Four-wave mixing in semiconductor optical amplifiers for terahertz spectroscopy and wavelength conversion

Author: Zhou, Jianhui

Year: 1995

Degree: Dissertation (Ph.D.)

Advisor: Vahala, Kerry J.

Committee Member: Unknown, Unknown

Option: Applied Physics

DOI: 10.7907/vmke-sz45

Abstract

Four-wave mixing in semiconductor gain media from GHz to THz detuning rates was used as a frequency-domain technique for analysis of carrier relaxation mechanisms having relaxation times extending from nanosecond to femtosecond time scales. Measurements of four-wave mixing in various semiconductor traveling-wave amplifiers were performed for detuning frequencies as large as 1.7 THz. Ultrafast intraband mechanisms having relaxation time constants of 650 fs, in agreement with dynamic carrier heating, and of less than 100 fs, in agreement with intraband carrier-carrier scattering, were determined in the measurements.

A novel cross-polarized four-wave mixing technique was also developed to study the inter quantum well carrier transport process in quantum well amplifiers. A semiconductor optical amplifier having a structure of alternating tensile and compressively strained quantum wells was used. Polarization selection rule of the strained quantum wells enables selective excitation and probing of adjacent quantum wells according to polarization, thereby enabling study of inter-well carrier transport. A one-dimensional diffusion model was developed to illustrate the different transport efficiencies for carrier number and temperature modulations, thereby qualitatively explaining the experimental data. The inter-well carrier number transport rate in the device measured was determined to be greater than 100 GHz.

Four-wave mixing in semiconductor optical amplifiers was also studied as a wavelength conversion technique. Conversion efficiency over spans up to 65 nm was measured, and wavelength conversion with gain was also demonstrated. It was found theoretically and confirmed experimentally that the conversion efficiency varies with the cube of the saturated amplifier gain. Noise characteristics of four-wave mixing wavelength converters and their dependence on various device and operational parameters were also studied. Noise reduction by introducing a filter between the preamplifier and the mixer was demonstrated and significant noise reduction was achieved. Finally, wavelength conversion of modulated signals at data rates of 2.5 Gb/s and 10 Gb/s was demonstrated.

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