Abstract

This paper reports different proposals in the field of theSuper-structured Fiber Bragg Gratings for Coherent DirectSequence OCDMA applications providing enhanced fea-tures in terms of available spectral bandwidth, spectralefficiency and inter-channel rejection suitable for WDMand OCDMA combined applications. The reported de-vices cover the multiband en-decoders covering differentbands on the same device, the almost rectangular enve-lope en-decoders demonstrated for both 1 and 5 ITU-100GHz bands providing flat response and a roll-offbetter than 5 dB/GHz, and finally a multidimensionalWDM/CODE/SPACE multiplexing proposal based on theconcatenation of rectangular SSFBGs.

Keywords: Coherent Direct Sequence (CDS) OpticalCode Division Multiple Access (OCDMA), Super-struc-tured Fiber Bragg Gratings (SSFBG). Wavelength DivisionMultiplexing (WDM).

1.Introduction to CDS-OCDMA systems

Coherent Direct Sequence (CDS) Optical Code DivisionMultiple Access (OCDMA) is presented as a promisingtechnique that has attracted increasing attention for theimplementation of FTTH over passive optical networks(PON) [1-3] or employed for optical en/decoding of head-ers (or labels) in Photonic Label Switching (PLS) networks[4-5]. CDS-OCDMA techniques has been demonstratedemploying either integrated technology on Silica en-coders [5-7] or Super Structured Fibre Bragg Gratings(SSFBG) [4,5,8,9]. Although Code division multiplexing(CDM) could be some times considered as an approach

too complex compared with their competitors as WDM-PON, it must be assumed as complementary technic forthe future high bit-rate symmetric FTTH networks. It canbe exploited in combination with WDM signals or con-veyed into WDM bands as has been previously proposedby several authors [8-9], reducing the traditionally ultra-high bandwidth requirements and therefore the cost ofthe final devices. Moreover OCDMA techniques provideadvantage in security against eavesdroppers on the phys-ical medium. One example of the recent achievements toalleviate the practical limitations in the cost-sensitive fieldof access networking is the integrated multi-channel en-coder [7] that can encode or decode numerous opticalCDM channels simultaneously, and is suitable to beplaced at the remote distribution node sharing the costby the whole network. In this sense this paper focus onthe SSFBG designs with upgraded features to be moreefficiently employed in PON-WDM networks. We willpresent the multi-band en/decoder on the same deviceconcept and its refinement on the rectangular envelopemultiband en/decoder leading to the demonstration ofa single band rectangular en/decoding device. Finally themulti-band & multi-code device is also proposed anddemonstrated with clear application on optical en/decod-ing of headers in PLS networks.

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Super-structured Fiber Bragg Gratings withimproved features for Coherent Direct Sequence OCDMARocío Baños1, Daniel Pastor1, Victor Garcia-Munoz2 and Waldimar Amaya1

1 Instituto de Telecomunicaciones y Aplicaciones MultimediaUniversitat Politècnica de València8G Building - access DCamino de Vera s/n - 46022 Valencia (Spain).

2 Phoenix Photonics Ltd. Sarre, CT7-0JZ ,(UK).

Corresponding author: dpastor@dcom.upv.es

Figure 1. OCDMA PON.

In this section we present the basic concepts supportingthe encoding and decoding processes and we define themain parameters that we will refer along the paper.These fundamental concepts are independent of the net-work application or technology employed. The simplestscheme of OCDMA-PON is shown in Fig. 1. The encodingprocess begins with a short optical pulse that we can as-sume as a data bit from the OCDMA network user orowning to the label information sequence in PLS appli-cations. This pulse must be encoded into a sequence ofN sub pulses named “chips” that will be transmitted andreconstructed or decoded at the receiver nodes. The im-pulse response for the CDS device used for code “p” canbe expressed as:

(1)

where hchip ( t ) is the individual chip impulse responsegiven by the technology or the fabrications limitations,ap,k and �p,k are the amplitude and phase defined by thecode word “p” at the position “k” and tch is the time sep-aration between input pulses. The spectral response canbe written as:

(2)

Hchip (�) is the global spectral envelope and correspondsto the Fourier transform of hchip ( t ) the summation termin (2) imposes a spectral periodic function with a Fre-quency Repetition Period (FRP) defined by 1/tch. To ac-complish the encoding and decoding process, thedecoder devices should implement the reverse and con-jugated code on it (3).

(3)

Thus, the global system response can be expressed as theconvolution of the input signal x(t) and the impulse res -ponse of the encoder hp (t) and the decoder hq (t):

(4)

Moreover, for simplicity the equation (4) can be rewritten as:

(5)

Where the first term is defined as , which is the part

related with the input pulse shape x(t) and those of theencoder and the decoder. The part corresponding to thecoding is:

where ap,k and �p,k correspond to the code word “p” atthe position “k” imposed by the encoder, whereas ap,land �p,l correspond to the code word “q” at the position“l” imposed by the decoder.

At the receiver end after the optical decoding the correctdecoded signals (proceeding from correct encoder anddecoder pairs) will exhibit a strong peak named Autocor-relation Peak (ACP) surrounded of a low level like-noisesignal named “wings”. Whereas, non-correct combina-tions will generate just only the low level like-noise signalnamed in this case the Cross Correlation (XC) signal. Fi-nally, in order to properly discern ACP from XC signals, itis required an electronic or optical time gating with du-ration of Tg [10] (with typical value around tch) and thefinal electronic processing and detection.

As we demonstrated in [11], the spectral content of theencoded signal (compound signal h pulses) must have abandwidth at least the order of FRP in order to take ad-vantage of the complete encoding potential according tothe code length (N). Furthermore, if this signal overpassesthe FRP range, the ACP/XC ratio saturates to its theoret-ical maximum, only obtaining an inefficient use of thespectrum. This concept will be explored along the paperwhere we describe different proposals for more efficientWDM-OCDMA multi-channel utilization.

2.SSFBG Fabrication Process and Optical Bandwidth

As we said before, the non-limited spectral response ofthe ideal component hi,j , is reduced by the fre-quency response of the individual technological elementsthat accomplish the en/decoding process hchip ( t ) whichare defined by the fabrication process. The most em-ployed technology based on the phase mask techniqueconsists in the use of SSFBG structures that provide alocal and distributed reflectivity along the whole inter-chip separation (tch) [7-9]. In this case, the device globalspectral envelope Hchip (�) corresponds to a “sinc-like”function [12] whose main lobe FWHM bandwidth is ap-proximately equal to 0.9·FRP having strong notches at±FRP. Consequently, only the main lobe can be employedto encode the signals. In order to increase the SSFBGbandwidth, we have proposed in [11] an SSFBG in whichonly a narrow region of the fiber (�chip,z ) is inscribed, giv-ing rise to a device whose bandwidth is independent ofthe inter-chip separation (tch ), as it is illustrated in Fig. 2.

An example is depicted in Fig 3, which is a simulation fora 16-chip code length and summarizes two representa-tive cases for a device with tch=10 ps with Continuouschips and Gaussian chips with �chip,t =2 ps. Note that thevariation pattern in Fig. 3 is determined by the summa-tion term which contains the code information (2). Based

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WDM and Code Division Multiplexing must be assumedas complementary technics for the future bit-ratesymmetric FTTH networks.

hp (t) = hchip ap,k e j �p,k • �(t-ktch)�k=0N

Hp (�) = Hchip (�) ap,k e j �p,k • e j k� tch�k=0N

hdecod (t) = {hcod (-t)}*

Cod Decod

Cod / Decod

yp,q (t) = x(t) hp (t) hq (t)system Cod Decod

hpulses (t) = x(t) hchip,p (t) hchip,q (t)

yp,q (t) = hpulses (t) hp,q system Cod /Decod

hp,q (t) = hp hq Cod /Decod Ideal Ideal

hp,q (t) ={ ap,k e j �p,k • �(t-ktch)} { aq,l e j �q,l • �(t-ltch)}Cod /Decod �k=0

N �l=0N

(6)

on this behavior, broader FWHM bandwidth can be ob-

tained if we are capable to minimizes the chip temporal

width (�chip,t ), which is defined by the ultraviolet laser

beam width (�UV ) employed (�chip,t =(2·n/c)·�UV, where

n is the fiber core refractive index and c the speed of

light). We proposed the use of convergent lens placed

between the UV laser and the phase mask to reduce the

ultraviolet laser beam width as represented in Fig 2.

2.1.Multi-band en/decoding experimental verificationThe multi-band (MB) en/decoding operation was verifiedemploying the system setup shown in Fig. 4. Seven Multi-Band SSFBG en/decoders (two encoders and 5 decoders)were fabricated chip by chip with a focused Gaussian UVfringe pattern (~0,2 mm aprox.) and a chip separationfixed to 1 mm (tch=10ps).

Figure 5 shows the spectral characterization of each fab-ricated devices for code 1. We can clearly identify thespectral repetition period of 100 GHz (0.8 nm) and theslow decaying envelope lower than 2 dB at 0.8 nm frommaximum and 4 dB for 1.6 nm. Note that the obtainedbroadband spectral envelope can be employed for codinga single very broad band pulsed signal (like in a standardapproach), or divided in sub-bands, as we propose here,in a WDM-OCDMA system employing narrower opticalsources.

To ensure a stable operation of the devices were placed intothermal boxes to compensate their detuning after fabrica-tion. The seven MB-SSFBG devices are feed through the re-spective circulators. We employed four adjacent channelsof an Array Waveguide Grating (AWG) router with 0.8 nmchannel spacing and 0.4 nm 3dB bandwidth (channels Ato D). The sources used were three DFB lasers pulsed bygain switching technique [13] at 1.25 Gpulses/s, and a

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The broadband spectral envelope can be employed forcoding multiple sub-bands in a WDM-OCMA system.

Figure 2. (a) Continuous chip shape, (b) Short chips.

Figure 4. System Setup.

Figure 5. Spectral response of the en/decoder devicesimplementing the code 1.

Figure 3. (a) Multi-Band proposal by shortening thechip temporal width chip,t. (b) Chip temporal shapes.

Mode Locked Laser (MLL) at 5 Gpulses/s rate before a PulsePatter Generator (PPG) to reduce the pulse rate to 1.25Gp/s. DFBs were combined by a splitter (4x1) and tuned tothe three sub-bands (B to D), being codified in the sameMulti-Band SSFBG C1 covering different portions of itsspectrum. The MLL source was tuned from channels A toD and codified by Code 2. The en/decoding process wasverified recovering the Auto-Correlation Peak (ACP) for thematched pairs (C1*C1c & C2*C2c) and the Cross-Correla-tion (XC) (C2*C1c & C1*C2c). See figures 6 and 7.

ACP power was adjusted to the same value for all thecases to perform the ACP/XC ratio in the same interferingconditions and it was about 10 dB for the worst case.

3.Rectangular Envelope SSFBG En-Decoders

In the previous section Multi-Band SSFBG devices basedon a Gaussian envelope were addressed, however, theslow decaying global envelope of the fabricated devicesreduces the useable number of bands due to the powerimbalanced among them. To solve this shortcoming, wehave proposed [14] a more accurate design of the chipshape taking into account the influence of the fabricationprocess in order to reduce as much as possible its impacton the final device. The proposed solution compensatesthe Gaussian shape of the focalized UV beam to producea new rectangular spectral envelope.

Taking up again the equation (2), we can rewrite it re-placing Hchip by a Gaussian function G (�):

(7)

Therefore, the system must be apodized with the inverseof the function G (�), to mitigate the effect of the fabri-cation process. However, the inverse of G (�) has veryhigh values at frequencies separated from the central fre-quency due to it is a band pass signal. Consequently, thespectral response must be gated with a squared windowfunction W (�) [14]. Hence, the device to be fabricatedshould have the form described in (8), where the firstterm correspond to the ideal response, and the secondterm, W(�) / G(�) named window apodization function(Hapod (�)).

(8)

In the time domain hapod (t) is given by the convolutionof the window with the inverse of the Gaussian function,where w (t)= (W (�)).

(9)

where w(t)= FT (W(�)). This window apodization func-tion with amplitude and phase imposes that the fiber isilluminated all along the complete chip during and ideally,if the focused UV beam corresponds with the employedG (�), the device response after the fabrication can bewritten as [14]:

(10)

obtaining the ideal response of the device only limited bythe squared window function imposed. Figure 8a showsthe schematic of the fabrication process where the hapodfunction has a “sinc-like” shape for each individual chip.Figure 8b shows the rectangular envelope encoder for 5bands equivalent to that shown in figure 2 without anycompensation.

Additionally, in Fig 9 we can see the simulation results forthe first five chips of the impulse response, the amplitudeof the flat function hp, the effective apodization obtai -ned when the Gaussian sampling is performed hp andthe sampling points to avoid overlapping in the centralband and to perform a correct reconstruction.

These components open the feasibility to compact andspectrally efficient DWDM applications. In Figure 10 thedifferent structures are compared in order to analyze theirbehavior in terms of crosstalk and spectral efficiency. Thethree spectral envelopes under consideration for an arbi-trary 16 chips code are: a) Sinc-like envelope (rectangularchip shape caused by continuous illumination), b) Gauss-ian spectral envelope as designed before and c) Rectan-gular envelope (sinc-like shape for the chips). In all the

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Figure 6. ACP and XC signal for code 1.

Figure 7. ACP signal for code 2 using MLL source.

Hp (�) = G(�) ap,k e j �p,k •e j k�tchfabricated �k=0N

Hp (�) = ap,k e j �p,k •e j k�tch • flat �k=0N W(�)

G(�)

hapod (t) = w (t) FT-1 1

G(�)

-1 ��

-1

Hp (�) = Hfabricada (�) •Hapod (�)reconstrusted

Hp (�) = Hideal (�) •G(�)) •reconstrusted W(�)

G(�)

Hp (�) = ap,k e j �p,k •e j k�tch •W(�)reconstrusted �k=0N

flat

rec

cases tch=10 ps that correspond with a Frequency Repeti-tion Period (FRP) of 100GHz. The maximum spectral effi-ciency will be bounded by the maximum inter-channelcrosstalk and therefore by the spectral overlapping. Thethree different cases depicted in Fig. 10 show deviceswith different spectral separations and also with differentnumber of available encoding bands. Notice that this isa generic WDM/multi-band OCDMA scenario where dif-

ferent devices could also have different codes. Figure10(d) show the averaged power crosstalk (xtalk) for themost affected channels as a function of the optical fre-quency separation of the two WDM devices, and more-over the cases (a) to (c) corresponds with -20dB of xtalkillustrating the achievable Spectral Efficiency defined asEn-Decoding bandwidth / Total bandwidth which areS=1/3, ~2/3 and 1 respectively.

3.1. Experimental Results of Rectangular EnvelopedevicesDifferent devices were fabricated in order to show thepractical feasibility of the proposed technique improvingthe performance in presence of crosstalk signals. In Fig11, we can see the final devices fabricated using 5 and 1sub-bands of 100GHz ITU Channels. The fabricated de-vices present less than 0.6 dB of total variation in reflec-tivity and a roll-off better than 5 dB/GHz. Experimentalresults using 5 and 1 sub-bands en/decoder combinationsand their very good features of ACP/XC ratio demonstratethat these devices are suitable for both broadcasting andpoint-to-point applications, as we can see in Fig 12.

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Figure 8. Rectangular Envelope fabrication process (a)and results (b).

Figure 9. Simulated impulse response of a 5 sub-bandC1 encoder.

Figure 10. Spectral efficiency and crosstalk.

The rectangular envelope devices as demonstrated pre-viously open the possibility of compact DWDM multi-band and multi-code devices. More specifically we haverecently designed [15] a Dual-Code and Dual-Band deviceimplementing two different codes in the same device. InFig 13 a) we can see the final devices fabricated imple-menting different codes in order to accomplish the de-coding process in a system where the encoding processis performed by a code-tunable Integrated En/Decoder(IED) device based on Silicon On Insulator. In this case theSSFBG and the IED implements an 8-length code, with achip length of 1 mm (0.8 nm). The SSFBGs where de-

signed according to the inter-chip time tch=10.5 ps meas-ured on the fabricated SOI devices. The selected spectralseparation of the two different codes in each device wasthe double of the Frequency Repetition Period (FRP)

(1/tch ), i.e. 2(1/tch )≈190GHz (~1.5 nm), in order to reservea intermediate zone as guard-band to prevent interfer-ences and the time separation was fixed to 2.5Ntch (~210

ps) in order to avoid overlapping of the ACP wings andXC signals. We fabricated 3 different device implement-ing 5 different code-words. The spectral response of theDual Code SSFBGs fabricated and IED response areshown in Fig. 13 a), and the results obtained for theen/decoding process are shown in the Figure 13 b). In allthe cases, the ACP/XC ratios obtained are in good agree-ment with the theory.

4.Conclusions

We have presented in this paper the recent achievementson Super-Structured Fiber Bragg Gratings designed for Co-herent Direct Sequence OCDMA. The proper design andfabrication of the individual code element or “chip” insidethe whole device represented a key aspect to construct thespectral envelope response giving rise to different propos-als increasing the number of available channels and thespectral efficiency for the combined WDM-OCDMA sys-tems. In the first proposal, the shortening of the chip du-ration led to broadband en-decoders with spectralenvelopes embracing up to 5 encoding bands (FRP) on thesame device. In order to increase the spectral efficiency forWDM approaches, it was proposed a complex chip profileto compensate the natural Gaussian envelope determinedby the ultraviolet beam of the fabrication. In this case thedesigned and fabricated devices provided almost rectan-gular envelope presenting power uniformity better than0.6 dB along of its five ITU-100GHz encoding channelsand a roll-off better than 5 dB/GHz at the device edgeswith an out of band rejection higher than 25dB. Finally wedescribe the proposal of multi-band and multi-code de-vices based on multiple almost rectangular SSFBGs inchain. This structure integrates over a single device amultidimensional WDM/CODE/SPACE multiplexing.

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Fabricated devices provided almost rectangular enve-lope with uniformity better than 0.6 dB, roll-off at edgesbetter than 5 dB/GHz and out of band rejection higherthan 25 dB.

Figure 11. Fabricated device for 5 and 1 sub-bands.

Figure 12. ACP and XC signals.

Figure 13. Dual Code Rectangular Envelope SSFBG.

Acknowledgments

This work was supported by the Spanish Governmentproject TEC 2009-12169, and the Valencian Governmentunder the project ACOMP/2010/023.

References

[1] P. Green, “Paving the last mile with glass,” IEEE Spec-trum, vol. 39, no. 12, 13–14 (2002).

[2] L. H. Spiekman, “Active Devices in Passive OpticalNetworks”, J. Lightwave Technology, vol. 31, no. 4,488-495 (2013)

[3] K Kitayama, et al. “OCDMA over WDM PON-solutionpath to gigabit-symmetric FTTH,” J. Lightwave Tech-nology. 24, 1654-1662 (2006).

[4] X. Wang, et al. “Experimental demonstration of 511-chip 640 Gchip/s superstructured FBG for high perform-ance optical code processing,” in Proceedings of theEuropeam Conference Optical Communication (ECOC),(Academic, Stockholm, Sweden, 2004), Paper Tu1.3.7.

[5] X. Wang and N. Wada, “Experimental Demonstrationof OCDMA Traffic Over Optical Packet Switching Net-work With Hybrid PLC and SSFBG En/Decoders,” J.Light. Technol., 24, 3012-3020, 2006.

[6] Xu Wang ; Naoya Wada ; T. Miyazaki ; G. Cincotti ;Ken-ichi Kitayama; Hybrid WDM/OCDMA for nextgeneration access network. Proc. SPIE 6783, OpticalTransmission, Switching, and Subsystems V, 678328(November 26, 2007);

[7] N. Kataoka, N. Wada, G. Cincotti, and K.-I. Kitayama,“2.56 Tbps (40-Gbps 8-wavelength 4-OC 2-POL)asynchronous WDM-OCDMA-PON using a multi-portencoder/decoder,” in Proc.ECOC, 2011, Postdeadlinepaper Th.13.B.6.

[8] P. C. Teh, et al., “Demonstration of a Four-ChannelWDM/OCDMA System Using 255-Chip 320-Gchip/sQuaternary Phase Coding Gratings,” IEEE Photon.Technol. Lett., 14, 227-229, 2002.

[9] H. Zheng et al; “Investigation of DWDM over OCDMASystem Based on Parallelly Combined SSFBG En-coder/Decoders,” in Proceedings of Symposium onPhotonics and Optoelectronics (SOPO), (Academic,Wuhan, China, 2011), pp. 1-3.

[10] W. Amaya, et al. “Modeling of a Time-SpreadingOCDMA System Including Nonperfect Time Gating,Optical Thresholding, and Fully AsynchronousSignal/Interference Overlapping,” J. Light. Technol.,26, 768-776 (2008).

[11] W. Amaya, D. Pastor, R. Baños and V. Garcia-Munoz,“WDM-Coherent OCDMA over one single devicebased on short chip Super structured fiber Bragg grat-ings,” Opt. Express, OSA, 19, 2011, pp. 24627-24637.

[12] M. Ibsen, M. Durkin, M. Cole, and R. Laming, “Sinc-sampled fiber Bragg gratings for identical multiplewavelength operation” Photonics Technology Letters,IEEE, vol. 10, n. 6, pp. 842 -844, June 1998.

[13] D. Pastor, et al. "Coherent Direct Sequence opticalen/decoding employing low cost DFB lasers with narrowoptical band consumption – towards realizable photonic

label switching," in Proceedings of 12th InternationalConference on Transparent Optical Networks (ICTON),(Academic, Munich, Germany, 2010), pp. 1-4.

[14] Baños, R.; Garcia-Munoz, V.; Pastor, D.; Amaya, W.,"Rectangular Global Envelope Super Structured FBGs forMultiband Coherent OCDMA," Photonics TechnologyLetters, IEEE , vol.25, no.5, pp.512,514, March1, 2013.

[15] Baños, R; Pastor, D.; Domenech, D.; " Code-TunableDirect Sequence Coherent OCDMA device based onSilicon On Insulator," (Submitted to Transparent Op-tical Networks, 2013. ICTON '13).

Biographies

Rocío Baños, was born in Alba-cete, Spain, in 1986. She receivedthe degree in TelecommunicationEngineering from the UniversidadPolitécnica de Valencia, in 2010and the MSc. degree in Telecom-munication Technologies in 2012.In March of 2011 she joined theOptics and Quantum Communica-tions Group at the Universidad Po-

litécnica de Valencia. Currently, she is working on herresearch toward the Ph.D degree, which involves the de-sign, fabrication and characterization of devices for opti-cal code division multiple access (OCDMA) systems. Herresearch interests include Fiber Bragg Gratings for opticalsignal processing, optical networks and optical commu-nications technologies.

Daniel Pastor, was born in Elda,Spain, on Novenber 5, 1969. He re-ceived the Ingeniero de Telecomuni-cacion degree in 1993, from theUniversidad Politécnica de Valencia(UPV), and the Doctor Ingeniero deTelecomunicacion degree (Ph.D.) in1996, from the Universidad Politéc-nica de Valencia, Spain. He joined

the Departamento de Comunicaciones at the UniversidadPolitécnica de Valencia in 1993, where he was engaged tothe Optical and Quantum Communications Group. From1994 to 1998 he was a Lecturer at the TelecommunicationsEngineering Faculty and he became an Associate Professorsince 1999. He is co-author of more than 120 papers injournals and international conferences in the fields of Op-tical Delay Line Filters, Fiber Bragg Gratings, MicrowavePhotonics, WDM and SCM ligthwave systems. He has beenleader of national projects, related with Metro and Accessoptical Networks and Optical Code Division Multiple Access(OCDMA), and he has been leader of particular work pac-kages in IST-LABELS (Ligthwave Architectures for the pro-cessing of Broadband Electronics Signals), or GLAMOROUS(Glass-based modulators, Routers and Switches). His cu-rrent technical interests include Microwave Photonics,Complex Fiber Bragg Grating Fabrication for optical signalprocessing applications, WDM-SCM networks, RoFsystems, and OCDMA techniques.

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Victor Garcia-Muñoz received theM. Sc. in physics degree from theUniversidad de Valencia, Spain andthe Nuclear Physics Master Degreefrom the Université de Paris XI,France both in 2001. In 2002 hewas at the Universita di Pavia wor-king in the field of microwaves. Hecompleted his Ph.D. in the Photo-

nics Technology Group at the Universidad Politécnica deMadrid in 2008. His dissertation subject was related withthe applications of Fiber Bragg Gratings (FBGs) to theprocessing of ultrafast optical signals. From June 2008 toAugust 2009 we worked at the Université Polytechniquede Mons, Belgium where he was involved in the studyand reduction of the polarization related properties ofFGBs and in the applications of in-fiber sensing techni-ques to the fabrication of composite pieces. In Aeptem-ber 2009 he joined the Optics and QuantumCommunications Group at the Universidad Politecnica deValencia as a Juan de la Cierva fellow where he workedon the fields of Quantum Key Distribution and OpticalCode Division Multiple Access (OCDMA). In May 2012he joined Phoenix Photonics Ltd where he develops po-larization related devices and passive optical devices foroptical Space Division Multiplexing communications.

Waldimar Amaya, was born inBogotá, Colombia. He received theElectronics Engineer, Mobile Tele-communications Specialist, andM.Sc. degrees from the DistritalUniversity, Bogotá, Colombia, in1999, 2000, and 2006, respecti-vely. For two years, he was a HybridFiber Coaxial Community Access

Television Operator. Later, he was an Assistant Lecturerat two universities in Colombia. In 2005, he joined theOptical and Quantum Communications Group (OQCG),Institute of Telecommunications and Multimedia Rese-arch Institute - iTEAM, where he developed his PhD thesisand he obtained his PhD degree in telecommunicationsfrom the Universidad Politecnica de Valencia (UPV) Va-lencia, Spain, in 2008. Since 2009 he works with theOCQG – iTEAM as fellow research where he has conti-nued with his work in optical signal processing and morerecently in the field of quantum key distribution.

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