Andrew Grieco

Optical Bistability in a Silicon Waveguide Distributed Bragg Reflector Fabry–Pérot Resonator

We demonstrate optical bistability in a silicon waveguide Fabry-Pérot resonator formed by a pair of distributed Bragg reflectors. In the bistable regime, the output power of the resonator ceases to be uniquely determined by the input power because multiple powers within the cavity satisfy the resonance condition. Pulsating behavior is observed within the resonator output, and is attributed to noise within the experimental setup driving the resonator between the multiple allowed output powers.

Femtosecond micromachining of internal voids in high explosive crystals for studies of hot spot initiation

Femtosecond micromachining was used to produce controlled patterns of internal voids in high explosive single crystals of 1,3-dinitrato-2,2-bis(nitratomethyl) propane (PETN), 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) and 1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX). The micromachined voids were characterized with optical microscopy and confocal Raman microscopy. Optical microscopy established that the voids generated near the threshold energy were localized to submicrometer diameters. Increasing the micromachining energy above threshold led to microcracking along preferred crystalline planes. Consolidation of hundreds to thousands of individual voids allowed creation of defined two- and three-dimensional structures. Production of three-dimensional consolidated structures led to extended crystal damage or residual strain over tens to hundreds of micrometers. Confocal Raman microscopy established that the defects generated were voids, with no chemical products observable and with diminished crystal spectr...

Towards 100 channel dense wavelength division multiplexing with 100GHz spacing on silicon

A 1 by 4 wavelength division multiplexer with 0.5nm bandwidth and no free spectral range limitation is demonstrated on silicon. The device utilizes wide bandwidth filters cascaded with ring resonators in order to select specific ring resonator modes and route each resonant mode to a separate port. This technology will enable dense wavelength division multiplexing covering the C - and L - bands with up to 100 10GB/s channels separated by 100GHz to be implemented for optical interconnects applications. A 1 by 4 wavelength division multiplexer with 3dB channel bandwidths as small as 0.5nm and 1dB insertion loss are demonstrated with 16dB inter-channel crosstalk suppression. A second wavelength division multiplexer scheme with four channels, each spaced 0.5nm apart without any free spectral range limitations is also demonstrated using wide bandwidth filters centered at the same wavelength to select resonances from four different ring resonators with slightly different widths.

Integrated Space-Division Multiplexer for Application to Data Center Networks

The prospect of creating integrated space-division multiplexing (SDM) on a chip, utilizing the orthogonal degrees of freedom of numerous guided spatial modes in a multimode waveguide, promises a substantial reduction in the cost, complexity, and scalability of networking systems by augmenting or replacing the commonly used approach of wavelength-division multiplexing (WDM). As a demonstration of the SDM approach, we introduce and experimentally characterize a periodically nanostructured resonant coupler integrated with a multimode waveguide that selectively transfers energy between arbitrary waveguide modes. Compared to alternative schemes, this device possesses advantages in terms of packing density, control of operating bandwidth, tunability to operate with numerous orthogonal spatial modes, and support of a large number of switching ports.

Silicon nanophotonic devices for chip-scale optical communication applications [Invited]

This paper reviews recent work in the area of silicon photonic devices and circuits for monolithic and heterogeneous integration of circuits and systems on a chip. In this context, it presents fabrication results for producing low-loss silicon waveguides without etching. Resonators and add-drop distributed filters utilizing sidewall modulation fabricated in a single lithography and etching step are demonstrated. It also presents an optical pulse compressor that monolithically integrates self-phase modulation and anomalous dispersion compensation devices on a silicon chip. As an example of heterogeneous integration, we demonstrate vertical emitting metallo-dielectric nanolasers integrated onto a silicon platform. Future research directions toward large-scale photonic circuits and systems on a chip also are discussed.

Design and analysis of a narrowband filter for optical platform

This paper presents an approach to designing narrowband digital filters that are realizable using optical allpass building blocks. We describe a top-down design method by explicitly examining the derivation of an Infinite Impulse Response (IIR) architecture. Our result demonstrates a design that can achieve a 0.0025π passband edge while providing 60dB stopband attenuation. The design is aimed to reduce filter pole magnitudes, providing tolerance for waveguide losses and fabrication errors. The narrowband filter is based on the foundation of latticed allpass sections, which makes it naturally realizable using basic photonic components. Furthermore, analysis is performed on delay length variations that can result from the fabrication process.

Characterization of Distributed Bragg Reflectors

We propose and demonstrate a novel method to characterize the coupling coefficient and loss coefficient of a distributed Bragg reflector (DBR). The method is based on a coupled-mode analysis of periodic structures, and involves the linewidth comparison of a pair of DBR Fabry-Pérot resonators. The method is shown to be independent of coupling efficiency and wavelength dependence of the DBR parameters.

Allpass filter design with waveguide loss compensation

A major artifact of realistic photonic filters is the waveguide power loss. Its detrimental effect on the allpass structure is particularly alarming because the phase response is highly sensitive to perturbations. While the loss can be simply captured into a variation on the unit delay in signal processing analysis, its non-linearity makes it mathematically difficult to address. We present an allpass filter design algorithm that is able to provide filter coefficients that compensate for the waveguide power loss. By absorbing the loss parameter into the design cost function, the optimization problem becomes non-convex and NP hard. Our approach solves this problem by utilizing an iterative algorithm in conjunction with the branch and bound global optimization technique. The proposed algorithm is expected to improve the performance and increase the utilization of allpass filters for optical signal phase based applications such as distortion compensation and group delay equalization.

Hybrid multimode resonators based on grating-assisted counter-directional couplers

Research thrusts in silicon photonics are developing control operations using higher order waveguide modes for next generation high-bandwidth communication systems. In this context, devices allowing optical processing of multiple waveguide modes can reduce architecture complexity and enable flexible on-chip networks. We propose and demonstrate a hybrid resonator dually resonant at the 1st and 2nd order modes of a silicon waveguide. We observe 8 dB extinction ratio and modal conversion range of 20 nm for the 1st order quasi-TE mode input.

Multichannel optical filters in nanoscale silicon waveguides

We design and characterize asymmetric Bragg gratings in waveguides which possess multiple reflected wavelengths. We experimentally demonstrate devices with two independent stopbands, then use finite-difference time domain software to characterize more complex grating designs.