FEATURE: PHOTONIC INTEGRATION


THE EXISTING SEMICONDUCTOR MODULATORS ARE SIMPLY NOT FAST ENOUGH, AND CONSUME TOO MUCH POWER


Infinera has invested in building its own state-of-the-art InP PIC fabrication facility


circuits with beter performance and lower cost’. He highlighted the fact that, in ‘pluggables,’ this capability also enables higher transmit power (0 dBm compared to –10 dBm) in QSFP- DD form factors since ‘they do not have room for an external micro-EDFA, which is key for compatibility with the many existing DWDM line systems’. He added: ‘By comparison, silicon photonics


relies on external (InP) lasers and amplifiers.’ When it comes to challenges, Momtahan


observes that it takes ‘time, expertise and up-front investment’ to establish an indium phosphide manufacturing facility capable of delivering commercial volumes of high- performance coherent InP-based PICs. ‘For vendors that do not have experience


with indium phosphide-based PICs, and do not own or have access to an indium phosphide fab, the ability to leverage existing CMOS foundries with legacy (~130nm to 45nm process node) equipment provides an option for vendors to bring photonic integrated circuits to market more quickly and with a lower up-front investment,’ he added. In terms of current and potential telecoms


applications, Momtahan observed that both InP and silicon photonics will continue to be used in coherent DWDM embedded and pluggable optical engine designs – but stressed that, for high-end embedded optical engines, superior modulation effect and greater photonic integration give indium phosphide an ‘inherent performance advantage’. He added: ‘For coherent pluggables, InP’s


ability to integrate amplification into the photonic integrated circuit enables higher transmit power in a QSFP-DD form factor relative to silicon photonics.’ Moving forward, Momtahan confirmed


Infinera is investing in InP PICs for its embedded optical engines – enabling evolution to ‘even higher baud rates’ – and continues to invest in InP PICs for coherent pluggables, including the ICE-XR line of XR optics coherent pluggables.


Polymer PIC systems Elsewhere, Colorado-based technology platorm company, Lightwave Logic is exploring


18 FiBRE SYSTEMS n Issue 35 n Spring 2022


the use of high-performance optical polymers as part of polymer PIC systems for telecoms applications. Building on its experience in organic materials, particularly those with electro-optical properties, the company has refined its proprietary chromophore materials for a range of applications, including fibre optic communication. As Michael Lebby, CEO at Lightwave


Logic, explained, some key properties of the materials include ‘low loss at 1310nm and 1550nm wavelengths, a high pockels effect, high glass transition temperature and excellent material stability.’ When the electro-optic polymers are fabricated into Mach Zehnder optical modulators – a device that is common in the internet – and optical networks, Lebby observed that ‘extremely fast optical switching speeds and low drive voltages are achieved’. Although other semiconductor-based Mach


Zehnder modulators are in commercial use today, Lebby said they suffer from ‘relatively low speed of operation and significantly higher power consumption through their higher voltage drive’ – restricting the industry on a plateau of modulator device speed and power consumption for the past decade. ‘We are now at a point in time where the


PIC chips need to be turbo-boosted,’ he said. ‘Te existing semiconductor modulators are simply not fast enough, and consume too much power. Our Polymer Plus optical polymer platorm addresses these issues directly by allowing electro-optic polymers to be fabricated using standard silicon semiconductor techniques. For example, the polymer material can be spun onto silicon photonics circuits, so that the polymer modulators increase the speed of the PIC chip, while keeping power consumption low.’ He added: ‘Our Polymer Slot technology


can also be fabricated into a PIC platorm with increased performance and with a very small footprint, saving cost through the use of less real estate. It doesn’t mater if the transceiver is pluggable or on-board, both need high-speed modulation at lower power consumption levels.’ For Lebby, the performance advantages


of using electro-optic polymers ‘can be seen through the performance Mach Zehnder modulator devices’ – with modulators featuring the material ‘easily achieving’ electro- optical bandwidths of 70-100GHz, two to three times more than existing semiconductor devices. Moreover, when the modulators are driven at one volt or less, Lebby observes that the low voltage ‘eliminates the need for dedicated drivers, which in turn allows the optical system architect to drive directly from the CMOS electronics, saving the system power and money’. Although both the Polymer Plus and


Polymer Slot technology platorms are currently based on the use of large CMOS silicon foundries – fabrication plants that focus on silicon semiconductors, and have traditionally set up their process design kits (PDKs) for integrated circuits (ICs) – Lebby revealed that, over the past few years, many silicon foundries have been ‘looking at increasing their wafer throughput by servicing silicon photonics solutions’. He said: ‘It is these foundries that are the


catalyst for volume scale when polymers are added to silicon photonics. Electro-optic polymers are being used to create polymer modulators at our facility in Colorado, and in a small fabrication plant. Transporting the standard semiconductor fabrication techniques to a large foundry in terms of a PDK is relatively straightorward, as the processes are amenable.’ To make polymer modulators ‘ubiquitous


across the industry’, Lebby also pointed out that challenges are being addressed at ‘record pace’ – including advanced and mature electro-optic polymers, simple and standard fabrication in large-scale volumes, and packaged modulator device implementation into commercial applications. ‘Te polymer industry for fibre


communications is growing quickly, and with the correct positioning for scale, volume and performance, electro-optic polymers are poised very well to enable optical network system businesses to be much more competitive,’ he added.n


www.fibre-systems.com @fibresystemsmag


Infinera


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