MOGlabs CEX - Reverse Beam: Using a Visual Fault Locator; Mirror Adjustment

4.4 Fibre coupling 25
fibre, andthe mirrorsadjusted sothat the beamis clearlytransmitted by
the coupler (see below for detailed instructions).
An eccentric keyis provided foradjusting the couplinglens focus.Please
contactMOGLabsifyourfibrecouplingefficiencyismuchlowerthanstated
in your laser test report.
4.4.1 Reverse beam: using a visual fault locator
Avisual fault locator isaveryusefuldeviceforquicklyachievinginitial
couplingofthelaserbeamtothefibre.Avisualfaultlocator(seefigure4.3)
is a low-power red laser that injects a beam intothe exit end of the fibre
patchcord,thuspropagatingvisiblelightbackwardsalongthefibreand
thenintofreespace,formingabeambackintothelasercavity. These
devices are very low in cost (search on eBay for visual fault locator; they
are typically less than $20).
Figure 4.3: Fibrelaserpen,orvisualfaultlocator.Injectsvisiblelaserbeaminto
fibre, which allows basic alignment and mode matching.
Aligning theMOGLabslaserbeamtothe fibreisthensimplyamatterof
adjustingthemirrorssothattheMOGLabslaserbeam andthevisualfault
locator beam overlap inside the laser.
4.4.2 Mirror adjustment
Tomaximisethe fibrecoupling efficiency,theincidentangle andlocation
ofthelaserbeamatthefibrecouplermustbeoptimisedbywalkingthe
mirrors.
LetM1bethemirrorclosesttothefibrecoupler, andM2beclosesttothe
laser (see figure 3.6).