In-fiber modal Mach-Zehnder interferometer based on the locally post-processed core of a photonic crystal fiber

We demonstrate a novel, compact and low-loss photonic crystal fiber modal Mach-Zehnder interferometer with potential applications to sensing and WDM telecommunications. By selectively collapsing a ~1-mm-long section of a hole next to the solid core, a pair of modes of the post-processed structure are excited and interfere at its exit. A modulation depth of up to ~13 dB and an insertion loss as low as 2.8 dB were achieved. A temperature sensitivity of -53.4 pm/°C was measured, making the device suitable for temperature sensing.