Bernard Journet

A low-cost laser range finder based on an FMCW-like method

The purpose of this paper is to present the prototype of a low-cost laser range finder. It belongs to the flight time measurement category. In this case, the time of flight is converted into a beat frequency proportional to the distance to be measured. This physical conversion is realized with an optical power modulation of the laser beam by a chirped wave. The experimental set-up is detailed with the main functional blocks. Experimental results are provided and the main possible improvements are discussed.

Refractive Index Measurement by Using an Optoelectronic Oscillator

The purpose of this letter is to present a preliminary experiment, showing that an optoelectronic oscillator can be used for measuring refractive index by detecting the change of the oscillation frequency. The uncertainty of the measurement is of about 10-2. However, this value can decrease to 10-3 or less if the mechanic vibrations, the temperature control of liquid, and the long-term stability of the oscillator are improved. Measurements have been performed for acetonitrile, acetone, dioxane, and chloroform at the wavelength of 1535 nm and at 25°C approximately.

A twofold modulation frequency laser range finder

The purpose of this paper is to present the conception of a twofold modulation frequency laser range finder. The system is based on the phase-shift measurement method with two modulation frequencies, one giving the distance within a wide range and a second one leading to high resolution measurement. The measurement method is based on intermediate frequency sampling associating the under-sampling technique with digital synchronous detection. Its main advantage is a global simplification of the electronic system, leading to a quite simple development and low cost system. There is only one phase-shift measurement stage but the twofold modulation frequency is possible thanks to the heterodyne technique. The emission and detection parts are designed for wideband operation and are digitally controlled. The whole system has been designed with only one digital phase locked loop reducing the phase noise and improving the resolution. Because of the global structure and the different digitally controlled parts the necessary calibration process could be introduced. From the design of the prototype it is possible to move towards a smart laser range finder.

Exact calculation of the optical path difference and description of a new birefringent interferometer

A new Fourier transform spectrometer is presented. The novelty of this work comes from the interferometer designed with two identical Wollaston prisms. Thus, the interferogram, formed at infinity in the spatial domain, is independent of the size of the source and of its position. In order to know the characteristics of the apparatus and especially its resolution, we propose the complete calculation of the optical path difference introduced by such an interferometer. Then, by associating the birefringent interferometer with a lens and a linear CCD sensor, we realize a spectrometer with a theoretical resolution about 230 cm-1. Finally, an experimental result is presented, proving the feasibility of the system.

A new laser range-finder based on FMCW-like method

A synthesis on laser range-finding techniques is first presented, giving the methods, the performance and the correlated applications. Then, a research in progress in our laboratory on a new laser range-finder method is focused on: the frequency beat detection, derived from the FMCW radar ranging technique. The beam intensity is modulated by a sine-wave wobulated by a chirped waveform, and final detection after mixing the emitted and echoing waves gives a frequency beat proportional to the distance. The experimental set-up is described in details with the main functional blocks. Experimental results and performance are finally discussed to find improvements and specific applications.

Novel MIMO antenna using Complementary Split Ring Resonator(CSRR) for LTE applications

A small multiband-printed antenna for multi-input and multi-output (MIMO) communication system using metamaterial structure is proposed as well as the whole concepts of miniaturization are introduced. To reduce the mutual coupling between two multi-band antennas, we develop a compact stop-band filter loaded with Complementary Split Ring Resonator Transmission Line (CSRR-TL) on ground plane. A resonant frequency obtained with high isolation value is f0 = 2.33GHz. Total small patch size is 0.20λ0 × 0.11λ0 with 1.6 mm thickness. The novel MIMO antenna for Long Term Evolution (LTE) is fabricated by using low cost FR4 (εr = 4.4) substrate. Both the simulated and measured results are shown to illustrate the performances of the proposed antenna.

Laser range-finding by phase-shift measurement: moving toward smart systems

The systems presented in this paper are based on phase-shift measurement. The first solution developed here is the heterodyne technique associated with direct counting. An improvement of the system consists in using digital PLL to reduce the phase noise. A second technique based on under-sampling technique, applied to digital synchronous detection, is described. Its main advantage is a global simplification of the electronic system, leading to a quite simple development of a twofold modulation system. This new technique is also very interesting to move towards a kind of smart range finder able to adapt different parameters to the different steps of the measurement.

Direct laser writing of polymeric nanostructures via optically induced local thermal effect

We demonstrate the fabrication of desired structures with feature size below the diffraction limit by use of a positive photoresist. The direct laser writing technique employing a continuous-wave laser was used to optically induce a local thermal effect in a positive photoresist, which then allowed the formation of solid nanostructures. This technique enabled us to realize multi-dimensional sub-microstructures by use of a positive photoresist, with a feature size down to 57 nm. This mechanism acting on positive photoresists opens a simple and low-cost way for nanofabrication.

Instrumentation system for determination and compensation of electro-optic modulator transfer function drift

This paper presents an instrumentation system developed to improve the operation of an electro-optic modulator (EOM). During their operating time, EOM are subject to a drift of the optical transfer function; therefore the initial tuning of the bias point no longer corresponds to the best characteristics of the device. Because of this drift the EOM no longer behaves linearly and there is degradation during time of the performances of the system in which the EOM is included. To determine the drift, a low frequency modulation signal (at 500 Hz) is applied to the EOM and the second harmonic component at 1 kHz is detected. A new criterion is introduced for estimating the nonlinearity and for compensating the drift of the transfer function, keeping the optical bias point at the quadrature position. Temperature changes significantly influence the EOM characteristics. Thus, the instrumentation system has to be simultaneously developed with temperature control and drift compensation of the optical transfer function. The design is based on PSOC microcontrollers for tuning the different parameters, for data acquisition and regulation process. By setting the temperature to some specific values, it is possible to test the behaviour of the modulator. Finally, by using both temperature and bias point control, a significant reduction of the nonlinearity can be obtained during 2 h of experiment: the biasing point at the quadrature point of the transfer function which corresponds to the most linear behaviour can be stabilized within ±0.22% of the half-wave voltage. All the works presented here were carried out with a Mach–Zehnder intensity modulator made of lithium niobate, but it is also possible to apply this method to other kinds of material, for example polymer material.

Time evolution of an electro-optic modulator by detection of its nonlinear behavior

The stability of an electro-optic modulator has been significantly improved by implementing an original temperature control system. In particular, the evolution of the modulator characteristics can be followed through its nonlinear behavior by detecting the second harmonic of a low-frequency modulation signal; the evolution can be investigated with a higher accuracy by measuring also the phase-shift of this harmonic signal. Two digital boards have been developed with PSOC microcontrollers. The first one is associated with a small power amplifier for the temperature control; the second board is used to analyze the behavior of the electro-optic modulator. By thermal control of the modulator it is possible to reduce significantly the drift of its optical bias point.