PIC development and deployment for fibre sensing

Photonic integration brings significant advantages in performance, environmental endurance and reliability. Rolf Evenblij, Program Manager at Technobis Fibre Technologies, looks at the key components enabling the detection of extremely small variations in temperature, vibration (and other parameters) for monitoring applications in aerospace, energy and nuclear industries, semiconductor and medical sectors.

Significant investments have been made in the development of fibre optic sensing systems based on integrated photonics and by doing so achieving technology readiness in a demanding market. Photonic integrated circuits have proven to be enabling and bring significant advantages in sensing performances (resolution, speed, sensor multiplexing), environmental endurance (high-tech industry, aeronautics, space, medical and other sectors) and reliability (solid state, thermally and mechanically stable). Together with the demonstrated capacity from Technobis to bring this (fibre optic) sensing technology to the market, these benefits have convinced large companies to regard this as a leap forward for applications in demanding environments where size, weight, reliability and cost, are key requirements, and where conventional systems do not apply anymore.

Figure 1. ASPIC: application specific photonic integrated circuit

For the purpose of fibre sensing using Fibre Bragg Gratings at high performance, a modified AWG (Arrayed Waveguide Grating) has been developed. A modified spectrometer principle allows an extremely high and stable wavelength shift detection resolution. Adding PIC interferometry functionality allows detection of even smaller wavelength shifts in the attometer order of magnitude. Using proper thermal management packaging mechanisms assures temperature stability as required within ranges of at least 70°C.

Figure 2. PIC devices can be configured to suit extreme high-resolution measurement.

These chips are packaged and so by definition thermally, mechanically and/or EMI isolated from the environment (within requirements) allowing electronic interfacing or data processing without affecting the optical system performance. This means that once having a good packaging concept, different ASPICs can be used with the same packaging concept without having to deal with the back-end electronics for interfacing/acquisition. As an intermediate between chip output and back-end electronics Technobis has developed extremely low-noise front-end electronics in order to preserve the signal quality provided by the chip for further data processing. The demonstrated versatility of measurement capabilities makes this technology favourable for many existing and new applications.

Applications landscape

It's probably not a surprise that with integrated photonics as an enabling technology a vast amount of applications can be supported throughout all markets segments. The number of applications is growing as we speak and new opportunities present themselves on a daily basis. Technobis has a strong focus on providing highly reliable, small sized PIC based devices for fibre sensing. Markets such as High-tech Industry, Aerospace, Space, Medical will benefit from these innovations, also applications in Automotive, Civil, Energy and Nuclear.

Figure 3. High-tech industry

Manufacturing

At Technobis, the path to using optical chips was paved by requests from the High-tech Industry. The everlasting growing need to increase performances in the semiconductor industry desperately seeks means to deal with mechanical and thermal vibrations in orders that are barely noticeable by human observation, but greatly affect system performance. Multiple iterations led to sensing equipment to measure wavelength shifts of less than 100 attometer. For many high-tech applications and environments it is of great importance to measure extremely small variations in temperature (and vibrations for that matter) to assure proper critical behavior of structures and objects. High resolution thermal mapping helps to detect weak spots and provides feedback information for optimized control of systems and structures. Different types of sensors and fibre optic sensing techniques based on spectrometry and interferometry have been assessed successfully for extreme measurement resolutions.

Figure 4. Packaged device

Two fibre sensing systems, the T100 Gator and the Chiroptera are specifically designed for that purpose; Thermal Mapping for detecting thermal deformation of structures as wafer tables and lens systems, and sub-nanometer displacement sensing for object positioning.

Aerospace

The Aerospace sector will benefit greatly from smaller sized and more reliable devices. Fibre optics for telecom and sensing has been targeted in Aerospace for many years already for its obvious advantages of being light weight, immunity to EMI, etc. But solutions must also include readout equipment capable of sustaining the stringent environmental conditions of Aerospace. The Fibre Bragg Grating technology seems to be the most promising since it allows a wide range of varieties in different performance aspects. Applications of interest are damage and impact detection, load monitoring shape sensing (for instance on morphing structures), multi-point temperature sensing, and in general Structural Health Monitoring, Prognostic Health Monitoring (PHM) and Condition Based Maintenance (CBM), i.e. determining indicators as State of Health (SoH) and Remaining Useful Life (RUL). In the years to follow legacy systems will be replaced by their fibre optic equivalents and new applications will rise to reduce costs of flight in general.

Space

In many ways, space is the ultimate environment with regard to endurance and other extreme lifetime conditions. Here, PIC technology seems the perfect last piece of the puzzle to fit the need for miniaturisation and reliability of measurement devices. A general approach towards the assessment of fibre sensing systems for space applications was recently performed as being the first steps towards the assessment of the radiation hardness of ASPIC interrogators for FBG sensing. Both active and passive PIC functionality on Indium Phosphide was investigated for GEO and LEO mission conditions. Preliminary results show that both active and passive components endure a radiation hard environment.

Medical

In the medical field, huge interest is growing for shape monitoring functionality in guide wire and catheter systems as well as intravascular monitoring capabilities on force, temperature, pressure. One of the most recent innovations examples is a laparoscopic grasper with enhanced fibre optic based haptic feedback mechanism for minimal invasive surgery, allowing visco-elastic tissue feeling. Such exemplary innovations are made possible by high-end and still affordable fibre optic sensing capabilities. Again integrated photonics plays an enabling role here.

Next steps

The landscape for PIC based systems, and in particular for sensing applications, is huge and expanding. Based on what has been done so far, it barely scratches surface of what is possible. The PIC based development platform allows complex optical systems on just a few square millimeters, packaging innovations make PICs work in stringent environments and the Optical Fibre appears to demonstrates an increasingly number of sensing capabilities almost on a daily basis.

For PIC technology in general, one of the tendencies in order to consolidate new technologies is standardisation as a means to reduce costs and improve efficiency in the supply chain. Generic processing is one of the ambitions for integrated photonics in order to reach this state. The advantages are reduced costs and lead-time in the supply of PIC based components. A well balanced interaction capability on a technical level within the supply chain is imperative towards touching high skies.