Cantilever couplers for fiber coupling to silicon photonic integrated circuits are presented. The couplers consist of
silicon inverse width tapers embedded within silicon dioxide cantilevers that are deflected out-of plane by residual stress.
Coupling efficiencies of 1.6 dB per connection for TE polarization and 2 dB per connection for TM polarization are
achieved. Finite difference time domain simulations are conducted to assess coupling loss as a function of cantilever
geometry and fiber-to-cantilever misalignment. The cantilever couplers enable high efficiency propagation of light from
optical fibers to photonic integrated circuits directly on a chip surface without dicing or cleaving.
Due to their high electrical bandwidth and good signal-to-noise ratio, optical receivers that utilize a combination
of PIN photodetectors and erbium-doped fiber amplifiers (EDFAs) have emerged as an attractive technology for
high-speed optical communication. However, the drawbacks of this technology are cost and bulkiness. Since
avalanche photodiodes (APDs) are capable of amplifying the photocurrent internally, without the need for
optical preamplification, they may offer a cost-effective and compact alternative to the PIN-EDFA combination.
Unfortunately, this internal optoelectronic gain comes at the expense of uncertainty in the APD's gain, and more
importantly, at the expense of reduced speed due to the notorious avalanche buildup time. The relatively slow
response time of an APD, compared to a PIN photodiode, introduces significant inter-symbol interference (ISI)
at high operational transmission rates. In this work, an equalization approach is undertaken to compensate for
buildup-time-induced ISI by means of either the transversal equalizer (TE) or the decision-feedback equalizer
(DFE). To design the equalizers, the APD-based receiver is viewed as a random linear channel whose impulseresponse
function is a stochastic process. The mean and the correlation matrix of the receiver's random impulseresponse
function are numerically determined by utilizing a recently developed analytical model. It is revealed
that these equalizers can reduce the bit-error-rate (BER) remarkably at high transmission rates; this makes
current InP APDs potentially suitable for near 40-Gbps digital operation.