The history, fabrication, theory, numerical modeling, optical properties, guidance mechanisms, and applications of photonic-crystal fibers are reviewed

Photonic-Crystal Fibers

On-chip optical buffers based on waveguide delay lines might have significant implications for the development of optical interconnects in computer systems. Silicon-on-insulator (SOI) submicrometre photonic wire waveguides are used, because they can provide strong light confinement at the diffraction limit, allowing dramatic scaling of device size. Here we report on-chip optical delay lines based on such waveguides that consist of up to 100 microring resonators cascaded in either coupled-resonator or all-pass filter (APF) configurations. On-chip group delays exceeding 500 ps are demonstrated in a device with a footprint below 0.09 mm2. The trade-offs between resonantly enhanced group delay, device size, insertion loss and operational bandwidth are analysed for various delay-line designs. A large fractional group delay exceeding 10 bits is achieved for bit rates as high as 20 Gbps. Measurements of system-level metrics as bit error rates for different bit rates demonstrate error-free operation up to 5 Gbps.

Ultracompact optical buffers on a silicon chip

A review of some properties of chalcogenide glasses and the current status of their applications is given. Techniques to characterize the linear and non-linear properties of these glasses are introduced and used to measure the optical constants of chalcogenide glasses in the form of bulk, thin film and fiber. Different techniques for the fabrication of gratings and waveguides in these glasses are described. Achievable efficiencies of gratings, as well as propagation losses of fabricated waveguides, are presented. The possibilities of fabricating active devices, such as fiber amplifiers and lasers, are presented. Finally, a novel application of chalcogenide glasses, namely all-optical switching for the fabrication of efficient femtosecond switches, is introduced.

Optical properties and applications of chalcogenide glasses: a review

Discrete Solitons in Optics

Within the last several years, the field of terahertz science and technology has changed dramatically. Many new advances in the technology for generation, manipulation, and detection of terahertz radiation have revolutionized the field. Much of this interest has been inspired by the promise of valuable new applications for terahertz imaging and sensing. Among a long list of proposed uses, one finds compelling needs such as security screening and quality control, as well as whimsical notions such as counting the almonds in a bar of chocolate. This list has grown in parallel with the development of new technologies and new paradigms for imaging and sensing. Many of these proposed applications exploit the unique capabilities of terahertz radiation to penetrate common packaging materials and provide spectroscopic information about the materials within. Several of the techniques used for terahertz imaging have been borrowed from other, more well established fields such as x-ray computed tomography and synthetic aperture radar. Others have been developed exclusively for the terahertz field, and have no analogies in other portions of the spectrum. This review provides a comprehensive description of the various techniques which have been employed for terahertz image formation, as well as discussing numerous examples which illustrate the many exciting potential uses for these emerging technologies.

https://iopscience.iop.org/article/10.1088/0034-4885/70/8/R02/pdf

Imaging with terahertz radiation

Optical delay lines have some important applications, notably in optical communication systems and in phased arrays. These devices are based on the concept of optical group delay, which, in turn, can be understood as the property of an optical filter. Optical filters are well-understood devices and, in particular, their dispersive properties determine the group delay response. We review these dispersive properties and point out some of the inherent tradeoffs involved in generating large group delay. Fiber Bragg gratings and recent results on optical all-pass filters are used as examples.

Optical delay lines based on optical filters

Third-order Kerr nonlinearities and Raman gain are studied experimentally in high-purity As2Se3 optical fibers for wavelengths near 1.55 μm. Kerr nonlinear coefficients are measured to be nearly 1000 times higher than those for silica fibers. In pulsed mode, nonlinear phase shifts near 1.2-π rad are measured in fibers only 85 cm long with peak pulse powers near 3 W. However, there are nonlinear losses near 20% for nonlinear phase shifts near π. By use of a cw optical pump, large Raman gains nearly 800 times that of silica were measured. In the cw case there were losses in the form of index gratings formed from standing waves at the exit face of the fiber. Discrete Raman amplifiers and optical regenerators are discussed as possible applications.

Large Raman gain and nonlinear phase shifts in high-purity As 2 Se 3 chalcogenide fibers

High-speed optical communication requires ultrafast all-optical processing and switching capabilities. The Kerr nonlinearity, an ultrafast optical nonlinearity, is often used as the basic switching mechanism. A practical, small device that can be switched with ∼1‐pJ energies requires a large Kerr effect with minimal losses (both linear and nonlinear). We have investigated theoretically and experimentally a number of Se-based chalcogenide glasses. We have found a number of compounds with a Kerr nonlinearity hundreds of times larger than silica, making them excellent candidates for ultrafast all-optical devices.

Large Kerr effect in bulk Se-based chalcogenide glasses.

Lossless all-pass optical filters are introduced, which can approximate any desired phase response while maintaining a constant, unity amplitude response. Architectures using cascade and lattice structures based on ring resonators and cavities defined by reflectors are discussed. Two applications are presented: 1) for fiber dispersion compensation and 2) for compensation of the nonlinear phase response of narrow bandpass optical filters such as thin-film or Bragg grating filters. All orders of dispersion can be compensated in principle, and the filters are periodic so multiple channels can be compensated with a single device. The architectures are very compact compared to alternatives such as chirped Bragg gratings.

Optical all-pass filters for phase response design with applications for dispersion compensation

New integrated optical all-pass filters are presented that can be used for tunable dispersion compensation, dispersion slope compensation, and as building blocks in tunable bandpass filters. The dispersion slope compensation capability is demonstrated using ring resonators in /spl Delta/=2% Ge-doped silica planar waveguides. In addition, a tunable four-stage filter with free-spectral range (FSR)=25 GHz, a passband width of 14 GHz (0.56/spl times/FSR), and D=1800 ps/nm is reported.

Gadi Lenz

Papers

Optical delay lines based on optical filters

Large Raman gain and nonlinear phase shifts in high-purity As 2 Se 3 chalcogenide fibers

Large Kerr effect in bulk Se-based chalcogenide glasses.

Optical all-pass filters for phase response design with applications for dispersion compensation

Integrated all-pass filters for tunable dispersion and dispersion slope compensation