First Demonstration of WDM-enabled All-Optical Wavelength Conversion with a SOA and a 2nd Order Micro-

ring Resonator ROADM

C. Stamatiadis1, D. Petrantonakis1, P. Bakopoulos1, E. Kehayas1, P. Zakynthinos1, Ch. Kouloumentas1, L. Stampoulidis1, R. Dekker2

, E. J. Klein3 and H. Avramopoulos1

(1) National Technical University of Athens – School of Electrical and Computer Engineering

9 Iroon Polytechniou Street, Zografou 15773, Athens, Greece Tel. +30-10-7722057, Fax +30-10-7722077, Email: cstamat@mail.ntua.gr

(2) LioniX BV, P.O. Box 456, 7500 AE Enschede, The Netherlands (3) XiO Photonics BV, P.O.Box 1254, 7500 BG Enschede, The Netherlands.

Abstract: We present the RAWC, the first Ring Resonator Assisted Wavelength Converter employing a SOA and a tunable, Si3N4–SiO2 micro-ring resonator ROADM. We demonstrate inverted, non-inverted and WDM-enabled wavelength conversion with low power penalties. ©2009 Optical Society of America OCIS codes: (060.4510) Optical communications; (230.7405) Wavelength conversion devices;

1. Introduction The realization of large scale photonic routers requires scalable and power efficient all-optical wavelength converters (WCs). In this context photonic integration efforts have focused on integrated arrays of WCs: recently the silica-on-silicon integration system has provided the first hybrid photonic chip that hosts 4 SOA-MZI WCs and consumes only 12W [1]. In order to enable even larger and faster integrated WC devices, power consumption, thermal crosstalk and heat dissipation should be further reduced. One possible way is to reduce the number of active components per WC and the technique that employs a single SOA and a band-pass filter (BPF) offers such capability [2]. However, the SOA-BPF scheme is limited to single wavelength operation and is inappropriate for wavelength routing in a high-capacity photonic router. The first attempt towards WDM-enabled wavelength conversion with optical filtering employs a single QD-SOA and a bulk AWG [3]. The technique is promising, but for optimum performance and chip real-estate efficiency in integrated WCs, ultra-small and tunable filters must be utilized. Following this rationale, we present the RAWC (Ring Resonator-Assisted Wavelength Converter) - the first all-optical WC that employs a single SOA followed by a compact and integrated micro-ring resonator ROADM. The ROADM is fabricated using the TriPleXTM waveguide technology [4, 5] and features two coupled and tunable micro-ring resonators that provide both a periodic spectral response and a filter profile suitable for high-speed chirp filtering. We present error-free inverted and non-inverted wavelength conversion and demonstrate WDM capability by converting an incoming packet-mode data stream into serially, time-domain multiplexed CW signals. The successful bonding of SOAs on silicon boards [6], as well as the high integration potential of micro-ring resonators [7] makes this WC promising for large scale photonic integration.

Figure 1: a) RAWC concept, b) mask image of the ROADM, c) SEM image of the coupled ring resonators, d) TE-TM spectral profile.

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2. Concept and experimental setup

Figure 1a) shows the RAWC concept: 40Gb/s packets enter the SOA synchronized with CW packet signals that are generated by the router controller. The SOA has a 1/e nominal recovery time of 80 ps. The transmission peaks of the ROADM are detuned with respect to the CW wavelengths, speeding up the effective system recovery time. In the case of the blue-shift filtering, an inverted signal at the output of the ROADM is obtained, so a Delay Interferometer (DI) with a suitable periodic response is required for polarity inversion. The ROADM consists of two coupled Si3N4–SiO2 TriPleXTM microring resonators that can be tuned independently by thermal heaters (Figure 1b)). Figure 1c) shows a scanning electron microscope (SEM) image of the ROADM: the ring radius is 50 um, yielding a total chip footprint of <2.5mm2 (Figure 1b), where most of the footprint is used for the bondpads. Figure 1d) shows the TE and TM spectral characterization: the ROADM has an FSR of 4nm and a FWHM bandwidth of 0.6nm. The DI was implemented using standard polarization maintaining (PM) panda fiber and provided a differential delay of 2 ps. The performance of the circuit was evaluated under two operating conditions: firstly, converting continuous data streams on a single CW signal and secondly, converting packet-mode data on different CW signals. Figure 2 shows the experimental setup. It consists of the 40 Gb/s Transmitter, the RAWC and the 40-to-10 Gb/s demultiplexer. The data stream is RZ formatted with 3ps pulses at 1556.55 nm, and is combined with a CW signal at 1562.75 nm at the input of the RAWC.

Figure 3: Experimental results: a) input signal, b) inverted WC signal with detuned ROADM and inset inverted signal at the output of the

SOA c) WC signal after DI and d) non-inverted WC signal. Time scale is 10 ps/div.

3. Results and Discussion

Single Wavelength conversion of continuous data The eye diagram of the incoming data is depicted in Figure 3a). Firstly, the ROADM is detuned by 0.1nm for selecting the lower signal wavelength (blue-shift chirp) and the inverted signal of figure 3b) is obtained. The inset of figure 3b) shows the signal directly at the output of the SOA indicating the SOA slow recovery. The inverted signal at the output of the ROADM is launched in the PM DI and the pulse polarity is restored (figure 3c). The same setup was also employed for non-inverted WC. By de-tuning the ROADM by 0.3 nm the non-inverted eye diagram of figure 3d) was obtained. Both eye diagrams verify the increase of the effective system operational speed. The spectrum for both inverted and non inverted WCs is shown in figure 5(c) and 5(d). Packet-mode WDM-enabled Wavelength Conversion Figure 4 illustrates the experimental results for the WDM-enabled operation. Two TDM multiplexed data packets of the same wavelength enter the RAWC, synchronized with two different CW packets. Due to the temporal synchronization of the packet stream, the first data packet is converted to 1555 nm and the second packet to 1559,1 nm. Figures 4A(a) and 4B(a) show the inverted WC packets and figures 4A(b) and 4B(b) show the converted data packets after the DI. The detuning of the ROADM was 0.1nm. BER measurements were obtained for both cases. Figure 5a) shows the BER curves for the continuous, single wavelength operation. The inverted converted signal exhibits a power penalty of 0.84 dB whereas a power penalty of 1.5 dB is measured for the non-inverted converted signal.

Figure 2: Experimental set-up

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Figure 4: Experimental results for WDM-enabled RAWC. Trace and eye diagrams of A(a) inverted WC at 1555nm , B(a) inverted WC at 1559,16nm, A (b) DI output at 1555 nm and B(b) DI output at1559,16nm. Time scales are 2ns/div (traces) and 10 ps/div (eyes).

Figure 5b) shows the BER curves obtained for the packet-mode WDM-enabled operation. Error free operation was obtained with a 0.8 dB power penalty for the data packet at 1559,1 nm and 1 dB power penalty for the data packet at 1555 nm. The optical power requirements were 7 dBm for the CW and 3 dBm for the data signal. The RAWC requires approximately 1.5W of electrical power to operate, which includes the SOA bias and TEC as well as driving requirements for the micro-ring resonator heaters.

Figure 5: a) BER results for continuous operation, b) BER for WDM-enabled, packet-mode operation, c) and d) optical spectra of inverted and non-inverted wavelength converted signals. 4. Conclusion

We demonstrate for the first time micro-ring resonator assisted wavelength conversion with WDM routing capabilities. The RAWC can perform inverted and non-inverted all-optical wavelength conversion and convert incoming data packets on different wavelengths exploiting the periodic response of a 2nd order TriPleXTM ring resonator ROADM. Error free operation was obtained with low penalty levels. The scheme can be integrated on a single photonic chip and operates with low optical and electrical power.

References [1] L. Stampoulidis, et al.: “Enabling Tb/s Photonic Routing”, JSTQE, vol. 14, pp. 849-860, May/June 2008. [2] Y. Liu, et al.: “Error-free 320 Gbit/s SOA-based wavelength conversion using optical filtering” in Proc. OFC, Anaheim, CA, USA, 2006. [3] O. Raz, et al.: “Non-inverted multiple wavelength converter at 40 Gbit/s using 1550 nm quantum dot SOA” Electron.s Lett., 44(16),pp. 988-989, (2008). [4] R. Heideman, et al., "Large-scale integrated optics using TriPleXTM waveguide technology: from UV to IR" (Invited), SPIE Photonics West, San Jose, California, 24–29 January 2009, p. 7221-26. [5] F. Morichettiet al., "Box-Shaped Dielectric Waveguides: A New Concept in Integrated Optics?", JLT, vol. 25, Sep. 2007, pp 2579-2589. [6] T. Aalto, et al.: “Integration of InP-based optoelectronics with silicon waveguides (Invited)”, in SPIE Photonics West 2009,San Jose (2009). [7] E. J. Klein, et al.,” Densely integrated microring resonator based photonic devices for use in access networks. Opt. exp., 15 (16). pp. 10346-10355.

Acknowledgment

This work was supported by the European Commission through ICT-BOOM project under the 7th Framework Programme and by the Dutch Government under the Freeband BB Photonics project BSIK 03025.

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