At&t Intellectual Property I, LP

Tel Aviv University

US Government As Represented by the Secretary of the Army

Cristian Antonelli

Jungmi Oh

Michael Brodsky

Mikhail Brodsky

Antonio Mecozzi

Peter David Magill

Mikhail Boroditsky

Mark Shtaif

Paul Shala Henry

Lynn Nelson

Daniel E Jones

Gabriele Riccardi

Systems, apparatus and methods for defining an impairment profile along a polarization quantum channel such as in terms of modal loss and decoherence. The disclosed impairment profile or characterization methods may be used as part of a tool such as to inform a network operator of a weakest span of the communication channel, thus facilitating optimal signal routing decisions.

Method and apparatus for mapping out sources of decoherence in quantum channels

A quantum key distribution system is deployed in an optical fiber network transporting classical data traffic. A source of entangled photon pairs is used to generate quantum keys. Classical data traffic is typically transported over channels in the C-band. If a pair of channels for transport of quantum data is available within the C-band, then the source of entangled photon pairs is tuned to emit in a pair of channels in the C-band. If a pair of channels for transport of quantum data is not available within the C-band, then the source of entangled photon pairs is tuned to emit in a pair of channels in a combined S-band and L-band. When a periodically-poled lithium niobate waveguide pumped with a laser is used for the source of entangled photon pairs, the output spectral properties are tuned by varying the temperature of the waveguide.

Bandwidth provisioning for an entangled photon system

There is provided a Kramers-Kronig receiver, comprising a reception path; wherein the reception path comprises: a Stokes receiver that is configured to receive a polarization-multiplexed signal and to output a Stokes vector; wherein the polarization-multiplexed signal comprises a first modulated signal, a second modulated signal and a continuous wave signal; wherein the first modulated signal is of a first polarization; wherein the second modulated signal is of a second polarization; wherein the continuous wave signal is of the first modulation or of the second modulation; a set of analog to digital converters that are configured to generate a digital representation of the Stokes vector; and a digital processor that is configured to process the digital representation of the Stokes vector to provide a reconstructed polarization-multiplexed signal, wherein the processing is based on a Kramers-Kronig relationship related to the polarization-multiplexed signal.

Kramers-Kronig receiver

A Kramers-Kronig receiver that may include a reception path; wherein the reception path may include a photodiode that is configured to receive a received signal and output a photocurrent that represents the received signal; wherein the received signal comprises a continuous wave (CW) signal and a modulated signal; wherein a frequency gap between the CW signal and the modulated signal is smaller than a bandwidth of the modulated signal; an analog to digital converter that is configured to generate a digital representation of the photocurrent; and a digital processor that is configured to process the digital representation of the photocurrent to provide a reconstructed modulated signal, wherein the processing is based on a Kramers-Kronig relationship related to the received signal.

Operational parameters of a single-photon detector are determined with a continuous wave laser source. At a fixed trigger, a dark count probability and a series of count probabilities at different optical powers are determined. A particular optical power is selected by using a wide-range variable attenuator to attenuate the optical power of the continuous wave laser. The dark count probability and the count probabilities are determined for different trigger rates. The operational parameters include efficiency, afterpulsing constant, and detrap time. The operational parameters are computed by fitting the computed dark count probabilities and count probabilities to a user-defined relationship.

Characterization of single-photon detectors using a continuous wave laser source

Bandwidth provisioning for the entangled photon system by adjusting the phase matching conditions

A quantum key distribution system comprises a source of entangled photon pairs and two single-photon detectors. The source is coupled to each of the single-photon detectors by optical fiber. Operational systems parameters include the efficiency of the first single-photon detector, the efficiency of the second single-photon detector, and the maximum average number of photon pairs per unit time generated by the source. To characterize the operational systems parameters, the transmittances between the source and each single-photon detector are determined. The dark count probability of the first single-photon detector and the dark count probability of the second single-photon detector are determined. The count probability at the first single-photon detector, the count probability at the second single-photon detector, and the coincidence count probability are determined as a function of the optical power from the source. By fitting the values to a set of relationships, the operational systems parameters are computed.

Characterization of an entangled photon system

Operational parameters of a single-photon detector are determined with a source of photon pairs. At a fixed trigger, a dark count probability and a series of count probabilities at different optical powers are determined. A particular optical power is selected by adjusting the optical power of the source of photon pairs. The dark count probability and the count probabilities are determined for different trigger rates. The operational parameters include efficiency, afterpulsing constant, and detrap time. The operational parameters are computed by fitting the computed dark count probabilities and count probabilities to a user-defined relationship.

Characterization of single-photon detectors using a source of photon pairs

Systems and methods are described that derive a relationship between an optical transmitter's extinction ratio (E) and its interferogram wing-to-peak ratio (I). The change in an optical transmitter's Icorrelates with a change in measured E. As the Eof a telecom signal changes, the power of the modulated signal's interferogram wings change. After a relationship between Iand measured Ehas been derived for an optical transmitter, the relationship may be used after deployment to determine an Eby measuring an I.

System and method for measuring the extinction ratio of an optical transmitter using an interferogram wing-to-peak ratio

Disclosed is a method and apparatus for determining the birefringence autocorrelation length of a fiber in a non-destructive manner. The PMD of an optical fiber is measured over a first optical spectrum. A Faraday rotation angle is measured over a second optical spectrum. The birefringence autocorrelation length is determined from the measuring of the PMD and the Faraday rotation angle.

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Cristian Antonelli