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IR imageguide with As-S glass fibers
]OIIRNA
I T,L ELSEVIER
L OF
III
Journal of Non-Crystalline Solids 184 (1995) 40-43
IR imageguide with As-S glass fibers Kewu Yang *, Peilan Wu, Guosheng Wei, Baoting Yu Beijing Glass Research Institute, Beijing 100062, People's Republic of China
Abstract Coherent fiber bundles with 1000 and 4000 pixels made from glass-clad chalcogenide fiber were prepared. Their transmittance reached 40% in the spectral region 3-5 txm. Coupling this imageguide to an infrared TV system, the thermal image of a character 'A' delivered through the bundle has been detected.
1. Introduction In recent years rapid progress in the technology of infrared (IR) thermal imaging has enabled us to measure and display the temperature distribution of various objects both in daylight and in the dark. However, in some unfavourable conditions, such as nuclear radiation, high intensity of electromagnetic fields, or restricted space, it is difficult to measure this temperature distribution by the IR TV in situ. So the research and development of the IR image guide bundle for these situations is needed. It was reported by Nishii et al. that 1550 and 8400 pixels of A s - S coherent fiber bundles have been prepared [1,2]. The bundle was connected to an infrared television camera (AVIO IVS 2100) and the thermal images of an operating integrated circuit and human hand were detected. The fiber materials they used w e r e A s 2 S 3 glass for the core and Teflon for the cladding. The diameter ratio of core to fiber was 5 5 / 7 5 and the length of the bundle was 1 m. This fiber bundle can detect and transmit the lower tern-
* Corresponding author. Tel: + 86-1 701 5765. Telefax: + 86-1 511 2478.
perature thermal image in restricted space and could be widely used in many fields. By using the A s - S core/clad fiber, we have prepared 1000 and 4000 pixels coherent fiber bundles. Their transmissive wavelength range was at 3 - 5 txm. In this paper we present the techniques for preparation of A s - S glass clad fiber, A s - S coherent fiber bundle, and their transmission characteristics. The primary research on examination of the image quality delivered by the bundle is also described.
2. Experimental
2.1. Glass preparation Commercially available high-purity As and S elements of 6N were used. Prior to synthesis the As was purified by baking under vacuum to exclude oxygen and S was distilled under Ar. The purified elements were weighed depending on glass composition in a glovebox and sealed in a dehydrated silica ampoule under vacuum. The ampoule was heated in a rocking furnace at 750-800°C. The compositions of core and clad glass w e r e A s 3 8 S 6 2 and AS35565 respectively. The refractive index difference was 2.3% [3].
0022-3093/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved
SSDI 0 0 2 2 - 3 0 9 3 ( 9 4 ) 0 0 6 8 9 - X
K. Yang et al. /Journal of Non-Crystalline Solids 184 (1995) 40-43 2.2. F i b e r d r a w i n g
41
5
The fiber was drawn by a double-crucible technique with argon gas pressure designed by the authors [4]. Core glass A s 3 8 5 6 2 and clad glass AS35865 were put in the core tube and clad tube of the pyrex glass double crucible respectively. The upper and lower heaters were both connected with the power source under an Ar atmosphere. When the glasses were melting and flowing in the concentric tube, different Ar pressures of core and clad tube were selected, and different diameter A s - S fibers, having different core and clad ratio, were obtained. A suitable fiber diameter was achieved by changing the fiber take-up speed and modifying the temperature of the lower port of the drawing furnace. Fibers (diameter 50-90 Ixm) with 5 - 1 0 Ixm clad were selected for preparing the coherent fiber bundle. The deviation of the fiber diameter was normally __+2 txm. By means of the IR fiber loss spectrometer (spectral region 1-12 ~xm, made at the Shanghai Institute of Optics and Fine Mechanics), the loss spectra in the range of 1-6 Ixm wavelength has been measured by the cutback method on 250 /xm diameter fiber. 2.3. B u n d l e p r e p a r a t i o n and m e a s u r e m e n t
A s - S IR coherent fiber bundles with 32 × 34 (1000) and 64 × 64 (4000) pixels, length 300 mm were prepared by regularly arranging the fiber layer and lamination method. The equipment used for transmittance measurement of these bundles is shown in Fig. 1. From Fig. 1 there was an aperture on the IR radiation source. The size of this hole should be slightly less than the end face of the bundle, thus
3 v m m o ..J
2 1
3
4
5
W a ~ z t b (~m)
Fig. 2. Loss spectrum of As-S clad IR optical fiber. enabling it to make the radiation output of the hole, I h, the same as the radiation input from the bundle end face, I 0. Measuring the I h and the radiation output of the bundle, I, the transmittance, T, could be calculated: T = I/I o = I/I h.
3. Results
The loss spectrum of A s - S clad IR optical fibers prepared is shown in Fig. 2. The losses of the fiber al wavelengths 2.4, 3.35, 4.75 and 5.7 ~m were all less than 1 d B / m . In order to increase the measurin~ precision, the loss at single wavelengths was measured. The results are 0.2, 0.4 and 0.7 d B / m at 3.35, 4.75 and 5.7 p~m respectively. The loss at 4 Ixm was larger than 5 d B / m , because there exist impurities as absorption of HS. The losses are about 2 d B / m at
concave [R radiation source ~ ,,. / /
I c o ~ t e . t cur-
Lrent supply
co.~ ~ir~o~
mirror ~
Fiber
3-5 ~m filter \.
n~l~ ~ / x.Y.z r ~ i t i o ~
Target area /
I [
z zA ] LP |
[[0 . . . . .
ter|
Fig. 1. The equipment used for transmittance measurement of fiber bundle.
Fig. 3. Microscope photograph of cross-section of a single clad A s - S fiber with 130 p~m diameter.
42
K. Yang et al. /Journal of Non-Crystalline Solids 184 (1995) 40-43 Table 1 The transmittance of A s - S IR fiber bundle at 3 - 5 ~ m wavelength
Fig. 4. Coherent bundles of 300 mm length and 1000 pixels.
Fig. 5. 1000 pixels bundle array. Single fiber core/fiber diameter is 7 5 / 9 0 fxm.
No.
Core/fiber diameter (l~m)
Number of pixels
Array
Transmittance (%)
1 2 3 4 5
75/90 75/90 70/80 60/70 45/60
1000 1000 1000 4000 4000
32 X 34 32 X 34 32 X 34 64 × 64 64 X 64
34 34 40 40 37
both 2.8 and 2.9 t~m which are due to the absorption peaks of H 2 0 and OH groups. Fig. 3 shows a micrograph of the cross-section of a single clad A s - S fiber. The prepared coherent bundles of 300 mm length and 1000 pixels is shown in Fig. 4. The pixel array of this bundle is shown in Fig. 5. The transmittance of the A s - S IR fiber bundle is given in Table 1. While coupling one end face of the bundle to the target area of the IR TV camera by the lens system, the other end was aimed at a black character ' A ' cut out of thick paper. This character had been homogeneously injected by an IR radiation source; the thermal image was delivered through the bundle and was clearly observed on the TV monitor. Fig. 6 shows the picture taken from the TV screen. The skew striae in the picture were caused by electric interference.
4. Discussion
Fig. 6. The thermal image of a character ' A ' taken from coupling the 1000 pixels bundle with an IR TV.
It is simple and easy to draw A s - S glass clad fiber by the double-crucible method using Ar pressure. Experiments showed that, when the core is prepared from the same batch of glass, the loss of the glass clad fiber is less than that of the unclad fiber. This fact indicated that good conditions were achieved at the core clad interface. The concentricity of clad fiber is affected by the size precision of the lower port of the pyrex glass double crucible. Under good conditions, 1% inconcentricity could be achieved. The spectral region of A s - S IR optical fiber application is 3 - 5 p~m, but there is an absorption band of H - S impurity at 4.01 txm. This extinction coefficient is as large as 2.3 X 10 3 d B / ( k m ppm)
K. Yang et al. /Journal of Non-Crystalline Solids 184 (1995) 40-43
[5], making the fiber ineffective and unfavourable. We will carry out further investigation in order to further decrease the hydrogen impurities in the fiber. Moreover, the inclusion of silica impurities into the glass from the walls of the silica container during the A s - S glass synthesis at high temperature is a major cause of fiber scattering loss. It is clear that if one could reduce fiber loss greatly and make the size of fiber more homogeneous, the quality of coherent fiber bundle could be improved. From Fig. 5 it is shown there are a few blackened and darkened fibers in this 1000 pixels bundle. Most of the pixels are arranged hexagonally and are dense. If adding a fiber selecting step prior to fiber arrangement and improving the technology of laminating were included, the quality of the fiber bundle could be improved. This paper reports only a primary experiment in the use of the IR fiber bundle for delivery of thermal images. We plan to design a unit for estimating the image quality delivered by the A s - S IR fiber bundle. In this unit the sensor for 3 - 5 txm radiation detection was a P t S i - S B I R CCD focal plane array (128 X 128). Matched with this array was an IR lens system which could couple with the fiber bundle. We will do further experiments on cross talk affected by the fiber clad thickness.
43
As an application, a 4000 pixels bundle was used to measure the distribution of temperature in a flame.
5. Conclusion Using the glass clad A s - S fiber which was drawn
using AS38562 as core, As35565 as clad, and a newly designed pyrex glass double crucible with Ar pressure, IR coherent fiber bundles with 1000 and 4000 pixels and 300 mm length were prepared. The transmittance at 3 - 5 p,m wavelength without antireflective films on the end face was 34-40%. Coupling the 1000 pixels bundle with an IR TV, the thermal image picture of a character ' A ' has been taken.
References [1] J. Nishii, New Glass 6 (1991) 277. [2] J. Nishii, S. Morimoto, I. Inagawa, R. Iizuka, T. Yamashita and T. Yamagishi, J. Non-Cryst. Solids 140 (1992) 199. [3] T. Kanamori, Y. Terunuma and T. Miyashita, Rev. Electrical Commun. Labs. 32 (1984) 469. [4] K. Yang, P. Wu and G. Wei, J. Chinese Ceram. Soc. 21 (1993) 70. [5] M.F. Churbanov, J. Non-Cryst. Solids 140 (1992) 324.
I T,L ELSEVIER
L OF
III
Journal of Non-Crystalline Solids 184 (1995) 40-43
IR imageguide with As-S glass fibers Kewu Yang *, Peilan Wu, Guosheng Wei, Baoting Yu Beijing Glass Research Institute, Beijing 100062, People's Republic of China
Abstract Coherent fiber bundles with 1000 and 4000 pixels made from glass-clad chalcogenide fiber were prepared. Their transmittance reached 40% in the spectral region 3-5 txm. Coupling this imageguide to an infrared TV system, the thermal image of a character 'A' delivered through the bundle has been detected.
1. Introduction In recent years rapid progress in the technology of infrared (IR) thermal imaging has enabled us to measure and display the temperature distribution of various objects both in daylight and in the dark. However, in some unfavourable conditions, such as nuclear radiation, high intensity of electromagnetic fields, or restricted space, it is difficult to measure this temperature distribution by the IR TV in situ. So the research and development of the IR image guide bundle for these situations is needed. It was reported by Nishii et al. that 1550 and 8400 pixels of A s - S coherent fiber bundles have been prepared [1,2]. The bundle was connected to an infrared television camera (AVIO IVS 2100) and the thermal images of an operating integrated circuit and human hand were detected. The fiber materials they used w e r e A s 2 S 3 glass for the core and Teflon for the cladding. The diameter ratio of core to fiber was 5 5 / 7 5 and the length of the bundle was 1 m. This fiber bundle can detect and transmit the lower tern-
* Corresponding author. Tel: + 86-1 701 5765. Telefax: + 86-1 511 2478.
perature thermal image in restricted space and could be widely used in many fields. By using the A s - S core/clad fiber, we have prepared 1000 and 4000 pixels coherent fiber bundles. Their transmissive wavelength range was at 3 - 5 txm. In this paper we present the techniques for preparation of A s - S glass clad fiber, A s - S coherent fiber bundle, and their transmission characteristics. The primary research on examination of the image quality delivered by the bundle is also described.
2. Experimental
2.1. Glass preparation Commercially available high-purity As and S elements of 6N were used. Prior to synthesis the As was purified by baking under vacuum to exclude oxygen and S was distilled under Ar. The purified elements were weighed depending on glass composition in a glovebox and sealed in a dehydrated silica ampoule under vacuum. The ampoule was heated in a rocking furnace at 750-800°C. The compositions of core and clad glass w e r e A s 3 8 S 6 2 and AS35565 respectively. The refractive index difference was 2.3% [3].
0022-3093/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved
SSDI 0 0 2 2 - 3 0 9 3 ( 9 4 ) 0 0 6 8 9 - X
K. Yang et al. /Journal of Non-Crystalline Solids 184 (1995) 40-43 2.2. F i b e r d r a w i n g
41
5
The fiber was drawn by a double-crucible technique with argon gas pressure designed by the authors [4]. Core glass A s 3 8 5 6 2 and clad glass AS35865 were put in the core tube and clad tube of the pyrex glass double crucible respectively. The upper and lower heaters were both connected with the power source under an Ar atmosphere. When the glasses were melting and flowing in the concentric tube, different Ar pressures of core and clad tube were selected, and different diameter A s - S fibers, having different core and clad ratio, were obtained. A suitable fiber diameter was achieved by changing the fiber take-up speed and modifying the temperature of the lower port of the drawing furnace. Fibers (diameter 50-90 Ixm) with 5 - 1 0 Ixm clad were selected for preparing the coherent fiber bundle. The deviation of the fiber diameter was normally __+2 txm. By means of the IR fiber loss spectrometer (spectral region 1-12 ~xm, made at the Shanghai Institute of Optics and Fine Mechanics), the loss spectra in the range of 1-6 Ixm wavelength has been measured by the cutback method on 250 /xm diameter fiber. 2.3. B u n d l e p r e p a r a t i o n and m e a s u r e m e n t
A s - S IR coherent fiber bundles with 32 × 34 (1000) and 64 × 64 (4000) pixels, length 300 mm were prepared by regularly arranging the fiber layer and lamination method. The equipment used for transmittance measurement of these bundles is shown in Fig. 1. From Fig. 1 there was an aperture on the IR radiation source. The size of this hole should be slightly less than the end face of the bundle, thus
3 v m m o ..J
2 1
3
4
5
W a ~ z t b (~m)
Fig. 2. Loss spectrum of As-S clad IR optical fiber. enabling it to make the radiation output of the hole, I h, the same as the radiation input from the bundle end face, I 0. Measuring the I h and the radiation output of the bundle, I, the transmittance, T, could be calculated: T = I/I o = I/I h.
3. Results
The loss spectrum of A s - S clad IR optical fibers prepared is shown in Fig. 2. The losses of the fiber al wavelengths 2.4, 3.35, 4.75 and 5.7 ~m were all less than 1 d B / m . In order to increase the measurin~ precision, the loss at single wavelengths was measured. The results are 0.2, 0.4 and 0.7 d B / m at 3.35, 4.75 and 5.7 p~m respectively. The loss at 4 Ixm was larger than 5 d B / m , because there exist impurities as absorption of HS. The losses are about 2 d B / m at
concave [R radiation source ~ ,,. / /
I c o ~ t e . t cur-
Lrent supply
co.~ ~ir~o~
mirror ~
Fiber
3-5 ~m filter \.
n~l~ ~ / x.Y.z r ~ i t i o ~
Target area /
I [
z zA ] LP |
[[0 . . . . .
ter|
Fig. 1. The equipment used for transmittance measurement of fiber bundle.
Fig. 3. Microscope photograph of cross-section of a single clad A s - S fiber with 130 p~m diameter.
42
K. Yang et al. /Journal of Non-Crystalline Solids 184 (1995) 40-43 Table 1 The transmittance of A s - S IR fiber bundle at 3 - 5 ~ m wavelength
Fig. 4. Coherent bundles of 300 mm length and 1000 pixels.
Fig. 5. 1000 pixels bundle array. Single fiber core/fiber diameter is 7 5 / 9 0 fxm.
No.
Core/fiber diameter (l~m)
Number of pixels
Array
Transmittance (%)
1 2 3 4 5
75/90 75/90 70/80 60/70 45/60
1000 1000 1000 4000 4000
32 X 34 32 X 34 32 X 34 64 × 64 64 X 64
34 34 40 40 37
both 2.8 and 2.9 t~m which are due to the absorption peaks of H 2 0 and OH groups. Fig. 3 shows a micrograph of the cross-section of a single clad A s - S fiber. The prepared coherent bundles of 300 mm length and 1000 pixels is shown in Fig. 4. The pixel array of this bundle is shown in Fig. 5. The transmittance of the A s - S IR fiber bundle is given in Table 1. While coupling one end face of the bundle to the target area of the IR TV camera by the lens system, the other end was aimed at a black character ' A ' cut out of thick paper. This character had been homogeneously injected by an IR radiation source; the thermal image was delivered through the bundle and was clearly observed on the TV monitor. Fig. 6 shows the picture taken from the TV screen. The skew striae in the picture were caused by electric interference.
4. Discussion
Fig. 6. The thermal image of a character ' A ' taken from coupling the 1000 pixels bundle with an IR TV.
It is simple and easy to draw A s - S glass clad fiber by the double-crucible method using Ar pressure. Experiments showed that, when the core is prepared from the same batch of glass, the loss of the glass clad fiber is less than that of the unclad fiber. This fact indicated that good conditions were achieved at the core clad interface. The concentricity of clad fiber is affected by the size precision of the lower port of the pyrex glass double crucible. Under good conditions, 1% inconcentricity could be achieved. The spectral region of A s - S IR optical fiber application is 3 - 5 p~m, but there is an absorption band of H - S impurity at 4.01 txm. This extinction coefficient is as large as 2.3 X 10 3 d B / ( k m ppm)
K. Yang et al. /Journal of Non-Crystalline Solids 184 (1995) 40-43
[5], making the fiber ineffective and unfavourable. We will carry out further investigation in order to further decrease the hydrogen impurities in the fiber. Moreover, the inclusion of silica impurities into the glass from the walls of the silica container during the A s - S glass synthesis at high temperature is a major cause of fiber scattering loss. It is clear that if one could reduce fiber loss greatly and make the size of fiber more homogeneous, the quality of coherent fiber bundle could be improved. From Fig. 5 it is shown there are a few blackened and darkened fibers in this 1000 pixels bundle. Most of the pixels are arranged hexagonally and are dense. If adding a fiber selecting step prior to fiber arrangement and improving the technology of laminating were included, the quality of the fiber bundle could be improved. This paper reports only a primary experiment in the use of the IR fiber bundle for delivery of thermal images. We plan to design a unit for estimating the image quality delivered by the A s - S IR fiber bundle. In this unit the sensor for 3 - 5 txm radiation detection was a P t S i - S B I R CCD focal plane array (128 X 128). Matched with this array was an IR lens system which could couple with the fiber bundle. We will do further experiments on cross talk affected by the fiber clad thickness.
43
As an application, a 4000 pixels bundle was used to measure the distribution of temperature in a flame.
5. Conclusion Using the glass clad A s - S fiber which was drawn
using AS38562 as core, As35565 as clad, and a newly designed pyrex glass double crucible with Ar pressure, IR coherent fiber bundles with 1000 and 4000 pixels and 300 mm length were prepared. The transmittance at 3 - 5 p,m wavelength without antireflective films on the end face was 34-40%. Coupling the 1000 pixels bundle with an IR TV, the thermal image picture of a character ' A ' has been taken.
References [1] J. Nishii, New Glass 6 (1991) 277. [2] J. Nishii, S. Morimoto, I. Inagawa, R. Iizuka, T. Yamashita and T. Yamagishi, J. Non-Cryst. Solids 140 (1992) 199. [3] T. Kanamori, Y. Terunuma and T. Miyashita, Rev. Electrical Commun. Labs. 32 (1984) 469. [4] K. Yang, P. Wu and G. Wei, J. Chinese Ceram. Soc. 21 (1993) 70. [5] M.F. Churbanov, J. Non-Cryst. Solids 140 (1992) 324.