H. D. Liu

Multi-wavelength operation of an erbium-doped fiber ring laser using a dual-pass Mach-Zehnder comb filter

Abstract We propose and demonstrate a novel multi-wavelength erbium-doped fiber ring laser. A dual-pass Mach–Zehnder (M–Z) interferometer fiber device is used as a comb filter inside the fiber laser cavity. Simultaneous oscillation of nine wavelengths is obtained when the erbium-doped fiber is immersed in liquid nitrogen. Tuning of the peak wavelengths and the spacings between adjacent modes in this laser is also demonstrated by controlling the optical path difference between the two arms of the M–Z device.

Effects of ion clusters on the performance of a heavily doped erbium-doped fiber laser

A cluster model is proposed for study of the effects of the number of ions per cluster on the performance of a heavily erbium-doped fiber laser. The results indicate that both the threshold pump power and the unstable-operation region of the fiber laser increase with increasing numbers of ions per cluster.

Ultraviolet-initiated reactions of H 2 with germanosilicate fibers and H 2 concentration dependence of the Bragg wavelength of a fiber grating: errata

We present a model with which to calculate the index increase induced in standard single-mode fiber by hydrogen loading. Also, we propose that the dominant products of reaction in UV-written hydrogenated standard communication fibers are GeE′ and Si-OH. Based on the above models, we calculate the Bragg wavelength shifts that are due to hydrogen diffusion out of the fiber gratings. The relative effective index change that is due to hydrogen dissolved in fiber can be as much as 6×10-4 if standard telecom fiber is hydrogen loaded with a concentration of ∼1.44 mol.%. Theoretical results agree with experimental results.

Four-wave mixing in a fiber loop mirror constructed from two polarization-maintaining dispersion-shifted fibers

A fiber loop mirror constructed from two polarization-maintaining dispersion-shifted fibers is proposed and four-wave mixing (FWM) in this loop is theoretically investigated. Our results show that this fiber loop can inherently suppress the pump and signal waves even without optical filtering in continuous-wave or long-pulse cases. The difference between one-pump (nearly degenerate) and two-pump (nondegenerate) FWMs is also presented.

Compact Single-Mode Distributed Bragg Reflector Fiber Laser

A compact single-mode distributed Bragg reflector (DBR) fiber laser with narrow spectral linewidth is investigated. Firstly, based on our theoretical analysis the single longitudinal mode operation domain is obtained. Then, a single-mode DBR fiber laser of 7.9 cm long with master oscillator power amplifier (MOPA) configuration is designed and constructed to operate in the single-mode domain. The fiber laser is pumped by a semiconductor laser at 975.5 nm. The master oscillator operates at 1556.91 nm with a cw output power of 1.43 mW for a pump power of 55.35 mW. Its slope efficiency is 2.7% and the spectral linewidth is less than 1.2 MHz (instrument resolution limited). With the MOPA configuration the laser output power and slope efficiency are increased to 7.8 mW and 16.9%, respectively.

Four-wave mixing and all-optical switching in a fiber loop mirror constructed from two dispersion-shifted fibers

A fiber loop mirror constructed from two polarization- maintaining dispersion-shifted fibers with different zero- dispersion wavelengths is theoretically investigated. Our results show that this fiber loop can be used for both four- wave mixing without optical filtering and all-optical switching.

Intensity-noise suppression by ytterbium codoping in heavily erbium-doped fiber lasers with partly clustered erbium ions.

The effect of ytterbium codoping in heavily erbium-doped fibers with partly clustered erbium ions on the intensity noise stemming from both pump-rate and cavity-loss fluctuations is theoretically investigated with a modified ion-cluster model. Numerical results indicate that low-frequency (below 1 MHz) noise can be greatly suppressed by ytterbium codoping.

Multi-wavelength Operation of an Er3+-doped Fiber Laser at Room Temperature with a Novel Optical Fiber Mach-Zehnder Interferometer

A novel multi-wavelength erbium-doped fiber laser with a double-pass Mach-Zehnder fiber interferometer acting both as a comb filter and as a reflection mirror is demonstrated. The spatial hole burning effect introduced by the standing wave cavity configuration enables the simultaneous operation of multiple wavelengths in the homogeneously broadened erbium-doped fiber at room temperature. In the experiment, simultaneous oscillation of four wavelengths at room temperature has been obtained.

Photosensitivity and Hydroxyl in Hydrogenated Silica Fibers

Optical loss spectra and refractive index changes have been measured in the hydrogenated standard telecommunication fiber and photosensitive fiber. The index changes due to ultraviolet exposure were found to be closely related with the OH formation in both types of fibers. A direct photolytical model is proposed to explain the effect of hydrogen loading on the enhancement of the photosensitivity in silica fibers.

HYDROGEN CONCENTRATION DEPENDENCE OF BRAGG WAVELENGTH OF UV-WRITTEN FIBER GRATING

Hydrogen loading provides highly enhanced photosensitivity in Ge-doped fiber. But the Bragg wavelength of UV-written fiber grating will shift from its initial value as the remaining hydrogen diffuses out of such fiber. A simple model to calculate the index change of hydrogenated fibers is presented. The theoretical model is in good agreement with experimental results and it can well predict the final wavelength position of UV-written weak fiber grating.