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The design, fabrication, and demonstration of a planar two-dimensional-crossed reflective diffractive grating are proposed to construct a novel optical configuration, to the best of our knowledge, potentially applied for atom cooling and trapping in a magneto-optical trap. Based on the proposed single-beam single-exposure scheme by means of an orthogonal two-axis Lloyd’s mirrors interferometer, we rapidly patterned a ∼ 1 µ m period grating capable of providing a uniform intensity of the diffracted beams. The key structural parameters of the grating including the array square hole’s width and depth were determined, aiming at providing a high energy of the diffracted beams to perform the atom cooling and trapping. To guarantee the diffracted beams to be overlapped possibly, we adopted a polarized beam splitter to guide the optical path of the incident and zero-order diffracted beams. Therefore, one zero-order diffracted beam with a retroreflected mode and four first-order diffracted beams with appropriate optical path constructed a three-dimensional optical configuration of three orthogonal pairs of counterpropagating beams. Finally, three pairs of the counterpropagating cooling laser beams with 9 mm diameter and > 10 % diffraction efficiencies were achieved, and the circular polarization chirality, purity, and compensation of the desired diffracted beams are further evaluated, which preliminarily validated a high applicability for the magneto-optical trap system.

The free vibration of a fluid-conveying nanotube composed of carbon nanotube and boron nitride (BN) nanotube is studied in this paper. The nonlocal Euler-Bernoulli beam model is adopted to describe the transverse displacement of the hybrid nanotube, and the governing equation is segmented because of the material properties' change at the junction. Then the dynamic stiffness method is used to solve the governing equation, and we investigated the effects of length ratio and nonlocal parameter on the vibration behavior and stability of the fluid-conveying hybrid nanotube. It can be concluded that the instability of the nanotube is significantly dependent on the length ratio and the nonlocal parameter. The increase of length ratio or nonlocal parameter will both make the system more unstable, in particularly, the nonlocal parameter has a great effect on the second-mode divergence. And we also find that the extra support at the junction will lead a great increment to the first two order frequencies and critical flow velocity.

Stimulated Raman adiabatic passage (STIRAP) is an effective technique to transfer state coherently with the features of both high fidelity and robustness in the field of quantum information and quantum precise measurement. In this note, we present a simple method to generate arbitrary laser shapes for STIRAP by controlling the modulation depth of the electro-optic modulator (EOM) and the diffraction efficiency of the acoustic–optic modulator (AOM) simultaneously. The EOM and AOM are used to control the power ratio between the two Raman lasers (pumping laser and Stokes laser) and the total power, respectively. Compared with the traditional method by combining two Raman lasers separated in space, this method has the advantage of simple structure and insensitivity to the environment disturbance, which would degrade the relative phase noise between two Raman lasers.

Light shift produced by the AC Stark effect is one of the major factors limiting the accuracy and long-term stability of a cold atom interferometer. The first order light shift can be canceled by fixing the power ratio of the Raman beams at a specified value. We report here a new method to stabilize the power ratio of the two Raman lasers with ∼100 kHz locking bandwidth, suppressing the effect of the first order light shift. We first mixed the two Raman lasers (at different optical frequencies) with a reference beam and then used two Schottky diode detectors to extract the corresponding beat note signals for each beam, which are much easier to be manipulated and processed as they are in the microwave band. The stability of the power ratio is improved by three orders of magnitude from 5.84 × 10-3 to 3.51 × 10-6 at 1 s averaging time and reaches 1.59 × 10-7 at 10 000 s integrating time when the servo loop is engaged. This method can be used in other precise quantum measurement based on the stimulated Raman transition and can be applied to compact inertial sensors.

Ocean economy plays a crucial role in the strengthening maritime safety industry and in the welfare of human beings. Electric Submersible Pumps (ESP) have been widely used in floating platforms on the sea to provide oil for machines. However, the ESP fault may lead to ocean environment pollution, on the other hand, a timely fault diagnosis of ESP can improve the ocean economy. In order to meet the strict regulations of the ocean economy and environmental protection, the fault diagnosis of ESP system has become more and more popular in many countries. The vibration mechanical models of typical faults have been able to successfully diagnose the faults of ESP. And different types of sensors are used to monitor the vibration signal for the signal analysis and fault diagnosis in the ESP system. Meanwhile, physical sensors would increase the fault diagnosis challenge. Nowadays, the method of neural network for the fault diagnosis of ESP has been applied widely, which can diagnose the fault of an electric pump accurately based on the large database. To reduce the number of sensors and to avoid the large database, in this paper, algorithms are designed based on feature extraction to diagnose the fault of the ESP system. Simulation results show that the algorithms can achieve the prospective objectives superbly.

This paper reports on an experimental realization of an automatic laser locking scheme using the artificial intelligence algorithm. We design a classifier based on the support vector machine to recognize the pattern of the saturated absorption spectroscopy signal of a laser and to locate its lockable points. We experimentally investigated our intelligent locking scheme on an external-cavity-diode-laser (ECDL) at 780 nm through the rubidium (Rb) cell and Rb saturated absorption lines. Test results show that the laser frequency can be automatically locked or relocked to the desired point within 11.6 s, either from free running state or from unlocked state, where the entire locking and relocking process is managed by the machine itself rather than human operations. The intelligent method reported in this paper provides a robust and smart solution for laser locking in unmanned conditions, e.g., space-borne experiments.

Radar correlated imaging (RCI) is a novel modality to obtain high resolution target images by correlated process of stochastic radiation field and the received signals. Conventional RCI methods neglect the inherent structure information of complex extended target, which makes the quality of recovery result degraded. Thus a clustered sparse Bayesian learning with Laplace prior (La-CSBL) algorithm for extended target imaging is proposed in this paper. A hierarchical correlated Laplace prior model is introduced to consider both the sparse prior and the cluster prior, and the prior for each coefficient not only involves its own hyperparameter, but also its immediate neighbor hyperparameters. Then the algorithm alternates between steps of target reconstruction and parameter optimization by cyclic minimization method under the Bayesian maximum a posteriori framework. Experimental results show that the proposed algorithm could realize high resolution imaging efficiently for extended target.

Vibration-based monitoring is one approach used to perform structural condition assessment. By measuring structural response, such as displacement, dynamic characteristics of a structure may be estimated. Often, the primary dynamic responses in civil structures are below 5 Hz, making accurate low frequency measurement critical for successful dynamic characterization. In addition, static deflection measurements are useful for structural capacity and load rating assessments. This paper presents a DC coupled continuous wave radar to accurately detect both dynamic and static displacement. This low-cost radar sensor provides displacement measurements within a compact, wireless unit appropriate for a range of structural monitoring applications. The hardware components and operating mechanism of the radar are introduced and a series of laboratory experiments are presented to assess the performance characteristics of the radar. The laboratory and field experiments investigate the effect of factors such as target distance, motion amplitude, and motion frequency on the radar\'s measurement accuracy. The results demonstrate that the radar is capable of both static and dynamic displacement measurements with sub-millimeter accuracy, making it a promising technology for structural health monitoring.

Radars are among the best exponents of radio-frequency (RF)/microwave devices for remote sensing [1], [2]. Long-range radars have demonstrated outstanding potential not only for defense/security environments, such as the detection, location, and tracking of targets, but also on a plurality of civilian scenarios, such as meteorological/weather measurement tasks, imaging of the Earth's surface through synthetic aperture radar (SAR) techniques, monitoring of animal migrations, and many others [3]-[7].

The gold-coated cross-grating is investigated to simultaneously improve the diffraction efficiency, signal contrast and optical subdivision in heterodyne grating interferometer (HGI). Based on the theories of Fresnel–Kirchhoff diffraction integral and rigorous coupled wave analysis (RCWA), the diffractive characteristics related to diffraction efficiency, wavelength selectivity and polarization dependency are analyzed. The analysis reveals that grating pitch less than twice of the incident wavelength ought to be adopted here to avoid the second-orders, and longer wavelength is preferred to achieve high diffraction efficiency in the visible region. Meanwhile, the equivalent efficiency for TE and TM polarization, probably up to 18.32% at the wavelength of 632.8 nm, can be obtained with normal incidence which results in a signal contrast of 100% theoretically. Additionally, an eightfold optical subdivision method with cross-gratings is proposed for HGIs, and it is applicable to nearly all the existing two-dimensional (2D) optical configurations. The experimental tests on diffraction field, polarization dependency and signal contrast are performed. The results show reasonable consistency with the theoretical analysis, which validates the capability of cross-gratings for HGIs.

One of the problems with the chemical exfoliation of graphite to graphene via oxidation and reduction, is the excessive oxidation of graphite and incomplete reduction of graphene oxide, which introduce many defects and unnecessary oxygen-containing groups into the graphene sheets. Therefore, it is difficult to create high quality graphene sheets with few defects on a large scale by chemical exfoliation. Here, a simple and convenient method is developed to prepare graphene with a little fluorine by ultrasonicating fluorinated graphite in hydrazine hydrate. For comparison, reduced graphene oxide (RGO) was also prepared by Hummers method. The results showed that thin and flat graphene prepared from fluorinated graphite has a monocrystalline structure, while RGO presents turbostratic stacking. Moreover, the thermal stability and electrical conductivity of the as-prepared graphene sheets (GS) are much higher than those of the RGO sheets.

This paper presents a hybrid radar system that incorporates a linear frequency-modulated continuous-wave (FMCW) mode and an interferometry mode for indoor human localization and life activity monitoring applications. The unique operating principle and signal processing method allow the radar to work at two different modes for different purposes. The FMCW mode is responsible for range detection while the interferometry mode is responsible for life activities (respiration, heart beat, body motion, and gesture) monitoring. Such cooperation is built on each mode's own strength. Beam scanning is employed to determine azimuth information, which enables the system to plot 360° 2-D maps on which the room layout and objects' location can be clearly identified. Additionally, the transmitted chirp signal is coherent in phase, which is very sensitive to physiological motion and allows the proposed technique to distinguish human from nearby stationary clutters even when the human subjects are sitting still. Hence, the proposed radar is able to continuously track the location of individuals and monitor their life activities regardless of the complex indoor environment. A series of experiments have been carried out to demonstrate the proposed versatile life activity monitoring system.

This paper presents a Doppler radar vital sign detection system with random body movement cancellation (RBMC) technique based on adaptive phase compensation. An ordinary camera was integrated with the system to measure the subject's random body movement (RBM) that is fed back as phase information to the radar system for RBMC. The linearity of the radar system, which is strictly related to the circuit saturation problem in noncontact vital sign detection, has been thoroughly analyzed and discussed. It shows that larger body movement does not necessarily mean larger radar baseband output. High gain configuration at baseband is required for acceptable SNR in noncontact vital sign detection. The phase compensation at radar RF front-end helps to relieve the high-gain baseband from potential saturation in the presence of large body movement. A simple video processing algorithm was presented to extract the RBM without using any marker. Both theoretical analysis and simulation have been carried out to validate the linearity analysis and the proposed RBMC technique. Two experiments were carried out in the lab environment. One is the phase compensation at RF front end to extract a phantom motion in the presence of another large shaker motion, and the other one is to measure the subject person breathing normally but randomly moving his body back and forth. The experimental results show that the proposed radar system is effective to relieve the linearity burden of the baseband circuit and help compensate the RBM.

A novel imaging method based on temporal-spatial stochastic radiation field is a super-resolution imaging technique without the limitation of relative motion between the target and radar. For the novel microwave staring coincidence imaging of the moving target, in addition to the distribution of the target scattering coefficient, we also need to estimate the target velocity. When the target movement information is ignored or failing to estimate, the imaging result will appear serious defocusing and affect the imaging resolution performance. Inspired by dictionary learning, we use sparse representation-based classifier (SRC) to assess a velocity from the target velocity range in the compressed sensing framework. We propose PSO-SRC algorithm which utilize Particle Swarm optimization (PSO) to find the optimal velocity which is assessed by SRC algorithm. The simulations that the target velocity is within the speed of sound illustrate the effectiveness of the proposed method.

A prototype laser distance interferometer is demonstrated by incorporating the frequency comb of a femtosecond laser for mass-production of optoelectronic devices such as flat panel displays and solar cell devices. This comb-referenced interferometer uses four different wavelengths simultaneously to enable absolute distance measurement with the capability of comprehensive evaluation of the measurement stability and uncertainty. The measurement result reveals that the stability reaches 3.4 nm for a 3.8 m distance at 1.0 s averaging, which further reduces to 0.57 nm at 100 s averaging with a fractional stability of 1.5 × 10−10. The uncertainty is estimated to be in a 10−8 level when distance is measured in air due to the inevitable ambiguity in estimating the refractive index, but it can be enhanced to a 10−10 level in vacuum.

Summary Continuous wave (CW) radar sensors are a promising technology for structural displacement measurement. However, the commonly employed passive backscattering measurement configuration has some limitations for low-power applications of CW radar. To improve displacement measurement performance using the low-power CW radar, an active transponder configuration is introduced. Compared with passive backscattering, the active transponder configuration is capable of increasing the radar's signal power, thereby increasing the signal to noise ratio for more accurate displacement measurement. A series of laboratory experiments to demonstrate the performance of the transponder configuration was conducted, and the experimental results were compared with the results of using the backscattering configuration. The investigation revealed that the signal improvement provided by the transponder is a function of the distance between the transponder and the radar. In addition, a full-scale bridge test with the active transponder configuration was conducted to verify the improved performance. An oblique angle test using the transponder was conducted in the laboratory to demonstrate the potential for flexible installation strategies when deploying the radar/transponder pair for bridge displacement measurements. Copyright © 2016 John Wiley & Sons, Ltd.

Ti-based bulk metallic glass (BMG) plates have been successfully welded together by laser welding process. The tensile strength of the welded sample reaches up to 93% of the base material. Based on calculations and numerical simulations, the mechanism of successful welding of the BMG has been discussed in terms of the thermal history of weld fusion zone (WFZ) and heat affected zone (HAZ).

Doppler radar has been used for small-scale displacement detection, e.g. respiration and heartbeat. The motion amplitude is less than half a carrier wavelength. In this letter, a novel Doppler radar technique is presented for accurate tracking of large-scale displacement of several carrier wavelengths, e.g., the water level variation. The DC-coupled architecture is used to ensure precise measurement of slow motions even with stationary moment. A novel signal processing approach is proposed to increase the demodulation linearity to deal with inconstant signal amplitude, dynamic dc offset and phase ambiguity in large-scale displacement tracking. Experiments have been carried out in the outdoor environment to monitor the relative water level position in a rain barrel when the water was pumped in or drained out. It is shown that the proposed technique can accurately gauge the relative water level variation of 3.5 wavelengths with mm accuracy.

A novel low-noise front-end electronics was proposed for detection of light signals with intensity about 10 μW and frequency above 2.7 MHz. The direct current (DC) power supply, pre-amplifier and main-amplifier were first designed, simulated and then realized. Small-size components were used to make the power supply small, and the pre-amplifier and main-amplifier were the least capacitors to avoid the phase shift of the signals. The performance of the developed front-end electronics was verified in cross-grating diffraction experiments. The results indicated that the output peak-topeak noise of the ±5 V DC power supply was about 2 mV, and the total output current was 1.25 A. The signal-to-noise ratio (SNR) of the output signal of the pre-amplifier was about 50 dB, and it increased to nearly 60 dB after the mainamplifier, which means this front-end electronics was especially suitable for using in the phase-sensitive and integrated precision measurement systems.

We measure absolute distances by performing multi-wavelength interferometry (MWI) using four different wavelengths generated simultaneously from the frequency comb of a femtosecond laser. The measurement precision is estimated to be less than 63 nm in peak-to-valley over a distance of 1 m as compared to an incremental HeNe laser interferometer. We also evaluate the operational stability and robustness of the interferometer hardware system over a time period of 12 hours. Finally, it is concluded that the proposed frequency-comb-referenced multi-wavelength interferometry is capable of providing fast, precise and high stable absolute distance measurements, being well suited for industrial precisionengineering applications and near-future space missions.

We report on a frequency-comb-referenced absolute interferometer which instantly measures long distance by integrating multi-wavelength interferometry with direct synthetic wavelength interferometry. The reported interferometer utilizes four different wavelengths, simultaneously calibrated to the frequency comb of a femtosecond laser, to implement subwavelength distance measurement, while direct synthetic wavelength interferometry is elaborately introduced by launching a fifth wavelength to extend a non-ambiguous range for meter-scale measurement. A linearity test performed comparatively with a He–Ne laser interferometer shows a residual error of less than 70.8 nm in peak-to-valley over a 3 m distance, and a 10 h distance comparison is demonstrated to gain fractional deviations of ~3 × 10−8 versus 3 m distance. Test results reveal that the presented absolute interferometer enables precise, stable, and long-term distance measurements and facilitates absolute positioning applications such as large-scale manufacturing and space missions.

Frequency modulated continuous wave (FMCW) radar is moving from long range detection to indoor short distance target monitoring and has already demonstrated its unique advantages over other approaches. The state-of-the-art coherent FMCW radar, especially, can provide very accurate result in small motion signal detection. However, the performance is sensitive to the clutters that surround the target. In this paper, a clutter reduction technique is developed to further enhance the performance and the robustness of coherent FMCW radar for physiological signal detection. Both theoretical and experimental results are presented to demonstrate the feasibility of the adopted solution.

The ability to accurately measure bridge deflections is an important aspect of bridge monitoring and maintenance, both in the US and internationally. Static deck deflections are used to provide load ratings while dynamic deflection measurements may be used to track changes in the dynamic behavior of the bridge due to environmental, loading, and condition changes. Directly measuring bridge deflection has proven challenging, requiring either a fixed reference point or the use of non-contact laser sensors. This presentation introduces wireless, continuous wave radar sensors developed for bridge monitoring applications. The small, bridge-mounted sensors provide a practical and low-cost solution for a range of measurement conditions. As the bridge moves, the radars send a continuous wave that is reflected by a stationary target (either the ground below or a fixed transponder, depending on the application). The reflected signal contains the information necessary to extract the bridge motion. While the theoretical operation is straightforward, there are challenges associated with signal demodulation and data processing in the presence of noise due to interference or long detection ranges. Characterization of the static and dynamic performance of the radar is presented, as well as guidelines for their practical application. The audience of this presentation will be both researchers and practitioners working to improve bridge inspection and monitoring practices. Specifically, the audience will learn about a novel technology to improve bridge testing, gain an understanding of the advantages and challenges of applying radar technology to structural monitoring, and be presented with strategies for achieving a network of distributed radar sensors to capture bridge responses.

Doppler radar has the capability to remotely monitor human respiration. However, in real applications random body movements during measurement will cause drift of “DC” level in the experiment results. Also, the dc level will shift slowly with the temperature change of the radar circuit. Those DC drifts will cause inaccurate measurement results. To solve the dc drift issue during the experiments, an automatic DC-correction algorithm is developed. Experiment results show that this algorithm eliminates undesirable DC drifts and offset while recovering useful information of the original respiration signal. It is able to provide reliable respiration measurement even if there are large body movements that otherwise overwhelm the desired signal.

Based on the detailed derivation of the displacement measurement principle with Jones matrix method, the optical system of the heterodyne grating interferometry that we previously proposed was modified. A reflection phase grating with smaller grating pitch was designed with rigorous coupled-wave analysis (RCWA) to improve the measurement performance. The first order diffraction efficiency of 47.35% and 56.24% were obtained for TE and TM polarization, respectively. Therefore the TM polarization was chose to enhance the signal-to-noise ratio (SNR) of the beat signal. Meanwhile, the errors of the optical system resulting from grating non-uniformity, frequency mixing, polarization mixing and polarization-frequency mixing were discussed as well. It was shown that the frequency mixing was the main source of the errors, and the modified heterodyne grating interferometry had the potential to realize nanometer resolution for displacement measurement.

This paper presents a Doppler radar sensor system with camera-aided random body movement cancellation (RBMC) techniques for noncontact vital sign detection. The camera measures the subject's random body motion that is provided for the radar system to perform RBMC and extract the uniform vital sign signals of respiration and heartbeat. Three RBMC strategies are proposed: 1) phase compensation at radar RF front-end, 2) phase compensation for baseband complex signals, and 3) movement cancellation for demodulated signals. Both theoretical analysis and radar simulation have been carried out to validate the proposed RBMC techniques. An experiment was carried out to measure a subject person who was breathing normally but randomly moving his body back and forth. The experimental result reveals that the proposed radar system is effective for RBMC.

A hybrid FMCW-interferometry radar sensor is presented. The proposed measurement system incorporates the linear frequency-modulated continuous-wave (FMCW) mode and the continuous wave (CW) interferometry mode. The radar system works in 5.8 GHz ISM band with a bandwidth of 160 MHz. Equipped with a special signal processing method, the hybrid system is capable of detecting absolute distance as well as slow motion. Experiments show that the absolute position detection has an average accuracy of 1.65 cm, and the accuracy of relative motion tracking is better than 2 mm.

A novel water level monitoring technique using continuous-wave (CW) Doppler radar is presented. The CW radar works with a DC-coupled baseband that allows accurate monitoring of the slow-varying water level. Ray tracing model has been used to simulate and validate the feasibility of water level monitoring in the presence of ripple. The proposed technique is robust against clutter interference and the fluctuation of water ripples by properly choosing the carrier frequency. Experiment was carried out to monitor the water level in a rain barrel when the water was draining out. Both simulation and experiment shows that the proposed technique can accurately monitor the water level with a high accuracy in millimeter-scale.

A continuous wave (CW) radar sensor system with active transponders is designed for Structural Health Monitoring (SHM) to accurately measure the structures' vibration while rejecting clutters reflected from the surrounding environment. The radar sensor, designed with a coherent heterodyne architecture, transmits a single-tone 2.4 GHz signal and receives a returning signal at 3.3 GHz, thus rejecting the backscattered clutters at 2.4 GHz. The active transponder was designed to convert the received 2.4 GHz signal up to 3.3 GHz and transmits a 900 MHz reference to synchronize the radar sensor. The proposed radar with active transponders was tested in lab environment to successfully capture vibration movements from 4.1 m with SNR over 35 dB. Experiments also showed that the radar sensor can isolate the target motion from the interferences from surrounding shaking bodies and sinusoidal phantom motions.

In this paper, the Doppler radar non-contact sensing technology is extended from measurement of one dimensional movement to a practical application in measuring rotational movement. Both simulation and experiment show that Doppler radar can detect the speed of angular movement such as electric fans or motor rotation. It has been shown that in Doppler radar based non-contact rotational movement measurement, the baseband output will have a dominant fundamental frequency that is multiple of the rotation frequency that depends on the structure of reflectors on the target.

Magnetorheological (MR) disk-type isolating dampers are the semi-active control devices that use MR fluids to produce controllable squeezing force. In this paper, the analytical endeavor into the fluid dynamic modeling of an MR isolating damper is reported. The velocity and pressure distribution of an MR fluid operating in an axisymmetric squeeze model are analytically solved using a biviscosity constitutive model. Analytical solutions for the flow behavior of MR fluid flowing through the parallel channel are obtained. The equation for the squeezing force is derived to provide the theoretical foundation for the design of the isolating damper. The result shows that with the increase of the applied magnetic field strength, the squeezing force is increased.

Displacement measurement by dual wavelength and single grating integrates the single grating diffraction theory and the heterodyne interference theory. By taking advantage of the two theories, it solves the contradiction between large range and high precision in grating displacement measurement quite well. In order to obtain nanometer resolution and nanometer precision, high-power subdivision of interference fringe must be realized accurately. According to phase demodulation theory for heterodyne interference signal, a digital phase measuring method is proposed by combining frequency-mixing technique and pulse-filling method. The whole signal processing part, which is based on FPGA and PLL, has been designed to realize the integer period measurement and high-powered subdivision of the decimal phase. Through experiments, it is validated that the phase range is [-180°, 180°], and the phase measurement resolution and the phase precision are above 0.03° and 0.1°, respectively. Moreover, the displacement measurement resolution and the displacement precision, corresponding to the phase indexes, are 0.167nm and 0.556nm, respectively.

Principle of the dual-wavelength single grating nanometer displacement measuring system, with a long range, high precision, and good stability, is presented. As a result of the nano-level high-precision displacement measurement, the error caused by a variety of adverse factors must be taken into account. In this paper, errors, due to the non-ideal performance of the dual-frequency laser, including linear error caused by wavelength instability and non-linear error caused by elliptic polarization of the laser, are mainly discussed and analyzed. On the basis of theoretical modeling, the corresponding error formulas are derived as well. Through simulation, the limit value of linear error caused by wavelength instability is 2nm, and on the assumption that 0.85 x T = , 1 T y = of the polarizing beam splitter(PBS), the limit values of nonlinear-error caused by elliptic polarization are 1.49nm, 2.99nm, 4.49nm while the non-orthogonal angle is selected correspondingly at 1°, 2°, 3° respectively. The law of the error change is analyzed based on different values of T x and T y .

A multi-wavelength interferometer utilizing the frequency comb of a femtosecond laser as the wavelength ruler is tested for its capability of ultra-precision positioning for machine axis control. The interferometer uses four different wavelengths phase-locked to the frequency comb and then determines the absolute position through a multi-channel scheme of detecting interference phases in parallel so as to enable fast, precise and stable measurements continuously over a few meters of axis-travel. Test results show that the proposed interferometer proves itself as a potential candidate of absolute-type position transducer needed for next-generation ultra-precision machine axis control, demonstrating linear errors of less than 61.9 nm in peak-to-valley over a 1-meter travel with an update rate of 100 Hz when compared to an incremental-type He-Ne laser interferometer.