Study of the Errors in Interpolated Fast Fourier Transform for Interferometric Applications

Frequency estimation is often the basis of various measurement techniques, among which optical distance measurement stands out. One of the most used techniques is interpolated fast Fourier transform due to its simplicity, combined with good performance. In this work, we study the lim-its of this technique in the case of real signals, with reference to a particular interferometric tech-nique known as self-mixing interferometry. The aim of this research is the better understanding of frequency estimation performances in real applications, together with guidance on how to im-prove them in specific optical measurement techniques. An optical rangefinder, based on self-mixing interferometry, has been realized and characterized. The simulation results allow us to explain the limits of the interpolated fast Fourier transform applied to the realized instrument. Fi-nally, a method for overcoming them is proposed by decorrelating the errors between the meas-urements, which can provide a guideline for the design of frequency-modulated interferometric distance meters

Overview of self-mixing interferometer applications to mechanical engineering

We present an overview of the applications of self-mixing interferometer (SMI) to tasks of interest for mechanical engineering, namely high-resolution measurement of linear displacements, measurements of angles (tilt, yaw, and roll), measurements of subnanometer vibrations, and absolute distance, all on a remote target-representative of the tool-carrying turret of a tool-machine. Along with the advantages of SMI-compactness, low cost, minimum invasiveness, ease of use, and good accuracy, we illustrate the typical performance achieved by the basic SMI sensors, that is, the versions requiring a minimum of signal processing and discuss special features and problems of each approach

Overview of self-mixing interferometer applications to mechanical engineering

We present an overview of the applications of self-mixing interferometer (SMI) to tasks of interest for mechanical engineering, namely high-resolution measurement of linear displacements, measurements of angles (tilt, yaw, and roll), measurements of subnanometer vibrations, and absolute distance, all on a remote target-representative of the tool-carrying turret of a tool-machine. Along with the advantages of SMI-compactness, low cost, minimum invasiveness, ease of use, and good accuracy, we illustrate the typical performance achieved by the basic SMI sensors, that is, the versions requiring a minimum of signal processing and discuss special features and problems of each approach

Evaluation of Self-Mixing Interferometry Performance in the Measurement of Ablation Depth

This paper studies self-mixing interferometry (SMI) for measuring ablation depth during laser percussion drilling of TiAlN ceramic coating. The measurement performance of SMI was investigated in a large processing range producing blind microholes with depths below and beyond the average coating thickness. Signal characteristics of the measurement system were evaluated indicating sources of disturbance. The SMI measurements were compared with a conventional measurement device based on focus variation microscopy to evaluate the measurement error. The measurement error classes were defined, as well as defining the related error sources. The results depict that the measurement error was independent of the processing condition, hence the hole geometry and ablation rate. For 76% of cases, measurement error was below the intrinsic device resolution obtainable by simple fringe counting of half a wavelength (λ/2 = 0.393 μm)

Optical proximity sensor based on self-mixing interferometry

A proximity detector based on self-mixing technique, well suited for different industrial applications, is demonstrated. Instead of using a light-source plus a detector, the proposed sensor is realized by a single laser source. Two different physical effects in the laser diode allow for a continuous detecting range, from 10 mm up to 80 mm. The main advantages of the sensor are target detection from just one point of view; multiple sensors configuration does not need optical filters; separation of source and detector is eliminated; and background rejection is intrinsically given by the self-mixing effect, which shows a sharp cut-off after the focus

Application of self-mixing interferometry for depth monitoring in the ablation of TiN coatings

Among possible monitoring techniques, self-mixing interferometry stands out as an appealing option for online ablation depth measurements. The method uses a simple laser diode, interference is detected inside the diode cavity and measured as the optical power fluctuation by the photodiode encased in the laser diode itself. This way, self-mixing interferometry combines the advantages of a high resolution point displacement measurement technique, with high compactness and easiness of operation. For a proper adaptation of self-mixing interferometry use in laser micromachining to monitor ablation depth, certain optical, electronical, and mechanical limitations need to be overcome. In laser surface texturing of thin ceramic coatings, the ablation depth control is critically important to avoid damage by substrate contamination. In this work, self-mixing interferometry was applied in the laser percussion drilling of TiN coatings. The ∼4 μm thick TiN coatings were drilled with a 1 ns green fiber laser, while the self-mixing monitoring was applied with a 785 nm laser diode. The limitations regarding the presence of process plasma are discussed. The design criteria for the monitoring device are explained. Finally, the self-mixing measurements were compared to a conventional optical measurement device. The concept was validated as the measurements were statistically the same

Yb,Er:glass Microlaser at 1.5 μm for optical fibre sensing: Development, characterization and noise reduction

A fiber-pumped single-frequency microchip erbium laser was developed and characterized with the aim of using it in coherent Optical Time Domain Reflectometry (OTDR) measurements and sensing. The laser is pumped by a fiber-coupled 976 nm laser diode and provides 8 mW TEM00 single-frequency output power at 1.54 μm wavelength, suitable for efficient coupling to optical fibers. The amplitude and phase noise of this 200 THz oscillator were experimentally investigated and a Relative Intensity Noise (RIN) control loop was developed providing 27 dB RIN peak reduction at the relaxation oscillation frequency of 800 kHz

Yb,Er:glass Microlaser at 1.5 µm for optical fiber sensing: development, characterization and noise reduction

A fiber-pumped single-frequency microchip erbium laser was developed and characterized with the aim of using it in coherent Optical Time Domain Reflectometry (OTDR) measurements and sensing. The laser is pumped by a fiber-coupled 976 nm laser diode and provides 8 mW TEM00 single frequency output power at 1.54 µm wavelength, suitable for efficient coupling to optical fibers. The amplitude and phase noise of this 200 THz oscillator were experimentally investigated and a Relative Intensity Noise (RIN) control loop was developed providing 27 dB RIN peak reduction at the relaxation oscillation frequency of 800 kH