Laser doppler velocimeter
A laser Doppler velocimeter is formed using a fiber laser as the lasing medium. Within the velocimeter, all optical signals, transmitted and received, are conveyed by optical fibers. An amplifier amplifies a source laser, which is then transmitted to one or more transceivers. The one or more transceivers, each projecting along a different axis, and each with a single optical fiber input/output interface act as both the transmission device to focus the radiation at a target region, and as the receiving system for collecting reflected radiation. The transceivers each include an amplifier to further amplify the radiation received from the laser source. The one or more transceivers transmit radiation simultaneously to the target region, and may be located remotely from the laser source. The portion of the reflected radiation collected by the receiving system is analyzed to determine the Doppler shift caused by targets at the focal point of the one or more transceivers.
1. A velocimeter comprising:
a coherent source configured to produce a coherent beam;
a modulation system configured to add a frequency shift to the coherent beam to produce a modulated beam;
an optical amplifier configured to amplify the modulated beam;
a transceiver configured to receive the amplified beam via a first optical fiber, the transceiver including an amplifier configured to further amplify the amplified beam, and the transceiver configured to transmit the further amplified light to a target region and to receive reflected light from the target region;
wherein the modulation system is located between the coherent source and the transceiver, and
a receiver coupled to the transceiver via a second optical fiber and coupled to the coherent source via a third optical fiber, the receiver configured to:
receive the reflected light from the transceiver,
receive a reference light from the coherent source, and
determine a Doppler shift based on the reflected and reference light.
2. The velocimeter of claim 1 , wherein the modulation system is further configured to perform modulations of the beam from the coherent source.
3. The velocimeter of claim 1 , further comprising:
a splitter configured to split the modulated beam from the optical amplifier into n amplified beams, n being a positive integer; and
n transceivers and n first optical fibers,
wherein the n transceivers are configured to receive respective ones of the n amplified beams via the n first optical fibers, to further amplify the n amplified beams, and to transmit and receive the n further amplified beams to the target area.
4. The velocimeter of claim 1 , wherein at least one of the optical amplifier and the amplifier is comprised of a rare earth doped fiber.
5. The velocimeter of claim 1 , wherein the receiver comprises a signal processor configured to perform the determining of the Doppler shift.
6. The velocimeter of claim 1 , wherein the receiver is further configured to determine a velocity of one or more objects in the target region based on the determined Doppler shift.
7. The velocimeter of claim 6 , wherein the receiver is further configured to adjust the determined velocity by accounting for movement of the transceiver.
8. The velocimeter of claim 7 , wherein the receiver further comprises an altitude heading reference system, an inertial measurement unit, a global positioning system, or a ground speed detection device configured to determine the movement.
9. The velocimeter of claim 1 , wherein the transceiver further comprises a switch configured to allow transmission of the further amplified light through a lens in a transmission position and to allow reception of the reflected light through the lens in a receipt position.
10. The velocimeter of claim 1 , wherein at least one of the velocimeter and transceiver is arranged as a handheld device.
11. The velocimeter of claim 1 , wherein the coherent source is configured to operate based on a received operational status of the transceiver.
12. The velocimeter of claim 3 , wherein the n transceivers are configured to substantially simultaneously transmit respective ones of the n further amplified beams to different ranges from the transceiver.
13. A method of determining a velocity of scatterers in a target region, comprising:
generating a coherent beam:
adding a frequency shift to the coherent beam with a modulation system;
amplifying the modulated beam with at least first and second amplifiers;
transmitting the amplified beam from a transceiver towards the target region;
receiving reflected radiation from the target region at the transceiver;
combining the received reflected radiation with a reference radiation beam; and
determining the velocity of the scatterers in the target region based on the combined received and reference beams.
14. The method of claim 13 , further comprising generating the coherent beam using an erbium clad fiber.
15. The method of claim 13 , further comprising conveying the coherent beam using optical fibers between at least one of the frequency shift, the amplification, and the receiving.
16. The method of claim 13 , wherein the amplifying further comprises using a rare earth doped fiber for at least one of the first and second amplifiers.
17. The method of claim 13 , wherein the determining further comprises compensating for any motion of the transceiver.
18. The method of claim 13 , further comprising generating the coherent beam based on receiving information regarding an operational status of the transceiver.
19. The method of claim 13 , further comprising:
splitting the coherent beam between the at least first and second amplifiers, such that a plurality of transmitters are utilized to transmit the amplified beam to a plurality of target regions and to receive the reflected radiation from the plurality of the target regions.
20. The method of claim 19 , wherein the amplified beams are substantially simultaneously transmitted from the plurality of the transceivers towards the plurality of the target regions at different ranges.