Abstract: A semiconductor optical amplifier (SOA) apparatus and related methods are described. The SOA comprises a signal waveguide for guiding an optical signal along a signal path, and further comprises one or more laser cavities having a gain medium lying outside the signal waveguide, the gain medium being sufficiently close to the signal waveguide such that, when the gain medium is pumped with an excitation current, the optical signal traveling down the signal waveguide is amplified by an evanescent coupling effect with the laser cavity. When the gain medium is sufficiently pumped to cause lasing action in the laser cavity, gain-clamped amplification of the optical signal is achieved.

Abstract: An optical return-to-zero (RZ) signal generator and related methods are described in which a phase modulator causes a phase change in an optical signal responsive to a transition in a driving signal, and in which an interferometer receives the optical signal from the phase modulator and generates an optical pulse responsive to that phase change. Preferably, the interferometer introduces a fixed, unmodulated time delay between its two signal paths, the fixed time delay being selected such that destructive interference occurs at an output of the interferometer when the phase of the optical signal received from the phase modulator remains constant. However, when a rising or falling edge of the driving signal causes phases changes in the optical signal, the destructive interference at the output of the interferometer is disturbed, and an optical pulse is generated. The driving signal is a differentially encoded version of an input information signal.

Abstract: An integrated optical cross-connect device and associated methods are described, the cross-connect device comprising a plurality M of input waveguides formed in a first material layer of an integrated circuit, a plurality N of output waveguides formed in a second material layer of the integrated circuit, and a plurality MN of micromechanically actuated bridge elements formed in at least one intermediate layer lying between the first and second material layers. Responsive to an electrical control signal, each bridge element establishes an index-guided, nonreflecting optical path between its associated input waveguide and its associated output waveguide. Preferably, the bridge element comprises an arcuate waveguide structure substantially surrounded by air or other nonsolid material, the arcuate waveguide structure being twistably connected to a remainder of the intermediate layer by a narrow neck portion.

Abstract: An optical interleaver is described, comprising a splitting element for splitting an incident beam into a first optical signal directed along a first path and a second optical signal directed along a second path, a first resonant element positioned along the first path, a second resonant element positioned along the second path, and a combining element positioned to receive and to interferometrically combine the outputs of the first and second resonant to produce the output signal. The optical interleaver may be implemented using a free-space configuration using a beamsplitter and a plurality of resonant cavities such as asymmetric Fabry-Perot resonators or Michelson-Gires-Tournois resonators. In an alternative preferred embodiment, the optical interleaver may be implemented in a Mach-Zender-style configuration using couplers and fiber ring resonators.

Abstract: A vertical cavity surface-emitting laser (VCSEL) structure and related fabrication methods are described, the VCSEL comprising amorphous dielectric distributed Bragg reflectors (DBRs) while also being capable of fabrication in a single-growth process. Beginning with a substrate such as InP, a first amorphous dielectric DBR structure is deposited thereon, but is limited in width such that some substrate material remains uncovered by the dielectric material. A lateral overgrowth layer is then formed by epitaxially growing material such as InP onto the substrate, the lateral overgrowth layer eventually burying the dielectric DBR structure as well as the previously-uncovered substrate material. Active layers may then be epitaxially grown on the lateral overgrowth layer, and a top dielectric DBR may be deposited thereon using conventional techniques. To save vertical space between DBRs, the first DBR may be deposited in a non-reentrant well formed in the surface of a substrate.

Abstract: A vertical cavity surface emitting laser (VCSEL) structure and fabrication method therefor are described in which a subsurface air, gas, or vacuum current confinement method is used to restrict the area of electrical flow in the active region. Using vertical hollow shafts to access a subsurface current confinement layer, a selective lateral etching process is used to form a plurality of subsurface cavities in the current confinement layer, the lateral etching process continuing until the subsurface cavities laterally merge to form a single subsurface circumferential cavity that surrounds a desired current confinement zone. Because the subsurface circumferential cavity is filled with air, gas, or vacuum, the stresses associated with oxidation-based current confinement methods are avoided. Additionally, because the confinement is achieved by subsurface cavity structures, overall mechanical strength of the current-confining region is maintained.

Abstract: An index-guiding microstructured optical fiber, having a majority of the cross-section of the core and cladding regions occupied by voids. The voids are dimensioned such that an effective index of refraction of the cladding region is less than an effective index of the core region, the optical fiber propagating light by an index-guiding effect. The attenuation and dispersion characteristics of the microstructured optical fiber, when expressed in dB/km and ps/(nm-km), respectively, each decrease in approximate proportion to the percentage of cross-sectional area occupied by the voids. An appropriate void-to-cross-sectional area ratio may be selected so as to provide an optical communications link that provides substantially increased data throughput using today's installed base of conduit and communications relay stations.

Abstract: A semiconductor optical amplifier (SOA) apparatus and related methods are described. The SOA comprises a signal waveguide for guiding an optical signal along a signal path, and further comprises one or more laser cavities having a gain medium lying outside the signal waveguide, the gain medium being sufficiently close to the signal waveguide such that, when the gain medium is pumped with an excitation current, the optical signal traveling down the signal waveguide is amplified by an evanescent coupling effect with the laser cavity. When the gain medium is sufficiently pumped to cause lasing action in the laser cavity, gain-clamped amplification of the optical signal is achieved.

Abstract: A WDM demultiplexer/multiplexer comprising a plurality of narrow band reflective filters linearly disposed along an optical axis, each narrow band reflective filter reflecting a single channel or group of channels and transmitting the remaining channels, is described. In a demultiplexing mode, an optical signal initially carrying channels at &lgr;1&lgr;2 . . . &lgr;N travels along the optical axis. Each narrow band reflective filter reflects a distinct channel and is tilted with respect to the optical axis such that it directs the reflected beam away from the optical axis to an output. Each narrow band reflective filter is substantially transparent to the remaining channels of the optical signal, such that the remainder of the optical signal proceeds along the optical axis substantially undisturbed.

Abstract: A vertically lasing semiconductor optical amplifier (SOA) apparatus for amplifying an optical signal and related methods are described. The SOA comprises an integrated plurality of vertical cavity surface emitting lasers (VCSELs) having a common gain medium layer, and a signal waveguide extending horizontally through the VCSELs near the gain medium layer such that the optical signal is amplified while propagating therethrough. Although integrated onto a common substrate, the VCSELs are functionally isolated from each other, each building up its own distinct lasing field responsive to a distinct electrical pump current therethrough. Each VCSEL is configured and dimensioned to achieve smooth, single transverse mode lasing action for promoting spatially uniform and temporally stable gain of the optical signal as it propagates along the signal waveguide. Preferably, the SOA comprises several dozens to several hundreds of functionally isolated VCSELs, each providing only a small portion of the overall signal gain.

Abstract: A ballast-powered semiconductor optical amplifier (SOA) apparatus and related methods are described. The SOA comprises a signal waveguide for guiding an optical signal along a signal path, and further comprises one or more ballast lasers positioned with respect to the signal waveguide such that the optical signal is amplified using energy from the lasing fields of the one or more ballast lasers. The problem of relative intensity noise (RIN) transfer from the ballast lasers into the optical signal is avoided by ensuring that the relaxation oscillation frequency (ROF) of each ballast laser is sufficiently higher than the signal modulation rate such that the RIN spectrum is tolerably low at the signal modulation rate. The ROFs themselves are manipulated by methods including adjustment of excitation current densities within the ballast lasers.

Abstract: A vertically lasing semiconductor optical amplifier (SOA) apparatus for amplifying an optical signal and related methods are described. The SOA comprises an integrated plurality of vertical cavity surface emitting lasers (VCSELs) having a common gain medium layer, and a signal waveguide extending horizontally through the VCSELs near the gain medium layer such that the optical signal is amplified while propagating therethrough. Although integrated onto a common substrate, the VCSELs are functionally isolated from each other, each building up its own distinct lasing field responsive to a distinct electrical pump current therethrough. Each VCSEL is configured and dimensioned to achieve smooth, single transverse mode lasing action for promoting spatially uniform and temporally stable gain of the optical signal as it propagates along the signal waveguide. Preferably, the SOA comprises several dozens to several hundreds of functionally isolated VCSELs, each providing only a small portion of the overall signal gain.

Abstract: An optical fiber having extended single-mode capabilities is described in which subwavelength microstructural voids are introduced into the core and/or cladding to allow a fine tuning of the difference between their effective refractive indices. The introduction of subwavelength microstructures into the optical material, preferably through a photolithographic process at the preform stage, allows for control of the effective refractive index difference between the core and the cladding that is more precise than the control afforded by chemical doping processes (e.g., flame hydrolysis) alone. Accordingly, the specified effective refractive index difference between the core and the cladding may be made smaller than that allowed by chemical doping processes alone, thereby allowing the optical fiber to exhibit single-mode properties for larger core diameters.

Abstract: A vertical cavity surface emitting laser (VCSEL) structure and fabrication method therefor are described in which a subsurface air, gas, or vacuum current confinement method is used to restrict the area of electrical flow in the active region. Using vertical hollow shafts to access a subsurface current confinement layer, a selective lateral etching process is used to form a plurality of subsurface cavities in the current confinement layer, the lateral etching process continuing until the subsurface cavities laterally merge to form a single subsurface circumferential cavity that surrounds a desired current confinement zone. Because the subsurface circumferential cavity is filled with air, gas, or vacuum, the stresses associated with oxidation-based current confinement methods are avoided. Additionally, because the confinement is achieved by subsurface cavity structures, overall mechanical strength of the current-confining region is maintained.

Abstract: A ballast-powered semiconductor optical amplifier (SOA) apparatus and related methods are described. The SOA comprises a signal waveguide for guiding an optical signal along a signal path, and further comprises one or more ballast lasers positioned with respect to the signal waveguide such that the optical signal is amplified using energy from the lasing fields of the one or more ballast lasers. The problem of relative intensity noise (RIN) transfer from the ballast lasers into the optical signal is avoided by ensuring that the relaxation oscillation frequency (ROF) of each ballast laser is sufficiently higher than the signal modulation rate such that the RIN spectrum is tolerably low at the signal modulation rate. The ROFs themselves are manipulated by methods including adjustment of excitation current densities within the ballast lasers.

Abstract: A semiconductor optical amplifier (SOA) apparatus and related methods are described. The SOA comprises a signal waveguide for guiding an optical signal along a signal path, and further comprises one or more laser cavities having a gain medium lying outside the signal waveguide, the gain medium being sufficiently close to the signal waveguide such that, when the gain medium is pumped with an excitation current, the optical signal traveling down the signal waveguide is amplified by an evanescent coupling effect with the laser cavity. When the gain medium is sufficiently pumped to cause lasing action in the laser cavity, gain-clamped amplification of the optical signal is achieved.

Abstract: A method of fabricating a microstructured optical fiber is described in which a plurality of solid silica wafers are generated corresponding to longitudinally consecutive portions of the optical fiber, separately etched with void patterns in a lithographic process, and bonded together into a preform. The preform is then drawn to form the optical fiber. The lithographic process used to form the void patterns in the wafers may be any of several processes currently or prospectively used in VLSI fabrication. Such lithographic process may be used because the wafers comprise silica glass or other material common in VLSI devices and, in accordance with a preferred embodiment, are generated with thicknesses highly amenable to such fabrication methods. The wafers are preferably generated by creating a preliminary preform having the desired material refractive index profile using conventional preform fabrication methods, the wafers then being sliced from the preliminary preform.

Abstract: An optical fiber having a strongly negative dispersion characteristic that is well suited for use as a dispersion compensating fiber is described. The optical fiber comprises a primary core, a primary cladding surrounding the primary core, a secondary core surrounding the primary cladding, and a secondary cladding surrounding the secondary core, wherein a plurality of voids is formed within the secondary core. The voids in the secondary core are elongated and run parallel to the fiber axis, and form a spatially periodic pattern when viewed in cross-section. In one preferred embodiment, the voids are circular and the spatially periodic void pattern comprises hexagonal unit cells having central members, whereby each void is the same distance from each of its six nearest neighbors. The optical fiber exhibits a strongly negative dispersion characteristic, thereby reducing the required length of dispersion compensating fiber per unit distance of optical fiber span.

Abstract: A WDM demultiplexer/multiplexer comprising a plurality of narrow band reflective filters linearly disposed along an optical axis, each narrow band reflective filter reflecting a single channel or group of channels and transmitting the remaining channels, is described. In a demultiplexing mode, an optical signal initially carrying channels at &lgr;1&lgr;2 . . . &lgr;N travels along the optical axis. Each narrow band reflective filter reflects a distinct channel and is tilted with respect to the optical axis such that it directs the reflected beam away from the optical axis to an output. Each narrow band reflective filter is substantially transparent to the remaining channels of the optical signal, such that the remainder of the optical signal proceeds along the optical axis substantially undisturbed.

Abstract: A vertical cavity surface emitting laser (VCSEL) structure and fabrication method therefor are described in which a subsurface air, gas, or vacuum current confinement method is used to restrict the area of electrical flow in the active region. Using vertical hollow shafts to access a subsurface current confinement layer, a selective lateral etching process is used to form a plurality of subsurface cavities in the current confinement layer, the lateral etching process continuing until the subsurface cavities laterally merge to form a single subsurface circumferential cavity that surrounds a desired current confinement zone. Because the subsurface circumferential cavity is filled with air, gas, or vacuum, the stresses associated with oxidation-based current confinement methods are avoided. Additionally, because the confinement is achieved by subsurface cavity structures, overall mechanical strength of the current-confining region is maintained.