US 12,259,240 B1 · Distance measurement device and method based on secondary mixing of inter-mode self-interference signals of optical frequency combs

Abstract

A distance measurement device and method based on secondary mixing of inter-mode self-interference signals of optical frequency combs are provided, which relate to the field of high precision laser distance measurement technologies. A dual-comb light source emits a dual-comb laser into a detection optical module to obtain the inter-mode self-interference signals carrying the to-be-measured distance information. The detection optical module outputs the inter-mode self-interference signals into a generation, acquisition and calculation module of inter-mode self-interference secondary mixing signals to generate the inter-mode self-interference secondary mixing signals, to thereby achieve signal acquisition and obtain a distance measurement result. In this device, coarse and fine distance measurements at different scales are achieved, measurement range and accuracy can be effectively balanced by combing intermediate transition measurement scales and inter-stage transition method, strong real-time property of measurement is achieved, and the light source has low cost and the scale of the system is small.

A distance measurement method based on secondary mixing of inter-mode self-interference signals of optical frequency combs, comprising:

step 1, starting a dual-comb light source (1), and setting repetition rates fr1 and fr2 of dual combs to make a to-be-measured distance/not exceed a half of a measurement unambiguous range LNAR, and to make frequencies of secondary mixing coarse measurement signals respectively generated at a coarse measurement signal generating mixer (16) at a reference end of an interferometer and a coarse measurement signal generating mixer (20) at a measurement end of the interferometer lower than a half of an acquisition frequency of a data acquisition card (21);
and
starting a local oscillator (18) to emit a local oscillator signal with a frequency of fLo, and setting the frequency fLo to make frequencies of mixing fine measurement signals respectively generated at a fine measurement signal generating mixer (17) at the reference end and a fine measurement signal generating mixer (19) at the measurement end lower than the half of the acquisition frequency of the data acquisition card (21);
step 2, placing a target reflector (10) at a zero position;
acquiring and calculating, by using the data acquisition card (21) and an upper computer (22), the mixing fine measurement signals respectively generated at the fine measurement signal generating mixer (17) at the reference end and the fine measurement signal generating mixer (19) at the measurement end to obtain a first fine phase difference φfine0 between the measurement end and the reference end;
and acquiring and calculating, by using the data acquisition card (21) and the upper computer (22), the secondary mixing coarse measurement signals respectively generated at the coarse measurement signal generating mixer (16) at the reference end and the coarse measurement signal generating mixer (20) at the measurement end to obtain a first coarse phase difference φcoarse0 between the measurement end and the reference end;
step 3, moving the target reflector (10) to a position of the to-be-measured distance L;
acquiring and calculating, by using the data acquisition card (21) and the upper computer (22), the mixing fine measurement signals respectively generated at the fine measurement signal generating mixer (17) at the reference end and the fine measurement signal generating mixer (19) at the measurement end to obtain a second fine phase difference φfine between the measurement end and the reference end;
and acquiring and calculating, by using the data acquisition card (21) and the upper computer (22), the secondary mixing coarse measurement signals respectively generated at the coarse measurement signal generating mixer (16) at the reference end and the coarse measurement signal generating mixer (20) at the measurement end to obtain a second coarse phase difference φcoarse between the measurement end and the reference end;
step 4, calculating a fine measurement distance Lfine and a coarse measurement distance Lcoarse, wherein calculation formulas of the fine measurement distance Lfine and the coarse measurement distance Lcoarse are expressed as follows:
L
fine
=
φ
f
⁢
i
⁢
n
⁢
e
-
φ
fine
⁢
0
2
⁢
π
·
c
2
⁢
n
1
⁢
N
⁢
f
r
⁢
1
;
L
c
⁢
o
⁢
a
⁢
r
⁢
s
⁢
e
=
φ
c
⁢
o
⁢
a
⁢
r
⁢
s
⁢
e
-
φ
c
⁢
o
⁢
a
⁢
r
⁢
s
⁢
e
⁢
0
2
⁢
π
·
c
2
⁢
❘
"\[LeftBracketingBar]"
n
1
⁢
N
⁢
f
r
⁢
1
-
n
2
⁢
M
⁢
f
r
⁢
2
❘
"\[RightBracketingBar]"
;
wherein N represents an order number of a Nth order repetition rate component of inter-mode self-interference signals of the first optical frequency comb, M represents an order number of a Mth order repetition rate component of inter-mode self-interference signals of the second optical frequency comb, c represents a speed of light in vacuum, n1 represents a group refractive index of the first optical frequency comb, and n2 represents a group refractive index of the second optical frequency comb;
step 5, calculating the to-be-measured distance L, wherein a calculation formula of the to-be-measured distance L is expressed as follows:
L
=
L
fine
+
c
2
⁢
n
1
⁢
N
⁢
f
r
⁢
1
·
floor
[
2
⁢
n
1
⁢
N
⁢
f
r
⁢
1
(
L
c
⁢
o
⁢
a
⁢
r
⁢
s
⁢
e
-
L
f
⁢
i
⁢
n
⁢
e
)
c
+
1
2
]
;
wherein floor[ ] represents rounding down, and a prerequisite for establishment of the calculation formula of the to-be-measured distance L satisfies an inter-stage transition condition;
step 6, determining, by using the inter-stage transition condition, whether the calculation formula of the to-be-measured distance L is established;
wherein a formula of the inter-stage transition condition is expressed as follows:
U
⁡
(
L
c
⁢
o
⁢
a
⁢
r
⁢
s
⁢
e
)
<
λ
f
⁢
i
⁢
n
⁢
e
4
=
c
4
⁢
n
1
⁢
N
⁢
f
r
⁢
1
;
wherein U(Lcoarse) represents a coarse measurement uncertainty, and λfine represents a fine measurement scale;
selecting, in response to the secondary mixing coarse measurement signals and Nth order inter-mode self-interference fine measurement signals of a first optical frequency comb not satisfying the inter-stage transition condition, a Pth order inter-mode self-interference signal of the first optical frequency comb and a Qth order inter-mode self-interference signal of the second optical frequency comb, and taking an inter-mode self-interference secondary mixing signal with a frequency of |Pfr1−Qfr2| as an intermediate transition measurement scale to satisfy an inter-stage transition condition of a coarse measurement scale and the intermediate transition measurement scale;
wherein a formula of the inter-stage transition condition of the coarse measurement scale and the intermediate transition measurement scale is expressed as follows:
U
⁡
(
L
c
⁢
o
⁢
a
⁢
r
⁢
s
⁢
e
)
<
λ
middle
4
=
c
4
⁢
n
⁢
❘
"\[LeftBracketingBar]"
Pf
r
⁢
1
-
Q
⁢
f
r
⁢
2
❘
"\[RightBracketingBar]"
=
c
·
❘
"\[LeftBracketingBar]"
Nf
r
⁢
1
-
M
⁢
f
r
⁢
2
❘
"\[RightBracketingBar]"
4
⁢
❘
"\[LeftBracketingBar]"
n
1
⁢
N
⁢
f
r
⁢
1
-
n
2
⁢
M
⁢
f
r
⁢
2
❘
"\[RightBracketingBar]"
·
❘
"\[LeftBracketingBar]"
Pf
r
⁢
1
-
Q
⁢
f
r
⁢
2
❘
"\[RightBracketingBar]"
;
wherein λmiddle represents a wavelength of the inter-mode self-interference secondary mixing signal with the frequency of |Pfr1−Qfr2|, and n represents an equivalent refractive index of the inter-mode self-interference secondary mixing signals;
performing step 2 to step 5 to measure a phase difference φmiddle0 between the measurement end and the reference end of the inter-mode self-interference secondary mixing signal with the frequency of |Pfr1−Qfr2| at the zero position and a phase difference φmiddle between the measurement end and the reference end of the inter-mode self-interference secondary mixing signal with the frequency of |Pfr1−Qfr2| at the position of the to-be-measured distance L, and calculating a distance measurement result of the intermediate transition measurement scale by using a formula expressed as follows:
L
middle
=
φ
middle
-
φ
middle
⁢
0
2
⁢
π
.
c
·
❘
"\[LeftBracketingBar]"
Nf
r
⁢
1
-
M
⁢
f
r
⁢
2
❘
"\[RightBracketingBar]"
2
⁢
❘
"\[LeftBracketingBar]"
n
1
⁢
N
⁢
f
r
⁢
1
-
n
2
⁢
M
⁢
f
r
⁢
2
❘
"\[RightBracketingBar]"
·
❘
"\[LeftBracketingBar]"
Pf
r
⁢
1
-
Q
⁢
f
r
⁢
2
❘
"\[RightBracketingBar]"
;
making the intermediate transition measurement scale satisfy an inter-stage transition condition of the intermediate transition measurement scale and a fine measurement scale, wherein a formula of the inter-stage transition condition of the intermediate transition measurement scale and the fine measurement scale is expressed as follows:
U
⁡
(
L
middle
)
<
λ
fine
4
=
c
4
⁢
n
1
⁢
N
⁢
f
r
⁢
1
;
taking, by selecting the Pth order inter-mode self-interference signal of the first optical frequency comb and the Qth order inter-mode self-interference signal of the second optical frequency comb, the inter-mode self-interference secondary mixing signal with the frequency of |Pfr1−Qfr2| as the intermediate transition measurement scale to satisfy the inter-stage transition condition of the coarse measurement scale and the intermediate transition measurement scale and the inter-stage transition condition of the intermediate transition measurement scale and the fine measurement scale, to thereby achieve accuracy transmission among the coarse measurement scale, the intermediate transition measurement scale and the fine measurement scale;
and
step 7, calculating, by using an inter-mode self-interference secondary mixing signal with a frequency of f2nd as a coarse measurement scale, a corresponding coarse measurement distance Lcoarse0, and calculating, by using the inter-mode self-interference secondary mixing signal with the frequency of |Pfr1−Qfr2| as the intermediate transition measurement scale, a corresponding intermediate distance Lmiddle after the intermediate transition measurement scale satisfies the inter-stage transition condition of the coarse measurement scale and the intermediate transition measurement scale and the inter-stage transition condition of the intermediate transition measurement scale and the fine measurement scale;
and substituting the coarse measurement distance Lcoarse0 and the intermediate distance Lmiddle into the formula of step 5 to obtain a transition distance, and recording the transition distance as Lcoarse-new;
wherein a formula for calculating the transition distance Lcoarse-new is expressed as follows:
L
coarse
-
new
=
L
middle
+
c
2
⁢
n
⁢
❘
"\[LeftBracketingBar]"
Pf
r
⁢
1
-
Q
⁢
f
r
⁢
2
❘
"\[RightBracketingBar]"
·
floor
[
2
⁢
n
⁢
❘
"\[LeftBracketingBar]"
Pf
r
⁢
1
-
Q
⁢
f
r
⁢
2
❘
"\[RightBracketingBar]"
⁢
(
L
coarse
⁢
0
-
L
middle
)
c
+
1
2
]
;
wherein f2nd represents a frequency difference of the inter-mode self-interference secondary mixing signals of the optical frequency combs;
calculating, by using an inter-mode self-interference signal with a frequency of Nfr1 as a fine measurement scale, the fine measurement distance Lfine;
and substituting the transition distance Lcoarse-new and the fine measurement distance Lfine into the formula of step 5 to obtain the to-be-measured distance L;
wherein a formula of the to-be-measured distance L is expressed as follows:
L
=
L
fine
+
c
2
⁢
n
1
⁢
N
⁢
f
r
⁢
1
·
floor
[
2
⁢
n
1
⁢
N
⁢
f
r
⁢
1
(
L
coarse
-
new
-
L
fine
)
c
+
1
2
]
.

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Distance measurement device and method based on secondary mixing of inter-mode self-interference signals of optical frequency combs

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Distance measurement device and method based on secondary mixing of inter-mode self-interference signals of optical frequency combs

Life of this patent

Abstract

Claims7