Optoelectronics


semiconductors; such as InP, to more novel materials with extremely attractive electro- optics characteristics like Barium Titanate (BTO) or polymers.


While there is much development and progress on these fronts, there is not a commercial solution today that can be scaled in the way silicon photonics can.


InP: A versatile material with existing strengths and opportunities for scalability


The direct bandgap nature of Indium Phosphide (InP) makes it especially attractive as it can form lasers, optical amplifi ers, and detectors. Furthermore, it is a well-understood material widely used in telecom and datacom industries for many years. Nevertheless, InP is relatively expensive and harder to scale to large numbers of components than silicon, necessitating hermetic packaging to prevent long-term environmental degradation.


Heterogeneous integration: bridging the gap for high-performance optics Heterogeneous integration provides a pathway to circumvent these limitations by intelligently integrating diverse material functionalities. Here, most of the circuit is realized in silicon


and during fabrication small dies or chiplets of InP are bonded to the silicon to then be processed using photolithography to create individual devices, avoiding the need for precise alignment of each device, enabling wafer scale production. The InP material is fully encapsulated removing the need for hermetic packages and now circuits with lasers and detectors can be tested electrically rather than needing to couple light into and out of wafers, greatly enhancing the testability. Light is coupled into and out of InP devices from the silicon waveguides using adiabatic tapers to minimize the loss through the circuit which also removes the need for facets, one of the main causes of laser failure.


OpenLight’s breakthrough: high- speed modulation with integrated InP InP also enables different modulator structures. Mach-Zehnder modulators are certainly possible with high bandwidths. Additionally, electro-absorption modulators based on the Quantum Confi ned Stark Effect, which effectively shifts bandgap absorption as a function of voltage applied across a section


References 1


of quantum wells, are also available. This kind of device has been used ubiquitously for externally modulated lasers. The devices are small, thermally insensitive and, with proper design consideration, can support bandwidths beyond what silicon alone can support. EAMs also have low drive swings making them ideal candidates for existing pluggable transceivers, dense CPO where power and footprint are at a premium and for shorter reach applications where cost and power consumption are critical. OpenLight has recently demonstrated modulation bandwidths greater than 90GHz with heterogeneously integrated devices with performance on a par with best-in- class EMLs using a commercially available process, PH18DA, available from Tower Semiconductor. PH18DA is an open platform that allows users to tape in their own designs using a combination of active and passive structures. Other elements within the PDK include tuneable and DFB lasers, semiconductor amplifi ers and detectors allowing users to create a single Photonic ASIC with all of the needed components


on chip. Using this toolkit, OpenLight has demonstrated PICs using 65GHz EAMs to support 1.6T which are available as reference designs that customers can use to short cut their development times and have a route to both supporting CWDM and 3.2T solutions.


The breakthrough: integrated InP for high-speed modulation


The relentless demands of AI are propelling a revolution in optical interconnect technology, pushing beyond the limitations of traditional electrical solutions. Silicon photonics has emerged as a crucial platform for achieving the necessary scale and cost effi ciencies. However, the quest for even higher bandwidth and lower power consumption requires integrating advanced materials like InP, often through cutting-edge heterogeneous integration techniques. This evolution will enable the next generation of high- performance optical interconnects to meet the growing demands of modern computing and AI-driven applications.


https://openlightphotonics.com/ https://www.yolegroup.com/yole-group-actuality/yole-group-shaping-the-future-of-the-semiconductor-industry/


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www.cieonline.co.uk Components in Electronics June 2025 45


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