Abstract

Surface-emitting nonlinear waveguide devices, based on coherent sum-frequency (SF) mixing of two counter-propagating guided waves, have attracted increasing interest for their potential applications in future high throughput all-optical fiber communication networks. Several authors have recently reported success with the proof-of-concept demonstrations of passive and laser-integrated nonlinear waveguide devices as wavelength sensors for frequency control of DFB lasers.[1], parametric spectrometers for DWDM demultiplexing [2] and serial-to-parallel-convertors for 100Gb/s TDM demultiplexing [3]. From the view point of practical systems implementation, one key parameter for these devices is the overall SF conversion efficiency because it ultimately dictates the signal-to-noise ratio and bit error rate (BER). For devices using quasi-phase-matched (QPM) AlGaAs multilayers structure, the efficiency is further affected by two somewhat related factors: the absorption of the SF light by the waveguide materials and the coupling efficiency of the input signal. Since the band gap of GaAs is smaller than the SF light photon energy for the wavelength that we are interested in, strong absorption occurs as the SF light propagating towards the waveguide surface. On the other hand, for thin guides, large mismatchs between waveguide thickness and fiber core size results large coupling losses. In order to improve the optical coupling, we have recently demonstrated a device employing a nonlinear antiresonant reflecting optical waveguide (NARROW) geometry [4]. The NARROW structure allows large coupling efficiency with fibers by providing a thick guiding core with high modal discrimination. We have obtained coupling efficiency of ~15% from a 8-μm core diameter fiber to a 2.6 μm thick NARROW device. Further improvement in coupling efficiency, however, is limited by the SF light absorption of the thick nonlinear layers.

© 1995 Optical Society of America