Filter tap for optical communications systems

An optical filter tap for directing an optical signal in a selected band of frequencies from a main trunk to a branch line while blocking optical signals in other than said selected band of frequencies from said branch line, comprising:

• an optical resonant cavity comprising a length of optical fiber having mirrors coupled to opposite ends thereof, said cavity being resonant at said selected band of frequencies, said mirrors having a nonzero transmission characteristic in said selected band of frequencies;
• first means for optically coupling the power in said main trunk to one of said mirrors with minimal perturbation of the power flow in said main trunk;
• and
• second means for optically coupling the power in said selected band of frequencies passing through the other of said mirrors to said branch line.

A fiber optic filter tap comprising;

• a fiber optic resonant cavity comprising a length of optical fiber having dielectric mirrors coupled to opposite ends thereof and resonant at a selected band of frequencies;
• a pair of main trunk optical fibers optically coupled to one mirror of said resonant cavity and positioned to permit evanescent coupling therebetween over a portion of their lengths, one of said trunk optical fibers acting as an input trunk and the other of said trunk optical fibers acting as an output trunk;
• and
• a branch optical fiber optically coupled to the other mirror of said resonant cavity for supplying the selected band of frequencies to a branch circuit.

An optical communication system comprising:

• an optical transmitter;
• at least one optical filter tap;
• a main trunk line carrying optical signals from said transmitter on a plurality of bands of channels and having an input portion directing said signals to said filter tap and an output portion directing said signals away from said filter tap;
• at least one branch line for carrying optical signals from said filter tap to a user;
• said optical filter tap comprising an optical resonant cavity comprising first and second mirrors spaced to permit resonance at a selected one of said bands of channels, said first and second mirrors having a nonzero transmission characteristic for said selected band;
• first means for optically coupling the optical signals from said input portion of the main trunk line to said first mirror and from said first mirror to said output portion with minimal reduction in optical signals in nonselected bands;
• and
• second means for optically coupling the optical signal in said selected band from said second mirror to said branch line.

An optical filter tap comprising;

• an optical resonant cavity comprising first and second mirrors spaced to permit resonance at a selected band of channels, said first and second mirrors having a nonzero transmission characteristic for said selected band;
• first coupling means for optically coupling the optical signals from an input portion of a main trunk line carrying optical signals on a plurality of bands of channels to said first mirror at an end face of said resonant cavity and from said first mirror to an output portion of said main trunk line with minimal reduction in optical signals in nonselected bands;
• and
• second coupling means for optically coupling the optical signal in said selected band from said second mirror at the other end face of said resonant cavity, to a branch line.