TWI853339B - Coupled optical path structure and optical module - Google Patents

Abstract

The present invention relates to a coupled optical path structure and an optical module. The coupled optical path structure comprises the laser emission unit, the spatial coupling unit, and the optical chip. The laser emission unit is used to output the first horizontally polarized light. The spatial coupling unit is used to change the polarization state of the first horizontally polarized light and output the vertically polarized light. Along the propagation direction of the optical signal, the optical chip includes the spot size converter unit, the polarization rotation unit, and the optical processing unit. The spot size converter unit is used to change the spot size of the vertically polarized light and output the converted vertically polarized light. The polarization rotation unit is used to change the polarization state of the vertically polarized light and output the second horizontally polarized light. The optical processing unit is used to receive and process the second horizontally polarized light. Compared with the transmission of horizontally polarized light, the transmission of the vertically polarized light can greatly reduce the nonlinear loss caused by optical transmission in optical chips. And it can prevent problems such as heat accumulation and burnout of optical chips caused by nonlinear loss.

Description

Coupling optical path structure and optical module

The present invention relates to the field of semiconductor integrated circuit technology, and in particular to a coupled optical path structure and an optical module.

Silicon photonic chips can effectively reduce the cost and power consumption of modules in optical communications and are a key technology for achieving optical interconnection. The size of a typical single-mode silicon waveguide is 350 nm×155 nm, and the diameter of the optical mode field output by the laser is 2~4 μm. The mode fields between the two do not match, and the direct coupling alignment tolerance is small, but the loss is large. Therefore, in order to achieve a large alignment tolerance and low loss coupling between the two, it is necessary to increase the optical field of the laser and the optical field at the coupling point between the silicon photonic chip and the laser at the same time, generally to about 9 μm. The optical field expansion of the laser is generally achieved using a lens, and the optical field expansion at the coupling point of the silicon photonic chip is achieved by designing a mode converter.

In the prior art, the coupling optical path structure between the laser and the light emitting chip is shown in Figure 1. The laser 1 outputs horizontally polarized (TE) light, which passes through the lens 21, isolator 22 and wave plate 23. The light field is amplified, and the polarization state is still horizontal. Then it is coupled into the mode converter 31 of the light emitting chip, and then outputs horizontally polarized light through the silicon waveguide and integrated device. However, in actual applications, the light emitting chip needs to input a large optical power, and the mode converter of the silicon waveguide and the single-mode silicon waveguide will produce large nonlinear losses when transmitting horizontally polarized light under large optical powers. The heat accumulation caused by the nonlinear loss may even burn the chip.

The purpose of the present invention is to provide a coupled optical path structure and an optical module to reduce the nonlinear loss caused by optical transmission.

In order to achieve the above-mentioned invention purpose, the present invention provides a coupling optical path structure, the coupling optical path structure comprises a laser emitting unit, a spatial coupling unit and an optical chip; the laser emitting unit is used to output a first horizontal polarized light; the spatial coupling unit is arranged between the laser emitting unit and the optical chip, and is used to receive the first horizontal polarized light, and change the polarization state of the first horizontal polarized light to output vertically polarized light; the optical chip is sequentially connected along the propagation direction of the optical signal The invention comprises: a mode conversion unit, a polarization rotation unit and a light processing unit; the mode conversion unit is used to receive vertically polarized light, perform mode conversion on the vertically polarized light, and output the converted vertically polarized light; the polarization rotation unit is used to receive the converted vertically polarized light, change the polarization state of the vertically polarized light, and output a second-level polarized light; the light processing unit is used to receive the second-level polarized light and process the second-level polarized light.

As a further improvement of the present invention, the optical processing unit includes an optical power monitoring unit and an optical modulator, and the input ends of the optical power monitoring unit and the optical modulator are both connected to the output end of the polarization rotation unit.

As a further improvement of the present invention, the optical chip further includes a first beam splitting unit connected to the output end of the mode conversion unit for splitting the converted vertical polarized light into at least two paths for transmission to the polarization rotation unit.

As a further improvement of the present invention, the first beam splitting unit is a 3dB coupler, which divides the vertically polarized light after the conversion into two transmission paths, each of which is connected to a polarization rotation unit and an optical processing unit.

As a further improvement of the present invention, the aforementioned mode conversion unit is a double-tip mode converter, which is used to perform mode conversion on the aforementioned vertically polarized light and evenly output two paths of converted vertically polarized light, each of which is connected to a polarization rotation unit and an optical processing unit.

As a further improvement of the present invention, the aforementioned mode conversion unit is an inverted wedge structure.

As a further improvement of the present invention, the aforementioned mode conversion unit is a sub-wavelength structure.

As a further improvement of the present invention, the optical processing unit further includes a second beam splitting unit, which is a 3dB coupler that splits the second horizontal polarized light into two transmission paths, each of which is connected to an optical power monitoring unit and an optical modulator.

As a further improvement of the present invention, the aforementioned spatial coupling unit includes a lens, an isolator and a wave plate. The aforementioned lens is arranged close to the aforementioned laser emitting unit, and the aforementioned wave plate is arranged close to the aforementioned optical chip, and is used to convert the aforementioned first horizontal polarized light into vertically polarized light for output; the aforementioned isolator is arranged between the aforementioned lens and the aforementioned wave plate.

To achieve the aforementioned purpose, the present invention further provides an optical module, wherein the optical module has any one of the aforementioned coupling optical path structures.

Compared with the prior art, the optical chip in the coupled optical path structure of the present invention receives vertically polarized light at one end optically coupled with the output light of the laser source, and a polarization rotation unit is arranged in the optical chip to convert the received vertically polarized light into horizontally polarized light for output. Compared with the technical solution in the prior art that the optical chip receives and outputs horizontally polarized light, the mode conversion unit in the optical chip and the silicon waveguide for transmitting the optical signal can greatly reduce the nonlinear loss caused by optical transmission in the optical chip when the input optical power is relatively large by transmitting vertically polarized light rather than horizontally polarized light, thereby preventing problems such as heat accumulation and burning of the optical chip caused by nonlinear loss.

In order to make the purpose, technical solution and advantages of this application clearer, the technical solution of this application will be described clearly and completely in combination with the specific implementation methods of this application and the corresponding drawings. Obviously, the implementation methods described are only part of the implementation methods of this application, not all of the implementation methods. Based on the implementation methods in this application, all other implementation methods obtained by ordinary technicians in this field without creative labor are within the scope of protection of this application.

The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

In order to reduce the nonlinear loss caused by light transmission in the coupling optical path, the present invention provides the following five embodiments for specific description.

Embodiment 1

As shown in FIG. 2 , it is a schematic diagram of the coupling optical path structure in Embodiment 1 of the present invention. The coupling optical path structure includes a laser emitting unit 1, a spatial coupling unit 2 and an optical chip 3. The spatial coupling unit 2 is disposed between the laser emitting unit 1 and the optical chip 3.

The laser emitting unit 1 outputs a first horizontal polarized light with high power. In this embodiment, the laser emitting unit 1 uses a 1310 nm DFB laser. Of course, in other embodiments of the present invention, the laser emitting unit 1 can also use other lasers capable of outputting a first horizontal polarized light with high power.

The aforementioned spatial coupling unit 2 is used to receive the first horizontal polarized light output by the aforementioned laser emitting unit 1, expand the mode field diameter of the first horizontal polarized light output by the aforementioned laser emitting unit 1, and change the polarization state of the first horizontal polarized light output by the aforementioned laser emitting unit 1 to convert it into vertically polarized light.

Specifically, the spatial coupling unit 2 includes a lens 21, an isolator 22 and a wave plate 23. The lens 21 is arranged close to the laser emitting unit 1, and is used to expand the mode field diameter of the first horizontal polarized light output by the laser emitting unit 1. Here, it is a spherical glass lens. The wave plate 23 is arranged close to the optical chip 3. The first horizontal polarized light output by the laser emitting unit 1 can be converted into a vertically polarized light output by setting relevant parameters of the wave plate 23. The isolator 22 is arranged between the lens 21 and the wave plate 23.

The optical chip 3 is optically coupled with the spatial coupling unit 2 to receive the vertically polarized light output by the spatial coupling unit 2. Specifically, the optical chip 3 includes a mode conversion unit 31, a polarization rotation unit 32 and an optical processing unit 33 in sequence along the optical signal propagation direction.

The aforementioned mode conversion unit 31 is used to receive the vertically polarized light output by the aforementioned spatial coupling unit 2, perform mode conversion on the aforementioned vertically polarized light, and output the converted vertically polarized light. Since the optical chip 3 is coupled with a high-power light beam, the high-power light beam is vertically polarized light. Compared with horizontally polarized light, under the same optical power, the energy density of vertically polarized light is smaller, especially when the height of the silicon waveguide is low, for example, less than 200 nm, so that the nonlinear loss caused by the transmission of light on the mode conversion unit 31 and the silicon waveguide can be greatly reduced.

In one embodiment of the present invention, the aforementioned mode conversion unit 31 is a mode converter of an inverse wedge structure, which gradually reduces the width of the waveguide at one end for coupling the optical waveguide with the input light, so that the mode field originally confined in the waveguide leaks into the cladding, thereby expanding the mode field, achieving matching with the mode field of the output light of the spatial coupling unit 2, and reducing coupling loss.

In another embodiment of the present invention, the mode conversion unit 31 is a mode converter of a sub-wavelength grating structure. Similarly, the structure is used to expand the mode field diameter of the end that is optically coupled with the output light from the chip, to achieve matching with the mode field of the output light from the spatial coupling unit 2, and to reduce coupling loss. Compared with the mode converter of the reverse wedge structure, the mode converter of the sub-wavelength grating structure can expand the mode field to a greater extent, but it has high process requirements and is difficult to manufacture.

The polarization rotation unit 32 is used to receive the converted vertically polarized light, change the polarization state of the vertically polarized light, and output a second horizontally polarized light.

The optical processing unit 33 is used to receive the second horizontal polarized light, and process and output the second horizontal polarized light. Specifically, in this embodiment, the optical processing unit 33 includes an optical power monitoring unit 331 and an optical modulator 332. The input ends of the optical power monitoring unit 331 and the optical modulator 332 are both connected to the polarization rotation unit 32. The optical power monitoring unit 331 is used to monitor the optical power on the optical transmission path. The optical modulator 332 receives the second horizontal polarized light, and modulates and outputs the second horizontal polarized light.

Embodiment 2

As shown in FIG3 , it is a schematic diagram of the coupling optical path structure in Embodiment 2 of the present invention. Different from Embodiment 1, in this embodiment, the optical chip 3 further includes a first beam splitting unit 34. The input end of the first beam splitting unit 34 is connected to the output end of the mode conversion unit 31, and is used to split the vertically polarized light converted by the mode conversion unit 31 into at least two paths to the polarization rotation unit 32.

Specifically, the first beam splitting unit 34 is a 3dB coupler, which divides the converted vertical polarized light into two transmission paths. Each transmission path is connected to a polarization rotation unit 32 and an optical processing unit 33. The polarization rotation unit 32 receives 50% of the vertical polarized light with optical power split by the 3 dB coupler, and is used to change the polarization state of the 50% vertical polarized light with optical power, and outputs the horizontal polarized light with optical power of 50%. The optical processing unit 33 is connected to the output end of the polarization rotation unit 32, and specifically includes an optical power monitoring unit 331 and an optical modulator 332. The input ends of the optical power monitoring unit 331 and the optical modulator 332 are both connected to the polarization rotation unit 32. The optical modulator 332 receives the horizontal polarized light of 50% optical power and performs optical signal modulation and output on the horizontal polarized light of 50% optical power.

Of course, the aforementioned first beam splitter unit 34 can also be designed as a multi-way beam splitter structure, as long as the optical power of each transmission path meets the transmission requirements of the subsequent silicon-based optical devices.

Furthermore, in this embodiment, the input end of the optical power monitoring unit 331 can also be connected to an output end of the first beam splitting unit 34, the output end of the optical power monitoring unit 331 can be connected to the input end of the polarization rotation unit 32, and the input end of the optical modulator 332 can be connected to the output end of the polarization rotation unit 32. In this embodiment, the optical power on the optical transmission path is first monitored, and then the polarization state of the light is changed for output. The polarization rotation unit 32 changes the polarization state of the 50% vertical polarized light split by the first beam splitting unit 34, and outputs 50% horizontal polarized light. The optical modulator 332 receives the 50% horizontal polarized light, and modulates the 50% horizontal polarized light for output.

Furthermore, a combiner may be designed after the output end of the optical modulator 332 in this embodiment to combine the two optical transmission paths into one output, and the specific design may be based on actual needs.

Embodiment 3

As shown in FIG4 , it is a schematic diagram of the coupling optical path structure in Embodiment 3 of the present invention. Different from Embodiment 2, the aforementioned optical processing unit 33 further includes a second beam splitting unit 333, which is connected to the output end of the aforementioned polarization rotation unit 32, receives the horizontal polarized light of 50% optical power output by the aforementioned polarization rotation unit 32, and is used to split the horizontal polarized light of 50% optical power into at least two transmission paths, thereby further reducing the optical power on each optical transmission path.

Specifically, the second beam splitting unit 333 is a 3dB coupler, which divides the received 50% optical power horizontal polarized light into two transmission paths. Similarly, each optical transmission path is connected to an optical power monitoring unit 331 and an optical modulator 332. The optical modulator 332 receives the 25% optical power horizontal polarized light split by the second beam splitting unit 333, and modulates the 25% optical power horizontal polarized light into an optical signal for output.

Of course, the aforementioned second beam splitter unit 333 can also be designed as a multi-channel beam splitter structure, and it is only necessary to ensure that the optical power of each channel of transmission meets the transmission requirements of the subsequent silicon-based optical device.

Furthermore, a combiner can be designed after the output end of the optical modulator 332 in this embodiment to combine the two optical transmission paths into one output, which can be specifically designed according to actual needs.

Embodiment 4

As shown in FIG5 , it is a schematic diagram of the coupling optical path structure in Embodiment 4 of the present invention. Different from Embodiment 1, the aforementioned mode conversion unit 31 is a double-tip mode converter structure, which receives the vertically polarized light output by the spatial coupling unit 2 and performs mode conversion on the aforementioned vertically polarized light, which can greatly reduce the nonlinear loss caused by the light passing through the mode conversion unit 31. At the same time, the aforementioned double-tip mode converter can evenly output the two paths of converted vertically polarized light, further reducing the nonlinear loss caused by the light transmission on the silicon waveguide.

Specifically, each optical transmission path is connected to a polarization rotation unit 32 and an optical processing unit 33. The polarization rotation unit 32 receives 50% of the vertically polarized light of the optical power split by the double-tip mode converter, and is used to change the polarization state of the 50% of the vertically polarized light of the optical power, and outputs the horizontally polarized light of the 50% of the optical power. The optical processing unit 33 is connected to the output end of the polarization rotation unit 32, and specifically includes an optical power monitoring unit 331 and an optical modulator 332. Similarly, the input ends of the optical power monitoring unit 331 and the optical modulator 332 are both connected to the polarization rotation unit 32. The optical power monitoring unit 331 is used to monitor the optical power on the optical transmission path, and the optical modulator 332 receives the horizontal polarized light and performs optical signal modulation on the horizontal polarized light for output.

Furthermore, in this embodiment, the input end of the optical power monitoring unit 331 can also be connected to an output end of the mode conversion unit 31, the output end of the optical power monitoring unit 331 can be connected to the input end of the polarization rotation unit 32, and the input end of the optical modulator 332 can be connected to the output end of the polarization rotation unit 32. In this embodiment, the optical power on the optical transmission path is first monitored, and then the polarization state of the light is changed for output. The optical power monitoring unit 331 receives the vertically polarized light split by the mode conversion unit 31, and the polarization rotation unit 32 changes the polarization state of the vertically polarized light split by the mode conversion unit 31, and outputs horizontally polarized light. The optical modulator 332 receives the horizontally polarized light, and modulates the horizontally polarized light for output.

Furthermore, a combiner may be designed after the output end of the optical modulator 332 in this embodiment to combine the two optical transmission paths into one output, and the specific design may be based on actual needs.

Compared with Embodiment 2, Embodiment 4 can reduce the number of integrated devices on the optical chip and simplify the optical transmission path, and can further reduce the transmission loss of optical power and the nonlinear loss caused by optical transmission.

Embodiment 5

As shown in FIG6 , it is a schematic diagram of the coupling optical path structure in Embodiment 5 of the present invention. Different from Embodiment 4, the aforementioned optical processing unit 33 further includes a second beam splitting unit 333, which is connected to the output end of the aforementioned polarization rotation unit 32, receives the horizontal polarized light of 50% optical power output by the aforementioned polarization rotation unit 32, and is used to split the horizontal polarized light of 50% optical power into at least two transmission paths, further reducing the optical power on each optical transmission path, and reducing the nonlinear loss caused by the transmission of light on the silicon waveguide. Specifically, the aforementioned second beam splitting unit 333 is a 3 dB coupler, which evenly splits the received horizontal polarized light of 50% optical power into two transmission paths.

Of course, the aforementioned second beam splitter unit 333 can also be designed as a multi-way beam splitter structure, as long as the optical power of each transmission path meets the transmission requirements of the subsequent silicon-based optical devices.

Furthermore, a combiner may be designed after the output end of the optical modulator 332 in this embodiment to combine the two optical transmission paths into one output, and the specific design may be based on actual needs.

The present invention also provides an optical module, wherein the optical module has the coupling optical path structure described above in any one of the above embodiments.

In summary, the optical chip in the coupling optical path proposed by the present invention receives vertically polarized light at one end optically coupled with the output light of the laser source, and a polarization rotation unit is arranged in the optical chip to convert the received vertically polarized light into horizontally polarized light for output. Compared with the technical solution in the prior art that the optical chip is horizontally polarized light from reception to output, the mode conversion unit in the optical chip and the silicon waveguide for transmitting the optical signal are more efficient under the condition of large input optical power. In this case, the nonlinear loss caused by light transmission in the optical chip can be greatly reduced by transmitting with vertical polarized light rather than transmitting with horizontal polarized light; at the same time, by setting up the first beam splitting unit and the second beam splitting unit, the input light is evenly divided into at least two transmission paths, and the optical power on each optical transmission path is reduced, so as to further reduce the nonlinear loss caused by light transmission on the silicon waveguide, and prevent the accumulation of heat and burning of the optical chip caused by the nonlinear loss.

In the aforementioned embodiments, the description of each embodiment has its own emphasis. For parts not described in detail in a certain embodiment, reference can be made to the relevant description of other embodiments.

The above is a detailed introduction to the coupled optical path structure and optical module provided by the present application in combination with the embodiments. This article uses specific examples to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the technical solutions and core ideas of the present application. Ordinary technical personnel in this field should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some of the technical features therein with equivalents; and such modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

1: Laser emission unit 2: Spatial coupling unit 21: Lens 22: Isolator 23: Wave plate 3: Optical chip 31: Mode conversion unit 32: Polarization rotation unit 33: Optical processing unit 331: Optical power monitoring unit 332: Optical modulator 333: Second beam splitting unit 34: First beam splitting unit

Figure 1 is a schematic diagram of the coupling optical path structure in the prior art; Figure 2 is a schematic diagram of the coupling optical path structure in embodiment 1 of the present application; Figure 3 is a schematic diagram of the coupling optical path structure in embodiment 2 of the present application; Figure 4 is a schematic diagram of the coupling optical path structure in embodiment 3 of the present application; Figure 5 is a schematic diagram of the coupling optical path structure in embodiment 4 of the present application; Figure 6 is a schematic diagram of the coupling optical path structure in embodiment 5 of the present application.

1: Laser launch unit

2: Spatial coupling unit

21: Lens

22: Isolator

23: Wave plate

3: Optical chip

31: Mode conversion unit

32: Polarization rotation unit

33: Light processing unit

331: Optical power monitoring unit

332: Light modulator

Claims (10)

A coupled optical path structure, wherein the coupled optical path structure comprises a laser transmitting unit, a spatial coupling unit and an optical chip; the laser transmitting unit is used to output a first horizontal polarized light; the spatial coupling unit is arranged between the laser transmitting unit and the optical chip, and is used to receive the first horizontal polarized light, and change the polarization state of the first horizontal polarized light to output vertically polarized light; the optical chip comprises in sequence along the propagation direction of the optical signal: a mode conversion unit; ... The invention relates to a mode conversion unit, a polarization rotation unit and a light processing unit; the mode conversion unit is used to receive the vertically polarized light, perform mode conversion on the vertically polarized light, and output the converted vertically polarized light; the polarization rotation unit is used to receive the converted vertically polarized light, change the polarization state of the vertically polarized light, and output the second horizontal polarized light; the light processing unit is used to receive the second horizontal polarized light and process the second horizontal polarized light. As described in claim 1, the aforementioned coupled optical path structure, wherein the aforementioned optical processing unit includes an optical power monitoring unit and an optical modulator, and the input ends of the aforementioned optical power monitoring unit and the aforementioned optical modulator are both connected to the output end of the aforementioned polarization rotation unit. As described in claim 2, the optical chip further comprises a first beam splitting unit connected to the output end of the mode conversion unit for splitting the converted vertical polarized light into at least two paths for transmission to the polarization rotation unit. As in the coupling optical path structure mentioned in claim 3, the first beam splitting unit is a 3dB coupler, which divides the converted vertical polarized light into two transmission paths, each of which is connected to a polarization rotation unit and an optical processing unit. As described in claim 2, the coupled optical path structure, wherein the mode conversion unit is a double-tip mode converter for performing mode conversion on the vertically polarized light and evenly outputting two paths of converted vertically polarized light, each path being connected to a polarization rotation unit and an optical processing unit. As described in claim 5, the coupled optical path structure, wherein the aforementioned mode conversion unit is an inverted wedge structure. As described in claim 5, the coupled optical path structure, wherein the aforementioned mode conversion unit is a sub-wavelength structure. As in claim 4 or 5, the aforementioned coupled optical path structure, wherein the aforementioned optical processing unit further includes a second beam splitting unit, the aforementioned second beam splitting unit is a 3dB coupler, which divides the aforementioned second horizontal polarized light into two transmission paths, each path is connected to an optical power monitoring unit and an optical modulator. As described in claim 1, the aforementioned coupling optical path structure, wherein the aforementioned spatial coupling unit includes a lens, an isolator and a wave plate, the aforementioned lens is arranged close to the aforementioned laser emitting unit, and the aforementioned wave plate is arranged close to the aforementioned optical chip, and is used to convert the aforementioned first horizontal polarized light into vertically polarized light for output; the aforementioned isolator is arranged between the aforementioned lens and the aforementioned wave plate. An optical module, comprising a coupling optical path structure as described in any one of claims 1 to 9.