Temperature-insensitive, gain flattened erbium-doped photonic crystal fiber amplifier: a compatible solution

An all-silica, erbium-doped photonic crystal fiber (PCF) has been investigated numerically to achieve temperature insensitive amplification for optical communication applications. The careful engineering of PCF microstructured air-hole cladding offers two distinct advantages over conventional fibers, namely, compatible mode area and large modal overlap which can be controlled accurately to lower the splice loss and shorten the fiber length respectively. Splice loss as low as 0.22 dB and fiber length as short as 3.25 m for 190 mW pump power and 1 µW signal power, have been achieved in this work. Apart from these two existing advantages, a third advantage has been highlighted and numerically verified in this paper. This third advantage concerns the realization of an athermal long period grating (LPG) filter to flatten the amplifier’s gain spectrum. The LPG which exhibits a gain ripple of 0.29 dB over a 25 nm wavelength band at room temperature (20 °C), does not respond significantly with temperature and sub-dB ripples within 0.64 dB are maintained when temperature changes over a 80 °C range (−20 to +60 °C). This athermal nature of the flattened gain spectrum is attributed to the single material composition of the PCF, which is clearly unachievable with conventional fibers.