We have developed a miniaturized silicon photonics short-wave infrared spectrophotometer that fits in a wrist-based wearable device. Our device has the capability for non-invasive and real-time measurement of various physiologic biochemistries that cannot be interrogated with the same accuracy when using light emitting diodes (LEDs) and common photoplethysmography (PPG) applications. By producing many discrete and individually addressable laser diodes on a single photonics integrated circuit together with wavelength multiplexing and on-chip wavelength and power monitoring, our platform enables novel commercial applications, including the ability to sense hydration status, core body temperature, alcohol consumption, lactate threshold, and glucose levels.
Effect of relaxation time on the performance of photonic crystal optical bistable switches based on Kerr nolinearity is
discussed. This paper deals with optical pulses with the duration of about 50 ps. In such cases the steady state response
of the optical device can be used to approximate the pulse evolution if the nonlinearity is assumed instantaneous, hence
analytical solutions such as the coupled mode theory can be used to obtain the time evolution of the electromagnetic
fields. However if the relaxation time of the material nonlinear response is also considered, changes in the power levels
and in the shape of the hystersis loop is observed. In this case, we use the nonlinear finite difference time domain method
(NL-FDTD) to follow the system dynamics and get the bistability hystersis loop. Codes are developed to analyze the
instantaneous Kerr materials and the Kerr materials with finite response times. Depending on the material, the relaxation
times of the order of 1-10fs should be considered in studying bistability to obtain the right shape of the output pulses. It
is observed that the relaxation leads to larger input power and threshold and hence degrades the performance of the
switch in pulse shaping.
Low power operation and high speed have always been desirable in applications such as data processing and
telecommunications. While achieving these two goals simultaneously, however, one encounters the well-known powerbandwidth
trade-off. This is here discussed in a typical bistable switch based on a two-dimensional photonic crystal
with Kerr type nonlinearity. The discussion is supported by the nonlinear finite difference time domain (FDTD)
simulation of a direct coupled structure with a home-developed code. Two cases of working near resonant and offresonant
are simulated to compare the power and the speed of the device in the two cases. It is shown that working nearresonance
reduces the power levels at the expense of reducing the settling time, i.e. the bandwidth limitation. The
hystersis loops for the device are also obtained with both coupled-mode theory and quasi-steady state FDTD simulation.
The impact of operating near/off resonance on the shape of the hystersis loop is discussed as a confirmation of the
previous results. Alternative ways of reducing the power while saving the bandwidth are also examined. The discussion
is general and one may investigate other optical switches to obtain similar results.
Differential transfer matrix method is extended to analyze nonuniform nonlinear distributed feedback structures. The
input-intensity dependence of the reflectivity and transmissivity of inhomogeneous nonlinear dielectric slabs is
investigated for TE polarized and TM polarized incident waves.
Optical code division multiple access (OCDMA) is a promising multiple-access technique for future all optical networks.
In this manuscript, the usefulness of exploiting bistable optical elements as threshold devices in coherent OCDMA
systems is analytically investigated, in which the bistability effect is modeled by a simple square loop.
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