CN107947867B - Single-sideband spectrum generation device and method based on multi-frequency phase modulation - Google Patents

Abstract

The invention provides a single-sideband frequency spectrum generating device and method based on multi-frequency phase modulation, and relates to a single-sideband frequency spectrum generating device and method. The device comprises a narrow-linewidth laser source, an electro-optic modulator, a spectrum measuring system, an arbitrary waveform generator and a radio frequency signal amplifier; the method comprises the following steps: firstly, introducing a single-frequency signal output by a narrow-line-width laser source into an electro-optic modulator; secondly, obtaining a multi-frequency modulation electrical signal waveform based on the spectrum analysis reverse calculation, and setting an arbitrary waveform generator to generate a corresponding multi-frequency modulation electrical signal; amplifying the modulated electric signal by a radio frequency signal amplifier, and then transmitting the amplified modulated electric signal to an electro-optical modulator; and step four, outputting the optical signal formed after modulation to a spectrum measurement system for spectrum structure analysis. The invention solves the problems of low energy conversion efficiency and complex structure of signals in the prior art. The invention can be applied to wireless communication.

Description

A single sideband spectrum generation device and method based on multi-frequency phase modulation

technical field

The invention relates to a single sideband frequency spectrum generation device and method.

Background technique

With the increasing demand for broadband wireless communication, wireless communication continues to expand towards high-frequency bands. However, due to the limitation of the processing rate, the traditional electronic technology is a bit powerless for the processing of high-speed microwave signals. In addition, as the frequency increases, the transmission loss of microwave signals in the air also increases, making long-distance transmission impossible. Photons have a huge bandwidth, and the use of photon technology to process high-speed microwave signals can get rid of the bottleneck of electronic technology processing speed, and has a strong ability to resist electromagnetic interference. In addition, the transmission loss of the signal in the optical fiber is extremely low, and the long-distance transmission of the microwave signal can be realized by means of the optical fiber communication technology, a typical representative is Radio over fiber (ROF).

In the ROF system, due to the influence of fiber link dispersion, the signal measured by the optical receiver will periodically fade. If the single-frequency carrier signal is converted into an optical double-sideband signal (ODSB), the upper and lower sidebands have the same amplitude and phase. After the optical fiber dispersion, the upper and lower sidebands experience different delays, which will produce a phase shift related to the dispersion. If the phase shift is π, when detecting at the receiving end, the two side frequencies are respectively beat with the carrier frequency to generate two radio frequency (RF) signals with the same amplitude and opposite phases. Signal power is 0. When the phase shift varies from 0 to π, the total RF signal will fade to different degrees. The periodic fading of the detection signal will affect the efficiency and reliability of optical fiber communication.

The most economical and effective way to solve this RF signal periodic fading problem is to use optical single sideband modulation technology (OSSB-modulator). The specific idea is to eliminate the influence of the dispersion of the modulated light wave signal in the optical fiber, so that the signal received by the optical detector is a beat frequency signal that modulates the sideband and the carrier, improves the utilization of the frequency band, and increases the transmission capacity. .

At present, people use a variety of methods to obtain OSSB signals. According to their realization principles, they can be classified into three categories: (1) use an optical filter to filter out a sideband in the ODSB signal to obtain an optical single sideband signal output; (2) Amplify one sideband in ODSB to obtain optical single sideband signal; (3) Obtain optical single sideband signal directly by using OSSB modulator.

In 2005, Spanish Capmany et al. used two series of fiber Bragg grating arrays (FBGA) to generate multi-wavelength OSSB signals. The multi-wavelength fiber laser is generated by the tunable fiber laser array, injected into the electro-optic modulator, and each vertical and horizontal modulation is made into a double-sideband laser signal, and then one of the sidebands is filtered by FBGA to obtain a multi-wavelength OSSB signal. This method has better performance in insertion loss, carrier rejection effect, bandwidth and so on. As long as high-quality, high-reflectivity FBG filters are used, the frequency range of the application can extend from millimeter waves to the entire microwave bandwidth range. In 2012, Tang et al. used a phase modulator to generate an ODSB signal, and then used a tunable optical bandpass filter to filter out one of the sidebands to obtain an OSSB signal. And it is used in the optical vector network analyzer to achieve a higher resolution. In 2016, Song et al. in Australia proposed a single-sideband modulator based on a coupled resonator optical waveguide filter on an insulating silicon chip. After the OSSB signal is transmitted through a dispersive element, the fluctuation of the RF signal measured by the photodetector Less than 2dB. The disadvantage of the above method of using an optical filter to realize a single sideband modulation signal is that the use of the filter will permanently lose a part of the sideband energy, and the energy conversion efficiency of the signal is not high.

In 2005, Y.Shen et al proposed a ROF system that produces 11GHz optical single sideband modulation. Using the stimulated Brillouin scattering effect in the optical fiber, the modulation signal of the lower sideband is amplified, while the modulation signal of the upper sideband is weakened, thereby improving the performance of the system and obtaining a 2dB signal-to-noise ratio gain. Since the Brillouin frequency shift in the optical fiber is about 11 GHz, the frequency of the modulated radio frequency signal is 11 GHz. This OSSB signal generation method is essentially to transfer the energy on one sideband to the other sideband through the stimulated Brillouin scattering effect of the fiber, which has higher efficiency than the scheme using optical filters; but This method is developed based on the nonlinear optical effect, and the stability of the obtained single-sideband modulation signal is limited.

In 2008, B.Masella et al. in Canada proposed a linear single sideband Mach-Zehnder electro-optic modulator. This OSSB uses a dual-driver Mach-Zehnder modulator biased at the quadrature transmission point, which consists of two Driven by an RF signal with a phase shift of π. Through proper design, better modulation results are obtained. A phase shifter is needed in the system to control the phase shift of the two RF driving signals, and its structure and operation are not simple enough.

The intensity ratio of each order modulation signal in the sideband can be controlled by using multi-frequency phase modulation technology, which has been used to generate special spectral line structure. The research group of Professor Lv Zhiwei from Harbin Institute of Technology realized the generation of equal-amplitude spectral structure by using multi-frequency phase modulation technology, and obtained dozens of equal-amplitude spectral line outputs by rationally designing the ratio of each frequency component in the modulation signal (patent number: 200710144442.3 ).

Contents of the invention

In order to solve the problems of low energy conversion efficiency and complex structure of signals in the prior art, the present invention provides a single sideband spectrum generation device and method based on multi-frequency phase modulation.

A SSB spectrum generating device based on multi-frequency phase modulation according to the present invention includes: a laser source with a narrow linewidth, an electro-optic modulator, a spectrum measurement system, an arbitrary waveform generator, and a radio frequency signal amplifier;

The output fiber of the narrow linewidth laser source is connected to the input end of the electro-optic modulator, and the single-frequency signal output by the narrow linewidth laser source is introduced into the electro-optic modulator;

The input end of the radio frequency signal amplifier is connected to an arbitrary waveform generator, the output end of the radio frequency signal amplifier is connected to the electro-optic modulator, and the output end of the electro-optic modulator is connected to the spectral measurement system; the arbitrary waveform generator generates multi-frequency modulation The electrical signal is amplified by the radio frequency signal amplifier, and then transmitted to the electro-optic modulator; the electro-optic modulator performs phase modulation on the single-frequency signal entering the electro-optic modulator according to the multi-frequency modulation electrical signal, and outputs the modulated optical signal to the spectrum measurement system middle.

A kind of SSB spectrum generation method based on multi-frequency phase modulation described in the present invention is realized by the following technical solutions:

Step 1, importing the single-frequency signal output by the narrow-linewidth laser source into the electro-optic modulator;

Step 2. Obtain the waveform of the multi-frequency modulated electrical signal based on spectral analysis reverse calculation, and set the arbitrary waveform generator to generate the corresponding multi-frequency modulated electrical signal according to the calculation result;

Step 3, the multi-frequency modulated electrical signal is first amplified by a radio frequency signal amplifier, and then transmitted to the electro-optic modulator; the electro-optic modulator is driven by the multi-frequency modulated electrical signal amplified by the radio frequency signal amplifier to the electro-optic modulator. The single frequency signal is phase modulated, and the single frequency signal is modulated;

Step 4. Output the optical signal formed after modulation to the spectral measurement system for spectral structure analysis; the single spectral line of the original single-frequency signal carrier is split into multiple spectral lines, and the intensity of one spectral line is much greater than that of other spectral lines The intensity of the spectrum shows a single sideband structure.

The most prominent features and remarkable beneficial effects of the present invention are:

The invention has a simple structure, and only uses one electro-optical modulator and one radio frequency driver to realize the output of the single sideband modulation signal. The energy conversion efficiency is high, no optical filter is used in the present invention, and the corresponding insertion loss is reduced; in addition, the multi-frequency phase modulation transfers the signal power of one sideband of ODSB to another sideband instead of filtering it directly, and the two All together lead to the extremely high energy conversion efficiency of the present invention. In the simulation experiment, the edge frequency intensity is only 0.56dB lower than that of the carrier signal intensity before modulation, and the energy conversion efficiency reaches 88%.

Description of drawings

Fig. 1 is the structural representation of the SSB spectrum generation device based on multi-frequency phase modulation of the present invention;

Fig. 2 is a waveform diagram of a modulated electrical signal for realizing SSB modulation;

Fig. 3 is the power spectrum image of signal light before and after single-frequency signal modulation;

1. Laser source with narrow line width, 2. Electro-optic modulator, 3. Spectral measurement system, 4. Arbitrary waveform generator, 5. Radio frequency signal amplifier.

Detailed ways

Specific Embodiment 1: As shown in Figure 1, a single sideband spectrum generation device based on multi-frequency phase modulation provided in this embodiment includes a laser source 1 with a narrow linewidth, an electro-optic modulator 2, and a spectral measurement system 3 , arbitrary waveform generator 4 and radio frequency signal amplifier 5;

The output fiber of the laser source 1 of the narrow line width is connected to the pigtail of the input end of the electro-optic modulator 2, and the single-frequency signal output by the laser source 1 of the narrow line width is introduced into the electro-optic modulator 2;

The input end of the radio frequency signal amplifier 5 is connected to the arbitrary waveform generator 4, and the output end of the radio frequency signal amplifier 5 is connected to the electro-optic modulator 2, and the output end of the electro-optic modulator 2 is connected to the spectral measurement system 3; The generator 4 generates a multi-frequency modulation electrical signal, which is amplified by the radio frequency signal amplifier 5, and then transmitted to the electro-optic modulator 2; the electro-optic modulator 2 performs phase modulation on the single-frequency signal entering the electro-optic modulator 2 according to the multi-frequency modulation electrical signal , and output the modulated optical signal to the spectrum measuring system 3 .

In this device, when no phase modulation is performed or the amplitude of the modulated electrical signal applied to the electro-optic modulator 2 is 0, the spectrum measured in the spectrum measurement system 3 only contains carrier components; when a modulated electrical signal is applied to the electro-optical When the modulator 2 is on, the single-frequency signal output by the narrow-linewidth laser source 1 is modulated, and the single spectral line of the original single-frequency signal is split into multiple spectral lines. With the adjustment of the modulated electrical signal, the modulated The spectrum is able to show a single sideband structure.

Embodiment 2: The difference between this embodiment and Embodiment 1 is that the spectral measurement system 3 is a spectrum analyzer, a spectrum analyzer or a scanning F-P interferometer.

Other steps and parameters are the same as those in the first embodiment.

Embodiment 3: This embodiment is different from Embodiment 1 in that the narrow linewidth laser source 1 is provided by a narrow linewidth semiconductor laser. The wavelengths of the commonly used communication bands are 1550nm and 1310nm, and the wavelengths of the commonly used bands for laser medical treatment are 1064nm.

Other steps and parameters are the same as those in the first embodiment.

Specific embodiment four: according to Fig. 1, present embodiment is described, and a kind of SSB spectrum generation method based on multi-frequency phase modulation that present embodiment provides, specifically comprises the following steps:

Step 1, importing the single-frequency signal output by the narrow-linewidth laser source into the electro-optic modulator;

Step 2. Obtain the waveform of the multi-frequency modulated electrical signal based on spectral analysis reverse calculation, and set the arbitrary waveform generator to generate the corresponding multi-frequency modulated electrical signal according to the calculation result;

Step 3, the multi-frequency modulated electrical signal is first amplified by a radio frequency signal amplifier, and then transmitted to the electro-optic modulator; the electro-optic modulator is driven by the multi-frequency modulated electrical signal amplified by the radio frequency signal amplifier to the electro-optic modulator. The single frequency signal is phase modulated, and the single frequency signal is modulated;

Step 4. Output the optical signal formed after modulation to the spectral measurement system for spectral structure analysis; the single spectral line of the original single-frequency signal is split into multiple spectral lines, and the intensity of one spectral line is much greater than that of other spectral lines Intensity, the spectrum exhibits a single sideband structure.

Embodiment 5: The difference between this embodiment and Embodiment 4 is that the process of calculating the multi-frequency modulation electrical signal waveform in step 2 includes:

Step 21, the fundamental frequency of the multi-frequency modulated electrical signal m(t) is f _m , and the Fourier series expansion of m(t) is:

In formula (1), γ _k and φ _k are the modulation index and initial phase of the kth harmonic in the multi-frequency modulated electrical signal, and t represents time;

Step 22, set the multi-frequency modulation electrical signal waveform γ _k = 0, φ _k = 0, the multi-frequency modulation electrical signal waveform is the value combination of the modulation index γ _k of the k harmonic and the initial phase φ _k ;

Step 23: Under the action of the modulated electrical signal, the DC component in the multi-frequency modulated electrical signal is ignored, that is, the DC component γ ₀ =0, and the time-domain expression of the modulated single-frequency signal is:

Among them, fc is the frequency of the single-frequency signal output by the narrow linewidth laser source, and j is the imaginary number unit; E( _t ) refers to the amplitude of the modulated optical signal;

The Fourier series expansion on the right side of formula (2) gives:

Among them, n ₁ , n ₂ , n _k are integers of (-∞ _, ∞), is a Bessel function; the optical signal after multi-frequency phase modulation is a series of discrete spectral lines with a frequency interval of f _m ;

Calculate the spectral structure of the modulated optical signal satisfying formula (2) and formula (3) by mathematical simulation software;

Step two and four, compare the spectral structure obtained in step two and three with the set target SSB modulation signal, if the error of the two is within the set precision requirement range, then select this multi-frequency modulated electrical signal waveform as the calculation Result; if the comparison error is not within the accuracy requirement range, then γ _k =γ _k +0.01, that is, the value of γ _k is increased by 0.01, and steps 23-24 are repeated until a multi-frequency modulated electrical signal waveform meeting the conditions is obtained.

The target single-sideband modulation signal, that is, the preset optical signal is a series of discrete spectral lines with a frequency interval of f _m and the single-sideband modulation signal in which the intensity of one spectral line is much greater than the intensity of other spectral lines. The above steps increase the value of γ _k by equal steps, and select and obtain a multi-frequency modulated electrical signal waveform. Compared with the target single-sideband modulated signal, the optical signal generated after modulation can meet the range of accuracy requirements.

The set accuracy requirement range includes the carrier suppression ratio R1 range and the side frequency suppression ratio R2 range.

Other steps and parameters are the same as those in Embodiment 4.

Embodiment 6: This embodiment is different from Embodiment 4 in that the fundamental frequency of the multi-frequency modulated electrical signal ranges from 1 kHz to 40 GHz.

Other steps and parameters are the same as those in Embodiment 4 or 5.

Embodiment 7: This embodiment is different from Embodiment 6 in that the fundamental frequency of the multi-frequency modulated electrical signal is 10.8 GHz.

Other steps and parameters are the same as those in Embodiment 4, 5 or 6.

Embodiment 8: The difference between this embodiment and Embodiment 4 is that the multi-frequency modulation electrical signal applied to the electro-optical modulator in step 3 includes f _m , 2f _m , ..., kf _m , k frequencies, k∈ [2,10], the phase φ _k of each frequency component is 0.

Other steps and parameters are the same as those in Embodiment 4, 5, 6 or 7.

Example

Adopt the following examples to verify the beneficial effects of the present invention:

A method for generating SSB spectrum based on multi-frequency phase modulation described in this embodiment is carried out according to the following steps:

As shown in Figure 1, first connect the device: connect the output fiber of the laser source 1 with a narrow linewidth to the pigtail at the input end of the electro-optic modulator 2, and introduce the single-frequency signal output by the laser source 1 with a narrow linewidth into the In the electro-optic modulator 2; the input end of the radio frequency signal amplifier 5 is connected to the arbitrary waveform generator 4, the output end of the radio frequency signal amplifier 5 is connected to the electro-optic modulator 2, and the output end of the electro-optic modulator 2 is connected to the spectrum measurement System 3, the spectral measurement system 3 in the present embodiment adopts a spectral analyzer;

The narrow-linewidth laser light source is provided by a narrow-linewidth semiconductor laser with a wavelength of 1550nm. As shown in Figure 2, the arbitrary waveform generator 4 is set to generate multi-frequency modulation electrical signals as follows: including f _m , 2f _m , 3f _m , 4f _m , 5f _m , 6f _m , 7f _m , 8f _m , 9f _m , 10f _m and other 10 frequency multi-frequency modulated electrical signals, the value of the fundamental frequency f _m of the multi-frequency modulated electrical signal is 10.8 GHz, set The fixed carrier suppression ratio R1 range is greater than or equal to 20dB and the side frequency suppression ratio R2 range is greater than or equal to 18dB, and the multi-frequency modulation electrical signal waveforms that meet the requirements are calculated and obtained: γ ₁ =1.9900, γ ₂ =0.9800, γ ₃ =0.6400, γ ₄ =0.4700, γ ₅ =0.3600, γ ₆ =0.2900, γ ₇ =0.2300, γ ₈ =0.2700, γ ₉ =0.2800, γ ₁₀ =0.2400, and the phase φ _k of each frequency component is 0.

When the amplitude of the multi-frequency modulation electrical signal is 0, that is, no modulation signal is applied, the spectral line structure measured in the spectrum analyzer is shown in the dotted line in Figure 3, and only the carrier component exists. If the calculated multi-frequency modulation electrical signal waveform is added to the electro-optic modulator 2, the modulation spectrum shown by the solid line in Fig. 3 can be obtained. It can be seen that the components of the upper side frequency in the spectral line structure are effectively suppressed. The side frequency suppression ratio is about 18.5dB, and the carrier is also well suppressed at the same time. The carrier suppression ratio is about 24.3dB, and a better single sideband signal is obtained. Another advantage is the high utilization rate of the signal. It can be clearly seen from Figure 3 that the strength of the first-order lower side frequency of the modulated signal is only 0.56dB lower than that of the pre-modulated carrier signal.

The present invention can also have other various embodiments, without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and deformations according to the present invention, but these corresponding changes and deformations are all Should belong to the scope of protection of the appended claims of the present invention.

Claims (8)

1. The single-sideband spectrum generating device based on the multi-frequency phase modulation is characterized by comprising a narrow-linewidth laser source, an electro-optical modulator, a spectrum measuring system, an arbitrary waveform generator and a radio-frequency signal amplifier;

the output optical fiber of the narrow-linewidth laser source is connected with the input end of the electro-optical modulator, and a single-frequency signal output by the narrow-linewidth laser source is led into the electro-optical modulator;

the input end of the radio frequency signal amplifier is connected with an arbitrary waveform generator, the output end of the radio frequency signal amplifier is connected with the electro-optical modulator, and the output end of the electro-optical modulator is connected with a spectrum measurement system; the random waveform generator generates a multi-frequency modulation electric signal, the multi-frequency modulation electric signal is amplified by a radio frequency signal amplifier and then is transmitted to the electro-optic modulator; the electro-optical modulator carries out phase modulation on a single-frequency signal entering the electro-optical modulator according to the multi-frequency modulation electric signal, and outputs the modulated optical signal to the spectrum measurement system.

2. The apparatus for generating single sideband spectrum based on multifrequency phase modulation of claim 1, wherein: the spectrum measuring system is a spectrum analyzer, a spectrum analyzer or a scanning Fabry-Perot interferometer.

3. the apparatus for generating single sideband spectrum based on multifrequency phase modulation of claim 1, wherein: the narrow linewidth laser source is provided by a narrow linewidth semiconductor laser.

4. A method for generating a single sideband spectrum using the apparatus of claim 1, said method comprising the steps of:

Firstly, introducing a single-frequency signal output by a narrow-line-width laser source into an electro-optic modulator;

Secondly, obtaining a multi-frequency modulation electrical signal waveform based on the spectral analysis reverse calculation, and setting an arbitrary waveform generator to generate a corresponding multi-frequency modulation electrical signal according to the calculation result;

Amplifying the multi-frequency modulation electric signal by a radio frequency signal amplifier, and then transmitting the multi-frequency modulation electric signal to an electro-optical modulator; the electro-optical modulator is driven by a multi-frequency modulation electric signal amplified by the radio-frequency signal amplifier to perform phase modulation on a single-frequency signal entering the electro-optical modulator, and the single-frequency signal is modulated;

Step four, outputting the optical signal formed after modulation to a spectrum measurement system for spectrum structure analysis; a single spectral line of an original single-frequency signal is split into a plurality of spectral lines, the intensity of one spectral line is far greater than that of other spectral lines, and a spectrum presents a single-sideband structure.

5. The method of generating a single sideband spectrum of claim 4, wherein the step two of calculating the waveform of the multi-frequency modulated electrical signal comprises:

Step two, the fundamental frequency of the multi-frequency modulation electric signal m (t) is f_mthe Fourier expansion of m (t) is as follows:

in the formula (1) < gamma >, (_kand phi_kRespectively representing the modulation index and the initial phase of the k-th harmonic in the multi-frequency modulation electric signal, wherein t represents time;

Step two, setting a multi-frequency modulation electric signal waveform gamma_k＝0、φ_k0, modulation index gamma of the waveform of the multi-frequency modulated electric signal, i.e. the k-th harmonic_kand an initial phase phi_kValue combination of (1);

Step two and step three, neglecting the direct current component in the multi-frequency modulation electric signal, namely the direct current component gamma₀0, the time domain expression of the modulated single-frequency signal is:

wherein f is_cthe frequency of a single-frequency signal output by a narrow-linewidth laser source, j is an imaginary number unit; e (t) refers to the amplitude of the modulated optical signal;

performing Fourier series expansion on the right side of the formula (2) to obtain:

Wherein n is₁、n₂、n_kIs an integer of (-infinity, ∞),Is BesselA function; the optical signal after multi-frequency phase modulation has a series of frequency intervals f_mdiscrete spectral lines of (a);

Calculating the frequency spectrum structure of the modulated optical signal satisfying the formula (2) and the formula (3) through mathematical simulation software;

step two, the spectrum structure obtained in the step two is compared with a set target single-sideband modulation signal, and if the error between the spectrum structure and the target single-sideband modulation signal is within a set precision requirement range, the waveform of the multi-frequency modulation electrical signal is selected as a calculation result; if the contrast error is not in the precision requirement range, gamma is determined_k＝γ_k+0.01, i.e. gamma_kThe value of (2) is increased by 0.01, and the steps two, three, two and four are repeated until the multi-frequency modulation electric signal waveform meeting the conditions is obtained.

6. Method for generating a single sideband spectrum according to claim 4, characterized in that: the value of the fundamental frequency of the multi-frequency modulation electric signal is 1 kHz-40 GHz.

7. The method of generating a single sideband spectrum of claim 6, wherein: the fundamental frequency of the multi-frequency modulation electric signal takes 10.8 GHz.

8. Method for generating a single sideband spectrum according to claim 4, characterized in that: the electrical multi-frequency modulated signal applied to the electro-optical modulator in step three comprises_m、2f_m、...、kf_mK frequencies, k ∈ [2,10 ]]Phase of each frequency component phi_kAre all 0.