CN106526899A - Microwave photon filter based on cross-polarization modulation - Google Patents

Abstract

The invention discloses a microwave photon filter based on cross-polarization modulation. The microwave photon filter comprises an input module, an upper branch module, a lower branch module and an output module. The upper branch module and the lower branch module are generated by modulating the intensity of light carriers through microwave signals of an intensity modulator, raster treatment is carried out on the upper branch module and the lower branch module, and the treated microwave signals of the upper branch module and the lower branch module are combined and then input in the output module. The microwave photon filter has the advantages of being high in tuning speed, high in bandwidth, low in loss, high in electromagnetic interference resisting capacity and the like, and meanwhile has the tunable and reconfigurable flexible operating characteristics.

Description

Microwave photonic filter based on cross-polarization modulation

technical field

The invention relates to the field of microwave photonics, in particular to a microwave photon filter based on cross polarization modulation.

Background technique

Microwave photonic filters have the advantages of low loss, high bandwidth, anti-electromagnetic interference, etc., and at the same time have flexible operating characteristics such as tunable and reconfigurable, so they can replace traditional electrical filters in radio-over-optical, microwave signal generation and There are huge advantages in high-frequency microwave signal processing. Improving the tuning speed of microwave photonic filters is of great significance. However, the tuning speed of microwave photonic filters is often limited by the bandwidth of devices such as electro-optic modulators in microwave photonic systems. How to break through this limitation is a big problem.

Contents of the invention

(1) Technical problems to be solved

The technical problem to be solved by the invention is that the tuning speed of the microwave photonic filter is limited by the bandwidth of the electro-optical modulator and other devices in the microwave photonic system.

(2) Technical solutions

In order to achieve the above object, the present invention adopts following technical scheme:

A microwave photonic filter based on cross polarization modulation, comprising an input module, an upper branch module, a lower branch module and an output module, wherein:

The input module is used to generate an optical signal and send the optical signal to the upper branch module and the lower branch module, and the optical signal is generated by modulating a microwave signal onto an optical carrier;

The upper branch module is used to time delay the optical signal and send it to the output module;

The lower branch module is used to generate a pulse signal and combine it with the optical signal to perform cross-polarization modulation and send the microwave signal to the output module;

The output module is used for interfering and outputting the optical signal generated by the upper branch module and the microwave signal generated by the lower branch module.

As a preferred mode of the present invention, the input module includes a first laser source, a micro light source, an intensity modulator and a first optical coupler;

The intensity modulator modulates the microwave signal input by the microwave source to the optical carrier input by the first laser source, and outputs the modulated signal to the first optical coupler; the first optical coupler sends the optical signal to Upper branch module and lower branch module.

As a preferred mode of the present invention, the upper branch module includes an adjustable optical delay line and an adjustable optical attenuator;

The adjustable optical delay line is used to increase or decrease the distance of light transmission to achieve the purpose of time delay; the adjustable optical attenuator is used to control the power of the laser.

As a preferred mode of the present invention, the delay time T of the adjustable optical delay line satisfies: F=1/T, and F is a free spectral range.

As a preferred mode of the present invention, the lower branch module includes a pulsed laser source, a second optical coupler, a first polarization controller, a second laser source, a second polarization controller, a third optical coupler, a high nonlinear optical fiber;

The second optical coupler is used to combine the optical signal output by the first optical coupler and the laser pulse output by the pulsed laser source, as a control light to induce the Kerr effect in the highly nonlinear optical fiber;

The third optical coupler is used to combine the control light output by the first polarization controller and the detection light output by the second polarization controller to output to the high nonlinear optical fiber;

The lower branch module uses the cross-polarization modulation effect in the highly nonlinear optical fiber to perform binary phase encoding on the microwave signal;

The detection light generated by the second laser source is linearly polarized light, and the wavelength of the light is different from that of the upper branch module. Adjust the second polarization controller to control the polarization state of the detection light so that it is different from that of the high nonlinear optical fiber. The axis is at an angle of 45 degrees, which produces asymmetric phase modulation in the two directions of the fast axis and the slow axis of the highly nonlinear fiber;

As a preferred mode of the present invention, the lower branch module further includes a third polarization controller;

The third polarization controller is used to control the polarization state of the laser output from the highly nonlinear fiber.

As a preferred mode of the present invention, the lower branch module further includes a polarizer;

The polarizing direction of the polarizer is at an angle of 45 degrees to the slow axis of the highly nonlinear fiber, and the polarization-modulated detection optical signal output by the highly nonlinear fiber is projected onto the polarizing direction of the polarizer and converted into an intensity-modulated Signal.

As a preferred mode of the present invention, the lower branch module further includes an optical bandpass filter;

The detection light is inside the passband of the optical bandpass filter, and the control light is outside the passband. In the laser output by the highly nonlinear optical fiber, the polarization modulated detection light signal is retained, while the control light is filtered out.

As a preferred manner of the present invention, the optical signal of the upper branch module and the microwave signal of the lower branch module are respectively subjected to optical domain processing.

As a preferred mode of the present invention, the output module includes a fourth optical coupler and a photodetector;

The fourth optical coupler combines the optical signal of the upper branch module and the microwave signal of the lower branch module and then inputs it to the photodetector;

The photodetector is used for outputting the microwave signal obtained by combining beams after being interfered in the photodetector.

(3) Beneficial effects

The microwave photon filter based on cross-polarization modulation of the present invention uses the cross-polarization modulation effect of highly nonlinear optical fibers to replace the electro-optic modulator, and its bandwidth far exceeds that of the electro-optic modulator, breaking through the electronic bottleneck of the electro-optic modulator, and can The signal is modulated at very high speed. Utilizing this advantage, the invention can realize ultra-high-speed tuning of the central wavelength of the microwave photon filter.

Description of drawings

FIG. 1 is a block diagram of a microwave photonic filter based on cross-polarization modulation according to the present invention.

Fig. 2 is a schematic structural diagram of a microwave photonic filter based on cross-polarization modulation according to the present invention.

Fig. 3 is a schematic diagram of the central wavelength tuning principle of the microwave photonic filter based on cross-polarization modulation according to the present invention.

detailed description

For the above situation, the present invention provides a microwave photonic filter based on cross polarization modulation, including an input module, an upper branch module, a lower branch module and an output module, the input module is used to generate an optical signal and send the optical signal to The upper branch module and the lower branch module, the optical signal is generated by modulating the microwave signal onto the optical carrier; the upper branch module is used to send the optical signal to the output module after time delay; the lower branch module Used to generate a pulse signal and combine it with the optical signal and send the microwave signal obtained by cross-polarization modulation to the output module; the output module is used to combine the optical signal generated by the upper branch module and the microwave generated by the lower branch module The signal interferes and is output.

The invention can change the free spectral range of the microwave photon filter by adjusting the adjustable optical delay line of the upper branch module, and adjust the laser power of the upper branch module by adjusting the adjustable optical attenuator. The lower branch module uses the cross-polarization modulation of the highly nonlinear optical fiber to encode the phase of the microwave signal, which can solve the problem of the tuning speed of the microwave photonic filter.

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

FIG. 1 is a block diagram of a microwave photonic filter based on cross-polarization modulation according to the present invention. As shown in Figure 1, the microwave photonic filter based on cross-polarization modulation is composed of four modules, which are input module, upper branch module, lower branch module and output module. The input module generates an optical signal and sends the optical signal to the upper branch module and the lower branch module, and the optical signal is generated by modulating the microwave signal onto the optical carrier. The upper branch module delays the optical signal before sending it to the output module. The lower branch module generates the pulse signal and combines it with the optical signal to perform cross-polarization modulation and sends the microwave signal to the output module. The output module interferes and outputs the optical signal generated by the upper branch module and the microwave signal generated by the lower branch module.

Fig. 2 is a schematic structural diagram of a microwave photonic filter based on cross-polarization modulation according to the present invention. As shown in FIG. 2 , the input module includes a first laser source 1 , a microwave source 2 , an intensity modulator 3 and a first optical coupler 4 .

The first laser source 1 generates laser light and outputs it to the light input port gate of the intensity modulator 3;

The microwave source 2 generates a microwave signal and outputs it to the radio frequency input port of the intensity modulator 3;

The intensity modulator 3 modulates the microwave signal input by the microwave source 2 onto the optical carrier input by the first laser source 1, and outputs the modulated signal to the first optical coupler 4;

The first optical coupler 4 sends the optical signal output by the intensity modulator 3 to the upper branch module and the lower branch module. The output of the upper branch module is to the adjustable optical delay line 6 , and the output of the lower branch module is to the second optical coupler 8 .

The upper branch module includes an adjustable optical delay line 6 and an adjustable optical attenuator 7;

The adjustable optical delay line 6 is used to increase or decrease the distance of light transmission to achieve the purpose of time delay;

The adjustable optical attenuator 7 is used to control the laser power of the upper branch module.

The lower branch module includes a pulsed laser source 5, a second optical coupler 8, a first polarization controller 9, a second laser source 10, a second polarization controller 11, a third optical coupler 12, a highly nonlinear optical fiber 13. A third polarization controller 14, a polarizer 15 and an optical bandpass filter 16;

The second optical coupler 8 is used to combine the optical signal output by the first optical coupler 4 and the laser pulse output by the pulsed laser source 5, as a control light to induce the Kerr effect in the highly nonlinear optical fiber 13;

The first polarization controller 9 controls the polarization state of the laser light output by the second optical coupler 8, and outputs it to the third optical coupler 12;

The second laser source 10 is used to output continuous wave detection light;

The second polarization controller 11 controls the polarization state of the probe light output by the second laser source 10;

The third optical coupler 12 combines the control light output by the first polarization controller 9 and the detection light output by the second polarization controller 11 and outputs them to the highly nonlinear optical fiber 13;

The highly nonlinear optical fiber 13 is used to generate the Kerr effect under the action of the control light, so as to perform cross-polarization modulation on the detection light;

The third polarization controller 14 controls the polarization state of the laser output from the highly nonlinear optical fiber 13;

A polarizer 15, whose polarization direction is at an angle of 45 degrees to the slow axis of the highly nonlinear optical fiber 13, converts the input laser light into linearly polarized light and outputs it to the optical bandpass filter 16;

The optical bandpass filter 16 is used to filter out the control light in the laser output from the highly nonlinear optical fiber 13 , retain the detection light and output it to the fourth optical coupler 17 .

The output module includes a fourth optical coupler 17 and a photodetector 18;

The fourth optical coupler 17 combines the optical signal of the upper branch module and the microwave signal of the lower branch module and outputs it to the photodetector 18;

The photodetector 18 is used for photoelectric conversion of the input signal to generate two microwave signals, which are output from the radio frequency output port of the photodetector 18 after interference.

Fig. 3 is a schematic diagram of the central wavelength tuning principle of the microwave photonic filter based on cross-polarization modulation according to the present invention. In Fig. 1, the signals of the upper branch module and the lower branch module interfere in the output module due to different delays, so the transmission response of the microwave photonic filter is a periodic bandpass filter shape, and its period is the free Spectral range F. Adjust the adjustable optical delay line 6 of the upper branch module in Figure 2, and the free spectral range F changes (F=1/T); adjust the adjustable optical attenuator 7 of the upper branch module in Figure 2, and the transmission response is within the band The depth of the resistance position changes. When the laser pulse jumps from 1 to 0, the phase of the microwave signal in the lower branch is shifted by pi, and the transmission response of the microwave photonic filter changes accordingly, and the central wavelength fluctuates as shown in Figure 3, and the fluctuation range is Half of the free spectral range F.

The specific embodiments described above have further described the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above descriptions are only specific embodiments of the present invention, and are not intended to limit the present invention. Within the spirit and principles of the present invention, any modifications, equivalent replacements, improvements, etc., shall be included in the protection scope of the present invention.

Claims (10)

1. A microwave photonic filter based on cross polarization modulation, comprising an input module, an upper branch module, a lower branch module and an output module, wherein: The input module is used to generate an optical signal and send the optical signal to the upper branch module and the lower branch module, and the optical signal is generated by modulating a microwave signal onto an optical carrier; The upper branch module is used to time delay the optical signal and send it to the output module; The lower branch module is used to generate a pulse signal and combine it with the optical signal to perform cross-polarization modulation and send the microwave signal to the output module; The output module is used for interfering and outputting the optical signal generated by the upper branch module and the microwave signal generated by the lower branch module. 2. the microwave photonic filter based on cross-polarization modulation according to claim 1, is characterized in that, described input module comprises the first laser source (1), microlight source (2), intensity modulator (3) and the first An optical coupler (4); The intensity modulator (3) modulates the microwave signal input by the microwave source (2) onto the optical carrier input by the first laser source (1), and outputs the modulated signal to the first optical coupler (4); The above-mentioned first optical coupler (4) sends the optical signal to the upper branch module and the lower branch module. 3. the microwave photonic filter based on cross polarization modulation according to claim 1, is characterized in that, described upper branch module comprises adjustable optical delay line (6) and adjustable optical attenuator (7); The adjustable optical delay line (6) is used to increase or decrease the distance of light transmission to achieve the purpose of time delay; the adjustable optical attenuator (7) is used to control the power of the laser. 4. the microwave photonic filter based on cross polarization modulation according to claim 3, is characterized in that, the delay time T of described adjustable optical delay line (6) satisfies: F=1/T, F is free spectral range . 5. The microwave photonic filter based on cross polarization modulation according to claim 1, characterized in that, the lower branch module comprises a pulsed laser source (5), a second optical coupler (8), a first polarization control Device (9), second laser source (10), second polarization controller (11), third optical coupler (12), highly nonlinear optical fiber (13); The second optical coupler (8) is used to combine the optical signal output by the first optical coupler (4) and the laser pulse output by the pulsed laser source (5), as a control light-induced high nonlinear optical fiber (13) produce the Kerr effect; The third optical coupler (12) is used to output the control light output by the first polarization controller (9) and the detection light output by the second polarization controller (11) into a high nonlinear optical fiber (13); The lower branch module utilizes the cross-polarization modulation effect in the highly nonlinear optical fiber (13) to perform binary phase encoding on the microwave signal, and the phase of the signal is controlled by a pulsed laser source. When the pulsed laser changes from presence to absence, the phase of the signal A precise pi phase shift occurs; The detection light generated by the second laser source (10) is linearly polarized light, the wavelength of the light is different from that of the upper branch module, and the second polarization controller (11) is adjusted to control the polarization state of the detection light so that it is the same as The slow axis of the highly nonlinear optical fiber (13) forms an angle of 45 degrees, which generates asymmetric phase modulation in the two directions of the fast axis and the slow axis of the highly nonlinear optical fiber (13). 6. the microwave photonic filter based on cross polarization modulation according to claim 5, is characterized in that, described lower branch module also comprises the 3rd polarization controller (14); The third polarization controller is used to control the polarization state of the laser output from the highly nonlinear fiber. 7. the microwave photonic filter based on cross polarization modulation according to claim 5, is characterized in that, described lower branch module also comprises polarizer (15); The polarizing direction of the polarizer (15) forms an angle of 45 degrees with the slow axis of the highly nonlinear optical fiber (13), and the detection optical signal of the polarization modulation output by the highly nonlinear optical fiber (13) is projected onto the polarizer ( 15) In the polarizing direction, it is converted into an intensity modulation signal. 8. the microwave photonic filter based on cross polarization modulation according to claim 5, is characterized in that, described lower branch module also comprises optical bandpass filter (16); In the passband of the optical band-pass filter (16) is the detection light, and outside the passband is the control light. In the laser output by the highly nonlinear optical fiber (13), the polarization-modulated detection light signal is retained, while the control Light is filtered out. 9. The microwave photonic filter based on cross-polarization modulation according to claim 1, wherein the optical signal of the upper branch module and the microwave signal of the lower branch module are respectively subjected to optical domain processing. 10. the microwave photonic filter based on cross polarization modulation according to claim 1, is characterized in that, described output module comprises the 4th optical coupler (17) and photodetector (18); The fourth optical coupler (17) combines the optical signal of the upper branch module and the microwave signal of the lower branch module and then inputs it to the photodetector (18); The photodetector is used for outputting the microwave signal obtained by combining beams after being interfered in the photodetector.