Patent ID: 7139446

Claim:
A dual chirp laser apparatus for precision distance measurement comprising: a) a first coherent light beam linearly polarized in a first direction and passing through a first optical path; b) a second coherent light beam linearly polarized in a second direction, the second direction being orthogonal to the first direction and passing through a second optical path; c) a linear polarization maintaining fiber having a first transmission axis and a second transmission axis, said first transmission axis being capable of transmitting light polarized in said first direction and said second transmission axis being capable of transmitting light polarized in said second direction, said linear polarization fiber having a proximal end and a distal end; d) a polarization splitter capable of diplexing said first coherent light beam and said second coherent light beam and conducting said coherent light beams into the proximal end of said linear polarization maintaining fiber; e) an interface at the distal end of the linear polarization maintaining fiber capable of reflecting a fraction of said first coherent light beam into said first axis and of reflecting a fraction of said second coherent light beam into said second axis and further capable of transmitting both coherent light beams to a target and further capable of receiving reflected portions of both coherent light beams and transmitting them respectively into said first transmission axis and said second transmission axis, whereby a first interference signal is established in a first optical path comprising said first axis and a second interference signal is established in a second optical path comprising said second axis; f) a first detector capable of detecting said first interference signal and producing a first beat frequency output and a second detector capable of detecting said second interference signal and producing a second beat frequency output; g) digital signal processing apparatus capable of producing a first measured frequency from the first beat frequency output and capable of producing a second measured frequency from the second beat frequency output; and h) computing apparatus capable of computing a first relative distance measurement from the first measured frequency and a second relative distance measurement from the second measured frequency and further capable of combining said first relative distance measurement and said second relative distance measurement to produce a composite relative distance measurement, whereby uncertainty in the composite relative distance measurement is substantially reduced.