Demonstration of an all-digital 7-bit 33-channel photonic delay line for phased-array radars

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 . Hz and a spurious free dynamic range of 105 dB . Hz(2/3) are presented.     

Micromechanics-based wavelength-sensitive photonic beam control architectures and applications

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.     

Acousto-optic liquid-crystal analog beam former for phased-array antennas

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.     

一种数字化可调光衰减器的设计

设计了一种具有自锁功能,可实现数字化的电磁驱动可调光衰减器。该衰减器以电磁驱动 微加工齿轮/齿条机构,带动偏心轮以及与偏心轮点接触的移动挡光片,从而实现数字化电控调节光衰减量。性能测试表明该器件的插入损耗小于 0.5 dB,衰减动态范围为0～50dB。     

Optical characteristics of a refractive optical attenuator with respect to the wedge angles of a silicon optical leaker

We design, fabricate, and characterize the micromachined refractive variable optical attenuator (VOA) with a wedge-shaped silicon optical leaker (SOL). The vertical structures of the VOA device can be simply fabricated by deep reactive ion etching with no sidewall metallization, and the 8 degrees angled fibers are employed for a high return loss even in air-ambient conditions. The SOL successively transmits and refracts part of the incident light far outside the acceptance angle of the output fiber, showing an effective optical attenuation. The fabricated VOA gives high optical performances, such as a response time of 6 ms, a return loss of 39 dB, an insertion loss of 0.6 dB, an attenuation range of 43 dB, and a polarization-dependent loss (PDL) of a 10% attenuation level, including a wavelength-dependent loss. The optical characteristics of the VOA are also theoretically investigated with respect to the wedge angles of the SOL. The experimental characteristics are in good agreement with the theoretical values calculated, considering light scattered from the endface of an optical fiber and sidewall of the SOL. The PDL estimation was confirmed especially to sufficiently explain the fundamental characteristic of the PDL for the refractive VOA.     

Phased-array antenna, maximum-compression, reversible photonic beam former with ternary designs and multiple wavelengths

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.     

Manipulation of polarization-dependent effects by magnetostrictive stress on silicon-on-insulator rib waveguides

Polarization dependent loss (PDL) can cause deterioration in optical network performance owing to the resultant fluctuation in received power because of random changes in fiber polarization. We describe the use of a magnetostrictive layer integrated on a planar light-wave circuit that can offer the functionality of modifying the variable PDL or differential group delay produced within the typical tolerances of volume manufacturing. This approach provides an alternative to the sizable delay lines and splitters that were previously employed for polarization compensation. We demonstrate adjustment of polarization-dependent parameters by the application of an external magnetic field to a ferromagnetic layer adjacent to the waveguide.     

Optimum antenna configurations for millimetre-wave communications from high-altitude platforms

Clustering sizes, power control strategies and antenna beamwidths, and orientations are investigated for quasi-stationary high-altitude platforms (HAPs) or other aerial platforms operating in the millimetre-wave band. It is shown that considering the carrier-to-noise and interference ratios (CNIRs) when optimising antenna beamwidths and directions can lead to significant increases in minimum CNIR levels (e.g. from 8.7 to 16.9 dB) over the coverage area. It is also shown that the optimum antenna configurations and transmit powers are a function of the weather, and should (if possible) be adjusted during periods of cloud cover and rainfall. In more practical situations in which only the transmit powers from the HAP antennas can be adjusted dynamically, it is shown that the loss in performance is <2 dB relative to the optimum scheme with dynamically adjustable antenna beamwidths and orientations over a wide range of rainfall conditions     

Polymer‐Based Photonic Crystals

In this report, we highlight the development of polymers as 1D photonic crystals and subsequently place special emphasis on the activities in self‐assembled block copolymers as a promising platform material for new photonic crystals. We review recent progress, including the use of plasticizer and homopolymer blends of diblock copolymers to increase periodicity and the role of self‐assembly in producing 2D and 3D photonic crystals. The employment of inorganic nanoparticles to increase the dielectric contrast and the application of a biasing field during self‐assembly to control the long‐range domain order and orientation are examined, as well as in‐situ tunable materials via a mechanochromic materials system. Finally, the inherent optical anisotropy of extruded polymer films and side‐chain liquid‐crystalline polymers is shown to provide greater degrees of freedom for further novel optical designs.     

Compact optical-fiber variable attenuator arrays with polymer-network liquid crystals

Electrically controlled fiber variable-optical-attenuator arrays with polymer-network liquid crystals are shown to be compact and to have a large attenuation range (30-40 dB) and low residual loss (0.55 dB) at wavelengths from 1.3 to 1.6 mum. Their estimated power consumption is very low (<30 nW/channel), and arrays with more than ten channels can be made. The manufacturing process is simple: Trenches 30-100 mum wide are cut across parallel conductive-layer-coated optical fibers and are filled with a polymer-network liquid crystal. The attenuation properties depend on UV-curing conditions and on trench width.     

Enhanced antenna-pattern measurements for Satellite systems

This paper describes an enhanced measurement technique for earth-station antennas in a satellite communication system. A new data-acquisition algorithm improves the dynamic range of the measurements by increasing the signal-to-noise ratio in the test setup. The resolution limitation of conventional techniques is eliminated without any modifications to the ground station setup. The proposed approach improves the conventional measurement techniques by utilizing pulse modulation of the test-signal amplitude and its synchronous detection. The noise floor in the pattern is reduced by biasing out the average noise power calculated during the OFF cycle of the pulse. In addition, a randomly fluctuating local mean in the receiver output is reduced. Experimental results show improvements of as much as 25 dB in the noise variance and over 11 dB in the dynamic range of the antenna pattern.     

Towards the improvement of attenuation range and response time of electrochromic polymer-based variable optical attenuators

A solid–liquid electrochromic variable optical attenuator device consisting of a thin layer of LiClO₄-doped poly(3,4-ethylenedioxythiophene) (PEDOT) and ferrocene in propylene carbonate has been demonstrated to exhibit a large dynamic range of optical attenuation at the telecommunication wavelength of 1550 nm. Doping of PEDOT film with an electrolyte greatly improves the device performance in terms of optical attenuation or color efficiency at 1550 nm and response time. An optimized single-layer device consisting of LiClO₄-doped PEDOT film (440 nm) shows a 10-dB dynamic range of optical attenuation at 1550 nm, a low optical loss of 0.86 dB for the bleached state, and a response time of 5–7 s at the switching potential of 0–2 V.     

Optical BEAMTAP beam-forming and jammer-nulling system for broadband phased-array antennas

We present an approach to receive-mode broadband beam forming and jammer nulling for large adaptive antenna arrays as well as its efficient and compact optical implementation. This broadband efficient adaptive method for true-time-delay array processing (BEAMTAP) algorithm decreases the number of tapped delay lines required for processing an N-element phased-array antenna from N to only 2, producing an enormous savings in delay-line hardware (especially for large broadband arrays) while still providing the full NM degrees of freedom of a conventional N-element time-delay-and-sum beam former that requires N tapped delay lines with M taps each. This allows the system to adapt fully and optimally to an arbitrarily complex spatiotemporal signal environment that can contain broadband signals of interest, as well as interference sources and narrow-band and broadband jammers-all of which can arrive from arbitrary angles onto an arbitrarily shaped array-thus enabling a variety of applications in radar, sonar, and communication. This algorithm is an excellent match with the capabilities of radio frequency (rf) photonic systems, as it uses a coherent optically modulated fiber-optic feed network, gratings in a photorefractive crystal as adaptive weights, a traveling-wave detector for generating time delay, and an acousto-optic device to control weight adaptation. Because the number of available adaptive coefficients in a photorefractive crystal is as large as 10(9), these photonic systems can adaptively control arbitrarily large one- or two-dimensional antenna arrays that are well beyond the capabilities of conventional rf and real-time digital signal processing techniques or alternative photonic techniques.     

Electronically controlled agile lens-based broadband variable photonic delay line for photonic and radio frequency signal processing

To the best of our knowledge, proposed for the first time is the design of an optically broadband variable photonic delay line (VPDL) using an electronically controlled variable focus lens (ECVFL), mirror motion, and beam-conditioned free-space laser beam propagation. This loss-minimized fiber-coupled VPDL design using micro-optic components has the ability to simultaneously provide optical attenuation controls and analog-mode high-resolution (subpicoseconds) continuous delays over a moderate (e.g., <5 ns) range of time delays. An example VPDL design using a liquid-based ECVFL demonstrates up to a 1 ns time-delay range with >10 dB optical attenuation controls. The proposed VPDL is deployed to demonstrate a two-tap RF notch filter with tuned notches at 854.04 and 855.19 MHz with 22.6 dB notch depth control via VPDL attenuation control operations. The proposed VPDL is useful in signal conditioning applications requiring fiber-coupled broadband light time delay and attenuation controls.     

Tunable photonic nanojet achieved using a core–shell microcylinder with nematic liquid crystal

A tunable photonic nanojet achieved using a core–shell microcylinder with nematic liquid crystal is reported. The core–shell microcylinder can be obtained by the infiltration of liquid crystal into the air core of a microcylinder. The refractive indices of the liquid crystals can be changed by rotating the directors of the liquid crystals. Therefore, we were able to control the flow direction of the photonic nanojet in two-dimensional core–shell microcylinder structures. Using high resolution finite-difference time-domain simulation, we demonstrate that the photonic nanojet can be continuously tuned in the core–shell microcylinder. The horizontal and vertical shifts of photonic nanojet depend strongly on the director of the liquid crystals. Such a mechanism of nanojet adjustment should open up a new application for using visible light to detect nanoparticles, optical gratings, and single molecules with subwavelength spatial resolution.     

Development and field demonstration of a hardware-compressive fiber-optic true-time-delay steering system for phased-array antennas

We describe the design, fabrication, testing, and antenna-range demonstration of a photonic wavelengthmultiplexed true-time-delay steering system for use with broadband phased-array antennas. The prototype system is based on a unique hardware-compressive architecture and can drive 16 antenna elements over the 0.35-2.1-GHz band with 6-bit angular resolution over a ±45° scan angle.     

Modelling of a variable optical switch based on the parametric amplification in a photonic crystal fibre

We model an optical switch with a variable gain based on the optical parametric amplification in a photonic crystal fibre (PCF). By solving the coupled amplitude equations, the switch gain as a function of the power, wavelength and the state of polarization (SOP) of the control wave as well as the signal wavelength is simulated. The results show that the switch gain is increased by increasing the control power and the maximum gain is obtained for a specific SOP of the control wave. Also, the proposed switch has ultrahigh speed and provides a very wide and flat gain over the C-band without changing the operating wavelength.     

Adaptive beam shaping by controlled thermal lensing in optical elements

We describe an adaptive optical system for use as a tunable focusing element. The system provides adaptive beam shaping via controlled thermal lensing in the optical elements. The system is agile, remotely controllable, touch free, and vacuum compatible; it offers a wide dynamic range, aberration-free focal length tuning, and can provide both positive and negative lensing effects. Focusing is obtained through dynamic heating of an optical element by an external pump beam. The system is especially suitable for use in interferometric gravitational wave interferometers employing high laser power, allowing for in situ control of the laser modal properties and compensation for thermal lensing of the primary laser. Using CO(2) laser heating of fused-silica substrates, we demonstrate a focal length variable from infinity to 4.0 m, with a slope of 0.082 diopter/W of absorbed heat. For on-axis operation, no higher-order modes are introduced by the adaptive optical element. Theoretical modeling of the induced optical path change and predicted thermal lens agrees well with measurement.     

Optical properties caused by periodical array structure with colloidal particles and their applications

High quality opal films have been attracting much attention due to their novel properties and applications, such as smart materials with structural color, novel photonic/optical devices and three-dimensional photonic crystals. In this article, the author reported a colloidal crystal consisting of cubic closely packed (ccp) polystyrene particles and filled with polydimethylsiloxane (PDMS) elastomer. The array of ccp (111) planes diffracts light of selective wavelengths according to Bragg’s law. The PS-PDMS hybrid opal films exhibit dynamic tuning structural colors. The lattice distance of ccp (111) planes is variable by swelling PDMS elastomer with hydrophobic liquid or by applying mechanical deformation. The hybrid opal films have potential applications in wide fields, for example, in smart sensing materials, color imaging without pigments and strain mapping of plastic deformation.     

High performance photonic microwave frequency down-conversion using a dual-drive dual-parallel Mach-Zehnder modulator

Photonic microwave frequency down-conversion based on carrier suppression single sideband (CS-SSB) modulation via an integrated dual-drive dual-parallel Mach-Zehnder modulator (DP-MZM) is proposed. The MZM on the up path of the DP-MZM is used to generate SSB modulation signal, while the MZM on the bottom path of the DP-MZM is unmodulated. By adjusting the amplitude and phase of the unmodulated optical carrier, two optical carriers are cancelled out, which improves the performance of the system with reduced local oscillator (LO) power and large suppression of mixing spurious sidebands. The frequency down-conversion approach is theoretically analyzed and verified by simulation. Simulation results show that the power of frequency down-conversion signal is at least 39?dB higher than that of the mixing spurious sidebands. Besides, 9.5?dB gain, 2.8?dB noise figure (NF) and 1.9?dB spurious-free dynamic range (SFDR) improvements can be obtained compared with the previous OCS modulation frequency down-conversion scheme while the required LO power is 10?dB, 5?dB and 5?dB lower than that of the OCS modulation scheme, respectively.