Optoelectronics
Many people associate fibre-optics with telecoms, and therefore glass fibre. For fast signals, or transmission distances of hundreds of metres or more, glass is usually preferred, because it has lower attenuation, and smaller core diameters minimise signal distortion caused by modal dispersion. However, for shorter links with the modest signal speeds often typical of industrial datalinks, polymer (plastic) fibre can prove a better choice, as it’s more rugged and easier to install – and can deliver lower overall link cost. Two kinds of transmission technology are typically used: LEDs or lasers. While lasers deliver higher bandwidths and longer transmission via very small core fibre, for shorter links and speeds up to around 50MHz, LEDs are often the better choice, being cheaper and easier to drive, more durable, and offering longer life-expectancy. However, even LEDs degrade over time eventually, and this is exacerbated by drive current and temperature, so if the drive current can be kept down, the system will last longer. So, while it’s critical to transmit enough light that the receivers can still distinguish those zeros and ones at end-of-life, it’s also just as important not to overdo it. As well as hastening its deterioration, simply driving the LED chip hard to ‘flood’ the system with light can also lead to unreliability. An overly powerful transmitter can saturate the receiver such that it can’t recover before the next pulse – similar to eyes being dazzled by car headlights. Also, excess light may bounce back and forth between receiver and transmitter, and if the receiver is sensitive enough, it may be double-triggered by back-reflections.
Another important consideration is that while ‘typical’ specifications may be helpful when prototyping, that’s where their usefulness ends. Large industrial complexes may have thousands of datalinks. Due to manufacturing tolerances, most receivers will be less or more sensitive than typical, and transmitters lower or higher power. It’s usually neither practical nor cost-effective to try to pair up the lowest power transmitters with the highest sensitivity receivers. So, the designer must ensure that even once the system has aged, every receiver will still respond appropriately to each transmitted pulse – even if, say, the lowest output LED happens to be paired with the lowest sensitivity receiver. To achieve this, the designer needs to know that the launch power of every transmitter falls within specified limits on day one of
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system operation at the chosen LED drive current and into the precise fibre type that will be used in the application. This last point is crucial because even if a defined performance window is provided for a given device, often this is only at a given nominal (or maximum) current, and/ or for one specific fibre type. Any usage outside these conditions plunges the designer back into the treacherous realm of relying on ‘typical’ performance figures. To help solve this problem, OMC developed its proprietary ACA (Active Component Alignment) technology, in which each transmitter or receiver is powered up and aligned during manufacture. Our alignment rigs continuously measure device performance with the customer’s specified drive current and fibre type, allowing it to be optimised, recorded, and fixed within the required performance window. The batch’s test data then shows the actual performance of each device under relevant application conditions. This allows much tighter performance tolerances to be achieved, leading to greatly enhanced long-term reliability, giving the customer confidence that every device meets the specific performance window their application requires.
Calculating optical budget OMC has published a technical white paper, ‘Industrial Fibre Optic Datalinks: Consider Your Optical Budget’, that details the importance of carefully calculated optical budgets in the design of industrial fibre-optic datalink systems for long-life high-reliability (hi-rel) applications – and includes a worked example.
Aimed at engineers designing industrial fibre-optic systems for a wide range of mission-critical and high-reliability applications – from braking systems in railway networks to interference-resistant and electrically isolated communications in the defence and high voltage sectors, this white paper explains why determining the optical budget for your application is critical, before outlining how to do so, using a worked example.
Supporting requirements for both new optical links and replacements for legacy components in systems that require maintenance, OMC’s comprehensive understanding of the different components of industrial fibre-optics – transmitters, receivers, connectors and cable assemblies – backed up by its vertically-integrated, in- house manufacturing capabilities, is unique in the industry. Established over 40 years ago, OMC offers world-class technical
capability for the design and manufacture of complete optical links – and can help engineers reliably incorporate fibre-optics into their industrial system designs, from component selection to optical budget calculation, right through to customer- specific component manufacture at its UK facility.
Many off-the-shelf fibre-optic components struggle to meet the standards of performance, robustness and consistency needed in long-life industrial applications. This is why OMC has designed and developed a range of proprietary components that interface with industry standards while offering much- enhanced features. The company also offers a device optimisation facility where each transmitter or receiver can be honed during the manufacturing process to ensure that its optical characteristics fall within a customer-specific performance window. OMC’s white paper (available for download at:
www.omc-uk.com/dynamic/ omc_optical_budgets_white_paper_ bf14601045bb82f7.pdf) helps engineers understand the factors and process involved in calculating the best optical budget for their application.
www.omc-uk.com Components in Electronics September 2025 37
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