Precise measurement of ultra-narrow laser linewidths using the strong coherent envelope

Shihong Huang,Min Liu,Wei Huang,Tao Zhu

doi:10.1038/srep41988

Shihong Huang, Min Liu + Show 2 more

Open Access

https://doi.org/10.1038/srep41988

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Abstract

Laser linewidth narrowing down to kHz or even Hz is an important topic in areas like clock synchronization technology, laser radars, quantum optics, and high-precision detection. Conventional decoherence measurement methods like delayed self-heterodyne/homodyne interferometry cannot measure such narrow linewidths accurately. This is because a broadening of the Gaussian spectrum, which hides the laser’s intrinsic Lorentzian linewidth, cannot be avoided. Here, we introduce a new method using the strong coherent envelope to characterize the laser’s intrinsic linewidth through self-coherent detection. This method can eliminate the effect of the broadened Gaussian spectrum induced by the 1/f frequency noise. We analyze, in detail, the relationship between intrinsic laser linewidth, contrast difference with the second peak and the second trough (CDSPST) of the strong coherent envelope, and the length of the delaying fiber. The correct length for the delaying fiber can be chosen by combining the estimated laser linewidth (Δfest) with a specific CDSPST (ΔS) to obtain the accurate laser linewidth (Δf). Our results indicate that this method can be used as an accurate detection tool for measurements of narrow or super-narrow linewidths.

Highlights

Laser linewidth narrowing down to kHz or even Hz is an important topic in areas like clock synchronization technology, laser radars, quantum optics, and high-precision detection
We have previously proposed an accurate method to obtain the Lorentzian linewidth by comparing the contrast difference between the second peak and the second trough (CDSPST) of the coherent envelope of the power spectrum using SDSHI22
The detected 3-dB linewidth is much larger than that given by the manufacturer because of the broadening Gaussian linewidth induced by the 1/f noise and the delaying fiber[9,24,25,26,27,28,29,30]

Summary

Introduction

Laser linewidth narrowing down to kHz or even Hz is an important topic in areas like clock synchronization technology, laser radars, quantum optics, and high-precision detection. Conventional decoherence measurement methods like delayed self-heterodyne/homodyne interferometry cannot measure such narrow linewidths accurately This is because a broadening of the Gaussian spectrum, which hides the laser’s intrinsic Lorentzian linewidth, cannot be avoided. We introduce a new method using the strong coherent envelope to characterize the laser’s intrinsic linewidth through selfcoherent detection This method can eliminate the effect of the broadened Gaussian spectrum induced by the 1/f frequency noise. Huang[9,12,21,22,23] demonstrated that short delay self-heterodyne interferometry (SDSHI) is a good method to filter out 1/f noise It is still not clear how long the delaying fiber should be to eliminate the effect of 1/f noise to obtain the accurate Lorentzian linewidth for different levels of the laser linewidth.

Methods

Results

Conclusion