Showing papers on "Optical communication published in 2001"

Indoor visible communication utilizing plural white LEDs as lighting

Abstract: Future electric lights will be composed of white LED (light emitting diodes). Indoor wireless optical communication systems utilizing white LED lights have been proposed in our laboratory and we have been studying it. Generally, plural lights are installed in our room. Therefore, their optical path difference must be considered. In this paper, the influence of optical path difference has been investigated and two approaches for this problem are introduced. One uses OOK-RZ (on-off keying, return-to-zero) coding and the other uses optical OFDM (orthogonal frequency division multiplexing). From the results of computer simulations, we have found that these approaches are feasible for wireless optical communication systems utilizing white LED lights.

Integrated optical micro-electromechanical systems and methods of fabricating and operating the same

Abstract: An apparatus and method of fabricating and operating a micro-electromechanical systems (MEMS) integrated optical structure is disclosed. Micro-optics is integrated with MEMS actuators to provide a building block for a micro-optical communication device. Such micro-optical communication device may realize a variety of optical communication systems including optical interconnects, laser communications, or fiber optic switches. In accordance with one aspect of the present invention, a micro-optical element such as a micro-lens is advantageously integrated with an actuator such as MEMS comb drive actuator to form a MEMS lens assembly. The MEMS lens assembly is further coupled to an optical source which may provide a MEMS integrated micro-optical communication device. This integration substantially obviates the generally needed external or manual positioning of the micro-optical element to align a light beam or an optical signal being emitted from the optical source. The MEMS comb drive actuator, responsive to an actuation force, selectively positions the micro-optical element. By appropriately micro positioning a micro-optical element such as a micro-lens relative to an optical source, such as an input optical fiber or a laser diode, a focused light beam or an optical signal may be coupled to a respective optical fiber or a detector. In one embodiment, a commonly used flip chip module assembly technique may be adapted for bonding the MEMS lens assembly to a carrier substrate, which preferably receives the optical source. The carrier substrate is generally disposed on a host assembly. A flip chip based passive alignment of the MEMS lens assembly could be provided. Additionally, an active alignment of the light beam or optical signal with an optical detector may be provided, which can be maintained through a feedback loop.

Electro-opto-mechanical assembly for coupling a light source or receiver to an optical waveguide

Abstract: A novel electro-opto-mechanical assembly is provided. The electro-opto-mechanical assembly comprising: a first wafer, the wafer having a top and bottom surface; at least one optical element disposed on one surface of the first wafer; at least one discrete opto-electronic transducer element disposed on the bottom surface of the first wafer and in optical communication with the optical element; and an optical waveguide; wherein the first wafer and the optical element form an optical relay which relays light between the discrete opto-electronic transducer and the optical waveguide and thereby forms an efficient optical coupling between the discrete opto-electronic transducer and the optical waveguide.

Wavelength division multiplexing optical communication system and wavelength division multiplexing optical communication method

Abstract: The object of the present invention is to provide a WDM optical communication system and a WDM communication method wherein deviation of transmission characteristics of optical signals of respective wavelengths is reliably controlled, based on reception information such as the OSNR, BER and the like measured at the receiving end, thereby enabling optimal transmission conditions to be realized. For this purpose, the present WDM optical communication system transmits WDM signal light of wavelengths λ1˜λn, which has been generated by the transmitting end of one terminal station, to the receiving end of the other terminal station through an optical transmission path. At the receiving end, the OSNR and BER of the optical signals of wavelengths λ1˜λn are measured, and the result is superimposed on overhead information transmitted along the opposing line of the optical transmission path as reception information. At the transmitting end, the settings of pre-emphasis and a parameter α are feedback controlled based on the reception information about each wavelength transmitted, and deviation of transmission characteristics of respective wavelengths is thus suppressed.

Optical heterodyne detection in optical cavity ringdown spectroscopy

Abstract: The present invention relates to optical heterodyne detection cavity ringdown spectroscopy. In one aspect the invention relates to an optical system (1) comprising a ringdown cavity cell (3) defining a resonant optical cavity, means for directing coherent light selected from the group consisting of continuous or quasi-continuous light into said optical cavity (8, 9, 10, 11 and 12), means for altering the resonant optical cavity so as to generate a frequency shift of the coherent light in the optical cavity (6, 7), means for coupling said coherent light into the optical cavity and means for decoupling the frequency shifted coherent light out of said optical cavity (5, 6, 7), means for optically combining (10, 11, 12) said decoupled frequency shifted coherent light with another portion of coherent light not in optical communication with the optical cavity and means for optical heterodyne detection (13) of the intensity of said combined light. A method for optical detection is also described as well as methods and apparatus for detecting a parameter of a sample.

Synchronization and communication using semiconductor lasers with optoelectronic feedback

Abstract: Semiconductor lasers provide an excellent opportunity for communication using chaotic waveforms. We discuss the characteristics and the synchronization of two semiconductor lasers with optoelectronic feedback. The systems exhibit broadband chaotic intensity oscillations whose dynamical dimension generally increases with the time delay in the feedback loop. We explore the robustness of this synchronization with parameter mismatch in the lasers, with mismatch in the optoelectronic feedback delay, and with the strength of the coupling between the systems. Synchronization is robust to mismatches between the intrinsic parameters of the lasers, but it is sensitive to mismatches of the time delay in the transmitter and receiver feedback loops. An open-loop receiver configuration is suggested, eliminating feedback delay mismatch issues. Communication strategies for arbitrary amplitude of modulation onto the chaotic signals are discussed, and the bit-error rate for one such scheme is evaluated as a function of noise in the optical channel.

Optical module, method for manufacturing optical module and optical communication apparatus

Abstract: An optical module for an optical device and an optical fiber is constituted by a pre-molded plastic package. In forming the plastic package, the main flowing direction of the molding resin is substantially parallel with the optical axis of the optical fiber. The optical module is formed by molding the resin by an injection method using pressure and then solidifying the resin. When the plastic package is formed by comprehensive molding, the flowing direction of the resin is parallel with the optical axis direction of the optical fiber to be installed in the optical module. As a result, for comprehensive molding, the molding pressure applied to the optical fiber is reduced. By using the resin case that is formed, the resulting package exhibits high rigidity and low thermal expansion properties in connection with the flowing direction of the resin, thus reducing the external stress and thermal stress applied to the optical fiber.

Optical communication device

Abstract: An optical communication device including optoelectronic (LD, PD, LD/PD) elements allocated to a top surface of a circuit board and electronic, electric elements (IC, R/C) allocated to a bottom surface and to the top surface of the circuit board.

Protection switching for an optical network, and methods and apparatus therefor

Abstract: An optical communications network having at least one optical switch connected to a network access device. The optical switch includes a first line card disposed along a first communications path over which a first optical signal is transmitted. The first line card is connected to the network access device. A second line card is disposed along a second communications path over which a second optical signal is transmitted. An inter-card communication channel is provided for bridging the second path to the first line card. The system enables the rapid switching of traffic from the first optical path to the second optical path.

Transceiver, system, and method for free-space optical communication and tracking

Abstract: A transceiver, method, and system for optical communication. The system including at least a first and second optical transceivers each having an optical assembly unit with a single-aperture for transmitting and receiving optical communication signals and receiving beacon signals, and the optical assembly unit having one or more light sources attached thereto for emitting beacon signals. The transceiver, method, and system providing for superior tracking of optical communication signals/light beams transmitting information in free-space.

Secure communication scheme using chaotic laser diodes subject to incoherent optical feedback and incoherent optical injection

Abstract: We propose a secure communication scheme based on anticipating synchronization of two chaotic laser diodes, one subject to incoherent optical feedback and the other to incoherent optical injection. This scheme does not require fine tuning of the optical frequencies of both lasers as is the case for other schemes based on chaotic laser diodes subject to coherent optical feedback and injection. Our secure communication scheme is therefore attractive for experimental investigation.

Optical communication system

Abstract: A method for transferring information within a cellular communications network ( 20 ), consisting of transmitting an optical carrier from a first network-element ( 26 A) of the network, modulating the optical carrier ( 57, 59 ) with the information, and detecting the modulated optical carrier in an avalanche photo-diode (APD) ( 150 ) in a second network-element ( 24 A) of the network so as to recover the information The method includes altering a gain of the APD responsive to a level of the optical carrier so as to prevent saturation of the APD Other methods and apparatus are also provided for transferring the information via the optical carrier, and also for using the information transferred

On the capacity of intensity modulated systems using optical amplifiers

Abstract: We study the information capacity and the information density of communication systems using optical amplifiers, in the direct detection intensity modulation case. Our results are compared with Shannon's formula for coherent detection, where we find that in the relevant range of parameters the information density of intensity modulated systems is equal to one half of the density of coherent systems minus 1 bit/s/Hz. We show that with typical values of optical signal-to-noise ratio of the order of 20 dB, multilevel signaling can increase the information density by no more than a factor of 3.5 relative to binary modulated systems. The highest information density is obtained with a symmetric optical spectrum and it cannot be improved by removing one sideband as in the single sideband modulation case.

Miniature monolithic optical add-drop multiplexer

Abstract: A miniature monolithic optical add-drop multiplexer that comprises a dispersive optical element, a wavelength filter array and a diverter. The miniature monolithic optical DWDM add-drop multiplexer can be fabricated using micro- and nano-scale techniques common to the semiconductor industry. The operating principles and some characteristics of the DWDM add-drop multiplexer are described. The device will be useful in the field of optical communication as a component within networks that perform all of the necessary switching, adding, dropping, and manipulating of optical signals entirely in the optical domain.

Hybrid WDM-TDM optical communication and data link

Abstract: A hybrid WDM-TDM optical link employing a hybrid modelocked multi-wavelength semiconductor which provides approximately 4 to approximately 20 wavelength channels that makes possible modulated multiplexed data which when demultiplexed by ultra fast optical demultiplexing provides rates suitable for conventional electronic photo receivers. The link uses single-stripe GaAs/AlGaAs semiconductor optical amplifiers which simultaneously generate from approximately four to more than approximately twenty tunable WDM channels. Diode laser can also include InP, InGaAlP, InGaAsP, InGaP, InGaAs. A four channel version transmits approximately 12 picosecond pulses at approximately 2.5 GHz for an aggregate pulse rate of 100 GHz. When generating approximately 20 wavelength channels, each transmitting approximately 12 picosecond pulses at a rate of approximately 600 MHz, there is provided optical data and transmission systems operating at rates in excess of 800 Gbits/s.

Free space optical communications link tolerant of atmospheric interference

Abstract: Free space optical communications systems which resist atmospheric attenuation of optical beams is presented Very long link distances remain highly reliable despite fog and other inclement weather conditions which otherwise tend to hamper optical transmissions in an atmospheric air column Systems include primary elements as follows: a plurality of transceivers and at least one air column optical path Each transceiver includes specialized light sources which produce radiation in the Mid-IR spectral region In addition, these sources are very compact and well organized in view of their intended deployment environment Further, special modulation means are joined with particular light sources to address high bandwith needs In addition, specialized detection strategies are presented whereby sensitivity is improved Alternative versions and configurations directed to specialized function are also described in detail

Fully stabilized electroabsorption-modulated tunable DBR laser transmitter for long-haul optical communications

Abstract: We report on a fully functional 2.5-Gb/s electroabsorption (EA)-modulated wavelength-selectable laser module meeting all long-haul transmission requirements for stability, chirp, power and linewidth over 20 channels on a 50-GHz grid. Based on a highly integrated InP chip comprising a distributed Bragg reflector (DBR) laser, semiconductor optical amplifier, power monitor, and EA-modulator, the compact transmitter module also contains optics and control circuits necessary to ensure simultaneous long-term wavelength and mode stability. We have achieved 2.5-Gb/s transmission on all 20 channels over 680 km of standard fiber.

Receiver designs and channel characterization for multi-spot high-bit-rate wireless infrared communications

Abstract: This paper addresses one of the most promising candidates for high-speed in-house wireless communications, namely, the multi-spot diffusing configuration (MSDC). Since it uses the optical infrared medium for data transmission, it has the inherent potential for achieving very high capacities. The channel characteristics in MSDC are simulated and the causes for channel distortion are analyzed. Then, conditions for creation of a virtually ideal channel are derived. It is shown that the 3-dB channel bandwidth can be extended up to beyond 2 GHz. This bandwidth comes at the cost of a poor power efficiency. In order to compensate for that, a novel receiver optical front-end design is proposed and its performance is analyzed. Taking advantage of the unique properties of the holographic optical elements, the conventional optical front-end, consisting of a concentrator and a filter, is replaced by a single holographic curved mirror. The utilization of such a holographic optical element improves the signal-to-shot noise ratio by up to 18.5 dB.

Cost-effective wavelength division multiplexer and demultiplexer

Abstract: A cost-effective wavelength division multiplexer and demultiplexer for use in optical communication consists of three modules, including a fiber array (20), a lens array (30) and a filter array/reflector (40). Each array is made in wafer level with very precise position control and is bonded to an adjacent wafer by conventional wafer bonding techniques. In addition to eliminating the need for active alignment in the manufacturing process of a wavelength division multiplexer (WDM) transceiver, the invention reduces the footprint of such a device to the order of a few millimeters and the process is suitable for low-cost, large quantity manufacturing. The fiber array (20) is connected to the light sources (10, 12, 14, 16), which optimally are fiber pig-tailed semiconductor lasers to enable repeatable and accurate placement in reference to the lens array (30). The input lenses (32, 34, 36, 38) are used to collimate the beams such that light traveling from them at an angle will zigzag between the reflector (49) and the filters of the filter array/reflector combination (40). In the multiplexer configuration, an output lens (39) is used to focus and couple the beams from each different laser (10, 12, 14, 16) into a fiber (18).

Programmable optical multiplexer/demultiplexer

Abstract: A programmable optical demultiplexer can independently assign every input optical channel in a WDM optical communications signal to depart from any desired output port. The demultiplexer device can also be operated in the reverse direction, and thus achieve programmable optical multiplexer functionality, by accepting different wavelengths at each of multiple input ports and efficiently combining the wavelength channels at the multiplexer output port. The programmable multiplexer/demultiplexer device has an optical arrangement for spatially dispersing the optical wavelengths, and tunable micro-mirrors for beam steering each channel independently. Controlling the beam reflection direction determines the connectivity between the input and output ports at the wavelength level.

Optical communication system with co-propagating pump radiation for raman amplification

Abstract: A fiber Raman amplifier is configured to use a co-propagating Raman pump source, which may be beneficial in a variety of system configurations (for example, in bidirectional communication systems). By carefully configuring the pump source characteristics, sufficient optical gain can be achieved in the co-propagating arrangement, the characteristics including: (1) using an optical pump power of at least 50 mW, (2) having a relatively large spectral bandwidth within the pump (to suppress SBS); and (3) a frequency difference between all longitudinal pump modes of each pump laser being separated by at least the walk-off frequency between the pump laser frequency and the signal frequency, and all intense longitudinal modes between different pump lasers being separated by at least the electrical bandwidth of the communication system.

Method and apparatus for locking the transmission wavelength in optical communication laser packages

Abstract: The present invention is directed toward a monitoring and control system for an optical system. In one aspect of the present invention the system may include an interferometer that splits an input beam into a transmitted portion and a reflected portion. The interferometer introduces a path length difference between at least a segment of the transmitted and reflected portions that recombine to form an output beam having an intensity that varies as a function of wavelength of the input beam.

Precise operation-frequency control of monolithic mode-locked laser diodes for high-speed optical communication and all-optical signal processing

Abstract: We describe a method for pulse-repetition-frequency tuning of mode-locked laser diodes (MLLDs) monolithically integrated with a distributed Bragg reflector (DBR). The pulse-repetition frequency, i.e., the cavity-roundtrip time, is tuned through loss-induced change in the effective length of the DBR. The frequency-tuning range as large as the chip-to-chip frequency deviation caused by cavity-length fabrication variation of 10 μm has been confirmed experimentally, and the MLLDs operate at SDH (synchronous digital hierarchy) frequencies of 9.953, 19.906 and 39.813 GHz. Synchronization with an external system-clock through the hybrid mode-locking operation reduces the timing jitter of the optical pulses to less than 0.3 ps. As an optical pulse source for optical communication, error-free 20-Gbps transmission over 3000 km has been demonstrated, confirming that the MLLD properties satisfy the requirements for use in real systems. The novel application of MLLDs to all-optical clock extraction, one of the essential functions required in all-optical signal processing, has been demonstrated at the 40-GHz SDH frequency.

Communication using synchronization of optical-feedback-induced chaos in semiconductor lasers

Abstract: A communication system based on the synchronization of optical chaos in semiconductor lasers is proposed. The optical chaos is generated in a single-mode semiconductor laser with external ring optical feedback. Synchronization of chaos is performed by a direct optical-injection scheme that consists of a transmitter laser with an external optical feedback and a receiver laser with optical injection from the transmitter laser. Both numerical and experimental results on synchronization of giga-hertz chaotic signals are presented. Direct encoding of 2.5 Gbps messages on the chaotic waveform is numerically demonstrated. The bit-error rate shows a sensitive dependence on the frequency detuning.

Method and apparatus for optimizing SBS performance in an optical communication system using at least two phase modulation tones

Abstract: A method of optimizing SBS suppression is disclosed for use in an optical communication system including a light guide for transmitting light and means for producing phase modulation of the light using at least first and second tones. In the method, an operational region of SBS suppression is established as a function of the phase modulation of the light such that the operational region identifies combinations of first and second phase modulation levels at which optimum SBS suppression is achieved for the first and second tones. Thereafter, based on the operational region, the first and second phase modulation levels are adjusted such that the system operates with optimum SBS suppression. In one aspect, a contour map and associated method are introduced. The contour map is especially suited for use in optimizing SBS suppression in an optical communication system in which light is phase modulated using at least first and second tones for transmission of the phase modulated light via media which exhibits an SBS threshold. In another aspect, one of the sub-regions identified by the contour map may be selected as the operating point of the system based on certain characteristics of the contour map at and around the location of the selected operating point. In this manner, for example, the stability of the optical communication system may be improved in the event that the selected operating point is subject to drift.

In-orbit measurements of short term attitude and vibrational environment on the Engineering Test Satellite VI using laser communication equipment

Abstract: Morio ToyoshimaNational Space Development Agency ofJapan2-2-1 SengenTsukuba, Ibaraki 305-8505JapanE-mail: toyoshima.morio@nasda.go.jpKenichi ArakiCommunications Research Laboratory4-2-1 Nukui-KitamachiKoganei, Tokyo 184-8795JapanE-mail: araki@crl.go.jpAbstract. Angular microvibrations of platform jitter on a three-axisattitude-stabilized satellite are measured in space using an onboard la-ser communication terminal. Stable optical tracking control allows themeasurement of relative angular variations from the reference line ofsight of the optical link. The tracking accuracy in this measurement isless than 1 mrad rms. The angular variation and the drift rate on thesatellite are measured at a sampling rate of 500 Hz, and these data aredownlinked to a ground station via a satellite-to-ground optical commu-nication link. The power spectral density of the satellite microvibration iscalculated by a Fourier transform analysis. The frequency spectrum ofthe gimbal mirror’s angular variation is also obtained when the coarsetracking control is operational. The rms value agrees with the residualcoarse tracking error estimated before launch of the satellite. These re-sults will be useful for the future design of a tracking control loop foroptical communication systems.

Mutual alignment errors due to the variation of wave-front aberrations in a free-space laser communication link

Abstract: Optical devices in free-space laser communication systems are affected by their environment, particularly in relation to the effects of temperature while in orbit. The mutual alignment error between the transmitted and received optical axes is caused by deformation of the optics due to temperature variation in spite of the common optics used for transmission and reception of the optical beams. When a Gaussian beam wave for transmission is aligned at the center of a received plane wave, 3rd-order Coma aberrations have the most influence on the mutual alignment error, which is an inevitable open pointing error under only the Tip/Tilt tracking control. As an example, a mutual alignment error of less than 0.2 µrad is predicted for a laser communication terminal in orbit using the results from space chamber thermal vacuum tests. The relative power penalty due to aberration is estimated to be about 0.4 dB. The results will mitigate surface quality in an optical antenna and contribute to the design of free-space laser communication systems.

Optical amplifier for wide band raman amplification of wavelength division multiplexed (WDM) signal lights

Abstract: A Raman amplifier providing a wideband gain for use in a wavelength division multiplexing (WDM) optical communication system. In one embodiment, a first optical amplifier Raman amplifies a wavelength division multiplexed signal light in both a first wavelength band and a second wavelength band in accordance with a plurality of excitation (pumping) lights provided to the first optical amplifier, the first and second wavelength bands being different from each other. A divider divides the amplified signal light into first and second lights in the first and second wavelength bands, respectively. A second optical amplifier amplifies the first light and has a gain band in the first wavelength band. The third optical amplifier amplifies the second light and has a gain in the second wavelength band. In various embodiments, a gain equalizer and/or an optical isolator is used in combination with the first optical amplifier providing the Raman amplification. A controller is also provided to control the excitation lights provided to the first optical amplifier to achieve specific effects.

Multiplexed transmission of optical signals

Abstract: In an optical communication system, a train of optical pulses is transmitted such that each pulse carries a set of multiplexed channels. In a receiver, the error rate for each channel is monitored and a subset of channels having the most favorable rate is selected to carry a first data stream. The remaining channels carry a second data stream. Error rate performance is determined on the basis of error detecting codes carried by the channels in the first and second data streams.

Multi-wavelength locking method and apparatus for wavelength division multiplexing (WDM) optical communication system

Abstract: Disclosed is a multi-wavelength locking method for a wavelength division multiplexing (WDM) optical communication network, and in particular, a multi-wavelength locking method and apparatus for a WDM optical communication system that can lock wavelengths of optical signals by producing pilot tones by applying a sine-wave current to a plurality of transmission lasers having different wavelengths, passing the optical signal through a Fabry-Perot etalon filter, and then Fourier-transforming the filtered optical signal. The multi-wavelength locking method includes frequency-modulating an optical signal by applying a small and specified sine-wave current to a bias current for driving WDM lasers, detecting pilot tones produced after filtering the optical signal through a filtering section and converting the detected signal into a digital signal by performing a sampling of the detected signal, detecting a magnitude and phase of the pilot tones by performing a fast Fourier transform, providing Fourier-transformed data as a first derivative signal of the filtering section, and locking an operation wavelength of WDM channels by controlling the temperature or current if resonance frequencies of the filtering section coincide with respective standard frequency.