  Recently, a type of curved light beams, photonic hooks (PHs), was
theoretically predicted and experimentally observed. The production of photonic
hook (PH) is due to the breaking of structural symmetry of a plane-wave
illuminated microparticle. Herein, we presented and implemented a new approach,
of utilizing the symmetry-broken of the microparticles in material composition,
for the generation of PHs from Janus microcylinders. Finite element method
based numerical simulation and energy flow diagram represented theoretical
analysis were used to investigate the field distribution characteristics and
formation mechanism of the PHs. The full width at half-maximum (FWHM) of the PH
(~0.29$\lambda$) is smaller than the FWHM of the photonic nanojet
(~0.35$\lambda$) formed from a circular microcylinder with the same geometric
radius. By changing the refractive index contrasts between upper and lower
half-cylinders, or rotating the Janus microcylinder relative to the central
axis, the shape profiles of the PHs can be efficiently modulated. The
tunability of the PHs through simple stretching or compression operations, for
the Janus microcylinder constituted by one solid inorganic half-cylinder and
the other flexible polymer half-cylinder, was studied and discussed as well.
