CN115639646A - A silicon optical chip end-face coupler and its output control method - Google Patents

Abstract

The invention discloses a silicon optical chip end face coupler, comprising: the device comprises an input unit, a transmission waveguide, an output waveguide and a beam splitting module; the input unit includes: two inverted cone waveguides which are arranged in parallel and are mutually symmetrical. The invention also discloses an output control method of the silicon optical chip end face coupler, which is applied to the end face coupler. The structural design of the invention can effectively reduce the optical power density in the optical waveguide, not only improves the upper limit of the input optical power bearing of the end face coupler, but also increases the alignment tolerance of the integral loss of the device, simplifies the optical path, reduces the cost and improves the reliability of the system. Under the condition that the whole insertion loss of the device is not obviously degraded, the control of the power division ratio of the output port changing within a certain range is realized by controlling the distance delta x from the central line of the light source to the central line of the end face coupler in the horizontal direction, and meanwhile, under the condition that the delta x is changed, multichannel balanced output is realized.

Description

A silicon optical chip end-face coupler and its output control method

technical field

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

Background technique

The performance of the end face coupler directly affects the coupling efficiency between the silicon photonics chip and the external light source. At present, the silicon waveguide used in the end-face coupler has strong second-order nonlinear optical effects in the communication band. As the power of the incident light source increases, these nonlinear optical effects increase, resulting in an increase in the loss of the silicon waveguide, causing end-face coupling. If the input optical power is further increased, it may even cause irreversible damage to the silicon waveguide.

Contents of the invention

In view of this, the present invention provides a silicon photonic chip end face coupler and its output control method to solve the technical problem that the current traditional end face coupler has limited input optical power, which further limits the application scenarios of silicon photonic chips.

In order to provide a basic understanding of some aspects of the disclosed embodiments, a brief summary is presented below. This summary is not an overview, nor is it intended to identify key/critical elements or delineate the scope of these embodiments. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is presented later.

The present invention adopts following technical scheme:

The present invention provides a silicon optical chip end-face coupler, comprising: an input unit used for light source mode spot conversion, and the input unit comprises: two inverted tapered waveguides arranged side by side and symmetrical to each other.

In an embodiment, the input unit further includes: two parallel front-end waveguides; the front-end waveguides are arranged at one end of the inverted tapered waveguide facing the light source.

In one embodiment, the input unit etches the substrate to form deep trenches.

In one embodiment, the width of the tips of the inverted tapered waveguides is 60-180 nm, and the distance between the tips of the two inverted tapered waveguides matches the pattern spot of the light source.

In an 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 through the transmission waveguide.

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

In an embodiment, the silicon photonic chip end-face coupler further includes: a beam splitting module, the beam splitting module divides the light output by the input unit into several beams and then outputs it through the output waveguide.

In one embodiment, the beam splitting module is composed of several power splitting units that are connected in multiple levels; One of the output ends of the power splitting unit is connected through the transmission waveguide.

The present invention also provides an output control method of a silicon photonic chip end-face coupler, which is applied to the silicon photonic chip end-face coupler, including:

The light source performs mode spot conversion through the input unit of the end face coupler;

By adjusting the distance from the centerline of the light source to the centerline of the end coupler in the horizontal direction, the power split ratio of the output port of the end coupler is adjusted, wherein the center line of the end coupler is the two inverted tapered waveguides in the input unit axis of symmetry.

In one embodiment, the method for controlling the output of a silicon photonic chip end-face coupler further includes: when the distance between the centerline of the light source and the centerline of the end-face coupler in the horizontal direction is not 0, setting the The cumulative phase difference transmitted on the two front-end waveguides at the front end 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 two inverted tapered The front end of the waveguide refers to the end of the inverted tapered waveguide facing the light source.

The beneficial effects brought by the present invention:

1. Two inverted tapered waveguides arranged side by side and symmetrical to each other in the input unit split the light, effectively reducing 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 overall loss of the device. alignment tolerance;

2. The beam splitting module combined with the structural design of the input unit realizes multi-port output on the premise of reducing the number of input light sources, which not only simplifies the optical path on the chip, reduces costs, but also improves system reliability;

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

4. In the case that the overall insertion loss of the device does not deteriorate significantly, by controlling the distance Δx from the centerline of the light source to the centerline of the end coupler in the horizontal direction, the control of the power split ratio of the output port within a certain range is realized;

5. By designing the input unit, multi-channel balanced output can be realized when Δx changes.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. Those skilled in the art can also obtain other drawings based on these drawings without creative work.

Fig. 1 is a structural block diagram of a silicon photonic chip end-face coupler with multiple output ports of the present invention;

Fig. 2 is a structural block diagram of a silicon photonic chip end-face coupler with two output ports of the present invention;

Fig. 3 is a schematic diagram of simulation of optical transmission mode field distribution of a silicon optical chip end-face coupler with two output ports of the present invention;

Fig. 4 is a structural block diagram of a silicon photonic chip end-face coupler with four output ports of the present invention;

Fig. 5 is a structural side view of the input unit of the present invention;

Fig. 6 is a structural side view of the power splitting unit of the present invention;

Fig. 7 is a schematic diagram of the mode field distribution simulation of the power beam splitting unit of the present invention;

Figure 8 shows the variation of insertion loss with incident optical power of silicon photonic chip end face couplers with different structures

Fig. 9 is a schematic diagram of the distance Δx from the centerline of the light source to the centerline of the end coupler in the horizontal direction when the light source is coupled to the input unit;

Figure 10 is a graph of the variation curve of the insertion loss of the two output ports and the total insertion loss of the device as a function of Δx in a silicon photonic chip end-face coupler with two output ports

Fig. 11 is a schematic diagram of the positions of the front-end waveguide and the inverted tapered waveguide.

Detailed ways

Embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings. It should be clear that the described embodiments are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

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

The light source 50 performs mode speckle conversion through the input unit 10, and efficiently couples the light source to the end face coupler, wherein the external light source can be directly output by the laser, or output by an optical fiber connected to the laser. The input unit 10 includes: two inverted tapered waveguides 101 arranged side by side and symmetrical to each other.

The inverted tapered waveguide 101 is specifically a slowly changing adiabatic inverted tapered waveguide with a very narrow tip. The width of the waveguide at the tip of the inverted tapered waveguide is determined by the size of the light source mode spot and the process conditions, specifically 60-180nm, and the two inverted tapered The pitch of the tip of the waveguide matches the mode spot of the light source, so as to ensure the coupling efficiency. When the input spot is large, such as single-mode fiber input (the spot diameter is 10.4um), as shown in FIG. bottom, increasing the insertion loss of the end face coupler.

The strength of the nonlinear absorption of the silicon waveguide is determined by the nonlinear coefficient of the material and the optical power density. In this embodiment, the input unit 10 adopts two inverted tapered waveguides 101 arranged side by side and symmetrical to each other. With the transmission of light, the light source is divided into two parts, which are respectively coupled into the two waveguides, reducing the light intensity in each waveguide. Power density, thereby reducing the nonlinear absorption intensity of the silicon waveguide. Compared with the traditional single-port output end-face coupler, the invention can significantly improve the withstand optical power of the end-face coupler. As shown in Figure 8, the solid line is the variation of insertion loss IL of the traditional end face coupler with the incident light power, and the dotted line is the change of the insertion loss IL of the two output port face coupler of the present invention with the change of the incident light power, as can be seen from Figure 8 It can be seen that the structural design of the present invention enables the insertion loss to remain unchanged when the incident optical power increases to a larger value, and the present invention has a higher optical power tolerance than the traditional end coupler.

Traditional end-face couplers often have only one output port for one input port. For scenarios that require multiple outputs, one of the ways is to add a beam splitter structure to split the beam, which not only increases the complexity of the optical path, but also increases the chip area. ; The second way is to use multi-channel end-face couplers to realize N-port input and N-port output, but this way needs to match multiple light sources, which increases the complexity of the optical chip system, also increases the cost of the entire optical module and reduces the reliability. performance, performance stability cannot be guaranteed.

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 adopts two inverted tapered waveguides 101 arranged side by side and symmetrical to each other. Therefore, the input unit 10 itself can realize the beam splitting function of splitting into two. At this time, as shown in FIG. 2, the input unit 10 is directly connected to the output waveguide 40 through the transmission waveguide 30 to form an end-face coupler with two output ports. The simulation diagram of the mode field distribution of the end-face coupler with two output ports is shown in FIG. 3 .

As shown in Figure 9, 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 overall insertion loss of the device does not deteriorate significantly. The power division ratio of the two ports is controlled within a certain range; wherein, the center line of the end face coupler is the symmetry axis of the two inverted tapered waveguides 101 in the input unit 10 .

When the light source 50 is connected with the end face coupler, when Δx changes, the respective insertion losses of the two output ports will change, but the overall loss of the device does not change much within a certain range, as shown in Figure 10, Δx is -1.5 um～+1.5um, the overall insertion loss of the device changes less than 0.5dB. However, in a traditional cutting-edge end-face coupler structure, the change of Δx in the range of -1.5um to +1.5um will cause the overall insertion loss of the device to change by more than 1dB. Therefore, the input unit of the present invention 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 through the structural design of two inverted tapered waveguides arranged in parallel and symmetrical to each other.

Among them, in Fig. 10, the two dotted lines are the variation curves of the insertion loss IL of the two output port end face couplers with Δx, respectively, and the solid line is the variation curve of the total insertion loss IL of the device with Δx.

For the end-face coupler with two output ports whose structural parameters are determined, there is a specific Δx ₀ that makes the insertion loss of the two output ports consistent, and then makes the output port of the device reach a power split ratio of 50:50. Ideally, Δx ₀ is 0, that is, when the centerline of the light source is aligned with the centerline of the end face coupler, 3dB light splitting is achieved. However, due to manufacturing errors in the actual process, Δx ₀ may deviate from 0. When Δx is not equal to Δx ₀ and the insertion losses of the two output ports are no longer equal, the structural design of the present invention can realize the power division ratio of the two output ports of the device to change within a certain range by controlling the size of Δx.

When multi-channel output is required, the light output by the input unit 10 is divided into several beams by the beam splitting module and then output through the output waveguide 40 . The beam splitting module is composed of several power splitting units 20 connected in multiple levels; wherein, the multi-level connection refers to the connection between the input end of the power splitting unit 20 at the high level and the power splitting unit 20 at the low level One of the outputs is connected via a transmission waveguide 30 . Specifically, the power beam splitting unit 20 can be divided into several stages, and the function of the higher order power beam splitting unit 20 is to split the beam output by the lower order power beam splitting unit 20 again, finally forming Multi-channel output.

Among them, the power splitting unit 20 at the lowest level is connected to the input unit 10 through the transmission waveguide 30 ; the power splitting unit 20 at the highest level is connected to the output waveguide 40 through the transmission waveguide 30 . As shown in FIG. 4 , when the input unit 10 is connected to the transmission waveguide 30, two power splitting units 20 are respectively connected after the transmission waveguide 30, and each power splitting unit 20 is respectively connected to two output waveguides 40 respectively, thus forming four End coupler for the output port. By analogy, as shown in FIG. 1 , increasing the cascade number N of power splitting units 20 (N is 0 or a positive integer) can realize that the end coupler has 2 (N+1) output ports.

When it is a silicon photonic chip end-face coupler with multiple output ports, the power division ratio of one part of the output port and the other part of the output port of the device can also be changed within a certain range by controlling the size of Δx. The above is only based on the end-face coupling of two output ports device as an example.

Through the above structural design, this embodiment realizes multi-port output on the premise of reducing the number of input light sources, which not only simplifies the optical path on the chip, reduces the cost, but also improves the reliability of the chip system. Moreover, the structural design and device arrangement of this embodiment can significantly improve the performance of the end face coupler, and at the same time, the structure is simple. Based on the existing silicon photonics process platform, mass production can be achieved without introducing additional process steps.

Among them, the power splitting unit 20 is based on the principle of mode coupling, and realizes the splitting function of splitting into two. As shown in FIG. 6 and FIG. 7, the power splitting unit 20 adopts a completely symmetrical structure, which is easy to manufacture. The multi-mode interferometer does beam splitting without considering the phase matching problem, and the process tolerance is higher.

Wherein, the transmission waveguide 30 is one or more of a straight waveguide, an S-curved waveguide, an Euler curve waveguide, and an arc curve waveguide, that is, the transmission waveguide 30 is not limited to the shape shown in FIG. S-bend waveguides, Euler curve waveguides, arc-curve waveguides and their various combinations only need to meet the single-mode transmission conditions and device layout requirements.

Wherein, by designing the input unit 10, multi-channel equalized output can be realized under the condition that Δx changes. As shown in FIG. 11 , the input unit 10 further includes: two parallel front-end waveguides 102 ; the front-end waveguides 102 are disposed at one end of the inverted tapered waveguide 101 facing the light source 50 . Compared with the input unit 10 mentioned above, by adding two 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 respectively, 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 powers of the output ports are equal. That is, the effective refractive indices neff _sys and neff _asys of the two modes and the length L of the front-end waveguide 102 satisfy the following formula:

The multi-output port end-face 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 multiple outputs. For example, in a high-speed short-distance data center communication scenario, a 400G or even 800G intensity modulation/direct detection scheme is used, usually using a laser array or a hybrid integration of multiple light sources and silicon photonic chips to meet the multi-channel parallel requirements of the scheme. However, if the end face coupler of this embodiment is used, one light source can directly output multiple channels to meet the requirements of multi-channel parallelism. On the one hand, the light path is simplified to improve the reliability of the chip system. On the other hand, the number of light sources is reduced, the cost is reduced, and the overall module is also simplified. package. For most of the current application scenarios, end couplers with two output ports and four output ports can meet most application scenarios.

Wherein, the waveguides of all unit modules in this embodiment may be SOI waveguides, silicon nitride waveguides or waveguides made of other CMOS platform compatible materials. Compared with silicon waveguides, silicon nitride waveguides have smaller transmission loss, thermo-optic coefficients and nonlinear coefficients, and end-face couplers based on silicon nitride waveguides can achieve smaller transmission losses, higher temperature insensitivity and more High withstand optical power. If a silicon nitride waveguide is used, only an additional interlayer coupling structure is needed to couple the signal to the subsequent silicon waveguide without any additional impact on the overall silicon photonics solution chip.

In some illustrative embodiments, the present invention also provides an output control method of a silicon-optical chip end-face coupler, which is applied to the above-mentioned silicon-optic chip end-face coupler, and the two are the same inventive concept, so reference can be made to the above-mentioned end-face coupler Implementation of the coupler Understanding the control method of this embodiment, the control method includes:

The light source 50 performs mode speckle conversion through the input unit 10 of the end face coupler;

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

For the end-face coupler whose structural parameters are determined, there is a specific Δx ₀ , so that the insertion loss of each output port is consistent, and then the output port of the device has a balanced power division ratio. Ideally, Δx ₀ is 0, that is, when the centerline of the light source is aligned with the centerline of the end face coupler, 3dB light splitting is achieved. However, due to manufacturing errors in the actual process, Δx ₀ may deviate from 0. When Δx is not equal to Δx ₀ , the insertion loss of the output port is no longer equal. The present invention makes the power division ratio of the output port of the device change within a certain range by controlling the size of Δx.

The control method further includes: when Δx is not 0, making the cumulative phase difference transmitted on the two front-end waveguides 102 arranged at the front ends of the two inverted tapered waveguides 101 satisfy an integer multiple of π/2, so that each of the end-face couplers The optical power output by the channels is equal; where, the front ends of the two inverted tapered waveguides 101 refer to the end of the inverted tapered waveguides 101 facing the light source 50 .

By adding two front-end waveguides 102 parallel to each other and extremely narrow in width at the front-end of the inverted tapered waveguide 101, the multi-channel balanced output under the change of Δx is realized. 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 respectively, 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 powers of the output ports are equal.

The above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Anyone skilled in the art can easily think of changes or substitutions within the technical scope disclosed in the present invention. All should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims (10)

1. A silicon photonic chip end-face coupler, characterized in that it comprises: an input unit for spot conversion of a light source, and the input unit comprises: two inverted tapered waveguides arranged side by side and symmetrical to each other. 2. A silicon photonic chip end-face coupler according to claim 1, wherein the input unit further comprises: two parallel front-end waveguides; the front-end waveguides are arranged on the face of the inverted tapered waveguide end of the light source. 3. A silicon photonic chip end face coupler according to claim 1 or 2, wherein the input unit etches the substrate to form a deep trench. 4. A silicon photonic chip end face coupler according to claim 3, characterized in that, the width of the tip of the inverted tapered waveguide is 60-180nm, and the distance between the tips of the two inverted tapered waveguides is equal to Light source pattern matching. 5. A silicon photonic chip end-face coupler according to claim 1 or 2, further comprising: a transmission waveguide and an output waveguide; the input unit is connected to the output waveguide through the transmission waveguide. 6. A silicon-optical chip end-face coupler according to claim 5, wherein the transmission waveguide is one or more of straight waveguide, S-bend waveguide, Euler curve waveguide, arc curve waveguide . 7. A silicon photonic chip end face coupler according to claim 5, further comprising: a beam splitting module, the beam splitting module divides the light output by the input unit into several beams and passes through the Output waveguide output. 8. A silicon photonic chip end-face coupler according to claim 7, wherein the beam splitting module is composed of several power splitting units connected in multiple stages; The multi-level connection means that the input end of the high-level power splitting unit is connected to one of the output ends of the low-level power splitting unit through the transmission waveguide. 9. An output control method of a silicon photonic chip end face coupler, which is applied to the silicon photonic chip end face coupler according to claims 1-8, characterized in that it comprises: The light source performs mode spot conversion through the input unit of the end face coupler; By adjusting the distance from the centerline of the light source to the centerline of the end coupler in the horizontal direction, the power split ratio of the output port of the end coupler is adjusted, wherein the center line of the end coupler is the two inverted tapered waveguides in the input unit axis of symmetry. 10. The output control method of a silicon photonic chip end-face coupler according to claim 9, further comprising: when the distance from the centerline of the light source to the centerline of the end-face coupler in the horizontal direction is not 0, set The cumulative 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-face coupler is equal; Wherein, 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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