Anders Sig Olesen

Frequency Stepped Pulse Train Modulated Wind Sensing Lidar

In this paper a wind sensing lidar utilizing a Frequency Stepped Pulse Train (FSPT) is demonstrated. One of the advantages in the FSTP lidar is that it enables direct measurement of wind speed as a function of distance from the lidar. Theoretically the FSPT lidar continuously produces measurements as is the case with a CW lidar, but at the same time with a spatial resolution, and without the range ambiguity originating from e.g. clouds. The FSPT lidar utilizes a frequency sweeping source for generation of the FSPT. The source generates a pulse train where each pulse has an optical carrier frequency shifted a set quantity relative to the carrier frequency of the previous pulse. In the scheme presented here, the measured frequency depends on the distance from which the signal originates. The measured frequency is related to the Doppler frequency shift induced by the wind and an integer number of frequency shifts corresponding to a specific distance. The spatial resolution depends on the repetition rate of the pulses in the pulse train. Directional wind measurements are shown and compared to a CW lidar measurement. The carrier to noise ratio of the FSPT lidar compared to a CW lidar is discussed as well as the fundamental differences between the two systems. In the discussion we describe the most dominant noise sources in our system and what influences these have on the FSPT lidars ability to measure under different scattering conditions.

Spatial filtering velocimetry for real-time measurements of speckle dynamics due to out-of-plane motion.

This paper describes an optical spatial filtering velocimetry technique that converts an expanding or contracting speckle pattern into a photocurrent. This photocurrent will have a quasi-sinusoidal dependency on this specific speckle motion. The spatial filter consists of a series of concentric rings. Each ring divides the incoming light into two radial-wise, almost even contributions and directs them by refraction toward two half-rings of photodetectors. The corresponding two photocurrents are balanced and provide a differential photocurrent. In this paper the optical spatial filtering velocimetry technique is used to demonstrate real-time measurements of speckle dynamics due to out-of-plane motion.

Accurate simulation of Raman amplified lightwave synthesized frequency sweeper

A lightwave synthesized frequency sweeper using a Raman amplifier for loss compensation is presented together with a numerical model capable of predicting the shape of individual pulses as well as the overall envelope of more than 100 pulses. The generated pulse envelope consists of 116 pulses with constant peak power and no significant growth of noise. The numerical simulation is based on careful measurements of the physical properties of the individual components and a well established Raman amplifier model. Very good agreement between the measured and the simulated data is found.

Fast visual part inspection for bin picking

In this paper we present a novel 3D sensing approach for industrial bin-picking applications that is low-cost, fast and precise. The system uses a simple laser-line emitter. While a robot arm moves the object through the laser light, a synchronized camera captures the laser line image on the object. A full point cloud as well as an edge point cloud suitable for subsequent pose estimation is generated by the developed system. The aim of this work is to deliver an accurate point cloud based on which an object pose can be generated to support a manufacturing robot to deliver an object with high precision. The experimental evaluation of our system shows robust and accurate scanning results.

Spatial filtering velocimetry for real-time out-of-plane displacement measurements

We probe the dynamics of objective laser speckles as the axial distance between the object and the observation plane changes. With the purpose of measuring out-of-plane motion in real time, we apply optical spatial filtering velocimetry to the speckle dynamics. To achieve this, a rotationally symmetric spatial filter is designed. The spatial filter converts the speckle dynamics into a photocurrent with a quasi-sinusoidal response to the out-of-plane motion. The selectivity of the sensor relates directly to the uncertainty on sensor measurements. The selectivity most be derived from a temporal power spectrum of the photocurrent produced by this filter. This main contribution of this paper is a model, which describe the selectivity of the sensor, applied to speckle dynamics generated by an object moving out-of-plane. To motivate our interest in these filters we also present an all optical element which implements the spatial filter and experimentally demonstrate the ability of the technology to obtain displacement measurements of a vibrating object in real-time.

Sensing roughness and polish direction

As a part of the work carried out on a project supported by the Danish council for technology and innovation, we have investigated the option of smoothing standard CNC machined surfaces. In the process of constructing optical prototypes, involving custom-designed optics, the development cost and time consumption can become relatively large numbers in a research budget. Machining the optical surfaces directly is expensive and time consuming. Alternatively, a more standardized and cheaper machining method can be used, but then the object needs to be manually polished. During the polishing process the operator needs information about the RMS-value of the surface roughness and the current direction of the scratches introduces by the polishing process. The RMS-value indicates to the operator how far he is from the final finish, and the scratch orientation is often specified by the customer in order to avoid complications during the casting process. In this work we present a method for measuring the RMS-values of the surface roughness while simultaneously determining the polishing direction. We are mainly interested in the RMS-values in the range from 0 – 100 nm, which corresponds to the finish categories of A1, A2 and A3. Based on simple intensity measurements we estimates the RMS-value of the surface roughness, and by using a sectioned annual photo-detector to collect the scattered light we can determine the direction of polishing and distinguish light scattered from random structures and light scattered from scratches.

Fast and cheap prototyping of nonstandard optical components for sensing speckle dynamics

As a part of the work carried out a project supported by the Danish council for technology and innovation, we have investigated the option of smoothening standard CNC machined surfaces. In the process of constructing optical prototypes, involving custom-designed optics, the development price and time can become a prohibitively large part of a research budget. Machining the optical surfaces of a molding tool may be done directly using diamond turning, but it is expensive and time consuming. Alternatively, a more standardized and cheaper machining method can be used, however, calling for manual polishing afterwards. Particularly, this last process is expensive as well, and will introduce an uncertainty in precisely how much material the polishing process will remove, introducing roughness on a larger lateral scale, such as waviness. Therefore, we have investigated the possibilities of smoothening surfaces of various shapes succeeding a standard CNC machining process. Different coatings have been tested for their abilities to fill and smoothen out structures of larger scales, while removing the small-scale roughness, which is critical for optical uses. In this work we will present an optical element, designed for optical spatial filtering velocimetry. The spatial filter is the key component in an optical sensor for non-contact measurement of surface vibrations, based on speckle dynamics. The optical element is casted in silicon. The results of smoothing an optical element will be demonstrated, and the sensor will be demonstrated for real-time measurements.

Analytic model utilizing the complex ABCD method for range dependency of a monostatic coherent lidar

In this work, we present an analytic model for analyzing the range and frequency dependency of a monostatic coherent lidar measuring velocities of a diffuse target. The model of the signal power spectrum includes both the contribution from the optical system as well as the contribution from the time dependencies of the optical field. A specific coherent Doppler wind lidar system measuring wind velocity in the atmosphere is considered, in which a Gaussian field is transmitted through a simple telescope consisting of a lens and an aperture. The effects of the aperture size, the beam waist position, and pulse duration are analyzed.

Wind Sensing Doppler LIDAR, Improving Wind Turbines

In recent years, the focus on alternative energy has grown and with that the interest in optimizing of known alternative energy sources. It has been shown by Catch The Wind inc. that wind sensing Doppler LIDAR mounted on a wind turbine can be used to optimize the performance of wind turbines up to 10%. This project investigates a novel technique of Doppler LIDAR and its pros and cons. In addition to this, other uses of the LIDAR will be investigated. This could be temperature measurements, ash detection, or detection of atmospheric composition such as CO2 concentrations.