Over-85-GHz-Bandwidth InP-Based Coherent Driver Modulator Capable of 1-Tb/s/λ-Class Operation

We developed an InP-based coherent driver modulator (CDM) with a flexible printed circuit (FPC) RF interface. The CDM has a 3-dB electro-optic (EO) bandwidth of over 85 GHz, including the evaluation board loss, which is sufficient for 1-Tb/s/λ-class operation. Furthermore, we obtained good back-to-back bit-error-rate (BER) performance in modulations up to 144-Gbaud dual-polarization 16-QAM, and we confirmed the CDM's capability for operation over the 150-Gbaud class. With the FPC RF interface, a package's roll-off frequency above 100 GHz was demonstrated in both measured and simulated results. The CDM includes an InP-based n-i-p-n heterostructure modulator chip with a differential capacitively loaded traveling-wave electrode (CL-TWE) and a 4-channel linear SiGe BiCMOS driver IC with an open-collector configuration and low wire inductance. The modulator chip has an EO 3-dB bandwidth of over 70 GHz, which is an improvement of about 30 GHz over that of a conventional p-i-n structure. In addition, to facilitate future 200-Gbaud-class operation, a simulation with a reduced GND via diameter confirmed that the package's roll-off frequency can be improved to more than 120 GHz. Moreover, by reducing the CL-TWE period and the metal's DC resistance, the n-i-p-n modulator chip achieve an EO 3-dB bandwidth of 90 GHz or more.