Showing papers on "Optical Carrier transmission rates published in 1994"

Optical time division multiplexing: systems and networks

Abstract: The recent advances in optical time division multiplexed (OTDM) systems and components research show the technique to be highly suited to the generation and transmission of high capacity data on a single optical carrier. This approach uses a single wavelength to carry capacities of at least 40 Gb/s. Such systems are based on a clock frequency and tributary data rates which are easily accessible using electronic components. Short optical pulses are used in a return-to-zero data transmission format with temporal interleaving to map a number of optical data channels into a single electronic clock cycle. It is an approach that can be used to achieve extremely high data-rate bit interleaved systems. This article summarizes the developments in this field and outlines a possible methodology to evolve transport networks to encompass the potential that both WDM and OTDM have to offer. >

Optical carrier filtering for high dynamic range fibre optic links

Abstract: Optical carrier filtering is used with an externally modulated fibre optic link to maintain high dynamic range operation with significantly reduced optical power levels. A spur-free dynamic range of 115 dBHz/sup 2/3/ is achieved for a frequency of 17 GHz with a received optical power of only 1.5 mA. An external filter is used to demonstrate a 10 dB improvement in dynamic range for a fixed optical power level.

Device for extraction and re-insertion of an optical carrier in optical communications networks

Abstract: The device includes a first optical circulator connected in series with the line (1e, 1u) in order to receive a signal stream including a carrier to be extracted, modulated by an information signal, and to transmit a signal stream including the same carrier, re-inserted into the stream after having being modulated with another information signal, and a second optical circulator connected to local information processing means, to which it supplies the extracted carrier and from which it receives the carrier to be re-inserted. Between the two circulators there is an optical-fibre bandpass filter that can be tuned to the carrier wavelength.

Low-loss fiber optic time-delay element for phased-array antennas

Abstract: We present a novel concept, the fiber optic Bragg grating true- time-delay (TTD) element, for implementing true time delay in the distribution network of an optically fed phased array antenna. the device utilizes narrowband optical Bragg reflection gratings written holographically into the core of a single-mode fiber at various positions along its length. An optical carrier is modulated by the RF signal of interest and launched into this delay-line fiber. The desired RF time delay may be realized by wavelength-selectable nature of the TTD device offers the possibility for simplified beamsteering control and channel multiplexing.

Optical circuits for equalizing group delay dispersion of optical fibers

Abstract: Optical circuits are synthesized for equalizing the group delay dispersion of single-mode fibers. The transfer function of the equalizing circuits are given by Chebyshev polynomials of the second kind. The various realization methods for the group delay equalizer are shown, including periodic structures using birefringent crystals, birefringent fibers, and Mach-Zehnder interferometric planar optical circuits. An optical equalizer employing TiO/sub 2/ birefringent crystals was fabricated and evaluated by using an optical network analyzer, which operates by making modulation-envelope phase and amplitude measurements while scanning the optical carrier frequency. The measured optical equalizer characteristics show excellent agreement with the simulation analysis. The effectiveness of the equalizer for substantial reduction of the dispersion penalty for a 10 Gb/s signal transmitted over 30 km of normal dispersion fiber was demonstrated. The periodicity of the equalizer results in periodic dispersion-free bands, and hence, the equalizer is suitable for use in future multichannel FDM systems. >

Composite second order distortion due to self-phase modulation in externally modulated optical AM-SCM systems operating at 1550 nm

Abstract: Self-phase modulation due to fibre nonlinearity can significant composite second order distortion in modulated AM-SCM video systems. However, it is shown that this can be minimised by phase modulating the optical carrier. Analytic expressions are derived which are in good agreement with numerical simulations. >

Wavelength-selectable optical signal processor

Abstract: A wavelength-selectable optical signal processor for creating a predetermined optical delay pattern in a signal. The system includes a succession of optical delay pathways each receiving a portion of a modulated optical beam having a predetermined wavelength. The distance each beam traverses through each delay pathway varies as a function of the predetermined wavelength of the optical beam. As a result, the distance of the optical path for any of the predetermined wavelengths creates a predetermined delay pattern across the succession of optical delay pathways. In signal processing applications the delayed optical beam can be recombined in the time domain to construct a superposition of time delayed signals yielding an agile signal processor implemented using a wavelength-reconfigurable transversal filter design. In a phased-array antenna, the present invention results in a time delay network which establishes a one-to-one correspondence between antenna beam direction and optical carrier wavelength. This permits an antenna to change beam direction simply by changing the wavelength of the optical carrier.

A 50 Mbit/s Optical Wireless LAN Link Using Novel Optical and Electronic Enabling Technologies

Abstract: Optical wireless transmission is proposed for the implementation of broadband wireless LANs. An optical cellular structure, which uses holograms to define optical cells and high levels of optical concentration in the receivers, will maximise the performance of such a system. The bootstrapping circuit technique can be used in the optical receiver design to give wideband and low noise operation in the presence of a large photodiode capacitance. Results for a 50Mbit/s link that operates over a 5m2 cell size are given.

Transmission station, intermediate repeater and receiver station for a fibre-optic communications-transmission system

Abstract: The invention relates to a transmitting station (SS), and intermediate repeater (ZV1 to ZVn) and a receiving station (ES) for an optical communications-transmitting system for transmitting useful data of a high bit rate by means of at least one optically narrow-band carrier signal, and for transmitting additional data, for example service information, of a low bit rate. In order to operate the communications-transmitting system with the lowest possible outlay, an optically wide-band carrier signal, for example from a super-luminescence diode, which is located in the wavelength range of the narrow-band optical carrier signal, is used for transmitting the additional data. Both the optically narrow-band carrier signal of the useful data and the optically wide-band carrier signal of the additional data are located within the amplifying range of an optical fiber amplifier disposed in the intermediate repeater (ZV1 to ZVn). Both carrier signals can be selected with simple means.

Sensitivity enhancement using coherent heterodyne detection

Abstract: This paper focuses on some heretofore overlooked advantages of coherent detection (CD) over direct detection (DD) in optical fiber communication systems. The basis for these sensitivity improvements is the fact that the local laser in coherent fiber optic systems adds a large number of photons to the net received optical signal. Under these conditions, the Bohr correspondence principle enables us to treat the photodiode output signal classically. Specifically, the usual CD environment yields a photodiode output that can be regarded as a classical signal disturbed by Gaussian noise (central limit theorem). This detection process has been studied extensively, and there exist many powerful signal processing techniques that may be used to enhance system sensitivity. In particular, we utilize a sum of digitally modulated subcarriers to frequency modulate an optical carrier along with the aid of coherent detection to achieve 11.1 photons/b sensitivity as determined by computer simulation. >

Method of and device for the fine synchronization of aim cells in optical ATM nodes

Abstract: Within an optical ATM node, an ATM cell to be synchronized is sent into a segment of pre-determined length of an optical fiber with a high time dispersion (FD), after having been associated, in a tunable wavelength converter (CL), to an optical carrier with a wavelength that is different from that with which the cell itself was received and such that, as an effect of the transit the fiber (FD), the cell reaches the input side of a switching element (Eml . . . Emh) of the node (NC) at a predetermined instant.

4x4 polymer thermo-optic directional coupler switch at 1.55 µm

Abstract: Future telecommunication systems will take advantage of the almost unlimited transmission capacity of optical fibers by optical-frequency-division-multiplex (OFDM) techniques. Transparent photonic networks need transparent optical crossconnects for switching optical carrier frequency signals in the frequency-space domain [1]. The space switching stage of a crossconnect for a high number of channels may be realized in an integration technology delivering low power consumption, insertion loss and crosstalk as well as a high degree of integration and polarization independence.

Two-dimensional optical beam-forming networks

Abstract: This paper presents recent advances toward the experimental demonstration and the far field pattern characterization of an optically controlled phased array antenna operating at 3 GHz. The 2D optical architecture is based on polarization switching by N (N equals 6) spatial light modulators of pxp pixels (p equals 4). It provides 2N-1 time delays values and an analog control of the 0 to 2(pi) phase for each of the pxp microwave signals actuating an active antenna. These signals originate from the coherent detection of a dual frequency laser beam obtained with an acousto-optic frequency shifter. Furthermore, we also present the principle of a new photodetector based on the synchronous drift of photogenerated carriers with a moving interference pattern. This moving pattern results from the interference of the two components of the dual frequency optical carrier of the microwave signal used in the above architecture. It provides a large detection volume which could yield a high saturation intensity. A theoretical analysis is detailed and followed by an experimental demonstration in GaAs at a frequency f equals 210 MHz.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Broadband optical local area network technologies

Abstract: Summary form only given. We will present recent work on all optical technologies for ultrahigh bit rate optical TDM transmission. These results include a demonstration of a new ultrafast source, an 80 Gb/s optical transmission, rate conversion and demultiplexing, and a prototype optical network unit. The system experiments are combined with computer simulation studies to investigate transmission architectures for a 100 Gb/s local area optical network.

High-speed optical detectors for monolithic millimeter wave integrated circuits

Abstract: Metal-semiconductor-metal photo-diodes with interdigitated Schottky barrier fingers have been 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 incorporated 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 have been integrated with short-gate MODFET amplifiers to form the complete monolithic integrated optical receiver circuit. The circuits comprise of the active devices and coplanar waveguide matching/filter networks for optimal MMW performance. DC bias networks have also been integrated with the circuits.

Broadband microwave fiber optic link with a compact transmitter

Abstract: A microwave fiber optic link is developed for operation from 8 to 18 GHz. Modulation of a 1.3-μm wavelength optical carrier is accomplished using a lithium niobate Mach-Zehnder interferometer modulator that was designed for broadband operation up to 19 GHz. The link transmitter components, which consist of a high-power semiconductor laser, an optical isolator, and a modulator with polarization-preserving fiber pigtails, are spliced together to fit into a 10.16- x 5.08- x 2.54-cm3 (4- x 2- x 1-in.) box for applications where space is critical. The average link electrical gain is 45 dB, the frequency response is flat to within ±4 dB across the 10-GHz band, and the spur-free dynamic range of the link is 84 dB.

Optical transmission system

Abstract: PURPOSE: To avoid the deterioration phenomenon of transmission quality connected with a Brillouin effect by providing a means for increasing the modulating speed of an optical carrier wave from a zero value as necessary when modulation is the one other than the intensity modulation. CONSTITUTION: In an optical transmission system including a transmission terminal equipment 1, optical link 2, and receiving terminal equipment 3 a comparator 10 compares the number of the valid carrier waves of an incident multiplex counted by a scanner 9 with a prescribed limit value. Then, when the number of the valid carrier waves of the incident multiplex is detected as less than the prescribed limit value, a control instruction is made active, and the gain of an adjustable gain amplifier 11 is increased and/or an auxiliary carrier wave is added through an auxiliary carrier wave generator 12 and a multiplexer 13. Thus, when a strong transmission light power is connected, reflection is generated inside the fiber of an optical link 2, and as a result, a phenomenon in which additional attenuation, deformation, and disturbance is introduced to a transmitted signal can be avoided or limited.

Multiplex optical space transmission system

Abstract: PURPOSE:To simultaneously utilize plural optical carrier waves inside the same space without mutual interference by allocating them to the multiple systems of optical space transmission systems. CONSTITUTION:Polarizing boards a1, b1, a2 and b2 are respectively provided at transmitters A1 and B1 and receivers A2 and B2, and optical space transmission is performed by using respectively linearly polarized optical carrier waves. In this case, the installation angles of respective polarizing boards a1, b1, a2 and b2 are adjusted so that the optical carrier waves transmitted/received inside the same system can make the polarizing angles parallel and the polarizing angles can be respectively different between different systems.

Effect of four‐wave mixing on the performance of subcarrier multiplexing (scm) catv systems

Abstract: The effect of four-wave mixing on the performance of CATV-SCM systems, in which the optical carrier is either amplitude or phase modulated, has been evaluated, considering both direct and coherent detection. Four-Wave-Mixing is a nonlinear phenomenon arising in single-mode fibers when input optical power is too high and / or channel spacing is excessively narrow. The penalty induced by this phenomenon on the carrier-to-noise ratio has been evaluated assuming the FWM as a noise process that affects the amplitude and phase of the useful signal. © 1994 John Wiley & Sons, Inc.

Bidirectional single-wavelength optical fiber communication links

Abstract: PURPOSE: To enable operation due to a minimum loss wavelength while using the optical carriers of the same frequency in both the directions for a bidirectional optical fiber communication link by modulating the optical carrier with demodulate signals having various frequency spectrums, and making these optical carriers incident on an optical fiber. CONSTITUTION: At a moving body 120, the optical carrier is modulated by the 1st modulate signal having the 1st frequency spectrum, made incident from a transmission section 260 through a coupler 220 and a connector 200 on a fiber 160 and sent out to a control station 140. At the control station 140, on the other hand, the optical carrier of the same wavelength is modulated by the 2nd modulate signal having the 2nd frequency spectrum, made incident on the fiber 160 and advanced in a reflecting direction by a transmission section 270. These modulated signals are respectively extracted by receiving means 440 and 420 and converted to electric signals. Thus, the carrier of minimum fiber loss wavelength can be shared and the efficiency of bidirectional optical fiber communication link can be improved.

Integrated quantum well modulators for very high speed transmission systems

Abstract: This paper summarises work currently performed within the European program RACE, under contract R2006 WELCOME, Quantum Well Components for High Speed Transmission Systems. The introduction of Integrated Broadband Communication (IBC) services requires solutions that enable high capacity transmission and distribution of information at low cost, including the integration and possible upgrade of existing networks. A currently discussed approach is based on direct detection schemes at very high bit rates on one optical carrier. Optical communication systems based on standard fibres presently achieve data rates of 10 Gbit/s. The most stringent limitation appears to be the dispersion of standard fibres which limits the bridgeable fibre length. Residual chirp which always accompanies intensity modulation has not only to be minimised. For adjustable low negative chirp, however, the maximum fibre length can be even increased above the dispersion limit of chirp-free fibre transmission. In the WELCOME project several approaches for transmission with direct detection and low chirp intensity modulation at bit rates of 10 Gbit/s and above have been successfully demonstrated. Among them, electroabsorption (EA) modulators have shown their potential to fulfil these requirements. >

An Experimental High Definition Videoconference System

Abstract: Publisher Summary This chapter describes an experimental high definition videoconference (VC) system. Two main kinds of VC services can be distinguished. One uses an analog technique without any video data reduction, the other applies digital techniques with data reduction. The analogue service is provided through a public fiber network which is capable to carry the broadband video data stream of about 100 Mbit/s. As the video technique is based on the conventional TV transmission standard PAL, the quality of service is only moderate, and is not appropriate to the high transmission bandwidth. In contrast, digital systems are promising the combination of bandwidth and power efficiency and are thus cost efficient as well. The most advanced digital videoconferencing service is based on the international H. 261 coding standard. It is found that as the data rate is scalable from 64 kbit/s to 2 Mbit/s, this service is suited for the transmission in the narrowband ISDN.