Xinyong Dong

Multiwavelength Raman fiber laser with a continuously-tunable spacing

A spacing-tunable multiwavelength Raman fiber laser with an independently-adjustable channel number is proposed and demonstrated. It uses a novel free-spectral-range (FSR)-tunable comb filter based on a superimposed chirped-fiber Bragg grating (CFBG) and a linear cavity formed by a bandwidth-tunable CFBG reflector, a pumped highly-nonlinear fiber for Raman gain, and an optical circulator based loop mirror. Multiwavelength laser operations with spacing tuning from 0.3 to 0.6 nm and channel number adjustment from 2 to 10 have been achieved.

A novel temperature-insensitive fiber Bragg grating sensor for displacement measurement

This paper presents the design and development of an optical fiber Bragg grating based displacement sensor. A fiber Bragg grating is glued at a slant orientation onto the lateral side of a specially designed cantilever beam. It is found that the bandwidth of the FBG based sensor changes linearly with the variation of the displacement at the free end of the beam due to the displacement-induced strain gradient. Displacement sensing is realized by measuring the reflected optical power of the signal from the grating with a photodetector. A linear response of 37.9 mV mm−1 was obtained within a displacement range of 9.0 mm. This sensor is also cost-effective due to the use of a simple demodulation method and is inherently temperature insensitive, eliminating the need for temperature compensation.

A largely tunable CFBG-based dispersion compensator with fixed center wavelength.

A largely tunable chirped fiber Bragg grating (CFBG)-based dispersion compensator with fixed center wavelength is demonstrated. Tunable dispersion ranging from 178 to 2126 ps/nm, corresponding to a large range of 3-db bandwidth from 0.42 to 5.04 nm, is realized by using a 10 cm-long CFBG with an original bandwidth of 1.61 nm. The variation in center wavelength is less than 0.2 nm.

Multiwavelength erbium-doped fiber laser with 0.8-nm spacing using sampled Bragg grating and photonic crystal fiber

We propose and demonstrate a novel room-temperature multiwavelength erbium-doped fiber laser (EDFL) with a 0.8-nm wavelength spacing based on four-wave mixing (FWM) in a length of high-nonlinear photonic crystal fiber and sampled-fiber Bragg grating. The FWM processes suppress the wavelength competition of the EDFL and increase the number of lasing wavelength. By adjusting the FWM efficiency, the number of the concurrent lasing wavelengths can be changed, and the peak power differences among the main oscillation wavelengths are less than 2.0 dB.

Polyvinyl alcohol-coated hybrid fiber grating for relative humidity sensing.

A relative humidity (RH) sensor based on a hybrid fiber grating coated with polyvinyl alcohol is proposed and demonstrated experimentally. The hybrid fiber grating is formed by superimposing a normal fiber Bragg grating (FBG) and a tilted-FBG around the same position of a single-mode fiber so that it can work in the reflection mode. Optical power of the reflected signal changes with the refractive index of the moisture sensitive polyvinyl alcohol, and humidity measurement can be realized. Experimental results show that the measurement range is 30 to 95% with the maximum sensitivity of 0.737 nW∕% RH. The average response time is ∼2 s and the measurement is nearly insensitive to temperature. Compared with the wavelength detection method used in normal FBG-based relative humidity sensors, the intensity demodulation method in this report is simpler and more cost-efficient.

A Dual-Wavelength Fiber Laser Sensor System for Measurement of Temperature and Strain

A strain and temperature-sensing scheme based on a dual-wavelength fiber laser is demonstrated experimentally. By measuring the change in the wavelength separation of the two lasing wavelengths and the shift of any of two lasing wavelengths, the measured strain and temperature are very linear and have a strain sensitivity of 0.15 pm/muepsiv over a range of 0-2400 muepsiv and a temperature sensitivity of 14.3 pm/degC over a range of 22degC-230degC, respectively.

Passive mode locking at harmonics of the free spectral range of the intracavity filter in a fiber ring laser.

We report the passive mode-locking at harmonics of the free spectral range (FSR) of the intracavity multi-channel filter in a fiber ring laser. The laser uses a sampled fiber Bragg grating (SFBG) with a free spectral range (FSR) of 0.8 nm, or 99 GHz at 1555 nm, and a length of highly nonlinear photonic crystal fiber with low and flat dispersion. Stable picosecond soliton pulse trains with twofold to sevenfold enhancement in the repetition rate, relative to the FSR of the SFBG, have been achieved. The passive mode-locking mechanism that is at play in this laser relies on a dissipative four-wave mixing process and switching of repetition rate is realized simply by adjustment of the intracavity polarization controllers.

Multi-wavelength linear-cavity tunable fiber laser using a chirped fiber Bragg grating and a few-mode fiber Bragg grating

A novel and simple multi-wavelength linear-cavity tunable fiber laser source using a chirped fiber Bragg grating (CFBG) and a few-mode fiber Bragg grating (FMFG) is demonstrated using erbium-doped fiber (EDF) as the gain medium. In our linear-cavity configuration, the FMFG acts as full-reflecting mirror and wavelength selector while the CFBG with the 3-dB bandwidth of over 30 nm acts as a broadband partially reflecting mirror. The number of lasing wavelengths can be controlled by changing the state of polarization inside the cavity using a polarization controller. The large bandwidth of the CFBG enables continuous tuning of the lasing wavelengths by application of mechanical strain or thermal heating on the FMFG.

Linear cavity erbium-doped fiber laser with over 100 nm tuning range.

We report a widely tunable single-frequency linear-cavity erbium-doped fiber laser covering both the conventional wavelength band (C-band) and the long wavelength band (L-band). The laser has low threshold, high slope efficiency and high signal-to-noise radio. A large tuning range of over 100 nm is realized by optimization of the active fiber length.

Continuously spacing-tunable multiwavelength semiconductor-optical-amplifier-based fiber ring laser incorporating a superimposed chirped fiber Bragg grating

We investigate a flexibly tunable multiwavelength semiconductor-optical-amplifier-based fiber ring laser with continuous wavelength spacing controllability incorporating a superimposed chirped fiber Bragg grating (CFBG). The wavelength spacing of a superimposed CFBG can be continuously controlled by symmetrically modifying the chirp bandwidth of the grating with the specially designed apparatus. We achieve a wide and continuous tuning range of the wavelength spacing from 0.35 to 0.78 nm. The continuous tunability of the wavelength spacing is measured to be ~ +/-0.033 nm/mm. By controlling the reflection bandwidth of the tunable CFBG, we can independently adjust the number of lasing channels from 2 to 23 at the wavelength spacing of 0.51 nm.