Domestic self-developed FIS4 series four wave shear wavefront sensor: ushering in a new era of quantitative phase imaging and micro nano measurement

1、 Introduction: When Wavefront Measurement Meets the 'Four Waves' Revolution

In cutting-edge fields such as semiconductor lithography, precision optical manufacturing, laser beam diagnostics, and biomedical imaging, the demand for measuring wavefront aberration, surface shape, and beam quality is becoming increasingly stringent. Although traditional interferometric measurement technology has extremely high measurement accuracy, it has long been limited by core pain points such as complex optical path structure, high sensitivity to environmental vibrations, and difficulty in aligning and adjusting reference mirrors. It is difficult to step out of the constant temperature vibration isolation laboratory and face the real environment of industrial sites.

The research and development team led by Professor Yang Yongying from Zhejiang University has made great efforts to develop and officially launched the FIS4 series four wave shear wavefront sensor. Based on the principle of four wave transverse shear interferometry (QWLSI), it is redefining the technical boundary of quantitative phase imaging and wavefront measurement with the unique advantages of single optical path self interference, no reference mirror, and no isolation platform.

2、 Principle Unveiled: The 'Decoding Secret Language' of Four Beams of Light

The core of FIS4 lies in a precise randomly encoded hybrid grating. When the incident beam passes through the grating, it is decomposed into four symmetrically propagating transverse shear coherent wavelets, which are superimposed on the detector plane to form an interferogram containing rich wavefront gradient information.

The system only requires a single interferogram to calculate the wavefront gradient, and then reconstruct quantitative parameters such as optical path difference (OPD), phase distribution, surface morphology, and refractive index difference of the target.

The brilliance of this architecture lies in the fact that all optical paths are designed as a common optical path, greatly suppressing the impact of vibration and temperature drift on measurement. Without the need for precise reference mirror calibration with traditional interferometers, high-precision wavefront detection can truly achieve 'test as you want'.

3、 Six core advantages: redefining the measurement experience

① Non contact non-destructive measurement

Completely non-contact measurement, without damaging the surface of wafers, optical components or biological samples, especially suitable for non-destructive testing of fragile or expensive samples. A beam of light is the gentlest probe.

② Common light path anti-interference, bidding farewell to 'vibration anxiety'

Adopting a common optical path interference architecture, no reference mirror or isolation platform is required. The four shear waves of FIS4 share the same source and path - the vibration is synchronized and shifted, and the phase difference between them remains unchanged. It's not about using algorithms to 'filter' vibrations, but about making them less likely to affect the interference results. Even under normal workshop conditions or temperature and humidity fluctuations, it can still maintain a high phase resolution of ≤ 2nm RMS, truly achieving the goal of 'testing as needed, testing as needed'.

③ Plug and play, easily integrated into existing microscopes

The FIS4 series sensors adopt a standard interface design, are compact in size, and can be directly installed in existing optical systems or microscopes without the need for complex optical path modifications, making them ready to use. Instantly upgrade ordinary optical platforms to quantitative phase imaging systems, significantly reducing user upgrade costs.

④ Wide spectral range, fearless of coherent noise, adaptable to multiple scenarios

The FIS4 series covers the 200nm to 1400nm wavelength range - FIS4-UV (200-400nm) is designed specifically for UV lithography detection, FIS4-HR (400-1100nm) covers visible to near-infrared universal detection, FIS4-UHR (400-1100nm) provides 512 × 512 ultra-high resolution, and FIS4-NIR (900-1200nm) is suitable for near-infrared detection of internal lattice distribution of materials. Support continuous laser, pulse laser LED、 Multiple light sources such as halogen lamps, with wide spectral adaptability. When using a broadband light source, coherent noise can be effectively suppressed, resulting in purer interference images. Match different frequency band scene requirements.

⑤ Single frame imaging, with speed reaching the camera frame rate limit

Traditional interferometric measurements often require multiple phase shifts, which are time-consuming and unable to capture dynamic processes. The FIS4 series single frame interferogram can complete wavefront reconstruction, with a camera sampling rate of up to 32fps (real-time processing rate of 5-10Hz at full resolution), meeting real-time application requirements such as dynamic observation of live cells, transient flow field monitoring, and laser transient process analysis.

⑥ Domestic self-developed, independently controllable

From randomly encoded hybrid grating design to wavefront reconstruction algorithm, the FIS4 series achieves full technology chain autonomous controllability. The technology originates from Professor Yang Yongying and his team's years of accumulation in four wave shear interferometry technology at Zhejiang University, and has obtained multiple national invention patents.

4、 Diversified Applications: A Wide Field from Semiconductors to Biomedicine

（1） Semiconductor and Microelectronics Manufacturing

▶ Surface roughness detection of wafers: nanometer level resolution, precise evaluation of polishing quality

▶ Measurement of silicon wafer surface shape: non-destructive measurement of wafer surface flatness and warpage

▶ Characterization of Microlens Array: Quickly Obtaining the Surface Shape and Curvature Radius of Each Lens in the Array

（2） Precision optical manufacturing

▶ Optical lens surface measurement: accuracy testing of flat, spherical, and non spherical surfaces, with measurement repeatability better than 1/1000 λ

▶ Optical window detection: Transmission wavefront measurement, evaluation of imaging quality

▶ Laser damage micro defect detection: quantitative analysis of laser-induced micro damage pit depth and volume

（3） Laser Beam Diagnosis and Adaptive Optics

▶ Laser beam wavefront detection: real-time measurement of wavefront distortion and waist position, supporting beam quality analysis

▶ Adaptive optics closed-loop feedback: providing real-time wavefront data for deformable mirrors to achieve precise correction

（4） Biomedical imaging

▶ Unlabeled dynamic observation of live cells: no staining labeling required, real-time recording of cell growth, division, and migration processes

▶ Phase imaging of tissue slices: providing a new quantitative method for drug screening and tumor research

（5） Frontier scientific research

▶ Metasurface and meta lens wavefront characterization: precise quantification of phase modulation characteristics of subwavelength structures

▶ Pneumatic optics and high-speed flow field measurement: combined with high-speed cameras to achieve kHz level transient wavefront capture

5、 Speak with data, verify with actual testing

In a recent grating sample transmission wavefront testing, engineers used FIS4-NIR (working band 1064nm) to systematically detect the 0-level and ± 1-level beam splitting spots of the grating sample under normal optical platform and non isolated conditions. The lowest RMS in the 0-level region is 2.74nm, and the wavefront data in the ± 1-level region is stable and reproducible. The entire testing process can be completed within tens of minutes without the need for vibration isolation or complex optical path debugging.

Have you tried the FIS4-NIR wavefront sensor for grating device wavefront detection?

6、 Let the measurement go out of the isolation laboratory

The emergence of FIS4 wavefront sensor is not only a major technological breakthrough in the field of wavefront detection, but also a precise response to the pain points of industry demand:

▶  Lowering the entry threshold: Without the need for complex optical path modifications, high-precision interferometric measurement capabilities can be obtained on ordinary desktops and production lines.

▶  Improve measurement efficiency: single frame imaging, no need for phase shift, easy capture of dynamic processes, and significantly reduced beat time.

▶  Expanding application boundaries: Extending from traditional optical measurement to cover multiple cutting-edge emerging fields such as biomedical, semiconductor manufacturing, aerospace, etc., to achieve nanoscale stable wavefront detection in industrial fields.

▶  Promote domestic substitution: With independently developed core technologies, provide reliable and controllable measurement solutions for high-end manufacturing and scientific research in China.

7、 Conclusion: Using light as a ruler, measure every inch of the microscopic world with brilliance

From nanoscale surface shape detection of semiconductor wafers to high-precision wavefront characterization of ultraviolet lithography objectives; From the full lifecycle quality control of precision optical components to the label free dynamic observation of living biological cells, the FIS4 four wave shear interference wavefront sensor sets a new measurement standard for the microscopic world with the most precise ruler of 'light'.