Fabrication of 7×6 multimode optical fiber gratingdemultiplexer-star coupler using a single GRIN-rod lens

A multimode optical fiber grating demultiplexer-star coupler having seven demultiplexing channels and six fan-out channels is demonstrated. This device consists of an input-output fiber array, in which 42 output fibers are aligned radially around an input fiber, a single gradient-index (GRIN)-rod lens and a multifacet blazed reflection grating. In this device, the incident light beam is split into six beams, each of which is diffracted at the multifacet grating and couples to the output fibers. The device has a working band from 0.62 to 0.88 μm, channel separation from 36 to 45 nm and 3 dB bandwidth from 13 to 24 nm. We also evaluate the unevenness in the center wavelength and the minimum excess loss among the fan-out channels and discuss the relationship between the unevenness and the fabrication accuracy of the optical components in detail