Stabilization of microwave signal generated by a dual-polarization DBR fiber laser via optical feedback.

Yizhi Liang,Bai-Ou Guan,Long Jin,Linghao Cheng

doi:10.1364/oe.22.029356

Abstract

Microwave signals can be generated by beating the two orthogonal polarization modes from a dual-frequency fiber grating laser. In this paper, we present that the phase noise of the microwave signal can be significantly reduced via optical feedback by cascading an external cavity. This is achieved as a result of the bandwidth narrowing of each polarization laser mode when introducing phase-matched feedbacks into the laser cavity. By optimizing the external cavity length and the feedback ratio, the noise level over low frequencies has been reduced by up to 30 dB, from -42 to -72 dBc/Hz at 1 kHz, and from -72 to -102 dBc/Hz at 10 kHz. Meanwhile the relaxation resonant peaks can be eliminated. Compared with the existing techniques, the present method can offer a cost-effective, low-noise microwave signal, without the requirement for complex electrical feedback system.

Highlights

The generation of optically carried microwave signals is of great interest for a wide range of applications
The phase noise level is a significant measure of signal quality which reflects the purity and bandwidth of a microwave signal
We have demonstrated the generation of microwave signals by use of a dual-polarization distributed Bragg reflector (DBR) fiber laser with a signal-to-noise ratio (SNR) over 60 dB, a temperature dependency as low as 10−5 /°C, and an intrinsic tunability with a range over 15 GHz [10]

Summary

Introduction

The generation of optically carried microwave signals is of great interest for a wide range of applications. The coherence of the signals is better as a result of the common resonant cavity This method does not need any reference source and greatly reduces system cost. When phase-matched feedbacks are introduced, each polarization laser mode is stabilized, yielding a significant reduction in the phase noise level of the beat signal. By optimizing the external cavity length and the feedback ratio, the noise level is reduced by 30 dB, from −42 to −72dBc at 1 kHz, and from −72 to −102dBc at 10kHz. Compared with the existing techniques in literature, the present method offers a costeffective, high-quality optically generated microwave source

Methods

Discussion

Conclusion