Tiehui Su

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.

Free-space coherent optical communication with orbital angular, momentum multiplexing/demultiplexing using a hybrid 3D photonic integrated circuit

We demonstrate free-space space-division-multiplexing (SDM) with 15 orbital angular momentum (OAM) states using a three-dimensional (3D) photonic integrated circuit (PIC). The hybrid device consists of a silica planar lightwave circuit (PLC) coupled to a 3D waveguide circuit to multiplex/demultiplex OAM states. The low excess loss hybrid device is used in individual and two simultaneous OAM states multiplexing and demultiplexing link experiments with a 20 Gb/s, 1.67 b/s/Hz quadrature phase shift keyed (QPSK) signal, which shows error-free performance for 379,960 tested bits for all OAM states.

Ultra-Compact Silicon Photonic 512 × 512 25 GHz Arrayed Waveguide Grating Router

This paper discusses design, fabrication, and characterization of a 512 × 512 arrayed waveguide grating router (AWGR) with a channel spacing of 25 GHz. The dimensions of the AWGR is 16 mm × 11 mm and is fabricated on a 250 nm silicon-on-insulator platform. The measured channel crosstalk is approximately -4 dB without any compensation for the phase errors in the arrayed waveguides. The AWGR spectrum in the arrayed waveguide grating arms were characterized by using an optical vector network analyzer. Fabrication details of obtaining low loss silicon ridge waveguides are also discussed.

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.

Monolithic InP 100-Channel

We demonstrate monolithic integration of a 100-channel arrayed-waveguide grating (AWG) with 10-GHz channel spacing and 100 optically controlled Michelson-interferometer-based phase and amplitude modulators. The high-resolution AWG showed better than -15-dB crosstalk, and the modulator extinction ratio was better than 20 dB with either electrical or optical modulation control. The twin-integrated devices comprise a 50-mm diameter InP wafer with 1200 independent optoelectronic components.

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Conventional elastic optical networking, EON, uses elasticity in two domains, time and frequency, to optimize utilization of optical network resources in the presence of fluctuating traffic demand and link quality. Currently, networking exploiting a third domain, space, is the focus of significant research efforts since space-division multiplexing, SDM, has the potential to substantially improve future network capacity and spectral efficiency. This article extends 2D-EON to include elasticity in all three domains: time, frequency, and space. We introduce enabling technologies, architectures, and algorithms for 3D-EONs. Based on sample network topologies, we investigate algorithms for routing, spectrum, spatial mode, and modulation format assignment - RSSMA. In particular, we investigate fragmentation-aware RSSMA and how the constraints in the formation of super-channels in MIMO-based SDM systems can impact the network performance in terms of blocking probability.

10-GHz Device for Optical Arbitrary Waveform Generation

Spatial heterodyne spectrometers (SHS) can achieve high resolution with excellent optical throughput. We demonstrate a planar waveguide SHS incorporating 64 asymmetric Mach-Zehnder interferometers and show measurements that verify 1 GHz resolution across a 64 GHz measurement range.

3D elastic optical networking in the temporal, spectral, and spatial domains

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.

Fourier-transform, integrated-optic spatial heterodyne spectrometer on a silica-based planar waveguide with 1 GHz resolution

We present a free-space coherent communication link employing orbital angular momentum (OAM) multiplexing using polarization diversified 2D-3D hybrid photonic integrated circuits (PICs). The PICs support multiplexing/demultiplexing of up to 15-OAM states with dual polarizations. We characterize the hybrid device, including phase errors and crosstalk performance. Then, we use two hybrid PICs for a free-space coherent communication link demonstration. We utilize polarization, frequency, quadrature, and space dimensions to achieve a 1.68-Tb/s link bandwidth and a 9.6-b/s/Hz spectral efficiency.

Fully reconfigurable silicon CMOS photonic lattice filters

This paper demonstrates rapidly reconfigurable, high-fidelity optical arbitrary waveform generation (OAWG) in a heterogeneous photonic integrated circuit (PIC). The heterogeneous PIC combines advantages of high-speed indium phosphide (InP) modulators and low-loss, high-contrast silicon nitride (Si3N4) arrayed waveguide gratings (AWGs) so that high-fidelity optical waveform syntheses with rapid waveform updates are possible. The generated optical waveforms spanned a 160 GHz spectral bandwidth starting from an optical frequency comb consisting of eight comb lines separated by 20 GHz channel spacing. The Error Vector Magnitude (EVM) values of the generated waveforms were approximately 16.4%. The OAWG module can rapidly and arbitrarily reconfigure waveforms upon every pulse arriving at 2 ns repetition time. The result of this work indicates the feasibility of truly dynamic optical arbitrary waveform generation where the reconfiguration rate or the modulator bandwidth must exceed the channel spacing of the AWG and the optical frequency comb.