An optical switch, comprising: a first optical waveguide, a first optical add path, a second optical add path and a micro-ring resonator. The micro-ring resonator is operable to add a first optical signal at a preselected wavelength received from the first optical add path to the first optical waveguide to travel in a first direction through the first optical waveguide. The micro-ring resonator is further operable to add a second optical signal at the preselected wavelength received from the second optical add path to the first optical waveguide to travel in a second direction through the first optical waveguide opposite to the first direction. There is also provided an optical drop switch, an optical switching apparatus, an optical communications network node and an optical communications network.

Aspects of the present disclosure describe systems, methods, and structures for passive optical add/drop multiplexing (POADM) architectures that remove the prior art requirement of an optical amplifier (i.e., repeater-less) at the POADM nodes.

The present disclosure discloses a method and device for channel switching, an Optical Network Unit (ONU) and a system for Time Wavelength Division Multiplexing (TWDM). The method for channel switching includes that: an ONU acquires channel information of a first TWDM channel, wherein the channel information of the first TWDM channel is used for indicating an uplink wavelength and/or downlink wavelength of the first TWDM channel; and the ONU tunes the uplink wavelength and/or downlink wavelength of the ONU into the uplink wavelength and/or downlink wavelength of the first TWDM channel according to the channel information of the first TWDM channel. By means of the present disclosure, the problem of high cost caused by specially building a standby channel for each TWDM channel in a system for TWDM Passive Optical Network (PON) to provide service protection is solved, and the cost of deploying the TWDM PON system is reduced.

An optical communications network has an interconnecting node (100) coupled in between at least one hub node (130) and at least first (140) and second (150) access nodes, to provide working and protection optical paths. The interconnecting node has a working wavelength selective switch (110) to select which working wavelengths are coupled. A corresponding protection wavelength selective switch (120) is also provided for the protection wavelengths. In the event of detection of a fault, protection switching (230) is carried out at the access node and the hub node without altering the selections made by the wavelength selective switches in the interconnecting node. Thus protection schemes across the interconnecting node for more than one access node can be handled. By not needing to alter wavelength selections at the interconnecting node during protection switching operation, the complexity and thus costs can be reduced.

In some embodiments, an apparatus includes an optical transceiver that includes a first set of electrical transmitters operatively coupled to a switch. Each electrical transmitter from the first set of electrical transmitters is configured to transmit an electrical signal from a set of electrical signals. In such embodiments, the switch is configured to switch an electrical signal from the set of electrical signals such that the set of electrical signals are transmitted via a second set of electrical transmitters. Each electrical transmitter from the second set of electrical transmitters is operatively coupled to an optical transmitter from a set of optical transmitters. The set of optical transmitters is operatively coupled to an optical multiplexer. In such embodiments, at least one electrical transmitter from the second set of electrical transmitters is associated with a failure within the optical transceiver.

A method of establishing communication between an optical line terminal and an optical network unit within an optical access network includes receiving a signal indication from an optical transceiver of an optical line terminal. The signal indication includes: (i) a loss-of-signal indication indicating non-receipt of an upstream optical signal from the optical network unit; or (ii) a signal-received indication indicating receipt of the upstream optical signal from the optical network unit. The method includes determining whether the signal indication includes the loss-of-signal indication. When the signal indication includes the loss-of-signal indication, the method includes instructing the optical transceiver to cease signal transmission from the optical transceiver to the optical network unit. Moreover, when the signal indication includes the signal-received indication, the method includes instructing the optical transceiver to transmit a downstream optical signal from the optical transceiver to the optical network unit.

In a case where a failure occurs in a part of an optical fiber in an optical cable, when attempting to switch to a redundant configuration, the stable use of an optical transmission system is impaired, so that the wavelength band cannot be used effectively. Accordingly, the optical transmission system of the present invention includes a first optical device configured to change the transmission line of a wavelength band signal propagating through a first optical transmission line to a second optical transmission line that is the same path as the first optical transmission line, in the stage before a faulty part in the first optical transmission line, and a second optical device configured to change the transmission line of the wavelength band signal from the second optical transmission line to the first optical transmission line, in the stage after the faulty part.

An optical transmission system includes: a first light source configured to output a light wave of a first wavelength among a plurality of wavelengths; a second light source configured to output a light wave of a second wavelength; and a first detection section configured to detect abnormality in the light wave from the first light source, wherein upon detection of abnormality, a multiplexed optical signal including an optical signal of a modulated light wave generated using the light wave from the second light source in place of an optical signal of a modulated light wave generated using the light wave from the first light source is transmitted.

An optical line terminal for use in a multi-wavelength network to operatively connect via a PON port by a first connection to a first network node and to operatively connect via the PON port by a second connection to a second network node, the optical line terminal being configured to operate under first network conditions by sending no data via the second connection, and to operate under second network conditions by sending data via the second connection.

An optical switch, comprising: a first optical waveguide, a first optical add path, a second optical add path and a micro-ring resonator. The micro-ring resonator is operable to add a first optical signal at a preselected wavelength received from the first optical add path to the first optical waveguide to travel in a first direction through the first optical waveguide. The micro-ring resonator is further operable to add a second optical signal at the preselected wavelength received from the second optical add path to the first optical waveguide to travel in a second direction through the first optical waveguide opposite to the first direction. There is also provided an optical drop switch, an optical switching apparatus, an optical communications network node and an optical communications network.