D. Starodubov

40-nm-wide tunable fiber ring laser with single-mode operation using a highly stretchable FBG

We demonstrate a 750-Hz linewidth single-mode erbium-doped fiber (EDF) ring laser with wide tunability using a widely tunable fiber Bragg grating (FBG). The stable single-mode operation is realized by using the FBG as a narrow wavelength-selective element and 4 m of unpumped EDF as a saturable absorber in the cavity. The 40-nm continuous tuning range of 1522-1562 nm is achieved using a highly stretchable FBG that exhibits a filter tuning range of over 52 nm. The grating is prepared with chemically stripped deuterium-loaded fiber to eliminate degrading factors for the grating strength, thereby achieving the wide tunability. The tuning range represents a 3.5-fold increase in wavelength tuning over previous use of FBGs.

Dynamic dispersion compensation in a 10-Gb/s optical system using a novel voltage tuned nonlinearly chirped fiber Bragg grating

We experimentally demonstrate dynamic dispersion compensation using a novel nonlinearly chirped fiber Bragg grating in a 10-Gb/s system. A single piezoelectric transducer continuously tunes the induced dispersion from 300 to 1000 ps/nm. The system achieves a bit-error rate=10/sup -9/ after both 50 and 104 km of single-mode fiber by dynamically tuning the dispersion of the grating between 500 and 1000 ps/nm, respectively. The power penalty after 104 km is reduced from 3.5 to <1 dB.

Reconfigurable optical packet header recognition and routing using time-to-wavelength mapping and tunable fiber Bragg gratings for correlation decoding

We achieve reconfigurable optical header recognition and penalty-free routing of a 2.5 Gb/s packet stream with a 1.6-ns guard time. Our method uses cross-gain compression in a semiconductor optical amplifier for time-to-wavelength mapping, and two fiber Bragg grating arrays for tunable correlation decoding. This technique may be of value in future high-speed optical packet-switching nodes.

Simultaneous tunable dispersion compensation of many WDM channels using a sampled nonlinearly chirped fiber Bragg grating

We fabricated and characterized a tunable dispersion compensator for multiple wavelength-division-multiplexed (WDM) channels using a sampled nonlinearly chirped fiber Bragg grating, the channel dispersion can be adjusted from -200 to -1200 ps/nm, we demonstrate tunable dispersion compensation for three channels in a 10-Gb/s WDM system. All three channels achieve a BER=10/sup -9/ after propagating through either 60 or 120 km of standard single-mode fiber.

All-fiber bandpass filter with adjustable transmission using cladding-mode coupling

We demonstrate an all-fiber bandpass filter with 2-nm bandwidth and more than 25 dB of nonresonant light suppression (ignoring sidelobes) in a 60-nm-wide spectral range around its central wavelength. This novel device uses a pair of long-period gratings to couple resonant light from the fiber core into the cladding and then back into the core. The amplitude transmission through the filter is dynamically adjustable over a 20-dB range.

Adjustable compensation of polarization mode dispersion using a high-birefringence nonlinearly chirped fiber Bragg grating

We demonstrate an adjustable polarization-mode-dispersion (PMD) compensator. The device uses a nonlinearly chirped fiber Bragg grating written into a high-birefringence photosensitive fiber. By mechanically stretching the grating, the device generates a time delay between different polarizations that is adjustable from 100 to 320 ps and is tunable over 2.3 nm. We demonstrate tunable PMD compensation of a 10-Gb/s signal that has an initial delay between the two polarization states of 127 or 302 ps.

Bragg grating fabrication in germanosilicate fibers by use of near-UV light: a new pathway for refractive-index changes.

Using 334-nm light, we demonstrate side writing of Bragg gratings with an index change of ~10(-4) in germanium-doped fibers. No hydrogen loading of the fibers was required. These gratings have the same temperature stability as gratings fabricated with 240-nm light. Our results suggest that photoionization is not needed for formation of gratings in Ge-doped glass. We observe an enhancement of the 334-nm photosensitivity in boron-codoped fibers and suggest that B facilitates a structural transformation of the glass.

Behavior of fibre Bragg gratings under high total dose gamma radiation

We report on the effect of MGy dose level /spl gamma/-irradiation on the parameters of fibre Bragg gratings intended for sensing applications. The /spl gamma/-radiation sensitivities of gratings written with near-UV 330 nm light in hydrogen loaded Ge-doped fibres and of a grating written in a N-doped fibre were found to be higher than that of gratings written in a 10 mol.% Ge-doped fibre without hydrogen loading. In the former cases, changes in the amplitude and the width of the Bragg peak were observed during /spl gamma/-irradiation while no change was observed in the latter case. For the grating written in the N-doped fibre, the radiation-induced shift of the Bragg peak did not saturate while for gratings written in hydrogen-loaded Ge-doped fibres it saturated to a higher level than for gratings written in unloaded Ge-doped fibre.

Fabrication of long-period fiber gratings with no harmonics

We demonstrate a method to fabricate spectrally clean long-period gratings in optical fibers. Because the photosensitivity of glass is nonlinear, even a sinusoidal light pattern will generate harmonic gratings, and these higher order gratings can cause unwanted resonances. We solve this problem by first measuring the photosensitivity of the glass and then scanning the fiber across an ultraviolet light beam at a variable speed under computer control. The resulting spectra are free from extraneous resonances caused by harmonics of the fundamental grating period.

Wavelength-selective coupler and add-drop multiplexer using long-period fiber gratings

We demonstrate a low-insertion-loss wavelength-selective coupler that uses cladding-mode coupling between two identical fibers. The device is simple to manufacture, has >40 dB of channel isolation and no back-reflection.