Angular adjustable variable beamsplitter

An optical beam splitter comprising:

• an input port for launching an input optical signal at a first wavelength along an input path;
• a frame rotatable about a rotation axis perpendicular to the input path;
• a first arm extending from the frame;
• an etalon mounted on the first arm disposed in the input path at a first variable acute angle of incidence, whereby the input optical signal is split into a transmitted sub-beam, comprising a first portion of the input beam, passing through the etalon, and a reflected sub-beam, comprising a second portion of the input beam, reflected at a first variable angle of reflection from the etalon;
• a second arm extending from the frame;
• a mirror positioned on the second arm for receiving the reflected sub-beam at a second variable acute angle of incidence for reflecting the reflected beam at a second variable acute angle of reflection along an output path;
• a first output port for receiving the transmitted sub-beam;
• and
• a second port for receiving the reflected sub-beam;
• wherein rotation of the frame about the rotation axis changes the first variable acute angle of incidence, thereby enabling the first portion of the input beam to be adjusted to between 0% and 90% of the input beam, and the second portion of the input beam to be adjusted to between 10% and 100% of the input beam.