  We present a robust, fiber based endoscope with a silver direct-laser-written
(DLW) structure for radio frequency (RF) emission next to the optical fiber
facet. Thereby, we are able to excite and probe a sample, such as nitrogen
vacancy (NV) centers in diamond, with RF and optical signals simultaneously and
specifically measure the fluorescence of the sample fully through the fiber. At
our targeted frequency-range around 2.9 GHz the facet of the fiber-core is in
the near-field of the RF-guiding silver-structure, which comes with the
advantage of an optimal RF-intensity decreasing rapidly with the distance. By
creating a silver structure on the cladding of the optical fiber we achieve the
minimal possible distance between an optically excited and detected sample and
an antenna structure without affecting the optical performance of the fiber.
This allows us realizing a high RF-amplitude at the sample's position when
considering an endoscope solution with integrated optical and RF access. The
capabilities of the endoscope are quantified by optically detected magnetic
resonance (ODMR) measurements of a NV-doped microdiamond that we probe as a
practical use case. We demonstrate a magnetic sensitivity of our device of 17.8
nT/$\sqrt{\mathrm{Hz}}$ per when measuring the ODMR exclusively through our
fiber and compare the sensitivity to a measurement using a confocal microscope.
Moreover, such an endoscope could be used as a powerful tool for measuring a
variety of fluorescent particles that can otherwise only be measured with bulky
and large optical setups. Furthermore, our endoscope points toward precise
distance measurements based on Rabi oscillations.
