Magnetically controllable wavelength-divisionmultiplexing fiber coupler Wei Lin,1 Hao Zhang,1,3 Binbin Song,1 Yinping Miao,2 Bo Liu,1,4 Donglin Yan,1 and Yange Liu1 1

Key Laboratory of Optical Information Science and Technology, Ministry of Education, Institute of Modern Optics, Nankai University, Tianjin 300071, China 2 Tianjin Key Laboratory of Film Electronic & Communication Devices, School of Electronics Information Engineering, Tianjin University of Technology, Tianjin, 300384 China 3 [email protected] 4 [email protected]

Abstract: In this paper, a magnetically controllable wavelength-divisionmultiplexing (WDM) fiber coupler has been proposed and experimentally demonstrated. A theoretical model has been established to analyze the influences of the weak as well as strong couplings to the wavelength tunability of this coupler. Experimental results show that the operation wavelength tunability of the proposed WDM coupler could be fulfilled for an applied magnetic field intensity range of 0 Oe to 500 Oe, and particularly it possesses high operation performances within the magnetic field intensity ranging from 25 Oe to 125 Oe when additional transmission loss and isolation are both considered. Within this range, the two selected channels show the wavelength tunability of 0.05 nm/Oe and 0.0744 nm/Oe, respectively, and the isolation between the two branches is higher than 24.089 dB. Owing to its high isolation, good splitting ratio stability, and high wavelength tunability, the proposed controllable WDM coupler is anticipated to find potential applications in such fields as fiber laser, fiber sensing and fiber-optic communications. Moreover, the fiber coupler integrated with the magnetic fluid would be valuable for the design of magnetically controllable mode-division-multiplexing devices. ©2015 Optical Society of America OCIS codes: (060.2310) Fiber optics; (060.2340) Fiber optics components; (160.3820) Magneto-optical materials; (230.3810) Magneto-optic systems.

References and links 1. 2. 3. 4. 5. 6. 7. 8. 9.

H. Ishio, J. Minowa, and K. Nosu, “Review and status of wavelength-division-multiplexing technology and its application,” J. Lightwave Technol. 2(4), 448–463 (1984). Y. Zhang and C. Zhou, “High-efficiency reflective diffraction gratings in fused silica as (de)multiplexers at 1.55microm for dense wavelength division multiplexing application,” J. Opt. Soc. Am. A 22(2), 331–334 (2005). M. Lequime, R. Parmentier, F. Lemarchand, and C. Amra, “Toward tunable thin-film filters for wavelength division multiplexing applications,” Appl. Opt. 41(16), 3277–3284 (2002). H. G. Iocco, H. G. Limberger, R. P. Salathe, L. A. Everall, K. E. Chisholm, J. A. R. Williams, and I. Bennion, “Bragg grating fast tunable filter for wavelength division multiplexing,” J. Lightwave Technol. 17(7), 1217– 1221 (1999). U. Tiwari, S. M. Tripathi, K. Thyagarajan, M. R. Shenoy, V. Mishra, S. C. Jain, N. Singh, and P. Kapur, “Tunable wavelength division multiplexing channel isolation filter based on dual chirped long-period fiber gratings,” Opt. Lett. 36(19), 3747–3749 (2011). J. B. Eom, H. R. Lim, K. S. Park, and B. H. Lee, “Wavelength-division-multiplexing fiber coupler based on bending-insensitive holey optical fiber,” Opt. Lett. 35(16), 2726–2728 (2010). B. S. Kawasaki, K. O. Hill, and R. G. Lamont, “Biconical-taper single-mode fiber coupler,” Opt. Lett. 6(7), 327– 328 (1981). M. Eisenmann and E. Weidel, “Single-mode fused biconical couplers for wavelength division multiplexing with channel spacing between 100 and 300 nm,” J. Lightwave Technol. 6(1), 113–119 (1988). M. N. McLandrich, R. J. Orazi, and H. R. Marlin, “Polarization independent narrow channel wavelength division multiplexing fiber couplers for 1.55 μm,” J. Lightwave Technol. 9(4), 442–447 (1991).

#233554 - $15.00 USD © 2015 OSA

Received 11 Feb 2015; revised 13 Apr 2015; accepted 15 Apr 2015; published 21 Apr 2015 4 May 2015 | Vol. 23, No. 9 | DOI:10.1364/OE.23.011123 | OPTICS EXPRESS 11123

10. S. W. Yang, T. L. Wu, C. W. Wu, and H. C. Chang, “Numerical modeling of weakly fused fiber-optic polarization beamsplitters—part ii: the three-dimensional electromagnetic model,” J. Lightwave Technol. 16(4), 691–696 (1998). 11. K. Morishita and K. Yamazaki, “Wavelength and polarization dependences of fused fiber couplers,” J. Lightwave Technol. 29(3), 330–334 (2011). 12. J. Teng, J. Yang, C. Lv, T. Chen, J. Guo, J. Feng, and P. Wu, “Guidelines for design and fabrication of fused fiber coupler based wavelength division multiplexings,” Opt. Fiber Technol. 20(3), 239–244 (2014). 13. M. J. F. Digonnet and H. J. Shaw, “Analysis of a tunable single mode optical fiber coupler,” IEEE J. Quantum Electron. 18(4), 746–754 (1982). 14. H. Choi, Y. Jeong, and K. Oh, “Wide, tunable band rejection filter based on micro-optical waveguide on microactuating platform covering O, E, S, C, L, and U bands,” Opt. Lett. 36(4), 484–486 (2011). 15. R. G. Lamont, D. C. Johnson, and K. O. Hill, “Power transfer in fused biconical-taper single-mode fiber couplers: dependence on external refractive index,” Appl. Opt. 24(3), 327–332 (1985). 16. K. T. Kim, K. J. Cho, and B. H. Lee, “Empirical analysis of widely tunable fused fiber coupler assisted by external medium of high thermo-optic coefficient,” Fiber Integrated Opt. 30(1), 61–72 (2011). 17. M. Velazquez-Benitez and J. Hernandez-Cordero, “Optically Controlled Wavelength Tunable Fused Fiber Coupler,” in Workshop on Specialty Optical Fibers and their Applications, (Optical Society of America, 2013), paper W3.25. 18. S. Y. Yang, J. J. Chieh, H. E. Horng, C. Y. Hong, and H. C. Yang, “Origin and applications of magnetically tunable refractive index of magnetic fluid films,” Appl. Phys. Lett. 84(25), 5204–5206 (2004). 19. S. Y. Yang, Y. P. Chiu, B. Y. Jeang, H. E. Horng, C. Y. Hong, and H. C. Yang, “Origin of field-dependent optical transmission of magnetic fluid films,” Appl. Phys. Lett. 79(15), 2372–2374 (2001). 20. P. C. Scholten, “The origin of magnetic birefringence and dichroism in magnetic fluids,” IEEE T. Magn. 16(2), 221–225 (1980). 21. R. Gao, Y. Jiang, and S. Abdelaziz, “All-fiber magnetic field sensors based on magnetic fluid-filled photonic crystal fibers,” Opt. Lett. 38(9), 1539–1541 (2013). 22. A. Candiani, A. Argyros, S. G. Leon-Saval, R. Lwin, S. Selleri, and S. Pissadakis, “A loss-based, magnetic field sensor implemented in a ferrofluid infiltrated microstructured polymer optical fiber,” Appl. Phys. Lett. 104(11), 111106 (2014). 23. Y. Zhao, R. Lv, D. Wang, and Q. Wang, “Fiber optic Fabry-Perot magnetic field sensor with temperature compensation using a fiber Bragg grating,” IEEE Trans. Instrum. Meas. 63(9), 2210–2214 (2014). 24. J. Zheng, X. Dong, P. Zu, J. Ji, H. Su, and P. S. Perry, “Intensity-modulated magnetic field sensor based on magnetic fluid and optical fiber gratings,” Appl. Phys. Lett. 103(18), 183511 (2013). 25. H. E. Horng, C. S. Chen, K. L. Fang, S. Y. Yang, J. J. Chieh, C. Y. Hong, and H. C. Yang, “Tunable optical switch using magnetic fluids,” Appl. Phys. Lett. 85(23), 5592–5594 (2004). 26. Y. Gu, G. Valentino, and E. Mongeau, “Ferrofluid-based reconfigurable optofluidic switches for integrated sensing and digital data storage,” Appl. Opt. 53(4), 537–543 (2014). 27. P. Zu, C. C. Chan, L. W. Siang, Y. Jin, Y. Zhang, L. H. Fen, L. Chen, and X. Dong, “Magneto-optic fiber Sagnac modulator based on magnetic fluids,” Opt. Lett. 36(8), 1425–1427 (2011). 28. S. Pu, X. Chen, Y. Chen, Y. Xu, W. Liao, L. Chen, and Y. Xia, “Fiber-optic evanescent field modulator using a magnetic fluid as the cladding,” J. Appl. Phys. 99(9), 093516 (2006). 29. T. Liu, X. Chen, Z. Di, J. Zhang, X. Li, and J. Chen, “Tunable magneto-optical wavelength filter of long-period fiber grating with magnetic fluids,” Appl. Phys. Lett. 91(12), 121116 (2007). 30. S. Dutt, S. K. Varshney, and S. Mahapatra, “Design of tunable couplers using magnetic fluid filled three-core optical fibers,” IEEE Photon. Technol. Lett. 24(3), 164–166 (2012). 31. W. Lu, Z. Chen, and Q. Guo, “A fiber magneto-optical switch for NGN,” in Proceedings of IET International Conference on Wireless, Mobile and Multimedia Networks, (IET, 2006), pp. 1–4. 32. Y. Chen, Q. Han, T. Liu, X. Lan, and H. Xiao, “Optical fiber magnetic field sensor based on single-modemultimode-single-mode structure and magnetic fluid,” Opt. Lett. 38(20), 3999–4001 (2013). 33. C. Y. Hong, H. E. Horng, and S. Y. Yang, “Tunable refractive index of magnetic fluids and its applications,” Phys. Status Solidi 1(7), 1604–1609 (2004). 34. S. Lacroix, F. Gonthier, and J. Bures, “Modeling of symmetric 2 × 2 fused-fiber couplers,” Appl. Opt. 33(36), 8361–8369 (1994).

1. Introduction As one of the most efficient methods to expand the transmission spectral window, wavelength division multiplexing (WDM) is one of the key technologies for optical communications as well as optical sensing systems [1]. Due to the great demands of data exchange applications in multi-channel optical networks, much efforts have been put on the development of multiplexing/demultiplexing components, including diffraction grating [2], dielectric film filter [3], fiber Bragg grating [4], long period fiber grating [5], and fiber coupler [6]. Amongst these components, fiber coupler plays a particularly significant role in building up all-fiber

#233554 - $15.00 USD © 2015 OSA

Received 11 Feb 2015; revised 13 Apr 2015; accepted 15 Apr 2015; published 21 Apr 2015 4 May 2015 | Vol. 23, No. 9 | DOI:10.1364/OE.23.011123 | OPTICS EXPRESS 11124

optical systems and have attracted increasing research interests in the past few decades [7~12]. The wavelength tunability of fiber couplers provides convenient, fiber-compatible and hence low loss approaches for wavelength channel selection and add/drop in fiber-optic systems, and they have found various applications in such ever-growing fields as fiber laser, fiber sensor, and fiber-optic communications technologies. In the past few years, wavelength tunability of fiber couplers has been fulfilled by employing the micro-mechanical platform or thermo-optical medium [13–17]. Fiber-optic couplers could be generally classified into two categories: the mechanically tunable [13, 14] and evanescent-field-assisted ones [15–17]. The latter would be of special attraction as the evanescent field is highly sensitive to the environmental medium. This property makes it possible to achieve a tunable WDM coupler with high performances by integrating the fiber-optic coupler with various functional materials. As an attractive functional material, the magnetic fluid (MF) possesses many intriguing magneto-optical properties such as tunable refractive index [18], tunable transmission [19], tunable birefringence and dichroism [20], etc. By using these properties, a good variety of magneto-optical devices have been proposed, including magnetic field sensors [21–24], optical switches [25, 26], and optical modulators [27, 28], etc. The variation in refractive index of the MF could normally reach a magnitude of 10−2 when external magnetic field is applied [29]. This property could be exploited to tune the coupling coefficient of fiber-optic couplers. Actually some works have been engaged on the design of MF-based tunable couplers [30, 31]. These works aim to theoretically design the magnetically controlled coupler operating at one particular wavelength. In the work presented in this paper, we have theoretically proposed and experimentally validated a magnetically controllable wavelength-selective fiber coupler for WDM applications. Its wavelength tunability is achieved by integrating the fiber coupler with the MF. A theoretical model has been set up to analyze the operation principle of the proposed WDM coupler, which is verified by our experimental observation on the transmission spectral evolution in response to the applied magnetic field intensity. Our proposed magnetically controllable WDM coupler has high channel wavelength tunability and splitting ratio with high isolation, which ensures its applicability for potential applications in fiber laser and fiber-optic communications systems, as well as fiber sensing occasions. Furthermore, our proposed schemes also support the magnetically controllable mode division multiplexing by using the MF-integrated fiber coupler. 2. Theory 2.1 Fundamental principle Several schemes have been proposed to analyze the coupling mathematically of tapered fiber couplers [10–12]. According to the fusion degree, the coupling region of the fiber coupler can be classified into weakly coupling and strong coupling regions, as shown in Fig. 1. Under weakly coupling condition, the two fibers are not fused together. When the light propagating through the two fibers is constrained inside the core area, the coupling between the two fibers is rather weak and could be actually neglected. As the fiber radius further reduces during the pulling process and the fiber core would no longer thoroughly constrain the light, and the fiber cladding would turn to serve as the waveguide core with ambient medium working as the waveguide cladding. In this case the coupling coefficient could be expressed as [12]: 1/ 2


2  Δ  ⋅  r  2π D 

3 − U∞ λ 2 −V (2 D − 2) U V e = ∞ V 5/ 2 eV (2 D − 2) 2π r 2 n2 π D


where, Δ = (n22-n32)/2n22 and V = 2πr(n22-n32)1/2/λ refer to the relative refractive index difference and normalized propagation constant, respectively. Here n2 and n3 represent the

#233554 - $15.00 USD © 2015 OSA

Received 11 Feb 2015; revised 13 Apr 2015; accepted 15 Apr 2015; published 21 Apr 2015 4 May 2015 | Vol. 23, No. 9 | DOI:10.1364/OE.23.011123 | OPTICS EXPRESS 11125

refractive indices of the cladding and the external medium, respectively, and r is the fiber radius which depends on the fusion degree and length of the tapering region. The eigenvalue U∞, is 2.405 when the fundamental core mode is far from cut-off region. D is defined as D = d/2r to describe the fusion degree, where d is the inter-core distance.

Fig. 1. Schematic diagram of a symmetrical 2 × 2 tapered coupler.

For the strong coupling case, the fibers are fused together and Eq. (1) is no longer valid. Under this condition, the coupler could be considered as a hybrid waveguide and the coupling coefficient can be calculated by half of the propagation constant difference between the even and odd modes. In other words, the fiber fusion region is simplified as a rectangular waveguide and the coupling coefficient can be described as [12]:

β 0 − β1

3πλ 1 ⋅ (2) 2 2 32n2 r (1 + 1/ V ) 2 Therefore, the phase difference between the light at the two output ports can be calculated by integrating the coupling efficient along z-axis over the coupling region, as expressed by the following equation [12]: CSC =


ϕ (λ , n3 ) =  CWC (λ , n3 , z)dz +  CSC (λ , n3 , z)dz

(3) = ϕWC (λ , n3 ) + ϕ SC (λ , n3 ) Thus the normalized powers of the output ports could be acquired using PC (λ) = 1- sin2 φ (λ, n3) and PD (λ) = sin2 φ (λ, n3) [12]. It should be noted that the transmission loss is neglected in the above calculation. However, with the reduction of fiber radius, stronger evanescent field would be excited and will be absorbed or scattered by ambient medium, causing considerable transmission loss when the light propagates though the fiber fusion region. Besides, the modal phase difference between the two fibers should be also taken into account as it is rather difficult to maintain identical fiber geometry during the pulling process. Considering these factors, the output powers normalized to the input power should be modified as: WC


PC (λ ) = 10−α (1 − F sin 2 ϕ (λ , n3 ))


PD (λ ) = 10−α F sin 2 ϕ (λ , n3 )


where, α = α0 + αext (H) is the transmission loss introduced during the pulling process and the ambient medium, and F≡|κ|2/φ2 (0≤F≤1) is the phase matching degree. Here, κ is the coupling coefficients between the two fibers. For an ideal fiber coupler, the phase is well matched and in practical applications it is reasonable to assume that F≈1. The performance of the coupler can be theoretically evaluated by the following parameters, including insertion loss L, additional loss Ladd, and splitting ratio SR, which could be expressed below: LX = −10 lg

#233554 - $15.00 USD © 2015 OSA

PX = −10 lg PX (λ ) ; X = C or D Pin


Received 11 Feb 2015; revised 13 Apr 2015; accepted 15 Apr 2015; published 21 Apr 2015 4 May 2015 | Vol. 23, No. 9 | DOI:10.1364/OE.23.011123 | OPTICS EXPRESS 11126

Ladd = −10 lg

Pout ,total Pin

= −10 lg( PC (λ ) + PD (λ ))


− L /10 = α = −10 lg 10( C ) + 10( − LD /10)   


PX × 100% = 10− ( L − Ladd )/10 × 100% ; X = C or D Pout ,total


When sin2 φ (λ, n3) = 1, the minimum PC (λ) could be reached while the maximum could be acquired when sin2 φ (λ, n3) = 0. Thus, for port C, the band-pass or band-rejection operations can be achieved when the following conditions are respectively satisfied: π 2 + kπ ϕ (λ , n3 ) =   kπ

band-rejection channel ; k is integer band-pass channel

(1 − F ) × 100% SRC − channel =  1 

band-rejection channel band-pass channel



2.2 Theoretical analysis As the applied magnetic field intensity varies, the refractive index and transmission loss of the magnetic fluid would change accordingly [18, 19]. And therefore, the phase difference of the coupler φ (λ, n3), the phase matching degree F as well as the transmission loss α would change accordingly. Since the transmission loss increases with the increment of the magnetic field intensity, the additional loss would increase according to Eq. (7) [19]. While, the insertion losses are affected by the transmission loss α, the phase difference φ (λ, n3) and the phase matching degree F. However, the channel splitting ratio SR only depends on the phase matching degree F. Additionally, the channel wavelength would also shift with the variation in the refractive index of the magnetic fluid, and the corresponding sensitivity can be expressed as:  ∂ϕ ∂ϕ  ∂ϕ −  WC + SC  ∂n3 ∂n3  ∂n ∂λ (11) =− 3 =  ϕ ϕ ϕ ∂ ∂ ∂ ∂n3 WC + SC ∂λ ∂λ ∂λ According to Eqs. (1) and (2), it is easy to deduce that ∂φSC/∂n3 0 and ∂φWC/∂n3>0. And in order to ensure good light constraint ability, the eigenvalues V of the tapered fiber should be larger than 2.045, which means that ∂φSC/∂λ >0. Thus, if weak coupling is the major factor that account for the coupling mechanism, ∂λ/∂n30 and ∂φWC/∂n3>0. Under the strong coupling condition, in order to maintain good light constraint ability, the eigenvalue V of the tapered fiber should be larger than 2.045, and ∂φSC/∂λ is larger than 0. Hence according to Eqs. (11)-(15), the channel wavelength would shift toward longer wavelength region with the increment of ambient refractive index when -∂φSC/∂n3>∂φWC/∂n3, while it will turn out blue shift when -∂φSC/∂n3

Magnetically controllable wavelength-division-multiplexing fiber coupler.

In this paper, a magnetically controllable wavelength-division-multiplexing (WDM) fiber coupler has been proposed and experimentally demonstrated. A t...
3MB Sizes 2 Downloads 6 Views

Recommend Documents

Magnetically controllable 3D microtissues based on magnetic microcryogels.
Microtissues on the scale of several hundred microns are a promising cell culture configuration resembling the functional tissue units in vivo. In contrast to conventional cell culture, handling of microtissues poses new challenges such as medium exc

Double-clad fiber coupler for partially coherent detection.
Double-clad fibers (DCF) have many advantages in fibered confocal microscopes as they allow for coherent illumination through their core and partially coherent detection through their inner cladding. We report a double-clad fiber coupler (DCFC) made

Hybrid fiber resonator employing LRSPP waveguide coupler for gyroscope.
Polarization error and temperature noise are two main limits to the performance of resonant fiber optic gyroscope (RFOG). To overcome these limits, we demonstrated a hybrid resonator consisting of a polymer-based long-range surface plasmon polariton

Design and fabrication of magnetically functionalized flexible micropillar arrays for rapid and controllable microfluidic mixing.
Magnetically functionalized PDMS-based micropillar arrays have been successfully designed, fabricated and implanted for controllable microfluidic mixing. The arrangement of PDMS micropillar arrays inside the microchannel can be flexibly controlled by

Controllable orientation of single silver nanowire using two fiber probes.
We report a strategy for realizing precise orientation of single silver nanowire using two fiber probes. By launching a laser of 980 nm wavelength into the two fibers, single silver nanowire with a diameter of 600 nm and a length of 6.5 μm suspended

All-optical logical gates based on pump-induced resonant nonlinearity in an erbium-doped fiber coupler.
In this paper, we theoretically investigate all-optical logical gates based on the pump-induced resonant nonlinearity in an erbium-doped fiber coupler. The resonant nonlinearity yielded by the optical transitions between the (4)I(15/2) states and (4)

Differential twin receiving fiber-optic magnetic field and electric current sensor utilizing a microfiber coupler.
A magnetic field and electric current meter is proposed based on a differential twin receiving microfiber coupler (MC) sensor. The sensor is fabricated by bonding a MC and an aluminium (Al) wire together. With the small diameter of several micrometer

Highly efficient and perfectly vertical chip-to-fiber dual-layer grating coupler.
A novel high-efficiency silicon-chip-to-fiber grating coupler is investigated here. By introducing a dual layer grating structure with an inter-layer lateral shift to mimic 45° tilted mirror behavior, perfectly vertical coupling is successfully demon

All-fiber fused directional coupler for highly efficient spatial mode conversion.
We model and demonstrate a simple mode selective all-fiber coupler capable of exciting specific higher order modes in two- and few-mode fibres with high efficiency and purity. The coupler is based on inter-modally phase-matching the propagation const

An integrated photoluminescence sensing platform using a single-multi-mode fiber coupler-based probe.
We demonstrate an integrated fiber optic photoluminescence sensing platform using a novel single-multi-mode fiber coupler (SMFC)-based probe with high collection efficiency for fluorescence signals. The SMFC, prepared using fused biconical taper tech