Optical reconfigurable demultiplexer based on Bragg grating assisted ring resonators

Transcription

1 Optial reonfigurable demultiplexer based on Bragg grating assisted ring resonators Salvador Vargas 1,,* and Carmen Vazquez 1 1 Department of Eletroni Tehnology, Universidad Carlos III de Madrid, Ave. Universidad No. 30, C.P: 8911, Leganés, Madrid, Spain Eletrial Engineering Faulty, Universidad Tenológia de Panamá, Ave. Universidad Tenológia, El Dorado , Panamá, Panama * salvador.vargas@utp.a.pa Abstrat: A polarization independent reonfigurable optial demultiplexer with low rosstalk between adjaent hannels and high number of potential alloated hannels is designed on silion on insulator tehnology. On to off state transitions an be implemented by hanging the oupling fator or the ring length. Wavelength seletive swith units are asaded to form the demultiplexer. Crosstalks below 30dB with 50GHz hannel spaing and losses below 1.5dB in the off state are obtained from simulations. Designs using arrier dispersion effet and power onsumption estimations are inluded. 014 Optial Soiety of Ameria OCIS odes: ( ) Buffers, ouplers, routers, swithes, and multiplexers; (30.310) Integrated optis devies; ( ) Resonators; (30.090) Eletro-optial devies. Referenes and links 1. H. Zang, J. P. Jue, and B. Mukherjeea, Review of Routing and Wavelength Assignment Approahes for Wavelength-Routed Optial WDM Networks, Opt. Netw. Mag. 1, (000).. T. E1-Bawab, Optial Swithing (Springer, 010). 3. I. Kiyat, A. Aydinli, and N. Dagli, Low-Power Thermooptial Tuning of SOI Resonator Swith, IEEE Photon. Tehnol. Lett. 18(), (006). 4. E. J. Klein, P. Urban, G. Sengo, L. T. H. Hilderink, M. Hoekman, R. Pellens, P. van Dijk, and A. Driessen, Densely integrated miroring resonator based photoni devies for use in Aess networks, Opt. Express 15(16), (007). 5. S. J. Emelett and R. A. Soref, Analysis of dual-miroring-resonator ross-onnet swithes and modulators, Opt. Express 13(0), (005). 6. R. Boek, N. A. F. Jaeger, N. Rouger, and L. Chrostowski, Series-oupled silion raetrak resonators and the Vernier effet: theory and measurement, Opt. Express 18(4), (010). 7. F. Xia, M. Rooks, L. Sekari, and Y. Vlasov, Ultra-ompat high order ring resonator filters using submiron silion photoni wires for on-hip optial interonnets, Opt. Express 15(19), (007). 8. Y. Zhang, P. Chowdhury, M. Tornatore, and B. Mukherjee, Energy Effiieny in Teleom Optial Networks, IEEE Commun. Surveys Tuts. 1(4), (010). 9. L. Shuai, W. Yuanda, Y. Xiaojie, A. Junming, L. Jianguang, W. Hongjie, and H. Xiongwei, Tunable filters based on an SOI nano-wire waveguide miro ring resonator, J. Semiondu. 3, (011). 10. R. Soref and B. Bennett, Eletrooptial Effets in Silion, IEEE J. Quantum Eletron. 3(1), (1987). 11. Q. Xu, B. Shmidt, S. Pradhan, and M. Lipson, Mirometre-sale silion eletro-opti modulator, Nature 435(7040), (005). 1. C. Li, L. Zhou, and A. W. Poon, Silion miroring arrier-injetion-based modulators/swithes with tunable extintion ratios and OR-logi swithing by using waveguide ross-oupling, Opt. Express 15(8), (007). 13. P. Dong, W. Qian, H. Liang, R. Shafiiha, X. Wang, D. Feng, G. Li, J. E. Cunningham, A. V. Krishnamoorthy, and M. Asghari, 1x4 reonfigurable demultiplexing filter based on free-standing silion raetrak resonators, Opt. Express 18(4), (010). 14. S. Vargas and C. Vazquez, Synthesis of optial filters using miroring resonators with ultra-large FSR, Opt. Express 18(5), (010). 15. C. Vázquez, S. Vargas, and P. Contreras, Low power onsumption in silion photonis tuning filters based on ompound ring resonators, in Silion Photonis VIII, Photonis West, Pro. SPIE 869, (013). 16. D. Dai, J. Bauters, and J. E. Bowers, Passive tehnologies for future large-sale photoni integrated iruits on silion: polarization handling, light non-reiproity and loss redution, Light: Si. Appl. 1(3), 1 14 (01). 17. S. Ghosh, S. Keyvaninia, W. Van Roy, T. Mizumoto, G. Roelkens, and R. Baets, Adhesively bonded Ce:YIG/SOI integrated optial irulator, Opt. Lett. 38(6), (013). (C) 014 OSA 11 August 014 Vol., No. 16 DOI: /OE OPTICS EXPRESS 19156

2 18. C. Vázquez, S. Vargas, J. M. S. Pena, and P. Corredera, Tunable Optial Filters Using Compound Ring Resonators for DWDM, IEEE Photon. Tehnol. Lett. 15(8), (003). 19. J. G. Proakis and D. G. Manolakis, Digital Signal Proessing, (Pearson Prentie Hall, 006). 0. Y. A. Vlasov and S. J. MNab, Losses in single-mode silion-on-insulator strip waveguides and bends, Opt. Express 1(8), (004). 1. S. P. Chang, C. E. Png, S. T. Lim, V. M. N. Passaro, and G. T. Reed, Single mode and polarization independent SOI waveguides with small ross setion, J. Lightwave Tehnol. 3, (005).. W. Headley, G. Reed, S. Howe, A. Liu, and M. Paniia, Polarization-independent optial raetrak resonators using rib waveguides on silion-on-insulator, Appl. Phys. Lett. 85(3), (004). 3. F. Sun, J. Yu, and S. Chen, Diretional-oupler-based Mah-Zehnder interferometer in silion-on-insulator tehnology for optial intensity modulation, Opt. Eng. 4, (007). 4. P. Dong, S. Liao, H. Liang, R. Shafiiha, D. Feng, G. Li, X. Zheng, A. V. Krishnamoorthy, and M. Asghari, Submilliwatt, ultrafast and broadband eletro-opti silion swithes, Opt. Express 18(4), (010). 5. J. Dziewior and W. Shmid, Auger oeffiients for highly doped and highly exited silion, Appl. Phys. Lett. 31(5), (1977). 6. M. Hossein-Zadeh and K. J. Vahala, Optomehanial Osillator on a Silion Chip, IEEE J. Sel. Top. Quantum Eletron. 16(1), (010). 1. Introdution Wavelength-Division Multiplexing (WDM) in optial fiber networks has been rapidly gaining aeptane as a means to handle the ever-inreasing bandwidth demands of network users. In a wavelength-routed WDM network, end users ommuniate with one another via all-optial WDM hannels, whih are referred to as lightpaths. Wavelength seletive optial swithes are needed to set up lightpaths at different wavelengths [1]. There are several types of optial swithes depending on the fabriation tehnologies used to onstrut them, like lithium niobate, aousto-opti, thermo-opti, liquid rystal, miroeletromehanial systems (MEMS), semiondutor optial amplifiers (SOA) and ring resonators (RR) []. From all these types, the RR WDM swithes are very versatile as they an be integrated with other devies using integrated optis tehnology, like silion on insulator (SOI) tehnology. This tehnology permits the maximum integration due to its high refrative index ontrast. These WDM swithes have appliations working individually [3], or as part of optial multiplexers/demultiplexers [4], optial routers and optial ross onnets [5]. Nevertheless, beause of its periodi transfer funtion the number of hannels they an swith is limited by its free spetral range (FSR). To avoid this restrition, it has been proposed strutures using the Vernier effet [6] to inrease the FSR. Also to improve the on-off ratio and redue the rosstalk have been asaded RR to realize higher order transfer funtions [7], although this tehnique inrease the footprint in the wafer in the integrated optis devie. On the other hand, due to the rapid growth of energy onsumption in ICT (Information and Communiation Tehnologies), lot of attention is being devoted towards green ICT solutions [8]. Energy onsumption in optial networks will be redued by using omponents onsuming a lower amount of energy. In RR based WDM swithes most of the power is onsumed to swith and maintain any optial path hange, whih indue a ommutation of the WDM swith state. This optial path hange an be done by means of the thermo-opti effet [3, 9], or by mean of eletro-optial effets like eletri field or harge arrier effets [10 1]. To save energy it has been designed strutures with free standing waveguides with underut strutures [13] highly effiient, whih signifiantly redues the tuning power. In this paper, we propose and design a reonfigurable optial demultiplexer based on RR WDM swithes tehnology, assisted with Bragg Gratings (BG). Simulations to desribe its features are reported. The demultiplexer is omposed by individual WDM swithes tuned to proper wavelengths. Avoiding the restrition imposed by the periodi funtion of the RR with a non periodi transfer funtion inside the ring [14], the BG. The number of hannels to be demultiplexed an be inreased beyond the limit of a single RR FSR, by asading more WDM swithes. The rosstalk and on off ratio are also, dereased and inreased respetively, (C) 014 OSA 11 August 014 Vol., No. 16 DOI: /OE OPTICS EXPRESS 19157

3 in omparison with the demultiplexers based on single RRs, as the basi unit of the swith has a seond order transfer funtion. It an provide a similar performane to demultiplexers based on double RR, but using a smaller footprint with greater manufaturing tolerane as they operate with only one physial ring [15]. Finally, two ontrol mehanisms are analyzed, the hange in the oupling fator and the hange in the ring optial path length.. WDM Swithes N WDM swith units, as the one shown in Fig. 1, an be asaded to form the demultiplexer. This basi unit is a RR BG assisted WDM swith. There is one of these units by eah wavelength to demultiplex and being tuned at a speifi information hannel frequeny. Fig. 1. WDM swith unit. The basi unit, see Fig. 1, onsists of a RR with a Mihelson interferometer (MI) plaed inside. The MI is made of a diretional oupler, with oupling fator K and idential BGs as frequeny seletive mirrors. The BG entral frequeny is tuned to the frequeny of the maximum RR transfer funtion amplitude, the information hannel frequeny. The basi unit has also a irulator to rediret the signal refleted from the ring to the drop output port. Optial irulators and isolators are non-reiproal optial devies. Optial isolators based on ring resonators have already being manufatured using a speial bonding tehnology to ombine magneto opti materials with silion integrated photoni iruits [16]. Reently, 3- port optial irulators in a SOI ompatible fabriation proess based on a Mah-Zehnder interferometer were reported in [17]. The most important part of the basi unit is the RR with a Mihelson interferometer (RRMI). The MI ats as a transmitting-refleting funtion allowing the lokwise and ounterlokwise propagation of light inside the ring. There are two outputs for the RRMI, the through output (TO) and the drop output (DO), beause of this double reirulation. Both are seond order transfer funtions, non-periodi in frequeny, due to the BG transfer funtion. This onfiguration permits lower rosstalk than a single RR plaed in series with a BG [14]. The transfer funtions of the RRMI an be alulated using the transfer matrix formalism in the z domain [18]: 1/ 1 1 ( 1 γ ) ( 1 Z1z )( 1 Zz ) 1 1 ( 1 p ) ( 1 p ) A = A Z z Z z 1 1 ( 1 γ )( 1 γ ) ( 1 ) ( Ω) A j K K r e z A Z z Z z 1R = ( 1 p ) ( 1 p ) α L 1 where A /A 1 and A 1R /A 1, are the TO and DO transfer funtions respetively, where (1-γ ), K and (1-γ), K are the exess loss oeffiient and oupling fators of the input and MI ouplers respetively; /r(ω)/ is the BG modulus, α is the attenuation oeffiient of the waveguides and (1) () (C) 014 OSA 11 August 014 Vol., No. 16 DOI: /OE OPTICS EXPRESS 19158

4 L is the round trip length in the ring. Z 1 and Z are the zeroes of the through transfer funtion: 1/ ( 1 γ ) ( 1 γ) r( Ω) ( 1 K ) (( 1 )( 1 ) ( )) ( )( ) α L e Z = j K K K K K + K K K 1/ 1/ 1 1/ (3) Z 1/ ( 1 γ ) ( 1 γ) r( Ω) e = 1/ ( 1 K ) j( ( 1 K )( 1 K) K ( K K )) + ( K )( K K ) (4) α L 1/ 1/ Z p1 and Z p are the omplex onjugated poles of both transfer funtions and their modulus and phase are given by: 1/ ( γ ) ( γ )( ) L Z p = K r( Ω) e α (5) 1 (1 K) ϕ p =± tan ( K K ) All transfer funtion simulations are based on Matlab software..1 Transfer funtion disussion The drop output, see Eq. () has a fix zero at the origin. The zeroes of the through transfer funtion, see Eq. (1), an be plaed at different positions in the Z plane by means of the hange in the oupling fators K and K. The modulus of these zeroes an be omplex onjugated, or real and they an be different depending on the values of K and K. The zeroes are omplex onjugated if K is smaller than K lim : K lim 1 K 0 K < K = K < K 1 K Otherwise, the zeroes are real positives and different. In Fig., see the zeroes modulus of the RRMI through transfer funtion evolution versus the K fator, at a fix K. This modulus is less than 1 for omplex zeroes and its value greatly inrease for real zeroes, see Eq. (3). This property of the through transfer funtion an be used to ontrol the WDM swith status. If a zero of any transfer funtion is mapped onto the unit irle line, the transfer funtion magnitude is zero at the frequeny that orresponds to an angle given by the zero phase [19]. Then by plaing a zero of the through transfer funtion, given in Eq. (1), at the unit irle line, the signal amplitude at the frequeny that orresponds to the angle given by this zero phase, in this ase the information hannel frequeny, is highly attenuated. From Fig., this an be fulfilled adjusting K to a value slightly higher than K lim, where the modulus of the zero is 1. For proper operation of the WDM swith, the same frequeny hannel at the drop output need to be dropped, see Eq. (). The pole phases must be equal to 0, or to the nearest possible value. This is fulfilled when K equals 0.5, see Eq. (6), but in this ase the transmittingrefleting funtion beomes only a transmitting funtion. Beause of this a K value of 0.49 is hosen for this oupler in the basi unit. (6) (7) (C) 014 OSA 11 August 014 Vol., No. 16 DOI: /OE OPTICS EXPRESS 19159

5 Fig.. Poles and Zeroes Modulus of the RRMI through transfer funtion, with K = 0.5, γ = γ = 0.05 and losses in the RR less than 0.01 db. For the hosen K value of 0.49 the orresponding K lim is 0.039, see Eq. (7). In this ase, the swith is working at the on state, the frequeny hannel at whih the swith is tuned, is rejeted at the through output and dropped at the drop output. For the off state, the hannel rejetion on the through output must be avoided. A way to fulfill this is by anelling the zeroes with the poles of the through transfer funtion, to have an all pass filter response. The modulus and phases of the omplex onjugated zeroes of the through transfer funtion [18] are given by: Z r e α L = Ω (8) 1/ ( 1 γ ) ( 1 γ ) ( ) (( 1 K)( 1 K) K ( K K )) 1/ 1 ϕ =± tan (9) ( K ) K K From Eqs. (5)-(6) and Eqs. (8)-(9), it an be seen that they are aneled for K values tending to 0, where Z p Z and φ p φ. In this design a K value of 0.01 is taken. Swithing from the off to the on state an be ahieved by hanging the oupling fator K from 0.01 to a higher value that depends on K, BG, ring losses and the desired rosstalk between hannels. By hanging the optial path in the ring, this swithing from off to on an also be ahieved.. Waveguides design A design on a SOI platform is going to be performed, its high index ontrast enables better mode onfinement and smaller bending radius, inreasing the integration density against others tehnologies. (C) 014 OSA 11 August 014 Vol., No. 16 DOI: /OE OPTICS EXPRESS 19160

6 Fig. 3. Shemati layout of the proposed rib waveguide with w = 0.67 μm, H = 1 μm and D = 0.6 μm. Other design onstraint is that the waveguides need to be single mode and polarization independent. The single mode ondition is more diffiult to fulfill in strip type waveguides beause the ross setionals dimensions must be signifiantly smaller than 1 μm. The roughness of the side walls is very important at these dimensions beause it inreases the losses for TE mode [0], and the devie will be polarization dependent. The single mode ondition is more relaxed by using rib waveguides with surfae ladding of air with width (w) and height (H) on the order of 1 μm. The dimensions of the waveguides are hosen to have a single mode and zero birefringene waveguide [1-]. From simulations using a FDTDbased FullWAVE software from RSoft, a rib waveguide with w = 0.67 μm, H = 1 μm and eth depth (D) of 0.6 μm, is seleted see Fig WDM swith ontrol WDM swith ontrol an be done by hanging the oupling fator K, or the ring resonator optial path. In any ase, a oupler with a speifi oupling oeffiient has to be designed. In the first ase, it is also neessary to design a variable oupler. A variable oupler based on a Mah-Zehnder (MZ) onfiguration as in [3] is not adequate, beause of the different arms lengths of the interferometer with various delay paths from the input to the output. This affets the frequeny response of the devie in a omplex form. A variable diretional oupler (DC) with a p-i-n onfiguration in one of the DC waveguides is seleted. By hanging the refrative index, the propagation onstants of the waveguides are desynhronized, and the oupling fator hanges. The oupling fator of a DC at desynhronism is given by: ξ 1 K = sin δ 1+ δ ξ 1+ δ where δ = κ L C, being κ the oupling oeffiient, and L C the length of the oupler, ξ is given by Δβ L C /, where Δβ = β 1 - β, is the differene between the propagation onstants at the two waveguides of the oupler. At synhronism ξ = 0, and the oupling fator K is given by: K ( κ L ) sin C (10) = (11) At synhronism, the WDM swith is at on state. A polarization independent diretional oupler is designed using a RSoft s BeamPROP software tool. Simulations at both polarizations are shown in Figs. 4(a) and 4(b). A waveguide separation of μm is onsidered. From Fig. 4, it an be seen that the neessary length for omplete optial power transfer between waveguides is L π/ = μm. From this parameter and using Eq. (11), κ = m 1 is obtained. (C) 014 OSA 11 August 014 Vol., No. 16 DOI: /OE OPTICS EXPRESS 19161

7 Fig. 4. Polarization independent diretional oupler: a) TE polarization and b) TM polarization. Cross setion of the waveguides is shown in Fig. 3. From Eq. (10) it an be onluded that the state of the WDM swith at synhronism is on, beause it needs the larger oupling fator. This oupling fator K, in the on state an be extrated from the expeted rosstalk for adjaent hannels. In Fig. 5 there is a simulation of the swith rosstalk at the through output versus K for 50 GHz, and 5 GHz hannel separations. The WDM swith parameters are a total length L of 100 μm, γ = γ = 0.05, 0.5 db/m waveguide losses and a BG maximum refletivity of 1. The minimum rosstalk is found for K value of , the value that plaes the zero at the unitary irle. For rosstalks lower than 50dB, the oupling fator in the on state should be in the viinity of Crosstalk lower than 30 db for hannel spaing of 5 GHz and 50 GHz, an be obtained for this design with K = Crostalk (db) Ch. Spaing 50 GHz Ch. Spaing 5 Ghz K Fig. 5. Crosstalk for adjaent hannels with separations of 50 GHz, and 5 GHz. The oupling length of the first oupler to get K = 0.08 is found from Eq. (11), whih results in δ = Here we take the seond zero beause it minimizes the ξ (Δβ) hange needed to swith the state, due to the fat that the two fators in Eq. (10) are dereasing funtions at this point. As κ is already alulated, this results in a oupler length L C = 1.36 μm. The next step is to find the refrative index hange (Δn) needed to swith from on to off state. This an be found solving numerially Eq. (10) with K = 0.01, to find the ξ and then the needed hange between the propagation onstants of the oupler (Δβ). This results in ξ = and Δβ = m 1. The relation of Δβ vs Δn is approximately linear, as it an be seen in Fig. 6 at 1550 nm, and the Δn needed is (C) 014 OSA 11 August 014 Vol., No. 16 DOI: /OE OPTICS EXPRESS 1916

8 4 x 105 Propagation Constants Differene (1/m) Refrative Index Change Fig. 6. Dependene of Δβ with Δn for the proposed waveguides at 1550 nm. The waveguide refrative index (Δn) and losses (Δα (Np/m)) hange depends on the arrier onentration. They are given by [10]: 18 e ( ) 0.8 Δ n = ΔN Δ N (1) Δ α = Δ N Δ N (13) e where ΔN e and ΔN h the hange in the eletrons and holes onentrations in m 3. From Eq. (1) with a ΔN e = ΔN h = ΔN and solving numerially for Δn = 0.036, we derive a arrier onentration hange of ΔN = m 3. It is in the margin of arrier onentration from to 10 0 m 3, where Eq. (1) and Eq. (13) are appliable [4]. Finally, optial loss hanges due to the arrier onentration injetion are found using Eq. (13), being Δα = Np/m. For a oupler length of 1.36 μm, this hange represents 1.4 db of attenuation at the upper waveguide of the oupler. This attenuation appears only at the off state. It an be treated as an insertion loss of (1.4) db at the drop output transfer funtion, and an insertion loss of 1.4 db at the through output transfer funtion. In the ase of hanging the optial path in the ring, by injeting free arriers on a length of 80 μm, we need to produe a Δβ = π/80μ. From Fig. 6, we need a Δn = , whih means a ΔN = m 3 ; so lesser optial losses an be obtained. 3.1 Spetral response The spetral responses of both outputs of the WDM swith at the on state are shown in Figs. 7(a) and 7(b). The parameters on those simulations are: γ = γ = 0.05, α = 0.5 db/m, L = 100 μm, and BG maximum refletivity of 1, K = 0.49 and K = As we an see in Figs. 7(a) and 7(b), an attenuation of 34 db and 1 db for the enter frequeny f 0 of the hannel, at the through and drop output respetively and a rosstalk 37 db for 50 GHz hannel spaing, at the drop output are obtained. For the through output, the rest of frequeny hannels are attenuated a maximum of 0.5 db, having a rejetion bandwidth at 3 db of 3 GHz, and of 8.3 GHz at 10 db. In the drop output, there is a full width at half maximum (FWHM) of 16. GHz. These bandwidths an be inreased without hanging the spetral responses only by dereasing the light transit time in the RR. h h (C) 014 OSA 11 August 014 Vol., No. 16 DOI: /OE OPTICS EXPRESS 19163

9 Fig. 7. WDM swith spetral response simulations at on state, of the drop a), and through b) outputs. In Figs. 8(a) and 8(b) are shown the spetral responses of the WDM swith at the off state. There is an attenuation of 4 db for the tuned hannel frequeny at drop output, 1 db more than in the on state, and a FWHM of 10 GHz, 6 GHz less than in the on state. In the through output, there is a maximum attenuation of 3.4 db for the tuned hannel frequeny f 0, while the others hannels are attenuated a maximum of 1.6 db, due to the oupler waveguide losses. Fig. 8. WDM swith spetral response, at off state on the drop a), and through b) outputs. 3. Power onsumption The swithing of the basi unit is obtained by forward biased of a p-i-n diode, either on the oupler waveguides or in the loop length. The urrent needed for the free arrier hange ΔN e = ΔN h = ΔN, is given by [4]: ΔNeSL I = (14) τ where τ is the free arrier reombination time, e is the eletron harge, S is the silion area of the waveguide ross setion and L C is the oupler length. S an be found from the distribution of the waveguide mode profile obtained from RSoft s BeamProp tool, see Fig. 9. Then S is approximated to 0.75 μm, the area of the trapezoid shown at Fig. 9 in dashed lines. (C) 014 OSA 11 August 014 Vol., No. 16 DOI: /OE OPTICS EXPRESS 19164

10 Fig. 9. Transverse mode profile. The reombination time an be obtained from the eletrons and holes reombination rate whih have three omponents, the band to band, the trap assisted or SRH (Shokley, Read and Hall) and the Auger reombination. In Silion, for arrier or doping onentrations higher than m 3, the reombination rate is dominated by the Auger proess [5], whih is given by: ( )( ) R = C n+ C p np n (15) Aug n p i where the C n and C p are the Auger oeffiients for eletrons and holes reombination, with approximated values of m 6 /s and m 6 /s respetively [5]; n and p are the onentrations of eletrons and holes, and n i is the intrinsi onentration and ould be negleted. The reombination time is given by: ΔN τ = (16) RAug In the oupling oeffiient hange ase ΔN, and L C are equal to m 3 and 1.36 μm respetively, From Eq. (15) it is obtained that R Aug is equal to m 3 s 1 and τ = 3.13 ns, a time in the order of ns as the one measured in [4]. From Eq. (14) the urrent needed depends on the reombination time τ and is given by I = /τ so it is equal to 1.18 ma. In the ase of hanging the optial path in the ring, the needed ΔN is m 3, therefore a urrent of 0.14 ma for the off state. The hange of the oupling fator an also be done as in optomehanial osillators [6], whih ould lead to smaller losses and power onsumptions. 4. WDM demultiplexer Four WDM swithes are asaded to form a 1x4 WDM demultiplexer. Eah swith is tuned at a different hannel, see Fig. 10. Eah frequeny hannel an be routed to its orresponding drop output or it an be passed to the through output depending on the state of eah one of the WDM swithes. (C) 014 OSA 11 August 014 Vol., No. 16 DOI: /OE OPTICS EXPRESS 19165

11 Fig x4 WDM demultiplexer, with eah WDM Swith tuned to different wavelengths. When all the WDM swithes are at the off state, a total onsumption of 4 times the onsumption of eah WDM swith is expeted. In this state, all WDM swithes pass all the hannel frequenies to the through output. In Figs. 11(a) and 11(b), an be seen the through output and the four drop outputs for a 50 GHz hannel spaing and being the x-axis referred to f, the enter frequeny of the information hannels band of the demultiplexer. Fig. 11. Spetral response of WDM demultiplexer with all the WDM swithes at the off state. Through output a) and the four drop outputs b). In the following the tuning of the devie by hanging the oupling oeffiient through arrier injetion, as reported in setion 3. Fig. 1. Spetral response of WDM demultiplexer with all the WDM swithes at the on state. Through output a) and drop outputs b). (C) 014 OSA 11 August 014 Vol., No. 16 DOI: /OE OPTICS EXPRESS 19166

12 The maximum attenuation expeted at the through output is given when all the swithes are at the off state. In this ase, eah one ontributes to the insertion loss with 1.59 db, so a total attenuation of 6.36 db, in the frequeny bands out of the information hannels band, as we an see in Fig. 11(a). And an attenuation higher than 4 db for all hannel frequenies at the drop outputs of the demultiplexer. There is an attenuation inrease of 1.67 db at eah suessive stage, see Fig. 11(b). Fig. 13. Spetral response of WDM demultiplexer: for one (fourth) hannel extrating a) through output b) drop outputs. For two (seond and fourth) hannels extrating ) through output d) drop outputs. For three (first, seond and third) hannels extrating e) through output f) drop outputs. # $15.00 USD Reeived 5 Jun 014; revised 18 Jul 014; aepted 19 Jul 014; published 31 Jul 014 (C) 014 OSA 11 August 014 Vol., No. 16 DOI: /OE OPTICS EXPRESS 19167

13 Another speial ase to be analyzed is when all the swithes are at the on state. In this ase, the through output rejets all the hannels, and eah hannel is extrated by its drop output. The spetral response for this ase is shown in Fig. 1. From Fig. 1(a), an be seen a rejetion of 35 db, for eah of the four frequeny hannels at the through output. And from Fig. 1(b), an be seen that the rosstalk is lower than 37 db at the drop port, with a FWHM of 16. GHz. For the drop outputs we have an attenuation inreasing by 0. db at eah suessive stage. This value is less than the one obtained for all the swithes at off state beause the losses due to free arrier injetion are not present. Also from Fig. 11 and Fig. 1, we an extrat the on off ratio parameter being of 7 db and 1 db for the through and drop output respetively. Finally we explore some examples when one, two and three frequeny hannels are extrated at the drop outputs. In Figs. 13(a) 13(f) are shown through and drop outputs for those examples. The attenuation of the frequeny bands out of the information hannels dereases for eah extrated hannel, being respetively 5. db, 4.1 db and 3 db for one, two and three extrated hannels, see Figs. 13(a), 13() and 13(e). This is beause for eah non extrated hannel there is one extra WDM swith at the off state, with an extra attenuation due to the injeted arriers. As before, rejetions better than 35 db on the rejeted hannels at through output and rosstalks lower than 37 db at the drop hannel outputs are obtained. This rosstalk is only for the next stage side hannel, the previous stage side hannel after the first on state swith, have a rosstalk of 37 db less than the attenuation of 35 db, this is 7 db, as it an be seen in Figs. 1(b) and 13(f). Again the on state drop outputs have a FWHM of 16. GHz. 5. Conlusions A polarization independent reonfigurable optial 1xN demultiplexer with low rosstalk between adjaent hannels is designed on silion on insulator tehnology. On to off state transitions an be implemented by hanging the oupling fator or the ring length. Wavelength seletive swith units, based on a Mihelson onfiguration embedded on a Ring Resonator are asaded to form the demultiplexer. Designs using arrier dispersion effet and power onsumption estimations are inluded. Crosstalks below 30dB with 50GHz hannel spaing and losses below 1.5dB in the off state are obtained for a 1x4 demultiplexer. Rejetion ratio between the two states is 6 db. Drop hannels with Full Width at Half Maximum of 16 GHz are obtained. Power onsumption ould be redued using other oupling tehniques based on miro-eletromehanial tehnologies or optomehanial osillators. Aknowledgments This work has been sponsored by the Spanish Eonomy and Eduation Ministries through grants (Ref.TEC C03-0) and by a SENACYT grant given to one of the authors. We thank to Dr. Dimitrios Zografopulos for his helpful disussions. (C) 014 OSA 11 August 014 Vol., No. 16 DOI: /OE OPTICS EXPRESS 19168