Radiation tolerant passive and active optical fiber products for use in space environments

Transcription

1 Radiation tolerant passive and active optical fiber products for use in space environments Mark Hill, Judith Hankey, Rebecca Gray

2 Introduction Space radiation environment space weather Orbital dose rates Radiation tolerant HB-G fiber (PM) AstroGain TM concept photo-annealing of radiation damage through 980nm pump only Radiation testing HB-G results Photo-annealing tests AstroGain results continuous and discontinuous use gain spectra Conclusions/summary

3 Space Weather Courtesy NASA/JPL-Caltech Solar Wind Solar Particle Events (SPE) Flares Prominences Coronal Mass Ejections (CME) Galactic Cosmic Rays (GCR) All interact with Earth s magnetosphere and impact on the local radiation environment. Geomagnetic Storms. Courtesy NASA/JPL-Caltech -

4 Space Weather Spacecraft travels through sea of ionised plasma and radiation. Materials on board can experience: Lattice deformation through Ionisation Direct collision Courtesy NASA/JPL-Caltech Creation of impurities by neutron capture Build up of charge Distort lattice Dangerous discharges

5 Orbits Dose Rates Orbit Low Earth Orbit (LEO) Medium Earth Orbit (MEO) Geosynchronous Orbit (GEO) Geosynchronous Transfer Orbit (GTO) Typ. mission duration (yrs.) Av. Dose Rate (Gy/hr.) Total dose for mission (Gy) x x x x Total doses are calculated assuming EDFAs are behind a 10mm thick aluminium spherical shield. Courtesy of Berné et al. (2004), calculated using OMERE 2.0 software.

6 Highly Birefringent, Radiation Tolerant Fiber Phosphorous free Bow-Tie structure optimised for: High Birefringence Low Attenuation Ideal for use as high precision gyroscopes Courtesy NASA/JPL-Caltech -

7 AstroGain TM EDF for space applications Erbium-doped fiber (EDF) Proprietary trivalent core matrix Designed to accelerate photo-annealing recovery of radiation damage Targets photo-annealing of point defects using 980nm optical pump source photon energies. Courtesy NASA/JPL-Caltech - No need for secondary optical source at higher photon energy. Other authors suggest use of 532nm photo-anneal source

8 PM fiber tests

9 Radiating the Samples 60 Co Source Dose rate varied by distance from source Gy/hr Radiation dose rate within 10% tolerance level

10 RIA (db/km) Standard HB-G (non-rt) vs HB-G RT samples Non-RT samples radiated at a dose rate of 50Gy/hr up to a total dose of 200Gy. P-free RT samples also tested to 200Gy, and to higher levels ,1 0,12 0,14 0,16 0,18 0,2 0,22 0,24 NA Phosphorus Rad Tolerant - No Phosphorus

11 Higher dose HB1500G-RT samples 3 HB1500G-RT samples radiated at a dose rate of 250Gy/hr up to a total dose of 5000Gy.

12 AstroGain EDF tests

13 AstroGain Photo-annealing Setup (EDFA) 3 Samples with differing trivalent compositions (A-1, A-2 & A-3). radiated at 50Gy/hr to a total dose of 200Gy. Post-radiation, fixed 80dB absorption lengths of each sample placed into EDFA setup 175mW pump power at 974nm results in photo-annealing effect EDFA output power monitored for 7 day photo-annealing period. RIA and spectra re-measured post photo-annealing. Input Signal WDM FUT WDM O/P Pump Res. Pump

14 Photo-annealing Worst case test of photo-annealing response: Highly accelerated dose rate Many years of accumulated dose in 4 hours All radiation damage is done before photo-annealing is performed Total accumulated dose higher than expected in orbit Equivalent to 30 years in GEO Or 60 years in LEO

15 Photo-annealing Results

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17 AstroGain TM sample results AstroGain TM sample number Peak 1531nm Absorption (db/m) Trivalent material % (scaled to fiber A-3) RIA pre 7 day photo-anneal (db/km) RIA post 7 day photo-anneal (db/km) EDFA power output recovery after 20 years A % % A % % A % %

18 Normalized Signal O/P Recovering output of AstroGain TM samples over 20 years anneal time 100% 90% 80% 70% 60% 50% 40% 30% 20% A-1 A-2 A Time elapsed (min)

19 Normalized Signal O/P Normalized Signal O/P Recovering output of AstroGain TM samples over 20 years anneal time 100% 90% 80% 70% 60% 50% 40% 30% 20% 80% 70% 60% 50% 40% 30% 20% Time elapsed (min) Anneal Time (years) A-1 A-2 A-3

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21 Normalized Signal O/P after 20 years AstroGainTM amplifier output recovery under discontinuous use 100% 90% 80% 70% 60% 50% 40% 30% A-1 A-2 A-3 20% 0,01% 0,10% 1,00% 10,00% 100,00% Percentage time that amplifier is active

22 Gain (db/m) A-3 fiber gain spectra pre, post irradiation and post 7 day anneal Control Sample (no rad) Radiated Sample Radiated Sample after 7 day photo anneal Wavelength (nm)

23 Conclusions Phosphorous free, HB-G fibers have shown two orders of magnitude improvement over the radiation resistance of standard PM fibers. After 5000Gy effective dose, attenuation of Fibercore HB1500G-RT: < 9dB/km at 1310nm < 7dB/km at 1550nm Equivalent to an overall RIA of: db/km/krad at 1550nm db/km/krad at 1310nm. Attenuation consistently low across the full operation wavelength range.

24 Conclusions AstroGain TM has demonstrated effective photo-annealing of radiation damage that can be expected in a space environment. using only a 980nm pump in a standard EDFA configuration Results suggest over a 20 year mission lifetime: Efficiency maintained Spectral performance maintained For discontinuous use: Proprietary trivalent dopant content of AstroGain TM can be fine-tuned to optimise performance. Effective photo-annealing under standard EDFA configuration Saves the need for costly secondary pump sources Mass budget Power consumption Reliability

25 Thank you for listening UK AND WORLDWIDE Fibercore House University Parkway Southampton Science Park Southampton Hampshire SO16 7QQ UK T: +44 (0) F: +44 (0)

26 Van Allen Radiation Belts