An optical network is disclosed which includes an optical fiber shared by a plurality of transmitters using code division multiple access techniques. The transmitters are connected by tributary optical fibers to the shared optical fiber. In code division multiple access techniques, each communication is encoded with a distinctive code which enables a receiver to extract the communication intended for it from amongst communications intended for other receivers. It is found that synchronizing the communications on the optical fiber improves the ability of a receiver to extract the communication intended for it. Injecting an optical pulse signal into the optical network, and using the tributary optical fibers to carry the clock signal to the transmitters provides an inexpensive method of synchronizing the transmitters which feed signals onto the optical fiber. The technology is of use in optical networks, and other transmission line networks, and is well-suited to use in local area networks.

The present application relates to an optical communication transmitting apparatus and receiving apparatus. The optical communication transmitting apparatus includes: an encoder, configured to encode and shunt an input signal, to generate multiple synchronous encoded signals; a driver, configured to amplify the multiple encoded signals, to generate multiple drive signals; and multiple light sources, configured to generate multiple synchronous optical signals when driven by the multiple drive signals. The optical communication transmitting apparatus and receiving apparatus provided in the present application make full use of advantages of visible light communication, achieving a rapid communication speed and high security.

An apparatus comprises: a first clock; a receiver configured to: receive a first packet via a first channel corresponding to a first wavelength, and receive a third packet via a third channel corresponding to a third wavelength; and a processor coupled to the receiver and configured to: implement channel bonding using the first channel and the third channel, synchronize the first clock based on the first packet, and calculate a channel skew between the first channel and the third channel based on the first clock.

An apparatus includes a receiver configured to receive a signal that has traveled an optical transmission line without returning output from an optical transmitting device and synchronize with the optical transmitting device in order to demodulate the signal; a dispersion compensator configured to compensate for wavelength dispersion caused by transmission of the signal; an acquisition circuit configured to acquire a transmitting timing at which the signal has been transmitted from the optical transmitting device; a calculation circuit configured to calculate a transmission time period from the optical transmitting device to the receiver from the transmitting timing and a receiving timing at which the signal has been received with the receiver; and an amount setting circuit configured to adjust a dispersion compensation amount of the dispersion compensator in accordance with the transmission time period.

Systems and methods for reducing total skew in optical signals transmitted by optical coherent transponders without measuring the total skew are disclosed. The method may compensate for the in-phase/quadrature (I/Q) skew of optical signals in complex modulation formats. It may include providing input to a transponder to produce a periodic (and generally sinusoidal) output signal, providing the signal to an optical power meter, measuring the optical power of positive and negative harmonics of the signal while varying the amount of skew introduced by a de-skewing filter in the transponder, identifying the amount of skew introduced by the de-skewing filter when the minimum optical power measurement is taken, and causing the amount of skew introduced by the de-skewing filter to equal the identified skew offset by a one-half symbol delay. The system may provide better skew compensation using less expensive equipment than de-skewing methods based on existing skew measurement methods.

A system for an installation and a method for operating a system, including stationary transceiver modules and a vehicle having a transceiver module, the individual transceiver module having a controllable light source and a light sensor, so that a data transmission is able to be carried out between the vehicle and the stationary modules.

An object is to provide a dispersion compensating system with a large amount of dispersion compensation and reduced operation costs. Disclosed is a dispersion compensating system in which a core node and an access node are connected through a ring network, the access node includes a delay measurement unit configured to receive delay measurement signals from the core node to measure a delay between the core node and the access node, an average dispersion amount calculation unit configured to calculate an amount of dispersion compensation to be applied to an optical burst signal prior to transmission to the ring network, based on the delay thus measured, and a real-part inverse dispersion application unit configured to perform pre-equalization on a waveform of the optical burst signal prior to the transmission, based on the calculated amount of dispersion compensation.

Systems and methods for quantum clock synchronization are provided. Various embodiments can use time-energy and polarization entangled photons to securely extract the absolute time difference between two remote clocks. In some embodiments, two parties can each have a source of entangled photons. Each party can detect one member of the pair locally and time stamp the detection time, while the other photon gets sent over a common channel (single optical mode) to the other party where the transmitted photon is detected and time stamped. The time stamp values can be shared over an open authenticated channel and each receiver can run a cross-correlation of the detection times. The authenticity and non-spoofability of the timing signal are ensured if each party does not just perform a simple time of arrival measurement but also incorporate polarization measurements whose joint values constitute a Bell test.

A time synchronization apparatus and method for automatically detecting the asymmetry of an optical fiber. The apparatus comprises an OTDR asymmetry detecting module (12), a time delay compensating module (14) and a time synchronization correcting module (16), the OTDR asymmetry detecting module (12) comprises an emitting unit (122) used for emitting a detection signal to the optical fiber, a receiving unit (124) used for receiving the detection signal returned by the optical fiber, a transmission time delay determining unit (126) used for determining the transmission time delay of the detection signal in the optical fiber according to the time difference between the emitting detection signal and the returned detection signal, and the determining transmission time delay of a service signal in the optical fiber according to the transmission time delay of the detection signal; The time delay compensating module (14) is used for calculating asymmetric time delay value between the first optical fiber and the second optical fiber according to the transmission time delay of the first optical fiber and the transmission time delay of the second optical fiber; The time synchronization correcting module (16) is used for synchronization correcting time according to the asymmetry time delay. The apparatus and method can improve the time synchronism precision.

In various embodiments, a method is provided. In this method, a first signal is received from a master node, and is sampled to obtain a first sample. The first sample is then quantized to obtain a quantized form of the first sample. A first synchronization sequence is detected from the quantized form of the first sample at T2. First information is received from the master node and the first information is used to indicate a moment T1 at which the master node sends the first synchronization sequence. A second synchronization sequence is sent to the master node at T3. Second information received from the master node and the second information is used to indicate a moment T4 at which the master node detects a quantized form of the second synchronization sequence. Time synchronization is performed based on T1, T2, T3, and T4.