[Problem] A signal distortion generated when a multi-level modulated optical signal is transmitted through an optical transmission path where optical amplifiers are scattered is suppressed and transmission quality is improved. [Solution] An optical transmission system 20 includes Tx 21a to Tx 21n configured to transmit a multi-level modulated optical signal 32 to an optical fiber 25, optical amplifiers 26a to 26f configured to amplify the optical signal 32 transmitted through the optical fiber 25, the optical amplifiers 26a to 26f being scattered on the optical fiber 25, and Rx 24a to Rx 24n configured to receive the amplified optical signal 32 via the optical fiber 25. A pre-dispersion compensation unit 27 of each of the Tx 21a to Tx 21n performs pre-dispersion compensation on the transmitted optical signal 32, based on a pre-dispersion compensation ratio for determining a percentage of dispersion compensation to be performed in advance on a wavelength dispersion to be accumulated in the optical fiber 25, with respect to the dispersion compensation to narrow a bandwidth to be widened by the wavelength dispersion during transmission of the optical signal 32 through the optical fiber 25.

An optical network device includes a receiver that receives a polarization multiplexed optical signal and a processor. The processor separates an electric field information signal indicating the polarization multiplexed optical signal into first and second polarization components orthogonal to each other, generates third and fourth polarization components by controlling the first and second polarization components, calculates an evaluation value corresponding to a power of the third or fourth polarization component for each of a plurality of positions on a transmission line, calculates a variation in the evaluation value for a control amount for each of the plurality of positions, and decides whether a first position is a position to be detected based on a result of comparing a variation in an evaluation value for the first position with a variation in an evaluation value for a second position adjacent to the first position.

An optical network device includes a receiver that receives a polarization multiplexed optical signal and a processor. The processor separates an electric field information signal indicating the polarization multiplexed optical signal into first and second polarization components orthogonal to each other, generates third and fourth polarization components by controlling the first and second polarization components, calculates an evaluation value corresponding to a power of the third or fourth polarization component for each of a plurality of positions on a transmission line, calculates a variation in the evaluation value for a control amount for each of the plurality of positions, and decides whether a first position is a position to be detected based on a result of comparing a variation in an evaluation value for the first position with a variation in an evaluation value for a second position adjacent to the first position.

A link extender configured to extend a range of an optical transceiver module is provided. The link extender includes an array of semiconductor optical amplifiers (SOAs) configured to amplify an optical signal received from the optical transceiver module, a first plurality of variable optical attenuators (VOAs) configured to control a power output of the amplified optical signal output from the array of SOAs, and a plurality of dispersion compensation and filtering (DC&F) devices configured to compensate for chromatic dispersion of the optical signal.

A link extender configured to extend a range of an optical transceiver module is provided. The link extender includes an array of semiconductor optical amplifiers (SOAs) configured to amplify an optical signal received from the optical transceiver module, a first plurality of variable optical attenuators (VOAs) configured to control a power output of the amplified optical signal output from the array of SOAs, and a plurality of dispersion compensation and filtering (DC&F) devices configured to compensate for chromatic dispersion of the optical signal.

All-optical multi-rate systems and methods include and use a continuous wave (CW) light source for providing a CW carrier signal, a plurality of modulators used for modulating the CW carrier signal to form a plurality of modulated optical signals, an inverse filter bank for multiplexing the plurality of modulated optical signals to form a multiplexed optical signal, and a post distortion filter (PDF) for obtaining a narrowed multiplexed optical signal and, optionally, for eliminating inter-symbol interference (ISI) in the narrowed multiplexed optical signal.

All-optical multi-rate systems and methods include and use a continuous wave (CW) light source for providing a CW carrier signal, a plurality of modulators used for modulating the CW carrier signal to form a plurality of modulated optical signals, an inverse filter bank for multiplexing the plurality of modulated optical signals to form a multiplexed optical signal, and a post distortion filter (PDF) for obtaining a narrowed multiplexed optical signal and, optionally, for eliminating inter-symbol interference (ISI) in the narrowed multiplexed optical signal.

Methods and systems relating to administration of access credentials for electronic access control are disclosed. Web resources are provided for rendering a webpage including an access credential. A server device receives an access instruction authorizing a user to access an electronic lock associated with the access credential. A client device of the user transmits a first request for the access credential. The first request may be generated by a browser application of the client device. The server device provides the web resources and a browser cookie to the client device. Responsive to subsequent requests for the access credential, the server device determines whether the client device is authorized to receive the access credential based on the client device providing the browser cookie. When the server device determines that a subsequent request authorizes the client device to receive the access credential, the web resources are provided to the browser application.

Methods and systems relating to administration of access credentials for electronic access control are disclosed. Web resources are provided for rendering a webpage including an access credential. A server device receives an access instruction authorizing a user to access an electronic lock associated with the access credential. A client device of the user transmits a first request for the access credential. The first request may be generated by a browser application of the client device. The server device provides the web resources and a browser cookie to the client device. Responsive to subsequent requests for the access credential, the server device determines whether the client device is authorized to receive the access credential based on the client device providing the browser cookie. When the server device determines that a subsequent request authorizes the client device to receive the access credential, the web resources are provided to the browser application.

An optical link for a communication network, the optical link having an optical fibre link, a downstream transmitter, a downstream receiver, an upstream transmitter and an upstream receiver. The upstream and downstream transmitters are configured to transmit a respective pilot tone on a respective optical carrier and are configured to tune a frequency of the pilot tone within a preselected frequency range. The upstream and downstream receivers are configured respectively to determine an upstream notch frequency, f.sub.notch-US, and a downstream notch frequency, f.sub.notch-DS, of respective detected photocurrents from at least one respective pilot tone frequency at which the respective detected photocurrent is equal to or lower than a photocurrent threshold. The optical link also includes processing circuitry configured to receive the upstream and downstream notch frequencies and configured to estimate a propagation delay difference of the optical link depending on the upstream and downstream notch frequencies.