阅读说明：本技术 一种级联式啁啾光栅辅助反向耦合器型光色散延时线 (Cascaded chirped grating auxiliary reverse coupler type optical dispersion delay line ) 是由 胡国华 汪冬宇 邓春雨 黄磊 孙彧 恽斌峰 崔一平 于 2021-08-12 设计创作，主要内容包括：本发明涉及一种级联式啁啾光栅辅助反向耦合器型光色散延时线,包括基于SOI材料制备的直波导、弯曲波导和多个交错级联的啁啾光栅辅助反向耦合器；所述啁啾光栅辅助反向耦合器由单侧壁调制波导光栅和锥形波导构成反向耦合区,所述单侧壁调制波导光栅在邻近锥形波导一侧具有周期性矩形光栅尺,所述锥形波导宽度沿波导长度方向线性改变；相邻啁啾光栅辅助反向耦合器由直波导和弯曲波导连接。本发明可以实现对输入光信号的滤波作用,并使选通波长范围内的光具有随波长线性变化的群延时量,能够在紧凑的芯片尺寸下提供高色散值,可应用于色散补偿、光缓存、光学真延时网络、集成化微波光子信号产生。(The invention relates to a cascade chirped grating auxiliary reverse coupler type optical dispersion delay line, which comprises a straight waveguide, a curved waveguide and a plurality of alternately cascaded chirped grating auxiliary reverse couplers, wherein the straight waveguide and the curved waveguide are prepared on the basis of an SOI material; the chirp grating auxiliary reverse coupler is characterized in that a reverse coupling region is formed by a single-side-wall modulation waveguide grating and a tapered waveguide, the single-side-wall modulation waveguide grating is provided with a periodic rectangular grating ruler at one side adjacent to the tapered waveguide, and the width of the tapered waveguide is linearly changed along the length direction of the waveguide; the adjacent chirped grating auxiliary counter-couplers are connected by a straight waveguide and a curved waveguide. The invention can realize the filtering effect on the input optical signal, enables the light in the gating wavelength range to have the group delay amount which is linearly changed along with the wavelength, can provide high dispersion value under the compact chip size, and can be applied to the generation of dispersion compensation, optical cache, optical true delay network and integrated microwave photon signals.)

1. A cascaded chirped grating auxiliary reverse coupler type optical dispersion delay line is characterized by comprising SiO₂Cladding, SiO₂A waveguide layer which is horizontally arranged is arranged in the cladding layer and is prepared by adopting Si materials and comprises a plurality of transverse straight waveguides, a plurality of semi-annular waveguides and at least two sections of chirp grating auxiliary reverse couplers; the upper transverse straight waveguide on the left side serves as the input end of the whole structure, the lower transverse straight waveguide on the left side serves as the output end of the whole structure, the chirped grating auxiliary reverse coupler is gradually increased in the number of stages from top to bottom, the first-stage chirped grating auxiliary reverse coupler is arranged on the top, the reverse coupler is connected with the input end, the last-stage chirped grating auxiliary reverse coupler is arranged on the bottom, and the reverse coupler is connected with the output end.

2. The cascaded chirped grating auxiliary back coupler type optical dispersion delay line according to claim 1, wherein the chirped grating auxiliary back coupler is characterized in that a back coupling region is formed by a single-side wall modulation waveguide grating and a tapered waveguide, wherein the single-side wall modulation waveguide grating is formed by introducing periodic rectangular grating teeth into one side of a straight waveguide adjacent to the tapered waveguide, the longitudinal tooth width is modulated by an apodization function, the transverse grating period is kept unchanged, and the tapered waveguide width is linearly changed along the waveguide length direction; the left side of each section of chirped grating auxiliary reverse coupler is connected with two sections of transverse short straight waveguides to serve as an input end and an output end of the section, two ports have different waveguide widths, the right side is connected with two sections of straight waveguides to serve as transmission ends, and the semi-annular waveguides are used for connection between structures.

3. The cascaded chirped grating auxiliary counter-coupler type optical dispersion delay line according to claim 2, wherein at least two sections of chirped grating auxiliary counter-couplers are adopted, each chirped grating auxiliary counter-coupler is connected by a half-ring waveguide with the same bending radius and different waveguide widths in an interleaving cascading manner, and the length-width ratio of the whole structure is optimized by increasing the number of the chirped grating auxiliary counter-couplers used for cascading.

4. The cascaded chirped grating auxiliary back coupler type optical dispersion delay line according to claim 2, wherein adjacent chirped grating auxiliary back couplers are connected in an interleaving manner, and have opposite input and output ports, and the structures are inverted from top to bottom.

5. The cascaded chirped grating assisted back coupler type optical dispersive delay line according to claim 1, wherein the input end of the integral structure is connected with the tapered waveguide in the first stage chirped grating assisted back coupler.

6. The cascaded chirped grating-assisted back-coupler type optical dispersion delay line according to claim 2, wherein an average waveguide width of a single-sidewall modulation waveguide grating in the chirped grating-assisted back-coupler is kept constant in a back-coupling region.

7. The cascaded chirped grating auxiliary back coupler type optical dispersion delay line according to claim 2, wherein the width of the tapered waveguide in the chirped grating auxiliary back coupler is linearly changed from left to right in the transverse direction, the change trend determines the positive and negative of the dispersion value, and the widths of the left end and the right end of the tapered waveguide are both smaller than the average waveguide width of the single-side-wall modulation waveguide grating.

8. The cascaded chirped grating-assisted counter-coupler type optical dispersion delay line of claim 2, wherein the waveguide pitch between the single-side-wall modulation waveguide grating and the tapered waveguide is constant and is set to be about half of the width of the narrow waveguide, and the large waveguide pitch is used to further suppress the co-directional coupling between the waveguides.

9. The cascaded chirped grating auxiliary back coupler type optical dispersion delay line according to claim 2, wherein the longitudinal grating tooth width of the single-side wall modulation waveguide grating is weighted by a sine apodization function in the left part region of the back coupling region, and the rest grating tooth widths are fixed to the maximum tooth width of the apodization region.

Technical Field

The invention relates to a delay line, in particular to a cascaded chirped grating auxiliary reverse coupler type optical dispersion delay line, and belongs to the technical field of optical communication.

Background

With the rapid development of optical communication technology towards high speed and large capacity, the requirements on information transmission efficiency and accuracy are higher and higher, and the dispersion delay technology has become the key for improving the performance of an information system. The optical dispersion delay line can enable an output optical signal to have group delay amount changing along with wavelength, delay values and the wavelength generally accord with linear change relation, and the optical dispersion delay line can be applied to dispersion compensation, optical cache, optical true delay network, integrated microwave photon signal generation and the like. Common non-integrated optical dispersion delay lines mainly include optical fiber devices such as dispersion compensation optical fibers and chirped fiber gratings, and in order to provide a required high dispersion value, the length of such devices usually reaches more than several kilometers, which is not beneficial to miniaturization of a system, while dispersion delay lines based on an optical waveguide technology are generally concerned by students due to their high integration level and low loss characteristics.

Compared with the traditional optical material, the optical waveguide device prepared based on the Silicon On Insulator (SOI) material has the advantages of low transmission loss, good polarization characteristic, compatibility of the device process and the standard CMOS process, convenience in realizing photoelectric hybrid integration and the like; in particular, the large refractive index difference between the silica cladding and the silicon device layer enables the optical signal to be well confined in silicon, which is beneficial to further reducing the waveguide size and realizing large-scale integration.

According to different principles, the current integrated waveguide dispersive delay line schemes mainly include a micro-ring resonator type, a photonic crystal waveguide type and a bragg grating type. Among them, the micro-ring resonator and the photonic crystal waveguide are affected by the high insertion loss of the device itself, and are difficult to be practical in practical systems; the single waveguide Bragg chirp grating adopts a spiral on-chip layout, and can realize a larger group delay range and a high dispersion value in a very small device size, however, the reflection type dispersion delay line needs to adopt an independent circulator or design an on-chip Y branch to convert the reflection type dispersion delay line into a two-port device so as to separate out a reflection signal, the former increases the complexity of a system and is not beneficial to miniaturization, and the latter introduces extra 3dB insertion loss; the other dispersion delay line based on the grating auxiliary reverse coupler skillfully utilizes a double-waveguide structure, and replaces a single-waveguide reflection output mode by a reverse coupling mode, so that the separation problem of output signals is effectively solved, however, the requirement of large dispersion value inevitably requires the increase of the length of a reverse coupling area of a device, and the integration difficulty is greatly improved. On the premise of not increasing the complexity and the loss of a system, the design of an optical dispersion delay line with the smallest device size and the optimized length-width ratio has great practical significance.

Disclosure of Invention

The invention provides a cascaded chirped grating auxiliary counter-coupler type optical dispersion delay line aiming at the problems in the prior art, and the technical scheme provides an integrated dispersion compensation module for an optical communication system, and has larger dispersion value, more reasonable length-width ratio of the device and higher design flexibility than the existing two-port device; the method is also suitable for being used as a large-delay optical buffer, building an optical true delay network or providing an easily-integrated wavelength-time domain mapping component for the generation of integrated microwave photon signals.

In order to achieve the purpose, the technical scheme of the invention is as follows: a cascade chirp grating auxiliary reverse coupler type optical dispersion delay line comprises a SiO2 cladding, wherein a horizontally arranged waveguide layer is arranged in the SiO2 cladding, is prepared from a Si material and comprises a plurality of transverse straight waveguides, a plurality of semi-annular waveguides and at least two sections of chirp grating auxiliary reverse couplers; the upper transverse straight waveguide on the left side serves as the input end of the whole structure, the lower transverse straight waveguide on the left side serves as the output end of the whole structure, and the chirped grating auxiliary reverse couplers are gradually increased in series from top to bottom, wherein the first-stage chirped grating auxiliary reverse coupler on the top is connected with the input end, and the last-stage chirped grating auxiliary reverse coupler on the bottom is connected with the output end; the chirp grating auxiliary reverse coupler is a reverse coupling region formed by a single-side wall modulation waveguide grating and a tapered waveguide, wherein the single-side wall modulation waveguide grating is formed by introducing periodic rectangular grating teeth on one side of a straight waveguide adjacent to the tapered waveguide, the longitudinal tooth width is modulated by an apodization function, the transverse grating period is kept unchanged, and the width of the tapered waveguide is linearly changed along the length direction of the waveguide; the left side of each section of chirped grating auxiliary reverse coupler is connected with two sections of transverse short straight waveguides to serve as an input end and an output end of the section, two ports have different waveguide widths, the right side is connected with two sections of straight waveguides to serve as transmission ends, and the semi-annular waveguides are used for connection between structures. When the wavelength of an input optical signal meets a reverse coupling condition, reversely coupling the input end passing through each section of chirped grating auxiliary reverse coupler to the output end, and finally outputting the output end from the output port below the left side; because the chirped grating auxiliary reverse coupler has different reverse coupling wavelengths at different positions of the reverse coupling area, and the wavelengths approximately satisfy a linear variation relation from left to right along the transverse direction, the output optical signal has a group delay amount linearly varied along with the wavelengths, and the light with the wavelengths not satisfying the reverse coupling condition is output from the right transmission end.

As a preferred technical scheme of the invention: at least two sections of the chirped grating auxiliary reverse couplers are connected in a cascading mode, the length-width ratio of the whole structure is optimized by increasing the cascading quantity, the chip size is reduced, the sidelobe suppression ratio of an output spectrum is improved, and larger on-chip total group delay quantity and dispersion value can be obtained conveniently.

As a preferred technical scheme of the invention: the adjacent chirp grating auxiliary reverse couplers are connected in a staggered mode, namely the adjacent chirp grating auxiliary reverse couplers have opposite input and output ports, the structure is inverted up and down, so that the ports with the same waveguide width are connected with each other, and a tapered waveguide is not needed to be used for matching different waveguide widths, so that the on-chip loss is reduced.

As a preferred technical scheme of the invention: the input end of the integral structure is connected with the tapered waveguide in the first-stage chirped grating auxiliary reverse coupler so as to inhibit the reflected light intensity in a single waveguide caused by the periodic grating and increase the free spectral range of the integral structure.

As a preferred technical scheme of the invention: the widths of the left end and the right end of the tapered waveguide in the chirped grating auxiliary reverse coupler are smaller than the average waveguide width of the single-side-wall modulation waveguide grating, so that the homodromous coupling efficiency between the two waveguides is reduced, the resonance effect generated by the homodromous coupling efficiency is inhibited, and the power loss of the reverse coupling light is reduced.

As a preferred technical scheme of the invention: the waveguide distance between the single-side-wall modulation waveguide grating and the tapered waveguide is kept unchanged and is set to be about half of the width of the narrow waveguide, and the large waveguide distance is utilized to further inhibit the homodromous coupling between the waveguides.

As a preferred technical scheme of the invention: the longitudinal grating tooth width of the single-side-wall modulation waveguide grating is weighted by a sine apodization function in a left part area of the backward coupling area, and the tooth widths of other gratings are fixed as the maximum tooth width of the apodization area, so that the side lobe suppression ratio of an output spectrum is improved, and the group delay jitter is reduced.

Compared with the prior art, the invention has the advantages that 1) the technical scheme provides a cascade chirped grating auxiliary counter coupler type optical dispersion delay line, the on-chip length-width ratio of the long waveguide delay line is optimized through the staggered cascade multi-section chirped grating auxiliary counter coupler, group delay jitter is reduced by means of a partial apodization technology, output spectrum side lobes are inhibited, and the optical dispersion delay function with large dispersion value and high linearity is realized under the compact device size; 2) the invention does not need to adopt an independent circulator or convert the optical fiber into a two-port device by designing the on-chip Y branch, has lower insertion loss compared with reflection type dispersion delay lines such as single-waveguide spiral chirped gratings and the like, and is more suitable for the monolithic integration of a multifunctional optical module. The integrated large-dispersion-value delay chip has the main advantages that the characteristics of separation of input and output ports of a reverse coupler are inherited, the contradiction between long-wave conductance requirements and integrated chip space limitation of the large-dispersion delay chip is effectively relieved by properly increasing the cascade stage number, and the integrated large-dispersion-value delay chip can better adapt to the requirements of application fields of dispersion compensation, optical cache, optical true delay networks, integrated microwave photon signal generation and the like on the integrated large-dispersion-value chip; 3) the manufacturing process adopted by the invention is compatible with the COMS process, and has the potential characteristics and advantages of low transmission loss, good polarization characteristic and convenience for realizing hybrid integration of photoelectric devices.

Drawings

FIG. 1 is a schematic three-dimensional structure of the present invention.

Fig. 2 is a schematic top view of the waveguide of the present invention.

FIG. 3 is a diagram of the output signal spectrum of the output port when different cascade stages are used in the present invention.

FIG. 4 is a group delay spectrum of output signals from the output port when different cascade stages are used in the present invention.

The specific implementation mode is as follows:

for the purpose of enhancing an understanding of the present invention, the present embodiment will be described in detail below with reference to the accompanying drawings.

Example 1: referring to fig. 1, as shown in fig. 1 and fig. 2, the present invention designs a cascaded chirped grating auxiliary counter-coupler type optical dispersion delay line prepared based on SOI material, wherein a waveguide layer is embedded in SiO₂The strip Si waveguide in the cladding 6, fig. 1 and 2 show the case of using three-stage chirped grating to assist the staggered cascade connection of the back couplers, it should be noted that the cascade stage number can be adjusted according to the actual chip size and the required dispersion value. The waveguide layers under the condition of the three-level cascade comprise a first straight waveguide to a fourteenth straight waveguide 1-1 to 1-14, a first semi-annular waveguide 4-1, a second semi-annular waveguide 4-2, a first-level chirped grating auxiliary counter-coupler 5-1, a second-level chirped grating auxiliary counter-coupler 5-2 and a third-level chirped grating auxiliary counter-coupler 5-3. The left ends of the first straight waveguide 1-1 and the second straight waveguide 1-2 are respectively an input port (Inport) and an output port (Outport) of a dispersion delay line; the third straight waveguide 1-3, the sixth straight waveguide 1-6 and the seventh straight waveguide 1-7 are respectively connected with the left ends of the first tapered waveguide 2-1, the second tapered waveguide 2-2 and the third tapered waveguide 2-3, the fourth straight waveguide 1-4, the fifth straight waveguide 1-5 and the eighth straight waveguide 1-8 are respectively connected with the left ends of the first-stage single-side-wall modulation waveguide grating 3-1, the second-stage single-side-wall modulation waveguide grating 3-2 and the third-stage single-side-wall modulation waveguide grating 3-3, and the fourth, the fifth and the eighth straight waveguides 1-4, 1-5 and 1-8 have the same width and are the same as the first-stage and the second-stage straight waveguides 1-4, 1-5 and 1-8The average width of the third-stage single-side-wall modulation waveguide grating 3-1, 3-2 and 3-3 is the same, and the third-stage to eighth-stage straight waveguides 1-3 to 1-8 are used as buffer areas before the left input end and after the output end of the first-stage to third-stage chirped grating auxiliary backward couplers 5-1 to 5-3; and the ninth to fourteenth straight waveguides 1-9 to 1-14 are connected with the right ends of the first to third-stage chirped grating auxiliary counter couplers 5-1 to 5-3 to serve as transmission ends. The first tapered waveguide 2-1, the second tapered waveguide 2-2 and the third tapered waveguide 2-3 respectively form a first-stage chirped optical grating auxiliary counter-coupler 5-1, a second-stage chirped optical grating auxiliary counter-coupler 5-2 and a third-stage chirped optical grating auxiliary counter-coupler 5-3 with fixed intervals with a first-stage chirped optical grating 3-1, a second-stage chirped optical grating auxiliary counter-coupler 5-2 and a third-stage chirped optical grating auxiliary counter-coupler 5-3, wherein the upper sides of the first-stage chirped optical grating auxiliary counter-coupler 5-1 and the third-stage chirped optical grating auxiliary counter-coupler 5-3 are tapered waveguides, the lower sides of the first-stage chirped optical grating auxiliary counter-couplers 5-2 are single-side-wall modulated waveguide gratings, the second-stage chirped optical grating auxiliary counter-couplers 5-2 are opposite to form a staggered cascade framework, and the first semi-annular waveguide 4-1 and the second semi-annular waveguide 4-2 are used for connecting adjacent chirped optical grating auxiliary counter-couplers A device.

The principle of the invention for providing the dispersion delay function is as follows: when the wavelength of light incident into the back coupling region satisfies the local Bragg conditionWhen the light with the wavelength is transmitted, the light with the wavelength can be coupled into the output waveguide by the input waveguide of the chirped grating auxiliary counter-coupler, and the transmission direction of the output signal is opposite to the incident direction. Wherein λ is incident light wavelength, Λ is grating period, n_eff1For single-sidewall modulation of the average effective refractive index, n, of a waveguide grating within a grating period_eff2And (z) is the local effective refractive index of the tapered waveguide, wherein z represents a horizontal position coordinate at any position in the backward coupling area by taking the left end of the backward coupling area as an origin. As the effective refractive index of the waveguide basically conforms to the linear change relation with the width of the waveguide in a smaller change range, and the width of the tapered waveguide is linearly increased or decreased from left to right, the effective refractive index of the core region of the tapered waveguide is correspondingly increased or decreased from leftAnd linearly increasing or decreasing to the right, so that the wavelength of the back coupling light linearly changes along the horizontal direction of the chirp grating auxiliary back coupler, and the light with different wavelengths meeting the local Bragg condition is back coupled in different grating regions. Under the condition of three-level cascade, incident light with the wavelength meeting the local Bragg condition enters a straight waveguide from an Inport, sequentially passes through a first-level, a second-level and a third-level chirped grating auxiliary reverse couplers 5-1, 5-2 and 5-3, is reversely coupled to a first-level single-side-wall modulation waveguide grating 3-1, a second-level single-side-wall modulation waveguide grating 3-2 and a third-level single-side-wall modulation waveguide grating 3-3 serving as output waveguides through a first tapered waveguide 2-1, a second-level single-side-wall modulation waveguide grating 3-2 and a third-level single-side-wall modulation waveguide grating 3-3 serving as input waveguides of the reverse couplers at all levels, and is finally output from an Outport, and the group delay amount of output optical signals is in direct proportion to the length of the waveguides passing through, so that the group delay which linearly changes along with the wavelength is generated. Light having a wavelength that does not satisfy the local bragg condition due to the previous design and manufacturing errors will be output from the ninth to fourteenth straight waveguides 1-9 to 1-14 as the transmission ends.

In order to verify that the present invention can realize the function, a description will be given with specific reference to a verification example.

The verification example adopts a time domain finite difference method for calculation and analysis, and the main parameters used in simulation calculation comprise: the thickness of the Si waveguide layer is 220 nm; the widths of a first straight waveguide 1-1 and a second straight waveguide 1-2 which are used as an input end and an output end are 500 nm; the width of the tapered waveguide 2 in each stage of chirped grating auxiliary reverse coupler is linearly increased from 460nm to 500nm from left to right, the average waveguide width of the single-side wall modulation waveguide grating 3 is 580nm, the distance between the single-side wall modulation waveguide grating and the tapered waveguide is 248nm, the transverse period and the longitudinal maximum tooth width of the grating are 308nm and 104nm respectively, the period number is 1500, and the apodization region accounts for 1/3 of the length of the whole reverse coupler; the semi-annular waveguide 4 for connection has a bending radius of 20 nm; and the cascade stage number is respectively selected from one stage, two stages and three stages for simulation comparison.

Fig. 3 shows the spectral response of the output signal of the output port calculated by using different cascade stages, where the thick solid line, the thin solid line, and the dotted line are output spectral lines of Outport in the case of first-stage, second-stage, and third-stage cascade, respectively. It can be seen that, under three cascade stages, the central wavelength and the working bandwidth of the backward coupling spectrum are basically kept unchanged at 1554.5nm and 14nm, and as the cascade frequency increases, the sidelobe suppression ratio of the output signal gradually increases through multiple filtering of each stage of the chirped grating auxiliary backward coupler, and is respectively 6dB, 11dB and 39 dB. Because the first-stage grating auxiliary reverse coupler takes the tapered waveguide as the optical signal input end and no periodic grating is introduced on the two side walls of the input waveguide, the self-reflection light intensity possibly existing in the input waveguide can be well inhibited, and the transmission spectrum output by the ninth straight waveguide 1-9 (under the condition of three-stage cascade) which is taken as the upper side transmission end of the first-stage chirped grating auxiliary reverse coupler 5-1 has a larger free spectrum range, so the first-stage grating auxiliary reverse coupler also has application potential in a wavelength division multiplexing system.

Fig. 4 shows the efficacy of the present invention, in which the thick solid line, the thin solid line, and the dotted line are the group delay spectral lines of the output optical signal at the output port end under the first-stage, second-stage, and third-stage cascade conditions, respectively, the maximum group delay differences generated within the corresponding gating wavelength ranges are 9ps, 17.3ps, and 25.5ps, respectively, the dispersion values are 0.75ps/nm, 1.44ps/nm, and 2.13ps/nm, respectively, and increase substantially in proportion to the cascade stage number. It can be seen that, under the same device length, the cascaded chirped grating auxiliary reverse coupler can achieve a larger dispersion value than the single-stage chirped grating auxiliary reverse coupler; similarly, in order to reach a certain specific dispersion value, the length of a required device is effectively reduced by adopting a cascading mode, and the length-width ratio of the structure can be optimized by reasonably designing the cascading series of the dispersion delay line and the length of each stage of chirp grating auxiliary counter coupler, so that the size of the device is reduced.

In conclusion, the cascade chirped grating auxiliary reverse coupler type optical dispersion delay line provided by the invention can realize the filtering effect on an input optical signal, enables light in a gating wavelength range to have group delay amount linearly changed along with the wavelength, has higher side lobe suppression ratio and optimized length-width ratio of a device compared with a conventional single-stage grating auxiliary reverse coupler, can provide a high dispersion value under a compact chip size, and can be better applied to integrated dispersion compensation, optical cache, an optical true delay network and microwave photon signal generation; the device has the capability of inhibiting self-reflection light, so that the first-stage chirped grating auxiliary counter coupler has a larger free spectral range, and the device can be further expanded and applied to a wavelength division multiplexing communication system; meanwhile, the invention also has the potential characteristics and advantages of low transmission loss, good polarization characteristic, simple manufacture, compatibility with CMOS process and convenient realization of hybrid integration of photoelectric devices.

It should be noted that the above-mentioned embodiments are not intended to limit the scope of the present invention, and all equivalent modifications and substitutions based on the above-mentioned technical solutions are within the scope of the present invention as defined in the claims.