Showing papers on "Optical Carrier transmission rates published in 1991"

Quadrature optical phase modulators for lightwave systems

Abstract: Optical communication methods and apparatus are disclosed for transmitting two or more optical signals with different optical carrier frequencies on a single optical fiber with high spectral efficiency. Each optical carrier is typically modulated with multiple modulated subcarriers. In one embodiment, an optical phase modulator provides cancellation of second order intermodulation products in each optical signal, thereby permitting the optical carrier frequencies to be spaced by 2f max , where f max is the maximum modulation frequency. In another embodiment, a single sideband optical phase modulator provides cancellation of second order intermodulation products and one signal sideband, thereby permitting the optical carrier frequencies to be spaced by f max . Quadrature optical phase modulators for simultaneous transmission of two independent baseband digital data signals or two independent subcarrier multiplexed signals are disclosed.

Differential quadrature phase shift keying encoder for subcarrier systems

Abstract: This invention features a differential QPSK digital communications apparatus and method, suitable for optical communications systems, where a pair of synchronous binary input data streams S 0 (t) and S 1 (t) are encoded into a pair of encoded binary data streams d 0 (t) and d 1 (t) which QPSK modulate the phase φ(t) of a carrier signal. An encoder features time delay circuits for delaying d 0 (t) and d 1 (t) by a period T to produce d 0 (t-T) and d 1 (t-T) respectively. A logic circuit produces d 0 (t) and d 1 (t) from S 0 (t), S 1 (t), d 0 (t-T) and d 1 (t-T) according to logical relationships. A microwave subcarrier is modulated by a microwave QPSK subcarrier modulator. The microwave QPSK subcarrier modulator includes an in-phase and quadrature subcarrier signal source, a mixer for mixing the in-phase subcarrier with d 0 (t), a second mixer for mixing the quadrature subcarrier with d 1 (t), and a combiner circuit for combining the two mixer outputs to produce a QPSK modulated microwave subcarrier signal. An optical modulator modulates the QPSK modulated microwave subcarrier signal onto an optical carrier signal, an optical detector detects the modulated subcarrier from the optical carrier signal to produce a detected subcarrier signal, and a QPSK demodulator recovers S 0 (t) and S 1 (t) from the detected subcarrier signal.

Fiber optic microcellular radio

Abstract: A distributed antenna system using optical fiber subcarrier transmission is proposed. The system consists of many small canisters which radiate and receive radio signals to and from mobile phones. An optical-fiber connected canister antenna can also serve as a supplement to cover dead spots of imperfect base station antenna coverage. Linear end-to-end transmission between the base station and canister antennas can be provided by direct modulation and direct detection of a 1.3- mu m optical carrier with 850 MHz subcarriers. Both radio and optical link budgets together with the required dynamic range of widely varying mobile signals have been analyzed. Technical feasibility has been verified by signal-to-noise ratio and intermodulation distortion measurements. A prototype canister transceiver has been constructed and tested. Using the above components with existing base-station and mobile equipment, a two-way audio link via 12 km of optical fiber and mobile radio path has been successfully demonstrated. >

A multilevel coherent optical system

Abstract: A multilevel coherent optical system is disclosed in which a multilevel signal with a coherent optical carrier is provided by means of a modulation of the phase and the polarization of the electromagnetic field propagating through a single-mode optical fibre, a heterodyne transmitter and receiver for said signal being also disclosed. The transmitter comprises a coherent light source (1) providing the optical carrier, a phase modulator (2) modulating the phase of the carrier, a polarization modulator (3-8), and a modulation signal generator (10) providing control signals to the phase modulator (2) and the polarization modulator. The receiver comprises a first stage (12-23) carrying out the heterodyne detection of the phase component and the phase quadrature component of the polarization of the signal received through an optical fibre (11), a second stage demodulating the received signal to provide the multilevel signal, and a processing circuit comparing the received multilevel signal with predetermined reference signals. Such a system exploits the four degrees of freedom of the electromagnetic field propagating through the optical fibre so as to approach closer to the theoretical Shannon limit than conventional systems.

Radio communication system

Abstract: In a cellular mobile-radio system with radio stations and transmission facilities remote therefrom, the radio stations send out radio signals and receive radio signals which, in each case, contain information signals. According to the invention, as many as possible of the processing functions are shifted from the radio stations to the transmission facilities. The radio signal to be sent out by the radio station is easily generated in the radio station because in the transmission facility, an unmodulated carrier and a carrier modulated with the information signal is produced, in which case the carriers differ in frequency by the amount of the carrier frequency of the radio signal. These two optical carriers are transmitted to the radio station and are mixed there in an optical receiver, so that the radio signal containing the information signal is generated. A radio signal that is received in a radio station is transmitted optically to a the transmission facility and is processed further there. This transmission is carried out by the fact that an optical transmitter present in the transmission facility generates an unmodulated optical carrier and transmits it to an optical modulator located in the radio station. In the optical modulator, the light, modulated with the received radio signals, is sent back and the radio signal is recovered by optical heterodyne reception of the unmodulated and modulated carrier.

Electro-optic system

Abstract: An electro-optic system for mixing and/or transmitting electrical signals using an optical carrier is described in which the electrical signals are applied to an electro-optic intensity modulator with a nonlinear transfer function, preferably of the Mach-Zehnder interferometric type biased at the transmission null point. The modulator output optical signal is transmitted to a receiver where it is detected and voltage products of the applied electrical signals are recovered.

Fiber optic external modulator

Abstract: An improved external optical modulator provides reduced noise and distortion. An optical carrier to be modulated is split into a plurality of portions. A first portion of the carrier is modulated with an information signal. A second portion of the carrier is processed to provide an attenuating signal. The modulated carrier portion is combined with the attenuating signal to provide an attenuated optical carrier having improved apparent percentage modulation. In a preferred embodiment, the first carrier portion comprises a substantially greater amount of optical carrier power than the second carrier portion.

Demonstration of photonic fast packet switching at 700 Mbit/s data rate

Abstract: Selfrouting of optical data through a photonic packet switch, with user data at 700 Mbit/s, is demonstrated. The switch is transparent to the bandwidth of the optical data thus allowing essentially unlimited payload bit rate.

Self-organizing photorefractive frequency demultiplexer.

Abstract: We demonstrate a self-organizing photorefractive circuit that demultiplexes a beam that has two signals imposed on separate optical carrier frequencies into two beams, each containing one of the signals on its carrier. Unlike conventional demultiplexing techniques, this method requires little a priori knowledge about the carrier frequencies. The signal channels must be spatially uncorrelated, and their frequency separation must be more than the photorefractive response bandwidth (hertz to kilohertz). The optical circuit uses no local oscillator, and the photorefractive response bandwidth places no upper bound on the channel bandwidth. Experimental results for demultiplexing a beam that has two signals, with a BaTiO3 circuit, show contrast ratios of better than 40:1 at the outputs.

Single wavelength bidirectional optical fiber communication link

Abstract: A bidirectional communication link and a method of contemporaneously transmitting signals having an optical carrier of a common wavelength along an optical fiber are disclosed. The link comprises an optical fiber (160) having a first and a second end. A transmitter (260) is provided for launching a first optical carrier of a first wavelength onto the fiber (160) at the first end thereof, the transmitter (160) including a modulator (300) for modulating the first carrier with a first modulating signal (D) confined to a first frequency spectrum upon the first carrier. Further, a second transmitter (270) is provided for launching a second optical carrier of the same wavelength along the fiber (160) at the second end thereof. The second transmitter (270) includes a modulator (360) for modulating upon the second carrier a second modulating signal (U) confined to a second frequency spectrum not overlapping the first spectrum. A first receiver (440) is coupled to the second end of the fiber (160) for extracting the first modulating signal (D) from the first optical carrier, and a second receiver (420) is coupled to the first end of the fiber (160) for extracting the second modulating signal (U) from the second optical carrier.

Long range bidirectional optical fiber communication link

Abstract: A long-range optical fiber communication link overcoming certain constraints on signal transmission range imposed by fiber-induced loss is disclosed herein. A first embodiment of the communication link (10) of the present invention includes an optical fiber (16) having a first and a second end wherein the attenuation of optical energy passing therethrough at wavelengths included within a transmission window is substantially minimized. The inventive link (10) further includes a first arrangement (22) and (36) for launching a first optical carrier of a first wavelength onto the first end of the fiber (16). Provision is made within the launching arrangement (22) and (36) for impressing a first modulating signal spanning a first frequency spectrum upon the first carrier. The first embodiment also includes a second arrangement (26) and (37) for launching a second optical carrier of a second wavelength onto the second end of the fiber, wherein the second wavelength is included within the transmission window. The second launching arrangement (26) and (37) is further disposed to impress upon the second carrier a second modulating signal spanning a second frequency spectrum segregated from the first spectrum. A first receiver (64) of a first bandwidth encompassing the first frequency spectrum is coupled to the second end of the fiber (16). The first receiver (64) is operative to extract the first modulating signal from the first optical carrier. A second receiver (58) having a second bandwidth encompassing the second frequency spectrum is coupled to the first end of the fiber (16).

450 Mbit/s BPSK and 1 Gbit/s QPSK throughput subcarrier multiple-access networks using 790 nm selfpulsating laser transmitter network for computer applications

Abstract: Experimental results are presented which describe the use of commercially-available 790 nm selfpulsating lasers in subcarrier multiple-access, computer networking applications. At selfpulsation frequencies of 1.8 and 2.2 GHz, error-free aggregate data throughputs of 450 Mbit/s and 1 Gbit/s were obtained over a mode-selective, eight-way star optical network with baseband plus two channel BPSK and five channel QPSK modulation formats, respectively.

Analog optical FM receiver

Abstract: An analog Optical FM Receiver which includes an optical delay for shifting the phase of a received modulated optical carrier signal as a function of the modulating analog signal so that the phase variation between the shifted optical signal and the received frequency modulated carrier signal can be determined and the modulating analog signal can be extracted.

Optical transmission process and system

Abstract: In a frequency shift keyed direct detection (FSKDD) optical transmission system, an optical carrier 14 is frequency modulated with a higher frequency part 16 of an input signal. The frequency modulation is converted in an optical frequency discriminator 18 (eg Mach Zehnder or Fabry Perot interferometer) to an intensity modulation and the carrier is further intensity modulated with a lower frequency part 17 of the input signal, eg by phase modulating the discriminator. The doubly modulated carrier is then transmitted to a receiver station for demodulation and recovery of the original signal. The technique overcomes the problem of poor low frequency response of semiconductor injection lasers.

Integrated optical mixer for RF applications

Abstract: An integrated optical modulator is shown to operate in a manner analogous to that of a conventional electronic mixer. The integrated optical mixer has been used to perform a spectral analysis on a subcarrier RF signal, modulated on an optical carrier, and demonstrates a novel signal processing application of such devices.

Optical carrier synthesis in coherent lightwave systems

Abstract: The requirements for the optical sources for future coherent lightwave systems employing phase modulation techniques have been identified. A technique for generating many narrow linewidth optical channels has been proposed using an optical frequency-locked loop. This is seen as an interim solution until inexpensive moderately narrow linewidth monolithic lasers can be acquired. Then the option of designing a narrowband optical phase-locked loop with the possibility of line-narrowing and precise frequency offsets becomes available. Finally, the use of this optical frequency synthesiser has been considered in the design of a high capacity optical network.

Optical FM modulation system

Abstract: An optical FM modulation system includes a continuous wave optical light source for producing an optical carrier wave; integration means, responsive to an FM modulating signal, for generating a phase signal representative of the phase variations corresponding to the frequency variations of the FM modulating signal; and an electro-optic phase modulator, responsive to the electrical signal representative of the phase variations, for shifting the phase of the optical carrier wave to modulate the frequency of the optical carrier wave as a function of the modulating signal.

Optical FM and heterodyne detection of two-channel 560 Mbit/s subcarrier multiplexed ASK signal using three-electrode DFB-LDs

Abstract: An optical carrier was frequency-modulated by directly modulating a three-electrode DFB laser diode using two-channel 560 Mbit/s subcarrier multiplexed ASK signals, and was transmitted through 122•3 km of single-mode fibre. Both channels were heterodyne-detected and selected simultaneously by a bandpass filter. A receiver sensitivity of −32•4 dBm was obtained and a crosstalk penalty was less than 0•8 dB with channel spacing of 1•8 GHz

A field demonstration of wavelength routed optical networks

Abstract: These experimental demonstrations have taken wavelength routing from the laboratory into British Telecom's (BT's) London Main Optical Fibre Network. It shows the ability of this technique to form effective transparent optical networks. Components and sub-assemblies that are available commercially have been used throughout to emphasise the practicality of constructing the networks without the use of state of the art technology. The significant multiplexing and demultiplexing losses at the network nodes limit the range of basic wavelength routed networks. However, this demonstration has shown that useful ranges of up to 40 km for 622 Mbit/s data can be achieved even without amplification. With optical amplification, large networks are possible and in this demonstration amplification allowed transmission lengths of 88.8 km to be demonstrated for the 622 Mbit/s signals. This was achieved with an optical power margin of 12 dB. This distance corresponds to twice the diameter of the existing London Main Fibre Network.

Coherent analog FM-SCM video transmission using direct frequency modulation of semiconductor lasers

Abstract: : An analog coherent subcarrier multiplexing system for video transmission using frequency modulation of both the subcarrier and optical carrier is analyzed. Theoretical receiver sensitivity for realistic values of receiver noise and phase noise is approximately -41 dBm for 50 channels and -25 dBm for 100 channels.

Experimental 9 Gbit/s transmitter and receiver for optical transmission systems

Abstract: By combining monolithic integrated GaAs and Si ICs, DFB (distributed feedback) lasers, and ternary avalanche photodiodes, it was possible to realize a 4.5-Gbit/s optical transmission system and experimental 9-Gbit/s equipment. The current bit rate in the Deutsche Bundepost network of 139.264 Mbit/s was used as input and output base. The 4.5 Gbit/s transmission signal is multiplexed from 32 input signals, and a 4-bit scrambler serves as line encoder. The 9 Gbit/s are obtained by multiplexing the 4.52-Gbit/s signal and a pseudorandom signal. Hybrid thick- and thin-film circuits and microwave-suited layouts are the necessary requirements for it. >

Performance evaluation of coherent subcarrier multiplexed optical distribution systems with common local oscillators

Abstract: Coherent subcarrier multiplexed local distribution systems using a common local oscillator (LO) in which the LO is provided by a distribution centre instead of locally generated at the subscriber premise are described. Both single and multiple optical carrier systems are considered. Because of the low path loss in a local optical network, a common LO system is possible with a LO shared by many subscribers, and indeed provides many advantages. First, a simplified receiver is achievable which eliminates a tunable LO, an automatic frequency control (AFC) circuit, a polarisation controller, and an optical coupler. Secondly, the system cost is decreased due to the reduction of components. Thirdly, laser phase noise and intermediate frequency (IF) drift are expected to be minimised. Fourthly, because no active optical components are placed at the subscriber premises, the system reliability is increased. Fifthly, the common LO system can be expanded with optical amplifiers without increasing the number of LO and simultaneous amplification of the message, and LO signals are achievable. By sharing high power, highly frequency stabilised, and very narrow linewidth LO lasers provided by the centre, it is expected that a simple and reliable coherent optical distributing network can be constructed by using common LO.

Optical carrier generator

Abstract: PURPOSE:To offer an optical carrier generator whose optical carrier frequency interval is easily controlled and variable by using >= stage of an acoustooptic element which is modulated by a sine wave signal generator to shift the optical frequency of input signal light. CONSTITUTION:Output light L from a light source 21 such as a semiconductor laser is inputted to an optical amplifier 23 through an optical coupler and ampli fied, and the amplification output L1 is inputted to acoustopptic elements 24a, 24b - 24n which are modulated by sine wave signal generators 26a, 26b - 26n with high stability; and the output light L2 of a final state where the frequency is shifted by the sum fo(f1+f2+-+fn) of modulation frequencies is fed back to the optical amplifier 23 by the optical coupler 22 to compensate the light loss of a feedback path 27. The output light 25 which is thus obtained is an optical carrier having a constant frequency interval. Thus, the optical frequency interval can be controlled with the oscillation frequencies (f1-fn) of the sine wave signal generator 26a - 26n which are electric signals, so the control is easy and high accuracy and high stability are obtained.

A method for transporting sdh signals using existing transmission systems

Abstract: This paper discusses a signal transmission method based on the existing digital hierarchical transmission system that transmits signals as defined in the network node interface (NNI) of the new CCITT synchronous digital hierarchy (SDH). The method transmits the information corresponding to two virtual containers (VC-3s) with the capacity of 28 of 1.5 Mbit/s over existing transmission systems using the fourth digital level, which is the basic unit of operation in the existing network. The fourth digital level signal in Japan has a bandwidth of 97.728 Mbit/s as specified in Rec. G.702. If two VC-3s are to be contained according to the basic SDH philosophy of NNI, the required transmission capacity is 103.68 Mbit/s. The method that allows two VC-3s to be transmitted at 97.728 Mbit/s should be considered. It is shown first that the use of the pointer introduced in SDH is adequate. A pointer scheme with a fourmultiframe structure is proposed, aiming at efficient information transmission. The characteristics of the fourmultiframe-type pointer are then discussed, and the assignment of the overhead required in the transfer of maintenance/operation information is considered. Based on those discussions, the frame structure for the 97.728 Mbit/s signal is derived, which is the fourth level of the existing digital hierarchy.

System considerations in multiplexed addressing using an optical time-of-flight technique

Abstract: An unconventional method of multiplexing data in a fiber-optic network is described. The method uses a linearly swept optical carrier frequency and physical distances in fiber as addresses to create frequency division multiplexed signals at the receivers. As it is a coherent self-heterodyne or -homodyne method, wide network bandwidth is available without the need for receiver local oscillator lasers or wide bandwidth electronics. As an example, a 2-Gb/s system that allows each of 200 nodes to access a 10-Mb/s channel without network blocking is described. Such a system could be used as a LAN or a backbone network for existing LANs. >

Wavelength division and subcarrier system based on Brillouin amplification

Abstract: This paper analyzes an optical wavelength division multiplexing system (WDM) with subcarrier multiplexing (SCM). The pump laser is tuned to amplify the corresponding optical carrier by fiber Brillouin amplification (FBA) in WDM for the desired group of SCM signals and then a microwave tuner is used to select the desired channel in this group. This system has the benefits of eliminating the need of polarization control, the ability of phase noise cancelling due to the 'squaring' photodetection process of the selected optical carrier together with its SCM channels, and enhancement of optical receiver sensitivities by amplification of the carrier.

Final progress report

Abstract: /2. Technical Objectives: The principal objective of this project is to determine the most efficient means of encoding a microwave/millimeter wave signal from a patch antenna onto an optical carrier in an electrooptical substrate for subsequent optical processing of the microwave/millimeter wave signal. 3. Approac: . . Our approach was to develop design models that would relate the performance of integrated electro-optic devices to the fabrication parameters used in making them and then experimentall) verify their performance. Where lack of agreement was observed, the models were rethought and modified to improve their predictive behavior. Such performance characteristics included modal field distributions, propagation constants, coupling coefficients of channel waveguides and coupling lengths of proton exchanged directional couplers. This information was then used to design patch antennas and integrated optical modulators using various fabrication techniques and substrates. Similar design methods were used to determine the depth of modulation of electrooptic modulators. 4. Accomplishments: In order to achieve optically-controlled integrated millimeter-wave receiving phase arrays, single sideband modulation of an optical carrier by an incoming millimeter wave must be performed. Our research in this area began with the investigation of traveling wave structures used to obtain 90 degree phase shifts in millimeter wave signals. These structures consisted of slots in microstrip O - lines and were analyzed using a numerical (moment method) program. A theoretical model describing the interaction of a millimeter or microwave signal with an optical carrier was developed and used to determine the optical depth of modulati, n. A strip dipole was fabricated onto one o arm of an integrated optical Mach Zender interferometer. Modeling and fabrication of electrooptic devices in LiNbOa was then initiated. This led to the