Optical wavelength meter

An optical wavelength meter for measuring an optical wavelength of an optical beam comprising:

• a) coarse optical filter means and first optical power measurement means for measuring output of the coarse optical filter means and second optical power measurement means for measuring an unfiltered reference beam for coarse wavelength measurement;
• b) fine optical filter means comprising first and second periodic optical filters in quadrature having a finesse of substantially 2 and free spectral range of substantially 100 GHz, such that peaks and troughs of the first filter coincide with substantially linear ranges between peaks and troughs of the second filter, and third and fourth optical power measurement means for measuring output of the first and second periodic optical filters in quadrature for fine wavelength measurement, respectively;
• c) beam splitting means for splitting the optical beam between the unfiltered reference beam and the coarse and fine optical filter means;
• d) synchronized clock signal measurement means for synchronized measurement of the output of the first, second, third and fourth optical power measurement means;
• and
• e) processing means for determining the optical wavelength of the optical beam from a predetermined transmissivity-wavelength relationship of the coarse filter and the first and second optical power measurement means for coarse wavelength measurement and from predetermined transmissivity-wavelength relationships of the first and second periodic optical filters and at least one of the third and fourth optical power measurement means for fine wavelength measurement.

A method of determining wavelength of an optical beam comprising:

• a) splitting the optical beam into first, second, third and fourth sub-beams;
• b) presenting the first sub-beam to reference first photodetector means;
• c) presenting the second sub-beam to coarse filter means having an output to second photodetector means;
• d) presenting the third sub-beam to a first fine periodic filter having an output to third photodetector means;
• e) presenting the fourth sub-beam to a second fine periodic filter having an output to fourth photodetector means, wherein the first fine periodic filter and the second fine periodic filter are in quadrature and have a finesse of substantially 2 and free spectral range of substantially 100 GHz, such that peaks and troughs of the first fine periodic filter coincide with substantially linear ranges between peaks and troughs of the second fine periodic filter;
• f) using synchronized clock signal measurement means to read outputs from the first, second, third and fourth photodetector means;
• g) identifying from predetermined transmissivity-wavelength characteristics of the coarse filter means and the first and second photodetector means outputs a limited range of wavelength in which the wavelength of the optical beam lies, to determine from their predetermined transmissivity-wavelength sensitivities which of the first fine filter and the second fine filter has a greater sensitivity to wavelength in that limited range;
• and
• h) using predetermined transmissivity-wavelength characteristics of the first or second fine filter having the greater sensitivity in the limited range of wavelength and the corresponding third or fourth photodetector means output, corresponding to the fine filter means having the greater sensitivity, to determine the wavelength of the optical beam.

A computer program comprising code means for performing all the steps of:

• a) splitting the optical beam into first, second, third and fourth sub-beams;
• b) presenting the first sub-beam to reference first photodetector means;
• c) presenting the second sub-beam to coarse filter means having an output to second photodetector means;
• d) presenting the third sub-beam to a first fine periodic filter having an output to third photodetector means;
• e) presenting the fourth sub-beam to a second fine periodic filter having an output to fourth photodetector means, wherein the first fine periodic filter and the second fine periodic filter are in quadrature and have a finesse of substantially 2 and free spectral range of substantially 100 GHz, such that peaks and troughs of the first fine periodic filter coincide with substantially linear ranges between peaks and troughs of the second fine periodic filter;
• f) using synchronized clock signal measurement means to read outputs from the first, second, third and fourth photodetector means;
• g) identifying from predetermined transmissivity-wavelength characteristics of the coarse filter means and the first and second photodetector means outputs a limited range of wavelength in which the wavelength of the optical beam lies, to determine from their predetermined transmissivity-wavelength sensitivities which of the first fine filter and the second fine filter has a greater sensitivity to wavelength in that limited range;
• and
• h) using predetermined transmissivity-wavelength characteristics of the first or second fine filter having the greater sensitivity in the limited range of wavelength and the corresponding third or fourth photodetector means output, corresponding to the fine filter means having the greater sensitivity, to determine the wavelength of the optical beam.
• when the program is run on one or more computers.