We report on the electrical-to-optical modulation bandwidths of non-mesa-etched semipolar (112¯2) InGaN/GaN light-emitting diodes (LEDs) operating at 430-450 nm grown on high-quality (112¯2) GaN templates, which were prepared on patterned (101¯2) r-plane sapphire substrates. The measured frequency response at -3 dB of the LEDs was up to 1 GHz. A high back-to-back data transmission rate of above 2.4 Gbps is demonstrated using a non-return-to-zero on-off keying modulation scheme. This indicates that (112¯2) LEDs are suitable gigabit per second data transmission for use in visible-light communication applications.
The thermal performance of Fabry-Perot InP lasers integrated onto different silicon photonics substrates by microtransfer printing is assessed. 500-µm-long ridge waveguide lasers on the original 350-µm-thick InP have an experimental thermal impedance, Z E X P , of 57 K/W that is reduced to 38 K/W after printing to a 500-µm-thick Si substrate. Z E X P for lasers printed on silicon-on-insulator wafers is ∼94 K/W, which is more than two times higher than that of the laser printed on the Si substrate. Z E X P of lasers printed on thermally insulating layers like benzocyclobutene (BCB) or SiO 2 increases with the thickness of the layer. BCB adhesive layers as thin as 50 nm limit Z E X P to be greater than 55 K/W. The thermal properties for the different situations were modeled using finite-element simulations which confirmed the experimental results within 10% accuracy. The simulations show how changes in the geometry and the materials of the integration platform can influence the resulting thermal impedance.
Pulse wave velocity (PWV) is a reference measure for aortic stiffness, itself an important biomarker of cardiovascular risk. To enable low-cost and easy-to-use PWV measurement devices that can be used in routine clinical practice, we have designed several handheld PWV sensors using miniaturized laser Doppler vibrometer (LDV) arrays in a silicon photonics platform. The LDV-based PWV sensor design and the signal processing protocol to obtain pulse transit time (PTT) and carotid-femoral PWV in a feasibility study in humans, are described in this paper. Compared with a commercial reference PWV measurement system, measuring arterial pressure waveforms by applanation tonometry, LDV-based displacement signals resulted in more complex signals. However, we have shown that it is possible to identify reliable fiducial points for PTT calculation using the maximum of the 2 nd derivative algorithm in LDV-based signals, comparable to those obtained by the reference technique, applanation tonometry.
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