GIPO newsletter

Multi-resonant optical parametric oscillator based on 2D-PPLT nonlinear photonic crystal

Professor Lung-Han Peng

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

In a recent collaborative work of Prof. Lung-Han PENG with Prof. Azzedine BOUDRIOUA (Galilee Institute, U. Paris 13, France) via Dr. Lazoul, and Prof. Simohamed of Ecole Militaire Polytechnique (Algeria), the authors made a report on Optic Letters regarding a multi-resonant optical parametric oscillator based on 2D nonlinear photonic crystals (NPC) periodically poled lithium tantalate (PPLT). This work takes advantage of the abundant multi-reciprocal lattice vectors uniquely prevailed in 2D-PPLT (developed at NTU) such that simultaneous multi-wavelength optical parametric oscillations (OPO) can take place. In comparison, for the conventional 1D case, wavelength tuning of OPO has to be taken by sequentially changed the grating vectors of the transversely-displaced quasi-phase-matching structures of the NPC, or by angle- or temperature-tuning of a single-QPM grating NPC. Figure 1 illustrated the experimental setup performed at the Laboratory of Laser Physics, Galilee Institute of U. Paris 13, and Fig.2 demonstrated multi-wavelength coverage when the incident power of a 532nm green pump laser is (a) below the oscillation threshold for optical parametric generation (b) near the oscillation threshold, and (c) 1.5 times of the oscillation threshold.

Ref: Mohamed Lazoul, Azzedine Boudrioua, Lotfy-Mokhtar Simohamed, and Lung-Han Peng, “Multi-resonant optical parametric oscillator based on 2D-PPLT nonlinear photonic crystal,” Opt. Lett. 40, 1861 (2015).

Laser-diode pumped glass-clad Ti:sapphire crystal fiber laser

Professor Sheng-Lung Huang’s laboratory

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

Titanium (Ti):sapphire crystals have become one of the most widely used solid-state laser gain media. Their broadband emission spectra are suitable for a wide range of applications, such as tunable lasers and mode-locked lasers, although their low absorption cross section and short lifetime prevent them from low threshold operations. In this work, efficient glass-clad crystal fiber lasers were demonstrated using a Ti:sapphire crystalline core as the gain medium. With a core diameter of 18 μm, the laser diode (LD) pump source can be effectively coupled and guided throughout the crystal fiber for a low threshold and high slope efficiency laser operation. The advantage of high heat dissipation efficiency of the fiber structure can be derived from the low core temperature rising measurement (i.e. 17 K/W) with passive cooling. At an output transmittance of 23%, the lowest absorbed threshold of 118.2 mW and highest slope efficiency of 29.6% were achieved, with linear laser polarization.

Fig. 1. SEM images of (a) end face of a glass-clad Ti:sapphire crystal fiber and (b) side face of a Ti:sapphire crystalline core; TEM images of (c) crystalline sapphire core and (d) interface of core and borosilicate clad. Dashes outline the 2-nm overlapping layer.

Fig. 2. (a) 520-nm LD pumped glass-clad Ti:sapphire crystal fiber laser scheme, (b) L-I curve by 520-nm LD pumping, (c) lasing spectra at different pump powers, (d) laser polarization measurement, and (e) lasing transverse mode profile. LPF: long wavelength pass filter; the red line in (b) is the simulation result. PM: power meter; OSA: optical spectrum analyzer.

Reference:

S. C. Wang, C. Y. Hsu, T. T. Yang, D. Y. Jheng, T. I Yang, T. S. Ho, and S. L. Huang, “Laser-diode pumped glass-clad Ti:sapphire crystal fiber laser,” Optics Letters, 41, pp. 3217–3220, 2016.

Noninvasive third harmonic generation microscopy reveals the dietary evolution in the ultrastructure of dinosaur teeth

Professor Chi-Kuang Sun

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

Fossilized teeth are primary tools in the study of vertebrate evolution, but standard imaging modalities have not been able to provide high-quality image contrast and 3D information inside dentin, the main component of teeth, owing to small refractive index differences in the fossilized tissues. Our first attempt to use third harmonic generation (THG) microscopy in numerous fossil teeth, spanning 300 Ma of vertebrate history, has yielded significant submicron level anatomy, with an unexpectedly strong THG signal contrasting fossilized tubules from the surrounding dentin. Morphometric analyses of dentinal tubule diameter, density, and branching rates provide strong phylogenetic signatures and reveal patterns consistent with evolutionary relationships among various groups of amniotes, including dinosaurs. These morphometric analyses reveal a strong signal for dietary preferences, with herbivorous saurischian and ornithischian dinosaurs consistently having higher dentinal tubule density than their carnivorous relatives. We hypothesize that this relates to the hardness of the dentine, where herbivorous taxa have dentine that is more resistant to breakage and wear at the dentine-enamel junction than carnivorous taxa. Our results also represent the only successful imaging of dentinal tubules in fossilized tissues while maintaining a sub-micron resolution, providing non-invasive 3D histological reconstruction in intact fossil teeth, demonstrating the great potential of our developed harmonic generation microscopy for the evolutionary studies of vertebrates. This work is in collaboration with Robert R. Reisz, University of Toronto Mississauga, Canada, Dar-Bin Shieh, National Cheng Kung University, and Timothy D. Huang, a dinosaur lover.

Figure 1: One of the Harmonic Generation Microscopes (HGM) built and designed in Prof. Sun’s laboratory. HGM was designed for noninvasive clinical microscopy imaging on human skin and mucosa, while with a world-record performance on resolution, penetration depth, and bio-viability. Its operating wavelength is at 1260 nm, and can penetrate even the darkest skin. Obviously it is also perfect for fossil studies.

Figure 2: Optically-sectioned 2D third-harmonic-generation microscopic images of the dentine-enamel junction from various fossil teeth. All scale bars, 20 μm. For animal’s outlook and their ages, please refer to Figure 3 and Figure 4. For 3D images, please refer to our references.

Figure 3: The imagination reconstruction of the ancient vertebrates where our fossil teeth came from. One to one correspondence on the relative position with respect to Figure 2 can be found. We appreciate all the sources where the pictures are from.

Figure 4: Results of morphometric analysis of dentinal tubules. (A) Bivariate plot of dentinal tubule density mean, tubule branching mean, and diameter. The sizes of the colored circles are representative of tubule diameter. The colors of the circles match the taxa in the phylogeny (B), which contains all taxa examined in this study. a, Cotylosauria; b, Amniota; c, Synapsida; d, Archosauria; e, Crocodylia; f, Dinosauria; g, Ornithischia; h, Saurischia. Abbreviation: Ma, Millions of years.

Reference:

Y.-C. Chen, S.-Y. Lee, Y. Wu, D.-B. Shieh, K. Brink, T. D. Huang, R. R. Reisz, and C.-K. Sun, “Third harmonic generation microscopy reveals dental anatomy in ancient fossils,” Optics Letters 40 (7), pp. 1354-1357 (2015).

K. S. Brink, Y.-C. Chen, Y.-N. Wu, W.-M. Liu, D.-B. Shieh, T. D. Huang, C.-K. Sun, and R. R. Reisz, “Dietary adaptions in the ultrastructure of dinosaur dentine,” to appear in Journal of the Royal Society Interface.

Localized surface plasmon-enhanced photoluminescence of amorphous silicon quantum dots through plasmonic subwavelength crossed metallic gratings

Professor Hoang-Yan Lin

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

We investigate experimentally the enhancing effect of plasmonic subwavelength crossed Ag gratings on photoluminescence (PL) from the amorphous silicon quantum dots (a-Si QDs) embedded in a central silicon-rich SiO_x film of the Ag/SiO_x:a-Si QDs/Ag sandwich nanostructures (Fig. 1). The use of the crossed Ag grating structure as the top layer in the sandwich nanostructures results in a 2-fold increase in the PL peak intensity and a 1.34-fold increase in the integrated emission intensity compared with the use of a one-dimensional (1D) Ag grating top layer, and a 1.53-fold peak intensity increase compared with that of a SiO_x:a-Si QDs/Ag structure without a Ag top layer (Fig. 2). These significant PL enhancements can be attributed to the high light-extraction efficiency of the polarization-independent crossed metallic grating structure, the strong out-coupling of localized surface plasmons (LSPs), and the strong a-Si QD–LSP coupling. (Japanese Journal of Applied Physics 55, 04EH15 (2016))

Fig. 1. Schematic structures of the trilayer Ag=SiO_x:a-Si QDs=Ag sandwich nanostructures on a Si substrate with (a) 1D Ag grating and (b) symmetric crossed Ag grating on the top.

Fig. 2. (a) PL spectra of the sample without Ag top layer, and the planar Ag thin film, 1D Ag grating, and crossed Ag grating MIM samples. (b) Polarization-dependent PL spectra of the 1D and crossed Ag grating samples.

Laser Diode LiFi and MMW-Over-Fiber Link

Professor Gong-Ru Lin’s Laboratory

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

Phosphorous Diffuser Diverged Blue Laser Diode for Indoor Lighting and Communication

A phosphorous diffuser diverged blue GaN laser diode (LD) is successfully demonstrated for both indoor luminescent white-lighting and optical wireless communication over a 60-cm free-space link, which represents a current state-of-the-art performance for carrying orthogonal frequency-division multiplexed 16-quadratureamplitude modulation (16-QAM OFDM) data at 5.2 Gbit/s, as illustrated in Fig. 1. As a result, the luminescent phosphor doped diffuser diverges the blue laser beam to a white-light spot covering a radiant angle of 120 degree with CIE coordinates of (0.34, 0.37), as shown in Fig. 2. As displayed in Fig. 3, the phosphorous diffuser diverged luminescent light spot exhibits its ability to carry the 5.2-Gbit/s 16-QAM OFDM data with an error vector magnitude of 17.3%, a signal-to-noise ratio (SNR) of 15.3 dB and a bit error rate (BER) of 3.6×10⁻³.

Fig. 1 The blue LD with phosphorous diffuser for luminescent white-lighting and optical wireless OFDM communication over a 60-cm free-space link.

Fig. 2 The light distribution in polar coordinate and the chromaticity coordinates result.

Fig. 3 The subcarrier SNRs and related constellation plot of the 5.2-Gbit/s 16-QAM OFDM data.

60-GHz Millimeter-wave Over Fiber with Directly Modulated Dual-mode Laser Diode

A directly modulated dual-mode LD (DMLD) with third-order intermodulation distortion (IMD₃) suppression is proposed for a 60-GHz millimeter-wave over fiber (MMWoF) architecture, enabling new fiber-wireless communication access to cover 4-km single-mode-fiber (SMF) and 3-m wireless 16-QAM OFDM transmissions, as depicted in Fig. 4. By dual-mode injection-locking, the DMLD mitigates its throughput degradation with saturation effect to reduce the threshold, IMD₃ power and relative intensity noise to 7.7 mA, −85 dBm and −110.4 dBc/Hz, respectively. After 4-km SMF and 3-m free space transmissions, the optical receiving power is optimized to restrict the power fading effect for improving the BER to 1.9×10⁻³ and the receiving power penalty to 1.1 dB, as shown in Fig. 5. Such DMLD based hybrid architecture for 60-GHz MMW fiber-wireless access can directly cover the current optical and wireless networks for next-generation indoor and short-reach mobile communications.

Fig. 4 The DMLD based hybrid architecture for 60-GHz MMW fiber-wireless access can cover the current optical and wireless networks for indoor communications.

Fig. 5 (Left) The schematic diagram for 60-GHz wireless access architecture. (Right) The BER response and constellation plots of the DMLD carried 16-QAM OFDM data after SMF and 3-m free space transmissions.