Robert P. Moeller

Fully packaged, broad-band LiNbO 3 modulator with low drive voltage

A low drive voltage of /spl sim/5 V at 40 GHz has been achieved in a fully packaged, broad-band LiNbO/sub 3/ modulator. The excellent response is attributed to nearly perfect velocity and impedance matching, along with very long electrodes (41 mm), low electrode losses, and minimal packaging effects. Very accurate frequency-dependent drive voltages are obtained by the use of independent sets of measurements.

Polarization holding in birefringent single-mode fibers

Perturbations in highly birefringent single-mode fibers couple the two polarization modes and degrade the polarization-holding ability. With a broadband source we demonstrate wavelength averaging of the power in either mode, permitting a simple measurement of the power transfer to the cross-polarized mode as a function of fiber length. Using this technique, we confirm experimentally the theory of random mode coupling between the polarization modes.

Open-loop output and scale factor stability in a fiber-optic gyroscope

An all-fiber open-loop, fiber-optic interferometric gyro with polarization-preserving fiber with 14-dB insertion loss and 20-dB polarization extinction is described. The random drift coefficient is 3.2*10/sup -40// square root h for a 1-km coil length on a 16-cm radius. Bias drift is within 0.03 degrees /h over three days. Source coherence effects and optical feedback are shown to result in additional terms in the demodulated output, which can be corrected for. A procedure for obtaining scale-factor coefficients is described. With modeling for temperature and source drive current, these coefficients are measured to be stable within 32 p.p.m. over 12 days. >

Linear interferometric waveguide modulator for electromagnetic-field detection

A channel-waveguide interferometer with asymmetric arms, suitable for electromagnetic-field detection, is described. A π/2 intrinsic phase differential makes the output linearly proportional to the applied voltage (electromagnetic field). Horizontal and vertical electrode sets provide polarization-independent operation, with electrode lengths chosen to make the voltages approximately equal. In Ti-diffused devices in Z–X-cut LiNbO3, the TE- and TM-mode outputs are equally modulated with the horizontal voltage 43% of the vertical. Output linearity over a 40-dB range and operation up to 300 MHz are demonstrated.

High-stability Er/sup 3+/-doped superfluorescent fiber sources

Data are presented on Er/sup 3+/-doped superfluorescent fiber sources showing the dependence of output characteristics on pump wavelength and power, fiber length, fiber temperature, and feedback. In particular, the broadband operation and mean wavelength stability required for fiber optic gyroscope applications are evaluated. Substantial improvements in the mean wavelength stability with pump power have been achieved by optimizing the fiber length. An all-fiber superfluorescent fiber source utilizing a fiber-pigtailed 980-nm diode pump laser is demonstrated, with a 1-h mean wavelength stability better than 0.9 ppm RMS and /spl les/8 ppm drift over 20 h. The intrinsic mean wavelength variation versus fiber temperature is measured, with values of 4.8 and 3.0 ppm//spl deg/PC obtained for fiber lengths of 23 and 78 m, respectively. >

High‐power low‐divergence superradiance diode

Using a combination of antireflection coating and proton implantation techniques, GaAlAs double‐heterostructure lasers are fabricated to operate in superradiant mode. Light output, in excess of seven milliwatts, is obtained with spectral half‐power widths of 15–20 nm. This implies extremely short coherence lengths of less than 50 μm. Such a short coherence length light source should be very useful for many applications in fiber sensors and fiber optic communications. In particular, it has produced marked reduction (better than 15 dB) of coherent Rayleigh backscattering noise in a single‐mode fiber. Since the laser operates in superradiant mode, the output light is only partially polarized, another unique characteristic that is important for fiber gyroscopes. The typical light output angle of 30°×50° also provides easy coupling into fibers. Coupling efficiencies of 80% into multimode fiber and over 20% into single‐mode fiber have been achieved.

Low drive voltage, broad-band LiNbO/sub 3/ modulators with and without etched ridges

Frequency dependent drive voltage is reported in velocity matched, packaged, Mach-Zehnder interferometers, made on Z-cut, Y-propagating LiNbO/sub 3/, with and without etched ridges. Drive voltages of /spl sim/7 V at 40 GHz are demonstrated, with the etched ridge device showing a 1/2-1 V advantage. Microwave modeling allowed the extraction of the effects of dispersion in material properties, occurring near the acoustic resonance, on bandwidth and drive voltage.

1.06-μm all-fiber gyroscope with noise subtraction

An all-fiber gyroscope that uses a 1.06-microm multicore Nd-doped fiber source pumped by a laser-diode array is demonstrated. Intensity noise subtraction is used to reduce the excess noise that arises from a source bandwidth limitation. The random walk coefficient is improved by a factor of 3, to 2.5 x 10(-4) deg radicalh (1-km fiber, 16-cm radius).

Fiber-optic gyroscope with polarization-holding fiber.

A fiber gyroscope is reported that uses polarization-holding fiber in the coil, the phase modulator, and the coupler. The random-drift coefficient, calculated from rms noise levels, was 8.10−4deg/h, within a factor of 2 of an experimentally determined quantum and thermal limit. White-noise behavior was observed for integration time constants from 1 to 40 sec. Device characteristics and performance are presented.

High-power superfluorescent source with a side-pumped Yb-doped double-cladding fiber

A compact superfluorescent source based on an Yb-doped double-cladding fiber amplifier is described. The packaged amplifier is pumped at 975 nm by side-coupling emission from a 2.0-W broad-stripe laser diode through an imbedded V groove. The fiber source generates 485 mW of broadband emission centered at 1055 nm with a 41-nm FWHM flat power spectrum.