Insights Into Silicon Photonics Mach–Zehnder-Based Optical Transmitter Architectures

Slow light with interleaved p-n junction to enhance performance of integrated Mach-Zehnder silicon modulators

“…The energy dissipation is then 0.26 pJ/bit for SLOW50 and 0.45 pJ/bit for SLOW150. These values are reduced up to one order of magnitude compared to typical modulators based on normal rib waveguides [14,19], and are comparable to those obtained with PhC waveguides [37].…”

“…As for the insertion loss, a common figure of merit is IL(L π ), obtained as the propagation loss per unit length α times the length L π . Here, α is calculated at V = 0, while L π depends on the voltage: this should again be viewed as a quantification of losses in a worst-case scenario, and it applies to MZ modulators in a push-pull configuration where one of the two phase shifters is always kept at V = 0 [19]. A typical modulator operates with a phase shift ~0.15π in each arm, thus the length has to be L = 0.15L π and the actual insertion loss is ~0.15 · IL(L π ).…”

“…For high-speed operation required for optical communication, the most appropriate modulation mechanism exploits the plasma dispersion effect in a reversebiased p-n junction, namely the change of the refractive index due to a variation of the free-carrier concentration [17]. Standard MZ modulators have two arms made of rib waveguides, which include sections with a lateral p-n junction that act as on optical phase-shifter [18,19]. The main limitation of such a device is the poor overlap between the depletion region of the p-n junction and the optical mode profile.…”

Building blocks of silicon photonics

“…Despite its theoretical interest, a hybrid III-V/Si PN junction phase shifter is difficult to integrate in practice due to the strong lattice mismatch between Si or SiGe and InP or InGaAsP. Nonetheless, SIS structure can be made using molecular bonding [162]. A typical example is shown in Fig 14.…”

Silicon photonic modulators for PAM transmissions

“…A number of low-power, distributed amplifiers can then be used to drive a long segmented optical phase shifter [42]. The delay between the amplifiers can be synchronized using TW transmission lines [43] and digitally controlled delay blocks [34].…”