Three aspects of polymer-based external cavity tunable lasers are investigated. First, the tuning efficiency is increased from 0.29 nm/mW to a record 0.52 nm/mW by improving the microheater thermal design. Second, the long-term reliability of such tunable laser modules is investigated through two batches of stress tests at 25 °C and 45 °C, respectively. No degradation effect is observed in terms of output power drop and wavelength drifting after thousands of hours of continuous operation at tuned wavelength of 20 nm. Finally, a novel TM-emitting tunable laser is demonstrated by inserting a half-wave plate into the polymer output waveguide. Index-matching techniques and the intrinsic curved waveguide design guarantee robust single mode operation. The TM laser exhibits excellent side mode suppression ratio (>40 dB), large tuning range (>20 nm), and high output power (>5 mW at 100-mA drive current).

To fulfill the functionality demands from the fast developing optical networks, a hybrid integration approach allows for combining the advantages of various material platforms. We have established a polymer-based hybrid integration platform (polyboard), which provides flexible optical input/ouptut interfaces (I/Os) that allow robust coupling of indium phosphide (InP)-based active components, passive insertion of thin-film-based optical elements, and on-chip attachment of optical fibers. This work reviews the recent progress of our polyboard platform. On the fundamental level, multi-core waveguides and polymer/silicon nitride heterogeneous waveguides have been fabricated, broadening device design possibilities and enabling 3D photonic integration. Furthermore, 40-channel optical line terminals and compact, bi-directional optical network units have been developed as highly functional, low-cost devices for the wavelength division multiplexed passive optical network. On a larger scale, thermo-optic elements, thin-film elements and an InP gain chip have been integrated on the polyboard to realize a colorless, dual-polarization optical 90° hybrid as the frontend of a coherent receiver. For high-end applications, a wavelength tunable 100Gbaud transmitter module has been demonstrated, manifesting the joint contribution from the polyboard technology, high speed polymer electro-optic modulator, InP driver electronics and ceramic electronic interconnects.

We report for the first time the successful wavelength stabilization of two hybrid integrated InP/Polymer DBR lasers through optical injection. The two InP/Polymer DBR lasers are integrated into a photonic integrated circuit, providing an ideal source for millimeter and Terahertz wave generation by optical heterodyne technique. These lasers offer the widest tuning range of the carrier wave demonstrated to date up into the Terahertz range, about 20 nm (2.5 THz) on a single photonic integrated circuit. We demonstrate the application of this source to generate a carrier wave at 330 GHz to establish a wireless data transmission link at a data rate up to 18 Gbit/s. Using a coherent detection scheme we increase the sensitivity by more than 10 dB over direct detection.

Recently developed photonic components for nextgeneration datacenter systems based on the Heinrich Hertz Institute's PolyBoard integration platform are reviewed. Hybridintegrated transmitters and receivers, including optical functionalities, such as tunable lasers, polarization manipulators,1 x 2 switches, and variable optical attenuators, are presented. The flexibility of those devices provides the possibility of generating, routing and detecting multiple optical data flows, offering the potential of aggregating traffics of 1 Tb/s and beyond. In addition, vertically stacked polymer waveguide structures are presented, opening the way towards the third dimension in photonic integration and allowing increasing the transmission capacity beyond the physical limit of standard single mode fibers. The freedom in the arrangement of the polymer waveguides allow for the matching of different multicore fiber types, providing the possibility of processing in parallel the different optical flows. By means of micromachining 45° mirrors on the different stack levels, the three-dimensional (3-D) stacked waveguide structure can act as an interface between multicore fibers and planar optoelectronic devices such as photodiodes and laser diodes. Furthermore, a novel concept for a 4 x 4 3-D optical switch based on 3-D multimode interferometers is presented and numerically proven, showing potential for its application as the interface between multicore fibers and planar optoelectronic devices, as well as offering the possibility of reconfigurable N x N switching matrices.

A graphene-based electro-absorption modulator has been integrated into a passive polymer waveguide platform for the first time. The opto-electronic properties of the structure are investigated with numerical simulations and measurements of a fabricated device. The graphene layers transferred to the polymer substrate were analyzed by means of Raman spectroscopy and the results indicate a high crystalline quality of the two-dimensional material. The voltage-dependent transmission through a 25 µm long device has been measured in the telecommunications-relevant wavelength range between 1500 nm and 1600 nm yielding an extinction ratio of 0.056 dB/µm.

Optical waveguides have been fabricated and investigated that employ silicon nitride as core and polymer as surrounding cladding material. Buried single-mode waveguides showed a propagation loss of ∼0.7 dB/cm at 1550 nm. Depending on the thickness of the silicon nitride core, the optical mode can be designed to expand largely into the polymer cladding. Using such a low-confinement structure and a metal strip heater embedded in the polymer cladding material beneath the core region, efficient thermally tunable waveguide Bragg grating filters were demonstrated. Wavelength tuning >57 nm was achieved at ∼220 mW of electrical heating power.