Mr. Jinchao Lu Profile

Jinchao Lu

at Suzhou Univ

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Publications (4)

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Proceedings Article | 9 October 2021 Poster + Paper

Study on the immersion grating with dielectric film

Zongqing Wu, Quan Liu, Jinchao Lu, Nenghua Zhou, Bin Huang

Proceedings Volume 11898, 1189820 (2021) https://doi.org/10.1117/12.2602757

KEYWORDS: Diffraction gratings, Diffraction, Spectroscopy, Refractive index, Polarization, Prisms, Atomic layer deposition

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Imaging spectrometer is an important optical instrument for monitoring the content of carbon dioxide (CO2) in the atmosphere. Using an immersion grating as the dispersive element in the spectrometer can significantly reduce the size of the grating while maintaining the same spectral resolution. The immersion grating with dielectric film is one of the key elements in greenhouse gases imaging spectrometer. In this paper, the quartz immersed grating was designed for weak CO₂ band. The rectangular groove structure with high refractive index dielectric film was designed in consideration of possible fabrication errors. In the 1.595 ~ 1.625 μm band, the duty cycle of the rectangular groove is 0.3 to 0.35, the thickness of TiO₂ is 110 to 125 nm, and the grating groove depth is 560 to 640 nm, the diffraction efficiency can reach more than 80%. When the duty cycle is 0.4~0.45, the TiO₂ thickness is 95~105 nm, and the grating groove depth is 570~700 nm, the diffraction efficiency can reach more than 80%. For the trapezoidal groove, when the duty cycle is 0.3~0.35, the bottom angle of the trapezoid is 82°~86°, the thickness of TiO₂ is 120~125 nm, and the grating groove depth is 565~620 nm, the diffraction efficiency can reach more than 80%. When the thickness of TiO₂ is 115~120 nm, the overall degree of polarization is less than 0.1.The immersed grating with the period of 697nm in a quartz substrate of 245 mm × 138mm will be fabricated by holographic lithography - ion beam etching in late 2021. The TiO₂ film will be deposited by atomic layer deposition.

Proceedings Article | 4 December 2020 Paper

Study on the silica immersed grating for the short-wave infrared

Quan Liu, Jinchao Lu, Zongqing Wu, Jianhong Wu

Proceedings Volume 11617, 116173I (2020) https://doi.org/10.1117/12.2585464

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Due to the addition of immersion medium, when the diffraction happens in high refractive index medium, the optical path difference and angular dispersion will increase proportionally. Therefore, when immersed grating is used in imaging spectrometer, it will have higher resolution, higher angular dispersion and more compact instrument structure. In this sense the immersed grating is one of the key elements in greenhouse gas hyperspectral spectrometers. In this paper, we have designed the immersed grating with high diffraction efficiency for the atmosphere methane spectral band (the shortwave infrared). The diffraction characteristics of the immersed grating have been investigated by using rigorous coupled wave theory. The simulation showed: the groove depth and duty cycle of the immersed grating must be controlled within the range of 1050nm-1100nm and 0.3-0.36 respectively, in order to guarantee the 1 order diffraction efficiency would be over 80% at wavelength 2300nm. The immersed grating with the period of 1319nm in a silica substrate of 120 mm x 95mm will be fabricated by holographic lithography - ion beam etching in late 2020.

Proceedings Article | 18 November 2019 Paper

Research on slanted trapezoidal surface relief grating

Jinchao Lu, Quan Liu, Shuangshuang Huang

Proceedings Volume 11188, 1118828 (2019) https://doi.org/10.1117/12.2538776

KEYWORDS: Diffraction gratings, Diffraction, Planar waveguides, Waveguides, Holography, Augmented reality, Superposition, Virtual reality, Head-mounted displays, Optical design

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With the rapid development of augmented reality technology, people can clearly see the superposition of virtual and real world images at the same time. The diffractive optical waveguide has obvious advantages over the geometric optical waveguide because of its high diffraction efficiency, light weight and difficulty in generating ghost images. Therefore, the use of holographic gratings as coupling elements for planar waveguides has been widely used in head-mounted display systems. Because high efficiency grating is required as coupling element in coupling, we use slanted trapezoidal surface relief grating as coupling element of the planar waveguide. In this paper, a slanted trapezoidal surface relief grating has been designed as a high-efficiency coupling element with a grating period of 520 nm and a material of BaK₃ glass with a refractive index of 1.54. By optimizing the structure of the slanted grating, the relationship between the groove parameters and the diffraction efficiency of the slanted rectangular grating and the slanted trapezoidal grating is analyzed in detail. The results show that under the normal incidence of light at 630 nm, the groove depth is 450 nm, and the slant angle θ1 is 40°, when the -1 order diffraction efficiency of the TE polarized light is higher than 80%, the ranges of the slant angle θ₂ and of the maximum diffraction efficiency value would be obtained. This can greatly improve the coupling efficiency of the holographic planar waveguide.

Proceedings Article | 18 November 2019 Paper

Research on high efficiency immersed holographic grating

Shuangshuang Huang, Quan Liu, Jinchao Lu

Proceedings Volume 11188, 111881Z (2019) https://doi.org/10.1117/12.2537684

KEYWORDS: Polarization, Holography, Carbon dioxide, Diffraction gratings, Diffraction, Quartz, Sensors, Optical design, Spectroscopy, Climate change

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Nowadays, the monitoring of CO₂ concentration has gradually become the focus of scientists all over the world. In order to study the effects of CO₂ on climate change and global ecosystems, hyperspectral and high spatial resolution CO₂ detectors are necessary. Holographic grating is the core element of that CO₂ detectors, and the immersion holographic grating can greatly improve the resolution of grating and reduce the volume of spectrometer. Therefore, it is necessary to take research on immersion grating. In this paper, we have designed and optimized a quartz immersion grating used in the CO₂ detectors. We have designed and optimized the parameters of the grating, such as the width ratio and groove depth, according to the requirements of the spectrometer used and the actual fabrication errors, we designed and optimized rectangular and trapezoidal groove with different bottom angles to obtain high efficiency and low polarization-dependent immersion gratings. In the 2.04-2.08 μm band, with rectangular groove, the groove depth of the quartz immersion grating is 950 nm, the duty cycle is 0.7, the -1 order diffraction efficiency is over 82%, and the degree of polarization is below 12%. When the groove is trapezoidal and the bottom angle is 85 degrees, the -1 order diffraction efficiency is over 79% and the degree of polarization is below 10% at duty cycle of 0.63 and groove depth of 1050 nm. Then under the trapezoidal groove with a bottom angle of 80 degrees, when the duty cycle is 0.62 and the groove depth is 1100 nm, the -1 order diffraction efficiency is over 81% and the degree of polarization is less than 9%. Finally, we will fabricate a sample of immersion grating with a period of 1117 nm on a quartz substrate by holographic ion beam etching in late 2019.

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