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Propagation loss, degradation and protective coating of long drawn microfibers
Optics Communications 284 (2011) 2825–2828
Contents lists available at ScienceDirect
Optics Communications j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / o p t c o m
Propagation loss, degradation and protective coating of long drawn microfibers Shih-Min Chuo a, Lon A. Wang a,b,⁎ a b
Graduate Institute of Photonics and Optoelectronics, National Taiwan University, Taipei 10617, Taiwan Department of Electrical Engineering, National Taiwan University, Taipei 10617, Taiwan
a r t i c l e
i n f o
Article history: Received 26 December 2010 Received in revised form 31 January 2011 Accepted 10 February 2011 Available online 26 February 2011 Keywords: Microfiber Propagation loss Optical degradation Protective coating
a b s t r a c t Propagation losses, transmission spectra and optical degradation attributed to surface scattering, crack propagation and water absorption were characterized for long microfibers fabricated by using a drawing tower. The propagation losses and optical degradation at 1550 nm wavelength were found increasing as the diameters decreased for the microfibers. A coating setup was established where polydimethylsiloxane (PDMS) was used as coating material and a CO2 laser as curing source to form a cylindrical film layer along the surface of microfiber. It was confirmed that no optical degradation was observed for the long drawn microfibers with protective coating over a long period of 18 h. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Microfibers have been studied as a potential building block in various optical components including sensors, resonators, filters, interferometers, and so on [1–5]. We reported the fabrication of microfibers by using a modified fiber drawing tower and obtained the length up to 165 cm with a diameter smaller than 5 μm [6]. The propagation loss, transmission spectra and optical degradation of such a long drawn microfiber, however, need to be characterized before it can be applied to making useful microfiber components. A microfiber usually refers to the fiber type waveguide of silica with diameter slightly larger than 1 μm, and the light will be guided in the whole microfiber rather than the reduced core region. The strong guiding mechanism of microfibers caused by high index difference between silica and air will make the guided light in microfibers more sensitive to the particles attached to their surfaces, which greatly increases the scattering loss [7]. Besides, the crack propagation and the generation of hydroxyl bond under humid conditions will optically degrade microfibers and increase the volume scattering loss [8,9]. Optical degradation is related to the surface area of microfibers because the aforementioned factors all take place from the surface. Therefore, the loss of long drawn microfibers will increase more rapidly than shorter ones and the induced large loss may make some microfiber-based optical components impractical. Many researchers have studied the preservation of microfibers to keep their optical performance from further deterioration [9–12]. Xu et. al. accomplished the packaging of microfiber-based devices by
⁎ Corresponding author. E-mail address: [email protected] (L.A. Wang). 0030-4018/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.optcom.2011.02.018
covering low index materials such as Teflon [9]. Lou et. al. discussed the required thickness of outer packaging materials to make microfibers fully or partially embedded [10]. Though the fully embedded microfibers can be protected from the optical degradation, partially embedded ones with thin coating thickness are desired for sensing applications. Kakarantzas et. al. covered the microfiber with sol–gel silica films of 90 nm thickness and formed a long period grating [11]; however, the silica films were too thin to protect the microfibers. Xiao et. al. proceeded to use a rigid block of aerogel to embed the microfibers [12]. The porous structure of the aerogel not only protects but also allows the gases and dopants to interact with microfibers. Unlike the previously reported studies, our aim is to make a cylindrical protective coating layer along the long drawn microfibers [6], which are hard to be entirely preserved by the aforementioned methods. Instead a conventional coating method frequently used in a fiber drawing tower is adapted to form a coating layer on the surface of a microfiber. This method is particularly suitable for coating long drawn microfibers. 2. Propagation loss and optical degradation of a long drawn microfiber A long drawn microfiber was made by drawing an optical fiber preform down to a few micron diameter wire through a modified fiber drawing tower. The preform used in the experiment was a singlemode optical fiber with cut-off wavelength of 1260 nm, NA of 0.14 and core/cladding diameter of 8.2 μm/125 μm. The fiber preform with both ends fastened to a fiber feeder and a drawing wheel respectively passed through a hot zone where the silica material became viscous liquid. Both the feeder and the wheel moved in the same direction at
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rapidly, and the transmitted power would return to the previous value. After measuring the power evolution of microfibers in different diameters, we obtained the distribution of propagation losses as shown in Fig. 1(b). The loss was approximately 0.001 dB/mm for 2 μm diameter microfibers, and would increase as the diameter decreased. The environment will also severely affect the loss of microfibers. Particles would adhere to microfibers and hydroxyl bonds would generate to increase the losses of microfibers under humid condition. Fig. 2(a) shows the measured transmission spectrum of a 2 μm diameter microfiber one day after it was made. Note that the loss increase at 1383 nm wavelength indicates the formation of OH− bond caused by water absorption during and after drawing process [8]. The loss was larger for longer wavelength because of larger mode field influenced by surface roughness and particles. The increase of loss around and shorter than 800 nm wavelength resulted from the disappearance of higher-order modes in microfibers [13]. Fig. 2(b) indicates the seriousness of the microfiber degradation. The loss would increase enormously with tens of decibels after the fabrication for one day for 300 mm long, 2 μm diameter microfiber. The smaller the diameter of a microfiber was, the larger the loss would be induced
Fig. 1. (a) Transmitted power evolution at 1550 nm wavelength of a 300 mm long microfiber being drawn, and the slope represents the propagation loss. (b) Distribution of propagation losses of microfibers in different diameters at 1550 nm wavelength.
different speeds but with the desired constant ratio. By controlling the feed velocity (Vf) into the hot zone to be much slower than the drawing velocity (Vd), the fiber perform would be narrowed down based on the principle of mass conservation; therefore, the resultant diameter reduction Df/Dd can be related to the speed ratio Vd/Vf as 2
2
Vf × Df = Vd × Dd
ð1Þ
where Df and Dd are the diameters of fiber preform and microfiber, respectively. The propagation loss at 1550 nm wavelength was in situ measured when a microfiber was drawn with its length increasing at constant speed. The power evolution of a microfiber being drawn is shown in Fig. 1(a). The large variation at the beginning resulted from the formation of a fiber tapering section connecting a conventional singlemode optical fiber with a microfiber. The section length was about 5 mm, and the induced 0.7 dB loss could be attributed to the nonadiabatic tapering shape. The ensued slope represents the propagation loss. Note that the sudden transmission drops came from the change of fiber taper profiles caused by the instability of drawing mechanism. Such slight shape variations would recover
Fig. 2. (a) Transmission spectrum of a one-day old, 2 μm diameter microfiber. The water absorption at 1383 nm wavelength is observable. (b) Degradation of microfibers of different diameters at 1550 nm wavelength.
S.-M. Chuo, L.A. Wang / Optics Communications 284 (2011) 2825–2828
2827
Fig. 3. Experimental setup for coating microfibers and in-situ measurement. The coating die is placed after the microfiber fabrication and CO2 laser is used to cure PDMS. For the measurement of coated microfiber performance, the light is guided from the lower side and transmitted the coated region. The photodetector is placed beside the top of coated microfiber to capture scattered light.
because of larger evanescent fields. Therefore, the coating of microfibers to protect them from degradation is essential for practical applications. 3. Microfiber coating Polydimethylsiloxane (PDMS) was chosen as the coating material due to its lower refractive index (n = 1.402) than silica. Furthermore, PDMS is a kind of silicone frequently used as coating material for a conventional optical fiber [14]. However, PDMS is hard to remove completely from a microfiber because of its crosslink property. Only a few chemicals such as sulfuric acid, trifluoroacetic acid or dipropylamine can dissolve PDMS when immersed for 24 h [15]. The experimental setup of microfiber coating is shown in Fig. 3. A funnel shaped coating die installed in the microfiber drawing platform was placed between the fiber feeder and the drawing wheel so that the drawing and coating could be carried out simultaneously to minimize the fiber degradation. The preform passed through the hole of die, and the coating material PDMS was then injected into the die with no leak because of its high viscosity. The fiber preform was heated by a butane flame and directly drawn to a microfiber while immediately being dipped in PDMS. PDMS in the die would be dragged with microfiber and formed a cylindrical film layer along its surface. An unfocused CO2 laser with power of 10 W and beam diameter of 3.5 mm was used to irradiate the place after the microfiber passing through the coating die to thermally cure the PDMS layer. The time between a microfiber coating and curing should be less than 100 ms; otherwise, the coating would shrink into ball shape owing to the surface tension of PDMS. It required the microfiber drawing speed as fast as about 65 mm/s. The total length of coated microfiber was approximately 200 mm, and it should be kept straight to avoid bending for loss measurement. A PDMS coated microfiber is shown in Fig. 4(a). The surface of coating was very smooth due to rapid curing. The coating diameter was in the range of 50 to 150 μm depending on the viscosity of PDMS and the hole dimension of the die.
Fig. 4. (a) A photograph of coated microfiber with smooth surface; (b) the coating is uniform over a 2 mm long microfiber; (c) the 2 μm diameter microfiber can be clearly observed inside 50 μm diameter coating.
As an illustration, the microfiber would have uniform coating over 2 mm long as depicted in Fig. 4(b). For the observation of microfiber inside the coating, the coated microfiber was placed on a microscope slide glass and covered with a few drops of index matching oil before sealed with a cover glass [16]. Then it could be viewed by using Nomarski microscopy [17] as shadow image. Fig. 4(c) shows the image of a 2 μm diameter microfiber in the 50 μm diameter coating.
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with the result shown in Fig. 2(b). These values are comparable to what have been reported in References [5] and [6]. 5. Conclusion The propagation loss and degradation of long drawn microfibers in different diameters made by a modified fiber drawing tower have been characterized. The large losses caused by surface scattering, crack propagation and water absorption necessitate the coating along the surface of such microfibers. We successfully installed an experimental coating setup, and the resultant coatings were found uniform in diameters of about 50 to 150 μm. A coated microfiber showed effective protection from transmission loss as compared with an uncoated one. A long drawn microfiber with coated layer can be regarded as a much smaller diameter optical fiber. Therefore, it can be also used in the applications demanding long length optical fibers such as telecommunication, fiber optic gyroscope, distributed fiber sensors, etc. Fig. 5. The power evolutions of coated and bare microfibers over 18 hours at 1550 nm wavelength. The coated microfiber has a diameter of 50 μm, and the diameter of bare microfiber is 2 μm.
4. Loss measurement for a coated microfiber The loss measurement for a coated microfiber was carried out in situ and modified to measure the scattering light. When the microfiber drawing stopped, there was a small region of uncured PDMS between the coating die and the laser curing spot where a PDMS microball would be formed by surface tension. The microball would scatter light and make direct loss measurement impossible. Hence, the 1550 nm wavelength light was guided from the lower side of the single-mode fiber and went through the coating region of microfiber as shown in Fig. 3. To prevent measuring the uncoated microfiber, the scattered light from the microball was captured by a photodetector placed beside the top of coating region. The power evolutions of a 2 μm diameter microfiber with and without 50 μm diameter coating over 18 h are shown in Fig. 5. Though a variation of ±1 dB was observed owing to some air flow perturbation, the overall slope comparison between two indicates the efficacy of added coating. The uncoated microfiber was seen to degrade at the speed of 0.264 dB/h or equivalently 0.032 dB/mm/day, which is consistent
Acknowledgment The authors are grateful to the National Science Council for financial support under grant number 95-2221-E-002-327-MY3. References [1] L. Tong, R.R. Gattass, J.B. Ashcom, S. He, J. Lou, M. Shen, I. Maxwell, E. Mazur, Nature 426 (2003) 816. [2] Y.K. Lizé, E.C. Mägi, V.G. Ta'eed, J.A. Bolger, P. Steinvurzel, B.J. Eggleton, Opt. Express 12 (2004) 3209. [3] M. Sumetsky, Y. Dulashko, A. Hale, Opt. Express 12 (2004) 3521. [4] G. Brambilla, F. Xu, P. Horak, Y. Jung, F. Koizumi, N. Sessions, E. Koukharenko, X. Feng, G. Murugan, J. Wilkinson, D. Richardson, Adv. Opt. Photon. 1 (2009) 107. [5] G. Brambilla, Opt. Fiber Technol. 16 (2010) 331. [6] S.M. Chuo, M.H. Wan, L.A. Wang, J. Wang, J. Lightwave Technol. 27 (2009) 2983. [7] S. Wang, X. Pan, L. Tong, Opt. Commun. 276 (2) (2007) 293. [8] L. Ding, C. Belacel, S. Ducci, G. Leo, I. Favero, Appl. Opt. 49 (2010) 2441. [9] F. Xu, G. Brambilla, Jpn. J. Appl. Phys. 47 (2008) 6675. [10] N. Lou, R. Jha, J. Domínguez-Juárez, V. Finazzi, J. Villatoro, G. Badenes, V. Pruneri, Opt. Lett. 35 (2010) 571. [11] G. Kakarantzas, S.G. Leon-Saval, T. Birks, P. Russell, Opt. Lett. 29 (2004) 694. [12] L. Xiao, M. Grogan, S.G. Leon-Saval, R. Williams, R. England, W. Wadsworth, T. Birks, Opt. Lett. 34 (2009) 2724. [13] Y. Jung, G. Brambilla, D. Richardson, Opt. Express 16 (2008) 14661. [14] T.J. Miller, A.C. Hart, W.I. Vroom, M.J. Bowden, Electron. Lett 14 (1978) 603. [15] J.N. Lee, C. Park, G.M. Whitesides, Anal. Chem. 75 (2003) 6544. [16] M.H. Wan, L.A. Wang, Proc. SPIE 7503 (2009) 750373. [17] R.D. Allen, G.B. David, G. Nomarski, Z. Wiss. Mikrosk. 69 (1969) 193.
Contents lists available at ScienceDirect
Optics Communications j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / o p t c o m
Propagation loss, degradation and protective coating of long drawn microfibers Shih-Min Chuo a, Lon A. Wang a,b,⁎ a b
Graduate Institute of Photonics and Optoelectronics, National Taiwan University, Taipei 10617, Taiwan Department of Electrical Engineering, National Taiwan University, Taipei 10617, Taiwan
a r t i c l e
i n f o
Article history: Received 26 December 2010 Received in revised form 31 January 2011 Accepted 10 February 2011 Available online 26 February 2011 Keywords: Microfiber Propagation loss Optical degradation Protective coating
a b s t r a c t Propagation losses, transmission spectra and optical degradation attributed to surface scattering, crack propagation and water absorption were characterized for long microfibers fabricated by using a drawing tower. The propagation losses and optical degradation at 1550 nm wavelength were found increasing as the diameters decreased for the microfibers. A coating setup was established where polydimethylsiloxane (PDMS) was used as coating material and a CO2 laser as curing source to form a cylindrical film layer along the surface of microfiber. It was confirmed that no optical degradation was observed for the long drawn microfibers with protective coating over a long period of 18 h. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Microfibers have been studied as a potential building block in various optical components including sensors, resonators, filters, interferometers, and so on [1–5]. We reported the fabrication of microfibers by using a modified fiber drawing tower and obtained the length up to 165 cm with a diameter smaller than 5 μm [6]. The propagation loss, transmission spectra and optical degradation of such a long drawn microfiber, however, need to be characterized before it can be applied to making useful microfiber components. A microfiber usually refers to the fiber type waveguide of silica with diameter slightly larger than 1 μm, and the light will be guided in the whole microfiber rather than the reduced core region. The strong guiding mechanism of microfibers caused by high index difference between silica and air will make the guided light in microfibers more sensitive to the particles attached to their surfaces, which greatly increases the scattering loss [7]. Besides, the crack propagation and the generation of hydroxyl bond under humid conditions will optically degrade microfibers and increase the volume scattering loss [8,9]. Optical degradation is related to the surface area of microfibers because the aforementioned factors all take place from the surface. Therefore, the loss of long drawn microfibers will increase more rapidly than shorter ones and the induced large loss may make some microfiber-based optical components impractical. Many researchers have studied the preservation of microfibers to keep their optical performance from further deterioration [9–12]. Xu et. al. accomplished the packaging of microfiber-based devices by
⁎ Corresponding author. E-mail address: [email protected] (L.A. Wang). 0030-4018/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.optcom.2011.02.018
covering low index materials such as Teflon [9]. Lou et. al. discussed the required thickness of outer packaging materials to make microfibers fully or partially embedded [10]. Though the fully embedded microfibers can be protected from the optical degradation, partially embedded ones with thin coating thickness are desired for sensing applications. Kakarantzas et. al. covered the microfiber with sol–gel silica films of 90 nm thickness and formed a long period grating [11]; however, the silica films were too thin to protect the microfibers. Xiao et. al. proceeded to use a rigid block of aerogel to embed the microfibers [12]. The porous structure of the aerogel not only protects but also allows the gases and dopants to interact with microfibers. Unlike the previously reported studies, our aim is to make a cylindrical protective coating layer along the long drawn microfibers [6], which are hard to be entirely preserved by the aforementioned methods. Instead a conventional coating method frequently used in a fiber drawing tower is adapted to form a coating layer on the surface of a microfiber. This method is particularly suitable for coating long drawn microfibers. 2. Propagation loss and optical degradation of a long drawn microfiber A long drawn microfiber was made by drawing an optical fiber preform down to a few micron diameter wire through a modified fiber drawing tower. The preform used in the experiment was a singlemode optical fiber with cut-off wavelength of 1260 nm, NA of 0.14 and core/cladding diameter of 8.2 μm/125 μm. The fiber preform with both ends fastened to a fiber feeder and a drawing wheel respectively passed through a hot zone where the silica material became viscous liquid. Both the feeder and the wheel moved in the same direction at
2826
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rapidly, and the transmitted power would return to the previous value. After measuring the power evolution of microfibers in different diameters, we obtained the distribution of propagation losses as shown in Fig. 1(b). The loss was approximately 0.001 dB/mm for 2 μm diameter microfibers, and would increase as the diameter decreased. The environment will also severely affect the loss of microfibers. Particles would adhere to microfibers and hydroxyl bonds would generate to increase the losses of microfibers under humid condition. Fig. 2(a) shows the measured transmission spectrum of a 2 μm diameter microfiber one day after it was made. Note that the loss increase at 1383 nm wavelength indicates the formation of OH− bond caused by water absorption during and after drawing process [8]. The loss was larger for longer wavelength because of larger mode field influenced by surface roughness and particles. The increase of loss around and shorter than 800 nm wavelength resulted from the disappearance of higher-order modes in microfibers [13]. Fig. 2(b) indicates the seriousness of the microfiber degradation. The loss would increase enormously with tens of decibels after the fabrication for one day for 300 mm long, 2 μm diameter microfiber. The smaller the diameter of a microfiber was, the larger the loss would be induced
Fig. 1. (a) Transmitted power evolution at 1550 nm wavelength of a 300 mm long microfiber being drawn, and the slope represents the propagation loss. (b) Distribution of propagation losses of microfibers in different diameters at 1550 nm wavelength.
different speeds but with the desired constant ratio. By controlling the feed velocity (Vf) into the hot zone to be much slower than the drawing velocity (Vd), the fiber perform would be narrowed down based on the principle of mass conservation; therefore, the resultant diameter reduction Df/Dd can be related to the speed ratio Vd/Vf as 2
2
Vf × Df = Vd × Dd
ð1Þ
where Df and Dd are the diameters of fiber preform and microfiber, respectively. The propagation loss at 1550 nm wavelength was in situ measured when a microfiber was drawn with its length increasing at constant speed. The power evolution of a microfiber being drawn is shown in Fig. 1(a). The large variation at the beginning resulted from the formation of a fiber tapering section connecting a conventional singlemode optical fiber with a microfiber. The section length was about 5 mm, and the induced 0.7 dB loss could be attributed to the nonadiabatic tapering shape. The ensued slope represents the propagation loss. Note that the sudden transmission drops came from the change of fiber taper profiles caused by the instability of drawing mechanism. Such slight shape variations would recover
Fig. 2. (a) Transmission spectrum of a one-day old, 2 μm diameter microfiber. The water absorption at 1383 nm wavelength is observable. (b) Degradation of microfibers of different diameters at 1550 nm wavelength.
S.-M. Chuo, L.A. Wang / Optics Communications 284 (2011) 2825–2828
2827
Fig. 3. Experimental setup for coating microfibers and in-situ measurement. The coating die is placed after the microfiber fabrication and CO2 laser is used to cure PDMS. For the measurement of coated microfiber performance, the light is guided from the lower side and transmitted the coated region. The photodetector is placed beside the top of coated microfiber to capture scattered light.
because of larger evanescent fields. Therefore, the coating of microfibers to protect them from degradation is essential for practical applications. 3. Microfiber coating Polydimethylsiloxane (PDMS) was chosen as the coating material due to its lower refractive index (n = 1.402) than silica. Furthermore, PDMS is a kind of silicone frequently used as coating material for a conventional optical fiber [14]. However, PDMS is hard to remove completely from a microfiber because of its crosslink property. Only a few chemicals such as sulfuric acid, trifluoroacetic acid or dipropylamine can dissolve PDMS when immersed for 24 h [15]. The experimental setup of microfiber coating is shown in Fig. 3. A funnel shaped coating die installed in the microfiber drawing platform was placed between the fiber feeder and the drawing wheel so that the drawing and coating could be carried out simultaneously to minimize the fiber degradation. The preform passed through the hole of die, and the coating material PDMS was then injected into the die with no leak because of its high viscosity. The fiber preform was heated by a butane flame and directly drawn to a microfiber while immediately being dipped in PDMS. PDMS in the die would be dragged with microfiber and formed a cylindrical film layer along its surface. An unfocused CO2 laser with power of 10 W and beam diameter of 3.5 mm was used to irradiate the place after the microfiber passing through the coating die to thermally cure the PDMS layer. The time between a microfiber coating and curing should be less than 100 ms; otherwise, the coating would shrink into ball shape owing to the surface tension of PDMS. It required the microfiber drawing speed as fast as about 65 mm/s. The total length of coated microfiber was approximately 200 mm, and it should be kept straight to avoid bending for loss measurement. A PDMS coated microfiber is shown in Fig. 4(a). The surface of coating was very smooth due to rapid curing. The coating diameter was in the range of 50 to 150 μm depending on the viscosity of PDMS and the hole dimension of the die.
Fig. 4. (a) A photograph of coated microfiber with smooth surface; (b) the coating is uniform over a 2 mm long microfiber; (c) the 2 μm diameter microfiber can be clearly observed inside 50 μm diameter coating.
As an illustration, the microfiber would have uniform coating over 2 mm long as depicted in Fig. 4(b). For the observation of microfiber inside the coating, the coated microfiber was placed on a microscope slide glass and covered with a few drops of index matching oil before sealed with a cover glass [16]. Then it could be viewed by using Nomarski microscopy [17] as shadow image. Fig. 4(c) shows the image of a 2 μm diameter microfiber in the 50 μm diameter coating.
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S.-M. Chuo, L.A. Wang / Optics Communications 284 (2011) 2825–2828
with the result shown in Fig. 2(b). These values are comparable to what have been reported in References [5] and [6]. 5. Conclusion The propagation loss and degradation of long drawn microfibers in different diameters made by a modified fiber drawing tower have been characterized. The large losses caused by surface scattering, crack propagation and water absorption necessitate the coating along the surface of such microfibers. We successfully installed an experimental coating setup, and the resultant coatings were found uniform in diameters of about 50 to 150 μm. A coated microfiber showed effective protection from transmission loss as compared with an uncoated one. A long drawn microfiber with coated layer can be regarded as a much smaller diameter optical fiber. Therefore, it can be also used in the applications demanding long length optical fibers such as telecommunication, fiber optic gyroscope, distributed fiber sensors, etc. Fig. 5. The power evolutions of coated and bare microfibers over 18 hours at 1550 nm wavelength. The coated microfiber has a diameter of 50 μm, and the diameter of bare microfiber is 2 μm.
4. Loss measurement for a coated microfiber The loss measurement for a coated microfiber was carried out in situ and modified to measure the scattering light. When the microfiber drawing stopped, there was a small region of uncured PDMS between the coating die and the laser curing spot where a PDMS microball would be formed by surface tension. The microball would scatter light and make direct loss measurement impossible. Hence, the 1550 nm wavelength light was guided from the lower side of the single-mode fiber and went through the coating region of microfiber as shown in Fig. 3. To prevent measuring the uncoated microfiber, the scattered light from the microball was captured by a photodetector placed beside the top of coating region. The power evolutions of a 2 μm diameter microfiber with and without 50 μm diameter coating over 18 h are shown in Fig. 5. Though a variation of ±1 dB was observed owing to some air flow perturbation, the overall slope comparison between two indicates the efficacy of added coating. The uncoated microfiber was seen to degrade at the speed of 0.264 dB/h or equivalently 0.032 dB/mm/day, which is consistent
Acknowledgment The authors are grateful to the National Science Council for financial support under grant number 95-2221-E-002-327-MY3. References [1] L. Tong, R.R. Gattass, J.B. Ashcom, S. He, J. Lou, M. Shen, I. Maxwell, E. Mazur, Nature 426 (2003) 816. [2] Y.K. Lizé, E.C. Mägi, V.G. Ta'eed, J.A. Bolger, P. Steinvurzel, B.J. Eggleton, Opt. Express 12 (2004) 3209. [3] M. Sumetsky, Y. Dulashko, A. Hale, Opt. Express 12 (2004) 3521. [4] G. Brambilla, F. Xu, P. Horak, Y. Jung, F. Koizumi, N. Sessions, E. Koukharenko, X. Feng, G. Murugan, J. Wilkinson, D. Richardson, Adv. Opt. Photon. 1 (2009) 107. [5] G. Brambilla, Opt. Fiber Technol. 16 (2010) 331. [6] S.M. Chuo, M.H. Wan, L.A. Wang, J. Wang, J. Lightwave Technol. 27 (2009) 2983. [7] S. Wang, X. Pan, L. Tong, Opt. Commun. 276 (2) (2007) 293. [8] L. Ding, C. Belacel, S. Ducci, G. Leo, I. Favero, Appl. Opt. 49 (2010) 2441. [9] F. Xu, G. Brambilla, Jpn. J. Appl. Phys. 47 (2008) 6675. [10] N. Lou, R. Jha, J. Domínguez-Juárez, V. Finazzi, J. Villatoro, G. Badenes, V. Pruneri, Opt. Lett. 35 (2010) 571. [11] G. Kakarantzas, S.G. Leon-Saval, T. Birks, P. Russell, Opt. Lett. 29 (2004) 694. [12] L. Xiao, M. Grogan, S.G. Leon-Saval, R. Williams, R. England, W. Wadsworth, T. Birks, Opt. Lett. 34 (2009) 2724. [13] Y. Jung, G. Brambilla, D. Richardson, Opt. Express 16 (2008) 14661. [14] T.J. Miller, A.C. Hart, W.I. Vroom, M.J. Bowden, Electron. Lett 14 (1978) 603. [15] J.N. Lee, C. Park, G.M. Whitesides, Anal. Chem. 75 (2003) 6544. [16] M.H. Wan, L.A. Wang, Proc. SPIE 7503 (2009) 750373. [17] R.D. Allen, G.B. David, G. Nomarski, Z. Wiss. Mikrosk. 69 (1969) 193.