Rapid optical frequency detection device, demodulation parameter calibration method and optical frequency demodulation method

Abstract

The invention provides a rapid light frequency detection device which comprises a Michelson interferometer, and the Michelson interferometer comprises a 3 * 3 optical coupler. The 3 * 3 optical coupler divides an input optical path into three paths, two paths respectively enter two interference arms with optical path difference, and the other path enters one wavelength division multiplexer; two Faraday rotating mirrors are arranged at the tail ends of the two interference arms, the Faraday rotating mirrors reflect a light path back to the 3 * 3 optical coupler, the reflected light path is divided into three paths of output light, the three paths of output light are received by three first photoelectric detectors, and a first photoelectric detection signal is generated and used for calculating the light frequency variation of the input light; and two paths of light output by the wavelength division multiplexer are received by two second photoelectric detectors to generate a second photoelectric detection signal for calculating the absolute light frequency of the input light. The invention further provides a demodulation parameter calibration method and an optical frequency demodulation method of the rapid optical frequency detection device.

Description

Technical Field

[0001] The present invention belongs to the technical field of photonics, and in particular relates to a fast optical frequency detection device, a demodulation parameter calibration method and an optical frequency demodulation method. Background Art

[0002] The detection of optical frequency information has a wide range of applications, such as laser frequency measurement and control, frequency-modulated continuous-wave lidar, optical coherence tomography, optical frequency domain reflectometry, optical sensing based on fiber Bragg gratings, and optical computing based on microring resonators. In these applications, accurately measuring or obtaining high-resolution, large-scale, and rapid optical frequency variation information is extremely important, even playing a decisive role.

[0003] In the prior art, the detection of optical frequency information can be achieved through many different methods, such as: (1) Spectrum analyzers based on diffraction gratings or tunable narrowband filters have extremely high measurement accuracy, but their measurement speed, measurement accuracy, and resolution are mutually restricted, and they cannot achieve simultaneous and accurate measurement of the three parameters; (2) Optical frequency measurement methods based on unbalanced Mach-Zehnder interferometers have a resolution that is inversely proportional to the delay τ, but they have the problem of polarization fading. At the same time, long-distance optical fibers will cause increased laser frequency noise, resulting in the erroneous generation of f clocks with equal frequency intervals; (3) Optical frequency measurement methods based on Hilbert transforms can correct the nonlinearity of laser frequency scanning in data processing, but require obtaining very long phase data before Hilbert transform, which is not suitable for real-time optical frequency measurement; (4) Optical frequency measurement methods based on differential group delay (DGD) elements can achieve high-resolution, large-range, and high-speed optical frequency measurement, but their optical elements are large in size and sensitive to polarization state changes during transmission.

[0004] Therefore, the above optical frequency measurement methods all have certain disadvantages in frequency measurement resolution, frequency measurement range, and frequency measurement speed. Therefore, a device and measurement method for high-resolution, fast, real-time optical frequency change and absolute optical frequency measurement are needed. Summary of the Invention

[0005] The present invention provides a fast optical frequency detection device, a demodulation parameter calibration method and an optical frequency demodulation method, which can quickly and in real time measure optical frequency changes and absolute optical frequency measurements.

[0006] Other purposes and advantages of the present invention can be further understood from the technical features disclosed in the present invention.

[0007] To achieve one or part or all of the above-mentioned purposes or other purposes, a technical solution of the present invention provides a fast optical frequency detection device, including a Michelson interferometer with an input optical path, the Michelson interferometer including a 3*3 optical coupler, and the input light enters the Michelson interferometer from the 3*3 optical coupler; the 3*3 optical coupler divides the input optical path into three paths, two of which enter two interference arms with optical path difference respectively, and the remaining path enters a wavelength division multiplexer; two Faraday rotators are arranged at the ends of the two interference arms, the Faraday rotator reflects the optical path back to the 3*3 optical coupler, and the reflected optical path is divided into three output lights, which are received by three first photodetectors to generate a first photodetection signal for calculating the optical frequency change of the input light; the two light paths output by the wavelength division multiplexer are received by two second photodetectors to generate a second photodetection signal for calculating the absolute optical frequency of the input light.

[0008] One of the three output optical paths shares the input optical path and is divided into two optical paths by a 1*2 optical coupler. The optical paths divided by the 1*2 optical coupler are respectively used for inputting input light and connecting to the first photodetector.

[0009] The phase difference between the output signals of the three output optical paths after splitting by the 3*3 optical coupler is approximately 120°; the intensities of the three first photoelectric detection signals change according to a sine function or a cosine function, and the change in the sine function or the cosine function corresponds to the change in the optical frequency of the input light.

[0010] The working center wavelength of the wavelength division multiplexer is located at both ends of the wavelength of the light to be measured, and the ratio of the two output signals of the wavelength division multiplexer corresponds to the absolute optical frequency of the input light.

[0011] The optical path difference between the two interferometer arms is a variable optical path difference.

[0012] Another technical solution of the present invention provides a method for calibrating demodulation parameters of a fast optical frequency detection device, which is used for calibrating the demodulation parameters of the optical frequency variation of the Michelson interferometer in the fast optical frequency detection device described above and calibrating the splitting ratio of the wavelength division multiplexer at different wavelengths. The calibration method for the demodulation parameters of the optical frequency variation of the Michelson interferometer comprises: using a laser to input an optical signal into the fast optical frequency detection device to obtain a three-way output interference signal; collecting the three-way interference signal and the laser output wavelength monitoring pulse; determining the specific wavelength value and the three-way interference signal at the corresponding wavelength through the wavelength monitoring pulse; selecting a wavelength near which the optical frequency variation is equal to the Michelson frequency; Three Lissajous ellipse fittings are performed on three groups of interference signals corresponding to the time period of the free spectrum range of the Kerson interferometer to obtain demodulation parameters of all wavelength-related optical frequency changes at a certain wavelength; the method for calibrating the splitting ratio of the wavelength division multiplexer at different wavelengths includes inputting a continuous spectrum in a large wavelength range into the fast optical frequency detection device, inputting one spectrum signal separated by a 3*3 optical coupler into the wavelength division multiplexer, and outputting two spectrum signals; collecting the spectrum of the two spectrum signals, calculating the spectrum result difference and ratio of the two spectrum signals at the same wavelength, and obtaining a wavelength lookup table of the result difference and ratio of the two output signals of the wavelength division multiplexer at different wavelengths.

[0013] The continuous wavelength scanning mode of a wide wavelength swept laser is used to output an optical signal into a Michelson interferometer.

[0014] The wavelengths at intervals of 0.1 nm to 10 nm within a large wavelength range are calibrated to obtain a lookup table of optical frequency variation demodulation parameters and wavelength.

[0015] In the method for calibrating the splitting ratio of a wavelength division multiplexer at different wavelengths, calibration is performed on wavelengths at intervals of 0.1 nm to 10 nm within a large wavelength range, and the difference and ratio of the spectrum results of two spectral signals at the same wavelength are calculated to obtain a wavelength lookup table of the difference and ratio of the results at different wavelengths at intervals of 0.1 nm to 10 nm for the two output signals of the wavelength division multiplexer.

[0016] Another technical solution of the present invention provides a fast optical frequency demodulation method, which uses the calibration results obtained by the above-mentioned fast optical frequency detection device demodulation parameter calibration method to calculate the absolute optical frequency and the optical frequency variation, including: using a wide wavelength swept laser as a light source input into the fast optical frequency detection device to collect three-way interference signals and two-way wavelength division multiplexer signals; calculating the difference, ratio and sum of the two output signals of the wavelength division multiplexer; obtaining the absolute wavelength of the input light by comparing the difference and sum ratio of the two output signals of the wavelength division multiplexer at different wavelengths obtained by calibration with a wavelength lookup table, and calculating the absolute frequency of the input light; based on the obtained absolute frequency of the input light and the calibrated optical frequency variation demodulation parameter and the wavelength lookup table, determining the optical frequency variation demodulation parameter corresponding to each sampling point point by point; calculating the optical frequency variation based on the three-way interference signals and the optical frequency variation demodulation parameter; and calculating the absolute frequency of the light to be measured based on the obtained optical frequency variation and the absolute frequency of the input light.

[0017] Compared with the prior art, the present invention has the following advantages: 1. The present invention divides the optical frequency to be measured into two parts, one of which is connected to the interferometer and the other to the wavelength division multiplexer. By using the sine / cosine demodulation algorithm and the absolute frequency demodulation algorithm, the optical frequency variation and absolute optical frequency can be measured simultaneously;

[0018] 2. The present invention can achieve high-frequency, large-range, and rapid measurement of optical frequency changes;

[0019] 3. The present invention proposes a demodulation parameter calibration method for an optical frequency detection device, which can calculate the actual phase deviation and optical frequency demodulation parameters corresponding to different wavelengths of a 3*3 coupler, thereby calibrating the non-ideality of the device and improving the robustness of the measurement.

[0020] In order to make the above and other objects, features and advantages of the present invention more clearly understood, preferred embodiments are given below with reference to the accompanying drawings for detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the specific embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0022] Figure 1 Schematic diagram of a fast optical frequency detection device according to embodiment 1 of the present invention.

[0023] Figure 2These are ideal output signal results of the three photodetectors of the Michelson interferometer of the fast optical frequency detection device of Example 1 of the present invention when the input light is in the wavelength range of 1500-1630 nm.

[0024] Figure 3 These are the actual output signal results of the three photodetectors of the Michelson interferometer in the fast optical frequency detection device of Example 1 of the present invention when the input light has a wavelength range of 1500-1630 nm and a wavelength step change interval of 10 nm.

[0025] Figure 4 These are actual output signal results of the two photodetectors of the wavelength division multiplexer in the fast optical frequency detection device of Example 1 of the present invention when the input light has a wavelength range of 1500-1630 nm and the wavelength step change interval is 10 nm.

[0026] Figure 5 This is a flow chart of the method for calibrating the demodulation parameters of the optical frequency variation of the Michelson interferometer in the demodulation parameter calibration method of the fast optical frequency detection device according to embodiment 2 of the present invention.

[0027] Figure 6 This is a diagram showing the ellipse fitting result of calculating the optical frequency variation demodulation parameter corresponding to 1550nm by using the Lissajous ellipse fitting method in the Michelson interferometer optical frequency variation demodulation parameter calibration method according to Example 2 of the present invention.

[0028] Figure 7 This is a graph showing the experimental results of optical frequency variation demodulation parameters C1(λ) and B1(λ) corresponding to each 1 nm wavelength in the range of 1500 to 1630 nm, obtained by calibrating the optical frequency variation demodulation parameter calibration method of the Michelson interferometer in Example 2 of the present invention using the Lissajous ellipse fitting method.

[0029] Figure 8 These are the optical frequency variation demodulation parameter phase differences β2(λ) and β3(λ) corresponding to each 1 nm wavelength in the range of 1500 to 1630 nm, obtained by calibrating the optical frequency variation demodulation parameter calibration method of the Michelson interferometer in Example 2 of the present invention using the Lissajous ellipse fitting method.

[0030] Figure 9 This is a flow chart of a method for calibrating the splitting ratio of a wavelength division multiplexer at different wavelengths in a method for calibrating demodulation parameters of a fast optical frequency detection device according to embodiment 2 of the present invention.

[0031] Figure 10 This is a relationship diagram between the ratio of the light intensity difference to the light intensity sum at two output ports of the wavelength division multiplexer and the input light wavelength within the wavelength range of 1500-1630nm obtained by the splitting ratio calibration method of the wavelength division multiplexer at different wavelengths in Example 2 of the present invention.

[0032] Figure 11 This is a flow chart of a fast optical frequency demodulation method according to embodiment 3 of the present invention.

[0033] Figure 12 The absolute optical frequency of the input light with a wavelength range of 1500-1630 nm and a wavelength step change interval of 10 nm and an optical frequency change diagram are calculated using the fast optical frequency demodulation method of Example 3 of the present invention.

[0034] Figure 13 The absolute optical frequency of the input light and the optical frequency variation diagram with a wavelength range of 1500-1630 nm, continuous wavelength variation, and a sweep speed of 200 nm / s (25 THz / s) calculated by the fast optical frequency demodulation method of Example 3 of the present invention.

[0035] Figure 14 This is an optical frequency variation diagram of input light with a wavelength step change interval of 10 pm, obtained by calculating the fast optical frequency demodulation method according to Example 3 of the present invention. DETAILED DESCRIPTION

[0036] The foregoing and other technical aspects, features, and functions of the present invention are clearly presented in the following detailed description of a preferred embodiment with reference to the accompanying drawings. Directional terms such as up, down, left, right, front, and back, used in the following embodiments, are intended solely to refer to the directions in the accompanying drawings. Therefore, the directional terms used are for illustrative purposes only and are not intended to limit the present invention.

[0037] Example 1

[0038] Example 1 provides a fast optical frequency detection device, including a Michelson interferometer with an input optical path, the Michelson interferometer including a 3*3 optical coupler, and the input light enters the Michelson interferometer from the 3*3 optical coupler; the 3*3 optical coupler divides the input optical path into three paths, two of which enter two interference arms with optical path difference, respectively, and the remaining path enters a wavelength division multiplexer; two Faraday rotators are arranged at the ends of the two interference arms, and the Faraday rotator reflects the optical path back to the 3*3 optical coupler, and the reflected optical path is divided into three output lights, which are received by three first photodetectors, and the three first photodetectors are used to obtain the optical frequency change of the input light; the two lights output by the wavelength division multiplexer are received by two second photodetectors, and the two second photodetectors are used to obtain the absolute optical frequency of the input light.

[0039] The following is a detailed explanation of the fast optical frequency detection device in Example 1 with reference to the accompanying drawings. Figure 1The fast optical frequency detection device of the present invention includes a Michelson interferometer 113 having an input optical path, and the Michelson interferometer 113 includes a 3*3 optical coupler 102. The 3*3 optical coupler 102 divides the input light into three paths, which enter the first interferometer arm 103 and the second interferometer arm 104 respectively. There is a variable optical path difference ΔL between the first interferometer arm 103 and the second interferometer arm 104. The ends of the first interferometer arm 103 and the second interferometer arm 104 are respectively the first Faraday rotator mirrors. 106 and second Faraday rotator mirror 107. First Faraday rotator mirror 106 and second Faraday rotator mirror 107 interfere with the incident light and reflect it back to 3*3 optical coupler 102, where it is split into three paths. One of the paths overlaps with the input light path and is split into two paths by a 1*2 optical coupler 101. One path is the input light path, and the other path is connected to first photodetector 110. The other two paths reflected by 3*3 optical coupler 102 are connected to two first photodetectors 111 and 112, respectively. Three first photodetectors 110, 111, and 112 generate first photodetection signals, which are used to calculate the optical frequency change of the input light.

[0040] After the input light path is split by the 3*3 optical coupler 102, in addition to entering the first interferometer arm 103 and the second interferometer arm 104, another light path enters the wavelength division multiplexer 105. The two light paths output by the wavelength division multiplexer 105 are received by two second photodetectors 108 and 109 to generate second photodetection signals for calculating the absolute optical frequency of the input light.

[0041] The 3*3 optical coupler has a phase difference of about 120°, which facilitates the subsequent demodulation of phase information. The three first photodetection signals change with a sine function or a cosine function, and the change of the sine function or the cosine function corresponds to the optical frequency change information of the input light.

[0042] The working center wavelength of the wavelength division multiplexer is located at both ends of the wavelength of the light to be measured, and the ratio of the two output signals of the wavelength division multiplexer corresponds to the absolute frequency information of the input light.

[0043] Figure 2 The ideal output signal results of the three photodetectors of the Michelson interferometer of the fast optical frequency detection device of Example 1 are demonstrated when the input light has a wavelength range of 1500 to 1630 nm.

[0044] Figure 3 These are the actual output signal results of the three photodetectors of the Michelson interferometer in the fast optical frequency detection device of Example 1 of the present invention when the input light has a wavelength range of 1500-1630 nm and a wavelength step change interval of 10 nm.

[0045] Figure 4These are actual output signal results of the two photodetectors of the wavelength division multiplexer in the fast optical frequency detection device of Example 1 of the present invention when the input light has a wavelength range of 1500-1630 nm and the wavelength step change interval is 10 nm.

[0046] Example 2

[0047] Example 2 provides a method for calibrating demodulation parameters of a fast optical frequency detection device, which is used to calibrate the demodulation parameters of the optical frequency variation of a Michelson interferometer in a fast optical frequency detection device of Example 1 and to calibrate the splitting ratio of a wavelength division multiplexer at different wavelengths.

[0048] See also Figure 5 The method for calibrating demodulation parameters of optical frequency variation of a Michelson interferometer includes: using a laser to input an optical signal into a fast optical frequency detection device to obtain three-way output interference signals; collecting the three-way interference signals and a laser output wavelength monitoring pulse; determining a specific wavelength value and the three-way interference signals at the corresponding wavelength through the wavelength monitoring pulse; selecting three groups of interference signals with an optical frequency variation near a certain wavelength equal to a period corresponding to the free spectrum range of the Michelson interferometer, and performing three-times Lissajous ellipse fitting to obtain all wavelength-related optical frequency variation demodulation parameters at the certain wavelength;

[0049] See also Figure 9 The invention discloses a method for calibrating the splitting ratio of a wavelength division multiplexer at different wavelengths, comprising inputting a continuous spectrum in a large wavelength range into a fast optical frequency detection device, inputting one spectrum signal separated by a 3*3 optical coupler into the wavelength division multiplexer, and outputting two spectrum signals; collecting the spectrum of the two spectrum signals, calculating the spectrum result difference and ratio of the two spectrum signals at the same wavelength, and obtaining a wavelength lookup table of the result difference and ratio of the two output signals of the wavelength division multiplexer at different wavelengths.

[0050] The input light uses a wide-wavelength swept laser in continuous wavelength scanning mode to output an optical signal to the Michelson interferometer. Simultaneously, wavelengths are calibrated at intervals of 0.1nm to 10nm over a wide wavelength range to generate a lookup table of optical frequency variation demodulation parameters and wavelength intervals of 0.1nm to 10nm at different wavelengths.

[0051] In the method for calibrating the splitting ratio of a wavelength division multiplexer at different wavelengths, calibration is performed on wavelengths at intervals of 0.1nm to 10nm within a large wavelength range, and the spectrum results difference and ratio of two spectral signals at the same wavelength are calculated. A parameter lookup table of the results difference and ratio and wavelength at different wavelengths at intervals of 0.1nm to 10nm for the two output signals of the wavelength division multiplexer is obtained.

[0052] The following describes a specific calculation process for demodulation parameter calibration by taking the delay imbalance of 2ΔL between the two interference arms of the Michelson interferometer 113 as an example.

[0053] The three output signals of the Michelson interferometer 113 are:

[0054]

[0055] Among them, V i (t)(i=1, 2, 3) is the output voltage of the three output channels of the interferometer; C i (λ)(i=1, 2, 3) is the bias coefficient caused by the DC bias of the circuit in each channel; B i (λ)(i=1, 2, 3) is the amplitude of the sine and cosine functions received in each channel; β i (λ)(i=1, 2, 3) is the phase change of the three lasers caused by the coupler. Ideally, the difference between them is 120°. Is the phase change caused by the measured light frequency Δf(t). i , β i Usually weakly wavelength dependent.

[0056] The above C i 、B i , β i is the demodulation parameter of the optical frequency variation of the Michelson interferometer.

[0057] The interferometer free spectral range (FSR) is defined as:

[0058] FSR=1 / τ=c / Δl (4)

[0059] Here, τ is the delay time between the two arms of the Michelson interferometer, and the optical path length difference Δ1 between the two arms of the interferometer is set to 2ΔL.

[0060] is the phase change caused by the light frequency Δf(t) to be measured, which can be expressed as:

[0061]

[0062] Figure 2 Shown from Figure 1 The phase relationship between the three output light paths of the Michelson interferometer in the fast optical frequency detection device can be used to determine the optical frequency change Δf(t) from the three output signals according to the following formula 6:

[0063]

[0064] During the demodulation process, β1 is set to 0. At this point, β2 and β3 are the phase differences between their respective channels and the channel corresponding to β1. The phase demodulation algorithm can be used to calculate phase changes exceeding 2π, thereby determining the optical frequency change Δf and the direction of the frequency change. Optical frequency calculation requires demodulation parameters, so these parameters must be calibrated first. Three photodetectors are used to obtain voltages within multiple channels. These voltages are then substituted into the calculation to determine the optical frequency change. Furthermore, due to the small FSR, ultra-high frequency resolution can be achieved. The relationship between frequency resolution and FSR is: frequency resolution is FSR / (2^M), where M is the number of bits on the acquisition card plus one. Therefore, a smaller FSR results in a higher resolution.

[0065] The above formula 6 is used to calculate the optical frequency change and the direction of frequency change, where the demodulation parameter B i 、C i , β i The demodulation parameter B is wavelength-dependent. i 、C i , β i The calibration method is as follows Figure 5 The method includes using laser wavelength scanning input, collecting three-way interference signals and laser output wavelength monitoring pulses, determining the specific wavelength value and the three-way interference signals at the corresponding wavelength through the wavelength monitoring pulse, and selecting an interference signal with a time length corresponding to an FSR within the wavelength range for Lissajous ellipse fitting to calculate the demodulation parameter B. i 、C i , β i Repeat the above steps until all wavelengths are calculated. The following explains the calculation process of Lissajous ellipse fitting for the selected wavelengths.

[0066] Figure 6 The demodulation parameters are calibrated using the Lissajous ellipse fitting method at 1550nm, taking V1(t) and V2(t) as an example, with an ideal phase difference of 120°. For any two interference signals with a phase difference of α (α≠π), they can be expressed using trigonometric functions as follows:

[0067]

[0068] Where C1(λ) and C2(λ) are the DC components of the interference signals, B1(λ) and B2(λ) are the amplitudes of the interference signals, and α is the actual phase difference between the two interference signals. Expanding the above formulas 7 and 8 yields:

[0069]

[0070] According to trigonometric formulas:

[0071]

[0072] Substituting into the above formula we can get:

[0073]

[0074] Meanwhile, the standard equation of an ellipse is:

[0075]

[0076] Where A, B, C, D, and E are the coefficients of the standard ellipse equation. Equation 11 is derived by fitting V1(t) and V2(t) using a Lissajous ellipse. By comparing the derived equation 11 with the standard ellipse equation 12, the demodulation parameters of the interference signal DC component, amplitude, and actual phase difference can be obtained. The calculation results are shown in Equations 13 to 17.

[0077]

[0078] Therefore, all demodulation parameters in the calculation of optical frequency variation at a certain wavelength can be obtained by the Lissajous ellipse fitting method of the two-way interference signal. Figure 7-Figure 8 The calibration results of the demodulation parameters C1(λ), B1(λ), β2(λ), and β3(λ) for the optical frequency variation per 1 nm wavelength interval for one output of the Michelson interferometer in the wavelength range of 1500 to 1630 nm are shown. β2(λ) is the phase difference between the phase interference signals V1(t) and V2(T), and β3(λ) is the phase difference between the phase interference signals V1(t) and V3(t). The demodulation parameters C1(λ) obtained by calibrating the other two outputs of the Michelson interferometer are i (λ), B i (λ) and Figure 7 consistent.

[0079] In the process of measuring absolute frequency, the splitting ratio of the wavelength division multiplexer at different wavelengths needs to be calibrated in advance. The method for calibrating the splitting ratio of the wavelength division multiplexer at different wavelengths is as follows: Figure 9 , including using a supercontinuum spectrum with a large wavelength range as the device input, the wavelength division multiplexer obtains two output lights, which are connected to a spectrum analyzer to obtain the spectra of the two output signals, and calculating the difference ratio and sum of the two at the same wavelength. The lookup table of the difference ratio and sum of the two output signals of the wavelength division multiplexer at different wavelengths and the wavelength λ can be obtained. Figure 10 The figure shows the relationship between the ratio R1(t) of the light intensity difference to the sum of the light intensities at the two output ports of the wavelength division multiplexer and the input light wavelength λ.

[0080] All demodulation parameters in the calculation of the optical frequency variation obtained by calibration in Example 2 and a lookup table of the difference ratio and wavelength λ of the two output signals of the wavelength division multiplexer at different wavelengths are used for optical frequency demodulation.

[0081] Example 3

[0082] Example 3 provides a fast optical frequency demodulation method, which uses the calibration results obtained by the demodulation parameter calibration method of a fast optical frequency detection device in Example 2 to calculate the absolute optical frequency and the optical frequency variation, such as Figure 11 As shown, the method includes: using a wide wavelength swept laser as a light source to input into a fast optical frequency detection device, collecting three-way interference signals and two-way wavelength division multiplexer signals; calculating the difference, ratio and sum of the two-way output signals of the wavelength division multiplexer; obtaining the absolute wavelength of the input light by comparing the difference and sum ratio of the two-way output signals of the wavelength division multiplexer obtained by calibration at different wavelengths with a wavelength lookup table, and calculating the absolute frequency of the input light; repeatedly inputting the light source at different time points and calculating the absolute frequency of the input light to obtain the initial absolute frequency of the input light, and establishing a relationship between the absolute frequency of the input light and time; based on the obtained absolute wavelength of the input light and the lookup table of the optical frequency variation demodulation parameter and the wavelength obtained by calibration, determining the optical frequency variation demodulation parameter corresponding to each sampling point point by point; and calculating the optical frequency variation according to the three-way interference signal and the optical frequency variation demodulation parameter.

[0083] The specific calculation process is as follows:

[0084] Depend on Figure 10 It can be seen that R1(t) reaches its minimum value at 1260nm and its maximum value at 1480nm. It changes unidirectionally with the wavelength in the range of 1260nm to 1480nm and 1480nm to 1700nm, and has a one-to-one correspondence with the wavelength, that is:

[0085]

[0086] Where λ is the input light wavelength, and f1 and f2 are reversible functions.

[0087] When measuring the absolute frequency of the input light, the ratio of the difference to the sum of the output signals of the two second photodetectors connected to the two output ports of the wavelength division multiplexer is:

[0088]

[0089] Wherein, P1(t) is the output voltage of the photodetector 108 , and P2(t) is the output voltage of the photodetector 109 .

[0090] If the input light wavelength band is known to be in a specific range, the absolute wavelength λ(t) of the input light can be quickly and in real time by calculating the ratio of the light intensity difference to the sum of the light intensities at the two output ports at the current moment, R1(t), and then matching it with R1(λ). That is,

[0091]

[0092] The absolute frequency of the input light f0 and λ(t) satisfy the following relationship:

[0093] f0(t)=c / λ(t)(21)

[0094] Formula 6 in Example 2 is used to calculate the optical frequency variation. The demodulation parameter C in Formula 6 is i 、B i , β i Are related to the wavelength, according to the absolute wavelength f0 (t) call the demodulation parameter C i 、B i , β i This can reduce the effect of wavelength on the measurement of optical frequency variation. In the previous section, we calibrated the demodulation parameters for relative frequency at different wavelengths. Here, we use the relative wavelength demodulation parameters corresponding to the absolute wavelength to reduce the effect of wavelength variations on relative frequency demodulation. Otherwise, only one set of demodulation parameters would be used to demodulate relative frequency variations across the entire wavelength range, resulting in significant errors.

[0095] Figure 4 Demonstrated use Figure 1 The optical frequency detection device measures the actual signals measured by two photoelectric detectors when the TSL-570 laser is scanned in a unidirectional step-by-step manner in the wavelength range of 1500~1630nm with a wavelength step change interval of 10nm.

[0096] The second photodetector on the wavelength division multiplexer output path receives the optical signal and generates a second photodetection signal, which is then used to calculate the absolute frequency of the input light f0(t). The three signals output by the Michelson interferometer are received by the first photodetector and generate a first photodetection signal. Combined with the optical frequency increment demodulation parameter, the optical frequency change Δf(t) is then calculated. The absolute optical frequency can be obtained by calculating the absolute input light frequency f0(t) and the optical frequency change Δf(t), that is:

[0097] f(t)=f0(t0)+Δf(t) (22)

[0098] Where t0 is the point where Δf(t) is 0, which is generally set as the starting time.

[0099] The absolute frequency of the first point measured by the wavelength division multiplexer is used as the starting point of the relative frequency. The absolute frequency of the light to be measured has higher accuracy and resolution than the absolute frequency measured only by the wavelength division multiplexer.

[0100] Figure 13Figure 3 shows the absolute optical frequency of input light, calculated using the fast optical frequency demodulation method of Example 3, for a wavelength range of 1500-1630 nm, continuously varying wavelengths, and a sweep rate of 200 nm / s (25 THz / s), as well as a graph of the optical frequency variation. As can be seen from the figure, the fast optical frequency detection device of Example 1 is capable of measuring the absolute optical frequency of continuously varying wavelengths from 1500-1630 nm.

[0101] Figure 14 This is the optical frequency variation diagram of the input light with a wavelength step change interval of 10pm calculated by the fast optical frequency demodulation method of Example 3 of the present invention. Figure 14 It can be seen that the fast optical frequency detection device in Example 1 can achieve optical frequency change measurement with ultra-high optical frequency resolution. At the same time, the transient dynamic process of the transition between wavelengths can be clearly seen, reflecting the deviation of the laser wavelength tuning.

[0102] The above describes in detail the rapid optical frequency detection device, demodulation parameter calibration method, and optical frequency demodulation method provided by the present invention. Specific examples are used herein to illustrate the structure and operating principles of the present invention. The description of the above embodiments is intended only to facilitate understanding of the method and core concepts of the present invention. It should be noted that those skilled in the art will be able to make various improvements and modifications to the present invention without departing from the principles of the present invention, and such improvements and modifications fall within the scope of protection of the claims.

Claims

1. A fast optical frequency detection device, characterized in that: A Michelson interferometer having an input optical path, wherein the Michelson interferometer includes a 3*3 optical coupler, and input light enters the Michelson interferometer from the 3*3 optical coupler; The 3*3 optical coupler divides the input light path into three paths, two of which enter two interference arms with optical path difference, and the remaining path enters a wavelength division multiplexer; Two Faraday rotators are provided at the ends of the two interferometer arms. The Faraday rotators reflect the light path back to the 3*3 optical coupler. The reflected light path is divided into three output lights, which are received by three first photodetectors to generate first photodetection signals for calculating the optical frequency change of the input light. The two paths of light output by the wavelength division multiplexer are received by two second photodetectors, generating second photodetection signals for calculating the absolute optical frequency of the input light.

2. A fast optical frequency detection device according to claim 1, characterized in that: One of the three output optical paths shares the input optical path and is divided into two optical paths by a 1*2 optical coupler. The optical paths divided by the 1*2 optical coupler are respectively used for inputting input light and connecting to the first photodetector.

3. A fast optical frequency detection device according to claim 1, characterized in that: The phase difference between the output signals of the three output optical paths after light splitting by the 3*3 optical coupler is approximately 120°; The intensities of the three first photoelectric detection signals vary according to a sine function or a cosine function, and the variation of the sine function or the cosine function corresponds to the variation of the optical frequency of the input light.

4. A fast optical frequency detection device according to claim 1, characterized in that: The working center wavelength of the wavelength division multiplexer is located at both ends of the wavelength of the light to be measured, and the ratio of the two output signals of the wavelength division multiplexer corresponds to the absolute optical frequency of the input light.

5. A fast optical frequency detection device according to claim 1, characterized in that: The optical path difference between the two interferometer arms is a variable optical path difference.

6. A method for calibrating demodulation parameters of a fast optical frequency detection device, characterized in that: Used for calibrating the demodulation parameters of the optical frequency variation of the Michelson interferometer in the fast optical frequency detection device according to any one of claims 1 to 5, and for calibrating the splitting ratio of the wavelength division multiplexer at different wavelengths; The method for calibrating the demodulation parameter of the optical frequency variation of the Michelson interferometer comprises: using a laser to input an optical signal into a fast optical frequency detection device to obtain three output interference signals; Collect three-way interference signals and laser output wavelength monitoring pulses; Determine the specific wavelength value and the three-way interference signal at the corresponding wavelength through the wavelength monitoring pulse; Three groups of interference signals with optical frequency variations equal to the period corresponding to the free spectrum range of the Michelson interferometer are selected near a certain wavelength and Lissajous ellipse fitting is performed three times to obtain the demodulation parameters of all wavelength-related optical frequency variations at a certain wavelength. The method for calibrating the splitting ratio of the wavelength division multiplexer at different wavelengths includes inputting a continuous spectrum in a large wavelength range into the fast optical frequency detection device, inputting one spectrum signal split by a 3*3 optical coupler into the wavelength division multiplexer, and outputting two spectrum signals; The spectra of the two spectral signals are collected, the spectrum results difference and ratio of the two spectral signals at the same wavelength are calculated, and a wavelength lookup table of the results difference and ratio of the two output signals of the wavelength division multiplexer at different wavelengths is obtained.

7. A method for calibrating demodulation parameters of a fast optical frequency detection device according to claim 6, characterized in that: The continuous wavelength scanning mode of a wide wavelength swept laser is used to output an optical signal into a Michelson interferometer.

8. The method for calibrating demodulation parameters of a fast optical frequency detection device according to claim 6, wherein: The wavelengths at intervals of 0.1 nm to 10 nm within a large wavelength range are calibrated to obtain a lookup table of optical frequency variation demodulation parameters and wavelength.

9. The method for calibrating demodulation parameters of a fast optical frequency detection device according to claim 6, wherein: In the method for calibrating the splitting ratio of a wavelength division multiplexer at different wavelengths, calibration is performed on wavelengths at intervals of 0.1 nm to 10 nm within a large wavelength range, and the difference and ratio of the spectrum results of two spectral signals at the same wavelength are calculated to obtain a wavelength lookup table of the difference and ratio of the results at different wavelengths at intervals of 0.1 nm to 10 nm for the two output signals of the wavelength division multiplexer.

10. A fast optical frequency demodulation method, characterized in that: Calculating the absolute optical frequency and the optical frequency variation using the calibration result obtained by the demodulation parameter calibration method of a fast optical frequency detection device according to any one of claims 6 to 9, comprising: A wide wavelength swept laser is used as a light source to input into a fast optical frequency detection device to collect three-way interference signals and two-way wavelength division multiplexer signals; Calculate the difference, ratio and sum of the two output signals of the wavelength division multiplexer; The absolute wavelength of the input light is obtained by comparing the difference and ratio of the two output signals of the wavelength division multiplexer at different wavelengths obtained by calibration with the wavelength lookup table, and the absolute frequency of the input light is calculated; Based on the acquired absolute frequency of the input light and the calibrated lookup table of optical frequency variation demodulation parameters and wavelength, the optical frequency variation demodulation parameters corresponding to each sampling point are determined point by point; Calculate the optical frequency variation according to the three-way interference signal and the optical frequency variation demodulation parameter; The absolute frequency of the light to be measured is calculated based on the obtained optical frequency variation and the absolute frequency of the input light.

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