Showing papers on "Optical Carrier transmission rates published in 1995"

Fiber-optic tunable microwave transversal filter

Abstract: A fiber-optic finite impulse response filter with continuously tunable unit time delays is developed and studied. The filter consists of eight taps with progressively longer segments of high-dispersion fiber, but completed with dispersion-shifted fiber to nominally identical overall lengths. The time delays through each tap are tuned by varying the wavelength of the optical carrier. The constructed 8-tap filter exhibits bandpass characteristics with a Q of 30. The bandpass band is continuously tuned over a full octave from under 9 GHz to over 18 GHz with a single low-voltage control signal that demonstrates the technique's applicability to adaptive systems. >

Ring network communication structure on an optical carrier and reconfigurable node for said structure

Abstract: In a ring network communication structure for communication on an optical carrier (3A, 3B), a plurality of nodes (2A, ..., 2E) are interconnected by means of connections comprising at least a first (3A) and a second (3B) optical carrier, such as an optical fibre. Transmission occurs on the ring according to a WDM scheme, by utilising a first wavelength (λ₁) for communication in one direction on the first carrier (3A) of said pair, while communication in the opposite direction occurs by employing a second wavelength (λ₂) on the other optical carrier (3B). In the presence of a failure on one of the connections, the nodes adjacent (2B, 2C) to the failed connection reconfigure themselves to ensure the continuation of communication on the alternative path provided by the ring, by utilising the first wavelength (λ₁) on the second carrier (3B) and the second wavelength (λ₂) on the first carrier (3A). Preferential application to SDH optical fibre ring networks.

Remote millimeter-wave antenna fiber optic communication system using dual optical signal with millimeter-wave beat frequency

Abstract: The transmitter or receiver of the remote antenna system of the present invention includes a fiber optic link connecting the receiver or transmitter station with a remote antenna station. The optical carrier for the fiber optic link is produced by a dual optical signal generator, preferably in the form of two narrow-linewidth lasers frequency offset by a difference frequency corresponding to the millimeter-wave or microwave signal. If the invention is employed to convey a baseband signal from the transmitter station to the antenna station, a modulator at the transmitter station modulates the dual optical signal carrier with the baseband signal. The modulated signal is carried over the optical fiber to a photodetector at the remote antenna station which detects the millimeter wave difference frequency modulated by the baseband signal. If the invention is employed to convey a received millimeter wave signal from the remote antenna station to the receiver station, then a modulator at the remote antenna station modulates the dual optical signal carrier with the received millimeter wave signal. The modulated signal is carried over the optical fiber to a photodiode at the receiver station which detects the baseband contained in the millimeter wave signal.

Parametric wavelength interchanging cross-connect

Abstract: A wavelength-interchanging cross-connect for use as an optical switch within a wavelength-division multiplexing (WDM) communications network in which multiple optical carrier signals at different optical wavelengths are switched in an all-optical process according to their wavelength. The cross-connect of the invention further allows the optical wavelength of the signal being switched to be changed to another WDM wavelength. The cross-connect includes a series of multi-wavelength 2×2 spatial optical switches. One serial path is directly connected between the spatial switches. The other serial path leads through intermediate wavelength-interchanging modules that interchange the carrier wavelengths of at least one pair of signals. Preferably, the wavelength interchanging is performed by difference frequency generation relying on second-order non-linear susceptibilities and a pump signal providing parametric gain. The frequency of the pump signal is chosen to be the sum of the frequencies of whatever optical signals are to be interchanged, and more than one pair can simultaneously be interchanged. The placement of the pumping frequencies is determined by a design process using a modified version of a recursively designed Benes network. As a result, the wavelength-interchanging cross connect can be controlled by the well known looping algorithm known for Benes networks to be rearrangeably non-blocking.

Optical wavelength converters

Abstract: Devices and techniques for shifting the frequency/wavelength of an optical carrier wave are reviewed, with particular reference to applications in wavelength/frequency division multiplexed optical communication systems. Considered first are devices which make use of semiconductor laser amplifiers or oscillators. Some of these techniques come close to satisfying the requirements for a suitable wavelength shifter, though none appear to offer the potential for a transparent network independent of data modulation format. A second main category, using nonlinear optical materials, promises to satisfy the requirements for frequency translation in a network which is fully transparent to the modulation format. However, the conversion efficiencies currently available appear too low for cost-effective communication systems engineering so that further advances in nonlinear optical materials/techniques are still required. It seems likely that guided wave techniques will provide the best means of improving the efficiency by increasing the interaction length and the optical intensity for a given power. Schematic examples of such a converter are discussed. All of the existing techniques have some deficiencies compared to an ideal system so that wavelength conversion for optical communication systems is still a problem in search of a good solution.

Modulator LIDAR system

Abstract: A modulated LIDAR system is disclosed, in which a laser for generating an tical carrier signal and a microwave generator for generating a coded microwave signal are provided. A modulator is further provided for modulating the carrier signal with the microwave signal, whereby a modulated signal is generated. A method of detecting a reflective surface is also disclosed, in which an optical carrier signal is generated, the carrier signal is modulated with a coded microwave signal, the modulated signal is reflected off of a reflective surface and the reflected signal is recovered.

Optical transmission method with reduced sensitivity to dispersion, transmission device and system for implementing this method

Abstract: An embodiment of said method comprises coding a binary information sequence (SI) to be transmitted, in the form of a second binary signal (SM) by differential coding; filtering the second binary signal (SM) to obtain a duobinary signal (SMF) having three significant values (-a, O±e, +a) and a smaller bandwidth; modulating an optical carrier in accordance with the values taken by the filtered signal (SMF), by providing the modulated carrier with a maximum amplitude to represent the maximum value (+a) and the minimum value (-a) of the duobinary signal (SMF), by offseting the phase of the modulated carrier by υ1 and by υ2 = υ1 + 180° respectively; and providing the modulated carrier with a minimum amplitude to represent the values (O±e) which are close to O. The method of the invention is suitable for long distance fibre-optics transmissions.

Dispersion compensation for homodyne detection systems using a 10-Gb/s optical PSK-VSB signal

Abstract: This letter demonstrates fiber chromatic dispersion compensation for optical homodyne detection systems, using a VSB filtered optical PSK signal. An optical PSK signal suitable for SSB and VSB filtering is newly employed. A 10-Gb/s optical PSK-VSB signal is transmitted with an optical carrier through 126 km conventional single-mode fiber. Penalty-free transmission is achieved by fiber chromatic dispersion compensation in the baseband with a 10-cm microstrip line. >

Experimental investigation of fiber optic microwave link with monolithic integrated optoelectronic mixing receiver

Abstract: A fiber optic microwave link with a monolithic integrated optoelectronic mixing receiver (OEM) is demonstrated experimentally. The OEM consists of a GaAs metal semiconductor metal photodetector (MSM-PD) mixer and a MESFET transimpedance preamplifier. By modulating the bias of the MSM-PD with an electrical local oscillator, the information signals on an optical carrier are detected and converted to a desired electrical frequency simultaneously. Experimental results of a fiber optic microwave link with the OEM as a frequency up-converter are shown and the potential application of the OEM in fiber optic millimeter wave links is discussed. >

An optical intensity modulation transmission system

Abstract: In a transmitter side in an optical transmission system, an input binary signal is converted to duobinary signal, and said duobinary signal is applied to an optical modulation means which provides optical intensity modulation signal, wherein optical intensity for a center value of said duobinary signal is the minimum, optical intensity for other two values of said duobinary signal is the maximum, and optical phase for those two values is opposite with each other. In a receiver side, simple direct detection is carried out for receiving optical signal through an optical transmission line to provide demodulated binary signal. Thus, original binary signal is recovered without duobinary decoder and receiver sensitivity degradation. In the optical transmission system, optical carrier frequency component in signal spectrum is suppressed, signal bandwidth of modulated light is reduced as half as that of a prior art, so an optical transmission system for long distance, high bit rate and large traffic capacity is obtained.

Fiber optic Bragg grating true-time-delay generator for broadband rf applications

Abstract: A fiber-optic approach for low-loss true time delay of wideband RF signals for phased-array-antenna beamsteering is presented. An optical carrier modulated by the RF signal of interest is launched into a delay-line fiber composed of optical Bragg reflection gratings written holographically into the core of a single-mode fiber. The desired beam steering is realized by tuning the optical carrier wavelength for reflection from the appropriate grating. Radiation testing of various fibers with Bragg gratings has been performed indicating preferable fiber types. True time delay offers much reduced beam squint and sharper antenna superior nulling compared to phase shift scanned antenna. Examples of applications of this concept showing its advantages are presented.

Wideband fiber-optic signal processor

Abstract: In the transmission electrical signals using an optical carrier the signal power carried by an optical carrier is proportional to the optical power. High optical power levels are desired for optical carriers that are modulated by weak electrical signals, however, significant unmodulated power is left in the original carrier after processing. To maximize the radio frequency (RF) signal power generated by a given (maximized) photodetector current (for a given input power), in this invention, the optical carrier power is reduced. This is accomplished by the addition of a narrowband optical filter, such as a Fabry-Perot filter, to reduce the average optical carrier power without reducing the modulation sidebands, which results in an increased modulation depth. Therefore, greater RF and microwave power is generated by a photodetector with the same photocurrent. With a laser source exhibiting a beam whose linewidth is narrow compared to the filter bandwidth, the filter is tuned, or frequency locked, to match the filtering resonance with the optical carrier wavelength. With the high finesse filter and narrow-linewidth laser beam, the frequency range of operation is extended from the filter half-bandwidth to the next resonance of the filter. Thus, broadband effective gain results without introducing additional noise.

Method for low sensitivity optical transmission, transmission device and system for carrying out said method

Abstract: An embodiment of said method comprises coding a binary information sequence (SI) to be transmitted, in the form of a second binary signal (SM) by differential coding; filtering the second binary signal (SM) to obtain a duobinary signal (SMF) having three significant values (-a, O±e, +a) and a smaller bandwidth; modulating an optical carrier in accordance with the values taken by the filtered signal (SMF), by providing the modulated carrier with a maximum amplitude to represent the maximum value (+a) and the minimum value (-a) of the duobinary signal (SMF), by offseting the phase of the modulated carrier by υ1 and by υ2 = υ1 + 180° respectively; and providing the modulated carrier with a minimum amplitude to represent the values (O±e) which are close to O. The method of the invention is suitable for long distance fibre-optics transmissions.

Optical fiber feed system for a phased array antenna

Abstract: A signal feed system for a phased array antenna having a plurality of antenna elements arranged in an array with each antenna element being connected to a transmit/receive T/R module, the system having transmitter and receiver Tx/Rx equipment with an optical fiber signal feed between the Tx/Rx equipment and the T/R modules. A first opto-electronic interface converts signals from transmitter Tx to optical signals which are applied, via an optical fiber, to an optical coupler that couples those optical signals to a first group of optical fibers, each of which is connected to another opto-electronic interface where the optical signals are converted to electric signals and applied to the transmitter T in an associated T/R module which feeds an appropriate signal to its associated antenna element. Signals received by each antenna element are applied to a receive section R in a r/R module and then, from the receiver, to an associated opto-electronic interface where they are converted to optical signals and transferred by optical fibers in a second group of optical fibers to a second optical coupler that transfers those signals to the first opto-electronic interface. The first opto-electronic interface then converts those received optical signals into electrical signals that are applied to receiver Rx in the Tx/Rx equipment. This design allows for the use of a single high power laser as an optical carrier whose light can be remoted (i.e. distributed)to all the opto-electronic interfaces so that the optical carrier at each will be of the same wavelength.

Comparative evaluation of optical and conventional approaches for array antenna beamforming

Abstract: Microwave radar array antennas generally employ a beamformer which functions as the interface between the array elements and the transmitter-receiver, distributing signals to the array elements on transmit, and coherently combining the elemental signal components on receive. A conventional beamformer typically consists of corporate feed manifolds comprised of waveguide or coaxial cables, stripline combiner circuits, etc. These manifolds grow increasingly large and heavy in proportion to the number of elements in the array. Optical bemaformers, which utilize manifolds made up of optical fibers, promise a lightweight and very compact alternative approach. In an optoelectronic implementation the electrical signals are first converted to a modulation on an optical carrier frequency, and then the distribution and combining manifolds are configured with optical fibers. This paper compared conventional and optical implementations for a large, dual band (S and UHF) radar array. A detailed dual band beamformer design is developed for each technology and the two designs are compared with respect to weight, volume and power consuption. Both designs meet the same set of dynamic range, noise figure, bandwidth, power output, and sidelobe weighting requirements.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Method and apparatus for precise synchronization of atm cell in optical atm node

Abstract: PURPOSE: To compensate the delay caused by possible difference in optical routes in a node by utilizing dispersion dependence on wavelength in an optical fiber. CONSTITUTION: In an optical ATM node, a synchronized ATM cell is sent into the segment of an optical fiber (FD) having high time dispersion and a prescribed length. ATM cell transmission is performed after the cell is converted into such an optical carrier at a tunable wavelength converter (CL) that reaches the input sides of the switching elements (Em1,..., Emh) of a node (NC) at a prescribed moment as a result of the fact that the cell has a wavelength different from the original wavelength of the cell and passes through the optical fiber (FD).

Multi-wavelength, optical code-division-multiplexing based on passive, linear, unitary, filters

Abstract: The opportunity exists to apply spread spectrum concepts into the enormous bandwidth of optical fibers. We introduce a new optical CDMA network architecture based on passive linear unitary filtering of the optical carrier signals.

Method for dispersion compensation in an optical communication medium

Abstract: An electric baseband signal (IN) is divided between two parallel transmission circuits each incorporating a low-pass filter (LPF) between input and output modulators (M1,M2;MA,MB). An electric carrier frequency (fo) is inserted at the input, with 90 deg. phase shift (PSE) between the parallel circuits, and an optical carrier frequency (Fo) is inserted (To) with similar phase shift (PSO) for the output. The two optically modulated signals are added (ADD). The output modulators may be Mach-Zehnder interferometers.

Spatial optical communication equipment and spatial optical communication method thereof

Abstract: PURPOSE:To provide a spatial optical communication equipment and a spatial optical communication method thereof capable of reducing communication interruption due to the interruption of an optical transmission line between a transmitter and a receiver and the attenuation of optical carrier waves, surely transmitting information by minimizing the omission of transmission information and improving the reliability of communication. CONSTITUTION:This spatial optical communication equipment transmits optical pilot signals from an optical transmission part 4, receives the optical, pilot signals in an optical reception part 5 and detects and judges the level of the received optical pilot signals (the optical carrier waves) in an optical carrier wave detection and judgement part 6. The spatical optical communication equipment is used for a transmission side equipment and a reception side equipment and optical data signals are transmitted and received only when the detection levels of the optical pilot signals in the optical carrier wave detection and judgement parts 6 of both equipments are higher than a specified level.

High dynamic range applications of integrated optic modulators

Abstract: We review current 18 gigahertz optic link technology with a spurious free dynamic range of 110 dB/Hz2/3. The dynamic range of an externally modulated optic link increases with increasing optical power on the photodetector. One of the limiting factors for dynamic range is the amount of optical power that the photodiodes can handle. A method to allow greater optical information sideband power throught the link by filtering out some of the optical carrier will be discussed. The I/O modulator is normally run with an otpcial modulation depth of 4%. It should be possible to increase this by reducing the amount of optical carrier sent to the detector. This increase in the depth of modulation will reduce the RF loss and noise figure of the optic link thereby reducing the preamplifier requirements to obtain maximum dynamic range. This should make possible a spurious free dynamic range of 120 (db/Hz)2/3 with commercially available 18 GHz photodetectors. This technique could also be used to reduce problems caused by stimulated Brillouin scattering in long lengths of SM fiber.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A multiaccess coherent optical communication system using common optical carrier with star configuration

Abstract: A variety of multiaccess optical communication systems with common carrier have been reported recently This paper proposes a new type of multiaccess coherent optical communication system with star configuration in which a common optical carrier from a single source is distributed by a star coupler In this system, the carrier is phase-modulated at each user by an external modulator through a subcarrier signal and the signal is received by an optical heterodyne receiver A feature of the system is that the distributed optical carrier and the modulated light are directional-division multiplexed Theoretical analysis of the carrier-to-noise power ratio (CNR) of the system is carried out in this paper taking into account the effect of interference light caused by reflections, backscattering, or insufficient isolation of a circulator used in the system, followed by discussions on the allowable value of the signal-to-interference light power ratio and on the relation between transmitter power and maximum user numbers

Equipment for carrier wave extraction and re-insertion in optical communication network

Abstract: PURPOSE: To operate optical carrier extracting and reinserting equipment without relying upon polarization by making the equipment applicable to a wavelength division system by using a filter which can be adjusted finely for wavelength. CONSTITUTION: Various kinds of carriers existing at the branch 1e of a transmission line reach a fiber section after passing through the ports P1 and P3 of a circulator C1. A filter FP passes carriers having a wavelength and the carriers reach a receiver Rxi through a fiber 5. Carriers having the another wavelength are reflected by the filter FP and reach the output branch 1u of the transmission line through the ports P3 and P2 of the circulator C1. Similarly, carriers λwhich are transmitted from a transmitter and rely upon the input 3 of another circulator C2 pass through the filter FP in the reflecting direction and are inserted into a wavelength division multiplexing system at the output 1u of optical carrier extracting and reinserting equipment along a route (the ports P1' and P3' of the circulator C2, the fiber 5, and ports P3 and P2 of the circulator C1).

1.5 GHz time‐to‐wavelength converter

Abstract: The time‐to‐wavelength converter (TWC) is a fiber‐based system that converts time‐dependent voltage variations in a single‐transient electrical pulse into wavelength‐dependent power variations in an optical carrier pulse. This system is unique because its 1.5 GHz bandwidth is independent of signal transmission distance and the optical detector is a low‐bandwidth gated spectrophotometer. The TWC system uses a 50‐nm‐wide carrier pulse centered at 810 nm. It is capable of remotely measuring a transient analog signal with a pulse width between 0.20 and 3.0 ns full width at half‐maximum and has a −3 dB bandwidth from 104 MHz to 1.56 GHz. The system’s dynamic range is 12 dB for transient signals but it can be increased to about 30 dB by averaging multiple pulses. Its operation is based on the generation of an optical carrier pulse by self‐phase modulation in a flexible capillary filled with carbon disulfide; wavelength dispersion in a fused‐silica single‐mode fiber; optical intensity modulation using a Pockels cell; and spectral analysis of the modulated optical signal.

The design and fabrication of monolithic millimeter wave optical receivers

Abstract: The optical receiver circuits were fabricated monolithically on GaAs based materials. The optical receivers were to detect the modulated signal at 44 GHz transmitted through optical carrier. MSM photodetectors and P-MODFET's were employed in the receiver circuits. The photodetector layer was specially designed for the high quantum efficiency for 770 nm light by using Bragg reflector layers and cap layer. InGaAs channel P-MODFET's, adapted for the post-detection amplifiers, exhibited f/sub t/ of 90 GHz and f/sub max/ of 100 GHz. For DC bias lines and isolations, ground plane capacitors and thin film isolated bias lines were used. The circuit was designed and fabricated by conjugately matching the S-parameters of each device at 44 GHz through CPW transmission lines. The receivers were measured up to 40 GHz, showing about 3 dB gain at 39 GHz.

Crosstalk measurement and reduction in dense WDM systems using subcarrier tone channel identification and linear cancellation

Abstract: Proposes a scheme for the monitoring and reduction of crosstalk arising front the limited stop-band rejection of optical bandpass filters in dense WDM systems. The optical carrier at each wavelength is modulated with a subcarrier tone unique to that wavelength. The crosstalk level can be determined by measuring the power of the tone. The crosstalk from other channels can be cancelled by weighing and summing the photocurrents of several adjacent channels. Assuming a Gaussian passband for example, the channel density can be increased by 30% to 50%, depending on the number of adjacent channels detected, and the system can achieve a BER <10/sup -9/ even if the signal-to-interference ratio is less than 10 dB.