Chunlei Sun

Integrated dual-mode 3 dB power coupler based on tapered directional coupler

A dual-mode 3 dB power coupler based on silicon-on-insulator platform for mode division multiplexing system is proposed and demonstrated. The device, which consists of a tapered directional coupler and two output bend waveguides, has a 50:50 coupling ratio around the wavelength of 1550 nm for both fundamental and first order transverse magnetic (TM0 and TM1) modes. Based on asymmetrical tapered structure, a short common coupling length of ~15.2 μm for both modes is realized by optimizing the width of the tapered waveguide. The measured insertion loss for both modes is less than 0.7 dB. The crosstalks are about −14.3 dB for TM0 mode and −18.1 dB for TM1 mode.

Integrated switchable mode exchange for reconfigurable mode-multiplexing optical networks

We propose and experimentally demonstrate an on-chip switchable mode exchange utilizing a Mach-Zehnder interferometer assisted by a phase shifter. The switchable functionality, which is essential for an advanced and reconfigurable optical network, can be realized by controlling the induced phase difference. The measured extinction ratio is ∼24  dB over the C band for OFF-ON switchover. For demonstration, open and clear-eye diagrams can be observed when processing non-return-to-zero on-off keying signals at 10 Gb/s. The bit error rate measurements indicate a reasonable power penalty of less than 1 dB for two-mode exchange. The proposed device can further promote advanced and flexible mode-multiplexing optical networks.

On-chip data exchange for mode division multiplexed signals.

Data exchange is an important function for flexible optical network, and it has been extensively investigated for the time and wavelength domains. The mode division multiplexing (MDM) has been proposed to further increase the transmission capacity by carrying information on different modes with only single wavelength carrier. We propose and experimentally demonstrate a novel on-chip data exchange circuit for the MDM signals by utilizing two micro-ring resonator (MRR) based mode converters. For demonstration, single and four wavelengths non-return-to-zero on-off-keying (NRZ-OOK) signals at 10 Gb/s carried on different modes are successfully processed, with open and clear eye diagrams. Measured bit error ratio (BER) results show reasonable power penalties. The proposed circuit can be potentially used in advanced and flexible MDM optical networks.

On-chip switch for reconfigurable mode-multiplexing optical network.

The switching and routing is essential for an advanced and reconfigurable optical network, and great efforts have been done for traditional single-mode system. We propose and demonstrate an on-chip switch compatible with mode-division multiplexing system. By controlling the induced phase difference, the functionalities of dynamically routing data channels can be achieved. The proposed switch is experimentally demonstrated with low insertion loss of ~1 dB and high extinction ratio of ~20 dB over the C-band for OFF-ON switchover. For further demonstration, the non-return-to-zero on-off keying signals at 10 Gb/s carried on the two spatial modes are successfully processed. Open and clear eye diagrams can be observed and the bit error rate measurements indicate a good data routing performance.

An ultra-low crosstalk and broadband two-mode (de)multiplexer based on adiabatic couplers

A novel adiabatic couplers (ACs) based broadband and fabrication-tolerant two-mode multiplexer (MUX) is designed using silicon-on-insulator (SOI) platform. Being different from the previously reported ACs-based scheme, the converted and multiplexed signals are on conventional modes, rather than supermodes. The experimental results are in good agreement with the simulations. Over a wavelength range of 75 nm measured, the crosstalk is lower than −20 dB, and the insertion loss is ~1 dB. The eye diagram and bit error rate measurements validate the good performance of the proposed mode MUX. The investigation on fabrication tolerance indicates reasonable performance degradation for a large gap deviation from −30 to 30 nm and etching depth deviation from −50 to 50 nm.

A Low Crosstalk and Broadband Polarization Rotator and Splitter Based on Adiabatic Couplers

A low crosstalk and broadband polarization rotator and splitter (PRS) consisting of a bi-level adiabatic taper, a symmetric micro Y-junction and adiabatic couplers is proposed and demonstrated using a silicon-on-insulator platform. Due to the principle of mode evolution, the proposed PRS exhibits superior performance over a broad bandwidth. The waveguide with a thin ridge layer is introduced to reduce the crosstalk from TM0 mode and increase the coupling strength of TE0 mode. The proposed PRS is experimentally demonstrated with a loss about 1 dB and a crosstalk about -14 dB over a wavelength range of 100 nm.

Silicon chip-scale space-division multiplexing: from devices to system

Space-division multiplexing (SDM) technique has attracted increasing attentions recently, because it provides an effective way to increase transmission capacity. With the continuous and exponential increase in data demands, high-density integration of silicon photonic components is of significant interest in terms of link price, performance and power consumption. The multimode/mutlicore devices applied to achieve diverse functionalities are key building blocks to construct a chip-scale SDM system based on a silicon on insulator (SOI) platform. This study reviews the recent progress of multimode/multicore devices, which enable coupling, multiplexing/demultiplexing, transmitting switching, as well as modulation and detection. Based on these devices, a complete on-chip SDM system is constructed and discussed.

De-multiplexing free on-chip low-loss multimode switch enabling reconfigurable inter-mode and inter-path routing

Abstract Switching and routing are critical functionalities for a reconfigurable bandwidth-dense optical network, and great efforts had been made to accommodate mode-division multiplexing technology. Although the reconfigurable routing for spatial-mode groups between different optical paths was realized recently, a demultiplexing-switching-multiplexing process is necessary. Here we present a simplified and compact on-chip 2×2 multimode switch that can be easily upgradable to a larger scale. Fully and reconfigurable routing between not only optical paths but also spatial modes is achieved. To obtain a low loss multimode processing, a novel structure free from demultiplexing and re-multiplexing operations is adopted. The switch enables minimum and maximum insertion losses of 0.3 and 1.2 dB, with a compact footprint of 433 μm×433 μm and low crosstalk of <−16.6 dB for all channels. It is further extended to two types of 4×4 switch fabrics with cross-bar and ring-bus architectures, as demonstrations of high-level integration. System characterization with 32 Gb/s high-speed modulated signals is also carried out, reaching up to 256 Gb/s aggregate throughput. These results verify a general solution of 2×2 multimode switch for reconfigurable inter-mode and inter-path routing applicable in large-scale and high-density multimode optical network.

A novel sharply bent silicon multimode waveguide with ultrahigh mode extinction ratio

We propose a sharply bent (5 μm) multimode Silicon waveguide with mode extinction ratio over 22.8 dB from 1500 to 1600nm. A comparable performance can be achieved compared with conventional scheme with 40 μm radius.

An integrated mode (de)multiplexer based on adiabatic couplers

A novel broadband mode-division multiplexing link based on adiabatic couplers is proposed and experimentally demonstrated with crosstalk <; -20 dB, insertion loss <; 1 dB and power penalty <; 1 dB, using Silicon integrated platform.