Phase sensitive preamplification method based on electroabsorption modulated laser

Abstract

The application discloses a phase-sensitive pre-amplification method based on an electro-absorption modulated laser, and is applied to a star-ground laser communication system receiving end. A distributed feedback laser in the electro-absorption modulated laser amplifies weak pump light after long distance transmission, and generates idler light under the nonlinear effect of a laser cavity; an electro-absorption modulator in the electro-absorption modulated laser detects phase error information between signal light, pump light and idler light, and constructs an optical injection phase-locked loop through a feedback loop, so that stable control of the three-wave phase relationship is realized. Under the phase stability condition, the output light of the electro-absorption modulated laser is fed into a later-stage nonlinear medium to complete phase-sensitive pre-amplification. The phase-sensitive pre-amplification method based on the electro-absorption modulated laser has the advantages of simple structure and easy integration, can realize pump light amplification, idler light generation and phase error suppression under the condition of weak pump light, and effectively improves the receiving sensitivity performance of the star-ground laser communication system.

Description

Technical Field

[0001] This invention relates to the field of space optical communication, and more particularly to a phase-sensitive preamplification method based on an electro-absorption modulated laser. Background Technology

[0002] Space-to-ground laser communication boasts advantages such as high bandwidth, strong security, and robust anti-interference capabilities, making it a crucial component of future space information networks. However, signals experience significant power attenuation and phase jitter when traversing the atmosphere, highlighting the growing need for highly sensitive detection of optical signals at receivers under extremely low signal-to-noise ratio conditions. Traditional erbium-doped fiber amplifiers or semiconductor optical amplifiers, when used as preamplifiers, are limited by the 3 dB quantum noise limit, making them unsuitable for the demands of high-sensitivity space-to-ground laser communication. Phase-sensitive amplifiers can achieve lower noise amplification performance while maintaining a specific phase relationship between the signal light, pump light, and idler light; however, they struggle to operate stably under conditions of severe pump light attenuation.

[0003] Existing technologies often employ external high-power local oscillator lasers or complex optical phase-locked loop structures to recover pump light and achieve phase locking. These systems are complex, have low integration, are heavy, and consume a lot of power, making it difficult to meet the size, weight, and power requirements of satellite payloads. Summary of the Invention

[0004] In view of the aforementioned shortcomings of the prior art, the technical problem to be solved by the present invention is that existing phase-sensitive amplification methods are complex in structure, low in integration, heavy in weight, and high in power consumption. Therefore, the present invention provides a phase-sensitive pre-amplification method based on an electro-absorption modulated laser, which has the advantages of simple structure and easy integration. It can realize pump light amplification, idler light generation, and phase error suppression under weak pump light conditions, thereby improving the receiving sensitivity performance of the satellite-to-ground laser communication system. By inserting a virtual carrier at the transmitting end to generate pump light coherent with the signal light, and using an electro-absorption modulated laser at the receiving end to realize pump light amplification, idler light generation, and light injection into a phase-locked loop, a stable phase condition is provided for subsequent phase-sensitive amplification, achieving small size, lightweight, low power consumption, and low noise phase-sensitive pre-amplification.

[0005] To achieve the above objectives, the present invention provides a phase-sensitive preamplification method based on an electro-absorption modulated laser, which is applied to a satellite-to-ground laser communication system. The satellite-to-ground laser communication system includes a signal generation module, a digital-to-analog conversion module, an electro-optic modulation module, a preamplification module, a photoelectric detection module, an analog-to-digital conversion module, and a digital processing module.

[0006] The signal generation module generates a modulated signal in the digital domain and inserts a virtual carrier. The digital-to-analog conversion module converts the digital signal into an analog signal. The electro-optic modulation module modulates the analog signal onto the optical carrier. The preamplifier module uses an electro-absorption modulated laser and a highly nonlinear optical fiber to achieve phase-sensitive preamplification. The photoelectric detection module converts the phase-sensitive preamplified optical signal into an electrical signal. The analog-to-digital conversion module samples the analog signal and converts it into a digital signal. The digital processing module demodulates the digital signal.

[0007] Furthermore, a phase-sensitive preamplification method based on an electro-absorption modulated laser, executed by the preamplification module of a satellite-to-ground laser communication system, includes the following steps:

[0008] Step 1: At the receiving end, the received optical signal containing the signal light and pump light is injected into the electro-absorption modulated laser in the preamplifier module. The electro-absorption modulated laser consists of a distributed feedback laser and an electro-absorption modulator.

[0009] Step 2: By adjusting the bias current and operating temperature of the distributed feedback laser, it is locked to the pump light frequency, thereby amplifying the pump light;

[0010] Step 3: In the injection-locked state, the nonlinear effect of the distributed feedback laser is used to generate an idler light that is phase-locked with the signal light;

[0011] Step 4: Detect the multi-frequency optical field output by the distributed feedback laser using an electro-absorption modulator, and extract the phase error signal between the signal light and the pump light;

[0012] Step 5: After the phase error signal is down-converted and filtered, it is fed back to the bias current port of the distributed feedback laser to construct an optical injection phase-locked loop and eliminate the phase error;

[0013] Step 6: Under the condition of stable locking of the optical injection phase-locked loop, feed the output light of the electro-absorption modulated laser into the subsequent nonlinear medium in the preamplifier module to realize phase-sensitive preamplification of the signal light.

[0014] Furthermore, in step one, the distributed feedback laser and the electro-absorption modulator are integrated in a monolithic manner to form an electro-absorption modulated laser.

[0015] Furthermore, in step two, the locking range of the injection lock is determined by the injection power of the pump light and the frequency detuning between the pump light frequency and the free oscillation frequency of the distributed feedback laser.

[0016] Furthermore, in step three, the nonlinear effect refers to the four-wave mixing effect that occurs between the pump light and the signal light in the resonant cavity of the distributed feedback laser, which is a nonlinear medium, thereby exciting the generation of harmonic components as idler light.

[0017] Furthermore, in step four, the electroabsorption modulator utilizes the quantum-confined Stark effect for photoelectric conversion and detects the phase error signal between the signal light and the pump light in real time.

[0018] Furthermore, in step five, the feedback signal adjusts the bias current of the distributed feedback laser using a proportional-integral-derivative control algorithm or its equivalent control algorithm.

[0019] Furthermore, in step six, the subsequent nonlinear medium includes highly nonlinear optical fiber or integrated nonlinear optical waveguide.

[0020] Furthermore, the output of the distributed feedback laser is:

[0021]

[0022] in, For signal amplitude, The ratio of the frequency difference between the master laser and the slave laser to the maximum frequency offset that satisfies the locking condition. It is an intermediate variable, and its value is... , Main laser frequency, The beat frequency between the master laser and the slave laser. This is phase noise.

[0023] Furthermore, by down-converting and low-pass filtering the output electrical signal of the electroabsorption modulator, the phase error signal between the three waves is extracted. The phase error signal is processed by the proportional-integral-derivative control algorithm and then fed back to the bias current port of the DFB laser to construct an optical injection phase-locked loop, thereby realizing dynamic tracking and compensation of phase drift and maintaining a stable phase relationship between the signal light, pump light and idler light.

[0024] Technical effect

[0025] This invention provides a phase-sensitive preamplification method based on an electro-absorption modulated laser, which achieves phase-sensitive preamplification suitable for space-to-ground laser communication without requiring an external high-power pump source or complex local oscillator structure. It utilizes an electro-absorption modulated laser to simultaneously achieve pump amplification, idler generation, and phase error detection, offering advantages such as compact structure and ease of integration. An optical injection phase-locked loop effectively suppresses phase drift between the pump light and the signal light, improving the stability of the phase-sensitive amplification. Under weak signal reception conditions, it significantly reduces the equivalent noise at the receiver, enhancing the receiving sensitivity of the space-to-ground laser communication system.

[0026] The following will further explain the concept, specific structure, and technical effects of the present invention in conjunction with the accompanying drawings, so as to fully understand the purpose, features, and effects of the present invention. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of a free-space laser communication transmission system based on a phase-sensitive preamplification method of an electro-absorption modulated laser, according to a preferred embodiment of the present invention.

[0028] Figure 2 This is a schematic diagram of a free-space laser communication transmission device based on a phase-sensitive preamplification method of an electro-absorption modulated laser, according to a preferred embodiment of the present invention.

[0029] Figure 3 This is a schematic diagram of the principle structure of an electroabsorption modulated laser based on a phase-sensitive preamplification method of an electroabsorption modulated laser, according to a preferred embodiment of the present invention.

[0030] Figure 4 This is a preferred embodiment of the present invention, which describes the input and output signals of an electroabsorption modulated laser based on a phase-sensitive preamplification method for an electroabsorption modulated laser.

[0031] Figure 5 This is a schematic diagram of the complete phase-sensitive preamplification process of a phase-sensitive preamplification method based on an electro-absorption modulated laser, which is a preferred embodiment of the present invention. Detailed Implementation

[0032] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0033] In the following description, specific details, such as particular internal procedures and techniques, are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of the invention. However, those skilled in the art will appreciate that the invention may be practiced in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods have been omitted so as not to obscure the description of the invention with unnecessary detail.

[0034] This invention provides a phase-sensitive preamplification method based on an electrically absorbed modulated laser, applicable to satellite-to-ground laser communication systems. For example... Figure 1 As shown, the satellite-to-ground laser communication system includes a signal generation module, a digital-to-analog conversion module, an electro-optic modulation module, a preamplifier module, a photoelectric detection module, an analog-to-digital conversion module, and a digital processing module.

[0035] At the transmitting end, a signal generation module generates a modulated signal in the digital domain and inserts a virtual carrier. A digital-to-analog converter (DAC) module converts the digital signal into an analog signal. An electro-optic modulation module modulates the analog signal onto an optical carrier, and the resulting signal light and pump light are transmitted in a free-space laser link. At the receiving end, a preamplifier module uses an electro-absorption modulated laser and a highly nonlinear fiber to achieve phase-sensitive preamplification. A photodetector module converts the phase-sensitive preamplified optical signal into an electrical signal. An analog-to-digital converter (ADC) samples the analog signal and converts it into a digital signal. A digital processing module demodulates the digital signal.

[0036] In this embodiment of the invention, a phase-sensitive preamplification method based on an electro-absorption modulated laser, executed by the preamplification module of a satellite-to-ground laser communication system, includes the following steps:

[0037] Step 1: At the receiving end, the received optical signal containing the signal light and pump light is injected into the electro-absorption modulated laser in the preamplifier module. The electro-absorption modulated laser is composed of a distributed feedback laser and an electro-absorption modulator. The distributed feedback laser and the electro-absorption modulator are integrated in a monolithic manner to form the electro-absorption modulated laser.

[0038] Step 2: By adjusting the bias current and operating temperature of the distributed feedback laser, it is locked to the pump light frequency, thereby amplifying the pump light. The locking range is determined by the injection power of the pump light and the frequency detuning between the pump light frequency and the free oscillation frequency of the distributed feedback laser.

[0039] Step 3: In the injection-locked state, the nonlinear effect of the distributed feedback laser is used to generate idler light that is phase-locked with the signal light; the nonlinear effect refers to the four-wave mixing effect of the pump light and the signal light in the resonant cavity of the distributed feedback laser, which is a nonlinear medium, to excite the generation of harmonic components as idler light.

[0040] Step 4: The multi-frequency optical field output by the distributed feedback laser is detected by an electro-absorption modulator to extract the phase error signal between the signal light and the pump light; the electro-absorption modulator uses the quantum-confined Stark effect for photoelectric conversion and detects the phase error signal between the signal light and the pump light in real time.

[0041] Step 5: After the phase error signal is down-converted and filtered, it is fed back to the bias current port of the distributed feedback laser to construct an optical injection phase-locked loop and eliminate the phase error; the feedback signal is used to adjust the bias current of the distributed feedback laser through a proportional-integral-derivative control algorithm or its equivalent control algorithm.

[0042] Step 6: Under the condition of stable locking of the optical injection phase-locked loop, the output light of the electro-absorption modulated laser is fed into the subsequent nonlinear medium in the preamplifier module to realize phase-sensitive preamplification of the signal light; the subsequent nonlinear medium includes highly nonlinear optical fiber or integrated nonlinear optical waveguide.

[0043] Specifically, such as Figure 2 The diagram shown is a schematic of a free-space laser communication transmission device according to an embodiment of the present invention. At the transmitting end, an arbitrary waveform generator (AWG) generates a modulation signal and a virtual carrier, which are then modulated onto the optical carrier emitted by a tunable semiconductor laser (TSL) via an IQ modulator (IQM), thereby generating signal light and pump light. After transmission through the free-space laser link, the received optical signal containing the signal light and pump light is injected into an electrically absorbed modulated laser (EML) through an optical circulator (OC). The EML simultaneously amplifies the pump light, generates idler light, and detects phase error. Specifically, the pump light is amplified using the injection-locked characteristic of the distributed feedback laser in the EML; in the injection-locked state, the nonlinear effect of the distributed feedback laser generates idler light that is phase-locked with the signal light; the output of the distributed feedback laser is detected by the electrically absorbed modulator in the EML, the phase error signal between the signal light and the pump light is extracted, and it is fed back to the bias current port of the distributed feedback laser to construct an optical injection phase-locked loop (OPILL) and eliminate the phase error. The output of the EML is fed into a highly nonlinear fiber (HNLF) via an optical circulator, thereby achieving phase-sensitive preamplification. An integrated coherent receiver (ICR) performs coherent detection on the received signal after passing through an optical bandpass filter (OBPF), a digital real-time oscilloscope (DSO) performs analog-to-digital conversion on the probe signal, and finally, digital signal processing (DSP) demodulates the acquired signal.

[0044] like Figure 3 The diagram shows a schematic of the EML optical injection phase-locked loop structure according to an embodiment of the present invention. The received optical signal is optically coupled and injected into the electro-absorption modulated laser in the preamplifier module. The electro-absorption modulated laser consists of a distributed feedback laser and an electro-absorption modulator, both fabricated monolithically on the same semiconductor substrate. In this embodiment, by adjusting the bias current and operating temperature of the distributed feedback laser, the pump light frequency in the received optical signal is made close to the oscillation frequency of the distributed feedback laser. Under the action of the pump light, the distributed feedback laser enters a locked state, thereby realizing the recovery and amplification of the weak pump light after long-distance transmission. The signal light (S) and pump light (P) in the received optical signal propagate together in the resonant cavity of the distributed feedback laser. Due to the nonlinear effect of the semiconductor gain medium, an idler light (I) phase-locked with the signal light is generated, and the signal light is also amplified by the gain medium. The output of the distributed feedback laser is:

[0045]

[0046] in, For signal amplitude, The ratio of the frequency difference between the master laser and the slave laser to the maximum frequency offset that satisfies the locking condition. It is an intermediate variable, and its value is... , Main laser frequency, The beat frequency between the master laser and the slave laser. This is phase noise. Therefore, the output of a distributed feedback laser includes not only its own oscillation signal but also the injected signal and its harmonic components, with all spectral components having a frequency interval of 1. This results in a multi-frequency optical field at the output of the distributed feedback laser, comprising amplified signal light, amplified pump light, and phase-locked idler light.

[0047] like Figure 4 As shown, (a) and (b) are the spectra of the input and output signals of the electro-absorption modulated laser according to an embodiment of the present invention, respectively. The input signal includes pump light and signal light. Since the oscillation frequency of the distributed feedback laser is 193.42 THz, the frequency of the pump light is set to 193.42 THz, and the frequency interval between the signal light and the pump light is set to 5 GHz. The output light signal includes the pump light and signal light amplified by the laser gain medium, as well as the idler light generated under the nonlinear effect of the laser cavity. The measured spectra of the input and output signals of the electro-absorption modulated laser are consistent with the theoretical analysis.

[0048] Subsequently, the electroabsorption modulator in the EML performs direct photoelectric detection on the multi-frequency optical field, obtaining an electrical signal formed by the beat of the signal light, pump light, and idler light. The output of the electroabsorption modulator can be expressed as:

[0049]

[0050] This is the normalized intensity ratio between the pump light and the signal light or idler light. This refers to the angular frequency of the signal light or idler light. By down-converting and low-pass filtering (LPF) the output electrical signal of the electroabsorption modulator, the phase error signal between the three waves can be extracted. The phase error signal is processed by a proportional-integral-derivative (PID) control algorithm and then fed back to the bias current port of the DFB laser, thereby constructing an optical injection phase-locked loop to achieve dynamic tracking and compensation of phase drift, and maintain a stable phase relationship between the signal light, pump light and idler light.

[0051] like Figure 5The diagram shown illustrates the complete process of phase-sensitive preamplification based on an electro-absorption modulated laser according to an embodiment of the present invention. After the EML optical injection phase-locked loop is stably locked, the output optical signal of the electro-absorption modulated laser is fed into a highly nonlinear fiber. The output optical signal includes amplified signal light (S), amplified pump light (P), and phase-locked idler light (I). Under the condition of satisfying the phase matching condition, the three components undergo a four-wave mixing effect in the nonlinear medium, and the signal light obtains phase-related gain, realizing phase-sensitive preamplification. In a typical implementation, the phase-sensitive gain of the signal light is:

[0052]

[0053] The maximum gain under phase-matching conditions. The minimum gain when it is orthogonal to it. This refers to the relative phase between the pump light, signal light, and idler light.

[0054] After phase-sensitive preamplification, the signal light is filtered out by an optical bandpass filter, then fed into a coherent receiver for photoelectric conversion, and finally demodulated by an analog-to-digital converter and digital processing module.

[0055] As can be seen from the above embodiments, the present invention can complete pump light amplification, idler light generation and phase error detection using a monolithic integrated electro-absorption modulated laser. The stability of the phase-sensitive preamplifier is ensured by the optical injection phase-locked loop. It has the advantages of compact structure and easy integration, and is suitable for weak signal receiving application scenarios such as satellite-to-ground laser communication.

[0056] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A phase-sensitive preamplification method based on an electro-absorption modulated laser, characterized in that, This technology is applied to a satellite-to-ground laser communication system, which includes a signal generation module, a digital-to-analog conversion module, an electro-optic modulation module, a preamplifier module, a photoelectric detection module, an analog-to-digital conversion module, and a digital processing module. The signal generation module generates a modulated signal in the digital domain and inserts a virtual carrier. The digital-to-analog converter converts the digital signal into an analog signal. The electro-optic modulation module modulates the analog signal onto an optical carrier. The preamplifier uses an electro-absorption modulated laser and a highly nonlinear optical fiber to achieve phase-sensitive preamplification. The photoelectric detection module converts the phase-sensitive preamplified optical signal into an electrical signal. The analog-to-digital converter samples the analog signal and converts it into a digital signal. The digital processing module demodulates the digital signal.

2. The phase-sensitive preamplification method based on an electro-absorption modulated laser as described in claim 1, characterized in that, Performed by the preamplifier module of the aforementioned satellite-to-ground laser communication system, the steps include: Step 1: At the receiving end, the received optical signal containing the signal light and the pump light is injected into the electro-absorption modulated laser in the preamplifier module. The electro-absorption modulated laser is composed of a distributed feedback laser and an electro-absorption modulator. Step 2: By adjusting the bias current and operating temperature of the distributed feedback laser, it is locked to the pump light frequency, thereby amplifying the pump light; Step 3: In the injection-locked state, the nonlinear effect of the distributed feedback laser is used to generate idler light that is phase-locked with the signal light; Step 4: Detect the multi-frequency optical field output by the distributed feedback laser using the electro-absorption modulator, and extract the phase error signal between the signal light and the pump light; Step 5: After the phase error signal is down-converted and filtered, it is fed back to the bias current port of the distributed feedback laser to construct an optical injection phase-locked loop and eliminate the phase error; Step Six: Under the condition that the optical injection phase-locked loop is stably locked, the output light of the electro-absorption modulated laser is fed into the subsequent nonlinear medium in the preamplifier module to realize phase-sensitive preamplification of the signal light.

3. The phase-sensitive preamplification method based on an electro-absorption modulated laser as described in claim 2, characterized in that, In step one, the distributed feedback laser and the electro-absorption modulator are integrated in a monolithic manner to form an electro-absorption modulated laser.

4. The phase-sensitive preamplification method based on an electro-absorption modulated laser as described in claim 2, characterized in that, In step two, the locking range of the injection lock is determined by the injection power of the pump light and the frequency detuning between the pump light frequency and the free oscillation frequency of the distributed feedback laser.

5. The phase-sensitive preamplification method based on an electro-absorption modulated laser as described in claim 2, characterized in that, In step three, the nonlinear effect refers to the four-wave mixing effect that occurs between the pump light and the signal light in the resonant cavity of the distributed feedback laser, which is a nonlinear medium, to excite harmonic components as idler light.

6. The phase-sensitive preamplification method based on an electro-absorption modulated laser as described in claim 2, characterized in that, In step four, the electroabsorption modulator uses the quantum-confined Stark effect for photoelectric conversion and detects the phase error signal between the signal light and the pump light in real time.

7. The phase-sensitive preamplification method based on an electro-absorption modulated laser as described in claim 2, characterized in that, In step five, the feedback signal is used to adjust the bias current of the distributed feedback laser through a proportional-integral-derivative control algorithm or its equivalent control algorithm.

8. The phase-sensitive preamplification method based on an electro-absorption modulated laser as described in claim 2, characterized in that, In step six, the subsequent nonlinear medium includes highly nonlinear optical fiber or integrated nonlinear optical waveguide.

9. The phase-sensitive preamplification method based on an electro-absorption modulated laser as described in claim 5, characterized in that, The output of the distributed feedback laser is: ， in, For signal amplitude, The ratio of the frequency difference between the master laser and the slave laser to the maximum frequency offset that satisfies the locking condition. It is an intermediate variable, and its value is... , Main laser frequency, The beat frequency between the master laser and the slave laser. This is phase noise.

10. The phase-sensitive preamplification method based on an electro-absorption modulated laser as described in claim 7, characterized in that, By performing down-conversion and low-pass filtering on the output electrical signal of the electroabsorption modulator, the phase error signal between the three waves is extracted. The phase error signal is processed by the proportional-integral-derivative control algorithm and then fed back to the bias current port of the DFB laser to construct an optical injection phase-locked loop, thereby realizing dynamic tracking and compensation of phase drift and maintaining a stable phase relationship between the signal light, pump light and idler light.

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