Optical fiber (800-Mbit/sec) transmission experiment at 1.05 microm

Stable fiber-optic time transfer by active radio frequency phase locking

In this Letter we demonstrate a fiber link capable of stable time signal transfer utilizing our active long-distance radio frequency (RF) stabilization technology. Taking advantage of the chromatic dispersion in optical fiber, our scheme compensates dynamically the link delay variation by tuning the optical carrier wavelength to phase lock a round-trip RF reference. Since the time signal and the RF reference are carried by the same optical carrier, a highly stable time transfer is achieved at the same time. Experimentally, we demonstrate a stability of the time signal transfer over 50-km fiber with a time deviation of 40 ps at 1-s average and 2.3 ps at 1000-s average. The performance of the RF reference delivery is also tested, with an Allan deviation of 2×10(-15) at 1000-s average. According to our proposal, a simultaneous stable time and frequency transfer is expected.

Radiation losses of step-tapered channel waveguides

We compute the radiation losses of a rectangular dielectric waveguide (integrated optics channel waveguide) that is tapered so that its wider cross-sectional dimension increases by roughly a factor of three while its narrow dimension remains constant. As the waveguide widens its refractive index decreases to ensure that the waveguide supports only one guided mode. The taper is approximated by a discontinuous staircase curve. A rectangular waveguide taper of 2-microm thickness, tapering from 3- to 10-microm width through fourteen steps of 0.25-microm height, has a minimum loss (at 0.6328-microm wavelength) of 0.13 dB for a 200-microm taper length.

Optical properties of titanium-diffused LiNbO(3) strip waveguides and their coupling-to-a-fiber characteristics

Optical propagation losses and coupling losses in Ti-diffused strip waveguides, fabricated in y-plate and z-plate LiNbO(3), have been examined at 1.15-,microm wavelength. Propagation losses for y-plate and z-plate waveguides are ~0.5 dB/cm. Coupling losses in the y-plate and z-plate waveguides for a single-mode fiber are 2.5 and 1 dB, respectively. This difference is due to the large surface diffusion anisotropy; it is expressed by near-field pattern overlap calculations.

Semiconductor laser to single-mode fiber coupler

Promising results of various coupling experiments between laser diodes and single-mode fibers to determine the optimum coupling method are reported. The cylindrical lens method is shown to be most efficient, with a coupling loss of 1.8 dB under optimum alignment conditions. More than -2 dB coupling efficiency is attained with a cylindrical lens whose radius is less than 8 microm. The laser to fiber coupling characteristics are estimated by Gaussian beam approximation. The optimum radius of a cylindrical lens, which gives maximum coupling efficiency, is derived by theoretical calculation, using the ray matrix method. The cylindrical lens alignment tolerance is also shown theoretically and experimentally.