We provide detailed analysis of a four terminal p+pnn+ optical modulator integrated into a silicon-on-insulator (SOI) rib waveguide. The proposed depletion device has been designed to approach birefringence free operation. The modulation mechanism is the carrier depletion effect in a pn junction; carrier losses induced are minimised in our design and because we use a depletion device, the device is insensitive to carrier lifetime. The rise time and fall time of the proposed device have both been calculated to be 7 ps for a reverse bias of only 5 volts. A maximum excess loss of 2 dB is predicted for TE and TM due to the presence of p type and n type carriers in the waveguide.
The integration of nanophotonics components with advanced complementary metal-oxide-semiconductor (CMOS) electronics requires drive voltages as low as 1 V for enabling next-generation CMOS electrophotonics transceivers. Slow-light propagation has been recently demonstrated as an effective mechanism to enhance the modulation efficiency in free-carrier-based electrooptical silicon modulators. Here, we exploit the use of slow light to reduce the driving voltage of carrier-depletion-based Mach-Zehnder modulators. The slowlight phase shifter consists of a p-n junction positioned in the middle of a corrugated waveguide. A modulation efficiency as high as V L $ 0:6 V Á cm is achieved, thus allowing data transmission rates up to 10 Gb/s with a 1.5-V pp drive voltage and an insertion loss of $12 dB. The influence of the drive voltage on the modulation speed as well as the variation of the insertion losses with a group index is also analyzed and discussed.
We propose and numerically demonstrate a versatile strategy that allows designing highly efficient dual-level grating couplers in different silicon nitride-based photonic platforms. The proposed technique, which can generally be applied to an arbitrary silicon nitride film thickness, is based on the simultaneous optimization of two grating coupler levels to obtain high directionality and grating-fibre mode matching at the same time. This is achieved thanks to the use of two different linear apodizations, with opposite signs, applied to the two grating levels, whose design parameters are determined by using a particle swarm optimization method. Numerical simulations were carried out considering different silicon nitride platforms with 150, 300, 400 and 500 nm thicknesses and initially employing silicon as the material for the top level grating coupler. The use of Si-rich silicon nitride with a refractive index in the range 2.7–3.3 for the top layer material enabled to obtain similar performance (coupling efficiency exceeding − 0.45 dB for the 400 nm thick silicon nitride platform) with relaxed fabrication tolerances. To the best of our knowledge, these numerical results represent the best performance ever reported in the literature for silicon nitride grating couplers without the use of any back-reflector.
Photonic integrated circuits currently use platform intrinsic thermo-optic and electrooptic effects to implement dynamic functions such as switching, modulation and other processing. Currently, there is a drive to implement field programmable photonic circuits, a need which is only magnified by new neuromorphic and quantum computing applications. The most promising non-volatile photonic components employ phase change materials such as GST and GSST, which had their origin in electronic memory. However, in the optical domain, these compounds introduce significant losses potentially preventing a large number of applications. Here, we evaluate the use of two newly introduced low loss phase change materials, Sb 2 S 3 and Sb 2 Se 3 , on a silicon nitride photonic platform. We focus the study on Mach-Zehnder interferometers that operate at the O and C bands to demonstrate the performance of the system. Our measurements show an insertion loss below 0.04 dB/µm for Sb 2 S 3 and lower than 0.09 dB/µm for Sb 2 Se 3 cladded devices for both amorphous and crystalline phases. The effective refractive index contrast for Sb 2 S 3 on SiNx was measured to be 0.05 at 1310 nm and 0.02 at 1550 nm, whereas for Sb 2 Se 3 , it was 0.03 at 1310 nm and 0.05 at 1550 nm highlighting the performance of the integrated device.
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