We experimentally demonstrate the wavelength conversion of three wavelength multiplexed 40 Gbit/s Differential Phase Shift Keyed (DPSK) signals in a 2.2m length of highly nonlinear, dispersion tailored W-type lead-silicate optical fibre

Camerlingo, Angela

Feng, X.

Horak, P.

Loh, Wei H.

Parmigiani, F.

Petropoulos, P.

Poletti, F.

Richardson, D.J.

English

Southampton (e-Prints Soton)

Multichannel Wavelength Conversion of 40Gbit/s NRZ DPSK Signals in a Highly Nonlinear Dispersion Flattened Lead Silicate Fibre  Angela Camerlingo, Francesca Parmigiani, Xian Feng, Francesco Poletti, Peter Horak, Wei H. Loh, Periklis Petropoulos and David J. Richardson  Optoelectronics Research Centre, University of Southampton, Southampton SO17 1BJ, United Kingdom Email: anc@orc.soton.ac.uk  Abstract: We experimentally demonstrate the wavelength conversion of three wavelength multiplexed 40 Gbit/s Differential Phase Shift Keyed (DPSK) signals in a 2.2m length of highly nonlinear, dispersion tailored W-type lead-silicate optical fibre. OCIS codes: (060.2280) Fiber design and  fabrication; (060.4370) Nonlinear optics,  fibers; (190.4380) Nonlinear optics, four-wave mixing;   1. Introduction  Wavelength conversion is a crucial operation in high speed wavelength division multiplexed (WDM) optical  networks  for  the  implementation  of  essential  applications,  such  as  routing  or  switching. Efficient  wavelength  conversion  of  signals  can  be  realised  by  exploiting  nonlinear  processes  in  a medium and amongst them four-wave-mixing (FWM) is regarded as the most promising, especially because of its modulation format-agnostic nature. The most important fibre parameters for achieving efficient FWM are a high effective nonlinear coefficient, a low and flat dispersion profile and a short length.  Highly  nonlinear  soft  glass  fibres  have  already  proven  to  be  highly  suitable  candidates  to accomplish this task [1-3], offering the possibility to combine a high effective nonlinearity coefficient with a tailored dispersion profile. Here we consider a small-core W-type soft glass fibre comprising three commercial (Schott) lead-silicate glasses that has been designed to have low dispersion in the 1.55 mm  band.  We  demonstrate  simultaneous  FWM-based  wavelength  conversion  of  three  WDM 40 Gbit/s non-return to zero (NRZ) differential phase shift keyed (DPSK) signals in a 2.2m length of this fibre.         2. Experimental setup and results The experimental setup for the FWM-based wavelength converter is shown in Fig. 1. The nonlinear medium in the system was a lead-silicate W-type fibre, an SEM of which is also shown in the figure. The fibre core (1.6mm in diameter) was made of a high index glass, Schott SF57 (n=1.82 @ 1550 nm) which was surrounded by a first cladding (6.7mm in diameter) made of a low index glass, Schott LLF1 (n=1.53 @ 1550 nm). The outer cladding was made of a different glass with a higher refractive index, Schott SF6, (n=1.76 @ 1550nm). The insertion of the ring of LLF1 glass allowed manipulation of the fibre dispersion, whereas the inclusion of the outer cladding ensured single mode operation at telecoms wavelengths. This fibre design was the same as the one reported in [4]; however optimisation in the fabrication procedures has allowed a significant decrease in the fibre propagation losses from 4.8dB/m    Wavelength [nm]1531 1541 1551 1561 1571Spectral Densty [10dB/div]lch1 lch2 lch3li3 li2 li1lpDl=0.5nmReceiver and diagnosticsCoupling efficiency ~25.5%Monitor2.2m fibreHP-EDFACWl=1550.85nmDl=2nm231-1@40GbpsDPSKmodPCPC10%90%AWGPCPCPCCW3CW2CW1 lch1lch2lch3Wavelength [nm]1300 1400 1500 1600 1700Dispersion [ps/km/nm]-25-20-15-10-50Fig.1: Experimental setup of the FWM-based wavelength converter. Insets: SEM image of the W-type fibre; numerical simulation of the fibre dispersion as a function of wavelength; optical spectrum obtained at the output of the W-type fibre.        a562_1.pdf   OSA / NP 2010       NThA3.pdf          NThA3.pdf   to 2.1±0.2 dB/m in this instance, as measured using the cut-back method. By measuring the self-phase-modulation (SPM) response of the fibre, the nonlinear coefficient was found to be ~ 820 W-1km-1. The dispersion of the fibre was evaluated to be ~-3ps/nm/km at 1.55 mm through FWM measurements. The simulated dispersion profile of the fibre is shown in the inset to Fig.1.  The  outputs  of  three  continuous  wave  (CW)  lasers  (lch1=1556.86nm,  lch2=1558.58nm, lch3=1560.20nm)  were  multiplexed  together  using  an  arrayed  waveguide  grating  (AWG)  and modulated with a 231-1 pseudorandom bit sequence (PRBS) at 40Gbit/s. The pump signal for the FWM process was generated by a CW laser (lp=1550.85nm) and amplified using a high power erbium-doped fibre amplifier (HP-EDFA). A bandpass filter (BPF) was employed at the output of the high power EDFA to reject any undesired out-of-band amplified spontaneous emission (ASE) noise. In order to control the relative power levels of the signals and the pump and to avoid any nonlinear interaction in the EDFA, the three data channels were amplified separately from the pump using a second EDFA. The states of polarisation of the two beams were controlled by two polarization controllers (PCs) and were aligned to a common polarization axis of the fibre. The CW pump and the data channels were then combined in a 90/10 coupler and free-space launched into the fibre. The coupling efficiency was estimated to be ~25.5% and the average powers of the CW pump and the three DPSK signals at the very input of the fibre were 23dBm and 8.7dBm, respectively.  The inset to Fig.1 shows the optical spectra recorded after the W-type fibre. The idlers exhibited an optical signal to noise ratio (OSNR) greater than 25 dB and a uniform conversion efficiency (defined as the  ratio  of  the  idler  power  to  the  corresponding  channel  power)  of  -12dB.  The  output  spectrum indicates  the  existence  of  some  low-power  spurious  frequency  components,  which  were  mixing products  between  the  various  WDM  channels  and  the  pump.  These  components  were  clearly  at different wavelengths to the WDM channels, or their idlers, and did not affect the performance of the system. Additional measurements on the converted idlers also showed negligible nonlinear cross-talk. Each of the idlers was carefully filtered and characterised in terms of eye diagrams and bit error ratio (BER) measurements. Fig. 2 (left) shows a comparison between the DPSK demodulated eye diagrams of each channel at the transmitter output with that of its corresponding idler. The good quality of the conversion process was reflected in the BER measurements (Fig. 2 (right)), which showed a power penalty between 0.5dB and 2dB for the three converted channels.   Fig 2 (Left): Eye diagrams of each channel and of the corresponding filtered idlers. (Right): BER of each channel and of the corresponding filtered idler.  3. Conclusions We  have  experimentally  demonstrated  a  FWM-based  multichannel  conversion  scheme  using  three DPSK channels at 40Gbit/s in a 2.2m length of highly nonlinear, dispersion flattened soft glass fibre.  This work was partially funded by the European Union STREP project PHASORS (FP7-ICT-2007-2 22457).  4. References [1]  S. Asimakis et al., “Towards efficient and broadband four-wave-mixing using short-length dispersion tailored lead silicate holey fibres”, Opt. Exp., vol. 15, no. 2, pp 596-601, 2007. [2]  K. K. Chow et al., “Four-wave-mixing based widely tunable wavelength conversion using 1-m dispersion-shifted bismuth-oxide photonic crystal fibre”, Opt. Exp., vol. 15, no. 23, pp 15418-15423, 2007.    [3]  A. Camerlingo et al., “Four-wave mixing-based wavelength conversion in a Short-Length of a Solid 1D Microstructured Fibre, ECOC 2009, Vienna.  [4]  A. Camerlingo et al., “Wavelength Conversion in a Short Length of a Solid Lead-Silicate Fibre”, IEEE Photon. Technology Lett, vol. 22, no. 9, pp. 628-630, 2010. lch1lch2lch3li1Average Optical Power [dBm]-24 -22 -20 -18 -16-log(BER)34567891011Ch1 1556.86nmCh2 1558.58nm Ch3 1560.20nm Idler 1Idler 2Idler 3<2dBli2li3lch1lch2lch3li1Average Optical Power [dBm]-24 -22 -20 -18 -16-log(BER)34567891011Ch1 1556.86nmCh2 1558.58nm Ch3 1560.20nm Idler 1Idler 2Idler 3<2dBli2li3       a562_1.pdf   OSA / NP 2010       NThA3.pdf          NThA3.pdf   

Camerlingo et al., “Four-wave mixing-based wavelength conversion in a Short-Length of a Solid 1D Microstructured Fibre,

Four-wave-mixing based widely tunable wavelength conversion using 1-m dispersion-shifted bismuthoxide photonic crystal fibre”,

Towards efficient and broadband four-wave-mixing using short-length dispersion tailored lead silicate holey fibres”,

Wavelength Conversion in a Short Length of a Solid Lead-Silicate Fibre”,

Multichannel wavelength conversion of 40 Gbit/s NRZ DPSK signals in a highly nonlinear dispersion flattened lead silicate fibre

Multichannel wavelength conversion of 40 Gbit/s NRZ DPSK signals in a highly nonlinear dispersion flattened lead silicate fibre

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