All-fiber laser feedback interferometer using a DBR fiber laser for effective sub-picometer displacement measurement.

A fiber autodyne laser feedback displacement sensor based on the effect of the frequency shift is demonstrated. The all-fiber structure enables our system to be easily employed in diverse complex and narrow scenes. By virtue of adopting an ultra-high sensitivity distributed Bragg reflector (DBR) fiber laser as the laser source and the frequency-shift technology to avoid the phenomenon that the measured signal of the low frequency is submerged in the noise, the measurement of the sub-picometer displacement under weak feedback condition has been achieved, which shows a great potential in the field of micro-vibration measurement. Moreover, the proposed system has advantages such as simplicity in system structure, low cost of implementation, and immunity to electromagnetic interference.

Optical feedback interferometry with 40 km transmission distance based on a distributed feedback fiber laser.

This Letter proposes an all-fiber self-mixing interferometric method based on laser feedback technology with long transmission distance, which has advantages of high sensitivity and compact structure. We theoretically and experimentally verify that the measurement distance of the self-mixing sensor is not limited to the coherence length of the solitary laser used. In the experiment, the velocity of a non-cooperative target was successfully measured with 40 km transmission distance. Therefore, the all-fiber self-mixing Doppler velocimeter has a great application prospect in the field of remote sensing measurement. Its unique flexibility can be applied to a variety of complex environments of non-cooperative target measurement.

Coherent laser detection of the femtowatt-level frequency-shifted optical feedback based on a DFB fiber laser.

The theoretical basis and experimental realization of an all-fiber self-mixing laser Doppler velocimetry based on frequency-shifted feedback in a distributed feedback (DFB) fiber laser are presented, which employs a pair of fiber-coupled acousto-optic modulators to adjust the modulation intensity and frequency of the laser self-mixing effect. Moreover, the minimum optical feedback intensity for the velocity signal successfully measured by the interferometer is 5.12 fW, corresponding to 0.16 photons per Doppler cycle. The results demonstrate that the proposed scheme can adapt to the non-contact measurement requirements of the wide-range speed and weak feedback level in the complex environment.

Relaxation characteristics for efficient fluorescence lifetime detection of gain media in the fiber laser.

By using different active materials as gain media, we demonstrate a system aimed to measure the fluorescence lifetime of gain media in the fiber laser by utilizing the correlation between the laser's relaxation oscillation characteristics and the fluorescence lifetime of the active materials. As the advantages of extremely compact configuration, non-destructive and real time of the system, the fluorescence lifetime of gain media composed of materials of erbium-ytterbium-doped or erbium-doped have been measured, whose results are 20.2 µs and 1.62 ms, respectively. The proposed method provides a new, to the best of our knowledge, idea for real-time monitoring of fluorescence lifetime in the fiber laser.

All-fiber self-mixing laser Doppler velocimetry with much less than 0.1 pW optical feedback based on adjustable gain.

The all-fiber self-mixing laser Doppler velocimetry with adjustable gain is experimentally investigated based on a distributed Bragg reflector fiber laser. In the measurement system, the modulation gain of the injected light in the laser cavity is adjusted by a pair of fiber-coupled acousto-optic modulators (AOMs) in the external cavity, which can change the intensity and frequency of the self-mixing modulation effect. Simultaneously, the minimum feedback intensity from the target to the laser for successful measurements is 0.063 pW. Thus, the all-fiber laser velocimetry can adapt to the detection of ultraweak optical feedback and wide-range velocity measurements in various complex scenes.