Diamond's nitrogen-vacancy (NV) defect shows great promise as a quantum bit because of their long electron spin coherence time and since they can be located, manipulated and read out using optical methods. However due to its chemical inertness, a photonic manufacturing toolkit akin to silica and silicon photonics has yet to be developed for diamond. We describe how femtosecond laser fabrication can be applied to form 3D integrated optical circuits in diamond, which can optically link NV centers and help make the diamond-based quantum computer a reality. We apply mu Raman spectroscopy to show amorphization in the laser-modified tracks, allowing us to produce waveguides by compressive stress between two closely spaced damage tracks. In addition, we apply confocal fluorescence microscopy to show that within the laser-inscribed waveguides, the bulk properties of the NV centers are preserved.