C+L-Band InP-Based Coherent Driver Modulator Enabled Net-1.8 Tbps/λ Transmission

We developed the world's first InP-based C+L-band coherent driver modulator (CDM) that has a 3-dB electro-optic (EO) bandwidth of over 90 GHz. The CDM consisted of an InP-based n-i-p-n heterostructure twin IQ modulator chip with a differential capacitively loaded traveling-wave electrode, a SiGe BiCMOS driver in an open-collector configuration, and an RF package with a flexible printed circuit as the RF interface, with 3-dB bandwidths exceeding 105, 97, and 77 GHz, respectively. In terms of optical characteristics, by using a waveguide with a middle-ridge structure and optimizing the epitaxial structure of the InP modulator chip, the wavelength dependence of the absorption loss, which has been a problem with conventional InP modulators, is suppressed, and the insertion loss per polarization at maximum transmission, including a bias loss of V_π = 2.0 V, is less than 11 dB over the C+L band. In addition, by using the newly developed CDM, we achieved a single-carrier net bit rate of 1.8 Tbps after 80-km of standard single-mode fiber transmission in the C+L band.