Stevan S. Djordjevic

Demonstration of free space coherent optical communication using integrated silicon photonic orbital angular momentum devices

We propose and demonstrate silicon photonic integrated circuits (PICs) for free-space spatial-division-multiplexing (SDM) optical transmission with multiplexed orbital angular momentum (OAM) states over a topological charge range of -2 to +2. The silicon PIC fabricated using a CMOS-compatible process exploits tunable-phase arrayed waveguides with vertical grating couplers to achieve space division multiplexing and demultiplexing. The experimental results utilizing two silicon PICs achieve SDM mux/demux bit-error-rate performance for 1‑b/s/Hz, 10-Gb/s binary phase shifted keying (BPSK) data and 2-b/s/Hz, 20-Gb/s quadrature phase shifted keying (QPSK) data for individual and two simultaneous OAM states.

CMOS-compatible, athermal silicon ring modulators clad with titanium dioxide

We present the design, fabrication and characterization of athermal nano-photonic silicon ring modulators. The athermalization method employs compensation of the silicon core thermo-optic contribution with that from the amorphous titanium dioxide (a-TiO(2)) overcladding with a negative thermo-optic coefficient. We developed a new CMOS-compatible fabrication process involving low temperature RF magnetron sputtering of high-density and low-loss a-TiO(2) that can withstand subsequent elevated-temperature CMOS processes. Silicon ring resonators with 275 nm wide rib waveguide clad with a-TiO(2) showed near complete athermalization and moderate optical losses. Small-signal testing of the micro-resonator modulators showed high extinction ratio and gigahertz bandwidth.

Demonstration of a fast-reconfigurable silicon CMOS optical lattice filter

We demonstrate a fully-reconfigurable fourth-order optical lattice filter built by cascading identical unit cells consisting of a Mach-Zehnder interferometer (MZI) and a ring resonator. The filter is fabricated using a commercial silicon complementary metal oxide semiconductor (CMOS) process and reconfigured by current injection into p-i-n diodes with a reconfiguration time of less than 10 ns. The experimental results show full control over the single unit cell pole and zero, switching the unit cell transfer function between a notch filter and a bandpass filter, narrowing the notch width down to 400 MHz, and tuning the center wavelength over the full free spectral range (FSR) of 10 GHz. Theoretical and experimental results show tuning dynamics and associated optical losses in the reconfigurable filters. The full-control of each of the four cascaded single unit cells resulted in demonstrations of a number of fourth-order transfer functions. The multimedia experimental data show live tuning and reconfiguration of optical lattice filters.

Fully Reconfigurable Silicon Photonic Lattice Filters With Four Cascaded Unit Cells

We present a fully reconfigurable optical filter built by cascading four identical unit cells. The devices are fabricated using two distinct methods: a complementary metal-oxide-semiconductor (CMOS) compatible process utilizes deep ultraviolet (DUV) lithography with tuning elements defined by ion implantation to make lateral p-i-n diodes for current injection regions, while an electron beam (E-beam) lithography process uses nickel chrome (NiCr) heaters as tuning elements. The fabricated devices are characterized using swept optical vector network analyzer (OVNA) coherent measurements.

Continuously Tunable, Wavelength-Selective Buffering in Optical Packet Switching Networks

This letter investigates system performance of slow-light variable optical buffer based on cascaded stages of tunable silica microresonator rings. Continuous tunability is achieved by adjusting the resonance of each ring on the compact photonic integrated circuit. The all-pass configuration allows selectively applying variable delays to wavelengths of choice without losing any packets in an optical packet switching network.

Fully reconfigurable silicon photonic lattice filters with four cascaded unit cells

We present a fully-reconfigurable CMOS-compatible silicon-photonic lattice-filter with four cascaded unit cells consisting of resonant rings and Mach-Zehnder interferometers. The measurements show high-quality filter responses including IIR and FIR filter characteristics matching theoretical predictions.

CMOS Compatible Reconfigurable Silicon Photonic Lattice Filters Using Cascaded Unit Cells for RF-Photonic Processing

This paper presents an overview of a complementary metal-oxide-semiconductor-compatible, programmable, analog optical lattice filter based on silicon unit cells arrayed in large-scale photonic integrated circuits. The unit cell employs a combination of a ring resonator and a Mach-Zehnder interferometer with tunable phase elements in both of the paths. Each proposed unit cell contributes a separately controllable pole and zero pair. Under various configurations, we experimentally achieved >60-dB two-tone spurious-free dynamic range. For more sophisticated signal processing, we experimentally demonstrated an optical lattice filter with four cascaded unit cells capable of dynamically reconfiguring between a bandpass filter and a notch filter. The reconfiguration of the unit-cell and four-cell silicon lattice filter is based on a recursive algorithm, which brings new possibilities to RF photonic processing and a wide range of applications with design scalability to a large number of poles and zeros. The experimental results and the recursive algorithms show potentials for scaling to higher order filter designs.

Low-loss and high contrast silicon-on-insulator (SOI) arrayed waveguide grating

We report high-extinction and low-loss 40-channel × 100-GHz arrayed waveguide grating (AWG) fabricated on silicon-on-insulator using high quality etching condition resulting in <; 0.8 dB/cm loss and low phase errors.

Silicon microring resonator-based reconfigurable optical lattice filter for on-chip optical signal processing

We present a silicon microring resonator-based reconfigurable optical lattice filter for on-chip signal processing. The device design employs a novel infinite impulse response (IIR) structure with high flexibility for rapid reconfiguration. Preliminary measurement results show high-quality filter response.

Fully reconfigurable silicon CMOS photonic lattice filters

We present reconfigurable CMOS-compatible silicon-photonic lattice-filters consisting of Mach-Zehnder structures and ring resonators configured as high resolution bandpass and notch filter shapes. Arbitrary filter synthesis and CMOS-compatible fabrication process are also discussed.