This paper reports the findings of a study of an optoelectronic oscillator (OEO) with large delay under proportional and proportional integral control by a phase-locked loop (PLL). The study is the first to fully account for the OEO delay in responding to a tuning stimulus including the location of all the countable infinity of poles of the system function.

A panoramic ultra-high resolution photonic integrated circuit spectrometer is under development by the authors. The architecture comprises a tunable ring resonator stage and an AWG stage. The resolution defines the bandwidth of the ring resonator determined by the cross-coupled power and hence the gap between the access and ring waveguides. The AWG channel frequency spacing determines the required free-spectral range (FSR) and hence the perimeter of the ring resonator. The specified < 1GHz resolution combined with a FSR of 50 GHz render accurate simulation difficult obstructing the design process. In this report, a simplified design rule to determine the minimum gap between straight access waveguides and a circular ring waveguide is proposed. Realistic assumptions such as existence of local bisymmetry and adiabatic mode evolution throughout the coupling region permit a simple mode solver to determine the relationship between the cross-coupled power and the minimum gap size. A parameter extraction method is also formulated for add-drop rings equipped with two nominally identical couplers that disentangles the loss and coupling ring parameters from intensity-only transmission measurements. The proposed rule is applied to the design of ring resonators fabricated on a Si3N4 platform. The parameter extraction method is used to analyze the measured characterization data of the ring resonators. The results show good agreement between the design rule and parameters extracted from the measured data (measurement shows maximum deviation of ~43 nm from the design rule estimation) and provide experimental confirmation of the technological viability of the ring resonators required by the spectrometer.

A means of applying an adjustable RF phase shift over a broad band of frequencies is a requirement of diverse application. Photonic solutions to the generation of RF phase shifts have receive significant attention for reasons of reduced cost, compactness and simplicity, yet the achievement of a phase shift extending beyond 360˚ range remains a challenge. The circuit architecture of a compact and broadband RF phase shifter with unbounded range based on two parallel DP-MZM architecture is presented and verified by simulation verification and emulated using off the shelf low frequency electronic components. Results demonstrate that the complex transmission of the phase shifter follows a trajectory that may encircle the origin an arbitrary number of times in either direction. The proposed architecture can be implemented using commercially available DP-QPSK modulator or can be integrated in any material platform that offers linear electro-optic phase modulators.

A multi-functional photonic circuit implemented on silicon on insulator (SOI) platform is reported. Eight phase modulators are connected to provide four Mach-Zehnder interferometer structure in parallel. Multimode interference couplers are used as the splitter/combiner of the MZI structures to provide static DC bias. This architecture generates two principle spatially separated 1st order harmonics from a single light source, which may be collected from separate ports without using any optical demultiplexing filters which permits remote heterodyning. A carrier suppression of >20 dB and spurious sideband suppression > 12 dB relative to the principle harmonics is achieved with bias voltage tuning only. In addition to the frequency conversion, the circuit can also perform as a sub-carrier generator, IQ modulator and frequency multiplier.