A silicon photonic chip end coupler and output control method thereof

Abstract

The present invention discloses a silicon photonic chip end coupler, comprising: an input unit, a transmission waveguide, an output waveguide, and a beam splitting module; the input unit comprises: two inverted tapered waveguides arranged in parallel and symmetrical to each other. The present invention also discloses an output control method for a silicon photonic chip end coupler, which is applied to the end coupler. The structural design of the present invention can effectively reduce the optical power density in the optical waveguide, which not only improves the upper limit of the input optical power of the end coupler, but also increases the alignment tolerance of the overall loss of the device, while simplifying the optical path, reducing costs, and improving system reliability. In the case that there is no obvious degradation in the overall insertion loss of the device, by controlling the distance Δx from the center line of the light source to the center line of the end coupler in the horizontal direction, the output port power division ratio can be controlled within a certain range, and when Δx changes, multi-channel balanced output can be achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of silicon photonic integrated chips, and in particular to a silicon photonic chip end face coupler and an output control method thereof. Background Art

[0002] The performance of the end coupler directly affects the coupling efficiency between the silicon photonic chip and the external light source. The silicon waveguide used in the current end coupler has a strong second-order nonlinear optical effect in the communication band. As the power of the incident light source increases, these nonlinear optical effects are enhanced, resulting in increased silicon waveguide loss and insertion loss degradation of the end coupler. If the input optical power is further increased, it may even cause irreversible damage to the silicon waveguide. Summary of the invention

[0003] In view of this, the present invention provides a silicon photonic chip end coupler and an output control method thereof to solve the technical problem that the current traditional end coupler has limited input light power, thereby limiting the application scenarios of silicon photonic chips.

[0004] In order to have a basic understanding of some aspects of the disclosed embodiments, a brief summary is given below. This summary is not intended to be a general review, nor is it intended to identify key / important components or to delineate the scope of protection of these embodiments. Its only purpose is to present some concepts in a simple form as a preface to the detailed description that follows.

[0005] The present invention adopts the following technical solution:

[0006] The present invention provides a silicon photonic chip end face coupler, comprising: an input unit for light source mode spot conversion, and the input unit comprises: two inverted tapered waveguides which are arranged in parallel and symmetrical to each other.

[0007] In one embodiment, the input unit further includes: two parallel front end waveguides; the front end waveguide is arranged at one end of the inverted tapered waveguide facing the light source.

[0008] In one embodiment, the input unit etches the substrate to form a deep trench.

[0009] In one embodiment, the tip width of the inverted tapered waveguide is 60-180 nm, and the distance between the tips of two inverted tapered waveguides matches the light source mode spot.

[0010] In one embodiment, the silicon photonic chip end face coupler further includes: a transmission waveguide and an output waveguide; the input unit is connected to the output waveguide via the transmission waveguide.

[0011] In one embodiment, the transmission waveguide is one or more of a straight waveguide, an S-bend waveguide, an Euler curve waveguide, and a circular arc curve waveguide.

[0012] In one embodiment, the silicon photonic chip end face coupler further includes: a beam splitting module, which splits the light output by the input unit into several beams and outputs the light through the output waveguide.

[0013] In one embodiment, the beam splitting module is composed of a plurality of power beam splitting units connected in multiple levels; the multiple levels of connection means that the input end of a power beam splitting unit at a higher level is connected to one of the output ends of a power beam splitting unit at a lower level through the transmission waveguide.

[0014] The present invention also provides an output control method for a silicon photonic chip end face coupler, which is applied to the silicon photonic chip end face coupler, and comprises:

[0015] The light source undergoes mode spot conversion through the input unit of the end coupler;

[0016] The power division ratio of the output port of the end coupler is adjusted by adjusting the distance from the center line of the light source to the center line of the end coupler in the horizontal direction, wherein the center line of the end coupler is the symmetry axis of the two inverted tapered waveguides in the input unit.

[0017] In one embodiment, the output control method of a silicon photonic chip end coupler further includes: when the distance from the center line of the light source to the center line of the end coupler in the horizontal direction is not 0, the accumulated phase difference transmitted on the two front end waveguides arranged at the front ends of the two inverted tapered waveguides satisfies an integer multiple of π / 2, so that the optical power output by each channel of the end coupler is equal; wherein the front end of the two inverted tapered waveguides refers to the end of the inverted tapered waveguide facing the light source.

[0018] The beneficial effects brought by the present invention are:

[0019] 1. The two inverted tapered waveguides that are arranged in parallel and symmetrically in the input unit perform light splitting, which effectively reduces the optical power density in the optical waveguide, not only improving the upper limit of the input optical power of the end coupler, but also increasing the alignment tolerance of the overall loss of the device;

[0020] 2. The beam splitting module is combined with the input unit structure design to achieve multi-port output while reducing the number of input light sources, which not only simplifies the optical path on the chip, reduces costs, but also improves system reliability;

[0021] 3. The structural design and device arrangement of the present invention significantly improve the performance of the end coupler, and the structure is simple. Based on the existing silicon photonic process platform, large-scale mass production can be achieved without introducing additional process steps;

[0022] 4. When the overall insertion loss of the device is not significantly degraded, the power division ratio of the output port can be controlled within a certain range by controlling the distance Δx from the center line of the light source to the center line of the end coupler in the horizontal direction;

[0023] 5. By designing the input unit, multi-channel balanced output can be achieved when Δx changes. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 It is a structural block diagram of a silicon photonic chip end face coupler with multiple output ports of the present invention;

[0026] Figure 2 It is a structural block diagram of a silicon photonic chip end face coupler with two output ports of the present invention;

[0027] Figure 3 It is a schematic diagram of the simulation of the light transmission mode field distribution of a silicon photonic chip end face coupler with two output ports of the present invention;

[0028] Figure 4 It is a structural block diagram of a silicon photonic chip end face coupler with four output ports of the present invention;

[0029] Figure 5 is a structural side view of the input unit of the present invention;

[0030] Figure 6 is a structural side view of the power beam splitting unit of the present invention;

[0031] Figure 7 is a schematic diagram of the simulation of the mode field distribution of the power beam splitting unit of the present invention;

[0032] Figure 8 The insertion loss of silicon photonic chip end couplers with different structures varies with the incident light power.

[0033] Fig. 9 is a schematic diagram of the distance Δx from the center line of the light source to the center line of the end face coupler in the horizontal direction when the light source is coupled to the input unit;

[0034] Fig.10 This is a graph showing the insertion loss of each of the two output ports and the total insertion loss of the device as a function of Δx in a silicon photonic chip end coupler with two output ports.

[0035] Fig.11 This is a schematic diagram of the positions of the front-end waveguide and the inverted tapered waveguide. DETAILED DESCRIPTION

[0036] The embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. It should be clear that the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] In some illustrative embodiments, Figure 1 , 2 As shown in Figure 4, the present invention provides a silicon photonic chip end coupler, including: an input unit 10, a transmission waveguide 30, an output waveguide 40, and a beam splitting module.

[0038] The light source 50 is converted into a mode spot through the input unit 10, and the light source is efficiently coupled to the end coupler, wherein the external light source can be directly output by the laser or output by the optical fiber connected to the laser. The input unit 10 includes: two inverted tapered waveguides 101 arranged in parallel and symmetrical to each other.

[0039] The inverted cone waveguide 101 is a gradually changing adiabatic inverted cone waveguide with an extremely narrow tip. The waveguide width at the tip of the inverted cone waveguide is determined by the light source mode spot size and process conditions, specifically 60-180nm, and the spacing between the tips of the two inverted cone waveguides matches the light source mode spot, thereby ensuring the coupling efficiency. When the input spot is large, such as single-mode fiber input (spot diameter is 10.4um), Figure 5 As shown, the substrate of the input unit 10 needs to be etched to form a deep groove 103 to prevent the optical power from leaking into the substrate and increasing the insertion loss of the end face coupler.

[0040] The intensity of silicon waveguide nonlinear absorption is determined by the nonlinear coefficient of the material and the optical power density. In this embodiment, the input unit 10 uses two parallel and mutually symmetrical inverted tapered waveguides 101. As the light is transmitted, the light source is divided into two parts and coupled to the two waveguides respectively, which reduces the optical power density in each waveguide, thereby reducing the nonlinear absorption intensity of the silicon waveguide. Compared with the traditional single-port output end coupler, the present invention can significantly improve the optical power tolerance of the end coupler. Figure 8 As shown, the solid line is the variation of the insertion loss IL of the traditional end face coupler with the incident light power, and the dotted line is the variation of the insertion loss IL of the end face coupler with two output ports of the present invention with the incident light power. Figure 8 It can be seen that the structural design of the present invention can keep the insertion loss unchanged when the incident light power increases to a larger value. Compared with the traditional end face coupler, the present invention has a higher light power tolerance.

[0041] Traditional end-face couplers usually have only one output port for one input port. For scenarios that require multi-channel output, one method is to add a beam splitter structure for beam splitting, which not only increases the complexity of the optical path, but also increases the chip area. The second method is to use a multi-channel end-face coupler to achieve N-port input and N-port output, but this method requires matching multiple light sources, which increases the complexity of the optical chip system, increases the cost of the entire optical module, reduces reliability, and cannot guarantee performance stability.

[0042] In order to solve the above technical problems, the present invention realizes multi-port output through structural design without increasing the number of light sources. In this embodiment, the input unit 10 uses two inverted tapered waveguides 101 arranged in parallel and symmetrical to each other. Therefore, the input unit 10 itself can realize a one-to-two beam splitting function. Figure 2 As shown, the input unit 10 is directly connected to the output waveguide 40 through the transmission waveguide 30 to form an end coupler of two output ports. The simulation schematic diagram of the mode field distribution of the end coupler of the two output ports is shown in FIG. Figure 3 shown.

[0043] like Fig. 9 As shown, when the implementation scheme is an end coupler with two output ports, by controlling the distance Δx from the center line of the light source to the center line of the end coupler in the horizontal direction, the power division ratio of the two ports can be controlled within a certain range without obvious degradation of the overall insertion loss of the device; wherein the center line of the end coupler is the symmetry axis of the two inverted tapered waveguides 101 in the input unit 10.

[0044] When the light source 50 is connected to the end coupler, when Δx changes, the insertion loss of the two output ports will change, but the overall loss of the device will not change much within a certain range, such as Fig.10 As shown in the figure, when Δx changes in the range of -1.5um to +1.5um, the overall insertion loss of the device changes by less than 0.5dB. However, for a traditional tip end coupler structure, a change in Δx in the range of -1.5um to +1.5um will cause a change of more than 1dB in the overall insertion loss of the device. Therefore, the input unit of the present invention not only improves the upper limit of the input optical power of the end coupler through the structural design of two inverted tapered waveguides arranged in parallel and symmetrical to each other, but also increases the alignment tolerance of the overall loss of the device.

[0045] Among them, Fig.10 In the figure, the two dotted lines are the curves of the insertion loss IL of the two output ports of the two output port end coupler changing with Δx, and the solid line is the curve of the total insertion loss IL of the device changing with Δx.

[0046] For a two-port end coupler with certain structural parameters, there is a specific Δx 0, so that the insertion loss of the two output ports is consistent, and thus the device output port achieves a 50:50 power split ratio. Ideally, Δx 0 When the center line of the light source is aligned with the center line of the end face of the end face coupler, 3dB light splitting is achieved. However, due to the manufacturing error of the actual process, Δx 0 May deviate from 0. When Δx is not equal to Δx 0 , the insertion losses of the two output ports are no longer equal, then the structural design of the present invention can achieve the change of the power division ratio of the two output ports of the device within a certain range by controlling the size of Δx.

[0047] When multi-channel output is required, the light output from the input unit 10 is divided into several beams by a beam splitting module and then outputted through an output waveguide 40. The beam splitting module is composed of several power beam splitting units 20 connected in multiple levels; wherein, the multi-level connection means that the input end of the power beam splitting unit 20 at a higher level is connected to one of the output ends of the power beam splitting unit 20 at a lower level through a transmission waveguide 30. Specifically, the power beam splitting unit 20 can be divided into several levels, and the function of the power beam splitting unit 20 at a higher level is to split the light beam outputted by the power beam splitting unit 20 at a lower level again, and finally form a multi-channel output.

[0048] The power beam splitting unit 20 at the lowest level is connected to the input unit 10 through the transmission waveguide 30; the power beam splitting unit 20 at the highest level is connected to the output waveguide 40 through the transmission waveguide 30. Figure 4 As shown, when the input unit 10 is connected to the transmission waveguide 30, the transmission waveguide 30 is respectively connected to two power beam splitting units 20, and each power beam splitting unit 20 is respectively connected to two output waveguides 40, a four-output port end coupler can be formed. Figure 1 As shown, by increasing the cascade number N (N is 0 or a positive integer) of the power beam splitting units 20, the end face coupler can have 2 (N+1) output ports.

[0049] When it is a silicon photonic chip end coupler with multiple output ports, the power division ratio of one output port and another output port of the device can also be changed within a certain range by controlling the size of Δx. The above is just an example of an end coupler with two output ports.

[0050] Through the above structural design, this embodiment realizes multi-port output while reducing the number of input light sources, which not only simplifies the optical path on the chip, reduces costs, but also improves the reliability of the chip system. In addition, the structural design and device arrangement of this embodiment can significantly improve the performance of the end coupler. At the same time, the structure is simple and based on the existing silicon photonic process platform, large-scale mass production can be achieved without introducing additional process steps.

[0051] The power beam splitting unit 20 realizes a one-to-two beam splitting function based on the principle of mode coupling. Figure 6 and Figure 7 As shown, the power beam splitting unit 20 adopts a completely symmetrical structure and is easy to manufacture. Compared with the commonly used multi-mode interferometer for beam splitting, it does not need to consider the phase matching problem and has a higher process tolerance.

[0052] The transmission waveguide 30 is one or more of a straight waveguide, an S-bend waveguide, an Euler curve waveguide, and an arc curve waveguide. That is, the transmission waveguide 30 is not limited to Figure 2 The shape shown can be a straight waveguide, an S-bend waveguide, an Euler curve waveguide, an arc curve waveguide, and various combinations thereof, as long as the single-mode transmission conditions and device arrangement requirements are met.

[0053] The input unit 10 can also be designed to achieve multi-channel balanced output when Δx changes. Fig.11 As shown, the input unit 10 also includes: two parallel front-end waveguides 102; the front-end waveguide 102 is arranged at the end of the inverted tapered waveguide 101 facing the light source 50. Compared with the input unit 10 mentioned above, by adding two mutually parallel and extremely narrow front-end waveguides 102 at the front end of the inverted tapered waveguide 101, the structure can achieve multi-channel balanced output under the change of Δx. When Δx=0, due to the symmetry of the structure, the device can achieve multi-channel balanced output; when Δx≠0, the light source 50 will excite two main modes at the end face of the front-end waveguide 102, which are symmetric mode and antisymmetric mode. When the cumulative phase difference of the two modes transmitted on the front-end waveguide 102 satisfies an integer multiple of π / 2, the output optical power of the output port is equal. That is, the effective refractive index neff of the two modes sys and neff asys The length L of the front waveguide 102 satisfies the following equation:

[0054]

[0055] The multi-output port end coupler of this embodiment can reduce the number of light sources, which is very meaningful for application scenarios that need to reduce the number of light sources and achieve multi-channel output. For example, in high-speed short-distance data center communication scenarios, 400G or even 800G intensity modulation / direct detection solutions are adopted, and laser arrays or hybrid integration of multiple light sources and silicon photonic chips are usually adopted to meet the multi-channel parallel requirements of the solution. However, if the end coupler of this embodiment is adopted, one light source can directly output multiple channels to meet multi-channel parallelism. On the one hand, it simplifies the optical path and improves the reliability of the chip system. On the other hand, it reduces the number of light sources, reduces costs, and simplifies the packaging of the overall module. For most of the current application scenarios, end couplers with two output ports and four output ports can meet most application scenarios.

[0056] Among them, the waveguides of all unit modules in this embodiment can be SOI waveguides, or they can be silicon nitride waveguides or waveguides made of other CMOS platform compatible materials. Compared with silicon waveguides, silicon nitride waveguides have smaller transmission loss, thermo-optical coefficient and nonlinear coefficient. The end coupler based on silicon nitride waveguide can achieve smaller transmission loss, higher temperature insensitivity and higher optical power tolerance. If silicon nitride waveguides are used, only an additional interlayer coupling structure needs to be added to couple the signal to the subsequent silicon waveguide, without any additional impact on the overall silicon photonic solution chip.

[0057] In some illustrative embodiments, the present invention further provides an output control method of a silicon photonic chip end coupler, which is applied to the above-mentioned silicon photonic chip end coupler, and the two are the same inventive concept, so the control method of this embodiment can be understood with reference to the implementation of the above-mentioned end coupler, and the control method includes:

[0058] The light source 50 is subjected to mode spot conversion through the input unit 10 of the end coupler;

[0059] The power division ratio of the output port of the end coupler is adjusted by adjusting the distance Δx from the center line of the light source to the center line of the end coupler in the horizontal direction, wherein the center line of the end coupler is the symmetry axis of the two inverted tapered waveguides 101 in the input unit 10 .

[0060] For the end coupler that determines the structural parameters, there is a specific Δx 0 , so that the insertion loss of each output port is consistent, thereby making the power split ratio of the device output port balanced. Ideally, Δx 0 When the center line of the light source is aligned with the center line of the end face of the end face coupler, 3dB light splitting is achieved. However, due to the manufacturing error of the actual process, Δx 0 May deviate from 0. When Δx is not equal to Δx 0 , the insertion loss of the output ports is no longer equal. The present invention controls the size of Δx so that the power division ratio of the device output port changes within a certain range.

[0061] The control method also includes: when Δx is not 0, the accumulated phase difference transmitted on the two front end waveguides 102 arranged at the front ends of the two inverted tapered waveguides 101 satisfies an integer multiple of π / 2, so that the optical power output by each channel of the end face coupler is equal; wherein the front end of the two inverted tapered waveguides 101 refers to the end of the inverted tapered waveguide 101 facing the light source 50.

[0062] By adding two mutually parallel and extremely narrow front waveguides 102 at the front end of the inverted tapered waveguide 101, balanced output of multiple channels is achieved under the change of Δx. When Δx=0, due to the symmetry of the structure, the device can achieve balanced output of multiple channels; when Δx≠0, the light source 50 will excite two main modes at the end face of the front waveguide 102, namely, the symmetric mode and the antisymmetric mode. When the accumulated phase difference of the two modes transmitted on the front waveguide 102 satisfies an integer multiple of π / 2, the output optical power of the output port is equal.

[0063] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A silicon photonic chip end coupler, characterized in that: The silicon photonic chip end face coupler comprises: An input unit for light source pattern spot conversion, wherein a substrate of the input unit is etched to form a deep groove, and the input unit comprises: Two inverted tapered waveguides arranged in parallel and symmetrical to each other, wherein the inverted tapered waveguide is a gradually varying adiabatic inverted tapered waveguide with an extremely narrow tip, the tip width of the inverted tapered waveguide is 60-180 nm, and the spacing between the tips of the two inverted tapered waveguides matches the light source mode spot; Two parallel front waveguides with extremely narrow width, wherein the front waveguide is arranged at one end of the inverted tapered waveguide facing the light source; A beam splitting module, which splits the light output by the input unit into several beams and outputs the beams through the output waveguide, and the beam splitting module is composed of several power beam splitting units connected in multiple stages; When the distance from the center line of the light source to the center line of the end coupler in the horizontal direction is not 0, the light source excites the symmetric mode and the antisymmetric mode at the end face of the front waveguide, and when the cumulative phase difference between the symmetric mode and the antisymmetric mode transmitted on the front waveguide satisfies an integer multiple of π / 2, so that the optical power output by each channel of the end coupler is equal, The effective refractive index neff of the symmetric mode and the antisymmetric mode sys and neff asys The length L of the front waveguide satisfies the following formula: 。 2. The silicon photonic chip end coupler according to claim 1, characterized in that: The center line of the end face coupler is the symmetry axis of the two inverted tapered waveguides in the input unit.

3. The silicon photonic chip end coupler according to claim 2, characterized in that: When the distance from the center line of the light source to the center line of the end face coupler in the horizontal direction changes within the range of -1.5 μm to 1.5 μm, the overall insertion loss of the silicon photonic chip end face coupler changes by less than 0.5 dB.

4. The silicon photonic chip end coupler according to claim 1, characterized in that: The silicon photonic chip end face coupler further includes: a transmission waveguide and an output waveguide; the input unit is connected to the output waveguide via the transmission waveguide.

5. The silicon photonic chip end coupler according to claim 4, characterized in that: The transmission waveguide is one or more of a straight waveguide, an S-bend waveguide, an Euler curve waveguide, and an arc curve waveguide.

6. The silicon photonic chip end coupler according to claim 4, characterized in that: The transmission waveguide is a SOI waveguide or a silicon nitride waveguide.

7. The silicon photonic chip end coupler according to claim 4, characterized in that: The output waveguide is a SOI waveguide or a silicon nitride waveguide.

8. The silicon photonic chip end coupler according to claim 1, characterized in that: The multi-level connection means that the input end of the power beam splitting unit at a high level is connected to one of the output ends of the power beam splitting unit at a low level through the transmission waveguide.

9. An output control method for a silicon photonic chip end coupler, applied to the silicon photonic chip end coupler according to any one of claims 1 to 8, characterized in that: The output control method comprises: The light source undergoes mode spot conversion through the input unit of the end coupler; The power division ratio of the output port of the end coupler is adjusted by adjusting the distance from the center line of the light source to the center line of the end coupler in the horizontal direction, wherein the center line of the end coupler is the symmetry axis of the two inverted tapered waveguides in the input unit.

10. The output control method of the silicon photonic chip end coupler according to claim 9, characterized in that: The output control method further comprises: when the distance from the center line of the light source to the center line of the end coupler in the horizontal direction is not 0, making the accumulated phase difference transmitted on the two front end waveguides arranged at the front ends of the two inverted tapered waveguides meet an integer multiple of π / 2, so that the optical power outputted by each channel of the end coupler is equal; The front ends of the two inverted tapered waveguides refer to the ends of the inverted tapered waveguides facing the light source.

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