A laser linewidth measurement device and method based on switchable channel delay self-heterodyne interferometry

By using a laser linewidth measurement device with switchable channel delayed self-heterodyne interferometry, the problems of noise and polarization state jitter introduced by long-distance delayed optical fibers are solved, enabling accurate measurement of laser linewidth and improving system stability and measurement range.

CN122306378APending Publication Date: 2026-06-30BEIHANG UNIV
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Patent Information

Authority / Receiving Office
CN · China
Patent Type
Applications(China)
Current Assignee / Owner
BEIHANG UNIV
Filing Date
2026-04-24
Publication Date
2026-06-30

AI Technical Summary

Technical Problem

In existing laser linewidth measurement schemes based on delayed self-heterodyne interferometry, long-distance delayed optical fibers introduce additional low-frequency phase noise, increase transmission loss, and increase system cost and size. Furthermore, random polarization jitter in the optical path causes fluctuations in beat frequency signal power and measurement errors, while fixed-length delayed optical fibers limit the measurement range.

Method used

A laser linewidth measurement device employing switchable channel delayed self-heterodyne interferometry utilizes components such as isolators, fiber couplers, optical switches, and Faraday rotating mirrors. By switching between delay fibers of different lengths and polarization control, combined with a spectrum analysis module and a computer fitting program, the Lorentz linewidth, Gaussian linewidth, and composite linewidth of the laser are obtained.

Benefits of technology

It effectively suppresses polarization fading during optical fiber transmission, improves the system's anti-interference capability and stability, broadens the linewidth measurement range, reduces measurement errors, shortens the length of delay fiber, and reduces system hardware costs and size.

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Abstract

This invention discloses a laser linewidth measurement device and method based on switchable channel delay self-heterodyne interferometry, belonging to the field of laser linewidth measurement technology. The laser to be measured is incident on a first fiber coupler via an isolator and splits into two paths: one path enters a computer-controlled first and second optical switches via a three-port fiber circulator, switching between different lengths of delay fiber via the first and second optical switches, rotating the polarization state by 90° via a Faraday rotating mirror before returning along the original path, and then restoring the original polarization state via a polarization controller; the other path undergoes frequency shifting via an acousto-optic frequency shifter. The two paths are combined via a second fiber coupler to generate a beat frequency optical signal, which is then acquired by a photodetector for photoelectric conversion and a spectrum analysis module. The computer fits the beat frequency power spectrum corresponding to different delay lengths to obtain the laser linewidth to be measured. This invention has strong anti-interference capabilities and can simultaneously acquire Lorentz linewidth, Gaussian linewidth, and composite linewidth, with a wide linewidth measurement range.
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