Photo-production microwave method and device based on light injection semiconductor laser

Abstract

The invention discloses a photo-production microwave method based on a light injection semiconductor laser. An output optical signal of injecting the light in the single-period oscillation state into the semiconductor laser is transmitted through an optical fiber to generate an electric feedback signal, the electric feedback signal is used for performing electro-optical modulation on the injected light, and finally, the output optical signal is subjected to photoelectric detection to obtain a low-noise photo-generated microwave signal; the electric feedback signal generation method comprises the following steps: firstly, converting a transmitted output optical signal into an electric signal and dividing the electric signal into two paths; performing frequency division on the first electric signal to obtain a frequency-divided electric signal; performing feedback control adjustment on the phase of the second path of electric signal by taking the constant phase difference between the frequency division electric signal and a reference signal with the same frequency as a control target; and combining the second path of electric signal after feedback control adjustment with the reference signal into one path to obtain the electric feedback signal. The invention further discloses a photo-generated microwave device based on the light injection semiconductor laser. The frequency spectrum purity and the frequency stability of the signal can be effectively improved.

Description

Technical Field

[0001] This invention relates to a method for generating microwaves by light, and more particularly to a method and apparatus for generating microwaves by light-injected semiconductor lasers. Background Technology

[0002] Semiconductor lasers are devices that convert energy directly between electrons and photons through current injection excitation. Under external perturbations, semiconductor lasers can be excited into different nonlinear dynamic states. Optical injection, by introducing an external laser source as a perturbation, is injected into the semiconductor laser through an optical circulator, transforming the semiconductor laser from a free-running state to a nonlinear state. Optical injection offers advantages such as optical controllability, a wide frequency range, and flexible operation, and has gradually become the preferred method for exploring the nonlinear mechanisms of semiconductor lasers and generating microwave signals. However, due to the inherent noise of semiconductor lasers and the fact that optically injected semiconductor lasers are not strongly phase-locked systems, the generated microwave signals have a large linewidth. Furthermore, the injected laser exhibits certain frequency and power perturbations, further deteriorating the frequency stability of the generated signal. This significantly limits the practical application of microwave signals generated by optically injected semiconductor lasers in fields such as communication, radar, navigation, and test and measurement.

[0003] To address this issue, researchers have proposed a photogenerated microwave scheme based on photoelectric feedback and light-injected semiconductor lasers (T. Zhang). et al ., "Tunable Optoelectronic Oscillator Using FWM Dynamics of an Optical-Injected DFB Laser," IEEE Photonics Technology Letters , 2015,27(12): 1313-1316), the basic structure is as follows Figure 1 As shown, the output optical signal of a light-injected semiconductor laser operating in a single-cycle oscillation state is transmitted via optical fiber. The transmitted output optical signal is then photoelectrically converted into a feedback electrical signal, which is used to electro-optically modulate the injected light from the light-injected semiconductor laser. Finally, photoelectric detection is performed on the output optical signal of the light-injected semiconductor laser to obtain a low-noise optically generated microwave signal with significantly suppressed noise. This scheme utilizes energy storage components such as long optical fibers combined with electro-optic modulation to construct a delayed photoelectric feedback loop, which can improve the spectral purity of the signal. However, because the long optical fibers and other devices introduced in the loop are sensitive to external disturbances such as ambient temperature and oscillations, the frequency stability of the generated microwave signal is severely limited. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the existing optically injected semiconductor laser-based optical microwave generation scheme, and to provide an optically injected semiconductor laser-based optical microwave generation method that can effectively improve the spectral purity and frequency stability of the generated microwave signal.

[0005] The present invention specifically adopts the following technical solutions to solve the above-mentioned technical problems: A method for generating microwaves based on an optically injected semiconductor laser involves transmitting the output optical signal of the laser, which operates in a single-cycle oscillation state, via optical fiber. Then, an electrical feedback signal is generated from the transmitted output optical signal, and this feedback signal is used to electro-optically modulate the injected light from the laser. Finally, the output optical signal of the laser is photodetected to obtain a low-noise generated microwave signal. The specific method for generating the electrical feedback signal from the transmitted output optical signal is as follows: First, the output optical signal after optical fiber transmission is converted into an electrical signal and split into two paths; the first electrical signal is frequency-divided to obtain a frequency-divided electrical signal; the phase of the second electrical signal is adjusted by feedback control with the phase difference between the frequency-divided electrical signal and the reference signal of the same frequency remaining constant as the control target; the second electrical signal after feedback control adjustment is combined with the reference signal to obtain the electrical feedback signal.

[0006] Based on the same inventive concept, the following technical solutions can also be obtained: A photogenerated microwave device based on an optically injected semiconductor laser, comprising: The light-injected semiconductor laser operates in a single-cycle oscillation state; Optical fiber is used to transmit the output optical signal of an optically injected semiconductor laser. The electrical feedback module is used to generate an electrical feedback signal using the output optical signal transmitted through the optical fiber. An electro-optic modulator for electro-optically modulating the injected light of an optically injected semiconductor laser using the electrical feedback signal; The microwave signal output module is used to perform photoelectric detection on the output optical signal of the light-injected semiconductor laser to obtain a low-noise optically generated microwave signal; The electrical feedback module includes: A photodetector is used to convert the output optical signal transmitted through optical fiber into an electrical signal. The first power divider is used to split the electrical signal output by the photodetector into two paths; A frequency divider is used to divide the first electrical signal to obtain a frequency-divided electrical signal. Harmonic phase-locked loop (PLL) is used to perform feedback control and adjustment of the phase of a second electrical signal, with the control objective of keeping the phase difference between the frequency-divided electrical signal and a reference signal of the same frequency constant. The second power divider is used to combine the second electrical signal after feedback control adjustment with the reference signal into one channel, thus obtaining the electrical feedback signal.

[0007] Preferably, the harmonic phase-locked loop comprises: A frequency and phase detector is used to distinguish the frequency and phase of a frequency-divided electrical signal and a reference signal of the same frequency to obtain the phase difference signal between the two. A servo controller is used to generate feedback control signals with the goal of keeping the phase difference between the frequency-divided electrical signal and the reference signal constant. A voltage-controlled phase shifter is used to adjust the phase of the second electrical signal based on the feedback control signal.

[0008] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: This invention employs injection locking combined with harmonic phase-locked loop, which has a good noise suppression effect on optically generated microwave signals based on optically injected semiconductor lasers, and can significantly improve the linewidth, side-mode rejection ratio, phase noise and frequency stability of the generated microwave signals. Attached Figure Description

[0009] Figure 1 A schematic diagram of the structure and principle of an existing optically generated microwave scheme based on photoelectric feedback and optical injection semiconductor laser. Figure 2 This is a schematic diagram of a specific embodiment of the optically generated microwave device based on an optically injected semiconductor laser according to the present invention; Figure 3 This is a schematic diagram of the principle of the optically generated microwave device based on an optically injected semiconductor laser of the present invention; Figure 4 The spectrum of microwave signals generated by a traditional optically generated microwave scheme based on optically injected semiconductor lasers; Figure 5(a) and Figure 5(b) are the spectrum diagram and frequency drift diagram of the microwave signal generated by the existing photoelectric feedback-based optical injection semiconductor laser scheme, respectively. Figures 6(a) and 6(b) are the spectrum diagram and frequency drift diagram of the microwave signal generated by the optically generated microwave device based on the optically injected semiconductor laser of the present invention, respectively. Detailed Implementation

[0010] To address the problem of insufficient frequency stability in existing optically generated microwave schemes based on photoelectric feedback and optically injected semiconductor lasers, the present invention aims to improve upon these schemes by employing injection locking combined with a harmonic phase-locked loop to enhance the linewidth, side-mode rejection ratio, phase noise, and frequency stability of the generated microwave signal.

[0011] The present invention specifically adopts the following technical solutions to solve the above-mentioned technical problems: A method for generating microwaves based on an optically injected semiconductor laser involves transmitting the output optical signal of the laser, which operates in a single-cycle oscillation state, via optical fiber. Then, an electrical feedback signal is generated from the transmitted output optical signal, and this feedback signal is used to electro-optically modulate the injected light from the laser. Finally, the output optical signal of the laser is photodetected to obtain a low-noise generated microwave signal. The specific method for generating the electrical feedback signal from the transmitted output optical signal is as follows: First, the output optical signal after optical fiber transmission is converted into an electrical signal and split into two paths; the first electrical signal is frequency-divided to obtain a frequency-divided electrical signal; the phase of the second electrical signal is adjusted by feedback control with the phase difference between the frequency-divided electrical signal and the reference signal of the same frequency remaining constant as the control target; the second electrical signal after feedback control adjustment is combined with the reference signal to obtain the electrical feedback signal.

[0012] Based on the same inventive concept, the following technical solutions can also be obtained: A photogenerated microwave device based on an optically injected semiconductor laser, comprising: The light-injected semiconductor laser operates in a single-cycle oscillation state; Optical fiber is used to transmit the output optical signal of an optically injected semiconductor laser. The electrical feedback module is used to generate an electrical feedback signal using the output optical signal transmitted through the optical fiber. An electro-optic modulator for electro-optically modulating the injected light of an optically injected semiconductor laser using the electrical feedback signal; The microwave signal output module is used to perform photoelectric detection on the output optical signal of the light-injected semiconductor laser to obtain a low-noise optically generated microwave signal; The electrical feedback module includes: A photodetector is used to convert the output optical signal transmitted through optical fiber into an electrical signal. The first power divider is used to split the electrical signal output by the photodetector into two paths; A frequency divider is used to divide the first electrical signal to obtain a frequency-divided electrical signal. Harmonic phase-locked loop (PLL) is used to perform feedback control and adjustment of the phase of a second electrical signal, with the control objective of keeping the phase difference between the frequency-divided electrical signal and a reference signal of the same frequency constant. The second power divider is used to combine the second electrical signal after feedback control adjustment with the reference signal into one channel, thus obtaining the electrical feedback signal.

[0013] Preferably, the harmonic phase-locked loop comprises: A frequency and phase detector is used to distinguish the frequency and phase of a frequency-divided electrical signal and a reference signal of the same frequency to obtain the phase difference signal between the two. A servo controller is used to generate feedback control signals with the goal of keeping the phase difference between the frequency-divided electrical signal and the reference signal constant. A voltage-controlled phase shifter is used to adjust the phase of the second electrical signal based on the feedback control signal.

[0014] To facilitate public understanding, the technical solution of the present invention will be described in detail below through a specific embodiment and in conjunction with the accompanying drawings: like Figure 2 As shown, the optically generated microwave device based on an optically injected semiconductor laser in this embodiment includes: a master laser, an optical circulator, a slave laser, an optical fiber, two photodetectors, two power dividers, an electric amplifier, a frequency divider, a microwave source, a frequency and phase detector, a servo controller, a voltage-controlled phase shifter, and an electro-optic modulator; wherein the frequency and phase detector, the servo controller, and the voltage-controlled phase shifter constitute a harmonic phase-locked loop.

[0015] The main laser outputs a continuous optical signal with a frequency of f m The light is injected into the slave laser through an optical circulator. The slave laser has a free resonant frequency of . f s Semiconductor lasers exhibit rich nonlinear dynamic states when subjected to external disturbances. By controlling the injection parameters to keep the laser in a single-cycle oscillation state, the output spectrum of the laser includes the injected regenerated signal. f m and redshift signal f s’ The redshift phenomenon is due to the consumption of charge carriers within the cavity under light injection conditions, causing a change in the refractive index of the gain medium, which in turn leads to a change in the cavity resonant wavelength from [the previous wavelength]. f s Redshift to f s’ The optical signal output from the laser is transmitted through optical fiber and then converted by a photodetector to produce a signal with a frequency of [frequency value missing]. f o ( f o = f m - f s The signal is a noisy microwave signal. It is then amplified by an amplifier and split into two paths by a power divider. One path is then divided by a frequency divider to output a frequency of... f o The harmonic signal is / N (where N is the division ratio of the frequency divider, and N is a positive integer). At this time, the frequency of the reference signal output by the microwave source is also set to... fo / N, along with the harmonic signal output from the frequency divider, is simultaneously sent to the frequency and phase detector to obtain the phase difference signal. This phase difference signal is then fed back to the servo controller. The servo controller generates a feedback control signal with the goal of maintaining a constant phase difference, which in turn controls the voltage-controlled phase shifter to adjust the phase of the other electrical signal output from the power divider in real time. This other electrical signal, after feedback control adjustment by the voltage-controlled phase shifter, is combined with the reference signal output from the microwave source and fed back to the RF port of the electro-optic modulator. The electro-optic modulator performs electro-optic modulation on the injected optical signal. At this time, the regenerated carrier signal injected from the laser cavity will generate a series of modulation sidebands, such as... Figure 3 As shown, the Nth-order sideband is related to the redshift sideband in the frequency domain. f s’ By getting close enough, injection locking can be achieved, thus enabling noise suppression and frequency stability improvement of the generated microwave signal.

[0016] To demonstrate the effectiveness of the technical solution of this invention, experimental verification was conducted on the aforementioned photogenerated microwave device. When the delay photoelectric feedback loop and harmonic phase-locked loop are disconnected, the system operates as a traditional photogenerated microwave scheme based on an optically injected semiconductor laser, and the generated microwave signal spectrum is as follows: Figure 4 As shown, the signal frequency is 19.52 GHz, and a large 3 dB linewidth, on the order of MHz, can be observed. When the delayed photoelectric feedback loop is closed and the harmonic phase-locked loop is opened, i.e., the microwave source does not output a signal, the system is a photoelectric microwave scheme based on photoelectric feedback and optical injection semiconductor laser. The spectrum of the generated microwave signal is shown in Figure 5(a). The signal linewidth is significantly narrowed, but due to the presence of the long fiber loop, the generated microwave signal has a large side-mode rejection ratio, which is measured to be 13.87 dB. The frequency drift of the peak frequency of the generated signal during the measurement time was measured using the "Max Hold" function of the spectrum analyzer, as shown in Figure 5(b). It can be seen that the generated microwave signal drifted by about 18 kHz during the 10-minute measurement time.

[0017] By closing the time-delay photoelectric feedback loop and connecting it to a harmonic injection phase-locked loop, the photogenerated microwave scheme of this invention is formed. A division ratio of 4 is selected for the frequency divider, and the microwave source output signal frequency is 4.88 GHz. The spectrum of the generated microwave signal is shown in Figure 6(a). The measured signal side-mode rejection ratio is 95.11 dB, an improvement of 81.24 dB compared to the experimental results without the harmonic injection phase-locked loop. Figure 6(b) shows the frequency drift of the signal peak frequency over a 30-minute measurement period. The frequency shift is <1 Hz, demonstrating that the proposed structure can improve the frequency stability of the photogenerated microwave signal based on the light-injected semiconductor laser.

Claims

1. A method for generating microwaves based on an optically injected semiconductor laser, comprising: transmitting the output optical signal of the optically injected semiconductor laser operating in a single-cycle oscillation state via an optical fiber; then generating an electro-feedback signal using the output optical signal transmitted through the optical fiber; using the electro-feedback signal to electro-optically modulate the injected light of the optically injected semiconductor laser; and finally performing photoelectric detection on the output optical signal of the optically injected semiconductor laser to obtain a low-noise optically generated microwave signal; characterized in that... The specific method for generating an electrical feedback signal using the output optical signal transmitted through optical fiber is as follows: First, the output optical signal after optical fiber transmission is converted into an electrical signal and split into two paths; the first electrical signal is divided into frequencies to obtain a frequency-divided electrical signal; the phase of the second electrical signal is adjusted by feedback control with the phase difference between the frequency-divided electrical signal and a reference signal of the same frequency remaining constant as the control target. The second electrical signal, after feedback control adjustment, is combined with the reference signal to obtain the electrical feedback signal.

2. A photogenerated microwave device based on an optically injected semiconductor laser, comprising: The light-injected semiconductor laser operates in a single-cycle oscillation state; Optical fiber is used to transmit the output optical signal of an optically injected semiconductor laser. The electrical feedback module is used to generate an electrical feedback signal using the output optical signal transmitted through the optical fiber. An electro-optic modulator for electro-optically modulating the injected light of an optically injected semiconductor laser using the electrical feedback signal; The microwave signal output module is used to perform photoelectric detection on the output optical signal of the light-injected semiconductor laser to obtain a low-noise optically generated microwave signal; The electrical feedback module is characterized in that it comprises: A photodetector is used to convert the output optical signal transmitted through optical fiber into an electrical signal. The first power divider is used to split the electrical signal output by the photodetector into two paths; A frequency divider is used to divide the first electrical signal to obtain a frequency-divided electrical signal. Harmonic phase-locked loop (PLL) is used to perform feedback control and adjustment of the phase of a second electrical signal, with the control objective of keeping the phase difference between the frequency-divided electrical signal and a reference signal of the same frequency constant. The second power divider is used to combine the second electrical signal after feedback control adjustment with the reference signal into one channel, thus obtaining the electrical feedback signal.

3. The photogenerated microwave device based on an optically injected semiconductor laser as described in claim 2, characterized in that, The harmonic phase-locked loop includes: A frequency and phase detector is used to distinguish the frequency and phase of a frequency-divided electrical signal and a reference signal of the same frequency to obtain the phase difference signal between the two. A servo controller is used to generate feedback control signals with the goal of keeping the phase difference between the frequency-divided electrical signal and the reference signal constant. A voltage-controlled phase shifter is used to adjust the phase of the second electrical signal based on the feedback control signal.

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