|Abstract : ||The thesis has dealt with the techniques in optical design & subsequent application on designing the optics for one of the backend instruments for the 2.5 m telescope at PRL. NISP (Near-IR Imager, Spectrometer & Polarimeter) is a new multi-function near-infrared instrument for PRL’s upcoming 2.5 m telescope at Mount Abu. The major part of the thesis covers the instrumentation aspects and includes the optical design of NISP which has been completed with optimization at each step. The instrument will offer a multimode capability of imaging, spectroscopy, and polarimetry in a single package. The different modes in the instrument have been realized using custom-designed components to achieve the required specifications. The collimator optics design is an F/8 system with a collimated beam width of 38 mm, and the camera design necessary for our instrument specifications is F/5. The design has achieved a full unvignetted imaging field of view of 10′ x 10′, and a spectral resolving power ∼ 2150 across all filters in the near-infrared. It implements single-shot imaging polarimetry using wedged double Wollaston as an analyzer. The dual-beam polarimetry technique, will benefit many scientific projects with improved precision (compared to our earlier NICSPOL instrument at PRL). The thesis work illustrates the intricate details of the optical design of a near-infrared multimode instrument and its fulfillment with robust attributes, in terms of the implementation of the various modules, in the NISP instrument for PRL’s upcoming 2.5 m telescope.