Optical noise reduction apparatus and method

A noise reduction apparatus adapted to improve signal-to-noise ratio in an input optical signal containing a coherent component having a coherent signal power and an incoherent component having an incoherent signal power, the apparatus comprising:

• an input optical splitter, M optical transmission paths, and an output optical coupler, where M>=2;
• wherein the input optical splitter is adapted to split the input optical signal into M path signals each having a respective coherent path component and a respective incoherent path component, wherein each one of the M path signals propagates through a respective one of the M optical transmission paths resulting in a respective phase adjustment to the respective path signal;
• and
• a fine phase adjustment device in at least one of the optical transmission paths adapted to apply a fine phase adjustment to a respective one of the M path signals;
• wherein the phase adjustment applied by the transmission media in combination with the fine phase adjustment applied by the at least one fine phase adjustment device results in an optical path length difference, ΔLo, between the two optical transmission media selected such that the incoherent path components are substantially not correlated with each other at the output optical coupler;
• wherein the output optical coupler couples the path signals such that substantially all of the coherent signal power is produced at a main output, while the incoherent signal power is substantially divided between the main output and one or more subsidiary outputs.

A noise reduction apparatus adapted to improve SNR in an input optical signal having a coherent component and an incoherent component, the apparatus comprising:

• an optical coupler, two optical transmission media, and two optical reflectors;
• wherein the optical coupler is adapted to split the input optical signal into two path signals each having a respective coherent path component and a respective incoherent path component, wherein each one of the two path signals propagates through a respective one of the two optical media to a respective one of the two optical reflectors where the respective path signal is reflected, and propagates back through the respective one of the two optical media to the optical coupler;
• and
• at least one fine phase adjustment device adapted to apply a respective phase adjustment to at least one of the two path signals wherein the respective phase adjustment is applied in a manner that at the optical coupler the coherent path components are coupled substantially into a single output of the coupler, and the incoherent component is coupled to multiple outputs.

A noise reduction apparatus for improving the signal-to-noise ratio of an optical signal, comprising:

• an input optical splitter adapted to split the optical signal into M path signals transmitted along respective M optical transmission paths, wherein M>=2;
• a phase adjustment device in at least one of the M optical transmission paths adapted to apply a phase adjustment relative the M path signals;
• and
• an output optical coupler adapted to combine the M path signals into an output optical signal having a portion of incoherent components of each of the M path signals substantially uncorrelated and having coherent components of each M path signal constructively combined.

A method of improving the signal-to-noise ratio of an optical signal comprising:

• splitting the optical signal into a plurality of path signals, each path signal having a coherent path component and an incoherent path component;
• adjusting the phase of at least one of the plurality of path signals such that, at a combination point, the coherent path components are combinable constructively and each incoherent path component is substantially uncorrelated with each other incoherent path component;
• and
• combining the path signals at said combination point.

A noise reduction apparatus for an optical signal comprising:

• an optical splitter for splitting an input optical signal having a coherent signal component and an incoherent signal component into a plurality of path signals transmitted along a plurality of respective transmission paths;
• a phase adjustment device associated with at least one of the plurality of transmission paths for applying a phase difference between the plurality of path signals;
• and
• an optical coupler for combining the plurality of path signals into a main output optical signal and at least one subsidiary output optical signal, wherein the main output optical signal comprises substantially all of the coherent signal component and the subsidiary output signal comprises at least a portion of the incoherent signal component.