As a result, obtained emission spectrum in the visible range (k exc = 976 nm) at the
end of optical fiber consists of the dominant band in the range of blue (481 nm,
Tm
3+ :
1 G 4 !
3 H 6 ), green (Ho
3+ :
5 S 2 (
5 F 4 ) !
5 I 8 ), and red (655 nm) colors.
Luminescence in the range of the red color is the result of the superposition of
transitions among Ho
3+ :
5 F 5 !
5 I 8 and Tm
3+ :
1 G 4 !
3 F 4 .
According to the CIE 1931 model, the analysis of chromatic coordinates was
conducted based on obtained luminescence spectra. The increase of the length of
studied optical fiber causes the shift of chromatic coordinates from the region of
blue color toward the point corresponding to the emission of white color. What is
more, changing the power of pumping radiation in the range from 0.5 to 1.5 W
showed the possibility of changing the luminescence spectra. The increase of power
of the pump up to 1.5 W causes the shift of chromatic coordinates toward the center
of the triangle of CIE 1931.
Other developed construction of active optical fiber enabling the emission of
white light is double-clad one core optical fiber co-doped with Yb
3+ /Tm
3+ /Ho
3+ ions
[40]. The antimony-germanate glass, in which luminescence of white color was
obtained (0.5Yb 2 O 3 /0.1Tm 2 O 3 /0.2Ho 2 O 3 , mol%), has been used as a core of the
fabricated optical fiber. Chromatic coordinates in this case were x = 0.35, y = 0.32,
which locates the point in the center of the CIE 1931 diagram. Optical fiber was
characterized by the following parameters: outer diameter = 330 µm, diameter of
the core = 10 µm, offset of the core = 60 µm, NA cladding = 0.58, NA core = 0.29.
Analysis of mechanisms that have the impact on the differences of luminescence
properties of core glass and optical fiber shows that the luminescence spectrum
(k exc = 976 nm) of fabricated optical fiber consists of—similarly to glass—three
emission bands: 479 nm (Tm
3+ :
1 G 4 !
3 H 6 ), 545 nm (Ho
3+ :
5 S 2 (
5 F 4 ) !
5 I 8 ) and
656 nm (Ho
3+ :
5 F 5 !
5 I 8 + Tm
3+ :
1 G 4 !
3 F 4 ).
However, the strong luminescence quenching was observed in the optical fiber
in the range of blue color and decrease of the luminescence intensity in the band of
656 nm relatively to the intensity on the band of 545 nm. It is caused by phenomena of optical trapping of ASE signal propagating in optical fiber resulting from
the presence of Tm
3+ :
1 G 4 !
3 H 6 , Ho
3+ :
5 I 8 !
5 G 6 and Ho
3+ :
5 I 8 !
5 F 5 transitions.
Furthermore, in the set of Yb
3+ /Tm
3+ /Ho
3+ ions, the resonance energy transfer
Tm
3+
! Ho
3+ limits the population of higher metastable levels of Tm
3+ . Finally,
the change of geometry of the interaction of radiation of the pump (glass sample vs.
optical fiber) caused a significant shift of the coordinates on the CIE diagram (inset
Fig. 14.25).
The calculated chromatic coordinates in the case of optical fibers are x = 0.37,
y = 0.49, which locates the point of the color in the area of green color [40]. The
practical aspect of carried out research is the description of mechanisms that have
the impact on the shape of luminescence spectrum of optical fiber co-doped with
Yb
3+ /Tm
3+ /Ho
3+ ions, enabling to change obtained chromatic coordinates and
simultaneously the color temperature of the emission spectrum of fiber.
14 The Luminescent Properties of Photonic Glasses …
449
end of optical fiber consists of the dominant band in the range of blue (481 nm,
Tm
3+ :
1 G 4 !
3 H 6 ), green (Ho
3+ :
5 S 2 (
5 F 4 ) !
5 I 8 ), and red (655 nm) colors.
Luminescence in the range of the red color is the result of the superposition of
transitions among Ho
3+ :
5 F 5 !
5 I 8 and Tm
3+ :
1 G 4 !
3 F 4 .
According to the CIE 1931 model, the analysis of chromatic coordinates was
conducted based on obtained luminescence spectra. The increase of the length of
studied optical fiber causes the shift of chromatic coordinates from the region of
blue color toward the point corresponding to the emission of white color. What is
more, changing the power of pumping radiation in the range from 0.5 to 1.5 W
showed the possibility of changing the luminescence spectra. The increase of power
of the pump up to 1.5 W causes the shift of chromatic coordinates toward the center
of the triangle of CIE 1931.
Other developed construction of active optical fiber enabling the emission of
white light is double-clad one core optical fiber co-doped with Yb
3+ /Tm
3+ /Ho
3+ ions
[40]. The antimony-germanate glass, in which luminescence of white color was
obtained (0.5Yb 2 O 3 /0.1Tm 2 O 3 /0.2Ho 2 O 3 , mol%), has been used as a core of the
fabricated optical fiber. Chromatic coordinates in this case were x = 0.35, y = 0.32,
which locates the point in the center of the CIE 1931 diagram. Optical fiber was
characterized by the following parameters: outer diameter = 330 µm, diameter of
the core = 10 µm, offset of the core = 60 µm, NA cladding = 0.58, NA core = 0.29.
Analysis of mechanisms that have the impact on the differences of luminescence
properties of core glass and optical fiber shows that the luminescence spectrum
(k exc = 976 nm) of fabricated optical fiber consists of—similarly to glass—three
emission bands: 479 nm (Tm
3+ :
1 G 4 !
3 H 6 ), 545 nm (Ho
3+ :
5 S 2 (
5 F 4 ) !
5 I 8 ) and
656 nm (Ho
3+ :
5 F 5 !
5 I 8 + Tm
3+ :
1 G 4 !
3 F 4 ).
However, the strong luminescence quenching was observed in the optical fiber
in the range of blue color and decrease of the luminescence intensity in the band of
656 nm relatively to the intensity on the band of 545 nm. It is caused by phenomena of optical trapping of ASE signal propagating in optical fiber resulting from
the presence of Tm
3+ :
1 G 4 !
3 H 6 , Ho
3+ :
5 I 8 !
5 G 6 and Ho
3+ :
5 I 8 !
5 F 5 transitions.
Furthermore, in the set of Yb
3+ /Tm
3+ /Ho
3+ ions, the resonance energy transfer
Tm
3+
! Ho
3+ limits the population of higher metastable levels of Tm
3+ . Finally,
the change of geometry of the interaction of radiation of the pump (glass sample vs.
optical fiber) caused a significant shift of the coordinates on the CIE diagram (inset
Fig. 14.25).
The calculated chromatic coordinates in the case of optical fibers are x = 0.37,
y = 0.49, which locates the point of the color in the area of green color [40]. The
practical aspect of carried out research is the description of mechanisms that have
the impact on the shape of luminescence spectrum of optical fiber co-doped with
Yb
3+ /Tm
3+ /Ho
3+ ions, enabling to change obtained chromatic coordinates and
simultaneously the color temperature of the emission spectrum of fiber.
14 The Luminescent Properties of Photonic Glasses …
449