Nanophotonics or nano-optics is a part of nanotechnology that investigates the behavior of light on nanometer scales as well as interactions of nanometer-sized objects with light. Nanophotonics often includes metallic components that can transport and focus light through surface plasmon polaritons. Silicon photonics is a silicon-based subfield of nanophotonics in which nano-scale structures of the optoelectronic devices realized on silicon substrates and that are capable to control both light and electrons. They allow to couple electronic and optical functionality in one single device. Nanophotonics is the study of understanding and engineering light at a nanometer scale. By understanding how these photons behave on a nanoscale, we can start controlling and manipulating their interactions, leading to inventions like a new way for cancer diagnosis and treatment or photonic quantum computing.

Nanophotonic devices are crucial to control the properties of quantum emitters and improve their functionality. Here, nanophotonic devices using the GeV centers will be shown. Diamond nanophotonic waveguides and metal-based plasmonic waveguides have been fabricated based on the GeV centers. As another application, temperature sensing using optical properties of the group-IV color centers will be also discussed.Quantum non-linear optics at a single photon level has been demonstrated using a GeV center incorporated in a diamond waveguide. The single GeV center was fabricated in one dimensional waveguide made of diamond using nanofabrication techniques. Resonant excitation using a Bragg mirror resulted in a transmission by 18% in a single pass. From an interferometer experiment, the non-linearity at a single photon level was confirmed. In addition, it was also found that the excited state lifetime of the GeV center was not significantly affected by the measurement temperature ranging from cryogenic temperatures to 450 K. This observation suggests that the GeV center possesses a higher quantum efficiency due to less multi-phonon relaxation. A MEMS-based structure enables to control the properties of color centers. One important optical characteristic for the quantum applications is indistinguishability of multiple quantum emitters. When two quantum emitters possess precisely same fluorescence wavelength and width, they are not optically distinguishable, called indistinguishability. In the group-IV emitters with the D_3d symmetry, the permanent electrical dipole moment vanishes, and thus, we can expect the stable optical emission. However, due to strain and defects in a diamond crystal remained after the diamond growth process and/or induced during the emitter and device fabrication processes, different quantum emitters frequently do not show identical optical properties. Thus, the control of the optical properties is an important function for quantum emitters. Such a control has been demonstrated using a diamond cantilever structure including single GeV centers. Upon the application of the voltage to the cantilever, it bends by electrostatic force and strain is generated in the structure. Then, the wavelength of the incorporated single GeV centers can be tuned by the strain, leading to their spectral alignment.