阅读说明：本技术 用于单极化或双极化的薄膜全内反射衍射光栅 (Thin film total internal reflection diffraction grating for single or dual polarization ) 是由 J.M.米勒 G.威尔斯 L.田 M.奥莱瑞 于 2017-06-30 设计创作，主要内容包括：用于单极化或双极化的薄膜全内反射衍射光栅,可以包括基板。所述衍射光栅可以包括蚀刻停止层,以防止蚀刻所述基板。所述蚀刻停止层可以沉积在所述基板上。所述衍射光栅可以包括指示与电介质层的蚀刻相关联的蚀刻终点的标记层。所述标记层可以沉积在所述蚀刻停止层的一部分上。所述衍射光栅可以包括所述电介质层,所述电解质层在被蚀刻之后形成光栅层。所述电介质层可以至少沉积在所述标记层上。(A thin film total internal reflection diffraction grating for single or dual polarization may include a substrate. The diffraction grating may include an etch stop layer to prevent etching of the substrate. The etch stop layer may be deposited on the substrate. The diffraction grating may include a marker layer that indicates an etch endpoint associated with etching of the dielectric layer. The marker layer may be deposited on a portion of the etch stop layer. The diffraction grating may comprise the dielectric layer, the electrolyte layer forming a grating layer after being etched. The dielectric layer may be deposited at least on the marker layer.)

1. A diffraction grating, comprising:

the layer may be etched, an endpoint marked during the etching of the dielectric layer,

the etchable layer is located between the dielectric layer and a substrate; and

the dielectric layer, after being etched, forms a periodic grating layer,

the dielectric layer is at least on the etchable layer.

2. The diffraction grating of claim 1 further comprising:

an etch stop layer to prevent etching of the substrate,

the etch stop layer is located between the etchable layer and the substrate.

3. The diffraction grating of claim 1 further comprising:

a protective layer at least on the periodic grating layer.

4. The diffraction grating of claim 1 wherein the etchable layer comprises tantalum oxide, silicon dioxide, or silicon nitride.

5. The diffraction grating of claim 1 wherein the etchable layer is less than about 0.1 microns thick.

6. The diffraction grating of claim 1 wherein the dielectric layer comprises silicon or tantalum oxide.

7. The diffraction grating of claim 1 wherein the etchable layer marks an endpoint by producing a detectable reactant when the etch penetrates the etchable layer.

8. The diffraction grating of claim 7 wherein the detectable reactant comprises silicon fluoride.

9. A diffraction grating operating based on total internal reflection, comprising:

a dielectric grating layer between the substrate and the protective layer;

the dielectric grating layer is a periodic grating; and

a protective layer protecting the dielectric grating layer,

the protective layer has a total internal reflection planar surface spanning the width of the dielectric grating layer, and

the protective layer has a thickness greater than a thickness of the dielectric grating layer while maintaining a diffraction efficiency of at least 96%.

10. The diffraction grating of claim 9 further comprising:

an etchable layer, an end point being marked during etching of the dielectric grating layer,

the etchable layer is located between the dielectric grating layer and the substrate.

11. The diffraction grating of claim 9 wherein the protective layer comprises fused silica or glass.

12. The diffraction grating of claim 9 wherein a Total Internal Reflection (TIR) interface of the diffraction grating is located at a surface of the protective layer.

13. The diffraction grating of claim 9 wherein the diffraction grating is included in a rib grating assembly.

14. The diffraction grating of claim 9 wherein the difference between the thickness of the dielectric grating layer and the thickness of the protective layer is equal to or less than 0.28 microns.

15. A method of manufacturing a diffraction grating, the method comprising:

depositing a marker layer on a portion of a substrate;

depositing a dielectric layer on the marker layer;

etching the dielectric layer to form a grating layer;

etching the marking layer; and

detecting a reactant during the etching of the marker layer,

the reactant indicates an etch endpoint.

16. The method of claim 15, further comprising:

depositing an encapsulation layer associated with protecting the grating layer,

the encapsulation layer is to be deposited on the grating layer.

17. The method of claim 16 wherein the difference between the thickness of the encapsulation layer and the thickness of the grating layer is about 0.25 microns.

18. The method of claim 16, wherein a Total Internal Reflection (TIR) interface of the diffraction grating is at a surface of an encapsulation layer.

19. The method of claim 15, wherein the marker layer has a thickness of less than about 0.1 microns.

20. The method of claim 15, wherein the reactant comprises silicon fluoride.

Technical Field

The present disclosure relates to a reflective diffraction grating, and more particularly, to a thin film Total Internal Reflection (TIR) diffraction grating. The present disclosure also relates to a method of making such a thin film TIR diffraction grating.

Background

Reflective diffraction gratings are used to provide wavelength dispersion in wavelength selective optical devices such as Wavelength Selective Switches (WSS). The reflective diffraction grating may be applied in a two-channel configuration (e.g., within a prism grating) such that the optical path of the WSS causes light to pass through the reflective diffraction grating twice.

Disclosure of Invention

According to some possible embodiments, a diffraction grating may include a substrate; an etch stop layer to prevent etching of the substrate, wherein the etch stop layer may be deposited on the substrate; a marker layer indicating an etch endpoint associated with etching of the dielectric layer, wherein the marker layer may be deposited on a portion of the etch stop layer; and a dielectric layer that forms the grating layer after being etched, wherein the dielectric layer may be deposited at least on the marker layer.

According to some possible embodiments, a diffraction grating operating based on total internal reflection may include: a substrate; an etch stop layer to prevent etching of the substrate, wherein the etch stop layer may be formed on the substrate; a dielectric grating layer on the etch stop layer; and an encapsulation layer protecting the dielectric grating layer, wherein the encapsulation layer may be formed at least on the dielectric grating layer.

According to some possible embodiments, a method of manufacturing a diffraction grating may include: depositing an etch stop layer on a substrate; depositing a marker layer on a portion of the etch stop layer; depositing a dielectric layer on the marker layer; and etching the dielectric layer to form the grating layer, during etching the dielectric layer, the method may include preventing etching of the substrate by the etch stop layer; and determining that etching is to be stopped based on the etch marker layer.

Drawings

FIG. 1 is a diagram of an example of a prior art reflective diffraction grating;

FIG. 2 is a diagram of a first embodiment of a thin film diffraction grating designed to operate based on TIR;

3A-3F are diagrams associated with the design and performance of the first embodiment of FIG. 2;

FIG. 4 is a diagram of a second embodiment of a thin film diffraction grating designed to operate based on TIR;

5A-5C are graphical representations associated with the design and performance of the second embodiment of FIG. 4;

FIGS. 6A and 6B are illustrations of third and fourth embodiments of thin film diffraction gratings designed to operate based on TIR;

7A-7C are graphical illustrations associated with the design and performance of the fourth embodiment of FIG. 6B; and

FIG. 8 is a flow chart of an exemplary process for fabricating a thin film TIR diffraction grating as described herein.

Detailed Description

The following detailed description of embodiments refers to the accompanying drawings. The same reference numbers in different drawings may identify the same or similar elements. The embodiments described below are merely examples and are not intended to limit the embodiments to the precise forms disclosed. Rather, these embodiments are chosen and described to enable one of ordinary skill in the art to practice the embodiments.

A typical reflective diffraction grating includes a substrate and a reflective grating layer. Such reflective diffraction gratings are typically designed to achieve high Diffraction Efficiencies (DE) in the-1 st order for a particular polarization of light, such as transverse-magnetic (TM) polarization, when the reflective diffraction grating is in a first order Littrow installation. A typical reflective diffraction grating may be attached to a prism (e.g., using an optical epoxy) to form a grism.

Fig. 1 is an illustration of an example of an existing reflective diffraction grating 100 (referred to herein as an existing diffraction grating 100) attached to a prism 120. As shown in fig. 1, the conventional diffraction grating 100 includes a substrate 105 and a reflective grating layer 110, and is attached to a prism 120 using an optical epoxy 115. As shown in fig. 1, reflective grating layer 110 is embedded in optical epoxy 115 such that the binary grating profile of reflective grating layer 110 (e.g., a series of grooves etched in reflective grating layer 110 to form a series of ridges) is between substrate 105 and prism 120. In some cases, reflective grating layer 110 may have a profile other than a binary grating profile, such as a sinusoidal grating profile, a triangular grating profile, and so forth. A typical single-polarization existing diffraction grating 100 is designed such that DE in a particular order (e.g., ≧ 90%) for TM polarization is high and DE in a particular order (e.g., ≦ 8%) for transverse-electric (TE) polarization.

The substrate 105 is typically formed of a dielectric material, such as fused silica (SiO2) or other types of glass. In some cases, reflective grating layer 110 is formed from and/or coated with a reflective metallic material (e.g., gold). However, existing diffraction gratings having a gold reflective grating layer 110 (referred to herein as existing gold diffraction grating 100) may introduce a significant amount of insertion loss. For example, the existing gold diffraction grating 100 may have a single channel insertion loss in the range from about-0.2 decibels (dB) to about-0.3 dB. Thus, in a typical dual channel configuration, the existing gold diffraction grating 100 may have an insertion loss in the range from about-0.4 dB to about-0.6 dB.

The insertion loss of the existing gold diffraction grating 100 is due to at least two factors. One factor contributing to this insertion loss is that the gold reflectivity of reflective grating layer 110 is less than 100%. In other words, gold of reflection grating layer 110 does not reflect all light incident on reflection grating layer 110. This results in a maximum obtainable DE of less than 100% for the prior art gold diffraction grating 100. For example, for incident light having a wavelength of 1550 nanometers (nm), the reflectivity of gold reflective grating layer 110 is about 97%, which causes an insertion loss of about-0.13 db.

Another factor causing insertion loss associated with the existing gold diffraction grating 100 is imperfect-1 order blaze (blazing) caused by the binary grating profile of the reflective grating layer 110 on which light is incident (i.e., the uneven surface of the reflective grating layer 110 formed by grooves and ridges). For example, for light having a wavelength of 1550nm, the binary grating surface of reflective grating layer 110 causes imperfect-1 st order blaze, which results in an insertion loss of about-0.12 dB or greater. Thus, based on these two factors, the overall single-channel insertion loss of the existing gold diffraction grating 100 may be in the range of about-0.25 dB to-0.31 dB, which means that the DE in the-1 st order for TM polarization may range from about 93.2% to 94.4%.

One way to improve the DE of the existing diffraction grating 100 is to improve the reflectivity of the metallic material (e.g., gold) of the reflective grating layer 110. Thus, in some cases, one or more reflective dielectric thin film layers (e.g., rather than metal layers) are used to form the reflective grating layer 110. However, while relatively few (e.g., less than five) dielectric thin film layers may achieve near perfect blaze (e.g., about 100% DE) in the-1 st order for the TE polarization, a large number of reflective dielectric thin film layers (e.g., more than 30) are required to achieve high DE (e.g., greater than 94%) in the-1 st order for the TM polarization when the light has a high angle of incidence (e.g., when the existing diffraction grating 100 is in a first order littrow installation, as is typically the case). Thus, when a reflective dielectric thin film layer is used to achieve a high DE in the-1 st order for TM polarization, the fabrication of the existing diffraction grating 100 is expensive, time consuming, and/or complex.

In addition, the DE associated with the reflective dielectric thin film layer in the existing diffraction grating 100 may have a significant roll-off (e.g., a sharp drop in DE) as the wavelength of light deviates from the design wavelength (e.g., a wavelength near the center of the conventional band (C-band), a wavelength near the center of the long wavelength band (L-band), etc.). In addition, unlike the metallic (e.g., gold) reflective grating layer 110, the reflective dielectric thin film layer 110 allows at least two transmission orders (transmitted orders) to propagate into the substrate 105. This results in additional insertion loss (e.g., when light leaks in the transmission order), and thus, it is possible to further reduce the DE of the existing diffraction grating 100. Such transmission levels are illustrated in fig. 1 by the dashed lines for "0 th transmission" and "1 st transmission".

Embodiments described herein provide various embodiments of thin film dielectric reflective diffraction gratings (referred to herein as thin film TIR diffraction gratings) that operate based on Total Internal Reflection (TIR). The thin film TIR diffraction gratings described herein include a small number (e.g., one, two) of reflective dielectric thin film layers while still achieving a high DE (e.g., greater than 94%) in the-1 st order for TM polarization and/or for TE polarization. In addition, the thin film TIR diffraction gratings described herein prevent the propagation of transmission orders, thereby preventing insertion loss due to light leakage in such transmission orders. In some embodiments, thin film TIR diffraction gratings may be designed to achieve high DE for single polarization (e.g., TM polarization or TE polarization) or dual polarization (e.g., TM polarization and TE polarization) of light, as described elsewhere herein.

In some embodiments, the manufacturability and/or reliability of thin film TIR diffraction gratings may be improved by including: an etch stop layer associated with protecting the substrate during etching, a marker layer associated with marking or indicating an etch endpoint during etching, and/or an encapsulation layer associated with protecting a thin film grating layer of a thin film TIR diffraction grating (e.g., during an optical fitting process, during shipping, during cleaning, etc.), as described below.

Figure 2 is an illustration of an embodiment of a thin film diffraction grating 200 designed to operate based on TIR. As shown in fig. 2, thin film TIR diffraction grating 200 may include a substrate 205, an etch stop layer 210, and a thin film grating layer 215. As shown, the thin-film TIR diffraction grating 200 may be attached to an optical element 220 (e.g., to form a grism when the optical element 220 is a prism). In some implementations, the optical element 220 can have a triangular shape (e.g., the optical element 220 can be a prism) or a non-triangular shape (e.g., the optical element 220 can be a multi-surface trapezoid, a sphere, etc.).

Substrate 205 includes layers on which additional layers of thin film TIR diffraction grating 200 may be deposited. In some embodiments, the substrate 205 may be formed of a dielectric material, such as fused silica, or other types of glass.

The etch stop layer 210 includes a layer formed of an etch resistant material. For example, the etch stop layer 210 may comprise aluminum oxide (Al) resistant to Reactive Ion Etching (RIE)₂O₃) The layers formed. In this case, the etch stop layer 210 may ensure that gases associated with the RIE process do not penetrate the substrate 205, thereby preventing the substrate 205 from being etched (which may adversely affect the DE of the thin film TIR diffraction grating 200 if allowed). As shown, an etch stop layer 210 may be disposed between the substrate 205 and the thin film grating layer 215.

Thin film grating layer 215 (sometimes referred to as a dielectric grating layer) is a reflective dielectric grating layer that diffracts incident light. As shown, the thin film grating layer 215 may have a binary grating profile comprising ridges separated by grooves, wherein the grooves may be formed in a layer of dielectric material to form the thin film grating layer 215 by etching, as described below. In some embodiments, the cross-section of the ridge may be rectangular. Additionally or alternatively, the cross-section of the ridges may be trapezoidal, or take on other shapes. In some embodiments, the top of the ridge of the thin film grating layer 215 is substantially parallel to the top surface of the substrate 205 and the sidewalls of the ridge are substantially perpendicular to the top surface of the substrate 205 (e.g., when the cross-section of the ridge is rectangular). In some embodiments, the grating profile may be sinusoidal, triangular, trapezoidal, or take on other periodic shapes. A binary staircase may be a preferred grating profile because it is easily fabricated by photolithographic etching.

In some embodiments, the thin-film grating layer 215 may be formed from a dielectric layer that includes a small number (e.g., one or two) of layers of dielectric material having a refractive index (n) greater than that of air (n ═ 1), such as silicon (Si, n ═ 3.60), tantalum pentoxide (Ta)₂O₅N 2.10), silicon dioxide (SiO)₂N ═ 1.45), and so on. In some embodiments, the dielectric material forming the thin film grating layer 215 may be selected or determined based on the desired DE, as described below.

The arrangement of the layers of thin-film TIR diffraction grating 200 allows thin-film TIR diffraction grating 200 to operate based on TIR of light incident above a critical angle (e.g., as shown in fig. 2). Here, light incident beyond the critical angle is not refracted, but is totally internally reflected (e.g., in the specular reflection (0 th) order, in the ± 1 reflection diffraction order present when the thin film grating layer 215 is attached to the bottom of the etch stop layer 210), which may have 100%% reflectivity in both TM and TE polarizations. The arrangement of layers shown in fig. 2 allows for such TIR operation by forming a TIR interface (e.g., a flat, planar grating/air interface, rather than the non-planar surface of the prior art diffraction grating 100) at the lower surface of the etch stop layer 210. TIR operation of thin-film TIR diffraction grating 200 is possible when the pitch of thin-film TIR diffraction grating 200 is less than or equal to half the design wavelength. The grating pitch is the distance from an edge of a groove of the thin film grating layer 215 to a corresponding edge of an adjacent groove. The groove width is the distance between the edges of the groove. The normalized groove width is a fraction (e.g., a percentage) of the grating pitch as a groove (the pitch is not a part of the ridge). The grating height is the depth of the grooves (i.e., the height of the ridges).

Due to the TIR operation of thin-film TIR diffraction grating 200 and the arrangement of the layers of thin-film TIR diffraction grating 200, substrate transmission orders are eliminated (e.g., due to thin-film grating layer 215 being positioned on the outer surface of substrate 205, rather than between optical element 220 and substrate 205). In addition, the thin film grating layer 215 need not be embedded in the epoxy between the optical element 220 and the substrate 205. Without the need to embed thin film grating layer 215 in epoxy (e.g., to attach thin film TIR diffraction grating 200 to optical element 220), bending or warping of thin film grating layer 215 (e.g., due to expansion or contraction of the epoxy) caused by the use of such epoxy is eliminated.

The height, width, and thickness of the layers shown in fig. 2 are provided as examples and are exaggerated for illustrative purposes. In addition, thin-film TIR diffraction grating 200 may include additional layers, fewer layers, different layers, or layers arranged in a different manner than the layers shown in fig. 2.

Fig. 3A-3F are graphical representations associated with the design and performance of the thin film TIR diffraction grating 200 of fig. 2. FIG. 3A is a graphical representation 300 of an exemplary graph showing the profile area required to achieve various minimum DE's in the-1 st order for the TM polarization of a thin-film TIR diffraction grating 200, the thin-film TIR diffraction grating 200 including a thin-film grating layer 215 formed from one of silicon oxide, tantalum pentoxide, and silicon. Other materials with sufficiently high refractive indices are also feasible for wavelengths of light that are desired. As shown, the thin film grating layer 215 of fig. 3A corresponds to a pitch of 1624 lines per millimeter (lines/mm) (i.e., a repeating pattern, such as binary ridges and gaps), and is arranged in a littrow installation. The profile area may refer to the width of the groove of thin film grating layer 215 multiplied by the depth of the groove (i.e., the height of the ridge of thin film grating layer 215).

As shown in fig. 3A, the size of the profile area is typically larger for thin film grating layer 215 formed of silicon or tantalum pentoxide (rather than silicon dioxide). In other words, the manufacturability of the thin film grating layer 215 formed of silicon or tantalum pentoxide may be increased (e.g., due to the need for less fine etching) as compared to the thin film grating layer 215 formed of silicon dioxide. Thus, in some cases, therefore, in some cases, silicon or tantalum pentoxide may be selected for the thin film grating layer 215 to increase the manufacturability of the thin film grating layer 215. As shown in fig. 3A, when the desired ED in the-1 st order of TM polarization is greater than about 95%, the thin film grating layer 215 should not be formed of silicon dioxide.

As further shown, as the minimum DE required increases, the size of the profile area generally decreases (e.g., for silicon, tantalum pentoxide, and silicon dioxide). In other words, as the desired minimum DE increases, finer etching is required. For example, when the thin film grating layer 215 is formed of silicon, a profile area with dimensions of about 0.055 square microns is required in order to achieve a DE of 90% in the-1 st order of TM polarization. In contrast, when thin film grating layer 215 is formed of silicon, a profile area of about 0.005 square microns in size is required in order to achieve a DE of 99% in the-1 st order of TM polarization. Thus, the manufacturability of the thin film grating layer 215 generally decreases as the desired DE increases.

Nonetheless, as shown in fig. 3A, silicon dioxide, silicon, or tantalum pentoxide may be selected to form the thin film grating layer 215 so as to achieve a DE of from about 94% to about 95% (the most difficult to fabricate is the silicon dioxide thin film grating layer 215 because of the smaller profile area required). Silicon or tantalum pentoxide may be selected for forming thin film grating layer 215 to achieve a DE of greater than about 95%. In particular, the profile area of silicon thin film grating layer 215 required to achieve 98% DE or 99% DE is greater than the profile area of tantalum pentoxide thin film grating layer 215 required to achieve 98% DE or 99% DE. Thus, in some cases, silicon (rather than tantalum pentoxide) may be selected for thin film grating layer 215 (e.g., due to the larger profile area of silicon thin film grating layer 215 being easier to fabricate). However, while the embodiments described below describe the thin film grating layer 215 being formed of silicon, in some embodiments, the thin film grating layer 215 may be formed of silicon dioxide, tantalum pentoxide, or other suitable materials.

As mentioned above, fig. 3A is provided as an example associated with various DE's in the-1 st stage that achieve TM polarization of the thin film grating layer 215 formed of silicon dioxide, tantalum pentoxide, and silicon, where the thin film grating layer 215 is extended by 1624 lines/mm and arranged in a littrow installation. In practice, the thin film grating layer 215 may be formed of different materials, have different pitches (may have additional or fewer lines/mm), may be designed for high DE in different stages (e.g., stage 0), or may be configured differently than described above with respect to FIG. 3A.

Figure 3B is an exemplary thin film TIR diffraction grating 200 with certain parameters for a thin film grating layer 215 formed of silicon dioxide that includes 1624 lines/mm and an etch stop layer 210 with a thickness of 0.05 microns.

As shown in fig. 3B, exemplary thin film TIR diffraction grating 200 may include a silicon thin film grating layer 215 with a standard groove width of 0.4 (i.e., 40% of the grating pitch of exemplary thin film TIR diffraction grating 200 is a groove) and a grating height of 0.88 microns. As further shown in fig. 3B, thin film TIR diffraction grating 200 may comprise an etch stop layer 210 having a thickness of 0.05 microns.

In some embodiments, thin-film TIR diffraction grating 200 may be designed based on a design space associated with parameters identifying thin-film grating layer 215 in order to achieve a high DE in the-1 st order of the TM polarization and a low DE in the-1 st order of the TE polarization, as described below with respect to FIG. 3C. DE in the-1 st order of TM and TE polarization of a single-polarized thin film TIR diffraction grating 200 (e.g., as described in fig. 3B) may depend on the wavelength of the incident light. In practice, thin-film TIR diffraction grating 200 may include different numbers of lines/mm, different normalized groove widths, and/or etch stop layers 210 having different thicknesses.

Fig. 3C is an illustration of an exemplary design space 310 associated with parameters (e.g., normalized groove width, pitch, groove width, grating height) identifying the thin film grating layer 215 of a single-polarized thin film TIR diffraction grating 200 or a dual-polarized thin film TIR diffraction grating 200. Figure 3C shows DE in the-1 st stage of a thin film grating layer 215 formed of silicon for both TM and TE polarization. Additionally, the exemplary design space 310 corresponds to wavelengths within the C-band that result in a worst-case polarization design space (i.e., a minimum polarization design space), as described below. It should be understood that all other wavelengths in the C-band will have a design space that overlaps in the same region and is at least the same size (if not larger) as the design space shown in fig. 3C. As shown in fig. 3C, the longitudinal axis of the exemplary design space 310 corresponds to a range from 0.0 microns to 1.0 microns of the grating height (e.g., height of the ridges, depth of the grooves) of the thin film grating layer 215. As further illustrated, the horizontal axis of the exemplary design space 310 corresponds to a range of groove widths (e.g., Air Groove Widths (AGWs)) of the thin film grating layer 215 that are normalized to the pitch of the thin film grating layer 215 (referred to herein as the normalized groove width). In other words, the normalized groove width corresponds to a percentage of the pitch of the thin film grating layer 215 that is a groove (e.g., rather than a ridge).

As shown in the legend on the right-hand portion of fig. 3C, the black to light gray gradient of the exemplary design space 310 represents DE (e.g., from 0% to 100%) into the-1 st order of TE polarization over the grating height range and normalized groove width range described above. As shown, DE in the-1 st level of TE polarization varies across the exemplary design space 310. For example, for a normalized groove width of 0.6 and a grating height of 0.1 microns, the DE in the-1 st order of TE polarization is about 100%. Similarly, for a normalized groove width of 0.5 and a grating height of 0.1 microns, the DE in the-1 st order of TE polarization is about 50%. In addition, DE in the-1 st order of TE polarization is about 0% for a normalized groove width of 0.2 and a grating height of 0.1 microns.

The transparent black area (surrounded by white dashed lines in fig. 3C) represents such an area of the exemplary design space 310: in this region, DE in the-1 st order of TM polarization is greater than or equal to 90%. For example, DE in the-1 st order of TE polarization is greater than or equal to 90% for a normalized groove width of 0.3 and a grating height of 0.35 microns.

As shown above, fig. 3C is provided as an exemplary design space 310 for DE in the-1 st stage of thin film grating layer 215 formed of silicon, and corresponds to a region with different DE for TE and TM polarizations for wavelengths within the C band that result in a worst case polarization design space. Exemplary design space 310 includes an overlap region between the high DE of the TM polarization and the low DE of the TE polarization (e.g., which may be used to design a single-polarized thin film TIR diffraction grating 200), or an overlap region between the high DE of the TM polarization and the high DE of the TE polarization (e.g., which may be used to design a dual-polarized thin film TIR diffraction grating 200). Other design spaces exist for other wavelengths (e.g., within the C-band, within the L-band, etc.), and/or for thin film grating layer 215 formed from other materials (e.g., having a wider range, a smaller range, and/or a different range of grating heights and/or standardized groove widths). In other words, the exemplary design space 310 is a single example of a feasible design space.

In some embodiments, exemplary design space 310 may be used to identify parameters of thin film grating layer 215 in order to design thin film grating layer 215 to achieve a desired DE associated with one or both polarizations of light. For example, where thin-film grating layer 215 is to achieve a high (e.g., greater than or equal to 94%) DE in the-1 st order of TM polarization and a low (e.g., less than 10%, about 0%) DE in the-1 st order of TE polarization (i.e., when thin-film TIR diffraction grating 200 is designed for single polarization), the parameters of thin-film grating layer 215 may be identified approximately based on the region labeled "single polarization design space" in fig. 3C. Within a single polarization design space, DE in the-1 st stage of TM polarization is high, while DE in the-1 st stage of TE polarization is low.

As a specific example, the silicon thin film grating layer 215 has a normalized groove width of 0.4 and a grating height of 0.88 microns (similar to that described above with respect to FIG. 3B, and by labeling "x" within a single polarization design space_s"is marked with dots), a high DE in the-1 st order of TM polarization and a low DE in the-1 st order of TE polarization may be achieved.

Fig. 3D is a graphical representation of an exemplary graph 320 showing DE in the-1 st order of TE polarization and DE in the-1 st order of TM polarization for incident light having wavelengths ranging from 1500nm to 1600nm (i.e., approximately across the C-band).

As shown in fig. 3D (e.g., by the line identified as TM R1, and using the corresponding left longitudinal axis), DE in the-1 st order of TM polarization ranges from about 96.8% (e.g., at 1500nm and 1600 nm) to about 99.9% (e.g., at about 1550 nm). As further shown (e.g., by the line identified as TE R1, and using the corresponding right vertical axis), DE in the-1 st level of TE polarization ranges from about 0.4% (e.g., at 1500 nm) to about 2.1% (e.g., at 1600 nm). Therefore, DE in the-1 st order of TM polarization of more than about 99% can be easily achieved in the C-band, as shown in fig. 3D. This may allow for an insertion loss improvement of about 0.4dB to about 0.6dB (e.g., as compared to the existing diffraction grating 100). Still as shown, a DE in the-1 st order of TE polarization of less than about 1% can be achieved in the C-band, which corresponds to an improvement of about 5% over the existing diffraction grating 100.

Returning to FIG. 3C, in the case where thin-film grating layer 215 is to achieve a high DE in the-1 st order of TM polarization (e.g., greater than or equal to 94%) and a high DE in the-1 st order of TE polarization (i.e., when thin-film TIR diffraction grating 200 is designed for dual polarization), the parameters of thin-film grating layer 215 may be approximately identified by the area labeled "dual polarization design space" in FIG. 3C. In the dual-polarization design space, DE in the-1 st level of TM polarization is high, and DE in the-1 st level of TE polarization is high. In the case where the thin film TIR diffraction grating 200 is to minimize Polarization Dependent Loss (PDL), the thin film grating layer 215 may be designed for dual polarization blaze (e.g., the polarization dependent loss is reduced due to the high DE achieved for both polarizations).

As a specific example, thin film grating layer 215 has a normalized groove width (e.g., 70% of pitch) of 0.7 and a grating height (by labeling "x" within the dual polarization design space) of 0.38 microns_d"is marked with dots), a high DE in the-1 st order of TM polarization and a high DE in the-1 st order of TE polarization can be achieved. Fig. 3E is an illustration of an exemplary thin-film TIR diffraction grating 200 having these parameters: a thin film grating layer 215 with 1624 lines/mm and an etch stop layer 210 with a thickness of 0.05 microns. In practice, thin-film TIR diffraction grating 200 may include different numbers of lines/mm and/or etch stop layers 210 having different thicknesses.

The DE in the-1 st order of TM and TE polarization of a dual-polarized thin film TIR diffraction grating 200 (e.g., as described in fig. 3E) may depend on the wavelength of the incident light. Fig. 3F is a plot of an exemplary graph 330 showing the DE in the-1 st stage of TM polarization, the DE in the-1 st stage of TE polarization, and the average DE in the-1 st stage (i.e., the average of the DE of TM polarization and TE polarization, shown by the line labeled "av.r 1") for incident light in the wavelength range from 1500nm to 1600 nm. Fig. 3F also shows DE in order 0 for both TM and TE polarization (shown by the lines labeled "TM R0" and "TE R0", respectively).

As shown in fig. 3F (e.g., by the line identified as "TM R1"), DE in the-1 st order of TM polarization ranges from about 88% (e.g., at 1600 nm) to about 100% (e.g., at 1520 nm). Further shown (e.g., by the line identified as "TE R1"), DE in the-1 st stage of TE polarization ranges from about 95.0% (e.g., at 1500 nm) to about 99.0% (e.g., at about 1560 nm). Thus, a high DE in the-1 st order can be achieved for both the TE and TM polarizations, while the DE in the 0 th order is relatively low for both the TM and TE polarizations (e.g., less than about 12% and 5% for the TM and TE polarizations, respectively).

Therefore, DE in-1 order of more than 95% can be easily achieved in the C-band for both TM polarization and TE polarization, as shown in fig. 3F. This corresponds to a worst-case insertion loss of about-0.14 dB, and a worst-case PDL of about 0.16 dB.

In particular, fig. 3A-3F are provided as examples only, and other possible examples may differ from those associated with fig. 3A-3F. For example, the thin film grating layer 215 may include additional or fewer lines/mm, may be formed of different materials, and so forth. As another example, thin-film TIR diffraction grating 200 may include etch stop layer 210 having different thicknesses, may include additional and/or different layers (e.g., marker layer 225, encapsulation layer 230, as described below), may be designed for high DE in different levels (e.g., level 0), may be designed for light in a larger wavelength range, in a smaller wavelength range, or in a different wavelength range (e.g., L-band), and so on. In other words, fig. 3A-3F are merely examples associated with a possible thin film TIR diffraction grating that operates based on TIR while achieving a high DE for TM and/or TE polarization.

FIG. 4 is an illustration of a second exemplary embodiment of a thin film diffraction grating 235 designed to operate based on TIR. As shown in fig. 4, thin film TIR diffraction grating 235 may include substrate 205, etch stop layer 210, thin film grating layer 215, and indicia layer 225. As shown, the thin-film TIR diffraction grating 235 may be attached to the optical element 220 (e.g., to form a prism grating). As shown in fig. 4, the diffraction grating 235 is attached to the optical element 220 through the side of the substrate 205 opposite the thin film grating layer 215 (e.g., the bottom of the substrate 205).

As shown, thin-film TIR diffraction grating 235 may have a structure similar to thin-film TIR diffraction grating 200 (e.g., a similar arrangement of substrate 205, etch stop layer 210, and thin-film grating layer 215). In addition to these layers, thin film TIR diffraction grating 235 may include a marker layer 225 disposed between etch stop layer 210 and thin film grating layer 215.

The marking layer 225 includesLayer of the sample: this layer is associated with marking, indicating and/or identifying an etch endpoint (e.g., a point at which etching should stop) during etching of the thin film dielectric material from which the thin film grating layer 215 is formed. In some embodiments, the marker layer 225 may be formed of an etchable material, such as silicon, silicon nitride (Si)₃N₄) Tantalum pentoxide, and the like. In some embodiments, the marking layer 225 may have a thickness of less than about 0.1 microns, such as 50 nm.

In some embodiments, manufacturability of thin-film TIR diffraction grating 235 may be improved by marker layer 225 (e.g., compared to manufacturability of thin-film TIR diffraction grating 200). For example, a groove may be etched (e.g., toward the substrate 205) in the thin film dielectric layer to form the thin film grating layer 215. In a typical RIE etch process (e.g., a process using fluorine-based chemistry), when the etch reaches the substrate 205, the reactants resulting from the etch (e.g., silicon fluoride (SiF), C-N, tantalum fluoride (TaF)) are detected by a mass spectrometer associated with the etch chamber. Here, the mass spectrometer causes the etch to stop when the mass spectrometer detects an increase, surge, or peak in the amount of reactant being produced, etc. (e.g., due to the etch reaching and penetrating the substrate 205). In other words, the mass spectrometer detects the etch endpoint based on the reactants generated when etching through the substrate 205, rather than by monitoring the amount of time etching is occurring.

However, as described above, since the etch stop layer 210 is resistant to etching, the reactants required to detect the etch endpoint are not generated (e.g., because the etching does not penetrate the substrate 205). In this case, a time-based etch may be used. However, to determine the endpoint, precise timing calibrated by etch rate may be employed. Such timing makes it difficult to ensure different etches (e.g., different etches using the same chamber, different etches using different chambers) due to natural variations in etch rate for a particular etch chamber, as well as variations in etch rate between different etch chambers. Thus, during etching on a given time basis, over-etching of the thin film grating layer 215 in the lateral direction (e.g., into the sidewalls of the ridge) and/or under-etching of the thin film grating layer 215 may occur. Such etch variations will affect the yield of the overall etch process because grating profile tolerances may not be reliably achieved. In other words, where a time-based approach is used, the etching process may not be repeatable.

When thin-film TIR diffraction grating 235 includes etch stop layer 210, indicia layer 225 may improve the manufacturability of thin-film TIR diffraction grating 235 by allowing the use of the reactant detection-based etching techniques described above for etching the dielectric layer from which thin-film grating layer 215 is formed. For example, the marker layer 225 may be formed of silicon dioxide or silicon nitride. Here, when the etch reaches and penetrates the marker layer 225, a reactant (e.g., silicon fluoride) may be generated due to the penetration of the marker layer 225. In other words, the etching of the marker layer 225 may cause the marker layer 225 to mark or indicate an etch endpoint (by producing a detectable reactant). Thus, the mass spectrometer is able to detect an increase, surge or peak in the amount of reactant and may therefore cause the etch to stop. This may improve the manufacturability of the thin film TIR diffraction grating 235 in a repeatable manner by ensuring that grating profile tolerances can be reliably achieved.

The height, width, and thickness of the layers shown in fig. 4 are provided as examples and are exaggerated for illustrative purposes. In practice, the thin-film TIR diffraction grating 235 may include additional layers, fewer layers, different layers, or layers arranged in a different manner than that shown in fig. 4.

In some embodiments, the DE of thin-film TIR diffraction grating 235 may not be significantly affected due to the inclusion of marker layer 225 in thin-film TIR diffraction grating 235. FIG. 5A is a graphical representation of an exemplary graph 500 showing DE in the-1 st order of the TM polarization of a thin film TIR diffraction grating 235 including a marker layer 225 formed of silicon dioxide and silicon nitride (with a thickness ranging from 0.001 microns to about 0.8 microns). As mentioned, fig. 5A corresponds to a pitch of 1624 lines/mm of the silicon thin film grating layer 215 and is arranged in a littrow installation.

As shown in fig. 5A (by the designation "minDE TM SiO₂Lines labeled "), when the marker layer 225 is formed of silicon dioxide, when the marker layer 225 has a thickness of less than or equal to about 0.0At 65 microns, the DE in the-1 st order of the TM polarization is greater than 98%, and when the marking layer 225 has a thickness of less than or equal to about 0.025 microns, the DE in the-1 st order of the TM polarization is greater than 99%.

Similarly, (e.g., as labeled "minDE TM Si₃N₄Lines labeled "indicate), when the marker layer 225 is formed of silicon nitride, DE in the-1 st stage of TM polarization is greater than 98% when the thickness of the marker layer 225 is less than or equal to about 0.81 microns, and DE in the-1 st stage of TM polarization is greater than or equal to 99% when the thickness of the marker layer 225 is less than or equal to 0.041 microns.

In particular, the roll-off of the DE produced by the silicon oxynitride marker layer 225 is less abrupt than the roll-off of the silicon dioxide marker layer 225 (e.g., when the thickness of the marker layer 225 exceeds 0.1 microns). However, as shown, DE in the-1 stage is not significantly affected when the marker layer 225 is less than or equal to about 0.05 microns (50nm), regardless of whether the marker layer 225 is formed of silicon dioxide or silicon nitride.

Thus, in some embodiments, indicia layer 225 may be deposited in the grating region of thin film TIR diffraction grating 235. In other words, during fabrication of the thin-film TIR diffraction grating 235, the indicia layer 225 may be deposited within the chip boundaries (i.e., in the areas on the chip) of the substrate 205 (e.g., wafer) on which the thin-film TIR diffraction grating 235 is formed. Here, portions of marking layer 225 remain in the ridges of thin film TIR diffraction grating 235 and are disposed between thin film grating layer 215 and etch stop layer 210 (e.g., as shown in fig. 4).

Additionally or alternatively, the indicia layer 225 may be deposited in an off-chip area (e.g., a process control detection (PCM) area, an area outside the chip boundary) of the substrate 205 (e.g., instead of or in addition to being deposited in an area on the chip) on which the thin-film TIR diffraction grating 235 is formed.

FIG. 5B is an illustration of an exemplary wafer 510 showing the marking layer 225 deposited in the off-chip region of the wafer on which a plurality of thin film TIR diffraction gratings 235 are formed. As shown in FIG. 5B, on an exemplary wafer 510, a marker layer 225 may be deposited in the off-chip region adjacent to the end of each chip boundary. As shown in fig. 5B, in this example, the marker layer 225 is not deposited within the chip boundaries of the wafer 510 (i.e., in areas that are not deposited on the chips). Here, wafer 510 may be masked such that etching occurs within a grating area within the chip boundaries (e.g., identified by white areas with vertical lines) and within an off-chip area where marker layer 225 is present (e.g., identified by gray areas with vertical lines). Here, as described above, when etching through the marker layer 225 in the off-chip region, a reactant detectable by the mass spectrometer may be generated (i.e., the marker layer 225 may mark or indicate an etch endpoint), and the etching may be stopped. In this example, the resulting thin-film TIR diffraction grating will not include indicia layer 225 and may be similar to thin-film TIR diffraction grating 200 described above with respect to fig. 2.

Fig. 5C is a partial cross-section of an exemplary wafer 510 that includes a marker layer 225 in an off-chip region and does not include a marker layer 225 in an on-chip region. As shown, the marker layer 225 is present in an off-chip region (e.g., outside the chip boundary) and is absent in a region on the chip (e.g., within the chip boundary). As further illustrated, in some embodiments, wafer 510 may include an unetched region between an off-chip region with marker layer 225 and an on-chip region without marker layer 225.

In particular, fig. 5A-5C are provided as examples only, and other possible examples may differ from those associated with fig. 5A-5C. For example, thin film grating layer 215 may include additional or fewer lines/mm, and may be formed of different materials, and so on. As another example, thin-film TIR diffraction grating 235 may include etch stop layer 210 and/or marker layer 225 having different thicknesses, may include additional and/or different layers (e.g., encapsulation layer 230, as described below), may be designed for high DE in different orders (e.g., -2 th order, 3 rd order), may be designed for use with light in a larger range of wavelengths, in a smaller range of wavelengths, in a different range of wavelengths, and so forth. As an additional example, indicia layer 225 may be included in the on-chip area off of thin-film TIR diffraction grating 235. In other words, fig. 5A-5C are merely examples associated with possible thin film TIR diffraction gratings that operate based on TIR while achieving high DE for TM and/or TE polarization and are fabricated using a marker layer associated with indicating an etch endpoint.

Fig. 6A and 6B are illustrations of exemplary embodiments of thin film diffraction gratings 240 and 245, respectively, designed to operate based on TIR. As shown in fig. 6A, thin film TIR diffraction grating 240 comprises substrate 205, etch stop layer 210, thin film grating layer 215, and encapsulation layer 230. As shown, a thin-film TIR diffraction grating 240 may be attached to the optical element 220 (e.g., to form a prism grating).

As shown, thin-film TIR diffraction grating 240 may have a structure similar to thin-film TIR diffraction grating 200 (e.g., a similar configuration of substrate 205, etch stop layer 210, and thin-film grating layer 215). In addition to these layers, thin-film TIR diffraction grating 240 includes an encapsulation layer 230.

Encapsulation layer 230 includes a permanent layer designed to cover, encapsulate, and/or protect thin film TIR diffraction grating 240's thin film grating layer 215. In some embodiments, the encapsulation layer 230 can be formed of a hard, scratch resistant dielectric material, such as fused silica, glass (e.g., spin-on glass, Atomic Layer Deposition (ALD) -deposited SiO), or the like₂) And so on. As shown in fig. 6A, the thickness of encapsulation layer 230 may be greater than the thickness of thin film grating layer 215 (e.g., the height of the ridges of thin film grating layer 215).

In some embodiments, the encapsulation layer 230 may prevent the thin film grating layer 215 from being contacted, damaged, scratched, contaminated, or otherwise contacted, for example, during: during prism grid assembly (e.g., during a bonding step, during a polishing step, when integrating a grating or prism grid into an optical mechanism/optical platform, etc.), during shipping, during human handling, etc. Here, the use of the encapsulation layer 230 eliminates the need to apply a removable protective material (e.g., canada balsam (protective paint)) to the thin film grating layer 215, which may be advantageous because the removable protective material may not fully protect the thin film grating layer 215, may be difficult to remove, or may cause damage during removal/cleaning, etc.

In addition, encapsulation layer 230 may be polished without damaging thin film grating layer 215 in order to planarize or planarize the encapsulation surface of thin film TIR diffraction grating 240 (e.g., the lowermost surface of thin film TIR diffraction grating 240 as shown in fig. 6A). For example, because of the use of encapsulation layer 230, the TIR interface of thin-film TIR diffraction grating 240 is located at the encapsulation surface of encapsulation layer 230, as shown in fig. 6A (e.g., rather than at the bottom of etch stop layer 210 as with thin-film TIR diffraction gratings 200 and 235). Thus, the package surface of the thin film TIR diffraction grating 240 may be planarized or flattened to prevent a reduction in DE caused by a non-planar or rough TIR interface. Here, the package surface of the thin film TIR diffraction grating 240 may be manipulated, contacted, polished, and cleaned without risk of damaging the thin film grating layer 215 that would negatively impact the DE of the thin film TIR diffraction grating 240. In some embodiments, the sides of the grating chip may be polished to coincide with the sides of the prism 22, in some embodiments, to form an input surface for the light beam.

In addition, the encapsulation layer 230 allows for the application of a removable protective material to the now flat encapsulation surface that can be easily removed (e.g., using a typical swab and solvent cleaning process).

In some implementations, the thin-film TIR diffraction grating may include a marker layer 225 and an encapsulation layer 230. For example, as shown in FIG. 6B, thin film TIR diffraction grating 245 may include substrate 205, etch stop layer 210, thin film grating layer 215, indicia layer 225, and encapsulation layer 230. As shown, thin-film TIR diffraction grating 245 may have a structure similar to thin-film TIR diffraction grating 235 (e.g., a similar arrangement of substrate 205, etch stop layer 210, thin-film grating layer 215, and indicia layer 225).

The height, width, and thickness of the layers shown in fig. 6A and 6B are provided as examples and are exaggerated for illustrative purposes. In practice, thin-film TIR diffraction grating 240 and/or thin-film TIR diffraction grating 245 may include additional layers, fewer layers, different layers, or layers arranged in a different manner than shown in fig. 6A and 6B.

In some embodiments, the DE of thin-film TIR diffraction grating 245 may depend on the thickness of encapsulation layer 230, but may not be significantly affected thereby. Figure 7A is an illustration of a thin film TIR diffraction grating 245 that includes an encapsulation layer 230 having a thickness greater than the thickness of thin film grating layer 215. As shown, the thickness difference between encapsulation layer 230 and thin film grating layer 215 is identified as d_T。

FIG. 7B is an illustration of an exemplary graph 710 showing DE in the-1 st order of TM polarization of a thin film TIR diffraction grating 245 including an encapsulation layer 230 with a thickness difference (d)_T) In the range of 0.00 microns to about 0.37 microns. As mentioned, the corresponding thin film TIR diffraction grating 245 of fig. 7B includes a silicon dioxide encapsulation layer 230, a silicon or silicon dioxide thin film grating layer 215, an aluminum oxide etch stop layer 210, and a silicon dioxide marker layer 225. In addition, fig. 7B shows DE in the-1 st order of TM polarization, and corresponds to the wavelength within the C-band that results in the worst-case DE (i.e., DE may be the same or higher for other wavelengths in the C-band).

As shown in fig. 7B (by the line labeled "minDE C band"), when d is greater than d_TAt 0.0 microns (i.e., when the thickness of encapsulation layer 230 is the same as thin film grating layer 215), DE in the-1 st order of TM polarization is about 98%, which is about 1% lower compared to thin film TIR diffraction grating 240 without encapsulation layer 230. As shown, for d between 0.0 microns and about 0.15 microns_TDE is further reduced (i.e., below 98%). However, as shown, for d between about 0.15 microns and about 0.28 microns_TDE recovery (i.e., to at least 98%) when d_TAt about 0.25 microns, there is a peak DE of about 99.5%. In other words, thin-film TIR diffraction grating 245 may have an increased DE as compared to thin-film TIR diffraction grating 235. As further shown, for d greater than about 0.28 microns_TDE is again reduced and there is a significant roll off of DE.

Fig. 7A and 7B are provided as examples only, and other possible examples may differ from those described in association with fig. 7A and 7B. For example, thin film grating layer 215 may include additional or fewer lines/mm, may be formed of different materials, and so forth. As another example, thin-film TIR diffraction grating 235 may include etch stop layer 210, marker layer 225, and/or encapsulation layer 230 having different thicknesses, may include additional and/or different layers, may be designed for high DE in different orders (e.g., -2 th order, 3 rd order), may be designed for use with light in a larger wavelength range, in a smaller wavelength range, or in different wavelength ranges, and so on. In other words, fig. 7A and 7B are merely examples associated with possible thin film TIR diffraction gratings that operate based on TIR while achieving high DE for TM and/or TE polarization, and that include an encapsulation layer associated with a protective thin film grating layer.

FIG. 7C is an illustration of an exemplary design space 720 associated with parameters (e.g., normalized groove width, pitch, groove width, grating height) identifying a single polarized thin film TIR diffraction grating 245 or a dual polarized thin film TIR diffraction grating 245, where d_TEqual to 0.25 micron. Figure 7C shows DE in the-1 st stage of a thin film grating layer 215 formed of silicon for both TM and TE polarization. Additionally, the exemplary design space 720 corresponds to the wavelength within the C-band that results in the worst case polarization design space (i.e., the smallest polarization design space).

As shown in fig. 7C, the longitudinal axis of the exemplary design space 720 corresponds to an encapsulated grating height in the range from 0.0 microns to 2.0 microns (e.g., the varying thickness of the thin film grating layer 215 plus a constant dT of about 0.25 microns). As further shown, the horizontal axis of the exemplary design space 720 corresponds to a normalized groove width in the range from 0.0 to 1.0.

As shown in the legend in the right-hand portion of fig. 7C (and similar to the exemplary design space 310 described above), the black-to-light gray gradient of the exemplary design space 720 represents DE (e.g., from 0% to 100%) in the-1 st level of TE polarization over the above-described range of package grating heights and standardized groove widths. The transparent black area (surrounded by white dashed lines in fig. 7C) represents such an area of the exemplary design space 720: in this region, DE in the-1 st order of TM polarization is greater than or equal to 90%.

In some embodimentsExemplary design space 720 may be used to identify parameters of thin-film TIR diffraction grating 245 (e.g., normalized groove width pitch, groove width, including d)_TGrating height) and/or to achieve a desired DE associated with one or both polarizations of light in a manner similar to that described above with respect to the exemplary design space 310.

As shown by exemplary design space 720, for thin-film TIR diffraction grating 245, a single-polarized design space region is created that has an encapsulated grating height equal to about 1.1 microns, which is about 0.2 microns thicker than the single-polarized design space of thin-film TIR diffraction grating 200 associated with exemplary design space 310. Furthermore, as shown, there is also dual polarization design space for a package grating height of 1.1 microns. Thus, in some embodiments, the same grating height may be used to implement a single polarized thin film TIR diffraction grating 245 or a dual polarized thin film TIR diffraction grating 245, which may reduce manufacturing costs. In other words, it is made possible to manufacture wafers with the same grating height and then process them in different ways, masking (masking) different groove widths associated with different design spaces.

As mentioned above, fig. 7C is provided as an exemplary design space 720 for DE in the-1 st order of the thin film grating layer 215 formed of silicon, and corresponds to the wavelength within the C-band that results in the worst-case polarization design space (i.e., the overlap region between the high DE of the TM polarization and the low DE of the TE polarization, the overlap region between the high DE of the TM polarization and the high DE of the TE polarization). Other design spaces exist for thin film grating layer 215 at other wavelengths (e.g., within the C-band, within the L-band, etc.) and/or formed from other materials (e.g., having a wider range, a smaller range, and/or a different range of grating heights and/or standardized groove widths). In other words, exemplary design space 720 is a single example of a feasible design space.

Fig. 7C is merely an example associated with a possible thin film TIR diffraction grating that can operate based on TIR while achieving high DE for TM and/or TE polarization, and includes an encapsulation layer associated with a protective thin film grating layer.

FIG. 8 is a flow chart of an exemplary process 800 for fabricating thin film TIR diffraction grating 245 as described herein. In particular, although exemplary process 800 is described in the context of fabricating thin-film TIR diffraction grating 245, other thin-film TIR diffraction gratings described herein (e.g., thin-film TIR diffraction gratings 200, 235, or 240) may be fabricated using similar processes (e.g., using a subset of the blocks of exemplary process 800).

At block 805, the exemplary process 800 may include providing a substrate 205 (i.e., a wafer) on which the thin-film TIR diffraction grating 245 is to be formed 205. At block 810, an etch stop layer 210 associated with preventing etching of the substrate 205 is deposited on the substrate 205. At block 815, a marker layer 225 associated with marking or indicating an etch endpoint during etching is deposited on or over the etch stop layer 210. In some embodiments, the marker layer 225 may be deposited on the substrate 205 in on-chip and/or off-chip regions, as described above. At block 820, a dielectric thin film layer forming the thin film grating layer 215 is deposited on or over the marker layer 225 and/or the etch stop layer 210.

At step 825, a photoresist layer is patterned over the dielectric thin film layer so as to mask portions of the dielectric thin film layer that are not etched during formation of the thin film grating layer 215. At block 830, the dielectric thin film layer is etched through the patterned photoresist layer to form the thin film grating layer 215. Here, the etch may be performed until the etch penetrates the marker layer 225, such that the marker layer 225 marks or indicates the etch endpoint by generating a reactant, for example, that is detected by a mass spectrometer. The mass spectrometer may stop the etching when an increase or peak in the amount of reactant is detected. At block 835, the photoresist layer is removed.

At block 840, the encapsulation layer 230 is deposited on or over the thin film grating layer 215, the exposed portions of the etch stop layer 210, and/or the marker layer 225 within the grooves of the thin film grating layer 215 (e.g., such that the grooves are filled by the encapsulation layer 230). The encapsulation layer 230 may be deposited such that the difference between the thickness of the encapsulation layer 230 and the thickness of the thin film grating layer 215 (e.g., the height of the ridges of the thin film grating layer 215) is a desired distance. In some embodiments, encapsulation layer 230 may be planarized after deposition. In some embodiments, the encapsulation layer may be planarized to reduce the thickness of the encapsulation layer to about 0.25 microns thicker than the thickness of the grating layer. In some embodiments, the marker layer is formed from tantalum pentoxide, silicon dioxide, or silicon nitride, and has a thickness less than or equal to about 50 nanometers. In some embodiments, the region corresponding to such portion of the etch stop layer is an off-chip region of the substrate: a marker layer is deposited on the portion.

In some embodiments, the process 800 may include attaching, bonding, or otherwise bonding the diffraction grating to the prism through the side of the substrate opposite the thin film grating layer (e.g., the bottom of the substrate 205) to form a gridline.

Although fig. 8 shows example blocks of the process 800, in some implementations, the process 800 may include additional blocks, fewer blocks, different blocks, or blocks arranged in a different manner than the blocks depicted in fig. 8. Additionally or alternatively, although exemplary process 800 describes that the layers of thin film TIR diffraction grating 245 are deposited, in some embodiments, the layers of thin film layer TIR diffraction grating 245 may be fabricated in another manner, such as by growing, molding, chemical reaction, sputtering, and the like.

Embodiments described herein provide various embodiments of thin film dielectric reflective diffraction gratings that operate based on Total Internal Reflection (TIR). The thin film TIR diffraction gratings described herein include a small number (e.g., one, two) of reflective dielectric thin film layers while still achieving a high DE (e.g., greater than or equal to 94%) in the-1 st order of the TM and/or TE polarization. In addition, the thin film TIR diffraction gratings described herein prevent the propagation of transmission orders, thereby preventing insertion loss due to light leakage in such transmission orders. In some embodiments, thin film TIR diffraction gratings may be designed to achieve a high DE for either single polarization (e.g., TM polarization or TE polarization) or dual polarization (e.g., TM polarization and TE polarization) of light.

The foregoing disclosure provides illustration and description, but is not intended to be exhaustive or to limit the embodiments to the precise form disclosed. Modifications and variations are possible in light of the above disclosure or may be acquired from practice of the embodiments.

Even if specific combinations of features are recited in the claims and/or disclosed in the description, these combinations are not intended to limit the disclosure of possible embodiments. Indeed, many of these features may be combined in ways not specifically recited in the claims and/or disclosed in the specification. Although each dependent claim listed below may depend directly on only one claim, the disclosure of possible embodiments includes the combination of each independent claim with each other claim in the set of claims.

No element, act, or instruction used herein should be construed as critical or essential unless explicitly described as such. In addition, as used herein, the articles "a" and "an" are intended to include one or more items, and may be used interchangeably with "one or more". Further, as used herein, the term "collection" is intended to include one or more items (e.g., related items, unrelated items, combinations of related and unrelated items, etc.) and may be used interchangeably with "one or more. If only one item is intended, the term "one" or similar language is used. Furthermore, as used herein, the terms "having," "containing," "carrying," and the like are intended to be open-ended terms. Further, the phrase "based on" is intended to mean "based, at least in part, on" unless explicitly stated otherwise.