Optimum Injection Current Waveform for a Laser Range Finder Based on the Self-Mixing Effect

In a self-mixing type laser range finder the current of the laser is modulated with a triangle wave to produce a range of optical frequencies. However, the electrical signal does not produce a perfect linear sweep in optical frequency due to thermal and other effects in the laser. This leads to errors in the accuracy and resolution of the range finder. In this paper, we describe and implement a method in software to systematically determine the optimal shape of the injected waveform needed to eliminate these thermally induced measurement errors. With this method we do not require the more complicated and expensive optical techniques used by other researchers to recover the optical frequency variations with regard to injection current. The averaging of a reasonable number of samples gave sub-millimeter accuracy when the optimal current shape was used. The uncertainty in the average measurements are improved by roughly six times compared to the conventional triangular modulation. The reshaping also results in the range finding system being less sensitive to changes in ambient temperature

A Massively Parallel Imaging System Based on the Self-Mixing Effect in a Vertical-Cavity Surface-Emitting Laser Array

In this work we propose a massively parallel self-mixing imaging system, based on an array of VCSELs, to measure surface profiles of displacement, distance, velocity and liquid flow rate. The feasibility of this concept is demonstrated by the successful operation of a small scale prototype consisting of eight individual commercial VCSELs with integrated photodetectors. The system is used to accurately measure the velocity at different radial points on a rotating disk. The results show no influence of crosstalk. A massive version of the system will be useful in many industrial and biomedical applications where real-time surface profiling, vibrometry and velocimetry will be very beneficial

The Effect of Multiple Transverse Modes in Self-Mixing Sensors Based on Vertical-Cavity Surface-Emitting Lasers

In this work we investigate the effect of multiple transverse modes, such as those found in Vertical-Cavity Surface-Emitting Lasers, in self-mixing sensors. We show that the sensitivity of the system and the accuracy of the measurement changes periodically with target distance

Research and Application of Measurement System Base on Laser Self-Mixing Interference

激光自混合干涉效应是指由于外部物体反射或者散射，而导致光反馈回激光腔内引起光功率波动的现象。该技术不仅保证了传统干涉的测量精度，还具备单光路、结构紧凑、易准直等优点，解决了传统干涉中存在的问题，因此受到了研究人员的关注，被广泛应用于速度、位移和振动、生物医学等领域的测量。 本文介绍了激光自混合干涉效应的发展历程和研究现状。通过三种不同的数学模型，详细阐述了自混合效应的机理，并对自混合干涉系统进行数值仿真，进而分析研究了系统模型中各参数对自混合干涉信号的影响。在此基础上，搭建半导体激光器自混合干涉测量系统，通过观察和研究实验现象，验证了理论仿真的结果。此外，本文还根据自混合基本数学模型，研究了...As a new laser technique called, self-mixing interference (SMI), which is based on the interaction of cavity field with the field backscatter from the remote target, has increasingly garnered intense attention. The SMI has advantages of simple and compact system structure and easy collimated light path. Therefore, the applications of the SMI have been popularized in many fields, including metrolog...学位：工学硕士院系专业：信息科学与技术学院_光学工程学号：2312013115309

Effect of multiple transverse modes in self-mixing sensors based on vertical-cavity surface-emitting lasers

We investigate the effect of coexisting transverse modes on the operation of self-mixing sensors based on vertical-cavity surface-emitting lasers (VCSELs). The effect of multiple transverse modes on the measurement of displacement and distance were examined by simulation and in laboratory experiment. The simulation model shows that the periodic change in the shape and magnitude of the self-mixing signal with modulation current can be properly explained by the different frequency-modulation coefficients of the respective transverse modes in VCSELs. The simulation results are in excellent agreement with measurements performed on single-mode and multimode VCSELs and on self-mixing sensors based on these VCSELs

Single-photon counting lidar for long-range three-dimensional imaging

Single-photon time-of-flight (ToF) distance ranging lidar is a candidate technology for high-resolution depth imaging for use, for example, from airborne platforms. This approach enables low average power pulsed laser sources to be used while allowing imaging from significantly longer target ranges compared to analogue imaging. The recent availability of Geiger-mode (Gm) arrays has revolutionised photon-counting lidar as they provide single-photon full-frame data in short acquisition times. This thesis presents work on the opto-mechanical design, tolerance analysis and performance evaluation of a re-configurable single-photon counting lidar which can accommodate either a single-element single-photon avalanche photodiode (SPAD) or a 32 × 32 Gm-array. By incorporating an inter-changeable lens, the two configurations were designed to provide identical pixel resolution for both the single-pixel system and the Gm-array configurations in order to permit a performance comparison to be conducted. This is the first time that such a comparison has been reported and the lidar is one of the earliest to assess the performance of a short-wave infra-red (SWIR) Gm-array. Both detection configurations used InGaAs/InP SPAD detectors and operated at a wavelength of 1550 nm. The main benefits of operating within the SWIR band include reduced solar background, lower atmospheric loss, improved covertness, as well as improved laser eye-safety thresholds. The system estimates target range by measuring the ToF using time-correlated single-photon counting (TCSPC) and was used to produce high-resolution three-dimensional images of targets at between 800 m and 10.5 km range. The single-element system has the potential to provide improved depth resolution over the array due to a smaller timing jitter but requires longer acquisition times due to the need for two-dimensional scanning. The acquisition time of the array configuration can be up to three orders of magnitude faster than the single-element configuration but requires significantly higher average laser power levels. The Gm-array provided a simultaneous estimation of angle-of-arrival and intensity fluctuations from which a comparable strength of atmospheric turbulence could be measured. This demonstrated that Gm-arrays provide a new way of high-speed turbulence measurement with time intervals much shorter than those offered by existing scintillometers

Two Dimensional Positioning and Heading Solution for Flying Vehicles Using a Line-Scanning Laser Radar (LADAR)

Emerging technology in small autonomous flying vehicles requires the systems to have a precise navigation solution in order to perform tasks. In many critical environments, such as indoors, GPS is unavailable necessitating the development of supplemental aiding sensors to determine precise position. This research investigates the use of a line scanning laser radar (LADAR) as a standalone two dimensional position and heading navigation solution and sets up the device for augmentation into existing navigation systems. A fast histogram correlation method is developed to operate in real-time on board the vehicle providing position and heading updates at a rate of 10 Hz. LADAR navigation methods are adapted to 3 dimensions with a simulation built to analyze performance loss due attitude changes during flight. These simulations are then compared to experimental results collected using SICK LD-OEM 1000 mounted a cart traversing. The histogram correlation algorithm applied in this work was shown to successfully navigate a realistic environment where a quadrotor in short flights of less than 5 min in larger rooms. Application in hallways show great promise providing a stable heading along with tracking movement perpendicular to the hallway

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

A scanning cavity microscope

Nano ist überall! Nanoskalige Systeme sind allgegenwärtig, wie in farbigen Gläsern, neuartigen Solarzellen oder in Lebewesen. Für ein umfassendes Verständnis des Nanokosmos ist es unabdingbar, Nanoteilchen einzeln zu untersuchen, um einen tiefen und faszinierenden Einblick in eine Welt, die dem Betrachter auf dem ersten Blick verborgen ist, zu erlangen. Optische Spektroskopie von einzelnen Nanosystemen liefert grundlegende Erkenntnisse von deren physikalischen und chemischen Eigenschaften. Quantitative Messungen von Extinktion und Dispersion an einzelnen Teilchen sind sehr schwierig, gleichzeitig sind solche Messungen sehr wünschenswert, da sich die Teilchen in Form, Größe oder Zusammensetzung unterscheiden können. Diese Arbeit zeigt eine Methode zur gleichzeitigen Messung von Extinktion und Dispersion einzelner Nanopartikel mit Ortsauflösung. Tausende Umläufe von Licht in einem optischen Resonator verstärken dieWechselwirkung von Licht mit Materie und ermöglichen sehr sensitive Messungen an einzelnen Teilchen. Die Mode eines Fabry-Pérot Resonators mit einer Finesse von bis zu 85 000 wird als Rastersonde verwendet, um die Extinktion von Nanoteilchen im Resonator zu bestimmen. Der Resonator ist aus einer mikrobearbeiteten und hochreflektiv beschichteten Glasfaser und einem makroskopischen Planspiegel, der gleichzeitig als Probenhalter dient, aufgebaut. Transversales Verschieben von Faser und Planspiegel zueinander liefert Ortsauflösung. Zur Messung der Verschiebung der Resonanzfrequenz aufgrund eines Teilchens im Resonator werden Transversalmoden höherer Ordnung genutzt. Die Kombination beider Messungen erlaubt es, die komplexe Polarisierbarkeit, die die optischen Eigenschaften eines Nanoteilchens im Rayleigh-Grenzfall vollständig beschreibt, zu bestimmen. In dieser Arbeit werden Extinktions-, Dispersions- und Polarisierbarkeitsmessungen an Goldnanoteilchen verschiedener Form und Größe gezeigt. Verglichen mit beugungsbegrenzter Mikrokopie liefert die Rasterresonatormikroskopie um mehr als 3200fach stärkere Messsignale, die zu einer Sensitivität für Extinktionsmessungen von 1.7 nm² und zu Frequenzverschiebungen aufgrund von Dispersion von weniger als 200 MHz, was der Verschiebung durch eine Glaskugel mit einem Durchmesser von 31.6 nm entspricht, führen. Darüber hinaus werden höhere Transversalmoden dazu verwendet, um die Ortsauflösung zu erhöhen. Durch die Kombination von Extinktionskarten, die mit der Grundmode und den darauf folgenden, höheren Transversalmoden aufgenommen wurden, ist eine signifikante Erhöhung der Ortsauflösung, gegebenenfalls sogar jenseits der Beugungsgrenze, möglich. Das Rasterresonatormikroskop ist zunächst für die Untersuchung von Nanoteilchen in einer trockenen Umgebung konzipiert worden. Viele Nanosysteme, darunter biologische Proben, zeigen ihre einzigartigen Eigenschaften jedoch erst in einer wässrigen Umgebung. Um den Untersuchungsbereich dorthin auszuweiten, wurde ein faserbasierter Resonator hoher Finesse mit einer mikrofluidischen Zelle kombiniert. Mit diesem System können nicht nur die Extinktion oder Dispersion von Teilchen gemessen, sondern auch Teilchen gefangen werden, um beispielsweise deren Reaktionsdynamik zu beobachten. In dieser Arbeit wird demonstriert, dass es möglich ist, einen Fabry-Pérot Resonator hoher Finesse in einer wässrigen Umgebung zu betreiben und es werden erste Messsignale von Teilchen, die den Resonator passieren, als auch vom Resonator gefangen werden, gezeigt. Dieses System, das optische Detektion mit einem kontrollierten Flüssigkeitsstrom vereint, öffnet Möglichkeiten für neuartige Experimente mit einzelnen, unmarkierten Nanosystemen.Nano is everywhere! All around us, there are nanoscaled systems such as in coloured glass, novel solar cells or in living beings. For a detailed understanding of the nanocosmos, studying it at a single particle level is indispensable, leading to deep and intriguing insights into a world that is at a first glance hidden to the eye. Optical spectroscopy of nanosystems at the single particle level provides profound insight into their physical and chemical properties. Retrieving quantitative signals for extinction as well as dispersion at this level is very challenging. At the same time it is desirable to investigate individual particles as they may vary in size, shape or composition. This work presents a spatially resolved method for simultaneous extinction and dispersion measurements of single nanoparticles. Harnessing thousands of round trips of light within an optical microresonator, the interaction of light with the particle gets enhanced and very sensitive quantitative measurements become possible. The cavity mode of a Fabry-Pérot cavity with a finesse up to 85 000 is used as a scanning probe to assess the extinction of nanoobjects placed into the cavity. The resonator consists of a micro-machined and high-reflectively coated end-facet of an optical fibre and a macroscopic plane mirror that serves as a sampleholder and that can be scanned transversally with respect to the fibre, allowing for spatially resolved measurements. Higher order transverse cavity modes are exploited to retrieve the cavity’s resonance frequency shift due to a particle inside. Combining both measurements allows to quantify the complex polarizability, which fully determines the particle’s optical properties at the Rayleigh limit. Extinction, dispersion and polarizability measurements of gold nanoparticles of various size and shape are presented in this work. Compared to diffraction limited microscopy, scanning cavity microscopy reaches a signal enhancement by a factor of more than 3200 resulting in a sensitivity for extinction of 1.7 nm² and for frequency shifts due to dispersion below 200 MHz which corresponds to the shift due to a glass sphere with a diameter of 31.6 nm. Furthermore, the higher order cavity modes are used to increase the spatial resolution of the scanning cavity microscope. By combining extinction maps taken with the fundamental and subsequent higher order modes, a significant increase in resolution potentially beyond the diffraction limit is demonstrated. The scanning cavity microscope is dedicated to investigate nanoparticles in a dry environment. Many nanosystems, especially biological samples, show their unique properties only in an aqueous environment. To extend the field of investigation to these nanosystems a fibre-based high-finesse microcavity has been combined with a microfluidic cell. This system would not only allow to measure the extinction or dispersion of a particle, but also to trap it to monitor e.g. reaction dynamics. In this work, the feasibility of bringing a high-finesse Fabry-Pérot cavity to an aqueous environment is demonstrated and first signals of trapping glass nanoparticles with the cavity mode as well as of particle transitions through the mode are shown. This combined system of optical detection and fluid control opens the perspective for novel experiments with label-free individual nanosystems