There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Orbital angular momentum (OAM), which describes the “phase twist” (helical phase pattern) of light beams, has recently gained interest due to its potential applications in many diverse areas. Particularly promising is the use of OAM for optical communications since: (i) coaxially propagating OAM beams with different azimuthal OAM states are mutually orthogonal, (ii) inter-beam crosstalk can be minimized, and (iii) the beams can be efficiently multiplexed and demultiplexed. As a result, multiple OAM states could be used as different carriers for multiplexing and transmitting multiple data streams, thereby potentially increasing the system capacity. In this paper, we review recent progress in OAM beam generation/detection, multiplexing/demultiplexing, and its potential applications in different scenarios including free-space optical communications, fiber-optic communications, and RF communications. Technical challenges and perspectives of OAM beams are also discussed.

Optical communications using orbital angular momentum beams

It is shown that the ordinary semiclassical theory of the absorption of light by exciton states is not completely satisfactory (in contrast to the case of absorption due to interband transitions). A more complete theory is developed. It is shown that excitons are approximate bosons, and, in interaction with the electromagnetic field, the exciton field plays the role of the classical polarization field. The eigenstates of the system of crystal and radiation field are mixtures of photons and excitons. The ordinary one-quantum optical lifetime of an excitation is infinite. Absorption occurs only when "three-body" processes are introduced. The theory includes "local field" effects, leading to the Lorentz local field correction when it is applicable. A Smakula equation for the oscillator strength in terms of the integrated absorption constant is derived.

a Quantum-Mechanical Theory of the Contribution of Excitons to the Complex Dielectric Constant of Crystals.

Optical Waveguide Theory

Driven by the increasing demand on handing microwave signals with compact device, low power consumption, high efficiency and high reliability, it is highly desired to generate, distribute, and process microwave signals using photonic integrated circuits. Silicon photonics offers a promising platform facilitating ultracompact microwave photonic signal processing assisted by silicon nanophotonic devices. In this paper, we propose, theoretically analyze and experimentally demonstrate a simple scheme to realize ultracompact rejection ratio tunable notch microwave photonic filter (MPF) based on a silicon photonic crystal (PhC) nanocavity with fixed extinction ratio. Using a conventional modulation scheme with only a single phase modulator (PM), the rejection ratio of the presented MPF can be tuned from about 10 dB to beyond 60 dB. Moreover, the central frequency tunable operation in the high rejection ratio region is also demonstrated in the experiment.

/pdf/photonic-crystal-nanocavity-assisted-rejection-ratio-tunable-1zeivpqv3v.pdf

Photonic crystal nanocavity assisted rejection ratio tunable notch microwave photonic filter

 All-optical single-to-dual channel format con-verter from non-return-to-zero NRZ to return-to-zero RZis proposed and demonstrated using cascaded sum- anddifference-frequency generation SFG+DFG in a periodi-cally poled LiNbO 3 PPLN waveguide The pump opticalclock is generated from the active mode locking in a reﬂec-tive semiconductor optical ampliﬁer RSOA -based ﬁber ringlaser We successfully observe 10- and 20-Gbit/s single-to-dual channel NRZ-to-RZ format conversions in theexperiment © 2007 Society of Photo-Optical Instrumentation Engineers DOI: 101117/12823496 Subject terms: nonlinear optics; all-optical format conversion;non-return-to-zero; return-to-zero; cascaded sum- and difference-frequency generation; periodically poled LiNbO 3  Paper 070495LR received Jun 14, 2007; revised manuscriptreceived Sep 6, 2007; accepted for publication Sep 6, 2007;published online Dec 21, 2007 1 Introduction An all-optical format converter is an essential element inall-optical signal processing for future high-speed telecom-munication The basic format conversion from non-return-to-zero NRZ to return-to-zero RZ is very important andhas been successfully implemented using devices based ona nonlinear optical loop mirror

https://www.spiedigitallibrary.org/journals/Optical-Engineering/volume-46/issue-12/120501/All-optical-single-to-dual-channel-non-return-to-zero/10.1117/1.2823496.pdf

All-optical single-to-dual channel non-return-to-zero to return-to-zero format converter using a periodically poled LiNbO3 and a reflective semiconductor optical amplifier

We present a specific plasmonic vortex lens (PVL) structure to focus the surface plasmon polariton wave on an arbitrary spatial position.

Optionally focusing with plasmonic vortex lens

In this paper, we propose the simplest one-dimensional grating waveguide to obtain the wideband slow light. An ideal band indicating group index of 18.3 and bandwidth of 10.3 nm is obtained by plane wave expansion method, which is also verified in the finite-difference time-domain numerical simulation when a Gaussian pulse with bandwidth of 10.3 nm is input into the grating waveguide. Thus, this simple one-dimensional grating waveguide is believed to be widely used as wideband and low loss slow light delay for optical buffering and signal processing.

Wideband slow light in one-dimensional grating waveguide

An on-chip terahertz bandpass filter is demonstrated with widely continuous tunability and a narrow bandwidth of 256.8 MHz at 0.47945 THz. This is the first time to achieve a tunable on-chip terahertz bandpass filer.

Tunable on-chip terahertz bandpass filter with narrow bandwidth

A novel bandwidth tunable bandpass filter based on a silicon microring-MZI structure is proposed and demonstrated. By thermally tuning the resonance offset between the two microring resonators, and adding the two drop transmissions together, the bandwidth of the microring-MZI filter can be easily linearly tuned with low in-band ripples. Key words—bandwidth tunable; thermal tunable; optical filter; microring; optical signal processing.

Xinliang Zhang

Papers

All-optical single-to-dual channel non-return-to-zero to return-to-zero format converter using a periodically poled LiNbO3 and a reflective semiconductor optical amplifier

Optionally focusing with plasmonic vortex lens

Wideband slow light in one-dimensional grating waveguide

Tunable on-chip terahertz bandpass filter with narrow bandwidth

Bandwidth tunable filter based on silicon microring-MZI structure