Novel laser frequency noise measuring device and method

Abstract

The invention discloses a novel laser frequency noise measuring device and method, and belongs to the technical field of lasers, the device comprises a laser, an optical isolator, a 1 * 2 optical fiber coupler, an optical circulator, a 2 * 2 optical fiber coupler, an acousto-optic modulator, a single-mode optical fiber, two Faraday rotating mirrors, three photoelectric detectors, a data acquisition card, piezoelectric ceramics and a computer. By adding the circulator in the optical path, the requirement for the length of the single-mode optical fiber is reduced, the integration level of the device is improved, and the size and cost of the device are reduced; by adding the acousto-optic modulator, the influence of low-frequency noise of the acquisition card on a measurement result is reduced, and the laser frequency noise measurement result of the device in a low-frequency range is improved; the piezoelectric ceramic is added into the Michelson interferometer to realize fine adjustment of the length difference of the interference arms, so that the optical path is ensured to be in the optimal interference state; the Faraday rotating mirror is added in the interference light path to reduce the influence of the change of factors such as environment on the polarization state of the interference light path.

Description

Technical Field

[0001] The invention belongs to the technical field of lasers, and in particular relates to a novel laser frequency noise measuring device and method. Background Art

[0002] At present, the measurement methods of laser frequency noise mainly include delayed self-beating frequency method, optical resonant cavity method and mutual beat frequency method. The traditional schemes for measuring laser frequency noise mainly include the following categories: the first category is to use the delayed self-beating frequency method to transfer the laser frequency noise into laser power jitter, so as to obtain the frequency noise of the laser to be measured; the second category is to use an optical resonant cavity to convert the laser frequency noise into optical power jitter, and then measure the laser frequency noise; the third category is to use a narrow linewidth laser with extremely low frequency noise as a reference source, beat the laser to be measured with the reference laser, and then obtain the frequency noise of the laser to be measured.

[0003] In 2011, Yang Fei and others from the Shanghai Institute of Optics and Precision Mechanics of the Chinese Academy of Sciences proposed a "laser noise characteristic measurement device based on 3×3 couplers". This device uses a 3×3 coupler to form an interferometer to collect the laser phase noise power spectrum density, and uses the phase noise power spectrum density to calculate and extract the laser frequency noise. This method can measure the laser frequency noise, line width and intensity noise at the same time, and has the advantages of high integration and simple structure. However, this method requires accurate calibration of the splitting ratio of the 3×3 fiber coupler, and the calibration process is very cumbersome; at the same time, the demodulation algorithm of the device is relatively complex, and the algorithm level of the device developers is extremely high.

[0004] In 2011, Yu Xuhui and others from Zhejiang University proposed a "device and method for testing the power spectral density of laser frequency noise based on a fiber resonant cavity". The method is to modulate the light output by the laser through a phase modulator, and then pass the modulated light through a fiber resonant cavity and a photodetector. Finally, the frequency noise is converted into amplitude fluctuations through the fiber resonant cavity, and the power spectral density of the laser frequency noise is detected on a spectrum analyzer. This method uses a steep slope of the resonance curve to convert the frequency fluctuation of the laser into amplitude fluctuations. Thanks to the high definition of the fiber resonant cavity, the device has high sensitivity and can quickly measure frequency noise fluctuations. However, this method requires a servo controller and a phase-locked amplifier to accurately extract the phase. The device is relatively complex, the cost is relatively high, and the scalability is not strong.

[0005] In 2016, Chen Xinwei and others from the 38th Institute of China Electronics Technology Group Corporation proposed a "device and method for measuring the frequency noise of a DFB laser based on the modulation phase shift method". The method uses an electro-optic modulator to modulate the DFB laser, and then uses a vector network analyzer to extract the phase change value transmitted in the optical fiber to calculate the frequency noise value of the laser under test. This method uses microwave photon technology to load the RF signal onto the light wave through an electro-optic modulator, and uses a vector network analyzer to analyze the phase change of the RF signal to achieve the measurement of the DFB laser frequency noise. Compared with existing optical measurement methods, this method has the advantages of fast measurement speed and is less affected by environmental factors. However, the frequency noise measurement sensitivity of this method is not high, and it cannot meet the measurement requirements of laser frequency noise in some application scenarios.

[0006] In 2017, Peng Huanfa and others from Peking University proposed a "measurement method for laser frequency noise based on optical comb modulator". The method uses the laser to be tested as the light source of an optoelectronic hybrid oscillator built based on an optical comb modulator, and then measures the phase noise of the radio frequency oscillation signal in the optoelectronic hybrid oscillator; the frequency noise of the laser to be tested is obtained based on the phase noise. This method indirectly measures the frequency noise of the laser by measuring the phase noise of the radio frequency oscillation signal, so it can distinguish between the frequency noise and intensity noise of the laser, and has extremely high measurement sensitivity. However, the optical path system of this method is relatively complex, and the addition of various low-phase noise microwave devices such as electric amplifiers to the system will introduce electrical noise, which leads to unsatisfactory accuracy in the measurement of laser frequency noise by this method.

[0007] In 2017, the Paris Observatory in France proposed a scheme to characterize the frequency noise of narrow linewidth lasers. This scheme uses two single-frequency lasers with extremely narrow linewidth and extremely low frequency noise as references. The laser to be tested is beat with the two reference lasers respectively, and the phase noise of the beat frequency electrical signal is measured to achieve the purpose of indirectly measuring the frequency noise of the laser to be tested. This method uses two extremely narrow linewidth lasers for beat frequency, and has the advantages of simple measurement principle and easy operation. However, this method requires two single-frequency lasers with extremely narrow linewidth and extremely low frequency noise, which has extremely high hardware requirements.

[0008] The prior art has the following disadvantages:

[0009] (1) The measurement of laser frequency noise using the modulation phase shift method requires the phase parameters of the microwave photonic link to be measured using a vector network analyzer. Although this method is not greatly affected by environmental factors, the measurement sensitivity of this method is not high and cannot meet the measurement requirements of laser frequency noise in some application scenarios.

[0010] (2) The principle of using two reference lasers to measure the beat frequency is simple and easy to operate. However, this method requires two single-frequency lasers with extremely narrow linewidth and extremely low frequency noise, which places extremely high demands on hardware.

[0011] (3) The method of testing the power spectrum density of laser frequency noise based on the fiber resonator is to convert the frequency noise into amplitude fluctuation through the fiber resonator. It has the advantages of high sensitivity and can quickly measure the frequency noise fluctuation. However, this method is complex, expensive, and has a small application range.

[0012] (4) The laser to be tested is used as the light source of an optoelectronic hybrid oscillator based on an optical comb modulator, and then the phase noise of the radio frequency oscillation signal in the optoelectronic hybrid oscillator is measured. This method can distinguish the frequency noise and intensity noise of the laser and has extremely high measurement sensitivity. However, the optical path system of this method is relatively complex, and the addition of various microwave devices such as low-phase noise electric amplifiers to the system will introduce electrical noise, which results in the method's low accuracy in measuring the laser frequency noise.

[0013] In this context, in view of the shortcomings of the above measurement methods, the present invention proposes a novel laser frequency noise measurement device and method, which is based on a Michelson interferometer combined with coherent detection demodulation. The test method has better measurement sensitivity, accuracy and stability. Summary of the invention

[0014] In view of the above problems existing in the prior art, the present invention proposes a novel laser frequency noise measurement device and method, which has a reasonable design, solves the shortcomings of the prior art and has good effects.

[0015] In order to achieve the above purpose 1, the present invention adopts the following technical solution:

[0016] A novel laser frequency noise measuring device comprises a laser, an optical isolator, a 1×2 optical fiber coupler, an optical circulator, a 2×2 optical fiber coupler, an acousto-optic modulator, a single-mode optical fiber, two Faraday rotation mirrors, three photodetectors, a data acquisition card, an optical fiber jumper, piezoelectric ceramics and a computer.

[0017] Furthermore, the output end of the laser is connected to the input end of the 1×2 fiber coupler through an isolator, the first output end of the 1×2 fiber coupler is connected to the first photodetector, the data acquisition card and the computer in sequence, the second output end of the 1×2 fiber coupler is connected to the input end of the optical circulator, and the output end of the optical circulator is connected to port 1 of the 2×2 fiber coupler.

[0018] Furthermore, port 2 and port 3 of the 2×2 fiber coupler are respectively connected to an acousto-optic modulator and an optical fiber jumper connected with piezoelectric ceramics, the acousto-optic modulator is connected to the single-mode optical fiber and the first Faraday rotator mirror in turn, and the optical fiber jumper is connected to the second Faraday rotator mirror.

[0019] Furthermore, the reflection end of the optical circulator and port 4 of the 2×2 fiber coupler are respectively connected to the second photodetector and the third photodetector, which are in turn connected to a data acquisition card and a computer, and the computer is also connected to the piezoelectric ceramic.

[0020] In order to achieve the above purpose 2, the present invention adopts the following technical solution:

[0021] A novel laser frequency noise measurement method adopts the novel laser frequency noise measurement device as described above, wherein the optical signal output by the laser enters a 1×2 optical fiber coupler through an optical isolator for light splitting, one path is converted into an electrical signal through a first photoelectric detector and then is used for data acquisition through a data acquisition card, and the other path enters an optical circulator and then enters a 2×2 optical fiber coupler, the 2×2 optical fiber coupler divides the measured light beam into two paths of light waves, one path directly enters an acousto-optic modulator and a single-mode optical fiber with a Faraday rotating mirror at the tail end, and the other path directly enters an optical fiber jumper with a Faraday rotating mirror at the tail end, and the length of the optical fiber jumper can be adjusted by piezoelectric ceramics; the signals reflected back by the Faraday rotating mirrors of the two paths are recombined at the 2×2 optical fiber coupler to cause interference, the interference signal is divided into two paths, and arrives at the second and third photoelectric detectors respectively for photoelectric conversion, the electrical signal converted by the photoelectric detector is used for data acquisition by a data acquisition card, and finally the collected data is analyzed and processed by a computer to obtain the frequency noise of the measured laser.

[0022] Beneficial technical effects brought by the present invention:

[0023] (1) By adding a circulator to the optical path, the requirement for the length of the single-mode optical fiber can be reduced, which can improve the integration of the device and reduce the size and cost of the device;

[0024] (2) By adding an acousto-optic modulator, the influence of the acquisition card's own low-frequency noise on the measurement results can be reduced, thereby improving the device's laser frequency noise measurement results in the low-frequency range;

[0025] (3) By adding piezoelectric ceramics (PZT) to the Michelson interferometer, the interferometer arm length difference can be fine-tuned to ensure that the optical path is in the optimal interference state;

[0026] (4) By adding a Faraday rotator in the interference light path, the influence of environmental factors and other factors on the polarization state of the interference light path can be reduced;

[0027] The measurement method of the present invention can realize the test of laser frequency noise within a wide frequency band, thereby solving the problem of laser frequency noise measurement and further ensuring the accuracy of tracing the frequency noise of lasers from different manufacturers. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a structural diagram of a new type of laser frequency noise measurement device; DETAILED DESCRIPTION

[0029] The specific implementation of the present invention is further described below in conjunction with specific embodiments:

[0030] A new laser frequency noise measurement device, such as Figure 1 As shown, it includes a laser, an optical isolator, a 1×2 fiber coupler, an optical circulator, a 2×2 fiber coupler, an acousto-optic modulator, a single-mode optical fiber, two Faraday rotator mirrors (FRM), three photodetectors, a data acquisition card, a fiber jumper, a piezoelectric ceramic (PZT) and a computer.

[0031] The output end of the laser is connected to the input end of the 1×2 optical fiber coupler through an isolator, the first output end of the 1×2 optical fiber coupler is connected to the first photodetector, the data acquisition card and the computer in sequence, the second output end of the 1×2 optical fiber coupler is connected to the input end of the optical circulator, and the output end of the optical circulator is connected to port 1 of the 2×2 optical fiber coupler.

[0032] Port 2 and port 3 of the 2×2 fiber coupler are respectively connected to an acousto-optic modulator and an optical fiber jumper connected with piezoelectric ceramics. The acousto-optic modulator is connected to a single-mode optical fiber and a first Faraday rotator mirror in turn, and the optical fiber jumper is connected to a second Faraday rotator mirror.

[0033] The reflection end of the optical circulator and port 4 of the 2×2 optical fiber coupler are connected to the second photodetector and the third photodetector respectively, and the second photodetector and the third photodetector are connected to the data acquisition card and the computer in turn. The computer is also connected to the piezoelectric ceramics. The computer controls the piezoelectric ceramics (PZT), so that the arm length of the reference interferometer arm can be dynamically adjusted.

[0034] A novel laser frequency noise measurement method adopts the novel laser frequency noise measurement device as described above, based on Michelson interferometer combined with coherent detection demodulation method to achieve the measurement of narrow linewidth laser frequency noise, and the measurement process is as follows:

[0035] The optical signal output by the laser enters the 1×2 optical fiber coupler for splitting through an optical isolator, one path is converted into an electrical signal through a first photodetector and then is collected through a data acquisition card, and the other path enters an optical circulator and then enters a 2×2 optical fiber coupler. In a Michelson interferometer composed of a 2×2 optical fiber coupler, the 2×2 optical fiber coupler divides the light beam to be measured into two paths of light waves, one path directly enters an acousto-optic modulator and a single-mode optical fiber with a Faraday rotating mirror at the tail end, and the other path directly enters an optical fiber jumper with a Faraday rotating mirror at the tail end, and the length of the optical fiber jumper is adjusted through piezoelectric ceramics; the signals reflected back by the two paths of the Faraday rotating mirror are recombined at the 2×2 optical fiber coupler to interfere, and the interference signal is divided into two paths, which respectively arrive at the second and third photodetectors for photoelectric conversion, and the electrical signal converted by the photodetector is collected by a data acquisition card, and finally the collected data is analyzed and processed by a computer to obtain the frequency noise of the laser to be measured.

[0036] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A novel laser frequency noise measurement device, characterized in that: It includes laser, optical isolator, 1×2 fiber coupler, optical circulator, 2×2 fiber coupler, acousto-optic modulator, single-mode optical fiber, two Faraday rotation mirrors, three photodetectors, data acquisition card, fiber jumper, piezoelectric ceramics and computer.

2. A novel laser frequency noise measuring device according to claim 1, characterized in that: The output end of the laser is connected to the input end of the 1×2 optical fiber coupler through an isolator, the first output end of the 1×2 optical fiber coupler is connected to the first photoelectric detector, the data acquisition card and the computer in sequence, the second output end of the 1×2 optical fiber coupler is connected to the input end of the optical circulator, and the output end of the optical circulator is connected to port 1 of the 2×2 optical fiber coupler.

3. A novel laser frequency noise measuring device according to claim 2, characterized in that: Port 2 and port 3 of the 2×2 fiber coupler are respectively connected to an acousto-optic modulator and an optical fiber jumper connected with piezoelectric ceramics; the acousto-optic modulator is sequentially connected to a single-mode optical fiber and a first Faraday rotator mirror; and the optical fiber jumper is connected to a second Faraday rotator mirror.

4. A novel laser frequency noise measuring device according to claim 3, characterized in that: The reflection end of the optical circulator and port 4 of the 2×2 optical fiber coupler are respectively connected to the second photodetector and the third photodetector, which are in turn connected to a data acquisition card and a computer, and the computer is also connected to the piezoelectric ceramic.

5. A novel method for measuring laser frequency noise, characterized in that: A novel laser frequency noise measuring device as claimed in any one of claims 1 to 4 is used, wherein the optical signal output by the laser enters a 1×2 optical fiber coupler for light splitting through an optical isolator, one path is converted into an electrical signal through a first photodetector and then is used for data acquisition through a data acquisition card, and the other path enters an optical circulator and then enters a 2×2 optical fiber coupler, the 2×2 optical fiber coupler divides the measured light beam into two paths of light waves, one path directly enters an acousto-optic modulator and a single-mode optical fiber with a Faraday rotator mirror at the tail end, and the other path directly enters an optical fiber jumper with a Faraday rotator mirror at the tail end, and the length of the optical fiber jumper is adjusted by piezoelectric ceramics; the signals reflected back by the two paths from the Faraday rotator are recombined at the 2×2 optical fiber coupler to cause interference, the interference signal is divided into two paths, and arrives at the second and third photodetectors respectively for photoelectric conversion, the electrical signal converted by the photodetector is used for data acquisition by a data acquisition card, and finally the collected data is analyzed and processed by a computer to obtain the frequency noise of the measured laser.

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