Light intensity modulator bias control device and method for light pulse selection system

Abstract

The invention discloses a light intensity modulator bias control device and method for a light pulse selection system. The control device comprises a reference pulse laser, an adjustable light delay line, a first wavelength division multiplexer, a second wavelength division multiplexer, a photoelectric detector, a trans-impedance amplifier, a low-pass filter, an analog-to-digital converter, a core controller and a digital-to-analog converter. A reference light pulse output by a reference pulse laser and a signal light pulse output by a signal pulse laser are staggered by a half period in a time domain by adjusting an adjustable light delay line, so that the power of the reference light pulse output by a light pulse selection system is only influenced by a direct current bias point of a light intensity modulator; by monitoring the reference light pulse power output by the system in real time and controlling the reference light pulse power at the minimum value, the bias point of the light intensity modulator can be stably controlled at the minimum point, the output signal light pulse has the highest extinction ratio, and the method can be better suitable for a light pulse selection scene under large signal modulation.

Description

Technical Field

[0001] The present invention relates to the field of microwave photon technology, and in particular to a light intensity modulator bias control device and method for an optical pulse selection system. Background Art

[0002] Optical pulses, due to their high peak power, low jitter, and short duration, have been widely used in optical communications, optical sensing, microwave photonics, and other fields. Different applications have varying requirements for the repetition rate of optical pulses. Currently, commonly used methods for adjusting the repetition rate of optical pulses are based on optical pulse selectors. High-speed optical pulse selectors typically employ acousto-optic modulators (AOMs) or optical intensity modulators (OIMs). Limited by the acoustic wave's propagation time across the beam diameter and circuit delays, the modulation response time of an AOM typically exceeds 10ns. Therefore, AOM-based pulse selection schemes are unsuitable for optical pulses with repetition rates exceeding 100MHz. Optical intensity modulators, such as the lithium niobate Mach-Zehnder OIM, offer advantages such as large modulation bandwidth and low drive voltage, and are often used in higher-speed optical pulse selection scenarios. In optical pulse selection systems, the OIM is typically operated at its minimum DC bias point, and the corresponding optical pulse is selected using a rectangular electrical signal synchronized with the optical pulse to achieve optical pulse selection. However, when the optical intensity modulator encounters interference factors such as vibration, temperature changes, and magnetic field radiation, its DC operating point will shift, which will significantly affect the extinction ratio of optical pulse selection.

[0003] Conventional optical intensity modulator (OIM) bias point control schemes rely on output optical power monitoring and scrambling signal monitoring. The output optical power monitoring scheme automatically adjusts the DC bias point by monitoring the optical power output of the OIM to maintain the minimum optical power. In optical pulse selection scenarios, when the bias point drifts from the minimum, the power of unselected optical pulses increases, while the power of selected optical pulses decreases. This results in inconspicuous changes in overall output power and makes it difficult to precisely control the bias point. Therefore, traditional schemes based on output optical power monitoring are not suitable for optical pulse selection scenarios, especially when the optical pulse selection frequency division ratio is small. The scrambling signal monitoring scheme uses a low-amplitude, low-frequency signal and uses the ratio of the fundamental signal to its harmonics as feedback to control the bias point. This method offers high control accuracy, but the scrambling signal introduces additional modulation into the output signal, resulting in a decrease in the picked-up pulse amplitude and an increase in leakage pulses. Furthermore, when the pulse selection frequency division ratio is large, the output optical power decreases significantly, significantly increasing the difficulty of extracting the scrambling signal and reducing the accuracy of bias point control. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, the present invention proposes an optical intensity modulator bias control device and method for an optical pulse selection system, which has the advantages of strong adaptability, little impact on signals, and high stability.

[0005] In order to achieve the above object, the technical solutions specifically adopted by the present invention are as follows:

[0006] A light intensity modulator bias control device for an optical pulse selection system comprises a target light pulse selection system and a bias control device, wherein the target light pulse selection system comprises a signal pulse laser, a light intensity modulator, and a signal generator; the bias control device comprises a reference pulse laser, an adjustable optical delay line, a first wavelength division multiplexer, a second wavelength division multiplexer, a photodetector, a transimpedance amplifier, a low-pass filter, an analog-to-digital converter, a core controller, and a digital-to-analog converter; the signal pulse laser, the first wavelength division multiplexer, the light intensity modulator, the second wavelength division multiplexer, the photodetector, the transimpedance amplifier, the low-pass filter, the analog-to-digital converter, the core controller, and the digital-to-analog converter are connected in sequence, the reference pulse laser is connected to the input port of the first wavelength division multiplexer via the adjustable optical delay line, and the signal generator is connected to the radio frequency modulation port of the light intensity modulator.

[0007] Furthermore, the adjustable optical delay line is used to enable the signal pulse laser and the reference pulse laser to respectively output signal light pulses and reference light pulses that are staggered in time by Δτ.

[0008] Furthermore, the first wavelength division multiplexer is used to collect signal optical pulses and reference optical pulses; and the second wavelength division multiplexer is used to demultiplex the output optical signal of the optical intensity modulator into signal optical pulses and reference optical pulses.

[0009] Furthermore, the power of the reference optical pulse output by the second wavelength division multiplexer is only affected by the DC bias point of the optical intensity modulator and is not affected by the rectangular electrical signal output by the signal generator. The photodetector is used to convert the obtained reference optical pulse into a current, the transimpedance amplifier is used to amplify the obtained current into a voltage, and the analog-to-digital converter is used to convert the filtered voltage into a digital signal for input into the core controller. The core controller detects the digital signal and outputs a control signal. The digital-to-analog converter is used to convert the control signal into a DC voltage to control the DC bias point of the optical intensity modulator.

[0010] Furthermore, the signal generator is used to output a rectangular electrical signal synchronized with the signal light pulse.

[0011] The present invention also provides a control method for the optical intensity modulator bias device of the optical pulse selection system, comprising the following steps:

[0012] S1, signal pulse laser and reference pulse laser output signal light pulse and reference light pulse with wavelengths λ1 and λ2 and periods T1 and T2 respectively;

[0013] S2. After the signal light pulse and the reference light pulse are converged by the first wavelength division multiplexer, the signals are input into the optical intensity modulator. Meanwhile, the signal generator outputs a rectangular electrical signal synchronized with the signal light pulse and inputs the signal into the optical intensity modulator.

[0014] S3, passing the output optical signal of the optical intensity modulator through a second wavelength division multiplexer to demultiplex it into a signal optical pulse and a reference optical pulse;

[0015] S4, converting the demultiplexed reference light pulses into current through a photodetector, then amplifying the current into voltage through a transimpedance amplifier, filtering out high-frequency noise through a low-pass filter, and converting the filtered voltage into a digital signal through an analog-to-digital converter and inputting it into the core controller;

[0016] S5. The core controller detects the digital signal and outputs a control signal, which is converted into a DC voltage by a digital-to-analog converter to control the DC bias point of the light intensity modulator.

[0017] Furthermore, in step S1, the optical delay line is adjusted so that the reference optical pulse and the signal optical pulse are staggered in time by Δτ, the reference optical pulse period T2 is an integer multiple of the signal optical pulse period T1, and the delay Δτ between the reference optical pulse and the signal optical pulse is T1 / 2.

[0018] Furthermore, in step S5, the core controller dynamically monitors the power of the output reference optical pulse to minimize it, thereby enabling the optical intensity modulator to stably operate at the minimum DC bias point and enabling the output optical pulse to have the highest extinction ratio.

[0019] The present invention has the following characteristics and beneficial effects:

[0020] 1) Compared with the optical intensity modulator bias point control scheme based on the average optical power of the signal light, it can better adapt to the optical pulse selection scenario with a small division ratio and is not affected by changes in the signal light power.

[0021] 2) Compared with the scrambling-based optical intensity modulator bias point control scheme, it can better adapt to the optical pulse selection scenario with a large division ratio and will not cause additional scrambling interference. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic structural diagram of a bias control device for an optical intensity modulator in an optical pulse selection system according to an embodiment of the present invention;

[0023] Figure 2Schematic diagram of the relative positions of the signal light pulse, the reference light pulse and the rectangular electrical signal in an embodiment of the present invention;

[0024] Figure 3 Schematic diagram of light pulse changes after a signal light pulse and a reference light pulse pass through an optical intensity modulator in an embodiment of the present invention;

[0025] Figure 4 Schematic diagram of power variation of reference optical pulses with and without bias point control in an embodiment of the present invention;

[0026] In the figure: 1. Signal pulse laser; 2. Light intensity modulator; 3. Signal generator; 4. Reference pulse laser; 5. Adjustable optical delay line; 6a. First wavelength division multiplexer; 6b. Second wavelength division multiplexer; 7. Photodetector; 8. Transimpedance amplifier; 9. Low-pass filter; 10. Analog-to-digital converter; 11. Core controller; 12. Digital-to-analog converter. DETAILED DESCRIPTION

[0027] The present invention is described in detail below in conjunction with specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

[0028] Example 1

[0029] like Figure 1As shown, the present invention provides an optical intensity modulator bias control device for an optical pulse selection system, comprising a target optical pulse selection system and a bias control device, wherein the target optical pulse selection system comprises a signal pulse laser 1 (Ca l amr), an optical intensity modulator 2 (EOSPACE) and a signal generator 3 (Keysight N4960A); the bias control device comprises a reference pulse laser 4 (Ca l amr), an adjustable optical delay line 5 (Genera l Photon ics), a first wavelength division multiplexer 6a (XYT-CWDM-4CH-01), a second wavelength division multiplexer 6b (XYT-CWDM-4CH-01), a photodetector 7 (THORLABS), a transimpedance amplifier 8 (OPA657), a low-pass filter 9 (AD825), an analog-to-digital converter 10 (AD7606), a core controller 11 (STC12C5A60S2), and a digital-to-analog converter 12 (DAC8562); a signal pulse laser 1, a first wavelength division multiplexer 6a, an optical intensity modulator 2, a second wavelength division multiplexer 6b, a photodetector 7, a transimpedance amplifier 8, a low-pass filter 9, an analog-to-digital converter 10, a core controller 11, and a digital-to-analog converter 12 are connected in sequence; a reference pulse laser 4 is connected to an input port of the first wavelength division multiplexer 6a via an adjustable optical delay line 5; and a signal generator 3 is connected to a radio frequency modulation port of the optical intensity modulator 2. During operation, the adjustable optical delay line 5 is adjusted so that the signal pulse laser 1 and the reference pulse laser 4 respectively output signal light pulses and reference light pulses with wavelengths λ1 and λ2 and periods T1 and T2 that are time-shifted by Δτ. The signal light pulses and the reference light pulses are converged by the first wavelength division multiplexer 6a and input into the optical intensity modulator 2. At the same time, the rectangular electrical signal output by the signal generator 3, which is synchronized with the signal light pulses, is input into the optical intensity modulator 2. The output optical signal of the optical intensity modulator 2 is demultiplexed into signal light pulses and reference light pulses by the second wavelength division multiplexer 6b. The photodetector 7 converts the obtained reference light pulses into current, and the transimpedance amplifier 8 amplifies the obtained current into voltage. The voltage is filtered out by the low-pass filter 9 and then input into the analog-to-digital converter 10. The analog-to-digital converter 10 converts the filtered voltage into a digital signal and inputs it into the core controller 11. The core controller 11 outputs a control signal by detecting the digital signal. The control signal is converted into a DC voltage by the digital-to-analog converter 12 and controls the DC bias point of the optical intensity modulator.

[0030] The present invention provides a method for controlling the bias of an optical intensity modulator in an optical pulse selection system. By adjusting an adjustable optical delay line, the reference optical pulse output by a reference pulse laser and the signal optical pulse output by a signal pulse laser are staggered by half a cycle in the time domain, so that the power of the reference optical pulse output by the optical pulse selection system is only affected by the DC bias point of the optical intensity modulator and is independent of the rectangular electrical selection signal output by the signal generator. The bias control circuit composed of a photoelectric converter, a transimpedance amplifier, an active low-pass filter, an analog-to-digital converter, a core controller, and a digital-to-analog converter monitors the power of the reference optical pulse output by the system in real time and controls it to a minimum value. This method can stably control the bias point of the optical intensity modulator to a minimum point and ensure that the output signal optical pulse has a maximum extinction ratio. The method specifically comprises the following steps:

[0031] The signal pulse laser 1 and the reference pulse laser 4 output signal light pulses and reference light pulses with wavelengths λ1 and λ2 and periods T1 and T2, respectively. In this step, the reference light pulse and the signal light pulse are staggered in time by Δτ by adjusting the adjustable optical delay line 5.

[0032] The reference optical pulse and the signal optical pulse are then converged by the first wavelength division multiplexer 6a and input into the optical intensity modulator 2. At the same time, the signal generator 3 outputs a rectangular electrical signal synchronized with the signal optical pulse and inputs into the optical intensity modulator 2 to achieve optical pulse selection.

[0033] The output optical signal of the optical intensity modulator 2 passes through the second wavelength division multiplexer 6b and is demultiplexed into signal optical pulses and reference optical pulses. The demultiplexed reference optical pulses are converted into currents by a photodetector. The current is then amplified into a voltage by a transimpedance amplifier. High-frequency noise is filtered out by a low-pass filter, and the filtered voltage is converted into a digital signal by an analog-to-digital converter and input into the core controller.

[0034] The core controller detects this digital signal and outputs a control signal. This control signal is converted by the digital-to-analog converter into a DC voltage, which then controls the DC bias point of the optical intensity modulator. During control, the core controller dynamically monitors the power of the output reference optical pulse and minimizes it. This controls the optical intensity modulator to operate stably at the minimum DC bias point, ensuring the output optical pulse has the highest extinction ratio.

[0035] The working principle of the present invention is as follows: First, the signal light pulse output by the signal pulse laser and the reference light pulse output by the reference pulse laser can be expressed as

[0036]

[0037]

[0038] Among them, P s0 and Pr0 represents the peak power of the signal light pulse and the reference light pulse, T1 is the period of the signal light pulse, σ s and σ r It indicates that the pulse width of the signal light pulse and the reference light pulse are both much smaller than T1. N is a positive integer, which is a multiple of the reference light pulse period and the signal light pulse period.

[0039] The signal optical pulse and the reference optical pulse after the delay line pass through the first wavelength division multiplexer. The output optical signal can be expressed as:

[0040]

[0041] Where Δt is the delay time of the reference optical pulse relative to the signal optical pulse. The composite optical pulse output by the first wavelength division multiplexer is input to the optical intensity modulator, and the output power P of the optical intensity modulator is MZM (t) can be expressed as:

[0042]

[0043] Among them, V DC and V(t) are the DC voltage signal and rectangular electrical signal input to the optical intensity modulator respectively. The duration τ of the rectangular electrical signal V(t) is greater than σ s and σ r , but is much smaller than T1 / 2, and its repetition period is N1 times that of the signal light pulse, where N1 is a positive integer representing the frequency division ratio of the pulse selection system. The rectangular electrical signal V(t) can be further expressed as:

[0044]

[0045] Where rect() is a rectangular function. When the light intensity modulator is performing pulse selection, the bias point control system is used to lock its DC operating point to the minimum point, that is, V DC Equal to the half-wave voltage V of the light intensity modulator π , so the output power P of the optical intensity modulator is MZM (t) can be further transformed into:

[0046]

[0047] By controlling the delay Δt between the signal and reference optical pulses to satisfy the condition τ / 2 < Δt < T1 - τ / 2, the rectangular electrical signal will not affect the output power of the reference optical pulse, but only the output power of the signal optical pulse. Specifically, Δt can be set to T1 / 2 to maximize the time interval between the signal and reference optical pulses.

[0048] The reference optical pulse and signal optical pulse output by the second wavelength demultiplexer can be expressed as:

[0049] P r，out (t)=0 (7)

[0050]

[0051] The repetition rate of the output signal optical pulses is equal to one-N1 of the input signal optical pulse repetition rate, meaning the pulse selection system's division ratio is N1. Ideally, the power of the output reference optical pulses is zero. Therefore, the bias control device only needs to monitor the power of the output reference optical pulses and maintain it at a minimum value through feedback control. This allows the modulator to be stably controlled at the minimum bias point, achieving pulse selection with a high extinction ratio.

[0052] exist Figure 1 In the experimental verification of the system shown, the signal and reference pulse lasers both produced optical pulses with an output power of 13 dBm, a frequency of 700 MHz, and wavelengths of 1550.92 nm and 1552.52 nm, respectively. The intensity modulator had a bandwidth of 10 GHz and a half-wave voltage of 1.7 V. The signal generator produced a rectangular electrical signal with an amplitude of 1.7 V and a frequency of 350 MHz. The delay between the control signal and reference pulses was half the period of the signal pulse laser, approximately 0.7 ns. Figure 2 The signal light pulse, reference light pulse, and rectangular electrical signal generated by the signal generator are input to the optical intensity modulator. After passing through the adjustable optical delay line, the reference light pulse is time-shifted with the rectangular electrical signal, so that the rectangular electrical signal only covers a portion of the signal light pulse. The bias control device controls the average power of the output reference light pulse signal to reach the minimum value, thus achieving the selection of the signal light pulse. Figure 3 As shown. The repetition rate of the output signal light pulse becomes 350MHz, and a high extinction ratio is maintained. In addition, we tested the stability of the bias control method. The frequency of the rectangular electrical signal is set to 140MHz, and two optical pulse selection experiments with a frequency division ratio of 5 are carried out, one with bias control and the other without bias control. Each experiment lasts for one hour. The experimental results are shown in Figure 4 As shown in the figure, after bias control is applied, the average power of the output reference optical pulse remains at around 10μW, with a maximum fluctuation of 11.3μW. Without bias control, the power of the output reference optical pulse continuously increases from 10μW to 41μW. The above process proves that the proposed scheme can control the intensity modulator bias to the minimum point, achieve optical pulse selection with a high extinction ratio, and maintain long-term stability.

[0053] The above shows and describes the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely preferred examples of the present invention and are not intended to limit the present invention. Various changes and improvements may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and improvements fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A light intensity modulator bias control device for an optical pulse selection system, comprising a target optical pulse selection system and a bias control device, characterized in that: The target optical pulse selection system comprises a signal pulse laser, an optical intensity modulator and a signal generator; the bias control device comprises a reference pulse laser, an adjustable optical delay line, a first wavelength division multiplexer, a second wavelength division multiplexer, a photodetector, a transimpedance amplifier, a low-pass filter, an analog-to-digital converter, a core controller and a digital-to-analog converter; the signal pulse laser, the first wavelength division multiplexer, the optical intensity modulator, the second wavelength division multiplexer, the photodetector, the transimpedance amplifier, the low-pass filter, the analog-to-digital converter, the core controller and the digital-to-analog converter are connected in sequence, the reference pulse laser is connected to the input port of the first wavelength division multiplexer through the adjustable optical delay line, and the signal generator is connected to the radio frequency modulation port of the optical intensity modulator.

2. The optical intensity modulator bias control device for an optical pulse selection system according to claim 1, characterized in that: The adjustable optical delay line is used to enable the signal pulse laser and the reference pulse laser to respectively output a signal light pulse and a reference light pulse that are staggered in time by Δτ.

3. The optical intensity modulator bias control device for an optical pulse selection system according to claim 1, characterized in that: The first wavelength division multiplexer is used to collect signal light pulses and reference light pulses; the second wavelength division multiplexer is used to demultiplex the output optical signal of the optical intensity modulator into signal light pulses and reference light pulses.

4. The optical intensity modulator bias control device for an optical pulse selection system as claimed in claim 3, characterized in that: The reference optical pulse power output by the second wavelength division multiplexer is only affected by the direct current bias point of the optical intensity modulator, and is not affected by the rectangular electrical signal output by the signal generator.

5. The optical intensity modulator bias control device for an optical pulse selection system as claimed in claim 1, characterized in that: The signal generator is used to output a rectangular electrical signal synchronized with the signal light pulse.

6. A light intensity modulator bias control method for an optical pulse selection system, characterized in that: The following steps are involved: S1, the signal pulse laser and the reference pulse laser output signal light pulses and reference light pulses with wavelengths of λ1 and λ2 and periods of T1 and T2 respectively; S2, after the signal light pulse and the reference light pulse are converged by the first wavelength division multiplexer, the signals are input into the light intensity modulator, and at the same time, the signal generator outputs a rectangular electrical signal synchronized with the signal light pulse and inputs the rectangular electrical signal into the light intensity modulator; S3, passing the output optical signal of the optical intensity modulator through a second wavelength division multiplexer, and demultiplexing it into a signal optical pulse and a reference optical pulse; S4, converting the demultiplexed reference light pulse into current through a photodetector, then amplifying the current into voltage through a transimpedance amplifier, filtering out high-frequency noise through a low-pass filter, and converting the filtered voltage into a digital signal through an analog-to-digital converter and inputting it into a core controller; S5. The core controller outputs a control signal by detecting the digital signal, which is converted into a DC voltage by a digital-to-analog converter to control the DC bias point of the light intensity modulator.

7. The optical intensity modulator bias control method for an optical pulse selection system according to claim 6, characterized in that: In step S1, the optical delay line is adjusted so that the reference optical pulse and the signal optical pulse are staggered in time by Δτ, the reference optical pulse period T2 is an integer multiple of the signal optical pulse period T1, and the delay Δτ between the reference optical pulse and the signal optical pulse is T1 / 2.

8. The optical intensity modulator bias control method for an optical pulse selection system according to claim 6, characterized in that: In step S5, the core controller dynamically monitors the power of the output reference optical pulse to make it at the minimum value, thereby making the optical intensity modulator stably operate at the minimum DC bias point and making the output optical pulse have the highest extinction ratio.

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