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Fiber Raman Amplifier Development for Laser Absorption Spectroscopy

Measurements of Atmospheric Oxygen near 1.26 Micron

J. T. Dobler1, J. A. Nagel2, V. Temyanko2, T.

Zaccheo3, B. Karpowicz3, and M. Braun1

1ITT Geospatial Systems, Fort Wayne, IN 2TIPD, LLC & College of Optical Sciences, University of Arizona, Tucson, AZ

3Atmospheric and Environmental Research, Inc, Lexington, MA

This document is EAR controlled. Use or disclosure of this information is subject to the restrictions on the Title Page of this document.

Overview

• Multifunctional Fiber-Laser Lidar (MFLL) overview

• Recent CO2 work

• Raman amplifier development

• Ground testing

• Preliminary results

• Current and future work

June 23, 2011 2


Active Sensing of CO2 Emissions over Nights, Days and Seasons [ASCENDS]: A Multi-Functional Fiber Laser Lidar for Climate Variability and Atmosphere Composition

• Comprehensive Instrument Suite:

• CO2 Lidar

• O2 Lidar

• PN Laser Ranger

• Passive Temperature Sounder

• Passive CO Sensor

• Dedicated Payload

June 23, 2011 3


CO2 EDU Instrument Overview

June 23, 2011 4

•Simultaneous transmit/receive of all wavelengths

•Software based digital lock-in separates channels

•Leverages highly reliable CW telecom laser components

•No free space optics allows for rugged design


EDU Flight History

June 23, 2011 5

DC-8UC-12Lear-25ITT EDU

The CO2 EDU has been deployed in 10 flight campaigns

since May 2005; with more than 50 flights spanning 3

different aircraft. Flights have been conducted over

various land types and over water, during both day and

night operations. Recent results for the CO2 instrument

as compared to high precision in-situ data have shown

absolute comparisons to better the 0.5 ppm with

standard deviation of ~2ppm.


Fiber Raman Amplifier Objectives

• Amplify a 50 kHz or greater modulated CW 1.26-1.27 µm seed

signal to Watt level average power (5 W goal)

• Simultaneously transmit online and offline wavelengths

• Design fibers to suppress stimulated Brillouin scattering (SBS)

to allow for narrow linewidth amplification

• Varying core diameter

• Reduce overlap between optical and acoustic modes

• Simple, efficient, and robust architecture

June 23, 2011 6

This document is EAR controlled. Use or disclosure of this information is subject to the restrictions on the Title Page of this document. June 23, 2011

First Generation Fiber Raman Amplifier

7

Galeener, et. al., Apl. Phys. Lett.,

32, 34, 1978.

Nagel, et. al., IEEE Photon. Technol. Lett., 23, 585, 2011.

• Core variation broadens SBS spectrum by

50 MHz for ~3 dB SBS suppression

• 1.8 W average power achieved

• 2.4 W peak online (~30% optical efficiency)

• 0.58 W peak offline (~10% optical efficiency)


First Amplifier and Test Setup

June 23, 2011 8

Data acquisition and control

done through integration

with ITT CO2 EDU

This document is EAR controlled. Use or disclosure of this information is subject to the restrictions on the Title Page of this document. June 23, 2011

After Integrating With the EDU Tests Were Performed at ITT’s Ground Test Facility

TX/RX

680 m

Path

Weather

TX/RX

680 m

Path

Weather

9


AER’s End-to-End Analysis Software, Previously

Developed For the CO2 EDU was Updated to

Include O2

Ingest/Analysis

Interface

User-Defined Model Results

Web Interface to

Current/Historical

Weather Conditions

Interactive

Analyses

The data is fed into LBLRTM to generate values of optical depth for a given pressure, temperature, relative

humidity, and distance to target. The values for optical depth are computed in wavelength range of the

IPDA instrument, and values for online/offline optical depth are selected based upon the measured

wavelengths provided by the IPDA system. The difference between online and offline optical depths are

taken to compare with measurements of differential optical depth taken with the IPDA.

June 23, 2011 10


Initial Testing Results First Gen Amplifier

June 23, 2011

y = 0.8898x - 0.0023R² = 0.9782

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45

Measu

red

Preliminary Model

Measured vs. Modeled Diff OD

y = -0.0001x + 0.9783R² = 0.9657

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 500 1000 1500 2000 2500 3000

Measu

red

Dif

f T

ran

sm

issio

n

Range to Target [m]

• Measurements were made

over ranges from 600 m –

2.7 km

•The preliminary model

comparisons show good

correlation with the O2 IPDA

measurements

11


Second Generation Fiber Raman Amplifier

• Reduced size by 2X

• Reduced weight by 40 lbs

• Reduced power by 110 VA

• Forward pumping produced 13.2 W peak

with 3 db bandwidth of <3 MHz, but out of

band ASE becomes significant @ ~10 dB

down

• Backward pumping produces clean

spectrum (>45 dB side-mode and ASE

suppression) but with output limited to

~ 3 W peak from the amplifier

• Implemented at 1262 nm to take advantage

of trough between two lines

• Clean modulation demonstrated for both

forward and backward pumping schemes

June 23, 2011 12

Forward Stimulated Raman Scattering Modulation After 170m Sinusoidally Varying Core Fiber at 38A Pump Current

0

0.05

0.1

0.15

0.2

0.25

0 5 10 15 20 25 30 35 40

Time (us)

Am

plitu

de (

V)


Spectrum Forward vs. Backward Pumping

Forward Pumping

13.2 W peak, 3 dB

bandwidth ~3 MHzForward Stimulated Raman Scattering Spectrum for 200m First Generation Raman Fiber and 29W

Pump Power

-80

-75

-70

-65

-60

-55

-50

-45

-40

-35

-30

1260 1260.5 1261 1261.5 1262 1262.5 1263 1263.5 1264 1264.5 1265

Wavelength (nm)

dB

m

Backward Pumping

2.4 W peak, 3 dB

bandwidth ~2 MHz

Offline Forward Raman Spectrum at Full Pump Power (60A) from 40dB Tap

-80

-70

-60

-50

-40

-30

-20

1260 1260.5 1261 1261.5 1262 1262.5 1263 1263.5 1264 1264.5 1265

Wavelength (nm)

dB

m

June 23, 2011 13

Major loss for backward pumping is efficiency. Need longer fibers/more SBS suppression


Initial Ground Measurements with 2nd

Generation Amplifier (Backward Pumping)

June 23, 2011 14

0.7

0.75

0.8

0.85

0.9

0.95

1

1.05

1262.49000 1262.50000 1262.51000 1262.52000 1262.53000 1262.54000 1262.55000 1262.56000 1262.57000 1262.58000

Dif

fere

nti

al T

ran

sm

iss

ion

Wavellength

Preliminary Stepped Sweep of O2 Absorption Feature vs Model Prediction for Target 680 m Away

Measured

model

Not calibrated for

Optical filter


Ongoing Fiber Development

First fiber with acoustic

guiding layer had irregular

core shape and guided

significant light in the

inner cladding

Adjustments were made

to the heating elements

used to collapse the

MCVD tube which has

resulted in circular cores

on subsequent fibers

June 23, 2011 15


Recent Work to Obtain Required SBS Suppression

Latest iterative fiber

design

Results from latest

preform

June 23, 2011 16

-60 -40 -20 0 20 40 60-8

-6

-4

-2

0

2

4

6x 10

-3

m

n


Optical Mode

m

m

0 5 10 15

0

2

4

6

8

10

12

14

16-3.5

-3

-2.5

-2

-1.5

-1

-0.5

0

m

m

Acoustic Mode 1

0 5 10 15

0

2

4

6

8

10

12

14

16 -2

-1.8

-1.6

-1.4

-1.2

-1

-0.8

-0.6

-0.4

-0.2

0

m

m

Acoustic Mode 2 (Degenerate Mode)

0 5 10 15

0

2

4

6

8

10

12

14

16

-2

-1.5

-1

-0.5

0

0.5

m

m


0 2 4 6 8 10 12 14 16

0

2

4

6

8

10

12

14

16 -2

-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

3

m

m


0 5 10 15

0

2

4

6

8

10

12

14

16

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

3

Fiber Design Performance Modeling

June 23, 2011 17


Packaging Amplifier for DC-8 Flights

• HP wave meter for

monitoring offline

wavelength

• Seed laser and modulation

box

• Bristol wave meter for

monitoring online

wavelength

• Polarization control

• Raman amplifier

• Pump Laser

June 23, 2011 18

Detector

is being

provided

by LaRC


Current and Future Work

• Second generation amplifier is currently at ITT and is being

packaged into a DC-8 rack and integrated with the CO2 EDU

• Ground tests are being conducted over the next two weeks.

• Flight testing is planned for July and August on the NASA DC-

8 aircraft.

• New single mode fibers compatible for splicing with Hi-1060

fiber have been manufactured and are being evaluated for

their acoustic profiles and doping concentrations.

• We are currently pursuing funding to exploit the progress we

have made in the design and manufacture of acoustic guided

fibers for this wavelength. With plans to combine the varying

core diameter approach for maximum SBS suppression.

June 23, 2011 19


Acknowledgements

• This work is supported by NASA, Earth Science Technology

Office (ESTO) under the Advanced Component Technology

Grant #NNGX09AD79G awarded to ITT Geospatial Systems.

• Additional collaborators:

• ITT – Doug McGregor, Mark Neal, Steve Horney

• TIPD, LLC, & College of Optical Sciences – Nasser

Peyghambarian and Robert Norwood

• AER – Hilary E. Snell

June 23, 2011 20


Questions?

June 23, 2011 21

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