0733-8724 (c) 2016 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/JLT.2017.2650678, Journal of Lightwave Technology > REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT) < 1 Abstract—We have demonstrated a 1300-nm short-cavity distributed reflector (DR) laser having 55 GHz bandwidth (BW), and successful 112-Gb/s transmission using 4-level pulse- amplitude-modulation (PAM-4), without any pre-equalization for the transmitter. Two effects were realized in the design and operation of the DR laser: photon-photon (P-P) resonance and detuned-loading. The P-P resonance effect was realized between the DFB and DBR modes that co-existed in the cavity of the DR laser. The Detuned-loading effect was used to effectively enhance the differential gain through the dynamic change in the mirror reflectivity that occurs on the flank of the DBR mirror due to the frequency chirp under modulation. Despite a limited RC cut-off frequency of 22 GHz, a wide modulation BW of 55 GHz was achieved. It is shown that the RC limitation was counteracted by the combined effect of the detuned-loading, which reduces the damping of relaxation oscillations, and an in-cavity FM-AM conversion effect that created a high-pass filter effect in the modulation response. This will be discussed by way of simulations and experimentally observed eye diagrams for 10 Gb/s NRZ and 28 Gbaud PAM-4. The short-cavity DR laser achieved 112-Gb/s PAM-4 transmission over links having a range of dispersions from -28 ps/nm to +7 ps/nm without pre-compensation on the transmitter. Index Terms—100Gbit/s Ethernet, distributed reflector lasers, direct modulation, Pulse Amplitude Modulation, PAM-4, transmitters, TOSA. I. INTRODUCTION uture data center optical networks will soon require optical transmitter technologies that support 100-Gb/s single channel transmission. Electro-absorption modulators and Mach-Zehnder modulators have shown a modulation speed bandwidth (BW) exceeding 60 GHz [1]-[3], and have Manuscript received Xxx x, 2016; revised Xxxxx xx, 2016; accepted Xxxxx 7, 2016. Date of publication Xxxx xx, 2017; date of current version Xxxxx 30, 2017. Y. Matsui, G. Carey, D. Adams, T. Sudo, and C. Roxlo are with the Active Devices, Finisar Corporation, Fremont, CA 94538 USA (e-mail: yasuhiro.matsui@finisar.com; Tsurugi.Sudo@finisar.com; glen.carey @finisar.com; bruce.young@finisar.com; charles.roxlo@finisar.com). R. Schatz is with the School of ICT, Royal Institute of Technology (KTH), Electrum 229, Kista, SE-164 40, Sweden. (e-mail rschatz@kth.se). T. Pham, W. A. Ling, and H. M. Daghighian are with the Transceiver Engineering, Finisar Corp., Sunnyvale, CA 94089 USA (e-mail: thang.pham@finisar.com; william.ling@finisar.com; henry.daghighian@finisar.com). 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/JLT.2017.xxxxxxx been identified as promising candidates for data center use at 100 Gb/s per channel, and also for future 400 Gb/s – 800 Gb/s systems. However as systems evolve to faster bit rates, the required energy per bit increases, and therefore it is essential to identify the most power efficient technology for any given data rate. The energy efficiency requirement becomes even more acute for the more advanced modulation formats, for example, 4-level pulse amplitude modulation (PAM-4) format. Direct-modulation lasers (DML) are known for their high energy efficiency, low cost, and small size, and therefore are a highly attractive choice for single-channel 100 Gb/s/ data communications systems if the required modulation bandwidth can be attained. In recent years, the modulation bandwidths (BW) of DMLs have been approaching that of high-speed externally modulated lasers [1]-[3]. For a passive-feedback laser (PFL), a passive waveguide is integrated with a DFB laser to provide optical feedback to the DFB section, forming an external cavity mode in the vicinity of the DFB mode that resonantly amplifies the modulation sideband of the DFB laser. As a result, the modulation BW can be enhanced, in what is known as a photon-photon (P-P) resonance effect [4], [5]. A wide modulation BW of 37 GHz was reported for a PFL operating at 1300 nm [6] by adjusting a current to the phase section to control the frequency detuning between the DFB mode and the extended-cavity mode. In this paper, a further improvement in the modulation BW to 55 GHz for a short-cavity distributed reflector (DR) laser is presented [7]. The DR laser consists of a short-cavity DFB section integrated with a Bragg reflector for filtered optical feedback. The modulation sidebands of the main DFB mode are resonantly amplified by the presence of the cavity resonance for one of the available the DBR modes, which is separated from the DFB mode by around 50 GHz. This enhances the modulation response around 50 GHz, the frequency difference between these two modes. At the same time, the DFB mode was located on the long wavelength (LW) flank of the DBR mirror peak. In this case, frequency up-chirp of the DFB mode is translated into a dynamic reduction in the cavity mirror loss, which can effectively enhance the differential gain by the “detuned- loading effect” [8]. As a result, a high intrinsic resonant frequency (F r ) of 30 GHz was obtained. A short laser cavity is particularly useful for harnessing the detuned-loading effect, 55 GHz Bandwidth Distributed Reflector Laser Yasuhiro Matsui, Richard Schatz, Thang Pham, William A. Ling, Glen Carey, Henry M. Daghighian, David Adams, Tsurugi Sudo, and Charles Roxlo (Invited Paper) F D