CN110824493A - A Coherent Lidar Using Optical Phase Locking Technology to Improve Detection Range - Google Patents

Abstract

The invention discloses a coherent laser radar which adopts optical phase locking technology to improve the detection distance, comprising a main laser (space coupling), a tunable local oscillator laser, a receiving optical system, a 3dB coupler, a balanced detector, and a frequency and phase detection module (PFD), charge pump and loop filter. The laser emitted by the main laser hits the target and the echo signal reflected by the target interferes with the local oscillator light to obtain the beat frequency signal, and the set reference signal is passed through the frequency and phase identification module to obtain the phase difference between the two signals, which is generated by the loop filter. The corresponding control voltage controls the frequency of the local oscillator laser, so that the beat frequency signal is locked to the set reference signal phase. At this time, the beat frequency signal satisfies the condition of coherent accumulation in the time domain, which is more conducive to the extraction of weak signals, and ultimately improves the the detection range of coherent lidar.

Description

A Coherent Lidar Using Optical Phase Locking Technology to Improve Detection Range

technical field

The invention belongs to the technical field of coherent laser radar, and in particular relates to a coherent laser radar which adopts optical phase locking technology to improve the detection distance.

Background technique

In coherent lidar, the echo signal light interferes with the local oscillator light to generate a beat frequency signal, and the echo signal is extracted by using the local oscillator gain, which greatly improves the detection sensitivity and the working distance of the lidar. The beat frequency signal is coherently accumulated.

At present, the frequency domain coherent accumulation method is mostly used, and the development is relatively mature. On this basis, the present invention considers the time domain coherent accumulation to further improve the detection sensitivity. However, due to the influence of the laser's own phase noise, platform vibration, atmospheric disturbance, Doppler frequency shift and other factors during the signal optical transmission process, the phase of the beat frequency signal is jittered. At this time, the echo signal is coherently accumulated in the time domain. It does not improve the signal-to-noise ratio of the echo signal. The signal-to-noise ratio will be improved only after the signals that satisfy the time-domain coherence are accumulated. Therefore, ensuring the stability of the echo signal phase is the basis for improving the detection sensitivity through the time-domain coherent accumulation.

SUMMARY OF THE INVENTION

In order to overcome the shortcomings and deficiencies of the prior art, the present invention proposes a coherent laser radar that adopts the optical phase locking technology to improve the detection distance, which can realize the detection of long-distance targets by means of time domain accumulation.

In order to achieve the above object, the technical solution adopted in the present invention is: a coherent laser radar that uses optical phase locking technology to improve the detection distance. The lidar includes a main laser (space coupling), a tunable local oscillator laser, a receiving optical system, a 3dB coupler, a balanced detector, a frequency and phase detection module, a charge pump and a loop filter.

The main laser is used for emitting a spatial continuous laser signal to the measured target;

The tunable local oscillator laser is used to generate a local oscillator optical signal, and the frequency of the local oscillator optical signal can be tuned by PZT;

The receiving optical system is used for receiving the laser echo signal reflected/scattered by the measured target;

The 3dB coupler is used to couple the echo optical signal and the local oscillator optical signal into two optical signals with a phase difference of 180°;

The balanced detector is used to respectively respond to the two optical signals output by the 3dB coupler, and perform transimpedance amplification on the difference between the two photocurrents;

The described frequency and phase identification module is used to generate the pulse difference between the frequency difference signal and the rising edge of the reference signal;

The charge pump is used to generate the corresponding charge/discharge current in response to the pulse width difference output by the frequency and phase detector module;

The loop filter is used to generate the control voltage of the tunable local oscillator laser and also to filter out high frequency signals.

Compared with the prior art, the advantages of the coherent laser radar that adopts the optical phase locking technology to improve the detection distance of the present invention are:

The coherent lidar adopts the optical phase locking technology to realize the phase stability of the beat frequency signal. probe.

The coherent laser radar adopts the frequency and phase detection module to form an optical phase-locked loop. The reference signal is introduced into the frequency and phase detection module to reduce the capture bandwidth of the loop, which ensures the suppression of loop noise and ensures the tracking performance of the loop. . In addition, compared with other phase detectors, because the output of the frequency and phase detection module is the pulse width difference between the two signals, the frequency and phase detection module can detect both frequency and phase, and the locking accuracy is high.

The coherent lidar adopts an optimized loop filter designed according to the loop bandwidth and phase margin, and realizes the fast acquisition of large bandwidth by the loop.

Description of drawings

1 is a schematic structural diagram of a coherent laser radar that adopts optical phase-locking technology to improve detection distance according to the present invention;

FIG. 2 is a simple schematic diagram of the time-domain coherent accumulation of echo signals according to the present invention.

In the figure: 1 is the main laser, 2 is the tunable local oscillator laser, 3 is the receiving optical system, 4 is the 3dB coupler, 5 is the balanced detector, 6 is the frequency and phase detection module, 7 is the charge pump, and 8 is the ring path filter.

Detailed ways

In order to make the objects, solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

As shown in Fig. 1, the coherent laser radar proposed by the present invention, which adopts optical phase locking technology to improve the detection distance, includes a 1064 nm solid-state laser with a line width of kHz as the main laser 1 (spatial coupling); it has the functions of temperature tuning and PZT tuning. The 1064nm solid-state laser is used as a tunable local oscillator laser 2, its temperature tuning coefficient can reach GHz/℃, and the PZT tuning coefficient is tens of MHz/V; a collimator is used as the receiving optical system 3, and the polarization-maintaining fiber 3dB coupler4 , a high-bandwidth balanced detector 5, ADI's frequency and phase detection module 6, a charge pump 7 and a loop filter 8, which finally constitute an optical phase-locked loop with a loop bandwidth of 100kHz and a phase margin of 45°. The beat frequency electrical signal is obtained through the balanced detector 5 by using the echo signal emitted by the main laser 1 to the target reflected/scattered and the local oscillator light generated by the tunable local oscillator laser 2 to interfere. The frequency discrimination and phase discrimination module 6 is used to generate the pulse width difference between the beat signal and the single edge of the set RF reference signal, and then the charge pump 7 is controlled to generate the corresponding charge/discharge current. The loop filter 8 is used to generate a control voltage signal for driving the tunable local oscillator laser 2 , and the output frequency of the tunable local oscillator laser 2 is regulated by means of PZT tuning. Then, the phase of the beat signal is locked with the reference signal, and a stable beat signal is obtained, and its signal-to-noise ratio is significantly improved, so that the coherent lidar can detect distant targets based on the optical phase-locked loop.

The beat frequency signal output by the coherent laser radar using the optical phase-locked loop is locked on the phase of the radio frequency reference signal of the frequency and phase detector module 6 . Therefore, the principle of improving the signal-to-noise ratio of the beat signal after coherent accumulation in the time domain can be approximated as shown in Figure 2. It can be clearly seen that the signal-to-noise ratio of the signal is improved, which further improves the detection of coherent lidar. Sensitivity, which can realize the detection of long-distance targets.

Claims (4)

1. a coherent laser radar that adopts optical phase locking technology to improve detection distance, it is characterized in that: this coherent laser radar comprises main laser (1), tunable local oscillator laser (2), receiving optical system (3), 3dB coupling device (4), balanced detector (5), frequency discrimination and phase discrimination module (6), charge pump (7) and loop filter (8), the main laser (1) is used for emitting a spatial continuous laser signal to the measured target; the tunable local oscillator laser (2) is used to generate a local oscillator optical signal, and the frequency of the local oscillator optical signal can be tuned by PZT; the receiving optical system (3) is used to receive the measured target The reflected/scattered laser echo signal; the 3dB coupler (4) is used to couple the echo optical signal and the local oscillator optical signal into two optical signals with a phase difference of 180°; the balanced detector (5) It is used to respectively respond to the two optical signals output by the 3dB coupler, and amplify the difference between the two photocurrents by transimpedance; Pulse difference; the charge pump (7) is used to generate the corresponding charge/discharge current in response to the pulse width difference output by the frequency and phase detector module; the loop filter (8) is used to generate a tunable current The control voltage of the vibrating laser is also used to filter out high-frequency signals. 2. the coherent laser radar that adopts optical phase locking technology to improve detection distance according to claim 1, it is characterized in that: adopt frequency discrimination phase discrimination module (6) to form optical phase locked loop, by frequency discrimination phase discrimination module (6) ) can reduce the capture bandwidth of the loop, can better suppress the loop noise, and ensure the tracking performance of the loop; It is the pulse width difference of the two signals, so the frequency and phase detection module (6) can detect both the frequency and the phase, and the locking precision is high. 3. the coherent laser radar that adopts optical phase locking technology to improve detection distance according to claim 1, it is characterized in that: adopt optimized loop filter (8), can make loop bandwidth and phase margin be optimized to Appropriate value, so that the loop can quickly capture the large bandwidth. 4. The coherent laser radar that adopts optical phase locking technology to improve detection distance according to claim 1, it is characterized in that: adopting optical phase locking technology, the phase stability of the beat frequency signal is realized, on this basis the echo signal is passed through. The signal-to-noise ratio can be significantly improved after time-domain coherent accumulation, which further improves the detection sensitivity of coherent lidar, and can realize the detection of long-distance targets.

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