Abstract: In one aspect, a frequency agile LADAR (laser detection and ranging) sensor includes a transmitter configured to provide laser pulses towards a target, a receiver configured to receive a reflected signal from the target and control circuitry configured to tune an optical frequency of a first laser pulse of the laser pulses to be different from an optical frequency of a second laser pulse of the laser pulses and tune an optical frequency of the receiver to be different than an optical frequency of a laser pulse most recently transmitted by the transmitter.

Abstract: A servo system includes multiple servo channels being driven by a common error signal. Each channel has a controller that receives an error signal and provides a drive signal to a driver. The servo channels are arranged serially, with a drive signal from one controller forming the error signal for a downstream controller. As a result, the downstream controller does not attempt to correct for phase error directly, but instead attempts to keep the upstream driver at or near its operational midpoint. The servo channels can be arranged in order of decreasing controller bandwidth, from fastest to slowest. In contrast with a parallel configuration, in which servo channels all simultaneously receive a common error signal, the serial configuration can allow each controller to use its full bandwidth, can eliminate crosstalk between servo channels, and can prevent saturation of upstream drive signals.

Abstract: In one aspect, a frequency agile LADAR (laser detection and ranging) sensor includes a transmitter configured to provide laser pulses towards a target, a receiver configured to receive a reflected signal from the target and control circuitry configured to tune an optical frequency of a first laser pulse of the laser pulses to be different from an optical frequency of a second laser pulse of the laser pulses and tune an optical frequency of the receiver to be different than an optical frequency of a laser pulse most recently transmitted by the transmitter.

Abstract: A laser system comprises a pump diode, fiber, relay optics, and a microchip laser crystal. The pump diode produces light at a first wavelength. The fiber receives the light from the pump diode and produces a round, homogeneous light spot at an output of the fiber. The relay optics receives the light from the fiber. The microchip laser crystal receives the light from the relay optics and produces a linearly polarized single frequency output at a second wavelength. The microchip laser crystal includes a first layer and a second layer. The first layer absorbs the light at the first wavelength and emits light at the second wavelength. The second layer receives the light at the second wavelength and either provides a polarization dependent loss at the second wavelength or maintains a polarization of the light at the second wavelength.

Abstract: A servo system includes multiple servo channels being driven by a common error signal. Each channel has a controller that receives an error signal and provides a drive signal to a driver. The servo channels are arranged serially, with a drive signal from one controller forming the error signal for a downstream controller. As a result, the downstream controller does not attempt to correct for phase error directly, but instead attempts to keep the upstream driver at or near its operational midpoint. The servo channels can be arranged in order of decreasing controller bandwidth, from fastest to slowest. In contrast with a parallel configuration, in which servo channels all simultaneously receive a common error signal, the serial configuration can allow each controller to use its full bandwidth, can eliminate crosstalk between servo channels, and can prevent saturation of upstream drive signals.

Abstract: A laser system comprises a pump diode, fiber, relay optics, and a microchip laser crystal. The pump diode produces light at a first wavelength. The fiber receives the light from the pump diode and produces a round, homogeneous light spot at an output of the fiber. The relay optics receives the light from the fiber. The microchip laser crystal receives the light from the relay optics and produces a linearly polarized single frequency output at a second wavelength. The microchip laser crystal includes a first layer and a second layer. The first layer absorbs the light at the first wavelength and emits light at the second wavelength. The second layer receives the light at the second wavelength and either provides a polarization dependent loss at the second wavelength or maintains a polarization of the light at the second wavelength.

Abstract: For systems which disperse individual wavelength components of a DWDM beam into an array of converging beams, the individual wavelength signals are modified for blocking, equalization or other purposes by reflective liquid crystal cells. Thus modulated or modified components are then recombined by the system into an output beam, as by reverse passage through the system. Controlled full extinction or linear attenuation may be introduced by converging asymmetrical beams of separate polarization components for each wavelength into superposed relation on zero twist nematic crystal cells which are voltage controlled so as to retard for extinction of greater than 40 dB or to transform the state of polarization to a selected angle for attenuation. Polarization sensitive elements in the return paths of the reflected beams then filter the rejected components.

Abstract: Systems and methods for modifying, switching, rearranging or otherwise controlling the individual wavelength components of DWDM optical signals are described, which employ compact refolding and reshaping of these dimensionally patterned beams within a confined volume. The wavelength components of the beam are diffractively dispersed with high diffraction efficiency, and then reversely converged to beam waists incident on different ones of an array of control elements such as liquid crystal cells, MEMs and other spatial light modulators, or fixed distributed patterns. With reflective control elements the wavelength components may be reversely refolded along reciprocal paths with rediffraction, to form a reconstituted and revised DWDM output signal. If the control elements transmit at least one of the wavelength components, a separate, adjacent three dimensional beam refolding path, with rediffraction, is used to feed recombined signals to a separate output.

Abstract: For systems which disperse individual wavelength components of a DWDM beam into an array of converging beams, the individual wavelength signals are modified for blocking, equalization or other purposes by reflective liquid crystal cells. Thus modulated or modified components are then recombined by the system into an output beam, as by reverse passage through the system. Controlled full extinction or linear attenuation may be introduced by converging asymmetrical beams of separate polarization components for each wavelength into superposed relation on zero twist nematic crystal cells which are voltage controlled so as to retard for extinction of greater than 40 dB or to transform the state of polarization to a selected angle for attenuation. Polarization sensitive elements in the return paths of the reflected beams then filter the rejected components.

Abstract: Systems and methods for modifying, switching, rearranging or otherwise controlling the individual wavelength components of DWDM optical signals are described, which employ compact refolding and reshaping of these dimensionally patterned beams within a confined volume. The wavelength components of the beam are diffractively dispersed with high diffraction efficiency, and then reversely converged to beam waists incident on different ones of an array of control elements such as liquid crystal cells, MEMs and other spatial light modulators, or fixed distributed patterns. With reflective control elements the wavelength components may be reversely refolded along reciprocal paths with rediffraction, to form a reconstituted and revised DWDM output signal. If the control elements transmit at least one of the wavelength components, a separate, adjacent three dimensional beam refolding path, with rediffraction, is used to feed recombined signals to a separate output.

Abstract: An optical signal filter for providing a periodic transfer function in transmitting signals within a selected bandwidth, by which passbands are interleavered into groups of separate outputs. The filter employs the transmissivity characteristic of birefringent crystals in conjunction with splitting the input beam into orthogonal and separate components, while compensating for temperature variations by pairing crystals of different types. The transmissivity functions are independent of the polarization of the input beam, and are shaped to flatten transmissivity peaks by the use of cascaded stages of birefringent crystal pairs.

Abstract: Optical components, particularly microoptic glass components used in synthesizing birefringence in filter systems based on polarization interferometer techniques, are fabricated using systems and methods which provide accurate frequency periodicity measurements. These measurements are derived from differential delays induced by in-process glass elements between beam components in a polarization interferometer unit and from progressive wavelength scanning across a wavelength band of interest. The consequent sinusoidal output variation has peak to peak spacings which are measured to provide frequency periodicity values from which precise length corrections for the optical elements can be calculated.

Abstract: A fast acting, low insertion loss switch for use in an optical fiber communication system includes a small diameter waist region incorporating a Bragg grating which is precisely tuned by tensioning to be reflective at a selective wavelength band. By a small physical shift of the waist, as by lateral displacement of an attached small magnetic element with a magnetic field, the periodicity of the grating is varied so that the selected wavelength is passed through the waist with virtually no loss. The incremental motion required can be introduced by a variety of devices, selected in accordance with cost, size and response time requirements. Modules having a number of such switches in close juxtaposition offer distinct advantages for wavelength division multiplexed systems.

Abstract: Optical components, particularly microoptic glass components used in synthesizing birefringence in filter systems based on polarization interferometer techniques, are fabricated using systems and methods which provide accurate frequency periodicity measurements. These measurements are derived from differential delays induced by in-process glass elements between beam components in a polarization interferometer unit and from progressive wavelength scanning across a wavelength band of interest. The consequent sinusoidal output variation has peak to peak spacings which are measured to provide frequency periodicity values from which precise length corrections for the optical elements can be calculated.

Abstract: An optical signal filter for providing a periodic transfer function in transmitting signals within a selected bandwidth, by which passbands are interleavered into groups of separate outputs. The filter employs the transmissivity characteristic of birefringent crystals in conjunction with splitting the input beam into orthogonal and separate components, while compensating for temperature variations by pairing crystals of different types. The transmissivity functions are independent of the polarization of the input beam, and are shaped to flatten transmissivity peaks by the use of cascaded stages of birefringent crystal pairs.

Abstract: Interleavers for optical systems, including multiplexers and demultiplexers, are based on the use of non-birefringent elements in combination with polarization beam splitter to provide differential retardation effects for generation of precise transmittance functions. The retardation elements, in one particular example, are non-birefringent glasses arranged in individually athermal stages but the optical beams propagated through them are maintained in selected polarization states in each stage. Between or within the stages the polarization vectors are varied to match phase to a selected standard, such as an ITU grid. Within the stages, selected beam angle adjustments are made to shape the output transmittance characteristic.

Abstract: Precisely tensioned optical fiber devices are held in a temperature compensated package, with a small diameter span of a fiber containing a Bragg grating of a needed periodicity being supported under tension at opposite ends between spaced apart end members whose thermal expansion characteristics differ from that of an underlying base. The direct points of attachment of the ends of the tensioned span are rotationally as well as axially movable, enabling fine tuning of periodicity and twisting to minimize polarization and dispersion effects. This configuration is also useful for unique methods of assembly of the components, and for use during writing the Bragg grating in the small diameter span.

Abstract: Substantial improvements in photorefractive device lifetimes are provided by control of electron migration which results in the decay of gratings in photorefractive materials due to diffusion and other effects. A new class of photorefractive devices using compensating electronic and ionic gratings having relatively low efficiency but nonetheless usable gratings is provided by arranging the gratings to be reflective in a wavelength band outside the photo-excitation band of the photorefractive material, as by using an infrared operating wavelength. Longer lifetimes in high efficiency gratings are achieved by constant or periodic illumination of photorefractive materials to assure uniform charged distribution of electrons and maintenance of the ionic backbone grating.

Abstract: A laser utilizes feedback from a volume holographic grating used as a wavelength standard to lock the laser output wavelength to its desired value. This feedback can be non-optical, wherein the holographic filter output is used to actively control the wavelength through an external control mechanism. This feedback can also be optical, wherein a volume hologram reflection grating is used to generate optical feedback into the laser gain.

Abstract: A method of writing plane holographic gratings Bragg-matched for reflection in the infrared in a photorefractive material using shorter wavelength light through a face perpendicular to the grating planes. The writing beam wavelength is selected to be within the photorefractive sensitivity range of the crystal and the angles are chosen relative to the wavelength to define a reflection grating with a period such that counter-propagating reflection occurs at the desired IR wavelength. For reflection gratings at different wavelengths, either the transmission or the reflection mode geometry may be used. In the transmission mode, the writing beams are incident on the same side face while in the reflection made the writing is on opposite faces in an off-axis (non-counter-propagating) configuration. Anti-reflection coatings of the appropriate wavelengths are used on the crystal surfaces to reduce reflection losses and improve the diffraction efficiency of the grating.