M. Bachmann

Optical bandwidth and fabrication tolerances of multimode interference couplers

Analytical expressions are derived which relate the optical bandwidth and the fabrication tolerances of multimode interference (MMI) couplers to their most important design parameters. These expressions compare adequately with mode analysis simulations. For strong guided structures, the optical bandwidth is shown to he inversely proportional to the number of input and output ports N and to the length of the device. The fabrication tolerances are independent of N and proportional to the output channel separation D. Measurements on MMI couplers in InP/InGaAsP corroborate the theoretical predictions. >

New 2/spl times/2 and 1/spl times/3 multimode interference couplers with free selection of power splitting ratios

We report on the concept and realization of new 2/spl times/2 and 1/spl times/3 multimode interference (MMI) couplers that offer the possibility of a free choice of the power splitting ratio. These MMI devices, using a new butterfly geometrical design, are compact, polarization-insensitive, and tolerant to fabrication parameters. Realized in InGaAsP/InP with large fabrication tolerances, they permit the control of the output powers within a few percentage points for both polarizations. The measurement results fit well the theoretical predictions. Extensions of the design are presented that assure a fully symmetrical geometry and therefore an optimal homogeneity of the device characteristics. Based on the same idea, a new compact mode converter-combiner is proposed.

Low-loss polarization-insensitive InP-InGaAsP optical space switches for fiber optical communication

High-performance InP-InGaAsP optical space switches are reported, which in monolithic four switch arrangements reach fiber-to-fiber losses as low as 5 dB. Polarization insensitivity is within /spl plusmn/0.5 dB. On-off ratios throughout the 1.53-1.56 /spl mu/m wavelength range exceed 15 dB. Switch rearrangement times are below 200 ps.

The integrated prism interpretation of multileg Mach-Zehnder interferometers based on multimode interference couplers

To simplify the driving conditions as well as to improve the wavelength response of multileg Mach-Zehnder interferometers (MZI) based on multimode interference (MMI) couplers we develop a new interpretation of these devices. Used for optical switching and for wavelength filtering, they are shown to work as active or passive integrated prisms. This analogy greatly facilitates the design of such components and simplifies the understanding of their functionality. The driving conditions of optical switches based on such multileg MZI are easility studied and will be reduced to basic active phase shifts. For wavelength filtering applications using such elements, a new design of the phased waveguide array is proposed which improves the characteristics of the filters.

Polarization-insensitive high-speed InP/InGaAsP access node space switch matrix for bidirectional optical ATM networks

An InP/InGaAsP optical space switch matrix with 5 polarization-insensitive Mach-Zehnder interferometers in 3 stages and with 6 inputs and 6 outputs for access network applications is reported. The switches, specially designed for a low polarization dependence and low insertion losses, typically show on-state polarization-sensitivities of less than 0.5 dB, nearly identical switching voltages of around 7 V for TE and TM polarization, insertion losses below 11 dB, on-off ratios above 15 dB and high-speed switching capabilities up to 3 Gb/s.