Showing papers on "Optical communication published in 1987"

Polarization independent coherent optical receiver

Abstract: This paper describes an optical heterodyne receiver for DPSK signals which can receive an optical signal having an arbitrary polarization state. This is achieved by splitting the received signal between two orthogonal polarization axes and processing the resulting two signals as in a conventional DPSK heterodyne receiver. The sum of the two demodulated signals provides a baseband signal independent of the polarization state of the received optical signal. When the receiver noise is dominated by the shot noise of the photodetectors, the receiver provides a BER of 10-9for an average number of 22 photon/bit. In comparison, a conventional optical heterodyne receiver requires under the same noise condition 20 photon/bit to achieve the same BER for a received optical signal polarized along the polarization axis of the local optical signal.

Computer simulation of high-bit-rate optical fiber transmission using single-frequency lasers

Abstract: Chirp-induced dispersion penalties in high-bit-rate optical fiber transmission are assessed using numerical integration of laser rate equations and a Fourier transform fiber dispersion routine. The roles of the imposed modulation waveform and laser design parameters are evaluated from computer generated eye diagrams and simple analytical observations. Consistent with experiment, we find device dependent optimum laser extinction ratios. In addition, we address the delicate balance between nonlinear chirp-induced dispersion penalties and the speed limitations imposed by linear current filtering on both the laser transmitter and the receiver. These considerations become increasingly important at higher bit rates such as 8 Gbit/s.

60-channel FM video subcarrier multiplexed optical communication system

Abstract: A subcarrier multiplexed (SCM) optical communication system is described which transmits 60 frequency-modulated (FM) video channels over 18 km of single-mode fibre with a 56 dB weighted signal/noise ratio.

Optical intensity modulation to 40 GHz using a waveguide electro‐optic switch

Abstract: We report the intensity modulation of an optical carrier at frequencies as high as 40 GHz using a Ti:LiNbO3 optical waveguide switch. A self-electrooptic sampling technique is used to observe the modulation.

New design concept for a narrowband wavelength-selective optical tap and combiner

Abstract: A novel design is proposed for a four-port optical tap that extracts efficiently from a fibre in which light containing several discrete wavelength bands is propagating only that light within one such band. The same device can be used simultaneously to combine light of the same wavelength as the extracted light with the other, unselected, wavelength bands.

Recent advances in coherent optical fiber communication systems

Abstract: Research and development of coherent optical fiber communications have been accelerated mainly because of the possibility of receiver sensitivity improvement reaching 20 dB, and partly because of the possibility of frequency-division multiplexing (FDM) with very fine frequency separation. In this paper, recent advances in the research on coherent optical fiber communication systems are reviewed, with emphasis on those reported in the past two years. The bit-error rate measurements so far reported are classified and investigated in four categories: PCM-ASK, PCM-FSK, PCM-PSK, and PCM-DPSK. The states-of-the-art of polarization-state stabilization techniques is also discussed.

Coherent optical fiber transmission

Abstract: Essential technologies for developing coherent optical fiber transmission systems are reviewed from the viewpoint of regenerative repeater spacing and transmission data rate improvements. After describing the system features behind these advantages, recent progress in individual device and system technologies is delineated. Such progress includes frequency stabilization and linewidth reduction of semiconductor lasers, optical phase or frequency modulation, AM and FM noise suppression in coherent receivers, optical polarization stabilization and control in signal transmission, and optical direct amplification. Also described is progress in coherent optical transmission experiments carried out in many laboratories. Finally, future problems are discussed on the basis of the current state of the art.

Development of a coherent OTDR instrument

Abstract: Optical time domain reflectometry (OTDR) is a commonly used technique for characterization and fault location of optical fiber transmission systems. It involves measuring the fraction of a probe pulse that is scattered back (by Rayleigh scattering) from a silica fiber. Because of the very small levels of backscatter in single-mode fiber at long wavelengths, very sensitive optical detection is necessary to achieve adequate range performance. This paper gives the principles of operation and performance of a coherent OTDR system designed for use at 1.3 μm and its realization as a robust field-portable instrument with a specified performance of better than 24-dB one-way range, and 0.2-dB fault loss resolution. Coherent detection gives ultimate receiver sensitivity and also reduces the dynamic range requirements of the electronic signal processing. To realize these advantages, a novel technique is used to provide the necessary highly coherent source from a semiconductor laser. Sophisticated Signal processing techniques are employed both pre- and post-detection to integrate the signal out of the noise and also to reduce coherent fading effects. The various components of the system and their development into a robust instrument are described, and the performance of the system over long lengths of fiber both in the laboratory and more importantly on installed transmission links is presented in detail, showing achieved performance considerably better than this specified minimum.

A 1.3-µm 35-km fiber-optic microwave multicarrier transmission system for satellite earth stations

Abstract: A field experiment that transmits a full bandwidth of C-band satellite downlink signals over 35 km of 1.3-μm single-mode fiber was demonstrated. The major requirements of this analog fiber-optic link for video transmission, including system linearity and carrier-to-noise ratio, were experimentally characterized. Assessment of the system performance was based on measurement of video signal quality. A complete system analysis is given and the results agree well with the measured data.

All-fiber 90° optical hybrid for coherent communications

Abstract: A 90° optical hybrid is a four-port optical device with two inputs and two outputs. The two output signals are proportional to E1 + E2 and E1 + E2 exp(j90°), respectively, where E1 and E2 are the complex amplitudes the two input signals. The 90° hybrids are needed in many applications, including homodyne optical receivers in both phase-locked and phase-diversity configurations. In this paper, the principle of operation of an all-fiber 90° hybrid is described, and an experimental unit using connectorized in-line single-mode fiber components is reported.

Retroreflective optical communication system

Abstract: A retroreflective optical communication system in which a laser at a control station is aimed at a retroreflector at a second position or station whose reflectivity can be varied so as to impress a signal onto the retroreflected beam, and then back to the first station for detection. The communication link is such that the laser and aiming capability are at the receiving or control station and, greatly reducing the aiming and power requirements and cost at the retroreflector end of the link. The retromodulator optical communication system provides a high data rate, secure, non-jammable line-of-sight communication link between the second station, which may be a remotely piloted vehicle (RPV) and its control station. The retromodulator maybe entirely passive and thus would not give its presence away as would RF transmitting and receiving stations.

12.5 Gbit/s fibre-optic network using all-optical processing

Abstract: A 12.5 Gbit/s fibre-optic network is implemented with a central mode-locked laser clock, integrated-optic waveguide modulators, optical time-multi/demultiplexing and an optical reservation protocol. The network accommodates 125 stations transmitting at 100 Mbit/s each, using receiver-fixed assignment time-division multiple access.

Space coherent optical communication systems--An introduction

Abstract: Critical technology and system issues for space optical heteroydyne communication systems using GaAlAs lasers are discussed. Heterodyne systems offers 10-20 dB better receiver sensitivities and thus smaller telescope sizes for the same laser power than direct detection systems. Based on present state-of-the-art technologies, it is concluded that an efficient optical intersatellite link can be realized with a few years of development.

Optical frequency-selective amplification in a distributed feedback type semiconductor laser amplifier

Abstract: Optical frequency‐selective amplification of an injected optical signal in a distributed feedback type semiconductor laser amplifier is studied. Based on this mechanism an optical demultiplexer with optical gain for optical frequency‐division multiplexing is developed. A 9 GHz spectrum selectivity and a 11 dB extinction ratio are observed.

Coherence multiplexing using a parallel array of electrooptic modulators and multimode semiconductor lasers

Abstract: The paper presents a rather new approach of electrooptic modulation of light suitable for coherence multiplexing N transmission channels. A parallel array of N electrooptic multiplexers powered by multimode semiconductor lasers is used for imprinting the signals on light simultaneously. It is shown that the electrooptic multiplexers have to generate optical time delays whose optimal values are ruled by the sequence 1/2N \cdot \delta f, 1/N \cdot \delta f, 3/2N \cdot \delta f , etc., where \delta f is the intermodal separation of the laser longitudinal modes. The performance of the system is discussed in terms of crosstalk, number of possible channels, and signal power. The demonstration of the method is reported in the area of optical communications with the transmission of base-band video signals.

Frequency stabilisation of FDM optical signals

Abstract: Frequency confinement of FDM optical signals to a comb of equally spaced frequencies has been demonstrated. The result was achieved by locking the frequencies of three optical sources to three different resonances of a fibre Fabry-Perot resonator. The frequency spacing between the frequency-locked signals was adjusted to be 500 MHz, the spacing between adjacent resonances, or a multiple of this value. Implementation of the frequency stabilisation circuit requires only a fibre Fabry-Perot resonator, a photodetector and simple electronics. Such a simple circuit provides the means to frequency-stabilise a large number of FDM optical signals originating from the same location.

Optical amplifier configurations with low polarisation sensitivity

Abstract: The sensitivity of optical amplifiers to signal polarisation is avoided with use of configurations in which two amplifiers are combined. We describe experiments with a series and a parallel arrangement of two optical amplifiers. The experiments demonstrate a polarisation-insensitive amplification for both configurations over a spectral range of at least 80 GHz.

Long distance fiber-optic transmission of C-band microwave signals to and from a satellite antenna

Abstract: We demonstrate here the use of high-speed semiconductor lasers and detectors with low loss optical fiber for the transmission of the 500-MHz C-band microwave signal spectrum to and from a satellite antenna. The optical system has low attenuation and large band, width, so the microwave signals can be transmitted directly at the microwave frequency (4 or 6 GHz) over 20 km of fiber without regeneration or qualization. The optical system introduces ≈ 1 dB or less of degradation for both low spectral density QPSK signals and high spectral density FM video signals present in typical satellite transmission systems. For the video signals, the signal to noise after AM conversion was reduced from 56 to 55 dB. The microwave drive level to the laser must be significantly larger (typically > -10 dBm) than the intensity noise of the laser, yet small enough (typically < 10 dBm) to reduce the intermodulation distortion signals to an acceptable level. The laser bias current must be several times threshold so that the resonance frequency is beyond the frequency band of interest (4-6 GHz in this case). A flat modulation response is then obtained, and the intensity noise and intermodulation levels are low.

Design of wide-band optical heterodyne balanced mixer receivers

Abstract: The optical heterodyne balanced mixer, or dual-detector receiver, offers significant advantages over a single detector receiver. Balanced mixer receivers are particularly attractive for use in optical heterodyne communication systems because they conserve local oscillator power and cancel excess intensity noise present in the local oscillator. Simple circuit models that illustrate the noise performance, small signal gain, and bandwidth of a balanced mixer receiver are developed. A figure-of-merit for receiver noise performance is also derived. An example design of a gigahertz bandwidth optical heterodyne balanced mixer receiver and the techniques used to characterize near-quantum-limited receiver performance are discussed.

Integrated-optic devices on LiNbO 3 for optical communication

Abstract: Integrated-optic components on LiNbO 3 for fiber-optical communication systems are reviewed with respect to technology, fiber coupling, and device configurations. Typical devices for communication applications, such as modulators/switches, multiplexers, switch arrays, and heterodyne receiver chips rely on electrooptically controlled waveguide structures. Their operation mechanisms and performance characteristics are described to highlight the present status of development and of system applications.

Optical Amplifier Applications in Fiber Optic Local Networks

Abstract: The number of waveguide taps N that a passive optical fiber bus can accommodate is typically quite low, due to significant attenuation of the signal in the taps and splices. In an effort to increase N substantially, this paper investigates the potential use of optical amplifiers to boost the signal along the bus. An analysis is performed for both direct detection and heterodyne detection. Values of N are determined for a wide range of system and device parameters, such as signal duration, amplifier noise bandwidth, and amplifier saturation power. It is found that the use of optical amplifiers can increase N by at least an order of magnitude, and by as much as two orders of magnitude under many circumstances.

Method and apparatus for receiving optical signals

Abstract: A method and apparatus for receiving optical signals is disclosed. The apparatus 10 comprises a primary mirror 14 to create an intermediate image 22 between the primary mirror 14 and a secondary mirror 16. The apparatus 10 further comprises a tertiary mirror 18 in optical communication with the secondary mirror 16.

An Optical Rangefinder For Autonomous Robot Cart Navigation

Abstract: A simple, low cost, infra-red rangefinder has been developed for investigation of autonomous robot cart navigation in factories and similar environments. A 2mW 0.84 LED source (not a laser) is 100% amplitude modulated at 5MHz and used to form a collimated 1" diameter transmit beam that is unconditionally eye-safe. Returning scattered radiation is focussed by a 4" diameter coaxial Fresnel lens onto a p-i-n silicon photodiode. Range is determined from the phase shift between the 5MHz modulation on the transmitted and received signals. Use of a rotating mirror provides 360° polar coordinate coverage of both distance and reflectance out to "20 ft. around the vehicle. Both radial and angular resolution correspond to ~l inch at a ranging distance of 5 ft., with an overall bandwidth of ~lKHz. The ranging resolution at 20 ft. is '2.5 inches, which is close to the theoretical limit possible for the radiated power, bandwidth, optics and receiver employed. The system is capable of reading wall bar codes "on the fly" and is in addition capable of simultaneously ranging and acting as a wideband optical communication receiver. Total parts cost for the optical transmitter, Fresnel lens, receiver and all the electronics is <$200. The remaining major parts, consisting of the rotating mirror, ring mounting, motor and incremental encoder, cost <$500.

The application of coherent optical techniques to wide-band networks

Abstract: The successful demonstration of optical heterodyne and homodyne techniques for point to point transmission links has led to an examination of their use in the context of wide-band systems. The high receiver sensitivity and frequency tuning ability potentially provide a means for accessing a significant part of the 50 000-GHz bandwidth provided by single-mode fiber. The possibilities for new network structures based on combinations of space, wavelength, and time switching are presented here, together with the concept of transparent networks which are not dependent on a particular modulation format or information rate.

Four-port homodyne receiver for optical fibre communications comprising phase and polarisation diversities

Abstract: A new four-port homodyne receiver for optical fibre communications is proposed and studied experimentally. It comprises phase-and polarisation-diversity schemes, removing the need for phase locking and polarisation control. The bit-error-rate measurement is also reported.

Photoelectric device with optical fiber and laser emitting chip

Abstract: In a photoelectric device, particularly, a photoelectric device for optical communication, an optical fiber is fixed at two fixing points so that the extremity of the optical fiber is disposed opposite to the light emitting surface of a laser diode chip and the optical fiber extends in a nonlinear shape, for example, in a moderate curve, between the two fixing points. Even though holding members fixedly holding the optical fiber at the two fixing points and a base member supporting the holding members are formed of a metal or metals having a coefficient of thermal expansion far greater than that of the optical fiber, and even if the distance between the two fixing points is varied due to the thermal expansion or contraction of the holding members and the base member, the optical fiber is obliged only to change the shape of extension. Therefore, the optical fiber and the solder fixing the optical fiber to the holding members at the two fixing points are not subjected to repeated stress, and hence the fatigue of the optical fiber and the solder is avoided. Accordingly, the photoelectric device is able to continue stable optical communication regardless of temperature variation.

Simultaneous amplification of wavelength-division-multiplexed signals by a highly efficient fibre Raman amplifier pumped by high-power semiconductor lasers

Abstract: We describe the first operation of a high-power semiconductor-laser pumped fibre Raman amplifier (FRA) using high-Raman-gain optical fibre in the 1.5?m region. A high optical gain of 5 dB for 60mW of pump power is obtained. We have also achieved simultaneous amplification of wavelength-division-multiplexed signals by the FRA.

Progress in fluoride fibres for optical communications

Abstract: Proprietes des materiaux, limites des pertes de transmission. Fabrication des fibres, dispersion, attenuation

Filter tap for optical communication systems

Abstract: A filter tap for optical communication systems includes an optical resonant cavity comprising generally parallel, facing dielectric mirrors spaced to permit resonance in a selected band of channels. Optical signals from an input portion of a main trunk line carrying optical signals on a plurality of bands are coupled to one of the mirrors at an end face of the resonant cavity and are coupled from the one mirror to an output portion of the main trunk line with minimal reduction in optical signals in nonselected bands. Optical signals in the selected band are coupled from the other of the mirrors on the other end face of the resonant cavity to a branch line. In one preferred embodiment, the cavity is a finer optic resonant cavity and trunk line optical fibers are coupled directly to one of the mirrors of the cavity. Power is coupled from the input portion to the output portion of the trunk line by evanescent coupling. A second resonant cavity can couple power in the same or a different band to a second branch line. Optical pumping can be utilized at the filter tap for optical signal amplification. The filter tap can include a macro-optical resonant cavity and lenses for directing optical signals between optical fiber cores and the resonant cavity.

Design of transparent optical networks by using novel quantum amplifiers and sources.

Abstract: It is shown how the photon-number amplifier may be used to make, for either novel or conventional sources, an efficient direct-detection receiver and transceiver in a local-area network environment and how the parametric amplifier may be used similarly for a homodyne-detection receiver.