Showing papers on "Optical Carrier transmission rates published in 1993"

Fiber-optic prism true time-delay antenna feed

Abstract: Experimental results for an optical-control technique for implementing a true time-delay function for array antennas are reported. A microwave signal is transmitted on a wavelength-tunable optical carrier through a fiber-optic prism-a set of nominally equal-delay fibers with differing net dispersion-to photodetectors that feed each antenna element. The relative interelement time-delay (beam angle) adjustment is accomplished by tuning the optical carrier wavelength. Measured antenna patterns of a two-element array clearly demonstrate beam steering and true time-delay operation over a two-octave bandwidth of 2-8 GHz. >

A coherent optically controlled phased array antenna system

Abstract: A true-time delay, optically controlled phased array antenna system whereby a large number (100-2500) of antenna elements can receive a series of microwave delays via use of a coherent optical carrier signal is described. Both transmit and receive antenna arrays are described, and the signal-to-noise ratio for a 128 channel system is calculated to be approximately 40 dB with an optical link loss of only approximately 3 dB for a 1 GHz instantaneous bandwidth at a wavelength of lambda 1.55 mu m. It is shown that the use of coherent optically controlled phased array antennas provides improved controllability and immunity from noise and system losses over other architectures currently being investigated. >

Pulse time modulation techniques for optical communications: a review

Abstract: The principal factor in realising a high-performance bandwidth-efficient fibre communication system at an acceptable cost is the choice of modulation format on the optical carrier. In this context, pulse time modulation (PTM) techniques represent an attractive alternative to purely digital or analogue methods. The PTM family is reviewed, a classification system is proposed and their potential for use in high-speed fibre systems intended for the transmission of analogue data is examined.

Optical carrier filtering for signal/noise and dynamic range improvement

Abstract: A method and apparatus for improving the signal-to-noise ratio (SNR) and dynamic range of an optical fiber system. An optical fiber system (10) includes a laser(12) that produces a coherent light signal conveyed over an optical fiber (14) to a Mach-Zehnder modulator (16). An input signal modulates the coherent light, producing modulated side bands, which together with the carrier comprise a modulated light signal. The modulated light signal is filtered using an integrated optical filter (24) that substantially attenuates the carrier frequency, while passing light at the frequency of the modulated side bands. A detector (28) demodulates the filtered light with a substantially greater SNR than would otherwise have been possible. In one preferred form of the invention, the integrated optical filter comprises an imbalanced interferometer (40), and in another embodiment, tile interferometer produces imperfect nulls aligned with the carrier frequency. A relatively higher power laser(12) can be used without damage to detector (28), since the integrated optical filter substantially reduces the average power of the modulated light by attenuating the carrier, thereby enhancing SNR and dynamic range of the system.

Method for linearizing an unbalanced Mach Zehnder optical frequency discriminator

Abstract: An unbalanced Mach Zehnder optical frequency discriminator is linearized to suppress third order nonlinear distortion. An optical carrier that is modulated in optical frequency is input to an unbalanced Mach Zehnder interferometer to discriminate RF information signals carried on the carrier. The Mach Zehnder interferometer has an adjustable operating point. The operating point is adjusted to a point where the output intensity of the Mach Zehnder interferometer is no more than about ten percent of its maximum value. In order to avoid problems with second order distortion, the optical carrier is modulated with RF signals that do not occupy more than a single octave. The operating point of the device can be adjusted by adjusting an electrical bias thereof, by adjusting the wavelength of the optical carrier, or by adjusting the temperature of the device.

Optical transmission system for transmission of signals with a continuous application of the signals during transmission

Abstract: An optical transmission system for the transmission of optical signals in a wave-division multiplex on a plurality of neighboring optical carrier wavelengths is characterized by the fiber being doped to form a continuously distributed waveguide amplifier over the entire length of the transmission waveguide. To pump the waveguide amplifier, which is continuously distributed along the transmission waveguide, several arrangements are provided. This system can be operated as a unidirectional system or a bidirectional system.

Linear electroabsorptive modulator and related method of analog modulation of an optical carrier

Abstract: Apparatus, and a corresponding method for it use, for directly modulating an optical carrier with a radio-frequency (rf) electrical signal. A semiconductor electroabsorptive modulator is operated at an optical wavelength and electrical bias voltage carefully selected to provide a near-linear electrical-to-optical transfer characteristic and to keep rf insertion loss low. Further reduction of insertion loss is achieved by use of an extremely short device, or a single quantum well device configuration, or both. Linearity is further optimized by choosing an appropriate combination of optical polarization mode, optical reflectivity of the device facets, and the number and physical properties of multiple quantum wells.

Fiber channel (FCS)/ATM interworking: a design solution

Abstract: The paper addresses the main functions of a gateway between the fibre channel standard (FCS) and an ATM network. The fibre channel provides a general transport vehicle for upper layer protocols such as the intelligent peripheral interface (IPI), small computer system interface (SCSI), high-performance parallel interface (HIPPI) data framing and others at scalable speeds of 265 Mbit/s, 531 Mbit/s and 1.06 Gbit/s. ATM wide area networks will provide cell based transmission and switching at rates of 155 Mbit/s and above. The paper describes design solutions to obtain very high throughput using hardware processing and careful protocol functions relaying between the two standards. >

Network interfacing method and a network interface for a digital transmission network

Abstract: A method for establishing a user-network interface in a digital transmission network for a cell-based digital 140 or 155 Mbit/s ATM signal, and a network interface embodying the method. The interface includes an input buffer controlled by a predetermined policing function for receiving the cell-based signal and adapting the transmission speed of the signal to the actual transmission speed of the transmission network; a mapper for forming cell blocks of N consecutive cells from the cell-based signal and for adding N overhead bytes to each cell block; and a multiplexer for multiplexing the output signal of the mapper byte by byte into N separate output signals of about 1.5 Mbit/s, 2 Mbit/s, 6 Mbit/s or 8 Mbit/s.

Optical demultiplexing system

Abstract: Optical demultiplexing system, wherein from an optical carrier modulated by a TDM data flow the wanted tributary is extracted as an optical signal. The system makes use of a semiconductor optical amplifier, whose gain is modulated due to saturation effect. The amplifier receives both the modulated optical carrier and one or a plurality of sampling optical carriers, with wavelengths different from that of the modulated carrier. One or a plurality of optical filters supply at the output the tributaries by extracting from the amplifier output the sampling carriers modulated by data signals.

Dual frequency optical carrier technique for transmission of reference frequencies in dispersive media

Abstract: Two different carrier frequencies modulated by a reference frequency are transmitted to each receiver to be synchronized therewith Each receiver responds to local phase differences between the two received signals to correct the phase of one of them so as to maintain the corrected signal as a reliable synchronization reference

Two optical-control techniques for phased array: interferometric and dispersive-fiber true time delay

Abstract: We describe and present experimental results for two optical control techniques for phased array antennas. The first technique is based on interferometric heterodyning of two narrow- linewidth YAG lasers for the generation of required microwave signal and for simultaneous steering of the radiated beam. The constructed system is simple and well-suited for narrowband applications, and it may be built without any active mechanical components. The measured radiated antenna patterns are in close agreement with the predicted ones. The second technique is a novel and elegant method for implementing a true time-delay function for optical control. It relies on using a wavelength-tunable laser to provide the optical carrier for the microwave signal and a fiber-optic prism--a set of equal delay fibers with differing net dispersion. The relative interelement time-delay (beam angle) adjustment is accomplished by tuning the optical carrier wavelength. The experimental results obtained on a compact antenna range clearly demonstrate beam-steering and true time-delay operation over a two-octave bandwidth.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

High speed optical detectors for monolithic millimeter wave integrated circuits

Abstract: Metal-semiconductor-metal photodiodes with interdigitated Schottky barrier fingers are being developed for applications in monolithic optical receiver circuits with the purpose of detecting millimeter-wave modulation signals being transmitted via an optical carrier. The devices are planar and incorporate submicron finger spacings and a thin absorption region for speed with a buried stack of tuned Bragg reflectors for enhanced sensitivity at the carrier wavelength. These devices are being integrated with short-gate MODFET (modulation-doped field-effect transistor) amplifiers to form the complete monolithic integrated optical receiver circuit. Device measurements indicate a top surface reflectance of 0.5% with an operation bandwidth in excess of 40 GHz and a dynamic range of 33 dB. >

Multifrequency modulation for high-sensitivity coherent optical systems

Abstract: A new instantaneous multilevel modulation format is proposed that allows the optical bandwidth to be fully exploited without requiring an electrical bandwidth of the same order of magnitude. The format is more efficient than multilevel wide-deviation frequency-shift-keying (FSK), suffering only a limited penalty with respect to coherent pulse position modulation. The modulated signal is generated by the same criterion adopted for multilevel wide-deviation FSK, but for each optical carrier a modulation format more efficient than binary amplitude-shift-keying (ASK) is chosen. Multilevel four-quadrature modulation is used. In order to obtain power-efficient signaling, the transmitted symbols are associated with the field configurations in such a way that just one frequency carrier at a time is modulated. >

Multigigabit, Multichannel Lightwave Networks Using Subcarrier Multiplexing

Abstract: A novel multigigabit, multichannel lightwave network is described which uses subcarrier multiplexing to place multiple information channels and a baseband control channel on a single optical carrier. The control channel uses an FDDI-like token-passing access protocol and a 100 Mb/s control channel to provide efficient access to many Gb/s of information. The subcarrier multiplexed network (SCM-NET) can simultaneously transport many forms of information including variable-length data-grams, ATM-cells, and connection-oriented video traffic. By channelizing the total throughput, the reduction in utilization efficiency caused by propagation delay between nodes is significantly improved relative to conventional single-channel gigabit networks.

Organic polymer integrated optical channel waveguide devices

Abstract: Results of e-beam-written electro-optic (EO) organic polymeric integrated optical (IO) channel waveguide devices developed for onboard satellite applications are reported. Processing for both strip-loaded and ridge guide structures was developed to fabricate several types of devices, such as linear and curved waveguides, optical power splitters, combiners, and phase modulators, on a 3-in.-diameter silicon wafer. A large number of polished, butt-coupled devices were tested for optical loss and EO modulation at 830- and 1,310-nm wavelengths. These devices are highly reproducible, capable of very high frequency modulation (currently at 18 GHz) with a small rf drive (0 dBm), and can be made reasonably long if required. For the optical phase modulation measurements, both subcarrier modulation with phase-sensitive detection by a lock-in amplifier, and direct detection of the rf-modulated optical carrier in a lightwave analyzer, were used. The short- and long-term stability of the corona-poled EO polymer films investigated by second harmonic generation were found to be good. IO channel waveguide development considerations leading to above performance characteristics also are presented.

Optical fiber communication method

Abstract: PURPOSE:To reduce the deterioration of the reception sensitivity and to extend the transmission available range by reducing or compensating waveform distortion due to self phase-modulation generated in an optical fiber. CONSTITUTION:A synthesizer 5 synthesizes outputs of the pre-chirp wave generators 1-1,... 1-n applying intensity modulation to information to be sent at the speed 1/n (n is a positive integer) of the speed of the information based on the data outputted from a data generator 4 and applying frequency modulation to the optical carrier in one time slot. Then the output of the synthesizer 5 is sent to an optical fiber 6 provided with optical amplifiers 7-1,..., 7-m (m is a positive integer) used as repeaters on the halfway. The transmission signal light is transmitted through the optical fiber 6 and subjected to envelope detection or square detection by an optical receiver 8. Then the deterioration in the reception sensitivity is reduced by using a frequency displacement adjusting device 3 to adjust the frequency displacement of the pre-chirp wave generators 1-1,..., 1-n.

Optimal transmission condition of nonlinear optical pulses in single-mode fibers

Abstract: Optimal conditions for transmission of nonlinear optical pulses in single-mode fibers are presented. When an optical pulse propagates in a fiber, it suffers fiber loss, group velocity dispersion, and self-phase modulation. An optimal output pulse can be obtained by choosing a suitable optical carrier wavelength and an initial input pulse. The system under optimal conditions not only has a more stable performance than the dispersion-free system, but also achieves maximum transmission bit rate for a fixed transmission distance. A bit-length product up to 8550 Gb/s-km or more can be achieved by using dispersion-shifted fibers without amplification. >

High speed optical detectors for monolithic millimeter wave integrated circuits

Abstract: Metal-semiconductor-metal photodiodes with interdigitated Schottky barrier fingers are being developed for applications in monolithic optical receiver circuits with the purpose of detecting millimeter wave modulation signals being transmitted via an optical carrier. The devices are planar and incorporate submicron finger spacings and a thin absorption region for speed with a buried stack of tuned Bragg reflectors for enhanced sensitivity at the carrier wavelength. These devices are being integrated with short-gate MODFET amplifiers to form the complete monolithic integrated optical receiver circuit. >

Space-qualified fiber optic link for radar altimeter applications

Abstract: This paper reports on the system design of an rf-modulated optical link for spaceborne radar altimeter applications and presents results of rf carrier phase noise and phase stability measurements. Our study involved the transmission of rf-modulated optical signals at 834 nm wavelengths using Bias-T and Mach-Zehnder modulators. The rf/microwave signals' phase coherence, modulation levels, and insertion loss are reported. Phase noise measurements revealed a noise floor of at least -118 dBc/Hz at frequencies greater than 100 Hz from a 5-MHz carrier with direct modulation. The phase noise was degraded by about 10 dBc/Hz for external modulation techniques. The rf insertion losses appear smallest for the Bias-T intensity modulators (approximately 30 dB at an 834 nm optical carrier with 5 MHz modulation). The results of modulation experiments with 320 MHz radar altimeter chirps are also presented with an emphasis on coherence, stability, and rise and fall time. The linear FM chirp signal ramps down at a rate of -3.125 MHz/microsecond(s) (+/- 0.5%) and is flat to within +/- 1 dB. Measurements show that this type of FM chirp modulated on optical carriers at 834 nm meets radar altimeter system requirements.

Device for generating feedback signals to regulate optical monitoring circuits (PLL)

Abstract: An optical device for generating a modulated, phase controlled RF carrier by combining a modulated optical carrier signal having a first frequency with an unmodulated optical reference signal having a second frequency. The modulated and unmodulated signals are polarized on orthogonal axes and are transmitted in a single optical waveguide. Modulation of the optical carrier is performed, for example, by means of an integrated optical device which modulates only one polarization direction.

A N+2 protection switching system for synchronous STM-1 signals and plesiochronous 140 Mbit/s signals by using two carrier technique

Abstract: The availability of a high capacity radio link mainly depends on the reliability of the radio system and the occurrence of fading events. For improving availability and quality of a radio relay link there are protection channels added to the operating channels. In the configuration 1+1 one protection channel is assigned to each operating channel. In the configuration n+2 two protection channels are provided for up to n operating channels. The article describes a protection switching system which was designed for line protection. The system is able to handle STM-1 signals (155 Mbit/s) as well as plesiochronous 140 Mbit/s signals. All special requirements concerning two-carrier systems were taken into consideration.

Implementing a flexible synchronous network

Abstract: The SYNET project, undertaken by Deutsche Telekom to modernize its transmission network, is discussed. The SYNET technology is based on the synchronous digital hierarchy (SDH), which uses synchronous transport modules of 155 Mbit/s (STM-1). The latter include a maximum usable bit rate of about 50 Mbit/s as well as a variety of additional information intended for network management. Since the transmission network is divided into several network levels characterized by different traffic loads and structures, a range of synchronous components geared to the requirements of the different network levels have been developed. The major differences between the trunk network and the local networks are described. The implementation of SYNET is reviewed. >

Low-distortion laser system for amplitude- modulated optical fiber communication use

Abstract: PURPOSE: To eliminate a distortion component generated by the laser transmitter of an analog optical transmission system CONSTITUTION: A first optical carrier is modulated by using an information signal and a second optical carrier is modulated by inverting the information signal The modulated first and second carriers are multiplexed into a single optical signal and the optical signal is transmitted through an optical-fiber transmission line A receiver divides the optical signal into the carriers and restores the information signal and the inverted information signal Then the receiver provides the information signal of an electrical area which is reduced in distortion by coupling both restored signals with each other Therefore, a double detector balanced photodiode pair can be used for providing an analog RF output by coupling the restored information signal and inverted information signal This device is practically suitable for the transmission of AM-VSB television signals

Comparison of chirped FM/CW and chirped AM/CW fiber optic position sensors for aerospace applications

Abstract: During the past five years, fiber optic position sensing for aerospace applications based on high bandwidth chirped modulation of laser diode sources has been explored by a number of organizations. These investigations can be classified into two primary approaches: chirped Frequency Modulated/Carrier Wave (FM/CW) and chirped Amplitude Modulated/Carrier Wave (AM/CW). In this paper, the results of a system level analysis, which compares these two approaches in light of aerospace position sensing requirements, is presented. Key strengths and weaknesses of each approach are reviewed and conclusions are drawn concerning the applicability of each approach to aerospace position sensing. The primary conclusion is that the Doppler frequency shift imposed upon the optical carrier by the dynamic aerospace environment, is a major obstacle to the deployment of sensors based on the chirped FM/CW approach. While, in contrast, the performance of the chirped AM/CW approach is relatively insensitive to Doppler frequency shifts.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Method and apparatus for transmitting amplitude- modulated signal on optical communication route

Abstract: PURPOSE: To attain low C/N and a low distortion component by using a block of a conventional AM channel signal to frequency-modulate an RF subcarrier in order to send an optical carrier through an optical communication path CONSTITUTION: A block converter 14 includes a broad band VCO for oscillating a frequency signal to modulate an RF subcarrier for an AM cable frequency band A Fabry-Perot laser 22 is luminance-modulated by the RF subcarrier with a frequency band including a frequency band 20 and a generated optical carrier is sent to an optical fiber receiver 26 via an optical fiber network 24 The frequency-modulated RF subcarrier including a block of an AM channel signal is extracted from the receiver 26 The extracted information is given to a block demodulator 28, mixer 30 converts it into information with a higher frequency by using a local oscillating frequency fed to a terminal 32 and the original Am frequency band is extracted by a broad band discriminator 34 The extracted signal with an AM cable frequency band 10 is outputted from a demodulator 28

System for generating feedback signals for regulating optical surveillance circuits (pll)

Abstract: An optical system superposes an optical carrier with modulation and an additional optical carrier. The system is designed in such a way that it supplies the superposed optical signal with modulation at one of its outputs and the superposed optical signal without modulation at an additionnal output. The generator is designed in such a way that it is as insensitive as possible to ambient influences. The optical signal without modulation constitutes the feedback signal for the frequency/phase control of the laser emitter. The optical signal with modulation is available for further processing, for example in a beam shaping network.

Optical transmission device for the transmission of optical signals in wavelength division multiplexing on a plurality of adjacent optical carrier wavelengths

Abstract: 2.1 It is intended to specify an optical transmission device for the said transmission of optical signals, by means of which the power limit which is caused by non-linear effects can be shifted upwards with respect to the data throughput. 2.2 A doped fibre which acts in an optically amplifying manner is used for this purpose, into which pumping radiation can be coupled for pumping a concentration (which determines the level of optical amplification) of the dopant in the fibre having a profile over the length of the fibre such that a signal level of the optical signals which are coupled in the fibre remains constant in at least one transmission direction during its passage through the pumped fibre or at least has a drop in the signal level which is reduced in comparison with the unpumped fibre. 2.3 For use in the case of high-power trunk (long-distance) transmission paths, underwater cables (submarine cables).

Composite network using PLC and SCM technologies

Abstract: The study of integrated opto-electrical circuits has lead to the evolution of silica-based planer lightwave circuit (PLC) technology. PLC technology can be applied to the filtering of optical signals. Optical filters for AM-FDM signals that use the subcarrier multiplexing (SCM) technique can access two optical carrier wavelengths simultaneously, and can be used with point-to-multipoint wiring using coaxial cable to home videos. The use of optical fibers in subscriber networks has become a priority in telecommunications and video transmissions. In our network, the optical network unit (ONU) which is installed in an outside plant is designed so that three kinds of optical fiber systems are terminated simultaneously. They are for the video fiber backbone, personal communications and narrow band ISDN. The radius of the service area offered by the ONU is a few hundred meters. This network configuration is suitable for powering and operation, administration and maintenance (OA&M) from the viewpoint of feeder fiber network design.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.