CN104749798A - High-speed tunable microwave photon filter - Google Patents

Abstract

The invention discloses a high-speed tunable microwave photon filter. It is mainly composed of a light source 100, an optical splitter 101, an intensity modulator 102, a dual-drive Mach-Zehnder modulator 103, an optical bandpass filter 104, a polarization beam combiner 105, and a photodetector 106. The microwave signal 107 is an input signal, and the digital signal 108 is a control signal. By directly loading the control signal on the optical modulator, the transfer function of the filter can be switched at a high speed in time. The invention has a simple structure, is easy to integrate, can realize picosecond-level high-speed tunability, and can be used as a high-speed switch and frequency-hopping signal processing in dynamic optical networks and cognitive radio systems.

Description

High-speed tunable microwave photonic filters

technical field

The invention relates to the technical field of microwave devices, in particular to a high-speed tunable microwave photon filter. It is suitable for solving high-speed dynamic signal processing of high-frequency and ultra-high-frequency microwave signals in frequency hopping communication and recognition of radio, such as high-speed switching and dynamic filtering.

Background technique

Microwave photonic filters are filters that realize microwaves through photonic systems. Compared with traditional microwave filters, microwave photonic filters have the advantages of low loss, wide bandwidth, large tunability, and no electromagnetic interference. They can be used in high High-frequency, ultra-high-frequency microwave signal processing, suitable for radar, radio and other systems. At the same time, with the introduction of the concept of cognitive radio, that is, cognitive radio refers to the fact that radio signals can adaptively select free frequency bands for communication according to the occupancy of the radio spectrum, so fast tunable microwave photonic filters have gradually become a research hotspot. .

At present, microwave photonic filter technology can be mainly divided into two types: one is a finite impulse response filter (FIR), and the other is a filter based on optical phase modulation. The main principle of the finite impulse response filter is to implement weighting and delay superposition of multiple copies of the microwave signal. According to different light sources, finite impulse response filters can be divided into two types based on single light source and multi-wavelength light source or comb-filtered broadband light source. The former has a simple structure and low cost, but its tunable range is limited. It is mainly used for Implement comb or bandpass filtering; the latter can already implement arbitrary filter functions. Microwave photonic filters based on optical phase modulation are realized by combining stimulated Brillouin effect and optical filters. It is mainly used to produce non-periodic ultra-narrowband microwave photonic filters. The above two technologies have achieved multi-parameter tunable static microwave photonic filters, but the development of dynamic (or high-speed) microwave photonic filter technology is still in its infancy. Existing dynamic microwave photonic filters are mainly based on MEMS (switching speed greater than 300 microseconds), and a system based on fast optical delay lines recently reported in Nature (switching speed greater than 40 nanoseconds).

The above schemes of microwave photonic filters are mainly researches on statically tunable microwave photonic filters. Although the research on high-speed tunable microwave photonic filters has begun, the scheme based on fast optical delay line is based on the The complex structure and limited high-speed adjustability restrict the further development of high-speed dynamic network and cognitive radio technology.

Contents of the invention

In view of the above shortcomings of the prior art, the object of the present invention is to provide a high-speed tunable microwave photonic filter.

The object of the present invention proposes and realizes based on following analysis and scheme:

A high-speed tunable microwave photonic filter, consisting of a light source 100, an optical splitter 101, an intensity modulator 102, a dual-drive Mach-Zehnder modulator 103, an optical bandpass filter 104, a polarization beam combiner 105, and a photodetector 106, it is characterized in that the optical signal is divided into two branches through the optical splitter 101, and the branch one is generated by the dual-drive Mach-Zehnder modulator 103 and the optical bandpass filter 104 under the action of the microwave signal Aeωt and the digital signal The phase encoding signal Aej[θ(t)+ωt], wherein the optical bandpass filter 104 is used to filter out a sideband of the modulated optical signal; the second branch is to modulate the microwave signal onto the optical signal by the intensity modulator 102; The two paths of signals are combined in two paths of orthogonal polarization states by the polarization beam combiner 105 to avoid interference of coherent light.

The high-speed tunable microwave photon filter of the present invention is proposed based on the finite impulse response microwave photon filter. The optical signal is divided into two branches by the optical splitter 101, one route modulates the microwave signal onto the optical signal by the intensity modulator 102, and the other route the dual-drive Mach-Zehnder modulator 103 and the optical bandpass filter 104 in the microwave signal Ae The phase encoding signal Ae ^j[θ(t)+ωt] is generated under the action of ^ωt and the digital signal, wherein the optical bandpass filter 104 is used to filter out a sideband of the modulated optical signal. In order to avoid coherent light interference, the two signals are combined into one in two orthogonal polarization states by the polarization beam combiner 105 . Due to the existence of electrical delay, there is a time difference (△τ) between the two signals when they beat on the photodetector. At the same time, the power ratio of the two signals can be adjusted by adjusting the polarization controller before the polarization beam combiner. Under the above conditions, a two-tap high-speed tunable comb microwave photonic filter can be realized, and its transfer function is

H(ω)＝1+e ^jθ(t) e ^-jωΔτ

It is worth noting that the time difference between the two signals needs to be less than the switching time of the control signal. At this time, the transfer function of the filter of the present invention is a trigonometric function, and the free spectrum distance of the filter function of the present invention can be adjusted by adjusting the time difference between the two signals. , the phase of the triangular transfer function can be controlled by adjusting the amplitude of the control signal. If the present invention is used for a high-speed microwave switch, the optical bandpass filter 104 can be removed, and a binary control signal with a suitable amplitude can be used to switch between two trigonometric functions with a phase difference of 180°, which can be applied to wavelength division multiplexing Signal switching or amplitude and frequency key modulation.

In addition, in the present invention, both parallel branches can adopt the structure of the branch 103, and beat frequency on the photodetector through two arbitrary phase modulation signals, so that the transfer function can be switched at a higher speed and diversified. In the present invention, the incoherent superposition of branches 103 and 102 is realized through orthogonal polarization states, and at the same time, multiple arbitrary phase modulation signals can be formed by connecting multiple light sources with different wavelengths to the dual-drive Mach-Zehnder modulator 103 , and then add a dispersive medium before the photodetector 106 to generate a delay difference, thereby realizing a multi-tap high-speed adjustable microwave photon delay line.

With the above structure, the transfer function of the filter is a tunable time-varying function generated by the superposition of multiple arbitrary phase modulation signals (that is, different transfer functions can be quickly switched in time according to the control signal information); the control signal can be directly loaded on the optical modulation Switching control is realized on the device.

Compared with the multi-tap delay line microwave photon filter, the present invention is also a microwave photon filter function realized by the principles of weighting, delay, and superposition. On the basis of being compatible with the adjustability of this type of filter, the present invention The high-speed switching of the filter transfer function is realized by loading a high-speed digital control signal on the optical modulator. Compared with the fast adjustable microwave photon filter based on the adjustable optical delay line, the highest switching speed is only millisecond level, the present invention realizes the switching of the transfer function based on the modulation mode, and has the switching speed of picosecond level. The invention has the advantages of simple structure, low cost and easy integration, and can be used as a high-speed microwave switch, a frequency hopping signal generator and the like.

Description of drawings:

Fig. 1 is the structural representation of high-speed tunable microwave photon filter of the present invention;

Fig. 2 is principle and functional schematic diagram of the present invention;

Fig. 3 is the structure schematic diagram of the high-speed tunable microwave photon filter that the present invention expands: (a) the two-tap filter that two-way arbitrary phase modulation signal superposition produces; (b) the multi-tap filter that multi-way arbitrary phase modulation signal superposition produces device;

Fig. 4 is the microwave photon filter experimental result figure of free spectral range (FSR) adjustable triangular transfer function of the present invention: (a) FSR=200MHz, (b) FSR=400MHz;

Fig. 5 is a schematic diagram of high-speed tunability of the present invention: an experiment diagram of frequency-hopping signals as a high-speed microwave switch, wherein (a) switching speed is 50 ns; (b) switching speed is 500 ps;

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings.

As shown in Figure 1, the present invention consists of a light source 100, an optical splitter 101, an intensity modulator 102, a dual-drive Mach-Zehnder modulator 103, an optical bandpass filter 104, a polarization beam combiner 105, and a photodetector 106 constitute. The microwave signal 107 is the input signal of the filter of the present invention, and the digital signal 108 is the control signal of the filter of the present invention.

Fig. 2 is the schematic diagram (a) and functional schematic diagram (b) of the microwave photon filter of the present invention, as shown in figure (a), the input microwave signal is modulated to the intensity modulator 102 and double-drive Mach-Zehnder modulation respectively On the device 103, the digital signal 108 is used as the control signal of the filter to control the fast switching of the filter transfer function in time. At the input end of the polarization beam combiner 105, a polarization controller is respectively connected to adjust the combined power ratio of the two branches where 102 and 103 are located. Due to the difference in the paths of the two branches (that is, there is a time difference) and the orthogonality of the polarization state, the basic conditions of the microwave photon filter based on IFR are satisfied, and a microwave photon filter can be realized. By adjusting the time difference of the two branch signals through an electrical or optical delay line, the tunability of the free spectrum range of the transfer function can be realized; by adjusting the polarization controller to adjust the power ratio of the two branches, the sideband suppression ratio of the transfer function can be realized. adjust. At the same time, due to the existence of the control signal 108, the signal of the branch 103 has different phase differences in different time periods, and the microwave photon filter transfer functions with different complex exponential factors are quickly switched in time, which can It is used as a high-speed microwave signal switch and frequency hopping communication, as shown in figure (b). In the figure (a), for a single frequency signal fc, due to the effect of the control signal 108, it is processed by the microwave photon filter with positive and negative factor switching of the present invention, and the output is a binary amplitude modulation signal.

According to the above principles, we give some experimental results of the high-speed tunable microwave photonic filter constructed by the present invention. In the experiment, the central wavelength of the single-wavelength light source is about 1556.05nm, and the digital signal 108 is provided by a high-speed digital signal generator. The experiment is divided into two parts: 1) static measurement of the transfer function of the filter proposed by the present invention under different time states; 2) measurement of the high-speed switching characteristics of the filter proposed by the present invention.

Fig. 3 is the schematic diagram of the extended high-speed microwave photon filter of the present invention: wherein Fig. (a) is the two-tap filter that two-way arbitrary phase modulation signal superposition produces, compared with Fig. 1 this block diagram, replace intensity modulator By making a dual-drive Mach-Zehnder modulator, the superposition of two phase modulation signals can be realized, so that the switching control of four different transfer functions can be realized by modulation of two binary digital signals. Figure 2 shows a two-tap filter generated by superposition of multiple channels of arbitrary phase modulation signals. In Figure 1, the non-coherent superposition of optical signals implemented by using the polarization state can only be used for two channels of signals. In order to achieve the superposition of multi-channel signals, a multi-tap high-speed microwave photon delay line filter is realized by using multiple independent light sources with different central wavelengths, and then realizing the delay difference through a dispersive medium. Compared with the two-tap microwave photon filter, the multi-tap filter has higher filter performance, such as higher carrier rejection ratio and Q value.

Fig. 4 is a kind of transfer function of the filter proposed by the present invention measured by experiment, by setting the control signal 108 to be all "1" or "0", respectively measure the transfer function of the microwave filter under two different time states. By adjusting the length of the electrical delay line, the free spectrum range (FSR) of the filter transfer function can be adjusted, where Figure (a) FSR = 200MHz, Figure (b) FSR = 400MHz.

Fig. 5 is the experimental result of the high-speed switching characteristic of the filter. In order to prove the high-speed adjustable characteristics of the filter, microwave signals of two frequencies respectively located in the passband and stopband of the transfer function in state 1 are selected as the microwave input signal 107 of the filter. After the high-speed tunable positive and negative exponential filter processing of the present invention, the frequency jump is generated by the switching of the filter function. By setting the code pattern of the control signal 108 as "101", the rate is 2 × 10 ⁷ Hz, and figure (a) is the frequency hopping signal output by the filter of the present invention, and now the switching speed of the filter is 50ns, and figure (b ) is the waveform diagram of the frequency hopping signal output when the code pattern of the control signal 108 is "100100" and the rate is 2×10 ¹⁰ Hz, and the switching speed of the filter is 500 ps at this time. It can be observed from the above experimental results that the present invention can realize a picosecond-level high-speed microwave photon filter.

Claims (4)

1. a high speed tunable microwave photon filter, by light source (100), optical branching device (101), intensity modulator (102), Dual Drive MZ Mach-Zehnder (103), optical band pass filter (104), polarization beam combiner (105), photodetector (106) is formed, it is characterized in that, light signal is divided into two branch roads through optical branching device (101), branch road one is by Dual Drive MZ Mach-Zehnder (103) and optical band pass filter 104) under the effect of microwave signal Ae ω t and digital signal, produce phase-coded signal Aej [θ (t)+ω t], wherein optical band pass filter (104) is for a sideband of light signal after filtering modulation, microwave signal is modulated on light signal by intensity modulator (102) by branch road two, two paths of signals is placed on two orthogonal polarization states by polarization beam combiner (105) and is combined into a road to avoid coherent light interference.

2. high speed tunable microwave photon filter according to claim 1, it is characterized in that, described Dual Drive MZ Mach-Zehnder (103) can be the unit that can produce arbitrarily digital phase modulated signal.

3. high speed tunable microwave photon filter according to claim 1, is characterized in that, described wave filter can expand to the multitap delay line filter that the light source of multiple different wave length and dispersive medium are formed.

4. high speed tunable microwave photon filter according to claim 1, is characterized in that, described control signal can be the microwave signal arbitrarily such as digital signal, Gauss pulse signal.