We review recent work on low-dose high-energy helium ion implantation into silicon-on-insulator (SOI) optical
waveguides. The important role of free carriers generated by two-photon absorption (TPA) in nonlinear silicon
waveguide devices is discussed and a generalized definition of the nonlinear effective length which takes into account
the presence of nonlinear losses is proposed. We describe experimental studies and simulations of helium ion
implantation for carrier lifetime reduction to increase the nonlinear effective lengths of silicon waveguides. Helium ion
implantation can also enhance the photodetection responsivity of silicon at below-bandgap wavelengths. We review our
work on a possible application of the helium ion implanted waveguides for in-line optical power monitors (ICPM) which
monitor the output from erbium doped fiber amplifiers (EDFA) and, when combined with silicon variable optical
attenuators, can perform EDFA gain tilt and gain transient compensation.
This paper presents an embedded wavelet packet image coding algorithm which is based on context classification and
quadtree ordering (CCAQO). To match up well with the quadtree-based embedded coder, a new cost function for the best
basis selection is adopted in discrete wavelet packet transform (DWPT). In addition, combined with the structure of the
best wavelet packet basis, a complete quadtree representation of wavelet packet coefficients is established to explore the
ordering procedure of embedded image coding. Since subband correlation is mainly captured by significance coding, our
focus is on significance coding. The significance probability of wavelet coefficient is estimated by convoluting a 9x9 FIR
filter matrix kernel with the significance states of neighboring coefficients, and then a context classifier based on Lloyd-
Max algorithm is used to categorize the wavelet coefficients with the same or similar significance probability into several
contexts. The significance state of wavelet coefficient with respect to a given threshold is encoded using adaptive arithmetic
coder based on the classified context. Due to the optimal context classifier and the flexible quadtree representation ability of
wavelet packet coefficients, the proposed CCAQO embedded image coder offers improvement in subjective and objective
quality for texture-rich images and experimental results show that it offers coding performance superior to or comparable
to the state-of-the-art image coders.
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