Real-time active optical phase locking system

Abstract

A real-time active optical phase locking system includes: a signal light source; a reference light source; a frequency modulator; an equal-arm interferometer; a polarization photodetector for receiving the interference signal between the signal light and the reference light and converting the optical signal into an electrical signal; a phase detection circuit for detecting the phase difference between the signal light and the reference light; a feedback circuit for promptly feeding back the electrical signal generated by the phase difference to a phase adjuster; and the phase adjuster adjusts the phase via control by the feedback circuit. The present invention is resistant to light source intensity jitter, polarization jitter noise, and detection efficiency noise, is applicable to a variety of light sources, and can be widely used in scenarios requiring optical phase locking.

Description

Technical Field

[0001] The present invention relates to the field of photoelectric control, and in particular to a real-time active optical phase locking system suitable for optical fiber communication, optical quantum information, photoelectric signal processing and other fields. Background Art

[0002] Optical phase locking is a technique used in coherent optical communications, quantum communications, and quantum computing. Phase locking is a technique in which the phase of a controlled oscillator is controlled by a standard or external signal, achieving phase synchronization with the external signal or tracking its frequency or phase. Phase locking, short for phase lock, refers to the phase synchronization between two signals. The most critical technology is the phase-locked loop (PLL). This is a negative feedback control system that uses a voltage generated by phase synchronization to adjust a voltage-controlled oscillator to produce a target phase. This is a typical feedback control circuit that uses an external reference signal to control the phase of the oscillating signal within the loop, automatically tracking the output signal's phase to that of the input signal. It is typically used in closed-loop tracking circuits. Existing optical phase locking techniques are affected by light intensity noise, polarization noise, and detection efficiency noise, resulting in inaccurate phase acquisition and making active, real-time optical phase locking difficult to achieve. Summary of the Invention

[0003] In view of this, the main object of the present invention is to provide a real-time active phase locking system, in order to partially solve at least one of the above technical problems.

[0004] In order to achieve the above object, as one aspect of the present invention, a real-time active phase locking system is provided, comprising:

[0005] signal light source;

[0006] Reference light source;

[0007] Frequency modulator;

[0008] equal-arm interferometer;

[0009] A polarization photodetector, used to receive the interference signal between the signal light and the reference light, and convert the optical signal into an electrical signal;

[0010] A phase detection circuit for detecting the phase difference between the signal light and the reference light;

[0011] A feedback circuit is used to feed back the electrical signal generated by the phase difference to the phase regulator in a timely manner;

[0012] The phase regulator adjusts the phase through the feedback circuit.

[0013] The signal light source includes: a continuous laser light source, a pulsed laser light source, a collinear or non-collinear parametric down-conversion crystal light source pumped by a pulsed laser or a continuous laser, and a collinear or non-collinear parametric up-conversion crystal light source pumped by a pulsed laser or a continuous laser.

[0014] Wherein, the reference light source includes: a continuous laser light source or a pulsed laser light source.

[0015] Wherein, the phase locking system further includes reference light, and the reference light and the reference light come from the same reference light source or light sources whose phases are locked to each other.

[0016] The equal-arm interferometer can separate the signal light and the reference light, and includes a reflector, a translation device, piezoelectric ceramics, and a regulator. The working process of the equal-arm interferometer is as follows:

[0017] An optical path difference adjustment mirror, a translation device for adjusting the position of the reflector, a piezoelectric ceramic driven reflector for fine-tuning the optical path, and a piezoelectric ceramic driven optical fiber stretching adjuster for fine-tuning the optical path.

[0018] The polarization photodetector includes a polarization controller, a fiber polarization beam splitter, and a photoelectric signal converter. The polarization photodetector can only retain the coherent parts of the interfering signal light and parametric light and remove the irrelevant parts.

[0019] The phase detection circuit further includes the following functions:

[0020] Convert continuous analog signals into discrete digital signals;

[0021] The microcontroller reads the phase change to obtain the phase difference between the signal light and the reference light.

[0022] The feedback circuit also includes the following functions: performing high-precision PID feedback on the circuit signal, outputting voltage in real time, and controlling the phase regulator.

[0023] The phase adjuster includes a free space phase adjuster or an optical fiber phase adjuster, and the phase adjuster adjusts the phase under the control of a feedback circuit.

[0024] Based on the above technical solution, it can be seen that the real-time active phase locking system of the present invention has at least one or part of the following beneficial effects compared with the prior art:

[0025] The real-time active optical phase locking system provided by the present invention can be used in large-scale optical signal phase locking scenarios. The present invention can resist light source intensity jitter, polarization jitter noise, and detection efficiency noise, is applicable to a variety of different light sources, and can be widely used in scenarios requiring optical phase locking. The present invention is easy to adjust and facilitates expansion, and can be applied to coherent optical communication, optical quantum communication, quantum computing, and other application fields. When the present invention is applied to a system requiring optical phase locking, phase locking between multiple optical paths can be achieved without being affected by light intensity noise, polarization noise, and detection efficiency noise. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The figure schematically shows a design diagram of a real-time active phase locking system according to an embodiment of the present invention. DETAILED DESCRIPTION

[0027] The present invention develops the principle of phase-locked loop in electronics to adjust the optical phase, uses equal-arm interferometer to realize a scalable and scalable array optical phase-locked structure, and combines the balanced detector optical path with the heterodyne method to solve the problems of intensity noise and polarization noise caused by uncontrollable fluctuations of optical signals.

[0028] Specifically, the present invention discloses a real-time active phase locking system, comprising: a signal light source; a reference light source; a frequency modulator; an equal-arm interferometer; a polarization photodetector for receiving the interference signal between the signal light and the reference light and converting the optical signal into an electrical signal; a phase detection circuit for detecting the phase difference between the signal light and the reference light; a feedback circuit for promptly feeding back the electrical signal generated by the phase difference to a phase adjuster; and the phase adjuster for adjusting the phase through control by the feedback circuit.

[0029] The signal light source includes: a continuous laser light source, a pulsed laser light source, a collinear or non-collinear parametric down-conversion crystal light source pumped by a pulsed laser or a continuous laser, and a collinear or non-collinear parametric up-conversion crystal light source pumped by a pulsed laser or a continuous laser.

[0030] Wherein, the reference light source includes: a continuous laser light source or a pulsed laser light source.

[0031] Wherein, the phase locking system further includes reference light, and the reference light and the reference light come from the same reference light source or light sources whose phases are locked to each other.

[0032] The equal-arm interferometer can separate the signal light and the reference light, and includes a reflector, a translation device, piezoelectric ceramics, and a regulator. The working process of the equal-arm interferometer is as follows:

[0033] An optical path difference adjustment mirror, a translation device for adjusting the position of the reflector, a piezoelectric ceramic driven reflector for fine-tuning the optical path, and a piezoelectric ceramic driven optical fiber stretching adjuster for fine-tuning the optical path.

[0034] The polarization photodetector includes a polarization controller, a fiber polarization beam splitter, and a photoelectric signal converter. The polarization photodetector can only retain the coherent parts of the interfering signal light and parametric light and remove the irrelevant parts.

[0035] The phase detection circuit further includes the following functions:

[0036] Convert continuous analog signals into discrete digital signals;

[0037] The microcontroller reads the phase change to obtain the phase difference between the signal light and the reference light.

[0038] The feedback circuit also includes the following functions: performing high-precision PID feedback on the circuit signal, outputting voltage in real time, and controlling the phase regulator.

[0039] The phase adjuster includes a free space phase adjuster or an optical fiber phase adjuster, and the phase adjuster adjusts the phase under the control of a feedback circuit.

[0040] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0041] like Figure 1 Figure 2 shows the design of a real-time active phase locking system. The signal and reference beams share the same optical path, and the reference beam is pre-splitted to produce the reference beam. The reference beam is detuned from the reference beam by a frequency modulator. The signal, reference, and reference beams enter an equal-arm interferometer, where a reflector array adjusts the optical path length of each beam to within the coherence length range. The reference beam is split in the interferometer into a quantity equal to the required reference beam. The equal-arm interferometer is designed with a coating that separates the signal beam as a phase-locked output, while the reference beam and the corresponding reference beam achieve spatial mode overlap in the interferometer.

[0042] Each reference light and reference light that overlap in the interferometer enters the photodetector after interference, and is converted into an electrical signal and used to lock the phase.

[0043] The electrical signal obtained from the photoelectric conversion enters the phase detection circuit. The circuit first undergoes sampling at a frequency twice the modulation frequency, and then the signal enters a voltage maintainer to ensure that a stable interference signal is obtained regardless of whether the input is a pulsed light signal or a continuous light signal. The electrical signals of the two coherent modes undergo balanced detection, that is, one mode is inverted and added to the other mode, thereby subtracting the background signal and obtaining a higher contrast signal, enabling the subsequent amplification process. The phase circuit takes the balanced detection signals obtained from two consecutive samples as a group. One of them is inverted and added to the other balanced detection signal. The final electrical signal obtained in this way will not be affected by light intensity, polarization, and detection efficiency noise with a frequency lower than the sampling frequency. This phase signal is sent to the feedback circuit.

[0044] The feedback circuit performs PID analysis on the phase signal obtained by the phase detection circuit, performs conversion and necessary amplification, obtains a high voltage signal, and sends it to the phase regulator.

[0045] The phase regulator receives the high-voltage signal from the feedback circuit in real time, and changes the phase of the signal light and the reference light in the optical path relative to the reference light through physical adjustment means, so that the entire feedback system reaches a steady state and completes real-time active optical phase locking.

[0046] The working process of the present invention is described in detail below through a specific embodiment.

[0047] Before the phase-locked part, a beam combiner is used between the reference light source and the signal light source to combine the reference light and the signal light into the same path. In the phase-locked interferometer part, a beam splitter is used to separate the signal light output from the reference light and the reference light.

[0048] In the phase-locked portion, a beam splitter is used to split the reference light source into three (or n) paths: one path is the reference path, and the other two (or n-1) paths are reference paths. The reference light in the reference path is frequency-shifted by fHz using two cascaded acousto-optic modulators. These two acousto-optic modulators utilize the +1st and -1st diffraction orders, respectively, to cascade the reference light frequency by fHz. A high-speed phase modulator is placed in each phase-locked path to receive control signals and modulate the phase.

[0049] A phase-locked interferometer is used to split the reference light into n-1 paths, which interfere with the reference light separated in the n-1 phase-locked paths respectively. The n-1 interference outputs are collected into optical fibers and sent to the controller.

[0050] The controller consists of a photoelectric tube, an analog-to-digital converter, a processor, a digital-to-analog converter and a signal amplifier.

[0051] For each phase-locked path, a photoelectric tube converts the optical signal into an electrical signal, and then uses an analog-to-digital converter and processor to read the signal strength. The signal sampling frequency is 2f Hz. When processing the signals, the processor groups the collected signals into pairs. Each group of signals corresponds to one cycle of the reference path phase change, and the two signals within each group have a phase difference of half a cycle.

[0052] The control goal is to ensure that the two signals in each signal group are equal in strength, which corresponds to a fixed relative phase. Using a feedback control algorithm, the required feedback amount is calculated based on the difference between the two signals in each signal group. This is then used to generate a control signal through a digital-to-analog converter and a signal amplifier.

[0053] The control signal is output to the phase regulator of the phase-locked circuit for phase feedback.

[0054] In general, the electrical signal output by the phototube may have insufficient dynamic range due to incomplete interference contrast. In this case, a balanced detector or a high-pass filter can be used to increase the dynamic range of the electrical signal.

[0055] Using this scheme, each phase-locked path can be locked to the reference path at the same time, thus completing the phase locking between the phase-locked paths.

[0056] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A real-time active optical phase locking system, characterized in that: include: A signal light source, used to generate multi-channel signal light; A reference light source is used to generate multiple reference lights, combine each signal light and each reference light, and split one of the reference lights to obtain a reference light; a frequency modulator for detuning the reference light from the reference light; The equal-arm interferometer receives the signal light, reference light, and reference light. The reflector array adjusts the optical path of each light path to be within the coherence length range. The reference light is split into the same number of beams as the required reference light in the equal-arm interferometer. The equal-arm interferometer is designed with a coating to separate the signal light as a phase-locked output; the reference light and the corresponding reference light complete spatial mode overlap in the equal-arm interferometer; a polarization photodetector for receiving the interference signal of each overlapping reference light and benchmark light, and converting each interference signal into an electrical signal; A phase detection circuit for detecting a phase difference between the reference light and the reference light based on an electrical signal obtained by photoelectric conversion; A feedback circuit is used to feed back the electrical signal generated by the phase difference to the phase regulator in a timely manner; The phase adjuster is set between the signal light source and the equal-arm interferometer. Through the feedback circuit control, the phase of each combined signal light and reference light is adjusted to achieve real-time active optical phase locking.

2. The real-time active optical phase locking system according to claim 1, characterized in that: The signal light source includes: a continuous laser light source or a pulsed laser light source.

3. The real-time active optical phase locking system according to claim 1, characterized in that: The reference light source includes: a continuous laser light source or a pulsed laser light source.

4. The real-time active optical phase locking system according to claim 1, characterized in that: The polarization photodetector includes a polarization controller, an optical fiber polarization beam splitter, and a photoelectric signal converter. The polarization photodetector can only retain the coherent parts of the interfering reference light and parametric light and remove the irrelevant parts.

5. The real-time active optical phase locking system according to claim 1, characterized in that: The phase detection circuit also includes the following functions: Convert continuous analog signals into discrete digital signals; The microcontroller reads the phase change to obtain the phase difference between the reference light and the reference light.

6. The real-time active optical phase locking system according to claim 1, characterized in that: The feedback circuit also includes the following functions: performing high-precision PID feedback on the circuit signal, outputting voltage in real time, and controlling the phase regulator.

7. The real-time active optical phase locking system according to claim 1, wherein: The phase adjuster includes a free space phase adjuster or an optical fiber phase adjuster, and the phase adjuster adjusts the phase under the control of a feedback circuit.

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