Jingya Xie

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.

Seven-bit reconfigurable optical true time delay line based on silicon integration

We design, fabricate, and characterize a 7-bit reconfigurable optical true time delay line consisting of Mach-Zehnder interferometer (MZI) switches on the silicon photonics platform. Variable optical attenuators (VOAs) are embedded to suppress the inter-symbol crosstalk caused by the finite extinction ratio of switches. The device can provide a maximum of 1.27 ns delay with a 10 ps resolution over a wide wavelength range. Eye diagram measurement of a 25 Gbps 2(51)-1 pseudo-random bit sequence (PRBS) signal reveals the power penalties only increase 0.17 dB and 0.77 dB after transmission through the shortest (reference) and the longest (1.27 ns delay) paths, respectively.

Continuously tunable reflective-type optical delay lines using microring resonators.

We present a reflective-type optical delay line using waveguide side-coupled 13 microring resonators terminated with a sagnac loop reflector. Light passes through the microring resonator sequence twice, doubling the delay-bandwidth product. Group delay is tuned by p-i-p type microheaters integrated directly in the microring waveguides. Experiment demonstrates that the delay line can potentially buffer 18 bits and the delay can be continuously tuned for 100 ps with a power tuning efficiency of 0.34 ps/mW. Eye diagrams of a 20-Gbps PRBS signal after 10 and 110 ps delays are also examined.

Tunable silicon Fabry-Perot comb filters formed by Sagnac loop mirrors.

We experimentally demonstrate tunable silicon comb filters based on Fabry-Perot (FP) resonators composed of two Sagnac loop mirrors. The comb filter resolves up to 54 comb lines with a 115 GHz channel spacing over a spectral range from 1510 to 1560 nm. The comb line extinction ratio is ~26.3 dB and the quality factor is ~57,000 around 1550 nm wavelength. Electrical tuning is enabled via periodically interleaved PN junctions embedded inside the FP resonator. The comb lines are blue shifted by ~0.92 nm (one channel spacing) with a 5 mA forward-bias current and red-shifted by ~0.05 nm with a -10 V reverse-bias voltage.

CMOS-compatible temperature-independent tunable silicon optical lattice filters.

We present a CMOS-compatible athermal tunable silicon optical lattice filter composed of 10 cascaded 2 × 2 asymmetric Mach-Zehnder interferometers. Active tuning experiments show that the filter central wavelength can be red-/blue-shifted by 13.1/21.3 nm with power consumption of 77/96 mW on top/bottom arms. Temperature shift measurements show that the thermal-sensitivity of the filter central wavelength before active tuning is as low as -1.465 pm/°C. The thermal-sensitivity is varied within 26.5 pm/°C to -27.1 pm/°C when the filter central wavelength is tuned in the wavelength range of 1534 nm to 1551 nm. We use the transfer matrix method to theoretically model the lattice filter and its thermal-sensitivity before and after tuning is analyzed and discussed.

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.

Continuously tunable ultra-thin silicon waveguide optical delay line

As light cannot be stopped or directly stored in any media, optical delay lines are usually used to temporally trap the optical signals. We report a wide-range continuously tunable optical delay line chip consisting of a ring resonator array and a Mach–Zehnder interferometer (MZI) switch array on the 60-nm-thick silicon waveguide platform. The ring delay line provides continuous delay tuning of more than 10 ps with a push–pull differential tuning method. The MZI switchable delay line provides digitally programmable delay tuning with a resolution of 10 ps upon reconfiguration of the MZI switches to establish different optical routing paths. Dual-stage MZI switches are used to ensure low crosstalk with an improved signal-to-noise ratio. The delay line chip can generate a maximum delay of >1  ns with an on-chip insertion loss of 12.4 dB. Optical pulse time-division multiplexing and quasi-arbitrary waveform generation are realized based on the delay line chip. These results represent a significant step towards the realization of highly reconfigurable optical signal processors enabled by optical delay manipulation with broad applications for optical communications and microwave photonics.

Optical signal processing using silicon resonance and slow-light structures

We present our recent work on silicon resonance and slow-light based devices for optical signal processing. Waveguide self-coupling and mutual coupling are used to tailor the waveguide spectral and dispersion characteristics. With selfcoupling, optical resonances are generated with unique transmission performances. Electromagnetically induced transparency (EIT)-like effect appears in cascaded self-coupled waveguides. With mutual coupling between ridge and slot waveguides, group velocity experiences a big jump and optical signal can be delayed for a large range with low distortion by using thermo-optic tuning.

Experimental demonstration of self-coupled optical waveguide (SCOW)-based resonators

We experimentally demonstrate a self-coupled optical waveguide (SCOW)-based optical resonator. Transmission spectra reveal the resonators can exhibit split, broadened, or enhanced resonance dips. The SCOW resonators can be used for second-order optical filters.

Selective excitation of microring resonances using a pulley-coupling structure

We present a method to selectively excite resonances in microring resonators by using a pulley-coupling structure. Experimental results reveal only certain resonances are excited, due to the dispersions of coupling-coefficient and microring internal-loss.