Saturated evanescent‐wave absorption of few‐layer graphene‐covered side‐polished single‐mode fiber for all‐optical switching

Using the evanescent‐wave saturation effect of hydrogen‐free low‐temperature synthesized few‐layer graphene covered on the cladding region of a side‐polished single‐mode fiber, a blue pump/infrared probe‐based all‐optical switch is demonstrated with specific wavelength‐dependent probe modulation efficiency. Under the illumination of a blue laser diode at 405 nm, the few‐layer graphene exhibits cross‐gain modulation at different wavelengths covering the C‐ and L‐bands. At a probe power of 0.5 mW, the L‐band switching throughput power variant of 16 μW results in a probe modulation depth of 3.2%. Blue shifting the probe wavelength from 1580 to 1520 nm further enlarges the switching throughput power variant to 24 mW and enhances the probe modulation depth to 5%. Enlarging the probe power from 0.5 to 1 mW further enlarges the switching throughput power variant from 25 to 58 μW to promote its probe modulation depth of up to 5.8% at 1520 nm. In contrast, the probe modulation depth degrades from 5.1% to 1.2% as the pumping power reduces from 85 to 24 mW, which is attributed to the saturable absorption of the few‐layer graphene‐based evanescent‐wave absorber. The modulation depth at wavelength of 1550 nm under a probe power of 1 mW increases from 1.2% to 5.1%, as more carriers can be excited when increasing the blue laser power from 24 to 85 mW, whereas it decreases from 5.1% to 3.3% by increasing the input probe power from 1 to 2 mW to show an easier saturated condition at longer wavelength.