bluuebunny/crossref_metadata_2025 huggingface dataset:
Integrated MQW DFB laser/EA modulator with low chirp for high-speed transmission systems
Authors: Satzke K. , Baums D. , Hache C. , Haisch H. , Klenk M. , Kühn E. , Schilling M. , Weber J. , Zielinski E.
Published: February 2023

High-speed long haul fibre transmission systems have found considerable interest in low chirp sources operating in the 1.55 µm wavelength region. This is because intensity modulation is accompanied by wavelength chirp, which in conjunction with fibre dispersion causes a penalty in bit error characteristics. Integrated multiquantum well DFB lasers/electroabsorption modulators (EAM) have shown their potential as high-speed low chirp sources for fibre transmission systems. Details on design, fabrication, and highspeed system performance of such integrated sources for digital high-speed transmission are presented.
Large scale application of multi-quantum-well reflective modulators for analogue lightwave links
Authors: Via C. Da , Vasey F. , Glick M.
Published: February 2023

Lightwave links will constitute a key issue in the front-ends of tracking detectors in the experiments at the Large Hadron Collider (LHC) presently under study at CERN, the European particle physics laboratory. The very large number of detector channels (over 10 M) will be preprocessed in the front-end electronics and multiplexed into fiberoptic links to readout stations at a distance of about 100 m. The severe constraints on the devices installed on the particle detectors include radiation hardness (10 Mrad and neutron fluence of 1014 n/cm2 over 10 years), low power dissipation (a few mW per channel), small size and low mass, minimum cabling bulk.1 Very limited accessibility will be possible only during machine shutdown periods.
Low-loss waveguide propagation characterization by high accuracy interferometric measurement technique
Authors: Feuchter Thomas , Thirstrup Carsten
Published: February 2023

In this paper a high precision measurement technique based on measuring the contrast of a Fabry-Perot cavity containing the optical waveguide is demonstrated. A similar approach has been employed for high index waveguides,1,2 but in the technique described here, the cavity has been extended by two optical fibers with a dielectric coated mirror on one end of each fiber and the other end coupled to the waveguide as shown in Fig. 1. The dielectric mirrors enhance the cavity finesse, leading to improved measurement accuracy. By changing the length of one of the fibers; either by heating a section of the fiber or by stretching it using a piezo-electric element, the optical length of the cavity is changed and the transmission characteristic exhibits Fabry-Perot resonances with maxima and minima as predicted by the Fabry-Perot intensity transmission equation.3 The modified reflection coefficient, R' = R exp(–αtot) can be calculated from the measured contrast K = (Imax – Imin)/(Imax + Imin), Imax and Imin being the maximum and minimum transmitted optical intensity, respectively. As the mirror reflection coefficient, R, is known, the total propagation loss αtot can be determined in this way.
Suppressions of signal spectral broadening and fading using a phase-conjugator at midway in amplified lightwave systems at zero-dispersion
Authors: Zhang Xiupu , Ebskamp F. , Jørgensen B. F.
Published: February 2023

Simulations have shown that the combined effect between the self-phase modulation (SPM) or Kerr nonlinear effect of fiber and accumulated amplified spontaneous emission (ASE) noise of in-line amplifiers in long-haul amplified systems at zero-dispersion degrades the system performance. On the one hand it leads to large broadening of the signal spectrum due to random phase modulation.1,2 On the other hand it causes the decay of the signal magnitude with exponential of a cubic power of the propagation distance.2 It is well-known that using a phase conjugator at mid-way can reduce the effects of the chromatic dispersion and self-phase modulation along a dispersive fiber. In this letter we show that using a phase conjugator can reduce the combined effect of the ASE noise and SPM; on the one hand it reduces the signal spectral broadening, on the other hand it reduces the fading of the signal magnitude.
Soliton amplification in inhomogeneously broadened fiber amplifiers
Authors: Martí-Panameño E. , Vysloukh V. A. , Torres-Cisneros G. , Torres-Cisneros M. , Sánchez-Mondragón J. J.
Published: February 2023

The use of EDFA with inhomogeneously broadened line (IBL) allows the amplification of multiplexed signals. It is known that in a fiber amplifier with IBL, the channels could be independently amplified by each other. The wavelength division multiplexing (WDM) technique could offer significant economic performance advantages for a network through improved capacity, reliability, and transparency. Up to now there are great advances in the study of WDM fiber systems.1,2
Laser-generated surface acoustic waves in material processing
Authors: Kolomenskii A. , Maznev A. , Mikhalevich V.
Published: February 2023

Intensive surface elastic pulses of short duration can be excited in a sample by focused laser radiation. Laser generation can produce much higher accelerations of the surface than conventional techniques. If the local acceleration and inertial forces exceed the adhesive and friction forces, the surface acoustic wave (SAW) pulse can push particles along the direction of propagation and detach them from the surface. This opens the opportunity to develop dry cleaning technology that may be used also in vacuum.
CO2 laser induced microcracking of glass and the analysis of ablation products
Authors: Allcock G. , Dyer P. E. , Snelling H. V.
Published: February 2023

TEA CO2 and modulated c.w. CO2 lasers are now commonly used to mark packaging materials by stencil mode projection and dot writing, respectively. In particular, glass containers can be marked directly by a combination of surface crazing and material removal. In order to help optimise this process and evaluate the possible debris, we have analysed the stress-stain state of laser irradiated glass using thermoelastic equations.1 Frozen-in stress caused by the thermal cycling of the material through a low-viscosity regime has been identified as the most likely cause of laser induced microcracking (Fig. 1). Studies of the laser irradiated area by x-ray fluorescence and emission spectroscopy of the luminous plume also indicate a loss of, in particular, sodium from soda-lime glass. This change in stoichiometry may be a complementary mechanism for the precipitation of surface crazing. Observed time delays before cracking begins are broadly consistent with the typical cooling time of the glass and are of the order ≈10−3 s. Similarly, surface features recorded by scanning electron microscopy suggest that crazing occurs after the viscosity of the glass has returned to its room temperature value. However, cracking may not occur at this time but may only happen when initiated by stress enhancement (surface defects, handling, etc.). Soda-lime glass has been observed to craze consistently at fluences ≥1 Jcm−2 when irradiated by TEA CO2 lasers.
Polishing of high Tc films by KF laser
Authors: Sobol E. , Sviridov A. , Bagratashvili V. , Burimov V.
Published: February 2023

Laser polishing of thin YBaCuO films has been observed for the first time. It was established that the threshold for laser ablation of HTSC films depends on the their thickness. The processing of films with an excimer laser at a certain level below the threshold can significantly reduce the surface roughness. Measurements of the optical properties of YBaCuO films before and after the laser treatment, combined with a subsequent annealing in an oxygen atmosphere, revealed that the modification of the thin films by the excimer laser can be either reversible or irreversible. An explanation for the observed effect is presented on the basis of the analysis of the various ablation mechanisms of HTSC. The novel low-energy ablation mechanism is studied. That mechanism is connected with the macroparticles ejection due to the pressure oscillation of oxygen liberated in the course of the laser-assisted HTSC thermodecomposition. The theoretical model for the calculation of macroparticle size and velocity is developed.
Selective ablation of the amorphous silicon layer by the second-harmonic wave of the TEA CO2 laser
Authors: Sumiyoshi Tetsumi , Ninomiya Yutaka , Shiratori Akira , Obara Minoru
Published: February 2023

TEA CO2 lasers operate efficiently with high output energy and are expected to open up new applications in the industrial field. The TEA CO2 laser can oscillate at a single line between 9 and 11 µm with a high peak power pulse which is strongly absorbed by a vibrational- rotational line of the organic polymer materials. The efficient ablation of the organic polymer materials such as polyether ether ketone and polyether sul- phone by single line selected TEA CO2 lasers was successfully demonstrated.1
Debris elimination in a laser plasma soft x-ray source
Authors: Rymell L. , Hertz H. M.
Published: February 2023

A major drawback of laser-plasma soft x-ray sources is the emission of debris. Thus, fragile components must be positioned far away from the source, resulting in low x-ray flux. We have investigated two debris shields: localized miniature gas jets and thin aluminium films. Both methods are developed to eliminate the residual debris from the droplet target laser-plasma x-ray source.1 This 10-Hz, high-brightness, line-emitting source utilises 10-µm ethanol droplets as target. The source produces 200300 times less debris than other low-debris targets, such as the thin film tape target.2 Furthermore, the debris seems to be dominated by ions and very small clusters while larger fragments are significantly reduced. This allows efficient debris elimination by two simple methods that both show high transmission for x- rays in the water window.
Measurement of SEW phase velocity by heterodyne interferometry method
Authors: Trubaev V. V. , Makin V. S. , Libenson M. N.
Published: February 2023

The surface electromagnetic wave (SEW) attenuation coefficient determined by the imaginary part of the SEW wave vector kiilb is generally measured to obtain information concerning the optical properties of metal surface layers and thin films by SEWs. However, the essential information can be obtained by measuring the real part of kiilb, which determines the phase velocity v by the relation v = ω/ Re(kiilb), where ω is the SEW frequency. Thus, for example, Re(kiilb) is directly determined by plasma frequency ωP for the case when -γ, ω ≪ ωP, where γ is the collision frequency. In the middle infrared, where the use of SEWs is particularly attractive due to large propagation distance, Re(kiilb) differs insignificantly from a bulk wave number kiilb = ω/c, and therefore measuring it is a problem. Schemes have been suggested1,2 where the interference of SEW and bulk radiation launched by the SEW were considered for measuring Re(kiilb). Such schemes have some disadvantages. In the present method for measuring Re(kiilb) the interference of SEW and the bulk radiation propagating along the surface of a sample is also used. However, unlike the usual methods, the bulk radiation is directed along the surface of the sample in the SEW propagation path from a laser. This enables the bulk radiation directed along the sample surface to pass first through a modulator that shifts the laser radiation frequency by the value Δω ≪ ω, and the optical heterodyning method can be used to determine Re(kiilb) and corresponding SEW phase velocity.
Range control system for robotically manipulated optical fibre beam delivery systems
Authors: Abdullah Hussein A. , Chatwin Chris R. , Huang Ming-Yaw
Published: February 2023

Consistent, repeatable high quality materials processing, using fibre optically delivered Nd3+:YAG Laser radiation requires precise local control of stand-off distance. Unless specifically designed for laser processing applications, many robots produce a jerking incremental trajectory and usually suffer from position dependent displacement of the end effector. With the addition of a focal height servomechanism the high-bandwidth optical range sensor described herein allows the use of such robots for fibre manipulation and hence facilitates high quality laser cutting and welding operations using equipment that may already exist. Radiation from a low power laser beam is focussed onto a workpiece surface, light reflected from the surface is collected through a main lens and directed into an imaging lens, which focuses the signal to two positions after being split by a beam splitter. The irradiances of the two beams are detected by photodiodes placed behind pinhole apertures positioned fore and aft of the two focal positions. A differential amplifier is used to generate an output signal that determines the magnitude and direction of any workpiece displacement. The system facilitates a measuring range of ±6 mm, its effectiveness in controlling the stand-off distance for laser materials processing applications is assessed.
Selective sensors to monatomic mercury and hydrogen based on the effect of surface plasmon-polariton resonance
Authors: Alimov O. A. , Kononov M. A. , Mikheev A. A. , Valjansky S. I. , Vinogradov S. V. , Savransky V. V.
Published: February 2023

Development of sensor on different environment pollution deals with the solution of two main problems. The first problem is the choice of sensitive element to the given pollution. The second problem is the application of such registration methods that are sensitive enough to detect the change of sensitive element condition after interaction with pollution. Our sensor operation is based on the measurement of change of surface plasmon polariton (SPP) dispersion, which is proportional to the number of pollution molecules added to sensitive element.
Simple fiber-optic autocollimation refractometer
Authors: Ilev I. K.
Published: February 2023

Combining the possibilities of the widely applied conventional autocollimation method for determining the refractive index of optical crystals1 and the possibilities of the fiber-optic refractometers2 leads to the creation of fiber-optic autocollimation refractometers featuring a simplified principal scheme, improved parameters, and possibilities for measuring the refractive index and dispersion of solid-state and liquid optical materials.
Electromagnetic field resonance at the interface of two concentric spheres
Authors: Kai Li , D'Alessio A.
Published: February 2023

For homogeneous spheres irradiated by infinite, electromagnetic plane waves (Fig. 1), existence of extremely strong sharp maxima in the extinction efficiency curves as a function of size parameter was found analytically by the so-called Mie theory for a long time.1 Excellent coincidences of the maxima of the calculated extinction efficiency as a function of wavelength for a homogeneous sphere with the spikes on the spectra of a laser power to levitate a homogeneous spherical particle at a fixed height when varying the wavelength of the laser beam have been found.2,3 Since the volume averaged electric density inside a sphere at a resonant state is several orders higher than that inside a sphere at a nonresonant state,4 even a laser beam of small intensity may cause nonelastic emissions. In fact, spikes on spectra of fluorescence emission and stimulated Raman scattering coincide excellently with the maxima of the calculated extinction efficiency spectra by using the Mie theory.3 According to Chylek,4 the basic period (Δx) of the double-peak structure on the Q
ext
- x curve is a monotonous function of refractive index m, given that x≫1, where the size parameter is defined by x = 2πα/λ, λ is the wavelength. Thereby, the MDRs have been used to measure sizes and refractive indices of spherical particles and optical fibres with an accuracy several orders higher than any other optical methods. The MDRs is seen to be a powerful tool in the field of particle characterisation.
Fast recognition of Young's fringe images via the indirect radon transform
Authors: Shapiro Vladimir A. , Kavardjikov Vassil I.
Published: February 2023

The Young's fringe images are a secondary product of speckle photography and particle image velocimetry techniques. The latter are utilized in experimental mechanics for measuring in-plane displacement fields of the specimen surface observed. Two exposures are recorded on a photograph, which is then probed by a narrow laser beam point by point, yielding the fringes with a certain spacing and orientation angle, which are subjects of recognition. The same fringes can be obtained digitally by a computer.
The timing jitter suppression of subpicosecond optical solitons during their transmission over long distant fibre
Authors: Luchnikov Alexander V. , Mel'nikov Igor V.
Published: February 2023

Limitation of the transmission rate in optical soliton high bit rate (5 Gbits/s and higher) and ultralong (up to 10,000 km) information transmission systems is mainly due to soliton timing jitter, which is concerned with interaction of solitons with the spontaneous noise of optical amplifiers (Gordon-Haus effect)1 and electrostrictional soliton long-range interaction.2 The methods of the soliton timing jitter suppression were proposed.3,4 Similar problems arise when teraherz sequence of subpicosecond solitons have to be transmitted through long fibre of up to 100 km length. In this paper we propose the original method of the timing jitter suppression of subpicosecond solitons. The method is based on the soliton frequency stabilization due to the joint action of differential spectral amplification of soliton and Raman self-frequency shift.
Infrared optical detectors operating in the 1.7- to 3-µm range based on lnxGa1−xSb for environmental gas-sensing
Authors: Mansoor F. , Haywood S. K. , Stavrinou P. N. , Mason N. J. , Nicholas R. J. , Walker P. J. , Hill G.
Published: February 2023

Devices operating in the 2-5 µm region are of potential importance for use in environmental sensing applications. Atmospheric pollutants such as CO, SOx, and NOx show absorption bands in the 2-5 µm range and passing any of these between a light source and detector will show a change in the detector signal. Strain-balanced GaSb/GaxIn1−xSb quantum well structures are being investigated to cover the 2-3 µm region grown on relaxed GaxIn1_xSb buffer layers. These provide low-strain structures while engineering the bandgap to realise the wavelength of interest. This paper is concerned mainly with the detector structure rather than the design of the active region. Hence bulk GaSb is used as the active region in some of the devices designed to ascertain the efficiency and sensitivity enhancement achievable from resonant structures.
Spectral selective (λ. = 1.06 µm) infrared detectors and quadrants
Authors: Dorogan V. , Snigur A. , Brinzari V. , Kosyak V. , Korotchenkov G.
Published: February 2023

In this paper were examined the results of a scientific investigation, which direct the research of selective photocells with sensitivity in the region 1.06 µm. At the same time we solved the problem of creation for both the quadrants for optical orientation in the air-space and photocells with low dark current and little capacity, which can fulfill the part of IR photodetectors with high detected ability.
Phase zone plate smoothing - theory and optimisation
Authors: Pepler D. A. , Bett T. H. , Danson C. N. , Ross I. N. , Stevenson R. M. , Rivers S.
Published: February 2023

The far-field intensity distributions of high-power laser systems play a critical role in determining beam-plasma coupling. Targets requiring large-area illumination have been placed in the quasi- near-field where the coherence of the beam produces a nonuniform and deeply modulated intensity distribution.
Comparison of analytical methods and simulation of optically preamplified receivers
Authors: Ribeiro L. B. , da Rocha J. R. F. , Ribeiro R. F.
Published: February 2023

Significant progress has been made concerning the statistical characterization of direct detection optically amplified communication systems1,2,4 Using the moment generating function of the electric current at the decision instant, optimum decision threshold as well as bit-error-rate (BER) estimates can be obtained.
The novel polarizing optical element
Authors: Bel'tyugov Vladimir N. , Protsenko Sergei G. , Leis Alexander V.
Published: February 2023

In recent years, the holographic optical elements (HOE) have been the subject of a great deal of interest. The HOE were found to possess the new optical properties.1,2 These elements are used in different spectral devices as narrow-band spectral filters, spectral-selective laser mirrors, etc.3 In this paper the novel polarizing optical element (POE) based on HOE is suggested.4
A comparison of material systems for quantum well 1.55 µm micro-resonator modulators
Authors: Guy P. , Woodbridge K. , Hopkinson M.
Published: February 2023

In designing the modulator we have considered separately the design of the mirrors and the active region.
Arrays of light emitting diodes with integrated diffractive microlenses for board-to-board optical interconnect applications: design, modelling, and experimental assessment
Authors: Dhoedt B. , De Dobbelaere P. , Biondelle J. , Van Daele P. , Demeester P. , Neefs H. , Van Campenhout J. , Baets R.
Published: February 2023

As the availability at low cost of array components is of crucial importance for the large-scale application of a number of parallel optical interconnect schemes, considerable research effort has been spent to design and model source-arrays offering properly shaped, collimated beams.1,2 In this framework, LED-arrays with diffractive lenses etched into the rear substrate side were fabricated for a board-to-board (a few mm) highly parallel (pitch 250 µm to 500 µm) free-space optical interconnect application (Fig. 1). The diffractive lenses were designed to image the LEDs at a distance of 2.5 mm behind the lens plane.
A comparative study on the clamped linear electro-optic effect in organic and inorganic crystals
Authors: Schiesser R. , Bernasconi P. , Bosshard Ch. , Zgonik M. , Günter P.
Published: February 2023

It is well known that the extraordinary large linear electro-optic effect in inorganic crystals of the perovskite class (e.g., BaTiO31, KNbO32) is significantly influenced by acoustic phonon contributions. The electro-optic response of these materials shows a strong dependence on the frequency of the applied electric field. The largest of the clamped electro-optic coefficients r
s
(valid at high modulation frequencies) is typically reduced to half of the unclamped effect (r
T
) occurring at low frequencies.
Conical diffraction in two-dimensional thin phase gratings
Authors: Kwak Chong Hoon , Suh Ho Hyung , Lee El-Hang
Published: February 2023

The diffraction of electromagnetic waves from a periodic structure has been intensively investigated both in classical and conical (off-plane) diffraction mountings.1−3 In this paper, we present the multiple diffraction rings of a two-dimensional planar phase grating (so-called Dammann grating4) for the conical diffraction mounting and propose a simple method for measuring the unknown period of the grating as a possible application. Consider a unit amplitude plane wave incident on a two-dimensional (cross) surface-relief grating at a spherical angle (θ1,ϕ1), as illustrated in Fig. 1: where the components of the incident wave vector k1 are (αo, — ßo, —γoo) = kon1 (sinθ,cosϕ1, —sinθ1,sinϕ1, —cosθ1, ko is the wave vector in vacuum, and ni is the refractive index of regions 1 and 3.
High-capacity transatlantic communications using soliton pulse-position modulation and sub-band coding
Authors: Arnold J. M.
Published: February 2023

All recent proposals for transatlantic soliton communication systems have assumed digital ASK as the modulation format, with the result that their capacity is limited by Gordon-Haus noise and intersoliton interactions. In this paper it is argued theoretically that pulse-position modulation (PPM) can achieve high transatlantic capacities by coding for immunity against intersoliton interactions.
Silicon implanted oxide multifunctional optical switches for smart pixel arrays
Authors: Thienpont H. , Peiffer W. , Veretennicoff I. , de Tandt C. , Randson W. , Vounckx R. , Koster A.
Published: February 2023

In this paper we report on the progress which has been made in the fabrication and use of 2-D optical logic planes consisting of silicon hybrid electrically assisted thermo-optic resonators (HEATORS).1
A high speed optoelectronic adder
Authors: Shu C. , She T. C. , Tam K. C.
Published: February 2023

Optoelectronic logic units have attracted much research interest1 owing to their potential applications in optical computing and optical signal processing. A simple way to implement the logic structures is by the use of metal-semiconductormetal (MSM) photodetectors.2 We have designed and fabricated logic gates including AND, OR, NAND, exclusive-OR (XOR), and exclusive-NOR (XNOR) on GaAs. A high-speed optoelectronic serial adder is also constructed from a combination of AND, OR, and XOR units.
Control of the polarization state of a vertical cavity surface emitting laser using polarized feedback
Authors: Robert F. , Besnard P. , Stéphan G. M. , Paddon P. , May A. D. , Vakshoori D.
Published: February 2023

Switching techniques with coherent optical sources are a challenge for telecommunications. One technique is to control the polarization eigenstate of the laser. We have examined the stability of polarized modes in quasi-isotropic laser, such as He-Ne laser at 3.39 μm1 and have proposed a general anisotropy model with applications.2 To test our calculations we have used He-Ne lasers as they are easy to construct in-house and are systems for which all the important parameters are known. For practical applications, however, it is clear that one must use more compact lasers, such as miniature solidstate lasers or semiconductor lasers. To control the polarization eigenstate of such a laser with Polarized Optical Feedback (POF), we need sources, which can run single mode and have weak anisotropies. Possible candidates that satisfy these criteria are microchip Nd:YAG lasers and Vertical Cavity Surface Emitting Lasers.3 However, the orientation of their polarization can vary from laser to laser. That could be a sign of weak anisotropy as the polarization states of quasi-isotropic lasers are highly sensitive to residual cavity anisotropies (most likely strain left during the fabrication process). Previously, we reported on the control of the polarization eigenstates of microchip YAG lasers using POF.4 Here we focus our study on adding POF in order to control the polarization eigenstate of gain-guided VCSELs. A schematic diagram of the experimental setup is shown in Fig. 1.
Optically controlled quantum well light modulator
Authors: Pelekanos N. T. , Deveaud B. , Gravey P. , Clérot F. , Gérard J. M. , Hebling J. , Kuhl J.
Published: February 2023

In this report, we present preliminary results on a light modulator based on the Quantum Confined Stark Effect (QCSE)1 but for the first time operating all-optically. The principle of operation of the device is as follows: every period of the heterostructure contains three quantum wells (QWs) designed in such a way that following above band-gap photoexcitation a large fraction of the photogenerated electrons and holes tend to separate and accumulate in the exterior QWs, creating a local space-charge field having its maximum in the region in between and acting via the QCSE on the exciton resonance of the central QW.
An approach to visual cortex operation: optical neuron model
Authors: Martín-Pereda J. A. , González-Marcos A.
Published: February 2023

Several works have been published in the last years concerning the modelling and implementation of the visual cortex operation. Most of them present simple neurons with just two different responses, namely inhibitory and excitatory. Some of the different types of visual cortex cells are simulated in these configurations.
Electro-optic, dielectric, and elasto-optic properties of photorefractive BaTiO3 crystal
Authors: Zgonik M. , Bernasconi P. , Günter P.
Published: February 2023

Measurements on high quality samples of top-seeded-solution-grown crystal BaTiO3 have been performed in order to complete the set of data, which is necessary to describe the optic response of this material to electric fields and elastic deformation.1 Improvements in the accuracy of some previously published results could be obtained because of better optical quality and larger size of the crystal samples that are available nowadays. The most important results are the values and the signs of the piezoelectric coefficients d311 and d333, the absolute values of the elasto-optic coefficients, and all the electro-optic measurements. Both low frequency electro-optic measurements in a stress-free sample and the measurements in the inertia-clamped samples using a step-like electric field were used to correct the previous results. The complete set of material parameters of the BaTiO3 crystals at room temperature has been afterwards determined by a numerical fitting procedure. The signs of the elasto-optic coefficients could also be determined with great confidence. We propose that the new calculated values are used as a consistent set of material parameters of the BaTiO3 crystal, in particular for describing its photorefractive properties, that is, to calculate its effective electro-optic and dielectric properties.
Brillouin fiber temperature sensor using two axial laser modes
Authors: Czarske J. , Müller H.
Published: February 2023

We present, for the first time to our knowledge, the use of axial laser modes in distributed temperature sensing based on stimulated Brillouin scattering. One axial mode stimulates a Stokes wave1 with a temperature dependent frequency shift in the 13-GHz range. Optical heterodyning of the stimulated Stokes wave with a second axial laser mode allows to generate and evaluate a beat signal in a lower frequency range. Using a Nd:YLF laser we have reduced the Brillouin beat frequency from the 13-GHz range to the 470-MHz range. Hence, low cost detectors and conventional signal processing techniques can be applied for beat signal processing.
In-line fibre-optic wavelength meter for sensing/monitoring applications
Authors: Tam Hwa-Yaw , Demokan Muhtesem Suleyman
Published: February 2023

The measurement of optical wavelength is generally performed by expensive and bulky optical spectrum analyzers. These instruments are not suitable to be employed as a dedicated or built-in device for monitoring/measuring wavelength in most optical sensing/monitoring applications.
Design and experimental optimisation of an evanescent-field fibre-optic refractometer
Authors: Fawcett Gordon , Johnstone Walter , Yim W. L. K.
Published: February 2023

A sensor architecture based on resonant evanescent coupling between a side polished single-mode (cut-off 1200 nm) fibre and a high index overlay waveguide is reported. A polarisation dependent channel dropping filter with an inverse response of a Fabry-Perot is exhibited by the structure. It is found that the resonance position (with respect to wavelength) is dependent on the refractive index of the superstate. This effect is utilised to demonstrate highly sensitive refractometry in an pseudo-continuous all fibre form. The device is constructed by spin coating a thin film (approximately 2 μm) of polymer (refractive index 1.6) onto a polished fibre half coupler, and curing this to form an asymmetric directional coupler. A thin protective coating of dielectric is then deposited on top of the polymeric waveguide. Various index matching oils are then placed on top of the structure (Fig. 1) and the effect on resonant wavelength position noted.
Measurements of nonlinear properties on semiconductor-doped sol-gel films
Authors: Fick J. , Vitrant G. , Pelli S. , Righini G. C. , Guglielmi M. , Martucci A.
Published: February 2023

Thin silica-titania planar waveguides doped with cadmium sulphide have been prepared on fused silica substrates using the sol-gel technique. Tetraethoxisylane (TEOS) and titanium butilate Ti(n-OBu)4 (30%) were used as precursors of the film.1 The semiconductor dopants have been introduced by adding cadmium nitrate and thiourea to the starting solution as precursors of cadmium and sulphur, respectively. The films have been produced by dipping the samples in the solution and withdrawing them at constant speed. Thereafter the samples have been densified at 300°C for 4 hours in nitrogen atmosphere in order to prevent outdiffusion of the dopants. The thickness of the films is typically about 1300 A and their refractive index is 1.63 at 633 nm.
Interactions of system requirements and laser design of Nd:YAG microcrystal lasers for absolute distance measurements
Authors: Schmitt N. P. , Bechstein K.-H. , Fuchs W. , Salewski K.-D.
Published: February 2023

Absolute measuring of distances larger than 10 m with an uncertainty of far less than 10-5 by laser interferometry points to a specific problem: The short optical wavelength makes a high precision feasible, but for absolute distance information the required wavelength has to be much longer. A well-known solution of this problem is to take use of multiple optical wavelengths to generate synthetic microwaves in a heterodyne arrangement.1 An alternative system we built in contrast is based on tunable solid-state lasers. It allows to tune one laser source against a reference laser about Δv = 0.60 GHz, generating a tunable synthetic wavelength2 of many meters down to 5 mm. Assuming a phase measuring uncertainty of 10-3 yields in a length measuring accuracy of 5 μm, which will match the requirements mentioned above.
Single-frequency operation of the diode-pumped partially inhomogeneously broadened Nd3+:GdVO4 laser
Authors: Sorokin E. , Sorokina I. , Wintner E.
Published: February 2023

In recent years a new simple method of single-frequency operation of solid-state lasers has been realized1 and studied theoretically.2 The technique requires short absorption length at pump wavelength and purely homogeneously broadened laser transition. In this paper, we report about single frequency operation experiments and theoretical consideration of a laser with partially inhomogeneously broadened line.
Comparison of neodymium-doped LaSc3(BO3)4 and CdVO4 crystals under diode laser pumping
Authors: Ostroumov V. G. , Jensen T. , Meyn J.-P. , Huber G. , Tsvetkov V. B. , Shcherbakov I. A. , Zagumennyi A. I.
Published: February 2023

Microchip lasers require a laser medium with high absorption and slope efficiency and a low threshold. From this point of view the materials of choice might be Nd: LaSc3(BO3)4 (Nd:LSB) and Nd:GdVO4 (Nd:GVO). The main features of these crystals are strong and broad absorption bands near 808 nm, a very high emission cross section at 1.06 μm for GVO, and broad emission line of LSB (Table 1). Under diode pumping 1-1.5 mm long GVO and LSB crystals demonstrate more than 850 mW of output power at 1.06 μm with a slope efficiency close to 60%.1,2 In order to achieve the same results with Nd:YAG it is necessary to use a 5-8 mm-long crystal. On the other hand both LSB and GVO suffer more from the thermal problems than YAG and require re-adjustment to compensate the thermal lens in order to maintain a good beam profile.
Optical pumping of the XeF(C→A) laser by a new VUV plasma source
Authors: Chazaud F. , Sentis M. L. , Rigneault H. , Paramonov A.
Published: February 2023

A new type of plasma light source produced by a sliding surface discharge on ferrite rods has been developed for various applications such as gas laser excitation. The current flow is first initiated through a conducting line written on the ferrite material.1 The electrical discharge leads to the formation of a long linear plasma channel emitting an intense VUV radiation.2 This device is capable of repetitive pulse operation in any atmosphere gas conditions. Side-on views obtained with a rapid CCD camera system have shown a plasma column of cylindrical form surrounded by a layer of a shock-compressed gas whose radial expansion have been well described.3
A new VUV laser: gain studies of Cs2+F- ionic excimer molecules photoexcited by laser produced plasmas
Authors: Tóth Cs. , Sauerbrey R. , Young J. F.
Published: February 2023

Laser produced plasma was used to excite alkali halide vapors to create a new class of excimer molecules, the alkali halide ionic excimers,1 which are promising laser sources in the VUV wavelength region. The soft x-rays emitted from a laser produced plasma on a metallic target were used to photoionize CsF vapor2 and produce excited state Cs2+F- molecules in a heat pipe cell (Fig. 1). The plasma pumping source was a Nd:YAG-based mode-locked oscillator/regenerative amplifier system providing 225 mJ, 100-psec pulses at 6 Hz in the basic experimental configuration.3 200-psec and 2-nsec duration laser pulses were also used to determine the effect of the pulse duration on the gain dynamics. The Nd laser beam was line-focused onto a rotating cylindrical target with grooved surface by a cylindrical mirror4 under 60 deg angle of incidence realizing a quasi-traveling wave excitation.
Long gas-lifetime operation of an ArF excimer laser
Authors: Saito T. , Ito S. , Tada A. , Arai M. , Kajiki Y. , Hotta K.
Published: February 2023

A number of techniques have been developed to maintain ArF excimer laser performance over long periods of time. Three dominant factors involved in the lifetime degradation are gas contamination, optics deterioration, and electrode abrasion. In this work, the lifetime degradation due to the electrode abrasion has been investigated. The longest gaslifetime of 9.5 × 105 shots for a developed ArF excimer laser with a gas purifier, which has copper electrodes, has been achieved.
Fanning effect and phase conjugation in Bi12TiO20 photorefractive fiber
Authors: Kamshilin Alexei A. , Tuovinen Hemmo , Prokofiev Victor V. , Jaaskelainen Timo
Published: February 2023

Study of photorefractive phase conjugate mirror is of great importance on account of various practical applications, such as optical implementation of neural network, associative memories, synchronization of several isolated lasers, interferometry, etc. A double phase conjugate mirror (DPCM) offers more advantages because no coherence between laser pump beams is needed. BSO-type crystals represent an important class of photorefractive materials due to their fast response time? Fiber-like samples have several advantages compared to the bulk crystal.2 We present here an experimental investigation of the double phase conjugation and of the fanning effect in fiberlike photorefractive Bi12TiO20 (BTO) crystal supplied by alternating electric field of square-wave form at the wavelength of He-Ne laser (λ = 632.8 nm). It was found that features of photorefraction in fiber-like samples are quite different with bulk crystals.
On-line sensing of particle distributions by measurement of scattered optical fluctuations
Authors: Smith P. R. , Green D. A. , Hopcraft K. I.
Published: February 2023

Accurate and automatic particle size distribution analysis is usually performed using either photon correlation spectroscopy, for the ~1 nm to ~1 micron range, or laser diffraction, for the ~1 micron to ~1 mm range.1 Such devices are not traditionally installed on-line, although the increasingly sophisticated process industries are approaching the need for such measurements.2 Optical sensors for particle sizing are required to upgrade the relatively crude and largely surrogate measurements, such as turbidity, that are currently employed.3 This paper addresses the on-line measurement of particle distributions by a novel measurement system based on the observation of non-Gaussian light fluctuations.
An application of laser-induced gratings for thermal diffusivity measurements of solids
Authors: Ivakin E. V. , Ben V. N. , Lazaruk A. M.
Published: February 2023

A success of practical implementation of the well known method of thermal dynamic grating (TDG)1-3 in the contactless measurements of thermal diffusivity x of solids essentially depends on acceptable thermal excitation of the sample in order to obtain a quite noticeable signal of diffraction and on suppression of forward probe beam scattering caused by sample imperfections. In addition a theoretical model should be simple enough with the number of controlled parameters as low as possible.
High-precision measurement of the period of diffraction gratings using a laser interference diffractometer
Authors: Korotkov V. I. , Pul'kin S. A. , Vitushkin L. F.
Published: February 2023

Existing methods for measurement of the period of diffraction gratings using diffractometers are based on the measurements of lengths or angles between the diffraction orders. These set a limit of over 10% on the relative accuracy of measurements of periods in the submicrometer range.
High speed all optical wavelength converters for photonic network applications
Authors: Erman Marko , Jacquet Joël
Published: February 2023

Wavelength converters, which transform information from one wavelength to another, accompanied by regeneration of the input signal, are promising components in the future optical broadband networks. In these large capacity wavelength-division-multiplexing (WDM) systems, wavelength conversion is used for routing and multiplexing. The objective is to achieve high speed operation simultaneously with regeneration of the input signal under a moderate input power within a large input and output wavelength range. Some of the different solutions to realize this function are reviewed in the following: absorption in bistable lasers,1 carrier depletion in distributed Bragg Reflector (DBR) lasers,2 injection locking in distributed feedback (DFB)3 or interferometric Y lasers,4 and gain saturation in semiconductor optical amplifiers (SOA).5,6
Q-switched pulses at 16 GHz from two-section semiconductor lasers
Authors: Barrow David A. , Marsh John H. , Portnoi Efim L.
Published: February 2023

We report the demonstration of efficient passive Q-switching in GaAs/AlGaAs and strained layer InGaAs MQW lasers containing a monolithic intracavity electroabsorption loss modulator. Self-pulsation was observed at repetition rates as high as 16 GHz with optical pulse energies as high as 5 pj (pulse width 25 ps FWHM).
Time- and frequency-domain theory of externally synchronised operation of a passively mode-locked laser diode
Authors: Avrutin E. A. , Khalfin V. B. , Arnold J. M. , Marsh J. H.
Published: February 2023

It has been recently proposed, and demonstrated in a fibre laser,1 that synchronising a laser in a passive mode-locking (PML) regime by an external signal can be used to solve an important practical task of the extraction of a clock frequency from a stream of digital data. Monolithic laser diodes (LDs) are known to have a number of advantages for many applications in communications, but since the present application would require a regime of operation and parameter values scarcely studied hitherto, a new insight into the underlying physics looks useful. We present here time- and frequency-domain studies of a PML LD synchronized by an external periodic signal. While both models are fairly general, the specific case in mind is that of a monolithic extended-cavity LD with gain, saturable absorber and passive sections, the external modulation being in the form of a train of optical pump pulses incident on the saturable absorber, encompassing a realistic clock-extraction scheme.
Inductive RF plasmas for high-power solidstate laser technology
Authors: Vitruk P. P. , Baker H. J. , Hall D. R.
Published: February 2023

Electrodeless RF inductive gas discharges of coaxial geometry are an attractive choice for long life flash-lamps, for use in Nd:YAG solid-state lasers, although the optimum operation parameters of such discharges remain still unclear.1-3 A deeper understanding of the physical properties of inductive RF discharges will facilitate wider applications in laser technology. In this paper we discuss discharge stability, excitation efficiency, and operating frequency scaling, aimed at the optimisation of coaxial RF excited flashlamps.
Beam fanning and self-starting oscillation in photorefractive InP:Fe at 1.06 μm
Authors: Ding Y. , Röpnack R. , Eichler H.-J.
Published: February 2023

Light-induced refractive index changes in photorefractive semiconductors have become comparable with those in the photorefractive oxides with the help of electric field enhancement, resonance excitation as well as exploitation of the electrorefraction. The two-wave mixing gain coefficient in InP has reached the values higher than 30 cm-1 at 970 nm.1 As a benefit from such strong beam couplings self-organization effects like beam fanning, photorefractive oscillation, double-phase conjugation, and self-pumped phase conjugation can be achieved in semiconductors. In this presentation we report the experimental investigation on such self-starting (or self-organization) effects in InP:Fe at 1.06 μm with an applied dc-electric field.
Near field optical microscopy and spectroscopy
Authors: Marti Othmar
Published: February 2023

Near-field optical microscopy and spectroscopy is a novel tool to image samples by light at a resolution better than 50 nm.1 The non-propagating or evanescent parts of optical near-fields contain information on the sample with intensity variations on a small fraction of the wavelength. To probe optical near-fields either detector apertures, light sources, or a combination thereof with nanometer size are brought to within a distance of a few nanometers of the sample surface. These apertures scan the sample surface, with the gap controlled by force measurement or by distance dependent reflection or transmission of light. The illumination can be used to measure reflection, transmission, or to stimulate spectroscopic processes, such as fluorescence or luminescence.
Scanning near-field fluorescence microscope using analysis of decay times
Authors: Pagnot Thierry , Pieralli Christian
Published: February 2023

Interest in scanning near-field fluorescence microscopes increases dramatically for a few years.1 Classically, they work using either fluorescence quenching or spectroscopic data. We present a new kind of microscope dealing with the analysis of fluorescence decay time. The latter depends strongly on the tip-to-sample distance2 and the theoretical bases are described. The decay times attached to each pixel leads to the determination of the distance between the tip and the sample. Moving the tip according to the two lateral directions yields an image of the investigated surface. The setup is essentially devoted to metal-coated samples but it can be applied to other materials.
Nuclear pumped Ar-Xe laser parameter measurements using 2 MeV proton beam excitation
Authors: Kononov V. N. , Bokhovko M. V. , Dyachenko P. P. , Smolskiy V. N.
Published: February 2023

Nuclear excitation by fission fragments can potentially be used to pump very large high-power gas lasers owing to a high energy capacity of fission reactor systems and a high penetration ability of neutrons in a multiplication media. The experimental investigations directed to search effective laser media for nuclear pumping and their parameter measurements are actual to date. In this work the observation of laser action and measurement of main laser parameters for 1.73-µm line in Ar-Xe medium excited by 2-MeV proton beam have been made.
Linear nonreciprocity in a ring gas laser
Authors: Radina T. V.
Published: February 2023

The effects of the differences in the frequencies and intensities of counter-propagating waves in a ring gas laser (diffraction and polarization nonreciprocity, nonreciprocity due to the transit-time effect) are known to be nonlinear.
Pulse gas lasers with intracavity spatial LC modulators
Authors: Danilov V. V. , Danilov O. B. , Sidorov A. I. , Zhevlakov A. P.
Published: February 2023

In this paper we present the results of our experimental investigations of pulse gas lasers with intracavity liquid crystal (LC) spatial modulators. For achieving laser beam direction controlling matrix spatial modulators have been used in lasers with conjugate resonators.