95-Gb/s NRZ-DPSK Modulation with Full-ETDM Technique Atsushi Kanno (1) , Takahide Sakamoto (1) , Akito Chiba (1) , Tetsuya Kawanishi (1) , Masaaki Sudo (2) , Kaoru Higuma (2) , Junichiro Ichikawa (2) (1) National institute of Information and Communications Technology, Japan, B kanno@nict.go.jp (2) New Technology Research Laboratory, Sumitomo Osaka Cement Co., Ltd., Japan Abstract We demonstrated 95-Gb/s NRZ-DPSK modulation by using high-speed modulator and full-ETDM tech- nique. The BER performance under a back-to-back condition is achieved to be 7.1 × 10 -4 at 95 Gb/s. For high-speed transmission link, optical communi- cation uses a combination of time-division multiplex- ing (TDM) and wavelength-division multiplexing (WDM) technologies to optimize a total capacity of the trans- mission. Optical TDM- (OTDM-) transmission tech- nology is one of the candidates for future high-speed transmission at a data rate greater than Tb/s 1,2 . How- ever, it is difficult to apply a dense WDM (DWDM) tech- nique due to its broad bandwidth of the OTDM signal. In addition, the footprint and the power consumption of an OTDM transmitter, which is consisted of a com- bination of lasers, modulators and optical multiplexers, become quite large because this technology is based on a parallelism. On the other hand, electrical TDM (ETDM) technique is the other candidate for the high-speed transmis- sion. One of the advantages for the ETDM is narrower bandwidth than that with the OTDM. Therefore, the DWDM technique is easily applicable. Recently, huge- capacity transmission experiments were reported with the ETDM and a multi-level modulation technique 3–5 . However, these schemes based on a slow baud-rate modulation could not realize a drastic increase of the transmission speed. This is because the bandwidth of the optical and electrical devices for the ETDM tech- nique is low below 50 GHz. The high-speed modulation technique is the power- ful candidate for both of the OTDM and the ETDM tech- niques. In the OTDM, the high-speed modulation tech- nique can realize a drastic reduction of a number of consisting devices, that is, the reduction of the footprint and the power consumption of the transmitter. The high baud-rate modulation technique increases the trans- mission speed in the ETDM technique directly. How- ever, in a conventional lithium niobate (LiNbO3, LN) op- tical modulator, there are some problems pertaining to the frequency response and the half-wave voltage Vπ. The development of the LN modulator for high-speed operation, whose functions are a high bandwidth and low Vπ, has been strongly desired. In this study, we demonstrated 95 Gb/s NRZ-DPSK modulation by using a full-ETDM technique and an high-speed LN modulator fabricated with a thin LN sub- strate and a ridge-type optical waveguide structure. An electrooptic bandwidth and a half-wave voltage of the fabricated modulator are achieved to be 28 GHz and 3.4 V at 20 GHz, respectively. A bit error rate (BER) at 95 Gb/s operation is achieved to be below 1 × 10 -3 under a back-to-back condition. High-speed modulator with high bandwidth and low Vπ The use of a modulator with the high bandwidth and the low half-wave voltage Vπ are desirable for high- baud-rate modulation. We propose two specific struc- tures of the modulator: using a thin LN substrate and a ridge-type optical waveguide structure. The thin sub- strate and a ridge waveguide realize the extension of the modulator bandwidth and a reduction in Vπ, respec- tively. The details are described as follows. For improvement of the bandwidth, the reduction of the propagation loss of incident electric signals in the electrode fabricated on the LN substrate is one of the most important issues. Especially, at operation fre- quencies greater than 10 GHz, a radiative loss due to a (a) (b) Au electrode 0.1-mm-thick LN substrate 0.8-mm-thick LN substrate adhesive (c) 0 10 20 30 40 50 60 70 0 -6 -12 -18 -24 2.0 4.0 6.0 5.0 3.0 Electric response S21 (dB) Frequency (GHz) Half-wave voltage Vπ [single end] (V) 0.1-mm-thick LN substrate 0.2-mm-thick LN substrate Fig. 1: (a) Electric frequency response curve of the modulator for substrate thickness of 0.1 mm and 0.2 mm, and the fre- quency dependence of Vπ for the substrate thickness of 0.1 mm. Cross sectional pictures of (b) modulator structure and (c) ridge-type waveguide structure on the LN substrate with a Z-cut LN substrate are shown. ECOC 2010, 19-23 September, 2010, Torino, Italy 978-1-4244-8535-2/10/$26.00 ©2010 IEEE Mo.2.F.5