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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.

Properties of silver metal nanoridge surface plasmon waveguide modes are investigated. It is found that semicircular top geometry nanoridges are optimal for supporting long range and high figure-of-merit surface plasmon modes.

This paper outlines the challenges and benefits of applying silicon-based photonic techniques in the 2 to 5 μm midinfrared (MIR) wavelength range for chem.-bio-physical sensing, medical diagnostics, industrial process control, environmental monitoring, secure communications, Ladar, active imaging, and high-speed communications at 2 μm. Onchip passive and active components, mostly waveguided, will enable opto-electronic CMOS or BiCMOS integrated “circuits” for system-on-a-chip applications such as spectroscopy and lab-on-a-chip. Volume manufacture in a silicon foundry is expected to yield low-cost (or even disposable) chips with benefits in size-weight-power and ruggedness. This is “long-wavelength optoelectronic integration on silicon” which we call LIOS. Room temperature operation appears feasible, albeit with performance compromises at 4 to 5 μm. In addition to the electronics layer (which may include RF wireless), a 3-D LIOS chip can include several inter-communicating layers utilizing the photonic, plasmonic, photoniccrystal and opto-electro-mechanical technologies. The LIOS challenge can be met by (1) discovering new physics, (2) employing “new” IV and III-V alloys, (3) scaling-up and modifying telecom components, and (4) applying nonlinearoptical wavelength conversion in some cases. This paper presents proposals for MIR chip spectrometers employing frequency-comb and Ge blackbody sources. Active heterostructures employing Si, Ge, SiGe, GeSn and SiGeSn are key for laser diodes, photodetectors, LEDs, switches, amplifiers, and modulators that provide totally monolithic foundry integration, while numerous III-V semiconductor MIR devices within the InGaAsSb and InGaAsP families offer practical hybrid integration on Si PICs. Interband cascade and quantum cascade lasers on Ge waveguides are important in this context.

This article presents an overview of trends and progress in group IV heterostructures for optoelectronics. The outlook is good in electronics because the commercialization of SiGe/Si heterotransitors is proceeding nicely. However, the pace of progress is slower in SiGe/Si photonics. This article covers five innovative topics in an effort to enhance the development of heterostructure photonics: (1) band‐gap studies of SiGeC, an alloy that can be lattice matched to Si, (2) direct‐band‐gap, strained heterostructures of GeSn upon GeSi/Si, (3) silicon‐based quantum‐well intersubband lasers (ISBLs) including SiGe/Si quantum‐cascade, Raman, and inversionless ISBLs, (4) 1.5 μm ISBLs based on Si quantum wells with high barriers, such as heterosystems of Si/ZnS, and Si with SiO2/Si strained superlattice barriers, and (5) low‐cost substrates of 3C SiC upon SiO2/Si, a platform for SiC heterodevices and for InGaN/AlGaN heterodevices.

This article presents theoretical designs for a beamsteerer that uses one laser source whose wavelength is electrically tuned. Transmit/receive beamsteering of a phased-array antenna is obtained with prism-shaped arrays of fiber Bragg gratings or with waveguided gratings integrated in a semiconductor chip. An analysis of chirped and uniform grating requirements is given.

This paper explores the challenges faced in developing efficient room temperature porous Si-based light emitting diodes. We experimentally demonstrate that porous Si is an excellent host material for erbium ions to emit strong, room temperature, sharp-line luminescence at 1.54 μm. A comparison of photoluminescence data for erbium implanted samples of bulk Si, porous Si, and quartz indicate that quantum confinement likely enhances the erbium IR luminescence efficiency. Due to the 650 to 850°C annealing, it is unlikely that the environment of erbium in our samples is amorphous Si.

A novel gain medium consisting of direct bandgap semiconductor quantum dots (QDs) embedded in a short-period superlattice of indirect bandgap as barrier material is proposed to produce QD lasers with extremely small linewidth enhancement factor /spl alpha/. Our analysis has shown that at least one order-of-magnitude reduction in /spl alpha/ can be achieved at room temperature compared to that of similar QDs embedded in direct-bandgap barriers, making low chirp, narrow linewidth semiconductor lasers feasible.

We propose the idea of making quantum dot lasers by embedding direct-band gap quantum dots in a short period superlattice whose band gap is indirect. This technique reduces the threshold current and its temperature dependence. We show that a higher characteristic-temperature T0 can be achieved in a quantum dot laser with indirect GaAs/AlAs superlattice barriers compared to that with direct GaAs barriers.

Spectral evolution of a photonic crystal waveguide under electro-optic tuning revealed interband scattering signature from the TM-like mode to the odd TE-like mode in active devices. The impact on novel optical isolators is discussed.

By multiplexing different sized structures within the unit cell of the gap-mode plasmon resonance structure, perfect light absorption has been achieved with broader near-perfect absorption of light.

Metal nanoridges can support well-confined propagating surface plasmon modes. Various geometries of silver nanoridges are investigated in this work. It is found that semicircular top nanoridges are optimal for supporting high figure-of-merit surface plasmon modes.

We report the experimental fabrication and testing of a GeSn-based 320×256 image sensor focal plane array operating at −15°C in the 1.6–1.9 μm spectral range. For image readout, the 2D pixel array of Ge/GeSn/Ge p-i-n heterophotodiodes was flip-chip bonded to a customized silicon CMOS readout integrated circuit. The resulting camera chip was operated using back-side illumination. Successful imaging of a tungsten-filament light bulb was attained with observation of gray-scale “hot spot” infrared features not seen using a visible-light camera. The Ge wafer used in the present imaging array will be replaced in future tests by a germanium-on-silicon wafer offering thin-film Ge upon Si or on SiO2/Si. This is expected to increase the infrared responsivity obtained in back-side illumination, and it will allow an imager in a Si-based foundry to be manufactured. Our experiments are a significant step toward the realization of group IV near-mid-infrared imaging systems, such as those for night vision.

We propose and experimentally demonstrate an ultra-compact and highly efficient polarization splitter and rotator based on a silicon bent directional coupler structure. The TM-to-TE cross-polarization coupling occurs between the two parallel bent waveguides, if the phase matching condition is satisfied. Efficient polarization splitting and rotating are simultaneously achieved. The device is fabricated by a single step of exposure and etching. The measured peak TM-to-TE polarization conversion efficiency reaches 96.9%. The TM-to-TE conversion loss is lower than 1 dB in the wavelength range of 1544 nm–1585 nm, and the insertion loss for the TE polarization is lower than 0.3 dB in the wavelength regime of 1530 nm–1600 nm. The cross talk values are lower than −20 and −18 dB for the TE- and TM-polarizations over a wavelength range of 70 nm, respectively. The coupling length of the polarization splitter and rotator is 8.77μm. To the best of our knowledge, our device achieves the shortest coupling length.

This paper reports the demonstration of optically pumped GeSn edge-emitting lasers grown on Si substrates. The whole device structures were grown by an industry standard chemical vapor deposition reactor using the low cost commercially available precursors SnCl4 and GeH4 in a single run epitaxy process. Temperature-dependent characteristics of laser-output versus pumping-laser-input showed lasing operation up to 110 K. The 10 K lasing threshold and wavelength were measured as 68 kW/cm2 and 2476 nm, respectively. Lasing characteristic temperature (T0) was extracted as 65 K.

GeSn/SiGeSn techniques are of great interest in the area of Si photonics due to: 1) the industry scalable growth; 2) compatible with current Si complementary metal-oxide semiconductor (CMOS) process; 3) capability of monolithic integration on Si; 4) the identified group-IV based direct bandgap materials; and 5) the tunable bandgap allowing the optoelectronic devices operation features broad wavelength coverage in near- and mid-infrared ranges. In the past a few years, the GeSn/SiGeSn material growth, the materials and devices characteristics have been comprehensively studied. Plenty of promising results are reported. In this work, the following aspects regarding GeSn/SiGeSn techniques are investigated: 1) low-defect material growth technique via Ultra High Vacuum Chemical Vapor Deposition (UHVCVD) system; 2) advanced material and optical characterizations of GeSn/SiGeSn thin films, Ge/GeSn/Ge double heterostructure (DHS), and GeSn/SiGeSn quantum well samples; 3) demonstration of GeSn-based optoelectronic devices including photodetectors and emitters.

Temperature-dependent characteristics of GeSn light-emitting diodes with Sn composition up to 9.2% have been systematically studied. Such diodes were based on Ge/GeSn/Ge double heterostructures (DHS) that were grown directly on a Si substrate via a chemical vapor deposition system. Both photoluminescence and electroluminescence spectra have been characterized at temperatures from 300 to 77 K. Based on our theoretical calculation, all GeSn alloys in this study are indirect bandgap materials. However, due to the small energy separation between direct and indirect bandgap, and the fact that radiative recombination rate greater than non-radiative, the emissions are mainly from the direct Γ-valley to valence band transitions. The electroluminescence emissions under current injection levels from 102 to 357 A/cm2 were investigated at 300 K. The monotonic increase of the integrated electroluminescence intensity was observed for each sample. Moreover, the electronic band structures of the DHS were discussed. Despite the indirect GeSn bandgap owing to the compressive strain, type-I band alignment was achieved with the barrier heights ranging from 11 to 47 meV.

In this paper we present a detailed theoretical investigation of second harmonic generation in strained germanium waveguides operating at the mid infrared pump wavelength of 4 μm. The effective second order susceptibility has been estimated through a multiphysics approach considering the residual stress of the SiNsubx/subcladding film. Furthermore, general physical features have been investigated by means of a comparative analysis of SHG performance as a function of input pump power, linear and nonlinear phase mismatching, effective recombination carrier lifetime, and temperature, taking into account both continuous and pulsed regimes. Finally, periodically poled germanium devices have been explored with the aim to improve the SHG efficiency. In the same operative conditions, efficiencies of 0.6% and 0.0018% have been obtained in poled and not-poled waveguides, respectively.

We report an investigation on the absorption mechanism of a GeSn photodetector with 2.4% Sn composition in the active region. Responsivity is measured and absorption coefficient is calculated. Square root of absorption coefficient linearly depends on photon energy indicating an indirect transition. However, the absorption coefficient is found to be at least one order of magnitude higher than that of most other indirect materials, suggesting that the indirect optical absorption transition cannot be assisted only by phonon. Our analysis of absorption measurements by other groups on the same material system showed the values of absorption coefficient on the same order of magnitude. Our study reveals that the strong enhancement of absorption for the indirect optical transition is the result of alloy disorder from the incorporation of the much larger Sn atoms into the Ge lattice that are randomly distributed.

We report an investigation of a GeSn-based p-i-n photodetector grown on a Ge wafer that collects light signal from the back of the wafer. Temperature dependent absorption measurements performed over a wide temperature range (300 K down to 25 K) show that (a) absorption starts at the indirect bandgap of the active GeSn layer and continues up to the direct bandgap of the Ge wafer, and (b) the peak responsivity increases rapidly at first with decreasing temperature, then increases more slowly, followed by a decrease at the lower temperatures. The maximum responsivity happens at 125 K, which can easily be achieved with the use of liquid nitrogen. The temperature dependence of the photocurrent is analyzed by taking into consideration of the temperature dependence of the electron and hole mobility in the active layer, and the analysis result is in reasonable agreement with the data in the temperature regime where the rapid increase occurs. This investigation demonstrates the feasibility of a GeSn-based photodio...

The absorption coefficient and refractive index of Ge1−xSnx alloys (x from 0% to 10%) were characterized for the wavelength range from 1500 to 2500 nm via spectroscopic ellipsometry at room temperature. By applying physical models to fit the obtained data, two empirical formulae with extracted constants and coefficients were developed: (1) Absorption coefficient. The absorption regarding Urbach tail, indirect and direct bandgap transitions were comprehensively taken into account; (2) refractive index. The Sellmeier coefficients associated with dispersion relationship were extracted. In these formulae, the Sn composition and strain percentage were the input parameters, by inputting which the spectral absorption coefficient and spectral refractive index can be obtained. Since the absorption coefficient is key information to determine the performance of the photodetectors including operation wavelength range, responsivity, and specific detectivity, and the refractive index is very useful for the design of the anti-reflection coating for photodetectors and the layer structure for waveguides, the developed formulae could simplify the optoelectronic device design process due to their parameter-based expressions.

In the first part of the paper, the changes in the complex index of refraction of quantum-well structures proportional to the applied dc electric field (F) and its square are obtained from stationary perturbation theory. Expressions are obtained for the linear and quadratic changes in index and absorption coefficients of asymmetric and symmetric quantum well structures. The triple resonance term does not contribute to the quadratic Kerr effect for a symmetrical well in an expansion about F=0. In the second part of the paper, these results are applied to several types of modulators. First we consider two kinds of silicon/silicon-germanium high-barrier asymmetric quantum well structures at 1.55 /spl mu/m. For the step well, the dominant triple resonant term of the quadratic Kerr effect adds to the linear electrooptic effect (LEG) to yield an intensity extinction ratio of 15 dB in switching from F=+8 V//spl mu/m to -8 V//spl mu/m and a very small insertion loss of 0.04 dB, for a modulator length of 200 pm and for narrow linewidths (FWHM=7.6 meV). For the case of asymmetric barriers confining silicon wells, a comparable insertion loss is obtained but with an extinction ratio of 44 dB for FWHM=20 meV, a clearly superior performance. For symmetrical silicon-based wells, the double-resonance modulation, though small at /spl lambda/=1.55 /spl mu/m, is appreciable at /spl lambda/=10.6 /spl mu/m. For the Kerr effect in symmetrical gallium arsenide wells at /spl lambda/=10.6 /spl mu/m reported by Sa'ar et al., we show that it is the double-resonance term which yields the six order-of-magnitude enhancement with respect to bulk and that an even larger enhancement of the Kerr effect can be obtained in an asymmetric GaAs structure together with the LEO. >

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.

For more than 40years silicon has been the mainstream material in the electronic industry,revolutionizing the way we live. The pioneering work by Soref and his colleagues in mid1980s opened exciting prospects for silicon to expand its dominance into the field of pho-tonics. Silicon photonics has been the subject of intense research activity in both industryand academia, covering diverse areas such as optical waveguides, light sources, modulators,switches, detectors, couplers, photonic crystals, diffraction gratings, subwavelength struc-tures,spectralfilters,wavelengthmultiplexers,polarizationcircuits,sensors,transceivers,andvarious sub-systems. Today, silicon photonics is an extremely active and firmly establishedresearch field and silicon photonics circuits are emerging as a compelling technology forenergy-efficient high-speed computing, signal processing and communications. Integrationand scaling advantages together with the added benefit of leveraging the enormous existingCMOS manufacturing infrastructure are obvious industrial benefits of silicon that no otherphotonic material presently can match.TheaimofthisSpecialIssueistorecordsomeoftheremarkablerecentprogressinsiliconphotonics and nanophotonics and point to future trends in this rapidly evolving field. All thearticles in this issue are invited review papers by leading authorities and research groups inthis field from universities, industry and government laboratories.

Group IV mid-infrared photonics is attracting more research interest lately. The main reason is a host of potential applications ranging from sensing, to medicine, to free space communications and infrared countermeasures. The field is, however, in its infancy and there are several serious challenges to be overcome before we see progress similar to that in the near-infrared silicon photonics. The first is to find suitable material platforms for the mid-infrared. In this paper we present experimental results for passive mid-infrared photonic devices realised in silicon-on-insulator, silicon-on-sapphire, and silicon on porous silicon. We also present relationships for the free-carrier induced electro-refraction and electro-absorption in silicon and germanium in the mid-infrared wavelength range. Electro-absorption modulation is calculated from impurity-doping spectra taken from the literature, and a Kramers-Kronig analysis of these spectra is used to predict electro-refraction modulation. We examine the wavelength dependence of electro-refraction and electro-absorption, finding that the predictions suggest longer-wave modulator designs will in many cases be different than those used in the telecom range.

Heavily doped n-type Ge and GeSn are investigated as plasmonic conductors for integration with undoped dielectrics of Si, SiGe, Ge, and GeSn in order to create a foundry-based group IV plasmonics technology. N-type Ge1-xSnx with compositions of 0 ≤ x ≤ 0.115 are investigated utilizing effective-mass theory and Drude considerations. The plasma wavelengths, relaxation times, and complex permittivities are determined as functions of the free carrier concentration over the range of 10(10) to 10(21) cm-3. Basic plasmonic properties such as propagation loss and mode height are calculated and example numerical simulations are shown of a dielectric-conductor-dielectric ribbon waveguide structure are shown. Practical operation in the 2 to 20 μm wavelength range is predicted.

Propagating two-dimensional plasmon modes guided by elliptical cross section silver nanoridges are investigated in this paper. Mode field profiles, dispersion curves, propagation distances, and figure-of-merits of the plasmon ridge modes are calculated for various elliptical cross sections. It is found that an elliptical cross section metal nanoridge, if designed properly, can support a well-confined plasmon mode with a longer propagation distance and a higher figure-of-merit than the flat-top nanoridge plasmon waveguide of the same width. The optimal ridge waveguide cross section is obtained when the elliptical ridge top has a semicircular cross section. When the curvature of the elliptical nanoridge is large, the mode approaches the tightly confined wedge plasmon mode., arXiv admin note: text overlap with arXiv:1202.2477

Mid-infrared group IV photonics is emerging as a field with possible applications ranging from gas sensing to free-space communications. Free-carrier induced electro-absorption and electro-refraction have become the most widely used modulation mechanisms in active near-infrared silicon photonic devices. This work examines the magnitude of this effect in group IV materials at mid-infrared wavelengths. In silicon electro-absorption effects are calculated from experimental absorption coefficient data, and electro-refraction is calculated through numerical Kramers-Kronig analysis of absorption spectra. In germanium the Drude-Lorentz equations are used to estimate both change in absorption and change in refractive index.

We experimentally demonstrate a wide band near perfect light absorber in the mid-wave infrared region using multiplexed plasmonic metal structures. The wide band near perfect light absorber is made of two different size gold metal squares multiplexed on a thin dielectric spacing layer on the top of a thick metal layer in each unit cell. We also fabricate regular non-multiplexed structure perfect light absorbers. The multiplexed structure IR absorber absorbs above 98% incident light over a much wider spectral band than the regular non-multiplexed structure perfect light absorbers in the mid-wave IR region.

We show a scalable and reconfigurable optical logic architecture based on a regular array of integrated optical switches. We present a proof-of-principle demonstration with a 2 ×2 switch array that can perform arbitrary two-input logic functions.

Perfect light absorptions can be achieved with metal-dielectric-metal structures. In this talk, we will discuss how multiplexed metal nanostructures can control the metamaterial absorption light spectral bands.

The mid-infrared wavelength region offers a plethora of possible applications ranging from sensing, medical diagnostics and free space communications, to thermal imaging and IR countermeasures. Hence group IV mid-infrared photonics is attracting more research interest lately. Sensing is an especially attractive area as fundamental vibrations of many important gases are found in the 3 to 14 μm spectral region. To realise group IV photonic mid-infrared sensors several serious challenges need to be overcome. The first challenge is to find suitable material platforms for the mid-infrared. In this paper we present experimental results for passive mid-infrared photonic devices realised in silicon-on-insulator (SOI), silicon-on-sapphire (SOS), and silicon on porous silicon (SiPSi). Although silicon dioxide is lossy in most parts of the mid-infrared, we have shown that it has potential to be used in the 3-4 μm region. We have characterized SOI waveguides with < 1 dB/cm propagation loss. We have also designed and fabricated SOI passive devices such as MMIs and ring resonators. For longer wavelengths SOS or SiPSi structures could be used. An important active device for long wavelength group IV photonics will be an optical modulator. We present relationships for the free-carrier induced electro-refraction and electro-absorption in silicon in the mid-infrared wavelength range. Electro-absorption modulation is calculated from impurity-doping spectra taken from the literature, and a Kramers-Kronig analysis of these spectra is used to predict electro-refraction modulation. We have examined the wavelength dependence of electro-refraction and electro-absorption, and found that the predictions suggest longer-wave modulator designs will in many cases be different than those used in the telecom range.

t has been found that the nano-ridge plasmon modes are quasi-TEM modes. The quasi-TEM mode profiles reveal that the propagation of free electron oscillation on the top of the metal nano-ridges contributes to the tightly confined plasmon ridge mode.

A quantum-mechanical scattering theory approach is taken to evaluate the capture probability from the continuum into the quantum wells in quantum-well infrared photodetectors. The calculations show that the capture probability is dependent on the well width, the barrier height, and bias. An additional tunnel barrier is introduced to disturb the continuum levels near the top of the quantum well. It is shown that this can be optimized to reduce the capture probability and thus increase the photoconductive gain of the device.

Electrical, optical and electro-optical simulations are presented for a waveguided, resonant, bus-coupled, p-doped Si micro-donut MOS depletion modulator operating at the 1.55 μm wavelength. To minimize the switching voltage and energy, a high-K dielectric film of HfO₂ or ZrO₂ is chosen as the gate dielectric, while a narrow ring-shaped layer of p-doped poly-silicon is selected for the gate electrode, rather than metal, to minimize plasmonic loss loading of the fundamental TE mode. In a 6-μm-diam high-Q resonator, an infrared intensity extinction ratio of 6 dB is predicted for a modulation voltage of 2 V and a switching energy of 4 fJ/bit. A speed-of-response around 1 ps is anticipated. For a modulator scaled to operate at 1.3 μm, the estimated switching energy is 2.5 fJ/bit.

The paper presents a new optical directed logic architecture that is based on a regular array of integrated optical switches. The same circuit can be reconfigured to perform different combinational logic functions. Its application in network routing is discussed.

Crystalline semiconductor nanomembranes (NMs), which are transferable, stackable, bondable and manufacturable, offer unprecedented opportunities for unique and novel device applications. We review here nanophotonic devices based on stacked semiconductor NMs on Si, glass and flexible PET substrates. Photonic crystal Fano resonance-based surface-normal optical filters and broadband reflectors have been demonstrated with unique angle and polarization properties. Flexible photodetectors and solar cells have also been developed based on the NM stacking processes. Such NM stacking process can lead to a paradigm shift on silicon photonic integration and hybrid organic/inorganic flexible photonics.

We propose integrated waveguides for terahertz (THz) and mid-infrared (MIR) applications on wafer platform. Based on the prototype of spoof plasmonic waveguides consisting of textured metallic surface, we explore the possibility of coating periodic metallic pattern with silicon (at 0.6 THz) or germanium (at MIR region of 30 THz) to further shrink the relative mode size of propagation spoof plasmonic waves. Numerical modeling via 3D finite-difference time-domain (FDTD) has shown deep sub-wavelength mode confinement in transverse directions to smaller than λ/50 by λ/50, with an estimated propagation loss of less than 0.1 dB for each repetitive unit.

We investigate surface plasmon modes supported by flat-top silver nano-ridges. We calculate the mode electromagnetic field distribution, the dispersion curve, the travel range, and the figure-of-merit of the nano-ridge mode. We find that the nano-ridge surface plasmon modes are quasi-TEM modes with longitudinal field components three orders of magnitude smaller than the transverse field components. The quasi-TEM nature of mode profiles reveals that the propagation of free electron oscillations on the top of the nano-ridge contributes mainly to the tightly confined ridge mode. We also find that as the width of the nano-ridge decreases, the ridge mode becomes more tightly confined on the ridge top. As the width of the nano-ridge increases, the nano-ridge mode approaches two decoupled right-angle wedge plasmon modes., Comment: 23 pages, 9 figures, journal article

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.

Modeling and design studies show that a strain-balanced Si1−xGex/Si superlattice on Si1−yGey-buffered Si can be engineered to give an inverted effective mass HH2 subband adjacent to HH1, thereby enabling a 77 K edge-emitting electrically pumped p–i–p quantum staircase laser for THz emission at energies below the 37 meV Ge–Ge optical phonon energy. Analysis of hole-phonon scattering, lifetimes, matrix elements, and hole populations indicates that a gain of 450 cm−1 will be feasible at f=7.3 THz during 1.7 kA/cm2 current injection.

We have investigated a SiGe/Si quantum-well laser based on transitions between the light-hole and heavy-hole subbands. The lasing occurs in the region of k space where the dispersion of ground-state light-hole subband is so nonparabolic that its effective mass is inverted. This kind of lasing mechanism makes total population inversion between the two subbands unnecessary. The laser structure can be electrically pumped through tunneling in a quantum cascade scheme. Optical gain as high as 172/cm at the wavelength of 50 μm can be achieved at the temperature of liquid nitrogen, even when the population of the upper laser subband is 15% less than that of the lower subband.

A simple technique for steering the microwave radiation beam of a phased-array antenna is proposed and analyzed. Chromatic dispersion in equal-length fibers is used.

A new technique is described for linking remote sensors by multimode optical fibers. It combines two well-known technologies and is compatible with multimode optical multiplexing. At the sensing location, the output of a transducer (such as a piezoceramic hydrophone) is connected directly to a low-voltage liquid-crystal light modulator that is coupled to fiber-optic transmission lines by graded-index rod lenses. Transducer voltages as low as 10 microV produce intensity modulation of the fiber light. An optical hydrophone based on the technique demonstrated a minimum detectable pressure of 39 dB re 1 [equiation] at 500 Hz. The device performance was evaluated over the 8-45 degrees C temperature range. Sensitivity was found to decrease linearly by 0.2 dB/ degrees C over that range. The technique provides a means by which rugged nonmechanical sensors can be constructed that are suitable for incorporation into practical fiber-optic sensor systems.

A multimode electrooptical switch that has high isolation between channels has been demonstrated experimentally in a 70-microm-thick plate of Z-cut LiTaO(3). The fiber-compatible four-port switch is intended for integration into an optical matrix. The crosspoint consists of an in-plane crossover, two simple optical switches, and a curved connecting waveguide. For convergent input light with a 0.07 numerical aperture, 10% of the initially channeled light was transferred into the crosschannel, and the optical switching ratio of that channel was 26 dB using 450-V dc for control.

Silicides, heavily-doped semiconductors, and semimetals are investigated theoretically and experimentally as surface plasmon hosts for infrared surface plasmon resonance biosensors. Tighter IR mode confinement than for usual Au gives better overlap with biological analytes.

We introduce a compact, low-power electro-optical switch on a silicon-on-insulator circuit through heterogeneous integration. A 10µm diameter III-V microdisk cavity is employed as the switching element. Switching of a 10Gbps optical signal is demonstrated by sweeping the bias between −1.1V and +0.9V with 15dB extinction ratio and 1.2ns switching speed.

A new silicon waveguide called ARROW-C is proposed and analyzed at the 1.3-microm wavelength. The silicon structure uses two buried layers of SiO(2) or beta-SiC with a thickness of 14-23 nm to permit optical tunneling for leakymode propagation. A propagation loss of ~0.5 dB/cm is predicted for the TE(0) or the TM(0) mode in a 5-microm-thick Sicore layer. Novel silicon ARROW-A and ARROW-B guides are also discussed. The former uses a pair of buried GeSi layers; the latter employs buried SiO(2) and GeSi films.

Low-loss waveguiding at lambda = 1.3 microm has been observed in a partially strained, 10-microm-thick, single-crystal layer of Ge(0.1)Si(0.9) grown by chemical-vapor deposition upon an intrinsic (100) silicon substrate. The TM-mode propagation loss in the multimode planar guide was 1.9 dB/cm.