This paper presents a hybrid photonic integration concept based on the use of a polymer motherboard, InP EML arrays and InP PD arrays to realize WDM and SDM Terabit optical engines operating at 100-Gb/s or even at 200-Gb/s per lane. The optical engines are aligned with the Ethernet roadmap, are cost-efficient by design and can find their place in the next generation Terabit IM/DD optical transceivers within Data Centers.

We demonstrate an EML-array for up to 4x200 Gb/s PAM4 modulation at 45°C. Its single MQW layer stack design allows for low-cost fabrication. The device is optimized for equal performance over four LAN-WDM wavelength channels.

We demonstrate an InP EAM chip with high (> 5 mW) fibre-coupled output power, large (> 35 GHz) bandwidth, and wide (>15 nm) wavelength range. The BH device includes integrated amplifiers with spot size converters at in- and output supporting hybrid integration with e.g. tunable lasers or PICs.

100 GBd is demonstrated from 30°C to 70°C with O-Band InP EML array chips. Modulation bandwidths are above 50 GHz, and an integrated SOA ensures 10 dBm, while a single active layer allows for cost effective manufacturing.

We demonstrate an EML for 200 Gb/s PAM4 modulation at uncooled conditions. The device has an identical MQW layer stack for the DFB, EAM and SOA section, which allows a simple fabrication process. The EML is designed for balanced performance from 20°C to 85°C.

Externally modulated DFB lasers (EML) and vertically illuminated photodetectors are presented. Because of their excellent high-speed behavior and operation wavelength of 1310 nm, the devices are of interest for intra-data center communication. Since the EML and the photodetector chips are compatible with current systems, these devices are candidates for upgrading existing transceivers to higher baud rates. Therefore, a proof of concept for 100 GBaud data transmission with the presented components is demonstrated. Even without predistortion, the experiments show clearly open eye diagrams.

Combining semiconductor optical amplifiers (SOA) on direct-bandgap III–V substrates with low-loss silicon or silicon-nitride photonic integrated circuits (PIC) has been key to chip-scale external-cavity lasers (ECL) that offer wideband tunability along with small optical linewidths. However, fabrication of such devices still relies on technologically demanding monolithic integration of heterogeneous material systems or requires costly high-precision package-level assembly, often based on active alignment, to achieve low-loss coupling between the SOA and the external feedback circuits. In this paper, we demonstrate a novel class of hybrid ECL that overcome these limitations by exploiting 3D-printed photonic wire bonds as intra-cavity coupling elements. Photonic wire bonds can be written in-situ in a fully automated process with shapes adapted to the mode-field sizes and the positions of the chips at both ends, thereby providing low-loss coupling even in presence of limited placement accuracy. In a proof-of-concept experiment, we use an InP-based reflective SOA (RSOA) along with a silicon photonic external feedback circuit and demonstrate a single-mode tuning range from 1515 to 1565 nm along with side mode suppression ratios above 40 dB and intrinsic linewidths down to 105 kHz. Our approach combines the scalability advantages of monolithic integration with the performance and flexibility of hybrid multi-chip assemblies and may thus open a path towards integrated ECL on a wide variety of integration platforms.

A novel tunable transmitter structure based on liquid crystal filter, to the best of our knowledge, is presented. The structure is designed for application to 5G fronthaul and supports 25 Gbps dense wavelength division multiplexing (WDM) transmission and tunable range of 35 nm. The design takes into account easy change of operation band over coarse WDM grid. Prototype samples are developed to test feasibility of the design.

Existing transceiver technology inside data centers will soon reach its limits due to the enormous traffic growth rates driven by new, bandwidth-hungry applications. Efforts to develop the next generation of 800Gbps and 1.6Tbps transceivers for intra-DC optical interconnects have already kicked-off to address the demands in traffic, the exhaustion of the ports at the digital switches and the power consumption limitations inherent to the use of many lower capacity modules. The new generation of optical modules must also provide Terabit capacities at low cost, necessitating the use of high-volume manufacturing processes. TERIPHIC is an EU funded R and D project that aims at developing transceiver modules with up to 1.6 Tbps capacity over 16 lanes in duplex fiber and cost less than 1 € per Gbps for distances up to 2 km, utilizing PAM-4 modulation for 100Gbps per lane and high-volume production compatible transceiver designs. At the component level, TERIPHIC will rely on arrays of high-speed electronics, InP Externally Modulated Lasers (EMLs) and InP photodetectors, and at the integration level it will rely on a polymer photonic platform as a host motherboard, leveraging its flexibility and powerful toolbox. A summary of the progress on the TERIPHIC transceiver modules concept, both at the component level and integration level is presented in this paper.

Two independent reports of directly modulated lasers with bandwidths of >60 GHz may help bring data rates beyond 200 Gb s –1 to low-cost optical communication systems. Key to the successes has been managing photonic feedback effects within the laser cavities.

Three-dimensional (3D) nano-printing of freeform optical waveguides, also referred to as photonic wire bonding, allows for efficient coupling between photonic chips and can greatly simplify optical system assembly. As a key advantage, the shape and the trajectory of photonic wire bonds can be adapted to the mode-field profiles and the positions of the chips, thereby offering an attractive alternative to conventional optical assembly techniques that rely on technically complex and costly high-precision alignment. However, while the fundamental advantages of the photonic wire bonding concept have been shown in proof-of-concept experiments, it has so far been unclear whether the technique can also be leveraged for practically relevant use cases with stringent reproducibility and reliability requirements. In this paper, we demonstrate optical communication engines that rely on photonic wire bonding for connecting arrays of silicon photonic modulators to InP lasers and single-mode fibres. In a first experiment, we show an eight-channel transmitter offering an aggregate line rate of 448 Gbit/s by low-complexity intensity modulation. A second experiment is dedicated to a four-channel coherent transmitter, operating at a net data rate of 732.7 Gbit/s - a record for coherent silicon photonic transmitters with co-packaged lasers. Using dedicated test chips, we further demonstrate automated mass production of photonic wire bonds with insertion losses of (0.7 ± 0.15) dB, and we show their resilience in environmental-stability tests and at high optical power. These results might form the basis for simplified assembly of advanced photonic multi-chip systems that combine the distinct advantages of different integration platforms.

InP technology is the principal enabler for implementing fully monolithic photonic integrated circuits (PIC), uniquely including transmitter elements. In this article we present an overview of recent achievements on ultra-high speed electro-absorption modulated lasers (EML) which represent a simple transmitter PIC comprising a single-mode laser diode and an electro-absorption modulator. Using a so-called identical-layer approach single-wavelength modulation rates up to 100 Gb/s have been accomplished. By additionally integrating an optical amplifier section modulated optical output power of > 10 dBm has been achieved. Multi-level amplitude modulation was successfully demonstrated. Extended EML chips designed for wavelength-division and space-division multiplexing, respectively, will be presented. For dual-polarization transmission a novel EML related transmitter as well as a corresponding receiver PIC have been introduced. The latter devices were made on a generic PIC platform that is available for open-access foundry service.

We demonstrate an InP/Silicon integrated ECL using a photonic wirebond as intra-cavity coupling element. In our proof-of-concept experiments, we demonstrate 50 nm tuning range, SMSR above 40 dB, and linewidths of 750 kHz.

Wafer-level probing of photonic integrated circuits is key to reliable process control and efficient performance assessment in advanced production workflows. In recent years, optical probing of surface-coupled devices such as vertical-cavity lasers, top-illuminated photodiodes, or silicon photonic circuits with surface-emitting grating couplers has seen great progress. In contrast to that, wafer-level probing of edge-emitting devices with hard-to-access vertical facets at the sidewalls of deep-etched dicing trenches still represents a major challenge. In this paper, we address this challenge by introducing a novel concept of optical probes based on 3D-printed freeform coupling elements that fit into deep-etched dicing trenches on the wafer surface. Exploiting the design freedom and the precision of two-photon laser lithography, the coupling elements can be adapted to a wide variety of mode-field sizes. We experimentally demonstrate the viability of the approach by coupling light to edge-emitting waveguides on different integration platforms such as silicon photonics (SiP), silicon nitride (TriPleX), and indium phosphide (InP). Achieving losses down to 1.9 dB per coupling interface, we believe that 3D-printed coupling elements represent a key step towards highly reproducible wafer-level testing of edge-coupled photonic integrated circuits.

We present a novel concept for an integrated silicon photonic coherent transceiver using vertical-emitting laser sources at 1550 nm. In a state of the art external modulation configuration, we deploy a VCSEL on the transmit and a HCSEL on the receive side. We demonstrate the feasibility of this approach by externally modulating the VCSEL with QPSK at up to 28 Gbaud. We also perform experiments with the VCSEL-HCSEL configuration in a slave-master optical injection locking setup for future data center interconnects. The results show stable locking conditions and the VCSEL is detuned to perform predominant phase modulation. To the best of our knowledge, this is the first time direct phase modulation of a VCSEL under optical injection locking was demonstrated using two vertically emitting laser sources as master - and slave laser.

We present a novel array of electroabsorption modulated lasers as compact and low-cost single-chip solution for future 200 Gb/s transmitters. The array is designed for high optical output power with semiconductor optical amplifiers at the front side of the chip. A common InGaAlAs-MQW active layer structure allows for simple and cost-effective monolithic integration. On chip RF transmission lines are implemented to bring all electrical contacts to the rear side of the array-chip which supports packaging with short wire bonds. The array operates at four different wavelengths spanning over 7.5 nm in the L-band. Uniformity of each wavelength channel is experimentally proven regarding modulation bandwidth >30 GHz, extinction ratio >7 dB, and output power up to 8 dBm. The influence of the semiconducting optical amplifiers on signal quality is investigated by back to back bit error ratio measurements. In transmission experiments over standard single mode fiber links, the array's performance at 4 × 56 GBd NRZ and 4 × 28 GBd PAM4 is demonstrated and the arrays capability for up to 7 km transmission in case of PAM4 signaling is shown.

Efficient coupling of III-V light sources to silicon photonic circuits is one of the key challenges of integrated optics. Important requirements are low coupling losses, as well as small footprint and high yield of the overall assembly, along with the ability to use automated processes for large-scale production. In this paper, we demonstrate that photonic wire bonding addresses these challenges by exploiting direct-write two-photon lithography for in-situ fabrication of three-dimensional freeform waveguides between optical chips. In a series proof-of-concept experiments, we connect InP-based horizontal-cavity surface emitting lasers (HCSEL) to passive silicon photonic circuits with insertion losses down to 0.4 dB. To the best of our knowledge, this is the most efficient interface between an InP light source and a silicon photonic chip that has so far been demonstrated. Our experiments represent a key step in advancing photonic wire bonding to a universal integration platform for hybrid photonic multi-chip assemblies that combine known-good dies of different materials to high-performance hybrid multi-chip modules.

Hybrid photonic integration combines complementary advantages of different material platforms, offering superior performance and flexibility compared with monolithic approaches. This applies in particular to multi-chip concepts, where components can be individually optimized and tested. The assembly of such systems, however, requires expensive high-precision alignment and adaptation of optical mode profiles. We show that these challenges can be overcome by in situ printing of facet-attached beam-shaping elements. Our approach allows precise adaptation of vastly dissimilar mode profiles and permits alignment tolerances compatible with cost-efficient passive assembly techniques. We demonstrate a selection of beam-shaping elements at chip and fibre facets, achieving coupling efficiencies of up to 88% between edge-emitting lasers and single-mode fibres. We also realize printed free-form mirrors that simultaneously adapt beam shape and propagation direction, and we explore multi-lens systems for beam expansion. The concept paves the way to automated assembly of photonic multi-chip systems with unprecedented performance and versatility.

A small footprint electroabsorption modulated DFB laser TOSA with an ultra-low power SiGe driver with a power efficiency of 3.59 pJ/bit is demonstrated. Good optical eye openings up to 56 GBd NRZ and 64 Gb/s PAM-4 were obtained. The novel SiGe EML driver consumes 84 mW only.

We demonstrate a high output power EML-array operating at 4 × 56 Gb/s NRZ. On chip RF transmission lines enable flexibility for packaging and driver integration. A common active layer structure allows for cost effective fabrication.