Optimum design of 1.55-microm double heterostructures and ridge-waveguide lasers

The dependence of threshold current density and lateral-index difference for transverse guiding in a 1.55-microm InGaAsP/InP ridge-waveguide laser on the number of cladding layers, their thicknesses, and their compositions is presented. It is found that two cladding layers of intermediate band-gap InGaAsP (lambda(g) = 1.2-1.3 microm) are desirable to reduce the threshold current density and to reduce its sensitivity to layer-thickness variations. The use of active- and cladding-layer thicknesses between 0.1 and 0.15 microm minimizes the threshold current density and its sensitivity to layer-thickness variations. This regime of layer thicknesses results in relatively strong lateral-index guiding (Deltan(eff) approximately 0.06) in the 1.55-microm ridge-waveguide laser structure.

Single-mode-fiber 1 x N directional coupler

We report the development of an adjustable single-mode-fiber multiterminal directional coupler that exhibits efficient coupling and uniform terminal output over a wide range of coupling coefficients. The device is made using a new technique that employs silicon V-groove substrates in the fabrication of arrays of evanescently coupled taps on single-mode fibers. The coupler is highly directional and polarization independent and exhibits excess loss as low as 0.09 dB per terminal in a 1 x 7 device. The fabrication technique may be extended to produce devices having large numbers of terminals. Applications include use in fiber data-bus systems and as a tapped delay line for broadband signal processing.

Fiber-optic signal processor with applications to matrix-vector multiplication and lattice filtering

A new fiber-optic signal processor is proposed to implement systolic matrix-vector multipliers and lattice filters. 10(9) multiplications/sec can be achieved with currently available components for matrix-vector multiplications that involve Toeplitz matrices. A 2 x 2 (Toeplitz) matrix-vector multiplier has been experimentally demonstrated using single-mode fibers and directional couplers. The filtering characteristics of the device are also discussed.