Showing papers on "Optical communication published in 1975"

Multi-core optical communications fiber

Abstract: Methods and apparatus are disclosed for providing a multipath optical communications system within a single fiber. One embodiment comprises a concentric multi-core optical fiber having an inner core for transmitting information and an outer core for transmitting a security signal. Attempted access to the inner core causes a decrease in the security signal intensity alerting the operator to the attempted intrusion.

Optical communication, switching and control apparatus and systems and modular electro-optical logic circuits, and applications thereof

Abstract: Optical communication, switching and control apparatus and systems are disclosed, including modular electro-optical logic circuits, methods of construction and assembly of such modules and applications thereof. Optical transmission lines are interconnected by convenient connectors, and are assembled with switches, and optical signals, including visible light radiation, ultra-violet radiation and infra-red radiation are transmitted over the lines for carrying data and/or central signals. The optical transmission and control systems are used to control illumination, vehicle equipment, manufacturing and chemical processes, machinery, home appliances, and are used to monitor medical conditions in the human body. The electro-optical modules are assembled together with their respective light radiation transmitting windows or optical ports in communication one with another in computer equipment.

Optical heterodyne receiver with phase or frequency lock

Abstract: An improved optical heterodyne receiver is disclosed. Novel control circuitry is utilized in the receiver to provide compensation and tracking for undesired phase and frequency excursions of both the received and the local oscillator signals. An optical heterodyne receiver such as that disclosed is especially useful in optical communications systems having wideband variations in the frequency of the received signal caused by Doppler shifts and angle-modulated noise components.

Optical couplers for light emitting diodes and detectors

Abstract: An optical coupler is provided for connecting between optical fibers and electro-optical elements in optical communication systems. The coupler comprises one element consisting of a connector fiber within a support tube fixedly attached to the electro-optical elements at one end and optically polished at the other end. Connection between the connector fiber and an optical communication fiber is provided by means of a second element consisting of a dual diameter connector tube. The dual diameter tube slidingly engages the support tube at one end and the systems fiber at an opposite end to provided close optical proximity between the systems fiber and the connector fiber.

Optical communications link

Abstract: The specification discloses a wireless optical communications link which includes a transmitter housing having circuitry for receiving electrical audio and video signals. A light emitting diode is mounted in the transmitter housing for generating a directional beam of light. Circuitry modulates the beam of light in accordance with the audio and video signals. A receiver housing is adapted to be located remote from the transmitter housing and includes an aspheric Fresnel lens for receiving and focusing the beam of light. A photodiode is mounted in the receiver housing for generating electrical output signals in response to the received beam of light. Circuitry is responsive to the electrical output signals for reconstructing the audio and video signals at the remote location.

Calculation of Coupling Losses Between Light Emitting Diodes and Low-Loss Optical Fibers

Abstract: We have investigated the problem of coupling light emitting diodes to contemporary low-loss multimode optical fibers (NA ~ 014) for optical communications We have calculated the maximum coupled light power and the coupling efficiencies for a disk geometry and a strip geometry with and without a lens In our calculations, we assumed that the homostructure LED has a radiance of 30 W/sr cm(2) and requires an electrical power input JV or 2 x 10(4) W/cm(2) In the disk geometry without a lens, the maximum coupled light power of 36 microW can be achieved With a lens the LED junction area can be reduced so that the coupled light power of 31 microW, which is 01% of the input electric power, is possible In the strip geometry with a lens a coupled light power of 260 microW is achievable

Glass Fibers for Optical Communications

Abstract: Glass fiber optics have been used for many years for flexible light distribution bundles, faceplates for cathode-ray tubes, medical endoscopes, and similar purposes. Only recently (1) has serious research been directed toward the use of glass fiber as a long distance communication medium (2, 3). Such a communication system requires three main components: a transmitter, a receiver, and a transmission medium. The transmitter will most likely consist of a GaAIAs laser or light emitting diode (LED) driven with a digital signal. Such transmitters can operate at a wavelength of 800-900 nm at data rates up to hundreds of megabits per second. Another possible transmitter is based on an externally modulated Nd: YAG laser operating at 1060 nm. The receiver of an optical communication system will probably be a semiconductor photodetector that can be part of an integrated circuit chip used for processing the signal. Silicon avalanche diodes and silicon PIN diodes are sensitive at the GaAIAs wavelengths, and they have been built with bandwidths of at least a few hundred megacycles. Using lasers and avalanche photodiodes, losses of about 75 dB can be tolerated between repeaters operating at 1 megabit/sec, but only 45 dB loss is tolerable at 1000 megabits/sec. An excellent review of 'transmission and receiving devices has been published by Miller, Marcatili & Li (2). The transmission medium will be an optical fiber waveguide, consisting of a core of relatively high refractive index surrounded by a cladding of relatively low refractive index, The maximum tolerable loss per kilometer is governed by the distance over which transmission must take place. Losses as high as 100 dB/km may be acceptable for very short systems, as on airplanes or ships, whereas losses as low as 4 dB/km or less may be required for long distance systems where expensive repeaters must be spaced many kilometers apart. In addition to loss, another important characteristic of glass fiber waveguides

Semiconductor Components for Monolithic Applications

Abstract: In monolithic integrated optics, all optical functions must be obtained in a single material These optical functions can be broadly categorized as light generation, guiding, coupling, modulation and detection Active functions such as light generation, modulation and detection generally require crystals rather than amorphous light guides The only material to date in which all functions have been obtained is GaAs The existence of continuous lasers in GaAs operating at room temperature is a prime incentive for considering this material This chapter will be devoted to the fabrication of optical circuit elements in crystals, with special importance placed on GaAs and related III-V semiconductor compounds The spectral region in the red or near infra-red will be emphasized, because this is a region of low loss for optical fibers and therefore of interest for optical communication systems We shall describe ways to produce optical waveguides in crystals, particularly of the semiconductor variety, both planar and channel guides being considered We shall discuss ways to fabricate active elements in GaAs which generate, modulate and detect the light Finally, the growth processes of liquid-phase epitaxy will be discussed in some detail, as crystal growth is a necessary step for the realization of integrated optics using GaAs

High-power long-lived double heterostructure LED's for optical communications

Abstract: The use of light emitting diodes (LED's) in optical communications systems is critically dependent on the availability of high power single fiber compatible devices capable of sustained operation, for times in excess of 105hours. In this paper, the design and evaluation of double heterojunction Burrus(1)type GaAlAs LED's optimized for coupling to large core multimode glass fibers is described.

Phase-locked optical homodyne receiver

Abstract: An improved homodyne receiver for use in wideband optical communications systems is disclosed. The invention provides phase-locked homodyne reception of non-suppressed carrier or suppressed carrier input signals. Novel means are provided in the receiver for generating an error signal to provide phase-locked operation in the presence of noise and frequency excursions of the received signal.

A Modified Receiver for Optical Transmission Systems

Abstract: A Percival coil connected between the photodetector and amplifier in the receiver of an optical communication system offers the possibility of improved signal-to-noise ratios (SNR's). When the photodetector is an avalanche diode, the modified receiver requires a lower value of avalanche gain for optimum performance.

Optical communication system with bipolar input signal

Abstract: A bipolar electrical signal of the type transmitted in the T1 digital transmission system is converted into an optical binary signal having pulses and spaces by translating each positive digital "1" in the bipolar signal into two digital pulses, each negative digital 1 in the bipolar signal into two spaces, and the digital 0 in the binary signal into an optical pulse followed by a space. The nonpermitted code of a space followed by an optical pulse is utilized at the receiving location for instantaneous framing. As a result of this particular code conversion, the balanced property of the bipolar input signal is maintained in the optical signal thereby preventing an offset bias from developing at the receiving location in the photodetector. In addition, the bipolar information is maintained in transmission, thus making the optical system "transparent" to bipolar signals.

Tunable laser oscillator

Abstract: A laser oscillator circuit is disclosed which allows the operating frequency of the laser to be tuned over a wide range of frequencies in response to a wideband control signal. A laser oscillator such as that disclosed is useful in optical communications systems and especially in optical receivers utilizing a phase-locked control loop for tracking out frequency variations due to noise and the Doppler shifts.

Dual channel phase locked optical homodyne receiver

Abstract: An improved homodyne receiver for use in wideband optical communications systems is disclosed. The receiver utilizes dual channelization of the optical input signal in the manner of a Costas two-phase synchronous receiver. A novel beam-splitting/phase-splitting optical assembly is used to channelize the received and the local oscillator beams and insure the desired phase relationships. The receiver is capable of phase-locked operation in the presence of noise and frequency variations in the received and local oscillator signals.

Apparatus for word synchronization in an optical communication system

Abstract: An optical communication system is disclosed in which a bipolar signal of the type transmitted in digital transmission systems is converted into a unipolar binary signal for transmission over an optical transmission medium. The three levels of the bipolar signal are converted into three pairs of bits in the binary signal. One pair of bits is not utilized in the conversion and is therefore labeled as a forbidden word. Synchronization is achieved at the receiving location for the purpose of decoding by detecting the presence of the forbidden word in the binary signal and in response to this detection an energizing pulse is produced. This energizing pulse drives a clock circuit which in turn drives a decoding apparatus utilized to translate the binary signal back into the bipolar signal. As a result of this type of word synchronization, individual errors introduced into the binary signal do not result in a framing error.

Radiation-resistant integrated optical signal communicating device

Abstract: An integrated optical signal communicating device associating an optical eguide for guiding a light wave with a light-emitting junction for emitting the light wave and a light-collecting junction for receiving at least a part of the light wave. The device utilizes the gallium aluminum arsenide alloy system in the fabrication of the waveguide, emitter and collector to produce a device with high radiation resistance.

Thin-film waveguide devices

Abstract: This paper reviews a variety of practical or potential uses of low optical loss thin-film waveguides for light modulation, deflection, and switching. Emphasis is given to those thin-film devices that most likely will become necessary replacements of the bulk for systems involving signal processing, imaging radar, and optical communication in the infrared.

Wide dynamic range analog signal optical communication system

Abstract: A system for transmitting low level analog signals wherein the analog sigs are converted into frequency modulated light amplitudes which are transmitted by means of an inexpensive fiber optic bundle, and the transmitted modulated light is demodulated at the receiving end to obtain an exact replica of the input signals. The system enables one to maintain a large amplitude dynamic range using an inexpensive photo-transistor.

A Modified Receiver for Digital Optical Fiber Transmission Systems

Abstract: A Percival coil connected between the photodetector and amplifier in the receiver of a digital optical communication system offers the possibility of a reduced signal power requirement for a given bit error rate. When the photodetector is an avalanche diode, the modified receiver requires a lower value of avalanche gain for optimum performance.

Method and apparatus to provide a secure optical communication system

Abstract: The intelligence on an optical communication system is made secure by launching an intelligence modulated optical beam into the input end of an optical waveguide at a small angle with respect to the axis of the waveguide and launching a masking signal modulated optical beam into the input end of the waveguide at a high angle with respect to the axis of the waveguide. At the output end of the waveguide only the intelligence modulated optical beam is transmitted to an optical detector with the masking signal modulated optical beam being blocked from the detector. This prevents an intruder from separating the intelligence signal from the masking signal when observing the waveguide radially.

Submarine optical communication system with fiber optic depth compensator

Abstract: A system for providing secure communication by use of optical frequency transmission between an aircraft or spacecraft and a deeply submerged submarine. The submarine extends at least one fiber optic cable terminated in a lens arrangement. A flotation unit insures that the cable is extended substantially vertically to a point approaching, but not penetrating the surface of the sea. The thickness of the water layer between the surface and the cable upper end is thereby such as to reduce the attenuation of transmitted and received optical signals. Submarine communications may thereby be effected through modulated light beams while the submarine itself remains at a greater and more secure depth.

Integrated Optics at 10.6-mu m Wavelength

Abstract: While the major objective of integrated optics at the visible-light and near-infrared wavelength is to provide thin-film components to obtain switching, modulation, source, detection, etc., for fiber-optics communication, the immediate objective of integrated optics at the 10.6-mu m wavelength is to improve the operational characteristics of conventional bulk components via guided-wave technology. This paper will discuss the properties of the waveguides, the modulators, the passive components, and the waveguide laser that have been made to date. The most significant advancement is probably guided-wave modulation. Both the analysis and the initial experimental measurements indicate that pi-phase or 100-percent amplitude UHF-VHF modulation could be obtained with only a few hundred watts of modulation drive power. Microwave modulation has also been experimentally demonstrated. Naturally, this is only an interim report. Many exciting developments will be obtained in the future.

A theoretical assessment of low and high bandwidth gallium arsenide, germanium and silicon avalanche photodiodes for optical communication systems

Abstract: A comparison is made of the relative properties of avalanche photodetectors for use in optical communication systems operating up to 1 GHz bandwidth over the wavelength range 730–1130 nm. Detectors for optical communications systems may have to operate at voltages limited by the electrical feeds to repeaters, hence the present comparison is for the specific case of diodes with a maximum operating voltage. The voltage used is generally 100V, but the analysis is also extended to 200V. The speed of the diodes is considered briefly then the main analysis compares the signal to noise performance of gallium arsenide, germanium and silicon diodes. The most recent noise theory is used incorporating the frequency dependence of multiplication and a detailed comparison is made of the results and their differences for the three materials analysed. In addition comparison is made with results using less accurate theories. The optimum diode material, for the simple uniformly doped 100V diodes considered, varies with wavelength and frequency. However the results show that there is no clear-cut choice and that, for instance, at long wavelengths (i.e. greater than 1·05 nm) germanium diodes, despite their high dark current, have comparable or better performance than silicon diodes for operation at 100V. Similarly in the conditions considered gallium arsenide photodiodes might provide an alternative detector for high frequency systems using gallium aluminium arsenide lasers.

Semiconductor laser for optical communication systems - with narrow band emission obtd. using interference filter

Abstract: A semiconductor laser, esp. a double-heterostructure laser of GaAs-Ga1xAlxAs, has one of the two cleaved crystal ends forming the optical resonator provided with a highly reflecting mirror layer. To restrict the spectral range of the emitted radiation, the opposite end to the mirror end is provided with a narrow band interference filter which exhibits high transmission and low reflection of the desired emitted wavelength, but which is virtually impermeable to adjacent wavelengths. The mirror is pref. a dielectric with 100% reflection whereas the interference filter is a Fabry-Perot filter, or a Fabry-Perot multi-filter of partial, dielectric layers. Used for transmitters and intermediate amplifiers in optical communication systems. The laser radiation is restricted to a very narrow frequency band, and thus an optical transmitter can be built for very large band widths.

The avalanche phototransistor—A novel type of radiation detector and its potential use in optical communication systems

Abstract: The possibility of triggering avalanche transistors by optical signals and the resulting electrical characteristics are presented. These avalanche phototransistor (APT) detectors are capable of generating nanosecond output pulses at high current levels. A series connection of an APT and injection laser is shown to operate as a simple PCM-regenerator circuit in optical communication systems.