Deutschetelekom Ag

Deutsche Telekom Ag Bonn

Heidrun Schmitzer

Wolfgang Dultz

Gisela Dultz

Leonid Alexseevich Beresnev

Erna Frins

Eric Hildebrandt

Joachim Vobian

Leonid Beresnev

Helmar A Becker

Werner Weiershausen

Franko Kueppers

Bernhard Hils

Kay Michael Schmid

Bernd Hils

A method and device for reducing the distortion of optical pulses caused by the polarization mode dispersion in optical communication systems is provided. When an optical pulse having any polarization is transmitted through an optical communication system, which is optically anisotropic, at least in sections, the optical pulse may become distorted due to the different velocities of the various polarization components. This distortion of the optical pulses may reduces the maximum transmission rate of the system. A method is provided for functioning in response to the detected transmission quality of the communication system where a polarization-controlling device for setting the polarization of the optical pulse is driven in such a way that the transmission quality is maximized. An optical communication system, including an optical transmission medium, involves a device for determining the transmission quality of the communication system, a regulating device, and a polarization-controlling device. The output signal from the device for determining the transmission quality of the communication system may be applied to the regulating device, which drives the polarization-controlling device to change the polarization of the optical pulses in such a way that the transmission quality is optimized.

Reducing the distortion of optical pulses caused by polarization mode dispersion in optical communication systems

A method and a device for reducing speckle formation on a projection display when working with a coherent light source. In this context, the light coming from the light source, before the projection, may strike an electrically controllable optical element having a spatially inhomogeneous refractive index, passing through the same, the refractive index being varied over time within the projection period. This may lead to an averaging out of the speckle pattern on the projection screen. For purposes of illumination, a multimode light source may be used, and/or the light coming from the light source is separated into a plurality of spatial modes, thereby reinforcing the effect. As an optical element, one may employ a liquid crystal element composed of at least two liquid crystal layers, to which a spatially dependent voltage is applied to generate a spatially dependent refractive index. Its birefringence may be compensated by orientating the layers to one another in appropriate fashion.

Method and device for reducing speckle formation on a projection screen

A device for generating, adding and subtracting digital sequences of optical pulses and a method for the secure transmission of information. An interferometer having at least one electro-optical switch or electro-optical modulator positioned in one of its branch sections is used so that binary optical pulse sequences may be added and/or subtracted in the context of an electro-optical device and a method for the secure transmission of information using optical signals.

Device for generating adding and subtracting digital sequences of optical pulses and method for secure transmission of information

A method and system for the secure transmission of messages between at least two users of a telecommunications network, using a secret, random binary encryption key, which is used once for encryption. The key is generated in a key generator recorded on at least two portable data media, such as CDs, and then output in this form to the users, each of whom receives one data medium containing the recorded key. The key is not stored in any other location. The users insert the recorded key media into reading devices, which are respectively assigned to telecommunications equipment, e.g., telephones, fax machines, or PCs, employed by the users. When a connection is established, logistics devices, which are also assigned to the telecommunications equipment, check whether the keys were entered properly and whether they correspond to each other. The logistics devices also synchronize the entered keys, or at least portions of the keys, when the information to be transmitted is encrypted and decrypted.

Method for the secure transmission of messages

A method and arrangement for generating binary sequences of random numbers uses the principle of random selection of the path of photons on a beam splitter and generating a random number by using two detectors (D, D) downstream from a beam splitter (ST). To generate photons, a light source (L) of a low power is used, and an additional beam splitter (ST) is connected upstream from the beam splitter (ST). The photons emitted by the light source (L) during a predefined measurement time are split by the beam splitters (ST, ST) arranged one after the other in the beam path of the light source (L). The random sequence is generated when the splitting of the photons matches a predefined photon scheme.

Method and arrangement for generating binary sequences of random numbers

To provide a phase modulator for introducing a topological phase, which is designed to produce any desired phase shift between zero and 360&#xb0;, the phase modulator has means, at least one double-refractive, electrooptical delay element having a rotatable indicatrix, which is/are used to direct the polarization of the light, during transmission through the modulator, over at the light one closed path on the Poincar&#xe9; sphere, the indicatrix rotating in accordance with the predefined phase shift, and the total encircled surface on Poincar&#xe9; sphere being equal in terms of absolute value to &#x3c6;.

Optical phase modulator

A method is provided for changing the polarization of at least one of the photons emitted from a photon pair source into various partial ray paths using an electro-optical modulator (EOM), which is positioned in the particular partial ray path being traversed by the photon to be influenced and which, in the activated state, is able to alter the polarization of a photon, the modulator being activated as a function of time such that the probability that the photon is found in the region of the electro-optical modulator in the activated state is at a maximum.

METHOD FOR CHANGING THE POLARIZATION OF AT LEAST ONE OF THE PHOTONS EMITTED FROM A PHOTON-PAIR SOURCE INTO VARIOUS PARTIAL PATHS OF RAYS, AND METHOD FOR OPTIONALLY GENERATING INDIVIDUAL PHOTONS OR PHOTON PAIRS IN AN OPTICAL CHANNEL

The present invention provides an optical communications link having at least one optical fiber, in particular for communications transmission, where the optical fiber is repeatedly bent. The fiber sections having a right-hand and left-hand curvature are distributed in such a way over the communications link that the average torsion of the fiber is approximately zero. The communications link in accordance with the present invention is compact, flexible, and variable in length. In addition, it reduces the sensitivity of the polarization state of the optical signal to changes in the form of the communications link.

Optical communications link

A quantum cryptography system using electrooptical liquid crystal modulators which change the polarization and which are designed as electrically rotatable retardation plates whose two birefringent axes are rotated by the applied electrical field around an angle &thgr; which depends on the strength of this field. A &lgr;/2 retardation plate rotates the elliptically polarized light striking the plate around an angle 2&thgr; at speeds in the microsecond range. The quantum cryptography system can be used for interception-proof data transmission over transmission links that are accessible to the public.

Quantum cryptography system for a secure transmission of random keys using a polarization setting method

The present invention is directed to a sensor for detecting changes in the distance between a first and a second location, having at, least one substantially helically coiled optical fiber, which is able to be mechanically connected to at least one of the locations, and having a light transmitter and a detecting device for optical signals, the detecting device being able to generate an output signal, which is dependent upon the polarization state of the optical signal transmitted via the optical fiber. The present invention is also directed to a method for detecting the changes in distance between a first and a second location, having the following features: at least one of the locations is mechanically coupled to a substantially helically coiled optical fiber; an optical signal having a known polarization state is launched into the optical fiber; following transmission over the connecting line, this is detected in such a way that information is obtained with respect to its polarization state; from this information, the change in distance is determined.

Sensor and method for detecting changes in distance

A method and an apparatus for generating a random number on a quantum-mechanics machanics basis using the fundamentally random choice of path of a quantum particle on a beam splitter. Detectors are provided for capturing the particles being assigned to the outputs of the beam splitter. The detectors or their counting events represent different number values of the random number, or random number sequence. The generation of a multi-particle state in the output channel of the beam splitter, and thus of several particles which impact on a detector (D , D &prime;, D , D &prime;), significantly and advantageously increases the response probability of the detector and thus the probability of obtaining a useable counting event for every multi-particle state generated by the particle source. In this way a random sequence can be obtained more rapidly and more reliably than with single-particle detection.

Method for generating a random number on a quantum-mechanical basis and random number generator

A method and device for generating a choice of individual photons or photon pairs in an optical channel. The generation of this choice involves generating a two-photon state corresponding to a photon pair and spatially separating the photon pair while preserving the quantum-mechanical correlation, in the event the photons are emitted in a collinear manner. One photon is coupled into one optical channel each, the one channel containing an interferometer with variable optical path-length difference &dgr; , and the other channel including an optical delay section having the optical length &dgr; The channels are spatially reunited through a beam splitter, and an adjustment of the quantities &dgr; , and &dgr; occurs in such a way that the probability K for coincidences between the outputs of the beam splitter is a choice of approximately K&equals;0 or approximately K&equals;1, or approximately a predetermined intermediate value, with K&equals;0 corresponding to a photon pair in one of the output channels of the beam splitter, and K&equals;1 corresponding to two individual photons in both output channels of the beam splitter. With this choice generation, an optical separating filter or gate can be implemented for a choice of one-photon or two-photon states, which is usable in quantum cryptography and as a basic element of a quantum-optical computing machine.

Method and device for producing a choice of either single photons or pairs of photons in an optical channel

A method and a device are described to compensate for polarization mode dispersion in an optical transmission link(,&prime;) having polarization-dependent transmission characteristics, in particular in optical fibers and cables with not only statistical, but preferred birefringence. A compensation element (,&Prime;), whose length is adjusted non-destructively using an interference device (,&Prime;), in particular a pressure mechanism, is connected upstream or downstream from the transmission link (,&prime;). The polarization states P,and P,of the compensation element are mixed by the interference and thus the length of the compensation fiber is defined at which a propagation time difference between the partial waves of polarization states P,and P,is increased or decreased so that it compensates for the propagation time difference &tgr; within the transmission link (,&prime;).

Method and device to compensate for polarization mode dispersion in an optical transmission link

A double-beam interferometer for electromagnetic radiation and a method for the compensation of dispersion or increase in the spectral resolution of such an interferometer. Using a polarizer, which is brought into the optical radiation path, a defined polarization state P,is produced for the electromagnetic partial waves flowing into the arms of the interferometer. This polarization state is wavelength-independent and can vary for both partial beams. Optical elements modify the polarization state P,of the electromagnetic partial waves as a function of wavelength &lgr; and each spectral component &lgr;,is coded with a polarization P,(&lgr;i). An analyzer, fitted to the output of the interferometer, transmits an adjustable polarization state P,, whereby an additional wavelength-dependent phase difference &ggr;(&lgr;) occurs between the partial waves of the spectral components. &ggr;(&lgr;) can be adjusted to obtain compensation of dispersion or an increase in the spectral resolution of the interferometer.

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Wuppertal, Germany

Heidrun Schmitzer