Guoyong Sun

Strain and Temperature Discrimination Using High Birefringence Fiber Sagnac Interferometer With Enhanced Sensitivities

Discrimination between the strain and temperature variations based on the Sagnac interferometer is newly proposed and demonstrated with much improved properties. It is achieved by containing five sections of high birefringence fibers (HBFs) in the Sagnac interferometer-three of them spliced together act as the compact sensing head and the other two are isolated from the strain and temperature changes. By properly setting all the HBF lengths and relative orientations of their primary polarization axes, the strain and temperature sensitivity coefficients of the two wavelength dips generated due to the Sagnac interference may be greatly enhanced with the effectively reduced cross sensitivity.

Broadly Tunable Fiber Laser Based on Merged Sagnac and Intermodal Interferences in Few-Mode High-Birefringence Fiber Loop Mirror

A broadly tunable fiber ring laser including a few-mode high-birefringence fiber (FM-HBF) loop mirror is proposed and demonstrated. The operation mechanism is based on simultaneous occurrence of Sagnac and intermodal interferences in the FM-HBF loop mirror and polarization dependence of the modal excitation in the FM-HBF. While adjusting only a polarization controller next to the FM-HBF in the loop arm, the lasing wavelength can be tuned at a discrete step defined by the intermodal interference. The tunable range exceeding 40 nm with sidemode suppression ratio over 40 dB and power uniformity better than 1 dB at a discrete step of about 2.2 nm has been successfully demonstrated for the proposed fiber ring laser.

Switchable and Tunable Dual-Line Erbium-Doped Fiber Ring Laser in the

A simple but novel concept of switchable and tunable dual-line erbium-doped fiber ring laser in the C - plus L -band is proposed and demonstrated. It is based on concurrence of the Sagnac and modal interferences in a fiber loop mirror including cascaded high birefringence few-mode fiber (HB-FMF) and polarization controller (PC). Random combination of the two lasing lines, one in the C-band and the other in the L-band, can be realized by adjusting only the PC next to the HB-FMF in the loop arm. In addition, they can be simultaneously tuned at a discrete step equal to the channel spacing of the modal interference. The output power flatness is better than ±0.5 dB for both the single- and dual-line emissions by carefully choosing the HB-FMF length with the 3-dB spectral linewidth narrower than 0.03 nm and signal-to-noise extinction ratio higher than 40 dB during the whole switching and tuning processes.

C

A tunable multiwavelength fiber ring laser based on a semiconductor optical amplifier and Sagnac loop mirror incorporating a piece of few-mode high birefringence fiber (FM-HBF) is proposed and experimentally demonstrated. It is accomplished by simply adjusting a polarization controller in the Sagnac loop mirror because birefringence of the FM-HBF is polarization dependent. Tunable multiwavelength operation up to 11 oscillating lines at about 2.1 nm interval is stably achieved with an optical side-mode suppression ratio over 35 dB.

- Plus

A multiwavelength switchable erbium-doped fiber laser with linear cavity is proposed and experimentally demonstrated. It is based on a fiber loop mirror incorporating a piece of high birefringence few-mode fiber and polarization controller. Due to dependence of its reflection properties on the polarization controllers, the fiber laser can operate in the random combination of three wavelengths by only adjusting the polarization controllers in the linear cavity. The wavelengths involved in the switching operation are determined by the merged Sagnac and intermodal interferences elicited in the fiber loop mirror. The optical signal to noise extinction ratio of every oscillation line is higher than 40 dB and power fluctuation less than 0.5 dB.

L

A simple and high-stress resistance fiber refractometer based on the multimode fiber (MMF) intervening between two single-mode fiber (SMF) half-tapers is interrogated and experimentally demonstrated. The generated interference fringe shifts toward longer wavelengths with the response sensitivity of 319.3 nm/RIU at the external refractive index (RI) of 1.333, and the response sensitivity monotonically increases to 500.6 nm/RIU when the RI varies from 1.333 to 1.411. More importantly, the endurable longitudinal strain of the fiber refractometer may exceed 4000 με before breaking, which is just a little lower than that of the traditional SMF-MMF-SMF configuration. In addition, the effect of the MMF length on the RI sensitivity is also investigated, and the theoretical analysis shows the same tendency with the experimental results.

-Band Based on Merged Interference Effects

A simple but novel concept of switchable dual-wavelength erbium-doped fiber ring laser is proposed and experimentally demonstrated. It is based on a Sagnac loop mirror incorporating a high birefringence few-mode fiber and polarization controller (PC). Since its transmission properties depend on the PC state, the proposed fiber ring laser can operate in the random combination of two wavelengths by adjusting only the PC settings. The potential lasing lines are determined by simultaneous occurrence of the Sagnac and intermodal interferences in the Sagnac loop mirror. All lasing emissions have the optical signal to noise extinction ratio higher than 45 dB and their power fluctuations lower than 0.5 dB.

Tunable multiwavelength SOA-fiber ring laser based on Sagnac loop mirror incorporating few-mode high birefringence fiber

A fiber sensor capable of discriminating the strain and temperature variations is presented and fully investigated. Its simple configuration is a Sagnac interferometer containing only one piece of high birefringence few-mode fiber and a polarization controller in the loop arm. The Sagnac and intermodal interferences are generated simultaneously. Based on the combined interferences, it is possible to decouple the strain and temperature changes by monitoring the wavelength and power of one localized peak originating from the intermodal interference in the spectral response of the Sagnac interferometer.

Polarization controlled multiwavelength switchable erbium-doped fiber laser based on high birefringence few-mode fiber loop mirror

Individual or simultaneous monitoring of the temperature and strain variations by use of the high birefringence fiber loop mirror is newly proposed and demonstrated with reduced cross sensitivity. It is accomplished by incorporating two types of high birefringence fibers in the loop arm, which are spliced together to act as the compact sensing head. By properly choosing their birefringence, cutting their lengths and setting their relative orientation with respect to the primary axes, the temperature and strain may be individually or simultaneously measured with the effectively reduced cross sensitivity.