David B. Patterson

Fiber Bragg gratings for dispersion compensation in transmission: theoretical model and design criteria for nearly ideal pulse recompression

We propose a transmission-based dispersion compensator employing an apodized, unchirped fiber Bragg grating (FBG). A theoretical model for dispersion compensation in transmission based on the dispersive properties of the periodic structure is developed. A figure of merit is defined for optimization of the grating parameters for maximum recompression of dispersion-broadened optical pulses in long-haul communication systems. Numerical examples confirm that nearly perfect compensation with very low insertion losses can be achieved for many practical cases of interest.

Acousto-optic modulators for optical fibers using Hertzian contact with a grooved transducer substrate

The authors describe acousto-optic modulators for optical fibers, fabricated by the deposition of thin zinc-oxide transducers onto specially lapped glass capillary tubes. By exposing the inner surface of the capillary and contacting it to an optical fiber of the same diameter, a good Hertzian contact can be easily attained, providing efficient throughput of acoustic energy at frequencies in excess of 1 GHz. A phase modulator for a single-mode fiber has been fabricated in such a manner, achieving a maximum phase retardation of 1.0 rad/W input electrical power at 416 MHz. Its frequency, power, and polarization characteristics are discussed. Also presented are data from a frequency shifter/modal coupler for a two-mode optical fiber. This device achieved 6% power coupling from the fundamental optical mode to the second-order mode with 500 mW input power at 1.03 GHz. Single sideband modulation was observed with >19-dB suppression of the unwanted sideband. The authors also describe the design of an optical tap using the same technology.<<ETX>>

Analysis of fiber Bragg gratings for dispersion compensation in reflective and transmissive geometries

Numerical analysis of the dispersion-compensating properties of fiber Bragg gratings (FBGs) in both reflective and transmissive modes is presented. First, the sensitivity of chirped, reflective gratings to the grating chirp parameter, index modulation, and grating length is examined, showing that apodization provides lower sensitivity to variations in these parameters. Second, we introduce a new transmissive geometry for grating-based dispersion compensation that utilizes the dispersive properties of a uniform Bragg grating in transmission.

Mode-locked fiber laser with a fiber phase modulator

FM mode-locked operation of a single-mode Nd(3+)-doped fiber laser has been achieved with an integrated fiber phase modulator. The technique permits a low-loss cavity configuration, resulting in low threshold and high slope efficiency. Pulses of ~200-psec duration are observed at a repetition rate of 417 MHz with an average output power of 15 mW.

Vector modal solution of evanescent coupler

We present a vector modal solution for the evanescent coupler comprising an optical fiber and a slab waveguide. We identify the normal vector ridge modes of the device for different configurations. The dispersion characteristics and the power transmission properties of these modes are presented. Also, the effect of the proximity between the waveguides on the ridge modes is investigated.

All-fiber acoustooptic phase modulators using zinc oxide films on glass fiber

Experiments with an acoustooptic phase modulator for single-mode optical fibers are described. The device, which operates in the 500-MHz frequency range, uses a zinc oxide transducer sputter-deposited on top of a gold film evaporated on the fiber. The device is heat cooled and partially acoustically terminated by gallium, which is also used as the top electrode of the transducer. The maximum modulation observed on a 2-mm length of fiber is 2 rad with an input power of 2 W. >

Detachable 400-MHz acousto-optic phase modulator for a single-mode optical fiber.

A single-mode-fiber phase modulator was constructed by contacting the fiber with a lapped glass capillary tube. The capillarys inner surface provides a long, effectively semicircular contact region to the fiber, allowing throughput of acoustic waves launched from a thin-film ZnO transducer fabricated directly onto the capillarys other lapped face. The device operated at a center frequency of 416 MHz with a FWHM bandwidth of 14 MHz. The maximum phase shift was 0.033 rad/ radicalmw, with a largest measured value of 1.2 rad at 1.3-W input electrical power.

Diode-pumped FM modelocked fibre laser with coupled cavity bandwidth selection

A diode-laser-pumped Nd3+-doped fibre laser has been actively mode-locked using an integrated fibre phase modulator. Pulses with a sub-80 ps duration are observed at a repetition rate of 417 MHz. Near bandwidth-limited operation is achieved by restricting the laser bandwidth by feedback off a diffraction grating in an external coupled cavity. Low intracavity losses support a submilliwatt laser threshold and a slope efficiency in excess of 48%.

Frequency shifting in optical fiber using a SAW horn

The authors present an in-fiber frequency shifter for optical fiber which uses flexural acoustic waves to induce mode coupling between the two optical modes of a dual-mode, elliptical-core fiber. A sharply tapered surface-acoustic-wave horn is used to excite these waves in the fiber, providing a robust, efficient acoustic source. Optical mode filters at the input and output ensure spectral purity of the frequency-shifted light. A 6.3-MHz frequency upshift in 1.3- mu m light with 400-mW input power, with a 35-dB sideband suppression, was demonstrated. Recently studied methods for improving the sideband suppression through mode-filtering techniques are also discussed.<<ETX>>

Switchable acoustooptic tap for optical fibers

We recently reported a new type of acoustooptic modulator for optical fiber1,2 which uses a glass capillary half to provide a semicylindrical contact region between the acoustic transducer and optical fiber. Phase modulation in single-mode fiber and mode coupling in two-mode fiber have been demonstrated. This paper presents an extension of the latter interaction to provide switchable tapping of light propagating in the fundamental mode of a two-mode fiber. Using a 1-GHz acoustic frequency, we observed up to –30-dB tapping of the fundamental mode with a 3-dB bandwidth of 20 MHz. We also discuss the tapping of light in a single-mode fiber via a similar coupling mechanism with low-order cladding modes.