Passive anti-sunlight glare traffic signs with non-axisymmetric freeform lens design.

This paper proposes a passive optical brightening element design, a non-axisymmetric freeform lens (NAFL), arranged and assembled on a traditional traffic sign. NAFL is the first optical design which can effectively solve the traffic problem that direct sunlight affects the driver's inability to look directly at the traffic sign. The NAFL can converge the sunlight behind the traffic sign and diverge forward to 150 meters away. In this way, the NAFL array combinations on the traffic sign can directly rely on sunlight as image information pixels. According to the simulation, the optical efficiency of the NAFL can be as high as 81.5%. Besides, the angular tolerance is also analyzed to evaluate the working hours of the NAFL. Finally, we made the prototype and proved that such passive brightening components could effectively improve the traffic sign's visibility in harsh sunlight.

Optical profile: A key determinant of antibacterial efficacy of photodynamic therapy in dentistry.

BACKGROUND: Periodontal disease effects 20-50% of the population worldwide, posing a global health challenge. It has been reported to be more prevalent among adults. Actinobacillus actinomycetemcomitans (A. actinomycetemcomitans) is an important organism associated with localized juvenile periodontitis. Photodynamic therapy (PDT) has been widely utilized for the treatment of periodontal disease; however, the effect of laser (light) profile on the antibacterial efficacy of PDT remains to be established. The quantitative measurement of laser profile is required to confirm the in vitro efficacy of PDT. AIM: In the present study, a low cost PDT system comprising of six copper tube waveguides (CTW) was developed to provide more uniform irradiation of the culture plate. METHODS: The antibacterial effect of PDT, in combination with 200 µg/mL methylene blue (MB) as photosensitizer and 60 sec of irradiation, was studied on A. actinomycetemcomitans and Streptococcus mutans (S. mutans). In the present case, 660 nm laser guided with unpolished CTW, polished CTW, and optical fiber waveguide (OFW) provided radiant exposure of 0.86, 1.38, and 1.36 J/cm2, respectively, for a 24-well culture plate. RESULTS: The designed PDT system provided antimicrobial efficacy of 98% and 91% for A. actinomycetemcomitans and S. mutans, respectively, which was significantly higher as compared to OFW guided PDT. CONCLUSION: The results of the study highlighted the importance of laser profile as a key parameter that determines the survival rate of bacteria at the edge of the culture plate. Thus, the dose of PDT at the margin of optical profile is important for antibacterial activity for in vitro evaluation.

Generation of a uniform-square focal spot by a compound lens for solar concentration applications.

This paper describes a compound lens for solar photovoltaic system applications, which is composed of a front aspheric or Fresnel surface and a back array of concave surfaces. In contrast to earlier designs, the proposed method can simultaneously focus and shape sun light into a uniform-square pattern on the solar cell. For a square solar cell, this approach can maximize the solar cell's opto-electric conversion efficiency by enhancing the concentrated pattern's uniformity. In this article, the theoretical models of the beam shaping focused lens is derived and then compared with experimental data. The tolerance in assembling the component of the concentrator is also analyzed and the corresponding simulation and experimental results are discussed in detail.

Dual-layer blazed grating fabricated by the roll-to-roll microreplication process for chromostereoscopy.

In this work we present the design and fabrication of a dual-layer blazed grating (DBG) to replace a single-layer blazed grating for chromostereoscopy. Based on the physiological and physical background, we first analyze the relationship between the performance of a grating pair and color-stereo effect. The DBG is composed of two materials of different indices and fabricated upon a polyethylene terephthalate film by two steps of a roll-to-roll microreplication process. With this dual-layer design, the fabrication tolerance in the blazed facets of the grating is three times looser and more achievable as compared with that of a grating composed of single material.

Surface-structured diffuser by iterative down-size molding with glass sintering technology.

In this paper, a down-size sintering scheme for making high-performance diffusers with micro structure to perform beam shaping is presented and demonstrated. By using down-size sintering method, a surface-structure film is designed and fabricated to verify the feasibility of the sintering technology, in which up to 1/8 dimension reduction has been achieved. Besides, a special impressing technology has been applied to fabricate diffuser film with various materials and the transmission efficiency is as high as 85% and above. By introducing the diffuser into possible lighting applications, the diffusers have been shown high performance in glare reduction, beam shaping and energy saving.

Enhanced rotational Bragg selectivity by use of random phase encoding in volume holographic filter.

An out-of-plane angular detection scheme with random phase encoding is proposed. A ground glass is attached on a rod, which is rotated around a center point, so that the rotation of the rod induces the displacement of the ground glass in a circular path. To enhance the rotational sensitivity we adjust the Bragg selectivity of the volume holographic optical element encoded by random phase. Therefore, the rotational sensitivity can be tuned over a large range from several degrees to ten thousandth degrees by changing the radius of rotation. The theoretical calculation, as well as experiment, is demonstrated.

Precise optical modeling for LED lighting verified by cross correlation in the midfield region.

A novel LED modeling algorithm for precise three-dimensional light pattern simulation is proposed and demonstrated. We propose to use normalized cross correlation to verify the validity of the simulation in one-dimensional intensity patterns as well as two-dimensional irradiance patterns in various midfield distances and to provide feedback to achieve a successful model. The model is demonstrated to obtain an average of 99% in normalized cross correlation between the simulation light pattern and experimental measurement for a truncated inverse pyramid LED.

Analysis of position-dependent light extraction of GaN-based LEDs.

The light extraction efficiency of GaN-based LEDs as a function of the position of the light source over the active layer is studied. Several parameters, including chip dimensions, absorption coefficients and package are analyzed on the basis of a Monte-Carlo ray tracing simulation. The light extraction efficiency of a Thin-GaN LED is studied with respect to a sapphire-based LED, including the surface texture.