of the fiber preform was about 4 nm in diameter (size distribution:
2.0 nm to 4.8 nm) obtained from the transmission electron
microscopy (TEM, FEI Tecnai G2 F30 S-TWIN) as shown
in Fig. 1, [19]. The TEM photograph clearly shows the morphology
of CdSe QDs in the optical fiber preform core retained
even after the high temperature MCVD process, which is crystalline,
to be roughly spherical without agglomeration. To verify
the existence of CdSe QDs in the CdSe doped optical fiber core
which was drawn from the preform at high temperature again,
the optical absorption spectrum of the CdSe QDs doped fiber
was measured. The absorption peaks due to CdSe QDs in the
fiber core was found to appear at 622 nm, 633 nm, and 662
nm as shown in Fig. 2. Note that the absorption spectrum with
multi-peaks was due to the size difference of the embedded QDs
as shown in Fig. 1 [21], which is also the evidence of the existence
of CdSe QDs in the fiber core after drawing the preform
into the fiber at high temperature of about 2150 . Absorption
coefficient of the fiber was about 0.0008 at 660 nm.