Fabrication of a Multimode Interference Device in a Low-Loss Flat-Fiber Platform Using Physical Micromachining Technique

A physical micromachining technique is demonstrated in a low-loss flat-fiber substrate to fabricate a multimode interference (MMI) device. The flat-fiber substrate is a low-index-contrast material; however, by making use of two physically micromachined trenches, lateral confinement is achieved providing high index contrast for the MMI region. A 1
$\,\times\,$
3 MMI device exhibiting 1.89 dB of excess loss has been demonstrated.