A space-division multiplexed optical fiber includes a relatively high refractive index optical core region surrounded by alternating regions of relatively low and relative high refractive index material, forming concentric high index rings around the core. The optical core region supports propagation of light along at least a first radial mode associated with the optical core region and a high index ring region supports propagation of light along at least a second radial mode associated with the high index ring region. The second radial mode is different from the first radial mode.

An ADD/DROP filter and an optical add/drop multiplexer are disclosed. An ADD/DROP filter includes an input port, an output port, an add port connecting to a modulator, and a drop port. The modulator is configured to load a pilot signal to a first optical signal to obtain a second optical signal, and transmit the second optical signal to the add port. A third optical signal is input to the input port. A wavelength difference between the second optical signal and the third optical signal is an integral multiple of a free spectral range. A power detector is connected to the output port and/or the drop port. The power detector is configured to obtain an output optical signal from the output port or the drop port and detect an optical power of the output optical signal.

Examples of a polarization independent optical device are described. One example polarization independent optical device includes an input/output preprocessing optical path and M add/drop optical paths. Any add/drop optical path can be configured to drop a first Q.sub.TE and a first P.sub.TE that meet a resonance condition of a microring included in the add/drop optical path such that each add/drop optical path can be configured to drop a desired optical signal. Any add/drop optical path can also be configured to transmit an input optical signal to the input/output preprocessing optical path. Therefore, when any of the M add/drop optical paths is configured to drop a desired optical signal, another add/drop optical path can be configured to add a desired optical signal.

Methods and systems for monitoring an optical network are described. An optical device may receive a data signal. The optical device may send the data signal to a test port. A measuring device may measure characteristics associated with the data signal.

An optical network including an input to receive from an optical network light comprising plural wavelength components. An optical wavelength selective filter, optically connected to the input, extracts a first wavelength component of the plural wavelength components from the light, thereby providing a first optical signal including the first wavelength component and a second optical signal including a remainder of the plural wavelength components a light emitter to provide a modulated broadband optical signal. A first output, optically connected to the optical wavelength selective filter, receives a first portion of the second optical signal for transmission to a light detector and a second output, optically connected to optical wavelength selective filter, receives a second portion of the second optical signal for transmission to the optical network.

An optical communications apparatus is configured to be connected to first, second, and third optical cables. In a branch connecting configuration, a branch optical path is enabled so that (i) signal wavelengths received over the first cable are routed to the third cable and (ii) signal wavelengths received over the third cable are routed to the second cable. The signal wavelengths received over the third cable include at least one of the signal wavelengths routed from the first cable to the third cable and returned via a loop connection at a distal portion of the third cable. In a bypass configuration, a connection via the branch optical path to the distal portion of the third cable is bypassed so that the signal wavelengths received over the first cable are routed to the second cable without first being routed through the distal portion of the third cable.

Systems and methods for controlling optical powers of optical channels in an optical communications network comprising a plurality of nodes is described herein. The method comprises obtaining a reference optical power. The method also includes determining an optical power of an optical channel generated by an optical transmitter of a node. The method further includes applying an attenuation to the optical channel to reduce the optical power of the optical channel to the reference optical power. In some implementations, the method is performed by a network controller operating in the optical communications network.

A transmission quality estimation system includes, three or more nodes and a transmission quality estimation device configured to estimate, transmission quality. A multi-core fiber having a plurality of cores, the multi-core fiber being used in at least a partial segment of a connection between the nodes. A node of the nodes includes a core connection unit configured to drop, add or relay light transmitted from, to or to each of to the plurality of cores of the multi-core fiber. The transmission quality estimation device includes an estimation unit configured to estimate transmission quality between the nodes on the basis of a transmission quality measurement light dropped by the core connection unit.

A space-division multiplexed optical fiber includes a relatively high refractive index optical core region surrounded by alternating regions of relatively low and relative high refractive index material, forming concentric high index rings around the core. The optical core region supports propagation of light along at least a first radial mode associated with the optical core region and a high index ring region supports propagation of light along at least a second radial mode associated with the high index ring region. The second radial mode is different from the first radial mode.

When a plurality of transport apparatuses perform their respective signal compensations using dummy lights, such compensations performed by the plurality of transport apparatuses affect each other in multiplex, with the result that such compensations produce no expected effects. A transport apparatus of the invention is characterized in that the transport apparatus comprises: a transmission unit that transmits a first signal; a generation unit that generates a dummy signal for compensating the first signal transmitted by the transmission unit; and a combination unit that combines the first signal with the dummy signal; wherein the generation unit adjusts the intensity of the dummy signal, which is to be generated, such that a second signal obtained by combining the first signal with the dummy signal will have a constant intensity.