Axial-graded-index (AGRIN) lens-based eight-channel wavelength division demultiplexer for multimode fiber-optic systems

We have designed and fabricated the first multimode wavelength division multiplexer (WDM) and demultiplexer (WDDM) based on axial graded index (AGRIN) lenses in conjunction with a volume holographic grating. The demonstration is made using a multimode fiber with a 50-μm core size. The diffraction-limited AGRIN lenses employed significantly increase the output coupling efficiency and reduce crosstalk when compared with the best homogeneous lens solutions previously reported. The volume holographic grating has a maximum diffraction efficiency of 92% at the center wavelength of 780 nm. An eight-channel WDDM device with a center wavelength of 780 nm and a channel separation of 4 nm is designed and demonstrated. The end-to-end insertion loss for each channel is between 2.8 and 3.8 dB. The maximum channel-to-channel crosstalk is -25 dB.