Reinhard Caspary

• Dr.-Ing. Dipl.-Phys.
• Technology Coordinator at Leibniz Universität Hannover

This paper presents a novel method for accelerating the computationally intensive process of point-based holography using consumer grade hardware. By leveraging the parallel processing capabilities of graphics processing units (GPUs) and implementing optimization techniques, the proposed method significantly reduces the time required to generate co...

News from the German Cluster of Excellence PhoenixD on Optics and Photonics at Leibniz University Hannover with reports, interviews, portraits and the PhoenixD chronicle. Scientific topics are integrated optics, optics production, optical materials and others.

To achieve better quality and generation speed, we generate holograms from adaptively sized and placed points, modeled as 2D Gaussians. We compute them with a Rayleigh-Sommerfeld convolution directly in a compact, radially symmetric look-up table.

We present a novel fast method to compute point-based Computer Generated Holograms with occlusion on the GPU, using modern hardware capabilities. Our method offers a promising new route towards real-time calculation of high-resolution holograms.

In this paper we show the equivalence of near-field beamforming and backward-wave reconstruction algorithm. The proof is carried out analytically with two different approaches, using the principle of stationary phase from a signal processing point of view and the angular spectrum representation as an electromagnetic point of view. A comparison of t...

In this Letter, the pump wavelength dependence of the amplified spontaneous emission (ASE) and the threshold of stimulated Brillouin scattering (SBS) in a typical single-frequency continuous wave Er 3 + : Yb 3 + -codoped fiber amplifier is investigated numerically. The Er 3 + : Yb 3 + system is modeled as coupled two- and three-level systems, linke...

Integrating highly efficient luminescent dyes into poly(methyl methacrylate) (PMMA) matrices with well‐defined parameters, such as degree of polymerization and dispersity, is a key step in the development of emerging technologies like fiber‐based solar collectors, sensors, contactless coupling devices, and integrated light sources. In this work, fo...

The production of short polymer optical fibers from small material batches is valuable for materials research, especially in the investigation of copolymers. A two‐step fiber drawing process is usually used for this purpose. The drawing temperature of the individual materials is an important parameter in this process. Temperature measurements using...

In this work, cost efficient hybrid polymer based Bragg grating ridge waveguide resonators were successfully fabricated by a cost-effective combined nanoimprint and photolithography process. By using this hybrid process, optical features with the size in the scale of nanometers (Bragg gratings) and micrometers (waveguides) could be defined simultan...

The growth mechanism and the barrier performance of Al 2 O 3 , SiO 2 and a binary Si-Al oxide (SiAl x O y ) deposited by spatial atomic layer deposition (SALD) were investigated. Alumina and silica were deposited by TMA and BDEAS with growth-per-cycles ( GPC ) of 0.16 and 0.013 nm, respectively. Interestingly a significant higher GPC of 0.225 nm wa...

Waveguides made of poly-methyl-methacrylate (PMMA) play a major role in the homogeneous distribution of display backlights as a matrix for solid-state dye lasers and polymer optical fibers (POFs). PMMA is favored because of its transparency in the visible spectrum, low price, and well-controlled processability. Nevertheless, technical drawbacks, su...

Alumina layers were grown from trimethylaluminum (TMA) and water, ozone as well as an oxygen plasma as co-reactants in low temperature spatial atomic layer deposition (ALD). The influence of the amount of precursor, the precursor exposure duration, and substrate temperature were investigated with respect to the growth rate while employing different...

The mid-infrared (MIR) spans the 3-25 m wavelength range. Rare-earth-ion doped selenide-chalcogenide glasses are being developed for direct-emission MIR fibre lasers. The true Pr3+ absorption cross-section in the 3.5-6 µm wavelength region of a Pr3+-doped (500 ppmw of Pr3+ i.e. 9.47 x 1019 Pr3+ ions cm-3) GeAsGaSe host-glass is presented, after nu...

Organic laser sources offer the opportunity to integrate flexible and widely tunable lasers in polymer waveguide circuits, e.g. for Lab-on-Foil applications. Therefore, it is necessary to understand gain and degradation processes for long-term operation. In this paper we address the challenge of life-time (degradation) measurements of photoluminesc...

We report on the preparation and characterization of a highly sensitive organic photodiode for the entire visible part of the spectrum. The photodiode is based on a small molecule heterojunction layer of zinc phthalocyanine (ZnPC) and fullerene C60 and is prepared by multistep vacuum deposition technique. Investigation is performed under different...

In summary, the investigation shows the temperature sensitivity of the POF splices restricted their use specifically to non-critical applications. However, avionic POF splice can be realized in the future with suggested modification.

We have developed WDM multiplexer and demultiplexer in the visible spectral range for POF transmission links and have carried out transmission experiments using different lengths of standard SI-POF. Our 4-channel WDM system with laser diode sources is operated in the violet, blue, green and red spectral range. Using discrete multitone modulation (D...

To integrate polymer fiber based physical layer for avionic data network, it is necessary to understand the impact and cause of harsh environments on polymer fiber optic components and harnesses. Since temperature and vibration have a significant influence, we investigate the variation in optical transmittance and monitor the endurance of different...

Wavelength division multiplexing (WDM) is a promising solution for upgrading the capacity of polymer optical fiber (POF)-based telecommunication networks. In this letter, we report on the successful realization of a four-channel high-speed WDM transmission system for 1-mm diameter step-index POF (SI-POF). For combining the optical signals coming fr...

The mechanical properties of polymer optical fibers (POF) make them very interesting candidates for fiber optical sensors. Today POFs are mainly used for short range data communication. These fibers have a very large core of 980 μm. This large core is beneficial for handling and maintenance in fiber networks. Fiber sensors however, often need high...

We improved our glue splicing method to join silica and fluoride glass fibers. It is now even more robust and stabile with a mean loss below 0.5 dB. Moreover, the splice reflection was reduced to about −42 dB when an index matching gel was used. Pieces of Pr$^{3+}$ /Yb$^{3+}$ doped ZBLAN fibers with lengths of 25 cm were connected to silica fibers....

Even though the melting temperatures of silica and fluoride glass are very different, a new thermal splicing method to join these fibers is presented here. The lowest attenuation achieved was about 0.2 dB. Moreover, this thermal splice was stabilized, packed and inserted in a simple fiber laser setup.

Wavelength division multiplexing (WDM) is a promising solution for upgrading the capacity of polymer optical fiber (POF)-based telecommunication networks. In this letter, we report on the successful realization of a four-channel high-speed WDM transmission system for 1-mm diameter step-index POF (SI-POF). For combining the optical signals coming fr...

Current developments regarding polymer optical fibers (POF) make them suitable for high speed data transfer in industrial and home applications. Recently few- and singlemode polymer optical fibers have been shown. These are useful for various sensing applications like temperature changes or elongation measurements and allow the construction of inte...

Lately copolymers are increasingly discussed as a starting material for high temperature resistant polymer optical fibers (HT-POFs) [1,2,3]. In this work copolymers based on methyl-methacrylate (MMA) were synthesized and their copolymerization parameters investigated. In order to increase the glass transition temperature, copolymers with bulky side...

Wavelength division multiplexing (WDM) is a promising solution for upgrading the capacity and/or transmission distance of polymer optical fiber (POF)-based telecommunication networks. This paper is focused on the implementation of low-loss multiplexer and demultiplexer in the 100 m long step-index POF (SI-POF) communication link with four laser dio...

Polymer optical fibers are a very good choice for flexible and robust short range optical data links. We have developed PMMA with Eu3+-doped polymer chains. From this optically active material we draw fibers. These fibers can be used for UV pumped polymer fiber amplifiers in cases where larger distances have to be bridged. This paper presents the f...

The paper reports on the current development status of a four-channel coarse WDM transmission system for the investigation of Multi-Gbit/s data links over SI-POF. A four-channel DEMUX with low insertion loss and low crosstalk is realized in the bulk optics technology at the Harz University. Multi-Gbit/s data transmission experiments are performed w...

In order to develop new materials for polymer optical fiber amplifiers, new rare-earth metal complexes are synthesized. These complexes feature a polymerizable functional group, which can be used to synthesize copolymers. In this work we present Eu3+- and Tb3+-complexes, which are embedded into a PMMA polymer. Synthesized rare-earth metal complexes...

Manufacturing of Organic Light Emitting Diodes (OLED) for lighting is still some distance from the industry recognized cost target of 100 € /m2. Within the government funded Light In-Line (LILi) project, a team of material supplier, machine manufacturers and basic researchers have investigated potential ways to reduce OLED manufacturing costs. The...

The realization of high-speed WDM systems on POF links requires high-speed high-power laser diodes with different wavelengths within the visible range. The RF characteristics of such laser diodes are not specified by the manufacturers. Therefore we have to determine the characteristics of several laser diodes in order to develop high-speed visible...

Direct written waveguides in Er3+:ZBLAN are analyzed with regard to laser applications. We present a simulation model for the absorption properties of the waveguides. The results from the simulation are compared with experimental results.

To fabricate polymer optical fibers (POF) we built a fiber drawing tower similar to the drawing towers used to produce glass fibers. Commercial undoped PMMA preforms were used as reference for the drawing process. Monomer free preforms are prepared by ourselves, from which optical fibers are drawn. In the next step we develop Europium complexes and...

This paper aims to provide reliable and basic measurement data on the influence of flat connectors with an airgap (SMA) and connectors with physical contact (ST, SC) on the power margin and system performance of polymer optical fiber link for avionic applications.

The tunability of a red and orange fiber laser was investigated using Pr 3+ /Yb 3+ doped ZBLAN fibers. A maximum output power of more than 20 and 10 mW for the red and the orange fiber laser was found, respectively. The total tuning range was 18 nm. The fiber lasers were pumped with two pigtailed laser diodes at 845 nm. No free space optics except...

The fast expanding market of micro fluidic reactor systems in the chemical industry demands for small spectrometers in the mid-infrared (MIR) as analyzer for automatic process control. Conventional free-space MIR spectrometers are usually large and conventional fiber spectrometers are limited to the near-infrared (NIR) range up to 2.5 µm. We develo...

This paper discusses the challenges and options in integrating commercial POF link and its passive/active components to the critical as well as non critical data communication in commercial aircraft. The paper focusses particularly on the relevant firm environmental requirements that have to be fulfilled to assure the reliability and safety of the...

A fibre-coupled mid infrared spectrometer would have a very broad range of potential applications. For example it could be used for process control of chemical production processes in micro reactors e.g. in the pharmaceutical industry. Because of the absence of an adequate fibre, we developed preforms and fibres for this purpose using ZBLAN glass (...

The tunability of Pr³⁺/Yb³⁺ doped ZBLAN fiber lasers has been investigated. A broad tuning range of 17 nm with narrow linewidth was obtained for red and orange wavelengths. The fiber lasers were pumped with pigtailed laser diodes at 845 nm. No free space optics except of the tuning block was used.

A compact green laser diode pumped rare earth laser source is interesting for a range of medical, spectroscopic and communications applications. Since such a device is not commercially available up to now we are working on the development of an erbium-doped fluoride glass up-conversion waveguide laser. The actual fabrication of fluoride glass, espe...

For angular scanning a true-time array is developed for UHF ultra-wideband (UWB) applications in time and/or frequency domain. It is based on a 4 × 4 array with antipodal exponentially tapered slot antennas (ETSA, Vivaldi) and a 3-bit phase shifter. Distances of antenna elements are designed to be compromise between gain, scanning angle, side/grati...

Fiber lasers based on praseodymium-ytterbium doped fluoride glass fibers with silica fiber pigtails offer a wide range of different configurations. Here we present results of such fiber lasers in different ring configurations in an all-fiber setup. The fiber lasers are pumped with pigtailed laser diodes at 845 nm and deliver output powers up to 20...

Fiber-coupled mid infrared spectrometers can be used for in-situ monitoring of the reaction progress in chemical production processes. The absence of an adequate fiber led to the exploration of thick fluoride glass fibers for this purpose. 670 μm thick fluoride fibers with 500 μm core diameter have been fabricated. The fibers showed a bending radiu...

Abstract Low loss fluoride glass planar waveguides on monocrystalline CaF2-substrates have been fabricated by hot dip spin coating. The surface of the 30 to 50 μm thick glass films was very smooth. Structuring by photolithography and etching led to additional losses, due to the edge roughness. Improvement of the etching process and the use of a pol...

Fiber lasers are on the way to substitute gas lasers and other types of solid state lasers. Even though the main focus in the field of fiber lasers actually is on high power Ytterbium-doped fiber lasers at 1064 nm and Erbium-doped fiber lasers at 1550 nm, a lot of interesting developments are found abroad in different wavelength regions. Here we re...

When calling for compact green laser sources, the green upconversion emission of IR pumped erbium-doped fluoride glass waveguides opens up a technologically and economically superior alternative to complex and costly frequency doubling techniques. Therefore, fluoride glass planar waveguides were fabricated with thicknesses down to 29 mum and a scat...

Since green laser diodes are still not commercially available, alternative technologies like frequency doubling have to be used for compact green laser sources. The goal of this work is to develop diode pumped green erbium-doped glass up-conversion waveguide lasers, instead. Planar fluoride glass waveguides are fabricated using a spin-coating techn...

We present the design and realization of a 4-channel 3-bit phase shifter system for ultra-wideband beam steering applications in a frequency range of 0.5-1 GHz. Design considerations leading to a small, cost-effective realization with very good phase accuracy are described employing switched-line phase shifters. An additional degree of freedom is i...

By decreasing the arc power and choosing the optimal arc time, we use the FSM-20PM ARC Fusion Splicer for joining fluoride(ZBLAN) and silica fibers. The best results of the splice loss is 1.58dB, and the results can be improved if the Fusion Splicer with more stable arc power. Then glue connection is used to fix the splicing point, and the minimal...

Optical frequency domain reflectometry (OFDR) is an interferometric method which allows to determine the spatial distribution of the gain along the active fiber in a fiber amplifier. As a non-destructive tool it is ideal to find the optimum fiber length especially of co-directional pumped fiber amplifiers. In this paper we explain the OFDR method a...

A systematic investigation was carried out on melting and casting of Zr-fluoride based glasses in order to find out the optimum fabrication conditions. Several rods were prepared with variation in compositions and melting/casting parameters. They were characterised to compare their optical homogeneity and stability. The results showed an appreciabl...

Photoluminescence (PL) spectra and intensities of thin N,N′-diphenyl-N,N′-bis(1-naphthylphenyl)-1,1′-biphenyl-4,4′-diamine (α-NPD) films have been measured at room temperature, during sample heating with various rates and annealing times at constant temperatures, and after annealing. It was found that the temperature of T = 80 °C being considerably...

For thulium-doped fiber amplifier (TDFA) design, knowledge of the gain distribution within the active fiber is of great value. For the first time, the distributed gain along highly thulium-doped fibers was measured with high-resolution reflectometry. The technique of coherent optical frequency-domain reflectometry is a nondestructive and noninvasiv...

The avalanche energy transfer in highly thulium doped fiber amplifiers (TDFA) pumped at 1056nm with laser diodes was investigated. Amplified spontaneous emission (ASE) at 800nm and 1470nm as well as the remaining pump power were measured as function of the pump power to explain the efficiency of the energy transfer between thulium ions. As proof of...

In the last years a lot of different pump configurations were investigated for thulium doped fiber amplifiers (TDFA) in the S-band. Since the TDFA is using a four-level transition with long lifetime of the lower amplifier level, it turned out, that pumping with two wavelengths was most effective. Comparing the results of fluoride fibers doped with...

We present data on the deposition of various organic materials using Organic Vapor Phase Deposition (OVPD®) for use in efficient red OLEDs. The long term stability of the OVPD process has been investigated, showing reproducibility of deposition rates to be better than ± 1.5% for a period of up to 30 days. Due to the highly reproducible process the...

The first praseodymium-ytterbium up-conversion ZBLAN fiber laser in an all-fiber ring configuration is reported. The laser operates at 635nm, is pumped at 835nm, and consists of only the active ZBLAN fiber and two-fused-fiber couplers.

The excited state absorption (ESA) transitions at 1050 and 1420nm play a fundamental role in thulium-doped fiber amplifiers (TDFA). We present a novel setup to measure the spectral cross-sections of these transitions in amplifier fibers and the results of this measurement in case of thulium-doped fluorozirconate (ZBLAN) fibers. Besides a standard s...

Up-conversion fiber lasers based on Pr3+/Yb3+ doped fluoride fibers and pumped at 835 nm can operate on emission lines in the red, orange, green, and blue spectral region. Up to now only Fabry-Perot configurations with two mirrors butt-coupled to the fiber ends were investigated. In this paper we present the first visible Pr3+/Yb3+ fiber lasers in...

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The spectroscopic properties of thulium-doped indium fluoride based bulk glasses with a novel glass composition (IBZP) have been analyzed and compared to the standard ZBLAN glass according to measured absorption and emission spectra in the ultraviolet, visible and infrared wavelength regions. Moreover, lifetime measurements have been done and compa...

Due to the growing bandwidth demands in photonic networks, new fiber amplifiers besides the C -and L-band (1530-1610 nm) will be necessary in the future. Thulium-doped fiber amplifiers (TDFA) provide gain in the S -and S + -band (1450-1530 nm) and are therefore important candidates for next generation photonic networks. As TDFAs usually need fluori...

We report on ZBLAN fiber based praseodymium-ytterbium upconversion fiber lasers operating in the blue, green and red spectral region. We discuss advantages of the fiber laser and the operation of the upconversion lasers is described in detail. A red fiber laser running without external mirrors is presented, too. We show an unique experiment where l...

Two configurations of thulium-doped fiber amplifiers (TDFA) are presented and the performance of the amplifier in these configurations is discussed. The measurements are compared with a simulation using a self-written model and compared with results reported in the literature. The problems during the design, their solutions and the possibilities to...

Summary form only given. Rare-earth doped glasses are used for many applications such as glass and fiber lasers and fiber amplifiers. In the field of active fiber applications, fluoride fibers are of special interest, because most optical transitions in the rich energy level system of rare-earth ions cannot be used in usual silica fibers. Because o...

The internet boom in the 1990's led to an exponential increase of the bandwidth demands on optical long-haul transmission links and the introduction of WDM and DWDM systems. However, the gain bandwidth of usual fiber amplifiers is limited to a maximum of 80 nm in the C- and L-band. Todays optical senders and receivers are limited to a spectral effi...

A new external laser cavity design that allows for wavelength tuning and controlled simultaneous two-mode oscillation is demonstrated for a fibre laser. The gain bandwidth and the position of the gain maximum are determined from the tunability and the minimum threshold, respectively. Two-mode oscillation is shown for different mode wavelength spaci...

Thesis (doctoral)--Technische Universität, Braunschweig, 2001.

Six important programs of commercially available software for erbium-doped fiber amplifiers are described with attention to advanced simulations. A more detailed description is given of two programs, EDFA Design(R) and VPIComponentMaker(R). The models included in the software are discussed, and their implicit assumptions are explained and examined

Lasermodelle, basierend auf den Ratengleichungen des aktiven Materials, sind schon für verschiedene Lasersysteme, darunter auch Faserlaser, veröffentlicht worden. Diese Modelle sind aber üblicherweise genau auf ein spezielles System zugeschnitten. Das hier vorgestellte Modell für Faserlaser im stationären Betrieb ist dagegen für beliebige Dotierung...

: We have developed a fixed beam direct writing laser lithography system with a resolution of 400 nm at 457 nm wavelength and a writing speed of 4.2 mm/s with total system costs of less than 100 000 US$. Keyword: Laser lithography system 1. Introduction Although research into lithographic systems in the past few years has mainly been carried out in...

To design fiber lasers with desired properties, a theoretical model with computer code is needed. In this article such a model is presented which can be used to compute the characteristics of a cw fiber laser. Fed with the spectroscopic parameters of all energy levels of interest, it yields the output powers of a theoretically unlimited number of l...