Parameter optimization of hollow-core optical fiber phase modulators

We studied the effect of varying gas concentration, buffer gas, length, and type of fibers on the performance of optical fiber photothermal phase modulators based on C₂H₂-filled hollow-core fibers. For the same control power level, the phase modulator with Ar as the buffer gas achieves the largest phase modulation. For a fixed length of hollow-core fiber, there exists an optimal C₂H₂ concentration that achieves the largest phase modulation. With a 23-cm-long anti-resonant hollow-core fiber filled with 12.5% C₂H₂ balanced with Ar, phase modulation of π-rad at 100 kHz is achieved with a control power of 200 mW. The modulation bandwidth of the phase modulator is 150 kHz. The modulation bandwidth is extended to ∼1.1 MHz with a photonic bandgap hollow-core fiber of the same length filled with the same gas mixture. The measured rise and fall time of the photonic bandgap hollow-core fiber phase modulator are 0.57 µs and 0.55 µs, respectively.