GIPO newsletter

MBE growth of the highly mismatched alloy InAsPSb

Professor Hao-Hsiung Lin

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

The two binaries consisting of alloy InPSb are very different in bond properties which make the bonds in the alloy suffer from very large distortion. In such alloy, the atoms deviate from their lattice points, resulting in peculiar electronic and optic properties. In this work we performed temperature dependent XRD measurement to probe Debye-Waller’s factor, from which the mean square of the atomic deviation can be extracted. For comparison, binary InAs and alloy InPSb were measured. The atomic deviation in binary InAs is attributed to thermal vibration. In addition to thermal vibration, InPSb shows a large static deviation, whose root mean square value is 0.28Å.

Fig.1 Bond distortion in InPSb

Fig.2 (a) Ω-2θ scans of (002), (b) Ω-2θ scans of (006) at 15K

Fig.3 Linewidths of different reflection

Fig.4 Mean square displacement <u²> versus temperature

Environmentally Friendly Fluorescent Materials without Rare-Earth Elements for Head-Up Display

Professor Ching-Fuh Lin

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

Head-up display nowadays can be divided into two main types: penetrating (with optical lens group) and projection (without optical lens group). The penetrating type mainly uses the lens group to design the optical path and project the information out of the windshield in front of driver about one meter. In general, this method requires a lens set to focus the optical path and increase the distance of the projected image. Since the lens set will reduce the intensity of the light, the light source needs to be equipped with a high brightness, so the design is complicated and costly. The projection type is mainly used by micro-projector, which projects the image on the reflective film on the windshield. However, the position of the sticking reflective film between the position of the head-up display must be adjusted so that the image can be correctly projected onto the driver's eye. In addition, reflection type is dependent on highly reflective surface to show the image. As a result, its transmission is low, so drivers cannot see the views outside of the windshield clearly.

In order to improve the low transmission and the strict limit of reflective angle, we proposed a non rare-earth fluorescence film to replace the reflective film. Also, we combine the non rare-earth fluorescence film with the blue display device as a head-up-display configuration. Compared with the reflective film, our self-made luminescent film has several advantages. For example, we take the mechanism of photoluminescence, so it possesses high transmission and high display effect. Furthermore, the film is based on photoluminescence. The viewing angle is much broader than the reflective film. In addition, we convert the less sensitive blue light of the human eye into the most sensitive green light of the human eye, so we can have a more obvious display effect under the same projection power. Finally, the fluorescent display film has a grain-free boundary in appearance, no uneven surface, no frosted glass, high transparency, hence providing the high potential for head-up display in the future.

Fig. 1. 2. The transmission between commercial film and fluorescence film; absorption of fluorescence film

Fig. 3. 4. The outward projection image of fluorescence film

Multiwavelength generation from multi-nonlinear optical process in a 2D PPLT

Professor Lung-Han Peng

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

In a collaboration with University of Paris 13, Prof. Lung-Han PENG and Prof. Azzedine BOUDRIOUA recently have a joint publication “Multiwavelength generation from multi-nonlinear optical process in a 2D PPLT,” published in Opt. Exp. 25, 30253 (2017)”

In this work, two-dimensional nonlinear photonic crystals made of lithium tantalite square lattice structures with periodicity of 8.5μm х 8.5μm, and size of 2cm long and 1cm wide were prepared for investigating the nonlinear optical processes. With increase of green pump intensity (Fig.1) from 50 MW/cm² to 260 MW/cm², we observed progressive multi-wavelength generation in spectral range from 400nm to 1650nm with increase of peak intensity and blue shifting in the newly generated wavelength. Further analyses indicate that the optical signals were ascribed to the quasi-phase-matching processes due to second harmonic generation, sum-frequency generation and other frequency conversion in a cascade process. These conversions are assisted by all the optical nonlinear process involving χ(2) and achieved by satisfying the quasi-phase matching conditions.

Reference: Zohra Yellas, Min Won Lee, Régis Kremer, Kai-Hsun Chang, Mahmoud R. Beghoul, Lung-Han Peng, and Azzedine Boudrioua, “Multiwavelength generation from multi-nonlinear optical process in a 2D PPLT,” Opt. Exp. 25, 30253 (2017).