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Optical Devices|119 Article(s)
Arbitrary focusing lens by holographic metasurface
Rongzhen Li, Zhongyi Guo, Wei Wang, Jingran Zhang, Keya Zhou, Jianlong Liu, Shiliang Qu, Shutian Liu, and Jun Gao
In this paper, an ultrathin metalens has been proposed based on a holographic metasurface that consists of elongated apertures in 40 nm gold film, which exhibit intriguing properties such as on- and off-axis focusing and also can concentrate light into multiple, discrete spots for circularly polarized incident lights. First, the spatial transmission phase distributions of the designed metalens with arbitrary focusing can be obtained by computergenerated holography. Then, the discrete phase distributions can be continuously encoded by subwavelength nanoapertures with spatially varying orientations in gold film. The simulation results show that our designed metalens can work efficiently for different types of focusing. Finally, our metasurface shows superior broadband characteristics between 670 and 810 nm, and the corresponding focal lengths of the designed lenses also can be efficiently modulated with the incident lights at different wavelengths. In this paper, an ultrathin metalens has been proposed based on a holographic metasurface that consists of elongated apertures in 40 nm gold film, which exhibit intriguing properties such as on- and off-axis focusing and also can concentrate light into multiple, discrete spots for circularly polarized incident lights. First, the spatial transmission phase distributions of the designed metalens with arbitrary focusing can be obtained by computergenerated holography. Then, the discrete phase distributions can be continuously encoded by subwavelength nanoapertures with spatially varying orientations in gold film. The simulation results show that our designed metalens can work efficiently for different types of focusing. Finally, our metasurface shows superior broadband characteristics between 670 and 810 nm, and the corresponding focal lengths of the designed lenses also can be efficiently modulated with the incident lights at different wavelengths.
Photonics Research
- Publication Date: Aug. 31, 2015
- Vol. 3, Issue 5, 05000252 (2015)
Faraday anomalous dispersion optical filter at 133Cs weak 459 nm transition
Xiaobo Xue, Duo Pan, Xiaogang Zhang, Bin Luo, Jingbiao Chen, and Hong Guo
A 459 nm Faraday anomalous dispersion optical filter (FADOF) working at the side wings of the cesium 6S1∕2 → 7P1∕2 transition with weak oscillator strength is achieved. The transmittance of the higher side wing reaches 98% at a temperature of 179°C and magnetic field above 323 G. The experimental results coincide with the theoretical predictions in 1982 and 1995, which were not realized in experiments for over three decades. Due to its high transmittance, high accuracy, and narrow linewidth, the 459 nm FADOF can be applied in underwater optical communications, the building of active optical clocks, and laser frequency stabilization in active optical clocks. A 459 nm Faraday anomalous dispersion optical filter (FADOF) working at the side wings of the cesium 6S1∕2 → 7P1∕2 transition with weak oscillator strength is achieved. The transmittance of the higher side wing reaches 98% at a temperature of 179°C and magnetic field above 323 G. The experimental results coincide with the theoretical predictions in 1982 and 1995, which were not realized in experiments for over three decades. Due to its high transmittance, high accuracy, and narrow linewidth, the 459 nm FADOF can be applied in underwater optical communications, the building of active optical clocks, and laser frequency stabilization in active optical clocks.
Photonics Research
- Publication Date: Sep. 11, 2015
- Vol. 3, Issue 5, 05000275 (2015)
Optical cross-talk reduction in a quantum-dot-based full-color micro-light-emitting-diode display by a lithographic-fabricated photoresist mold
Huang-Yu Lin, Chin-Wei Sher, Dan-Hua Hsieh, Xin-Yin Chen, Huang-Ming Philip Chen, Teng-Ming Chen, Kei-May Lau, Chyong-Hua Chen, Chien-Chung Lin, and Hao-Chung Kuo
In this study, a full-color emission red–green–blue (RGB) quantum-dot (QD)-based micro-light-emitting-diode (micro-LED) array with the reduced optical cross-talk effect by a photoresist mold has been demonstrated. The UV micro-LED array is used as an efficient excitation source for the QDs. The aerosol jet technique provides a narrow linewidth on the micrometer scale for a precise jet of QDs on the micro-LEDs. To reduce the optical cross-talk effect, a simple lithography method and photoresist are used to fabricate the mold, which consists of a window for QD jetting and a blocking wall for cross-talk reduction. The cross-talk effect of the well-confined QDs in the window is confirmed by a fluorescence microscope, which shows clear separation between QD pixels. A distributed Bragg reflector is covered on the micro-LED array and the QDs’ jetted mold to further increase the reuse of UV light. The enhanced light emission of the QDs is 5%, 32%, and 23% for blue, green, and red QDs, respectively. In this study, a full-color emission red–green–blue (RGB) quantum-dot (QD)-based micro-light-emitting-diode (micro-LED) array with the reduced optical cross-talk effect by a photoresist mold has been demonstrated. The UV micro-LED array is used as an efficient excitation source for the QDs. The aerosol jet technique provides a narrow linewidth on the micrometer scale for a precise jet of QDs on the micro-LEDs. To reduce the optical cross-talk effect, a simple lithography method and photoresist are used to fabricate the mold, which consists of a window for QD jetting and a blocking wall for cross-talk reduction. The cross-talk effect of the well-confined QDs in the window is confirmed by a fluorescence microscope, which shows clear separation between QD pixels. A distributed Bragg reflector is covered on the micro-LED array and the QDs’ jetted mold to further increase the reuse of UV light. The enhanced light emission of the QDs is 5%, 32%, and 23% for blue, green, and red QDs, respectively.
Photonics Research
- Publication Date: Jun. 23, 2017
- Vol. 5, Issue 5, 05000411 (2017)
Tunable narrowband antireflection optical filter with a metasurface
Luigi Bibbò, Karim Khan, Qiang Liu, Mi Lin, Qiong Wang, and Zhengbiao Ouyang
A narrowband tunable antireflection optical filter is proposed and numerically studied. The structure is a metasurface based on plasmonic nanoparticles on an electro-optic film in a three-layer configuration of metal-dielectric-metal (MDM) in the visible near-infrared range. By tuning the voltage and thus tuning the refractive index of the dielectric LiNbO3, one can shift the wavelength of minimum reflection as desired. The parameters of gold nanoparticles and other elements used for the filter design and refractive index of the dielectric are obtained by the finite-element method (FEM). An analytical theory is presented to explain the FEM simulation results, and they agree well with each other. It is found that the frequency of the plasmonic resonance wave on the metasurface should be equal to that of the Fabry–Perot resonator formed by the MDM to have a good filtering property. Theoretical spectra obtained by FEM simulation show that the structure has extensive potential for the design of tunable narrow-band filters for modulators, displayers, and color extraction for imaging. A narrowband tunable antireflection optical filter is proposed and numerically studied. The structure is a metasurface based on plasmonic nanoparticles on an electro-optic film in a three-layer configuration of metal-dielectric-metal (MDM) in the visible near-infrared range. By tuning the voltage and thus tuning the refractive index of the dielectric LiNbO3, one can shift the wavelength of minimum reflection as desired. The parameters of gold nanoparticles and other elements used for the filter design and refractive index of the dielectric are obtained by the finite-element method (FEM). An analytical theory is presented to explain the FEM simulation results, and they agree well with each other. It is found that the frequency of the plasmonic resonance wave on the metasurface should be equal to that of the Fabry–Perot resonator formed by the MDM to have a good filtering property. Theoretical spectra obtained by FEM simulation show that the structure has extensive potential for the design of tunable narrow-band filters for modulators, displayers, and color extraction for imaging.
Photonics Research
- Publication Date: Aug. 22, 2017
- Vol. 5, Issue 5, 05000500 (2017)
Theory of high-density low-cross-talk waveguide superlattices
Nan Yang, Huashan Yang, Hengrun Hu, Rui Zhu, Shining Chen, Hongguo Zhang, and Wei Jiang
Waveguide superlattices, a special type of waveguide arrays, can be designed to achieve very low cross talk at submicrometer/subwavelength pitches. The theoretical framework and design rationales for such waveguide superlattices will be presented in depth. Waveguide sidewall roughness can help to deter the coherent coupling between identical waveguides in nearby supercells, but it also induces random fluctuation of transmission. Statistical behavior of the transmission due to roughness in a waveguide superlattice is systematically treated. Complex transmission characteristics due to spectral oscillation and random roughness will be presented, and their evolution with the superlattice length will be analyzed.Institutions. Waveguide superlattices, a special type of waveguide arrays, can be designed to achieve very low cross talk at submicrometer/subwavelength pitches. The theoretical framework and design rationales for such waveguide superlattices will be presented in depth. Waveguide sidewall roughness can help to deter the coherent coupling between identical waveguides in nearby supercells, but it also induces random fluctuation of transmission. Statistical behavior of the transmission due to roughness in a waveguide superlattice is systematically treated. Complex transmission characteristics due to spectral oscillation and random roughness will be presented, and their evolution with the superlattice length will be analyzed.Institutions.
Photonics Research
- Publication Date: Nov. 15, 2016
- Vol. 4, Issue 6, 06000233 (2016)
All-fiber acousto-optic modulator based on a cladding-etched optical fiber for active mode-locking
Jihwan Kim, Joonhoi Koo, and Ju Han Lee
An all-fiber acousto-optic modulator (AOM), which features a compact structure and a low-driving voltage, is experimentally demonstrated for the active mode-locking of a fiber laser. The proposed AOM is based on the short length of the cladding-etched fiber, the ends of which are fixed on a slide glass. On top of the cladding-etched fiber, a piezoelectric transducer was overlaid. A chemical wet-etching technique, which is based on a mixed solution of NH4F and (NH4)2SO4, is used to reduce the fiber diameter down to ～25 μm, and the length of the etched section is only 0.5 cm. The fabricated device exhibited a modulation depth of 73.10% at an acoustic frequency of 918.9 kHz and a peak-to-peak electrical voltage of 10 V, while a laser beam was coupled at 1560 nm. By using the prepared AOM within an erbium-doped-fiber ring cavity, the mode-locked pulses with a temporal width of 2.66 ps were readily obtained at a repetition rate of 1.838 MHz. An all-fiber acousto-optic modulator (AOM), which features a compact structure and a low-driving voltage, is experimentally demonstrated for the active mode-locking of a fiber laser. The proposed AOM is based on the short length of the cladding-etched fiber, the ends of which are fixed on a slide glass. On top of the cladding-etched fiber, a piezoelectric transducer was overlaid. A chemical wet-etching technique, which is based on a mixed solution of NH4F and (NH4)2SO4, is used to reduce the fiber diameter down to ～25 μm, and the length of the etched section is only 0.5 cm. The fabricated device exhibited a modulation depth of 73.10% at an acoustic frequency of 918.9 kHz and a peak-to-peak electrical voltage of 10 V, while a laser beam was coupled at 1560 nm. By using the prepared AOM within an erbium-doped-fiber ring cavity, the mode-locked pulses with a temporal width of 2.66 ps were readily obtained at a repetition rate of 1.838 MHz.
Photonics Research
- Publication Date: Jul. 09, 2017
- Vol. 5, Issue 5, 05000391 (2017)
Tapering-induced enhancement of light extraction efficiency of nanowire deep ultraviolet LED by theoretical simulations
Ronghui Lin, Sergio Valdes Galan, Haiding Sun, Yangrui Hu, Mohd Sharizal Alias, Bilal Janjua, Tien Khee Ng, Boon S. Ooi, and Xiaohang Li
A nanowire (NW) structure provides an alternative scheme for deep ultraviolet light emitting diodes (DUV-LEDs) that promises high material quality and better light extraction efficiency (LEE). In this report, we investigate the influence of the tapering angle of closely packed AlGaN NWs, which is found to exist naturally in molecular beam epitaxy (MBE) grown NW structures, on the LEE of NW DUV-LEDs. It is observed that, by having a small tapering angle, the vertical extraction is greatly enhanced for both transverse magnetic (TM) and transverse electric (TE) polarizations. Most notably, the vertical extraction of TM emission increased from 4.8% to 24.3%, which makes the LEE reasonably large to achieve high-performance DUV-LEDs. This is because the breaking of symmetry in the vertical direction changes the propagation of the light significantly to allow more coupling into radiation modes. Finally, we introduce errors to the NW positions to show the advantages of the tapered NW structures can be projected to random closely packed NW arrays. The results obtained in this paper can provide guidelines for designing efficient NW DUV-LEDs. A nanowire (NW) structure provides an alternative scheme for deep ultraviolet light emitting diodes (DUV-LEDs) that promises high material quality and better light extraction efficiency (LEE). In this report, we investigate the influence of the tapering angle of closely packed AlGaN NWs, which is found to exist naturally in molecular beam epitaxy (MBE) grown NW structures, on the LEE of NW DUV-LEDs. It is observed that, by having a small tapering angle, the vertical extraction is greatly enhanced for both transverse magnetic (TM) and transverse electric (TE) polarizations. Most notably, the vertical extraction of TM emission increased from 4.8% to 24.3%, which makes the LEE reasonably large to achieve high-performance DUV-LEDs. This is because the breaking of symmetry in the vertical direction changes the propagation of the light significantly to allow more coupling into radiation modes. Finally, we introduce errors to the NW positions to show the advantages of the tapered NW structures can be projected to random closely packed NW arrays. The results obtained in this paper can provide guidelines for designing efficient NW DUV-LEDs.
Photonics Research
- Publication Date: Apr. 23, 2018
- Vol. 6, Issue 5, 05000457 (2018)
Embedded whispering-gallery mode microsphere resonator in a tapered hollow annular core fiber
Jiawei Wang, Xiaobei Zhang, Ming Yan, Lei Yang, Fengyu Hou, Wen Sun, Xiaotong Zhang, Libo Yuan, Hai Xiao, and Tingyun Wang
We propose and demonstrate a tapered hollow annular core fiber (HACF) coupler for excitation of whispering-gallery modes (WGMs) of an embedded microsphere resonator. The coupler is simply fabricated by fusion splicing of a segment of HACF with the single-mode fiber (SMF), and then improved by tapering the splicing joint to reduce the cone-apex angle. Therefore, the coupling efficiency from the SMF to the HACF is enhanced to excite various WGMs via evanescent field coupling. Normal positive, negative symmetrical Lorentzian and asymmetric Fano line shapes can be obtained by varying the resonator size and location. Another interesting phenomenon is observed that a higher Q-factor mode in a lower Q-factor mode has a contrast as high as 58. Temperature sensing with good stability is also demonstrated. This embedded WGM microsphere resonator in the tapered HACF is expected to promote environmental adaptability in practical applications due to its simplicity and robustness. We propose and demonstrate a tapered hollow annular core fiber (HACF) coupler for excitation of whispering-gallery modes (WGMs) of an embedded microsphere resonator. The coupler is simply fabricated by fusion splicing of a segment of HACF with the single-mode fiber (SMF), and then improved by tapering the splicing joint to reduce the cone-apex angle. Therefore, the coupling efficiency from the SMF to the HACF is enhanced to excite various WGMs via evanescent field coupling. Normal positive, negative symmetrical Lorentzian and asymmetric Fano line shapes can be obtained by varying the resonator size and location. Another interesting phenomenon is observed that a higher Q-factor mode in a lower Q-factor mode has a contrast as high as 58. Temperature sensing with good stability is also demonstrated. This embedded WGM microsphere resonator in the tapered HACF is expected to promote environmental adaptability in practical applications due to its simplicity and robustness.
Photonics Research
- Publication Date: Nov. 19, 2018
- Vol. 6, Issue 12, 12001124 (2018)
Graphene-loaded metal wire grating for deep and broadband THz modulation in total internal reflection geometry
Yiwen Sun, Riccardo Degl’Innocenti, David A. Ritchie, Harvey E. Beere, Long Xiao, Michael Ruggiero, J. Axel Zeitler, Rayko I. Stantchev, Danni Chen, Zhengchun Peng, Emma MacPherson, and Xudong Liu
We employed a metallic wire grating loaded with graphene and operating in total internal reflection (TIR) geometry to realize deep and broadband THz modulation. The non-resonant field enhancement effect of the evanescent wave in TIR geometry and in the subwavelength wire grating was combined to demonstrate a ～77% modulation depth (MD) in the frequency range of 0.2–1.4 THz. This MD, achieved electrically with a SiO2/Si gated graphene device, was 4.5 times higher than that of the device without a metal grating in transmission geometry. By optimizing the parameters of the metallic wire grating, the required sheet conductivity of graphene for deep modulation was lowered to 0.87 mS. This work has potential applications in THz communication and real-time THz imaging. We employed a metallic wire grating loaded with graphene and operating in total internal reflection (TIR) geometry to realize deep and broadband THz modulation. The non-resonant field enhancement effect of the evanescent wave in TIR geometry and in the subwavelength wire grating was combined to demonstrate a ～77% modulation depth (MD) in the frequency range of 0.2–1.4 THz. This MD, achieved electrically with a SiO2/Si gated graphene device, was 4.5 times higher than that of the device without a metal grating in transmission geometry. By optimizing the parameters of the metallic wire grating, the required sheet conductivity of graphene for deep modulation was lowered to 0.87 mS. This work has potential applications in THz communication and real-time THz imaging.
Photonics Research
- Publication Date: Nov. 21, 2018
- Vol. 6, Issue 12, 12001151 (2018)
Fabrication and properties of high quality InGaN-based LEDs with highly reflective nanoporous GaN mirrors
Dezhong Cao, Xiaokun Yang, Lüyang Shen, Chongchong Zhao, Caina Luan, Jin Ma, and Hongdi Xiao
Distributed Bragg reflectors (DBRs) are essential components for the development of optoelectronic devices. In this paper, we first report the use of the nanoporous GaN (NP-GaN) DBR as a template for regrowth of InGaN-based light-emitting diodes (LEDs). The wafer-scale NP-GaN DBR, which is fabricated by electrochemical etching in a neutral solution, has a smooth surface, high reflectivity (>99.5%), and wide spectral stop band width (>70 nm). The chemical composition of the regrown LED thin film is similar to that of the reference LED, but the photoluminescence (PL) lifetime, PL intensity, and electroluminescence intensity of the LED with the DBR are enhanced several times compared to those of the reference LED. The intensity enhancement is attributed to the light reflection effect of the NP-GaN DBR and improved crystalline quality as a result of the etching scheme, whereas the enhancement of PL lifetime is attributable to the latter. Distributed Bragg reflectors (DBRs) are essential components for the development of optoelectronic devices. In this paper, we first report the use of the nanoporous GaN (NP-GaN) DBR as a template for regrowth of InGaN-based light-emitting diodes (LEDs). The wafer-scale NP-GaN DBR, which is fabricated by electrochemical etching in a neutral solution, has a smooth surface, high reflectivity (>99.5%), and wide spectral stop band width (>70 nm). The chemical composition of the regrown LED thin film is similar to that of the reference LED, but the photoluminescence (PL) lifetime, PL intensity, and electroluminescence intensity of the LED with the DBR are enhanced several times compared to those of the reference LED. The intensity enhancement is attributed to the light reflection effect of the NP-GaN DBR and improved crystalline quality as a result of the etching scheme, whereas the enhancement of PL lifetime is attributable to the latter.
Photonics Research
- Publication Date: Nov. 19, 2018
- Vol. 6, Issue 12, 12001144 (2018)
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