Performance Improvement of 40-Gb/s Capacity Four-Channel WDM Dispersion-Supported Transmission by Using Broadened Passband Arrayed-Waveguide Grating Demultiplexers Mário M. Freire Department of Mathematics and Computer Science, University of Beira Interior Rua Marquês d'ávila e Bolama, P-6200 Covilhã, Portugal Telephone: +351 75 3101700, Fax: +351 75 26198, E-mail: mfreire@ alpha.ubi.pt Henrique J. A. da Silva Department of Electrical Engineering, Pole II of University of Coimbra Pinhal de Marrocos, P-3030 Coimbra, Portugal Telephone: +351 39 7006248, Fax: +351 39 7006247, E-mail: hjas@ci.uc.pt Abstract This paper describes the performance improvement of 10-Gb/s four-channel WDM dispersion-supported transmission systems by using broadened passband arrayed-waveguide grating demultiplexers. Multimode interference couplers are assumed to be used to broaden the passaband of these demultiplexers.
Performance Improvement of 40-Gb/s Capacity Four-Channel WDM Dispersion-Supported Transmission by Using Broadened Passband Arrayed-waveguide Grating Demultiplexers Mário M. Freire Department of Mathematics and Computer Science, University of Beira Interior Rua Marquês d'ávila e Bolama, P-6200 Covilhã, Portugal Telephone: +351 75 3101700, Fax: +351 75 26198, E-mail: mfreire@ alpha.ubi.pt Henrique J. A. da Silva Department of Electrical Engineering, Pole II of University of Coimbra Pinhal de Marrocos, P-3030 Coimbra, Portugal Telephone: +351 39 7006248, Fax: +351 39 7006247, E-mail: hjas@ci.uc.pt Summary Integrated N N wavelength multiplexers based on arrayed-waveguide gratings (AWG) are being developed for wavelength division multiplexing (WDM) systems and networks, since they can offer four basic functions: multiplexing, demultiplexing, add/drop multiplexing, and N N full-interconnection [1]. The use of this technology for demultiplexing in high density WDM systems may impose very stringent requirements on the alignment of signal wavelengths and demultiplexers due to their peaked (Gaussian-like) spectral passband. However, the passband of these demultiplexers may be broadened by the use of multimode
interference couplers (MMI), as proposed and demonstrated in [2]. In this paper, we describe the performance improvement due to the use of broadened passband AWG demultiplexers in 40-Gb/s capacity four-channel WDM dispersion-supported transmission (DST) systems with 0.5 nm channel spacing. The block diagram of the simulated 10-Gb/s four-channel WDM-DST system is shown in Fig. 1. The system model is broadly similar to the one reported in [3] and includes a rate equation model for quantum-well lasers, and the frequency responses of a PIN photodiode and of a standard singlemode fiber (SMF) with chromatic dispersion of 17 ps/(nm.km) at 1532 nm. The frequency response of the AWG filter is assumed to be Gaussian and the frequency response of the broadened passband AWG filter is modeled by the double Gaussian approximation [2] with r = 2, which is the ratio between the peak separation and the FWHM of each simple Gaussian profile. The optical amplifiers (EDFAs) have been considered as linear with a noise figure of 6 db and an equivalent noise bandwidth of 1 THz. A RC lowpass filter was used to provide the 3-dB bandwidth required by the DST method [4]. The receiver sensitivity was estimated taking into account the signal-ase and ASE-ASE beat noises, the thermal and shot noises, as well as the contribution due to frequency-to-intensity conversion of laser phase noise after propagation via dispersive fibers [5]. Fig. 2 shows the receiver sensitivity for channel 2 versus fiber length for single-channel DST, without optical filters, and for four-channel WDM-DST using an arrayed-waveguide grating demultiplexer with (BP-AWG) and without (AWG) broadened passband. For comparison purposes, the receiver sensitivity of four-channel WDM-DST using a three-mirror Fabry-Perot demultiplexer (TMF) is also shown. For distances larger than 80 km, the performance of four-channel WDM-DST systems using three-mirror Fabry-Perot demultiplexers is close to the performance of single-channel DST systems without optical filters. Compared with the performance of single-channel DST without optical filters, the use
of conventional arrayed-waveguide grating filters as demultiplexers in four-channel WDM- DST degrades the system performance at least 0.6 db for link lengths larger than 11 km. However, the use of broadened passband AWG demultiplexers instead of the conventional AWG demultiplexers improves the performance of the four-channel WDM-DST system at least 1.5 db, for link lengths larger than 11 km (see Fig. 2). Detailed BER characteristics for channel 2 are displayed in Fig. 3 for four-channel WDM-DST via 204 and 253 km SMF. For the 204 km transmission simulation, sensitivities of -23.886, -23.169 and -24.827 dbm have been estimated for TMF, AWG and BP-AWG demultiplexers, respectively. The BER curves for 253 km clearly indicate an error floor due to laser phase noise. In conclusion, the use of broadened passband AWG demultiplexers improves the performance of four-channel WDM-DST systems with 0.5 nm channel spacing, while conventional AWG demultiplexers are less suitable to operate at this channel spacing.
References [1] H. Takahashi, K. Oda, H. Toba, and Y. Inoue, Transmission Characteristics of Arrayed waveguide N N Wavelength Multiplexer, IEEE J. Lightwave Tech., Vol. 13, No. 3, pp. 447-455, 1995. [2] J. B. D. Soole, M. R. Amersfoort, H. P. LeBlanc, N. C. Andreadakis, A. Rajhel, C. Caneau, R. Bhat, M. A. Koza, C. Youtsey, and I. Adesida, Use of Multimode Interference Couplers to Broaden the Passband of Wavelength-Dispersive Integrated WDM Filters, IEEE Photon. Technol. Lett., Vol. 8, No. 10, pp. 1340-1342, 1996. [3] M. M. Freire, Á. M. F. de Carvalho and H. J. A. da Silva, Performance Implications of Three-Mirror Fabry-Perot Demultiplexers for 10-Gb/s WDM Dispersion-Supported Transmission with 0.5 nm Channel Spacing, IEEE Photon. Technol. Lett., Vol. 8, No. 9, pp. 1261-1263, 1996. [4] B. Wedding, B. Franz, and B. Junginger, 10-Gb/s Optical Transmission up to 253 km Via Standard Single-Mode Fiber Using the Method of Dispersion-supported Transmission, IEEE J. Lightwave Tech., Vol. 12, No. 10, pp. 1720-1727, 1994. [5] R. F. S. Ribeiro, J. R. F. da Rocha, and A. V. T. Cartaxo, Influence of Laser Phase Noise on Dispersive Optical Fiber Communication Systems, IEEE Photon. Technol. Lett., Vol. 7, No. 12, pp. 1510-1512, 1995.
Figure Captions Fig. 1. Block diagram of the simulated 10-Gb/s four-channel WDM-DST system. Fig. 2. Receiver sensitivity for channel 2 versus fiber length for single-channel DST, without optical filters, and for four-channel WDM-DST using arrayed-waveguide grating demultiplexers with (BP-AWG) and without (AWG) broadened passband. For comparison, the sensitivity of four-channel WDM-DST using a three-mirror Fabry- Perot demultiplexer (TMF) is also shown. Fig. 3. Average error probability for channel 2 versus mean optical power at the input of the EDFA preamplifier for four-channel WDM-DST, via 204 and 253 km SMF, using TMF, AWG, and BP-AWG demultiplexers.
DRIVER MQW PPG 7 2-1 bits PPG 7 2-1 bits PPG 7 2-1 bits PPG DRIVER DRIVER DRIVER 1531 nm MQW 1531.5 nm MQW 1532 nm MQW WDM MUX EDFA 7 2-1 bits 1532.5 nm SMF EDFA SMF EDFA SMF EDFA OF PIN PD AMP LPF
Sensitivity for channel 2 [dbm] -5-10 -15-20 -25-30 -35 DST (without optical filters) WDM-DST (TMF) WDM-DST (AGW) WDM-DST (BP-AWG) 0 50 100 150 200 250 300 Fibre length [km]
M. M. Freire and H. J. A. da Silva: Performance of 40-Gb/s Capacity WDM Dispersion-Supported Transmission log (BER) 10-1 -3-5 -7-9 -11 204 km (TMF) 204 km (AWG) 204 km (BP-AWG) 253 km (AWG) 253 km (BP-AWG) -13-40 -30-20 -10 0 Mean optical power [dbm]