eLISA Laser Development in the US
Jordan Camp
Kenji Numata
NASA Goddard Space Flight Center
LISA X Symposium
May 20, 2014
GODDARD SPACE FLIGHT CENTER
eeLISA
S laser
ase p
program
og a at GSFC
GS C
• Provide TRL 5 laser system
y
by
y 2016
– Modern, fiber-based design
– Technical details to be made available to all LISA
members
• Funding
– SBIR (Small Business Innovative Research)
– Internal GSFC R&D
– LISA project funds
– Strategic
St t i Astrophysics
A t
h i Technology
T h l
award
d
– ~ $3.5M over 6 years
GODDARD SPACE FLIGHT CENTER
2
GSFC
GS
C LISA
S laser
ase des
design
g
ECL + Pre-amplifier
Pump LD
Pump
p LD
~10mW
ECL
Power amplifier
WDM
Yb fiber
~40mW
TFB
Yb fiber
~1.2W
2W
MOPA design
E
External
l Cavity
C i Laser,
L
fiber
fib preamp, fib
fiber amplifier
lifi
1064 nm wavelength
p
2 Watt output
GODDARD SPACE FLIGHT CENTER
3
Oscillator:
Osc ato : External
xte a Ca
Cavity
ty Laser
ase
1550 nm
Simple, compact, low mass,
highly reliable laser
(butterfly package)
Numata, Camp, Krainak, Stolpner, OE 18, 22781
GODDARD SPACE FLIGHT CENTER
NPRO: $25K
ECL: $5K
Packaging
ac ag g of
o ECL
C aand
d Preamp
ea p
2 ECLs
2P
Preamp Di
Diodes
d
10 cm x 5 cm x 1 cm
50 mW output
Redundant ECL and Preamplifier package
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1550
550 nm ECL
C iss space qualified
qua ed
Fig. 5 Reliability testing of ECL a) thermal cycling b) proton irradiation
Other tests:
• Hermiticity
• Gamma-ray exposure
• Accelerated aging
GODDARD SPACE FLIGHT CENTER
 Robust design suitable
for space operation
6
Conversion of ECL wavelength to
1064 nm
Gain Chip
RWG (1064nm)
Complex
p e ep
epi design
des g
1 Co
a Use special design to expand beam size
BH (1550nm)
epi design
ep
des g is
s decoup
decoupled
ed from
o mode
ode size
s e converter
co e te
Beam defined by BH and mode size converter
2 Waveguide defined by RWG
a Weak index guiding
b Thermal and carrier lensing
g affect beam profile
p
c Beam profile dependes on operating current
d Excitation of TEM 01 could degrade noise
f High ellipticity
g High GC-PLC coupling loss
q
facet passivation
p
h Requires
i One-step growth
Waveguide defined by BH
Strong index guiding
No thermal and carrier lensing
g
Beam profile does not depend on operating current
Only TEM00
Almost circular
Low GC-PLC coupling loss
Does not require
q
facet passivation
p
Two-step growth
GC
 PLC = Planar linear cavity
y
 GC = gain chip
 BFM = back facet monitor
Numata, Alalusi, Stolpner, Camp,
Krainak, OL 39, 2101 (2014)
GODDARD SPACE FLIGHT CENTER
BFM
Mount
PLC
7
Frequency noise of world’s 1st 1064 nm
ECL (in Butterfly package)
Lowering phase noise: 1) optimize optical cavity reflectivity slope 
strong feedback low noise 2) optimize gain chip for low loss  low noise
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3)G Oselect
gain chip for lowest 1/f noise
8
Frequency
eque cy stabilizing
stab
g the
t e ECL
C
Need external AOM as frequency actuator to
suppress frequency noise
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Frequency Modulation of ECL on laser chip
(to be implemented)
 Modulation of the effective refractive index inside the cavity, results in
f
frequency
modulation
d l ti
off the
th external
t
l wavelength
l
th up to
t 100 MHz
MH
 FM section on the gain chip, separated from gain section by etching
Ia+Im
AR
PLC Grating
10-15m Isolation > 300
Ib
AR AR
HR
SCH/MQW
Active Region
Ia = bias current of section-a
Im = modulation current
GODDARD SPACE FLIGHT CENTER
2000m
Power
o e Amplifier
p e
• Design
Yb LMA DC fiber
MM Pump LD
– All fiber
fib coupled
l d
>40mW
– Large mode area, double-clad Yb fiber
– Forward pump to avoid risk and noise sources
From seed
Redundant LD
TFB
>1.4W
Isolator
90/10
coupler
99/1
coupler
Input mon.
Output mon.
• Noise p
performance
– No additional frequency noise
– eLISA requirement level
• Differential phase noise (@2GHz)
• Stabilized low frequency
q
y RIN with
feedback to pump diode
10
Differential phase noise (1.4W output, Liekki fiber)
NGO requirement
-3
10
-4
10
-5
10
-6
10
0.0001
0.001
0.01
0.1
1
10
Frequency [Hz]
GODDARD SPACE FLIGHT CENTER
Differential phase noise
10
-1
10
-2
10
-3
10
After amplifier (stabilized)
After amplfiier (freerun)
R
Requirement
i
t (LISA)
-4
-5
10
0.0001
0.001
0.01
Frequency [Hz]
0.1
1
Relattive intensity noise [[/rtHz]
-2
Relative intensity noise [[/rtHz]
Ph
hase noise [cycle//rtHz]
-1
10
-5
10
After amplifier (stabilized)
After amplifier (free-run)
(free run)
NPRO (seed) only
Shot noise
4
2
-6
10
4
2
-7
10
4
2
-8
10
3
10
4
10
5
10
6
10
Frequency [Hz]
RIN and its stabilization (low/high frequency ends)
7
10
8
10
Planned
a ed Systems
Syste s Tests
ests for
o FY 2015
0 5
1064 nm ECL oscillator, rebuilt power amplifier
Temperature stabilized environment
Tests: noise,
noise accelerated aging,
aging etc.
etc
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Laser
ase Development
e e op e t Sc
Schedule
edu e
• FY 2014 - 2015
– Iterate design of 1064 nm ECL gain chip, planar cavity
– Achieve final frequency noise performance
• FY 2015
– Laser system testing with 1064 nm ECL
• FY 2016
– Reliability testing of 1064 nm ECL
• Low risk since same packaging as 1550 nm, also
E l
Eagleyard
d data
d t indicates
i di t reliable
li bl 1064 nm gain
i chips
hi
– Implement on-chip frequency modulation
GODDARD SPACE FLIGHT CENTER
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