We have demonstrated a silicon traveling wave Mach-Zehnder modulator adopting the single-drive push-pull scheme. The traveling wave electrode is made of coplanar stripline structure. Several key parameters have been optimized to get a high-speed modulator. It is shown that using the coplanar stripline electrode, group velocity matching and impedance matching are achieved by careful design. After optimization, the VπL of the modulator is calculated to be 2.23 V·cm with the phase shifter length of 4.2 mm. The insertion loss of the modulator excluding the grating couplers loss is 3.4 dB. The 3 dB electro-optic bandwidth of the modulator is simulated to be 32 GHz at 0 V reverse bias. A modulation speed of 70 Gbps under the driving voltage of 1 Vpp is realized with an extinction ratio of 4.9 dB. A higher data transmission capability can be get when high modulation formats such as PAM-4, together with digital signal processing is implemented. Such high-speed silicon modulator can be utilized for next generation communication networks.
Germanium photodetectors have been considered to be mature components in the silicon photonics systems, especially for applications in the near infrared communication band. In order to avoid the restriction between quantum efficiency and carrier transit time, attentions should be payed to integrated waveguide photodetectors, which control the light transmission and the transmission of carriers in two perpendicular directions. Integrated waveguide coupling mainly include end-coupling and evanescent coupling. Compared with end-coupling, evanescent coupling is more easily realized though its coupling efficiency is lower than that of end-coupling. This paper reports an integrated waveguide photodetector exploiting evanescent coupling with some design that the center of silicon rib waveguide would be halfsurrounded by the germanium region. And light could be coupled from the top and both sides of the silicon rib waveguide into the germanium region. Simulations were carried out to compare our design with the conventional evanescent coupling configuration by finite difference time domain (FDTD) algorithm on the same condition such as the incident light power and the size of the light absorbing region. Compared with the conventional evanescent coupling configuration, the half-surrounded configuration could contribute a more substantial light absorption efficiency and responsivity.
The grating-assisted contradirectional couplers based delay line attracts a lot of attentions due to its advantages of continuously tunable delay, low insertion loss and fast beam switching. Though much progress in single delay line has been made, there are still several problems yet to be solved in the multi-channel delay lines array, such as overlong chip length and large chip footprint. In this paper, channel-shared delay line array is proposed to solve above problems based on cascade delay line and inserted power divider. For 6 channels array, the channel-shared delay line array in this paper has only 1/3 chip length and 1/3 footprint of the channel-separated delay line array adopted in other literatures. Beside, we simulated the transmission and group delay spectra of a channel-shared 6-channel delay line array, all the channels show a same passband between 1544 nm to 1556 nm, the inter-channel delay differences are almost equal and can be tuned by the wavelength of light carrier.
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