An optical frequency comb locking system that eliminates carrier envelope offset frequency

Abstract

The application discloses an optical frequency comb locking system for eliminating carrier envelope phase shift frequency, and the disclosed system comprises an optical frequency comb, a repetition frequency detector, a carrier envelope phase shift detector, an attenuator, an operational amplifier, a filter, a power divider, a double balanced mixer, a bias voltage and a phase-locked loop; the system extracts the sum and difference frequencies of the repetition frequency and the carrier envelope phase shift frequency of the optical frequency comb, and locks them to each other, so as to realize the carrier envelope phase shift frequency locking to zero frequency, and reduce the difficulty of the optical frequency comb locking. The application solves the problem of high locking difficulty of the traditional optical frequency comb, simplifies the carrier envelope phase shift frequency control, has the feasibility of productization and high integration, has universality, and can be widely applied to different types of optical frequency comb systems.

Description

TECHNICAL FIELD

[0001] The present application relates to a carrier envelope offset frequency elimination optical comb locking system, belonging to the technical field of optical frequency comb, which can be applied to laser technology, phase-locked loop technology and many other fields. BACKGROUND

[0002] As a bridge linking optical frequency and microwave frequency, optical frequency comb can realize broadband lossless frequency conversion and characteristic transmission from microwave to optical, optical to optical, and optical to microwave, and is the most precise frequency transfer tool at present, which has important application value in communication navigation, space precise ranging, and time-frequency transfer field.

[0003] Optical frequency comb is one of the important applications of ultrafast laser technology, and its essence is to detect and lock the frequency of the mode-locked laser. Detecting and locking the repetition frequency and the carrier envelope offset frequency are the key to realizing the function of optical frequency comb. Among them, the repetition frequency is determined by the laser cavity length and can be directly detected by a fast photoelectric probe. The stability of the repetition frequency is mainly affected by environmental factors such as temperature and vibration, and the drift degree is low, the signal line width is narrow, and it is relatively easy to lock. The carrier envelope offset frequency needs to be detected by building an additional optical path,

[0004] In order to simplify the locking difficulty of optical comb, eliminate the influence of carrier envelope frequency instability on optical comb, G. Krauss, D. Fehrenbacher, etc. published the articles of "All-passive phase locking of a compact Er:fiberlaser system", "Free-running performance and full control of a passively phase-stable Er:fiber frequency comb", etc. to introduce the optical frequency comb device with zero carrier envelope offset frequency realized by using difference frequency laser generation technology; S. Koke published the article of "Direct frequency comb synthesis with arbitrary offset and shot noise-limited phase noise" to introduce the method of eliminating carrier envelope frequency by pre-feedback technology; Han Hai-nian, etc. introduced an optical comb locking scheme for removing the influence of carrier envelope offset frequency by using pre-feedback in the invention patent "A low-noise fiber laser frequency comb device with controllable carrier envelope offset frequency". The above existing technologies still use complex optical means to lock the carrier envelope offset frequency to zero frequency, which has certain technical difficulty, and there is still certain difficulty in feasibility and productization. SUMMARY

[0005] In view of the defects or deficiencies of the prior art, the present application provides an optical frequency comb locking system for eliminating carrier envelope offset frequency.

[0006] To this end, the optical frequency comb locking system for eliminating carrier envelope offset frequency provided by the present application processes the repetition frequency signal (Repetition frequency, denoted as f r ) of the optical frequency comb and the carrier envelope offset frequency signal (Carrier envelope offset frequency, denoted as f0) to realize locking the carrier envelope offset frequency of the optical frequency comb to zero frequency; the system comprises a repetition frequency detector, a carrier envelope offset frequency detector, an attenuator, an operational amplifier, a filter, a power divider, a double balanced mixer, a bias voltage and a phase-locked loop.

[0007] The repetition frequency detector is used to detect the repetition frequency signal of the optical frequency comb and convert the repetition frequency signal into a corresponding electrical signal, outputting a first repetition frequency signal f r1 and a harmonic frequency signal of the first repetition frequency signal.

[0008] The carrier envelope offset frequency detector is used to detect the carrier envelope offset frequency signal of the optical frequency comb and convert the carrier envelope offset frequency signal into a corresponding electrical signal, outputting a second repetition frequency signal f r2 , a first carrier envelope offset frequency signal f 01 , a sum signal f r2 +f 01 of the signal f r2 and the signal f 01 , a difference signal f r2 -f 01 of the signal f r2 and the signal f 01 , a harmonic frequency signal of the signal f r2 , a harmonic frequency signal of the signal f 01 and a harmonic frequency signal of the signal f r2 -f 01 ; the signal strength of the second repetition frequency signal is less than that of the first repetition frequency signal.

[0009] The attenuator is used to attenuate the output signal of the repetition frequency detector, so that the signal strength of the first repetition frequency signal is equal to or close to that of the second repetition frequency signal; the attenuated first repetition frequency signal and the harmonic frequency of the attenuated first repetition frequency signal are outputted.

[0010] The operational amplifier is used to perform operational comparison processing on the output of the attenuator and the output of the carrier envelope offset frequency detector, outputting a third repetition frequency signal f r3, the second carrier envelope phase shift frequency signal f 02 , the signal f r3 , the signal f 02 , the sum signal f r3 +f 02 , the signal f r3 , the signal f 02 , the difference signal f r3 -f 02 , the harmonic frequency signal of the signal f r3 , the harmonic frequency signal of the signal f 02 , the harmonic frequency signal of the signal f r3 -f 02 ; the signal strength of the third repetitive frequency signal f r3 is less than the signal strength of the first repetitive frequency signal after attenuation.

[0011] The filter is used for filtering the output of the operational amplifier, and outputs a fourth repetitive frequency signal f r4 , the third carrier envelope phase shift frequency signal f 03 , the signal f r4 , the signal f 03 , the sum signal f r4 +f 03 , the signal f r4 , the signal f 03 , the difference signal f r4 -f 03 .

[0012] The power divider is used for signal power equalization processing on the output of the filter, and outputs two signals, both of which contain a fifth repetitive frequency signal f r5 , the fourth carrier envelope phase shift frequency signal f 04 , the signal f r5 , the signal f 04 , the sum signal f r5 +f 04 , the signal f r5 , the signal f 04 , the difference signal f r5 -f 04 , and the frequency and power of the signal f r5 in the two signals are the same, the frequency and power of the signal f r5 +f 04 are the same, and the frequency and power of the signal f r5 -f 04 are the same.

[0013] The double balanced detector is used for mixing processing on the two signals output by the power divider, and outputs a sixth repetitive frequency signal f r6 , the fifth carrier envelope phase shift frequency signal f 05, signal f r6 , signal f 05 , signal f r6 +f 05 , signal f r6 , signal f 05 , signal f r6 -f 05 , signal f r6 +f 05 , signal f r6 -f 05 error signal of signal f

[0014] The bias voltage is used for adjusting the error signal amplitude generated by the double balanced detector to generate a zero-crossing voltage for feedback control;

[0015] The phase-locked loop is used for phase demodulation filtering processing on the output of the double balanced detector with the bias voltage, and outputs a feedback control voltage with varying intensity, which is used for modulating the pump of the optical frequency comb, so that the difference between the repetition frequency signal and the carrier envelope phase shift signal of the output of the optical frequency comb is equal to the sum of the repetition frequency signal and the carrier envelope phase shift signal, thereby realizing the carrier envelope frequency locked to zero frequency.

[0016] An optional solution is that the repetition frequency detector adopts a photodetector, and the carrier envelope phase shift frequency detector adopts an avalanche photodetector. The difference between the signal intensity of the first repetition frequency signal and the signal intensity of the second repetition frequency signal is close within 5 dB.

[0017] A further solution is that the system further comprises an optical frequency comb, wherein the input ports of the repetition frequency detector and the carrier envelope phase shift detector are connected with the output port of the optical frequency comb, and the output port of the phase-locked loop is connected with the modulation port of the optical frequency comb.

[0018] The present application solves the problem of high difficulty in locking the conventional optical frequency comb, simplifies the carrier envelope phase shift frequency control, has the feasibility of productization and high integration, and has universality, and can be widely applied to different types of optical frequency comb systems.

[0019] The present application uses operational amplifiers, mixers and other electrical elements to extract the sum and difference frequencies of the repetition frequency and the carrier envelope phase shift frequency of the optical frequency comb and lock them to each other, so as to realize the carrier envelope phase shift frequency locked to zero frequency and reduce the difficulty in locking the optical frequency comb. In the present application, the selected devices are common microwave devices, the device selection is flexible, and the devices can be replaced as needed. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 It is a schematic diagram of the principle of the system of the present application.

[0021] Figure 2 Output signal of the filter in the system of the present application.

[0022] Figure 3 Error voltage before and after the carrier envelope offset frequency in the system of the present application. DETAILED DESCRIPTION

[0023] Unless otherwise defined, scientific and technical terms used herein have the meanings that would be understood by one of ordinary skill in the art.

[0024] The present application extracts the sum and difference frequencies of the repetition frequency and the carrier envelope offset frequency of the optical frequency comb, and locks them to each other, so as to realize the carrier envelope offset frequency locking to zero frequency, and reduce the difficulty of optical frequency comb locking.

[0025] The present application is applicable to optical frequency combs including but not limited to fiber optical frequency comb, titanium-sapphire optical frequency comb, all-solid-state optical frequency comb, microcavity optical comb, etc. The above optical frequency combs are all provided with two optical output ports and a modulation port. The two output ports are respectively a carrier envelope offset frequency output port and a repetition frequency output port, and are respectively used for outputting the carrier envelope offset frequency signal and the repetition frequency signal of the optical frequency comb. The modulation port is connected with the output of the phase-locked loop in the system, so as to connect the two output ports of the optical frequency comb with the repetition frequency detection and the carrier envelope offset frequency detection respectively. In a specific scheme, if the port of the optical frequency comb is a spatial light output, a lens is needed to focus into a photodetector detection module; if the port output is a fiber laser output, a fiber flange is needed to be connected to a photodetector.

[0026] In order to make the purpose, technical scheme and advantages of the embodiments of the present application more clear, the technical scheme of the present application will be described clearly and completely by embodiments in combination with the drawings.

[0027] Embodiment:

[0028] Based on the scheme of the present application, the system structure principle diagram of the present embodiment is shown in Figure 1 The system structure principle diagram of the present embodiment is shown in

[0029] The optical frequency comb 1 is an erbium-doped fiber optical frequency comb (Menlo Systems SmartComb), the repetition frequency is 100 MHz, and the optical frequency comb 1 contains two output ports. The output power of the repetition frequency port signal is 2 mW, and the output power of the carrier envelope offset frequency port signal is 0.5 mW.

[0030] The repetition frequency detection 2 is an optoelectronic detector, and a DET01CFC / M fiber-coupled InGaAs detector of Thorlabs Company is selected, a wavelength range is 800-1700nm, and a bandwidth is 1.2GHz; a signal detected by the repetition frequency detection 2 includes a 100MHz first repetition frequency signal f r1 and harmonic frequency signals thereof, the signal f r1 has a signal strength of -10dBm.

[0031] The carrier envelope phase detection 3 is an avalanche photodetector, and an FPD310-FC-NIR indium gallium arsenide photodetector of Thorlabs Company is selected, a wavelength range is 950-1650nm, and a bandwidth is 1MHz-1.5GHz; a signal detected by the carrier envelope phase detection 3 includes a first carrier envelope phase shift frequency signal f 01 , a 100MHz second repetition frequency signal f r2 , a signal f r2 -f 01 , a signal f r2 +f 01 , a signal f 01 , a signal f r2 , a signal f r2 -f 01 , and harmonic frequency signals of three signals; wherein the signal f r2 has a signal strength of -20dBm, the signal f 01 and the signal f r2 -f0 all have signal strengths of -40dBm.

[0032] The attenuator 4 is a 10dB attenuator of BW-S10W20+ of Mini-circuits Company, and the signal strength of the signal f r1 detected by the repetition frequency detection 2 is attenuated to -20dBm.

[0033] The operational amplifier 5 is an OPA357 operational amplifier of TI Company, and a bandwidth is 250MHz; the operational amplifier is used for operating and comparing the output signal of the carrier envelope phase detection 3 and the output signal of the attenuator 4, and outputting a 100MHz third repetition frequency signal f r3 , a second carrier envelope phase shift frequency signal f 02 , a signal f r3 , a signal f 02 , a sum signal f r3 +f 02 , a signal f r3 , a difference signal f 02 -f r3 , a signal f 02 , a signal f r3 , a harmonic frequency signal of the signal f 02harmonic frequency signal of signal f r3 -f 02 harmonic frequency signal of signal f r3 The signal strength of signal f

[0034] The filter 6 is a BPF-F100+ band-pass filter from Mini-circuits company, with a center frequency of 100 MHz and a bandwidth of 5 MHz. The filter filters the output of the operational amplifier and outputs a fourth repetitive frequency signal f r4 , a third carrier envelope phase shift frequency signal f 03 , signal f r4 and signal f 03 The sum signal f r4 +f 03 , signal f r4 and signal f 03 The difference signal f r4 -f 03 , signal f r4 -f 03 , signal f r4 , signal f r4 +f 03 The signal strengths of signal f

[0035] The power divider 7 is a ZFSC-2-1W+ power divider from Mini-Circuits company, with a bandwidth of 1-750 MHz. The signal output by the filter 6 is divided into two signals with the same frequency and power by the power divider 7.

[0036] The double balanced mixer 8 is an ADE-1+ mixer from Mini-Cicuits company. After mixing the two signals output by the power divider 7, the double balanced mixer outputs a sixth repetitive frequency signal f r6 , a fifth carrier envelope phase shift frequency signal f 05 , signal f r6 and signal f 05 The sum signal f r6 +f 05 , signal f r6 and signal f 05 The difference signal f r6 -f 05 , signal f r6 +f 05 and signal f r6 -f 05 The error signal or error voltage, i.e. signal f r6 +f 05 and signal f r6 -f05 a difference signal of the error signals;

[0037] 0.45V bias voltage 9 is applied to the double balanced detector to adjust the amplitude of the error signal generated to produce a zero crossing voltage for feedback control; in a specific embodiment, the bias voltage value is related to the range of the error signal output by the double balanced detector;

[0038] The phase-locked loop 10 is a UHF digital phase-locked amplifier of Zurich Instrument, and the error voltage is processed by the phase-locked loop circuit and output to modulate the pump source of the optical frequency comb and control the feedback voltage of the optical frequency comb. The result of the loop lock is that the difference between the repetition frequency signal output by the optical frequency comb and the carrier envelope phase shift signal is equal to the sum of the repetition frequency signal and the carrier envelope phase shift signal, so as to realize the frequency locking of the carrier envelope to zero frequency and achieve the purpose of eliminating the carrier envelope phase shift frequency.

[0039] During the working process of the above system, the error voltage in the system of the above embodiment is measured by using a DS2302A oscilloscope of RIGOL company. When the error voltage applied by the bias monitored by the oscilloscope changes from oscillation to stable around 0V, the elimination of the carrier envelope phase shift frequency is realized, and the result is shown in Figure 3 .

[0040] Finally, it should be noted that the present application is not limited to the above-described embodiments. The above description of specific embodiments is intended to illustrate the technical solutions of the present application and to help further understanding. The above-described specific embodiments are merely illustrative and are not restrictive. Without departing from the purpose of the present application and the scope protected by the claims, those skilled in the art can make many forms of replacement and modification under the inspiration of the present application, and these all belong to the protection scope of the present application.

Claims

1. An optical frequency comb locking system that eliminates carrier envelope offset frequency, characterized in that, The system processes the repetition frequency signal f of the optical frequency comb r The carrier envelope offset frequency signal f0 is processed to realize the carrier envelope offset frequency locking of the optical frequency comb to zero frequency. The system comprises a repetition frequency detector, a carrier envelope phase shift detector, an attenuator, an operational amplifier, a filter, a power divider, a double balanced mixer, a bias voltage and a phase locked loop. The repetition frequency detector is used for detecting a repetition frequency signal of the optical frequency comb and converting the repetition frequency signal into a corresponding electrical signal, and outputs a first repetition frequency signal f r1 and a harmonic frequency signal of the first repetition frequency signal. The aforementioned carrier envelope phase shift frequency detector is used to detect the carrier envelope phase shift frequency signal of the optical frequency comb, and converts the carrier envelope phase shift frequency signal into a corresponding electrical signal, outputting a second repetition frequency signal f. r2 The first carrier envelope phase shift frequency signal f 01 Signal f r2 With signal f 01 The sum signal f r2 +f 01 Signal f r2 With signal f 01 The difference signal f r2 -f 01 Signal f r2 Harmonic frequency signal, signal f 01 Harmonic frequency signals and signal f r2 -f 01 The harmonic frequency signal; the signal strength of the second repetition frequency signal is less than the signal strength of the first repetition frequency signal; The attenuator is used to attenuate the output signal of the repetition frequency detector, so that the signal strength of the first repetition frequency signal is equal to or close to the signal strength of the second repetition frequency signal, wherein the difference between the signal strength of the first repetition frequency signal and the signal strength of the second repetition frequency signal is within 5dB; the attenuated first repetition frequency signal and the harmonic frequency of the attenuated first repetition frequency signal are outputted. The operational amplifier is used for operational comparison processing of the attenuator output and the output of the carrier envelope phase shift frequency detector, and outputs a third repetitive frequency signal f r3 , a second carrier envelope phase shift frequency signal f 02 , a signal f r3 , a signal f 02 , a sum signal f r3 +f 02 , a signal f r3 , a signal f 02 , a difference signal f r3 -f 02 , a harmonic frequency signal of a signal f r3 , a harmonic frequency signal of a signal f 02 , a harmonic frequency signal of a signal f r3 -f 02 ; the signal strength of the third repetitive frequency signal f r3 is less than the signal strength of the first repetitive frequency signal after attenuation. The filter is used to filter the output of the operational amplifier, output the fourth repetitive frequency signal f r4 , the third carrier envelope phase shift frequency signal f 03 , the signal f r4 and the signal f 03 the sum signal f r4 +f 03 , the signal f r4 and the signal f 03 the difference signal f r4 -f 03 ; The power divider is used for signal power equalization processing of the output of the filter, and outputs two signals, both of which contain the fifth repeated frequency signal f r5 , the fourth carrier envelope phase shift frequency signal f 04 , the signal f r5 , and the signal f 04 , the sum signal f r5 +f 04 , the signal f r5 , and the signal f 04 , the difference signal f r5 -f 04 , and the frequency and power of the signal f r5 in the two signals are the same, the frequency and power of the signal f r5 +f 04 are the same, and the frequency and power of the signal f r5 -f 04 are the same. The double balanced detector is used to mix the two signals output from the power divider, outputting a sixth repetition frequency signal f r6 , a fifth carrier envelope phase shift frequency signal f 05 , a signal f r6 , a signal f 05 , a sum signal f r6 +f 05 , a signal f r6 , a difference signal f 05 -f r6 , a signal f 05 +f r6 , a signal f 05 +f r6 -f 05 , an error signal The bias voltage is used to adjust the amplitude of the error signal generated by the double balanced detector to generate a zero-crossing voltage for feedback control. The phase locked loop is used to perform phase demodulation filtering on the output of the double balanced detector with bias voltage, and output a feedback control voltage with varying intensity, which is used to modulate the pump source of the optical frequency comb, so that the difference between the repetition frequency signal and the carrier envelope phase shift signal of the output of the optical frequency comb is equal to the sum of the repetition frequency signal and the carrier envelope phase shift signal, thereby realizing the carrier envelope frequency locked to zero frequency.

2. The system for cancelling carrier envelope offset frequency according to claim 1, characterized in that, The repetition frequency detector adopts a photoelectric detector.

3. The system for cancelling carrier envelope offset frequency of claim 1, wherein, The carrier envelope phase shift frequency detector adopts an avalanche photoelectric detector.

4. The system for canceling carrier envelope phase shift frequency of claim 1, wherein, The system further comprises an optical frequency comb, wherein the input port of the repetition frequency detector and the carrier envelope phase shift detector is connected with the output port of the optical frequency comb, and the output port of the phase locked loop is connected with the modulation port of the optical frequency comb.

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