Adding New Functionalities to Optical Fiber Cavities by Direct Laser Writing

Abstract

Fiber Fabry–Pérot cavities (FFPCs) are fiber-based optical cavities, which find widespread applications, for example, in cavity quantum electrodynamics, spectroscopy, sensing, metrology, and in many more fields. They provide a range of advantages over other types of optical cavities: The input and output of the cavity are directly fiber-coupled, the cavity is easily tunable, additional components can be brought into the cavity region to study their interaction with the cavity mode, the overall cavity length can be reduced to micrometer sizes in order to reach high coupling strengths, and the setup allows for access to the cavity volume due to the comparably small diameter of the fibers. FFPCs can be assembled inside ferrules, which provide mechanical stability. In this configuration, FFPCs can be universally applied in various environments without worrying about mechanical damages or alignment-disturbance of the fragile fiber construct. This enables, for example, the installation of an FFPC in a cryostat. <br /> Direct laser writing (DLW) allows for the fabrication of polymeric structures on a wide range of surfaces. The process of two-photon absorption enables three-dimensional prints with features on the sub-micrometer scale. A large number of resists with different optical and mechanical properties have been developed and serve for applications in photonics, micromechanics, material science, and many more. <br /> In this thesis, we combine both areas by manipulating optical fibers, designed for the usage in FFPCs, by structures fabricated via DLW. In the following, a polymeric membrane is fabricated on top of a fiber mirror or on a distributed Bragg reflector substrate. It is suspended via its feet and therefore serves as a mechanical structure with characteristic eigenmodes. When this fiber/substrate is used in a Fabry–Pérot cavity setup, the radiative field in the cavity and the mechanical mode of the membrane interact. We extract the coupling strength between the fundamental mechanical mode and the radiative field and investigate the temperature-dependent behavior of the mechanical linewidth and the mechanical resonance frequency. Furthermore, we present the tunability of the mechanical resonance by using the optical spring effect. <br /> In the second part of this thesis, an approach for manipulation of optical fibers via equipping fiber with metallic electrodes is developed. The procedure involves the creation of a polymeric structure via DLW, here serving as a mask for a thermal evaporation procedure. In the experiment, a metallic coating is applied all around the fiber and on its endfacet. Upon removal of the mask, the fiber remains with the created shadow structure. This structure can be used to apply an electric or a magnetic field directly within the FFPC, making the usage of additional electrodes in the cavity region obsolete.