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A novel type of light controlled fiber Bragg gratings written in attenuation fiber is demonstrated. The spectral reconfiguration can be controlled by the pump power, the pumping configuration, the grating position and the fiber attenuation. IntroductionTunable, reconfigurable and actively controlled fiber Bragg gratings (FBG) are one of the key components for the agile optical networks and sensing systems. Most common tuning methods include piezo-electrical [1], mechanical [2] and, thermal actuation [3,4]. Thermal tuning is usually achieved using a thin metallic film, deposited on the fiber around the FBG and heated using externally supplied electrical power. Electrical heating requires deposition of a metallic coating, external electrical power supply and cabling, which altogether limits range of application, decreases device lifetime, and could prevent application in harsh environment. Ideally, spectral shaping and reconfiguration of the properties of optical gratings should be done via optical means. The idea of all-optical control was demonstrated using Er/Yb doped fiber and appropriate pump light. Index changes were induced based on nonlinear effect [5] or non-radiative absorption [6]. Recently, Chen et al. [7] demonstrated an optically tunable FBG where the grating is heated by pump light absorbed in the metallic coating. In addition to applications in telecommunications, actively optically controlled FBG could play an important role in the sensing area [8]. Here, we present a novel all-optically reconfigurable optical fiber grating, without mechanical and electrical components. The idea is based on the concept of writing an FBG in an attenuation fiber. We called this new family of Bragg gratings -attenuation fiber Bragg gratings (AFBG). Using the high power light source (at a wavelength outside the grating resonance), the FBG written inside the attenuation fiber is heated and actively controlled using optical means only. Non-uniform absorption of the pump power along the fiber induces nonuniform temperature distribution. Using optical low-coherence reflectometry we measure the temperature profile along the grating with high spatial distribution. Due to the simple design and heating of the grating with light propagating along the same fiber, this device offers a simple solution for remotely light-controlled FBGs.

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Monitoring biological relevant reactions on the single molecule level by the use of fluorescent probes has become one of the most promising approaches for understanding a variety of phenomena in living organisms. By applying techniques of fluorescence spectroscopy to labelled molecules a manifold of different parameters becomes accessible i.e. molecular dynamics, energy transfer, DNA fingerprinting, etc… can be monitored at the molecular level. However, many of these optical methods rely on oversimplified assumptions, for example a threedimensional Gaussian observation volume, perfect overlap volume for different wavelength, etc. which are not valid approximations under many common measurement conditions. As a result, these measurements will contain significant, systematic artifacts, which limit their performance and information content. Based on Fluorescence Correlation Spectroscopy (FCS) and Fluorescence Lifetime Spectroscopy we will present representative examples including a thorough signal analysis with a strong emphasis on the underlying optical principles and limitations. An outlook to biochip applications, parallel FCS and parallel Lifetime measurements will be given with cross links to optical concepts and technologies used in industrial inspection.