阅读说明：本技术 基于片上集成麦克斯韦半鱼眼透镜的超宽带模斑转换器 (Ultra-wideband mode spot converter based on-chip integrated Maxwell half fish-eye lens ) 是由 沈健 张永 苏翼凯 于 2021-09-10 设计创作，主要内容包括：一种基于片上集成麦克斯韦半鱼眼透镜的超宽带模斑转换器,包括：片上集成的麦克斯韦半鱼眼透镜、设置于麦克斯韦半鱼眼透镜圆心一侧的过渡区以及硅波导,该硅波导包括：第一波导和第二波导,其中：第一波导作为输入端设置于过渡区的外侧,第二波导作为输出端位于麦克斯韦半鱼眼透镜相对过渡区的圆周一侧。本发明通过优化麦克斯韦半鱼眼透镜梯度折射的结构,不仅减小了透镜尺寸,而且与硅波导集成,实现不同宽度波导中的模斑尺寸匹配。(An ultra-wideband mode spot converter based on an on-chip integrated Maxwell half-fisheye lens, comprising: the on-chip integrated Maxwell half fish-eye lens, set up transition area and silicon waveguide in Maxwell half fish-eye lens centre of a circle one side, this silicon waveguide includes: a first waveguide and a second waveguide, wherein: the first waveguide is used as an input end and arranged on the outer side of the transition area, and the second waveguide is used as an output end and is positioned on one side of the circumference of the Maxwell half fisheye lens relative to the transition area. By optimizing the gradient refraction structure of the Maxwell half fish-eye lens, the size of the lens is reduced, and the lens is integrated with a silicon waveguide to realize the size matching of mode spots in waveguides with different widths.)

1. An ultra-wideband mode spot converter based on an on-chip integrated Maxwell half fish-eye lens, comprising: the on-chip integrated Maxwell half fish-eye lens, set up transition area and silicon waveguide in Maxwell half fish-eye lens centre of a circle one side, this silicon waveguide includes: a first waveguide and a second waveguide, wherein: the first waveguide is used as an input end and arranged on the outer side of the transition area, and the second waveguide is used as an output end and is positioned on one side of the circumference of the Maxwell half fisheye lens relative to the transition area.

2. The ultra-wideband mode spot converter based on an on-chip integrated maxwell half fish-eye lens as claimed in claim 1, wherein the maxwell half fish-eye lens has a radial fill factor profile, and the refractive index profile satisfies:wherein: n is_maxIs the central maximum refractive index, R_lensIs the radius of the maxwell half fisheye lens, and R is the radial distance from the center of the maxwell half fisheye lens.

3. The ultra-wideband mode spot converter based on the on-chip integrated Maxwell half fisheye lens as claimed in claim 1, wherein the relationship between the maximum refractive index and the minimum refractive index of the Maxwell half fisheye lens is n_max＝2n_minWherein: n is_minIs the minimum refractive index value, n, of Maxwell half-fisheye lens_maxIs the maximum refractive index value in a maxwell half-fish eye lens.

4. The ultra-wideband spot-size converter based on the on-chip integrated maxwell half fish-eye lens as claimed in claim 1, wherein the ultra-wideband spot-size converter is prepared by a microelectronic CMOS compatible process, and comprises: preparing a device by adopting an SOI substrate with the top silicon layer being 220nm thick and the buried layer being 3 microns thick, defining a grating, a Maxwell half-fisheye lens and a waveguide on the photoresist by using an electron beam exposure photoetching technology, then carrying out development and multi-step etching and etching for 70nm to form the grating, partially and shallowly etching for 160nm to form a nano-pillar array to form a lens and an output waveguide, fully etching for 220nm to form a waveguide with the thickness of 220nm, and depositing a waveguide with the thickness of 1 micron by using a plasma enhanced chemical vapor deposition method after the etching step is finishedSiO₂And (7) cladding.

5. The ultra-wideband mode spot converter based on the on-chip integrated maxwell half fisheye lens as claimed in claim 1, wherein the maxwell half fisheye lens is of an upper and lower cladding structure, wherein: the upper and lower cladding layers are silicon metamaterial layers of silicon dioxide, and the silicon metamaterial layer is a silicon nanorod antenna array structure with gradient filling factors.

6. The ultra-wideband spot-size converter based on an on-chip integrated maxwell half-fisheye lens of claim 1, wherein the first waveguide is a rectangular structure with a width less than or equal to the diameter of the maxwell half-fisheye lens.

7. The ultra-wideband mode spot converter based on the on-chip integrated Maxwell half-fish-eye lens as claimed in claim 1 or 6, wherein the second waveguide is rectangular, and the width ratio of the first waveguide to the second waveguide is selected to be 16: 1.

8. The ultra-wideband mode spot converter based on the on-chip integrated maxwell half fisheye lens as claimed in claim 1, wherein the maxwell half fisheye lens is an anisotropic lens, so that the equivalent material refractive index in the plane direction is:in the vertical direction: wherein: n is_meta(R)、n_SiAndrespectively equivalent material, silicon and silicon dioxideRefractive index of (d), δ (R) ═ pr²/p²Is the packing factor of the nano-rod, and r is the radius of the nano-column.

9. The use of the maxwell half fisheye lens according to any of claims 1 to 8, wherein in a room temperature environment, a laser input light source is used, light is coupled into a silicon chip placed on a vertical coupling stage through a polarization controller, an inclined fiber lens and a grating on the chip, the light passing through the maxwell half fisheye lens is coupled out of the chip by the grating and enters an optical fiber of an output part, an output optical signal passes through a coupler, one path of the output optical signal is input into a readable optical power meter, the other path of the output optical signal is input into a sweep spectrum power meter, and after alignment, a computer controls the sweep spectrum power meter to sweep spectrum, so that a spectrum of the optical signal is finally obtained.

Technical Field

The invention relates to a technology in the field of integrated photonics, in particular to an ultra-wideband mode spot converter based on an on-chip integrated Maxwell half fish-eye lens.

Background

In an integrated optical circuit, in order to reduce the size of a chip and improve the performance of devices on the chip, it is necessary to design a photoelectric device with a compact structural size and high coupling efficiency, wherein an important passive device is a spot size converter. The spot size converter is a passive device used to match different spot sizes, and can change the spot size to realize low-loss coupling between waveguides with different widths. The silicon-based photonic device has the characteristic of strong mode field constraint, can be compatible with a complementary metal oxide semiconductor CMOS (complementary metal oxide semiconductor) process, and is an ideal choice for future large-scale integrated optical circuits.

Disclosure of Invention

Aiming at the defects that the occupied area of the conventional conical waveguide structure is large, and the manufacturing difficulty is large because a lens based on conversion optics needs to utilize a focused ion beam etching or gray level exposure technology, the invention provides the ultra-wideband mode spot converter based on the on-chip integrated Maxwell half fisheye lens.

The invention is realized by the following technical scheme:

the invention comprises the following steps: the on-chip integrated Maxwell half fish-eye lens, set up transition area and silicon waveguide in Maxwell half fish-eye lens centre of a circle one side, this silicon waveguide includes: a first waveguide and a second waveguide, wherein: the first waveguide is used as an input end and arranged on the outer side of the transition area, and the second waveguide is used as an output end and is positioned on one side of the circumference of the Maxwell half fisheye lens relative to the transition area.

The Maxwell half fish-eye lens has radial filling factor distribution, and the refractive index distribution meets the following requirements:wherein: n is_maxIs the central maximum refractive index, R_lensIs the radius of the maxwell half fisheye lens, and R is the radial distance from the center of the maxwell half fisheye lens.

The relation between the maximum refractive index and the minimum refractive index of the Maxwell half fish-eye lens is n_max＝2n_minWherein: n is_minIs the minimum refractive index value, n, of Maxwell half-fisheye lens_maxIn Maxwell half-fisheye lensThe maximum refractive index value of.

The ultra-wideband spot-size converter is prepared by a microelectronic CMOS compatible process, can support large-scale integration, and comprises the following components: preparing a device by adopting an SOI substrate with the top silicon layer being 220nm thick and the buried layer being 3 microns thick, defining a grating, a Maxwell half-fisheye lens and a waveguide on the photoresist by using an electron beam exposure photoetching technology, then carrying out development and multi-step etching and etching for 70nm to form the grating, partially shallow etching for 160nm to form a nano-pillar array to form a lens and an output waveguide, fully etching for 220nm to form a waveguide with the thickness of 220nm, and depositing SiO with the thickness of 1 micron by using a plasma enhanced chemical vapor deposition method after the etching step is finished₂And (7) cladding.

Technical effects

The invention uses the nanometer column array to form the metamaterial on the SOI substrate to realize the change of the effective refractive index to form the Maxwell half fish-eye lens, and realizes the adjustment of the light field mode spot size from two dimensions of height and width in a smaller occupied area.

Drawings

FIG. 1 is a schematic structural view of the present invention;

FIG. 2 is a graph of a simulated transmission spectrum of the present invention;

FIG. 3 is a simulated spectrum of the TE mode spot conversion of the embodiment at a wavelength of 1.55 μm;

FIG. 4 is a simulated spectrum of the TE mode spot conversion of the example at a wavelength of 1.26 μm;

FIG. 5 is a graph of a simulated spectrum of TE mode spot conversion at a wavelength of 2 μm according to an embodiment;

in the figure: the on-chip Maxwell half fish-eye lens comprises an on-chip Maxwell half fish-eye lens 1, a silicon waveguide 2, an input end 3, an output end 4, a first waveguide 5, a second waveguide 6 and a transition region 7.

Detailed Description

As shown in fig. 1, an on-chip integrated maxwell half fish-eye lens-based ultra-wideband spot-size converter that can be processed and implemented on an SOI platform according to this embodiment includes: the on-chip integrated Maxwell half fish-eye lens 1, the transition region 7 arranged at one side of the circle center of the Maxwell half fish-eye lens 1 and the silicon waveguide 2, wherein the silicon waveguide 2 comprises: a first waveguide 5 and a second waveguide 6, wherein: the first waveguide 5 is arranged as an input end 3 outside the transition area 7, and the second waveguide 6 is arranged as an output end 4 on one side of the maxwell half fish-eye lens 1 opposite to the circumference of the transition area 7.

The Maxwell half fish-eye lens 1 is of an upper cladding structure and a lower cladding structure, wherein: the upper and lower cladding layers are silicon dioxide silicon metamaterial layers, the silicon metamaterial layers are silicon nanorod antenna array structures with gradient filling factors, the effective refractive index depends on the filling factors of silicon nanorods with sub-wavelength structures, the silicon metamaterial layers realize the function of Maxwell half-fish-eye lenses, the occupied area of devices is reduced, and conversion of the size of a mode spot on the width and the height is realized at the same time with extremely low loss in the 740nm ultra-wideband range.

The period of the silicon nano rod is p.

The first waveguide 5 is a rectangular structure, the width of the first waveguide is less than or equal to the diameter of the Maxwell half fisheye lens 1, and the width of the first waveguide 5 and the diameter of the Maxwell half fisheye lens 1 can be adjusted according to actual use.

The second waveguide 6 is a rectangular structure, and the width ratio of the first waveguide 5 to the second waveguide 6 is selected from 16: 1, the ratio can be adjusted according to actual use.

The Maxwell half fish-eye lens 1 has radial filling factor distribution and is composed of a periodic silicon nano-pillar array, and silicon dioxide is deposited and filled in the etched part around the nano-pillar, wherein the refractive index distribution satisfies the following conditions:wherein: n is_maxIs the edge refractive index, R_lensIs the radius of the maxwell half fisheye lens 1 and R is the radial distance from the center of the maxwell half fisheye lens 1.

The relation between the maximum refractive index and the minimum refractive index of the Maxwell half fish-eye lens 1 is n_max＝2n_min。

The maxwell half fish-eye lens is specifically an anisotropic lens, so that the refractive index of an equivalent material in the plane direction is as follows:in the vertical direction: wherein: n is_meta(R)、n_SiAndrefractive indices of equivalent material, silicon and silicon dioxide, respectively, delta (R) ═ R²/p²Is the packing factor of the nano-rod, and r is the radius of the nano-column. The fill factor ranged from 0 to 100%, and the maximum fill factor was set to 67.9% for experimental feasibility.

The embodiment relates to a preparation method of the Maxwell half fish eye lens, which comprises the steps of setting the thickness of a silicon layer on the top of an SOI platform to be 220nm, the thickness of a buried oxide layer to be 3 mu m, and the thickness of a covering layer on the top of silicon dioxide to be 1 mu m; the width of the first waveguide 5 and the width of the second waveguide 6 were set to 8 μm and 0.5 μm, respectively; the minimum filling factor of the nanorods of the Maxwell half-fisheye lens is set to be 0.3%, the minimum effective refractive index is 1.8, the maximum effective refractive index is 2.7, the maximum filling factor is set to be 67.9%, the period is 200nm, and the length of the lens is 5.44 μm; calculating the coupling loss and the working bandwidth according to the set parameters: as shown in FIG. 2, the transmission spectrum has a coupling loss of less than 1dB in the wavelength range of 1.26 μm to 2 μm. The spot-size converter thus has an operating bandwidth of greater than 740nm and low insertion loss.

As shown in FIGS. 3, 4 and 5, electric fields (E) of TE-based modes at light wavelengths of 1.55 μm, 1.26 μm and 2 μm, respectively, are shown_y) The distribution of (a); the parameters of the silicon waveguide at the output end 4 of the input end 3 and the parameters of the Maxwell half fish-eye lens 1 can also be changed to conform to the TM fundamental mode transmissionEffective refractive index, thereby realizing the spot size matching of the TM fundamental mode.

The embodiment relates to the application of the Maxwell half fish-eye lens: under the specific environment setting of normal room temperature, a laser input light source (Santec TSL-550and Keysight 81960A) is used, light is coupled into a silicon chip arranged on a vertical coupling platform through a polarization controller, an inclined optical fiber lens and a grating on the chip, the light passing through a Maxwell half-fisheye lens is coupled out of the chip through the grating and enters an optical fiber of an output part, an output optical signal passes through a 3dB coupler, one path of the output optical signal is input into a readable optical power meter, the other path of the output optical signal is input into a spectrum sweeping power meter (Keysight N774 7744A), after the light is emitted, a computer controls an aligning spectrum power meter to sweep spectrum, a spectrogram of the optical signal is finally obtained, and the performances of the optical signal, such as insertion loss, bandwidth and the like in the device are researched.

Compared with the prior art, the device can realize the conversion of the size of the mode spot with the wavelength from 1.26 mu m to 2 mu m, the bandwidth reaches 740nm and is far higher than the performance of the existing taper (taper) structure; in the 740nm bandwidth range, the size of the optical field mode spot of the C wave band and the O wave band can be changed in height and width, the size conversion loss of the mode spot is within 1dB, and the loss is lower than the performance of the existing Hollowkeeper structure. 3. The invention has small occupied area, the length of the invention is 5.44 mu m, and the occupied area is smaller than that of the prior lens structure. 4. The invention can change the size of the optical field mode spot from two dimensions of the width and the height of the waveguide, and is superior to the prior planar waveguide lens technology.

The foregoing embodiments may be modified in many different ways by those skilled in the art without departing from the spirit and scope of the invention, which is defined by the appended claims and all changes that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.