CN106299977A - The device and method of two frequency multiplication photoelectric oscillator based on phase-modulation - Google Patents

Abstract

The invention discloses a tunable double-frequency photoelectric oscillator based on phase modulation. The invention relates to the field of microwave technology and the field of optical communication technology, and is mainly applied to generating microwave local oscillator signals. The method is shown in the accompanying drawings, including a laser source, a polarization controller, a circulator, a polarization beam splitter, a phase modulator, an optical coupler, a polarizer, a standard single-mode fiber, a photodetector, and a tunable bandpass Filters, electrical amplifiers, and electrical phase shifters. The phase modulator has the characteristics of forward modulation and reverse non-modulation. The optical signal output from the circulator is divided into two signals with equal power by the optical coupler. One of them is fed back to the phase modulator to form a photoelectric oscillator to obtain a fundamental frequency signal. The other way suppresses the optical carrier by adjusting the polarization controller to obtain double-frequency microwave signals. Combined with a tunable band-pass filter, a frequency-tunable double-frequency microwave signal can be obtained. The photoelectric oscillator has a large frequency tuning range and low phase noise, and can simultaneously obtain fundamental frequency oscillation signals and double frequency microwave signals. The scheme has a simple structure, flexible adjustment, and is not affected by bias voltage drift in traditional intensity modulation schemes.

Description

Device and method of double frequency photoelectric oscillator based on phase modulation

technical field

The invention relates to the technical fields of optical communication and microwave technology, and mainly relates to a device and method of a double frequency optical oscillator (OEO) based on phase modulation in the optical communication technology.

Background technique

With the continuous development of microwave photonic technology in the fields of aerospace, radar, wireless communication and electronic countermeasures, high-frequency and broadband tunable microwave signal generation technology has important application value. Compared with the traditional microwave signal generation technology, the photonics generation technology of microwave signal has the advantages of high frequency, low phase noise, tunable broadband and no electromagnetic interference, and the system structure is relatively simple, compatible with other optical systems, long-distance Good coverage and large transmission capacity.

With the development needs of military and civil applications, future microwave systems are required to have the characteristics of large bandwidth, large dynamic range and high sensitivity. Especially in the field of military radar and electronic countermeasures, the requirements for microwave systems will become higher and higher. At the same time, as the complexity of information increases and the amount of information becomes more and more abundant, higher and stricter requirements are put forward for the performance of information systems. Among them, it is very important to generate microwave local oscillator signals with high frequency, high spectral purity, tunable bandwidth and low phase noise.

OEO is an oscillator that uses photonics technology to generate microwave local oscillators. It can directly generate microwave and millimeter-wave microwave local oscillators. It has potential applications in radar, electronic warfare, and precise measurement. Compared with traditional microwave oscillators, OEO has lower phase noise, and the phase noise does not increase significantly with the increase of oscillation frequency. It is a potential choice for microwave, millimeter wave, and even terahertz wave low phase noise signal sources. OEO can provide electrical and optical input methods for information systems, and is compatible with various electronic systems, optical communications, and microwave photonics systems.

In recent years, the method of using OEO to generate microwave signals and frequency multiplied signal processing has received extensive attention. An optoelectronic oscillator is generally a positive feedback loop composed of a light source, an intensity modulator, a filter, and an amplifier. Due to the bias voltage drift of the intensity modulator, many OEO schemes using polarization modulators, polarization controllers, and polarizers as intensity modulators have emerged in recent years. However, the frequency range of microwave and millimeter wave signals generated by these OEO solutions is relatively small, the system is relatively complex, and the cost is expensive.

Contents of the invention

In order to solve the technical problems existing in the background technology, the present invention proposes a tunable double frequency OEO method based on a phase modulator combined with a Sagnac ring. The frequency selection of the photoelectric oscillator is realized by using the tunable band-pass filter, and the fundamental frequency microwave signal with low phase noise is obtained. In addition, the carrier wave is suppressed by simply adjusting the polarization controller, thereby generating frequency-tunable, low-phase-noise double-frequency microwave signals.

The technical solution adopted by the present invention to solve the technical problem is: the device includes a laser source, a polarization controller, a circulator, a polarization beam splitter, a phase modulator, an optical coupler, a polarizer, a photodetector, a tunable A bandpass filter, an electrical phase shifter, an electrical amplifier and a standard single-mode fiber; the two output ends of the polarization beam splitter are respectively connected to the input and output ends of the phase modulator to form a Sagnac ring; the output end of the laser source is connected to the The polarization controller is connected, the other end of the polarization controller is connected to the circulator 1 port, and the circulator 2 port is connected to the input end of the polarization beam splitter; the circulator 3 port is divided into two signals with equal power by an optical coupler. One of them is sequentially connected with polarization controller, polarizer, single-mode fiber, photodetector, electric amplifier, tunable bandpass filter, and electric phase shifter; the output of the electric phase shifter is input to the RF port of the phase modulator , thus forming OEO. The other path is sequentially connected to another polarization controller, a polarizer, and a photodetector. The output end of each photoelectric detector can be connected to a spectrum analyzer for electrical signal testing.

The present invention comprises the following steps when working:

(1) A light wave with a wavelength of λ emitted from the laser source is injected into the polarization controller;

(2) Adjust the polarization controller so that the polarization beam splitter outputs two optical signals with equal power, one path is transmitted to the phase modulator through the polarization maintaining fiber in the clockwise direction, and the other path enters the phase modulation through the polarization maintaining fiber in the counterclockwise direction device;

(3) The optical signal transmitted in the clockwise direction will be phase-modulated. Due to the inherent characteristics of the modulator, the optical signal transmitted in the counter-clockwise direction will not be modulated. The phase-modulated signal and the optical carrier form polarization multiplexed light, from the ring Device 3 port output;

(4) The optical signal output from port 3 of the circulator is divided into two signals with equal power through the optical coupler. After each channel respectively passes through the polarization controller and polarizer, the phase modulation signal interferes with the optical carrier to a polarization direction to form an intensity modulation signal. The phase modulator, Sagnac ring and polarizer are equivalent to the intensity modulator, and the working point of the equivalent intensity modulator can be changed arbitrarily by adjusting the polarization controller;

(5) One of the optical signals passes through the polarization control, the polarizer outputs the intensity modulation signal of the orthogonal point, and enters the photodetector after passing through the optical fiber, and the obtained electrical signal is fed back to the phase modulator after being electrically amplified, filtered, and phase-shifted The radio frequency port, thus forming the OEO loop. The electric filter realizes the frequency selection function, and the electric amplifier makes the link obtain a stable gain, and generates a fundamental frequency signal after the oscillation condition is met.

(6) The other optical signal is controlled by polarization, the polarizer outputs the intensity modulation signal at the minimum point, the optical carrier is suppressed, and the double frequency microwave signal is obtained through the beating frequency of the photodetector.

(7) By changing the center frequency of the tunable electric bandpass filter, the frequency of the fundamental frequency signal changes, and at the same time, the double frequency microwave signal also changes accordingly.

The invention proposes a device capable of tunable double-frequency OEO. The scheme uses a phase modulator, a Sagnac ring and a polarizer, combined with a tunable electric filter, to realize a frequency-tunable OEO, and through another polarization control, a tunable double-frequency microwave signal is obtained. The device of the invention is simple and has strong practical operability.

Due to the use of the phase modulator, the present invention does not require an external DC bias voltage, which eliminates the problems caused by the drift of the bias point.

This scheme does not require an optical filter, and the tunability of the photoelectric oscillator can be realized by simply adjusting the voltage applied to the band-pass filter, and the tuning range is large, so that the generated double-frequency microwave signal has tunability and a wide tuning range larger.

Description of drawings

Fig. 1 is the schematic diagram of the present invention based on phase modulator and Sagnac ring's tunable double frequency OEO; Fig. 2 is the electric spectrum whole picture and the thumbnail of the fundamental frequency signal that photodetector 1 outputs, (a-d) is oscillation respectively Electrospectrograms when the frequency is 5GHz, 10GHz, 15GHz, and 20GHz; Figure 3 is the overall image and thumbnail of the electric spectrum of the double frequency signal output by the electric amplifier, (a-d) are the oscillation frequencies of 5GHz, 10GHz, 15GHz, and 20GHz, respectively When the electric spectrogram; Fig. 4 is the phase noise comparison diagram of the fundamental frequency signal and the double frequency signal.

detailed description

The embodiments of the present invention are described in detail below in conjunction with the accompanying drawings: this embodiment is implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operating procedures are provided, but the protection scope of the present invention is not limited to the following The described embodiment:

FIG. 1 is a schematic diagram of a tunable frequency-doubled OEO based on a phase modulator and a Sagnac ring in the present invention. As shown in Figure 1, in this embodiment, the device includes: a laser source, a polarization controller 1, a circulator, a polarization beam splitter, a phase modulator, a polarization controller 2, a polarizer 1, a polarization controller 3, a polarizer Polarizer 2, optical coupler, standard single-mode fiber, tunable bandpass filter, electrical phase shifter, electrical amplifier, photodetector 1, photodetector 2.

In this example, the specific implementation steps of the method are:

Step 1: The light source generates a continuous optical carrier wave with an operating wavelength of 1552.16nm, which is input to the port 1 of the circulator after passing through the polarization controller 1, and the optical signal output from the port 2 of the circulator enters the polarization beam splitter. Adjust the polarization controller 1 to make the two output optical powers of the polarization beam splitter equal.

Step 2: The optical signal from one port of the polarization beam splitter enters the phase modulator in the forward direction through the polarization-maintaining fiber to obtain phase modulation, and the optical signal output from the other port enters the phase modulator in the reverse direction through the polarization-maintaining fiber, and is not effectively modulated. Still an optical carrier. The forward modulated optical signal and the reverse optical carrier are combined into polarization multiplexed light at the polarization beam splitter, and output through port 3 of the circulator.

Step 3: Two optical signals output from the optical coupler, one of which passes through the polarization modulator 2 and then enters the polarizer 1, and the optical signals of the two polarization states are synthesized into a beam of polarized light at the polarizer, and then pass through 1.98km Long lengths of standard single-mode fiber. Photodetector 1 has a conversion gain of 600V/W, and the obtained electrical signal passes through a 30dB electrical amplifier, a tunable bandpass filter, and an electrical phase shifter, and then feeds back to the RF port of the phase modulator to form a photoelectric oscillator loop.

Step 4: The bandwidth of the tunable bandpass filter is about 50MHz. Adjust the voltage applied to the filter. The tuning range is within 3-20GHz. In the experiment, the center frequencies of 5GHz, 10GHz, 15GHz, and 20GHz were selected for testing . Adjust the polarization controller 2 so that the polarizer 1 outputs the modulation signal at the orthogonal point. Figure 2 (a-d) is the electrospectrogram of the fundamental frequency signals of 5GHz, 10GHz, 15GHz and 20GHz respectively. It can be seen that the obtained fundamental frequency signals are harmonic The wave suppression ratios are 47dB, 44dB, 36dB, 34dB respectively.

Step 5: Another optical signal output from the optical coupler enters the polarizer 2 after passing through the polarization modulator 3 . The maximum suppression of the optical carrier can be achieved by adjusting the polarization controller 3 . After being beat by the photodetector 2, a double frequency microwave signal is obtained. Figure 3(a-d) are the electric spectrograms of double frequency signals at 10GHz, 20GHz, 30GHz, and 40GHz respectively. It can be seen that the harmonic rejection ratios of double frequency signals are 38dB, 40dB, 40dB, and 45dB, respectively.

Step 6: Figure 4 (a-d) is the comparison of the phase noise of the 5GHz, 10GHz, 15GHz, and 20GHz fundamental frequency signals and the corresponding 10GHz, 20GHz, 30GHz, and 40GHz double frequency signals. Theoretically, the phase noise of the double frequency signals will attenuate 6dB, it can be seen from the figure that the difference between the experimental results is about 6dB.

To sum up, the present invention realizes frequency-tunable OEO by utilizing the phase modulator and the Sagnac ring. The structure is simple and easy to implement, the price is low, and it is not affected by electronic bottlenecks. The fundamental frequency signal and the double frequency microwave signal generated by the OEO have a large tuning range and low phase noise. In addition, due to the phase modulation technology, no additional DC bias circuit is required, and various problems caused by the drift of the DC bias point are eliminated, and the system stability is good.

In a word, the embodiments described above are only examples of the present invention, and are not only used to limit the protection scope of the present invention. The tuning range can be increased. The frequency range of the fundamental frequency signal generated by the photoelectric oscillator is not limited to 3-20GHz, and the frequency range of the double frequency signal is not limited to 6-40GHz. If the 3dB bandwidth of the photodetector is used, the tuning range can be larger . These equivalent modifications and replacements as well as the adjustment of the frequency range should also be regarded as the protection scope of the present invention.

Claims (5)

1. A tunable double frequency photoelectric oscillator device based on phase modulation, comprising a laser source, a polarization controller, a circulator, a polarization beam splitter, a phase modulator, an optical coupler, a polarizer, a photodetector, Electric amplifier, tunable electric filter, electric phase shifter and standard single-mode optical fiber, characterized in that: the circulator is on the outgoing optical path of the light source, and the polarization multiplexed light synthesized at the output polarization beam splitter is split by the optical coupler It is two signals with equal power, one of which is connected to the polarization controller, polarizer, single-mode fiber, photodetector, electric amplifier, tunable electric filter, electric phase shifter, and the output terminal of the electric phase shifter in turn. The RF port to the phase modulator constitutes the optoelectronic oscillator feedback link. The other path is sequentially connected to another polarization controller, polarizer, and photodetector to form a frequency-doubling link of the photoelectric oscillator. The two output ports of the polarization beam splitter are respectively connected to the input and output ports of the phase modulator to form a Sagnac ring. In the Sagnac ring, the optical signal passing through the modulator in the forward direction is phase-modulated, and the optical signal passing through the phase modulator in the reverse direction is not modulated. The phase modulated signal is combined with the unmodulated optical carrier at the polarization beam splitter. The Sagnac ring combined with the polarizer can be equivalent to an intensity modulator, and the working point of the intensity modulator can be changed by adjusting the polarization controller in front of the polarizer. In the feedback link of the photoelectric oscillator, by adjusting the polarization controller, an equivalent quadrature point modulation signal is obtained, and a pure fundamental frequency signal is obtained after photoelectric detection. In the double frequency link of the photoelectric oscillator, by adjusting the polarization controller, an equivalent minimum point modulation signal is obtained, the optical carrier is suppressed, and a pure double frequency signal is obtained after photoelectric detection. 2. The device of the tunable double-frequency photoelectric oscillator based on phase modulation according to claim 1 is characterized in that, by adjusting the passband frequency of the electric filter, the fundamental frequency can be changed, and then the double frequency frequency follows Change. 3 . The phase modulation-based tunable double-frequency photoelectric oscillator device according to claim 1 , wherein the modulator is a phase modulator, and no additional DC bias control circuit is needed. 4 . 4. The tunable double frequency photoelectric oscillator device based on phase modulation according to claim 1, characterized in that: a polarization controller is used in combination with a polarizer to make it equivalent to quadrature point modulation. 5. The device of the tunable double-frequency photoelectric oscillator based on phase modulation according to claim 1, characterized in that: utilize a polarization controller in conjunction with a polarizer to make it equivalent to minimum point modulation, by simply adjusting the polarization The controller suppresses the carrier to achieve frequency doubling.