synthetic wavelength interferometry of an optical frequency comb for absolute distance measurement - high accuracy laser distance measurement

We showed a synthesis.
Optical frequency comb for wide continuous measurement range for absolute distance measurement is based on wavelength-based outside interference.
The synthetic wavelength is derived from two wavelengths obtained from two bands-pass filters.
The interference phase of the synthetic wavelength is used as a marker of the pulseto-
The accuracy of traditional peak search method is greatly improved.
By using long fiber to increase the path length difference between the reference arm and the measurement arm, the continuous measurement range is expanded.
According to the interference phase of the CW laser, the length of the long fiber is stable.
The experimental results show that the system can achieve the accuracy of 75 nm in the 350 continuous measurement range.
High-precision distance measurement is critical for a variety of applications, such as industrial sensing of critical dimensions and satellite formations in space missions.
Traditionally, these applications employ single-wavelength interference measurements with stripe counts.
However, the stripe count is prone to loss of absolute position. Multiple-
Absolute distance measurement can be achieved by wavelength interference method, and stripe counting is avoided.
However, to achieve a large measurement range, a large number of synthetic wavelengths are required, which will result in a complex system of multiple lasers, or a low measurement speed due to wavelength scanning.
Due to the appearance of optical frequency comb, the absolute distance measurement has made revolutionary progress.
Optical frequency comb emits ultra-uniform spacing
Broadband spectrum short pulse sequence composed of discrete and uniform modes-
Narrow line spacing.
When its mode frequency is referenced to the frequency standard, it becomes a super
An accurate ruler of the space, time, and frequency domain.
This inherent advantage is attractive for absolute distance measurement.
Since the first work in Mingdao County.
, Various methods of this research have been reported, E. G. g.
, Using comb as the wavelength or frequency standard of CW laser, using a pair of frequency comb to achieve time-of-
The comb is used as the light source for the dispersion interference measurement, and the adjacent pulse repeat interval length is used (APRIL)as a scale.
In the above method, April is a simple and effective scheme based on unbalanced Michael Johnson interference, which is widely used in absolute distance measurement.
By adjusting the repetition rate ()
In order to overlap the pulses from the reference and measurement arm, the target distance can be determined by accurate measurement.
Generally speaking, two factors are extremely important for the performance of this approach.
The first is how to judge pulse overlap because of the accuracy of pulse overlapto-
Pulse alignment determines the accuracy of distance measurement.
The second is that the limited tuning range limits the continuous measurement range, which results in a large "dead zone" of this method ".
The accuracy of this distance measurement mainly depends on the knowledge of the relative position of the two overlapping pulses, I . E. e. , pulse-to-Pulse alignment.
Usually, the peak position of the interference line of the overlapping pulse is used for the pulse-to-Pulse alignment.
The following method is called peak search method.
It can achieve even a thousand cents.
Since the pulse width can be very narrow, the millimetre is aligned horizontally, but the accuracy is affected by the noise of the intensity of the interference line.
In addition, this precision for super
Precision applications.
To improve the accuracy of the pulse,to-
Pulse alignment, several attempts were made in improving the peak finding method or linking peak finding to interference phase.
In our previous research, we proposed
Color optical difference interference measurement based on subharmonic and subharmonic (SH)
Optical frequency comb.
The synthetic wavelength derived from the virtual second harmonic (
Basic half-wavelength)
And the real second harmonic (
Produced by nonlinear crystals)
Used to bridge the gap between peak finding methods and single value finding methods
Interference method of wavelength optical difference
However, the system needs a fully stable comb, second harmonic generation and two sound and light
In practical applications, the light modulator is very complex.
When applying the April method, the continuous measurement range depends on the tuning range and optical path difference of the cavity length (OPLD)
Between the measuring arm and the reference arm.
For example, we represent the optical length of the cavity (
Equal to the light distance between adjacent pulses)
Indicates that its adjustable range is Delta.
Assuming that old is secondary, it can achieve a continuous measurement range of Delta/2 (
Consider the round trip of the beam)
For distance measurement.
Therefore, if the continuous measurement range is large enough and there is no "dead zone" if the measurement> u2009/Δ ".
When we measure the short distance, we can add additional length delay in the reference/measurement arm to increase the old to achieve the "multiplier effect" of eliminating the "dead zone ".
This concept has been applied in surface profile measurement and cavity tuning optical sampling.
It is also expected to be combined with the approach of April.
In this study, we propose a simplified synthesis-
Wavelength interference method for optical frequency comb for absolute distance measurement.
The synthetic wavelength is derived from two wavelengths obtained from two bands-pass filters.
The interference phase of the synthetic wavelength is used as a marker of the pulseto-Pulse alignment.
Therefore, the carrier-envelope-
Offset frequency ()
Not sensitive to the measurement results in this system.
To expand the continuous measurement range, we use long fiber optic to add the old of the reference arm and the measurement arm.
Therefore, the system can achieve high-precision continuous distance measurement in a wide range.