Method and apparatus for mapping and ranging based on coherent-time comparison
Provided is a system for range detection including at least one beam source arrangement configured to provide illumination of certain coherence length, an optical arrangement, and a detection arrangement including at least one detector unit.
1 . A system for measuring a distance to a target object comprising at least one light source configured to provide an illumination beam of a selected wavelength range and a defined coherence length, an optical arrangement, and a detection arrangement comprising at least one detector unit,
said optical arrangement comprises optical elements forming at least first and second interferometers, each of said first and second interferometers is formed of a reference path and an interrogating path, said interrogating path comprises optical arrangement adapted to direct interrogating beam portions of said illumination beam toward a target object and collect return beam portions reflected from said target object, wherein the interrogating beam portions of the interrogating paths of the first and second interferometers spatially overlap at least at a point of impinging on the target object such that the first and second detected signals correspond to interference signals formed using light reflected from a common location on the target object; said reference path and interrogating path generate an interference signal on at least one detector of the detection arrangement, thereby generating detection data comprising at least first and second detected signals indicative of interference signal of said first and second interferometers;
wherein said first and second interferometers are configured with respective first and second different coherence factors being associated with at least one of optical path of reference paths of the first and second interferometers, and coherence length of light passing in said first and second interferometers;
wherein said at least one light source comprises at least one laser unit configured to emit the illumination beam having the defined coherence length and a fixed instantaneous frequency, wherein the illumination beam being provided as a continuous-wave (CW) or a pulsed beam;
and wherein the system is configured to determine a coherence ratio term being a ratio between said at least first and second detected signals and uses said coherence ratio term to determine a distance to said target object.
2 . The system of claim 1 , wherein interrogating paths of said least first and second interferometers being at least partially overlapping.
3 . The system of claim 2 , wherein said at least partially overlapping portion of said interrogating paths further comprises a circulator configured to receive the interrogating signal in a first port thereof and direct it towards the target object via a second port thereof and receive the at least one return signal via said second port and direct it towards the detection arrangement via a third port thereof.
4 . The system of claim 1 , further comprising a controller-comprising one or more processors and memories configured for receiving and processing said detection data and to determine said coherence ration term, and to utilizes said coherence ratio term and determined a distance of said target.
5 . The system of claim 1 , wherein said optical arrangement comprises optical fibers or waveguides.
6 . The system of claim 1 , wherein said detection arrangement comprises at least two detector arrays, said interrogating paths is configured for illuminating a field of view and for collecting light reflected from said field of view to form image data on detection plane of said detection unit, thereby enabling detection of distance map of said field of view.
7 . The system of claim 1 , wherein said detection arrangement is configured to provide balanced detection of said interference signal, said at least one detector unit comprises respective one or more additional detector units, thereby enhancing signal to noise ratio and filtering out at least one of background noise and distance independent components from the measurement data.
8 . The system of claim 1 , wherein said light source comprises at least one broadband light source.
9 . The system of claim 1 , wherein said light source is adapted to emit light of at least first and second wavelength ranges to propagate in corresponding said at least first and second interferometers.
10 . The system of claim 9 , wherein said light source is adapted for sequentially emit light of said first and second wavelength ranges, and wherein said first and second wavelength ranges are associated with corresponding first and second different linewidths, thereby affecting coherence length of light of said first and second wavelength ranges.
11 . The system of claim 1 , wherein said at least first and second interferometers are overlapping along interrogating path and at least a portion of reference paths.
12 . The system of claim 11 , wherein said at least portion of overlapping reference path overlapping between said at least first and second interferometers, comprise one or more wavelength selective delay lines thereby differentiating optical path of light portions of at least first and second wavelength ranges.
13 . The system of claim 12 , wherein said at least portion of overlapping reference path comprises one or more fiber Bragg grating array (FBGA) elements configured to reflect selected one or more wavelength ranges, thereby varying optical path of said one or more wavelength selective delay lines.
14 . The system of claim 1 , formed within a photonic integrated circuit.
15 . The system of claim 1 , wherein the illumination beam has a Gaussian spectrum, and wherein the coherence ratio term is determined by
Γ
=
Δ
Coh
(
I
long
)
Coh
(
I
short
)
=
χ
eff
·
e
-
Δ
k
2
8
(
Δ
x
-
L
)
2
e
-
Δ
k
2
8
(
Δ
x
)
2
=
χ
eff
·
e
Δ
k
2
L
4
[
Δ
x
-
L
2
]
where χ eff represents the constants parameters of the coherence terms, L is the half of the OPD between the long and short reference arms, Δk is the bandwidth of the illumination beam, and Δx=x−x 0 is the distance between the system and the target object.
16 . A method for determining distance to a target, the method comprising:
Generating, by at least one light source, at least one electromagnetic beam having a defined coherence length and a selected fixed instantaneous wavelength, wherein the electromagnetic beam being emitted as a continuous-wave (CW) or as a pulsed beam;
directing a first reference portion of the beam along a first reference path having first length;
directing a second reference portion of the beam along a second reference path having a second length different than the first length; and
directing a third portion of the beam toward the target;
collecting reflection of said third portion from a common location on the target;
combining a first portion of collected reflected radiation from said location with said first reference portion to form a first interfered combined signal and a second portion of the collected radiation from said location with said second reference portion to form a second interfered combined signal and detecting intensity of said first and second interfered combined signals to generate corresponding first and second detected signals; and
processing said first and second detected signals and determining a coherence ratio term and using said coherence ratio term data on distance of said location on the target.