3 × 3 optical switch by exploiting vortex beam emitters based on silicon microrings with superimposed gratings.

A silicon-on-insulator microring with three superimposed gratings is proposed and characterized as a device enabling 3×3 optical switching based on orbital angular momentum and wavelength as switching domains. Measurements show penalties with respect to the back-to-back of <1 dB at a bit error rate of 10-9 for OOK traffic up to 20 Gbaud. Different switch configuration cases are implemented, with measured power penalty variations of less than 0.5 dB at bit error rates of 10-9. An analysis is also carried out to highlight the dependence of the number of switch ports on the design parameters of the multigrating microring.

High-directional vortex beam emitter based on Archimedean spiral adiabatic waveguides.

Integrated devices that emit light beams with orbital angular momentum (OAM) are becoming key components for wide-ranging applications. Here we propose and demonstrate a highly directional silicon photonic vortex beam emitter based on a 3-turn Archimedean spiral adiabatic waveguide integrated with an angular grating. Such a compact emitter is capable of generating vortex beams with small divergence angles and high directivity. Various orders of OAM modes can be selectively generated by the emitter at different wavelengths with a side-mode suppression ratio as large as 13.6 dB.

Integrated optical vortex beam receivers.

A simple and ultra-compact integrated optical vortex beam receiver device is presented. The device is based on the coupling between the optical vortex modes and whispering gallery modes in a micro-ring resonator via embedded angular gratings, which provides the selective reception of optical vortex modes with definitive total angular momentum (summation of spin and orbital angular momentum) through the phase matching condition in the coupling process. Experimental characterization confirms the correct detection of the total angular momentum carried by the vortex beams incident on the device. In addition, photonic spin-controlled unidirectional excitation of whispering-gallery modes in the ring receiver is also observed, and utilized to differentiate between left- and right-circular polarizations and therefore unambiguously identify the orbital angular momentum of incident light. Such characteristics provide an effective mode-selective receiver for the eigen-modes in orbital angular momentum fiber transmission where the circularly polarized OAM modes can be used as data communications channels in multiplexed communications or as photonic states in quantum information applications.

Tunable Q-factor silicon microring resonators for ultra-low power parametric processes.

A compact silicon ring resonator is demonstrated that allows simple electrical tuning of the ring coupling coefficient and Q-factor and therefore the resonant enhancement of on-chip nonlinear optical processes. Fabrication-induced variation in designed coupling fraction, crucial in the resonator performance, can be overcome using this post-fabrication trimming technique. Tuning of the microring resonator across the critical coupling point is demonstrated, exhibiting a Q-factor tunable between 9000 and 96,000. Consequently, resonantly enhanced four-wave mixing shows tunable efficiency between -40 and -16.3 dB at an ultra-low on-chip pump power of 0.7 mW.

Bandpass integrated Bragg gratings in silicon-on-insulator with well-controlled amplitude and phase responses.

Bandpass filters with square shape amplitude responses and well-controlled dispersion characteristics are achieved by accurate apodization of Bragg grating structures in silicon-on-insulator waveguides. For these devices, precise tailoring of their frequency response typically requires low coupling coefficients and relatively long on-chip propagation lengths. These challenges are addressed by implementing apodization by phase-modulation and using wider strip waveguides to reduce phase noise. This design approach is demonstrated with a dispersion-less narrowband filter and a chirped bandpass filter.

1.06-µm InGaAs/GaAs multiple-quantum-well optical thyristor lasers with a PiNiN structure.

InGaAs/GaAs multiple quantum well (MQW)-depleted optical thyristor lasers operating at 1.06 µm with a waveguide-type PiNiN structure is presented for the first time. The optical thyristor lasers clearly show nonlinear S-shaped current-voltage and lasing characteristics. The measured switching voltage and current are 5 V and 1 mA, respectively. The holding voltage and current are 2.6 V and 3.6 mA, respectively. A relatively high output light power of 30 mW per facet at room temperature is achieved. The lasing wavelength is 1.055 µm at a bias current of 80 mA at 25 °C.