Self-coupled Optical Waveguide Research Articles

Reconfigurable Silicon Photonic Processor Based on SCOW Resonant Structures

Reconfigurable photonic processors, which can be programmed to perform multiple photonic processing tasks by using the same hardware platform, own the advantages of higher flexibility and more cost-effectiveness compared with application-specific photonic integration circuits (ASPICs). In this paper, we present a novel programmable photonic processor based on two-dimensional meshes of self-coupled optical waveguide (SCOW) resonant structures. The proposed processor can be configured for realizing various basic optical components, as well as cascaded and coupled components. As a proof-of-principle, we experimentally demonstrate the concept with a 3 × 1 SCOW-based processor on the silicon platform, including tunable couplers, variable optical attenuators, and phase shifters. We implement eight different configurations using the chip, including ring resonators, Mach-Zehnder interferometers, Fabry-Perot resonators, and composite structures built of these basic components. These results demonstrate that the proposed processor can be a promising candidate for multi-functional photonic processors.

Programmable SCOW Mesh Silicon Photonic Processor for Linear Unitary Operator.

Universal unitary multiport interferometers (UMIs) can perform any arbitrary unitary transformation to a vector of input optical modes, which are essential for a wide range of applications. Most UMIs are realized by fixed photonic circuits with a triangular or a rectangular architecture. Here, we present the implementation of an N × N rectangular UMI with a programmable photonic processor based on two-dimensional meshes of self-coupled optical waveguide (SCOW) resonant structures. Our architecture shows a high tolerance to the unbalanced loss upon interference. This work enriches the functionality of the SCOW mesh photonic processors, which are promising for field-programmable photonic arrays.

Electromagnetically Induced Transparency in a Silicon Self-Coupled Optical Waveguide

We investigate the resonance property of a self-coupled optical waveguide (SCOW) with four coupling points. Under a special condition that the two outer couplers are in weak coupling and the two inner couplers are in strong coupling, an implicit standing-wave resonance mode is formed inside the SCOW structure. As the resonance is feedback coupled via an S-shape bus waveguide, electromagnetically induced transparency (EIT)-like resonance features are observed in the output transmission spectrum. The SCOW resonator is analyzed using the coupled mode theory and finite-difference time-domain simulation. The device is experimentally demonstrated on the silicon-on-insulator platform. The measurement results overall agree well with the theoretical calculation. The EIT-like peak can be tuned by a thermo-optic phase shifter made of a NIN-type silicon resistor integrated in the feedback waveguide. The results point to new ways of creating on-chip optical analog of the EIT phenomenon that can be utilized for various optical signal processing applications.

Compact silicon photonic interleaver based on a self-coupled optical waveguide.

We propose and experimentally demonstrate a new scheme to realize an on-chip silicon photonic interleaver by using a self-coupled optical waveguide (SCOW). Benefiting from the high-order filtering property of a multistage SCOW resonator, the device has a smaller footprint and higher extinction ratio compared to conventional ring-assisted Mach-Zehnder interferometer interleavers. Its high fabrication tolerance is also demonstrated in this paper. The operation principle of the proposed interleaver is theoretically analyzed. The designed device is fabricated on a silicon-on-insulator wafer under standard complementary metal oxide semiconductor compatible fabrication processes. Experimental results show that 20 dB extinction ratio and about 8 dB insertion loss can be achieved in the entire C-band without any thermo-optic tuning, verifying the effectiveness of the proposed device as an on-chip interleaver with a compact footprint and high extinction ratio.

A High-Speed Second-Order Photonic Differentiator Based on Two-Stage Silicon Self-Coupled Optical Waveguide

In this paper, we propose and demonstrate an all-optical second-order differentiator based on a two-stage self-coupled optical waveguide on a silicon-on-insulator platform. The transmission spectrum of the fabricated device has a parabola-like filtering notch with a 3-dB bandwidth of up to ~ 100 GHz and a depth of ~ 12 dB. Experiments are carried out for 10-, 20-, and 40-Gb/s optical time-domain multiplexing (OTDM) picosecond pulse trains, and the second-order differentiations are achieved using the fabricated device.

Investigation of Coupling Tuning in Self-Coupled Optical Waveguide Resonators

We investigate the influence of coupling strength on self-coupled optical waveguide (SCOW) resonators. Experimental results reveal that the SCOW resonator transmission spectrum can exhibit single-channel or dual-channel stopbands with the band splitting level determined by the two coupling coefficients. Electrically tunable SCOW resonators comprising 2×2 Mach-Zehnder interferometer couplers are also demonstrated, which shows a similar change trend upon coupling tuning.

Tunable two-stage self-coupled optical waveguide resonators

We report tunable two-stage self-coupled optical waveguide (SCOW) resonators composed of a pair of mirror-imaged single SCOW resonators connected by a phase shifter in between. Experimental results show that the coupled-resonator-induced-transparency and high-order bandstop filtering characteristics can be obtained in the transmission spectra of the devices with two different configurations. The resonance spectrum can be tuned by using either a p-i-p microheater or a p-i-n diode in the phase shifter. Our theoretical modeling based on the transfer matrix method has a good agreement with the experimental results.

Coherent interference induced transparency in self-coupled optical waveguide-based resonators

We propose a self-coupled optical waveguide (SCOW)-based resonator to generate an optical resonance analogous to electromagnetically induced transparency (EIT). The EIT-like effect is formed by the coherent interference between two resonance paths inherent to the SCOW resonator. For cascaded SCOW resonators, the spectrum they produce is significantly affected by the phase shift between them, with the EIT-like peak flattened or split as the two extreme cases. We also investigate the dispersion characteristics of an infinite array of SCOW resonators and show that the dispersion relation and group index in the EIT subband can be greatly changed by a small phase shift between the SCOW resonators.