Abstract: The present invention enables device downsizing by utilizing a light-emitting diode as a plurality of interfaces. A light-emitting diode 11 of a data communication unit using a light-emitting diode for data communication outputs light when a current flows therethrough. A transmission circuit 13 applies a forward bias to the light-emitting diode 11 based on transmission data. A separation circuit 14 outputs a voltage that changes according to a voltage which is generated in the light-emitting diode 11 when the transmission circuit 13 does not apply the forward bias to the light-emitting diode 11.

Abstract: A solution for detecting and recovering from a failure in a protected single-fiber passive optical network. A detector is used to detect the degradation in power level of optical signals. Furthermore, the invention discloses a variable symmetric split ratio approach to improve the number of splits (e.g. the number of ONUs). A single-fiber passive optical network is disclosed that uses a plurality of passive nodes connected in the optical fiber between the interfaces, wherein in the passive nodes 2-by-2 splitters/combiners are used to couple optical power from and into the optical fiber at a predetermined split ratio.

Abstract: Subterranean oilfield high-temperature devices configured or designed to facilitate downhole monitoring and high data transmission rates with remotely pumped lasers that are configured for operation downhole, within a borehole, at temperatures in excess of 115 degrees Celsius.

Abstract: An optoelectronic module for converting and coupling an information-containing electrical signal with an optical fiber including a housing having an electrical input for coupling with an external cable or information system device and for transmitting and receiving information-containing electrical signals over such input, and a fiber optic connector adapted for coupling with an external optical fiber for transmitting and receiving an optical signal; an electro-optic subassembly coupled to the information containing electrical signal and converting it to and/or from a modulated optical signal corresponding to the electrical signal; means disposed in the housing for determining the electrical and/or optical protocols or packet formats in use; and a processor for adapting the module to utilize the electrical and optical protocol or packet format.

Abstract: Included among the many structures described herein are photonic bandgap fibers designed to provide a desired dispersion spectrum. Additionally, designs for achieving wide transmission bands and lower transmission loss are also discussed. For example, in some fiber designs, smaller dimensions of high index material in the cladding and large core size provide small flat dispersion over a wide spectral range. In other examples, the thickness of the high index ring-shaped region closest to the core has sufficiently large dimensions to provide negative dispersion or zero dispersion at a desired wavelength. Additionally, low index cladding features distributed along concentric rings or circles may be used for achieving wide bandgaps.

Abstract: A modulator includes an electro-optical substrate and a first and second waveguide formed of a doped semiconductor material positioned on a surface of an electro-optical substrate forming a slot therebetween. A doping level of the semiconductor material being chosen to make the first and second waveguide conductive. A dielectric material is positioned in the slot which increases confinement of both an optical field and an electrical field inside the slot. A refractive index of the semiconductor material and a refractive index of the dielectric material positioned in the slot being chosen to reduce the V?·L product of the modulator.

Abstract: An apparatus for enabling transmission of signals and data via means of infrared (IR) light for a wind turbine includes a plurality of IR data communication elements configured to provide unidirectional and bidirectional IR data exchange between non-rotating portions of the wind turbine and the rotatable wind turbine hub.

Abstract: An optical transmission and reception control apparatus is provided. The present invention relates to an optical transmission and reception control apparatus for enabling smooth optical transmission and reception when a photo diode and/or a laser diode fail. The apparatus includes a plurality of laser diodes, a laser driver, a first switching unit, a plurality of photo diodes, an optical power amplifier, a second switching unit, an optical power detection module, and a control module.

Abstract: Embodiments of a system are described. This system includes an array of chip modules (CMs) and a baseplate, where the baseplate is configured to communicate data signals via optical communication. Moreover, the array includes first CMs mechanically coupled to first alignment features on the baseplate, and adjacent second CMs mechanically coupled to second alignment features on the baseplate. In this array, a given first CM is electrically coupled to a given set of electrical proximity connectors. Additionally, the array includes bridge components, wherein a given bridge component is electrically coupled to the second SCM and another set of electrical proximity connectors, which is electrically coupled to the set of electrical proximity connectors, thereby facilitating communication of other data signals between adjacent first CMs and second CMs via electrical proximity communication.

Abstract: An optical engine for providing a point-to-point optical communications link between a first computing device and a second computing device. The optical engine includes a modulated hybrid micro-ring laser formed on a substrate and configured to generate an optical signal traveling parallel to the plane of the substrate. The optical engine further includes a waveguide, also formed in a plane parallel to the plane of the substrate, that is configured to guide the optical signal from the modulated ring laser to a defined region, a waveguide coupler at the defined region configured for coupling the optical signal into a multi-core optical fiber, and a multi-core optical fiber at the defined region that is configured to receive and transport the optical signal to the second computing device.

Abstract: In a receiver suitable for an optical fiber link and comprising an optical receiver unit (1), which includes a radiation-sensitive detector (4) and a signal processing circuit (6,8), and an electrical receiver unit (2), the optical receiver unit comprises a power draining circuit (16) that drains power from a pull-up stage (R1-R4; Vpu) of the electrical receiver unit and supplies power to the electrical circuit of the optical receiver unit.

Abstract: An optical fiber network can include an outdoor laser transceiver node that can be positioned in close proximity to the subscribers of an optical fiber network. The outdoor laser transceiver node does not require active cooling and heating devices that control the temperature surrounding the laser transceiver node. The laser transceiver node can adjust a subscriber's bandwidth on a subscription basis or on an as-needed basis. The laser transceiver node can also offer data bandwidth to the subscriber in preassigned increments. Additionally, the laser transceiver node lends itself to efficient upgrading that can be performed entirely on the network side. The laser transceiver node can also provide high speed symmetrical data transmission. Further, the laser transceiver node can utilize off-the-shelf hardware to generate optical signals such as Fabry-Perot (F-P) laser transmitters, distributed feed back lasers (DFB), or vertical cavity surface emitting lasers (VCSELs).

Abstract: An optical receiver includes a demodulator having a delay interferometer comprising an optical input that receives a phase modulated optical signal from a bandwidth limited transmission system. The delay interferometer has a free spectral range that is larger than a symbol rate of the phase modulated optical signal by an amount that improves receiver performance. The receiver also includes a differential detector having a first and a second photodetector. The first photodetector is optically coupled to the constructive optical output of the delay interferometer. The second photodetector is optically coupled to the destructive optical output of the delay interferometer. The differential detector combines a first electrical detection signal generated by the first photodetector and a second electrical detection signal generated by the second photodetector to generate an electrical reception signal.

Abstract: An optical network and an optical signal modulation method thereof are provided. The optical network includes an optical fiber and a remote node (RN). The RN receives a continuous carrier wave from the optical fiber and modulates the continuous carrier wave to generate a first frequency offset carrier wave The frequency of the first frequency offset carrier wave is different from that of the continuous carrier wave. A first user device re-modulates and loads data to the first frequency offset carrier wave to generate a first upstream signal. The frequency of the first upstream signal is the same as that of the first frequency offset carrier wave. The RN inputs the first upstream signal into the optical fiber.

Abstract: An optical transceiver for converting and coupling an information-containing electrical signal with an optical fiber including a housing having an electrical connector with a plurality of XFI electrical interfaces for coupling with an external electrical cable or information system device and for transmitting and/or receiving an information-containing electrical signal having a data rate of at least 10 Gigabits per second on each interface, and a fiber optic connector adapted for coupling with an external optical fiber for transmitting and/or receiving an optical communications signal having a data rate at least 40 Gigabits per second; and at least one electro-optical subassembly in the housing for converting between an information-containing electrical signal and a modulated optical signal corresponding to the electrical signals.

Abstract: In one embodiment, a fiber optic link includes a combined optical link for transmitting high optical power and wide bandwidth signal through a single optical fiber. In one embodiment, a means is provided for combining a high power optical signal and a low power data signal with wavelength selective directional couplers so as to inhibit the low power data transmitter and the low power data receiver from being overloaded with too much power. In one implementation, a method of using double clad fiber is provided, which includes transmitting an optical data signal at an optical data wavelength along an inner core, the inner core being single mode at the optical data wavelength and simultaneously transmitting an optical power signal at a optical power wavelength through a cladding, the cladding serving as a multimode core for a power optical link at the optical power wavelength.

Abstract: An apparatus comprises an optical transmitter; an optical detector configured to receive optical signals from an optical fiber; an optical splitter having a first port, a second port coupled to the optical detector by the optical fiber, and a third port coupled to the optical transmitter; and a two stage amplifier system connected to an output of the optical detector. An input surface of the optical detector may have a diameter that is substantially equal to a diameter of a core in the optical fiber. The diameter of the input surface of the optical detector reduces capacitance and reduces signal distortion. The optical splitter may be configured to receive a first optical signal at the first port. The optical splitter may be configured to send the first optical signal to the second port and send a second optical signal received at the third port to the first port.

Abstract: A bidirectional interface for multimode optical fiber includes a receive/transmit optical fiber port operable to connect to a multimode optical fiber, a wavelength separating module in communication with the receive/transmit optical fiber port, an optical receiver module in communication with the wavelength separating module and configured to receive optical signals at a first wavelength via the wavelength separating module and the receive/transmit optical fiber port, and an optical transmit module in communication with the wavelength separating module and configured to transmit at a second wavelength via the wavelength separating module and the receive/transmit optical fiber port.

Abstract: An avionics system for a plane includes a plurality of nodes disposed throughout the plane, each node performing a function. The system includes an optical network in communication with the nodes and through which the nodes communicate. The system includes at least one of the nodes having a hardwired interpreter that interprets the information transmitted from another one of the nodes via the optical network. A method for operating a plane includes the steps of communicating information through an optical network between a plurality of nodes disposed throughout the plane, each node performing a function. There is the step of interpreting with at least one of the nodes having a hardwired interpreter the information transmitted from another one of the nodes via the optical network. A phostonic stack.

Abstract: In an integrated circuit device, such as a microprocessor, a device internal optical communication system is provided in order to enhance signal transfer capabilities while relaxing overall thermal conditions. Furthermore, the device internal optical data or signal transfer capabilities may result in superior operating speed and a high degree of design flexibility. The optical communication system may be applied as a chip internal system in single chip systems or as an inter-chip optical system in three-dimensional chip configurations provided in a single package.

Abstract: A device other than a projectile including: a casing, at least a portion of which contains a potting material acting as the optical waveguide material; a transmitter for transmitting a pulse based signal at least partially through the potting 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: The system includes: a two-light wave generator for generating light beams having wavelengths ?1 and ?2 that are spaced apart by a frequency of a signal M1 from a laser; a photodetector for detecting a signal M2 from the light beams transmitted through an optical fiber; an optical modulator for frequency-shifting the light beams by a frequency of a signal M3; a Faraday reflector for reflecting the light beams; an optical coupler for mixing the light beams that have been returned to a polarization beam splitter, with the generated light beams; a photodetector for converting the light beams into microwave signals; an image rejection mixer for frequency-converting the signals obtained through the conversion by using the signal M1 to output a two side bands; and a phase difference detector for detecting a phase difference between the side bands, and controlling a phase shifter so that the phase difference becomes 0.

Abstract: Input data is encoded using a look-up table and then transmitted over a transmission medium as a series of pulses. The look-up table includes data elements. The length of each pulse is calibrated to correspond to one of the data elements in the look-up table. Upon receipt at another end of the transmission medium, the data is decoded using a look-up table. This decoding includes measuring the length of each received pulse to match the measured length to a corresponding one of data elements in the look-up table.

Abstract: Systems and methods for manipulating light with high index contrast waveguides clad with substances having that exhibit large nonlinear electro-optic constants such as ?3. Waveguides fabricated on SOI wafers and clad with electro-optic polymers are described. Embodiments of waveguides having slots and input waveguide couplers are discussed. Waveguides having closed loop structures (such as rings and ovals) as well as linear or serpentine waveguides, are described. All-optical signal processing systems and methods for implementing devices such as variable delay lines, optical logic gates (for example an AND gate), optical multiplexers, optical self-oscillators, and optical clock generators are disclosed.

Abstract: A communication system, the communication system includes: a first decision entity; and a long laser that includes a first reflector and a second reflector; wherein a lasing characteristic of the long laser is responsive to: (i) first data unit that is provided by a first user and affects a reflection spectrum of the first reflector, and (ii) second data unit that is provided by a second user and affects a reflection spectrum of the second reflector; and wherein the first decision entity is adapted to receive the first data unit and information representative of the lasing characteristic, as well as to determine (i) a relationship between the first data unit and the second data unit, or (ii) a content of the second data unit.

Abstract: An optical signal low energy method for coupling electrical signals on-chip between component circuits of for example a CMOS circuit array. The described coupling method employs infrared signals communicated along a nano-scale resonant semiconductor waveguide between for example PIN diode signal transducers. The coupling may employ an electrically pumped laser, an electro absorption modulator and a photodetector all for typically the 1.5 to 2.0 micrometer spectral region with each formed using for example PIN heterodiode semiconductor devices. Each of these three devices includes active semiconductor crystal material situated in a resonator within a strip waveguide. The resonator is defined by two fabricated mirrors having a tapered location one dimensional photonic crystal lattice of oxide hole or slot apertures.

Abstract: An optical communication apparatus that can perform stable intensity and phase modulation on an optical pulse at high speed is provided, as well as a quantum key distribution system using the apparatus. Using multilevel signals for the electric signals (RF1, RF2) to be applied to two arms of a two-electrode Mach-Zehnder modulator, phase modulation is performed on an optical pulse in accordance with the average of the levels of the signals (RF1, RF2), and intensity modulation is performed on the optical pulse in accordance with the voltage difference between the signals (RF1, RF2), whereby stable high-speed multilevel modulation can be realized. The cryptographic key generation rate in a decoy quantum key distribution system is enhanced.

Abstract: An imaging system is provided that includes a optical pulse generator for providing an optical pulse having a spectral bandwidth and includes monochromatic waves having different wavelengths. A dispersive element receives a second optical pulse associated with the optical pulse and disperses the second optical pulse at different angles on the surface of the dispersive element depending on wavelength. One or more focal elements receives the dispersed second optical pulse produced on the dispersive element. The one or more focal element recombine the dispersed second optical pulse at a focal plane on a specimen where the width of the optical pulse is restored at the focal plane.

Abstract: Embodiments of the present invention relate to systems and methods for distributing an intentionally skewed optical-clock signal to nodes of a source synchronous computer system. In one system embodiment, a source synchronous system comprises a waveguide, an optical-system clock optically coupled to the waveguide, and a number of nodes optically coupled to the waveguide. The optical-system clock generates and injects a master optical-clock signal into the waveguide. The master optical-clock signal acquiring a skew as it passes between nodes. Each node extracts a portion of the master optical-clock signal and processes optical signals using the portion of the master optical-clock signal having a different skew for the respective extracting node.

Abstract: Various embodiments of the present invention are directed to photonic-based interconnects for transmitting data encoded in electromagnetic signals between electronic mosaics. In one embodiment of the present invention, a photonic-based interconnect comprises a first photonic node coupled to a second photonic node via a waveguide. The first photonic node is coupled to a first electronic mosaic and is configured to transmit electromagnetic signals encoding data generated by the first electronic mosaic to a second electronic mosaic and receive electromagnetic signals encoding data generated by the second electronic mosaic. The second photonic node is coupled to the second electronic mosaic and is configured to transmit electromagnetic signals encoding data generated by the second electronic mosaic to the first electronic mosaic and receive electromagnetic signals encoding data generated by the first electronic mosaic.

Abstract: The present invention relates to an installation for conveying electrical signals carried by a first triaxial cable (1) to a second triaxial cable (18). It comprises: a first interface (15) between the first triaxial cable (1) and a fiber optic cable (9) and a second interface (16) between the fiber optic (9) cable and the second triaxial cable (18). A television camera (17) is connected to a remote camera control unit (14) via this installation. The first triaxial cable (1) connects CCU (14) with the interface (15). The interface (15) comprises an adapter converting electrical signals, conveyed by the triaxial cable (1), to optical signals. The fiber optic cable (9) transmits optical signals to the second interface (16). The interface (16) comprises an adapter converting optical signals to electrical signals. The second triaxial cable (18) transmits the electrical signals to the television camera (17). A mirror image of the adapters allows transmitting electrical signals from the camera (17) to the CCU (14).

Abstract: A head-end circuit comprises first and second continuous light sources, first and second modulators. The first and the second continuous light sources provide first and second optical signals respectively corresponding to first wavelength and second wavelength, which is different from the first wavelength. The first modulator modulates the first optical signal based on first clock signal to generate an optical clock signal. The second modulator modulates the second optical signal based on downlink data to generate optical downlink data with the carrier of the second optical signal. The optical clock signal and the optical down link data are outputted to a remote antenna unit via first fiber path.

Abstract: An arrangement for generating beat notes with a relatively high signal-to-noise ratio (SNR) utilizes a pulsed laser source coupled into a section of post-processed highly-nonlinear optical fiber (HNLF) to generate a frequency comb having one or more regions of enhanced spectral power. A second laser signal source is overlapped with the frequency comb to form one or more “beat notes” at difference frequencies(y) between the second source and the continuum comb. By virtue of the post-processing, areas of spectral enhancement are formed along the comb, and are positioned to interact with the second laser signal to generate optical beat notes. The second laser signal may be from an external source (forming beat notes from a signal “outside” of the comb), or may be a frequency-multiplied version of the generated supercontinuum (forming beat notes from a signal “within” the comb).

Abstract: Various embodiments of the present invention are directed to methods and systems for transmitting optical signals from a source to a plurality of receiving devices. In one method embodiment, an optical enablement signal is transmitted (401) from the source to the plurality of receiving devices. The target receiving device responds to receiving the optical enablement signal by preparing to receive one or more optical data signals. The source transmits the one or more optical data signals to the target receiving device. The remaining receiving devices do not receive the one or more optical data signals.

Abstract: An optical link for communicating a payload data stream between a near end transceiver and a far end transceiver via an optical communication channel, the near end transceiver including a near end receiver (near-Rx) and a near end transmitter (near-Tx) and the far end transceiver including a far end receiver (far-Rx) and a far end transmitter (far-Tx), wherein the far-TX is adapted to transmit a link data stream to the near-RX beside the payload data stream from the far end to the near end.

Abstract: Included among the many structures described herein are photonic bandgap fibers designed to provide a desired dispersion spectrum. Additionally, designs for achieving wide transmission bands and lower transmission loss are also discussed. For example, in some fiber designs, smaller dimensions of high index material in the cladding and large core size provide small flat dispersion over a wide spectral range. In other examples, the thickness of the high index ring-shaped region closest to the core has sufficiently large dimensions to provide negative dispersion or zero dispersion at a desired wavelength. Additionally, low index cladding features distributed along concentric rings or circles may be used for achieving wide bandgaps.

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: A system may comprise a single wavelength laser; a modulator optically coupled to said laser; a length of multi-mode fiber optically coupled to said modulator; and a phase mask optically coupled to said fiber. The phase mask may be configured to filter out modes other than a selected mode.

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: An optical interconnection arrangement for use in high data applications is presented that eliminates the need for extensive serialization/de-serialization (SERDES) functionality by utilizing pulse amplitude modulation (PAM) techniques to represent the data in the optical domain while utilizing a separate channel for transmitting an optical clock signal, eliminating the need for clock recovery circuitry on the receive end of the arrangement.

Abstract: The present invention relates to advances in the field of reconfigurable optical networks. In particular, the present invention provides improvements in the technology of light sources for use in optical networks. The optical network according to the present invention includes a single light source that can be used to emit all of the bands and channels needed for transmission. In particular, the single light source in the optical network of the present invention is a mode-locked laser.

Abstract: Digital signal processing based methods and systems for receiving electrical and/or optical data signals include electrical receivers, optical receivers, parallel receivers, multi-channel receivers, timing recovery schemes, and, without limitation, equalization schemes. The present invention is implemented as a single path receiver. Alternatively, the present invention is implemented as a multi-path parallel receiver in which an analog-to-digital converter (“ADC”) and/or a digital signal processor (“DSP”) are implemented with parallel paths that operate at lower rates than the received data signal.

Abstract: A communication includes an analog input configured to receive an analog signal. An analog to digital converter is configured to provide a digital signal output based upon the analog input. A modulator is configured to modulate a laser based upon the digital signal thereby generating a modulated optical signal. An optical fiber carries the modulated optical signal and an optical detector arranged to receive the modulated optical signal from the optical fiber and provide a received output. A digital to analog converter digitizes the received output and provides an analog output based respective of the analog signal provided to the analog input.

Abstract: Provided is a digital camera module. The digital camera module includes an image sensor generating an electrical signal including a video signal and a clock signal and an optical interconnection unit converting the at least one of the video and clock signals into an optical signal to transmit the converted optical signal. The digital camera module further includes an image signal processor receiving the video signal restored from the optical signal to the electrical signal to convert the received video signal into a signal that is visually displayable.

Abstract: An image acquiring device includes a scanning module, an optical signal transmission medium and a mainboard module. In the scanning module having a rechargeable battery, a scanning unit scans a document to obtain an electrical document signal, a first signal converter is connected to the scanning unit and converts the electrical document signal into an optical document signal, and a first signal transmitting unit is connected to the first signal converter and receives and outputs the optical document signal. The optical signal transmission medium is connected to the first signal transmitting unit. On a mainboard of the mainboard module, a second signal input/output unit is connected to the optical signal transmission medium and receives the optical document signal, and a second signal converter is connected to the second signal input/output unit and converts the optical document signal into the electrical document signal.

Abstract: Embodiments of a system are described. This system includes an array of single-chip modules (CMs), which includes a first CM and a second CM which are coupled to each other. A given CM, which can be either the first CM or the second CM, includes a semiconductor die that is configured to communicate data signals with other CMs by capacitively coupled proximity communication and optical proximity communication using proximity connectors. These proximity connectors are proximate to a surface of the semiconductor die, and the semiconductor die includes an optical signal path configured to communicate on-chip optical signals.

Abstract: A signal processing system is disclosed having a detector for detecting an RF signal, wherein the detector has plural detection channels. A modulator modulates an optical signal with the detected RF signal and a processor processes the modulated optical signal to determine an azimuth or an elevation of the detected RF signal.

Abstract: A communication device includes an enclosure including a recess member including a bottom wall and an accommodating portion, a circuit board mounted on the bottom wall, and a light guiding member received in the accommodating portion. The circuit board includes a plurality of light sources arranged in a circular array. The light guiding member includes a light guiding portion to transmit light from the light sources to an outer surface of the communication device and a light shielding portion to shield the light to the outer surface and fix the light guiding portion in the accommodating portion. The light guiding portion includes a light guiding bottom wall surrounding the light sources and a light guiding sidewall. The light guiding sidewall includes an annular end surface to indicate signal strength and a strong signal orientation received by an antenna of the communication device.

Abstract: Various embodiments of the present invention are directed to systems and methods for all optical distributed arbitration for computer system components (1801-1804) communicatively coupled via a photonic interconnect in a computer system device. The embodiments of the optical arbitration in the computer system provides arbitration schemes with fixed priority (2000) and non-fixed priority (1830, 2200). The non-fixed priority scheme embodiments can provide fairness in arbitration. In some embodiments, delivery of light power and arbitration are combined (1830, 2001).

Abstract: The control of the transmission of useful optical signals on different line paths of an optical transmission device is accomplished via at least one of the following features: using signal sources and signal sinks, the useful optical signals are coupled into the line paths, or are coupled out of them; at least one portion of the optical line paths is configured as normal line paths having coupling nodes via which a switchover to an alternative line path can be undertaken if a normal line path is disturbed; in addition to the useful optical signals, test signals, whose evaluation is used for the switchover between the line paths, are transmitted bidirectionally section-by-section; at least two types of test signals can be transmitted, of which a first type is used as an indicator for an intact line path and a second type as an indicator for a disturbed line path; and any switchover to an alternative line path is only undertaken if, before the detection of the disturbance, a test signal of the first type has be