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

Abstract

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/-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 travelingwave 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.

Oscillation Suppression of EO Response in Coherent Driver Modulator for Over 160 Gbaud Operation

“…In detail, by controlling the cavity resonant frequencies away from the frequencies where the µ-factor <1, we can achieve smooth EO characteristics (without EO oscillation) and high baud-rate operation. Moreover, if the driver is stable (µ-factor >1) near the cavity resonance frequencies, the EO oscillation is not observed even in the same package with a distance of 1.75 mm [7].…”

“…The HB-CDM includes an InP-based n-i-p-n heterostructure twin-IQ modulator chip with a differential capacitively-loaded travelling-wave electrode (CL-TWE) and a 4-channel linear SiGe BiCMOS driver die with an open-collector configuration. The package and modulator chip used were the same as those previously reported; the characteristics of the package and modulator chip are an electrical (EE) 3-dB bandwidth of 80 GHz and a roll-off frequency of over 100 GHz, and a 3-dB bandwidth of over 72 GHz with V of 2 V, respectively [7].…”

“…In our assembly conditions, the wire inductance was controlled to be less than 120 pH, and the driver is designed to have sufficient RF characteristics even with 120 pH. Even with the inductance of 120 pH, the magnitude of the peaking at 80 GHz exceeds 10 dB, which is more than the sum of the RF losses (approximately -7 dB at 80 GHz) of our modulator chip (about -4 dB at 80 GHz) and the package (about -3 dB at 80 GHz) [7], which can achieve an HB-CDM with bandwidth above 80 GHz supporting 160 Gbaud operations. While sufficient bandwidth can be achieved, the EO response of the HB-CDM will have excessive peaking due to driver peaking.…”

“…The high-bandwidth coherent driver modulator (HB-CDM) [5] is a well-known form factor that utilizes high-speed modulator chips based on InP [6,7] and TFLN [8]. In the HB-CDM, a driver die and a modulator chip, previously packaged separately, are now assembled next to each other in a single package to enable high-speed operation.…”

“…In addition, using a flexible printed circuit (FPC) as the RF interface of the package enables excellent impedance J. Ozaki, Y. Ogiso, Y. Hashizume, and N. Nunoya, M. Ishikawa are with NTT Device Innovation Center, Nippon Telegraph and Telephone Corporation, Atsugi, Kanagawa 243-0198, Japan (e-mail: josuke.ozaki@ntt-devices.com; yoshihiro.ogiso@ntt-devices.com; yasuaki.hashizume @ntt.com; nobu.nunoya@ntt-devices.com; mitsuteru.ishikawa@ntt-devices.com). matching and minimized RF losses, and up to 144-Gbaud operation has been reported using the HB-CDM including the InP-based modulator chip [7].…”