Grating–fiber coupler as a high-resolution spectrometer

An in-line, single-mode fiber-optic spectrometer is described and analyzed. Its key element is a photoresist grating placed in the evanescent field near the core on a side-polished fiber. Fabrication and nearly diffraction-limited performance (resolution Deltalambda asymptotically equal to 1 nm) are reported, and means are proposed to increase the resolution by several orders of magnitude.