III. EXPERIMENTS
A fiber preform doped with CdSe QDS was fabricated
by using the modified chemical vapor deposition (MCVD)
process. Core layers of alumino-germano-silica glass deposited
onto inner surface of a silica glass tube was doped by the
solution doping process using a toluene solution containing
CdSe QDs (Sigma-Aldrich: Lumidot CdSe QDs in toluene,
peak absorption , 7.5 mg in 1.5 ml solution) at room
temperature [19]–[21]. It was observed during the experiments
that incorporation of CdSe QDs in the core of the optical fiber
preform was quite challenging. Although not fully stabilized,
we used a simple technique to deal with the problem. Initially
the core layers were deposited inside the silica glass tube in
the form of soot at 1400 and the soot was cooled to room
temperature. Then the doping solution was infiltrated into the
soot of core part for 1 hour to incorporate CdSe QDs. The
wet soot was then dried by flowing and He gases in the
tube. To reduce possible evaporation of the dopants during
sintering of the soaked layers of the core part at about 2100 ,
an additional silica glass layer was deposited onto them. Then
the tube was collapsed and sealed into a rod preform. Finally,
the preform was drawn into fibers with outer diameter of 125
at 2150 by using the draw tower. The core diameter and
the cut-off wavelength of the fabricated fiber were 5.4 and
560 nm, respectively. The mode field diameters (MFDs) of the
optical fiber were 13.1 and 13.6 at 1310 nm and 1550
nm, respectively, which were measured by using the optical
fiber analysis system (Model: 2500, PK Technology).
The concentration was about 1.5 mole% in the optical
fiber core and the estimated concentration of CdSe QDs was
about 2.2 . The average CdSe QDs size in the core