0
\$\begingroup\$

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?

\$\endgroup\$
5
  • \$\begingroup\$ Practically, at the wavelengths used for optical fiber communications, you can make accurate power measurements down to about -30 dBm pretty easily. So if you can pick off (for example with a coupler) a controlled fraction of the signal giving you about that much to measure, you should be good. Whether that is going to disturb the signal you're trying to measure depends on just what you're trying to measure and how it's being used. \$\endgroup\$
    – The Photon
    Jan 8 at 0:29
  • \$\begingroup\$ @ThePhoton If a coupler used this should follow a photodiode for detection? I want to detect when the laser radiation is ON for safety and show it with an LED. The 5W 1500nm laser module I use doesn't have any radiation ON indicator. So at the moment I use a current meter to indirectly detect radiation ON(by measuring module's current sink from its power supply wire). I don't know in commercial systems how they implement this radiation ON indicator. \$\endgroup\$
    – user16307
    Jan 8 at 0:38
  • \$\begingroup\$ High power laser diodes frequently have a monitoring photodiode. Use that if possible. Otherwise add a coupler or pick off some of the be once it's in free space and use a photodetector to see if it's emitting. \$\endgroup\$
    – user1850479
    Jan 8 at 1:01
  • \$\begingroup\$ @user1850479, I dunno where you got that laser, but you should be designing a power supply with an indicator, key lock-out, and only operating it with eye protection, etc. \$\endgroup\$
    – The Photon
    Jan 8 at 1:39
  • \$\begingroup\$ @user1850479 The module is a sealed pump source so I have no access to inners and shouldn't open it. I can only measure the current it draws from power supply. So when the pump module power is on the current is under 400mA and after that the radiation starts. Since I control the pump with SW gradually the only way Im sure there's radiation is when the current is above 400mA. So down side is Im in the mercy of the current sensors drift. Its also hard to convince people to use coupler in this case. I think at the moment I have no option. \$\endgroup\$
    – user16307
    Jan 8 at 1:42

2 Answers 2

Reset to default
1
\$\begingroup\$

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.

\$\endgroup\$
1
\$\begingroup\$

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.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.