optical active er doped waveguide...
TRANSCRIPT
POSTER 2017, PRAGUE MAY 23
Abstract – In the paper are presented the results of the gain
transmission characteristics measurement for the ion exchange
Ag-Na optical active planar waveguides realized on a glass
substrates. The attenuation measurements were performed by
the time impulse selective wavelength method using pulse
generator as well as broadband spectral measurement method
using supercontinuum optical source in the wavelength
domain. Both methods were compared and the results were
evaluated. It has been demonstrated, that pulse method can
very accurately measurement of the attenuation characteristics
in dependence on the pumping power, but only for one
wavelength. The minimum attenuation wavelength bandwidth
of the active waveguide can be determined by the broadband
spectral characteristic measurement.
I. INTRODUCTION
The active optical waveguides are currently the subject of
the intensive research. The active optical waveguides on
glass dotted by Er3+
– Yb3+
are known for the low losses,
optical transparency in the NIR spectrum, low weight and
excellent stability of the operating parameters. The simple
and cheap fabrication by two-stage ion exchange and an
easy setting of the optical attenuation parameters and focus
on the fiber determines the use of active optical waveguides
in many areas of information technology devices such as
optical amplifiers, active optical splitters, optical switches
and many others. This paper summarizes measurement
results of the spectral transmission characteristics of the
active optical planar waveguides, which were created using
the Ag-Na ion exchange on a glass substrate. The
measurement was realized using two methods - the pulse
method in the time area, and the broadband spectral
measurement method in the wavelength area. Both methods
were compared and the results were discussed. In the case of
the pulse method, it is possible to determine, quite precisely,
the transmission characteristics dependent on the pumping
power, but only for one wavelength. In the case of the
spectral characteristics measurements, it was possible to
determine the area, where the maximum amplification of the
active waveguide takes place. The spectral characteristics of
pumped and non-pumped waveguides were compared.
Optically active material makes use of the activator ions,
most commonly rare earth elements, specifically those that
are optically active in the area of the second (1300 – 1350
nm) or third (1530 – 1560 nm) optical attenuation windows
of silica waveguides. The used rare earth elements are
trivalent ions from the lanthanide group. The ability of ions
to generate optical radiation (photoluminescence) while
optically pumping is hidden in the insufficiently occupied 4f
subshell, which is localized inside the activation atoms. The
fully occupied subshells 5s a 5p work as a shield of the 4f
subshell from the external field perturbations (e.g., thermal)
from the atoms of the base material.
The three-orbital system of energy levels, where the Yb3+
ions are pumped to the 2F 5/2 level is shown in Fig. 1.
After a certain time, the electors pass through non-radiative
transition to a lower orbital 4I 13/2, and via radiation-
transition with stimulated emissions of photons 1550 nm to
the base state (4I 15/2).
Fig. 1. Energy levels of transitions in a complex of Er3+ - Yb3+ ions [ 4 ].
In regards to the optical amplifiers for the 1550 nm
wavelength, the most frequently used activators are Er3+
ions, which use electron transition in the 4f subshell. There
are eleven electrons for amplification, and three of the
valences electrons are unoccupied and therefore usable for
excitation. A part of the erbium ions is very frequently
replaced by Yb3+
, which can increase the optical activity
(intensity of luminescence) than the erbium itself. The
absorption cross-section of Yb3+
ions is larger by orders of
magnitude than Er3+
.itselves. The optimal activator
concentration finding is one of the most crucial tasks in the
research of optically active structure technology. The higher
concentration of activators causes the quenching of the
luminescence radiation. The activator atoms are clustering,
the energy migration or the cross-relaxation take place. As
an example, we present a planar configuration of a planar
optical amplifier (POA) depicted in Fig.2.
Fig. 2. The planar configuration of the optical amplifier [1].WDM - wavelength division multiplexer, AMP - amplifying waveguide, SPL –
splitter 1x4
Optical Active Er doped waveguide structures
Jiří Šmejcký
Faculty of Electrical Engineering, Technical University in Prague
POSTER 2017, PRAGUE MAY 23
w
h ns+n
nc
ns
The POA use the aluminum oxide waveguide doped with
Er3+
ions for the 1540 nm operation with the 1480 nm
pumping. The POA utilizes a planar interference WDM
filter at the input, which combines the pumping radiation
with the signal one. The mixed radiation is amplified in the
active planar waveguide. At the end of the waveguide is
wavelength divider, which splits the pumping and the signal
radiation. The signal part of the radiation is taken to an
interference splitter, and the pumping part is taken to a ring
resonator, which is tuned to the pump wavelength. The ring
resonator absorbs the energy of the pumping radiation.
II. TECHNOLOGY
A key part of an OPA used in our measurements was
samples of the diffused optical planar waveguide dotted by
Er3+
and Yb3+
realized in the glass.
Fig. 3. The planar diffused optical waveguide [2].
The planar diffused optical waveguide with ZnO precursor
after a first-degree ion exchange is depicted in Fig. 3. We
can see a gradient waveguide, in which the refractive index
changes continuously exponentially from the center to the
edge, according to the diffusion. The picture shows the first
Measurement procedure
The measurement of the samples was done by both the by
the time impulse selective wavelength method and the
spectral method with the aid of a broadband signal.
Fig. 4. The absorption characteristics waveguide dotted by Er,Yb [3].
Fig. 5. The luminescence characteristics of the waveguide dotted by
Er,Yb [3].
The comparison of the absorption and luminescence
spectrum the planar diffused optical waveguide with ZnO
precursor is shown in Fig. 4. It is clear that influence of the
ZnO concentration on the process of absorption (980 nm)
does not affect the absorption spectrum, where the
absorption takes place from the ytterbium ions. In opposite
to the luminescence spectrum, which arises from erbium
ions, where the increase of ZnO correlates to an increased
luminescence activity. This point to the fact that as the
concentration of ZnO increases so does the separation of
erbium ions, which prevents the clustering, so that more
energy is radiated (Fig.5).
III. MEASUREMENT AND RESULTS
The measurement of the samples was done by both the by
the time impulse selective wavelength method and the
spectral method with the aid of a broadband signal.
The measurement of transmission characteristics
at = 10 log (Ps,out/Ps,in) in dependence on the pumping power
Pp is shown in Fig. 6. In order to separate the spontaneous
emission a pulse modulation of the signal radiation was
used. The optical signal attenuation radiation component
was determined from the amplitude of the modulated
electrical signal at the output.
Fig. 6. The measurement of transmission characteristics
at = 10log Ps,out / Ps,in in dependence on the pumping power Pp.
POSTER 2017, PRAGUE MAY 23
Fig. 7. The modulated electrical signa at the oscilloscope. DC signal
component ASE represents the size of the amplified spontaneous emission.
at [dB] Ppumpid[mW]
Fig. 8. The transmission characteristics of samples M1 – 02 –C4 – K7 ,
M1 – 02 – C2 – K7 (type of glass-slice-chip-channel).
The measurement proved optical activity in samples M1 –
02 – C4 – K7 and M1 – 02 – C2 –K7 that also represent the
smallest attenuation. Time measurements of the M1 – 02 –
C4 – K7 and M1 – 02 – C2 – K7 samples reveal a static
attenuation of 1.27, for the maximum pumping of 20 dBm
and a differential gain of 18.55 W/mW of the pumping
power. The value of the differential gain does not depend on
the attenuation of the optical coupling to the waveguide and
the attenuation of the waveguide itself, so the real optical
activity of the sample can be considered. Saturation of this
parameter with pumping up to the power of 20dBm was not
observed during the measurements. The resulting
attenuation values of these samples, using this method, a
wavelength of 1550 nm, input power of – 1 dBm and zero
pumping are:
1. M1 – 02 – C4 – K7 ………… - 4,4 dB
2. M1 – 02 – C2 – K7 ………… - 4,8 dB
3. 2223 – C2 – K5 ………… - 9,5 dB
4. Y2 – 02 – C2 – K5 ………… - 17,2 dB
5. Y2 – 02 – C2 – K ………… - 16,8 dB
Measurements were done by the broadband method. The
sources of the measuring signal is a supercontinuum emitter.
Fig .9. Block scheme of measurement spectral characteristic.
Fig. 10. The spectral characteristic of wideband input signal
(supercontinuum)
The signal is broadband; its run is shown in Fig. 10. An
optical measuring IDIL amplifier (Safibra) was used as a
comparison in addition to the samples mentioned above
(Fig. 11). This method particularly allows searching for
those wavelengths that amplify the given sample. The
measurement proved an optical activity in samples M1 – 02
– C4 – K7 and M1 – 02 - C2 – K7 with the smallest
attenuation. The activity was not detected in other samples.
The following graphs show the spectral characteristics of the
input signal (green curve), spectral characteristics of the
measured sample without pumping and the spectral
characteristics of the measured sample with the wavelength
of 980 nm. The area where sample activity is specified is
marked by an ellipse. The areas of optical activity for the
individual samples are:
1. M1 – 02 – C4 – K7 ………… 1530 -1560 nm
2. M1 – 02 – C2 – K7 ………… 1540 -1590 nm
3. 2223 – C2 – K5 ………… non-measurable
4. Y2 – 02 – C2 – K5 ………… non-measurable
5. Y2 – 02 – C2 – K6 ………… non-measurable
y = 0,0102x - 4,6465
-5
-4,8
-4,6
-4,4
-4,2
-4
-3,8
0 20 40 60 80 100
izolator
Fianium
Example
SP. AQ6370c
Supercontinum
Input 980 nm
mux
Ps,in
-65
-55
-45
-35
-25
-15
800 1000 1200 1400 1600
Ps,in
[d
Bm
]
λ[nm]
POSTER 2017, PRAGUE MAY 23
Fig. 11. The spectral characteristic of an optical measuring IDIL amplifier.
In areas about the wavelength of 1550 nm happens at off
source pumping high inhibition, that is of incurred
absorption energy on erbium ions. At source pumping (laser
at 980 nm) then happens to expressive thickness signal 25
dB.
Fig.12. The spectral characteristic sample M1 – 02 – C2 – K7.
Fig. 13. The spectral characteristic sample M1 – 02 – C4 – K7.
A high attenuation, caused by the absorption of energy of
erbium ions, takes place around the 1550 nm wavelength
when the pumping source is turned off. A marked
strengthening of the signal (about 25dB) takes place with a
pumping source (laser at 980 nm).
IV MEASUREMENT EVALUATION AND
CONCLUTION
The time measurement method makes it possible to
determine attenuation and differential gain gd with very high
precision but only at one wavelength, in this case, the
wavelength of 1550 nm ( gd = Δ𝑎𝑡,𝑝𝑢𝑚𝑝𝑒𝑑
Δ𝑎𝑡,𝑢𝑛𝑝𝑢𝑚𝑝𝑒𝑑).
The spectral method enables to look up areas where the
samples attenuation strength (are optically active) and, with
lower exactness, also determine attenuation or gain.
Considering the measuring results using both the spectral
and the time method at the wavelength of λ = 1550 nm, the
samples with the lowest insertion loss have the biggest
differential gain. Insufficient pumping occurs at those
samples that have high insertion loss and thus signal
amplification is not achieved. According to our opinion, the
substantial attenuation is not caused by the composition of
the samples but the quality of the optical coupling. The need
for improvement of the optical coupling is indicated by an
evaluation of the results. There is a further need, based on
the extrapolation of the attenuation characteristic of the
active samples, to increase the power of the pumping define
to at least 320 mW to acquire an absolute positive gain
under the condition that saturation does not occur. This
hypothesis was not tested since a source of this power
output was not available. Another possibility of increasing
the gain is the lengthening of the active length of the
sample. Under the current parameters, it is necessary to
increase the active length of the sample to at least 10 cm to
get a positive gain.
ACKNOWLEDGMENT
Our research is supported by the Student Grant Competition
of the Czech Technical University in Prague under grant
number SGS16/162/OHK3/2T/13.
REFERENCES
[1] C.E.Chyssou,F.Di Pascale,C.W. Pitt:Improved gain performance
in𝑌𝑏3+ - sensitized 𝐸𝑟3+- doped aluminia (𝐴𝑙2𝑂3) channel optical
waveguide amplifiers.J. of Lightwave Technology,19,2001,
[2] O.Barkman,V.Prajzler,P.Nekvindova:Design and modeling of the
single mode optical Glass waveguides for passive photonics
structures, Optické komunikace 2011, Praha, 2011, p.101 – 104.
[3] P.G.KiK and A.Polman : Erbium-Doped Optical-Waveguide
Amplifiers on Silicon (MRS Bulletin/April 1998
[4] V.Prajzler, I. Hüttel, O. Lyutakov, J.Spirkova, J.Oswald, V. Jerabek:
Optical Properties of PMMA Polymer Doped with 𝐸𝑟3+ and
𝐸𝑟3+/𝑌𝑏3+ Ions, Journal of Physics, Conference Series 100, 2008,
p.1-4
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Ps,
ou
t,Ps,
in [
dB
m]
λ[nm]
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-75
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ou
t,Ps,
in [
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m]
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ou
t,Ps,
in [
dB
m]
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POSTER 2017, PRAGUE MAY 23