Integrated Nonlinear Photonics Using CROWs (Project Report 0642603-Y1)

This NSF-funded project [0642603] is a five-year (60 months) CAREER (Faculty Early Career Development Program) unified research and education development program. The full title of this project is “CAREER: Chip-scale low-power nonlinear optics using coupled resonators and CROWs”. The focus of this project is a study of the waveguiding principles and applications of a novel type of integrated photonics waveguide, the Coupled Resonator Optical Waveguide (CROW), in nonlinear optics at the milliwatt-scale power level, which is relevant for optical communications and signal processing.

PR_23_EA_ICOP Nonlinear Optics Using Coupled Resonators in Silicon Photonics (ICOP-15)

Extended abstract of an invited presentation at the ICOP Workshop on Silicon Photonics, 19 February 2015 at Kolkata India. This workshop was part of the Golden Jubilee Conference of the Optical Society of India.

Balancing of Coupled Piezoelectric NEMS Resonators

Micro and Nano Electro Mechanical systems (M/NEMS) have a lot of potential to be used for sensing in different schemes and operation modes. We focus here on the use of coupled resonators for sensing and address the major limitation that these systems face, which stems from a compromise between dynamic range and responsivity. When the system becomes unbalanced, the responsivity drops. To solve this issue, we propose the use of piezoelectric-based stress tuning of the stiffness of the resonators in order to rebalance the system of resonators. With this approach we expect to be able to extend the dynamic range of such systems by some orders of magnitude.

Design and Analysis of a Wide Stopband Microstrip Dual-band Bandpass Filter

A novel configuration of a dual-band bandpass filter (BPF) working as a harmonic attenuator is introduced and fabricated. The proposed filter operates at 3 GHz, for UHF and SHF applications, and 6.3 GHz, for wireless applications. The presented layout has a symmetric structure, which consists of coupled resonators. The designing of the proposed resonator is performed by introducing a new LC equivalent model of coupled lines. To verify the LC model of the coupled lines, the lumped elements are calculated. The introduced filter has a wide stopband up to 85 GHz with 28th harmonic suppression, for the first channel, and 13th harmonic suppression, for the second channel. The harmonics are attenuated using a novel structure. Also, the proposed BPF has a compact size of 0.056 λg2. Having several transmission zeros (TZs) that improve the performance of the presented BPF is another feature. The proposed dual-band BPF is fabricated and measured to verify the design method, where the measurement results confirm the simulations.

Multipole resonance and Vernier effect in compact and flexible plasmonic structures

Spoof surface plasmons in corrugated metal surfaces allow tight field confinement and guiding even at low frequencies and are promising for compact microwave photonic devices. Here, we use metal-ink printing on flexible substrates to construct compact spoof plasmon resonators. We clearly observe multipole resonances in the microwave frequencies and demonstrate that they are still maintained even under significant bending. Moreover, by combining two resonators of slightly different sizes, we demonstrate spectral filtering via the Vernier effect. We selectively address a target higher-order resonance while suppressing the other modes. Finally, we investigate the index-sensing capability of printed plasmonic resonators. In the Vernier structure, we can control the resonance amplitude and frequency by adjusting a resonance overlap between two coupled resonators. The transmission amplitude can be maximized at a target refractive index, and this can provide more functionalities and increased design flexibility. The metal-ink printing of microwave photonic structures can be applied to various flexible devices. Therefore, we expect that the compact, flexible plasmonic structures demonstrated in this study may be useful for highly functional elements that can enable tight field confinement and manipulation.

Highly Chiral Exceptional Point in Perturbed Coupled Resonators

Exceptional point (EP) is a non-Hermitian spectral degeneracy that has application in ultrasensitive sensors and laser mode selectivity. By employing strong chirality in an optical system, the direction of light propagation can be controlled and subwavelength particles can be detected. Here, we show that EP with high chirality can appear in the coupled resonators perturbed by a scatterer, in which both the distance and position of the scatterer can be tuned. We achieve strong chiral EP in two different distances between the resonators, with chirality around 0.99 in both cases.