This document provides supplementary information to "Silicon photonic transmitter for polarization-encoded quantum key distribution," http://dx.doi.org/10.1364/optica.3.001274. Details on the refractive index and absorption change as well as the electroluminescence in the forward-biased silicon (Si) PIN diodes are described. © 2016 Optical Society of America http://dx.doi.org/10.1364/optica.3.001274.s001 REAL AND IMAGINARY REFRACTIVE INDEX CHANGE IN SI WAVEGUIDE PIN DIODESThe modulation of the refractive index in silicon (Si) is typically through the plasma dispersion effect. The carrier density changes both the real and imaginary parts of the refractive index, which can cause, for example, a reduced extinction ratio in an optical attenuator or modulator, and polarization dependent loss in a polarization controller. According to [1], the changes in the refractive index Δn and absorption Δα of Si near a wavelength of 1550 nm arewhere ΔN e and ΔN h are changes in the free electron density and free hole density measured in cm −3 . By incorporating both Δn and Δα into a mode-solver, the coupled changes in the real and imaginary parts of the effective index as a function of carrier density can be modelled. Experimentally, for the Si waveguide PIN diode with the cross-section illustrated in Fig. S1(a), which is similar to the one used in the present work, the measured phase-shift and attenuation as function of the applied forward bias voltage are shown in Fig. S1(b) and Fig. S1(c), respectively [2]. The length of the Si PIN diode used for these measurements was 500 μm. The measured differential phase-shift was about −7.3π/(mm · V) and the corresponding differential absorption change was about 20 dB /(mm · V). These figures have been reproduced from [2]. The Si PIN diodes we have used in the current work had P++ and N++ regions that were 700 nm away from the waveguide core compared to 800 nm in Fig. S1. The reduced separation would lead to a slightly lower series resistance. ELECTROLUMINESCENCE FROM SI PIN DIODESWe observed that the Si waveguide PIN diodes in forward bias could generate weak electroluminescence. Fig. S2(a) shows the electroluminescence spectrum of a 1000 μm-long PIN diode at several forward bias voltages. The electroluminescence is broadband and centered near a wavelength of 1150 nm, close to the bandgap energy of Si (1.1 eV = 1130 nm). This electroluminescence is not power efficient due to the indirect bandgap of Si. Fig. S2(b) shows the current vs. voltage relationship of the diode. Fig. S2(c) shows the total optical power collected

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The electromagnetic resonances of optical microspheres-the so-called whispering gallery modes (WGMs)-can be used for refractometric sensing of surrounding fluids. Microspheres are attractive because they offer high sensitivity and can be utilized with fluorescent dyes or quantum dots. One issue with microspheres, however, is that they are difficult to integrate into microfluidic systems. Here, we develop a microfluidic structure that permits sensing applications using a single microsphere in a capillary. To achieve this, a microsphere formed on the end of a tapered fiber was first coated with fluorescent silicon quantum dots (QDs). The sphere was then inserted into a microcapillary and the fluorescence WGMs were monitored as different fluids were pumped through the channel. The sensitivity and detection limits for this sphere-in-a-capillary device were measured for several different QD film thicknesses and for two different microsphere sizes. Because of the relatively high-visibility mode structure, the sensitivity and detection limit can be defined by Fourier analysis of the free spectral range and WGM spectral shifts.

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We demonstrate foundry-fabricated O-band III-V-on-silicon discrete-mode lasers. The laser fabrication follows the back-side-on-buried-oxide laser integration process and is compatible with complex, multilayer, silicon-on-insulator based platforms. A series of devices were characterized, with the best devices producing on-chip powers of nearly 20 mW with Lorentzian linewidths below 20 kHz and a side mode suppression ratio of at least 60 dB.