The paper presents a construction of a wireless hybrid data link operates applying two transmission channels using optical radiation (FSO – Free Space Optics) and radio one (RF - Radio Frequency). Based on some parameters (e.g. laser power, optics aperture, photodetector detectivity, signal bandwidth, beam divergence) of the link components, its data range was determined for various operating conditions (visibility and turbulence). Preliminary tests of the link prototype (TRL 6) were carried out at the Military Communication Institute, Poland. The results showed that the use of FSO/RF technology systems can provide the increase in data transmission security, link availability, and immunity to intentional interference. Considering the features of this technology, high applicable potential to military activities was observed.
Military wireless communication systems provide services using radio transmission technologies. However, this technology is exposed to modern radio-electronic warfare devices. In some operational scenarios, an application of laser data link (Free Space Optics - FSO) makes it possible to increase data transmission reliability and security. Such capability could be obtain using so-called hybrid FSO/RF communication system. The development of optoelectronic devices (lasers and photodetectors) operated in the spectral range of 8 – 12 μm (Long Wavelength Infrared Radiation - LWIR) enabled to construct a new FSO link. Compared to currently used FSO systems operating in 700-900 nm (NIR) or 1300 – 1550 nm (SWIR) spectral ranges, this link is characterized by less sensitivity to atmospheric phenomena (fog, mists or turbulences) and by greater difficulty of detection. The performed analyses shown that the use of FSO/RF technology systems can provide increase in data transmission security, link availability, secretiveness of operation, and immunity to intentional interference. The paper presents virtues of some wireless communication technologies based on radio, optical and hybrid system configuration. The status of the research on FSO link operated at LWIR wavelength range is also described. This study has been performed in the frame of LasBITer project financed by The Polish National Center of Research and Development. The developed optical data link is a unique device in relation to the FSO technologies available today, because of its operation in LWIR spectrum using quantum cascade lasers and HgCdTe detectors. Scenario of FSO/RF data link works in military operation is also presented.
In this paper, the study of AlInAs/InGaAs/InP Quantum Cascade Lasers application in Free Space Optical data link is performed. Implementation of such FSO link operated in long-wavelength infrared (LWIR: 8-12 μm) will be unique for construction of so-called RF/FSO hybrid communication system. The range of longer wavelengths provides better data transfer performance in the case of severe weather conditions, especially, fog, low haze or air turbulence. In the frame of this work, series of QCLs for application in FSO system were examined. They are characterized by different geometries and constructions towards best performance in optical link systems operated in the wavelength range of 8-12 μm. The preliminary test of QCLs included electrical measurements of pulsed light-current-voltage characteristics and time-resolved spectra. The obtained results made it possible to determine operation point for FSO. Their modulation performances were tested using the laboratory laser drivers. Based on measurements, both power and time parameters of QCLs pulses were investigated. These results defined critical values for FSO system. The second part of the analysis concerned the spatial parameters of QCLs radiation. Knowledge of spatial characteristics of emission is vital for FSO optics construction. To characterize spatial properties of beams, far-field patterns of emission were registered. Finally, the obtained results made it possible to optimize the optical transmitter construction and further performance of FSO laboratory model. This research was supported by The Polish National Centre for Research and Development grant DOB-BIO8/01/01/2016.
The paper presents some aspects of approach to construct an optical detection system for laser absorption sensing. These aspects concern a designing procedure of the system, starting with a photodetector, preamplifier, and ending with a signal processing. There is also discussed a project of integrated preamplifier which can be applied in Cavity Enhanced Absorption Spectroscopy (CEAS). In the preamplifier, boxcar method was implemented using integrated circuit (IC) of switched integrator and a special synchronous block. Taking into account an idea of CEAS operation, selected methods of the exponential signal analyzing are described and tested. The main task of the methods is to determine decay time of this signal. The results of these tests make it possible to define some virtues of the designed boxcar technique that could be useful in CEAS sensing instrument.
A laboratory demonstrator of the optoelectronic sensor employing cavity enhanced spectroscopy has been designed to detect the trace amounts of carbon monoxide. High sensitivity of this sensor is provided by the use of optical cavity consisted of dielectric mirrors with extremely high reflectance. The instrument concept was taking into consideration the latest achievement of optoelectronic technology as a part of the ‘EDEN’ project, funded by the Polish National Centre for Research and Development. Preliminary tests using the sensor concept have shown that detection of carbon monoxide is possible using the developed devices. In this configuration, the sensor is characterized by high linear sensitivity in the concentration range of 10 ppb to 2.5 ppm.
The aim of this paper is to address some of the aspects of thermal management of QCLs. Results include electrical and spectral characterization of the devices. Results show shift of QCL emission mode towards lower wavenumbers during the pulse. Characteristics were registered at different temperatures of operation and driving conditions. Registered shift rates depend on operating temperature, being the highest at room temperature. Based on spectral tuning results, temperature increase rates for different modes of operations were evaluated, delivering information on thermal dynamics of investigated devices.
The article describes an application one of the most sensitive optoelectronic method – Cavity Enhanced Absorption
Spectroscopy in investigation of nitric oxide in exhaled breath. Measurement of nitric oxide concentration in exhaled
breath is a quantitative, non-invasive, simple, and safe method of respiratory inflammation and asthma diagnosis. For
detection of nitric oxide by developed optoelectronic sensor the vibronic molecular transitions were used. The
wavelength ranges of these transitions are situated in the infrared spectral region. A setup consists of the optoelectronic
nitric oxide sensor integrated with sampling and sample conditioning unit. The constructed detection system provides to
measure nitric oxide in a sample of 0-97% relative humidity.
The article describes application of cavity enhanced absorption spectroscopy (CEAS) for detection of nitrogen oxides and vapours of explosives. The oxides are important greenhouse gases that are of large influence on environment, living organisms and human health. These compounds are also markers of some human diseases as well as they are emitted by commonly used explosives. Therefore sensitive nitrogen oxides sensors are of great importance for many applications, e. g. for environment protection (air monitoring), for medicine investigation (analyzing of exhaled air) and finally for explosives detection. In the Institute of Optoelectronics MUT different types of optoelectronic sensors employing CEAS were developed. They were designed to measure trace concentration of nitrogen dioxide, nitric oxide, and nitrous oxide. The sensors provide opportunity for simultaneous measurement of these gases concentration at ppb level. Their sensitivity is comparable with sensitivities of instruments based on other methods, e.g. gas chromatography or mass spectrometry. Our sensors were used for some explosives detection as well. The experiment showed that the sensors provide possibility to detect explosive devices consisting of nitroglycerine, ammonium nitrate, TNT, PETN, RDX and HMX.
The paper presents the new infrared detection module developed at the VIGO System Ltd. Its high sensitivity of was
achieved by both matching the IR detector to the preamp and minimizing noises. High sensitivity of the detector was
achieved by using photodiodes with immersion lens. Immersion lens enables optimization of the detector area,
decreasing detector capacity and time constant. Detector noise was reduced as a result of photodiode cooling by means
of a thermoelectric cooler and reverse biasing. Developed module is dedicated to NOx optoelectronic sensors operates
basing on Cavity Enhanced Absorption Spectroscopy technique.
The article describes an application of cavity enhanced absorption spectroscopy for nitric oxide and nitrous oxide
detection. Both oxides are important greenhouse gases that are of large influence on environment, living organisms and
human health. These compounds are also biomarkers of some human diseases. They determine the level of acid rain, and
can be used for characterization of specific explosive materials. Therefore the sensitive detectors of these gases are of
great importance for many applications: from routine air monitoring in industrial and intensive traffic areas, to detection
of explosives in airports, finally for medicine investigation, for health care, etc.
Our compact detection system provides opportunity for simultaneous measure of both NO and N2O concentration at ppb
level. Its sensitivity is comparable with sensitivities of instruments based on other methods, e.g. gas chromatography or
The paper presents a model of a free space optical transmitter operating in the wavelength range of 8-12 μm. In the
transmitter, a quantum cascade laser controlled by a special driver was applied. The driver provides the control of the
energy, repetition rate and duration of radiation pulses. In the described transmitter, generation of pulses with high duty
cycle is also provided, making it possible to use the data link with either RZ or NRZ coding. In the frame of the study,
the impact of laser working conditions on the data link operation was determined.
The paper presents a construction and some investigations results of a new driver for quantum cascade (QC) lasers.
The driver is designed to control pulse and CW mode QC lasers. For both laser mode operations, there is the possibility
to set a laser current in the range of 0.1 A - 3 A and pulse duration of 30 ns at the frequencies to the level of 25 MHz.
The stabilization of the temperature in the range of 50°C ÷ -30°C with accuracy of 1.5 K is also achieved. A full
synchronization with external pulses makes the driver very useful in a construction of a free space optical transmission
system and of a laser spectroscopy setup.
The paper presents an application of an optical parametric generator (OPG) for cavity enhanced absorption spectroscopy
(CEAS) technique to nitric oxide (NO) detection. The principle of this method is based on an injection of a radiation
beam into an optical cavity at a very small angle. The radiation is multiple reflected inside the resonator equipped with
spherical and high reflectance mirrors. After each reflection a part of the radiation leaves the optical cavity due to
residual transmission of mirrors. In the case of NO detection the laser emitting at around 5.26 μm was applied. During
investigation of CEAS system with OPG, two-lenses collimator was required to improve OPG beam divergence. The Ge
and ZnSe lenses were used. Thanks to this decrease of about three times in beam diameter was achieved (at the distance
of 1 m from source). It make it possible to measure output signal from the CEAS optical cavity.
The paper presents construction of broadband optical system devoted to free space optical communication using long
wavelength quantum cascade laser and a heterostructural thermally cooled HgCdTe photodetector. This system should
characterize with lower sensitivity to adverse meteorological conditions when compared with the systems operating
in near IR.
The paper presents a procedure and laboratory setup for calibration of extreme ultraviolet detectors. The procedure
determinates a responsivity of a photodiode applied in the technology of EUV radiation. The main elements of the
described system are a gas-puff laser plasma source, metrology chamber with an optical beam splitter and a model
instrument. The applied measurement method is based on a comparison of the detected signals from the model
instrument and the tested detector. The reduction of an error resulting from instabilities of the source radiation is
ensured using a special construction of the optical beam splitter. Because of the cost and the metrology features,
the presented setup is future alternative for small factories and laboratories producing EUV detectors. In the paper,
analysis and preliminary research of the setup are described.
We present the study of potential application of Cavity Enhanced Absorption Spectroscopy (CEAS) for
construction of fully optoelectronic and portable NO2 detector which could replace the commonly used chemical
detectors. We demonstrate an experiment on detection of NO2 in the ambient air. The concentration of investigated
absorber was found by determination of decay time of pulse radiation trapped in the optical cavity constructed with two
mirrors of a very high reflectivity coefficient (R > 99,99%). As a light source a blue pulsed diode laser was applied. The
output signal was detected by a photomultiplier and analysed by a digital oscilloscope. For this construction the detection
limit better than 1 ppb was obtained. The cavity parameters and it's adjustment were controlled by a beam from a red
laser that is not absorbed by NO2. In order to perform the measurements in two spectral regions the special mirrors have
been developed. Study of influence of another NOx compounds (especially NO3) on final result was investigated as well.
The paper presents a measuring system of extreme ultraviolet radiation pulses (13.5 nm). The system is used for
monitoring a gas-puff laser-plasma source constructed at the Institute of Optoelectronics. The radiation source and the
system are used in metrology of EUV optics. The system consists of a detection head and a system of optical filters,
which are housing in a special construction. Additional element of the measuring system is a special processing unit.
The measuring system was used during investigations of the plasma-laser optimization. The results were comparable
with the ones from a spectrograph and an Emon energy meter.
This paper presents application of Cavity Ring-Down Spectroscopy (CRDS) and Cavity Enhanced Spectroscopic (CEAS) techniques with blue laser diodes-based system for nitrogen dioxide (NO2) detection. CES technique bases on integration of the light from a resonator. Since the integrated intensity is proportional to the decay time, the experimental signal can be related to the absorption process. The minimum detectable concentration of the absorber for a specific transition is inversely proportional to the effective sample-path length, and directly proportional to the minimum intensity fluctuation detected by a receiving system. In the presented system, the blue laser diode was mounted in a temperature-controlled housing. The light transmitted through the cavity was focused onto a PMT of H5783-03 type. The detector signal enters a lock-in amplifier and next a computer with a 16-bit data acquisition board.
The paper presents a detection method of laser radiation using photoacoustic converter. Mathematical-physical model of
the converter and its numerical analysis is described. Influence of selected design factors and operation conditions
on a level of a voltage signal produced at a converter output was analysed. The results of theoretical investigations have
been confirmed by the experimental ones.
The paper presents analyses of a testing system of extreme ultraviolet detectors. The testing procedure concerns determination of a quantum efficiency of photodiode detectors. The testing method is based on a comparison of the detected signals from the model detector and the tested one The system consists of a gas-puff laser plasma source, a metrology chamber with an optical system, and a model energy detector. Theoretical and experimental investigations, including optimisation of efficiency and stability of the radiation source, calculation of a charge measurement accuracy of the model detector, determination of mirrors reflectivity and its angle dependence are discussed.
We present an experiment on detection of nitrogen dioxide in free air using cavity enhanced spectroscopy. As a light source a blue pulsed diode laser was applied, while the output signal was detected with a photomultiplier. The absorber concentration was found by investigation of the optical resonator quality. It was done by determination of decay time of radiation pulse trapped in the cavity. Also the measurement of the phase shift between the output signal and modulation signal was used as the alternative method. The detection limit better than 1 ppb was demonstrated. The aim of this experiment was to study potential application of cavity enhanced absorption spectroscopy for construction of fully optoelectronic NO2 detector which could replace the commonly used chemical detectors.
In the paper, we present UV-detection system and it¢s noise model. It consist of GaN photodiode produced by ITME in Warsaw, and low noise preamplifier. The Schotttky barrier MSM and p-π-n visible blind detectors on gallium nitride were used. The main purpose was to analyse the first stage of UV receiver (photodetector plus low noise preamplifier) to optimise them providing maximal value of signal-to-noise ratio.
The paper describes principles of minimization of noises in infrared detection systems. An analysis of operating conditions affecting signal to noise ratio (S/N) has been carried out. Many practical solutions have confirmed theoretical predictions.
The paper presents the results of investigations on emitter and photoreceiver system of a laser rangefinder operating within the range of eye-safe radiation. The aim was to achieve maximal value of a signal to noise ratio in a photoreceiver and peak conditions of a laser. Fast photoreceiver and laser transmitter are described.
High power continuous wave semiconductor lasers (P > W) on the market give a great possibility for use in many fields of technology as well as in medical applications. Due to high price and vulnerability, these sources of radiation require especially detailed elaboration of supply, control, and protection systems. This work presents supply, control, and protection systems of the high power cw laser for medical application. The methods of control and supplying of protection for semiconductor cw laser and thermoelectric cooler were particularly described.
The meter of average energy of holmium laser radiation is a digital measuring instrument, made on the basis of a pyroelectric detector and single-system microprocessor from the MCS- 51 family. This device enables a measurement of a defined number of light pulses, total energy of n-laser pulses as well as the number of pulses received by a detector. The frequency of sampling signal is 25 Hz, the accuracy of measurement is 5%. This meter also enables introducing the defined transmission coefficient (measurement at the back mirror of the laser resonator) to the measurement results as well as control of operation of the output diaphragm of the laser (TTL levels).
The laser coagulator is assigned to the coagulation of an eye retina. It has been built on the basis of semiconductor cw laser, SDL-2482 P1 type. The laser is integrated with the monitoring photodiode, thermistor, and thermoelectric cooler. The electronic system ensures a continuous work (cw) and pulse work of the coagulative laser. For the continuous work, the time of laser operation depends on how long the operator presses a pedal. Exposure duration is displayed at the time-meter. The pulse operation enables previous setting of pulse duration. Time of laser switch on can be regulated from 0 to 5 s with the resolution of 0.1 s. The output laser power is regulated continuously from 1 mW to 3 W and it is displayed at the power meter display. The laser controller is equipped in the series of systems protected against the exceeding of permissible work conditions.
This paper presents the influence of background radiation on the properties of SPRITE detectors, thermoelectrically cooled at 200 K and operated within the spectral range of 3 - 5 micrometers for detectors with the field of view ranging from 0 to 90 degree(s) and background temperature 300 K.