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We present a methodology to systematically and analytically treat phonon-induced spin relaxation of conduction electron in silicon. All leading order contribution from all phonon modes and scattering processes are considered and the results for spin-flip matrix elements and spin lifetime are summarized. We show the explicit dependence of matrix elements on the electron wavevectors, spin orientation and phonon polarization. These results are shown to be powerful especially under symmetry-breaking conditions when an averaging rough evaluation of the matrix elements is not sufficient. Corrections due to the special two-band degeneracy in the X point (near the conduction valley minima) are also discussed. Numerical calculation are used to confirm the analytical results.

The spin polarization of carriers in a direct-gap semiconductor is readily quantified by measuring the circular polarization of the recombination light luminescence. However, in silicon, owing to its indirect band-gap, such a direct connection between spin polarization and luminescence has been conspicuously absent. This missing link is established with a theory that provides intuitive relations for phonon-assisted optical transitions between the conduction and valence band edges. The theory is applied to explain recent experiments on spin injection in silicon and further elucidate its desirable spin-dependent properties.

Semiconductor optical amplifiers (SOAs) based on nanostructure gain media such as quantum dots (QD) and quantum dashes (QDASH) have several basic characteristics which offer significant performance improvements over commonly used quantum well (QW) or bulk amplifiers. Among these are broadband optical gain bandwidth (which is two to three times broader than that of QW/bulk gain media), fast gain dynamics, large saturation powers, and low α parameter and population inversion factor. Originally, these properties have been demonstrated for QD/QDASH SOAs operating at 1000 nm and 1300 nm. However, it is imperative that QD/QDASH SOAs operating at 1550 nm be materialized in order for them to have the expected impact on fiber-optic communication. Operation at 1550 nm has been achieved using InAs / InP QD and QDASH laser structures. In this paper the unique gain and noise properties of InAs / InP QDASH SOAs operating at 1550 nm will be presented. Specifically, cross-gain-modulation, four-wave-mixing and chirp measurements which explore the complex spectral cross relaxation dynamics of these SOAs will be described and highlighted in the context of simultaneous, distortionless, high bit-rate multiwavelength data amplification, as well as wideband / high-speed optical signal processing applications. Also, an experimental study of the gain and noise in saturated QDASH SOAs will be described together with a theoretical analysis comprising both coherent and incoherent gain phenomena. The impact of the partially inhomogeneously broadened gain spectrum, fast population pulsation dynamics, α parameter and wetting layer density of states on the noise characteristics will be discussed.

We address basic issues related to the dynamical properties of low dimensionality semiconductor lasers. We concentrate on quantum dash lasers but many of the properties hold, with very few changes, to quantum dot lasers. We formulate a self consistent semiclassical model for a multimode laser field which interacts with an inhomogeneously broadened assembly of quantum dashes. The key advantage of this model is the fact that it spectrally resolves the gain and multimode laser field. We show that the differential gain and the nonlinear damping can not be optimized simultaneously.

Semiconductor lasers and amplifiers were developed based on self-assembled quantum-dot gain material. This paper gives an overview about the recent work on GaAs- and InP-based quantum-dot devices mainly dedicated for telecom applications. The major advantage of quantum-dot like gain material, i.e. the possibility to tailor the spectral and spatial gain properties of an amplifying material, was used to optimize different device aspects, like low threshold current, broad band amplification or low temperature sensitivity. High performance GaAs-based continuous wave (cw) operating quantum-dot lasers could be fabricated with threshold currents of about 2 mA (L = 400 μm). Single mode emitting devices with emission wavelengths > 1.3 μm were realized by laterally coupled feedback gratings with threshold currents below 5 mA, output powers > 5 mW and cw operation temperatures up to 85 °C. Modulation frequencies of up to 7.5 GHz were obtained for standard device structures. For long wavelength telecom applications quantum-dot like material with dash geometry was developed on InP substrates with basic properties in the transition region between quantum-dot and -wire systems. A very large tuning range of the emission wavelength between 1.2 and 2.0 μm (room temperature) was obtained which allow the realization of material with ultra-wide gain bandwidth. Quantum-dash laser structures reaches threshold current densities 2 . Ridge waveguide lasers with a cavity length of 1.9 mm show cw threshold currents of about 100 mA and maximum output powers > 40 mW per facet. With 300 μm long facet coated devices cw threshold currents of 23 mA and maximum operation temperatures in pulsed mode of 130 °C were achieved. Semiconductor optical amplifiers were fabricated by using broad band quantum-dash material. For a 1.9 mm long device, up to 22 dB gain was obtained with a three times larger spectral range than in comparable quantum well devices. High speed nearly pattern free signal amplification up to 10 GBit/s could be demonstrated and wavelength conversion experiments were performed.