An ultra-high bandwidth (BW) and a low V π InP Mach-Zehnder modulator with an n-i-p-n heterostructure is proposed. The combination of the n-i-p-n heterostructure and the capacitive-loaded travelling-wave electrode provides a modulator with extremely low electrical loss. The device exhibits a 3 dB electro-optic BW of over 67 GHz and a V π of 2.0 V. A 100 Gb/s non-return-to-zero on-off keying modulation with an extinction ratio of over 10 dB is also realised.
The authors obtained very good back‐to‐back bit error rate performance in up to 80 Gbaud DP‐16QAM operation by using their coherent driver modulator of a 3‐dB electro‐optic bandwidth of over 50 GHz. To achieve high bandwidth and good signal integrity, they used double ultra‐low loop wires between the driver IC and the modulator and a differential capacitively loaded travelling‐wave RF electrode based on straight coupled coplanar waveguide with a ground‐signal–signal‐ground configuration for their InP modulator. As far as they know, this is the highest bandwidth and baud rate operation so far for the high‐bandwidth coherent driver modulator configuration.
The authors used 65-nm CMOS technology to develop a linear four-channel driver IC with low temperature dependence and ultralow power dissipation for 64-Gbaud coherent optical transmitters. The driver showed more than a 48-GHz 3-dB electrical bandwidth and less than 1-W power consumption in four-channel operation. By employing a circuit that suppresses the temperature dependence, they achieved 3-dB electrical bandwidth variation of 3.0 GHz and the gain variation of 1.5 dB under the −5 to 75°C and ±5% supply voltage variation conditions. The CMOS driver has all the necessary functions for a high-bandwidth coherent driver modulator such as a gain control, peaking control, peak detection and temperature monitoring, all of which functions can be controlled by a serial peripheral interface. A fabricated sub-assembly consisting of the CMOS driver and an InP modulator showed a 48-GHz 3-dB electro-optic bandwidth.
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