The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

http://ieeexplore.ieee.org/iel5/6354/16969/00781867.pdf

Photonic crystals

Slow light with a remarkably low group velocity is a promising solution for buffering and time-domain processing of optical signals. It also offers the possibility for spatial compression of optical energy and the enhancement of linear and nonlinear optical effects. Photonic-crystal devices are especially attractive for generating slow light, as they are compatible with on-chip integration and room-temperature operation, and can offer wide-bandwidth and dispersion-free propagation. Here the background theory, recent experimental demonstrations and progress towards tunable slow-light structures based on photonic-band engineering are reviewed. Practical issues related to real devices and their applications are also discussed. The unique properties of wide-bandwidth and dispersion-free propagation in photonic-crystal devices have made them a good candidate for slow-light generation. This article gives the background theory of slow light, as well as an overview of recent experimental demonstrations based on photonic-band engineering.

/pdf/slow-light-in-photonic-crystals-59fjoaj79v.pdf

Slow light in photonic crystals

We report the fabrication and accurate measurement of propagation and bending losses in single-mode silicon waveguides with submicron dimensions fabricated on silicon-on-insulator wafers. Owing to the small sidewall surface roughness achieved by processing on a standard 200mm CMOS fabrication line, minimal propagation losses of 3.6+/-0.1dB/cm for the TE polarization were measured at the telecommunications wavelength of 1.5microm. Losses per 90 masculine bend are measured to be 0.086+/-0.005dB for a bending radius of 1microm and as low as 0.013+/-0.005dB for a bend radius of 2microm. These record low numbers can be used as a benchmark for further development of silicon microphotonic components and circuits.

/pdf/losses-in-single-mode-silicon-on-insulator-strip-waveguides-2xwu3irgp8.pdf

Losses in single-mode silicon-on-insulator strip waveguides and bends.

Nanophotonic waveguides and components are promising for use in the large-scale integration of photonic circuits. Coupling light between nanophotonic waveguides and a single-mode fiber is an important problem and many different solutions have been proposed and demonstrated in recent years. In this paper, we discuss a grating coupler approach. Grating couplers can be placed anywhere on a circuit and can easily be integrated. We have experimentally demonstrated >30% coupling efficiency with a 1 dB bandwidth of 40 nm on standard wafers. Theoretically, the coupling efficiency can be improved to >90% using an optimized grating design and layer stack. The fabrication of the couplers in silicon-on-insulator and in indium phosphide membranes is also discussed.

/pdf/grating-couplers-for-coupling-between-optical-fibers-and-242kb9dwcg.pdf

Grating Couplers for Coupling between Optical Fibers and Nanophotonic Waveguides

Silicon photonics could enable a chip-scale platform for monolithic integration of optics and microelectronics for applications of optical interconnects in which high data streams are required in a small footprint. This paper discusses mechanisms in silicon photonics for waveguiding, modulating, light amplification, and emission. These mechanisms, together with recent advances of fabrication techniques, have enabled the demonstration of ultracompact passive and active silicon photonic components with very low loss.

Guiding, modulating, and emitting light on Silicon-challenges and opportunities

A novel integrated mode size converter for single-mode Si wire waveguides is presented. The mode size converter is constructed with two-dimensional tapered Si waveguides and overlaid high-index polymer waveguides. We calculated the proposed mode size converter characteristics, and fabricated 1.09 mm length Si wire waveguides with the converters. The measured loss of the mode size converter was 0.8 dB per conversion, and the total insertion loss through the sample with an Si wire waveguide was 3.5 dB.

Low loss mode size converter from 0.3 [micro sign]m square Si wire waveguides to singlemode fibres

An Si wire array waveguide grating wavelength demultiplexer fabricated using immersion ArF lithography is reported. The tilt directions of the input and output star couplers are aligned in the same direction to avoid phase error generated at the curved waveguides. A 16 channel device with 200 GHz wavelength spacing was fabricated.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/el.2013.0206

Si wire array waveguide grating with parallel star coupler configuration fabricated by ArF excimer immersion lithography

Single-mode lightwave transmission was observed in novel line-defect photonic-crystal (PC) waveguides. The waveguide structure is constructed by adding phase-shifted holes in an ordinary missing-hole line defect. This device permits a fine single-mode lightwave transmission even though the waveguide structure is fabricated on silicon-on-insulator (SOI) substrate, which seriously promotes off-plane leakage of waveguiding modes.

Single-mode lightwave transmission in SOI-type photonic-crystal line-defect waveguides with phase-shifted holes

We demonstrate a monolithic integration of a silica-based arrayed waveguide grating filter and silicon variable optical attenuators. The integrated device perform wavelength demultiplexing in 16 channels and provide high-speed power-level adjustment with a response of <15 ns in each channel.

Monolithic integration of a silica-based arrayed waveguide grating filter and silicon variable optical attenuators based on p-i-n carrier-injection structures

We propose a novel polarization beam splitter (PBS) and rotator (PBR) for polarization diversity configuration to implement a polarization-independent silicon photonic circuit Our PBS, which is based on a directional coupler (DC), exhibits the polarization extinction ratio (PER) of 10 dB for the C-band, and the maximum PER is 23 dB For the PBR, which consists of a Si wire and an off-axis silicon oxinitride (SiOxNy) waveguide, the simulated PER exceeds 20 dB in the efficient wavelength range of over 6 THz

K. Yamada

Papers

Low loss mode size converter from 0.3 [micro sign]m square Si wire waveguides to singlemode fibres

Si wire array waveguide grating with parallel star coupler configuration fabricated by ArF excimer immersion lithography

Single-mode lightwave transmission in SOI-type photonic-crystal line-defect waveguides with phase-shifted holes

Monolithic integration of a silica-based arrayed waveguide grating filter and silicon variable optical attenuators based on p-i-n carrier-injection structures

Polarization Beam Splitter and Rotator for Polarization-Independent Silicon Photonic Circuit