We present the preliminary optical and optomechanical design of a high throughput, fiber spectrograph for the Gemini/Subaru Wide-Field, Fiber-Fed, Multi-Object Spectrograph (WFMOS) designed with the principle goal of studying the nature of dark energy via enormous high-redshift spectroscopic surveys. Developed from an original Sloan Digital Sky Survey design this multi-object spectrograph utilizes all-refractive cameras, volume phase holographic gratings, and state-of-the-art CCD detectors to produce a peak instrument throughput of ~ 70%. The instrument produces 292 spectra simultaneously in two channels covering the bandpass 390 < λ < 1000 nm with a mean spectral resolution, λ/FWHM, of R ~ 1700. WFMOS will employ approximately ten of these fiber spectrographs on an 8 m class telescope to capture nearly 3000 spectra simultaneously. When used in a nod & shuffle mode of operation these spectrographs will facilitate spectroscopy of faint 0.5 < z < 3.5 galaxies with unprecedented efficiency.© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.