We present a high power semiconductor Master Oscillator Power Amplifier monolithically integrated on InP, which includes a modulation section. This device can be used for random-modulation-continuous wave lidar systems or free-space communications

Esquivias Moscardo, Ignacio

Faugeron, Mickael

García Tijero, José Manuel

Krakowski, Michel

Pérez Hugalde, Carlos

Pérez Serrano, Antonio

Van Dijk, Frédéric

Vilera Suárez, María Fernanda

Servicio de Coordinación de Bibliotecas de la Universidad Politécnica de Madrid

Monolithic Integration of a High Power 
Semiconductor Master Oscillator Power Amplifier 
M. Faugeron , M. Vilera , A. Pérez-Serrano , J. M. G. Tijero , I. Esquivias , M. Krakowski and F. van Dijk 
Abstract— We present a high power semiconductor Master 
Oscillator Power Amplifier monolithically integrated on InP, 
which includes a modulation section. This device can be used for 
random-modulation-continuous wave lidar systems or free-space 
communications. 
Index Terms — Distributed feedback lasers, semiconductor 
optical amplifier, integrated optics devices, multi-section laser, 
master oscillator power amplifier. 
I. INTRODUCTION 
High power, single-mode semiconductor emitters at 
1.55 um are very promising devices for lidar systems and free-
space communications thanks to their low weight, 
compactness, high wall-plug efficiency and radiation 
hardness. To compete with fiber and solid-state lasers, they 
must exhibit output power > 0.5 W with a stable wavelength. 
II. DESIGN OF THE STRUCTURE 
We have investigated the Master Oscillator Power 
Amplifier (MOP A) architecture which usually consists of two 
sections, a distributed Bragg reflector (DBR) or distributed 
feedback (DFB) laser acting as a master oscillator and a power 
semiconductor optical amplifier (SOA). The MOPA 
architecture seems the more convenient solution to obtain both 
high power and single-mode operation [1], [2]. In that case, 
the SOA is often flared to increase its saturation power. 
Instabilities in MOPA devices mainly comes from 2 factors: 
the disturbance of the DFB laser due to the light which returns 
into it, the mode competition between the whole cavity 
defined by the 2 chip facets and the DFB laser (Fig. 1). To 
mitigate these 2 effects, one key parameter is the reduction of 
the reflections at the SOA facet. To decrease as much as 
possible the reflections coupled to the waveguide mode, we 
have tilted the SOA waveguide and we have included a bent 
between the DFB laser and the flared SOA (Fig. 2). One 
advantage of the bent MOPA architecture is that we can both 
control the reflectivity of the DFB laser back facet (waveguide 
perpendicular with the facet) and have a tilt for the SOA 
waveguide. The bent section can be used as a pre-amplifier 
SOA or as a modulation section (forward-biased). 
The MOPA chips were High Reflectivity (HR) / Anti 
Reflectivity (AR) coated. Then individual chips were mounted 
p-side up on Aluminum Nitride submounts (Fig. 3). 
Oscil lation on the whole cavity 
HR AR< 102 
Fig. 1. Schematic of a straight MOPA. 
HR AR<10 2 
Fig. 2. Schematic of a bent MOPA. 
Fig. 3. Picture of the bent MOPA mounted on a A1N submount. 
III. RESULTS 
For all the devices shown in the letter, the DFB laser, the 
modulator and the flared SOA lengths are respectively 1, 1 
and 3 mm. Fig. 4 is a plot of the output power as a function of 
the flared SOA bias current at 10° C (IDFB = 400 mA, 
Imod =300 mA). The maximum output power is 620 mW for 
5.7 A. With shorter device (same DFB laser and modulator 
length but only 2 mm long flared SOA), we have obtained a 
maximum output power of 430, 510 and 600 mW respectively 
at 18, 12 and 6° C (ISOA = 3 A). 
The optical spectrum is plotted Fig. 5 for IDFB = 400 mA, 
Imod = 300 mA and ISOA = 3 A. The device is single-mode with 
a side mode suppression ratio (SMSR) superior to 45 dB. The 
peak is blue-shifted (17 run) compared with the amplified 
spontaneous emission. Be closer or slightly red-shifted from 
the maximum of the ASE will be better to get a higher output 
power. For an application point of view, the stability of the 
peak wavelength is very important. Fig. 6 shows the evolution 
of the optical spectra as a function of the DFB laser bias 
current for Imod = 300 mA and ISOA = 3 A. Because the DFB 
laser is not A/4 phase-shifted there are 2 peaks close to the 
threshold (each side of the stop-band). From IDFB = 200 mA, 
the laser remains purely single-mode without any mode-
hopping. The parabolic evolution of the wavelength is due to 
heating effects (standard for DFB laser). 
700 
600 
500 
400 
300 
200 
100 
0 
IDFB = 400 mA, Imod = 300 mA 
2 3 4 
Amplifier current (A) 
Fig. 4. P-I measurement for a 5 mm long MOPA (T = 10° C). 
0 
-10 
-20 
-30 
-40 
-50 
-60 
-70 
— T = 18°C 
—— —-^, 
— — — """ ~~~~~~ 
1533 1553 1573 1593 
Wavelength (nm) 
Fig. 5. Optical spectrum (T 
1613 1633 
18° C). 
Fig. 6. Optical spectra (variation of IDFB, Imod = 300 mA and ISOA = 3 A). 
The optical linewidth measured using the delayed self-
heterodyne method (1 km SMF fiber) was in the 2 to 5 MHz 
range for high DFB bias currents. We have observed an 
increase of the linewidth with the increase of the flared SOA 
current (Fig. 7). We think this is due to an increase of the 
current source noise. 
Fig. 8 shows preliminary modulation results of a similar 
device with different grating pitch leading to a slightly 
different emission wavelength and a lower maximum output 
power (~ 180 mW). The CW bias conditions of this device 
are: IDFB = 300 mA and IPA = 2.5 A. The response to the 
superimposition of a dc bias current Imod = 100 mA and a 12.5 
MHz square signal (peak-to-peak voltage Vpp = 18 V) applied 
to the modulation section (bent section) is shown in Fig. 8a. 
Fig. 8b shows the optical modulation amplitude (OMA) and 
the Extinction Ratio (ER) as a function of the modulation 
amplitude Vpp. At 12.5 MHz a maximum OMA of ~ 170 mW 
with an ER of ~ 42 dB is obtained for Vpp = 20 V. This 
modulation results are encouraging for the application of the 
device as laser source for the detection of atmospheric CO2 by 
random modulation-continuous wave differential absorption 
lidar (RMCW DIAL) [3]. 
(a) ISOA = 2.2 A (b) ISOA = 5.0 A. 
Measured 
JL Lorentzian fit 
A J \ y v 
0* FWHM = 3,0 MHz ^ ^ ( É » , 
7\ 
Measured 
-Lorentzian fit 
FWHM = 4,4 MHz 
30 50 70 90 110 130 
Frequency (MHz) 
30 50 70 90 110 130 
Frequency (MHz) 
Fig. 7. Optical linewidth for ISOA = 2.2 (a) and ISOA = 5.0 (b). 
Fig. 8. (a) Modulation response to a square wave (Vpp = 18 V). (b) OMA 
and ER. f = 12.5 MHz, IDFB = 300 mA, Imod = 100 mA and ISOA = 2.5 A. 
I V . CONCLUSION 
We have fabricated a 3-section monothically integrated 
M O P A . The output power is in the 400-600 mW range and the 
wavelength emission peak is single-mode ( S M S R > 45 dB) 
and stable. The optical linewidth is below 5 MHz. Preliminary 
modulation results indicate the suitability of these devices for 
R M C W lidar applications. 
V . ACKNOWLEDGMENT 
The authors acknowledge the European Commission Directorate-General for 
Research and Innovation within the framework of the European Space Project 
B R I T E S P A C E under Grant 313200, the Communidad de Madrid within the 
Program S I N F O T O N - C M under Grant S2013/MIT-2790 and the Ministerio 
de Economia y Competitividad of Spain through the R A N G E R Project under 
Grant TEC2012-38864-C03-02. 
REFERENCES 
[ 1 ] M . L . Osowski, et al., “High-power semiconductor lasers at eye-safe 
wavelengths,” in proc. SPIE, Laser Technol. Defense Secur. V, vol. 
7325, p. 73250V, May 2009. 
[2] L. Hou, et al., “Narrow linewidth laterally coupled 1.55 µm 
AlGaInAs/InP distributed feedback lasers integrated with a curved 
tapered semiconductor optical amplifier,” Opt. Lett., vol. 37, no. 21, 
pp. 4525-4527, Nov. 2012. 
[ 3 ] I. Esquivias, et al, “High-brightness all semiconductor laser at 1.57 
μm for space-borne lidar measurements of atmospheric carbon 
dioxide: device design and analysis of requirements” in proc. SPIE 
9135, Laser Sources and Applications II, 913516 
doi:10.1117/12.2052191 (2014). 
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Monolithic integration of a high power semiconductor master oscillator power amplifier

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Monolithic integration of a high power semiconductor master oscillator power amplifier

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