Technical Insight
Reimagining PIC-fibre interfaces with engineered V-Groove technology
Engineered V-Groove technology is redefining fibre alignment in photonic integration, offering a cost-effective, scalable solution that bridges performance with manufacturability for next-generation optical interconnects.
BY: AURI RIPOLL, MARKET INTELLIGENCE & STRATEGIC MARKETING MANAGER, DIRK HAUSCHILD, SENIOR STRATEGIC MARKETING EXPERT, AND ZHICHAO HE, MARKETING MANAGER, FOCUSLIGHT
In the rapidly evolving world of photonics, PICs have emerged as a transformative force across industries – from ultra-fast datacentres to next-generation AI computing. But despite their potential, a fundamental challenge threatens to slow these chips’ adoption: how they connect to the outside world, especially via optical fibres.
At the heart of every photonic system lies the need to align optical fibres to PICs with sub-micron precision. Even a small misalignment can drastically degrade signal quality, introduce insertion losses, or compromise system performance.
Fibre-to-chip interfaces are often overlooked but are mission-critical. They must meet the dual demands of sub-micron precision and high-volume manufacturability, a combination that traditional fabrication techniques struggle to deliver. As PICs become more complex and integrated with AI workloads, datacentres, and quantum systems, the cost of even minor inefficiencies in these interfaces increases exponentially.
This is precisely where engineered V-Groove technology steps in – a quiet innovation with far-reaching implications.
A traditional solution for connecting PICs to fibres involves blade dicing – a mature and well-understood process in which a rotating blade sequentially cuts grooves into a substrate to hold individual fibres in place. But despite its widespread use, the method presents serious limitations for modern PIC applications.
First, there’s tool wear. As the blade cuts through glass or silicon, its geometry degrades, leading to inconsistent groove depth and pitch variation, especially across large channel counts (>16). The cumulative result is misalignment between the fibre and the PIC waveguide.
Second, sequential processing, whereby each groove is cut one at a time, introduces positional errors, with tiny inconsistencies accumulating, especially over large arrays. Add to this the impact of thermal drift, substrate warping, and material flaking, and the result is a high failure rate and increased need for active alignment and inspection.
Figures 1-3 show measurements that were made with commercially available components, illustrating some characteristic problems with current methods.
At the heart of every photonic system lies the need to align optical fibres to PICs with sub-micron precision. Even a small misalignment can drastically degrade signal quality, introduce insertion losses, or compromise system performance.
Fibre-to-chip interfaces are often overlooked but are mission-critical. They must meet the dual demands of sub-micron precision and high-volume manufacturability, a combination that traditional fabrication techniques struggle to deliver. As PICs become more complex and integrated with AI workloads, datacentres, and quantum systems, the cost of even minor inefficiencies in these interfaces increases exponentially.
This is precisely where engineered V-Groove technology steps in – a quiet innovation with far-reaching implications.
A traditional solution for connecting PICs to fibres involves blade dicing – a mature and well-understood process in which a rotating blade sequentially cuts grooves into a substrate to hold individual fibres in place. But despite its widespread use, the method presents serious limitations for modern PIC applications.
First, there’s tool wear. As the blade cuts through glass or silicon, its geometry degrades, leading to inconsistent groove depth and pitch variation, especially across large channel counts (>16). The cumulative result is misalignment between the fibre and the PIC waveguide.
Second, sequential processing, whereby each groove is cut one at a time, introduces positional errors, with tiny inconsistencies accumulating, especially over large arrays. Add to this the impact of thermal drift, substrate warping, and material flaking, and the result is a high failure rate and increased need for active alignment and inspection.
Figures 1-3 show measurements that were made with commercially available components, illustrating some characteristic problems with current methods.
Figure 1: Single-channel errors observed in typical >16 channels blade diced v-grooves.
Figure 2: Variation of the position and orientation of fibre arrays within blade diced V-grooves.
Figure 3: Random fibre pitch variation without a single centre of gravity value.
Cumulative errors
The singular random pitch and position errors limit the number of channels per product and require a 100 percent test procedure (both incoming quality control and outgoing quality control) to avoid defective products at functional inspection after assembly is finished. Due to the sequential positioning of the blade, individual cutting characteristics, and degradation of the blade, achieving a defect-free product means using a selection process that will affect the yield and the resulting cost structure of the product.
During assembly of connectors and PIC-fibre interfaces, the height and roll angles – key parameters defining how well the fibre is aligned to the groove – should be reproducible across the fibre array. However, current methods offer insufficient reproducibility. Not only does this result in lower overall performance and increased variation in performance within the array of channels, but it also requires some compensation for errors, increasing the assembly time and cost.
In addition, the larger variation of parameters has implications for using reproducibility and repeatability as a basis for a good process capability index (Cpk) – a statistical measure of how consistently a process can produce output conforming to specified limits. The combination of errors and the distribution of functional parameters gives a clear indication about the process capability and resulting yield in production. The errors and variation of parameters described above lead to a parameter distribution that is not comparable with a typical Gaussian normal distribution, which is based on the variation of blade geometry and positioning during V-groove processing. Figure 3 shows a typical distribution of functional parameters of a sequential process that does not show a single “centre of gravity” value with an even distribution on either side.
This observed non-Gaussian distribution is due to the limitations inherent in sequential blade dicing; this process suffers not only from blade wear but also from cumulative 2D positioning errors and environmental temperature drift. These factors lead to systematic degradation of groove geometry, affecting reproducibility and the overall process capability index. In addition, uncontrolled sharp edges and glass flakes from the cutting process can damage delicate optical fibres, further reducing yield.
These issues also compromise compatibility with emerging co-packaged optics (CPO) and multi-channel transceivers, where even a 1 µm deviation can degrade link performance.
Additionally, traditional V-groove arrays are often limited by their reliance on specific materials, usually constrained to glass types that are compatible with mechanical cutting. This restricts compatibility with a broader range of PIC materials, such as silicon, indium phosphide, silicon nitride, and lithium niobate, which are increasingly used in advanced photonic systems. Finally, traditional blade-diced grooves often struggle to support high-density integration. As industry trends shift toward greater channel counts and denser packaging formats, the limitations of sequential processing become even more pronounced. Blade cutting is not only slower but also more likely to introduce thermal stress and microfractures, especially when pushing toward edge-to-edge array configurations.
Innovation unveiled
Focuslight’s Engineered V-Groove technology solves these problems by rethinking the process from the ground up.
Instead of cutting grooves one by one, Focuslight uses a proprietary wafer-level simultaneous structuring approach. All grooves and alignment features are structured simultaneously across the entire wafer, processing all grooves and assembly features at the same time and thus avoiding cumulative errors inherent to sequential dicing. The process is conducted in a temperature-controlled environment, compatible with large substrates, and allows integration of concave/convex geometries, smooth transition zones, and customised v-angles. 100 percent in-line wafer-level testing ensures statistical reproducibility and Gaussian distribution of positional accuracy.
The benefits are immediate and profound, eliminating tool wear and geometric limitations of blade dicing, and reducing production time by 40 percent compared to sequential methods. Additionally, this approach offers flexibility for standard and application-adapted designs and mechanical positioning support, and allows customisation with a variable number of channels, and the potential to include assembly features to facilitate the packaging process.
Moreover, this process is fully compatible with wafer-level metrology. Focuslight inspects every unit on the wafer before dicing, ensuring quality control without needing downstream inspection.
Key performance specifications include a lateral grid error of ±0.25 µm in the high-accuracy version of the technology, and ±0.5 µm as standard, with a vertical alignment error of ±0.35 µm (high accuracy), or ±0.7 µm (standard). The single-mode fibre coupling efficiency is greater than 99.5 percent per channel. Additionally, the process is compatible with materials including fused silica, Borofloat 33, S-TIH53, N-BK7, and silicon, and supports pitches of 127 µm, 250 µm, and custom sizes.
In addition to standard features, Focuslight’s platform enables customers to design grooves with application-specific mechanical or optical features. These can include thermal compensation features to reduce drift, optical blocking or guiding elements, recessed or elevated plateau areas for dual-layer packaging, and built-in fiducials for vision alignment systems.
Focuslight’s platform also allows for scalable production with reduced waste, minimal edge chipping, and significantly reduced risk of microcracks, making it ideal for use in sensitive optical or high-voltage environments.
With wafer-level control, Focuslight can produce V-groove arrays scalable to 96 channels and higher, tailored to application needs, while ensuring consistency across every groove.
Figure 4: Wafer-level structured substrate with engineered V-grooves.
Designed for the real world
What truly differentiates engineered V-grooves from other high-precision technologies is their readiness for production. Focuslight’s process is built on an infrastructure originally developed for high-volume micro optics. With substrate sizes ranging from 0.4 to 300 mm and standard thickness tolerances of ±0.05 mm, it supports both custom and standardised product configurations.
Further capabilities include a fully customisable groove depth and step dimensions of ≥0.1 mm ± 0.02 mm. The solution also offers edge chipping of ≤0.1 mm on outer dimensions (minimised internally) and either a grinded or polished surface finish, depending on optical grade. Focuslight has also developed a wafer-level testing strategy that includes automatic quality mapping prior to back-end separation.
This ensures that 100 percent of units are tested, that the grid deviation and plateau height are within defined tolerances, and that there is no need for post-assembly active alignment.
Figure 5: Wafer test result showing Gaussian distribution of grid error.
The resulting process achieves high process capability (Cpk), low variation, and a reliable statistical distribution of performance characteristics – ideal for automation.
With its low-defect, high-throughput process and compatibility with a wide variety of substrates, Focuslight’s engineered V-groove platform enables cost-effective production of high-performance optical systems across the full spectrum of commercial photonics applications.
As photonic integration continues to push the boundaries of how fibres and chips are brought together, achieving reliable coupling is no longer only about precision – it is equally about scalability, manufacturability, and long-term system stability. We are entering an era of platformisation in photonics; much like CMOS enabled the rise of ubiquitous electronics, scalable packaging and interfacing solutions will be key to the next wave of optical systems. By removing complex alignment steps and minimising tolerance errors, Focuslight is enabling a future in which PIC modules are manufactured like electronic integrated circuits: reliably, rapidly, and affordably. By shifting from sequential blade dicing to wafer-level simultaneous structuring, the industry gains a platform that unites submicron alignment accuracy with volume production capability.
This convergence opens the door to new design freedoms, from customised geometries to integration with advanced PIC materials. These advantages will support the expansion of photonics into consumer devices, healthcare, edge computing, and satellites, where reliable and scalable interfaces are essential. Looking ahead, Focuslight continues to invest in next-generation manufacturing technology, including AI-driven process control and data-driven yield optimisation. These enhancements will further improve the consistency, cost-effectiveness, and sustainability of photonics manufacturing.
As photonic systems evolve toward higher density and broader application spaces – from AI accelerators to quantum communication – the role of engineered V-grooves will be central in ensuring that performance and scalability advance hand in hand.
Usage Statement: All images included in this article are the intellectual property of Focuslight Technologies and are provided with full publication rights for use in PIC Magazine Issue 2025.
