Patent ID: 8643844

Claim:
A laser distance measuring apparatus of the type which splits a laser beam into a measuring beam directed to a measuring reflector and a reference beam, generates interference light through interference between said measuring beam returned by reflection and said reference beam, and a counter to measures a distance of movement relative to said measuring reflector by counting changes in interference fringes formed by said interference light, the apparatus comprising: a first beam splitter which splits said laser beam into a first beam and a second beam; a second beam splitter which splits said second beam into a third beam and a fourth beam, the apparatus being so deployed that reflected beams, produced by reflection of said third and fourth beams and incident from directions reverse to the directions of said third and fourth beams, exit in a reverse direction to the direction of said second beam; a first reference reflector that, when either one of said third and fourth beams is emitted as said measuring beam, is moved by a first mover into a light path of said first beam and reflects said first beam incident thereon into a direction of incidence of said first beam, thereby producing said reference beam; a second reference reflector that, when said first beam is emitted as said measuring beam, is moved by a second mover into a light path of said third beam and reflects said third beam incident thereon into the direction of incidence; a beam switch further comprising a beam selector and a third mover, that, by movement of said beam selector between a first in-beam position and a second out-of-beam position, from among said reflected beams produced by reflection of said third and fourth beams and caused to exit said second beam splitter in the reverse direction to the direction of said second beam, selects one of said reflected beams to be combined in said first beam splitter with a reflected beam produced by reflection of said first beam and incident on said first beam splitter from a reverse direction to the direction of said first beam; and a light detector that generates an electrical signal corresponding to interference fringes formed by the interference light that is generated through interference between said beam selected by said beam switch and said reflected beam produced by reflection of said first beam; wherein said first and second beam splitters comprise respective polarization beam splitters; wherein said laser distance measuring apparatus comprises a first polarization rotator to rotate the direction of polarization of said second beam through 45 degrees, said first polarization rotator being located between said beam splitters; and wherein said beam selector comprises a second polarization rotator so that the direction of polarization of each of said reflected beams caused to exit said second beam splitter in the reverse direction to the direction of said second beam is rotated or not rotated through 90 degrees.