Update on irradiation effects in optical fibers and optoelectronic ... - IFA

Association EURATOM MEdC 

<strong>Update</strong> on irradiation effects 

in optical fibers and optoelectronic 

components 

Dan Sporea*, Adelina Sporea*, Constantin Oproiu*, 

Ion Vata**, Rodica Georgescu** 

Simonpietro Agnello***, Laura Nuccio*** 

*National Institute for Lasers, Plasma and Radiation Physics 

**“Horia Hulubei” National Institute for Physics and Nuclear Engineering 

***Universita degli Studi di Palermo, Italy 

*409 Atomistilor St., Magurele, RO-077125, Romania 

e-mail: sporea@ifin.nipne.ro 

Days of Association EURATOM/MEdC, October 10-11, 2006, Cluj-Napoca


Irradiation Effects in Ceramics for Heating and 

Current Drive, and Diagnostics Systems 

Subtasks 2006: 

A. Investigations on the gamma-ray and electron beam radiation 

effects on semiconductor optical detectors for sensing and 

optical communication applications 

B. In-situ thermal annealing and photobleaching of low dose rate/ 

low dose gamma and neutron irradiated aluminium jacketed 

silica optical fibers 

C. Complementary investigations on irradiated optical fibers 

In cooperation with: 

• Centre d’Etude de l’Energie Nucleaire – SCK/CEN Mol 

• University of Palermo, Department of Astronomy and Physics 



Optical fibers are expected to play an important role, along with other 

optical components (such as windows and mirrors) and 

optoelectronic components in plasma diagnostics set-ups, 

communication systems, distributed sensing and control installations 

to be used in ITER. They have to operate under high temperature and 

high radiation fields (gamma-rays, neutron), hence the interest 

towards the investigation of their radiation resistance capabilities. 

Under irradiation, optical fibers exhibit both the degradation of their 

optical transmission and radiation induced optical emission. 

All these effects are related to the generation of radiation induced color 

centers in optical fiber core. Color centers appear over the entire 

optical spectrum (UV, visible ranges) 



Presentation outline 

1. Irradiation conditions 

2. Irradiated components and devices 

3. Research results 

4. Conclusions 

5. References 



Electron beam and gamma-ray irradiation conditions: 

The electron beam and gamma-ray irradiations were done at the “Linear Accelerator 

Laboratory” - The National Institute for Lasers, Plasma and Radiation Physics. 

The electron beam irradiation was 

carried out at room temperature, in an axial 

geometry, the electron beam incident on the 

photodiode sensing surface; 

- the electron beam current – 1 μA; 

- the pulse repetition rate – 100 Hz; 

- the pulse duration – 3,5 μs; 

- the beam transversal area – 100 cm^2; 

- the spot uniformity - +/- 5 %; 

- the dose rate – 2 kGy/ min 

The gamma irradiation was 

carried out with a dose rate of 9 Gy/ 

min and was produced by the electron 

beam impinging on a tungsten target. 



Neutron irradiation: 

The neutron irradiation was done at the Department of Applied Nuclear Physics facility of the 

“Horia Hulubei” National Institute for Physics and Nuclear Engineering. 

- Based on the reaction Be + d n + X, using a deuteron beam (13 MeV) and a thick beryllium 

target of 165 mg.cm^-2; 

- The samples are located downstream at the distances from 10 to 40 cm from the Be target; 

- The neutrons mean energy was about 5.2 

MeV. The neutrons flux above 1 MeV is 

estimated with a relative error of about 20 %; 

- The maximum neutron flux achievable in 

our setup at a distance of 10 cm from the 

target was 2.109 n.cm^-2.s-1.μA^-1, 

corresponding to a deuteron beam intensity 

of 10 μA; 

- The maximum value for the fluence 

reached was 1.18 x 10^13 n.cm^-2 (on-line); 

3.152 x 10^13 n.cm^-2 (off-line). 



A. Investigations on the gamma-ray and electron beam 

radiation effects on semiconductor optical detectors for 

sensing and optical communication applications 

The characteristics of the investigated photodiodes 

Photodiode designation/ 

Characteristics 

Ph 1 (2) Ph 3 (4) Ph 5 (6) 

Material Si Si InGaAs 

Sensing area (mm) □ = 3 x 3 Φ = 0.991 Φ = 0.3 

Capacitance (pF) - 5.2 (V R 

= 3.3 V) 5 

Max. reverse voltage (V) 30 20 15 

Max. reverse current (mA) - - 5 

Max. Forward current (mA) - - 25 

Responsivity (A/W) 30 nA/lx 0.5 0.9 (1310 nm) 

0,95 (1550 nm) 

Dark current (nA) 50 0.3 6 

NEP (W/Hz 1/2 ) - - 6.28 x 10 -15 

Rise/ fall time (ns) 100 ms 1200 1.5 



The investigated photodiodes were subjected to 

• gamma-ray and 

• electron-beam irradiation 

The irradiation doses to which each photodiode was subjected: 

Photodiode/ 

Irradiation step 

Total gamma dose 

(kGy) – step 1 

Total gamma dose 

(kGy) – step 2 

Total electron beam 

dose (kGy) – step 1 

Total electron beam 

dose (kGy) – step 2 

Ph 1 Ph 2 Ph 3 Ph 4 Ph 5 Ph 6 

- 90 - 90 - 90 

- 100 - 100 - 100 

100 - 100 - 100 - 

200 - 200 - 200 - 



The photodiode evaluated characteristics are: 

• the dark current; 

• the spectral responsivity at different wavelengths; 

• the turn-on and turn-off time; 

• the spatial responsivity for large area photodiodes. 

The semiconductor lasers employed for the characterization of the spectral 

and spatial responsivity are emitting optical radiation at the following 

wavelengths: 

• for photodiodes 1-4 we used laser diodes operating at: 653 nm, 

650 nm, 670 nm, 780 nm, 808 nm and 850 nm; 

• for the photodiodes 5 and 6 the used laser diodes emitted at 808 nm 

850 nm, 1310 nm and 1550 nm. 



The set- ups for the responsivity measurements 

Setup for large area photodiodes: 

1 – laser diode mount and the laser diode; 

2 – photodiode mount and the photodiode; 

3 – current-to-voltage converter; 

4 – data acquisition board; 

5 – PC; 

6 – laser diver/ temperature controller. 

Setup for small area photodiodes: 

1 – semiconductor laser temperature 

mount; 

2 – integrating sphere operating in the 

visible range; 

3 – the mounting of the photodiode. 



Research results: dark current 

The temporal variation of the signal for the Si 

photodiode, not illuminated (the signal 

corresponding to the dark current), as it was 

subjected to electron beam irradiation 

The temporal variation of the signal for the 

Si photodiode, not illuminated (the signal 

corresponding to the dark current), as it 

was subjected to gamma irradiation 



Research results with the photodiode exposed to 

optical radiation 

The temporal variation of the Si photodiode 

signal, after electron beam irradiation, 

measured at a constant incident optical 

power, for the wavelength λ = 636 nm. 

The temporal variation of the Si photodiode 

signal, after gamma irradiation, measured at 

a constant incident optical power, for the 

wavelength λ = 653 nm.


Research results: spatial responsivity 

c 

b 

a 

The spatial responsivity for the Si photodiode, scanned along the Y axis with a laser beam spot 

of about 0.8 mm diameter (λ = 653 nm), after gamma irradiation: 

a – non-irradiated photodiode; 

b – 90 kGy total irradiation dose; 

c - 190 kGy total irradiation dose.


B. In-situ thermal annealing and photobleaching of low dose 

rate/ low dose gamma and neutron irradiated aluminium 

jacketed silica optical fibres 

Objective: 

The objective of this investigation was related to the development of the 

experimental setup and the associated software to be used for the 

in-situ evaluation of thermal annealing and photobleaching of 

gamma and neutron irradiated aluminium jacketed silica optical 

fibres, to asses their possible use for plasma diagnostics in fusion 

installations (i.e. ITER). 



Under irradiation, optical fibers exhibit: 

• radiation-induced absorption (RIA) and 

• radiation-induced luminescence (RIL) or radioluminescence 

Both effects are dependent on the wavelength, the irradiation conditions 

and the optical fiber type. 

We investigated specially designed optical fibers 

- with higher OH contents 

- solarization resistant type 

- hydrogen loaded 

- aluminum jacketed 



Characteristics of the investigated optical fibers 

Optical 

fiber 

designation 

OFS1 

Optical fiber type 

•Enhanced UV response, 

operational temperature < 150 O C 

•On-line measurements 

OFS2 •Solarization resistant, H 2 

loaded, 

operational temperature < 400 O C 

•On-line measurements 

OFS3 

•Solarization resistant 

•Off-line measurements 

Core 

diameter 

[μm] 

Cladding 

diameter 

[μm] 

Jacketing 

400 480 Tefzel 

590 μm 

200 210 Al 

280 μm 

600 - Polyimide 

790 μm 

Sample 

length 

[mm] 

580 

2000 

110 



Set-up for the in-situ measurement 

of the irradiation induced optical 

attenuation: 

1 – multi-channel fiber optic 

spectrometer; 

2 – deuterium-tungsten optical 

source; 

3 – optical fiber multiplexer; 

4 – optical fiber sample; 

5 – variable optical attenuator; 

6 – optical fiber probes; 

7 – gamma source. 



Schematic experimental setup for combined temperature and 

irradiation stress on optical fibers 

U(max24)V 

T 

1 

T 

2 

Heating wire (thermo-coax type) 

Nickel dosimeter 

Optical fiber samples 

Ceramic cylinders 



Silica optical fibers – comparative irradiation results for EH; SR;H2L; on 

line attenuation measurements during gamma irradiation 



Silica optical fibers (EH) – irradiation results: on-line attenuation 

measurements during neutron irradiation 



Silica optical fibers (H2L) – irradiation results: on-line attenuation 

measurements during neutron irradiation 

The optical attenuation 

for a neutron fluence of 

152.3 x 10^13 n/cm^2 ; 

after 6 hours heating at 

80 C 



601.1 x 10^13 n/cm^2; 

after 7 hours heating at 

160 C 



1.8 x 10^14 n/cm^2; after 

17 hours heating at 240 C 



Silica optical fibers (EH) – irradiation results: on-line attenuation 

measurements & room temperature recovery during gamma irradiation 



C. Complementary investigations on irradiated optical fibers 

Objective 

The objective of this investigation was to perform additional, 

complementary investigations on large diameter optical fibers to 

assess their possible use in plasma diagnostics tools in ITER 

The complexity of the problem resides both in the multitude of 

effects present in these interactions, and in the great variety of 

optical fibers proposed as possible candidates to operate in 

radiation environments. 



The change of optical attenuation in an UV enhanced transmission optical 

fiber, after electron beam irradiation followed by gamma-rays irradiation. 

In situ measurements: 

1- non-irradiated optical 

fiber; 

2- electron beam 

irradiated optical 

fiber (360 kGy); 

3- recovery of optical 

attenuation at room 

temperature; 

4- gamma rays 

irradiated optical 

fiber (468 kGy). 



Dynamics of the color centers during the irradiation 

The evaluation of the irradiation induced optical attenuation in the UV range is 

quite a difficult task as far as several color centers can be activated during the 

irradiation. In order to observe the dynamics of these color centers, as function 

of the total irradiation dose, we developed a programme for the deconvolution of 

the attenuation spectra corresponding to the color centers mentioned in the 

literature: 

• 215 nm (E’γ color center); 

• 230 nm (E’β color center); 

• 240 nm (B2β color center); 

• 250 nm (B2α color center); 

• 260 nm (D0 color center); 

• 280 nm (oxygen vacancy color center); 

• 318 nm (bound chlorine color center); 

• 330 nm (molecular chlorine color center). 



Silica optical fibers: the dynamics of the color centers for a gamma 

irradiated H2L optical fiber, during on-line attenuation measurements


Silica optical fibers: the dynamics of the color centers for a gamma 

irradiated SR optical fiber, during on-line attenuation measurements


Photoluminescence measurements* 

The emission band peaked at about 4.4 

eV related to the oxygen deficient centers 

for samples S15_2/1 and S15_10/1, under 

exitation energy at 5.0 eV (248 nm). 

Emission peaks around 3 eV for the samples 

S15_5/1 and S15_6/1, and around 3.6 eV for 

sample S15_9/1, under exitation energy at 5.0 

eV (248 nm). Their origin is not known. 

*Measurements performed by Dr.Simonpietro Agnello and Dr. Laura Nuccio, Dipartimento di Scienze Fisiche ed Astronomiche, Universita 

degli Studi di Palermo, Italy 



Photoluminescence measurements* 

A refined investigation in the fiber 

S15_6/1 shows that the emission 

peaked around 3 eV has a PLE 

with maximum at about 3,65 eV. 

Exciting at the energy of 3.65 eV, 

a clear emission is observed, 

peaked around 3 eV. 





Electron paramagnetic resonance (EPR) measurements* 

Sample S15_2/1 shows the EPR 

signal of the E’ center of silica. 

This spectrum shows the same 

features found in bulk commercial 

silica samples. 





Electron paramagnetic resonance (EPR) measurements* 

High sensitivity EPR measurements (2 nd harmonic detection) for lower concentration in 

samples S15_2/1, S15_8/1 and S15_10/1. The spectral characteristics of the detected signals 

are practically the same, considering the low signal-to noise ratio, with the exception of the 

sample S15_10/1 in which a broadening of line shape is detected. 





Conclusion 1 

• Three types of optical fibers were irradiated with neutrons. One optical fiber has an 

enhanced UV response, the other one was H2-loaded with Al-jacket. The first two types of 

optical fibers (OFS1, OFS2_A and OFS2_B) were measured on-line, while the third type of 

optical fiber (OFS3) was investigated only off-line. The irradiation of the OFS1 and OFS3 

samples was done at room temperature, while the Al-jacketed optical fibers (OFS2_A and 

OFS2_B) were irradiated at different temperatures. 

• The optical attenuation of the optical fiber with enhanced UV response (OFS1) changes by 

1.2 dB for a neutron fluence of 1.18 x 1013 n/cm2. The maximum attenuation increases 

slightly with the neutron fluence, and no significant broadening of the attenuation 

spectrum was noticed. 

• The optical attenuation of the third sample increases by 4 dB at a neutron flux of 2.1 x 1014 

n/cm2. 

• In the case of the H2-loaded optical fibers (OFS2_A and OFS2_B), a change of about 2 dB 

was observed for the optical attenuation in the UV range. In comparing the results 

obtained for OFS2 and OFS3 one have to consider the fact that in both cases almost the 

same length of optical fiber was irradiated (about 10 cm) but the overall length of each 

optical fiber sample OFS2 was 20 times longer than the OFS3 sample, so the attenuation 

induced by the non-irradiated part of the OFS2 samples has to be considered. 

Measurements carried out off-line in the spectral range of 600 – 1700 nm indicated no 

transmission changes. 



Conclusions 2 

• There is a difference between the values obtained on-line and off-line for samples OFS2 

as the length of the irradiated optical fiber as compared to the total length of the optical 

path over which the investigation is done has a greater contribution to the total 

attenuation for off-line measurements. 

• Off-line measurements indicated a slight influence of the temperature over the optical 

attenuation. The optical fiber sample kept at high temperature during the irradiation 

shows a high degradation than the optical fiber irradiated at room temperature. This 

phenomenon can be attributed to the H2 lose through thermal diffusion. 

• No irradiation induced emission was noticed for the H2-loaded optical fiber in the UVvisible 

spectral range. 

• The illumination of the irradiated optical fibers both during the irradiation and during the 

irradiation pause (but keeping the optical fiber heated at 240OC) with a broadband UV 

source and with a blue-emitting LED has no effects on the optical attenuation, as the 

effect of the irradiation over the optical transmission is very small. 

• For the UV spectral range, the H2-loaded optical fibers proved to be more radiation 

resistant than common solarization resistant optical fibers. 

• The project milestones were achieved as planned. 



References 

1. Dan Sporea, Adelina Sporea, B. Constantinescu, Optical fibers for plasma diagnostics under gamma-ray 

and UV irradiation, Fusion Engineering and Design, Vol.74, No 1-4, 2005, pp. 763-768. 

2. Dan Sporea, R. Sporea, Setup for the in situ monitoring of the irradiation-induced effects in optical fibers 

in the ultraviolet-visible optical range, Review of Scientific Instruments, Vol. 76, No. 11, 2005. 

3. Dan Sporea, R. Sporea, C. Oproiu, and I. Vata, Comparative study of gamma-ray, neutron and electron 

beam irradiated index-guided laser diodes, to be published in the Proceedings of the 8th European 

Conference on Radiation and its Effects on Components and Systems, Cap d’Agde, France, 19-23 

September 2005. 

4. Dan Sporea, Adelina Sporea, Bogdan Constantinescu, In-situ Measurements of Optical Fibers under 

Gamma-ray Irradiation, to be published in the Proceedings of the 12th International Conference on Fusion 

Reactor Materials, Santa Barbara, California, USA,4-9 December 2005. 

5. Dan Sporea, Reliability testing of laser diodes under irradiation, Proceedings of the 3rd International 

Conference on Materials Testing, Nurnberg, Germany, pp.135-140, 10-12 May 2005. 

6. Dan Sporea, Ion Vata, Radu Sporea, Hetero-junction Laser Diodes under Neutron Irradiation, 

Proceedings on the CD of the 13th International Conference on Nuclear Engineering, ICONE13, Beijing, 

China, 16-20 May 2005. 

7. Dan Sporea, Adelina Sporea, Evaluation of Solarization Resistant Optical Fibers under Gamma-Ray 

Irradiation and Temperature Stress, to be published in the Proceedings of the Workshop on Fibres and 

Optical Passive Components, Palermo, Italy, 22-24 June 2005. 

8. Dan Sporea, “Irradiation effects on the optical properties of silica and sapphire optical fibers”, Topical 

Meeting on Radiation Effects on Insulators, March 7, 2006, Garching, Germany. 

9. Dan Sporea, Adelina Sporea, “Comparative study of the irradiation induced degradation in large diameter 

optical fibers”, Conference on “Reliability of Optical Fiber Components, Devices, Systems, and Networks 

III”- SPIE Symposium on Photonics Europe, April 3 – 6, 2006, Strasbourg, France. 

10. Dan Sporea, Adelina Sporea, “Dynamics of the radiation induced color centers in optical fibers for plasma 

diagnostics”, 24th Symposium on Fusion Technology, September 11-15, 2006, Warsaw, Poland. 




Thank you

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