A chiral fiber laser implemented in a fiber Bragg grating mimicking the advantageous optical properties of a cholesteric liquid crystal structure is provided. The invention is characterized in that the power unit comprises a plurality of modular elements including at least one motor block, at least one upper roller box and at least one lower roller box. The tagged probe includes a molecular tag that is linked to a first binding compound through a cleavable linkage, and the cleaving probe includes a second binding agent and a cleavage-inducing moiety that can cleave the linkage when within a defined proximity thereto.