The development of optical gain in chemically synthesized semiconductor nanoparticles (nanocrystal quantum dots) has been intensely studied as the first step toward nanocrystal quantum dot lasers. We examined the competing dynamical processes involved in optical amplification and lasing in nanocrystal quantum dots and found that, despite a highly efficient intrinsic nonradiative Auger recombination, large optical gain can be developed at the wavelength of the emitting transition for close-packed solids of these dots. Narrowband stimulated emission with a pronounced gain threshold at wavelengths tunable with the size of the nanocrystal was observed, as expected from quantum confinement effects. These results unambiguously demonstrate the feasibility of nanocrystal quantum dot lasers.

http://science.sciencemag.org/content/sci/290/5490/314.full.pdf

Optical gain and stimulated emission in nanocrystal quantum dots.

Influences on the semiconductor laser properties of external optical feedback, i.e., return of a portion of the laser output from a reflector external to the laser cavity, have been examined. Experimental observations with a single mode laser is presented with analysis based on a compound cavity laser model, which has been found to explain essential features of the experimental results. In particular, it has been demonstrated that a laser with external feedback can be multistable and show hysteresis phenomena, analogous to those of non-linear Fabry-Perot resonator. It has also been shown that the dynamic properties of injection lasers are significantly affected by external feedback, depending on interference conditions between returned light and the field inside the laser diode.

External optical feedback effects on semiconductor injection laser properties

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

1. Introduction and overview 2. Film stress and substrate curvature 3. Stress in anisotropic and patterned films 4. Delamination and fracture 5. Film buckling, bulging and peeling 6. Dislocation formation in epitaxial systems 7. Dislocation interactions and strain relaxation 8. Equilibrium and stability of surfaces 9. The role of stress in mass transport.

Thin Film Materials: Stress, Defect Formation and Surface Evolution

An overview of analog microwave photonics will be presented. The performance requirements for externally-modulated analog microwave photonic links will be reviewed with specific emphasis placed on modulator efficiency, laser noise, detected photocurrent, and link linearity.

http://ieeexplore.ieee.org/iel5/6387506/6403300/06403360.pdf

Microwave photonics

Polarization control of the light output from single-mode fiber systems is very important in order to connect it to polarization-dependent integrated optical circuits and applications using a heretodyne detection system. In this paper, automatic control of the polarization of light transmitted through the fiber was demonstrated by an electrooptical and electrical feedback system. In this system, we used a 1.6 μm long wavelength semiconductor CW BH laser, low-loss single-mode optical fiber with a loss of 0.2 dB/km, and two thin z -cut LiNbO 3 modulators tilted 45° relative to each other. The output light from this polarization controller was maintained to be linear while that from the single-mode fiber was unstable and elliptically polarized.

Polarization control on output of single-mode optical fibers

The room-temperature operation of 1.5–1.6 μm GaInAsP/InP integrated twin-guide lasers with first-order distributed Bragg reflectors is reported. Single-longitudinal-mode oscillation was observed up to 1.4 times the threshold current. The temperature dependence of lasing wavelength was only 0.8 A/degree.

1.5-1.6 μm GaInAsP/InP Integrated twin-guide lasers with first-order distributed Bragg reflectors

Mode filter actions are found theoretically in an optical dielectric waveguide consisting of a core and a thin cladding layer which is further surrounded by an external higher index region. The propagating waves, which are usually considered to be cutoff modes, can be guided with a small amount of loss under a certain condition. These waves are defined here as quasi-guided modes. These modes tend to the guided modes of the guide when the cladding thickness increases infinitely. A method is given to estimate the losses. As an example, the radiation losses are formulated for a symmetric slab waveguide, and are found to be approximately proportional to the cube of the mode number of the quasi-guided mode. Therefore, losses of the quasi-guided modes depend strongly on the mode number. It is suggested that fibers with large core diameters can be used as quasi-single mode fibers by covering the clad-type multimode fibers with external higher index surroundings and choosing the parameters properly.

Chasi-Guided Modes and Related Radiation Losses in Optical Dielectric Waveguides with External Higher Index Surroundings

The reflection phenomenon of the guided mode in optical switches with intersecting single-mode waveguides is investigated by the wave approach. The guided mode is expanded into an infinite spectrum of plane waves and the condition of total internal reflection is applied. The power reflectivity of the guided mode is calculated and is used to estimate the extinction ratios. It is found that at refractive index variation of about 1 percent, large extinction ratios (>30 dB) are achievable if the refractive index difference between the waveguide core and cladding is smaller than the voltage induced refractive index variation by about one order of magnitude. The intersecting angle is found to be limited to about the critical angle and is required to be large enough to prevent degradation of the extinction ratios and to keep scattering losses small. It is also indicated that by displacing the electrode, to account for the Goos Haenschen shift, it is possible to further reduce the scattering losses. >

Analysis of reflection-type optical switches with intersecting waveguides

The dynamic spectral width of a CW GaInAsP/InP buried-heterostructure distributed-Bragg-reflector integrated-twin-guide (BH-DBR-ITG) laser operating at a wavelength of 1.58 μm was measured under direct modulation up to 3 GHz. The maximum dynamic spectral width at a modulation depth of 100% was measured to be 0.27 nm at the resonance-like frequency of 1.8 GHz. A possibility of wideband transmission of 1.55 μm conventional single-mode fibre at 185 Gbit km is suggested.

Yasuharu Suematsu

Papers

Polarization control on output of single-mode optical fibers

1.5-1.6 μm GaInAsP/InP Integrated twin-guide lasers with first-order distributed Bragg reflectors

Chasi-Guided Modes and Related Radiation Losses in Optical Dielectric Waveguides with External Higher Index Surroundings

Analysis of reflection-type optical switches with intersecting waveguides

Dynamic spectral width of rapidly modulated 1.58 m GaInAsP/InP buried-heterostructure distributed-Bragg-reflector integrated-twin-guide lasers