Public Progress Report 2

Transcription

1 Embedded Resonant and ModulablE Self- Tuning Laser Cavity for Next Generation Access Network Transmitter ERMES Public Progress Report 2 Project Project acronym: ERMES Project full title: Embedded Resonant and ModulabIE Self-Tuning Laser Cavity for Next Generation Access Network Transmitter Grant agreement no.: Funding scheme: Collaborative Project - STREP Project start date: Project duration: 36 months Call topic: ICT Core and disruptive photonic technologies (b) Project web-site: Deliverable Deliverable Title: Public Progress Report 2 Deliverable no.: D1.11 Lead beneficiary: POLIMI Nature: R Dissemination Level: PU Contractual Delivery Date: Month 27 Actual Delivery Date: Document version: 01 Authors: Lucia Marazzi, Paola Parolari, Mario Martinelli No of pages (including cover): 9 Public Progress Report 2 D1.8 1

2 TABLE OF CONTENTS Purpose...3 Publishable summary...4 Public Progress Report 2 D1.8 2

3 PURPOSE This document is deliverable D1.11 of ERMES Project. It is a document produced by Work Package 1 Project management and coordination and it provides an overview of the project from Month 19 to Month 27. Public Progress Report 2 D1.8 3

4 PUBLISHABLE SUMMARY, In the context of Next Generation Access Network (NGAN), the wavelength division multiplexed passive optical networks (WDM PON) architecture offers almost unlimited bandwidth similarly to point-to-point links, while allowing the advantages of fibre sharing. ERMES offers a disruptive approach to the ONU transmitter, which is required to be colourless, by using a significant portion of the network to implement an embedded self-tuning modulable laser cavity. The ERMES transmitter exploits an active element, which sustains the cavity lasing, overcoming the overall cavity losses. It is also the modulating element, through direct modulation of the active chip current and finally it allows recirculating modulation cancellation through the self-gain modulation mechanism, supporting new signal modulation. ERMES project targets 10 Gbit/s per-user data rate and, according to the different foreseen applications, different bridged distances. This target is to be pursued by the achievement of four objectives, here briefly listed, and which are mapped on the four technical work packages, also indicated in parentheses. Objective 1, Development of the active chip component (WP-3) Objective 2, Theoretical understanding and development of the simulation model (WP-4) Objective 3, Realization of a laboratory prototype operating at 10 Gbit/s (WP- 2) Objective 4, In-field demonstration (WP-5) These Objectives have been actively and successfully pursued up in these nine months of work. Significant experimental activity, partly presented in the Public report 2 (deliverable D1.8) has demonstrated the impact of chromatic dispersion of 10-Gb/s performances. Thus the experimental and theoretical activities of months have been devoted both to clarify this impact and to counteract it. Concerning the development of the active chip component, it has been Public Progress Report 2 D1.8 4

5 Consortium decision to operate in the O-band. New RSOA chips have been fabricated with III-V Lab Buried Ridge Stripe technology, from compressively strained InGaAsP Multi Quantum Wells (MQW). With respect to previously designed and realized RSOA operating in C band, some changes have been made to match the new operating wavelength band: in particular the ridge width and the spot-size converters design, as well as the barrier height have been adapted. Figure 1: Output optical spectrum of the O-band RSOA, centred at 1320 nm. In the inset a detail of the gain ripples. The actual O band chips offer a high small signal gain, above 25 db at 1.32 µm and comparable with the gain displayed by the same devices designed for the C band. The RSOA spectra are centred around 1320 nm and present gain ripples higher than 5 db, as it shown in the output spectrum recorded in Fig.1., Figure 2: Electro-optical measurements at various wavelength for the O-band RSOA. Fig. 2 displays the measured E/O response for one chip for various bias currents, which highlights the still limited bandwidth of this first generation O band RSOA in comparison with C-band results. Furthermore improved characteristics are expected from InGaAlAs MQW, mainly because of larger barrier height for electrons. Concerning the development of the device model, K activity has been carried on by ETH Zurich, which is a new partner. Focus has been placed on Public Progress Report 2 D1.8 5

6 the impact of chromatic dispersion (CD) on 10-Gb/s performance. Measurements of the RSOA chirp due to RSOA direct current modulation are shown in Fig. 3 in blue, together with the intensity of the applied direct modulation in red; they certainly explain the propagation penalties in SSMF at 10 Gb/s., Figure 3: Measured frequency chirp (blue) and intensity (red) of the signal obtained by direct modulation at 10 Gb/s of the RSOA bias current By modelling the cavity operation, another aspect of the impact of chromatic dispersion on the 10 Gb/s performance can be commented. The relatively long cavity of the RSOA-based self-seeded transmitter excites a large number of longitudinal modes. Such multi-mode nature of the transmitter must be included in the mathematical modelling of the cavity to fully understand the impact of chromatic dispersion. Therefore a multimode Reflective-SOA model, which considers the signal and amplified spontaneous emission (ASE) fields, is implemented. Then, it is combined with the AWG, which is modelled as a Gaussian optical bandpass filter (OBPF), and the optical fibre with CD and attenuation, as shown in the schematics of Fig. 4. Figure 4: Schematic of the RSOA-based self-seeded transmitter: The cavity is formed between the RSOA mirror Rh and a second mirror RRN. The gain medium is the RSOA with length l while the cavity is the distribution fiber of length L and frequency response Hfbr. HOBPF is the frequency response of the Gaussian shaped optical bandpass filter (OBPF). To clearly see the role CD plays, we simulated the CW operation of the RSOA-based self-seeded transmitter using dispersive cavity with CD = 16 ps/(nm km) and dispersionless cavity with CD = 0 ps/(nm km). Fig. 5 shows Public Progress Report 2 D1.8 6

7 the simulated signal spectra for the two types of cavities having 5 km length. One can see that the dispersion causes significant spectral broadening, which will affect propagation performance. In addition, the CD will induce strong mode partition noise. Figure 5: Plot of the CW output signal of the RSOA-based self-seeded transmitter with 5 km long dispersive (CD = 16 ps/(nm km) or dispersionless (CD = 0 ps/(nm km) cavities. The signal spectrum broadens due to the due to the accumulation of CD. Concerning the realization of a laboratory prototype, new experiments have been carried out involving the new chips. As the PDG is very high, higher than 20 db, a 2-Faraday rotator set up is needed to control the signal SOP evolution when re-entering the RSOA. The experimental set up in Fig. 6 has been exploited to compare the chips performance in C and O bands. Both set up in these two optical bands use the two-faraday rotators topology with Faraday elements operating in the respective spectral bandwidth., Figure 6. Schematic of a self-seeded transmitter. The cavities output couplers have a splitting ratio of 80/20 and 90/10 respectively for C and O band operation, being these best compromise between cavity losses and transmitter output power for the two cases. BER measurements at 10 Gb/s have been performed by an APD receiver followed by a commercially available clock and data recovery circuit with an electronic equalizer, namely a 9-taps FFE and a 4-taps DFE. Public Progress Report 2 D1.8 7

8 , Figure 7: C-band 10 Gb/s BER curves in back-to-back (open symbols) and after 20 km of DS fiber (full symbols). Diamonds and circles curves refer respectively to the transmitter with 220- GHz FWHM AWG and with 110-GHz FWHM AWG. Fig. 7 shows the BER measurements obtained in C band for a 420-m long cavity: diamonds relate to the transmitter with 220 GHz FWHM AWG, while circles relate to the transmitter with 110 GHz FWHM AWG. For the transmitter with 220 GHz FWHM AWG, the back-to-back curves (open symbols) show an error floor below 10-5 BER, negligible penalty is found after 20 km of propagation in a dispersion shifted (DS) fiber (full symbols). For the transmitter with 110 GHz AWG, both back-to-back and 20-km DS fiber curves present an error floor around 10-4 BER. In the previous public report we pointed out that the propagation over SSMF is on the other hand limited to a few kilometers. The proper comparison between O-band and C- band chips is to be performed with an equivalent amount of CD load, that is for C band using DSF. In particular Fig. 8 a) shows back-to-back performance when exploiting a 145-GHz FWHM optical tunable filter (OTF) with cavities of 420-m (squares) and 1-km (circles). The two curves show BER floors respectively below 10-9 and O band better performance can be ascribed both to the absence of chromatic dispersion in the drop fiber, which influences cavity build up, and to the very low cavity roundtrip losses associated to the OTF based cavity, which are 6 db lower with respect to the C-band AWG cavity, and which allow for better RIN suppression and higher output ER. Fig. 8 b) shows instead the performance of the cavity with 20-m drop fiber in back-to-back (squares), after propagation in 20-km SSMF (circles) and in 52 km SSMF (triangles). As expected no chromatic dispersion penalties can be found, confirming that O-band choice permits to bridge feeder fibers as long as allowed by the back-to-back performance and the cavity output power. Public Progress Report 2 D1.8 8

9 , Figure 8: 10 Gb/s BER curves a) back-to-back with 420-m drop fiber (squares) and 1-km drop fiber (circles). b) 20-m drop fiber back-to-back (open squares), after 20-km SSMF (circles), after 52-km SSMF (triangles). Concerning the in-field demonstration, after the field trial specifications have been defined in the previous report, last measurements in January and February 2014 will define the actual chip and MUX to be employed in the demo. Finally as a result of the ERMES dissemination activity many papers were published, which can provide further information on the ERMES results obtained so far: A. Gatto et al., Off-set filtering for enhanced transmission in RSOA based WDM-PON, Proceedings of ICTON S.D. Le et al., 16 X 2.5 Gbit/s and 5 Gbit/s WDM PON Based on Self- Seeded RSOA, Proceedings of ICTON Q. Deniel et al., 2Self-seeded RSOA based WDM-PON transmission capacities, Proceedings of OFC 2013 OW4D.2. P. Parolari, et al., 10-Gb/s Polarization-Insensitive RSOA-based Self-Tuning transmitter for WDM-PON bridging up to 52 km Proceedings of OFC 2013 OW1A.1 P.Chanclou et al., Optical fiber solution for mobile fronthaul to achieve cloud radio access network, Future Network and Mobile Summit 2013 S. O'Duill, et al., Simulating Self-Seeded Sources for WDM PON, Photonics Ireland; Belfast; Sept (2013) Public Progress Report 2 D1.8 9