An optical frequency comb generation system based on electro-optical modulator

Abstract

The present application discloses an optical frequency comb generation system based on an optoelectronic modulator, comprising: a signal generating unit, a radio frequency unit, a modulator unit, a power supply unit and an observation unit; the signal generating unit is used to generate an optoelectronic signal; the radio frequency unit is used to preprocess the optoelectronic signal; the modulator unit is used to modulate the optoelectronic signal; the power supply unit is used to provide a modulation voltage to the modulator unit; the observation unit is used to observe the optoelectronic signal information. By accurately adjusting the harmonic modulation index, phase and deviation of the DPMZM, a flat optical frequency comb can be generated. The solution using a single modulator is compact and easy to implement.

Description

Technical Field

[0001] The present application belongs to the field of microwave photon technology, and specifically relates to an optical frequency comb generation system based on an optoelectronic modulator. Background Art

[0002] Microwave photonics is the fusion of microwave technology and photonic technology. Microwave signals and optical signals influence and interact with each other, while taking advantage of the flexibility of microwave signals and the high bandwidth of optical fiber communication, overcoming the limitations of traditional microwave technology in terms of transmission bandwidth and processing speed. An important application of microwave photonics is the use of optical fiber in wireless communications to transmit microwave carrier signals and process data.

[0003] Optical frequency comb (OFC) is a special laser light source with multiple wavelengths and equally spaced comb-shaped frequency components. It is widely used in spectroscopy, astronomy, optical communications, radio frequency photonics and other fields. Currently, one of the methods to generate optical frequency combs is to use an intensity modulator or a cascaded intensity modulator and a phase modulator. The device used in this method has a complex structure, and the generated optical frequency comb has a single range and a narrow scope of application.

[0004] Currently, if an optical frequency comb with multiple spectral lines is to be generated based on an electro-optic modulator, multiple electro-optic modulators are needed or multiple harmonics are superimposed, where the harmonic phase needs to be precisely adjusted. In the current literature, optical frequency combs (OFCs) with more comb lines can be achieved by superimposing harmonics, where the harmonic phase needs to be precisely adjusted. Summary of the invention

[0005] This application proposes a new scheme to generate flat OFC using a dual parallel Mach-Zehnder modulator (DPMZM) with superimposed harmonics, where only one sub-MZM in the DPMZM is driven by superimposed harmonics. By precisely adjusting the harmonic modulation index and phase and deviation of the DPMZM, a flat optical frequency comb can be generated. The scheme using a single modulator is compact and easy to implement.

[0006] To achieve the above objectives, this application provides the following solutions:

[0007] An optical frequency comb generation system based on an electro-optical modulator comprises: a signal generation unit, a radio frequency unit, a modulator unit, a power supply unit and an observation unit;

[0008] The signal generating unit is used to generate a photoelectric signal;

[0009] The radio frequency unit is used to pre-process the photoelectric signal;

[0010] The modulator unit is used to modulate the photoelectric signal;

[0011] The power supply unit is used to provide a modulation voltage for the modulator unit;

[0012] The observation unit is used to observe the photoelectric signal information.

[0013] Preferably, the signal generating unit comprises: a first signal generating unit and a second signal generating unit;

[0014] The first signal generating unit is used to generate an optical signal;

[0015] The second signal generating unit is used to generate an electrical signal;

[0016] Preferably, the first signal generating unit comprises: a radio frequency source; the radio frequency source is used to generate a sinusoidal radio frequency signal having a frequency that is a multiple of the base frequency;

[0017] The second signal generating unit comprises: a laser; the laser is used to generate an optical carrier signal.

[0018] Preferably, the radio frequency unit comprises: a radio frequency phase shifter, a radio frequency amplifier, a coupler and a power divider;

[0019] The RF phase shifter is connected to the RF source, the operating frequency band of the RF phase shifter is the same as the output frequency of the RF source, and the RF phase shifter is used to adjust the phase of the RF signal;

[0020] The RF amplifier is connected to the RF phase shifter, the operating frequency band of the RF amplifier is the same as the output frequency of the RF source, and the RF amplifier is used to amplify the amplitude of the RF signal;

[0021] The coupler is connected to the radio frequency amplifier, and the coupler is used to superimpose the radio frequency signals after phase adjustment and amplitude amplification to form a modulated signal;

[0022] The power divider is connected to the coupler, and the power divider is used to divide the modulated signal into two paths to obtain a first modulated signal and a second modulated signal.

[0023] Preferably, the power supply unit includes a first bias power supply, a second bias power supply and a third bias power supply.

[0024] Preferably, the observation unit includes a first observation unit and a second observation unit;

[0025] The first observation unit is connected to the power divider, and the first observation unit is used to observe the first modulated signal;

[0026] The second observation unit is connected to the modulator unit, and the second observation unit is used to observe the second modulated signal.

[0027] Preferably, the first observation unit adopts an electric spectrometer;

[0028] The second observation unit adopts a spectrometer.

[0029] Preferably, the modulator unit comprises a double-balanced Mach-Zehnder modulator, and the double-balanced Mach-Zehnder modulator comprises: an input port, an output port, an upper branch modulator, a lower branch modulator and a third bias port;

[0030] The input port is connected to the laser, and the input port is used to receive the optical signal;

[0031] The upper branch modulator is connected to the power distributor, and the upper branch modulator comprises an upper branch modulation port and a first bias port;

[0032] The lower branch modulator is connected to the signal generating unit and the power supply unit; the lower branch modulator includes a second bias port.

[0033] The third bias port is connected to the lower branch modulator and the output port;

[0034] The output port is connected to the observation unit.

[0035] The beneficial effects of this application are:

[0036] The present application discloses an optical frequency comb generation system based on an electro-optical modulator, which generates a flat OFC using a dual parallel Mach-Zehnder modulator (DPMZM) with superimposed harmonics, wherein only one sub-MZM in the DPMZM is driven by superimposed harmonics. By precisely adjusting the harmonic modulation index, phase and deviation of the DPMZM, a flat optical frequency comb can be generated. The solution using a single modulator is compact and easy to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the technical solution of the present application, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0038] Figure 1 This is a schematic diagram of the structure of the optical frequency comb generation system based on the electro-optical modulator of this application;

[0039] Figure 2 This is a specific working flow chart of the optical frequency comb generation system based on the electro-optical modulator of this application. DETAILED DESCRIPTION

[0040] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0041] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0042] Embodiment 1

[0043] like Figure 1 As shown, it is a structural diagram of an optical frequency comb generation system based on an optoelectronic modulator of the present application, including: a signal generating unit, a radio frequency unit, a modulator unit, a power supply unit and an observation unit;

[0044] The signal generating unit is connected with the radio frequency unit and the modulator unit; the signal generating unit includes a first signal generating unit and a second signal generating unit; the radio frequency unit is also connected with the observation unit and the modulator unit, and the radio frequency unit includes: N radio frequency phase shifters, N radio frequency amplifiers, N-in-one couplers and a one-input and two-output power divider; the modulator unit is also connected with the power supply unit and the observation unit, and the modulator unit includes: a double-balanced Mach-Zehnder modulator, wherein the double-balanced Mach-Zehnder modulator includes: an input port, an output port, an upper branch modulator, a lower branch modulator and a third bias port; the power supply unit includes a first bias power supply, a second bias power supply and a third bias power supply; the observation unit includes a first observation unit and a second observation unit.

[0045] Specifically, the first signal generating unit is connected to the RF phase shifter, and the first signal generating unit includes N RF sources, and the RF sources are used to generate a sinusoidal RF signal with a frequency that is a multiple of the base frequency; wherein the frequency of one RF source among the N RF sources is selected as the base frequency, and the frequencies of the other RF sources are multiples thereof. The outputs of the N RF sources are respectively connected to N RF phase shifters, and the operating frequency band of the RF phase shifter is the same as the output frequency of the corresponding RF source. The RF phase shifter is used to adjust the phase of the RF signal generated by the RF source; the RF phase shifter is also connected to the RF amplifier, and the operating frequency band of the RF amplifier is the same as the output frequency of the corresponding RF source, and the RF amplifier is used to amplify the amplitude of the RF signal generated by the RF source.

[0046] The N-in-one coupler is connected to the RF amplifier, and is used to add up the RF signals that have been phase-adjusted and amplitude-amplified to form a modulated signal. The output end of the N-in-one coupler is connected to a one-input and two-output power divider, and the power divider divides the modulated signal into two paths, including a first modulated signal and a second modulated signal; wherein the first modulated signal is transmitted to the first observation unit through the power divider, and the first observation unit uses an electric spectrometer, which is used to observe the frequency and power information of the first modulated signal.

[0047] The second signal generating unit is connected to the modulator. The second signal generating unit adopts a laser. The laser is used to generate an optical carrier signal. The optical carrier signal is output by the laser and enters the upper branch modulator and the lower branch modulator through the input port of the dual parallel Mach-Zehnder modulator; the upper branch modulator includes an upper branch modulation port and a first bias port; the lower branch modulator includes a second bias port. The upper branch modulator is also connected to a power distributor. The second modulation signal is modulated by the upper branch through the power distributor; the first bias port is connected to the first bias power supply; the second bias port is connected to the second bias power supply, and the third bias port is connected to the third bias power supply. Finally, the optical carrier signal output by the upper branch modulator and the optical carrier signal output by the lower branch modulator through the third bias port are transmitted to the spectrometer. The spectrometer is used to observe the wavelength and power information of the optical signal.

[0048] Embodiment 2

[0049] like Figure 2 As shown, this is a specific working flow chart of an optical frequency comb generation system based on an optoelectronic modulator of the present application. The optical frequency comb generation system will be described in detail below in combination with the specific process.

[0050] The sinusoidal RF signal generated by the RF source is phase-adjusted and amplitude-amplified by the RF phase shifter and RF amplifier, and then superimposed by the RF signals generated by N RF sources through the coupler to form a modulated signal. The modulated signal is divided into two paths through a one-input and two-output power divider. One path enters the spectrometer to observe its frequency and power information; the other path enters the upper branch modulator.

[0051] The optical carrier signal generated by the laser enters a dual parallel Mach-Zehnder modulator;

[0052] Among them, the electric field of the continuous light output by the laser is:

[0053] E in (t) = E0exp(j2πf c t)

[0054] Among them, E0 and f c represent the amplitude and frequency of the output light respectively; j represents a complex number, and t represents time.

[0055] Output continuous light Ein (t) is divided into two branches and enters the upper branch and the lower branch of the dual parallel Mach-Zehnder modulator; the upper branch modulator is modulated by the second modulation signal ∑ i s i (t) drive; the lower branch modulator is not driven by any sinusoidal signal. The electric field at the output of the upper branch modulator is:

[0056]

[0057] in, The phase change of the continuous light in the upper branch modulator is determined by the first bias supply voltage V bias1 and half-wave voltage V π Determine; The i-th driving harmonic modulation index for phase modulation of each branch of the upper branch modulator is Where E i is the amplitude of the ith driving harmonic. Then the ith driving harmonic is:

[0058]

[0059] Where f0 is the fundamental frequency, is the phase of the ith driving harmonic.

[0060] The electric field at the output of the lower branch modulator is:

[0061]

[0062] in, The phase change of the continuous light input to the lower branch is determined by the second bias supply voltage V bias2 and V π Decide.

[0063] Then the electric field at the output port of the dual parallel Mach-Zehnder modulator is:

[0064]

[0065] in, The continuous light in the lower branch is due to the third bias supply voltage V bias3 The additional phase change produced.

[0066] The search for a set of parameters that minimizes the flatness of the system is considered as an optimization problem, and the differential optimization algorithm is used as its optimization algorithm to solve it;

[0067] The differential optimization algorithm is a simple but powerful random optimization algorithm that simulates the natural evolution mechanism. Like all evolutionary algorithms, it uses sets or populations to operate to find potential optimal solutions that can solve the optimization problem. The set can be represented as S = {x1, x2, ..., x N}, N means the size of the population remains unchanged. The central idea of ​​the algorithm is to continuously replace the points in the original population with better points to establish a new population. The specific working process of the DE algorithm will be introduced in detail below.

[0068] (1) Parameter initialization

[0069] It is generally believed that individuals in the population are uniformly distributed while being subject to boundary constraints, so the initialization formula can be expressed as:

[0070]

[0071] Among them, rand represents a random value ranging from 0 to 1, and u j and l j represent the upper and lower limits of the j-th variable respectively.

[0072] (2) Producing new individuals

[0073] The process of generating new individuals can be called mutation. In each generation g, individuals in the population S are replaced by better individuals. A mutant individual is obtained by adding the weighted difference of two individuals to a third individual. The mutation scheme is shown in the following formula:

[0074]

[0075] Where F is the scaling parameter, x p(1) 、x p(2) and x p(3) These points are randomly selected.

[0076] Through the origin x i,g and mutation point The new test point y is obtained by recombining i,g In this process, the binomial recombination method is used for crossover. The binomial recombination starts from the first component of the vector and generates a random number r for each component. j ∈[0,1]. If r j ≤c r ,y i,g The jth component of i,g Take it, otherwise when r j >c r When the jth component changes from Take until x i,g All considered, binomial recombination can be expressed mathematically as follows:

[0077]

[0078] In each iteration, the DE algorithm tries to replace individuals in the original population with better individuals. Therefore, in each generation, N competitions will be conducted to determine the individual members of the next generation. That is, the i-th competition is to replace x in the population S. i,g By comparing the test points The function value and target point The function value can be expressed as:

[0079]

[0080] The DE algorithm ensures that the current generation is equal to or better than the previous generation through the above selection scheme. When time tends to infinity, the random method converges to the optimal value with a probability of 1. Although the algorithm result will gradually tend to the optimal solution as the number of iterations increases, after the number of iterations reaches a high level, the algorithm's optimization of the result gradually slows down. Therefore, this embodiment terminates the algorithm by setting an upper limit on the number of iterations, saving time costs while obtaining as good flatness as possible.

[0081] In this embodiment, a set of parameters with the minimum flatness is as follows:

[0082] P1: minimize

[0083] subject to 0<β i ≤1.5,

[0084]

[0085] Under this scheme, multiple harmonics in two cases are studied by simulation and experiment. In the first case, the fundamental frequency and the third harmonic drive the DPMZM upper branch modulator to generate a 9-line optical frequency comb with a flatness of 0.26db. In the second case, the fundamental frequency, the second harmonic and the third harmonic are combined to drive the DPMZM upper branch modulator to generate a 13-line optical frequency comb with a flatness of 0.58. In both cases, the experimental and simulated spectra are consistent, proving the effectiveness of the scheme proposed in this application in generating flat OFC.

[0086] At the same time, through the DPMZM modulation scheme and differential optimization algorithm, the optimal solution under the constraints can be obtained, and then an optical frequency comb with the desired number of spectral lines and spectral flatness can be generated.

[0087] The embodiments described above are only descriptions of the preferred methods of the present application, and are not intended to limit the scope of the present application. Without departing from the design spirit of the present application, various modifications and improvements made to the technical solutions of the present application by ordinary technicians in this field should fall within the scope of protection determined by the claims of the present application.

Claims

1. An optical frequency comb generation system based on an electro-optical modulator, characterized in that: include: A signal generating unit, a radio frequency unit, a modulator unit, a power supply unit and an observation unit; The signal generating unit is used to generate a photoelectric signal, and the signal generating unit includes: a first signal generating unit and a second signal generating unit; The first signal generating unit is used to generate an electrical signal; The second signal generating unit is used to generate an optical signal; The first signal generating unit comprises: a radio frequency source; the radio frequency source is used to generate a sinusoidal radio frequency signal having a frequency that is a multiple of a base frequency; The second signal generating unit comprises: a laser; the laser is used to generate an optical carrier signal; The radio frequency unit is used to pre-process the electrical signal, and the radio frequency unit includes: a radio frequency phase shifter, a radio frequency amplifier, a coupler and a power divider; The RF phase shifter is connected to the RF source, the operating frequency band of the RF phase shifter is the same as the output frequency of the RF source, and the RF phase shifter is used to adjust the phase of the RF signal; The RF amplifier is connected to the RF phase shifter, the operating frequency band of the RF amplifier is the same as the output frequency of the RF source, and the RF amplifier is used to amplify the amplitude of the RF signal; The coupler is connected to the radio frequency amplifier, and the coupler is used to superimpose the radio frequency signals after phase adjustment and amplitude amplification to form a modulated signal; The power divider is connected to the coupler, and the power divider is used to divide the modulated signal into two paths to obtain a first modulated signal and a second modulated signal; The modulator unit is used to modulate the photoelectric signal, and the modulator unit includes a double-balanced Mach-Zehnder modulator, and the double-balanced Mach-Zehnder modulator includes: an input port, an output port, an upper branch modulator, a lower branch modulator and a third bias port; The input port is connected to the laser, and the input port is used to receive the optical signal; The upper branch modulator is connected to the power distributor, and the upper branch modulator comprises an upper branch modulation port and a first bias port; The lower branch modulator is connected to the signal generating unit and the power supply unit; the lower branch modulator includes a second bias port; The third bias port is connected to the lower branch modulator and the output port; The output port is connected to the second observation unit; The power supply unit is used to provide a modulation voltage for the modulator unit, and the power supply unit includes a first bias power supply, a second bias power supply and a third bias power supply; The observation unit is used to observe the photoelectric signal information, and the observation unit includes a first observation unit and a second observation unit; The first observation unit is connected to the power divider, and the first observation unit is used to observe the first modulated signal; The second observation unit is connected to the modulator unit, and the second observation unit is used to observe the optical signal; The first observation unit adopts an electric spectrometer; The second observation unit adopts a spectrometer; The workflow of the optical frequency comb generation system specifically includes: The sinusoidal RF signal generated by the RF source is phase-adjusted and amplitude-amplified by the RF phase shifter and RF amplifier, and then superimposed by the RF signals generated by N RF sources through the coupler to form a modulated signal. The modulated signal is divided into two paths through a one-input and two-output power divider. One path enters the spectrometer to observe its frequency and power information; the other path enters the upper branch modulator. The optical carrier signal generated by the laser enters a dual parallel Mach-Zehnder modulator; Among them, the electric field of the continuous light output by the laser is: E in (t)=E0exp(j2πf c t) Among them, E0 and f c They represent the amplitude and frequency of the output light respectively; j represents a complex number, and t represents time; Output continuous light E in (t) is divided into two branches and enters the upper branch and the lower branch of the dual parallel Mach-Zehnder modulator; the upper branch modulator is modulated by the second modulation signal ∑ i s i (t) drive; the lower branch modulator is not driven by any sinusoidal signal; the electric field at the output of the upper branch modulator is: in, The phase change of the continuous light in the upper branch modulator is determined by the first bias supply voltage V bias1 and half-wave voltage V π Determine; The i-th driving harmonic modulation index for phase modulation of each branch of the upper branch modulator is Where E i is the amplitude of the ith driving harmonic; then the ith driving harmonic is: Where f0 is the fundamental frequency, is the phase of the i-th driving harmonic; The electric field at the output of the lower branch modulator is: in, The phase change of the continuous light input to the lower branch is determined by the second bias supply voltage V bias2 and V π Decide; Then the electric field at the output port of the dual parallel Mach-Zehnder modulator is: in, The continuous light in the lower branch is due to the third bias supply voltage V bias3 The additional phase change caused by The search for a set of parameters that minimizes the flatness of the system is considered as an optimization problem, and the differential optimization algorithm is used as its optimization algorithm to solve it; The set of parameters with the minimum flatness is as follows: in,

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