I know that there are clamp meters to measure currents for electrical wires externally without almost not interfering the circuit.
I was wondering whether in the case of an optical fiber(single mode silica optical fiber), is there a technique or device/component which can detect the laser light power externally or wrapping a sensor around ect?
The light is trapped in the fibre due to the refractive index mismatch between the core and the cladding. Some light enters the cladding as an evanescent field and can be used to excite a thin film of fluorophore which may be externally detected.
Another method is to disolve or polish away the cladding and immerse the fibre into an fluid with an refractive index close to the core which allows light to escape the core and then can be detected.
Bending the fibre can cause light to enter the cladding and be externally detected.
The field in most SM fibers is contained within the core and surrounding cladding, so unless you're going to strip away the cladding you don't have access to the fields you're trying to measure. If you are willing to strip away the cladding you can make a coupler and measure energy by taking a few percent of the energy out of the core, but I think that's your only option.