All-optical devices based on carrier nonlinearities for optical filtering and spectral equalization.

摘要

InGaAsP-based quantum wells can display nonlinear refractive index changes of ∼0.1 near the band-edge for intrawell carrier density changes of 1 × 1018cm−3, due to effects like bandfilling and the plasma effect, which make these materials promising for the realization of all-optical signal processing devices, as demonstrated here.; A novel single passband filter with sub-gigahertz bandwidth and greater than 40nm of tunability was experimentally demonstrated. The filter uses the detuning characteristics of nearly degenerate four-wave mixing in a broad area semiconductor optical amplifier to obtain frequency selectivity. The key to this demonstration was the spatial separation of the filtered signal from the input signal, based on their different propagation directions. An analysis of an analogous integrated optic dual-order mode nonlinear mode-converter, with integrated mode sorters which separate the signal from the interacting modes, was also undertaken. This device is promising as a filter, a wavelength converter, notch filter, and a wavelength recognizing switch. Novel ways to prevent carrier diffusion, which washes out the nonlinear grating, were suggested. It is important to have a large mutual overlap to modal overlap ratio of the two interacting modes on the nonlinear medium, because the mixing efficiency scales as the fourth power of this number.; Three types of integrated optic limiters (based on Kerr-like nonlinearities) namely an all-optical cutoff modulator, a nonlinear Y-branch and an interferometer with an internal Kerr element, were theoretically investigated. A beam propagation program, which can solve the propagation of an optical field in a semiconductor in the presence of carrier diffusion, was developed for the numerical analysis of these structures. A negative feedback mechanism was identified in the Y-branch devices and a new limiting configuration was discovered in a Y-branch with a selectively placed defocusing nonlinearity. Dichroic materials like compressively strained quantum wells are a promising material for the limiters. A novel wavelength insensitive pulse limiter based on a polarization-maintaining fiber Sagnac loop with such an intraloop dichroic waveguide was demonstrated, and displays superior noise reduction characteristics compared to a saturating optical amplifier/two-photon absorption waveguide.