Abstract

The filtering characteristics of a waveguide grating are well known,^1,2 with the transmission being a function of the detuning from the center frequency Γ = (2βk₀ − K). For a material with an intensity-dependent refractive Index, n = n₀ + n₂l, the guided mode index β, and thus the detuning Γ, become power dependent. Thus, for a given incident wavelength, the transmission of the grating varies with guided wave power. The waveguides used consisted of a 6-μm thick MBE grown film of InSb on a GaAs substrate. Two gratings (period, 2.7 μm) for input and output coupling and one distributed feedback grating (DFBG) (period, 1.3 μm) between the couplers were fabricated using standard holographic and ion-milling techniques. The experiments were carried out using the TM₁ mode for which the DFBG resonance falls in the vicinity of a number of CO₂ laser lines. A tunable cw CO₂ laser was used, for which the nonlinearities can be either thermal or due to two-photon absorption. The variation in the transmission of the DFBG was measured at discrete CO₂ wavelengths and agrees with theoretical calculations. The grating throughput was monitored as a function of incident power at various wavelengths. The measured transmission coefficient increased monotonlcally with increasing power over the waveguide power range of 0 → 100 mW. For a system without a DFBG, the transmission coefficient decreases with increasing power due to nonlinear input coupling. These results show a power-dependent change in the center wavelength of the DFBG due to an optically controlled grating transmission coefficient.

© 1988 Optical Society of America