Recently, it becomes a tendency for cost-effective, portable spectrometers to have more applications from scientific research to daily life, e.g., in food safety and air pollution analysis. While most spectrometers utilize plane gratings, we demonstrate a more miniaturized, two-channel, broadband spectrometer based on variable-spacing concave gratings, combining the functionality of imaging optics and diffraction grating in one component. The added degree of design freedom in the micro-sized grating spacing further corrects most optical aberrations, thus the design achieves a tiny volume of <26 × 12 × 10 mm³ with a high spectral resolution. Simulation results show an optical resolution of <1.6 nm in the VIS-channel (400 to 790 nm) and <3.1 nm in the NIR-channel (760 to 1520 nm). The blazed structure of grating grooves provides a high overall diffraction efficiency in the whole spectral range, more than 50% on average. To further validate the feasibility for mass production, we successfully manufactured the variable-spacing concave gratings by using diamond tooling for fabricating the master mold and hot embossing for replication. Our fabricated variable-spacing grating replicas have a diffraction efficiency up to 70% in the VIS-channel and up to 60% in the NIR-channel. We built the prototype with fabricated concave gratings, and experimental results show a good match (error < 7 % ) in spectral resolution with the nominal design.

The photographic assessment of the optic nerve has been one of the original and most extensively used methods to evaluate patients for glaucoma. The depth evaluation of the optic disc in the retinal fundus is important for the early detection of glaucoma. Conventional fundus cameras have a limited field-of-view for imaging of the retina and its peripheral areas. In this article, we report the design and fabrication of a non-mydriatic wide-field fundus camera using a contact-free trans-scleral illumination that is capable of taking 3D images of the optic disc using oblique illumination. We demonstrate that, using oblique illumination through sclera, a quasi 3D image of the optic disc along with its shadow can be obtained. The shadow provides important information on the shape and depth of the optic disc. The depth values of the optic disc obtained by our proposed method using shadow length measurements are in good agreement with the values obtained using an optical coherence tomography device. The results indicate that our fabricated fundus camera could be an easy-to-handle and low-cost tool for remote detection and diagnosis of ocular diseases without the need of an ophthalmologist.