Optical frequency comb locking system for eliminating carrier envelope phase shift frequency

Abstract

The invention discloses an optical frequency comb locking system for eliminating carrier envelope phase shift frequency. The 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. According to the system, the sum value and the difference value frequency of the repetition frequency of the optical frequency comb and the carrier envelope phase shift frequency are extracted and mutually locked, so that the purposes of locking the carrier envelope phase shift frequency to zero frequency and reducing the locking difficulty of the optical frequency comb are achieved. According to the method, the defect that a traditional optical frequency comb is high in locking difficulty is overcome, carrier envelope phase shift frequency control is more simplified, feasibility of productization and high integration is achieved, meanwhile, universality is achieved, and the method can be widely applied to different types of optical frequency comb systems.

Description

Technical Field

[0001] The invention relates to an optical comb locking system for eliminating carrier envelope phase shift frequency, belongs to the technical field of optical frequency combs, and can be applied to many fields such as laser technology and phase-locked loop technology. Background Art

[0002] As a bridge connecting optical frequency and microwave frequency, the optical frequency comb can realize broadband lossless frequency conversion and characteristic transfer from microwave to optical, optical to optical, and optical to microwave. It is currently the most accurate frequency transfer tool and has important application value in the fields of communication navigation, space precision ranging, and time-frequency transfer.

[0003] Optical frequency comb is one of the important applications of ultrafast laser technology. Its essence is to detect and lock the frequency of mode-locked lasers. Detecting and locking the repetition frequency and carrier-envelope phase shift frequency are the keys 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. The drift degree is low, the signal line width is narrow, and it is easier to achieve locking. The carrier-envelope phase shift frequency requires the construction of an additional optical path for detection.

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

[0005] In view of the defects or shortcomings of the prior art, the present invention provides an optical frequency comb locking system for eliminating the carrier envelope phase shift frequency.

[0006] To this end, the optical frequency comb provided by the present invention for eliminating the carrier envelope phase shift frequency is locked by adjusting the repetition frequency signal (Repetition frequency, denoted as f) of the optical frequency comb. r ) and the carrier envelope phase shift frequency signal (Carrier envelope offset frequency, denoted as f0) are processed to lock the carrier envelope phase shift frequency of the optical frequency comb to zero frequency; the system includes: 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;

[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, and output a first repetition frequency signal f r1 and a harmonic frequency signal of the first repetition frequency signal;

[0008] The carrier envelope phase shift frequency detector is used to detect the carrier envelope phase shift frequency signal of the optical frequency comb, and convert the carrier envelope phase shift frequency signal into a corresponding electrical signal, and output 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 The harmonic frequency signal, signal f 01 The harmonic frequency signal and signal f r2 -f 01 The signal strength of the second repetition frequency signal is less than the signal strength 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 the signal strength of the second repetition frequency signal; output the attenuated first repetition frequency signal and the harmonic frequency of the attenuated first repetition frequency signal;

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

[0011] The filter is used to filter the output of the operational amplifier and output the fourth repetition frequency signal f r4 , the third carrier envelope phase shift frequency signal f 03 , signal f r4 With signal f 03 The sum signal f r4 +f 03 , signal f r4 With signal f 03 The difference signal f r4 -f 03 ;

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

[0013] The double balanced detector is used to mix the two signals output by the power divider and output the sixth repetition frequency signal f r6 , the fifth carrier envelope phase shift frequency signal f 05, signal f r6 With signal f 05 The sum signal f r6 +f 05 , signal f r6 With signal f 05 The difference signal f r6 -f 05 , signal f r6 +f 05 With signal f r6 -f 05 The error signal

[0014] 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;

[0015] The phase-locked loop is used to perform phase-detection filtering on the output of the double-balanced detector to which a bias voltage is applied, and output a feedback control voltage with varying output intensity, which is used to modulate the pump source of the optical frequency comb to achieve that the difference between the repetition frequency signal and the carrier-envelope phase shift signal output by the optical frequency comb is equal to the sum of the repetition frequency signal and the carrier-envelope phase shift signal, thereby locking the carrier-envelope frequency to zero frequency.

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

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

[0018] The present invention solves the shortcoming of high difficulty in locking traditional optical frequency combs, simplifies the carrier-envelope phase shift frequency control, and has the feasibility of productization and high integration. At the same time, it has universality and can be widely used in different types of optical frequency comb systems.

[0019] The present invention uses electrical components such as operational amplifiers and mixers to extract the sum and difference frequencies of the optical frequency comb repetition frequency and the carrier envelope phase shift frequency and lock them to each other, thereby locking the carrier envelope phase shift frequency to zero frequency and reducing the difficulty of locking the optical frequency comb. The devices selected in the scheme of the present invention are commonly used microwave devices, and the device selection is flexible and replaceable, and can be flexibly modified according to system requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the principle of the system of the present invention.

[0021] Figure 2 is the output signal of the filter in the system of the present invention.

[0022] Figure 3 This is the error voltage before and after the carrier phase shift frequency is eliminated in the embodiment system. DETAILED DESCRIPTION

[0023] Unless otherwise specified, the scientific and technical terms used herein are understood according to the knowledge of ordinary technicians in the relevant fields.

[0024] The present invention achieves the purpose of locking the carrier envelope phase shift frequency to zero frequency and reducing the difficulty of locking the optical frequency comb by extracting the sum and difference frequencies of the optical frequency comb repetition frequency and the carrier envelope phase shift frequency and locking them mutually.

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

[0026] In order to make the purpose, technical solution and advantages of the embodiments of the present invention more clear, the technical solution of the present invention will be clearly and completely described below through embodiments in conjunction with the accompanying drawings.

[0027] Example:

[0028] Based on the solution of the present invention, the system structure principle diagram of this embodiment is as follows: Figure 1 As shown, it includes an optical frequency comb 1, a repetition frequency detector 2, a carrier envelope phase shift detector 3, an attenuator 4, an operational amplifier 5, a filter 6, a power divider 7, a double-balanced mixer 8, a bias voltage 9 and a phase-locked loop 10.

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

[0030] The repetition frequency detector 2 is a photoelectric detector, which uses the DET01CFC / M fiber-coupled InGaAs detector from Thorlabs, with a wavelength range of 800-1700nm and a bandwidth of 1.2GHz. The signal detected by the repetition frequency detector 2 includes the 100MHz first repetition frequency signal f r1 and its harmonic frequency signal, signal f r1 The signal strength is -10dBm;

[0031] The carrier envelope phase shift detector 3 is an avalanche photodetector, FPD310-FC-NIR InGaAs photodetector from Thorlabs, with a wavelength range of 950-1650nm and a bandwidth of 1MHz-1.5GHz. The signal detected by the carrier envelope phase shift detector 3 includes a first carrier envelope phase shift frequency signal f 01 , 100MHz second repetition frequency signal f r2 , signal f r2 -f 01 , signal f r2 +f 01 and the signal f 01 , signal f r2 , signal f r2 -f 01 The harmonic frequency signals of the three signals; among which the signal f r2 The signal strength is -20dBm, signal f 01 and signal f r2 The signal strength of -f0 is -40dBm;

[0032] Attenuator 4 uses a 10dB attenuator BW-S10W20+ from Mini-circuits, which detects the signal f r1 The signal strength is attenuated to -20dBm;

[0033] The operational amplifier 5 is an OPA357 operational amplifier from TI with a bandwidth of 250MHz. The operational amplifier is used to compare the output signal of the carrier envelope phase shift detection 3 with the output signal of the attenuator 4, and output a 100MHz third repetition frequency signal f r3 , the second carrier envelope phase shift frequency signal f 02 , signal f r3 With signal f 02 The sum signal f r3 +f 02 , signal f r3 With signal f 02 The difference signal f r3 -f 02 , signal f r3 The harmonic frequency signal, signal f 02The harmonic frequency signal, signal f r3 -f 02 Harmonic frequency signal; where the signal f r3 The signal strength is -55dBm;

[0034] Filter 6 uses a BPF-F100+ bandpass filter from Mini-circuits, 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 repetition frequency signal f of 100 MHz. r4 , the third carrier envelope phase shift frequency signal f 03 , signal f r4 With signal f 03 The sum signal f r4 +f 03 , signal f r4 With signal f 03 The difference signal f r4 -f 03 , where the signal f r4 -f 03 , signal f r4 , signal f r4 +f 03 The signal strengths are -43dBm, -58dBm, and -43dBm respectively;

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

[0036] The double-balanced mixer 8 uses the ADE-1+ mixer of Mini-Cicuits Company; the two signals output by the power divider 7 are connected to the double-balanced mixer for mixing, and the 100MHz sixth repetition frequency signal f r6 , the fifth carrier envelope phase shift frequency signal f 05 , signal f r6 With signal f 05 The sum signal f r6 +f 05 , signal f r6 With signal f 05 The difference signal f r6 -f 05 , signal f r6 +f 05 With signal f r6 -f 05 The error signal or error voltage, that is, the signal f r6 +f 05 and signal f r6 -f05 The difference signal of

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

[0038] The phase-locked loop 10 is a Zurich Instruments UHF digital phase-locked amplifier. 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 locking is to control the difference between the repetition frequency signal and the carrier envelope phase shift signal output by the optical frequency comb to be equal to the sum of the repetition frequency signal and the carrier envelope phase shift signal, thereby locking the carrier envelope frequency to zero frequency and achieving the purpose of eliminating the carrier envelope phase shift frequency.

[0039] During the operation of the above system, the error voltage in the above embodiment system is measured using a DS2302A oscilloscope from RIGOL. When the error voltage applied with a bias monitored by the oscilloscope changes from oscillation to stability near 0V, the carrier envelope phase shift frequency is eliminated. The results are as follows: Figure 3 shown.

[0040] Finally, it should be noted that the present invention is not limited to the embodiments described above. The above description of the specific embodiments is intended to illustrate the technical solution of the present invention to help further understand that the above specific embodiments are merely illustrative and not restrictive. Without departing from the scope of the present invention and the scope of protection of the claims, those skilled in the art can also make many forms of replacement and modification under the enlightenment of the present invention, which all belong to the protection scope of the present invention.

Claims

1. An optical frequency comb locking system for eliminating carrier envelope phase shift frequency, characterized in that: The system undergoes a repetitive frequency signal f of the optical frequency comb. r Processing with the carrier-envelope phase shift frequency signal f0 to achieve locking the carrier-envelope phase shift frequency of the optical frequency comb to zero frequency; The system comprises: a repetition frequency detector (2), a carrier envelope phase shift detector (3), an attenuator (4), an operational amplifier (5), a filter (6), a power divider (7), a double-balanced mixer (8), a bias voltage (9) and a phase-locked loop (10); 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, and output a first repetition frequency signal f r1 and a harmonic frequency signal of the first repetition frequency signal; The carrier envelope phase shift frequency detector is used to detect the carrier envelope phase shift frequency signal of the optical frequency comb, and convert the carrier envelope phase shift frequency signal into a corresponding electrical signal, and output 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 The harmonic frequency signal, signal f 01 The harmonic frequency signal and signal f r2 -f 01 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; output the attenuated first repetition frequency signal and the harmonic frequency of the attenuated first repetition frequency signal; The operational amplifier is used to perform operational comparison processing on the attenuator output and the output of the carrier envelope phase shift frequency detector, and output a third repetition frequency signal f r3 , the second carrier envelope phase shift frequency signal f 02 , signal f r3 With signal f 02 The sum signal f r3 +f 02 , signal f r3 With signal f 02 The difference signal f r3 -f 02 , signal f r3 The harmonic frequency signal, signal f 02 The harmonic frequency signal, signal f r3 -f 02 The third repetition frequency signal f r3 The signal strength of is less than the signal strength of the attenuated first repetition frequency signal; The filter is used to filter the output of the operational amplifier and output the fourth repetition frequency signal f r4 , the third carrier envelope phase shift frequency signal f 03 , signal f r4 With signal f 03 The sum signal f r4 +f 03 , signal f r4 With signal f 03 The difference signal f r4 -f 03 ; The power divider is used to perform signal power equalization processing on the output of the filter, and output two signals, both of which contain the fifth repetition frequency signal f r5 , the fourth carrier envelope phase shift frequency signal f 04 , signal f r5 With signal f 04 The sum signal f r5 +f 04 , signal f r5 With signal f 04 The difference signal f r5 -f 04 , and the signal f in the two signals r5 The frequency and power of the signal f are the same. r5 +f 04 The frequency and power of the signal f are the same. r5 -f 04 The frequency and power are the same; The double balanced detector is used to mix the two signals output by the power divider and output the sixth repetition frequency signal f r6 , the fifth carrier envelope phase shift frequency signal f 05 , signal f r6 With signal f 05 The sum signal f r6 +f 05 , signal f r6 With signal f 05 The difference signal f r6 -f 05 , signal f r6 +f 05 With signal f r6 -f 05 The 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-detection filtering on the output of the double-balanced detector to which a bias voltage is applied, and output a feedback control voltage with varying output intensity, which is used to modulate the pump source of the optical frequency comb to achieve that the difference between the repetition frequency signal and the carrier-envelope phase shift signal output by the optical frequency comb is equal to the sum of the repetition frequency signal and the carrier-envelope phase shift signal, thereby locking the carrier-envelope frequency to zero frequency.

2. The system for eliminating carrier envelope phase shift frequency according to claim 1, characterized in that: The repetition frequency detector is a photoelectric detector.

3. The system for eliminating carrier envelope phase shift frequency according to claim 1, characterized in that: The carrier envelope phase shift frequency detector adopts an avalanche photodetector.

4. The system for eliminating carrier envelope phase shift frequency according to claim 1, characterized in that: The difference between the signal strength of the first repetition frequency signal and the signal strength of the second repetition frequency signal is close if it is within 5 dB.

5. The system for eliminating carrier envelope phase shift frequency according to claim 1, characterized in that: It also includes an optical frequency comb (1), wherein the input ports of the repetition frequency detector and the carrier envelope phase shift detector are connected to the output port of the optical frequency comb, and the output port of the phase-locked loop is connected to the modulation port of the optical frequency comb.

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