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A Generalized Optical Logic Element or GOLE is device that performs any of the 16 Boolean logic operations on signals in an optical beam with very fast switching among functions. The advantages of a generalized or universal gate in manufacturing are obvious. Extremely flexible functioning becomes possible if the GOLE functionality is switched in response to earlier computations. Likewise Field Programmable Gate Arrays or FPGAs can be used to fix the GOLE functions, making one of the most powerful and flexible processor units ever designed – called a Field GOLE. Such systems can be made in bulk optics to utilize Spatial Light Modulator or SLM capabilities, but integrated optics on silicon will be the choice for most applications. GOLEs can be generalized in several ways to become Fredkin gates and generalized Fredkin gates. They can also be cascaded similarly to electronic gates.

Two areas of intense current research, optical logic and silicon photonics, can be combined to create optical logic in silicon substrates. We describe a generic (universal) optical logic gate based on silicon components that can be programmed electronically to perform any logical operation on light beams confined in a silicon waveguide under control of the silicon electronics on the same chip. The effect is to create enhanced integration between optics and electronics.

The GaN/AlGaN active regions for terahertz (THz) quantum cascade lasers were grown by metal organic chemical vapor deposition (MOCVD). The surface of the sample was characterized by atomic force microscopy (AFM). The structure of this sample was evaluated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The XRD pattern and cross-sectional TEM images showed that a well-controlled quantum cascade GaN/AlGaN layers could be prepared. Optical properties of the active region of a terahertz GaN/AlGaN have been investigated by Fourier transform infrared (FTIR) spectrometer. It was found that the frequency of E 1 (LO) phonon decreased in quantum cascade GaN/AlGaN structures. The phonon frequency shift could be attributed to the effect of phonon zone folding.

We propose the idea of developing THz quantum cascade lasers (QCLs) with GaN-based quantum well (QW) structures with significant advantages over the currently demonstrated THz lasers in the GaAs-based material system. While the ultrafast longitudinal optical (LO) phonon scattering in AlGaN/GaN QWs can be used for the rapid depopulation of the lower laser state, the large LO-phonon energy (∼90 meV) can effectively reduce the thermal population of the lasing states at higher temperatures. Our analysis of one particular structure has shown that a relatively low threshold current density of 832 A/cm2 can provide a threshold optical gain of 50/cm at room temperature. We have also found that the characteristic temperature in this structure is as high as 136 K.

This work is motivated by the desire to extend the operating wavelength of contemporary quantum well infrared photodetectors from the mid- ( 20μm) or terahertz region of the electromagnetic spectrum without recourse to liquid helium temperatures. This apparently simple objective hides many challenges which stem from the parasitic current that flows even in the absence of any illumination—the so-called dark current.

An analysis, by a carrier scattering approach, of the thermionic emission contribution to the dark current is carried out in conventional bound-to-continuum quantum well infrared photodetectors (QWIPs). It is found that the thermionic emission increases with increasing temperature or when extending the detection wavelength from mid- to far-infrared. Considering p-type instead of n-type material, however, the increased effective mass decreases the thermionic emission. Designs for mid- and far-infrared p-type QWIPs based on the Si 1 − xGe x/Si system are discussed for both normal and non-normal incident geometries.

The critical design issues for unipolar silicon quantum-well intersubband lasers are investigated in this paper. Group IV lasing at near-infrared and middle-infrared wavelengths is analyzed for surface-emitting and edge-emitting geometries. Calculations show feasibility of SiGe/Si and SiGe/Si lasing. Silicon-on-insulator structures are proposed for index-guided lasers, vertical-cavity lasers and micro-cavity lasers

The creation of Si-based intersubband lasers in multiple quantum wells of Si/SiGeC, Si/ZnS, Si/Al 2 O 3 , Si/CaF 2 or Si/SiO 2 would have “spinoffs” in intersubband optical amplifiers, light emitting diodes, electro-optic modulators, switches, and photodetectors. SiGe/Si and SiGeC/Si quantum-cascade lasers appear feasible for 6 to 20 μm wavelength operation. The field-tunable Si Raman laser could operate over a wavelength range of 1.45 to 1.60 μm. A new non-cascaded intersubband laser, the Si charge-coupled laser, has a 1 V bias and a 1 μm optical waveguide height made possible by a p–i–p–i structure with selective contacts. Silicon nano-photonic structures rely upon a silicon-on-insulator platform. © 1997 Elsevier Science S.A. All rights reserved.

We propose the idea of making quantum dot (QD) lasers by embedding direct-bandgap QDs in a short-period superlattice whose bandgap is indirect. In comparison with similar QD lasers with barriers of direct band gap, this technique not only reduces the temperature dependence of threshold current, but also leads to extremely small linewidth enhancement factor, making low-temperature sensitivity, low chirp, and narrow linewidth semiconductor lasers feasible.

Our study indicates that there are significant advantages in developing THz quantum cascade lasers (QCLs) with GaN-based quantum well (QW) structures. While the ultrafast longitudinal optical (LO) phonon scattering in AlGaN/GaN QWs can be used for the rapid depopulation of the lower laser state, the large LO-phonon energy (∼90 meV) can effectively reduce the thermal population of the lasing states. Our investigation shows that GaN-based THz QCLs can potentially be operating cw at room temperature.

Design results are presented for electrically pumped quantum staircase intersubband p-i-p SiGe/Si strain-balanced superlattice lasers to be operated at 77 K or higher. The wavelength of laser emission will be in the THz range. Two approaches of quantum staircase lasers will be presented, one utilizes the inverted light-hole effective mass, while the other inverted heavy-hole mass. Optical gain on the order of a few 100 cm −1 can be achieved for both laser designs.

A theoretical proposal is given for creating direct-gap semiconductor layers in silicon-based Group IV heterostructures. Based upon recent bandstructure calculations for pseudomorphic Ge/GeSi and GeSi/Ge, we predict a strain-induced Γc-Lc direct-gap crossover (λg ∼ 2.2 μm) in tensile Ge/Ge0.87Sn0.13 and in compressive Ge0.98Sn0.02/Ge. We used linear extrapolation of band-edge curves. The direct-gap structures are potentially useful in laser diodes, electrooptic modulators, and photodetectors.