Apparatus and method for suppressing residual amplitude in frequency modulation spectrum based on polarization rotation

Abstract

The invention belongs to the field of laser trace gas detection, and mainly relates to a device and method for suppressing residual amplitude in frequency modulation spectrum based on polarization rotation. The invention solves the problem that in the prior art, when suppressing the residual amplitude modulation of the frequency modulation spectrum, the modulation signal is usually loaded on the electro-optical modulator (EOM), so that when used for trace gas detection, there is double modulation in the EOM, which causes radio frequency Due to the technical problem of signal fidelity reduction, a new scheme of residual amplitude modulation suppression in frequency modulation spectrum is proposed, which can be used for trace gas detection. Specifically, a polarization rotator is used as a feedback control device with a response bandwidth of 500kHz, which can be quickly Compensate the change of the polarization angle; at the same time, the angle between the polarization direction of the incident light of the EOM and the e-axis of the electro-optical modulation crystal is controlled by the feedback of the polarization controller, and no additional signal is applied to the EOM, which improves the fidelity of the radio frequency signal; the input and output light of the system The unique polarization state detection and feedback reduces the complexity of the whole device.

Description

technical field [0001] The invention belongs to the field of laser trace gas detection, and mainly relates to a device and method for suppressing residual amplitude in frequency modulation spectrum based on polarization rotation. Background technique [0002] Frequency modulation spectroscopy (FMS) technology is a high-sensitivity laser spectroscopy technology, which is often used in the field of trace gas detection. Compared with direct absorption spectroscopy10 -3 Order of magnitude detection sensitivity, FMS technology can increase the sensitivity to 10 under the same conditions -6 order of magnitude. However, in practical applications, the detection sensitivity of the FMS cannot reach the theoretical limit due to the appearance of residual amplitude modulation (RAM for short) generated in the modulation and demodulation process. In theory, if the sidebands on both sides of the carrier frequency due to modulation are not completely equal in amplitude and out of phase, R...

AI Technical Summary

Problems solved by technology

[0005] The present invention solves the problem that when suppressing the residual amplitude modulation of the frequency modulation spectrum in the prior art, the modulation signal is mostly loaded on the electro-optical modulator (EOM), so that there is double modulation in the EOM when used for trace and gas detection. The technical problem of reducing the fidelity of radio frequency signals, providing a device and method for suppressing residual amplitude in frequency modulation spectrum based on polarization rotator

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