Optics: measuring and testing – Velocity or velocity/height measuring – With light detector
Reexamination Certificate
2000-05-26
2003-06-17
Black, Thomas G. (Department: 3663)
Optics: measuring and testing
Velocity or velocity/height measuring
With light detector
Reexamination Certificate
active
06580497
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a laser radar apparatus. More specifically, the present invention is directed to a coherent laser radar apparatus capable of measuring physical information such as a distance of a target, a target velocity, a density distribution of a target, and a velocity of a target, while using as a light source a laser oscillated with having a single wavelength, for instance, is directed to such a coherent laser radar apparatus in which transmitted radiation is modulated by a pseudo-random sequence (PN code), while employing a CW laser radiation source oscillated with having a single wavelength. Furthermore, the present invention is related to a compact/highly reliable coherent laser radar apparatus mounted on a mobile object such as an aircraft and a vehicle. Also, the present invention is related to a system constituted by integrating an optical space communication apparatus with a coherent laser radar apparatus.
2. Description of the Related Art
There are various coherent laser radar apparatus using light waves (lasers) and also pulse Doppler radars with employment of microwaves and millimeter-waves, which may function as apparatuses designed to measure various physical information such as distances, velocities, density distributions, velocity distributions as to targets. Among these radar apparatuses, the pulse Doppler radars are capable of measuring targets over wide bands and also over long distances, whereas the coherent laser radar apparatuses are capable of realizing both high spatial resolution and high speed resolution, due to differences in frequencies under use. There is such a definition as to a target. That is, a single target which owns a certain dimension and also a boundary surface functioning as a reflection surface and a scattering surface is referred to as a “hard target”, for instance, an aircraft and a vehicle. Also, in such a case that scattered radiation is synthesized with each other to constitute received radiation and this scattered radiation is derived from a large number of very fine scattering members which are distributed in a certain space, this spatially distributed target is referred to as a “soft target”.
While measuring soft targets such as a wind velocity and a wind velocity distribution, a pulse Doppler radar measures a Doppler shift of an echo of a scattering object mainly including particles of rain droplets, fog, cloud in the atmosphere, and then acquires a wind velocity. As a result, in fine weather where no particles of rain droplets, fog, and cloud are present in the atmosphere, echoes having sufficiently large intensitys cannot be acquired. Therefore, there is such a drawback that the pulse Doppler radars cannot measure clean-air turbulence.
Since a coherent laser radar apparatus with employment of laser radiation may acquire a sufficiently high scattering intensity even from aerosol in the atmosphere, this laser radar apparatus may measure a wind velocity and a wind velocity distribution even in fine weather. As a result, such a coherent laser radar apparatus may be expected as an obstacle sensing apparatus capable of sensing various obstacles including air turbulence, which may be mounted on an aircraft, or in an airport.
As a coherent laser radar apparatus, there are a radar apparatus in which a pulse laser oscillated having a single frequency is employed as a light source, and another radar apparatus in which a CW laser is employed as a light source.
FIG. 29
schematically shows a structural diagram of a coherent laser radar apparatus in which the injection-seeded pulsed laser apparatus is employed a light source, which is disclosed in U.S. Pat. No. No. 5,237,331 issued to Sammy W. Henderson at al.
In
FIG. 29
, reference numeral
1
shows a laser radiation source oscillated having a single frequency, reference numeral
2
indicates a first optical dividing device, reference numeral
3
represents a frequency shifter, reference numeral
4
is an injection-seeded pulsed laser, reference number
5
shows a beam splitter, reference numeral
6
indicates a ¼ wavelength plate, reference numeral
7
denotes a transceiver optics, reference numeral
8
represents a scanning optics, reference numeral
9
indicates a first combining device, and reference numeral
10
shows a first photodetector. Also, reference numeral
11
is a second optical dividing device, reference numeral
12
shows a third optical dividing device, reference numeral
13
is a second combining device, reference numeral
14
is a second photodetector, reference numeral
15
shows an A/D converter, reference numeral
16
represents a signal processing apparatus, reference numeral
17
shows an adjusting mechanism constructed of a piezoelectric transducer of a resonator length of the injection-seeded pulse laser
4
, reference numeral
18
shows a control circuit of the adjusting mechanism, reference numeral
19
shows laser radiation emitted from the laser radiation source
1
, and reference numeral
20
denotes seed light. Also, reference numeral
21
indicates pulse laser radiation, reference numeral
22
is an optical axis of the transmitted/resceived radiation, reference numeral
23
shows transmitted radiation, reference numeral
24
represents received radiation, reference numeral
25
shows local radiation, and furthermore, reference numeral
26
shows mixture light made by combining the received radiation
24
with the local radiation
25
.
Next, operations will now be made.
The laser radiation
19
supplied from the laser radiation source
1
oscillated having a single wavelength “f
0
” is subdivided by the first optical dividing device
2
into two laser radiations. One laser radiation is employed as the local radiation
25
, and the other laser radiation is shifted by the frequency shifter
3
by a frequency “f
IF
” to become such laser radiation whose frequency is increased only by this frequency f
IF
. This frequency-shifted laser radiation is supplied as the seed radiation
20
to the injection-seeded pulsed laser
4
. The injection-seeded pulsed laser
4
oscillates a laser pulse having a single frequency (single wavelength) in an axial mode having such a frequency located at the nearest frequency of the seed radiation
20
.
Since the laser pulse radiation
21
emitted from the injection-seeded laser pulse
4
is linear-polarized, this laser pulse radiation
21
is reflected by the beam splitter
5
. After this reflected laser pulse radiation is converted into the circular-polarized laser radiation by the ¼ wavelength plate
6
, this circular-polarized laser radiation is traveled through both the transceiver optics
7
and the scanning optics
8
, and then is projected toward the target. The scattering radiation originated from the target is received via such an optical path opposite to the above-explained optical path of the transmitted radiation.
The received radiation
24
is traveled via both the scanning optics
8
and the transceiver optics
7
, and then, is processed by the ¼ wavelength plate
6
to become linear-polarized laser radiation which is shifted by 90 degrees with respect to the polarizing plane of the laser pulse radiation
21
. Then, the linear-polarized laser radiation passes through the beam splitter
5
so as to be conducted to the first combining device
9
. In the first combining device
9
, the received radiation
24
is mixed with the local radiation
25
. The combined radiation
26
is coherent-detected in the first photodetector
10
. The signal detected by the first photodetector
10
is sampled by the A/D converter
15
, and the signal processing apparatus
16
extracts the distance of the target from the temporal waveform of the intensity signal, and also extracts the velocity of the target from the Doppler signal.
As previously explained, since the injection-seeded pulse laser
4
oscillates the pulse having the single frequency in the axial mode having such a frequency located at the nearest frequency of the seed li
Asaka Kimio
Hirano Yoshihito
Wadaka Shusou
Birch & Stewart Kolasch & Birch, LLP
Hughes Deandra M.
LandOfFree
Coherent laser radar apparatus and radar/optical... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Coherent laser radar apparatus and radar/optical..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Coherent laser radar apparatus and radar/optical... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3136924