Using the Liquid Crystal Spatial Light
Modulators for Control of Coherence and Polarization of Optical Beams

309

22
12 0 0
22
00
1
(,) exp exp
22
xy
xy
xy
SS
SS















(,)
W
xx through a thin polarization-dependent screen whose
amplitude transmittance is given by the so-called Jones matrix (Yariv & Yeh, 1984)

() ()
()
() ()
xx xy
yx yy
tt
tt





xx
Tx
xx
, (9)
with elements ( )
ij
t x being the random (generally complex) functions of time. It can be
readily shown (Shirai & Wolf, 2004) that the cross-spectral density matrix of the beam just
behind the screen is given by the expression

12 1 12 2
(,) ()(,)()


where
()

x
is some real random function. To provide the desired statistical characteristics
of modulation, the function
()

x
has to be generated by computer. The most appropriate
candidate for physical realization of such a computer controled random phase screen is the
LC-SLM.
3. Elements of the theory and design of LC-SLMs
The LC represents an optically transparent material that has physical properties of both
solids and liquids. The molecules of such a material have an ellipsoidal form with a long
axis about which there is circular symmetry in any transverse plane. The spatial
organization of these molecules defines the type of LC (Goodman, 1996). From the practical
point of view, the most interesting type is so-called nematic LC, for which the molecules
have a parallel orientation with randomly located centres within entire volume of the
material. Further we will consider the LCs exclusively of this type.
Because of its geometrical structure the nematic LC exhibits anisotropic optical behaviour,
possessing different refractive indices for light polarized in different directions. From the
optical point of view the nematic LC can be considered as an uniaxial crystal with ordinary

Optoelectronics – Devices and Applications

310
refraction index
o
n along the short molecular axis and extraordinary refraction index

d
A z
Φ

Fig. 1. Twist of LC molecules due to the boundary conditions at the alignment layers.
According to (Yariv & Yeh, 1984), the amplitude transmittance of twisted LC cell with front
molecules aligned along x-axis is given by the Jones matrix



























R
, (14)
is the coordinate rotation matrix and parameter

is defined as

22


. (15)
Using the Liquid Crystal Spatial Light
Modulators for Control of Coherence and Polarization of Optical Beams

311
Bellow we consider two important particular cases, namely when
º0


and
º90

. In the
first case we will reffer to the LC cell as 0º-twist LC cell and in the second case we will refer
to it as 90º-twist LC cell.
For 0º-twist LC cell Eq. (13) takes the form





























sin
2
sincos
sincossin

Saleh, 1990).

A
z
A y
Ψ
1
Ψ
2
Polarizer 1 90° LC cell Polarizer 2

Fig. 2. 90º-twist LC cell sandwiched between two polarizers.
The Jones matrix for the system shown in Fig. 2 is given by

)()(
1PLC2P


JJJT

, (19)
where
LC
J
is the matrix given by Eq. (17) and

Optoelectronics – Devices and Applications

312


, we obtain













0sincos
00
)exp(





i
iT
. (21)
The matrix given by Eq. (21) contains the only non-zero element






















yx
t
, (24)
and argument










s
m
i
t
t
a
n
c
e
0
aπ
2
π
3
π
4
π
β
0.2
0.4
0.6
0.8
1
1
.
2
2
π
4
π

23

, the amplitude transmittance
yx
t
approachs to
Using the Liquid Crystal Spatial Light
Modulators for Control of Coherence and Polarization of Optical Beams

313
unity while the phase transmittance rises linearly having a slope of approximately

2
. Thus,
when the birefringence parameter satisfies the condition
23



, the matrix given by Eq.
(21) can be well approximated as











o
2
oee
cos)()( nnnn 

. (28)
It has been shown (Lu & Saleh, 1990) that the dependence between tilt angle and applied
voltage has the form
























, (29)
where
c
V
is the threshold voltage,
0
V
is the saturation voltage, and
rms
V
is the effective
voltage. Combining Eqs. (27) – (29), it is possible to show that the birefringence parameter

finds to be approximately proportional to the inverse value of the applied voltage.
Finally, we are ready to define a LC-SLM as an electro-optical device composed by a large
number of LC cells (pixels) whose birefringence indices are controlled by the electrical
signals generated by computer and applied individually to each cell by means of an array of
electrodes. The amplitude transmittance of 0º-twist LC-SLM or 90º-twist LC-SLM can be
described by Eqs. (16) and (26), respectively, replacing parameter

by spatial function
)(x

.
4. Techniques for control of coherence and polarization by means of LC-
SLMs
4.1 Single 0º-twist LC-SLM
We begin with the technique based on the use of a 0º-twist LC-SLM (Shirai & Wolf, 2004). It

2
2
2
2
1
2
021
sinsincos
sincoscos
4
exp),(
xx
xxW E
, (30)
where
0
E is the value of power spectrum at the beam centre, ε is the effective (rms) size of
the source, and

is the angle that the direction of polarization makes with the x axis. It can
be readily verified that for such a beam
1),(
21

xx

and
1)(

xP


has the form


)(
2
1
)(
01
xx


, (32)
where
0

is a constant and
)(x

is a computer generated zero mean random variable which
is characterized by the Gaussian probability density
















2
2
2
21
2
exp)()(





xx , (34)
where
21
xx 

and


is a positive constant characterizing correlation width of
)(x

.
On substituting from Eqs. (30) - (32) into Eq. (10), one obtains











2
2110
20
2
sin)]()([expsincos)](exp[)exp(
sincos)](exp[)exp(cos
xxx
x
iii
ii
. (35)
On making use of Eqs. (33) and (34), it can be shown that (Ostrovsky et al, 2009b, 2010)





















2
2
2
2121
2
exp1exp)()(exp)()(exp





xxxx ii . (37)
Using the Liquid Crystal Spatial Light
Modulators for Control of Coherence and Polarization of Optical Beams

315
Then, Eq. (35) can be rewritten as











































2
2
2
2
2
0
2
0
2
sin
2
exp1expsincos
2
exp)exp(
sincos
2
exp)exp(cos
i
i
. (38)
































exp),(
2
2
2
2
2
2
1
2
1
2
021



















2
2
2
sin
2
exp11)(


















, (42)


2cos)( 

xP

316

Fig. 4. Degree of coherence given by Eq. (42) for
4



and different values of


.
4.2 Two 0º-twist LC-SLMs coupled in series
To avoid the shortcomings mentioned above, the authors (Ostrovsky et al, 2009) proposed to
use instead of a single 0º-twist LC-SLM the system of two 0º-twist LC-SLMs coupled in
series as shown in Fig. 5. Fig. 5. System of two crossed 0º-twist LC-SLMs coupled in series. The bold-faced arrows
denote the extraordinary axis of liquid LC.
The transmittance of the first SLM is just the same as in previous technique, while the
transmittance of the second one, whose extraordinary axis is aligned in the x direction, is
given by matrix









xx


, (45)
with
0

and
)(x

of the same meaning as stated in the context of Eq. (32). The transmittance
of the system composed by two crossed 0º-twist LC-SLMs is given by matrix











)](exp[0
0)](exp[
)exp()()()(
01LC2LC
x
x
xTxTxT


xx
xxW E























































































.
sin0
0cos
2
exp
4
exp),(
2
2
2
2
2
2
1
2
1
2
021



















2
2
2
exp)(




, (49)


2cos)( 

xP
. (50)
As can be seen from Eqs. (49) and (50), the output degree of coherence in this case does not
depend on direction of the input polarization and changes in the whole desired range from
1 to 0.
4.3 Two 0º-twist LC-SLMs coupled in parallel
The result resembling the one given above can be also obtained using the system of two 0º-
twist LC-SLMs coupled in parallel. Such a system has been described in (Shirai et al, 2005).
Here we propose a somewhat modified version of this technique.
The technique is based on the use of two 0º-twist LC-SLMs with orthogonal orientations of
their extraordinary axes placed in the opposite arms of a Mach-Zehnder interferometer as it

space propagation within the interferometer, one can represent the considering system as a
thin polarization-dependent screen with the transmittance given by matrix












)](2exp[0
0)](2exp[
)(
2
1
x
x
xT


i
i
. (51)
As before, we assume that parameter

of each 0º-twist LC-SLM has the form

)(
2
x

are generated by two different computers so that
they can be considered as statistically independent with the separable joint probability
density


 


)()()()(
2121
xxxx




ppp

. (53)
Following Subsection 4.1 and using in addition relation (Ostrovsky et al, 2010)



2
1)1(22)2(1
exp)]}()([exp{


orthogonally aligned 90º-twist LC-SLMs are used in the opposite arms of the Mach-Zehnder
interferometer. Secondly, the conventional beam splitter at the output of interferometer is
replaced by the polarizing one. As a result, taking into account that two polarizing beam
splitters coupled in series act as crossed polarizers, each arm of interferometer can be
considered as the system shown in Fig. 2 with
º0
1


and
º90
2


. In accordance with
Section 3 such a system realizes the phase-only modulation of the correspondent orthogonal
component of the incident beam. Fig. 8. System of two crossed 90º-twist LC-SLMs coupled in parallel: PBS, polarizing beam
splitter; M, mirror. The bold-faced arrows and circled dots denote polarization directions.

Optoelectronics – Devices and Applications

320
Again disregarding the negligible changes of coherence and polarization properties of the
electric field induced by the free space propagation within the interferometer, the system
shown in Fig. 8 can be considered as a thin polarization-dependent screen with
transmittance given by matrix


technique the cross-spectral density matrix has a slightly different form, namely































and the degree of polarization
)(xP

are given again
by Eqs. (49) and (50).
Concluding, it is appropriate to mention here that the proposed technique, as well the one
presented before, provides generating the beam of a Gaussian Schell-model type given by
Eq. (6) with parameters

22
00
sinES
x

,

22
00
cosES
y

and






yx

of the matrix
),(
21
xxW

is realized by means of the
following four experiments. In the first experiment the polarizers P
1
and P
2
are aligned to
transmit only x components of the incident field without any subsequent rotation of the
plane of polarization. In the second experiment P
1
and P
2
are aligned to transmit only y
components of the incident field again without any subsequent rotation of the plane of
polarization. In the third and the fourth experiments the polarizers P
1
and P
2
cut off the
different orthogonal components of the incident field and the corresponding polarization
rotator R
1
or R
2
serves to allow the interference of these components.
Using the Liquid Crystal Spatial Light

yxji
ξ
,
ξ
αx
z
kξξ
,
ξ
W
ξ
S
ξ
SxS
ijijjiij

















and
j
S

are the power spectra of the field components in the pinhole position
2ξ/
,
k is the wave number,
0
z
is the geometrical path between the pinhole plane and the
observation plane, and
.arg
ijij
Wα


From the physical point of view, Eq. (57) describes an
image with periodic structure, known as the interference fringe pattern. The measure of the
contrast of the interference fringes is the so-called visibility coefficient defined as

.
)()(
)()(
)(ξ
minmax
minmax
xSxS
xSxS






















. (59)
The spectra
i
S

and
j
S


322
6. Experiments and results
To verfy the proposed technique in practice, we conducted some physical experiments. The
experimental setup used in experiments is sketched in Fig. 10. The principal part of the
experimental setup was composed of two Mach-Zehnder interferometers coupled by the
common beam splitter. The first interferometer realized the modulation of the incident beam
as it has been described in Subsection 4.4, while the second one served for measuring the
degree of coherence and the degree of polarization of the modulated beam as it has been
described in Section 5.
As the primary source we used a highly coherent linearly polarized beam generated by He-
Ne laser (Spectra-Physics model 117A, λ=633 nm, output power 4.5 mW) which can be well
described by the model given by Eq. (30). The laser was mounted in a rotary stage that
allowed changing the polarization angle

without any loss of light energy. As the 90º-twist
nematic LC-SLMs we used the computer controlled HoloEye LC2002 electro-optical
modulators which have resolution of 800 × 600 pixels (32 µm square in size) and can display
the control signal with 8 bit accuracy (256 gray levels). The control of LC-SLMs was realized
independently by two computers using a specially designed program for generating the
random signals which obey the desired Gaussian statistics. To realize the measurements of
the degree of coherence we used two pinholes with diameter of 200 µm mounted on
motorized linear translation stages. Fig. 10. Experimental setup: L, laser; BE, beam expander; ZL, zoom-lens; PD, photodiode;
the other abbreviations are just the same as in Figs. 8 and 9.
We realized two sets of experiments. In the first set we measured the degree of polarization
for different values of the polarization angle of incident beam and for the fixed value (
1
)




. Fig. 12. Results of measuring the degree of coherence for
4



and different values of
parameter


.
7. Conclusion
In this chapter the problem of modulating the coherence and polarization of optical beams
has been considered. It has been shown that the LC-SLM represents an ideal tool for
practical realizing such a modulation. We have analized the known techniques of optical
modulation based on the use of 0º-twist LC-SLM and have proposed a new technique based
on the use of two 90º-twist LC-SLMs. Because of the wide commercial availability of 90º-

Optoelectronics – Devices and Applications

324
twist LC-SLMs the proposed technique proves to be the most attractive one. The
justifiability of this technique has been corroborated by the results of physical experiments.
8. Acknowledgment
The authors gratefully acknowledge the financial support from the Benemérita Universidad

Wolf E. (2007). Introduction to the Theory of Coherence and Polarization of Light, Cambridge
University Press, ISBN 9780521822114, Cambridge, UK.
Yamauchi M. & Eiju T. (1995). Optimization of twisted nematic liquid crystal panels for
spatial light phase modulation. Optical Communications, Vol.115, No.1, (March
1995), pp. (19-25). ISSN 0030-4018.
Yariv, A. & Pochi, Y. (1984). Optical Waves in Crystals, Wiley, ISBN 0-471-09142-1, USA.
16
Recent Developments in
High Power Semiconductor Diode Lasers
Li Zhong and Xiaoyu Ma
National Engineering Research Center for Optoelectronic Devices,
Institute of Semiconductors, Chinese Academy of Sciences
Beijing
China
1. Introduction
Due to a number of advantages of diode lasers, such as small size, light weight, high
efficiency etc., it has been the focus of the laser field from the beginning of the birth and has
been widely used in industrial, military, medical, communications and other fields.
Especially, to a great extent, a tremendous growth in the technology of solid-state lasers has
been complemented by laser diode array designs for pumping such solid-state lasers.
Significant applications continue to exist at common solid state laser systems such as
yttrium aluminum garnet doped with neodymium or ytterbium (Nd:YAG or Yb:YAG,
respectively) requiring pump light in the 780 nm to 1000 nm range. Driven by the increasing
demands of high-performance high-power laser pumping source and direct industrial
processing applications, tremendous breakthrough have been realized in the main optical-
electronic performances of high power semiconductor diode lasers, such as ultra-high peak
power, super-high electro-optical conversion efficiency, low beam divergence, high
brightness, narrow spectrum linewidth, high operation temperature, high reliability,
wavelength stabilization and fundamental transverse mode operation etc. These
achievements are attributed to a combination of the maturity of semiconductor material

some thoughts on the future study directions and the developing tendency for high power
diode lasers.
2. Status of high-power diode laser technology and characteristics
2.1 Laser diode chip technology
Over the recent years, high power diode lasers have seen a tremendous evolution in
material epitaxial growth technology, epi-structure optimization technique, cavity surface-
passivation technology etc Epitaxial structure is designed for a specific range of operation
to optimize a combination of optical, electrical and thermal performance, generally
minimizing both operating voltage and internal loss to achieve high efficiency with long
cavities for high-average-power and high-brightness applications. The details of these
structures, such as material compositions, layer thicknesses, asymmetric or symmetric
waveguide structure design, and doping profiles are selected to ensure that
manufacturability and reliability are not compromised. Important developments in epitaxial
growth technology include the reporting of low loss materials (about 1 cm
–1
for AlGaAs for
example), the development of the strained materials with attendant benefits on gain and
bulk defect pinning, and the development of aluminum-free materials such as InGaAs and
InGaAsP with the latter material having been reported to wavelengths below 800 nm. A
number of careful studies are being reported on filament formation and current crowding in
semiconductor lasers and methods for avoiding their deleterious effects. With the
improvement of the high-quality, low defect density epitaxial growth technology of
semiconductor materials, the resonator cavity length of the existing cm bar has been
increased from 0.6 ~ 1.0 mm to 2.0 ~ 5.0 mm, making a significant increase of the output
power. The large cavity length ensured low thermal and electrical resistivities of the devices
by increasing their active area. The cavity length is selected mainly depending on desired
operation power and is optimized for best power conversion efficiency (PCE) at the given
condition.
In continuous wave (CW) operation the output power from high power laser bars usually is
limited by the thermal load that the assembly may dissipate. Failure modes, like wear out of

quality. Therefore the beam quality is under the direct control of the far field divergence
angle. Overall, the waveguide structure of semiconductor lasers leads to a serious
asymmetry far-field beam quality. In the fast axis direction, the output beam can be
considered to be fundamental mode, but the divergence angle is large. The compression
of the fast axis divergence angle can effectively reduce the requirements for the fast axis
collimator aperture. While in the slow axis direction, the output beam is multi-mode and
the beam quality is poor. The beam quality can be directly improved by reducing the
divergence angle in the slow axis direction, which is the research focus in the field of the
high-beam quality semiconductor laser.
The research focus in the control of the fast axis divergence angle is how to balance the
fast axis divergence angle and the electro-optical conversion efficiency. Although a
number of research institutions had press release of the continued access to fast axis
divergence angle of only 3° and even 1°, but based on the consideration of the power, the
electro-optical conversion efficiency and the cost, it is difficult to promote practical
applications in the short term. In the early year of 2010, the P. Crump etc. of German
Ferdinand-Braun Institute has reported the fast axis divergence angle of 30° (95% of the
energy range) obtained through the use of large optical cavity and low-limiting factors,
meanwhile the electro-optical conversion efficiency of the device is 55%, which is the basic
standards to practical devices. The fast axis divergence angle of the current commercial
high-power semiconductor laser devices are also dropped from the original of about 80°
(95% of the energy range) to below 50°, which substantially lower the requirements for the
numerical aperture of the collimator.
In the slow-axis divergence angle control, recent studies have shown that, in addition to
the device's own structure, the combination of the drive current density and the thermal
effects of semiconductor lasers affect the slow axis divergence angle. The slow axis
divergence of a single emitter with long cavity length is of the most easy to control,

Optoelectronics – Devices and Applications

328

Company has presented the development of high-temperature 8xx-nm diode laser bars
for diode laser long-pulse (>10 milliseconds) pumping within a high-temperature (130 ºC)
environment without any cooling.( Fan et al., 2011) The epi-structure is based on a large
optical cavity separate confinement heterostructure with Al-free active region. By
adjusting Aluminum concentration in the AlGaInP barrier, introducing strain in quantum
well (QW) and adjusting the width of QW, optimizing the strain and the width of
quantum well, the gain is maximized, the loss and carrier leakage especially at high
temperature is minimized and the optical confinement of the waveguide is also be
improved. Under the operation condition (130 ºC, 15 ms pulse width, 5 Hz frequency and
100-A current pulse), the high-temperature laser bars show robust and consistent
performance, reaching 60 W (peak) power and having good pulse shape, as shown in
Figure 1. The laser bars do not show any degradation after 310,000 15-millisecond current
pulse shots. They demonstrated over 40-millisecond long-pulse operation of the 8xx-nm
CS bars at 130 ºC and 100 A. Regardless of the pulse shape, this laser bar can lase at
extremely high temperature and output pulse can last for 8 ms/2ms at 170 ºC/180 ºC
respectively, both driven by 60 A current pulses with 5-Hz frequency, 10 millisecond
pulse width. This is the highest operating temperature for a long-pulse 8xx-nm laser bar.
Figure 2 shows the high-temperature performance of the 3-bar stack array and its pulse
shape at 130 ºC. The peak power of the 3-bar array reaches 165 kW at 100A and 130 ºC, but
the pulse shape is very sensitive to the current and the power of the array drops much
faster than that of the CS bar, which may be attributed to the package difference between
the CS bar and stack array.

Recent Developments in High Power Semiconductor Diode Lasers

329

Fig. 1. Pulsed (15 msec PW and 5 Hz frequency) L-I performance and wall-plug efficiency at
130°C.


cooling technology with the circulating water at 5-8°C (Li et al., 2008). These output power
are the maximum continuous output power level of the current laboratory. In addition,
many other semiconductor laser company, such as the German company JENOPTIK,
Switzerland company Oclaro also continued to prepare the kilowatt diode laser array. J.
Müller ect. of the Oclaro has made it clear that the access to 1.5 kW/bar array devices is not
a problem based on the existing technologies. At the same time, the output power of high
beam quality, low fill factor cm bar is also increasing. Table 1 gives the BPP value of cm bars
with different fill factors obtained by the Limo Company of German. From the results of
Table 1, it can be concluded that for a certain horizontal dimensions of semiconductor laser
array device, in the case of the same divergence angle, the BPP value is proportional to the
fill factor, i.e. the lower the fill factor, the smaller of the BPP value, and the better the beam
quality. Currently, In the 9xx-nm wavelength range 150 W or higher CW output power
levels have become the standard for high filling factor bars.( Lichtenstein et al., 2005; Krejci
et al., 2009; Crump et al., 2006) In the 80x range devices with 100 W and more output power
were demonstrated (Tu et al., 1996; Ziegler et al., 2006). The output characteristic of an 808
nm device optimized for 140-160 W CW output power is shown in Figure 4 (Müller et al.,
2010).An output power of 185 W is achieved for CW 200A drive current. For currents above
180 A the thermal limitation of the device is clearly visible in a pronounced rolling of the P-I
curve limiting the achievable brightness in this operation mode. The output power of 9xx-
nm cm bar with 20% fill factor is up to 180 W/bar in CW condition, the BPP value is down
to 5.9 mm·mrad after the symmetry of the fast and slow axis of the beam, and the
commercial devices can be work above the level of 80 W/bar with long-term stability; the

Recent Developments in High Power Semiconductor Diode Lasers

331
Emitter Width
(μ
m
)

19

19

49
Fillin
g
Factor
(
%
)

50

50

30

20

2.5
Beam Diver
g
ence FA
(
FW 90%
)

(
°

735 720 428 285 37
S
y
mmetrized BPP

(
mm·mrad
)

9.5 9.4 7.2 5.9 2.1
Beam Diameter at
NA=0.22
(μ
m
)

121 120 92 75 27
Table 1. the BPP of cm bars with different structures.
output power of 2.5 % fill factor cm bar is up to 50 W/bar in CW condition, the BPP value is
down to 2.1 mm·mrad after the symmetry of the fast and slow axis of the beam, the current
device is still under developing, and need to improve the stability further. The reliable output
power of CW operated bars is in first place limited by the cooling capability of the assembly.
Bars operated in a qCW mode deliver a significantly higher reliable output power, because the
thermal load is reduced by a factor which is inverse proportional to the duty cycle of the
operation mode. Figure 5 and 6 give the typical performance of our lab’s 808nm laser diode
bar packaged by conductive heatsink (qCW 300 W/barand 200 W/bar with 60% PCE) and
980nm laser diode bar packaged by micro-channel heatsink (CW 200W/bar), respectively. Fig. 4. PIV-PCE characteristic of a 50% filling factor 808 nm bar on micro channel cooler at 25


333
and micro-heat-pipe technology etc., it is difficult to satisfy the practical applications in the
short term because of the performance characteristics, the cost and the compatibility
problems. Due to the two constraints mentioned above, in recent years, the major research
institutions and high-power semiconductor laser suppliers no longer blindly pursue the
improvement of the output power of cm bars, but gradually shift the focus to develop single
emitter and mini bars with high power and good beam quality.
3.2 Developments of the single emitter
Compared with the cm bar, the single emitter, which possesses the independent electrical
and thermal operation environment, can avoid the thermal crosstalk between the emitting
units, so that to have the obvious advantages in life span and beam quality. In addition,
owing to the low drive current of the single emitter, the requirement for the drive power can
be reduced significantly even in the serial operation. Meanwhile, the heat from a single
emitter is relatively low, so the conduction heat sink can be used directly for heat dissipation
to avoid the short life span problem brought by the micro-channel heat sink. And the
independent thermal operation environment can make it operate under high power density.
Currently, optical power linear density of a single emitter can be up to above 200 mW/μm
with narrow spectral width, while that of a cm bar is only about 50~85 mW/μm. Especially,
the independent thermal and electrical operation environment can make a significant
reduction in the risk of device failure. Under the support of the high stable gold tin solder
packaging technology, average life of the commercial high-power single emitters can reach
to above 100 thousands hours, which is much higher than that of cm bars and hence reduces
the use-cost of devices. Based on the advantages listed above, the single emitter exhibits the
trend that it will replace the cm bar gradually to become the mainstream semiconductor
laser device with high power and high beam quality.
In recent years, single emitters have been developed rapidly. Especially driven by the
demand of high power fiber lasers for high-brightness fiber-coupled pumping modules, the
single emitters with 90~100 μm strip width, which is matched to the 105 μm/125 μm
multimode fiber tail, are improved significantly in output power and beam quality.