High-accuracy optical comb repetition frequency measuring device and method

Abstract

The invention discloses a high-accuracy optical comb repetition frequency measuring device and method. The device comprises an optical fiber beam splitter, a phase modulator, an optical fiber beam combiner, a detector, a frequency spectrograph, a radio frequency amplifier, a radio frequency source and an external clock. Pumping laser is connected into the optical fiber beam splitter, and the laser is divided into two paths to be connected into the optical comb generation system and the phase modulator. The phase modulator generates a secondary sideband of the pumping laser and inputs the secondary sideband into the optical fiber beam combiner, and an optical comb generated by the optical comb generation system is input into the optical fiber beam combiner; the detector detects beat frequency signals of a secondary sideband of the pumping laser and comb teeth of the optical comb and converts the beat frequency signals into electric signals, and the frequency spectrograph detects the beat frequency signals output by the detector and is connected with an external clock; the radio frequency source generates a microwave signal and refers to the microwave signal on an external clock, and the radio frequency source is connected to the radio frequency amplifier; the radio frequency amplifier is used for power amplification of microwave signals, and the output end is connected to the phase modulator. According to the invention, the problem of inaccurate high repetition frequency test of the optical comb generated by a microcavity and other devices with ultra-short cavity lengths can be solved.

Description

Technical Field

[0001] This invention belongs to the field of ultrafast lasers, and specifically relates to a high-accuracy optical comb repetition rate measurement device and method. Background Technology

[0002] Thanks to the ultra-short cavity length of the high-quality factor microcavity, when continuous pump light is coupled into the microring resonator, a high repetition rate broadband optical frequency comb output can be achieved through a four-wave mixing effect. The repetition rate level can be improved by 2 to 3 orders of magnitude compared with other traditional frequency comb systems. Its broad application prospects have attracted great attention from the fields of defense technology, electronic information, etc.

[0003] Microcavity optical combs typically have repetition rates (RFs) reaching hundreds of GHz or even THz. This presents a challenge: such high RFs lack matching high-bandwidth detectors and spectrum analyzers, making direct testing impossible. Currently, the common method for testing high RFs involves down-converting the RF using optoelectronic devices such as phase modulators, followed by detection with low-bandwidth detectors and spectrum analyzers. However, this method suffers from system complexity and measurement inaccuracies. Summary of the Invention

[0004] The purpose of this invention is to provide a relatively simple and highly accurate optical comb repetition rate measurement device and method, which can solve the problem of high repetition rate testing of optical combs generated by devices with ultra-short cavity lengths such as microcavities.

[0005] To achieve the above objectives, one aspect of the present invention provides a high-accuracy optical comb repetition rate testing device, comprising an optical fiber splitter, a phase modulator, an optical fiber combiner, a detector, a spectrum analyzer, an RF amplifier, an RF source, and an external clock. The input end of the fiber beam splitter is connected to the pump laser, which is generated by a narrow linewidth laser. The fiber beam splitter is used to split the laser into two paths, which are respectively connected to the optical comb generation system and the phase modulator. The phase modulator is used to generate the secondary sideband of the pump laser and input it into one port of the fiber combiner. The optical comb generated by the optical comb generation system is input into the other port of the fiber combiner. The output of the fiber combiner is connected to the detector. The detector is used to detect the beat frequency signal of the secondary sideband of the pump laser and the comb teeth and convert it into an electrical signal. The radio frequency output port of the detector is connected to the spectrum analyzer. The spectrum analyzer is used to detect the beat frequency signal output by the detector. The spectrum analyzer is connected to an external clock and referenced to the external clock. The radio frequency (RF) source is used to generate microwave signals, is connected to and referenced by an external clock, and its output is connected to the input of an RF amplifier. The frequency of the microwave signal output by the RF source constitutes the sideband spacing generated by the phase modulator. The RF amplifier is used to amplify the power of the microwave signal, and its output is connected to the RF port of the phase modulator.

[0006] Preferably, the narrow linewidth laser is frequency-locked by a frequency-locking system, and the locking methods include saturated absorption spectrum, MTS, and PDH.

[0007] Another aspect of the present invention provides a method for high-accuracy optical comb repetition rate testing, which utilizes the above-described apparatus to achieve high-accuracy testing of the optical comb repetition rate, the method comprising: Step S1: Set the frequency of the microwave signal output by the radio frequency source to... f 1. Set the output power to a small value and gradually increase the output power of the microwave signal until a beat frequency signal is observed on the spectrum analyzer. Record the frequency as follows: f b1 ; Step S2: Fine-tune the frequency of the microwave signal and observe the beat frequency signal on the spectrum analyzer. If the microwave signal frequency increases and the beat frequency signal frequency also increases, then the optical comb repetition rate is... f r The calculation formula is: f r = n × f 1- f b1 If the microwave signal frequency increases while the beat frequency signal frequency decreases, then the optical comb repetition rate will increase. f r The calculation formula is: f r = n × f 1+ f b1 ; Step S3: Set the frequency of the microwave signal output by the radio frequency source to... f 2. Set the output power to a small value and gradually increase the output power of the microwave signal until a beat frequency signal is observed on the spectrum analyzer. Record the frequency as follows: f b2 ; Step S4: Fine-tune the frequency of the microwave signal and observe the beat frequency signal on the spectrum analyzer. If the microwave signal frequency increases and the beat frequency signal frequency also increases, then the optical comb repetition rate is... f r The calculation formula is: f r = n × f 2-f b2 If the microwave signal frequency increases while the beat frequency signal frequency decreases, then the optical comb repetition rate will increase. f r The calculation formula is: f r = n × f 2+ f b2 ; Step S5, based on the optical comb repetition rate determined in steps S2 and S4 f r The two calculation formulas are used to solve for the order of the sideband. n Harmony Comb Frequency Repetition f r .

[0008] The high-accuracy optical comb repetition rate measurement device and method of the present invention can solve the problem of high repetition rate testing of optical combs generated by devices with ultra-short cavity lengths such as microcavities. Attached Figure Description

[0009] To more clearly illustrate the technical solutions of the present invention, the accompanying drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort: Figure 1 This is a schematic diagram of the structure of a high-accuracy optical comb repetition rate testing device according to an embodiment of the present invention. Detailed Implementation

[0010] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0011] One embodiment of the present invention provides a high-accuracy optical comb repetition rate testing device, such as... Figure 1 As shown, the high-accuracy optical comb repetition rate testing device of this invention includes an optical fiber splitter 2, a phase modulator 4, an optical fiber combiner 8, a detector 9, a spectrum analyzer 10, an RF amplifier 5, an RF source 6, and an external clock 7. The external clock 7 is, for example, a hydrogen clock. The RF source 6 and the spectrum analyzer 10 are both connected to the external clock 7 and referenced on the external clock 7. The input end of fiber beam splitter 2 is connected to a pump laser, which is generated by pump laser 1. Pump laser 1 is a narrow linewidth laser, and the wavelength of the pump laser can be locked by frequency locking system 11, and the output frequency... f 0. The output of the fiber beam splitter 2 is connected to the optical comb generation system 3 and the phase modulator 4, respectively. The frequency locking system 11 performs wavelength locking through frequency stabilization methods such as saturated absorption spectrum, MTS (modulation transfer spectrum), and PDH (Pound-Drever-Hall).

[0012] Phase modulator 4 is used to generate secondary sidebands of pump laser. The input of phase modulator 4 is one of the paths of pump laser source 1 of optical comb generating device through optical fiber beam splitter 2, and the output is connected to one of the ports of optical fiber combiner 8.

[0013] One of the inputs of the fiber optic combiner 8 is the output of the phase modulator 4, and the other input is the optical comb generated by the optical comb generation system 3. The output of the fiber optic combiner 8 is connected to the detector 9.

[0014] Detector 9 is used to detect the beat frequency signal of the secondary sideband of the pump laser and the comb teeth and convert it into an electrical signal. The radio frequency output port of detector 9 is connected to spectrum analyzer 10. The bandwidth of detector 9 generally does not need to be very large. By adjusting the output frequency of radio frequency source 6, the beat frequency signal can be reduced to the MHz level.

[0015] The spectrum analyzer 10 is used to detect the beat frequency signal output by the detector 9. After relevant calculations, the repetition frequency of the optical comb can be obtained. The calculation formula is shown below.

[0016] Radio frequency (RF) source 6 generates microwave signals and references a stable external clock 7. It is connected to the input of RF amplifier 5 to form the sideband spacing generated by phase modulator 4. RF amplifier 5 amplifies the power of the microwave signals; its input is the output of RF source 6, and its output is connected to the RF port of phase modulator 4.

[0017] The high-accuracy optical comb repetition rate testing device of the above embodiments of the present invention uses a narrow linewidth laser as the pump laser of the optical comb. The laser is frequency-locked by a frequency locking system. By using a frequency reduction method, the pump laser is used as the injection light, and a phase modulator is used to generate a high-order sideband close to the first-order comb teeth. The repetition rate is obtained by observing the beat frequency signal through a spectrum analyzer.

[0018] Embodiments of the present invention also provide a method for high-accuracy optical comb repetition rate testing, which utilizes the above-described apparatus to achieve optical comb repetition rate testing. f r High accuracy testing, f r The calculation formula is: f r =n × f Δ ± f b ,in n Represents the order of the sideband, and is the unknown quantity to be calculated. f Δ The frequency of the microwave signal output by the radio frequency source is a known quantity recorded in the experiment. f b The signal representing the beat frequency is a known quantity recorded in the experiment. The positive or negative sign in the formula indicates that it needs to be determined experimentally. By recording two sets of data and establishing two equations, the solution can be obtained. n and f r The method includes: Step S1: First, record the first set of data and establish the first equation to determine the frequency of the microwave signal output by the radio frequency source. f Δ Set as f 1. Set the output power to a small value and gradually increase the output power of the microwave signal until a beat frequency signal is observed on the spectrum analyzer. Record the frequency as follows: f b1 ; Step S2: Determine the sign in the first equation, fine-tune the frequency of the microwave signal and observe the beat frequency signal on the spectrum analyzer. Determine the sign based on whether the beat frequency signal frequency increases or decreases: If both the microwave signal frequency and the beat frequency signal frequency increase, then the first equation is denoted as: f r = n × f 1- f b1 If the microwave signal frequency increases while the beat frequency signal frequency decreases, then the first equation is denoted as: f r = n × f 1+ f b1 ; Step S3: Record the second set of data, establish the second equation, and determine the frequency of the microwave signal output by the RF source. f Δ Set as f 2. Set the output power to a small value and gradually increase the output power of the microwave signal until a beat frequency signal is observed on the spectrum analyzer. Record the frequency as follows: f b2 ; Step S4: Determine the sign in the second equation, fine-tune the microwave signal frequency and observe the beat frequency signal on the spectrum analyzer. Determine the sign based on whether the beat frequency signal frequency increases or decreases: If both the microwave signal frequency and the beat frequency signal frequency increase, then the first equation is denoted as: f r = n × f 2- f b2 If the microwave signal frequency increases while the beat frequency signal frequency decreases, then the first equation is denoted as: f r = n × f 2+ f b2 ; Step S5: Solve the two equations determined in steps S2 and S4 simultaneously to obtain the order of the sideband. n Harmony Comb Frequency Repetition f r .

[0019] According to the high-accuracy optical comb repetition rate (RFR) testing apparatus and method of the above embodiments of the present invention, the RFR calculation formula shows that the RFR magnitude is only related to the microwave signal output by the RF source and the beat frequency signal obtained by the spectrum analyzer. The present invention ensures the accuracy of both signals by referencing the RF source and the spectrum analyzer to an external clock, thereby further ensuring the accuracy of the RFR test. The locked laser, combined with the RF source referenced to an external clock, makes the comb teeth used for RFR measurement more stable, reducing sideband signal jitter. By beating the comb teeth generated by the optical comb generation system, the accuracy of the RFR test can be improved.

[0020] The high-accuracy optical comb repetition rate (RFR) testing device and method of this invention greatly simplifies existing optical comb RFR testing devices. It innovatively uses a narrow-linewidth pump laser from the optical comb generation system as the injection laser, eliminating the need for filters in existing devices, reducing the use of optical amplifiers, and significantly reducing system size and power consumption. Furthermore, by locking the laser wavelength, the RF source, and the external clock referenced by the spectrum analyzer, the accuracy of the tested RFR is ensured.

[0021] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A high-accuracy optical comb repetition rate testing device, characterized in that, Includes fiber optic beam splitters, phase modulators, fiber optic combiners, detectors, spectrum analyzers, RF amplifiers, RF sources, and external clocks; The input end of the fiber beam splitter is connected to the pump laser, which is generated by a narrow linewidth laser. The fiber beam splitter is used to split the laser into two paths, which are respectively connected to the optical comb generation system and the phase modulator. The phase modulator is used to generate the secondary sideband of the pump laser and input it into one port of the fiber combiner. The optical comb generated by the optical comb generation system is input into the other port of the fiber combiner. The output of the fiber combiner is connected to the detector. The detector is used to detect the beat frequency signal of the secondary sideband of the pump laser and the comb teeth and convert it into an electrical signal. The radio frequency output port of the detector is connected to the spectrum analyzer. The spectrum analyzer is used to detect the beat frequency signal output by the detector. The spectrum analyzer is connected to an external clock and referenced to the external clock. The radio frequency (RF) source is used to generate microwave signals, is connected to and referenced by an external clock, and its output is connected to the input of an RF amplifier. The frequency of the microwave signal output by the RF source constitutes the sideband spacing generated by the phase modulator. The RF amplifier is used to amplify the power of the microwave signal, and its output is connected to the RF port of the phase modulator.

2. The high-accuracy optical comb repetition rate testing device as described in claim 1, characterized in that, The narrow linewidth laser is frequency-locked by a frequency-locking system, and the locking methods include saturated absorption spectrum, MTS, and PDH.

3. A method for high-accuracy optical comb repetition rate testing, characterized in that, The method for achieving high-accuracy testing of optical comb repetition rate using the apparatus of claim 1 or 2 includes: Step S1: Set the frequency of the microwave signal output by the radio frequency source to... f 1. Set the output power to a small value and gradually increase the output power of the microwave signal until a beat frequency signal is observed on the spectrum analyzer. Record the frequency as follows: f b1 ; Step S2: Fine-tune the frequency of the microwave signal and observe the beat frequency signal on the spectrum analyzer. If the microwave signal frequency increases and the beat frequency signal frequency also increases, then the optical comb repetition rate is... f r The calculation formula is: f r = n × f 1- f b1 If the microwave signal frequency increases while the beat frequency signal frequency decreases, then the optical comb repetition rate will increase. f r The calculation formula is: f r = n × f 1+ f b1 ; Step S3: Set the frequency of the microwave signal output by the radio frequency source to... f 2. Set the output power to a small value and gradually increase the output power of the microwave signal until a beat frequency signal is observed on the spectrum analyzer. Record the frequency as follows: f b2 ; Step S4: Fine-tune the frequency of the microwave signal and observe the beat frequency signal on the spectrum analyzer. If the microwave signal frequency increases and the beat frequency signal frequency also increases, then the optical comb repetition rate is... f r The calculation formula is: f r = n × f 2- f b2 If the microwave signal frequency increases while the beat frequency signal frequency decreases, then the optical comb repetition rate will increase. f r The calculation formula is: f r = n × f 2+ f b2 ; Step S5, based on the optical comb repetition rate determined in steps S2 and S4 f r The two calculation formulas are used to solve for the order of the sideband. n Harmony Comb Frequency Repetition f r .

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