Single aperture multiple optical waveguide transceiver
A single-aperture, multi-axial transceiver is provided that is particularly useful in a LIDAR system for detecting low velocities at increased ranges. The system is particularly useful in systems that are required to measure very low velocities and very short distances as well as to provide an operating range of hundreds of meters. The transceiver uses closely spaced waveguides placed near the focal point of a single objective 8 to form input and detector apertures. Preferably the input and detector apertures are spaced from each other by less than about 80 μm. In an embodiment using light with a wavelength of 1550 nm, the spacing is preferably about 30 μm.
1. A transceiver comprising:
an objective;
a light source element configured to form a source aperture placed near a focal point of said objective such that said objective generates an illumination beam therefrom, the illumination beam being directed to reflect from a target;
a detector element placed near said light source element and configured to form a detector aperture to receive light reflected from the target; and
wherein said source aperture and said detector aperture comprise two separate, closely spaced single-mode optical waveguides, and
wherein said source aperture and said detector aperture are spaced from each other by a distance between about ten to sixty times a wavelength of said light.
2. The transceiver according to claim 1 , wherein said distance is about 80 μm.
3. The transceiver according to claim 1 , wherein:
said light source element comprises said source single-mode optical waveguide, which comprises an optical fiber coupled to a laser; and
said detector comprises said detector single-mode optical waveguide, which comprises an optical fiber coupled to a detecting element.
4. The transceiver according to claim 3 , wherein:
an end of said single-mode fiber waveguide forming said source aperture is held in a groove in a first plate;
an end of said single-mode fiber waveguide forming said detector aperture is held in a groove in a second plate; and
the ends have diameters of less than said distance.
5. The transceiver according to claim 3 , wherein ends of said single-mode optical fiber waveguides forming said source aperture and said detector aperture, respectively, are formed by a tapered fiber bundle.
6. The transceiver according to claim 1 , wherein the single-mode optical waveguides forming said source aperture and said detector aperture, respectively, are planar waveguides.
7. The transceiver according to claim 1 , further comprising:
a measuring device configured to determine a velocity of the target by comparing light from the source aperture with that received by the detector aperture.
8. The transceiver according to claim 7 , wherein:
said short distances are those distances R, obeying a relation 0<R≦R max ,
a maximum distance is given by R max =(Df)/(2d)+f,
D is a diameter of a source beam at the target, d is the distance between a transmitter and receiver waveguide, and f is a focal length of the objective,
the focal length of the objective being f=150 mm;
the distance is d=30 μm; and
the diameter of the illumination beam is D=50 mm;
whereby velocities are measured within distances less than R max =125 meters.