Design and characterisation of high-speed monolithic silicon modulators for digital coherent communication

Silicon-based phase shifters for high figure of merit in optical modulation

“…[2][3][4][5][6][7][8][9][10][11] In telecom applications, in particular, high-speed optical modulation beyond 100 Gb/s/λ for optical-fiber transmission in advanced modulation formats such as dual-polarization quadrature phaseshift keying (DP-QPSK) has been achieved by using lateral PN-junction carrier-depletion silicon MZMs, which were monolithically integrated with optical circuits such as waveguides for polarization-division multiplexing (PDM) on a silicon-on-insulator (SOI) wafer in small chip footprints. [2][3][4][5] Optical-fiber transmission up to 1000 km in 128-Gb/s DP-QPSK format has been demonstrated by using the monolithic silicon PDM IQ MZM copackaged with electrical modulator drivers in a ceramic-based metal package in a small form factor of 15x35 mm 2 in footprint and 4.5 mm in profile. 4,12 Peak-to-peak RF voltage (RF V PP ) of ~6.5 V or higher in 50-ohm impedance matching produces 180-degree phase shift in the silicon MZM, and further reduction in the drive voltage is required for the deployment of the compact silicon modulator in energy-efficient optical transport networks.…”

Graphene-based BPSK and QPSK modulators working at a very high bit rate (up Tbps range)

“…A high-speed monolithic Mach-Zehnder optical modulator was used in a coherent optical channel based on polarization-multiplexed quadrature-phase (DP-QPSK) with a bit rate of 128 Gb/s, for each wavelength channel, in a 1000 km long single-mode fiber link [3].…”

“…Hence, as the variation in the refractive index of silicon occurs due to the plasma dispersion effect, there is a change in the value of the effective index (neff) of the propagating mode, which provides a change in the value of the signal phase, at the output of the waveguide. Therefore, changing the value of the refractive index of silicon alters the values of the effective refractive index of the optical modes that propagate in the arms of the MZM, causing a change in the propagation speed of these propagating modes, which, consequently, causes a phase difference between the optical signals at the MZM output [3,8,9,10]. Indeed, the increase in the value of the refractive index is caused by increasing the reverse voltage, as in this case, the free charges move away from the depletion zone.…”