High Index Contrast Waveguides Research Articles

Switching light on a silicon chip

Abstract Optics on a silicon chip—provides a new platform for monolithic integration of optics and microelectronics and can open the door to a new technology that is free from conventional microelectronics. However, the difficulty in controlling light and diverting its path on silicon need to be addressed before this technology can successfully be used to resolve current microelectronics bottlenecks. Here we use highly confined photonic structures for enhancing the electro-optical and nonlinearities properties of silicon and achieving optical switching on-chip with very low powers. We demonstrate for the first time optical bistability in a highly integrated silicon device using a 5-μm radius ring resonator. The strong confinement nature of the resonator induces nonlinear optical response with low pump powers. We show that the optical bistability enables all-optical switching with microsecond time response and modulation depth of 10 dB, driven by pump power as low as 45 μW. We also present the first experimental demonstration of fast all-optical switching on silicon. The transmission of the structure is modulated by more than 97% in less than 500 ps using light pulses with energies as low as 40 pJ. Finally, we propose and analyze an electrically modulated silicon-on-insulator (SOI) submicron-size high index-contrast waveguide. The geometry of the waveguide provides high lateral optical confinement and defines a lateral p-i-n diode. Our calculations indicate that this scheme can be used to implement submicron high index-contrast waveguide active devices on SOI. As an example of application, a one-dimensional microcavity intensity-modulator is predicted to exhibit a modulation depth as high as 80% by employing a dc power consumption as low as ∼11 μW.

Fabrication and characterization of low loss rib chalcogenide waveguides made by dry etching

We report the fabrication and characterization of rib chalcogenide waveguides produced by dry etching with CF4 and O2. The high index contrast waveguides (Deltan ~1) show a minimum propagation loss of 0.25 dB/cm. The high refractive nonlinearity of 100 times silica in As2S3 allowed observation of a pi phase shift due to self-phase modulation of an 8 ps duration 1573 nm pulse in a 5 cm long waveguide.

Optimal waveguide dimensions for nonlinear interactions

We investigate strong light confinement in high core-cladding index contrast waveguides with dimensions comparable to and smaller than the wavelength of incident light. We consider oval and rectangular cross sections and demonstrate that an optimal core size exists that maximizes the effective nonlinearity. We also determine that waveguides with asymmetrical cross sections provide the maximum possible nonlinearity, although only a small improvement over the symmetric case. Furthermore, we find that for a specified waveguide shape the largest nonlinearity occurs for nearly the same core area in all cases. Calculations of the dispersion for the optimal-size waveguide at a particular wavelength indicate that the group-velocity dispersion is normal. Ultimately, such designs could be used to develop low-power all-optical devices and to produce waveguides for ultra-low threshold nonlinear frequency generation such as supercontinuum generation.

Silicon-based Integrated Optics: Waveguide Technology to Microphotonics

ABSTRACTUsing a waveguide spectrometer chip as an example, we describe how high index contrast waveguides systems such as silicon-on-insulator can be combined with microphotonic design rules to extend the performance of waveguide devices. The challenges arising in the implementation of silicon microphotonic technology are discussed, and recent work addressing the issues of waveguide coupling, polarization sensitivity, waveguide loss and massively parallel data acquisition is reviewed.

Geometric variations in high index-contrast waveguides, coupled mode theory in curvilinear coordinates

Perturbation theory formulation of Maxwell's equations gives a theoretically elegant and computationally efficient way of describing small imperfections and weak interactions in electro-magnetic systems. It is generally appreciated that due to the discontinuous field boundary conditions in the systems employing high dielectric contrast profiles standard perturbation formulations fail when applied to the problem of shifted material boundaries. In this paper we developed a novel coupled mode and perturbation theory formulations for treating generic non-uniform (varying along the direction of propagation) perturbations of a waveguide cross-section based on Hamiltonian formulation of Maxwell equations in curvilinear coordinates. We show that our formulation is accurate and rapidly converges to an exact result when used in a coupled mode theory framework even for the high index-contrast discontinuous dielectric profiles. Among others, our formulation allows for an efficient numerical evaluation of induced PMD due to a generic distortion of a waveguide profile, analysis of mode filters, mode converters and other optical elements such as strong Bragg gratings, tapers, bends etc., and arbitrary combinations of thereof. To our knowledge, this is the first time perturbation and coupled mode theories are developed to deal with arbitrary non-uniform profile variations in high index-contrast waveguides.

High-density integrated optics

This paper presents two dimensional (2-D) finite difference time domain (FDTD) simulations of low-loss right-angle waveguide bends, T-junctions and crossings, based on high index-contrast waveguides. Such structures are essential for the dense integration of optical components. Excellent performance characteristics are obtained by designing the waveguide intersection regions as low-Q resonant cavities with certain symmetries and small radiation loss. A simple analysis, based on coupled mode theory in time, is used to explain the operation principles and agrees qualitatively with the numerical results.