Optimized process for fabricating ultra-short tapered long period gratings

The process of fabricating tapered long period gratings (TLPGs) using a CO2 laser is described. The objective of this work is to optimize the CO2 laser based fabrication of TLPGs so that their transmission spectra are comparable with those made using the arc-discharge technique, which typically exhibits transmission losses below 2 dB. The losses currently observed with CO2 laser fabricated TLPGs are typically greater than 10 dB over the spectral waveband 650-1100 nm. In this work, the reduction in transmission loss was achieved by optimizing the micro-taper geometry and the duty-cycle of the device. TLPGs with a period of 378 μm were fabricated. The 6-period TLPGs exhibited a pass-band transmission loss of 0.6 dB, resonance band extinction values of 3 dB and had a physical length of 2.27 mm. The refractive index sensitivity of a 6 period TPLG was measured and found to be 372 nm/ RI.