阅读说明：本技术 一种基于频移反馈腔的宽带可调谐正弦调频激光信号产生方法及装置 (Method and device for generating broadband tunable sinusoidal frequency modulation laser signal based on frequency shift feedback cavity ) 是由 杨宏志 王磊 毛叶飞 高原 于 2020-04-22 设计创作，主要内容包括：本发明提供一种基于频移反馈腔的宽带可调谐调频激光信号产生方法及装置,通过简单调节相对于反馈腔基频的偏离量Δf,即可实现调频指数连续可调的宽带调频信号,并具有脉冲重复频率连续可调、调制指数大、宽带可调谐、结构简单,便于应用等特点。(The invention provides a frequency shift feedback cavity-based broadband tunable frequency modulation laser signal generation method and device, which can realize a broadband frequency modulation signal with continuously adjustable frequency modulation index by simply adjusting the deviation delta f relative to the fundamental frequency of a feedback cavity, and have the characteristics of continuously adjustable pulse repetition frequency, large modulation index, tunable broadband, simple structure, convenient application and the like.)

1. A method for generating a broadband tunable frequency-modulated laser signal based on a frequency-shift feedback cavity, the method comprising:

setting the modulation frequency f of the electro-optical phase modulation_m＝pf_c+ Δ f, i.e. making fm deviate from the feedback cavity fundamental frequency f_cAn integer p times, where the deviation is Δ f and satisfies Δ f < f_c；

Injecting seed laser into the feedback cavity, and generating a frequency modulation laser signal after electro-optic phase modulation;

and realizing the tunable broadband of the frequency modulation laser signal by adjusting the deviation delta f.

2. The method of claim 1, wherein the feedback cavity comprises a feedback loop, and wherein the seed laser is injected into the feedback loop to generate the frequency modulated laser signal after the electro-optic phase modulation.

3. The laser signal generation method according to claim 2, wherein the electro-optical phase-modulated modulation signal is a broadband sine-modulated signal, and the frequency-modulated laser signal is a sine-frequency-modulated laser signal; when the modulation depth of the electro-optic phase modulation is set to pi, the instantaneous frequency of the sine frequency modulation laser signal satisfies:

f_t＝|kf_msin(2πf_mt-πΔfτ)+f_i|；

wherein k is a frequency modulation index, and k is 1/(2 Δ f τ); τ is the time required for the seed laser to transmit in the feedback loop for one week; t is the current time; f. of_iFor the carrier frequency of the broadband sinusoidal modulation signal, the following conditions are satisfied:

f_i＝round{(ω₀τ-2pπ)/2πΔfτ}×f_m；

wherein round { } is an integer function; omega₀Is the angular frequency of the seed laser.

4. The method according to claim 3, wherein the seed laser is a single-frequency continuous laser, and the frequency-modulated laser signal is a broadband sinusoidal frequency-modulated double-pulse laser signal.

5. A device for generating a broadband tunable frequency-modulated laser signal based on a frequency shift feedback cavity, which is characterized by applying the laser signal generation method of any one of claims 1-4.

6. The laser signal generating apparatus according to claim 5, wherein the apparatus comprises:

a seed laser emission source (1) to emit and inject the seed laser into the feedback cavity;

the feedback cavity comprises a low-noise optical amplifier (4) for amplifying the seed laser and an electro-optic phase modulator (3) for performing electro-optic phase modulation on the seed laser;

a photodetector (6) for detecting the frequency modulated laser signal output by the feedback cavity;

a 2X2 coupler (2) including a first input IN1 connected to the seed laser emission source (1), a first output OUT1 connected to the photodetector (6), and a second input IN2 and a second output OUT2 connected to the feedback cavity.

7. The laser signal generation device according to claim 6, wherein a radio frequency driver (31) is arranged within the electro-optical phase modulator (3) to emit a radio frequency drive signal for the electro-optical phase modulation.

8. The laser signal generating device according to claim 7, wherein the feedback cavity further comprises an optical narrow-band filter (5), the center wavelength of the optical narrow-band filter (5) being the same as the wavelength of the seed laser.

Technical Field

The invention relates to the photoelectron technology, in particular to a method and a device for generating a broadband tunable frequency modulation laser signal based on a frequency shift feedback cavity.

Background

With the rapid development of modern communication technology, the application of radio technology is more and more extensive, and the application range of the radio technology covers various civil and military fields such as aerospace, communication, navigation, military equipment and the like, and becomes an indispensable means and tool for improving production capacity, improving living environment, accelerating economic development, improving military combat power and the like. The broadband sinusoidal frequency modulation signal has strong anti-interference capability, can realize the interchange of bandwidth and signal-to-noise ratio, and is widely applied to long-distance high-quality communication systems, such as space and satellite communication, frequency modulation stereo broadcasting, short-wave radio stations and the like. In addition, modern radars also widely use broadband frequency modulation signals, because of their characteristics of strong anti-interference ability, strong anti-interception ability, etc.

When the traditional electronic technology is used for generating the broadband sinusoidal frequency modulation signal, the broadband sinusoidal frequency modulation signal with high stability, large bandwidth and large modulation index is difficult to directly obtain under the influence of the bandwidth and the speed of an electronic device. Compared with an electronic method, microwaves are loaded onto light waves in a subcarrier mode through an optical method, microwave signals are processed in an optical domain, and electrical interference of the electrical domain can be avoided.

In addition, in the existing frequency modulation application based on the feedback cavity, the modulation frequency of the electro-optical phase modulation is usually equal to the integral multiple of the feedback cavity frequency, so that the modulation frequency is changed between several integral multiples of the feedback cavity fundamental frequency when the electro-optical phase modulation is implemented. In addition to this, other optoelectronics methods can also generate a broadband sinusoidal modulation signal, but there are a number of problems: 1) the modulation index k is small and cannot provide a sufficiently large modulation index; 2) the pulse repetition frequency cannot be continuously adjusted; 3) the structure is complex, the price is expensive, and the application is not facilitated.

Therefore, it is urgently needed to provide a method and a device for generating a broadband tunable frequency modulation laser signal, which have the advantages of continuously adjustable pulse repetition frequency, large modulation index, tunable broadband, simple structure and convenient application, aiming at the frequency modulation of a frequency shift feedback cavity.

Disclosure of Invention

In order to overcome the defects of the prior art, in a first aspect of the present invention, a method for generating a broadband tunable frequency-modulated laser signal based on a frequency-shift feedback cavity is provided, where the method includes:

setting the modulation frequency f of the electro-optical phase modulation_m＝pf_c+Δf, i order f_mDeviating from the fundamental frequency f of the feedback cavity_cAn integer p times, where the deviation is Δ f and satisfies Δ f < f_c；

Injecting seed laser into the feedback cavity, and generating a frequency modulation laser signal after electro-optic phase modulation;

and realizing the tunable broadband of the frequency modulation laser signal by adjusting the deviation delta f.

Further, the feedback cavity comprises a feedback loop, and the seed laser is injected into the feedback loop and generates the frequency modulation laser signal after being modulated by the electro-optic phase.

Further, the modulation signal of the electro-optic phase modulation is a broadband sine modulation signal, and the frequency modulation laser signal is a sine frequency modulation laser signal; when the modulation depth of the electro-optic phase modulation is set to pi, the instantaneous frequency of the sine frequency modulation laser signal satisfies:

f_t＝|kf_msin(2πf_mt-πΔfτ)+f_i|；

wherein k is a frequency modulation index, and k is 1/(2 Δ f τ); τ is the time required for the seed laser to transmit in the feedback loop for one week; t is the current time; f. of_iFor the carrier frequency of the broadband sinusoidal modulation signal, the following conditions are satisfied:

f_i＝round{(ω₀τ-2pπ)/2πΔfτ}×f_m；

wherein round { } is an integer function; omega₀Is the angular frequency of the seed laser.

Further, the seed laser is a single-frequency continuous laser, and the frequency modulated laser signal is a broadband sinusoidal frequency modulated double-pulse laser signal.

According to a second aspect of the present invention, there is provided a broadband tunable frequency modulated laser signal generation device based on a frequency shift feedback cavity, wherein the device is applied to the laser signal generation method as described above.

Further, the apparatus comprises:

a seed laser emission source to emit and inject the seed laser into the feedback cavity;

the feedback cavity comprises a low-noise optical amplifier for amplifying the seed laser and an electro-optic phase modulator for performing electro-optic phase modulation on the seed laser;

the photoelectric detector is used for detecting the frequency-modulated laser signal output by the feedback cavity;

a 2X2 coupler including a first input terminal IN1 connected to the seed laser emission source, a first output terminal OUT1 connected to the photodetector, and a second input terminal IN2 and a second output terminal OUT2 connected to the feedback cavity.

Further, a radio frequency driver is arranged in the electro-optical phase modulator to send out a radio frequency driving signal for the electro-optical phase modulation.

Further, the feedback cavity further comprises an optical narrow-band filter, and the central wavelength of the optical narrow-band filter is the same as the wavelength of the seed laser.

Therefore, the invention can realize the broadband frequency modulation signal with continuously adjustable frequency modulation index by simply adjusting the deviation delta f relative to the fundamental frequency of the feedback cavity, and has the characteristics of continuously adjustable pulse repetition frequency, large modulation index, tunable broadband, simple structure, convenient application and the like.

Drawings

FIG. 1 is a schematic diagram of a broadband tunable FM laser signal generating apparatus based on a frequency shift feedback cavity according to an embodiment of the present invention;

FIG. 2(a) shows the modulation frequency f of the present invention in the embodiment corresponding to FIG. 1_mThe time domain and instantaneous frequency distribution of the obtained frequency-modulated laser signal is shown as 10MHz +20 kHz.

FIG. 2(b) shows the modulation frequency f of the present invention in the embodiment corresponding to FIG. 1_mThe time domain and instantaneous frequency distribution of the obtained frequency-modulated laser signal is shown as 10MHz +10 kHz.

FIG. 2(c) shows the modulation frequency f of the present invention in the embodiment corresponding to FIG. 1_mThe time domain and instantaneous frequency distribution of the obtained frequency-modulated laser signal is shown as 10MHz +5 kHz.

Description of reference numerals:

1-seed laser emission source; a 2-2X2 coupler; 3-an electro-optic phase modulator; 31-a radio frequency driver; 4-low noise optical amplifier; 5-an optical narrow-band filter; 6-a photodetector; 7-high speed acquisition system.

Detailed Description

The technical solutions of the present invention will be described clearly and completely with reference to the accompanying drawings, and it should be understood that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.

In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.

Referring to fig. 1, a schematic structural diagram of a broadband tunable frequency modulation laser signal generation apparatus based on a frequency shift feedback cavity according to an embodiment of the present invention is shown.

IN this embodiment, a seed laser is emitted from a seed emission source 1, and is injected into a feedback cavity through a 2X2 coupler 2 (as shown IN fig. 1, the feedback cavity is a feedback loop IN this embodiment), and then sequentially passes through an electro-optical phase modulator 3 (including an rf driver 31 for outputting an rf driving signal), a low noise optical amplifier 4, and an optical narrow band filter 5, and then is fed back to an input terminal IN2 of the coupler 2, and another output terminal OUT1 of the coupler is directly connected to a photodetector 6. In addition, a high-speed acquisition system 7 can be arranged and connected to the photoelectric detector 6, so that the output frequency-modulated laser signal can be measured in real time at a high speed.

Preferably, the 2X2 coupler is a fiber coupler, which has certain advantages in terms of reliability, stability and volume.

Preferably, the center wavelength of the optical narrow-band filter 5 is the same as the seed laser wavelength, so as to perform the functions of spectral filtering and raising the loop self-excitation threshold.

Preferably, the seed laser is a single-frequency continuous laser, and the frequency modulated laser signal is a broadband sinusoidal frequency modulated double-pulse laser signal. Here, regarding the formation of the double-pulse laser signal, the seed laser may be injected into the feedback loop, the double-sideband frequency shift may be generated by the phase modulator 3, the seed laser after the double-sideband frequency shift may be fed back to the loop input end again, and the above process may be repeated, so that the double-pulse laser signal may be generated within one modulation period by using the double-sideband modulation characteristic of the electro-optic phase modulator.

The forming and implementing processes of the broadband tunable frequency-modulated laser signal generating method based on the frequency shift feedback cavity of the present invention are further described below with reference to the broadband tunable frequency-modulated laser signal generating apparatus provided in the embodiment:

first, a modulation frequency f of electro-optic phase modulation is set_m＝pf_c+ Δ f, i.e. f_mDeviating from the fundamental frequency f of the feedback cavity_c(corresponding to this embodiment, f)_cI.e., the fundamental frequency of the loop) by an integer p, where the deviation is Δ f and Δ f < f is satisfied_c(ii) a Here, the loop fundamental frequency f_cDepending on the loop length, it can be expressed as: f. of_c＝1/τ＝c/L, wherein c is the speed of light in vacuum and L is the loop length.

Thus, according to the theory model of delayed self-heterodyne interference, the light intensity I at the output of the frequency shift feedback cavity can be expressed as:

in the formula (1), real { } is the operation of the real part, t₂₂Transmission matrix representing 2X2 coupler 2(wherein front sides 1, 2 represent IN1 and IN2, respectively, and rear sides 1, 2 represent OUT1 and OUT2, respectively) of the transmission path portion from IN2 to OUT 2. The electric field expression of the seed laser is

Wherein the seed laser angular frequency is omega_o＝2πf_o，f_oThe seed laser frequency. The time required for the seed laser to transmit in the loop for one circle is tau, gamma is a gain coefficient (for example, gain is obtained by amplifier 4), and the transfer function of the electro-optical intensity modulation isWherein ═ pi V_m/V_πModulation depth (V) for electro-optical phase modulation_mRadio frequency voltage, V, for electro-optic phase modulators_πHalf-wave voltage of electro-optic phase modulator).

Since the modulation frequency satisfies f_m＝pf_c+ Δ f relationship and the modulation frequency is tunable, then the light intensity I expression in equation (1) above can be simplified as:

in the formula (2), the reaction mixture is,

representing a wideband sinusoidal fm signal. To further simplify the calculationThe modulation depth of the electro-optical phase modulation is set to pi (for example, the power of the radio-frequency driving signal of the radio-frequency driver 31 of the electro-optical phase modulator 3 is adjusted so that the modulation depth is equal to pi), so that the instantaneous frequency of the broadband sinusoidal frequency modulation signal at this time can be simply expressed as:

f_p＝(1/2π)dθ/dt＝kf_msin(2πf_mt-πΔfτ)

wherein k is 1/(2 Δ f τ) is the frequency modulation index of the wideband sinusoidal frequency modulated signal.

In the formula (2), the summation portion may be based on the formula (A) of Jacobian-Angel

Wherein J_n(k) Is a first class of nth order bessel function) and can be approximated as:

in which equation (3) is simulated, which represents a radio frequency modulated double pulse signal laser. The modulation frequency of the rf modulation (e.g. the rf frequency of the rf driving signal provided by the rf driver 31 in fig. 1, or the carrier frequency of the wideband sinusoidal modulation signal) can be expressed as: f. of_i＝round{(ω₀τ-2pπ)/2πΔfτ}×f_mIt can be seen that it is determined by the instantaneous frequency of the single-frequency continuous laser and the modulation frequency, where round { x } is an integer function.

According to the analysis, the single-frequency continuous laser outputs the double-pulse laser modulated by the broadband sinusoidal frequency after passing through the frequency shift feedback cavity by adjusting the modulation frequency to deviate from the integral multiple cavity fundamental frequency, and the deviation is far smaller than the cavity fundamental frequency, and the instantaneous frequency of the double-pulse laser meets the requirement

f_t＝|f_p+f_i|＝|kf_msin(2πf_mt-πΔfτ)+f_i| (4)

According to the above analysis, the carrier frequency of the wideband sinusoidal modulated signal is f_i(determined by both laser frequency and modulation frequency); maximum frequency offset kf_mFrom the frequency modulation index k and the modulation frequency f_mAnd (6) determining. By adjusting delta f, the change of the frequency modulation index can be realized, and the change of the instantaneous frequency of the output pulse signal is further realized; namely, the broadband sinusoidal frequency modulation signal with continuously adjustable frequency modulation index can be realized by simply adjusting delta f.

As a verification of the laser frequency modulation tunability of the above embodiment, reference is made to fig. 2(a), 2(b) and 2(c), which correspond to a set of experimental simulation verification results respectively. The common conditions on which these three sets of experimental simulation verifications are based are: the cavity fundamental frequency is 10MHz, and the gain loss comprehensive coefficient t in the cavity₂₂Gamma is 0.97, the seed laser frequency is constant and meets omega₀τ＝2kπ。

By adjusting the deviation amount deltaf, the modulation frequency f of the electro-optical phase modulation is adjusted_mAre respectively f_m10MHz +20kHz (in this case. DELTA.f 20kHz), f_m10MHz +10kHz (in this case. DELTA.f 10kHz) and f_m10MHz +5kHz (in this case Δ f 5 kHz). The frequency modulation results of their corresponding frequency modulated laser signals are shown in fig. 2(a), 2(b) and 2(c), respectively, and in fig. 2(a), 2(b) and 2(c), the upper half represents the time domain distribution of the frequency modulated laser signals, and the lower half represents the instantaneous frequency distribution thereof obtained by short-time fourier transform.

Therefore, the invention can realize the broadband sinusoidal frequency modulation signal with continuously adjustable frequency modulation index by simply adjusting delta f, and has the characteristics of continuously adjustable pulse repetition frequency, large modulation index, tunable broadband, simple structure and convenient application.

It should be noted that the above-mentioned embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above-mentioned embodiments, and any other changes, modifications, substitutions, combinations and simplifications which do not depart from the spirit and principle of the present invention should be regarded as equivalent substitutions and are included in the protection scope of the present invention.