Chi Yan Wong

Focusing subwavelength grating coupler for mid-infrared suspended membrane waveguide.

A mid-infrared (mid-IR)-focusing subwavelength grating (SWG) coupler and suspended membrane waveguide (SMW) on a silicon-on-insulator wafer are studied. For a transverse-electric mode uniform SWG, finite-difference time-domain simulation predicts 44.2% coupling efficiency with 1 dB bandwidth of about 220 nm and backreflection of 0.78% at 2.75 μm. Then the uniform SWG is curved to a focusing SWG using a phase-matching formula. The SMWs are analyzed by the finite element method and fabricated. An Er3+-Pr3+ co-doped mid-IR fiber laser is used for device characterization. The fabricated mid-IR SWG coupler has 24.7% coupling efficiency.

Mid-Infrared Grating Couplers for Silicon-on-Sapphire Waveguides

Theoretical and experimental results of mid-infrared (mid-IR) gratings for coupling between transverse-electric (TE)/transverse-magnetic (TM) mode silicon-on-sapphire (SOS) waveguides and zirconium, barium, lanthanum, aluminum, and sodium fluoride (ZBLAN) fibers are presented. The shallow-etched uniform grating, full-etched subwavelength grating, and apodized grating are analyzed theoretically. TE mode shallow-etched apodized gratings with coupling efficiency of 80.6% and TM mode full-etched apodized subwavelength gratings with coupling efficiency of 39.6% are predicted at the wavelength of 2.75 by finite-difference time-domain (FDTD) simulation. An co-doped ZBLAN fiber laser is set up to be used as a mid-IR light source at 2.75 . Coupling efficiencies of 32.6% and 11.6% to TE mode and TM mode SOS waveguides, respectively, were obtained experimentally with uniform grating couplers. The dependence of coupling efficiency on etch depth, grating period, fill factor, and incident angle are also studied.

Apodized focusing subwavelength grating couplers for suspended membrane waveguides

We demonstrate an apodized focusing subwavelength grating (SWG) for suspended membrane waveguides on silicon-on-insulator. Finite-difference time-domain simulation predicts −1.7 dB coupling efficiency and a 3 dB bandwidth of ∼50 nm for the transverse-magnetic mode apodized SWG, which has 98% field overlap with propagation mode in the single mode fiber. A modified phase matching formula is proposed to design the focusing apodized SWG. Better than −3.0 dB coupling efficiency and a 3 dB optical bandwidth of ∼50 nm is demonstrated experimentally.

Stable and wavelength-tunable silicon-micro-ring-resonator based erbium-doped fiber laser

In this work, we propose and demonstrate a stable and wavelength-tunable erbium-doped fiber (EDF) ring laser. Here, a silicon-on-insulator (SOI)-based silicon-micro-ring-resonator (SMRR) is used as the wavelength selective element inside the fiber ring cavity. A uniform period grating coupler (GC) is used to couple between the SMRR and single mode fiber (SMF) and serves also as a polarization dependent element in the cavity. The output lasing wavelength of the proposed fiber laser can be tuned at a tuning step of 2 nm (defined by the free spectral range (FSR) of the SMRR) in a bandwidth of 35.2 nm (1532.00 to 1567.20 nm), which is defined by the gain of the EDF. The optical-signal-to-noise-ratio (OSNR) of each lasing wavelength is larger than 42.0 dB. In addition, the output stabilities of power and wavelength are also discussed.

Tunable integrated variable bit-rate DPSK silicon receiver

We integrate a wavelength-tunable microring resonator with a monolithic Ge-on-Si photodetector for use as a variable bit-rate silicon receiver. The integrated receiver has a responsivity of 0.7 A/W. We achieved error-free operation for a wide range of bit rates from 5 Gb/s to 12.5 Gb/s. The wavelength tuning was realized by a TiN-based thermal heater, which enabled tuning of up to ~1 free spectral range.

Demodulation of 20 Gbaud/s differential quadrature phase-shift keying signals using wavelength-tunable silicon microring resonators

We experimentally demonstrate a demodulation scheme for 20 Gbaud/s nonreturn-to-zero differential quadrature phase-shift keying signals using a silicon microring resonator. Either the I or Q channel can be selected by electrical tuning using the carrier depletion effect. Error-free (bit error rate <10(-9)) operations can be achieved for both the I and Q channels with ~1.5 dB power penalty compared with a commercial 20 GHz Mach-Zehnder delay interferometer. The tuning range of the ring resonator can be up to 60 GHz, which enables operation over a wide range of data rates.

Enhanced optical Kerr nonlinearity of MoS 2 on silicon waveguides

A quasi-two-dimensional layer of MoS2 was placed on top of a silicon optical waveguide to form a MoS2–silicon hybrid structure. Chirped pulse self-phase modulation measurements were carried out to determine the optical Kerr nonlinearity of the structure. The observed increase in the spectral broadening of the optical pulses in the MoS2–silicon waveguide compared with the silicon waveguides indicated that the third-order nonlinear effect in MoS2 is about 2 orders of magnitude larger than that in silicon. The measurements show that MoS2 has an effective optical Kerr coefficient of about 1.1×10−16  m2/W. This work reveals the potential application of MoS2 to enhance the nonlinearity of hybrid silicon optical devices.

An Ultracompact OSNR Monitor Based on an Integrated Silicon Microdisk Resonator

Optical signal-to-noise ratio (OSNR) monitoring is essential for control and management of dynamic optical networks. Small footprint, low cost, and less power consumption are always desirable for such monitoring system. In this paper, we demonstrate an integrated dispersion-insensitive in-band OSNR monitor based on a compact silicon microdisk resonator (MDR) with only 5-μm radius. The MDR (Q ~ 54 000) functions as an ultranarrow bandpass filter in the measurement of the OSNR. The monitoring performance is evaluated in a 10-Gb/s return-to-zero differential phase-shift keying (RZ-DPSK) system and is shown to be insensitive to chromatic dispersion from 0 to 850 ps/nm. The input power requirement of the monitor is also studied, which is consistent with the desire for low-power operation. Finally, we analyze the sensitivity of this technique for various Q factors of the MDRs. The results indicate that the sensitivity of this scheme can be improved with higher Q factors.

In-plane saturable absorption of graphene on silicon waveguides

Using ultrafast pulses, in-plane saturable absorption in monolayer graphene placed on silicon waveguides is studied. A saturation response is observed at 15.8 pJ pulse energy and absorption decreases by 14.3% at 1.9 nJ pulse energy.

Performance of silicon coupled resonator waveguides for integrated Nyquist filter

We propose an integrated optical Nyquist filter based on silicon coupled resonator waveguides. The filter is designed for converting the 28 Gbaud QPSK spectrum to a low rolloff raised cosine shape with baud rate bandwidth.