On-chip Photonic Devices Research Articles

Combination of a spectrometer-on-chip and an array of Young's interferometers for laser spectrum monitoring.

This Letter presents the design and experimental results for an on-chip photonic device for laser spectrum monitoring that combines a nanospectrometer and an array of Young's interferometers. The array of Young's interferometers and the spectrometer measure the width and wavelength of a spectrum in visible light, respectively. The accuracy of spectral width measurements is around 10% for FWHM higher than 2.5 pm. The spectrometer-on-chip is based on a digital planar hologram, and provides a resolution around 145 pm within the spectral range of 719-861 nm (142 nm bandwidth). The performance of the device is demonstrated for distinguishing between the single- and two-longitudinal mode operation of a fiber Bragg grating laser diode with 23 pm mode separation.

(Invited) Narrow Linewidth, Highly Efficient, and Integrated Light Emitting Diodes Based on Ge Quantum Dots in Optical Microcavities

Room-temperature current-injected light emitting diodes with well-resolved and narrow emission peaks are demonstrated based on Ge self-assembled quantum dots embedded in optical microcavities, including photonic crystal cavities and microdisks. By using modified L3-type photonic crystal cavities, sharp resonant peaks with Q-factor over 800 are observed in the electroluminescence spectra around wavelength of 1.3 µm. Measurable output power on the level of pico-Watt is obtained under 3 mA injected current. In order to realize integration with other on-chip photonic devices, waveguide-coupled microdisk light emitting diodes are also demonstrated. Light emission is successfully coupled from the microdisk to waveguide. Sharp resonant peaks with Q-factor over 5000 are realized. As a further step to enhance the light emission efficiency of Ge quantum dots, n-type delta-doping at Ge/Si interfaces is performed and up to 3 times enhancement of emission intensity is obtained due to extra supply of extrinsic electrons.

Plasmon-Induced Transparency in the Visible Region via Self-Assembled Gold Nanorod Heterodimers

The phenomenon of plasmon-induced transparency holds immense potential for high sensitivity sensors and optical information processing due to the extreme dispersion and slowing of light within a narrow spectral window. Unfortunately plasmonic metamaterials demonstrating this effect has been restricted to infrared and greater wavelengths due to requisite precision in structure fabrication. Here we report a novel metamaterial synthesized by bottom-up self-assembly of gold nanorods. The small dimensions (≤ 50/20 nm, length/diameter), atomically smooth surfaces, and nanometer resolution enable the first demonstration of plasmon-induced transparency at visible wavelengths. The slow-down factors within the reduced symmetry heterodimer cluster are comparable to longer wavelength counterparts. The inherent spectral tunability and facile large-scale integration afforded by self-assembled metamaterials will open a new paradigm for physically realizable on-chip photonic device designs.

Holey-Metal Lenses: Sieving Single Modes with Proper Phases

We study a planar, holey-metal lens made as a set of concentric circular arrays (rings) of nanoscale holes milled in a subwavelength-thick metal film. Each nanohole-a finite-length, circular, single-mode waveguide with a radius-dependent mode index-is used as a phase-shifting element. Our experimental results confirm that the focusing properties of our polarization-independent, holey-metal lens milled in a 380-nm-thick gold film and illuminated with 531 nm light fits the analytical model well. The proposed concept could offer an alternative to conventional refraction microlenses and open up a vital path toward on-chip or fiber-end planar photonic devices for biosensing and imaging.

Planar achromatic multiple beam splitter by adiabatic light transfer

We introduce a novel achromatic and robust scheme for n-fold multiple beam splitting based on adiabatic light transfer in a planar geometry of coupled waveguides (WGs). The concept is experimentally verified for a one-to-three beam splitter by using a reconfigurable light-induced WG structure at two operating wavelengths. The demonstrated planar-type achromatic beam splitter opens new opportunities for the realization of ultra-high bandwidth on-chip photonic devices.

Graphene-based polymer waveguide polarizer

Planar-lightwave-circuit (PLC)-type graphene polarizers are fabricated by using a low loss optical polymer waveguide. The optical characteristics are investigated at a wavelength of 1.31 µm. By interface engineering with a UV-curable perfluorinated acrylate polymer resin, the graphene's electrical properties are tuned to support a transverse-magnetic (TM) or transverse-electric (TE) surface wave. Thus, the fabricated PLC-type graphene polarizer serves alternatively as a TM-pass or TE-pass polarizer depending on the absence or presence of the upper-cladding layer. The proposed planar-type graphene polarizer can be exploited further for on-chip photonic integrated circuit and devices.

Exciton Polaritons in 1D Organic Nanocrystals

Nanophotonic circuits meet exciton polaritons (EPs) in organic nanomaterials: Great possibilities for the use of organic 1D crystalline nanostructures as building blocks are emerging. These remarkable studies will contribute significantly to the development of EP-based on-chip photonic devices in the near future.

Near-field measurement of amplitude and phase in silicon waveguides with liquid cladding

Heterodyne near-field scanning optical microscopy (H-NSOM) has proven useful as a tool for characterization of both amplitude and phase of on-chip photonic devices in air, but it has previously been unable to characterize devices with a dielectric overcladding, which is commonly used in practice for such devices. Here we demonstrate H-NSOM of a silicon waveguide with a liquid cladding emulating the solid dielectric. This technique allows characterization of practical devices with realistic refractive index profiles. Fourier analysis is used to estimate the effective refractive index of the mode from the measured data, showing an index shift of 0.08 from air to water cladding, which is seen to correspond well to simulations.

Diffraction inhibition in two-dimensional photonic crystals

We show the existence of flat equal-frequency contour across the entire first Brillouin zone in two-dimensional photonic crystals. Under this condition, light diffraction can be inhibited. Moreover, the beam can be highly localized between two neighboring rows of the defect-free photonic crystal. Such a finding may have novel applications in light beam manipulations and on-chip integrated photonic devices.

Frequency-bin entangled comb of photon pairs from a Silicon-on-Insulator micro-resonator

We present a quantum-mechanical theory to describe narrowband photon-pair generation via four-wave mixing in a Silicon-on-Insulator (SOI) micro-resonator. We also provide design principles for efficient photon-pair generation in an SOI micro-resonator through extensive numerical simulations. Microring cavities are shown to have a much wider dispersion-compensated frequency range than straight cavities. A microring with an inner radius of 8 μm can output an entangled photon comb of 21 pairwise-correlated peaks (42 comb lines) spanning from 1.3 μm to 1.8 μm. Such on-chip quantum photonic devices offer a path toward future integrated quantum photonics and quantum integrated circuits.

Dynamic tuning of an optical resonator through MEMS-driven coupled photonic crystal nanocavities

We present dynamic tuning of optical resonance using microelectromechanical systems (MEMS)-driven coupled photonic crystal (PhC) nanocavities. The device consists of an air-suspended one-dimensional PhC nanocavity coupled to input and output waveguides and a perturbing nanocavity attached to a submicrometer MEMS comb drive. Resonance tuning is achieved through varying the gap between the two coupled cavities. We demonstrate experimentally that resonance can be tuned up to 8nm with no significant deterioration in the Q factor. The proposed mechanism potentially enables a new platform of on-chip photonic devices that can achieve a large tuning range with low power and small footprint and may find useful applications in tunable optical/photonic devices.

Design of nanoslotted photonic crystal waveguide cavities for single nanoparticle trapping and detection

We design and numerically simulate an on-chip photonic device that integrates both optical manipulation and detection functionalities for a single nanoparticle or macromolecule. A unique combination of a photonic crystal waveguide cavity and a nanoslot structure leads to a approximately 1300 times enhancement of the optical gradient trapping force compared with a conventional waveguide trapping device. Numerical simulations indicate that the designed device is capable of stably trapping a single nanoparticle inside the nanoslot cavity, and thus provides an ideal platform for single particle detection and analysis using cavity-enhanced spectroscopic technologies.

High-speed all-optical modulation using polycrystalline silicon microring resonators

We experimentally demonstrate on-chip active photonic devices fabricated from deposited polycrystalline silicon, which can be used for monolithic three-dimensional integration of optical networks. The demonstrated modulator is based on all-optical carrier injection in a micrometer-size resonator and has a modulation depth of 10dB and a temporal response of 135ps. Grain boundaries in the polycrystalline silicon (polysilicon) material result in faster electron-hole recombination, enabling a shortened carrier lifetime and a faster optical switching time compared to similar devices based on crystalline silicon.

Photonic-Fluidic Integrated Microstructures for Sensor and Photonic Device Applications

ABSTRACTThe design, fabrication and characterization of liquid-filled microchannels embedded in silica layers and integrated with optical waveguides for applications in on-chip sensors and novel photonic devices are presented. These integrated microstructures are formed using plasma-enhanced chemical vapor deposition (PECVD), photolithography and reactive ion etching (RIE). Surface accessible fluid introduction ports have been developed, and microfluidic circuits including bends, T-junctions and splitters are demonstrated. Coupling of light from integrated solid silica waveguides via directional coupling or direct end-fire coupling into fluid filled channels has been achieved on-chip, and optical losses assessed experimentally and theoretically. Optimization of the microstructures for sensor applications and for novel photonic devices based on nonlinear and other optical properties of fluids in integrated liquid waveguide segments is discussed.