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We propose and demonstrate hydrophobic photonic crystal fibers (PCFs). A chemical surface treatment for making PCFs hydrophobic is introduced. This repels water from the holes of PCFs, so that their optical properties remain unchanged even when they are immersed in water. The combination of a hollow core and a water-repellent inner surface of the hydrophobic PCF provides an ultracompact dissolved-gas sensor element, which is demonstrated for the sensing of dissolved ammonia gas.

Novel multiplexers–demultiplexers for dense wavelength-division multiplexing systems that use interleaved sampled gratings are presented. It is shown that, with the appropriate design, configurations ranging from hybrid to add–drop as well as all-grating-based multiplexers can easily be realized.

Novel multiplexers–demultiplexers for dense wavelength-division multiplexing systems that use interleaved sampled gratings are presented. It is shown that, with the appropriate design, configurations ranging from hybrid to add–drop as well as all-grating-based multiplexers can easily be realized.

We present experimental results of complex grating structures fabricated with uniform phase masks by the moving fiber–scanning beam approach. Pure apodized gratings with side-mode-suppression levels in excess of 40 dB, self-apodized linearly chirped gratings, and phase shifted gratings with narrow-band transmission peaks have all been realized.

Boron- and germanium-doped highly photosensitive cladding is used in a novel design to achieve photosensitive Er/Yb-doped fibers, permitting short, strong gratings (length ≈1 cm, reflectivity >99%) to be written without hydrogenation. The high absorption at 980??nm in Er/Yb fibers permits efficient pump absorption over a short device length, which is ideal for achieving highly efficient single-frequency fiber lasers. Both single-frequency Bragg-grating reflector and distributed-feedback lasers with slope efficiencies of 25% with respect to launched pump power have been realized in such fibers.

We demonstrate stable single-frequency and polarization operation of a traveling-wave, Er^3+-doped fiber loop laser by incorporating an unpumped Er^3+-doped fiber section butted against a narrow-band feedback reflector. The saturable absorber acts as a narrow bandpass filter that automatically tracks the lasing wavelength, thus ensuring single-frequency operation. Output powers up to 6.2 mW at 1535 nm were obtained for launched pump powers of 175 mW at 1064 nm. At this output, the relative intensity noise was less than −112 dB/Hz at frequencies above 200 kHz and a laser linewidth of less than 0.95 kHz, whereas the lasing frequency was observed to drift slowly (∼170 MHz/h) because of environmental effects.

A new approach to improving the stability of erbium-doped fiber lasers is presented. By use of a model based on ion-pair effects, spiking behavior is shown to be effectively suppressed by resonant pumping when the pump wavelength is sufficiently close to the lasing wavelength.

We study both experimentally and theoretically soliton interaction in the presence of a weak nonsoliton component and show that the existence of a frequency-shifted cw wave results in a temporal shift of the soliton.

The absorption spectra of clustered and isolated ions in erbium-doped germanosilicate fibers have been experimentally studied. The ground-state absorption spectra broaden as the degree of erbium-ion clustering increases, indicating that the absorption spectrum of clustered ions is significantly different from that of the homogeneous ions. This fact is confirmed by comparison of the broadened absorption spectra with the fiber's unbleachable loss spectrum, a direct measurement of the clustered ions. This is the first experimental evidence to the authors' knowledge that indicates different absorption cross sections for the two species of ions in germanosilicate glass, an assumption that is used in the theoretical description of self-pulsing in erbium-doped fiber lasers but is in direct contradiction to the pair-induced quenching model widely used to characterize erbium-doped fiber amplifiers.

We propose and demonstrate a polarimetric Er^3+-doped fiber distributed-feedback laser sensor in which a force applied transversely along the fiber laser induces a birefringence that gives rise to a change in the beat frequency between the two orthogonally polarized laser modes. We measure a sensitivity of ~9.6 GHz/(N/mm), a wide dynamic range with stable two-mode operation for frequency separations up to 50 GHz, and high sensor resolution owing to the narrow beat frequency bandwidth of <10 kHz. The temperature sensitivity is dominated by the temperature dependence of the inherent birefringence, which was measured to be −130 kHz/°C. The sensor permits independent pressure–force and temperature measurements.

Experimental results are presented showing that resonant pumping can significantly improve the stability of erbium-doped fiber lasers. In particular, it is observed that an erbium fiber laser that exhibits sustained spiking behavior when pumped at 980 nm will revert to stable cw operation when pumped at 1510 nm.

We have made an experimental study of the time jitter in a harmonic passively mode-locked fiber soliton ring laser. We demonstrate that jitter as low as 600 fs (100–550 Hz), which is less than the soliton pulse width, can be achieved at a repetition frequency of 463 MHz. The results support the suggestion that the stability of the laser is dependent on the long-range soliton interaction through the excitation of acoustic waves that is induced by the propagating pulses.

We present experimental results of complex grating structures fabricated with uniform phase masks by the moving fiber-scanning beam approach. Pure apodized gratings with side-mode-suppression levels in excess of 40 dB, self-apodized linearly chirped gratings, and phase shifted gratings with narrow-band transmission peaks have all been realized.

The spacing between optical amplifiers in a long-haul soliton system may be increased to 100 km by using only passive quantum-well saturable absorbers and narrow-band filters for soliton control. After transmission over 9000 km at 10 Gbits/s, the effects of soliton–soliton interaction and Gordon–Haus jitter in the proposed system yield bit error rates of better than 10^−9.