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

Although high-speed all-optical switches are expected to replace their electrical counterparts in information processing, their relatively large size and power consumption have remained obstacles. We use a combination of an ultrasmall photonic-crystal nanocavity and strong carrier-induced nonlinearity in InGaAsP to successfully demonstrate low-energy switching within a few tens of picoseconds. Switching energies with a contrast of 3 and 10 dB of 0.42 and 0.66 fJ, respectively, have been obtained, which are over two orders of magnitude lower than those of previously reported all-optical switches. The ultrasmall cavity substantially enhances the nonlinearity as well as the recovery speed, and the switching efficiency is maximized by a combination of two-photon absorption and linear absorption in the InGaAsP nanocavities. These switches, with their chip-scale integratability, may lead to the possibility of low-power, high-density, all-optical processing in a chip. All-optical switching energies as small as 0.42 fJ — two orders of magnitude lower than previously reported — are demonstrated in small photonic crystal cavities incorporating InGaAsP. These devices can switch within a few tens of picoseconds, and may therefore have potential for low-power high-density all-optical processing on a chip.

Sub-femtojoule all-optical switching using a photonic-crystal nanocavity

This paper reviews the recent progress of AlGaInP high brightness light-emitting diodes. After the discussion of some basic material properties and the general problem of light extraction we will discuss several approaches of high efficiency devices.

High brightness AlGaInP light-emitting diodes

A method for the production of a robust, chemically stable, crystalline, passivated nanoparticle and composition containing the same, that emit light with high efficiencies and size-tunable and excitation energy tunable color. The methods include the thermal degradation of a precursor molecule in the presence of a capping agent at high temperature and elevated pressure. A particular composition prepared by the methods is a passivated silicon nanoparticle composition displaying discrete optical transitions.

Light-emitting nanoparticles and method of making same

Transparent conducting oxides have recently gained great attention as CMOS-compatible materials for applications in nanophotonics due to their low optical loss, metal-like behavior, versatile/tailorable optical properties, and established fabrication procedures. In particular, aluminum doped zinc oxide (AZO) is very attractive because its dielectric permittivity can be engineered over a broad range in the near infrared and infrared. However, despite all these beneficial features, the slow (> 100 ps) electron-hole recombination time typical of these compounds still represents a fundamental limitation impeding ultrafast optical modulation. Here we report the first epsilon-near-zero AZO thin films which simultaneously exhibit ultra-fast carrier dynamics (excitation and recombination time below 1 ps) and an outstanding reflectance modulation up to 40% for very low pump fluence levels (< 4 mJ/cm2) at the telecom wavelength of 1.3 {\mu}m. The unique properties of the demonstrated AZO thin films are the result of a low temperature fabrication procedure promoting oxygen vacancies and an ultra-high carrier concentration. As a proof-of-concept, an all-optical AZO-based plasmonic modulator achieving 3 dB modulation in 7.5 {\mu}m and operating at THz frequencies is numerically demonstrated. Our results overcome the traditional "modulation depth vs. speed" trade-off by at least an order of magnitude, placing AZO among the most promising compounds for tunable/switchable nanophotonics.

Epsilon-Near-Zero Al-Doped ZnO for Ultrafast Switching at Telecom Wavelengths: Outpacing the Traditional Amplitude-Bandwidth Trade-Off

A high-power 690-nm AlGaInP laser for use in a high-density rewritable-optical-disk memory system is presented. The deterioration of its temperature characteristics, which results from the high-power-oriented laser structure, is improved by using compressively strained GaInP quantum wells as the active layer. Output power of 40 mW is achieved up to 80 degrees C. Stable fundamental-transverse-mode operation is obtained up to 50 mW. Output-power-induced facet degradation is suppressed by an Al/sub 2/O/sub 3/ facet coating. The lasers operate stably at 30 mW at 50 degrees C for over 2600 h. The mean extrapolated lifetime is 10000 h. >

30 mW 690 nm high-power strained quantum well AlGaInP laser

We modeled the PDSMZ-type (UNI-type) 3R scheme and studied its available degree of amplitude-noise suppression in both '1' and '0' signals and possible waveform distortion. For evaluating the noise distribution, bit-error rates were calculated to below 1E-6.

Theoretical Models of SOA-Based SMZ-Type Optical-3R Gates

A laser diode having high output power and good high-frequency characteristics is an attractive optical source not only for a digital system but also for an analog system Although the nonlinearity of the laser diode limits its application to an analog system, modulation methods, such as PIM, PFM, and FM, can be used to overcome this drawback But when a high C/N ratio is required, as in a long repeated line, the laser-diode noise cannot be neglected even if these modulation methods are used For example, C/N of 50 dB at laser-diode output is necessary to obtain video S/N of 60 dB in an FM system, as is shown in Fig 1 There are two kinds of laser-diode noise They are the inherent noise that is observed even in an ideal laser diode and the excess noise caused by operational imperfections Many discussions have been made on the inherent noise, mainly in the case of dc operation The excess noise has been studied in relation to mode instability, including the effect of the reflected wave on noise level But the dependence of the inherent noise on the operation condition including high frequency modulation and the effect of the reflected wave from a fiber line on the excess noise have not been examined sufficiently We have studied both laser-diode noise under direct-current, sine-wave, and pulse-wave operation in various bias current levels Further, the excess noise was measured with or without a fiber cable Two methods for reducing the excess noise induced by reflection were examined

Laser-diode noise in an FM signal-transmission system

Two photon absorption accompanied by a 25-ps-delayed nonlinear response was observed in nonlinear photonic crystal/quantum dot waveguides. Criterion for preventing such a delay time is studied for applications in ultrafast all-optical gates.

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Yoshiyasu Ueno

Papers

30 mW 690 nm high-power strained quantum well AlGaInP laser

Theoretical Models of SOA-Based SMZ-Type Optical-3R Gates

Laser-diode noise in an FM signal-transmission system

Criterion for Removing a Delayed Peak from the Ultrafast Nonlinear Response of Photonic Crystal / Quantum Dot Waveguides

Novel window-structure algainp visible LDs with non-absorbing facets formed by disordering of natural superlattice in gainp active layer