CN116124291B - Polarization measurement system and polarization measurement method based on silicon optical chip - Google Patents
Polarization measurement system and polarization measurement method based on silicon optical chip Download PDFInfo
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- 230000003287 optical effect Effects 0.000 title claims abstract description 151
- 230000010287 polarization Effects 0.000 title claims abstract description 92
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 title claims abstract description 45
- 229910052710 silicon Inorganic materials 0.000 title claims abstract description 45
- 239000010703 silicon Substances 0.000 title claims abstract description 45
- 238000005259 measurement Methods 0.000 title claims abstract description 43
- 238000000691 measurement method Methods 0.000 title claims abstract description 9
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims abstract description 70
- 239000000377 silicon dioxide Substances 0.000 claims abstract description 35
- 235000012239 silicon dioxide Nutrition 0.000 claims abstract description 26
- 239000000758 substrate Substances 0.000 claims abstract description 11
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- GQYHUHYESMUTHG-UHFFFAOYSA-N lithium niobate Chemical compound [Li+].[O-][Nb](=O)=O GQYHUHYESMUTHG-UHFFFAOYSA-N 0.000 description 3
- 239000000463 material Substances 0.000 description 3
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- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J4/00—Measuring polarisation of light
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Abstract
The invention discloses a polarization measurement system and a polarization measurement method based on a silicon optical chip, wherein the polarization measurement system comprises: silicon photochip and photodetector. The silicon optical chip includes: a silicon substrate; a silicon dioxide layer formed on the silicon substrate; a two-dimensional grating coupler formed on the silicon dioxide layer; a first phase modulation device formed on the silicon dioxide layer; a first multimode interferometer formed on the silicon dioxide layer; a second phase modulation device formed on the silicon dioxide layer; a second multimode interferometer formed on the silicon dioxide layer; and the one-dimensional grating coupler is formed on the silicon dioxide layer. The silicon optical chip is used for converting an input target optical signal into a polarized optical signal; and the photoelectric detector is used for measuring the polarization state of the output optical signal. The polarization measurement system based on the silicon optical chip disclosed by the invention improves the polarization state measurement rate and simultaneously ensures that the optical element has higher integration level.
Description
Technical Field
The invention relates to the field of integrated optics, in particular to a polarization measurement system based on a silicon optical chip and a polarization measurement method thereof.
Background
Polarization state is one of important properties of light, and a polarization state measuring instrument is also an important instrument required in the fields of optical sensing, light field regulation, laser communication, quantum key distribution and the like. In a coherent optical communication system and a polarization coding quantum key distribution system, the polarization state change introduced by a channel needs to be measured in real time; in fiber optic sensing systems, external shock events are detected by measuring changes in polarization state.
Most polarization measurement devices today typically use a polarizer and a wave plate to achieve polarization state measurement. A wave plate is an optical device that uses birefringence of a crystal to introduce a phase difference between the fast axis and the slow axis. The half-wave plate and the quarter-wave plate may introduce pi/2 and pi/4 phase differences between the fast axis and the slow axis, respectively. The polarizing plate is used for generating linearly polarized light and analyzing polarization. The polarization state of any light can be measured using a combination of wave plates and polarizers. Current commercial polarization measurement devices can be generally divided into two categories: one type consists of a rotating quarter wave plate, a fixed polarizer and a detector; the other type consists of a plurality of beam splitters, polarizers, waveplates and detectors. Among them, the first type of devices are relatively few, and the sampling rate is generally around several hundred Hz due to the limitation of the mechanical rotation structure; the second type of device adopts a beam splitter to divide a light beam to be measured into a plurality of beams to respectively measure each polarization component, the sampling rate can reach the MHz level generally, but the device is larger because of more equipment. In addition, the integrated polarization measuring device based on the lithium niobate thin film greatly reduces the equipment volume through the thin film lithium niobate process, but the preparation process of the lithium niobate thin film is complex, has higher cost and cannot be compatible with the existing CMOS process, so that the large-scale production cannot be realized at present.
Disclosure of Invention
In view of the above, the present invention provides a polarization measurement system based on a silicon optical chip, in which a plurality of grating couplers, a plurality of phase modulation devices, a plurality of multimode interferometers, and other structures are integrated on the same chip through a silicon optical integrated chip process.
To achieve the above object, a first aspect of the present invention discloses a polarization measurement system based on a silicon optical chip, comprising:
a silicon photodie, comprising:
a silicon substrate;
a silicon dioxide layer formed on the silicon substrate;
a two-dimensional grating coupler formed on the silica layer and adapted to divide a received target optical signal into a first polarized optical signal and a second polarized optical signal having a polarization direction perpendicular to the first polarized optical signal;
a first phase modulation device formed on the silica layer and adapted to modulate the first polarized light signal to obtain a modulated polarized light signal, the modulated polarized light signal and the second polarized light signal having a first phase difference;
a first multimode interferometer, formed on the silica layer, adapted to interfere the modulated polarized light signal with the second polarized light signal to obtain a first interference light signal, and to divide the first interference light signal into a first sub-interference light signal and a second sub-interference light signal;
a second phase modulation device formed on the silicon dioxide layer and adapted to modulate the first sub-interference optical signal to obtain a modulated interference optical signal, wherein the modulated interference optical signal has a second phase difference from the second sub-interference optical signal;
a second multimode interferometer, formed on the silicon dioxide layer, adapted to interfere the modulated interference optical signal with the second sub-interference optical signal, to obtain a second interference optical signal; and
a one-dimensional grating coupler formed on the silica layer and adapted to transmit the second interference optical signal to an output optical fiber; and
the photoelectric detector is suitable for detecting the second interference optical signal to obtain a detection electric signal, and the detection electric signal is suitable for obtaining the polarization state of the target optical signal.
According to an embodiment of the present invention, the detecting the polarization state of the electrical signal suitable for obtaining the target optical signal includes obtaining the polarization state of the target optical signal using the following formula:
wherein,,I 1 、I 2 、I 3 、I 4 a detection electric signal obtained by four times of detection for the photoelectric detector,
、/>
、/>
、
a stokes parameter for a target optical signal suitable for characterizing a polarization state of the target optical signal;θ 1 is the sum ofI 1 A first phase difference between the modulated polarized light signal and the second polarized light signal,θ 2 Is the sum ofI 2 A first phase difference between the corresponding modulated polarized light signal and the second polarized light signal,θ 3 is the sum ofI 3 A first phase difference between the corresponding modulated polarized light signal and the second polarized light signal,θ 4 is the sum ofI 4 A first phase difference between the corresponding modulated polarized light signal and the second polarized light signal,/and>
is the sum ofI 1 A second phase difference between the corresponding modulated interference light signal and the second sub-interference light signal,/or->
Is the sum ofI 2 A second phase difference between the corresponding modulated interference light signal and the second sub-interference light signal,/or->
Is the sum ofI 3 A second phase difference between the corresponding modulated interference light signal and the second sub-interference light signal,/or->
Is the sum ofI 4 And a second phase difference between the corresponding modulated interference optical signal and the second sub-interference optical signal.
According to an embodiment of the present invention, the first phase modulation device includes a first carrier depletion modulator and a second carrier depletion modulator that are disposed in parallel, and the first carrier depletion modulator, the second carrier depletion modulator, and the first multimode interferometer form a first mach-zehnder interferometer structure having an equal arm length;
the first carrier depletion modulator is adapted to modulate the first polarized light signal to obtain the modulated polarized light signal.
According to an embodiment of the present invention, the second phase modulation device includes a third carrier depletion modulator and a fourth carrier depletion modulator that are disposed in parallel, and the third carrier depletion modulator, the fourth carrier depletion modulator, and the second multimode interferometer form a second mach-zehnder interferometer structure having an equal arm length;
the third carrier depletion modulator is adapted to modulate the first sub-interference optical signal to obtain the modulated interference optical signal.
According to an embodiment of the present invention, the first carrier-depleted modulator, the second carrier-depleted modulator, the third carrier-depleted modulator, and the fourth carrier-depleted modulator have the same modulator structure;
the modulator structure includes: the P-type doped region and the N-type doped region are in butt joint to form a ridge structure.
According to an embodiment of the present invention, waveguides are used for communication between the two-dimensional grating coupler and the first phase modulation device, between the first phase modulation device and the first multimode interferometer, between the first multimode interferometer and the second phase modulation device, and between the second phase modulation device and the second multimode interferometer.
According to an embodiment of the present invention, the polarization measurement system further includes:
a driving module adapted to drive the first phase modulation device, the second phase modulation device, and the photodetector;
and the input optical fiber is suitable for inputting the target optical signal into the two-dimensional grating coupler.
According to an embodiment of the present invention, the first multimode interferometer and the second multimode interferometer structure have the same interferometer structure, the interferometer structure comprising:
the section of the mode field interference area is rectangular;
the mode spot conversion area is positioned at two opposite ends of the mode field interference area.
According to an embodiment of the present invention, the first multimode interferometer has a spectral ratio of 50:50, the second multimode interferometer has a spectral ratio of 50:50.
the second aspect of the present invention discloses a polarization measurement method for measurement by using the above polarization measurement system, comprising:
step A: dividing a received target optical signal into a first polarized optical signal and a second polarized optical signal with a polarization direction perpendicular to the first polarized optical signal by using a two-dimensional grating coupler;
and (B) step (B): receiving the first polarized light signal and the second polarized light signal by using a first phase modulation device, and modulating the first polarized light signal to obtain a modulated polarized light signal; wherein the modulated polarized light signal and the second polarized light signal have a first phase difference;
step C: utilizing a first multimode interferometer to make the modulated polarized light signal and the second polarized light signal interfere to obtain a first interference light signal, and dividing the interference light signal into a first sub-interference light signal and a second sub-interference light signal;
step D: receiving the first sub-interference optical signal and the second sub-interference optical signal by using a second phase modulation device, and modulating the first sub-interference optical signal to obtain a modulated interference optical signal, wherein the modulated interference optical signal has a second phase difference with the second sub-interference optical signal;
step E: utilizing a second multimode interferometer to interfere the modulated interference light signal and the second sub-interference light signal to obtain a second interference light signal;
step F: transmitting the second interference optical signal to an output optical fiber by using a one-dimensional grating coupler;
step G: detecting the second interference light signal by using a photoelectric detector;
step H: repeating the steps A-G at least four times to obtain at least four detected detection electric signals, wherein the detection electric signals are suitable for obtaining the polarization state of the target optical signals.
According to the embodiment of the invention, a silicon optical chip is formed by integrating a plurality of grating couplers, a plurality of phase modulation devices, a plurality of multimode interferometers and the like, so that a silicon optical chip type polarization measurement system with small volume and high integration level is obtained; and by introducing a plurality of carrier depletion modulators with GHz-order bandwidth, the polarization state measurement of hundred MHz sampling rate is further realized, and the technical defect of a polarization measuring instrument for measuring the polarization state by adopting a thermal effect in the existing silicon light polarization measuring technology is overcome.
Drawings
FIG. 1 is a schematic diagram of a silicon-based optical chip polarization measurement system provided by an embodiment of the present invention;
FIG. 2 is a cross-sectional view of a modulator structure provided by an embodiment of the present invention;
FIG. 3 is a top view of an interferometer structure provided by an embodiment of the present invention;
fig. 4 is a cross-sectional view of a waveguide provided by an embodiment of the present invention.
Reference numerals illustrate:
1: a silicon optical chip;
11: a two-dimensional grating coupler;
12: a first phase modulation device;
121: a first carrier depletion modulator;
122: a second carrier depletion modulator;
13: a first multimode interferometer;
14: a second phase modulation device;
141: a third carrier depletion modulator;
142: a fourth carrier depletion modulator;
15: a second multimode interferometer;
16: a one-dimensional grating coupler;
17: a silicon substrate;
18: a silicon dioxide layer;
19: a waveguide;
2: a photodetector;
3: a driving module;
4: an input optical fiber;
5: a modulator structure;
51: a P-type doped region;
52: an N-type doped region;
53: a P electrode;
54: an N electrode;
6: an interferometer structure;
61: a mode field interference region;
62: a spot-converting region;
7: and outputting an optical fiber.
Detailed Description
The present invention will be further described in detail below with reference to specific embodiments and with reference to the accompanying drawings, in order to make the objects, technical solutions and advantages of the present invention more apparent.
The invention provides a polarization measurement system and a polarization measurement method based on a silicon optical chip, which integrate a plurality of grating couplers, a plurality of phase modulation devices, a plurality of multimode interferometers and other structures on the same chip through a silicon optical integrated chip process so as to overcome the technical defect of a polarization measurement instrument for measuring the polarization state by adopting a thermal effect in the prior art.
Fig. 1 is a schematic diagram of a polarization measurement system based on a silicon optical chip according to an embodiment of the present invention.
According to an exemplary embodiment of the present invention, the present invention discloses a polarization measurement system based on a silicon optical chip 1, referring to fig. 1, comprising: a silicon photo chip 1 and a photodetector 2. The silicon optical chip 1 includes: a silicon substrate (not shown), a silicon dioxide layer (not shown), a two-dimensional grating coupler 11, a first phase modulation device 12, a first multimode interferometer 13, a second phase modulation device 14, a second multimode interferometer 15, and a one-dimensional grating coupler 16. A silicon dioxide layer (not shown) is formed on the silicon substrate. A two-dimensional grating coupler 11 formed on the silica layer, adapted to receive the target optical signal from the input optical fiber 4 and split into a first polarized optical signal and a second polarized optical signal having a polarization direction perpendicular to the first polarized optical signal. The first phase modulation device 12 is formed on the silica layer, and is adapted to modulate the first polarized light signal to obtain a modulated polarized light signal, and the modulated polarized light signal and the second polarized light signal have a first phase difference. A first multimode interferometer 13 formed on the silica layer, adapted to interfere the modulated polarized light signal with the second polarized light signal to obtain a first interference light signal, and to divide the first interference light signal into a first sub-interference light signal and a second sub-interference light signal. And a second phase modulation device 14 formed on the silicon dioxide layer and adapted to modulate the first sub-interference optical signal to obtain a modulated interference optical signal, wherein the modulated interference optical signal has a second phase difference from the second sub-interference optical signal. And a second multimode interferometer 15 formed on the silicon dioxide layer and adapted to interfere the modulated interference light signal with the second sub-interference light signal to obtain a second interference light signal. A one-dimensional grating coupler 16, formed on the silica layer, is adapted to transmit the second interference optical signal to the output optical fiber 7. The photodetector 2 is adapted to detect the second interference light signal to obtain the polarization state of the target light signal.
According to an embodiment of the invention, the input fiber 4 is connected to the input of a two-dimensional grating coupler 11; the output end of the two-dimensional grating coupler 11 is connected with the input end of the first phase modulation device 12; the output end of the first phase modulation device 12 is connected with the input end of the first multimode interferometer 13; the output end of the first multimode interferometer 13 is connected with the input end of the second phase modulation device 14; the output end of the second phase modulation device 14 is connected with the input end of the second multimode interferometer 15; the output end of the second multimode interferometer 15 is connected with the input end of the one-dimensional grating coupler 16; and the output end of the one-dimensional grating coupler 16 is connected with the input end of the photoelectric detector 2 through the output optical fiber 7.
According to an embodiment of the present invention, the two-dimensional grating coupler 11 and the first phase modulation device 12, the first phase modulation device 12 and the first multimode interferometer 13, the first multimode interferometer 13 and the second phase modulation device 14, the second phase modulation device 14 and the second multimode interferometer 15, the second multimode interferometer 15 and the one-dimensional grating coupler 16 are all communicated by using a waveguide 19.
According to an embodiment of the invention, the first polarized light signal and the second polarized light signal are coupled into a waveguide 19, and transmitted through the waveguide 19 into the first phase modulation means 12.
The invention provides a polarization measurement system and a polarization measurement method based on a silicon optical chip, which integrate a plurality of grating couplers, a plurality of phase modulation devices, a plurality of multimode interferometers and other structures on the same chip through a silicon optical integrated chip process so as to overcome the technical defect of a polarization measurement instrument for measuring the polarization state by adopting a thermal effect in the prior art.
According to an embodiment of the invention the phase modulation means comprise a first phase modulation means 12 and a second phase modulation means 14.
According to an embodiment of the present invention, the first phase modulation device 12 includes a first carrier-depleted modulator 121 and a second carrier-depleted modulator 122 arranged in parallel, and the first carrier-depleted modulator 121, the second carrier-depleted modulator 122, and the first multimode interferometer 13 constitute a first mach-zehnder interferometer structure having equal arm lengths; the first carrier depletion modulator 121 is adapted to modulate the first polarized light signal to obtain a modulated polarized light signal.
According to an embodiment of the present invention, the second phase modulation device 14 includes a third carrier-depleted modulator 141 and a fourth carrier-depleted modulator 142 arranged in parallel, and the third carrier-depleted modulator 141, the fourth carrier-depleted modulator 142 and the second multimode interferometer 15 constitute a second mach-zehnder interferometer structure having equal arm lengths; the third carrier depletion modulator 141 is adapted to modulate the first sub-interference optical signal to obtain a modulated interference optical signal.
According to an embodiment of the present invention, the first mach-zehnder interferometer structure and the second mach-zehnder interferometer structure are identical. The first Mach-Zehnder interferometer structure and the second Mach-Zehnder interferometer are arranged in an equal-arm-length structure, so that the filtering effect of optical signals can be avoided, the wavelength selectivity of the input optical signals is reduced, and the application range of the input optical signals is enlarged.
According to an embodiment of the present invention, the first carrier-depleted modulator 121, the second carrier-depleted modulator 122, the third carrier-depleted modulator 141, and the fourth carrier-depleted modulator 142 have the same modulator structure.
Fig. 2 is a cross-sectional view of a modulator structure provided by an embodiment of the present invention.
As shown in fig. 2, from bottom to top, a silicon substrate 17, a silicon dioxide layer 18, and a modulator structure 5, the modulator structure 5 comprising: the P-type doped region 51 and the N-type doped region 52 are abutted to form a ridge structure. A PN junction is formed between the P-type doped region 51 and the N-type doped region 52. The two sides of the doped region are respectively connected with the P electrode 53 and the N electrode 54, and different voltages are applied to the modulator structure so as to change the concentration of internal carriers, thereby changing the refractive index of the modulator structure for phase modulation. According to the embodiment of the invention, a plurality of carrier depletion modulators are adopted, and reverse voltages are applied to two ends of the P-N junction, so that the bandwidth of the phase modulation device is improved.
According to the embodiment of the invention, the technical defect of the polarization measuring instrument for measuring the polarization state by adopting the thermal effect is overcome by introducing a plurality of carrier depletion type modulators, and the polarization state measurement of the hundred MHz sampling rate is further realized by high-speed signal modulation due to the carrier depletion type modulators integrated on the silicon optical chip 1 having the bandwidth of the order of GHz.
According to the embodiment of the invention, the highest sampling rate of the polarization measurement system is equal to the bandwidth of the carrier depletion type modulator divided by 4, and the carrier depletion type modulator has the bandwidth of the GHz order, so that the carrier depletion type modulator provided by the embodiment of the invention can realize polarization state measurement of hundred MHz sampling rate. According to the embodiment of the invention, the structure and the size of the carrier depletion type modulator are optimized, so that the high-speed modulator with low half-wave voltage can be realized.
According to an embodiment of the present invention, the first multimode interferometer 13 and the second multimode interferometer 15 structure have the same interferometer structure. According to an embodiment of the present invention, the first multimode interferometer 13 has a spectral ratio of 50:50, the second multimode interferometer 15 has a spectral ratio of 50:50. according to an embodiment of the present invention, the first multimode interferometer 13 and the second multimode interferometer 15 are arranged in a symmetrical structure, so as to realize 50:50 spectral ratio.
FIG. 3 is a top view of an interferometer structure provided by embodiments of the present invention.
As shown in fig. 3, the interferometer structure 6 is located on the silicon dioxide layer, the interferometer structure 6 comprising: a mode field interference region 61 and a mode spot transition region 62. The mode field interference region 61 has a rectangular cross section. The spot-transfer regions 62 are located at opposite ends of the interference region. The mode spot converting region 62 converts the input transmission mode into an input mode adapted to the mode spot interference region 61. After passing through the mode field interference region 61, the mode spot converting region 62 converts the signal after interference into a transmission mode output corresponding to the waveguide 19. The interferometer structure is mainly determined by the length Lc of the mode field interference region 61, the height Hc of the mode field interference region 61, the length Lt of the mode spot-converting region 62, and the pitch S of the mode spot-converting region 62.
According to an embodiment of the present invention, the polarization measurement system further includes:
the driving module 3 is adapted to drive the first phase modulation means 12, the second phase modulation means 14 and the photodetector 2. The input optical fiber 4 is adapted to input a target optical signal to the two-dimensional grating coupler 11. The driving module 3 is connected with the first phase modulation device 12, the second phase modulation device 14 and the photoelectric detector 2; the input fiber 4 is connected to the input of a two-dimensional grating coupler 11.
According to an embodiment of the present invention, the driving module 3 drives the first phase modulation device 12, the second phase modulation device 14, thereby generating a phase difference between the corresponding optical signals of the two arms of the corresponding multimode interferometer.
According to an embodiment of the present invention, the phase difference generated by modulation by the first phase modulating means 12 may be + -pi/4 or + -3 pi/4. The phase difference generated by modulation by the second phase modulation device 14 may be
Or (b)
。
According to the embodiment of the invention, the output optical fiber 7 inputs the optical signal subjected to the two-stage Mach-Zehnder interferometer structure interference into the photoelectric detector 2, wherein the optical signal received by the photoelectric detector 2 is calculated by the following formula;
wherein,,
for detection by photodetectorsNumber of times (I)>
For the transmission matrix of the first phase modulation means 12, a transmission matrix of the first phase modulation means 12>
Transmission matrix for second phase modulation means 14>
For the transmission matrix of the first multimode interferometer 13 or of the second multimode interferometer 15, +.>
And->
Representing two polarized light signals with mutually perpendicular polarization directions.
The photoelectric detector 2 converts the received optical signal into an electrical signal, and the intensity of the optical signal received by the photoelectric detector 2 is calculated by the following formula;
wherein,,
、/>
、/>
、/>
for stokes parameters of the target optical signal suitable for characterizing the polarization state of the target optical signal, m is the number of detections corresponding to the photodetector 2, m=1, 2, 3, 4,/and m is the number of detections corresponding to the photodetector 2>
For modulating a first phase difference between the polarized light signal and the second polarized light signal +.>
For modulating a second phase difference between the interference light signal and the second sub-interference light signal.
To measure the entire stokes quantity, four different voltages are applied to the two arms of the first phase modulation device 12 and the second phase modulation device 14, respectively, to achieve four detection electric signal measurements. Detecting the polarization state of the electrical signal suitable for obtaining the target optical signal includes obtaining the polarization state of the target optical signal using the formula:
wherein,,I 1 、I 2 、I 3 、I 4 the detection electric signal obtained by four times of detection for the photodetector 2,
、/>
、/>
、/>
for a stokes parameter of the target optical signal that is suitable for characterizing the polarization state of the target optical signal, the four stokes yields may determine a polarization state;θ 1 is the sum ofI 1 A first phase difference between the corresponding modulated polarized light signal and the second polarized light signal,θ 2 Is the sum ofI 2 A first phase difference between the corresponding modulated polarized light signal and the second polarized light signal,θ 3 is the sum ofI 3 A first phase difference between the corresponding modulated polarized light signal and the second polarized light signal,θ 4 is the sum ofI 4 Corresponding modulated polarized light signal and second polarizationFirst phase difference between optical signals, +.>
Is the sum ofI 1 A second phase difference between the corresponding modulated interference light signal and the second sub-interference light signal, < ->
Is the sum ofI 2 A second phase difference between the corresponding modulated interference light signal and the second sub-interference light signal, < ->
Is the sum ofI 3 A second phase difference between the corresponding modulated interference light signal and the second sub-interference light signal, < ->
Is the sum ofI 4 A second phase difference between the corresponding modulated interference light signal and the second sub-interference light signal.
According to the embodiment of the invention, by applying different voltages to the two arms of the first phase modulation device 12 and the second phase modulation device 14 at the same time, when the optical signals pass through the two arms of the first phase modulation device 12 and the second phase modulation device 14 respectively, the refractive index of the optical waveguide changes due to the change of the carrier concentration in the phase modulation device, so that a first phase difference is generated between the modulated polarized optical signals and the second polarized optical signals, and a second phase difference is generated between the modulated interference optical signals and the second sub-interference optical signals.
According to an embodiment of the present invention, four different sets of first and second phase differences are generated between the modulated polarized light signal and the second polarized light signal and between the modulated interference light signal and the second sub-interference light signal by applying four different voltages across the first phase modulation device 12 and the second phase modulation device 14.
According to an embodiment of the invention, a phase modulator with a bandwidth of the order of GHz is preferably employed to achieve high-speed signal modulation, further enabling polarization state measurement at a hundred MHz sampling rate.
In accordance with an embodiment of the present invention, high-speed polarization state measurements are preferably made using a 20GHz bandwidth photodetector 2.
According to the embodiment of the invention, through a silicon optical integrated chip process, a plurality of grating couplers, a plurality of phase modulation devices, a plurality of multimode interferometers and other structures are integrated on the same chip, so that the integration level is higher; and by introducing a plurality of carrier depletion modulators, the technical defect of a polarization measuring instrument for measuring the polarization state by adopting a thermal effect in the prior art is overcome, and high-speed measurement is realized.
According to the embodiment of the invention, the silicon optical integration process is compatible with the complementary metal oxide semiconductor process, the plurality of optical elements are etched on the silicon optical chip 1, the processing cost is low, and large-scale mass production can be realized.
According to the embodiment of the invention, the input optical fiber 4 is a 1550nm single mode optical fiber, so that the target optical signal is ensured to work in a 1550nm band.
According to the embodiment of the invention, the center wavelength of the one-dimensional grating coupler 16 is 1550nm, the one-dimensional grating coupler 16 couples the optical signals subjected to two-stage interference into the output optical fiber 7, the silicon optical chip 1 is output through the output optical fiber 7, and the optical signals are further input into the photoelectric detector 2 to realize polarization state measurement.
According to an embodiment of the invention, the output optical fiber 7 is a 1550nm polarization maintaining optical fiber.
According to the embodiment of the invention, the connection angle between the input optical fiber 4 and the two-dimensional grating coupler 11 and the connection angle between one end of the output optical fiber 7 and the one-dimensional grating coupler 16 are approximately the same, so that the same optical fiber couples different grating couplers together, and the coupling efficiency is improved.
According to an embodiment of the present invention, preferably, the connection angle of the input optical fiber 4 and the two-dimensional grating coupler 11 is about 80 degrees; the connection angle between one end of the output optical fiber 7 and the one-dimensional grating coupler 16 is about 80 degrees, and the other end of the output optical fiber 7 is connected with the photoelectric detector 2.
Preferably, the two-dimensional grating coupler 11 is prepared in a wafer factory PDK device library, according to an embodiment of the present invention.
According to an embodiment of the present invention, the photodetector 2 converts the optical signal into an electrical signal and acquires it, thereby obtaining a polarization state measurement result.
Fig. 4 is a cross-sectional view of a waveguide provided by an embodiment of the present invention.
As shown in fig. 4, a silicon substrate 17, a silicon dioxide layer 18 and a waveguide 19 are sequentially arranged from bottom to top. In the case of a 500nm x 220nm waveguide 19 structure, this ensures that only a single transmission mode is present in the 1550nm band waveguide 19.
According to an embodiment of the invention, the waveguide 19, the two-dimensional grating coupler 11, the first multimode interferometer 13, the second multimode interferometer 15 and the two-dimensional grating coupler 11 are obtained by etching a silicon layer on a silicon dioxide layer in different shapes. The first phase modulation means 12 and the second phase modulation means 14 are obtained by doping a silicon layer with a further semiconductor material and etching. In addition, after the material is obtained by etching, the material obtained by etching is encapsulated by silicon dioxide.
The invention also provides a polarization measurement method, which comprises the following steps of:
step A: dividing the received target optical signal into a first polarized optical signal and a second polarized optical signal perpendicular to the first polarized optical signal by using a two-dimensional grating coupler 11;
and (B) step (B): receiving the first polarized light signal and the second polarized light signal by using the first phase modulation device 12, and modulating the first polarized light signal to obtain a modulated polarized light signal; wherein the modulated polarized light signal and the second polarized light signal have a first phase difference;
step C: utilizing a first multimode interferometer 13 to interfere the modulated polarized light signal and the second polarized light signal to obtain a first interference light signal, and dividing the interference light signal into a first sub-interference light signal and a second sub-interference light signal;
step D: receiving the first sub-interference optical signal and the second sub-interference optical signal by using the second phase modulation device 14, and modulating the first sub-interference optical signal to obtain a modulated interference optical signal, wherein the modulated interference optical signal has a second phase difference with the second sub-interference optical signal;
step E: utilizing a second multimode interferometer 15 to interfere the modulated interference light signal and the second sub-interference light signal to obtain a second interference light signal;
step F: transmitting the second interference light signal to the output optical fiber 7 by using the one-dimensional grating coupler 16;
step G: detecting the second interference light signal by using the photodetector 2;
step H: and (3) repeating the steps A-G at least four times to obtain at least four detected electric signals, wherein the detected electric signals are suitable for obtaining the polarization state of the target optical signals.
The foregoing description of the embodiments has been provided for the purpose of illustrating the general principles of the invention, and is not meant to limit the invention thereto, but to limit the invention thereto, and any modifications, equivalents, improvements and equivalents thereof may be made without departing from the spirit and principles of the invention.
Claims (9)
1. A silicon optical chip-based polarization measurement system, comprising:
a silicon photodie, comprising:
a silicon substrate;
a silicon dioxide layer formed on the silicon substrate;
a two-dimensional grating coupler formed on the silicon dioxide layer and adapted to divide a received target optical signal into a first polarized optical signal and a second polarized optical signal having a polarization direction perpendicular to the first polarized optical signal;
the first phase modulation device is formed on the silicon dioxide layer and is suitable for modulating the first polarized light signal to obtain a modulated polarized light signal, and the modulated polarized light signal and the second polarized light signal have a first phase difference;
a first multimode interferometer, formed on the silica layer, adapted to interfere the modulated polarized light signal with the second polarized light signal to obtain a first interference light signal, and to divide the first interference light signal into a first sub-interference light signal and a second sub-interference light signal;
the second phase modulation device is formed on the silicon dioxide layer and is suitable for modulating the first sub-interference optical signals to obtain modulated interference optical signals, wherein the modulated interference optical signals and the second sub-interference optical signals have a second phase difference;
the second multimode interferometer is formed on the silicon dioxide layer and is suitable for enabling the modulated interference optical signal and the second sub-interference optical signal to interfere to obtain a second interference optical signal; and
the one-dimensional grating coupler is formed on the silicon dioxide layer and is suitable for transmitting the second interference optical signal to an output optical fiber; and
the photoelectric detector is suitable for detecting the second interference optical signal to obtain a detection electric signal, and the detection electric signal is suitable for acquiring the polarization state of the target optical signal;
the detecting the polarization state of the target optical signal includes obtaining the polarization state of the target optical signal using the formula:
wherein,,I 1 、I 2 、I 3 、I 4 a detection electric signal obtained by four times of detection for the photoelectric detector,
、/>
、/>
、/>
a stokes parameter for a target optical signal adapted to characterize a polarization state of the target optical signal;θ 1 is the sum ofI 1 A first phase difference between the corresponding modulated polarized light signal and the second polarized light signal,θ 2 is the sum ofI 2 A first phase difference between the corresponding modulated polarized light signal and the second polarized light signal,θ 3 is the sum ofI 3 A first phase difference between the corresponding modulated polarized light signal and the second polarized light signal,θ 4 is the sum ofI 4 A first phase difference between the corresponding modulated polarized light signal and the second polarized light signal,φ 1 is the sum ofI 1 A second phase difference between the corresponding modulated interference light signal and the second sub-interference light signal,φ 2 is the sum ofI 2 A second phase difference between the corresponding modulated interference light signal and the second sub-interference light signal,φ 3 is the sum ofI 3 A second phase difference between the corresponding modulated interference light signal and the second sub-interference light signal,φ 4 is the sum ofI 4 A second phase difference between the corresponding modulated interference light signal and the second sub-interference light signal;
the detection electric signals obtained by four times of detection by the photoelectric detector are realized by respectively applying four different voltages to the first phase modulation device and the second phase modulation device.
2. The polarization measurement system of claim 1, wherein the first phase modulation device comprises a first carrier-depleted modulator and a second carrier-depleted modulator arranged in parallel, the first carrier-depleted modulator, the second carrier-depleted modulator, and the first multimode interferometer comprising a first mach-zehnder interferometer structure having equal arm lengths;
the first carrier depletion modulator is adapted to modulate the first polarized light signal to obtain the modulated polarized light signal.
3. The polarization measurement system of claim 2, wherein the second phase modulation device comprises a third carrier-depleted modulator and a fourth carrier-depleted modulator arranged in parallel, the third carrier-depleted modulator, the fourth carrier-depleted modulator, and the second multimode interferometer comprising a second mach-zehnder interferometer structure having equal arm lengths;
the third carrier depletion modulator is adapted to modulate the first sub-interference optical signal to obtain the modulated interference optical signal.
4. The polarization measurement system of claim 3, wherein the first carrier-depleted modulator, the second carrier-depleted modulator, the third carrier-depleted modulator, and the fourth carrier-depleted modulator have the same modulator structure;
the modulator structure comprises: the P-type doped region and the N-type doped region are in butt joint to form a ridge structure.
5. The polarization measurement system of claim 1, wherein waveguides are used for communication between the two-dimensional grating coupler and the first phase modulation device, between the first phase modulation device and the first multimode interferometer, between the first multimode interferometer and the second phase modulation device, and between the second phase modulation device and the second multimode interferometer.
6. The polarization measurement system of claim 1, further comprising:
the driving module is suitable for driving the first phase modulation device, the second phase modulation device and the photoelectric detector;
and the input optical fiber is suitable for inputting the target optical signal to the two-dimensional grating coupler.
7. The polarization measurement system of claim 1, wherein the first multimode interferometer and the second multimode interferometer structure have the same interferometer structure, the interferometer structure comprising:
the section of the mode field interference area is rectangular;
and the mode spot conversion areas are positioned at two opposite ends of the mode field interference area.
8. The polarization measurement system of claim 1, wherein the first multimode interferometer has a split ratio of 50:50, the second multimode interferometer has a spectral ratio of 50:50.
9. a polarization measurement method using the polarization measurement system according to any one of claims 1 to 8, the method comprising:
step A: dividing a received target optical signal into a first polarized optical signal and a second polarized optical signal with a polarization direction perpendicular to the first polarized optical signal by using a two-dimensional grating coupler;
and (B) step (B): receiving the first polarized light signal and the second polarized light signal by using a first phase modulation device, and modulating the first polarized light signal to obtain a modulated polarized light signal; wherein the modulated polarized light signal and the second polarized light signal have a first phase difference;
step C: utilizing a first multimode interferometer to make the modulated polarized light signal and the second polarized light signal interfere to obtain a first interference light signal, and dividing the interference light signal into a first sub-interference light signal and a second sub-interference light signal;
step D: receiving the first sub-interference optical signal and the second sub-interference optical signal by using a second phase modulation device, and modulating the first sub-interference optical signal to obtain a modulated interference optical signal, wherein the modulated interference optical signal and the second sub-interference optical signal have a second phase difference;
step E: utilizing a second multimode interferometer to enable the modulated interference light signal and the second sub interference light signal to interfere, so as to obtain a second interference light signal;
step F: transmitting the second interference optical signal to an output optical fiber by using a one-dimensional grating coupler;
step G: detecting the second interference light signal by using a photoelectric detector;
step H: repeating the steps A-G at least four times to obtain at least four detected detection electric signals, wherein the detection electric signals are suitable for obtaining the polarization state of the target optical signals.
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