CN110690646A - A Method for Generating Microwave Frequency Comb Based on Vertical Cavity Surface Emitting Laser - Google Patents

Abstract

The invention discloses a method for generating a microwave frequency comb based on a vertical cavity surface emitting laser. The optoelectronic feedback intensity and the optoelectronic feedback time simultaneously generate a linearly polarized microwave frequency comb with two power equalization, pure comb lines, ultra-wideband, optical signal and electrical signal, and orthogonal polarization directions; the optoelectronic feedback system consists of vertical Cavity Surface Emitting Laser (VCSEL), Optical Isolator (OI), Variable Optical Attenuator (VOA), Optical Beam Splitter (FC), Single Mode Fiber (SMF), Photodetector (PD), Electric Amplifier (EA) ) and an electric coupler (EC); the microwave frequency comb obtained by this method has the advantages of power equalization, pure comb lines, ultra-wideband, and orthogonal polarization directions, which can meet the application requirements in more fields.

Description

A Method for Generating Microwave Frequency Comb Based on Vertical Cavity Surface Emitting Laser

technical field

The invention relates to the technical field of microwave photonics, in particular to a method for generating a microwave frequency comb based on a vertical-cavity surface-emitting laser (VCSEL).

Background technique

Microwave frequency comb (MFC) refers to a microwave signal composed of a series of frequency components equally spaced like a comb in the frequency domain. Compared with single-frequency microwave signals, MFC has the advantages of a large number of spectral lines, a wide frequency range, and balanced spectral line intervals, which can provide both multi-frequency microwave signals and single-frequency microwave signals. It has broad application prospects in the fields of wireless hybrid communication, satellite communication, anti-jamming test, frequency and distance measurement.

In recent years, scholars at home and abroad have successively proposed many technical solutions for generating MFCs, mainly including electrical and optical methods. Due to the limitation of the bandwidth of electronic devices, the traditional method of generating electrical microwave frequency combs has defects such as sharply reduced amplitude of high-order harmonics and small bandwidth in the generated MFC signals. Therefore, it is difficult to obtain power-balanced, ultra-wideband MFC signals through electrical methods, and it is difficult to meet the needs of some application fields. The generation of MFC based on optical methods can overcome the bandwidth limitation of electronic devices in electrical methods, and can generate power-balanced and ultra-broadband MFC signals, so it has received extensive attention. The currently reported technical solutions for generating MFCs by optical methods mainly include the following two: (1) The MFCs are obtained by using the nonlinear effect of the tunnel junction of the scanning tunneling microscope. For example, in 2011, M.J.Hagmann and A.Efilmov et al. published the article "Microwave frequency-comb generation in a tunnelingjunction by intermode mixing of ultrafast laser pulses." in AppliedPhysics Letters, and proposed a 15fs ultrafast light pulse to The technical scheme of the tunnel junction of the lasing tunnel microscope, the MFC signal with a comb distance of 74.25MHz and a bandwidth of about 1GHz was obtained experimentally, and the typical output power of the fundamental frequency signal in the MFC was -146dBm. (2) Using photodetector (PD) to convert optical frequency comb to obtain MFC. For example, in 2015, W.T.Wang and J.G.Liu et al. published the article "Multi-band local microwave signal generation based on an optical frequency comb generator." in OpticsCommunications, and proposed an optical frequency comb under the injection locking of the optical sideband. The technical scheme of generating MFC after PD conversion, an MFC with a comb distance of 5 GHz and a bandwidth of about 40 GHz was obtained experimentally. The technical scheme of using the above two optical methods to generate microwave frequency combs has unique advantages, but its shortcomings are also more prominent. In addition to the above two methods, in recent years, the related research on the generation of MFC signals using the nonlinear dynamics exhibited by semiconductor lasers under external perturbation has attracted extensive attention. For example, in 2015, M.R.Zhao and Z.M.Wu et al. published the article "Tunable and broadband microwave frequency combs based on a semiconductorlaser with incoherent optical feedback." in Chinese Physics B, and proposed the nonlinear dynamic generation of semiconductor lasers using incoherent optical feedback The all-optical scheme of the ultra-wideband MFC can theoretically obtain an MFC with a 40GHz bandwidth varying in the range of ±5dB. In 2017, L.Fan and G.Q.Xia and others published the article "Tunable ultra-broadband microwave frequency combs generation based on a current modulated semiconductor laser under optical injection." on IEEE Access, and proposed a distributed method based on current modulation under optical injection. A technical solution for generating tunable ultra-broadband microwave frequency combs from a feedback semiconductor laser.

In addition, there are many patents on the generation method of microwave frequency combs published in recent years. For example, in 2014, Zhang Baofu of the Chinese People's Liberation Army University of Technology and others published the patent "Device and Method for Optical Frequency Comb Generation by Photoelectric Oscillator" (Patent Publication No. CN104092491A ) proposes a device and method for generating an optical frequency comb using an optoelectronic oscillator. In 2015, Deng Tao et al. of Southwest University published the patent "All-optical broadband microwave frequency comb generator" (patent publication number CN104577648A) and proposed an all-optical broadband microwave frequency comb generator based on distributed feedback semiconductor lasers. In 2017, Fan Li and others from Southwest University published the patent "Method for Generating Tunable Ultra-Broadband Microwave Frequency Combs Based on Semiconductor Lasers" (Patent Publication No. CN106981814A), and proposed a method that uses continuous light output from a tunable laser source to inject into In the current-modulated semiconductor laser, the bandwidth enhancement effect caused by optical injection is used to promote the semiconductor laser to produce a high-quality tunable ultra-broadband microwave frequency comb. The above technical solutions and devices have their own advantages and can be applied in many fields. However, the lasers used are edge-emitting distributed feedback lasers, and there are few methods and devices for generating microwave frequency combs using vertical cavity surface-emitting lasers. Compared with edge-emitting semiconductor lasers, vertical-cavity surface-emitting lasers have unique advantages such as low threshold current, high fiber coupling efficiency, dynamic single longitudinal mode output, low fabrication cost, and easy integration of high-density two-dimensional arrays. In recent years, patents using vertical cavity surface emitting lasers to generate microwave frequency combs have also been reported. For example, in 2015, Deng Tao and others published the patent "A Dual-Channel Microwave Frequency Comb Generator Based on Photoelectric Feedback VCSEL" (CN 105006727B). It is located in the short wavelength of 850nm in the first loss window. In addition, the optoelectronic feedback module adopts spatial optical components such as aspheric lens, beam splitter, half-wave plate and polarizing beam splitter, which makes the adjustment of the optical path relatively cumbersome.

Therefore, it is of great significance and practical value to explore new methods and devices for generating high-quality microwave frequency combs based on vertical cavity surface emitting lasers to meet application needs in more fields.

SUMMARY OF THE INVENTION

The object of the present invention is to overcome the deficiencies of the existing MFC generation technology, and to provide a method for generating a microwave frequency comb based on a vertical cavity surface emitting laser, so as to obtain the advantages of power balance, comb line purity, ultra-wideband, orthogonal polarization directions, etc. The linearly polarized microwave frequency comb can meet the application needs of more fields.

The technical scheme that realizes the object of the present invention is:

A method for generating a microwave frequency comb based on a vertical cavity surface emitting laser. Photoelectric feedback time, at the same time generate two-way power equalization, comb line pure, ultra-broadband, optical signal and electrical signal two forms, the polarization direction orthogonal linear polarization microwave frequency comb;

The optoelectronic feedback system is composed of a vertical cavity surface emitting laser (VCSEL), an optical isolator (OI), a variable optical attenuator (VOA), an optical beam splitter (FC), and a single-mode fiber (SMF) connected in sequence. , Photodetector (PD), Electric Amplifier (EA) and Electric Coupler (EC).

The photoelectric feedback system is that after the laser emitted by the VCSEL passes through OI, VOA and FC in sequence, 10% of the optical signal is used as the output detection signal, and 90% of the output optical signal is converted into electrical signals after passing through SMF and PD; electrical signals; After being amplified by the EA and passed through the EC, 20% of the electrical signal is used as the output detection signal, and 80% of the electrical signal is applied to the bias current of the VCSEL in the form of an irregular current disturbance signal, which makes the gain coefficient of the VCSEL change irregularly, prompting VCSELs exhibit nonlinear dynamic behavior, resulting in MFCs.

The photoelectric feedback effect is to use the bias current applied to the VCSEL after converting the optical signal into an irregular current disturbance signal, so as to cause the gain coefficient of the VCSEL to change irregularly, resulting in the VCSEL showing rich nonlinear dynamic behavior. .

The ultra-broadband refers to that the bandwidth can reach more than 180GHz within the range of 10dB of power.

The two forms of optical signal and electrical signal are that 10% of the optical signal output by the beam splitter (FC) in the photoelectric feedback system is in the form of microwave frequency comb optical signal; 20% of the output by the electrical coupler (EC) The electrical signal is in the form of a microwave frequency comb electrical signal.

The center wavelength of the VCSEL is 1550nm, and the 1550nm VCSEL can be controlled to output two linear x LP polarization modes and y LP polarization modes with orthogonal polarization directions by adjusting the temperature and bias current of the 1550 nm VCSEL.

The optoelectronic feedback system ensures the unidirectional transmission of the optical path by adjusting the OI; the optoelectronic feedback intensity of the optoelectronic feedback system is adjusted by adjusting the VOA; the optical signal is divided into two parts by the FC; the optoelectronic feedback time is adjusted by adjusting the SMF; The optical signal is converted into an electrical signal by using PD; the intensity of the electrical signal in the photoelectric feedback is regulated by using EA; the electrical signal is divided into two parts by using EC, in which 20% of the electrical signal is used as the output detection optical signal, and 80% of the electrical signal is used as the output detection optical signal. The bias current applied to the vertical cavity surface emitting laser in the form of an electrical signal current perturbation signal.

In the FC, 10% of the output optical signal is used as the output detection optical signal, and 90% of the optical signal is used for photoelectric feedback.

For the EC, 20% of the output electrical signal is used as the output detection light signal, and 80% of the electrical signal is applied to the bias current of the vertical cavity surface emitting laser in the form of a current disturbance signal.

Beneficial effects: The method for generating a microwave frequency comb based on a vertical cavity surface emitting laser provided by the present invention, because the photoelectric feedback belongs to incoherent feedback, it is not affected by the accumulation of the phase of the feedback external cavity, and can be very efficient through the existing electronic technology. Convenient and effective regulation has gradually become one of the effective ways to study the nonlinear dynamics of semiconductor lasers in recent years. By adjusting the optoelectronic feedback intensity and the optoelectronic feedback time, the present invention can simultaneously generate a linearly polarized microwave frequency comb (x LP MFC and y LP MFC), this method has the following advantages:

1. The microwave frequency comb is generated by the combination of VCSEL and photoelectric feedback loop;

2. Simple structure, small size, easy to control;

3. It can generate ultra-wideband microwave frequency combs with a power range of 10dB and a bandwidth of up to 180GHz;

4. Microwave frequency combs that can generate optical signals and electrical signals;

5. Two linearly polarized microwave frequency combs with orthogonal polarization directions can be generated simultaneously.

Description of drawings

Figure 1 is a schematic diagram of the structure of the photoelectric feedback system,

In the figure: VCSEL is a vertical cavity surface emitting laser, OI is an optical isolator, VOA is a variable optical attenuator, FC is an optical beam splitter, SMF is a single-mode fiber, PD is a photodetector, EA is an electrical amplifier, and EC is an electrical coupler;

Fig. 2 is a graph showing the variation of output power with normalized bias current μ when VCSEL is free-running. The solid line curve is the linear polarization mode (x LP) in the x direction, and the dotted curve is the linear polarization mode (y LP) in the y direction. );

Figure 3 shows the power spectrum of the VCSEL output when the normalized bias current μ=7, the photoelectric feedback time τ=0.1ns, and the photoelectric feedback coefficient ζ=0.667; Figure (a) is a microwave frequency comb linearly polarized in the x-direction (x LP MFC), panel (b) is a microwave frequency comb (y LP MFC) linearly polarized in the y direction.

Detailed ways

The content of the present invention will be further described below with reference to the accompanying drawings and embodiments, but it is not intended to limit the present invention.

Example:

A method for generating a microwave frequency comb based on a vertical cavity surface emitting laser. Photoelectric feedback time, at the same time generate two-way power equalization, comb line pure, ultra-broadband, optical signal and electrical signal two forms, the polarization direction orthogonal linear polarization microwave frequency comb;

As shown in Figure 1, the optoelectronic feedback system is composed of vertical cavity surface emitting laser (VCSEL), optical isolator (OI), variable optical attenuator (VOA), optical beam splitter (FC), It consists of a single-mode fiber (SMF), a photodetector (PD), an electric amplifier (EA) and an electric coupler (EC).

According to the spin inversion (SFM) model proposed in the article "Polarization properties of vertical-cavity surface-emittinglasers." by J.Martin-Regalado and F.Prati et al. in IEEE J.Quantum Electron. in 1997 The rate equation system, considering that under the action of photoelectric feedback, the rate equations of the two orthogonal polarization modes of the VCSEL can be described as:

是光电反馈系数，其前面符号为正时对应光电正反馈，为负时对应光电负反馈。τ是光电反馈时间。|Eox|²+|Eoy|²代表激光器自由运行时相应电流情况下的输出功率。n表示自旋向上和自旋向下能级对应的载流子密度之差，k表示光场衰减率，α为线宽增强因子。γ_a和γ_p分别表示二向色性系数和有源介质双折射系数，γN为总的载流子衰减速率，γ_s为自旋反转速率，μ为VCSEL上的归一化偏置电流。ξ₊和ξ_-是两个相互独立的高斯白噪声源(方差为1，平均值为0)，β_sp为噪声源自发辐射速率。通过调节光电反馈系数

与光电反馈时间τ，VCSEL可呈现出单周期、倍周期、准周期、混沌等丰富的非线性动力学状态。在合适的光电反馈系数

与光电反馈时间τ条件下，该光电反馈系统可产生梳线纯净、功率均衡、超宽带的微波频率梳信。In the above formula, the subscripts x and y represent the x LP mode and the y LP mode, respectively, E represents the slowly varying complex amplitude of the optical field, and N represents the total reverse carrier density between the conduction and valence bands in the VCSEL gain medium.

is the optoelectronic feedback coefficient. When the preceding symbol is positive, it corresponds to the optoelectronic positive feedback, and when it is negative, it corresponds to the optoelectronic negative feedback. τ is the photoelectric feedback time. |Eox| ² +|Eoy| ² represents the output power at the corresponding current when the laser is free-running. n is the difference between the carrier densities corresponding to the spin-up and spin-down energy levels, k is the optical field decay rate, and α is the linewidth enhancement factor. γ _a and γ _p denote the dichroic coefficient and the birefringence coefficient of the active medium, respectively, γ N is the total carrier decay rate, γ _s is the spin inversion rate, and μ is the normalized bias current on the VCSEL . ξ ₊ and ξ _- are two independent Gaussian white noise sources (variance is 1, mean value is 0), and β _sp is the emission rate of the noise source. By adjusting the photoelectric feedback coefficient

With the optoelectronic feedback time τ, VCSELs can exhibit rich nonlinear dynamic states such as single-period, period-doubling, quasi-periodic, and chaos. At the appropriate photoelectric feedback coefficient

Under the condition of photoelectric feedback time τ, the photoelectric feedback system can generate microwave frequency comb signal with pure comb line, balanced power and ultra-wideband.

The photoelectric feedback system is that after the laser emitted by the VCSEL passes through OI, VOA and FC in sequence, 10% of the optical signal is used as the output detection signal, and 90% of the output optical signal is converted into electrical signals after passing through SMF and PD; electrical signals; After being amplified by the EA and passed through the EC, 20% of the electrical signal is used as the output detection signal, and 80% of the electrical signal is applied to the bias current of the VCSEL in the form of an irregular current disturbance signal, which makes the gain coefficient of the VCSEL change irregularly, prompting VCSELs exhibit nonlinear dynamic behavior, resulting in MFCs.

The photoelectric feedback effect is to use the bias current applied to the VCSEL after converting the optical signal into an irregular current disturbance signal, so as to cause the gain coefficient of the VCSEL to change irregularly, resulting in the VCSEL showing rich nonlinear dynamic behavior. .

The ultra-broadband refers to that the bandwidth can reach more than 180GHz within the range of 10dB of power.

The two forms of optical signal and electrical signal are that 10% of the optical signal output by the beam splitter (FC) in the photoelectric feedback system is in the form of microwave frequency comb optical signal; 20% of the output by the electrical coupler (EC) The electrical signal is in the form of a microwave frequency comb electrical signal.

The center wavelength of the VCSEL is 1550nm, and the 1550nm VCSEL can be controlled to output two linear x LP polarization modes and y LP polarization modes with orthogonal polarization directions by adjusting the temperature and bias current of the 1550 nm VCSEL.

The optoelectronic feedback system ensures the unidirectional transmission of the optical path by adjusting the OI; the optoelectronic feedback intensity of the optoelectronic feedback system is adjusted by adjusting the VOA; the optical signal is divided into two parts by the FC; the optoelectronic feedback time is adjusted by adjusting the SMF; The optical signal is converted into an electrical signal by using PD; the intensity of the electrical signal in the photoelectric feedback is regulated by using EA; the electrical signal is divided into two parts by using EC, in which 20% of the electrical signal is used as the output detection optical signal, and 80% of the electrical signal is used as the output detection optical signal. The bias current applied to the vertical cavity surface emitting laser in the form of an electrical signal current perturbation signal.

In the FC, 10% of the output optical signal is used as the output detection optical signal, and 90% of the optical signal is used for photoelectric feedback.

For the EC, 20% of the output electrical signal is used as the output detection light signal, and 80% of the electrical signal is applied to the bias current of the vertical cavity surface emitting laser in the form of a current disturbance signal.

The present invention adopts the fourth-order Runge-Kutta algorithm to numerically solve the above-mentioned formula (1) to formula (4) rate equations, the time series length used in the simulation is 1000ns, and the calculation step is 1ps, The specific parameter values refer to the article "Polarization switching in long-wavelength VCSEL subject to orthogonaloptical injection." published in IEEE J.Quantum Electron. by MStorre and A. Hurtado in 2011, γ _N == 1ns ^-1 , γ _p = 192.1 ns ^-1 , γ _a = 1 ns ^-1 , γ _s = 1000 ns ^-1 , α = 3, k = 300 ns ^-1 , β _sp = 10 ^-6 , the output power of the VCSEL in free running varies with the normalized current μ The change curve is shown in Fig. 2. The solid line in Fig. 2 represents the x LP mode, and the dashed line represents the y LP mode. When the normalized current μ reaches 1, the y LP mode starts lasing, and the x LP is in a suppressed state; when the normalized current μ reaches 5.5, the polarization conversion between the y LP mode and the x LP mode occurs, and the x LP mode starts lasing, The y LP mode is in a suppressed state. Within the normalized bias current range under consideration (1<μ≤9), by adjusting the VCSEL normalized bias current μ, the y LP mode and x LP of the VCSEL output can be changed model.

In the optoelectronic feedback loop system shown in Figure 1, by adjusting the VOA, the optoelectronic feedback intensity can be regulated; by adjusting the length of the SMF, the optoelectronic feedback time can be changed. When the normalized bias current μ=7, the photoelectric feedback time τ=0.1ns, and the photoelectric feedback coefficient ζ=0.667, the power spectrum of the VCSEL output is shown in Figure 3, where Figure (a) is the microwave frequency of linear polarization in the x-direction Comb (x LP MFC), Figure (b) is a microwave frequency comb (y LP MFC) linearly polarized in the y direction. It can be seen from the figure that when μ=7, τ=0.1ns, ζ=0.667, the VCSEL simultaneously outputs two x LP MFC and y LPMFC with orthogonal polarization directions, and within 10dB amplitude range, the bandwidth of x LP MFC is about 180 GHz, and the bandwidth of y LP MFC is about 130 GHz.

To sum up, the present invention can simultaneously generate two linearly polarized microwave frequency combs with pure comb lines, balanced power, bandwidth up to 180 GHz (within an amplitude range of 10 dB), and orthogonal polarization directions. It can be applied to both low-frequency dense microwave communication and high-frequency high-speed microwave communication, which can meet the application requirements in more fields and solve the current difficulties of microwave technology.

Claims (9)

1. a method for producing a microwave frequency comb based on a vertical cavity surface emitting laser, is characterized in that, the method is to utilize the nonlinear dynamic characteristics that the vertical cavity surface emitting laser presents under the action of photoelectric feedback, by adjusting the photoelectric feedback system The photoelectric feedback intensity and the photoelectric feedback time in the two-way power balance, the comb line is pure, the ultra-wideband, the optical signal and the electric signal are two forms, and the polarization direction is orthogonal to the linearly polarized microwave frequency comb; The optoelectronic feedback system is composed of a vertical cavity surface emitting laser (VCSEL), an optical isolator (OI), a variable optical attenuator (VOA), an optical beam splitter (FC), and a single-mode fiber (SMF) connected in sequence. , photodetector (PD), electric amplifier (EA) and electric coupler (EC). 2. a kind of generation method based on the microwave frequency comb of vertical cavity surface emitting laser according to claim 1, is characterized in that, described photoelectric feedback system, is after the laser that is sent by VCSEL passes through OI, VOA, FC successively , 10% of the optical signal is used as the output detection signal, 90% of the output optical signal is converted into an electrical signal after passing through SMF and PD; after the electrical signal is amplified by EA and then passed through EC, 20% of the electrical signal is used as the output detection signal, 80% of the electrical signal is used as the output detection signal The electrical signal is applied to the bias current of the VCSEL in the form of an irregular current disturbance signal, which makes the gain coefficient of the VCSEL change irregularly, and causes the VCSEL to exhibit nonlinear dynamic behavior, thereby generating the MFC. 3. The method for generating a microwave frequency comb based on a vertical cavity surface emitting laser according to claim 1, wherein the photoelectric feedback effect is to convert the optical signal into an irregular current disturbance signal after using The bias current applied to the VCSEL causes an irregular change in the gain factor of the VCSEL, resulting in a nonlinear dynamic behavior of the VCSEL. 4. a kind of generation method based on the microwave frequency comb of vertical cavity surface emitting laser according to claim 1, is characterized in that, described ultra-broadband, refers to that the power bandwidth can reach 180 GHz in 10 dB amplitude range above. 5. The method for generating a microwave frequency comb based on a vertical cavity surface emitting laser according to claim 1, wherein the two forms of the optical signal and the electrical signal are a beam splitter in a photoelectric feedback system 10% of the optical signals output by (FC) are in the form of microwave frequency comb optical signals; 20% of the electrical signals output by the electrical coupler (EC) are in the form of microwave frequency comb electrical signals. 6. the generation method of a kind of microwave frequency comb based on vertical cavity surface emitting laser according to any one of claim 1,2,3, it is characterized in that, described VCSEL, center wavelength is 1550 nm, by adjusting 1550 nm The temperature and bias current of the VCSEL can control the 1550 nm VCSEL to output two linear x LP polarization modes and y LP polarization modes with orthogonal polarization directions. 7. the generation method of a kind of microwave frequency comb based on vertical cavity surface emitting laser according to any one of claim 1,2,4, it is characterized in that, described photoelectric feedback system, by adjusting OI to ensure the single-passage of the optical path By adjusting the VOA to control the photoelectric feedback intensity of the photoelectric feedback system; by FC to divide the optical signal into two parts; by adjusting the SMF to control the photoelectric feedback time; by using PD to convert the optical signal into an electrical signal; by using EA to The intensity of the electrical signal in the optoelectronic feedback is regulated; the electrical signal is divided into two parts by using EC, 20% of the electrical signal is used as the output detection light signal, and 80% of the electrical signal is applied to the bias of the vertical cavity surface emitting laser in the form of a current disturbance signal. set current. 8. the method for generating a microwave frequency comb based on a vertical cavity surface emitting laser according to any one of claims 1, 2, 5, 7, characterized in that, in the FC, the 10% optical signal of the output is used as Output detection light signal, 90% of the light signal is used for photoelectric feedback. 9. The method for producing a microwave frequency comb based on a vertical cavity surface emitting laser according to any one of claims 1, 2, 5, and 7, wherein the EC, the 20% electrical signal of the output is used as The detection light signal is output, and 80% of the electrical signal current disturbance signal is applied to the bias current of the vertical cavity surface emitting laser.

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