Spatial mode filters based on multimode interference couplers (MMI’s) that offer the possibility of splitting off antisymmetric from symmetric modes are presented, and realizations of these filters in InGaAsP/InP are demonstrated. Measured suppression of the antisymmetric first-order modes at the output for the symmetric mode is better than 18 dB. Such MMI’s are useful for monolithically integrating mode filters with all-optical devices, which are controlled through an antisymmetric first-order mode. The filtering out of optical control signals is necessary for cascading all-optical devices. Another application is the improvement of on-off ratios in optical switches.
© 1996 Optical Society of America
J. Leuthold, R. Hess, J. Eckner, P. A. Besse, and H. Melchior, "Spatial mode filters realized with multimode interference couplers," Opt. Lett. 21, 836-838 (1996)