1106 IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. 45, NO. 9, SEPTEMBER 2009 Suppressing Chirp and Power Penalty of Channelized ASE Injection-Locked Mode-Number Tunable Weak-Resonant-Cavity FPLD Transmitter Gong-Ru Lin, Senior Member, IEEE, Tzu-Kang Cheng, Yi-Hung Lin, Gong-Cheng Lin, and Hai-Lin Wang Abstract—Amplified spontaneous emission (ASE) power and injection-locked mode number dependent frequency chirp and bit error rate (BER) responses of a weak-resonant-cavity Fabry–Perot laser diode (WRC-FPLD) transmitter are characterized. Chirp analysis of upstream data from the 1.25 Gb/s directly modu- lated WRC-FPLD with two and three injection-locked modes after the 200-GHz AWG filtered ASE injection-locking is de- termined, which reveal similar peak-to-peak chirps of 0.8 and 1 GHz with corresponding negative chirp parameters of 1.6 and 2 MHz/ps for two- and three-mode lasing WRC-FPLD, respectively. Such a negative chirp further enlarges to 6.4 and 9 GHz after 25-km single-mode fiber (SMF-28) transmission. The BER of below 10 at receiving power below 30 dBm is obtained with mode number dependent power penalty of 0.25 dB before and after 25-km SMF 28 transmission. A chirp model involved the ASE injection induced power saturation effect is derived to explain the negatively fre- quency chirped WRC-FPLD, which reveals a reverse trend with increasing ASE injection power due to the power-saturation induced on/off extinction ratio reduction (from 10.5 to 8.2 dB) and rising-time broadening (from 120 to 180 ps) on WRC-FPLD transmitted data shape, which effectively reduces the peak-to-peak chirp by at least 2 GHz after 25-km SMF transmission. Index Terms—Amplified spontaneous emission (ASE), arrayed waveguide grating (AWG), chirp, Fabry-Perot laser diode (FPLD), injection-locking, weak-resonant-cavity (WRC). I. INTRODUCTION N OWADAYS, the channel capacity requirement of high-speed access network inevitably accelerates the ne- cessity in developing fiber-optic communication network with narrower channel spacing and/or higher channel data rate. The passive optical network is the practically used broadband access technology to reach the need of last-mile telecommunication, which is favorable among versatile approaches for network services demanding greater bandwidth [1], [2]. However, the exploitation on unified colorless transmitters are still crucial, thus remaining as a relatively expensive issue owing to the budget of location-specific wavelength sources at current stage. Manuscript received January 15, 2009; revised March 08, 2009. Cur- rent version published August 25, 2009. This work was supported in part by National Science Council under grants NSC96-2221-E-002-099 and NSC96-2752-E-009-008-PAE. G.-R. Lin, T.-K. Cheng, and Y.-H. Lin are with the Graduate Institute of Pho- tonics and Optoelectronics, and Department of Electrical Engineering, National Taiwan University, Taipei 106, Taiwan (e-mail: grlin@ntu.edu.tw). G.-C. Lin and H.-L. Wang are with the Advanced Technology Laboratory, Chung-Hwa Telecomunciation Company Ltd., Chungli, Taiwan (e-mail: gclin@cht.com.tw). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/JQE.2009.2021532 Using amplified spontaneous emission (ASE) injection-locked or specific-wavelength seeded long-cavity laser diodes [3]–[5] can essentially solve the mode-selection problem occurred in conventional Fabry–Perot laser diode (FPLD) based transmitter transmitters.[6] A bi-directional fiber-optic communication net- work using gain-saturated colorless reflective semiconductor optical amplifier (RSOA) based transmitter at 1.25 Gb/s for wavelength tunable upstream transmission over 20 km was also reported [7]. Nevertheless, the ASE injected RSOA benefits from color-free operation at a cost of suffering relatively large spontaneous emission noise figure as compared to the FPLD. Making the RSOA like a FPLD has thus emerged to deal the trade-off between noise reduction and color-free opera- tion. Therefore, the weak-resonant-cavity FPLD (referred as WRC-FPLD) placed at the transmitters enable a more cost-ef- fective and high-performance infrastructure for fiber-optic communication network. Besides, the RSOA usually exhibits negative chirp larger than that of FPLDs due to its unconfined spectral profile with an extremely large linewidth enhancement factor [8]. Thus, the bit error rate (BER) and chirp charac- teristics of such a WRC-FPLD with a front-facet reflectivity of 1% as compared to that 0.01% for RSOA are worthy of detailed investigation for improving its data transmission performance. In this letter, an injection-locked 200-GHz arrayed waveguide grating (AWG) based ASE fiber-optic communication network [9] using a directly modulated WRC-FPLD with end-face reflectance of 1% as an upstream transmitter is proposed. The ASE injection-locked dependent power saturation and data chirping phenomena are characterized. The injection-locking mode number dependent BER power penalty and dynamic chirp of upstream 1.25 Gb/s data transmitted before and after 25-km SMF spool are discussed. II. EXPERIMENTAL SETUP Fig. 1 schematically illustrates a fiber-optic communi- cation network constructing by the ASE injection-locked WRC-FPLDs based transmitter. The external injection-locking source is an Erbium-doped fiber amplifier (EDFA) based broad- band source, which passes through an AWG with 200-GHz mode spacing to inject the WRC-FPLD. The WRC-FPLD exhibits a threshold current of about 25 mA, a longitudinal mode spacing of 0.6 nm, the back and front facet reflectivity of 100% and 1%. In our experiment, the operating current of the FPLD is con- trolled at 35 mA corresponding to , the corresponding spectra for biased current enlarging from to reveal a significant enhancement on cavity mode lasing feature with peak-to-valley ratio increasing from 4 to 14 dB (see Fig. 2). 0018-9197/$26.00 © 2009 IEEE