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For Scientific Research & Industry Modernisation.
The rapid advancement of information technologies in the 21st century has indicated the approaching post-Moore’s law era. Moore’s law, which dictates the doubling of transistors on microchips every two years, has driven traditional computing technology for many years. The demand for higher speed, larger bandwidth, lower energy consumption, and improved security and stability in information technologies continues to grow. However, as we near the physical limits of miniaturization, new approaches are needed to continue advancing computation.
Integrated Photonic Chips (iPC) have emerged as a promising successor to silicon chips. With the continuous development, iPCs which offer the desired features including high speed and low power consumption, has become the best solution for high-throughput communication technology. However, as 3D photonic chips move towards commercialization and industrialization, existing fabrication capabilities face significant challenges concerning precision, reproducibility, and scalability to fulfill the needs for R&D and manufacturing. There is currently no effective measure to accurately characterize the three-dimensional structural changes formed inside an optical crystal by femtosecond laser, as well as the resulting refractive index distribution and morphology. To fabricate 3D optical structures in optical crystals, the difference in refractive index introduced by laser processing is particularly important, which determines the design of the component and its loss.
Therefore, to effectively characterize the fabricated nanostructure/nanopatterns and provide timely feedback to the fabrication process has become one of the key challenges in quality control for processing 3D photonics chips.
HoloView 3DRI, the 3D in-situ refractive index characterization system designed by Innofocus, has proved to enable characterize the 3D spatial refractive index distribution with our newly-developed optical imaging technology and image reconstruction algorithm. The system can precisely measure the refractive index distribution in material and effectively reconstruct the refractive index distribution, and form image of the 3D structure with an accuracy of 10-4. It is non-destructive and non-invasive, and it allows real-time monitoring the fabrication process, making it valuable for the applications in the disciplines of all-optical communications, sensors, biophotonic and micro/nano optical and photonic devices.
The key properties of an optical component are its refractive index distribution and surface morphology. High-performance optical components can only be fabricated when meeting requirements for both of the properties. Otherwise, distortion in electric field pattern, transmission loss and imperfection will occur, degrading the performance of the components.
Meanwhile, by understanding the refractive index variation and distribution, properties of the optical material and components are quantified, which can be used to indicate whether the material or component is damaged.
For those optical components that are sensitive to variation of refractive index, e.g. optical waveguide and optical fiber gratings, there is no standard quantitative method to characterize their 3D refractive index distribution. This issue has become a bottleneck for accurately designing and fabricating optical components like 3D photonic chips.
To solve, Innofocus has developed world-unique technology of 3D spatial characterization of refractive index to measure the refractive index difference between the structure designed and the substrate material, with an accuracy of 10-4. The system can not only precisely measure the distribution of refractive index differences, but also reconstruct the 3D surface morphology of the fabricated structure.
The main functions of the Innofocus HoloView 3DRI include:
along with the 3D spatial distribution of the refractive index and surface smoothness of femto-laser-processed optical components and structures. All of these can then contribute to optimizing laser processing parameters.
followed by a comparison with the original design input. This helps to ensure whether the fabrication outcome is optimal in terms of the desired quality requirements (e.g. self-inspection for defects and alignment with the design), allowing on-site correction of fabrication conditions of the optical components.
Therefore, the in-situ refractive index characterization system can be used to assess whether an optical component has been recharacterized. For example, in case of extreme conditions such as high temperatures or high humidity, it helps to examine if the component deform or sustain internal damage, and can identify which part of the component has suffered impairment.
While damage on the surface of components are easily detectable, internal damage caused by abrupt environmental temperature changes can hardly be found. However, such damage results in localized refractive index changes e.g. within the core of optical waveguide chips, or within FBGs, which can have detrimental impact on the performance of the optical components.
Currently, no other method can provide quantitative detection with high-resolution three-dimensional refractive index distribution measurements. This method stands as the sole approach for such detection in the industry.
HoloView 3DRI provides three-dimensional refractive index imaging display functionality which can visualize the observed refractive index distribution outcome. Based on the observed distribution, novel physical mechanisms of laser-material interactions can be discovered, displayed in a trustworthy and aesthetically pleasing manner through three-dimensional imaging.
