Optical frequency detection chip, demodulation parameter calibration method, and optical frequency demodulation method

Abstract

The present invention relates to an optical frequency detection chip, a demodulation parameter calibration method, and an optical frequency demodulation method. The optical frequency detection chip of the present invention is loaded on a substrate with a first coupler as an input port and a first Mach-Zehnder interferometer and a second Mach-Zehnder interferometer corresponding to the two outputs of the first coupler; the two interferometers each have four outputs, each output is detected by a photodetector, and the four outputs of each interferometer are divided into two pairs, the phase difference between the two interference signals of each pair is 180°, and the phase difference between the two pairs is 90°. The two pairs of signals change with a sine or cosine function, and the change corresponds to the measured optical frequency information. The present invention can measure the optical frequency in real time and quickly, and measure the optical frequency increment with ultra-high resolution. At the same time, the robustness of the chip measurement is improved by calibrating the non-ideal phase deviation of the two 90° mixers.

Description

Technical Field

[0001] This invention relates to a photonic integrated chip for measuring optical frequency changes and absolute optical frequency, specifically an optical frequency detection chip and its demodulation parameter calibration method and optical frequency demodulation method. Background Technology

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

[0003] The commonly used methods for detecting optical frequency information are as follows:

[0004] (1) Detection is performed using a spectrometer based on a diffraction grating or a tunable narrowband filter. The spectrometer used in this detection method has extremely high measurement accuracy, but its measurement speed, measurement accuracy, and resolution are mutually restrictive and mutually influential.

[0005] (2) Optical frequency measurement method based on unbalanced Mach-Zehnder interferometer. The resolution of this detection method is inversely proportional to the delay τ, so it is not suitable for photonic integration. At the same time, long-distance fiber optic transmission will increase the noise of the laser frequency, which can easily lead to errors in generating clocks with equal frequency intervals f.

[0006] (3) Optical frequency measurement method based on Hilbert transform. This detection method can correct the frequency scanning nonlinearity of the laser during data processing, but it requires a long phase data before the Hilbert transform, which is not suitable for real-time measurement of optical frequency.

[0007] (4) Optical frequency measurement method based on differential group delay (DGD) element. This detection method can achieve high resolution, wide range and high speed optical frequency measurement, but its optical element is large in size and is not suitable for photonic integrated systems.

[0008] All of the above-mentioned optical frequency measurement methods have disadvantages in terms of frequency measurement resolution, frequency measurement range, and frequency measurement speed. In addition, the detection system is large in size and expensive, so they are not suitable for integrated photonic chips. Summary of the Invention

[0009] One of the objectives of this invention is to provide an optical frequency detection chip to solve the problems of large device size, high cost, difficulty in integration, and mutual constraints between measurement speed, measurement accuracy, and resolution in existing optical frequency measurement technologies.

[0010] The second objective of this invention is to provide a method for calibrating the demodulation parameters of an optical frequency detection chip, so as to calibrate the non-ideal phase difference of the output signal of the 90° mixer in the chip, thereby improving the robustness of optical frequency measurement.

[0011] The third objective of this invention is to provide an optical frequency demodulation method for an optical frequency detection chip, which can be used for real-time and rapid optical frequency detection.

[0012] One of the objectives of this invention is achieved as follows:

[0013] An optical frequency detection chip, comprising:

[0014] Substrate, used to load the following devices;

[0015] The first coupler has two outputs connected to the first Mach-Zehnder interferometer and the second Mach-Zehnder interferometer, respectively, to receive the input light and split the input light into two beams, which are then output to the first Mach-Zehnder interferometer and the second Mach-Zehnder interferometer.

[0016] The first Mach-Zehnder interferometer has an input terminal connected to a first coupler. The optical path difference between the two interferometer arms is ΔL to generate an unbalanced delay in optical transmission. Each of the four output terminals is connected to a photodetector. The four outputs are divided into two pairs. One pair outputs an interference signal that varies with a cosine function and corresponds to the optical frequency increment information of the input light. The other pair outputs an interference signal that varies with a sine function and corresponds to the optical frequency increment information of the input light. The phase difference between each pair of output interference signals is 180°, and the phase difference between the two pairs of output interference signals is 90°.

[0017] The second Mach-Zehnder interferometer has an input terminal connected to the first coupler. The optical path difference between the two interferometer arms is ΔM, and ΔM << ΔL, to generate an unbalanced delay in optical transmission. Each of the four output terminals is connected to a photodetector. The four outputs are divided into two pairs. One pair outputs an interference signal that varies with a cosine function and corresponds to the absolute optical frequency information of the input light. The other pair outputs an interference signal that varies with a sine function and corresponds to the absolute optical frequency information of the input light. The phase difference between each pair of output interference signals is 180°, and the phase difference between the two pairs of output interference signals is 90°.

[0018] The first photodetector is connected to the first output terminal of the first Mach-Zehnder interferometer. It is used to detect the interference signal output from the first channel and generate the first output voltage signal V that varies with the cosine function and corresponds to the optical frequency increment information of the input light. u1 (t);

[0019] The second photodetector is connected to the second output terminal of the first Mach-Zehnder interferometer. It is used to detect the interference signal output from the second channel and generate a second output voltage signal V that varies with the cosine function and corresponds to the optical frequency increment information of the input light. u2 (t);

[0020] The third photodetector, connected to the third output terminal of the first Mach-Zehnder interferometer, is used to detect the interference signal from the third output and generate the first output voltage signal V that varies with a sine function and corresponds to the increment of the input light's optical frequency. u3 (t);

[0021] The fourth photodetector, connected to the fourth output terminal of the first Mach-Zehnder interferometer, is used to detect the interference signal from the fourth output and generate a second output voltage signal V that varies with a sine function and corresponds to the increment of the input light's optical frequency. u4 (t);

[0022] The fifth photodetector, connected to the first output of the second Mach-Zehnder interferometer, is used to detect the interference signal from the first output path and generate the first output voltage signal V that varies with a cosine function and corresponds to the absolute optical frequency information of the input light. l1 (t);

[0023] The sixth photodetector, connected to the second output terminal of the second Mach-Zehnder interferometer, is used to detect the interference signal from the second output and generate a second output voltage signal V that varies with a cosine function and corresponds to the absolute optical frequency information of the input light. l2 (t);

[0024] The seventh photodetector, connected to the third output of the second Mach-Zehnder interferometer, is used to detect the interference signal from the third output and generate the first output voltage signal V that varies with a sine function and corresponds to the absolute optical frequency information of the input light. l3 (t);

[0025] The eighth photodetector, connected to the fourth output of the second Mach-Zehnder interferometer, is used to detect the interference signal from the fourth output and generate a second output voltage signal V that varies with a sine function and corresponds to the absolute optical frequency information of the input light. l4 (t).

[0026] Furthermore, the first Mach-Zehnder interferometer of the present invention includes:

[0027] The second coupler is connected to the first coupler, the first optical waveguide, and the second optical waveguide, respectively. It is used to receive the input light transmitted from the first coupler and split the received input light into two beams and output them to the first optical waveguide and the second optical waveguide.

[0028] The first optical waveguide, connected between the second coupler and the first 90° mixer, serves as the first interferometer arm of the first Mach-Zehnder interferometer and is used to transmit the light beam to the first 90° mixer.

[0029] The second optical waveguide, connected between the second coupler and the first 90° mixer, serves as the second interferometer arm of the first Mach-Zehnder interferometer and is used to transmit the beam to the first 90° mixer.

[0030] The first 90° mixer is used to receive and combine two beams of light with an optical path difference of ΔL from the first and second optical waveguides to generate four interference beams, and output four interference signals through four output terminals.

[0031] Furthermore, the second Mach-Zehnder interferometer of the present invention includes:

[0032] The third coupler is connected to the first coupler, the third optical waveguide, and the fourth optical waveguide, respectively. It is used to receive the input light transmitted from the first coupler and split the received input light into two beams for output to the third and fourth optical waveguides.

[0033] The third optical waveguide, connected between the third coupler and the second 90° mixer, serves as the first interferometer arm of the second Mach-Zehnder interferometer and is used to transmit the beam to the second 90° mixer.

[0034] The fourth optical waveguide, connected between the third coupler and the second 90° mixer, serves as the second interferometer arm of the second Mach-Zehnder interferometer and is used to transmit the light beam to the second 90° mixer.

[0035] The second 90° mixer is used to receive and combine two beams of light with an optical path difference of ΔM from the third and fourth optical waveguides to generate four interference beams, and output four interference signals through four output terminals.

[0036] Furthermore, the optical frequency increment information is contained within multiple cycles of the four-channel sine-cosine function output signal of the first Mach-Zehnder interferometer.

[0037] Furthermore, the absolute optical frequency information is contained within a monotonic variation range of the phase change of the four sine-cosine functions of the second Mach-Zehnder interferometer.

[0038] The optical frequency detection chip of this invention includes two Mach-Zehnder interferometers, with the delay imbalance ΔL of the first Mach-Zehnder interferometer being significantly greater than the delay imbalance ΔM of the second Mach-Zehnder interferometer. Each Mach-Zehnder interferometer is generated by four photodetectors detecting and combining the input light from the two interferometer arms received by the interferometer through a 90° mixer, producing four outputs from each Mach-Zehnder interferometer. The four outputs of each Mach-Zehnder interferometer can be divided into two pairs. Ideally, the phase difference between the two interference signals in each pair is 180°, and the phase difference between the two pairs is 90°. The two pairs of signals vary with a sine or cosine function, corresponding to the measured optical frequency information. Using an optical frequency demodulation algorithm, the first Mach-Zehnder interferometer can obtain any optical frequency increment with ultra-high resolution, while the second Mach-Zehnder interferometer can obtain the absolute optical frequency.

[0039] The second objective of this invention is achieved as follows:

[0040] A method for calibrating demodulation parameters of an optical frequency detection chip includes a method for calibrating the incremental demodulation parameters of a first Mach-Zehnder interferometer and a method for calibrating the absolute optical frequency of a second Mach-Zehnder interferometer.

[0041] S1. The calibration method for the optical frequency increment demodulation parameters of the first Mach-Zehnder interferometer includes the following steps:

[0042] S1-1 inputs the output signal of the wide wavelength range scanning laser in continuous wavelength range scanning mode to the input terminal of the optical frequency detection chip.

[0043] S1-2 obtains four output interference signals through the first, second, third, and fourth photodetectors connected to the output of the first Mach-Zehnder interferometer: V uj (t),j=1,2,3,4.

[0044] S1-3 uses a wide-wavelength range scanning laser to monitor the output wavelength pulses, determining the specific wavelength values ​​corresponding to each of the four output interference signals. From these, a free spectral range (FSR) is selected that is near wavelength λ and has a frequency variation equal to that of the first Mach-Zehnder interferometer. u Interference signals of varying durations, ideally with a phase difference of 90°, are considered as interference signals V. u1 (t) and V u3 、V u2 (t) and V u3 (t), V u1 (t) and V u4 (t) Perform Lissajous ellipse fitting once for each wavelength to obtain all wavelength-related optical frequency increment demodulation parameters at that wavelength.

[0045] S1-4 repeats steps S1-1 to S1-3 for every 1nm wavelength in the wavelength range of 1480nm to 1640nm, thus obtaining a lookup table of optical frequency increment demodulation parameters and wavelength λ.

[0046] S2. The absolute optical frequency calibration method for the second Mach-Zehnder interferometer includes the following steps:

[0047] S2-1 inputs the output signal of the continuous wavelength range scanning mode of the wide wavelength range scanning laser to the input terminal of the optical frequency detection chip.

[0048] During a wide wavelength scan, S2-2 measures the interference signals output by the fifth, sixth, seventh, and eighth photodetectors connected to the output of the second Mach-Zehnder interferometer, respectively: V lj (t),j=1,2,3,4.

[0049] S2-3 solves for the phase of the sine-cosine functions of the four outputs. The phase corresponding to different wavelengths λ was obtained through calibration. The specific wavelength value is determined by monitoring the output pulses of a wide-wavelength scanning laser; for the measurement of unknown absolute optical frequency, it is determined by the calibrated wavelength λ and the corresponding phase. The lookup table will determine this.

[0050] The third objective of this invention is achieved as follows:

[0051] An optical frequency demodulation method for an optical frequency detection chip includes the following steps:

[0052] S3-1 uses a wide-wavelength scanning laser as the input light source. When light of unknown absolute frequency and optical frequency increment is input, the phase is calculated using the output signals from the fifth, sixth, seventh, and eighth photodetectors connected to the output of the second Mach-Zehnder interferometer.

[0053] S3-2 obtains the absolute light frequency information by using a pre-calibrated absolute light frequency lookup table, and obtains the change of absolute light frequency f with time t and the initial absolute light frequency f0.

[0054] S3-3 uses the absolute optical frequency f(t) to look up the optical frequency increment demodulation parameters and the lookup table of wavelength λ or absolute optical frequency f, and determines the corresponding optical frequency increment demodulation parameters for each sampling point point by point.

[0055] S3-4 outputs four signals V from the first, second, third, and fourth photodetectors connected to the output terminal of the first Mach-Zehnder interferometer. uj (t), calculate the light frequency increment Δf(t), and thus obtain the absolute light frequency f0 and the light frequency increment information Δf(t) of the measured light.

[0056] The advantages of this invention are as follows: 1. This invention divides the input optical frequency into two branches, each connected to an interferometer. Utilizing the sine / cosine demodulation algorithm in the optical frequency demodulation method, it can simultaneously measure both the optical frequency change and the absolute optical frequency. 2. This invention can simultaneously achieve high-resolution, wide-range, and rapid optical frequency change measurements without mutual constraints. 3. This invention, by integrating the optical path onto a photonic chip, significantly reduces the size, volume, and cost of the device. 4. The demodulation parameter calibration method for the optical frequency detection chip in this invention can calculate the actual phase deviation and optical frequency demodulation parameters corresponding to different wavelengths of the 90° mixer, thereby calibrating the non-ideal phase difference of the 90° mixer output signal in the optical frequency detection chip and improving the robustness of optical frequency measurement.

[0057] This invention relates to photonic integrated chips used in the fabrication of photonic integrated circuits for ultra-high resolution, rapid, real-time measurement of optical frequency changes and absolute optical frequencies. It effectively solves the problems of large device size, high cost, difficulty in integration, and the mutual constraints between measurement speed, accuracy, and resolution in existing optical frequency measurement technologies. This invention addresses equipment defects by calibrating and fixing device non-ideals. Attached Figure Description

[0058] Figure 1 This is a schematic diagram of the optical frequency detection chip of the present invention.

[0059] Figure 2 This is a graph showing the output signal results of the four photodetectors of the first Mach-Zehnder interferometer with a measurement range of 1519 nm.

[0060] Figure 3 This is a diagram showing the ideal output signal results of one photodetector in each of the first and second Mach-Zehnder interferometers within the measurement range of 1480nm to 1640nm.

[0061] Figure 4 This is a flowchart of the calibration procedure for the optical frequency increment demodulation parameters of the first Mach-Zehnder interferometer.

[0062] Figure 5 The figure shows the ellipse fitting results of the optical frequency increment demodulation parameters at 1519nm, calculated using the Lissajous ellipse fitting method.

[0063] Figure 6 The optical frequency detection chip of this invention is calibrated using the Lissajous ellipse fitting method, which yields the optical frequency increment demodulation parameter B corresponding to each 1nm wavelength within the wavelength range of 1480nm to 1640nm. u1 (λ) and m u1 B u1 The experimental results of (λ) are shown in the figure.

[0064] Figure 7 The optical frequency detection chip of this invention is calibrated using the Lissajous ellipse fitting method, which yields the optical frequency increment demodulation parameter phase deviation α corresponding to each 1nm wavelength within the wavelength range of 1480nm to 1640nm. u The result graph of (λ).

[0065] Figure 8 The optical frequency detection chip of this invention is calibrated using the Lissajous ellipse fitting method, which yields the optical frequency increment demodulation parameter phase deviation β corresponding to each 1nm wavelength within the wavelength range of 1480nm to 1640nm. u The result graph of (λ).

[0066] Figure 9 The optical frequency detection chip of this invention is calibrated using the Lissajous ellipse fitting method, which yields the optical frequency increment demodulation parameter phase deviation γ corresponding to each 1nm wavelength within the wavelength range of 1480nm to 1640nm. u The result graph of (λ).

[0067] Figure 10 This is a flowchart of the absolute optical frequency (or wavelength) calibration procedure for the second Mach-Zehnder interferometer.

[0068] Figure 11 The absolute optical frequency (wavelength) and phase at each 1nm wavelength within the 1490–1640nm wavelength range are obtained by calibrating the optical frequency detection chip of this invention. The monotonic correspondence results are shown in the graph.

[0069] Figure 12 This is a flowchart of the optical frequency demodulation algorithm program for the optical frequency detection chip of this invention.

[0070] Figure 13 The figure shows the experimental results of measuring the absolute optical frequency and optical frequency change in the wavelength range of 1500-1630nm with a wavelength step change interval of 10nm, using the optical frequency detection chip of this invention.

[0071] Figure 14 The figure shows the experimental results of measuring the absolute optical frequency and optical frequency variation in the wavelength range of 1520-1570nm with continuous wavelength variation and a frequency sweep speed of 20000nm / s (2500THz / s) using the optical frequency detection chip of this invention.

[0072] Figure 15 This is a graph showing the experimental results of measuring the optical frequency change of a laser modulated by a 100kHz high-frequency sine wave using the optical frequency detection chip of this invention.

[0073] Figure 16 This is a graph showing the experimental results of measuring the optical frequency change of a laser modulated by a 1Hz sine wave using the optical frequency detection chip of this invention.

[0074] In the diagram: 101, First Coupler; 102, Second Coupler; 103, Third Coupler; 104, First Optical Waveguide; 105, Second Optical Waveguide; 106, Third Optical Waveguide; 107, Fourth Optical Waveguide; 108, First 90° Mixer; 109, Second 90° Mixer; 110, First Photodetector; 111, Second Photodetector; 112, Third Photodetector; 113, Fourth Photodetector; 114, Fifth Photodetector; 115, Sixth Photodetector; 116, Seventh Photodetector; 117, Eighth Photodetector; 118, First Mach-Zehnder Interferometer; 119, Second Mach-Zehnder Interferometer. Specific implementation methods

[0075] The invention will now be described in further detail with reference to the accompanying drawings.

[0076] like Figure 1 As shown, the optical frequency detection chip of the present invention is configured as follows:

[0077] The substrate is loaded with devices including a first coupler 101, a first Mach-Zehnder interferometer 118, a second Mach-Zehnder interferometer 119, a first photodetector 110, a second photodetector 111, a third photodetector 112, a fourth photodetector 113, a fifth photodetector 114, a sixth photodetector 115, a seventh photodetector 116, and an eighth photodetector 117. Among these, the first coupler 101, the second coupler 102, and the third coupler 103 are all 3dB optical couplers; the first 90° mixer 108 and the second 90° mixer 109 are both 2×4 multimode interferometric couplers.

[0078] The first coupler 101 serves as the input port of the optical frequency detection chip, and its two outputs are connected to the first Mach-Zehnder interferometer 118 and the second Mach-Zehnder interferometer 119, respectively, to receive the input light and split the input light into two beams, which are then output to the first Mach-Zehnder interferometer and the second Mach-Zehnder interferometer.

[0079] The first Mach-Zehnder interferometer 118 includes a second coupler 102, a first optical waveguide 104, a second optical waveguide 105, and a first 90° mixer 108. The input of the second coupler 102 is connected to the first coupler 101, and its two outputs are connected to the first optical waveguide 104 and the second optical waveguide 105, respectively. It receives the input light transmitted from the first coupler 101 and splits the received input light into two beams, outputting them to the first and second optical waveguides 104 and 105. The first optical waveguide 104 connects the second coupler 102 and the first 90° mixer 108, serving as the first interferometer arm of the first Mach-Zehnder interferometer and transmitting the light beam to the first 90° mixer 108. The second optical waveguide 105 connects the second coupler 102 and the first 90° mixer 108, serving as the second interferometer arm of the first Mach-Zehnder interferometer and transmitting the light beam to the first 90° mixer 108. The first optical waveguide 104 has an optical path length of ΔL compared to the second optical waveguide 105, resulting in an imbalance in optical transmission delay. The first 90° mixer 108 serves as the output port of the first Mach-Zehnder interferometer 118, used to receive and combine two beams of light from the first optical waveguide 104 and the second optical waveguide 105 with an optical path difference of ΔL, to generate four interference beams, and outputs four interference signals through four output terminals.

[0080] A photodetector is connected to each of the four output terminals of the first Mach-Zehnder interferometer 118. These four photodetectors are: first photodetector 110, second photodetector 111, third photodetector 112, and fourth photodetector 113. The four outputs of the first Mach-Zehnder interferometer are divided into two pairs. One pair outputs interference signals that vary with a cosine function and correspond to the increment of the input light's optical frequency. The other pair outputs interference signals that vary with a sine function and correspond to the increment of the input light's optical frequency. The phase difference between each pair of output interference signals is 180°, and the phase difference between the two pairs of output interference signals is 90°.

[0081] The first photodetector 110 is connected to the first output terminal of the first 90° mixer 108, and is used to detect the interference signal of the first output, and generate the first output voltage signal V that varies with the cosine function and corresponds to the optical frequency increment information of the input light. u1 (t). The second photodetector 111 is connected to the second output terminal of the first 90° mixer 108, and is used to detect the interference signal of the second output, and generate a second output voltage signal V that varies with the cosine function and corresponds to the optical frequency increment information of the input light. u2(t). The third photodetector 112 is connected to the third output terminal of the first 90° mixer 108, and is used to detect the interference signal of the third output, and generate the first output voltage signal V that varies with a sine function and corresponds to the optical frequency increment information of the input light. u3 (t). The fourth photodetector 113 is connected to the fourth output terminal of the first 90° mixer 108 to detect the interference signal of the fourth output and generate a second output voltage signal V that varies with a sine function and corresponds to the optical frequency increment information of the input light. u4 (t). The optical frequency increment information is contained within multiple cycles of the four-channel sine-cosine function output signal of the first Mach-Zehnder interferometer.

[0082] The second Mach-Zehnder interferometer 119 includes a third coupler 103, a third optical waveguide 106, a fourth optical waveguide 107, and a second 90° mixer 109. The input of the third coupler 103 is connected to the first coupler 101, and its two outputs are connected to the third optical waveguide 106 and the fourth optical waveguide 107, respectively. The third coupler 103 receives the input light transmitted from the first coupler 101 and splits the received input light into two beams, outputting them to the third and fourth optical waveguides 106 and 107, respectively. The third optical waveguide 106 connects the third coupler 103 and the second 90° mixer 109, serving as the first interferometer arm of the second Mach-Zehnder interferometer and transmitting the light beam to the second 90° mixer 109. The fourth optical waveguide 107 is connected between the third coupler 103 and the second 90° mixer 109, serving as the second interferometer arm of the second Mach-Zehnder interferometer for transmitting the light beam to the second 90° mixer 109. The optical path length of the third optical waveguide 106 is ΔM longer than that of the fourth optical waveguide 107, and ΔM << ΔL, to generate an imbalance in optical transmission delay. The second 90° mixer 109 receives and combines two beams of light from the third optical waveguide 106 and the fourth optical waveguide 107 with an optical path difference of ΔM to generate four interference beams, and outputs four interference signals through four output terminals.

[0083] A photodetector is connected to each of the four output terminals of the second Mach-Zehnder interferometer 119. These four photodetectors are: fifth photodetector 114, sixth photodetector 115, seventh photodetector 116, and eighth photodetector 117. The four outputs of the second Mach-Zehnder interferometer are divided into two pairs. One pair outputs interference signals that vary with a cosine function and correspond to the absolute optical frequency information of the input light. The other pair outputs interference signals that vary with a sine function and correspond to the absolute optical frequency information of the input light. The phase difference between each pair of output interference signals is 180°, and the phase difference between the two pairs of output interference signals is 90°.

[0084] The fifth photodetector 114 is connected to the first output terminal of the second 90° mixer 109 to detect the interference signal output from the first channel and generate the first output voltage signal V that varies with the cosine function and corresponds to the absolute optical frequency information of the input light. l1 (t). The sixth photodetector 115 is connected to the second output terminal of the second 90° mixer 109 to detect the interference signal of the second output and generate a second output voltage signal V that varies with the cosine function and corresponds to the absolute optical frequency information of the input light. l2 (t). The seventh photodetector 116 is connected to the third output terminal of the second 90° mixer 109 to detect the interference signal of the third output and generate the first output voltage signal V that varies with a sine function and corresponds to the absolute optical frequency information of the input light. l3 (t). The eighth photodetector 117 is connected to the fourth output terminal of the second 90° mixer 109 to detect the interference signal of the fourth output and generate a second output voltage signal V that varies with a sine function and corresponds to the absolute optical frequency information of the input light. l4 (t). The absolute optical frequency information is contained within a monotonic range of the phase variation of the four sine-cosine functions of the second Mach-Zehnder interferometer.

[0085] The optical transmission delay imbalance between the two interferometer arms of the first Mach-Zehnder interferometer 118 is ΔL, and its four output signals are:

[0086]

[0087] Where the subscript u represents the first Mach-Zehnder interferometer; V uj (t)(j=1,2,3,4) represents the output voltages of the four channels of the first Mach-Zehnder interferometer; B uj It represents the amplitude of the sine and cosine functions related to optical power received in each channel; m uj It is the modulation depth of each channel; α u β u γ u This is the phase deviation of the 90° mixer; if the 90° mixer is ideal, it will be zero; where B uj α u β u γ u It is usually related to weak wavelengths.

[0088] Interferometer Free Spectral Range (FSR) u Defined as:

[0089] FSR u =1 / τ u=c / ΔL#(5)

[0090] Where, τ u ΔL and ΔL are the delay time and optical path length difference between the two interferometer arms of the first Mach-Zehnder interferometer 118, respectively.

[0091] The phase change caused by the measured optical frequency Δf(t) can be expressed as:

[0092]

[0093] according to Figure 2 The phase relationships and expressions (1) to (4) of the four outputs of the first Mach-Zehnder interferometer 118 shown can be used to determine the optical frequency increment Δf(t) from these four output signals:

[0094]

[0095] Among them, v uj =[V uj (t)-B uj ] / (m uj B uj (j=1,2,3,4), is the normalized voltage after subtracting the DC term of the interferometer. The phase demodulation algorithm can be used to calculate phase changes exceeding 2π, thereby obtaining the optical frequency increment Δf(t) and the direction of the frequency change. Simultaneously, due to FSR... u The amplitude is very small, enabling ultra-high frequency variation resolution. Furthermore, since the demodulation algorithm uses normalized voltage ratios, the calculated optical frequency increment is independent of the input light power.

[0096] In the optical frequency increment demodulation algorithm, the demodulation parameter B uj m uj ·B uj α u β u γ u All are related to the wavelength of light.

[0097] like Figure 4 As shown, the optical frequency increment demodulation parameter calibration method of the first Mach-Zehnder interferometer in the optical frequency detection chip demodulation parameter calibration method of the present invention includes the following steps:

[0098] S1-1 inputs the output signal of the wide wavelength range scanning laser in continuous wavelength range scanning mode to the input terminal of the optical frequency detection chip.

[0099] S1-2 obtains four output interference signals through the first, second, third, and fourth photodetectors connected to the output of the first Mach-Zehnder interferometer: Vuj (t),j=1,2,3,4.

[0100] S1-3 uses a wide-wavelength range scanning laser to monitor the output wavelength pulses, determining the specific wavelength values ​​corresponding to each of the four output interference signals. From these, a free spectral range (FSR) is selected that is near wavelength λ and has a frequency variation equal to that of the first Mach-Zehnder interferometer. u Interference signals of varying durations, ideally with a phase difference of 90°, are considered as interference signals V. u1 (t) and V u3 、V u2 (t) and V u3 (t), V u1 (t) and V u4 (t) Perform Lissajous ellipse fitting once for each wavelength to obtain all wavelength-related optical frequency increment demodulation parameters at that wavelength.

[0101] S1-4 repeats steps S1-1 to S1-3 for every 1nm wavelength within the wavelength range of 1480nm to 1640nm, thus obtaining a lookup table of optical frequency increment demodulation parameters and wavelength λ.

[0102] like Figure 5 As shown, a set of signals V with an ideal 90° phase difference u1 (t) and V u3 Taking (t) as an example, the demodulation parameters are calibrated using the Lissajous ellipse fitting method at 1519 nm. For any two interference signals with a phase difference of α (α≠π), they can be expressed using trigonometric functions as follows:

[0103]

[0104] Among them, B u1 (λ) and B u3 (λ) is the DC component of the interference signal, m u1 ·B u1 (λ) and m u3 ·B u3 (θ) represents the amplitude of the interference signal, and α represents the actual phase difference between the two interference signals. Expanding equations (10) and (11) yields:

[0105]

[0106] According to trigonometric function formulas: Substituting into equation (13), we get:

[0107]

[0108] Meanwhile, the standard equation of an ellipse is:

[0109]

[0110] Where A, B, C, D, and E are the coefficients of the standard equation of the ellipse, obtained by applying V... u1 (t) and V u3 (t) can be obtained by fitting a Lissajous ellipse. By analogy between the derived equation and the standard equation of an ellipse, the DC component, amplitude, and actual phase difference of the interference signal can be obtained. Then, the actual phase deviation can be calculated based on the known ideal phase difference and the actual phase difference.

[0111]

[0112]

[0113] Therefore, by using the Lissajous ellipse fitting method for the two interference signals, all demodulation parameters in the calculation of the optical frequency increment at a certain wavelength can be obtained. Figures 6-9 The optical frequency increment demodulation parameter B is given for every 1 nm wavelength interval in the wavelength range of 1480 nm to 1640 nm. u1 m u1 ·B u1 α u β u γ u The calibration results.

[0114] Based on the same inventive concept, the four output signal expressions of the second Mach-Zehnder interferometer 119 are similar to those of the four output signal expressions of the first Mach-Zehnder interferometer 118. The difference is that the first Mach-Zehnder interferometer 118 can only measure the change in optical frequency Δf, and cannot measure the absolute optical frequency. This is because the four output signals within the measurement range correspond to multiple periods. In contrast, the delay imbalance between the two interferometer arms of the second Mach-Zehnder interferometer 119 is ΔM, corresponding to the free spectral range FSR. l Much greater than FSR u This ensures that the absolute optical frequency (wavelength) corresponds one-to-one with the phase within a large measurement range, thereby enabling the measurement of the absolute optical frequency f0.

[0115] Here FSR l This determines the range of optical frequency measurements, because it is necessary to ensure a one-to-one correspondence between the absolute optical frequency (wavelength) and the phase monotonicity over a large measurement range.

[0116] Wavelength λ and phase in Mach-Zehnder interferometer 119 The relationship is:

[0117]

[0118] Where the subscript l represents the second Mach-Zehnder interferometer, vlj =[V lj (t)-B lj ] / (m lj B lj (j=1,2,3,4) is the four-way normalized output voltage after subtracting the DC term of the interferometer.

[0119] In optical frequency measurement, the optical frequency increment Δf(t) is measured using a first Mach-Zehnder interferometer, and the absolute optical frequency f0 is measured using a second Mach-Zehnder interferometer. By combining the measurements from the two interferometers, the absolute optical frequency f0 can be obtained.

[0120] f(t)=f0+Δf(t)#(22)

[0121] Under ideal conditions, the outputs of the first photodetector 110 and the fifth photodetector 114 in the optical frequency detection chip of the present invention are as follows: Figure 3 As shown, the first photodetector 110 corresponds to a smaller FSR. u The output of the first Mach-Zehnder interferometer corresponds to equation (1); the fifth photodetector 114 corresponds to a large FSR. l The output of the second Mach-Zehnder interferometer 119. Using a larger FSR. l The second Mach-Zehnder interferometer 119 with a smaller FSR u The first Mach-Zehnder interferometer 118 combination achieves optical frequency measurement. With a large FSR setting... l When the interferometer's delay is unbalanced, it is necessary to consider that the phase change range corresponding to the measured light frequency is limited to a monotonically changing interval of a sine-cosine function, for the purpose of roughly measuring the absolute light frequency. For example... Figure 3 As shown, within this monotonic period, the smaller FSR u The interferometer's interference signal corresponds to multiple periods, enabling high-resolution measurement of optical frequency variations. In Example 1, a larger FSR... l It can be set to tens of THz to achieve a large frequency measurement range and a small FSR. u It can be set to tens of GHz to achieve high frequency resolution.

[0122] like Figure 10 As shown, the absolute optical frequency calibration method of the second Mach-Zehnder interferometer in the demodulation parameter calibration method of the optical frequency detection chip of the present invention includes the following steps:

[0123] S2-1 inputs the output signal of the continuous wavelength range scanning mode of the wide wavelength range scanning laser to the input terminal of the optical frequency detection chip.

[0124] During a wide wavelength scan, S2-2 measures the interference signals output by the fifth photodetector 114, the sixth photodetector 115, the seventh photodetector 116, and the eighth photodetector 117, which are connected to the output of the second Mach-Zehnder interferometer: V lj (t), (j=1,2,3,4).

[0125] S2-3 solves for the phase of the sine-cosine functions of the four outputs. The phase corresponding to different wavelengths λ was obtained through calibration. The specific wavelength value is determined by monitoring the output pulses of a wide-wavelength scanning laser; for the measurement of unknown absolute optical frequency, it is determined by the calibrated wavelength λ and the corresponding phase. The lookup table will determine this.

[0126] Figure 11 The absolute optical frequency (wavelength) and phase at each 1nm wavelength within the calibrated wavelength range of 1490nm to 1640nm are determined. The monotonic one-to-one correspondence; the four outputs of the second Mach-Zehnder interferometer are used to calculate the change of the absolute phase of the input light over time. After determining the change of the absolute light frequency through the calibrated lookup table, the optical frequency increment demodulation parameter at the corresponding absolute light frequency is selected for the first Mach-Zehnder interferometer to accurately calculate the optical frequency increment.

[0127] like Figure 12 As shown, the optical frequency demodulation method of the optical frequency detection chip of the present invention includes the following steps:

[0128] S3-1 uses a wide-wavelength scanning laser as the input light source. When light of unknown absolute frequency and optical frequency increment is input, the phase is calculated using the output signals from the fifth, sixth, seventh, and eighth photodetectors connected to the output of the second Mach-Zehnder interferometer.

[0129] S3-2 obtains the absolute light frequency information by using a pre-calibrated absolute light frequency lookup table, and obtains the change of absolute light frequency f with time t and the initial absolute light frequency f0.

[0130] S3-3 uses the absolute optical frequency f(t) to look up the optical frequency increment demodulation parameters and the lookup table of wavelength λ or absolute optical frequency f, and determines the corresponding optical frequency increment demodulation parameters for each sampling point point by point.

[0131] S3-4 outputs four signals V from the first, second, third, and fourth photodetectors connected to the output terminal of the first Mach-Zehnder interferometer. uj(t), calculate the light frequency increment Δf(t), and thus obtain the absolute light frequency f0 and the light frequency increment information Δf(t) of the measured light.

[0132] Figure 13 The diagram illustrates experimental results of optical frequency measurement using the optical frequency detection chip of this invention, measuring wavelengths in the range of 1500nm to 1630nm with wavelength step intervals of 10nm. This demonstrates that the described optical frequency detection device achieves a large optical frequency (wavelength) measurement range of 1500nm to 1630nm, accurately measures optical frequency variations while simultaneously achieving absolute optical frequency measurement, and can distinguish the direction of optical frequency changes. By unfolding the wavelength step, a sinusoidal function change can be clearly observed, reflecting the details of laser wavelength tuning.

[0133] Figure 14 The diagram shows experimental results of optical frequency measurement using the optical frequency detection chip of this invention, measuring wavelengths in the range of 1520nm to 1570nm with continuous wavelength variation and a sweep rate of 20000nm / s (2500THz / s). This illustrates that the described optical frequency detection device can accurately measure optical frequency, achieve absolute optical frequency measurement, and measure rapid optical frequency changes. The unfolded measurement results clearly show the stepwise change in optical frequency, reflecting the laser wavelength tuning mechanism based on a stepper motor.

[0134] Figure 15 The diagram shows the experimental results of measuring the optical frequency of a laser modulated by a 100kHz sine wave using the optical frequency detection chip of this invention. The gray dashed line corresponds to the change in optical frequency, and the black solid line corresponds to the frequency sweep speed. This illustrates that the optical frequency detection device can accurately measure rapid optical frequency changes, and can achieve an optical frequency change rate of ±25THz / s under 100kHz high-frequency modulation.

[0135] Figure 16 The diagram shows the experimental results of measuring the frequency change of a laser 1Hz sinusoidal frequency modulated by the optical frequency detection chip of the present invention. The gray dashed line and the black solid line represent the results after filtering with a Butterworth third-order low-pass filter with cutoff frequencies of 5Hz and 50Hz, respectively. This illustrates that the optical frequency detection chip can achieve optical frequency change measurement with ultra-high optical frequency resolution, realizing an ultra-high optical frequency resolution of 2MHz (0.016pm).

Claims

1. An optical frequency detection chip, characterized in that, include: Substrate, used to load the following devices; The first coupler has two outputs connected to the first Mach-Zehnder interferometer and the second Mach-Zehnder interferometer, respectively, to receive the input light and split the input light into two beams, which are then output to the first Mach-Zehnder interferometer and the second Mach-Zehnder interferometer. The first Mach-Zehnder interferometer has an input terminal connected to a first coupler. The optical path difference between the two interferometer arms is ΔL to generate an unbalanced delay in optical transmission. Each of the four output terminals is connected to a photodetector. The four outputs are divided into two pairs. One pair outputs an interference signal that varies with a cosine function and corresponds to the optical frequency increment information of the input light. The other pair outputs an interference signal that varies with a sine function and corresponds to the optical frequency increment information of the input light. The phase difference between each pair of output interference signals is 180°, and the phase difference between the two pairs of output interference signals is 90°. The second Mach-Zehnder interferometer has an input terminal connected to the first coupler. The optical path difference between the two interferometer arms is ΔM, and ΔM << ΔL, to generate an unbalanced delay in optical transmission. Each of the four output terminals is connected to a photodetector. The four outputs are divided into two pairs. One pair outputs an interference signal that varies with a cosine function and corresponds to the absolute optical frequency information of the input light. The other pair outputs an interference signal that varies with a sine function and corresponds to the absolute optical frequency information of the input light. The phase difference between each pair of output interference signals is 180°, and the phase difference between the two pairs of output interference signals is 90°. The first photodetector is connected to the first output terminal of the first Mach-Zehnder interferometer. It is used to detect the interference signal output from the first channel and generate the first output voltage signal V that varies with the cosine function and corresponds to the optical frequency increment information of the input light. u1 (t); The second photodetector is connected to the second output terminal of the first Mach-Zehnder interferometer. It is used to detect the interference signal output from the second channel and generate a second output voltage signal V that varies with the cosine function and corresponds to the optical frequency increment information of the input light. u2 (t); The third photodetector, connected to the third output terminal of the first Mach-Zehnder interferometer, is used to detect the interference signal from the third output and generate the first output voltage signal V that varies with a sine function and corresponds to the increment of the input light's optical frequency. u3 (t); The fourth photodetector, connected to the fourth output terminal of the first Mach-Zehnder interferometer, is used to detect the interference signal from the fourth output and generate a second output voltage signal V that varies with a sine function and corresponds to the increment of the input light's optical frequency. u4 (t); The fifth photodetector, connected to the first output of the second Mach-Zehnder interferometer, is used to detect the interference signal from the first output path and generate the first output voltage signal V that varies with a cosine function and corresponds to the absolute optical frequency information of the input light. l1 (t); The sixth photodetector, connected to the second output terminal of the second Mach-Zehnder interferometer, is used to detect the interference signal from the second output and generate a second output voltage signal V that varies with a cosine function and corresponds to the absolute optical frequency information of the input light. l2 (t); The seventh photodetector, connected to the third output of the second Mach-Zehnder interferometer, is used to detect the interference signal from the third output and generate the first output voltage signal V that varies with a sine function and corresponds to the absolute optical frequency information of the input light. l3 (t); The eighth photodetector, connected to the fourth output of the second Mach-Zehnder interferometer, is used to detect the interference signal from the fourth output and generate a second output voltage signal V that varies with a sine function and corresponds to the absolute optical frequency information of the input light. l4 (t).

2. The optical frequency detection chip according to claim 1, characterized in that, The first Mach-Zehnder interferometer includes: The second coupler is connected to the first coupler, the first optical waveguide, and the second optical waveguide, respectively. It is used to receive the input light transmitted from the first coupler and split the received input light into two beams and output them to the first optical waveguide and the second optical waveguide. The first optical waveguide, connected between the second coupler and the first 90° mixer, serves as the first interferometer arm of the first Mach-Zehnder interferometer and is used to transmit the light beam to the first 90° mixer. The second optical waveguide, connected between the second coupler and the first 90° mixer, serves as the second interferometer arm of the first Mach-Zehnder interferometer and is used to transmit the beam to the first 90° mixer. The first 90° mixer is used to receive and combine two beams of light with an optical path difference of ΔL from the first and second optical waveguides to generate four interference beams, and output four interference signals through four output terminals.

3. The optical frequency detection chip according to claim 1, characterized in that, The second Mach-Zehnder interferometer includes: The third coupler is connected to the first coupler, the third optical waveguide, and the fourth optical waveguide, respectively. It is used to receive the input light transmitted from the first coupler and split the received input light into two beams for output to the third and fourth optical waveguides. The third optical waveguide, connected between the third coupler and the second 90° mixer, serves as the first interferometer arm of the second Mach-Zehnder interferometer and is used to transmit the beam to the second 90° mixer. The fourth optical waveguide, connected between the third coupler and the second 90° mixer, serves as the second interferometer arm of the second Mach-Zehnder interferometer and is used to transmit the light beam to the second 90° mixer. The second 90° mixer is used to receive and combine two beams of light with an optical path difference of ΔM from the third and fourth optical waveguides to generate four interference beams, and output four interference signals through four output terminals.

4. The optical frequency detection chip according to claim 1, 2 or 3, characterized in that, The optical frequency increment information is contained within multiple cycles of the four-channel sine-cosine function output signal of the first Mach-Zehnder interferometer.

5. The optical frequency detection chip according to claim 1, 2 or 3, characterized in that, The absolute optical frequency information is contained within a monotonic range of the phase changes of the four sine-cosine functions of the second Mach-Zehnder interferometer.

6. The optical frequency detection chip according to claim 1, 2 or 3, characterized in that, The first, second, and third couplers are all 3dB optical couplers.

7. The optical frequency detection chip according to claim 1, 2 or 3, characterized in that, Both the first 90° mixer and the second 90° mixer are 2×4 multimode interference couplers.

8. A method for calibrating demodulation parameters of the optical frequency detection chip according to any one of claims 1-7, characterized in that, This includes the calibration method for the optical frequency increment demodulation parameters of the first Mach-Zehnder interferometer and the absolute optical frequency calibration method of the second Mach-Zehnder interferometer; S1. The calibration method for the optical frequency increment demodulation parameters of the first Mach-Zehnder interferometer includes the following steps: S1-1 inputs the output signal of the wide wavelength range scanning laser in continuous wavelength range scanning mode to the input terminal of the optical frequency detection chip; S1-2 obtains four output interference signals through the first, second, third, and fourth photodetectors connected to the output of the first Mach-Zehnder interferometer: V uj (t), j = 1, 2, 3, 4; S1-3 uses the output wavelength monitoring pulse of the wide-wavelength range scanning laser to determine the specific wavelength values ​​corresponding to each of the four output interference signals, and selects a free spectral range (FSR) near wavelength λ with a frequency variation equal to that of the first Mach-Zehnder interferometer. u Interference signals of varying durations, ideally with a phase difference of 90°, are considered as interference signals V. u1 (t) and V u3 、V u2 (t) and V u3 (t), V u1 (t) and V u4 (t) Perform Lissajous ellipse fitting once for each wavelength to obtain all wavelength-related optical frequency increment demodulation parameters at that wavelength; S1-4 repeats steps S1-1 to S1-3 for every 1nm wavelength in the wavelength range of 1480nm to 1640nm, thus obtaining a lookup table of optical frequency increment demodulation parameters and wavelength λ. S2. The absolute optical frequency calibration method for the second Mach-Zehnder interferometer includes the following steps: S2-1 inputs the output signal of the continuous wavelength range scanning mode of the wide wavelength range scanning laser to the input terminal of the optical frequency detection chip; During a wide wavelength scan, S2-2 measures the interference signals output by the fifth, sixth, seventh, and eighth photodetectors connected to the output of the second Mach-Zehnder interferometer, respectively: V lj (t), j = 1, 2, 3, 4; S2-3 solves for the phase of the sine-cosine functions of the four outputs. The phase corresponding to different wavelengths λ was obtained through calibration. The specific wavelength value is determined by monitoring the output pulses of a wide-wavelength scanning laser; for the measurement of unknown absolute optical frequency, it is determined by the calibrated wavelength λ and the corresponding phase. The lookup table will determine this.

9. A method for optical frequency demodulation of the optical frequency detection chip according to any one of claims 1-7, characterized in that, Includes the following steps: S3-1 uses a wide-wavelength scanning laser as the input light source. When light of unknown absolute frequency and optical frequency increment is input, the phase is calculated using the output signals from the fifth, sixth, seventh, and eighth photodetectors connected to the output of the second Mach-Zehnder interferometer. S3-2 obtains the absolute light frequency information by using a pre-calibrated absolute light frequency lookup table, and obtains the change of absolute light frequency f with time t and the initial absolute light frequency f0. S3-3 uses the absolute optical frequency f(t) to look up the optical frequency increment demodulation parameter and the lookup table of wavelength λ or absolute optical frequency f, and determines the corresponding optical frequency increment demodulation parameter for each sampling point point by point; S3-4 outputs four signals V from the first, second, third, and fourth photodetectors connected to the output terminal of the first Mach-Zehnder interferometer. uj (t), calculate the light frequency increment Δf(t), and thus obtain the absolute light frequency f0 and the light frequency increment information Δf(t) of the measured light.

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