  Integrating two-dimensional (2D) crystals into optical fibers can grant them
optoelectronic properties and extend their range of applications. However, our
ability to produce complicated structures is limited by the challenges of
chemical vapor deposition (CVD) manufacturing. Here, we successfully
demonstrate a 2D-material heterostructure created on a fiber endface by
integrating a microscale multilayer graphene-MoS2-WS2 van der Waals (vdW)
heterostructure film on it. Hence, based on simple layer-by-layer transferring,
a visible-to-infrared gating-free all-in-fiber photodetector (FPD) is produced.
Our FPD exhibits an ultrahigh photoresponsivity of 6.6X107 A/W and a relatively
fast response speed of 7 ms at 400 nm light wavelength, due to the strong light
absorption and the built-in electric field of the heterostructure. Moreover,
owning to the type-II staggered band alignments in the MoS2-WS2
heterostructure, the interlayer optical transition between the MoS2 and WS2
layers enable our FPD to sense the infrared light power, displaying a
photoresponsivity of 17.1 A/W at 1550 nm. In addition, an inverse photoresponse
is observed under an illuminating power higher than 1 mW at 1550 nm, indicating
a competingphotocurrent generation mechanism, comprising the photoconductive
and photo-bolometric effects. These findings offer a new strategy for
developing broadband and gating-free photodetectors and other novel
optoelectronic devices based on 2D crystals. Furthermore, our fabrication
method may provide a new platform for the integration of optical fibers with
semiconducting materials.

Applied Physics