Showing papers on "Insertion loss published in 1996"

Long-period fiber gratings as band-rejection filters

Abstract: We present a new class of long-period fiber gratings that can be used as in-fiber, low-loss, band-rejection filters. Photoinduced periodic structures written in the core of standard communication-grade fibers couple light from the fundamental guided mode to forward propagating cladding modes and act as spectrally selective loss elements with insertion losses act as backreflections <-80 dB, polarization-mode-dispersions <0.01 ps and polarization-dependent-losses <0.02 dB.

A surface micromachined electrostatic ultrasonic air transducer

Abstract: Airborne ultrasound has many applications such as, ranging, nondestructive evaluation, gas flow measurement, and acoustic microscopy. This paper investigates the generation and detection of ultrasound in air at a few MHz. Conventional plane piston lead zirconium titanate (PZT) based transducers perform poorly for this application due to the lack of proper matching layer materials. Electrostatic, or capacitive, transducers promise higher efficiency and broader bandwidth performance. The device structure in this work consists of a capacitor where one plate is a circular silicon nitride membrane coated with gold and the other is a rigid silicon substrate. By applying a voltage between the membrane and the silicon substrate, an electrostatic force is exerted on the membrane which sets it in motion, thus generating a sound wave in air. Presented here is an electrical equivalent circuit model for electrostatic transducers which is based on the early work of Mason (1942). The electrostatic transducers were designed and constructed for operation at 1.8 and 4.6 MHz. The transducers were fabricated using standard micromachining techniques. An optical interferometer was used to measure the peak displacement of the 1.8 MHz electrostatic transducer at 230 /spl Aring//V. A transmit-receive system was built using two electrostatic transducers. The system had a signal to noise ratio of 34 dB at a transducer separation of 1 cm. Each transducer had a 3-dB bandwidth of 20%, and a one-way insertion loss of 26 dB. There is excellent agreement between the measured device performance and theoretical predictions.

Micro electromechanical RF switch

Abstract: A micro electromechanical RF switch is fabricated on a substrate using a suspended microbeam as a cantilevered actuator arm. From an anchor structure, the cantilever arm extends over a ground line and a gapped signal line that comprise microstrips on the substrate. A metal contact formed on the bottom of the cantilever arm remote from the anchor is positioned facing the signal line gap. An electrode atop the cantilever arm forms a capacitor structure above the ground line. The capacitor structure may include a grid of holes extending through the top electrode and cantilever arm to reduce structural mass and the squeeze damping effect during switch actuation. The switch is actuated by application of a voltage on the top electrode, which causes electrostatic forces to attract the capacitor structure toward the ground line so that the metal contact closes the gap in the signal line. The switch functions from DC to at least 4 GHz with an electrical isolation of -50 dB and an insertion loss of 0.1 dB at 4 GHz. A low temperature fabrication process allows the switch to be monolithically integrated with microwave and millimeter wave integrated circuits (MMICs). The RF switch has applications in telecommunications, including signal routing for microwave and millimeter wave IC designs, MEMS impedance matching networks, and band-switched tunable filters for frequency-agile communications.

Silica-based optical integrated circuits

Abstract: Silica-based integrated optical waveguide technology is reviewed. Low loss and manufacturable waveguides are made by chemical vapour, flame hydrolysis and electron beam deposition. Fibre to fibre insertion loss is as low as 0.3 dB for a 6 cm long waveguide. Bragg reflective add-drop filters are made with gratings formed by ultraviolet irradiation. The waveguide grating router has found important application as a multiplexer in dense wavelength multiplexed communications systems. Multiplexers with wide pass bands and stop bands are made with Fourier filters: these filters consist of a chain of alternating couplers and delaying arms. The good performance of waveguide grating routers and Fourier filters is due to the high degree of path delay and coupler control achievable by and processing in this technology.

16-channel optical add/drop multiplexer consisting of arrayed-waveguide gratings and double-gate switches

Abstract: An optical add/drop multiplexer that enables full access to 16 individual wavelength channels has been fabricated on the planar lightwave circuit (PLC). The device consists of four arrayed-waveguide gratings which are connected through 16 double-gate thermo-optic switches. The crosstalk characteristics of the optical switches have been improved by adopting a double-gate configuration. The on-off crosstalks from main input or add port to main output or drop port are less than -28.4 dB and the on-chip insertion losses are 7.8-10.3 dB, respectively.

WDM multiplexer-demultiplexer using Fabry-Perot filter array

Abstract: A compact WDM optical device can demultiplex an optical laser signal containing several different wavelengths corresponding to particular channels, and, in reverse operation operate as a multiplexer to interleave several different wavelengths into a multiplexed multi-channel optical laser signal with improved insertion loss characteristics. The optical device includes a linear array of passive resonant optical cavities, in the form of Fabry-Perot filters, extending in a lateral direction and an integral array of associated microlenses extending in the lateral direction. Each microlens has a center which is offset from the central longitudinal axis of an associated Fabry-Perot filter to reflect laser radiation through the device. Each optical cavity is tuned by adjusting the longitudinal dimension thereof to a particular wavelength contained in the multi-channel optical signal. A stepped-wavelength steered laser radiation source for the optical device uses a VCSEL array with offset microlenses. With an additional row of microlenses the optical device can be used for wavelength routing and channel dropping applications. A stepped-wavelength WDM VCSEL array can be similarly organized to form a WDM combiner or multiplexer.

Ultra-high-speed multiple-quantum-well electro-absorption optical modulators with integrated waveguides

Abstract: Integrating the input and output waveguides with a multiple-quantum-well (MQW) electro-absorption (EA) optical modulator is shown to achieve ultra-high-speed modulation while keeping the total device length long enough for easy fabrication and packaging. Testing with fabricated modulators showed that a shorter modulation region results in a larger modulation bandwidth. The additional loss due to the waveguide integration was less than 1 dB. An optimized modulator showed a large modulation bandwidth of 50 GHz, a low driving voltage of less than 3 V, and a low insertion loss of 8 dB. A prototype module of this modulator had a bandwidth of greater than 40 GHz. Optimizing the MQW structure makes the modulator insensitive to polarization. These results demonstrate that MQW-EA modulators with integrated waveguides are advantageous in terms of fabrication, packaging, and ultra-high-speed modulation.

Optical switching and routing system

Abstract: The present invention provides a free space optical switching and routing system utilizing a switchable grating based approach together with novel noise suppression techniques. This family of devices provides for an optical switching and routing system that is useful for interconnecting any of an input array's optical channels to any of an output array's optical channels. The incorporation of free space switched grating based routing in the present invention has several distinct advantages including compactness, a reduction in insertion loss and the number of required switching devices and control signals, and improvements in switch isolation, noise and crosstalk suppression, spurious reflections, data skew, and compactness.

Rapidly tunable narrowband wavelength filter using LiNbO/sub 3/ unbalanced Mach-Zehnder interferometers

Abstract: We demonstrate a rapidly tunable narrowband wavelength filter using unbalanced Mach-Zehnder interferometers in lithium niobate. It is designed to switch among eight channels spaced 50 GHz apart in optical frequency (approximately 0.4 nm in wavelength) in less than 50 ns. The insertion loss is 19 dB and crosstalk is less than -22 dB. The filter consists of a cascade of three electrooptically tunable unbalanced Mach-Zehnders and a feedback circuit to keep the filter centered on the desired wavelength.

Polarisation-independent InP arrayed waveguide filter using square cross-section waveguides

Abstract: The authors report a highly polarisation-independent InP arrayed waveguide filter using square cross-section waveguides. A TE-TM shift of <0.01 nm and polarisation-dependent loss of <0.1 dB was obtained for an 8/spl times/1.6 nm filter operating at 1.5 /spl mu/m. Fibre-to-fibre insertion loss was just 6.7-7.3 dB, with channel crosstalk <-26 dB.

Arrayed-waveguide grating multiplexer with loop-back optical paths and its applications

Abstract: We present a basic configuration of an unique integrated-optic arrayed-waveguide grating (AWG) multiplexer with loop-back optical paths and demonstrate an add-drop multiplexer (ADM), a network access terminal, and a wavelength channel selector for dense-WDM ring or bus networks, as three useful examples of its attractive applications. A key device in these components is a silica-glass based 1.55 /spl mu/m polarization-insensitive 32/spl times/32 AWG multiplexer chip with 0.8 nm channel spacing which is fabricated using planar lightwave circuit (PLC) technologies. Fine operation in their new functional components is achieved by using the AWG multiplexer module having low insertion loss of 3.9 dB and low interchannel crosstalk of less than -28 dB.

Fabrication of 128-channel arrayed-waveguide grating multiplexer with 25 GHz channel spacing

Abstract: A 128-channel arrayed-waveguide grating multiplexer with 0.2 nm (25 GHz) channel spacing at 1.55 /spl mu/m has been fabricated using a planar lightwave circuit (PLC). The authors obtained a crosstalk of less than -16 dB to neighbouring and all other channels. The on-chip insertion loss ranged from 3.5 to 5.9 dB for central and peripheral output ports, respectively.

Characterization of air-coupled transducers

Abstract: This paper describes a theoretical and experimental study for determination of the through-air system impulse response and insertion loss with different air-coupled ultrasonic transducers. Wide-band piezopolymer transducers (PVDF) are employed in both transmission and reception modes and their behavior assessed by means of mathematical modeling and experiment. Specifically, a linear systems approach, modified to include the influence of attenuation in the propagation medium, was used to design suitable PVDF transducers for wide-band operation in air. Suitable devices were then manufactured for determination of the transmission and reception response characteristics of piezocomposite and electrostatic transducers when operating in the air environment. A range of transducers was evaluated, including 1-3 connectivity composites of different ceramic volume fraction and mechanical matching conditions, in addition to electrostatic devices of varying design. To complement the investigation, relative performances for narrow-band operation are also presented under transmission and transmit-receive conditions. Despite the obvious measurement difficulties, good agreement between theory and experiment was observed and the methodology is shown to provide a convenient and robust procedure for comparison of through-air transducers operating in the frequency range 50 KHz to 2 MHz. Although highly resonant, the most effective composite transducers under consideration demonstrate an improvement in two-way insertion loss of 22.4 dB and 11.5 dB over a corresponding electrostatic pair, under narrow-band and wide-band operation, respectively.

High power DPDT antenna switch MMIC for digital cellular systems

Abstract: In this paper, we propose two new types of dual-pole double-throw (DPDT) switch GaAs JFET monolithic microwave integrated circuits (MMICs) for digital cellular handsets. These ICs have the excellent characteristics of low insertion loss and high power handling capability, even with a low control voltage by stacking three JFETs with shallow V/sub p/ and using a novel bias circuit using p-n junction diodes. One DPDT switch IC has two shunt FET blocks and can achieve high isolation without external parts. An insertion loss less than 0.6 dB and isolation over 25 dB up to 2 GHz were achieved. P/sub 1dB/ was about 35 dBm even with a control voltage of 0/3 V. Another DPDT switch IC utilizes parallel resonance of external inductors and parasitic capacitance between the drain and the source of the OFF-state FETs. By attaching 15 nH inductors, for example, the IC exhibited an insertion loss as low as 0.4 dB, an isolation of better than 40 dB at 1.5 GHz, a bandwidth of about 400 MHz for 20 dB isolation, and P/sub 1dB/ of about 34 dBm with the 0/3 V control.

Optical time domain reflectometer with internal reference reflector

Abstract: An optical time domain reflectometer suitable for determining its front panel insertion loss comprises a four-port coupler having first and second ports connected to a light source and an optical detector, respectively, and third and fourth ports connected to a front panel connector and a reference reflector, respectively. In use, a fiber-under-test is connected to the front panel connector. The coupler splits light from the light source between the front panel connector and the reference reflector and couples light returning from the front panel connector and reflector to the detector. The optical path between the front panel connector and the coupler is longer than the optical path between the reference reflector and the coupler by such a distance that a Fresnel reflection pulse from the reference reflector, produced by a pulse emitted by the light source, will be received by the detector before a corresponding reflection pulse returned from the front panel connector. In order to ensure that the two reflection pulses can be distinguished from each other, the difference between the two optical paths is greater than a distance equal to an event dead zone for the particular width of pulse supplied by said light source. The reference reflector comprises an end portion of a length of optical fiber, preferably encapsulated with a material having a refractive index different from that of the length of optical fiber. The OTDR facilitates miniaturization because it avoids the use of an internal length of reference fiber.

Fabrication and characterization of high-speed polyurethane-disperse red 19 integrated electrooptic modulators for analog system applications

Abstract: The fabrication and characterization of polymeric electrooptic modulators, made of a thermally crosslinkable polyurethane with Disperse Red 19 side chains, are summarized in this paper. Straight channel and Mach-Zehnder modulators have been fabricated, packaged and tested for the fiber-optic analog transmission system applications. Device performances including halfwave voltage, insertion loss, on-off ratio, and modulation frequency responses were measured. Long-term halfwave voltage stability, dc-bias voltage stability, and optical power handling capability at 1.3-/spl mu/m wavelength were investigated. A carrier-to-noise ratio of 53 dB and 80-channel television transmission have been demonstrated using the packaged polymer modulators.

A high-Q broad-band active inductor and its application to a low-loss analog phase shifter

Abstract: The proposed high-Q broad-band active inductor utilizes frequency-insensitive negative resistance to compensate constant internal losses caused by the drain-to-source conductance of the field-effect transistors (FETs), the dc bias circuit, and several other factors. The measured frequency range of the fabricated InAlAs/InGaAs/InP HEMT active inductor is 6 to 20 GHz for Q values greater than 100, and 7 to 15 GHz for Q values greater than 1000. A low-loss analog phase shifter is also fabricated at C-band. This is constructed with the active inductors, the varactor diodes and the low-loss multilayer broad-side coupler in a MIC structure. Since the constant negative resistance of the active inductors also compensates the line loss of the coupler and the varactor diodes' series resistance, the measured results show a good insertion loss performance with a large phase shift. A phase shift of more than 225/spl deg/ within a 0.8 dB insertion loss from 4.7 to 6.7 GHz, another of more than 180/spl deg/ within 1.3 dB insertion loss from 3.7 to 8.5 GHz, and one more of more than 90/spl deg/ within 1.4 dB insertion loss from 3.5 to 10.6 GHz were obtained.

High-speed polarization scrambler with adjustable phase chirp

Abstract: We report on the operation and performance of a novel electrooptic polarization scrambler that is capable of generating any desired combination of optical phase and polarization modulation. The scrambler comprises a dual-drive Mach-Zehnder-type intensity modulator on lithium niobate and an external microoptic polarization splitter which combines the two complementary outputs of the integrated-optic intensity modulator in orthogonal polarization states. The modulation indexes of the sinusoidal phase and polarization modulation in the output light can be varied independently of each other via the amplitudes and phases of the two drive voltages to the Mach-Zehnder modulator. The scrambler has a 3-dB modulation bandwidth of 14 GHz and operates in the 1.5-1.6-/spl mu/m wavelength range with an overall fiber-to-fiber insertion loss of less than 5 dB. At 5 GHz modulation frequency and electric drive powers between 390-2030 mW, we demonstrate phase-chirped and chirp-free depolarization with a residual degree of polarization of less than 0.02 and continuously variable phase modulation to 2.3-rad peak phase deviation.

Polymeric phased array wavelength multiplexer operating around 1550 nm

Abstract: A polymeric, optical fibre compatible, 8/spl times/8 phased array wavelength multiplexer with 400 GHz (3.2 nm) channel spacing, has been designed and realised for operation in the 1550 nm erbium doped fibre amplifier (EDFA) window. By using bending radii as small as 20 mm, the device measures only 64/spl times/4 mm. The fibre to fibre insertion loss in the passbands varies between 6.6 and 8.0 dB and the crosstalk is -25 dB.

Single-layer dipole array for linear-to-circular polarisation conversion of slotted waveguide array

Abstract: A single-layer linear-to-circular polarisation converter is proposed for an application to a slotted waveguide planar array. It consists of dipoles which closely couple to slot arrays. The method of moments clarifies the mutual coupling between the dipoles and the slots on the waveguide. Numerical results promise the use of a uniform and parallel dipole array as a single-layer linear-to-circular polarisation converter for an existing linearly polarised slotted waveguide array. The measurements using a linearly polarised slotted waveguide array in 22.0 GHz band confirm the prediction; the axial ratio less than 1 dB and a negligible insertion loss is realised.

Simultaneous bi-directional analogue fibre-optic transmission using an electroabsorption modulator

Abstract: Full-duplex analogue fibre-optic transmission is demonstrated using a single low-insertion-loss electroabsorption device as a simultaneous photodetector-receiver and modulator-transmitter at the remote end. Optimisation of the bias voltage results in an RF insertion loss of /spl sim/42 dB, each way, with minimal intermodulation distortion.

Filter-embedded wavelength-division multiplexer for hybrid-integrated transceiver based on silica-based PLC

Abstract: A thin film filter-embedded wavelength-division multiplexer is designed for a hybrid-integrated WDM transceiver based on a silica-based PLC platform. A compact multiplexer with a low insertion loss of 1.1 dB and a low crosstalk of <-50 dB is successfully fabricated.

2 × 2 Single-mode fiber routing switch

Abstract: An all-fiber 2 × 2 acousto-optic routing switch is described that has an insertion loss of 0.11 dB, a drive power of 1.5 mW, and a switching time of 80 μs. The switch has a very simple construction and so has the potential to be low in cost.

Design and realization of polarization independent phased array wavelength demultiplexers using different array orders for TE and TM

Abstract: A method for designing polarization independent phased-array wavelength demultiplexers, using different array orders for TE and TM, is described and analyzed with respect to fabrication variations. Flattening of the wavelength response is shown to improve fabrication tolerances. A four channel phased-array wavelength demultiplexer with at least 0.2 nm of polarization independent flattened response for each channel (spacing 1 nm) has been made with an insertion loss of 1.5-3 dB and a crosstalk of -17 to -19 dB.

L-band internally matched Si-MMIC front-end

Abstract: A 1.9 GHz-band internally matched Si-MMIC front-end, fabricated in standard 0.8 /spl mu/m BiCMOS process, was developed. This IC front-end contains a MOSFET T/R switch, a two-stage BJT low noise amplifier (LNA), and a down converter BJT mixer. Since the circuits are monolithically integrated on a low resistivity Si substrate, the coplanar waveguide (CPW) type spiral inductors are used to reduce the dielectric loss of on-chip matching circuits. The T/R switch has measured insertion loss of 2.5 dB and isolation of 25.5 dB at 0/3 V control voltage. The two-stage LNA has gain of 17.1 dB and noise figure (NF) of 2.9 dB at 2 V, 4 mA dc supply. The mixer has conversion gain of 5.9 dB and NF of 15 dB at 2 V, 1.7 mA dc supply. The measured performance of the fabricated Si-MMIC front-end indicates the possibility of application to mobile communication handset terminals.

Continuous-fiber modulator with high-bandwidth coplanar strip electrodes

Abstract: Operation of a continuous-fiber modulator based on coupling from a fiber side-polished beyond cut-off to a multimode planar waveguide has been demonstrated for the first time at gigahertz frequencies. The bandwidth of the modulator electrode structure was /spl sim/4 GHz while the optical insertion loss was measured at <0.5 dB. The device was used to produce mode-locked pulse trains in an erbium fiber laser at repetition rates of /spl sim/3 GHz.

W-band SPST transistor switches

Abstract: A single-pole, single-throw (SPST) transistor switch has been developed, Three types of switches, that is, GaAs MESFET, AlGaAs-GaAs HEMT, and pseudomorphic HEMT (PM-HEMT), have been fabricated, and the performances at W-band are compared. To reduce on-state resistance and off-state capacitance, gate length was varied as a parameter. Moreover, an inductance for resonance was installed in parallel to the off-state capacitance between source and drain to obtain a high isolation, A relatively low insertion loss of 1.6 dB and a high isolation over 20 dB at W-band have been obtained from the 0.8-/spl mu/m gate length PM-HEMT.

Novel low-loss delay line for broadband phased antenna array applications

Abstract: The microwave propagation velocity along a nonlinear transmission line is a function of dc bias, hence, a nonlinear transmission line (NLTL) can be utilized as a broadband delay line. A hybrid NLTL has been fabricated in a proof-of-principle experimental concept test where a 1.1-ns true time delay with <4-dB insertion loss has been measured in good agreement with theory. A 2/spl times/2 NLTL-based antenna array has been utilized to demonstrate beam steering at 5 GHz. Using parameters appropriate to varactors tested by our group at 60 GHz, a monolithic NLTL is predicted to exhibit <3.4-dB insertion loss and 200 ps delay at 20 GHz.

Passive DWDM components using MicroPlasma optical interference filters

Abstract: Summary form only given Thin-film resonant cavity filters have been incorporated into passive wavelength-division multiplexing (WDM) components by a number of vendors However, when conventional filter technology has been applied to narrow-band DWDM applications, several shortcomings become evident, such as poor temperature and environmental stability, high insertion loss, or poor bandpass spectral shape Typically, these problems can be traced primarily to defects with film morphology such as: porosity, scatter, absorption, columnar structure, inhomogeneity, or lack of accurate thickness control OCA has developed a technology to deposit ultranarrow band resonant cavity interference filters, which solves the performance problems associated with conventional thin films The technique, which goes by the trade name MicroPlasma, is an energetic high vacuum physical vapor deposition (PVD) process, which uses refractory metal-oxide coating materials such as silicon dioxide and tantalum pentoxide

Uniplanar power dividers using coupled CPW and asymmetrical CPS for MICs and MMICs

Abstract: Uniplanar coplanar waveguide (CPW), coplanar strip (CPS), and slotline on dielectric substrates have many applications in microwave integrated circuit (MIC) and monolithic microwave/millimeter wave integrated circuit (MMIC) designs. New power dividers using one-section and two-section coupled CPW have been developed. These circuits provide substantially improved performance over a wider bandwidth than conventional microstrip power dividers. Measured results show that the one-section CPW power divider has greater than 20-dB isolation, less than 0.3-dB insertion loss, a 0.2-dB power dividing imbalance, and a 20 phase imbalance over a bandwidth of more than 30% centered at 3 GHz. The two-section CPW power divider has greater than 24-dB isolation, less than 0.5-dB insertion loss, a 0.1 dB power dividing imbalance, and a 1.6/spl deg/ phase imbalance over a bandwidth of more than 66% centered at 3 GHz. Experimental results agree well with calculated ones. In-phase and 180/spl deg/ out-of-phase power dividers constructed by the circuit configuration method are described in this paper. The even-odd mode excited method is used to analyze the power dividers. Also two other power dividers using asymmetrical coplanar strip (ACPS) have been developed with good performance. A 180/spl deg/ out-of-phase power divider is demonstrated with an amplitude imbalance of 0.4 dB and a phase difference of 180/spl deg//spl plusmn/1/spl deg/ over a wide bandwidth.