Abstract: An optical fiber secure communication apparatus and a data encryption method therefor are provided. The apparatus comprises a transmitter and a receiver being connected with each other via an optical fiber. The transmitter comprises a PPC processor unit, a field programmable gate array test board, a light-emitting module, an optical fiber coupler and a connection optical fiber. The receiver comprises a wavelength division multiplexer, a connection optical fiber, a photodetector, a field programmable gate array test board, a PPC processor unit and a signal output interface. At the transmitter end, two or more paths of input data are forwarded by the PPC, encrypted by the FPGA and then transmitted to the light-emitting module of two or more wavelengths for conversion from electrical signals into optical signals. At the receiver end, signals of two or more wavelengths enter the photodetector for conversion into electrical signals, which are decrypted by the FPGA and then forwarded by the PPC for output.

Abstract: Simplified laser drivers for closed path digital optical cables and digital optical cables including the simplified laser drivers. The laser driver can include less transistors than conventional laser drivers for optical communication cables. The laser can include a bias source and modulation source. The bias source can have a single constant current bias point for all laser diodes. The modulation current source can have a single temperature coefficient for all laser diodes. The laser driver can exclude, for example, any one of or combination of temperature compensation of the modulation or bias current sources, external programming of the modulation or bias current sources, power control based on output of the laser diode, and/or control based on feedback received from a monitor device or other sensor within the cables.

Abstract: A computer including: a casing, at least a portion of which contains a potting material acting as an optical waveguide material; a transmitter for transmitting a pulse based signal at least partially through the potting material acting as the optical waveguide material; and a receiver for receiving the pulse based signal after one or more reflections of the pulse based signal from interior surfaces of the casing; the pulse based signal having a pulse rate configured such that a subsequent pulse doesn't interfere with reflections from an immediately previous pulse.

Abstract: A combined optical and electrical interconnection module includes a flat cable comprising an optical transmission line and an electrical wire, and a printed circuit board including a light receiving module for receiving optical signals and/or a light sending module for sending optical signals and an optical waveguide for the optical signals to be transmitted therethrough or an optical block for bending the optical paths of the optical signals. The printed circuit board is electrically and optically connected to both ends or one end of the flat cable.

Abstract: An optical to radio frequency detector comprises an optical guide for receiving two optical signal components having frequencies that differ by an amount corresponding to a radio frequency, and a radio signal guide coupled with an interaction zone of the optical guide for propagating a radio signal from the interaction zone at the radio frequency. The material of the interaction zone presents a second-order non-linear optical polarization characteristic to the propagation of the optical signal components, and the radio signal guide is in travelling-wave coupling with the interaction zone. A radio signal output is coupled with the radio signal guide.

Abstract: The invention pertains to optical fiber transmission systems, and is particularly relevant to optical transport systems employing optical amplifiers. In particular the invention teaches an apparatus and method that allows cost effective co-directional operation of an optical amplifier to support full duplex traffic on a single fiber, and the design of an optical fiber transmission system based on this optical amplifier technology.

Abstract: A method and apparatus is presented for reducing or eliminating pathological data patterns from signals for transmission over optical communications systems. One embodiment includes a decoder/deserializer configured to receive an encoded serial digital signal, a ditherer configured to dither a least significant bit of each digital data word, and a reserializer/encoder configured to serialize digital data and encode it, for example according to an applicable communication standard such as SMPTE 259M. The improvements may be provided in a single removable unit, such as a small form-factor pluggable (SFP) module compatible with existing optical communications equipment.

Abstract: A system and method for distributing high bandwidth signals is disclosed. The system and method use electrical transmission lines to distribute high bandwidth RF signals. The RF signals are sent along the electrical transmission lines using surface wave transmission. RF/Optical converters located along the electrical transmission lines are used to convert the RF signals into optical signals. Passive optical networks (PON) are used to transmit the optical signals between the RF/Optical converter and a customer site or location.

Abstract: An optical transmission assembly consists of an upper cladding; a lower cladding; a core formed between the upper cladding and the lower cladding; a surface light emitting device mounted to an upper surface at one end of the upper cladding, a light emitting surface of the surface light emitting device facing the core and emitting wavelength ?1 light thereto; a reflective surface formed in the core and at a position facing the light emitting surface of the surface light emitting device, and inclined in a longitudinal direction of the core; an inclined surface formed in the core and facing the reflective surface in a longitudinal direction of the core, and inclined in a thickness direction of the upper or lower cladding; a wavelength filter formed on the inclined surface and transmitting wavelength ?1 light incident in a longitudinal direction of the core while reflecting wavelength ?2 (?2??1) light incident in the opposite longitudinal direction of the core to the incident direction of the wavelength ?1 light,

Abstract: An apparatus for transmitting data at high data rates, between two systems that move relative to one another is provided. The apparatus includes an optical fiber and an axial module on one of the two systems for the purpose of axial data coupling, using the optical fiber and a lateral module on another of the two systems for the purpose of lateral data coupling using the optical fiber.

Abstract: An optical transmission system for transmitting an optical pulse in a dielectric waveguide, the system including a filter for altering a shape of the optical pulse in both amplitude and phase with respect to time so as to substantially suppress the generation of third-order nonlinearities and increase a power level of the optical pulse, the filter further providing a secure encrypted optical waveform that may be decrypted by a matching optical filter, the system allowing for energy sharing of the pulses to substantially increase system bandwidth.

Abstract: An optical/electrical composite cable in which a first connector having an optical transmission unit is connected to a second connector having an optical reception unit via an electrical wire and optical wiring line is provided. The optical transmission unit and optical reception unit are driven by electrical power supplied from an external electronic device. A detection unit that detects a removal/attachment operation of at least one of the first and second connectors and an interruption unit that interrupts supply of electrical power to the optical transmission unit and optical reception unit when the removal/attachment operation is detected by the detection unit are provided.

Abstract: Disclosed is an optical system including a polychromatic optical source emitting multiple transverse modes, an optical link having at least one portion of multimode optical fiber, and an optical device positioned between the optical source and the input of the multimode optical fiber. The optical device can modify the distribution of the energy coupling of the transverse modes emitted by the source in the propagation modes of the multimode optical fiber. The optical system makes it possible to use low-cost transverse multimode optical sources for producing high-bandwidth Ethernet transmission networks having excellent performance.

Abstract: Devices and systems are provided for free space optical communication using optical films. Some embodiments involve using an optical film for the transmission and/or reception of light in a free space optical communication system. Some free space optical communication systems may involve devices, such as laptop computers, desktop computers, mobile communications devices, etc., that are configured for communication via an optical film. The optical film may be disposed on a device, on a wall, a window, furniture, etc., according to the implementation. Many types of free space optical communication systems are provided, including line of sight and non line of sight free space optical communication systems.

Abstract: An optical communication system is provided for conveying signals between multiple housing elements of a device, where respective optical detectors and optical light sources interact via a light guide associated with each communication path, where an optical signal produced by the optical light source and received by the optical detector travels a path where at least a first light redirection unit redirects the optical signal between an angle in which the optical signal travels along at least a portion of the length of the light guide, and an angle which allows the optical signal to exit the light guide. In at least some instances, the multiple housing elements correspond to at least a pair of housing elements that are incorporated as part of a communication device having a slider configuration. In some of the same or still further instances, one or more of the light redirection units are diffractive optical elements. In some instances, one or more of the light redirection units are reflectors.

Abstract: A system and method for fabricating an electro-optical hybrid module (100). The electro-optical hybrid module (100) may comprise an electro-optical component, an electronic component (110), a planar light wave circuit (PLC) embedded with at least an optical waveguide (120). The electro-optical component may transmit or receive energy through a micro-folding mirror (160) while the electronic component may amplify and transfer an electric signal to the electro-optical component. The planar light wave circuit may typically provide an opto-electronic signal communication path via the plurality of optical waveguides that may be embedded in the planar light wave circuit.

Abstract: An optical transmission system includes an optical transmitting unit that outputs at least one optical signal having a wavelength included in an operation wavelength band and a holey fiber that is connected to the optical transmitting unit. The holey fiber includes a core and a cladding formed around the core. The cladding includes a plurality of holes formed around the core in a triangular lattice shape. The holey fiber transmits the optical signal in a single mode. A bending loss of the holey fiber is equal to or less than 5 dB/m at a wavelength within the operation wavelength band when the holey fiber is wound at a diameter of 20 millimeters.

Abstract: A low-cost, high-speed micro-connector replacement for current electrical inter-connects and intra-connects on printed circuit boards is provided. The invention permits fast and reliable information transmission over a single fiber through the utilization of an optical transmitter module or optical receiver module mounted in close proximity to a modulator used to encode optical signals from electrical impulses or decode optical signals to electrical impulses. The micro-connector is mounted on a PCB in alignment with the transmitting or receiving modules and provides appropriate alignment and stop positioning of an optical fiber used for optical transmitting between transmitting/receiving modules.

Abstract: An optical waveguide film of an optical reception and transmission module guides light. A first optical path converting part of an optical transmission unit guides light. A mirror surface of a first optical path converting part bends light which is emitted from a light emitting element and which enters the first optical path converting part. A first holding member holds the light emitting element and the first optical path converting part. A second optical path converting part of an optical reception unit guides light. A mirror surface of a second optical path converting part bends the guided light. A second holding member holds the light receiving element and the second optical path converting part. A first supporting member supports the first end portion of the optical waveguide film. A second supporting member supports the second end portion of the optical waveguide film.

Abstract: An optical network route and method are disclosed that mitigate distortion in a route having different types of fibers. For an optical network route that includes a plurality of fiber spans of a first type and a fiber span of a second type, assume that the optical network route is transporting optical signals having a plurality of original wavelengths where one or more of the original wavelengths is in a distortion wavelength region of the second type of fiber span. For optical signals entering the second type of fiber span, the original wavelength that is in the distortion wavelength region of the second type of fiber span is shifted to a temporary wavelength outside of the distortion wavelength region. The optical signals then travel over the second type of fiber span. For optical signals exiting the second type of fiber span, the temporary wavelength is shifted back to the original wavelength.

Abstract: An optical module comprising: a submount provided on a CAN stem; light-emitting device and a light-receiving device; a CAN cap or package; and an optical multiplexer/demultiplexer having a wavelength selective filter on a substrate that has transmissivity to passing light and a mirror, where an extending direction of the optical multiplexer/demultiplexer is fixed in the CAN cap or the package being tilted by an angle ? (??2N?, N=0, 1, 2, . . . ) in a two-dimensional cross section with respect to one surface of an optical device mounting board, outgoing light from the light-emitting device passes through the wavelength selective filter and the substrate and enters an optical fiber outside the cap, and outgoing light from the optical fiber enters the optical multiplexer/demultiplexer and is reflected by the wavelength selective filter and further reflected by the mirror, and then exits the optical multiplexer/demultiplexer to enter the light-receiving device.

Abstract: An optical transmitting/receiving apparatus capable of suppressing electrical crosstalk and magnetic crosstalk, includes: a laser diode/photo diode (LD/PD) integrated module that terminates a single-core bidirectional optical fiber; a circuit board electrically connected to a lead pin led out of the LD/PD integrated module; and a plastic case that accommodates the circuit board. At least a part of the plastic case abuts against the LD/PD integrated module, and impedance of the plastic case is controlled by mixing a conductive filler into the plastic case.

Abstract: A system and method for fabricating an electro-optical hybrid module (100). The electro-optical hybrid module (100) may comprise an electro-optical component, an electronic component (110), a planar light wave circuit (PLC) embedded with at least an optical waveguide (120). The electro-optical component may transmit or receive energy through a micro-folding mirror (160) while the electronic component may amplify and transfer an electric signal to the electro-optical component. The planar light wave circuit may typically provide an opto-electronic signal communication path via the plurality of optical waveguides that may be embedded in the planar light wave circuit.

Abstract: A POF (12) comprises a core (65) having a radius of R1, an outer shell (66) and an outermost shell (67). The core (65) includes concentric layers. A first layer (61) is at the periphery side and an nth layer (64) is at the center of the core (65). The refractive index increases from the first layer (61) to the nth layer (64).

Abstract: A process optically transports digital data over an all-optical long-haul communication path. The process includes transporting digital optical data signals at a selected bit rate and a selected wavelength over a sequence of transmission spans. The sequence includes 70 percent or more of the spans of the long-haul all-optical communication path. Each span of the sequence has a primary local maximum optical power point for the wavelength on a transmission fiber and nearest to an input of the span. The transporting causes a cumulative dispersion of each signal to evolve such that residual dispersions per span are positive over some of the spans and are negative over other of the spans. At the primary local maximum power points, magnitudes of cumulative dispersions of the signals in pico seconds per nanometer remain at less than 32,000 times the inverse of the bit rate in giga bits per second.

Abstract: A system and method for automatically determining a physical location of one or more units in a rack, including: using one or more physical cables between rack units; cascading a first signal through the one or more units located in the rack, the first signal being encoded with a unit number and a physical parameter; and creating a rack ID by utilizing hardware parameters, the hardware parameters being determined by: detecting a second signal that exists from a bottom unit, the bottom unit located at the bottom of the rack; and using a third signal to send data between the one or more units in the rack by manipulating void spaces within the rack, the third signal being either cabled or an optical signal.

Abstract: In an optical signal transmission system which can perform high-speed optical transmission not lower than 1 Gbps, VCSEL has light-emission points. A core diameter of an optical fiber GI-POF is set to not lower than 200 ?m, and the light-emission points of VCSEL are arranged inside an outer periphery at an end face of GI-POF. A polymerization composition material constituting the core of GI-POF is made of a compound containing deuterated poly methacrylic ester. A wavelength of the light beam of VCSEL is set to the range of 770 nm to 810 nm.

Abstract: A device including: at least two electronic/electrical components; and a casing, the casing having at least a portion thereof acting as a communication bus for connecting the at least two electronic/electrical components.

Abstract: An optical communication link has a plurality of light emitting elements and a plurality of light receiving elements associated with the respective light emitting elements, and a plurality of optical fibers each for conveying an optical signal emitted from one light emitting element to an associated light receiving element. The optical fibers have respective lengths that include at least two different lengths, and respective transmission losses per unit length that vary according the lengths of the optical fibers, so that variation of the transmission losses among the optical fibers due to difference in optical fiber length is prevented.

Abstract: The disclosure, in on aspect, provides a method for performing a laser operation in a wellbore that includes displacing a wellbore fluid with a laser-compatible medium proximate a location in the wellbore where a work is desired to be performed; positioning a laser head proximate the laser-compatible medium; and passing a laser beam via the laser-compatible medium to the location for performing the laser operation. In another aspect, the disclosure provides a laser apparatus for performing a laser operation at a worksite having a fluid that includes a laser power unit that supplies laser energy to a laser head placed proximate the worksite; a fluid displacement unit that displaces at least a portion of the fluid adjacent the worksite with a laser-compatible medium; and a controller that operates the laser head to pass the laser beam to the worksite through the laser-compatible medium. In another aspect, the disclosure provides an imager associated with the laser apparatus that provides images of the worksite.

Abstract: A single-to-multi mode converter and an optical code division multiple access system using the same. The mode converter includes first, second, and third optical waveguides. The first optical waveguide is formed of a single-mode optical fiber and outputs a single-mode optical signal. The second optical waveguide converts the single-mode optical signal output from the first optical waveguide to a multi-mode optical signal and allows the optical power of the single-mode optical signal to be coupled to each mode of the multi-mode optical signal. The third optical waveguide is formed of a multi-mode optical fiber and transmits the multi-mode optical signal output from the second optical waveguide.

Abstract: An optical beam diagnostic device includes one or more sets of coherent optical fiber bundles, wherein one end of the coherent optical fiber bundles is arranged to receive optical information from a dynamic moving or static optical beam or beams, and the other end of the coherent optical fiber bundles is arranged to transmit the optical information to a sensor array. Data from the sensor array can then be simultaneously acquired by an analysis system and analyzed to determine one or more characteristics of the optical beam.

Abstract: Provided is a black matrix light guide screen display. In a particular embodiment, provided are a plurality of aligned light guides, each having an input end, a midsection and a magnifying output end. A black matrix material is disposed adjacent to the light guides proximate to the magnifying output ends. The plurality of aligned light guides are arranged into a plurality of light guide layers, each layer one light guide thick. The magnifying output ends of each layer are aligned in substantially contiguous parallel contact with interposed black spacers to provide substantially the same magnification vertically and horizontally.

Abstract: Disclosed is a color optical link using a transparently jacketed plastic optical fiber that optically transmits data and uses light, scattered and emitted to the outside, for the purpose of illumination, and a method for achieving the color optical link. The color optical link includes a first driver that receives digital or analog signals and a coloring signal in parallel and converts these signals into optical signals through a plurality of light sources. These light sources emit light of different wavelengths. A first POF coupler, connected at one end of the optical fiber, inputs the received optical signals into the optical fiber. A second POF coupler at the other end separates the transmitted optical signals into a plurality of optical signals and inputs these optical signals into a plurality of optical detectors having filters for separating the received signals into plural signals according to wavelength. A second driver converts the received optical signals into electrical signals.

Abstract: A device including: at least two electronic/electrical components; and a casing, the casing having at least a portion thereof acting as a communication bus for connecting the at least two electronic/electrical components.

Abstract: A multi-mode optical fiber link is described. The multi-mode optical fiber link includes a first spatial mode converter that is coupled to a first single mode optical fiber. The first spatial mode converter conditions a modal profile of an optical signal propagating from the single mode optical fiber to the first spatial mode converter. A multi-mode optical fiber is coupled to the first spatial mode converter. A second spatial mode converter is coupled to an output of the multi-mode optical fiber and to a second single mode optical fiber. The second spatial mode converter reduces a number of optical modes in the optical signal. Both the first and the second spatial mode converters increase an effective modal bandwidth of the optical signal.

Abstract: An optical bus 30 optically connects each board of a signal processing section 22 and each board of a transmission/reception section 40 for transmitting an optical signal output to the optical bus 30 by each board of the signal processing section 22 to each board of the transmission/reception section 40 in a non-block state. In contrast, the optical bus 30 transmits an optical signal output to the optical bus 30 by each board of the transmission/reception section 40 to each board of the signal processing section 22 in a non-block state.

Abstract: An optical demultiplexer having at least one Bragg diffraction grating for minimizing crosstalk on the sides of transmitting and receiving optical signals, as well as an optical communication module using the optical demultiplexer. The optical demultiplexer has first and second waveguides arranged adjacent each other in a predetermined section in order to perform mode coupling, so that the optical signals input through one end of the first waveguide are transmitted to a light receiving element through the second waveguide, and in which output light waves inputted through the other end of the first waveguide are output through the one end of the first waveguide. A first Bragg diffraction grating is formed on the second waveguide and haa wavelength selectivity, for minimizing crosstalk by transmitting a reception wavelength of the optical signals at about 100% and by reflecting a wavelength of the output light waves at about 100%.

Abstract: A WDM system includes a transmission station, a receiving station, a first optical path and a second optical path. The first optical path includes a first section and a second section, the second section being capable of compensating at least partially the dispersion accumulated by a series of optical channels along the first section. The series of channels includes at least a first plurality of channels having an average dispersion of the same sign in the first optical path. The system also includes at least a first conversion device, capable of inverting the spectrum and modifying the wavelength of at least the first plurality of channels, to produce a second plurality of channels having an average chromatic dispersion of the same sign in the second optical path.

Abstract: A section of tapered optical fiber is provided to protect optical components from catastrophic damage that may propagate within an optical route. The tapered section functions as a fuse to arrest the propagation of optical power induced damage by leaking optical power from a waveguiding region below a threshold, below which further propagation of damage is not supported.

Abstract: The present invention discloses an optical transmission line constructing method comprising the steps of connecting a plurality of optical fibers differing from each other in terms of a transmission characteristic; making inspection light incident on an entrance end of the connected plurality of optical fibers; detecting, on the entrance end side, respective return light components of the inspection light occurring at individual positions of the plurality of optical fibers in its longitudinal direction; evaluating a characteristic information distribution of return light in the longitudinal direction of the plurality of optical fibers; and constructing an optical transmission line according to a result of the evaluation.

Abstract: A transmitting-end device generates a pilot signal with a pilot signal generation section, and transmits a pilot signal to a receiving-end device. At the receiving-end device, a transmission rate modification section detects the transmission band of an optical transmission line based on the amplitude of the pilot signal, and decides a data transmission rate acceptable to the receiving-end device by taking into account the transmission band of the optical transmission line. Based on a maximum data transmission data acceptable to the transmitting-end device and the data transmission rate thus decided, a control section in the receiving-end device arbitrates a data transmission rate between it and the transmitting-end device.

Abstract: A configuration for detecting optical signals of at least one optical channel of a planar optical circuit. At least one deflection device is provided, which couples the optical signals of at least one optical channel at least partly out of the plane of the circuit, and one detection unit is provided, which detects the signals that are coupled out outside the plane of the circuit. Therefore, a simple metrological monitoring of the signals of the optical channels of a planar optical circuit occurs with only slight signal losses and without undesirable crosstalk.

Abstract: An integrated optical circuit includes waveguides formed in the integrated optical circuit. One set of waveguides is a set of optical amplifiers doped with rare earth ions. A second set of waveguides is a multiplexer or demultiplexer, such as an arrayed waveguide grating (AWG). The set of optical amplifiers and the AWG are coupled together via waveguides formed in the integrated optical circuit. Other elements on the integrated optical circuit are coupled to the set of optical amplifiers and the AWG via optical fibers. The spectral response of the AWG is modified to compensate for the spectral gain of the AWG. The lengths of the individual optical amplifiers in the set of optical amplifiers may be varied to cause uniform power distribution across channels. The integrated optical circuit also has a pump coupler to couple a pump source to the set of optical amplifiers.

Abstract: An optical communication apparatus comprises an optical transmitter (1) which emits light signals corresponding to external electric signals (11) using light emitted from a short-wavelength light-emitting element (14) such as a yellow light-emitting diode of maximum wavelength in a range of 560–590 nm or a green light-emitting diode of maximum wavelength in a range of 490–550 nm; a plastic fiber (2) including a methacrylate polymer core free from benzene rings and having one end connected optically with the short-wavelength light-emitting element (14), the core containing less than 5 ppm free sulfur; and an optical receiver (3) having a photodetector element (31) connected optically with the other end of the plastic fiber (2) and adapted to producing an output electric signal (35) in accordance with the output from the photodetector element (31).

Abstract: An apparatus for switching optical signals, comprising a first group of port cards adapted to receive input optical signals to be switched by the apparatus and a second group of port cards adapted to provide switched optical signals to an entity external to the apparatus. Each of the port cards in the first group includes a plurality of optical transmitter elements operative to produce respective optical beams from the input optical signals, as well as a transmit beam steering element array operative to orient the optical beams into respective transmit directions. Each of the port cards in the second group includes a plurality of optical receive elements operative to detect the presence of respective optical beams received from the port cards in the first group and produce respective ones of the switched optical signals therefrom. Application of beam steering at the port cards in the first group permits the apparatus to be more compact and allows for greater manufacturing tolerances.

Abstract: A network for distributing signals to a plurality of user apparatuses having a distribution unit with a plurality of ports, and a plurality of optical-fiber cables connected to the ports and suitable to make the plurality of ports of the distribution unit communicate with the plurality of user apparatuses. At least one of the plurality of optical-fiber cables is an electrically terminated optical cable having an optical cable with a single-mode optical fiber and an opto-electronic end portion mechanically and permanently connected to an end of the optical cable, and the opto-electronic end portion has an opto-electronic conversion device having an optic port optically aligned with and mechanically connected to, an end of the single-mode optical fiber.

Abstract: A spread polarization transmitter for transmitting at least one light signal comprises a spread-spectrum communication apparatus and a polarization modulator. The spread-spectrum communication apparatus modulates the at least one light signal according to a spread-spectrum modulation technique. The polarization modulator comprises a polarizer and a magnetic bubble waveguide. The polarizer is capable of polarizing the at least one spread-spectrum modulated light signal in a polarized direction. And the magnetic bubble waveguide, which is configured in accordance with a pseudo-random polarization code sequence such that the plurality of magnetic bubble domains assume a time varying position representative of the pseudo-random polarization code sequence, is capable of receiving at least one polarized, spread-spectrum modulated light signal.

Abstract: Simulation of the transmission behavior of opto-electronic connections, by which the transmitter or the receiver is represented by at least two optical outputs or inputs and the optical line is represented by corresponding multi-poles, considers the spatial distribution of the emitted or received optical radiation.

Abstract: Methods and apparatus are disclosed for an intrusion detection system for secure fiber optic communication systems. A guard signal is transmitted over the optical fiber communication link and both the modal power and modal phase delay of this signal are monitored. Intrusions into the link for the purpose of intercepting information being transmitted, cause changes in the modal phase delay and power of the guard signal. These changes, when detected by the monitoring system, indicate the presence of an intruder. A fiber profile which is optimal for both transmission and intrusion detection purposes is described.