Multi-Cladding (MC) fibers with undoped silica core and alternating highly fluorine doped and undoped silica cladding layers are a new standard for high power laser beam transmission. Such MC-fibers allow tailoring the output beam profile of a single laser source to the desired application. An important factor for these applications is to avoid additional scattering of the guided light in the different regions leading to an increased output divergence, so-called Focal Ratio Degradation (FRD). In this work, we compare two possible measurement concepts to determine the beam divergence angle under controlled launch conditions to quantify FRD of MC fibers. One approach is the pinhole setup historically used in astronomy; another approach is the inverse far field method with selective excitation. The objective is to define a reliable setup for quality inspection. We show measurement results for FRD of MC fibers with both methods and evaluate the differences between the light-guiding sections. To our knowledge, this is the first time such data are presented. The objective described above is best fulfilled by a modified far field method with defined broad angular excitation.
Plasma outside deposition (POD) allows the incorporation of high fluorine contents in silica glass to manufacture multi-mode fibers. Due to all silica design and excellent material attributes, these so-called Fluosil fibers cover a wide spectrum of applications over a broad wavelength rage from UV to NIR including medical laser surgery, industrial materials processing, automotive, sensing, spectroscopy, and fiber bundles. These characteristics have allowed fiber designs to become more and more sophisticated in recent years. An overview of the current capabilities, characterization techniques, and fiber trends will be presented. Heraeus supports these new developments by offering a growing number of materials, preforms and services.
In this paper, we present our current work towards a highly efficient XLMA (extra-large mode area) fiber-based laser, which is being performed in the EKOLAS consortium within the BMBF-funded EffiLAS (efficient high-performance laser beam sources) research alliance. To this end, the complete manufacturing process chain of the XLMA fiber was reviewed and optimized. The work started with the material composition of the active XLMA preform with the goal of improving the purity and thus the background loss. A successfully implemented fluorine co-doping process allows refractive index adjustment of the active core material which improves the beam quality of the laser fibers without changing the concentration of active ions in the glass composition. The preform is subjected to a screening in which possible scatter centers, e.g. bubbles, inclusions or contaminants, are mapped and categorized, in order to identify defects, which could lead to a failure in the drawn fiber, already at an early production stage. The subsequent fiber drawing is monitored for scattering using the emissions from the heated preform as well as for inhomogeneities of the dopants using a phase measurement technique. Finally, the fiber is tested for residual impurities and background losses using a multi-mode OTDR to ensure that the fibers are free of any defects.
The ongoing development in microlithography towards further miniaturization of structures creates a strong demand for
lens material with nearly ideal optical properties. Beside the highly demanding requirements on homogeneity and stress
induced birefringence (SIB), low absorption is a key factor. Even a small absorption is associated with a temperature
increase and results in thermally induced local variations of refractive index and SIB. This could affect the achievable
resolution of the lithographic process.
The total absorption of the material is composed of initial absorption and of absorption induced during irradiation. Thus,
the optimization of both improves the lifetime of the material.
In principal, it is possible to measure transmission and scattering with a suitable spectrometer assembly and calculate
absorption from them. However, owing to the influence of sample surfaces and errors of measurement, these methods
usually do not provide satisfactory results for highly light-transmissive fused silica. Therefore, it is most desirable to find
a technique that is capable of directly measuring absorption coefficients in the range of (1...10)•10-4 cm-1 (base 10)
directly.
We report our first results for fused silica achieved with the LID technique. Besides a fused silica grade designed for 193
nm applications, grades with higher absorption at 193 nm were measured to test the LID technique. A special focus was
set on the possibility of measuring initial absorption without the influence of degradation effects.
Ongoing laser fusion experiments like the "Laser MegaJoule Project" and the "National Ignition Facility" have created a strong demand for large optical lenses of special grade fused silica. The required lens dimension poses several challenges to the manufacturing process. One of the key issues is to provide a suitable measurement technique, which is capable to fulfill the extreme demands for characterizing the optical homogeneity of those large fused silica blanks. We report on our first results achieved with an interferometer system that was installed to explore the potential and feasibility of stitching interferometry. Although the principle of stitching is well known, it had to be adapted to the special "oil-on measurement technique" that is necessary to characterize lens blanks without expensive surface polishing.
We report our investigations on interferometric precision measurements of fused silica for a required reproducibility of (sigma) ((Delta) (eta) )<EQ1x10-7 with special focus on thermal environmental conditions. An analytical description is proposed for a qualitative consideration of the thermalization process; numerical results are given for a quantitative prediction of temperature induced measurement errors. Experiments and numerical calculations point to the fact, that, apart from the thermal conductivity, the heat transfer between sample surface and environment has to be taken into account for precise process analysis. Reducing the thickness of the sample, the heat exchange rate between air and glass becomes more important. An effective heat conductivity can be introduced to describe the thermalization process of the sample more easily. Temperature stability of interferometric systems, as well as accuracy and reproducibility of measurement results, were analyzed experimentally in order to study their correlation. The reduction of environmental fluctuations by one magnitude has shown remarkable improvements in the interferometer stability.
Recent results on waveguide device fabrication by replication of inorganic-organic copolymers (ORMOCERs) are presented. The use of optimized ORMOCER resins offers advantages over conventional organic polymers. The organic as well as inorganic crosslinking is responsible to high thermal and chemical stability and thus an improved stability of the waveguide devices. Fluorination of ORMOCER side chains reduces the NIR absorption to < 0.4 dB/cm at 1.55 micrometers and < 0.3 dB/cm at 1.3 micrometers . Furthermore, the synthesis of purely inorganically crosslinked CH-free ORMOCER is possible. The refractive index can be tuned so that highly fluorinated core material can be combined with low-cost unfluorinated cladding material. The influence of the sidewall roughness of replication tools on scattering losses is investigated, and methods to fabricate smooth original structures have been developed leading to an additional scattering loss < 0.1 dB/cm in single-mode strip waveguides even at visible wavelengths. Furthermore, an improved deforming behavior is achieved. UV-patterning by UV-induced crosslinking is a second waveguide fabrication method used in ORMOCER. Applications of ORMOCERs in thermo- optical switching nodes are discussed.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.