Nicholas Madamopoulos

Synchronous amplitude and time control for an optimum dynamic range variable photonic delay line

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.

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.

High signal-to-noise ratio birefringence-compensated optical delay line based on a noise-reduction scheme

A multichannel fiber-optic delay-line architecture based on optical polarization switching is proposed that uses non-polarization-maintaining optical fibers. Critical birefringence-compensation and noise-reduction techniques are introduced and demonstrated for these delay lines, which show a high optical polarization extinction ratio (>39 dB) and a high electrical signal-to-noise ratio (>92 dB).

Directly modulated semiconductor-laser-fed photonic delay line with ferroelectric liquid crystals

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.

Polarization selective hologram-based photonic delay lines

Abstract The use of polarization selective holograms as optical signal routing elements for the implementation of photonic delay lines (PDLs) is proposed. A single bit PDL using ferroelectric liquid crystal (FLC) devices as active polarization switches and polymer dispersed liquid crystal (PDLC) devices as polarization selective holograms for optical path routing is experimentally demonstrated and characterized. Different within-channel leakage noise filters for improved PDL performance are discussed and experimentally demonstrated. Record high optical signal-to-leakage noise ratios (>45 dB) are obtained for both PDL settings using a combination of the proposed noise filters. An alternative reflective PDL architecture is also proposed. This reflective architecture requires half the physical length for each path compared with the transmissive design to obtain the same time delays. Other polarization dependent optical router designs based on birefringent-mode nematic liquid crystal (NLC) devices are also proposed.

All-fiber connectorized compact fiber optic delay-line modules using three-dimensional polarization optics

Compact and all-fiber connectorized photonic delay-line modules based on three-dimensional bulk polarization optics are proposed and experimentally demonstrated. The modules are built on a single optical microbench and demonstrate optical leakage noise performance of ?40 dB at switching speeds of 10 ?s. Insertion loss analysis is also performed. A special gradient-index lens fiber optic collimator design is proposed to further reduce the optical insertion loss of the delay-line module. A wavelength-dependent design is also proposed for expanding the applicability of the PDL module to multichannel operation.

Photonic time-delay beam-forming architectures using polarization switching arrays

Photonic time delay line (PTDL) architectures have been proposed for transmit/receive mode antenna applications. These architectures are based on two dimensional pixelated optical arrays that act as optical polarization switching elements. Such elements can be nematic liquid crystal (NLC) arrays, ferroelectric liquid crystal (FLC) arrays, and magneto-optic arrays. Optical delay lines can be formed using either free space or solid optics propagation, as well as non-polarization maintaining fiber propagation for the case of long time delays. In this paper, various optical array based optical beamformer architectures are presented and compared. These different architectures are based on Thompson polarization beamsplitters, and polarizing cube beamsplitters, for both transmissive and reflective geometries. A novel ternary time delay architecture is also introduced that can give 3N different time delay settings. In addition, a novel wavelength multiplexing architecture using a single channel dispersive fiber PTDL in cascade with multichannel PTDL is proposed for further hardware size and weight reduction.

Microwave band demonstration of a reflective geometry fiber and free-space binary photonic delay line

For the first time, a modulated 2-b, one-channel binary switched, photonic time delay system (PTDS) is demonstrated that is based on a compact reflective optical delay path geometry that consists of one free-space delay line and one non-polarization-maintaining (PM) fiber delay line. Polarization switching using birefringent-mode nematic liquid crystals and a polarization noise-reduction technique are used to minimize the optical noise when using the cube polarization beamsplitters (PBSs) required in the reflective geometry delay. This gives the high electrical signal-to-noise ratios measured from 52 to 89 dB for the four settings of the delay line.

Adaptable-delay balanced-loss binary photonic delay line architectures using polarization switching

Abstract A photonic delay line (PDL) architecture that gives balanced loss switched states is proposed and demonstrated. This balanced loss performance leads to balanced optical signal flow through the delay line, as is critically required in many signal processing applications. The balanced PDL module design also provides efficient usage of optical power. This module is based on a compact reflective and symmetric optical layout geometry. It is also adjustable to a wide range of time delays, from subpicoseconds to tens of nanoseconds, hence the adaptable nature of hardware. Theoretical analysis as well as experiments are performed to make comparisons with the previously demonstrated reflective PDL architecture. Issues such as electrical signal-to-noise ratio and relative output signal power between the two PDL settings are discussed. In addition to the new adaptable delay balanced loss PDL, two novel hardware compression techniques based on wavelength multiplexing and polarization multiplexing are proposed that can be used with the adaptable PDL architecture to realize multichannel PDLs.

Photonic security system using spatial codes and remote coded coherent optical communications

A novel photonic security system is described using 2-D spatialncodes based on both optical phase and amplitude information. Thisnsecurity system consists of an optical interferometric encoding subsystemnthat rapidly reads and encodes the 2-D complex-valued spatialncode, forming a wideband frequency modulated optical beam and ancolinear optical reference beam. After appropriate coherence coding ofnthis beam pair, the light is launched into a low probability of interceptncommunication channel such as an optical fiber or a narrow beamwidthnfree-space optical link. At the remote code receiving and data processingnsite, the received light beam pair is first coherently decoded. Then, anhigh speed photodetector via optical heterodyne detection generates annencoded wideband radio frequency signal that contains the original 2-Dncode. Decoding is implemented in parallel via two independent systems.nOne decoder uses a Fourier transforming lens to reconstruct an electronicnimage interferogram of the complex-valued user code. This imageninterferogram is sent to a high speed electronic image processor fornverification purposes. The other decoder is a high speed coherentnacousto-optic time integrating correlator that optically determines matchmismatchnbetween the received encoded signal and the code signalngenerated by the electronic database. Improved security to the overallncommunication network is added by using various keycodes such as antime varying keycode that determines the exact spatial beam scanningnsequence required for both proper encoding and decoding of the 2-Dncode information. This paper describes preliminary experiments using ansimple 1-D amplitude modulated spatial code.