Off-axis Fresnel Lens Research Articles

Wavefront measurement of a large aperture high image quality off-axis Fresnel lens.

Large aperture off-axis Fresnel lens will play an important role in the future 10 m scale aperture transmission space telescope system. Improving diffraction efficiency and wavefront image quality is always the goal of engineering applications. A 4-level off-axis fresnel lens with Ф350 mm effective aperture was fabricated through overlay etching technique by laser direct writing system. The wavefront aberration characteristics of the off-axis Fresnel lens at 632.8 nm wavelength are analyzed and discussed in detail, and the large aperture off-axis Fresnel lenses wavefront aberration measurement scheme, including a high-precision plane reflector, measured LAOFL, CGH, interferometer and laser tracker to compensate for certain low-order aberrations caused by LAOFL imperfect imaging, is proposed. Wavefront aberration of 0.020 λ(1/50 λ) RMS was achieved. This work presented the best results to our knowledge among the same field with similar aperture in open publications and provided a strong foundation for the future 10 m scale aperture transmission space telescope system.

Large aperture high diffraction efficiency off-axis Fresnel lens fabrication and analysis.

Large aperture high diffraction efficiency off-axis Fresnel lens is one of the most important optical elements in future 10m scale aperture transmissive space telescope systems. Improving diffraction efficiency and effective aperture are long-term goals and bottlenecks for engineering applications. A 4-level off-axis fresnel lens with Ф350 mm effective aperture and 2 µm critical dimension was fabricated through overlay etching technique bylaser direct writing system. Average diffraction efficiency of 75.9% was achieved and certain distribution pattern was observed. Influence of alignment errors on diffraction efficiency distribution was analysed and discussed in detail. This work presented the best results to our knowledge among the same field with similar aperture and critical dimension in open publications, and layed a solid foundation for future large aperture diffractive telescope development.

Transversely pumped solar Nd3+-doped fiber laser

In order to improve the coupling efficiency of solar fiber lasers, a new kind of transversely pumping geometry is proposed. A two-stage concentration system is designed to concentrate the sunlight into the Nd-doped fiber coiled in a ring chamber with high-reflective inner surfaces. The primary concentrator is an off-axis Fresnel lens with a radius of 600 mm, and the secondary concentrator is a compound parabolic optical waveguide. With this concentration configuration, the collection efficiency can be as high as 21.4%. 73.5 W solar power is absorbed by the fiber core according to ray-tracing simulation. Output characteristics of the solar fiber laser are further analyzed by calculating the rate equations. 2.6 W laser output is obtained and the slope efficiency reaches 3.7%.

Electronic holographic three-dimensional display with enlarged viewing angle using non-mechanical scanning technology

A non-mechanical scanning method based on a liquid-crystal spatial light modulator (LC-SLM) is proposed to increase the viewing angle of electronic holographic three-dimensional (3D) displays. A scanning off-axis Fresnel lens is simulated by the LC-SLM to deflect the reconstructed light beam. Using the time-division multiplexing method, the viewing zones are sequentially projected to different positions. When the eyes of the observer are located at the viewing zones, the reconstructed 3D images can be observed. The experimental results and analyses show the feasibility and advantages of the proposed method.

Depth of field multiplexing in microscopy

We demonstrate "depth of field multiplexing" by a high resolution spatial light modulator (SLM) in a Fourier plane in the imaging path of a standard microscope. This approach provides simultaneous imaging of different focal planes in a sample with only a single camera exposure. The phase mask on the SLM corresponds to a set of superposed multi-focal off-axis Fresnel lenses, which sharply image different focal planes of the object to non-overlapping adjacent sections of the camera chip. Depth of field multiplexing allows to record motion in a three dimensional sample volume in real-time, which is exemplarily demonstrated for cytoplasmic streaming in plant cells and rapidly swimming protozoa.

Diamond cutting of a large off-axis Fresnel lens Mold

The oxygen-free copper (OFC) is often used for the substrate material of the molds for the hot hydraulic press, the injection, and the light guide plate. The diamond cutting is usually used for the high precision finish process of the nonferrous metals. In this article, an OFC mold, which is used for testing the hot hydraulic press process of the large segmental double-side polymethyl methacrylate (PMMA) Fresnel lens, was designed. The rotary radius of this mold is about 1000mm and the mold must be fabricated to the high form accuracy and the low surface roughness. According to the conventional machining method, a rotary table with the radius larger than 1000mm is necessary for fabricating this mold. However, this mold is justly used for the first test of the hot hydraulic press of the large segmental double-side PMMA Fresnel lens. Thus, the fabrication of this mold should be carried out at the lower cost using the holding machine tool. In order to cut this mold on an ultraprecision air hydrostatic bearing rotary table of 500mm in diameter, a special method was proposed by the authors of this article. In this experiment, the diamond cutting process of the mold was investigated. The single crystal diamond cutting tool with the tip radius of 1μm was used at the depth of cut 1μm for the finish process in order to get the mold with the very small groove corner. After the finish cutting process, the surface has a very low roughness.

Assessment of integration of off-axis Fresnel lenses into a free-space interconnect

The integration of multiple optical functions into a single optical element is often seen as advantageous to improve practicality and/or performance. In free-space devices, a common way to achieve this is to use off-axis Fresnel lenses to simultaneously collimate and redirect light. We study the impact of this type of integration on assembly tolerances and performance of a free-space interconnect designed to format a one-dimensional set of inputs into a two-dimensional array. Two systems are built and compared: one where light collimation and redirection are performed by different elements and one where these functions were combined into off-axis Fresnel lenses. The integrated system has lower losses but exhibits higher polarization sensitivity.