Directional emission in X-cut lithium niobate microresonators without chaos dynamics
Ang Gao, Chen Yang, Likun Chen, Ru Zhang, Qiang Luo, Wei Wang, Qitao Cao, Zhenzhong Hao, Fang Bo, Guoquan Zhang, and Jingjun Xu
We systematically investigate the field distribution of the transverse electric modes in X-cut lithium niobate disks as an example of circular microcavities with anisotropic refractive index. A conserved quantity is discovered, which indicates the absence of chaos that generally exists in deformed microcavities and leads to a nontrivial directional emission. The emission directionality was theoretically investigated and experimentally verified by exciting high-order modes of an X-cut lithium niobate microresonator assisted with second harmonics. The field distribution analysis can enrich the knowledge in designing photonic devices that need precise control of field distribution, such as phase matching in nonlinear processes. Furthermore, the discovered emission phenomenon is momentous in enhancing and controlling communications between on-chip photonic devices.
  • Jan. 13, 2022
  • Photonics Research
  • Vol.10 Issue, 2 02000401 (2022)
  • DOI:10.1364/PRJ.447488
Micro-LED backlight module by deep reinforcement learning and micro-macro-hybrid environment control agent
Che-Hsuan Huang, Yu-Tang Cheng, Yung-Chi Tsao, Xinke Liu, and Hao-Chung Kuo
This paper proposes a micro-LED backlight module with a distributed Bragg reflector (DBR) structure to achieve excellent micro-LED backlight module quality and uses deep reinforcement learning (DRL) architecture for optical design. In the DRL architecture, to solve the computing environment problems of the two extreme structures of micro-scale and macro-scale, this paper proposes an environment control agent and virtual-realistic workflow to ensure that the design environment parameters are highly correlated with experimental results. This paper successfully designed a micro-LED backlight module with a DBR structure by the abovementioned methods. The micro-LED backlight module with a DBR structure improves the uniformity performance by 32% compared with the micro-LED backlight module without DBR, and the design calculation time required by the DRL method is only 17.9% of the traditional optical simulation.
  • Jan. 05, 2022
  • Photonics Research
  • Vol.10 Issue, 2 02000269 (2022)
  • DOI:10.1364/PRJ.441188
Mag-Optical Modulator Based on Parity-Time Symmetric Structure
Yi Lingjun, and Li Changhong
A mag-optical modulator based on periodic parity-time (PT) symmetry structure is proposed, which consists of hydro-based MnFe2O4 magnetofluid layer in the middle and periodic PT symmetry units on both sides. The high extinction ratio modulation with gain is realized by using the magneto-optic effect of the magnetic fluid. The transfer matrix method is used to simulate and analyze the structure, it turns out that, for the incident light wave whose wavelength is in the low transmission region of the structure gap band(in the wavelength range from 1513 nm to 1587 nm with 1550 nm as the center), the maximum gain of the modulator for incident light is close to 25 dB, the maximum and the minimum extinction ratio are close to 60 dB and 30 dB, respectively. Simultaneously, the average modulation sensitivity of incident light wave transmission and wavelength shift can reach the maximum of 74.51 dB and 108.2 nm, respectively.
  • Dec. 29, 2021
  • Acta Optica Sinica
  • Vol.42 Issue, 2 0223001 (2022)
  • DOI:10.3788/AOS202242.0223001
Design and Optimization of Half-Adder Based on Two-Dimensional Photonic Crystal
Zhang Yan, Li Mengfan, and Chen Deyuan
In this study, line defects and point defects are introduced in a complete two-dimensional triangular lattice silicon. Using waveguide coupling and linear interference, an all-optical half-adder structure based on photonic crystal is proposed. The half-adder consists of waveguide beam splitters, an all-optical logic AND gate and an all-optical logic XOR gate. Using Rsoft software, combined with the plane-wave-expansion method and the finite-difference time-domain method, the proposed half-adder is simulated. Results show that the contrast ratios of the "carry" and "sum" ports of the proposed half-adder are 4.67 dB and 10.77 dB when the input-light wavelength is 1530 nm, and the response time is about 2.67 ps. In order to improve the contrast ratio of the "carry" port, the structure of the half-adder is optimized. The contrast ratios of the "carry" and "sum" ports of the optimized half-adder are 8.26 dB and 15.34 dB, respectively, and the response time is 3.67 ps. Theoretically, it can reach a data transmission rate of 0.273 Tbps. The proposed half-adder with optimized structure has the characteristic of high contrast ratio, and plays an important role in all-optical signal processing systems and integrated optical circuits.
  • Dec. 23, 2021
  • Laser & Optoelectronics Progress
  • Vol.59 Issue, 1 0123001 (2022)
  • DOI:10.3788/LOP202259.0123001
Efficient, high-CRI white LEDs by combining traditional phosphors with cadmium-free InP/ZnSe red quantum dots
Bega Karadza, Hannes Van Avermaet, Leila Mingabudinova, Zeger Hens, and Youri Meuret
Quantum dots (QDs) offer an interesting alternative for traditional phosphors in on-chip light-emitting diode (LED) configurations. Earlier studies showed that the spectral efficiency of white LEDs with high color rendering index (CRI) values could be considerably improved by replacing red-emitting nitride phosphors with narrowband QDs. However, the red QDs in these studies were cadmium-based, which is a restricted element in the EU and certain other countries. The use of InP-based QDs, the most promising Cd-free alternative, is often presented as an inferior solution because of the broader linewidth of these QDs. However, while narrow emission lines are the key to display applications that require a large color gamut, the spectral efficiency penalty of this broader emission is limited for lighting applications. Here, we report efficient, high-CRI white LEDs with an on-chip color converter coating based on red InP/ZnSe QDs and traditional green/yellow powder phosphors. Using InP/ZnSe QDs with a quantum yield of nearly 80% and a full width at half-maximum of 45 nm, we demonstrate high spectral efficiency for white LEDs with very high CRI values. One of the best experimental results in terms of both luminous efficacy and color rendering performance is a white LED with an efficacy of 132 lm/W, and color rendering indices of Ra≈90, R9≈50 for CCT ≈ 4000 K. These experimental results are critically compared with theoretical benchmark values for white LEDs with on-chip downconversion from both phosphors and red Cd-based QDs. The various loss mechanisms in the investigated white LEDs are quantified with an accurate simulation model, and the main impediments to an even higher efficacy are identified as the blue LED wall-plug efficiency and light recycling in the LED package.
  • Dec. 14, 2021
  • Photonics Research
  • Vol.10 Issue, 1 01000155 (2022)
  • DOI:10.1364/PRJ.428843
Ultrahigh detectivity, high-speed and low-dark current AlGaN solar-blind heterojunction field-effect phototransistors realized using dual-float-photogating effect
Kai Wang, Xinjia Qiu, Zesheng Lv, Zhiyuan Song, and Hao Jiang
High detectivity is essential for solar-blind deep-ultraviolet (DUV) light detection because the DUV signal is extremely weak in most applications. In this work, we report ultrahigh-detectivity AlGaN-based solar-blind heterojunction-field-effect phototransistors fabricated utilizing dual-float-photogating effect. The p+-Al0.4GaN layer and Al0.4GaN absorber layer deposited on the Al0.6GaN barrier serve as top pin-junction photogate, while the thin Al0.4GaN channel layer with a strong polarization field inside acts as virtual back photogate. Due to the effective depletion of the two-dimensional electron gas at the Al0.6Ga0.4N/Al0.4Ga0.6N heterointerface by the top photogate, the dark current was suppressed below 2 pA in the bias range of 0 to 10 V. A high photo-to-dark current ratio over 108 and an optical gain of 7.5×104 were demonstrated at a bias of 5 V. Theoretical analysis indicates that the optical gain can be attributed to the joint action of the floating top and back photogates on the channel current. As a result, a record high flicker noise (Johnson and shot noise) limited specific detectivity of 2.84×1015(2.91×1017) cm Hz0.5 W-1 was obtained. Furthermore, high response speed at the microsecond level was also shown in the devices. This work provides a promising and feasible approach for high-sensitivity DUV detection.
  • Dec. 13, 2021
  • Photonics Research
  • Vol.10 Issue, 1 01000111 (2022)
  • DOI:10.1364/PRJ.444444
Rapid fabrication and characteristics analysis of high-filling-factor microlens array
Huang Shaoqi, Song Zeyuan, Pan Mingliang, Long Yan, Dai Bo, and Zhang Dawei
As a precise optical component, microlens array has applications in fields as optical information processing, optical sensing, optical computing, optical communications and high sensitivity imaging. Researchers have developed many advanced fabrication techniques, some of which already realized the preparation of the microlens array with required geometries, profile and optical properties. However, it would be extremely difficult to achieve a compact packing as such 3D micro-manufacturing techniques are hard to control. A novel rapid and low-cost microfluidic-manipulation based technique was proposed to fabricate high-filling-factor microlens array. A brief demonstration of the fabrication was given, which had excellence of suited to volume production and significant productivity boost. Meanwhile, the microlens arrays of three different properties were produced, which were realized by adjusting the size of the array of micro-posts whose sizes were 300, 500, 700 μm in diameter, respectively. The imaging system was set up to demonstrate the imaging performance of each of the microlens array, evaluating the precision of each microlens array and imaging uniformity of the microlens array. The results show that the fabricated microlens arrays have good imaging performance and have a promising prospect in the use of 3D imaging and optical uniformity.
  • Dec. 07, 2021
  • Infrared and Laser Engineering
  • Vol.50 Issue, 10 20200476 (2021)
  • DOI:10.3788/IRLA20200476
220 GHz sub-harmonic mixer integrated module
Hu Haifan, Ma Xuming, Ma Zhe, and Wang Zhibin
Based on the design of the 220 GHz sub-harmonic mixer, the vertical conversion structure of the IF transmission waveguide was proposed, and the four-channel mixer integration module was realized, the transverse size of the single channel of the mixer was shorten effectively. It provided a feasible scheme for the multi-channel linear array integration of the terahertz receiver system. In order to further optimize the accuracy of the system model, the three-dimensional semiconductor device modeling calculation was carried out for the Schottky-barrier diode based on TCAD, and the high-frequency electromagnetic wave simulation of the mixer was carried out according to the extracted key characteristic parameters. Through the test of the design scheme, the test results show that when the local frequency is 110 GHz, and the power is 7 dBm, the conversion loss of the mixer is 8.6-13 dB as the RF input is 200-240 GHz, and the conversion loss is 8.6-11.3 dB at 204-238 GHz. When the local frequency is 108 GHz, the driving power only needs 3 dBm. In addition, the 220 GHz receiver system based on the mixer module has a temperature sensitivity of 1.3 K as the integration time is 700 μs.
  • Dec. 07, 2021
  • Infrared and Laser Engineering
  • Vol.50 Issue, 10 20210078 (2021)
  • DOI:10.3788/IRLA20210078
Narrow linewidth high frequency microwave signal generator based on composite filter structure
Jia Qingsong, Xu Danfeng, Xu Yumeng, Lei Hao, and Liu Jianxu
In order to realize the output of single longitudinal mode dual-wavelength laser signal at lower pump power and obtain the high frequency microwave signal with narrow line width, the narrow linewidth high frequency microwave signal generator based on multiple filter compound structure was proposed and demonstrated. The dual-wavelength Stokes optical signal with four times Brillouin frequency shift interval was realized through the eight shaped Brillouin cavity structure and the wavelength selective filter composed by reflective fiber grating. The 200 m length single mode fiber was used as gain medium, and it forms a cascaded fiber ring structure with 50 m long single-mode fiber. A three-port coupler and 2 m long unpumped polarization-maintaining erbium-doped fiber was used to form a Sagnac ring structure. The cascaded fiber ring configuration and Sagnac ring configuration were designed to select mode for single longitudinal mode Stokes optical signal. The experiment proves that the high-frequency microwave signal of 42.85 GHz can be generated by the beat frequency detection of the output single-longitudinal-mode dual-wavelength Stokes optical signal, and the line width is 38 kHz; Changing the output wavelength of the tunable pump laser, frequency tuning in the range of 42.25-43.51 GHz can be achieved; Through the stability test, the frequency change of the 42.85 GHz high-frequency microwave signal is in the range of 0.83 MHz, and the peak power change is in the range of ±0.8 dB. It has good stability and meets the actual application requirements.
  • Dec. 07, 2021
  • Infrared and Laser Engineering
  • Vol.50 Issue, 10 20210074 (2021)
  • DOI:10.3788/IRLA20210074