3D In-situ Refractive Index Characterization Breakthrough in Laser Nanofabrication

For Scientific Research & Industry Modernisation.

Optical communication has been one of the fundamental driving forces for the development of the entire communication network. It is the foundation of modern telecommunication networks. With the increasing demand for high-throughput telecommunication today, optical communication, as the most critical backbone of the communication network, is under great pressure to advance. Consequently, high-speed, high-capacity optical communication systems and networks will be the main goals of the present optical communication technology.

The 3D photonic chip is one of the core devices of optical communication, which takes photons as information carrier and has the advantages of high-speed parallel fabricating ability and low power consumption. It is considered to be the most promising future solution for high-speed, large-volume data transmission processing by artificial intelligence computing. This photonic chip can solve multiple key problems in application areas, such as long processing time in data, inability to process in real time, and high-power consumption etc.

The study of fan-in/fan-out 3D photonic chips is one of the major challenges in the current optical communication research field. Optical waveguide is the basic structure of fan-in/fan-out 3D photonic chips. Its waveguide transmission characteristics can effectively eliminate beam divergence; maintain high optical density as well as uniformity in waveguide patterns over long transmission lengths. It helps enhance the interaction between light and waveguide materials and so does the optical properties of the substrate materials. Therefore, the fabrication of low-loss optical waveguide with flexible structures in different optical materials, and hence the realization of multifunctional high-performance waveguide optical devices has been a hot research topic in photonics chips.

Industry Challenge

Due to the limitations of the conventional waveguide fabrication process and the complexity of the crystal material structures, it is difficult to construct 3D optical waveguide structures in crystal materials. However, the rapidly growing femtosecond laser direct-writing technology in recent years has provided an effective solution.

The energy released by the femtosecond laser can change the structure of the material, thus causing a permanent change in the refractive index of the material. Therefore, understanding and characterizing the distribution of the refractive index is an important part in 3D photonics chip processing.

At the moment, there is no characterization method that can accurately characterize the refractive index distribution and morphology of the internal 3D structure of the optical crystals. It is one of the core challenges for quality control of the processing of fan-in and fan-out 3D photonics chips.

Solution Overview

The key property of an optical component is refractive index distribution and surface morphology. High-performance optical components can only be successfully fabricated when meeting both requirements. Otherwise, distortion in electric field pattern, transmission loss and imperfection will occur, degrading the performance. On this other hand by understanding the refractive index variation and distribution, we can understand the properties of optical material and devices, 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, such as optical waveguide and  fiber gratings, there is no standard quantitative method to characterize their 3D refractive index distribution. This issue becomes a bottleneck which hinders designing and fabricating optical components accurately. To solve this, Innofocus’s unique technology of 3D spatial characterization of refractive index is designed to accurately measure the modulation in refractive index with and without laser processing with an accuracy of 10-4. Furthermore, it can reconstruct the fabricated 3D structure. The main functions of the Innofocus HoloViewTM include:

1. In-situ measurement of the refractive index modulation, 3D distribution and surface smoothness of femtosecond laser processed optical waveguides, for optimizing parameters in fabrication process.

2. Quantitative measurement of the refractive index distribution both on surface and inside of the component, and evaluation on whether the fabrication can meet the desired quality requirements of the component through comparison with original design (e.g., detection of any defects and decide consistency with design)

3. Determine whether the material is modified by measuring the refractive index variation. Therefore, the method can be used to determine the property change of optical components when they expose to extreme conditions such as high temperature, high humidity etc., and it can display whether the components are deformed, or damaged inside. Additionally, it can run a quantitative determination to locate the damaged parts. Damage to the surface of the components can be easily identified, however, damage inside components caused by abrupt changes in working environment is challenging to detect. If a local refractive index variation occur inside an optical waveguide or FBG, it can be devastating to the performance of the components. At present, there is no other method that enables quantitative measurement and provides high-resolution 3D refractive index distribution profile. Our system is the only one available.

4. Quantitative design and measurement of refractive index distribution. Based on the measurement, the system can enable scientific researchers to study laser-material interactions and display the results in 3D image in a convincing way. It is a perfect choice for scientists and engineers.

Customer Value

In-situ characterization of refractive index for realization of optimal design and fabrication parameters.

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Application Scenario

A wide range of applications in for example: Characterization for laser fabrication, optimization of design and parameters, characterization of surface morphology of optical waveguide, characterization of material properties of optical components, characterization of material uniformity of optical components, characterization of internal damage of optical components and In-situ characterization of FBG and etc.

Optical Communications

Femtosecond laser processing with the NanoPrint 3D Intelligent Nano-fabrication system allows direct writing of micro-, sub-micron and even nano-scale 3D micro and nano structures in transparent media, with the advantages of maskless, flexible structure, simple design and fast processing speed. By combining with different optical materials, it can achieve a wide range of applications in the field of all-optical communication, especially in the fabrication of diffractive optics, integrated optics, on-chip optics, silicon photonics, nano-optics, and quantum optics, which stand out among the many micro and nano fabrication technologies and become increasingly important in enabling technology.


Three-dimensional micro-nano structures can be designed to enhance the interaction between the local optical field and matter, thus giving rise to a variety of linear and non-linear optical phenomena and shortening the scale of action, thus effectively achieving miniaturization, integration and low energy consumption of devices. For example, Nanoprint 3D Intelligent Laser Nano-Fabrication system can realize various miniature diffractive optical elements including micro-lens, integrated grating, and waveband sheet, which can play a great role in imaging, wavelength selection and dispersion compensation.


In addition, the NanoPrint system’s unique high-power femtosecond laser enables interaction with different materials such as glass, silicon, sulfur-based glass, and lithium niobate crystals. These materials can effectively introduce nonlinear optical interactions for wavelength conversion, optical switching, nonlinear tuning, etc. Nonlinear interactions in nanoscale waveguides can be exploited to generate effective sources of entangled photons for quantum optics. Femtosecond lasers can introduce ultra-high refractive index changes in optical fibers, bulk glass, and two-dimensional materials to form high-quality optical waveguides, ultra-thin devices, and complex three-dimensional integrated optical systems such as optical connectors and on-chip integration, which are essential enabling components for ultrafast, ultra-high-capacity, and quantum communications

Biological Application

In recent years, femtosecond pulsed lasers have been widely used in microfluidic devices, microsensors, biomedical and other micro and nano manufacturing fields. Especially in the biomedical field, the laser can realize complex and fine micro and nano structure processing, which can best meet the requirements of some special applications of biomedical products.


Compared with traditional fabrication methods, femtosecond pulsed laser micro-fabrication has the advantages of “cold” processing, low energy consumption, low damage, high precision, and strict positioning in 3D space, which has a good prospect in biological device fabrication. Laser micromachining technology gives new structures and functions to biological materials and can be used for cell culture to achieve permanent repair of damaged tissues or organs, which has become the development direction of contemporary biomedicine.


Although laser micro-fabrication technology can fabricate a new generation of implantable medical devices with extremely fine structures, making the next generation of implantable medical devices commercially viable, the development of laser micro-fabrication technology in the biomedical field is still immature, with low production efficiency and working stability to be improved.


For laser micro-fabrication, there is no complete set of theories to explain the physical nature of laser-material interaction under the extreme conditions of ultra-fast, ultra-short and ultra-intense, and the impact of laser micro-fabrication on the material structure and its physical and chemical properties cannot be well evaluated. The next step of work still needs a lot of basic and regular research, and at the same time, we need to develop simulation and analysis software to simulate the micro-fabrication process and optimize the parameters of the laser micro-fabrication process according to the characteristics of laser micro-fabrication and the properties of the fabricated material.


NanoPrint 3D Intelligent Laser Nano-Fabrication system can be widely used in biology for surface micro-fabrication of biomaterials, preparation of medical MEMS components, processing of vascular scaffold structures, rapid prototyping of biological scaffolds and cell feeding scaffolds.


Microfluidics means 1) the miniaturization of experimental instruments and equipment (tens to hundreds of microns in size); 2) the fact that the experimental object is a fluid (nanolitres to litres in volume); 3) the control, manipulation and handling of fluids on miniaturized equipment. Microfluidics is the integration of the basic operating units of sample preparation, reaction, separation, and detection of biological, chemical, and medical analytical processes onto a micron-scale chip, which automatically completes the entire analytical process.


The microfluidic chip is the main platform for the implementation of microfluidic technology. Its most important feature is that a multifunctional integrated system and a large number of composite systems of micro-all-analysis systems can be formed on a chip. The microfluidic chip uses micromachined electrical processing technology similar to that of semiconductors to build a microfluidic system on the chip, which reproduces experimental and analytical processes on a chip structure consisting of interconnected pathways and liquid-phase chambers, loaded with biological samples and reaction solutions followed by micromechanical pumps. Methods such as electrohydraulic pumping and electroosmotic flow drive the flow of the buffer in the chip, forming a microfluidic path to perform one or more consecutive reactions on the chip.


The NanoPrint 3D intelligent laser nano-fabrication system uses a variety of detection systems such as laser induced fluorescence, electrochemistry and chemistry as well as many assays combined with analytical tools such as mass spectrometry have been used in microfluidic chips for rapid, accurate and high throughput analysis of samples.