RESUMEN
A wavelength-multiplexed optical scanning scheme is proposed for deflecting a free-space optical beam by selection of the wavelength of the light incident on a wavelength-dispersive optical element. With fast tunable lasers or optical filters, this scanner features microsecond domain scan setting speeds and large- diameter apertures of several centimeters or more for subdegree angular scans. Analysis performed indicates an optimum scan range for a given diffraction order and grating period. Limitations include beam-spreading effects based on the varying scanner aperture sizes and the instantaneous information bandwidth of the data-carrying laser beam.
RESUMEN
Micromechanics-based wavelength-sensitive photonic delay and amplitude control modules are introduced for multiwavelength photonic applications such as hardware-compressed beam forming in phased-array antennas, timing-error compensation in high-speed long-haul fiber-optic communication networks, and pulse synchronization in photonic analog-to-digital converters and space-time code division multiplexed decoders. The basic delay structure relies on a single-circulator compact reflective parallel path design that features polarization insensitivity, independently controllable optical time-delay and amplitude settings, and fiber compatibility. Switched fiber time delays are proposed that use various micromechanical mechanisms such as mechanically stretched fiber Bragg gratings with comb-drive translational stages or magnetic levitation-based stretchers. Additional, shorter-duration variable time delays are obtained by means of the translational motion of external mirrors and the inherent delays in the zigzag reflective path geometry of the bulk-optic thin-film interference filter-based wavelength multiplexer used in our proposed design. Experiments are performed to test these concepts.
RESUMEN
A 7-bit multichannel photonic delay line for phased-array antenna control is demonstrated. Multichannel (33-pixel) ferroelectric liquid-crystal (FLC) devices are used as polarization rotation elements, and polarization beam-splitter cubes are used as polarization elements that route the optical signals to different paths. The controller is remotely fed by a unique fiber-optic-array design that uses gradient-index lens collimators for the input single-mode polarization-maintaining fibers. The optical signal is collected by a similar fiber array that uses multimode fibers for improved coupling efficiency. Photonic delay-line (PDL) design issues such as multiport assemblies, multipixel FLC designs, and delay-line architectures are discussed. Furthermore, various PDL parameters are examined. High electrical isolation numbers are obtained for both the within-channel leakage noise (e.g., less than -70 dB) and the interchannel cross talk (e.g., less than -90 dB). Optical and electrical insertion loss is examined for the PDL as well as for the overall system. A high-compression dynamic range of 149 dB x Hz and a spurious free dynamic range of 105 dB x Hz(2/3) are presented.
RESUMEN
A digitally controlled multiwavelength variable fiber-optic attenuator using a two-dimensional digital micromirror device (DMD) is introduced. The results from an experimental four-wavelength (i.e., 1546.92, 1548.52, 1550.12, and 1551.72 nm) proof-of-concept attenuator indicate a 26-dB dynamic range and 11-bit resolution. The measured attenuator average coherent optical cross talk per wavelength channel is -38 dB , limited by the additive noise resulting from the nonideal isolation of the optical circulator and the attenuator module. The average optical loss for our experimental attenuator is 15 dB and is limited mainly by the visible-mode DMD that is used as a 1550-nm infrared window device. Our theoretical estimate of a <8-dB loss optimized attenuator can be used for equalization in multiwavelength fiber-optic communications with as many as 108 wavelengths.
RESUMEN
A synchronous-amplitude-controlled and time-delay-controlled photonic controller for phased-array antenna applications is proposed and demonstrated. Amplitude control is based on a variable optical attenuator system that operates in synchronism with the photonic delay line (PDL). This amplitude control system can provide both the signal calibration for the different PDL channels and settings required for driving the antenna elements of a phased-array radar and the optimum optical power levels that impinge on the photodetector for optimum fiber-optic-link performance. Various variable amplitude control modules based on ferroelectric liquid crystals, polymer-dispersed liquid crystals, and photoconductive devices are proposed. We show that the dynamic range loss due to a switched-PDL inherent structure loss can be compensated when we control the optical power from the laser, using the synchronous optical attenuation system. For the first time to our knowledge, full dynamic range loss compensation is demonstrated for an external-modulation-fed 3-bit switched PDL with a structure optical insertion loss of 5.5 dB. A compression dynamic range of 158 dBxHz was measured at 6 GHz, and a spurious free dynamic range of 111 dBxHz(2/3) was estimated. Feasibility of the dynamic range compensation technique for multichannel, higher-insertion-loss PDL systems is discussed.
RESUMEN
A general formula for determining the coupling loss between two single-mode fiber collimators with the simultaneous existence of separation, lateral offset and angular tilt misalignments, and spot-size mismatch is theoretically derived by use of the Gaussian field approximation. Based on this general formula, the formulas for coupling losses that are due to the misalignment of insert separation, lateral offset, and angular tilt are given. The formula for the coupling loss that is due to Gaussian spot-size mismatch of two single-mode collimators is also given. Good agreement between these formulas and experimental results is demonstrated with gradient-index rod lens-based fiber collimators operating in the 1300-nm band.
RESUMEN
A new high-speed, ultrahigh cross-talk-suppression multiwavelength add-drop optical filter structure is demonstrated with two bulk acousto-optic tunable filters. With simple spatial blocks, an average -47-dB optical suppression is measured for the unwanted wavelengths at the filter output ports. The filter is tested for the three standard visible wavelengths, red, green, and blue, and demonstrates a switching time of 0.65micros and an average optical loss of 5 dB. Applications for this filter include multiwavelength switching applications such as wavelength-division-multiplexed optical communications.
RESUMEN
A 3-bit binary photonic delay line is demonstrated at 1 GHz by use of a directly modulated semiconductor laser and remote interconnection fiber optics. Three types of free-space delay-bit geometries are tested for 5.69-ns, 1.67-ns, and 8.8-ps designed delay bits. This is the first time, to our knowledge, that a photonic delay line is demonstrated with ferroelectric liquid-crystal optical on-off devices for optical path switching and active polarization noise filtering. Three-dimensional imaging optics and antireflection-coated optics (for all but five components) are used successfully to minimize photonic delay-line insertion losses and interchannel cross talk. The 3-bit system is fully characterized for measured and designed performance.
RESUMEN
A two-dimensional digital micromirror device- (DMD-) based add-drop filter is introduced for dense wavelength-division multiplexed applications. Features of the filter include polarization-insensitive operation, low interchannel cross talk parallel processing, and a fault-tolerant design. Experiments include evaluation of a parallel-beam-fed interchannel cross-talk with a 25-beam mask and a three-color (red, green, blue) filter operational test that indicates output-port average switching optical signal-to-noise and multiwavelength cross-talk ratios of 24 dB. The DMD-based average optical loss for the filter is -2.85 dB for visible-light free-space operation, whereas a -8.88-dB optical loss is measured for a fiber-coupled filter operating at 1319 nm.
RESUMEN
A high-speed, switched, binary photonic switching fabric based on two acousto-optic devices arranged in a compact self-aligning (by acousto-optic device-based Bragg matching) optical geometry is introduced for photonic signal processing and control. This fabric has the unique capability to provide simultaneously both high switching speeds and high optical isolation, a critical need for advanced low-noise high-speed signal-processing applications. The proof-of-concept experimental fabric demonstrated nearly 60% light throughput, a 39-dB optical isolation level for both states of the switching fabric, and a 138-ns switching time.
RESUMEN
A novel, switched, photonic delay-line ternary design combined with a wavelength-multiplexed transmit-receive beam-former architecture is proposed. One-dimensional antenna beam steering by use of a single-channel, wavelength-dependent switched photonic delay line in cascade with a multichannel wavelength-independent switched photonic delay line is proposed for hardware-compressed, phased-array antenna control with subarray antenna partitioning. Beam-former architecture extensions to two-dimensional antenna beam steering are described.
RESUMEN
A 1 mm x 1 mm nematic liquid-crystal three-terminal device for optical beam forming (focusing/spoiling) is fabricated. A thin-film-resistor network on the device substrate layer is used to control the voltages on the 98 internal lens electrodes by use of only one variable external driver. By using a high-resistance thin-film layer of amorphous silicon under the 98-element parallel electrode structure layer, we generate a near-continuous index perturbation to form a cylindrical lens. The focal length of this lens is continuously variable from inifinity to 12 cm by use of a variable 1-4-V-peak 1-kHz square-wave external terminal control signal.
RESUMEN
A bulk polarization-rotation-based 1 x 2 optical switch is demonstrated by use of a birefringent-mode parallel-rub nematic liquid-crystal cell and a calcite Thompson-prism polarizing beam splitter. With 633-nm linearly polarized light the switch output ports exhibit a >36-dB optical isolation with less than -0.75 dB of optical insertion loss. A >1.5-ms switching speed is demonstrated for a cascade cell optical arrangement by means of the transient nematic effect with >30 dB of optical isolation and -1.45 dB of optical loss.
RESUMEN
A novel, efficient, stable, in-line interferometric, two Bragg cell, acousto-optic architecture is introduced for signal correlation and spectrum analysis. The processor employs an image-inversion technique to produce a correlation output that does not have to be generated on a fast spatial carrier, thus reducing the burden on the required space-bandwidth product on the output time-integrating detector array. The system is particularly suited for wide-instantaneous-bandwidth signal processing and is demonstrated as an autocorrelator for dc-to-10-MHz AM signals on a 100-MHz carrier. A fixed-spatial-carrier outputbased correlator and spectrum-analyzer architecture that is particularly limited in the wideband mode is demonstrated for comparison purposes with the proposed flexible-spatial-carrier-design-based in-line acousto-optic correlator.
RESUMEN
A compact phased-array antenna acousto-optic beam former with element-level analog phase (0-2π) and amplitude control using nematic-liquid-crystal display-type technology is experimentally demonstrated. Measurements indicate > 6-bit phase control and 52.6 dB of amplitude-attenuation control. High-quality error calibration and antenna sidelobe-level control is possible with this low-control-power analog beam former. Optical system options using rf Bragg cells or wideband Bragg cells are discussed, with the rf design being the current preferred approach. Transmit-receive beam forming based on frequency upconversion-downconversion by electronic mixing is introduced for the rf Bragg-cell beam former, and comparisons with digital beam forming are highlighted. A millimeter-wave signal generation and control optical architecture is described.
RESUMEN
A novel in-line interferometric acousto-optic architecture for two-dimensional beam scanning of planar phased arrays is demonstrated experimentally for a 330-MHz carrier. The required modulo-2pi phase control along the two orthogonal antenna-array directions is achieved by using two independent control frequencies f(1) and f(2) with frequency variations of 0-170 and 0-210 kHz, respectively. A processor output carrier signal-to-noise ratio of 48 dB at + 1-MHz offset is measured in an analyzer bandwidth of 300 kHz, with a carrier tuning range of 90 MHz.
RESUMEN
Signaling by spatial coding is proposed for asynchronous multiple-access free-space optical communications and interference mitigation. The large spatial bandwidth (e.g., 10(6) pixels) of each laser transmitter aperture is utilized for user coding, while the transmitter temporal bandwidth is preserved for information signals. Signal recovery is based on incoherent optical detection, spatial sampling, and electronic or optical matched filtering of the remotely received transmit optical beam Fresnel or Fraunhofer diffraction pattern. The proposed signaling method is appropriate for multiple-access free-space laser links involving multiple transmitters that use a common receiver. With electronic filtering, low-to-medium (e.g., 3 Mbits/s) data-rate users are appropriate. With a lenslet-array-based incoherent optical correlator, higher (e.g., 100 Mbits/s) data rates can be achieved. Improved interference protection is achieved cby spatially distributed bit-duration-based processing. Preliminary simulation results are carried out to demonstrate operating principles.
RESUMEN
An efficient in-line additive acousto-optic architecture that can provide a high dynamic-range spectrum analysis and is suitable for an integrated optic design is introduced.
RESUMEN
An in-line additive acousto-optic architecture for very high speed ( asymptotically equal to0.4 s) two-dimensional, phasedarray antenna beam scanning is introduced that uses only two independent analog scan control signals. Features include up to K(u) band operation, intrapulse beam forming, and multiband, wide (2-GHz) tunable bandwidth capability.
