The station-side terminal apparatus for the optical access network includes: the station-side terminal apparatus; the subscriber-side terminal apparatuses connected to the station-side terminal apparatus via the optical transmission line; the terminal devices to which mutually different wavelengths are assigned; and the communication failure detecting unit. Each of the terminal devices includes the uplink communication state monitoring unit configured to monitor a state of uplink communication for each registered subscriber-side terminal apparatus, on the basis of the input uplink signal, and the downlink communication failure information extracting unit configured to extract information of a state of downlink communication, which is transmitted from the registered subscriber-side terminal apparatus. The communication failure detecting unit detects a failure of the uplink communication and a failure of the downlink communication, on the basis of the state of the uplink communication and the state of the downlink communication.

A method of implementing a stretched single optical communication span includes receiving one or more optical signals from an optical fiber span having high loss; adding a pilot signal to the one or more optical signals, subsequent to the receiving; and amplifying the one or more optical signals and the pilot signal with a pre-amplifier that is an Erbium Doped Fiber Amplifier (EDFA). Advantageously, the stretched single span operates below a Hazard 1M environment. A node in a stretched single optical communication span includes an optical multiplexer connected to an optical fiber span having high and a pilot signal, and configured to output a combination of one or more optical signals from the optical fiber span and the pilot signal; and a pre-amplifier that is an EDFA configured to receive the output of the optical multiplexer and provide amplification of the one or more optical signals and the pilot signal.

The present invention includes novel techniques, apparatus, and systems for optical WDM communications. Tunable lasers are employed to generate respective subcarrier frequencies which represent subchannels of an ITU channel to which client signals can be mapped. In one embodiment, subchannels are polarization interleaved to reduce crosstalk. In another embodiment, polarization multiplexing is used to increase the spectral density. Client circuits can be divided and combined with one another before being mapped, independent of one another, to individual subchannels within and across ITU channels. A crosspoint switch can be used to control the client to subchannel mapping, thereby enabling subchannel protection switching and hitless wavelength switching. Network architectures and subchannel transponders, muxponders and crossponders are disclosed, and techniques are employed (at the subchannel level/layer), to facilitate the desired optical routing, switching, concatenation and protection of the client circuits mapped to these subchannels across the nodes of a WDM network.

Embodiments of this application provide a service protection method, including: A first node determines that a fault occurs on a first working path; the first node generates a bandwidth activation message based on the fault, where the bandwidth activation message indicates a third node to adjust a bandwidth of a service from a protection bandwidth to a target bandwidth, the protection bandwidth represents a pre-occupied bandwidth of a first protection path before transmission of the service, and the target bandwidth represents an actual occupied bandwidth for transmission of the service; and the first node sends the bandwidth activation message on the first protection path.

According to an example aspect of the present invention, there is provided an apparatus comprising a first part (110) which comprises a first light-based communication port (114) and a network interface (112), a second part (120) which comprises a non-volatile memory (122) and a second light-based communication port (124), and wherein the apparatus is configured to deactivate at least one of the first light-based communication port (114) and the second light-based communication port (124) responsive to determining that a read or write operation in the non-volatile memory (122) is complete.

A method for operating an optical protection switching module to protect wave division multiplexed (WDM) optical signals. The method includes receiving a first WDM optical signal at a first receive port of the optical protection switching module, receiving a second WDM optical signal at a second receive port of the optical protection switching module, tapping off a portion of the first WDM optical signal to obtain a tapped portion of the first WDM optical signal, optically filtering the tapped portion of the first WDM optical signal to obtain a predetermined channel of the tapped portion of the first WDM optical signal, detecting a power level of the predetermined channel, and in response to the power level being below a predetermined threshold, causing a switch to enable the second WDM optical signal to pass through the optical protection switching module.

Techniques for protection switching mechanisms that use detection of power in baseband signals resulting from optical mixing of an optical signal (at a frequency of a particular channel to be protected) with the received WDM spectra to determine whether there is a failure on the particular channel, indicated by an average power at a resulting baseband signal from the optical mixing being less than a threshold.