Ultrafast optical switching using semiconductors for high-speed communication systems

مرکز و کتابخانه مطالعات اسلامی به زبان های اروپایی

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" Ultrafast optical switching using semiconductors for high-speed communication systems "
Y.-H. Kao M. N. S. Islam, Duncan

Document Type	:	Latin Dissertation
Language of Document	:	English
Record Number	:	1113149
Doc. No	:	TLpq304434400
Main Entry	:	M. N. S. Islam, Duncan
	:	Y.-H. Kao
Title & Author	:	Ultrafast optical switching using semiconductors for high-speed communication systems\ Y.-H. KaoM. N. S. Islam, Duncan
College	:	University of Michigan
Date	:	1998
student score	:	1998
Degree	:	Ph.D.
Page No	:	140
Abstract	:	In high-speed communication systems, nonlinear photonic switches are desired for ultrafast signal processing to overcome current electronic bottleneck. There have been several materials developed for these switches, such as optical fibers, organic waveguides, passive semiconductor waveguides, and semiconductor laser amplifiers. The focus of this thesis work is to develop high-speed (100 Gb/s) optical switches using semiconductor materials. Two materials studied are AlGaAs passive waveguides and InGaAsP semiconductor laser amplifiers (SLAs). For the passive AlGaAs waveguides, we report Raman gain coefficient at the pump wavelength of 1.55 usd\rm\mu musd (the wavelength for fiber communications) and find that this Raman gain gives rise to cross-talk between two orthogonally polarized subpicosecond pulses as well as pulse distortion. Both cross-talk and pulse distortion can degrade the performance of Al-GaAs waveguides for high-speed optical switching. Because the Raman effect scales inversely with pulse width, the Raman effect limits the minimum pulse width with which AlGaAs waveguides may be used for nonlinear refractive index applications. The main challenge for high-speed SLA switches is the slow recovery time of the inter-band nonlinearity. We studied two approaches to solve this problem. One is to bias the SLA at transparency current such that there is no net slow nonlinearity induced by control pulses. We find that with significant two photon absorption the SLA cannot always reach transparency condition if the control pulse width is shorter than the SLA transit time. Since the control pulse width is typically shorter than the SLA transit time for 100 Gb/s switching, it is necessary to avoid two photon absorption to achieve transparency operation. The second approach is to place the SLA in the middle of a nonlinear optical loop minor and use mainly the fast nonlinearity to perform switching. High-speed logic operations using a 100 Gb/s 8-bit packet are demonstrated at switching energy of 8 pJ. This device configuration is simple and can be potentially integrated on a chip. We have also studied subpicosecond pulse propagation in an SLA at high pulse energy (usd\approxusd12 pJ). We find that two photon absorption is important at this pulse energy and pulse width. It can deplete the pump pulse energy and cause pulse broadening. Finally, We apply gain saturation in SLA to a self-synchronization scheme for a 100 Gb/s packet network. The gain saturation creates an intensity difference between the first bit and the rest of the bits in a packet. This intensity difference is further enhanced by an intensity discriminator and the first pulse is extracted as the packet clock that is synchronized to the incoming packet. This synchronization technique does not require special clock pulse generation and hence simplifies packet generation and propagation.
Subject	:	Applied sciences
	:	High-speed communication
	:	Optical switching
	:	Optics
	:	Pure sciences
	:	Semiconductors