Laser Feedback Interferometer Research Articles

All-Fiber Laser Feedback Interferometry for Sequential Sensing of In-Plane and Out-of-Plane Displacements

In this paper, an all-fiber laser feedback interferometer (LFI) with a diffraction grating was developed for sequential measurement of in-plane and out-of-plane displacements without changing the optical arrangement. When the light emitted from an erbium-doped fiber ring laser is incident on a reflection grating at the Littrow angle, the diffracted light will return into the laser cavity along the original path, thus generating laser feedback interference. Experimental results reveal that the all-fiber system could achieve a precision of 40 nm in both in-plane and out-of-plane displacements sensing. Compared with the traditional all-fiber LFI, the proposed sensing system transfers the measuring scale from laser wavelength to grating period, and it has the advantages of good anti-interference performance and reliability.

Phase-interrogated surface plasmon resonance sensor based on laser feedback interferometry

This work reports a phase-interrogated surface plasmon resonance sensor based on a laser feedback interferometer to detect a small refractive index change. The laser feedback interferometer technique is introduced to demonstrate the sensing technique's performance, which offers several inherent advantages, such as compact, optically self-aligned, and high accuracy measurement. Moreover, this technique doubles the interrogating light beam propagation to the solution under the test, leading to an improvement of intrinsic sensitivity measurement up to two-fold. The proposed technique was characterized, and the performance was compared to another phase-interrogated surface plasmon resonance (SPR) based on the Mach-Zehnder interferometer. Laser feedback interferometer SPR has shown significant improvement to the performance parameter under test, namely sensitivity, drift, repeatability, and resolution.

正交偏振激光回馈干涉仪稳定性提高方法研究

正交偏振激光回馈干涉仪稳定性提高方法研究

Determining Ethanol Content of Liquid Solutions Using Laser Feedback Interferometry with a Terahertz Quantum Cascade Laser

Over the last decade, terahertz (THz) time-domain spectroscopy has been investigated as a technique for assaying the ethanol content of liquid solutionsindeed, operating at THz frequencies addresses some of the challenges that traditional optical refraction measurements face, such as delineation between sugarethanol content, florescence, and problems arising from carbonation or other dissolved gasses. In this article, we propose an alternative system and method for assaying ethanol content of liquid solutions at THz frequencies, which employs a laser feedback interferometer built around a 2.6-THz quantum cascade laser. The system is tested against a series of controlled waterethanol solutions, as well as a series of commercially available beverages. The accuracy of the estimated ethanol content compares favorably to THz time-domain spectroscopy techniques.

Measurement of the emission spectrum of a semiconductor laser using laser-feedback interferometry

The effects of optical feedback (OF) in lasers have been observed since the early days of laser development. While OF can result in undesirable and unpredictable operation in laser systems, it can also cause measurable perturbations to the operating parameters, which can be harnessed for metrological purposes. In this work we exploit this ‘self-mixing’ effect to infer the emission spectrum of a semiconductor laser using a laser-feedback interferometer, in which the terminal voltage of the laser is used to coherently sample the reinjected field. We demonstrate this approach using a terahertz frequency quantum cascade laser operating in both single- and multiple-longitudinal mode regimes, and are able to resolve spectral features not reliably resolved using traditional Fourier transform spectroscopy. We also investigate quantitatively the frequency perturbation of individual laser modes under OF, and find excellent agreement with predictions of the excess phase equation central to the theory of lasers under OF.

Multi-spectral terahertz sensing: proposal for a coupled-cavity quantum cascade laser based optical feedback interferometer.

We propose a laser feedback interferometer operating at multiple terahertz (THz) frequency bands by using a pulsed coupled-cavity THz quantum cascade laser (QCL) under optical feedback. A theoretical model that contains multi-mode reduced rate equations and thermal equations is presented, which captures the interplay between electro-optical, thermal, and feedback effects. By using the self-heating effect in both active and passive cavities, self-mixing signal responses at three different THz frequency bands are predicted. A multi-spectral laser feedback interferometry system based on such a coupled-cavity THz QCL will permit ultra-high-speed sensing and spectroscopic applications including material identification.

Laser Feedback Interferometry as a Tool for Analysis of Granular Materials at Terahertz Frequencies: Towards Imaging and Identification of Plastic Explosives.

We propose a self-consistent method for the analysis of granular materials at terahertz (THz) frequencies using a quantum cascade laser. The method is designed for signals acquired from a laser feedback interferometer, and applied to non-contact reflection-mode sensing. Our technique is demonstrated using three plastic explosives, achieving good agreement with reference measurements obtained by THz time-domain spectroscopy in transmission geometry. The technique described in this study is readily scalable: replacing a single laser with a small laser array, with individual lasers operating at different frequencies will enable unambiguous identification of select materials. This paves the way towards non-contact, reflection-mode analysis and identification of granular materials at THz frequencies using quantum cascade lasers.

Note: Design of a laser feedback interferometer with double diffraction system.

A novel laser feedback interferometer with double diffraction system is proposed in this paper. A beam emitted from the laser is incident onto a transmission grating. The mth order beam is vertically reflected by a mirror and diffracted again by the grating. The double-diffracted beam returns into the laser cavity and mixes with the light inside the active cavity, thus generating a modulation of both the amplitude and the frequency of the lasing field. Theoretical analysis and experimental observations show that the output signal of the proposed system depends on the grating pitch and the direction of the phase movement can be obtained from inclination of the interference signal. It provides a potential displacement sensor with high stability and quite a compact configuration.

Effect of the optical system on the Doppler spectrum in laser-feedback interferometry.

We present a comprehensive analysis of factors influencing the morphology of the Doppler spectrum obtained from a laser-feedback interferometer. We explore the effect of optical system parameters on three spectral characteristics: central Doppler frequency, broadening, and signal-to-noise ratio. We perform four sets of experiments and replicate the results using a Monte Carlo simulation calibrated to the backscattering profile of the target. We classify the optical system parameters as having a strong or weak influence on the Doppler spectrum. The calibrated Monte Carlo approach accurately reproduces experimental results, and allows one to investigate the detailed contribution of system parameters to the Doppler spectrum, which are difficult to isolate in experiment.

Note: Measurement speed improvement of microchip Nd:YAG laser feedback interferometer

We analyze the measurement speed limit of the quasi-common-path laser feedback interferometer and demonstrate a much improved measurement speed from 100 μm/s to 60 mm/s owing to the optimized system parameters and a novel signal processing method. The performance is experimentally verified by comparing to an Agilent 5529A dual-frequency laser interferometer.

A microchip laser feedback interferometer with nanometer resolution and increased measurement speed based on phase meter

We introduce a new signal processing method based on phase meter into heterodyne microchip Nd:YAG laser feedback interferometer. The nanometer resolution and a higher measurement speed are realized. The factors determining the accuracy are analyzed. The displacements of the Physik Instrumente nanopositioning system and two piezoelectric transducers were measured. Experimental results indicate laser feedback interferometer’s ability of measuring nanoscale displacement and present promising application prospects in noncooperative targets measurement.

Parallel multiplex laser feedback interferometry

We present a parallel multiplex laser feedback interferometer based on spatial multiplexing which avoids the signal crosstalk in the former feedback interferometer. The interferometer outputs two close parallel laser beams, whose frequencies are shifted by two acousto-optic modulators by 2Ω simultaneously. A static reference mirror is inserted into one of the optical paths as the reference optical path. The other beam impinges on the target as the measurement optical path. Phase variations of the two feedback laser beams are simultaneously measured through heterodyne demodulation with two different detectors. Their subtraction accurately reflects the target displacement. Under typical room conditions, experimental results show a resolution of 1.6 nm and accuracy of 7.8 nm within the range of 100 μm.

Note: High-performance HeNe laser feedback interferometer with birefringence feedback cavity scanned by piezoelectric transducer

We demonstrate a high-performance HeNe laser feedback interferometer (HLFI) based on a birefringence feedback cavity scanned by a piezoelectric transducer (PZT). The PZT scanning technique leads to a significant improvement in the HLFI's anti-jamming capability. The null drift under general laboratory conditions is approximately ±32 nm, corresponding to ±2 pulses. The phase difference between the two measurement signals does not vary when the feedback cavity length changes. This ensures a large measurement range for the HLFI. The HLFI presented here features a large measurement range (>1 m), nanometer-scale resolution (15.82 nm), a compact configuration, and low cost.

The frequency stabilization method of laser feedback interferometer based on external cavity modulation

Laser frequency stabilization is one of the foremost factors that influence the accuracy of measurement using a laser feedback interferometer, especially when the system is in the presence of strong optical feedback. In this paper, we use external cavity modulation to demonstrate a simple and effective method of frequency stabilization for laser feedback interferometer with strong optical feedback. The external cavity modulation is realized by oscillating a feedback mirror driven by a piezoelectric ceramic, the stable feedback optical field is obtained that has strong performance of anti-disturbance. Meanwhile, we stabilize the laser frequency by the thermal frequency-stabilizing. These lead to the realization of stable laser feedback interferometer. The relative uncertainty of the frequency stabilization is less than 1 part in 10(7).

Polarization flipping and hysteresis phenomenon in laser with optical feedback

We realize polarization control in He-Ne laser by optical feedback. Polarization flipping occurs when the length of the anisotropy feedback cavity is modulated. The relationship between polarization flipping and phase retardation of birefringence component placed in feedback cavity is built. The hysteresis effect of polarization flipping is observed. We build a system to measure the size of hysteresis loop based on Laser Feedback Interferometer (LFI). The variation of hysteresis loop with phase retardation is measured. The width of hysteresis loop decreases when phase retardation increases.

A laser feedback interferometer with an oscillating feedback mirror

A method is proposed to solve the problem of direction discrimination for laser feedback interferometers. By vibrating the feedback mirror with a small-amplitude and high-frequency sine wave, laser intensity is modulated accordingly. The modulation amplitude can be extracted using a phase sensitive detector (PSD). When the feedback mirror moves, the PSD output shows a quasi-sine waveform similar to a laser intensity interference fringe but with a phase difference of approximately ±π/2. If the movement direction of the feedback mirror changes, the phase difference sign reverses. Therefore, the laser feedback interferometer offers a potential application in displacement measurement with a resolution of 1/8 wavelength and in-time direction discrimination. Without using optical components such as polarization beam splitters and wave plates, the interferometer is very simple, easy to align, and less costly.

Phase Tuning Characteristics of a Double-Longitudinal-Mode He-Ne Laser with Optical Feedback

The phase tuning characteristics of a double-longitudinal-mode He-Ne laser with optical feedback are demonstrated. The phase behaviors of the two adjacent longitudinal modes are studied with different laser cavity lengths at the weak feedback level, and it is found that the phase difference of the two modes can be 0 to 180° along with the changing of the length of external cavity. The high-density intensity fringes are obtained with asymmetric feedback cavity at a strong feedback level. In particular, the phase difference is also observed between the two high-density fringes of adjacent modes, which have the potential to develop a direction sensitive laser feedback interferometer with high resolution. A simple theoretical analysis is presented, which fits well with the experimental results.

Orthogonally polarized dual frequency lasers and applications in self-sensing metrology

A review of the authors' work on orthogonally polarized lasers and their applications in self-sensing metrology is given. Zhang's group at Tsinghua University has been studying orthogonally polarized lasers, their phenomena and applications in metrology. Two kinds of dual frequency HeNe laser, which outputs a beam with two orthogonally polarized components, have been developed including (1) birefringence HeNe lasers (B-lasers) with 40 MHz to 1 GHz frequency difference and (2) birefringence-Zeeman HeNe lasers (BZ-lasers) with ∼0–1 GHz frequency difference. A large number of laser tuning characteristics and feedback effects in HeNe laser and Nd:YAG laser are discovered, which are the basis for utilizing the lasers to realize new sensors for measurement of displacement and phase retardation of optical elements. This paper introduces some original metrology instruments including (1) HeNe laser nanometer rulers, (2) frequency splitting wave-plate measurement system, (3) laser feedback wave-plate measurement system, (4) quasi-common-path Nd:YAG laser feedback interferometer and (5) microchip Nd:YAG laser feedback sensor with birefringence external cavity. These instruments are able to supplement or replace traditional sensors.

Distortion of optical feedback signals in microchip Nd:YAG lasers subjected to external multi-beam interference feedback

This paper proposes a theoretical analysis for the characteristics of an external cavity Nd:YAG laser with feedback of multiple-beam interference, which is induced by the multi-reentrance of the light from the external Fabry–Perot cavity. The theoretical model considers the multiple beam interference of the external Fabry–Perot cavity. It is found that the optical feedback signals are distorted to pulse waveforms instead of the sinusoidal ones in conventional feedback. The experimental results are in good agreement with the theoretical analysis. The obtained theoretical and experimental results can advance the development of a laser feedback interferometer.

Microchip Laser Feedback Interferometer with an Optical Path Multiplier

We present a microchip laser feedback interferometer with an optical path multiplier to enhance the resolution of traditional laser feedback interferometers (LFI). The optical path multiplier has a unique device, i.e. diffusive reflector. As class B microchip lasers have extremely high sensitivity to laser feedback, the diffusive reflector can easily reflect or diffuse back the laser beam without much manual adjustment to the optical system, which ensures the system's easy-adjustment and practical feature. The optical path multiplier is a two-mirror system which enables the laser beam to reflect between the two mirrors by N times. When the target shifts a distance of Δd, the variation of the optical path will be about (AN × Δd). Thus the system's resolution is about 4N times as high as the traditional LFI. Under typical room conditions, the optical path multiplier can effectively enhance the system's resolution by more than 26 times as high as a traditional LFI system and even to the level of 0.1 nm.