Page 60 - Fiber Bragg Gratings

TABLE 2.2: Routes to photosensitization of optical fibers.
Fabrication
Fiber type process Photosensitivity Advantages Disadvantages
Standard Standard CVD/ Very low: Easy production, Very low
telecommunications PECVD Photosensitive useful for low photosensitivity,
germania-doped index change, Sn reflectivity low birefringence,
fiber ~3 mol% ~ 1 X 10~^ gratings good quality fiber
(except one
report of 1 X
3
1(T [109])
High germania 10-30 Standard CVD/ Low photosensitive Good quality fiber, Birefringent,
mol% PECVD index change, easy production photosensitivity
slow growth of not enough to be
gratings, dn ~ 1 useful in
X 10 * untreated fiber
Reduced germania Production Good Low OH~ loss, Needs high germania
(—10 mol%) depleted oxygen photosensitivity, circular cored (—10 mol%)
atmosphere faster growth in fiber
index change, Sn
~ 5 X HT*
Boron-germania Needs additional Very good, faster Low OH~ loss, can Difficult preform
codoped calibration increase in be compatible fabrication, highly
since boron index, Sn ~ 8 X with standard stressed, increase
reduces core 10~ 4 telecommunication in boron induced
index fiber loss, elliptical core
Hot hydrogenated Preform cooked at Good Needs higher Slight increase in
germania-doped 750°C in photosensitivity, germania than OH loss
fiber hydrogen dn ~ 8c-4 standard tele-
atmosphere communications
fiber; easy to
store.