Optical equalization with beam counter-propagation

A method for processing an input optical signal having a first power spectrum among a plurality of wavelength channels, the method comprising:

• providing a plurality of filters along a path, each filter associated with an element in a frequency-domain series approximation of a target transfer function, the plurality of filters comprising a component assembly;
• separating the input optical signal into a first beam and a second beam;
• propagating the first beam through the component assembly via the path;
• counter-propagating the second beam through the plurality of filters of the component assembly via substantially the same path;
• and
• processing the first beam and the second beam using the component assembly to apply a first transfer function to the input optical signal such that an output optical signal formed using the processed first and second beams has a second power spectrum among the plurality of carrier wavelengths.

An optical device for processing an input optical signal having a first power spectrum among a plurality of carrier wavelengths, the optical device comprising:

• a beam displacer operable to separate the input optical signal into a first beam and a second beam and to re-combine the first and second beams to form an
• output optical signal having a second power spectrum among the plurality of carrier wavelengths after optical processing;
• a plurality of filters positioned such that the first beam passes through the plurality of filters in a first direction and the second beam passes through the plurality of filters in a second direction, and further positioned such that the first and second beams pass again through the beam displacer after being optically processed by the plurality of filters;
• and
• a controller operable to monitor the second power spectrum of the output optical signal and to adjust parameters of at least two of the plurality of filters in order to control the filters so that the second power spectrum approximates a predetermined target power spectrum.

A method for processing an input optical signal, the method comprising:

• separating the input optical signal into a first beam and a second beam;
• propagating the first beam through a component assembly having at least a first optical component and a second optical component, the first beam passing in a first direction through the first optical component and subsequently through the second optical component;
• propagating the second beam through the component assembly, the second beam passing in the first direction through the first optical component and subsequently through the second optical component;
• reflecting the first beam back through the component assembly, the reflected first beam passing in a second direction through the second optical component and subsequently through the first optical component;
• and
• reflecting the second beam back through the component assembly, the reflected second beam passing in the second direction through the second optical component and subsequently through the first optical component;
• whereby the optical processing performed on the first and second beams is performed by the passing of each of those beams in the first and second directions through at least the first and second optical components.

A method for filtering an input optical signal having a first power spectrum among a plurality of wavelength channels, the method comprising:

• separating the input optical signal into a first beam and a second beam;
• propagating the first beam through an optical filter comprising a polarization-dependent routing element and at least one crystal element, wherein the first and second beams pass in a first direction through the polarization-dependent routing element and subsequently through the at least one crystal element;
• propagating the second beam through the optical filter, the second beam passing in the first direction through the polarization-dependent routing element and subsequently through the at least one crystal element;
• reflecting the first beam back through the optical filter, the reflected first beam passing in a second direction through the at least one crystal element and subsequently through the polarization-dependent routing element;
• and
• reflecting the second beam back through the optical filter, the reflected second beam passing in the second direction through the at least one crystal element and subsequently through the polarization-dependent routing element;
• whereby the optical filtering performed on the first and second beams is performed by the passing of each of those beams in the first and second directions through at least the polarization-dependent routing element and the at least one crystal element.

An optical device for processing an input optical signal having a first power spectrum among a plurality of carrier wavelengths, the optical device comprising:

• an input which receives the input optical signal;
• a beam separator positioned to receive the input optical signal from the input and to separate the input optical signal into a first beam traveling along a first optical path and a second beam traveling along a second optical path;
• a reflector positioned to terminate both the first optical path and the second optical path, the reflector operable to reflect the first beam such that it travels along the second optical path and to reflect the second beam such that it travels along the first optical path;
• and
• a plurality of filter elements positioned along both the first optical path and the second optical path, optically between the beam separator and the reflector, such that the first beam travels through the plurality of filter elements along the first path before it is reflected, and again along the second path after it is reflected, such that the second beam travels through the plurality of filter elements along the second path before it is reflected and again along the first path after it is reflected.

An optical device for processing an input optical signal having a first power spectrum among a plurality of carrier wavelengths, the optical device comprising:

• an input which receives the input optical signal
• a beam separator positioned to receive the input optical signal from the input and to separate the input optical signal into a first beam traveling along a first optical path and a second beam traveling along a second optical path;
• a reflector positioned to terminate both the first optical path and the second optical path, the reflector operable to reflect the first beam such that it travels along the second optical path and to reflect the second beam such that it travels along the first optical path;
• a polarizer positioned adjacent to the beam separator along the first and second optical paths;
• a plurality of filter elements positioned along both the first optical path and the second optical path, optically between the polarizer and the reflector, such that the first beam travels through the plurality of filter elements along the first path before it is reflected and again along the second path after it is reflected, such that the second beam travels through the plurality of filter elements along the second path before it is reflected and again along the first path after it is reflected;
• and
• a redirecting element which is operable to receive the first beam when it is traveling along the second optical path after having been reflected and to receive the second beam when it is traveling along the first optical path after having been reflected and to redirect those beams away from their substantially coextensive common paths.