Yiwei Xie

Nyquist-Filtering (De)Multiplexer Using a Ring Resonator Assisted Interferometer Circuit

We present a Nyquist-filtering optical (de)multiplexer using a ring resonator-assisted interferometer circuit. It features a near-rectangular passband spectrum, scalable port count, and can be designed with sub-GHz spectral resolution. The circuit can be constructed using ordinary passive photonic-integrated circuit building blocks. In contrast to its counterparts using tapped-delay-line circuit topologies, this circuit has a chip area two-orders-of-magnitude smaller. The results of this study show the potential for realizing high-spectral-efficiency multicarrier transceivers and reconfigurable optical add-drop multiplexers in a fully integrated form.

Photonic integrated circuit implementation of a sub-GHz-selectivity frequency comb filter for optical clock multiplication

We report a photonic integrated circuit implementation of an optical clock multiplier, or equivalently an optical frequency comb filter. The circuit comprises a novel topology of a ring-resonator-assisted asymmetrical Mach-Zehnder interferometer in a Sagnac loop, providing a reconfigurable comb filter with sub-GHz selectivity and low complexity. A proof-of-concept device is fabricated in a high-index-contrast stoichiometric silicon nitride (Si3N4/SiO2) waveguide, featuring low loss, small size, and large bandwidth. In the experiment, we show a very narrow passband for filters of this kind, i.e. a -3-dB bandwidth of 0.6 GHz and a -20-dB passband of 1.2 GHz at a frequency interval of 12.5 GHz. As an application example, this particular filter shape enables successful demonstrations of five-fold repetition rate multiplication of optical clock signals, i.e. from 2.5 Gpulses/s to 12.5 Gpulses/s and from 10 Gpulses/s to 50 Gpulses/s. This work addresses comb spectrum processing on an integrated platform, pointing towards a device-compact solution for optical clock multipliers (frequency comb filters) which have diverse applications ranging from photonic-based RF spectrum scanners and photonic radars to GHz-granularity WDM switches and LIDARs.

Photonic Circuit Topologies for Optical OFDM and Nyquist WDM

Photonic circuits are the key to advanced functionality in future optical systems, as they efficiently process terabit/s data streams. This paper reviews how photonic circuit topologies have evolved to support high-spectral efficiency modulation formats, including: all-optical optical frequency division multiplexing (AO-OFDM), discrete Fourier transform spread OFDM (DFT-S-OFDM), Nyquist wavelength division multiplexing, (NWDM), orthogonal time division multiplexing (OrthTDM, OTDM), chirped-OFDM, and quasi-Nyquist signals. The importance of the order of components such as modulators, delays, and filters within these circuits is stressed, as simple changes to the circuit topology have significant impacts on the spectra of the signals, and the required bandwidths of the modulators.

Systems performance comparison of three all-optical generation schemes for quasi-Nyquist WDM.

Orthogonal time division multiplexing (OrthTDM) interleaves sinc-shaped pulses to form a high baud-rate signal, with a rectangular spectrum suitable for multiplexing into a Nyquist WDM (N-WDM)-like signal. The problem with generating sinc-shaped pulses is that they theoretically have infinite durations, and even if time bounded for practical implementation, they still require a filter with a long impulse response, hence a large physical size. Previously a method of creating chirped-orthogonal frequency division multiplexing (OFDM) pulses with a chirped arrayed waveguide (AWG) filter, then converting them into interleaved quasi-sinc pulses using dispersive fiber (DF), has been proposed. This produces a signal with a wider spectrum than the equivalent N-WDM signal. We show that a modification to the scheme enables the spectral extent to be reduced for the same data rate. We then analyse the key factors in designing an OrthTDM transmitter, and relate these to the performance of a N-WDM system. We show that the modified transmitter reduces the required guard band between the N-WDM channels. We also simulate a simpler scheme using an unchirped finite-impulse response filter of similar size, which directly creates truncated-sinc pulses without needing a DF. This gives better system performance than either chirped scheme.

Picosecond optical pulse processing using a terahertz-bandwidth reconfigurable photonic integrated circuit

Abstract Chip-scale integrated optical signal processors promise to support a multitude of signal processing functions with bandwidths beyond the limit of microelectronics. Previous research has made great contributions in terms of demonstrating processing functions and device building blocks. Currently, there is a significant interest in providing functional reconfigurability, to match a key advantage of programmable microelectronic processors. To advance this concept, in this work, we experimentally demonstrate a photonic integrated circuit as an optical signal processor with an unprecedented combination of two key features: reconfigurability and terahertz bandwidth. These features enable a variety of processing functions on picosecond optical pulses using a single device. In the experiment, we successfully verified clock rate multiplication, arbitrary waveform generation, discretely and continuously tunable delays, multi-path combining and bit-pattern recognition for 1.2-ps-duration optical pulses at 1550 nm. These results and selected head-to-head comparisons with commercially available devices show our device to be a flexible integrated platform for ultrahigh-bandwidth optical signal processing and point toward a wide range of applications for telecommunications and beyond.

Mitigation of electrical bandwidth limitations using optical pre-sampling

We propose a novel method to improve a system degraded by a low receiver electrical bandwidth. With optical pre-sampling, 4-dB sensitivity improvement at the 7% hard FEC limit is experimentally demonstrated.

Programmable optical processor chips: toward photonic RF filters with DSP-level flexibility and MHz-band selectivity

Abstract Integrated optical signal processors have been identified as a powerful engine for optical processing of microwave signals. They enable wideband and stable signal processing operations on miniaturized chips with ultimate control precision. As a promising application, such processors enables photonic implementations of reconfigurable radio frequency (RF) filters with wide design flexibility, large bandwidth, and high-frequency selectivity. This is a key technology for photonic-assisted RF front ends that opens a path to overcoming the bandwidth limitation of current digital electronics. Here, the recent progress of integrated optical signal processors for implementing such RF filters is reviewed. We highlight the use of a low-loss, high-index-contrast stoichiometric silicon nitride waveguide which promises to serve as a practical material platform for realizing high-performance optical signal processors and points toward photonic RF filters with digital signal processing (DSP)-level flexibility, hundreds-GHz bandwidth, MHz-band frequency selectivity, and full system integration on a chip scale.

Nyquist-WDM channel generation using an arrayed waveguide grating router

We propose a method for generating Nyquist sine pulses, based on an arrayed waveguide grating router (AWGR) preceded by a multimode interference coupler. This outperforms previous methods using a chirped AWGR and a dispersive fiber.

Compact 4×5 Gb/s silicon-on-insulator OFDM transmitter

We characterize an integrated silicon 4×5 Gb/s OFDM transmitter PIC (2.1×4.8 mm²) with four modulators and an optical Fourier transform. This PIC features a channel spacing of 5 GHz and an 80-GHz free spectral range.

Active photonic integrated circuits using semiconductor optical amplifiers

Active photonic circuits use combinations of active semiconductor devices and passive elements to support many applications. We present four functions on a single active photonic integrated circuit (4.5 mm × 4 mm).