Design and Development of a Lab Prototype of a Fiber-Based Integral Field Spectrograph

Integral Field Spectroscopy provides simultaneous spatial and spectral information, making it a powerful technique for studying both point like and extended astronomical sources. As part of our effort to develop a compact Integral Field Spectrograph (IFS) for optical astronomy, we have designed and realized a fiber based prototype with a resolving power of ~800 at the H-$\alpha$ wavelength. The front end optics, including the fore optics and lenslet based integral field unit (IFU), have been designed and optimized. In the present work, we focus on the design and laboratory verification of a fiber only IFU module consisting of 37 fibers arranged in a precise hexagonal geometry to match the lenslet pitch. The back end of the system forms a linear fiber slit that feeds a laboratory built spectrograph. The optical design was optimized using ZEMAX, and the system was experimentally tested using a Neon emission lamp and solar light. The measured spectra clearly show prominent features including the H-$\alpha$ lines, with dispersion and resolution consistent with theoretical predictions. Although lenslets are not yet integrated, this work establishes a validated methodology for accurate fiber alignment for IFS. This results form a crucial step toward the full implementation of a lenslet fiber based IFS for the 2.34 meter Vainu Bappu Telescope.