Abstract: A multijunction solar cell comprising a silicon solar cell with a germanium solar cell formed on the backside of the silicon solar cell. The silicon solar cell and germanium solar cell are directly coupled via a p-p junction to inactivate interface dislocations. Preferably, the silicon solar cell comprises a p++ type silicon layer; an intrinsic silicon layer formed on the p++ type silicon layer; an n++ type silicon layer formed on the intrinsic type silicon layer; and a p-type silicon layer formed on the n++ type silicon layer. The germanium solar cell preferably comprises an n-type germanium layer; and a p-type germanium layer form on the n-type germanium layer. The p-type germanium layer is coupled to the p++ type silicon layer.

Abstract: An optical cavity structure for bending optical signals is provided. The optical cavity structure includes an input port for receiving input optical signals from a first waveguide. The optical cavity structure also includes an interconnecting structure that receives said input optical signals and interconnects said first waveguide to a second waveguide, the interconnecting structure further includes at least four straight edges that orthogonal and of a finite width. The optical cavity structure further includes an output port coupled to the interconnecting structure for providing the second waveguide with the input optical signals. Further, the optical cavity structure may be used to create three dimensional splitter devices and resonators.

Abstract: An electromagnetic wavelength filter that allows the transmission of electromagnetic energy within a narrow range of wavelengths while reflecting incident electromagnetic energy at other wavelengths. The filter includes at least one cavity region; and at least two reflectors surrounding the at least one cavity region, at least one of the reflectors being an omni-directional reflector. The omni-directional reflector includes a structure with a surface and an index of refraction variation perpendicular to the surface, and the omni-directional reflector is specifically configured to exhibit high omni-directional reflection for a predetermined range of frequencies of incident electromagnetic energy for any angle of incidence and any polarization.

Abstract: A mode transformer that enables low-loss coupling between optical modes of two waveguides with different index difference. The mode size and the effective index are gradually changed between two waveguides to gradually transform the mode shape, size, and speed with minimum power loss. The mode transformer is useful for coupling the mode of an optical fiber waveguide with low index difference to the mode of a planar high index difference waveguide, and vice versa.

Abstract: An integrated optical sensor using optical waveguide micro-cavity resonators. Using a laser and a detector it is possible to detect changes in the position of the resonance position, in wavelength or frequency, of one or more modes of the resonator. The change in resonance can be made dependent on chemicals, which have been adsorbed by chemically or biologically sensitive material provided in close proximity to the resonator.

Abstract: An optical switch operating with an optical pumping source. The switch includes a microcavity structure that is resonant with both the pumping source and the input optical signal. The microcavity structure includes a cavity in between two reflectors. The input optical signal is switched from one to zero, by varying the pump source intensity. The microcavity provides amplification of the pumping energy allowing for a nonlocal optical power source. In addition it also provides a way for fast optical modulation of the input optical signal using continuous wave pumping source.

Abstract: Methods of tuning, switching or modulating, or, in general, changing the resonance of waveguide micro-resonators. Changes in the resonance can be brought about, permanently or temporarily, by changing the size of the micro-resonator with precision, by changing the local physical structure of the device or by changing the effective and group indices of refraction of the mode in the micro-resonator. Further changing the asymmetry of the index profile around a waveguide can alter the birefringence of the waveguide and allows one to control the polarization in the waveguide. This change in index profile may be used to change the polarization dependence or birefringence of the resonators.

Abstract: An optical device is provided. The optical device includes a plurality of high index layers. The optical device also includes a plurality of low index layers. The optical device is formed by creating alternating layers of the plurality of high layers and the plurality of low index layers, such that electricity and heat is allowed to be conducted through said optical device.

Abstract: Methods of tuning, switching or modulating, or, in general, changing the resonance of waveguide micro-resonators. Changes in the resonance can be brought about, permanently or temporarily, by changing the size of the micro-resonator with precision, by changing the local physical structure of the device or by changing the effective and group indices of refraction of the mode in the micro-resonator. Further changing the asymmetry of the index profile around a waveguide can alter the birefringence of the waveguide and allows one to control the polarization in the waveguide. This change in index profile may be used to change the polarization dependence or birefringence of the resonators.

Abstract: Methods of tuning, switching or modulating, or, in general, changing the resonance of waveguide micro-resonators. Changes in the resonance can be brought about, permanently or temporarily, by changing the size of the micro-resonator with precision, by changing the local physical structure of the device or by changing the effective and group indices of refraction of the mode in the micro-resonator. Further changing the asymmetry of the index profile around a waveguide can alter the birefringence of the waveguide and allows one to control the polarization in the waveguide. This change in index profile may be used to change the polarization dependence or birefringence of the resonators.

Abstract: Arrangements using air trench cladding enables minimization of the evanescent tail to suppress light coupling to radiation modes, resulting in low-loss bends and splitters. Structures including sharp bends and T-splitters without transmission loss, crossings without crosstalk, and couplers from/to fibers and with out-of-plane waveguides without substantial loss are provided with such air trench claddings. Air trench sidewall cladding of waveguides pushes evanescent tails toward top and bottom claddings to enhance coupling between vertically positioned waveguides. Fabrication processes using wafer bonding technology are also provided.

Abstract: A waveguide for amplifying electromagnetic radiation of a characteristic wavelength includes a first reflector, a second reflector, and a gain medium having a characteristic wavelength of emission disposed between the first and second reflectors. The first and second reflectors are spaced apart from each other to form a microcavity which is off-resonance with respect to the characteristic wavelength of light emitted by the excited gain medium.

Abstract: A mode coupler that enables low-loss coupling between optical modes of two waveguides with different index difference. The mode size and the effective index are gradually changed between two waveguides to gradually transform the mode shape, size, and speed with minimum power loss. The mode coupler is useful for coupling the mode of an optical fiber waveguide with low index difference to the mode of a planar high index difference waveguide, and vice versa.

Abstract: A method of reducing the scattering losses that involves smoothing of the core/cladding interface and/or change of waveguide geometry in high refractive index difference waveguides. As an example, the SOI-based Si/SiO2 waveguides are subjected to an oxidation reaction at high temperatures, after the waveguide patterning process. By oxidizing the rough silicon core surfaces after the patterning process, the core/cladding interfaces are smoothened, reducing the roughness scattering in waveguides.

Abstract: The invention provides processes for producing a high-quality silicon dioxide layer on a germanium layer. In one example process, a layer of silicon is deposited on the germanium layer, and the silicon layer is exposed to dry oxygen gas at a temperature that is sufficient to induce oxidation of the silicon layer substantially only by thermal energy. In a further example process, the silicon layer is exposed to water vapor at a temperature that is sufficient to induce oxidation of the silicon layer substantially only by thermal energy. It can be preferred that the exposure to dry oxygen gas or to water vapor be carried out in an oxidation chamber at a chamber pressure that is no less than ambient pressure. In one example, the chamber pressure is above about 2 atm. The temperature at which the silicon layer is exposed to the dry oxygen gas is preferably above about 500° C., more preferably above about 600° C., even more preferably above about 700° C., and most preferably above about 800° C.

Abstract: A planar waveguide that has a graded index layer at the core/cladding interface to reduce scattering losses due to core/cladding interface roughness. The refractive index at the core/cladding interface is changed from that of the core to that of cladding gradually by having a graded index layer. The graded index layer reduces the scattering of light traveling in the waveguide by reducing the effect of the roughness at the abrupt interface between the core and the cladding. Using a proper design, the graded index layer also minimizes the modal and polarization dispersion of the optical mode traveling in the waveguide.

Abstract: Methods of forming polycrystalline semiconductor waveguides include the steps of forming a first cladding layer (e.g., SiO.sub.2) on a substrate (e.g., silicon) and then forming a polycrystalline semiconductor layer (e.g., poly-Si) on the first cladding layer using a direct deposition technique or by annealing amorphous silicon (a-Si) to form a polycrystalline layer, for example. The deposited polycrystalline semiconductor layer can then be polished at a face thereof to have a root-mean-square (RMS) surface roughness of less than about 6 nm so that waveguides patterned therefrom have loss ratings of better than 35 dB/cm. The polished polycrystalline semiconductor layer is then preferably etched in a plasma to form a plurality of polycrystalline strips. A second cladding layer is then formed on the polycrystalline strips to form a plurality of polycrystalline waveguides which provide relatively low-loss paths for optical communication between one or more optoelectronic devices coupled thereto.

Abstract: Methods of forming polycrystalline semiconductor waveguides include the steps of forming a first cladding layer (e.g., SiO.sub.2) on a substrate (e.g., silicon) and then forming a polycrystalline semiconductor layer (e.g., poly-Si) on the first cladding layer using a direct deposition technique or by annealing amorphous silicon (a-Si) to form a polycrystalline layer, for example. The deposited polycrystalline semiconductor layer can then be polished at a face thereof to have a root-mean-square (RMS) surface roughness of less than about 6 nm so that waveguides patterned therefrom have loss ratings of better than 35 dB/cm. The polished polycrystalline semiconductor layer is then preferably etched in a plasma to form a plurality of polycrystalline strips. A second cladding layer is then formed on the polycrystalline strips to form a plurality of polycrystalline waveguides which provide relatively low-loss paths for optical communication between one or more optoelectronic devices coupled thereto.

Abstract: It has been discovered that co-doping of Er-doped Si with a light element such as C, N or F can result in substantially increased Er luminescence. A further increase in luminescence can result if, in addition, oxygen is present in the Si. Apparatus or systems according to the invention comprise a device (e.g., laser, optical ampifier, LED) that comprises a planar waveguide whose core region contains, in addition to at least 90 atomic % Si or SiGe alloy, Er, Pr and/or Nd, and further contains C, N and/or F, and preferably also contains oxygen. Currently preferred apparatus or systems according to the invention comprise means for electrically pumping the waveguide means.

Abstract: Disclosed is a broadly applicable method for making an article that, exemplarily comprises a superconductive oxide body, including a thin layer on a substrate, or powder particles. In a preferred embodiment, the method comprises forming a precursor melt and contacting at least a part of the melt with oxygen such that the concentration of oxygen in the part of the melt increase to a critical concentration, resulting in formation of the desired oxide, substantially without drop in temperature. The precursor melt comprises at least one metallic element M, and at least the part of the melt is at a temperature T, with T.sub.m <T<T.sub.o, where T.sub.m is the freezing temperature of the melt and T.sub.o is the melting temperature of the superconductive oxide. In an exemplary embodiment the melt consists essentially of Yb, Ba, and Cu in 1:2:3 atomic ratio, T is about 900.degree. C. A layer of superconductive oxide on a Sr-TiO.sub.3 substrate is formed by dipping the hot (900.degree. C.