Rare Earth Doped Photonic Glass Materials for the Miniaturization
and Integration of Optoelectronic Devices
Ju H. Choi1, Alfred Margaryan2, Ashot Margaryan2, Wytze van der Veer3 and Frank G. Shi1
University of California Irvine, Dept. of Chemical and Materials Science Irvine, CA 92697
AFO Research Inc., P.O. Box 1934, Glendale, CA 91209
University of California Irvine, Dept of Chemistry, Irvine, CA 92697
Phone: 949.824.7385, Fax: 949.824.2541
Er doped alkaline-free glass systems based on ,MgF2-BaF2-Ba(PO3)2-Al(PO3)3 (MBBA
system), was investigated with the aim of using as high gain media The absorption spectra were
recorded to obtain the intensity parameters (Ωt) which are found to be Ω2= 4.47×10-20 cm2,
Ω4=1.31×10-20 cm2, Ω6=0.81× 10-20 cm2 for the MBBA system. The emission cross section for the
I13/2 →4I15/2 transition is determined by the Fuchtbauer-Ladenburg method and found to be 2.35
×10-20 cm2 for the MBBA systems. Comparison of the measured spectroscopic values to those of
Er3+ transitions in other glass hosts suggests that new MBBA systems are good candidates for
broadband compact optical fiber and waveguide amplifier applications.
Keywords: Rare earth ion, Fluorophosphate glass
1.0 Introduction size. In order to evaluate the potential for
The use of compact lasers has attracted compact laser media, we conducted a
increasing interest operating in the infrared systematic investigation of the spectroscopic
region for optical communications, medical properties of Er3+ doped MBBA system. The
and eye-safe light detecting and ranging previous results on Nd3+, Yb3+ doped
applications in the visible region for data fluorophosphate glass systems already
storage, undersea communications [1-3]. showed the strong potentials for each
With the development of 980nm laser diodes, characteristics transitions of rare earth ions
the diode pumped solid state lasers can [5-9] to develop new host materials with a
provide a compact and efficient device with high emission cross section for compact gain
the advantage of easy coupling with fiber media. We obtained intensity parameters,
integrated optical systems. Specifically, the the radiative lifetime and gain coefficient for
optically excited luminescence originating the 4I13/2 →4I15/2 transition of Er3+. Finally,
from the dipole-forbidden 4I13/2 4
I15/2 the potential of these systems for short fiber
transition of Er has a wavelength of 1.54 amplifiers or planar waveguides is evaluated
µm that matches one of the minimum loss by comparison to other reported glass hosts.
windows of commercial silica-based optic
fibers. Typical Er3+ doped fiber amplifiers 2.0 Experimental procedures
utilize approximately several meters of silica 2.1 Glass formation:
fiber doped with a few hundred ppm weight The batch materials of 40MgF2-40BaF2-
Er3+ ions  10Ba(PO3)2-10Al(PO3)3 system (the MBBA
In the construction of integrated light system) was purchased from reagent grade
amplifiers it is desirable to obtain the materials (City Chemicals, except for Er2O3,
maximum gain with minimum component Spectrum Materials), all have better than
99.99% purity. The ingredients of the doped MBBA system was used in this work.
glasses were weighed with 0.1% accuracy The refractive index nD, and Abbe number
and mixed thoroughly for 3 hours. Next, the are 1.5885 and 68.1, respectively.
raw mixed materials were melted in a 3.2. Absorption spectrum properties
vitreous carbon crucible in Ar-atmosphere at of Er3+ in MBBA system.
1200 - 1250 °C. The melt was quenched by
pouring it in a room temperature stainless 3.00E-024
steel mold. Next, the samples were annealed
below the glass transition temperature, 2.00E-024
around 400 - 430 °C, to remove internal
stress, which was verified by examination 1.00E-024
with a polariscope (Rudolph Instruments).
400 600 800 1000 1200 1400 1600
The samples for optical and spectroscopic Wavelength (nm)
measurements were cut and polished to a
size of 15×10×2mm3. Figure 1: The absorption cross section of
2.2 Spectroscopic measurements: Er3+ in the range of 300nm to 1700nm.
The refractive index nd of the samples
was measured at 588 nm, using an Abbe The absorption spectrum of Er3+ ion
refractometer (ATAGO). The absorption consists of 11 absorption bands centered at
spectra were obtained at room temperature 1532, 804, 650, 544, 520, 488, 451, 406, 377,
in the range of 400-1700 nm with a Perkin- 365, and 356 nm, corresponding to the
Elmer photo spectrometer (Lambda 900). absorptions from the ground state 4I15/2 to
The lifetime and fluorescence spectrum of the excited states in the 4f11 electronic
both samples was recorded using a chopped configuration respectively. The radiative
Ti-Sapphire laser (Coherent 890) tuned to nature of trivalent rare earth ions in a variety
800 nm, pumped by the 514 nm line of an of laser host materials is usually investigated
Ar laser (Innova 300), see Figure 3. The using the Judd-Ofelt model [10, 11]. The
fluorescence signal was recorded with a 0.25 observed oscillator strengths fmed at each
m monochromator (Oriel 77200), using a absorption peak is calculated by integration
InGaAs PIN detector (Thorlabs DET 410), a the optical absorption spectra over each peak,
trans-impedance amplifier and a Lock-In as given by following expression Eq. (2):
amplifier (Oriel Merlin 70100). The
lifetimes of both samples, was recorded with
mc 2 α (λ )
the same system, recording the temporal f med = ∫ dλ
behavior of the fluorescence signal with a πe 2 N λ2 . (2)
100 MHz digital Oscilloscope.
Here c is the velocity of light, N is the Er3+
3.0 Results and discussion ion concentration (ion/cm3). α(λ)
3.1 Optical properties (=2.303Do(λ)/d) is the optical absorption
The value of (nF-nC) and Abbe number coefficient at a particular absorption
(νd) normally describes dispersion in glasses wavelength λ, which is calculated from the
as below sample thickness d and the measured
absorption density D0(λ). The oscillator
(n D − 1 ) (1) strengths as predicted by Judd-Ofelt model
(n F − n C ) fcal were also calculated. The oscillator
strengths of the observed electronic
where nD, nF and nC are the refractive indices transition are due to three interactions,
at the D, C and F spectral lines. The variation electrical dipole (ed), magnetic dipole (md)
of refractive index as a function of rare earth and electric quadrupole (eq). In most
dopant concentration was systematically instances in the Er3+ system, the oscillator
investigated in previous work. 2wt% of Er3+
strength of the eq component is of the order deviation δrms of the fits was 8.52 x 10-6,
of 10−10, and the md component is of the which indicates that these fits are reliable. In
order of 10−8. These contributions are thus Table I [12-15] these values are compared to
unimportant compared with the ed those for other reported laser glasses. The
contribution to the oscillator strength, which value of Ω2 indicates the strength of the
is in the order of 10−6 . However, a covalent binding between the tri-valent rare
significant contribution of the md earth ion and the host material [16, 17]. The
component is involved for the 4I15/2 → 4I13/2 value of Ω2 of the MBBA systems is smaller
absorption transition for the Er3+. Therefore, than those of BK20 oxide glass and
theoretical oscillator strengths f(aJ, bJ’) of phosphate glass, which show strong co-
the J → J’ transition at the mean frequency valent bonds. The measured value is higher
ν is given for both the electric and the than that of ZBLAN, which has a very high
magnetic dipole transition by below Eq. (3) fluoride content causing strong ionic bonds
and thus weaker co-valent bonds. The values
[ χedSed (aJ,bJ') + χmdSmd(aJ,bJ')] (3) of Ω2 of the MBBA, system are comparable
to those of other fluorophosphate glass with
similar fluorine content.
where me is the mass of the electron. e and h The effect of co-valent bonding between
are the charge of the electron and plank’s the Er3+ ions and the host material can be
constant, respectively. χed =n(n2+2)2/9 and understood in terms of the Judd-Ofelt
χmd =n3 are local field corrections and are parameters. In case of a Er3+ doped system
functions of the refractive index n of the the t=2 transition matrix elements [U(2)]2 of
medium. Sed and Smd are the electrical dipole the transitions between the 4I11/2, 4I13/2 and
and the magnetic dipole line strength 4
I15/2 states are very small. The quality of
respectively these transitions for laser operation is thus
3.2. Intensity parameters & quality factor characterized by Ω4 and Ω6 via the
The Judd-Ofelt intensity parameters spectroscopic quality factor Q (=Ω4/Ω6), as
were determined by a least squares fit of the introduced by Kaminskii . The Q values
theoretical (free ion) oscillator strengths to are found to be 1.62 for the MBBA system.
the measured (glass matrix) values obtained These values are larger than those found in
from optical absorption spectra. By fitting most laser glasses as well as in FP20, see
the measured oscillator strengths fmed to the Table I. The MBBA glass system is thus
calculated values fcal we obtained the better suitable for laser applications than
following values for three Judd-Ofelt other published glass systems
parameters Ω2= 4.47×10-20 cm2, Ω4= .
1.31×10-20 cm2 and Ω6= 0.81× 10-20 cm2 are
obtained for the MBBA system. The
Glasses Ω2 (10-20 cm2) Ω4 (10-20 cm2) Ω6 (10-20 cm2) Ω4 /Ω6 Ref
BK20 5.66 1.84 1.18 1.56 12
ZBLAN 2.20 1.40 0.91 1.54 13
Phosphate 6.65 1.52 1.11 1.34 14
FP20 4.71 1.61 1.62 0.99 15
MBBA 4.47 1.31 0.81 1.62 Current work
Table I: Comparison of Judd-Ofelt parameters of Er3+ doped MBBA system and other reported
3.3 The emission cross section and gain The efficiency of a laser transition is
coefficient of the 4I13/2 → 4I15/2 transition. evaluated by considering stimulated
emission cross-section (σem(λ)). In this work,
σem(λ) was determined from the emission 3 as a function of the population inversion γ,
spectrum using Fuchtbauer-Ladenburg using the relation below
method (FL) 
G(λ) = γσ em ( λ ) − (1 − γ )σ abs ( λ ) (5)
β J − > J ' λ 4p A ra
σ em =
8 π cn (λ p ) ∆ λ eff
(4) Using this equation, we calculated the gain
spectra as shown in Fig. 3.
where λp is the peak wavelength of the
emission, λeff is the width of the emission
line, βJ->J’ is the branching ration, which is in 4
case of the 4I13/2 → 4I15/2 transition equal to 1, 3 γ=0.8
c is the speed of light in vacuums, and n(λp)
Gain coefficient (x10 , cm )
is the refractive index at emission peak 1
wavelength. In our case an effective line 0
width is used instead of the full width at half
maximum to compensate for the a-
symmetric profile of the emission line. Fig. -2
2 shows the absorption cross section, σabs(λ), -3
and the emission cross section, σem(λ), -4
1400 1450 1500 1550 1600 1650 1700
determined by FL method. Wavelength (nm)
Figure 3: Gain coefficient in the eye-safe
range of Er3+ in the MBBA system
Note that the gain will be positive at 1536
Emission Intensity (a.u.)
nm, when the population inversion is larger
3 than 0.5. The maximum value for the gain is
0.4 achieved in the case of complete population
inversion (γ = 1), in this case cross section
1 0.3 for stimulated emission is 2.35 × 10−20 cm2
0 for the MBBA system.
1350 1400 1450 1500 1550 1600 1650 1700
Wavelength (nm) 4.0 Conclusions
The novel MBBA system was successfully
Figure 2: Absorption cross section and
developed and the absorption and emission
measured emission cross section of Er3+ in
spectra of Er3+ were measured and analyzed.
the MBBA system.
Three intensity parameters are found to be
For the MBBA system, the peak Ω2= 4.47×10-20 cm2 Ω4=1.31×10-20 cm2
absorption cross sections of σabs(λ) turned Ω6=0.81× 10-20 cm2 for the MBBA system.
out to be 1.58 × 10-20 cm2 and the peak The strong emission bands were observed at
1536 nm and the effective bandwidths were
emission cross sections of σem(λ) are 1.86 ×
found to be 91 nm. Emission cross section
10-20 cm2. Comparing the Er3+ ion to a
determined by FL method for the 4I13/2
simplified two level system, we assume the
→4I15/2 transition are found to be 2.35 ×
population is either in the 4I15/2 ground state
10−20 cm2 and population inversion of above
or the 4I13/2 excited state. In this case the
50 % were obtained. These spectroscopic
optical gain properties are directly
results show that these novel materials are
associated with the absorption and emission
strong candidates for developing broadband
cross sections. Gain spectra is shown in Fig.
optical amplifiers and compact fiber lasers.
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