Patent ID: 7295290

Claim:
A coherent laser radar device, comprising: a laser source that oscillates a laser beam which is linearly polarized; a first optical coupler that is formed of a polarization maintained type optical element that branches the laser beam from the laser source into two lights, a local light and a transmitted light; an optical modulator that is formed of a polarization maintained type optical element that modulates the transmitted light that is branched by the first optical coupler; a polarization controller that adjusts the polarization of the transmitted light that is outputted from the optical modulator such that a polarization monitor output becomes minimum; an optical fiber amplifier that amplifies the transmitted light which is outputted from the polarization controller; a polarization splitting coupler that splits the transmitted light which is amplified by the optical fiber amplifier to two linearly polarized components which are orthogonal to each other; a space type optical amplifier that amplifies the transmitted light which is outputted from the optical modulator over space propagation; a transmitting/receiving optical system that applies the transmitted light which is amplified by the space type optical amplifier toward a target and receives a scattered light from the target; a transmitting/receiving light splitting device that splits the transmitted light that is amplified by the space type optical amplifier and the received light that is scattered by the target; a second optical coupler that is formed of a polarization maintained type optical element that mixes the local light that is branched by the first optical coupler and the received light that is split by the transmitting/receiving light splitting device together; a photodetector that detects heterodyne of a mixed light from the second optical coupler to output a beat signal of the received light; a beat signal amplifier that amplifies the beat signal which is outputted from the photodetector; a signal processing device that processes a signal that is amplified by the beat signal amplifier; and a display device that displays a result processed by the signal processing device, characterized in that an optical path that extends from the laser source to the space type optical amplifier through the first optical coupler, an optical path that extends from the transmitting/receiving light splitting device to the photodetector through the second optical coupler, and an optical path that extends from the first optical coupler to the second optical coupler are connected by polarization maintained type single mode optical fibers.