Tunable microwave generation based on a dual-wavelength single-longitudinal-mode fiber laser using a phase-shifted grating on a triangular cantilever

Phase-Inserted Fiber Gratings and Their Applications to Optical Filtering, Optical Signal Processing, and Optical Sensing: Review

Phase-inserted fiber gratings (PI-FGs) refer to those gratings where there exist a number of the phase-shifts (spatial spacing) among different sections (or local periods) of the gratings themselves. All the PI-FGs developed to date can mainly be divided into three categories: phase-shifted gratings, phase-only sampled gratings, and phase-modulated gratings, of which the utilized gratings could be either the Bragg ones (FBGs) or the long-period ones (LPGs). As results of the proposed the PI-FGs where the numbers, quantities, and positions of the inserted phases along the fiber direction are optimally selected, PI-FGs have already been designed and used as various complex filters such as the ultra-narrow filters, the triangular (edge) filters, the high channel-count filters, and the flat-top band-pass/band-stop filters, which, however, are extremely difficult or even impossible to be realized by using the ordinary fiber gratings. In this paper, we have briefly but fully reviewed the past and recent advances on PI-FGs, in which the principles and design methods, the corresponding fabrication techniques, and applications of the different PI-FGs to the fields of optical filtering, optical signal processing, and optical sensing, etc., have been highlighted.

Tunable Spacing Dual-Wavelength Q-Switched Fiber Laser Based on Tunable FBG Device

A tunable spacing dual-wavelength Q-switched fiber laser is experimentally demonstrated based on a fiber Bragg grating tunable device incorporated in an erbium-doped fiber laser (EDFL). The system utilizes two identical fiber Bragg gratings (FBGs) at 1547.1 nm origin to enable two laser lines operation. The wavelength separations between two laser lines are controlled by fixing one of the FBGs while applying mechanical stretch and compression to the other one, using a fiber Bragg grating tunable device. The seven steps of wavelength spacing could be tuned from 0.3344 to 0.0469 nm spacing. Pulse characteristics for both close and wide spacing of dual-wavelength Q-switched fiber laser are successfully being recorded. The findings demonstrate the latest idea of dual-wavelength fiber laser based on FBG tunable device, which offers a wide range of future applications.

Implementation of a widely tunable microwave signal generator based on dual-polarization fiber grating laser

In this paper, we demonstrate the implementation of a widely tunable microwave signal generator based on a dual-polarization fiber grating laser. The laser contains two strong, wavelength-matched Bragg gratings photoinscribed in an Er-doped fiber and emits two polarization modes when pumped with a 980 nm laser diode. By beating the two modes, a microwave signal with a signal-to-noise ratio over 60 dB can be obtained. For a free running laser the fluctuations in intensity and frequency of the microwave signal are ±1  dB and ±5  kHz, respectively, and the noise level is about -40  dBc/Hz at 1 kHz. The frequency can be continuously tuned from 1.8 to 15.1 GHz, by transversely loading the laser cavity and changing the intracavity birefringence by use of a piezoelectric transducer-based mechanical device. The measured response time rate of tuning is about 90 MHz/μs and the intensity fluctuation at different frequencies is less than ±1.5  dB. The frequency fluctuation under loading is controlled within 1 MHz by introducing an electrical feedback.