Most Fourier Transform FT spectrometers use 2D optical plane interferometry and produce an interferogram by either a moving mirror (Michelson) or a static curved mirror (Sagnac). However, these spectrometers only use 50% of incoming light and rest is redirected towards the source. We present a new 3D optical layout for a modified Sagnac interferometer using all incoming light. This innovative design has no moving parts and uses tilted mirrors to raise the optical plane above the incoming light path. Many benefits can be gained from this configuration and here we demonstrate extending the spectral bandwidth. The spectrometer is aligned and calibrated using two laser diodes of known wavelengths; 404nm and 834nm. When a broadband tungsten-halogen light source is used, two complimentary interferograms are simultaneously measured from visible (400-1000nm) and SWIR (800-1700nm) spectral regions using two different detector arrays. The spectrometer performance was tested using multi-peak spectral bandpass filters and results are in good agreement with specifications data.