Method and apparatus for calibrating a polarization independent optical coherence domain reflectometer

Claim 1

A method for calibrating an optical system using an optical source for generating a light beam, the optical source being coupled to an input channel of an interferometer, the interferometer comprising means coupled to the input channel for splitting the light beam and coupling the split light beam into a reference beam path and a test beam path of the interferometer and means for combining light reflected back through the reference beam path and the test beam path and coupling the combined light into an output channel of the interferometer, the optical system comprising a polarization diversity receiver coupled to the output channel for receiving the combined light, the polarization diversity receiver having two channels, comprising the steps of: providing means for modulating the intensity of the light beam generated by the optical source; intensity modulating the light beam generated by the optical source; detecting any imbalance in the gains of the two channels of the polarization diversity receiver while the light beam generated by the optical source is being intensity-modulated; and storing data related to the imbalance in the gains of the two channels of the polarization diversity receiver as calibration factors to correct for any drift in electronic gains.

Claim 2

A method for calibrating an optical system using an optical source for generating a light beam, the optical source being coupled to an input channel of an interferometer, the interferometer comprising means coupled to the input channel for splitting the light beam and coupling the split light beam into a reference beam path and a test beam path of the interferometer and means for combining light reflected back through the reference beam path and the test beam path and coupling the combined light into an output channel of the interferometer, the optical system comprising a polarization diversity receiver coupled to the output channel for receiving the combined light, the polarization diversity receiver having two channels, comprising the steps of: providing means for modulating the intensity of the light beam generated by the optical source; intensity modulating the light beam generated by the optical source; detecting any imbalance in the gains of the two channels of the polarization diversity receiver while the light beam generated by the optical source is being intensity-modulated; and storing data related to the imbalance in the gains of the two channels of the polarization diversity receiver as calibration factors to correct for any drift in electronic gains.

Claim 4

A method for calibrating an optical system using an optical source for generating a light beam, the optical source being coupled to an input channel of an interferometer, the interferometer comprising means coupled to the input channel for splitting the light beam and coupling the split light beam into a reference beam path and a test beam path of the interferometer, a scanning reference mirror incorporated into the reference beam path for reflecting the split light beam in the reference beam path, and means for combining light reflected back through the reference beam path and the test beam path and coupling the combined light into an output channel of the interferometer, the optical system comprising a polarization diversity receiver coupled to the output channel for receiving the combined light, the polarization diversity receiver having first and second channels, comprising the steps of: providing means for modulating the intensity of the light beam generated by the optical source; providing means for controlling the polarization state of light received by the polarization diversity receiver; assuring that a device under test is not connected to the test beam path; terminating the test beam path with one of an optical absorber and a non-reflecting optical device; intensity modulating the light beam generated by the optical source; operating the polarization state controlling means to direct all of the modulated source power into the first channel of the polarization diversity receiver; measuring a signal level in the first channel; storing the signal level measured in the first channel as a first calibration parameter; operating the polarization state controlling means to direct all of the modulated source power into the second channel of the polarization diversity receiver; measuring a signal level in the second channel; storing the signal level measured in the second channel as a second calibration parameter; determining a calibration factor from the first and second calibration parameters to correct for any drift in electronic gains; storing the calibration factor; operating the polarization state controlling means so that the modulated source power is split between the first and second channels of the polarization diversity receiver such that signals produced by the first and second channels are approximately balanced; discontinuing the intensity modulation; disconnecting the one of the optical absorber and non-reflecting optical device from the test beam path; terminating the test beam path with an optical means having a known reflection coefficient; reciprocating the scanning reference mirror; measuring a peak signal produced by the first channel, while the earlier setting of the polarization state controlling means, which produced balanced outputs from the first and second channels when the one of the optical absorber and non-reflecting optical device is measured, is maintained; storing the measured peak signal produced by the first channel; measuring a peak signal produced by the second channel, while the earlier setting of the polarization state controlling means, which produced balanced outputs from the first and second channels when the one of the optical absorber and non-reflecting optical device is measured, is maintained; storing the measured peak signal produced by the second channel; combining the calibration factor to correct for any drift in electronic gains and the measured peak signals of the first and second channels to determine a combined calibration factor; and dividing the known reflection coefficient of the optical means having the known reflection coefficient by the combined calibration factor to determine a polarization independent magnitude calibration scaling factor.

Claim 5

A method for calibrating an optical system using an optical source for generating a light beam, the optical source being coupled to an input channel of an interferometer, the interferometer comprising means coupled to the input channel for splitting the light beam and coupling the split light beam into a reference beam path and a test beam path of the interferometer, a scanning reference mirror incorporated into the reference beam path for reflecting the split light beam in the reference beam path, and means for combining light reflected back through the reference beam path and the test beam path and coupling the combined light into an output channel of the interferometer, the optical system comprising a polarization diversity receiver coupled to the output channel for receiving the combined light, the polarization diversity receiver having first and second channels, comprising the steps of: providing means for modulating the intensity of the light beam generated by the optical source; providing means for controlling the polarization state of light received by the polarization diversity receiver; assuring that a device under test is not connected to the test beam path; terminating the test beam path with one of an optical absorber and a non-reflecting optical device; intensity modulating the light beam generated by the optical source; operating the polarization state controlling means to direct all of the modulated source power into the first channel of the polarization diversity receiver; measuring a signal level in the first channel; storing the signal level measured in the first channel as a first calibration parameter; operating the polarization state controlling means to direct all of the modulated source power into the second channel of the polarization diversity receiver; measuring a signal level in the second channel; storing the signal level measured in the second channel as a second calibration parameter; determining a calibration factor from the first and second calibration parameters to correct for any drift in electronic gains; storing the calibration factor; operating the polarization state controlling means so that the modulated source power is split between the first and second channels of the polarization diversity receiver such that signals produced by the first and second channels are approximately balanced; discontinuing the intensity modulation; disconnecting the one of the optical absorber and non-reflecting optical device from the test beam path; terminating the test beam path with an optical means having a known reflection coefficient; reciprocating the scanning reference mirror; measuring a peak signal produced by the first channel, while the earlier setting of the polarization state controlling means, which produced balanced outputs from the first and second channels when the one of the optical absorber and non-reflecting optical device is measured, is maintained; storing the measured peak signal produced by the first channel; measuring a peak signal produced by the second channel, while the earlier setting of the polarization state controlling means, which produced balanced outputs from the first and second channels when the one of the optical absorber and non-reflecting optical device is measured, is maintained; storing the measured peak signal produced by the second channel; combining the calibration factor to correct for any drift in electronic gains and the measured peak signals of the first and second channels to determine a combined calibration factor; and dividing the known reflection coefficient of the optical means having the known reflection coefficient by the combined calibration factor to determine a polarization independent magnitude calibration scaling factor.

Claim 17

A method for calibrating an optical system using an optical source for generating a light beam, the optical source being coupled to an input channel of an interferometer, the interferometer comprising means coupled to the input channel for splitting the light beam and coupling the split light beam into a reference beam path and a test beam path of the interferometer, a scanning reference mirror incorporated into the reference beam path for reflecting the split light beam in the reference beam path, and means for combining light reflected back through the reference beam path and the test beam path and coupling the combined light into an output channel of the interferometer, the optical system comprising a receiver coupled to the output channel for receiving the combined light, the receiver having at least one photodetector, comprising the steps of: providing means for controlling the polarization state of light received by the receiver; assuring that a device under test is not connected to the test beam path; terminating the test beam path with an optical means having a known reflection coefficient; reciprocating the scanning reference mirror; operating the polarization state controlling means, as the scanning reference mirror is reciprocated, to maximize fringe visibility; measuring the maximum peak-to-peak level of the fringe visibility; and storing the maximum peak-to-peak level of the fringe visibility as a calibration scaling factor.

Claim 18

A method for calibrating an optical system using an optical source for generating a light beam, the optical source being coupled to an input channel of an interferometer, the interferometer comprising means coupled to the input channel for splitting the light beam and coupling the split light beam into a reference beam path and a test beam path of the interferometer, a scanning reference mirror incorporated into the reference beam path for reflecting the split light beam in the reference beam path, and means for combining light reflected back through the reference beam path and the test beam path and coupling the combined light into an output channel of the interferometer, the optical system comprising a receiver coupled to the output channel for receiving the combined light, the receiver having at least one photodetector, comprising the steps of: providing means for controlling the polarization state of light received by the receiver; assuring that a device under test is not connected to the test beam path; terminating the test beam path with an optical means having a known reflection coefficient; reciprocating the scanning reference mirror; operating the polarization state controlling means, as the scanning reference mirror is reciprocated, to maximize fringe visibility; measuring the maximum peak-to-peak level of the fringe visibility; and storing the maximum peak-to-peak level of the fringe visibility as a calibration scaling factor.