Optical measurement system and measurement method based on sweep frequency laser

Abstract

The invention relates to an optical measurement system, in particular to an optical measurement system and method based on frequency sweeping laser. An optical measurement system based on frequency sweep laser comprises a frequency sweep laser, a second coupler, an S-path coherent receiving module, a P-path coherent receiving module, light to be measured, a polarization diversity device and a data processing module, and the data processing module carries out digital-to-analog conversion and digital signal processing on electric signals output by the above modules. And information such as frequency, light intensity, polarization state and phase of the to-be-measured light is obtained after calculation. According to the optical measurement system based on the sweep frequency laser, the frequency, the intensity, the phase and the polarization state of the light are measured at the same time through the low-complexity system, the detection precision is improved, the measurement speed is high, the cost is low, and the optical signal phase detection capacity is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to an optical measurement system, in particular, an optical measurement system and a measurement method based on a swept laser. BACKGROUND

[0002] Optical measurement systems are widely used in optical communication, photonic integrated circuits (PICs) and optical sensing, etc. The existing optical measurement systems are mainly spectrometers, which are divided into two categories: one is the classic spatial dispersion spectrometer with a long history, and the other is the new modulation transformation spectrometer developed in recent decades.

[0003] Ordinary spectrometers mainly separate light by wavelength through a dispersive element (such as a prism or a diffraction grating) and record the intensity of light at each wavelength using a detector. Such spectrometers have a contradiction between resolution and light flux, and the higher the resolution, the lower the energy of the detected spectral signal. Modulation spectrometers are non-spatially dispersive, which use a round hole to input light and a modulation transformation method to overcome the limitation of light flux of classic spectrometers, but their wavelength range is relatively narrow. In addition, both types of spectrometers cannot directly detect the phase information of light. If the phase information of light is to be measured, an optical spectrometer is needed, but the currently commercially available optical spectrometer mainly uses multiple single-frequency lasers as local light sources, which has a slow measurement speed, high cost and complex system. SUMMARY

[0004] To solve the problems of slow measurement speed, high cost and complex system, the present application provides an optical measurement system based on a swept laser, and the specific technical solution is as follows: An optical measurement system based on a swept laser, comprising: a swept laser for outputting swept light and displaying the power and frequency of the output light in real time; a second coupler for splitting the swept light signal into two swept light signals; an S-path coherent receiving module connected with the second coupler for receiving one of the swept light signals; a P-path coherent receiving module connected with the second coupler for receiving the other swept light signal; a polarization diversity unit connected with the S-path coherent receiving module, the P-path coherent receiving module and a light source to be measured, so that the S-path coherent receiving module obtains S-polarization state information of the light source to be measured and the P-path coherent receiving module obtains P-polarization state information of the light source to be measured; and a data processing module connected with the S-path coherent receiving module and the P-path coherent receiving module for obtaining spectral information of the light to be measured.

[0005] Preferably, the S-path coherent receiving module and the P-path coherent receiving module are both IQ receiving modules.

[0006] It also includes: a first coupler, connected to the swept laser module and the second coupler, for splitting the swept optical signal emitted by the swept laser into three paths, one of which enters the second coupler; and a frequency calibration module, connected to the first coupler, for obtaining information on the change of the swept laser frequency over time through one of the swept optical signals, and then calculating... ; and an optical power detection module, connected to the first coupler, for obtaining information on the power change of the swept-frequency optical signal over time through one of the swept-frequency optical signals. The frequency calibration module and the optical power detection module are both connected to the data processing module.

[0007] Preferably, the splitting ratio of the first coupler is 90:5:5; and the splitting ratio of the second coupler is 50:50.

[0008] Preferably, the frequency calibration module includes: a frequency reference module connected to the polarization diversity module, used to obtain the frequency information of the swept laser light at any time; and a photodetector connected to the frequency calibration module and the data processing module respectively, used to convert the light intensity signal into an electrical signal and send it to the data processing module.

[0009] Furthermore, the frequency reference module includes any one of an acetylene gas absorption chamber, a fiber optic grating, or a Fabry-Perot resonator.

[0010] An optical measurement method based on swept-frequency laser, used in the aforementioned optical measurement system based on swept-frequency laser, includes the following steps: Step 1: The swept-frequency laser generates a highly coherent linear swept-frequency laser: ,in, This represents the power of the sweep laser at time t. The sign representing the imaginary part of a complex number, t representing time. This indicates that the laser is in Phase of time; Step 2: Obtain information on the power variation of the swept-frequency optical signal over time using the display function of the swept-frequency laser. Information about frequency changes over time And information on phase changes over time The swept-frequency optical signal is split into two paths by the second coupler and enters the S-channel coherent receiving module and the P-channel coherent receiving module respectively to prepare for frequency matching with the light under test. Step 3: The light to be measured consists of two light waves: and , in, and Power of the to-be-tested light at time t, Phase of the to-be-tested light wave at time t, the frequencies of the two light waves are and ; The to-be-tested light is subjected to polarization diversity by a polarization diversity device, the signal light in the S polarization state and the sweep frequency light in the S polarization state are frequency-mixed in an S-path coherent receiving module to obtain the complex signal of the S path , the signal light in the P polarization state and the sweep frequency light in the P polarization state are frequency-mixed in a P-path coherent receiving module to obtain the complex signal of the P path ; The two complex signals are subjected to matched filtering by a matched filter, and the frequencies of the two to-be-tested light waves are obtained according to the pulse generation time and ; and ; The amplitudes of the output signals of the two polarization states of the first light wave are obtained: and , and the two phases are: and , and the intensity of the to-be-tested light is: ; wherein, the proportional coefficient K is calibrated to obtain the light intensity of the to-be-tested light at the frequency ; Similarly, the intensity and polarization state information of the second light wave are obtained; Step 4: Set a reference time , the phases of the S polarization states of the two to-be-tested light waves at the reference time are respectively: ; ; The phases of the P polarization states are respectively: ; .

[0011] Preferably, in step 2, the sweep frequency laser is divided into three paths by a first coupler, one of which enters a frequency calibration module to accurately obtain the information of the change of the sweep frequency laser frequency with time , and then calculate ; another path enters an optical wave power detection module to obtain the information of the change of the power of the sweep frequency light with time ; the third path is divided into two paths by a second coupler and enters an S-path coherent receiving module and a P-path coherent receiving module respectively to prepare for frequency-mixing with the to-be-tested light.

[0012] Preferably, the intensity and polarization state of the light wave to be measured in the entire frequency range are obtained by traversing different times t.

[0013] Preferably, the phase expression of the light wave to be measured at the time t is , the frequency is , and the phase of the S polarization state component of the light wave to be measured at the time t is , the frequency is , and the phase of the S polarization state component of the light wave to be measured at the time t is obtained: .

[0014] Preferably, the phase of the S polarization state and the P polarization state of the light wave to be measured at the time t in the entire frequency range is traversed, and the phase of the light wave to be measured is measured.

[0015] Compared with the prior art, the present application has the following beneficial effects: The optical measurement system based on the swept laser provided by the present application realizes the simultaneous measurement of the frequency, intensity, phase and polarization state of the light by using a low complexity system, improves the detection precision, and has the advantages of fast measurement speed, low cost and light signal phase detection capability.

[0016] The problem that the phase of the light signal cannot be measured in the general optical measurement system is solved, and the present application has the advantages of high resolution, fast measurement speed and low complexity. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is a structural block diagram of the optical measurement system based on the swept laser; Figure 2 is a structural block diagram of the frequency calibration module; Figure 3 is the test result of one experiment, and is a data graph of the beat frequency signal of one of the polarization lights of the light to be measured and the swept light source; Figure 4 is the test result of one experiment, and is a compressed pulse graph.

[0018] In the figure: 1 is a swept laser, 2 is a first coupler, 3 is a second coupler, 4 is an S polarization coherent receiving module, 5 is a P polarization coherent receiving module, 6 is light to be measured, 7 is a polarization diversity device, 8 is a frequency calibration module, 9 is a light wave power detection module, 10 is a data processing module, 11 is a frequency reference module, and 12 is a photodetector. DETAILED DESCRIPTION

[0019] The present application will be further described in combination with the accompanying drawings.

[0020] As​​​Figure 1 and Figure 2 As shown, an optical measurement system based on a swept-frequency laser includes: a swept-frequency laser 1, a first coupler 2, a second coupler 3, an S-channel coherent receiving module 4, a P-channel coherent receiving module 5, a light under test 6, a polarization diversity converter 7, a frequency calibration module 8, an optical power detection module 9, and a data processing module 10. The frequency calibration module 8 includes a frequency reference module 11 and a photodetector 12. The swept-frequency light signal emitted by the swept-frequency laser 1 is split into three paths after passing through the first coupler 2. One path is connected to the frequency reference module 11 in the frequency calibration module 8 and finally enters the data processing module 10 as an electrical signal through the photodetector 12. Another path is connected to the data processing module 10 through the optical power detection module 9. The last path is split into two paths again after passing through the second coupler 3. The light under test 6 is then processed by the polarization diversity converter 7 to obtain... and Two polarized states of light, Polarized light and The polarized light beats the two swept-frequency light beams and enters the S-channel coherent receiving module 4 and the P-channel coherent receiving module 5 respectively. The two coherent receiving modules convert the beat frequency signal into an electrical signal through the internal balanced photodetector, and transmit the electrical signal to the data processing module 10. After calculation and processing, the spectral information of the light under test is obtained, that is, the frequency, intensity, polarization state and phase of the light under test are obtained.

[0021] Information on the power variation of the swept-frequency optical signal over time Information on frequency changes over time And information on phase changes over time It can be obtained through the display function of the frequency sweep laser, or through the frequency calibration module 8 and the optical power detection module 9.

[0022] The optical signal generated by the frequency-sweeping laser 1 is a highly coherent frequency-sweeping laser, and the frequency sweep range can cover the wavelength range of the optical signal under test.

[0023] The frequency sweeping light source is a highly coherent linear frequency sweeping laser: Where t represents time, This represents the power of the sweep laser at time t. The sign representing the imaginary part of a complex number. This indicates that the laser is in The phase at time; the instantaneous frequency of the swept laser is The frequency sweep rate is .

[0024] The swept laser is split into four beams by a coupler. The first beam enters the gas cell, and the frequency of the swept laser is calibrated using the absorption peak of the gas cell, thus accurately obtaining information on the frequency change of the swept laser over time. , and then the frequency information of the swept light at any time is calculated ; the second beam of light enters the photodetector to obtain information about the power of the swept light changing with time , and the third and fourth beams of light enter the S-path coherent receiving module and the P-path coherent receiving module, respectively.

[0025] The frequency calibration module comprises a frequency reference module and a photodetector, the frequency reference module is connected with the polarization diversity module and is used to obtain the frequency information of the swept light at any time of the swept laser, and the photodetector is connected with the frequency calibration module and the data processing module, respectively, and is used to convert the light intensity signal into an electrical signal and send it to the data processing module. The frequency calibration module is used to calibrate the frequency of the swept laser and accurately obtain the information about the frequency of the swept laser changing with time .

[0026] The optical wave power detection module is used to detect the power of the swept light and accurately obtain the information about the power of the swept laser changing with time .

[0027] The laser frequency calibration module comprises a gas absorption chamber and a photodetector, wherein the swept light source is connected with the gas chamber through a coupler, and then the light intensity signal is converted into an electrical signal by the photodetector, and the electrical signal enters the data processing module. The gas chamber has strong absorption peaks at specific light frequencies, and the wavelengths of these absorption peaks hardly change with the environment, which are used to obtain the frequency information of the swept light at any time of the swept laser.

[0028] The first coupler 2 preferably has a splitting ratio of 90:5:5. The second coupler 3 preferably has a splitting ratio of 50:50.

[0029] The optical wave power detection module comprises a photodetector, which converts the input swept light power into an electrical signal output in a proportional manner, and is used to detect the power fluctuation information of the swept light.

[0030] The S-path coherent receiving module 4 and the P-path coherent receiving module 5 adopt the IQ coherent receiving mode.

[0031] The polarization diversity module divides the to-be-measured light signal into S and P two polarization states; the swept light is divided into two paths with equal light intensity, and the light intensity of each path is , and is placed in the S and P polarization states, respectively. The to-be-measured light in the S polarization state and the swept light in the S polarization state enter the S-path receiving module together, and the swept light in the P polarization state and the to-be-measured light in the P polarization state enter the P-path coherent receiving module.

[0032] The S-path coherent receiving module comprises a 90° IQ optical bridge and two balanced photodetectors. The in-phase beat signal of the local swept light and the to-be-measured light signal enters the balanced photodetector, and the output electrical signal is denoted as , the beat signal with 90° phase difference enters the balanced photo detector, and the output electric signal is recorded as ; the P-path coherent receiving module structure is the same as the S-path coherent receiving module, and the output electric signals and are obtained by the same reason. For the IQ receiving module of the S-path polarization state, the signal output by the I-path is converted into digital signal by the analog-digital converter, and the signal output by the Q-path is converted into digital signal by the analog-digital converter, which are respectively taken as the real part and the imaginary part to generate a complex signal . The complex signal is filtered by the matched filter to obtain signal , , which represents the intensity of the S-path polarization component of the measured light at frequency , , which represents the relative phase of the S-path polarization component of the measured light at frequency relative to the swept frequency light; the intensity and the relative phase of the P-path polarization component of the measured light at frequency are obtained by the same reason; and the intensity of the measured light at frequency is , and the polarization state of the measured light is obtained according to the intensity and the phase difference of the S-path and P-path polarization states.

[0033] The frequency reference module includes any one of acetylene gas absorption cell, fiber grating or Fabry-Perot resonant cavity. Preferably, the frequency reference module 11 adopts acetylene gas absorption cell.

[0034] The optical wave power detection module 9 is composed of photo detector.

[0035] The data processing module 10 carries out analog-digital conversion and digital signal processing on the electric signals output by the above laser frequency calibration module, optical wave power detection module, P-path coherent receiving module and S-path coherent receiving module, and obtains the frequency, light intensity, polarization state and phase of the measured light after calculation.

[0036] The frequency, intensity, phase and polarization state information of the measured light field are calculated by the following method: The electric signals and generated by the interference of the measured light wave and the swept frequency light are obtained to obtain the complex signals of the S-path and the P-path: ; ; A matched filter signal with a center frequency of 0 and a chirp rate of is generated , respectively with complex signals and After performing matched filtering, the amplitudes of the output signals are respectively and Phase is and Then the light to be measured has a frequency of At that point, the intensity of the S-polarized state is proportional to The phase difference relative to the swept-frequency laser is The intensity of the P-polarized state is proportional to... The phase difference relative to the swept-frequency laser is The polarization state information of the light under test can be obtained from the intensity and phase difference of the two polarization states. The intensity of the light under test is proportional to... After the proportionality coefficient is calibrated, the frequency of the light to be measured is obtained. The intensity of light at a given point can be obtained; similarly, the intensity and polarization state of light at other arbitrary frequencies can be obtained, thereby realizing the measurement of the optical power spectrum to be measured.

[0037] To measure the phase of light waves at different frequencies, a reference time is set. The frequency is The light wave to be measured at the reference time The phase of the polarization state of S is The phase of the P polarization state is Similarly, we can obtain the values ​​of light of any other frequency at the reference time. The phase of light is measured to determine the phase of light.

[0038] Specifically, an optical measurement method based on swept-frequency laser, used in an optical measurement system based on swept-frequency laser, includes the following steps: Step 1: The swept-frequency laser generates a highly coherent linear swept-frequency laser: ,in, This represents the power of the sweep laser at time t. The sign representing the imaginary part of a complex number, t representing time. This indicates that the laser is in Phase of time; Step 2: The swept laser is split into three paths by the first coupler 2, one of which enters the frequency calibration module 8 to accurately obtain information on the frequency change of the swept laser over time. Then calculate to get The other path enters the optical power detection module 9 to obtain information on the power change of the swept light over time. The third path is split into two paths by the second coupler 3, which enter the S-path coherent receiving module and the P-path coherent receiving module respectively to prepare for beat frequency with the light under test. Step 3: The test light 6 can contain multiple test light waves, taking two of them as examples, respectively: and , where and are the powers of the test light at time t, are the phases of the test light waves at time t, and the frequencies of the two light waves are and .

[0039] The test light 6 is subjected to polarization diversity by the polarization diversity device 7, and the S-polarized signal light and the S-polarized swept light are frequency-mixed in the S-path coherent detection module 4 to obtain the S-path complex signal , and the P-polarized signal light and the P-polarized swept light are frequency-mixed in the P-path coherent detection module 5 to obtain the P-path complex signal , and the frequency-mixed signal data is shown in Figure 3 .

[0040] Then, the two complex signals are matched filtered by using a matched filter, and according to the pulse generation times and , the frequencies of the two test light waves are obtained as and , where the results of one pulse output are shown in Figure 4 (the abscissa has been converted to frequency); In addition, the amplitudes of the output signals of the two polarization states of the first light wave are obtained as and , and the phases are and ; Therefore, the intensity of the test light is , and after the proportionality coefficient K is calibrated, the optical intensity of the test light at the frequency is obtained; Similarly, the intensity and polarization state information of the second light wave can be obtained.

[0041] Step 4: Set a reference time , then the phases of the S-polarized states of the two test light waves at the reference time are: ; ; The phases of the P-polarized states are: ; ; Thus, the measurement of the light phase is realized.

[0042] Compared with the prior art, the wavelength accuracy and resolution of the optical measurement system based on the sweep laser in the embodiment can reach sub-pico meter, the system has the measurement capability of light phase, the system complexity and cost are significantly reduced, and the system has good practical value.

[0043] The technical principles of the present application are described above in combination with specific embodiments. These descriptions are only for explaining the principles of the present application, and cannot be interpreted as limiting the protection scope of the present application in any way. Based on the explanations herein, other specific embodiments of the present application can be conceived by those skilled in the art without creative efforts, and these embodiments will all fall within the protection scope of the claims of the present application.

Claims

1. An optical measurement system based on a frequency-swept laser, characterized in that, The system comprises: a frequency-sweeping laser for outputting frequency-sweeping light and displaying the power of the output light and the frequency in real time; a second coupler for splitting the frequency-sweeping light signal into two frequency-sweeping light signals; an S-path coherent receiving module connected with the second coupler and used for receiving one of the two frequency-sweeping light signals; a P-path coherent receiving module connected with the second coupler and used for receiving the other of the two frequency-sweeping light signals; a polarization diversity device connected with the S-path coherent receiving module, the P-path coherent receiving module and a light source to be measured, so that the S-path coherent receiving module acquires S-polarization state information of the light source to be measured and the P-path coherent receiving module acquires P-polarization state information of the light source to be measured; a data processing module connected with the S-path coherent receiving module and the P-path coherent receiving module respectively and used for acquiring spectral information of the light to be measured.

2. The optical measurement system based on frequency-sweeping laser according to claim 1, wherein the S-path coherent receiving module and the P-path coherent receiving module are both IQ receiving modules.

3. The optical measurement system based on frequency-sweeping laser according to claim 1, further comprising: a first coupler connected with the frequency-sweeping laser module and the second coupler and used for splitting the frequency-sweeping light signal emitted by the frequency-sweeping laser into three frequency-sweeping light signals, one of which enters the second coupler; wherein the frequency calibration module and the light wave power detection module are both connected with the data processing module. The frequency calibration module is connected with the first coupler, and is configured to obtain information about the change of the swept laser frequency with time through one of the swept optical signals, and then calculate the information about the change of the swept laser frequency with time ; and The light wave power detection module is connected with the first coupler and is used for obtaining information about the change of the power of the sweep frequency light with time through one of the sweep frequency light signals ; 4. The optical measurement system based on frequency-sweeping laser according to claim 3, wherein the frequency calibration module comprises: a frequency reference module connected with the polarization diversity module and used for obtaining frequency information of the frequency-sweeping light at any time; and a photodetector connected with the frequency calibration module and the data processing module respectively and used for converting an optical intensity signal into an electrical signal and sending the electrical signal to the data processing module.

5. The optical measurement system based on frequency-sweeping laser according to claim 4, wherein the frequency reference module comprises any one of an acetylene gas absorption chamber, a fiber grating or a Fabry-Perot resonant cavity. The method comprises the following steps:

6. An optical measurement method based on a frequency-swept laser, for use in an optical measurement system based on a frequency-swept laser according to any one of claims 1 to 5, characterized in that, Step 3: The frequency-sweeping laser is split into two, which respectively enter the S-path coherent receiving module and the P-path coherent receiving module to prepare for frequency mixing with the light to be measured; the light to be measured comprises two light waves: Step 1: The swept-frequency laser generates a highly coherent linear swept-frequency laser: ,in, This represents the power of the sweep laser at time t. The sign for the imaginary part of a complex number, t, represents time. This indicates that the laser is in Phase at time; Step 2: get the information of the power of the swept light signal changing with time through the display function of the swept laser , the information of the frequency changing with time , and the information of the phase changing with time ; the swept light signal is divided into two paths through the second coupler and enters the S-path coherent receiving module and the P-path coherent receiving module respectively to prepare for beating with the light to be measured; Similarly, the intensity and polarization state information of the second light wave are obtained; and , wherein, and is the power of the light to be measured at time t, is the phase of the light wave to be measured at time t, the frequencies of the two light waves are and ; The to-be-tested light is subjected to polarization diversity through a polarization diversity device, and the signal light in the S polarization state and the sweep frequency light in the S polarization state are frequency-mixed in an S-path coherent receiving module to obtain a complex signal of the S path , and the signal light in the P polarization state and the sweep frequency light in the P polarization state are frequency-mixed in a P-path coherent receiving module to obtain a complex signal of the P path ; The two complex signals are matched filtered by a matched filter, and the pulse generation time is obtained according to the frequency And The frequencies of the two to-be-detected light waves are And ; The amplitudes of the output signals of the two polarization states of the first light wave are obtained: and and the two phases: and The intensity of the light to be measured is: ； Wherein, the proportionality coefficient K is calibrated to obtain the light intensity of the light to be measured at the frequency of 0. the P-polarization state phase is respectively: Step 4: Set a reference time Then the phase of the two light waves to be measured at the reference time is S ； ； in the step 2: ； 。 7. The method of claim 6, wherein the frequency of the laser is swept over a range of frequencies.

8. The optical measurement method based on frequency-sweeping laser according to claim 7, wherein The swept laser is split into three paths by the first coupler, one of which enters the frequency calibration module to accurately obtain information on the frequency change of the swept laser over time. Then calculate to get The other path enters the optical power detection module to obtain information on the power change of the swept-frequency light over time. The third path is split into two paths by the second coupler, which enter the S-path coherent receiving module and the P-path coherent receiving module respectively to prepare for beat frequency with the light under test. different times t are traversed to obtain the intensity and polarization state information of the light to be measured in the entire frequency range.

9. The optical measurement method based on frequency-sweeping laser according to any one of claims 6 to 8, wherein 10. The optical measurement method based on frequency-sweeping laser according to any one of claims 6 to 8, wherein According to the phase expression of the sweeping light wave at the reference time , the frequency is , the phase of the S polarization state component of the light to be measured at the frequency , the phase of the S polarization state component of the light to be measured at the reference time , the phase of the S polarization state component of the light to be measured at the reference time , the phase of the S polarization state component of the light to be measured at the reference time , the phase of the S polarization state component of the light to be measured at the reference time 。 ​ Traverse different time t, get the phase of the polarization state of the measured light wave S and P in the reference time at the whole frequency range, realize the measurement of the phase of the measured light wave.

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