## 6 Wavelength Tunable 100G Transmitter Module  
The polyboard technology has also contributed to the establishment of an advanced hybrid integration platform incorporating: (1) EO polymers for constructing low-complexity and low-cost Mach-Zehnder modulators (MZMs) with extremely high modulation bandwidth (\(>\)100 GHz); (2) InP components for light sources, detectors, but also high-speed electronics including MUX drivers and DEMUX circuits; (3) Ceramic (AlN) RF board and interposer that interconnects and terminates the electronic signals within the package. The entry of polyboard has not only enabled the functionalities such as wavelength tuning, polarization management, and light-flow (amplitude and direction) control, but also brought along well developed passive components (AWGs, MMIs and so on) and improved the integration compatibility with InP-based active devices and passive thin-film elements. On this hybrid integration platform, a wavelength tunable, 100 Gbaud, all-in-one transmitter module has been demonstrated [19]. The dissecting of the module is displayed in Figure 16. The passive polyboard includes a thermally-tunable Bragg grating section and an optically coupled interface with the InP-based gain element. An external-cavity tunable laser is hereupon assembled; the half-wave plate inserted at the output waveguide efficiently converts the TE emitting laser to the required TM polarization that feeds into the EO polymer MZM. Figure 16: Dissecting of the tunable 100G optical transmitter utilizing the merits of the four material systems. From lower-right counterclockwise: EO polymers for high-speed light modulation; InP-DHBTs for ultrafast driver electronics; ceramic RF board for electronic signal interconnects and termination; polyboard for wavelength tuning and polarization control. Electro-optical (EO) polymers have been known to possess extremely fast EO responses. A modulation bandwidth larger than 100 GHz has been achieved [37,38], paving way for the advanced, complex and high-fidelity signal generations in optical communications. The polymer modulator fabrication process replies on the low-temperature thin-film-polymer on silicon (TFPS) technology [38]. The fabrication can scale up with silicon wafer size and is compatible with industry-standard semiconductor manufacturing techniques. Within this technology a poling process is required with the electric field oriented perpendicular to the wafer and the ultrafast electro-optic effect only exists for the TM polarized light. Since most LDs are developed for the TE polarization, the direct attachment of a laser source raises some challenges. The previous solution replies on the 90 \({}^{\circ}\)rotated attachment [14, 15, 16]. Novel as this method is, the assembly process is complex and time-consuming. With the introduction of the polyboard, the polarization can be converted prior to the attachment. The assembly can be simplified and secured. The electronic signal multiplexers and drivers (MUX-DRV) are fabricated on an InP-double heterojunction bipolar transistor (InP-DHBT) process. The architecture choice for this application, operating at very high bit-rate, has been to monolithically integrate a multiplexing stage with 3R function (re-amplifying, re-shaping, and re-timing). In this architecture, the electrical input interface operates at lower, half-rate speed and the 100 Gb/s electrical interfaces on chip are shortened to the minimum. The clean multiplexed signal is directly applied to amplifying stage. Two versions of InP DHBT 2:1-selector-driver have been fabricated using the 0.7 \(\upmu\)m InP-DHBT technology [39]: with the compact lumped amplifier [40] and with distributed amplifier [41]. The differential output eye diagram of the distributed amplifier operating at 112 Gb/s has reached an amplitude of 5.9-Vpp, leading to a new record swing-speed product of 660 VGb/s. At high speed, the electronic interconnect becomes challenging.