Absolute distance meter that uses a fiber-optic switch to reduce drift

A dimensional measurement device configured to send a first beam of light to a remote target, the target having a position in space, the target returning a reflected portion of the first beam as a second beam, the measurement device comprising:

• a first light source configured to emit a first light;
• a fiber coupler assembly including a coupler input port, a coupler output port, a coupler measure port, and a coupler reference port, the fiber coupler assembly configured to receive a first portion of the first light through the coupler input port, to send a second portion of the first portion out of the coupler output port, and to send a third portion of the first portion out of the coupler reference port;
• a fiber-optic switch including a switch input port, a switch measure port, and a switch reference port, the fiber-optic switch configured to receive the second portion through the switch input port, to receive a first electrical signal in a first state or a second state, and to send the second portion out of the switch measure port if the first electrical signal is in the first state or to send the second portion out of the switch reference port if the first electrical signal is in the second state;
• an optical system configured to receive the second portion from the switch measure port and to send the second portion out of the dimensional measurement device as the first beam, the optical system further configured to receive the second beam as a fourth portion, to send the fourth portion into the switch measure port, the fiber-optic switch configured to receive the fourth portion and to send the fourth portion into the coupler output port, the fiber coupler assembly configured to send a fifth portion of the fourth portion out of the coupler measure port;
• a reference retroreflector configured to receive the second portion from the switch reference port and to return it to the coupler output port as a sixth portion, the fiber coupler assembly configured to send a seventh portion of the sixth portion to the coupler measure port;
• a first electrical circuit configured to provide the first electrical signal in the first state or the second state, to convert the third portion into a first reference value, to convert the fifth portion into a first measure value if the first electrical signal is in the first state, and to convert the seventh portion into a second reference value if the first electrical signal is in the second state;
• and
• a processor configured to determine a first distance from the dimensional measurement device to the target, the first distance based at least in part on the first measure value, the first reference value, and the second reference value.