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  • RESEARCH ARTICLE
    Xiaoxiao Wang, Ruizhe Gu, Yandong Li, Huixin Qi, Xiaoyong Hu, Xingyuan Wang, Qihuang Gong
    Frontiers of Optoelectronics, 2023, 16(4): 38. https://doi.org/10.1007/s12200-023-00094-z

    Nonreciprocal interlayer coupling is difficult to practically implement in bilayer non-Hermitian topological photonic systems. In this work, we identify a similarity transformation between the Hamiltonians of systems with nonreciprocal interlayer coupling and on-site gain/loss. The similarity transformation is widely applicable, and we show its application in one- and two-dimensional bilayer topological systems as examples. The bilayer non-Hermitian system with nonreciprocal interlayer coupling, whose topological number can be defined using the gauge-smoothed Wilson loop, is topologically equivalent to the bilayer system with on-site gain/loss. We also show that the topological number of bilayer non-Hermitian C6v-typed domain-induced topological interface states can be defined in the same way as in the case of the bilayer non-Hermitian Su–Schrieffer–Heeger model. Our results show the relations between two microscopic provenances of the non-Hermiticity and provide a universal and convenient scheme for constructing and studying nonreciprocal interlayer coupling in bilayer non-Hermitian topological systems. This scheme is useful for observation of non-Hermitian skin effect in three-dimensional systems.

  • RESEARCH ARTICLE
    Tao Wang, Bo Ren, Can Li, Kun Guo, Jinyong Leng, Pu Zhou
    Frontiers of Optoelectronics, 2023, 16(3): 30. https://doi.org/10.1007/s12200-023-00087-y

    In this work, a high-energy and high peak power chirped pulse amplification system with near diffraction-limited beam quality based on tapered confined-doped fiber (TCF) is experimentally demonstrated. The TCF has a core numerical aperture of 0.07 with core/cladding diameter of 35/250 μm at the thin end and 56/400 μm at the thick end. With a backward-pumping configuration, a maximum single pulse energy of 177.9 μJ at a repetition rate of 504 kHz is realized, corresponding to an average power of 89.7 W. Through partially compensating for the accumulated nonlinear phase during the amplification process via adjusting the high order dispersion of the stretching chirped fiber Bragg grating, the duration of the amplified pulse is compressed to 401 fs with a pulse energy of 126.3 μJ and a peak power of 207 MW, which to the best of our knowledge represents the highest peak power ever reported from a monolithic ultrafast fiber laser. At the highest energy, the polarization extinction ratio and the M2 factor were respectively measured to be ∼ 19 dB and 1.20. In addition, the corresponding intensity noise properties as well as the short- and long-term stability were also examined, verifying a stable operation of the system. It is believed that the demonstrated laser source could find important applications in, for example, advanced manufacturing and photomedicine.

  • RESEARCH ARTICLE
    Xiang Gao, Fengbo Sun, Xinzhu Tong, Xufan Zheng, Yinuo Wang, Cong Xiao, Pengcheng Li, Renqiang Yang, Xunchang Wang, Zhitian Liu
    Frontiers of Optoelectronics, 2023, 16(2): 8. https://doi.org/10.1007/s12200-023-00063-6

    Single perylene diimide (PDI) used as a non-fullerene acceptor (NFA) in organic solar cells (OSCs) is enticing because of its low cost and excellent stability. To improve the photovoltaic performance, it is vital to narrow the bandgap and regulate the stacking behavior. To address this challenge, we synthesize soluble perylenetetracarboxylic bisbenzimidazole (PTCBI) molecules with a bulky side chain at the bay region, by replacing the widely used “swallow tail” type alkyl chains at the imide position of PDI molecules with a planar benzimidazole structure. Compared with PDI molecules, PTCBI molecules exhibit red-shifted UV–vis absorption spectra with larger extinction coefficient, and one magnitude higher electron mobility. Finally, OSCs based on one soluble PTCBI-type NFA, namely MAS-7, exhibit a champion power conversion efficiency (PCE) of 4.34%, which is significantly higher than that of the corresponding PDI-based OSCs and is the highest PCE of PTCBI-based OSCs reported. These results highlight the potential of soluble PTCBI derivatives as NFAs in OSCs.

  • REVIEW ARTICLE
    Yong Yang, Zijie Wang, Xiaobei Zhang, Qi Zhang, Tingyun Wang
    Frontiers of Optoelectronics, 2023, 16(2): 10. https://doi.org/10.1007/s12200-023-00066-3

    In-fiber whispering gallery mode (WGM) microsphere resonators have received remarkable attention due to the superiorities of compact structure, high stability and self-alignment. As an in-fiber structure, WGM microsphere resonators have been demonstrated in various applications, such as sensors, filters and lasers, which have significant impacts on modern optics. Herein, we review recent progress of in-fiber WGM microsphere resonators, which involve fibers of diverse structures and microspheres of different materials. First, a brief introduction is given to in-fiber WGM microsphere resonators, from structures to applications. Then, we focus on recent progresses in this field, including in-fiber couplers based on conventional fibers, capillaries and micro-structure hollow fibers, and passive/active microspheres. Finally, future developments of the in-fiber WGM microsphere resonators are envisioned.

  • RESEARCH ARTICLE
    William Anderson Lee Sanchez, Shreekant Sinha, Po-Yu Wang, Ray-Hua Horng
    Frontiers of Optoelectronics, 2023, 16(4): 32. https://doi.org/10.1007/s12200-023-00086-z

    Thin film p-side up vertical-cavity surface-emitting lasers (VCSELs) with 940 nm wavelength on a composite metal (Copper/Invar/Copper; CIC) substrate has been demonstrated by twice-bonding transfer and substrate removing techniques. The CIC substrate is a sandwich structure with a 10 µm thick Copper (Cu) layer/30 µm thick Invar layer/10 µm thick Cu layer. The Invar layer was composed of Iron (Fe) and Nickel (Ni) with a proportion of 70:30. The thermal expansion coefficient of the composite CIC metal can match that of the GaAs substrate. It results that the VCSEL layers can be successfully transferred to CIC metal substrate without cracking. At 1 mA current, the top-emitting VCSEL/GaAs and thin-film VCSEL/CIC had a voltage of 1.39 and 1.37 V, respectively. The optical output powers of VCSEL/GaAs and VCSEL/CIC were 21.91 and 24.40 mW, respectively. The 50 µm thick CIC substrate can play a good heat dissipation function, which results in improving the electrical and optical characteristics of thin film VCSELs/CIC. The VCSEL/CIC exhibited a superior thermal management capability as compared with VCSEL/GaAs. The obtained data suggested that VCSELs on a composite metal substrate not only affected significantly the characteristics of thin film VCSEL, but also improved considerably the device thermal performance.

  • REVIEW ARTICLE
    Huaqing Qiu, Yong Liu, Xiansong Meng, Xiaowei Guan, Yunhong Ding, Hao Hu
    Frontiers of Optoelectronics, 2023, 16(3): 23. https://doi.org/10.1007/s12200-023-00076-1

    An optical phased array (OPA) is a promising non-mechanical technique for beam steering in solid-state light detection and ranging systems. The performance of the OPA largely depends on the phase shifter, which affects power consumption, insertion loss, modulation speed, and footprint. However, for a thermo-optic phase shifter, achieving good performance in all aspects is challenging due to trade-offs among these aspects. In this work, we propose and demonstrate two types of energy-efficient optical phase shifters that overcome these trade-offs and achieve a well-balanced performance in all aspects. Additionally, the proposed round-spiral phase shifter is robust in fabrication and fully compatible with deep ultraviolet (DUV) processes, making it an ideal building block for large-scale photonic integrated circuits (PICs). Using the high-performance phase shifter, we propose a periodic OPA with low power consumption, whose maximum electric power consumption within the field of view is only 0.33 W. Moreover, we designed Gaussian power distribution in both the azimuthal (ϕ) and polar (θ) directions and experimentally achieved a large sidelobe suppression ratio of 15.1 and 25 dB, respectively.

  • RESEARCH ARTICLE
    Qi Han, Yadong Jiang, Xianchao Liu, Chaoyi Zhang, Jun Wang
    Frontiers of Optoelectronics, 2023, 16(2): 9. https://doi.org/10.1007/s12200-023-00065-4

    Black phosphorus quantum dots (BPQDs) are synthesized and combined with graphene sheet. The fabricated BPQDs/graphene devices are capable of detecting visible and near infrared radiation. The adsorption effect of BPQDs in graphene is clarified by the relationship of the photocurrent and the shift of the Dirac point with different substrate. The Dirac point moves toward a neutral point under illumination with both SiO2/Si and Si3N4/Si substrates, indicating an anti-doped feature of photo-excitation. To our knowledge, this provides the first observation of photoresist induced photocurrent in such systems. Without the influence of the photoresist the device can respond to infrared light up to 980 nm wavelength in vacuum in a cryostat, in which the photocurrent is positive and photoconduction effect is believed to dominate the photocurrent. Finally, the adsorption effect is modeled using a first-principle method to give a picture of charge transfer and orbital contribution in the interaction of phosphorus atoms and single-layer graphene.

  • REVIEW ARTICLE
    Pengfei Liu, Hao Wen, Linhao Ren, Lei Shi, Xinliang Zhang
    Frontiers of Optoelectronics, 2023, 16(3): 18. https://doi.org/10.1007/s12200-023-00073-4

    Second-order (χ(2)) optical nonlinearity is one of the most common mechanisms for modulating and generating coherent light in photonic devices. Due to strong photon confinement and long photon lifetime, integrated microresonators have emerged as an ideal platform for investigation of nonlinear optical effects. However, existing silicon-based materials lack a χ(2) response due to their centrosymmetric structures. A variety of novel material platforms possessing χ(2) nonlinearity have been developed over the past two decades. This review comprehensively summarizes the progress of second-order nonlinear optical effects in integrated microresonators. First, the basic principles of χ(2) nonlinear effects are introduced. Afterward, we highlight the commonly used χ(2) nonlinear optical materials, including their material properties and respective functional devices. We also discuss the prospects and challenges of utilizing χ(2) nonlinearity in the field of integrated microcavity photonics.

  • RESEARCH ARTICLE
    Lu Zhang, Shijie Fu, Quan Sheng, Xuewen Luo, Junxiang Zhang, Wei Shi, Jianquan Yao
    Frontiers of Optoelectronics, 2023, 16(4): 33. https://doi.org/10.1007/s12200-023-00089-w

    976 nm + 1976 nm dual-wavelength pumped Er-doped ZBLAN fiber lasers are generally accepted as the preferred solution for achieving 3.5 µm lasing. However, the 2 µm band excited state absorption from the upper lasing level (4F9/24F7/2) depletes the Er ions population inversion, reducing the pump quantum efficiency and limiting the power scaling. In this work, we demonstrate that the pump quantum efficiency can be effectively improved by using a long-wavelength pump with lower excited state absorption rate. A 3.5 µm Er-doped ZBLAN fiber laser was built and its performances at different pump wavelengths were experimentally investigated in detail. A maximum output power at 3.46 µm of ∼ 7.2 W with slope efficiency (with respect to absorbed 1990 nm pump power) of 41.2% was obtained with an optimized pump wavelength of 1990 nm, and the pump quantum efficiency was increased to 0.957 compared with the 0.819 for the conventional 1976 nm pumping scheme. Further power scaling was only limited by the available 1990 nm pump power. A numerical simulation was implemented to evaluate the cross section of excited state absorption via a theoretical fitting of experimental results. The potential of further power scaling was also discussed, based on the developed model.

  • RESEARCH ARTICLE
    Chuancheng Zhang, Shoujun Ding, Miaomiao Wang, Hao Ren, Xubing Tang, Yong Zou, Renqin Dou, Wenpeng Liu
    Frontiers of Optoelectronics, 2023, 16(3): 31. https://doi.org/10.1007/s12200-023-00083-2

    Optical thermometry based on the upconversion (UC) luminescence intensity ratio (LIR) has attracted considerable attention because of its feasibility for achievement of accurate non-contact temperature measurement. Compared with traditional UC phosphors, optical thermometry based on UC single crystals can achieve faster response and higher sensitivity due to the stability and high thermal conductivity of the single crystals. In this study, a high-quality 5 at% Yb3+ and 1 at% Ho3+ co-doped Gd0.74Y0.2TaO4 single crystal was grown by the Czochralski (Cz) method, and the structure of the as-grown crystal was characterized. Importantly, the UC luminescent properties and optical thermometry behaviors of this crystal were revealed. Under 980 nm wavelength excitation, green and red UC luminescence lines at 550 and 650 nm and corresponding to the 5F4/5S25I8 and 5F55I8 transitions of Ho3+, respectively, were observed. The green and red UC emissions involved a two-photon mechanism, as evidenced by the analysis of power-dependent UC emission spectra. The temperature-dependent UC emission spectra were measured in the temperature range of 330–660 K to assess the optical temperature sensing behavior. At 660 K, the maximum relative sensing sensitivity (Sr) was determined to be 0.0037 K−1. These results highlight the significant potential of Yb,Ho:GYTO single crystal for optical temperature sensors.

  • RESEARCH ARTICLE
    Kareem J. Garriga Francis, Xi-Cheng Zhang
    Frontiers of Optoelectronics, 2023, 16(4): 44. https://doi.org/10.1007/s12200-023-00095-y

    The concept of Terahertz Field-Induced Second Harmonic (TFISH) Generation is revisited to introduce a single-shot detection scheme based on third order nonlinearities. Focused specifically on the further development of THz plasma-based sources, we begin our research by reimagining the TFISH system to serve as a direct plasma diagnostic. In this work, an optical probe beam is used to mix directly with the strong ponderomotive current associated with laser-induced ionization. A four-wave mixing (FWM) process then generates a strong second-harmonic optical wave because of the mixing of the probe beam with the nonlinear current components oscillating at THz frequencies. The observed conversion efficiency is high enough that for the first time, the TFISH signal appears visible to the human eye. We perform spectral, spatial, and temporal analysis on the detected second-harmonic frequency and show its direct relationship to the nonlinear current. Further, a method to detect incoherent and coherent THz inside plasma filaments is devised using spatio-temporal couplings. The single-shot detection configurations are theoretically described using a combination of expanded FWM models with Kostenbauder and Gaussian Q-matrices. We show that the retrieved temporal traces for THz radiation from single- and twocolor laser-induced air-plasma sources match theoretical descriptions very well. High temporal resolution is shown with a detection bandwidth limited only by the spatial extent of the probe laser beam. Large detection bandwidth and temporal characterization is shown for THz radiation confined to under-dense plasma filaments induced by < 100 fs lasers below the relativistic intensity limit.

  • RESEARCH ARTICLE
    Sergey N. Mantsevich, Ekaterina I. Kostyleva, Andrey N. Danilin, Vladimir S. Khorkin
    Frontiers of Optoelectronics, 2023, 16(3): 21. https://doi.org/10.1007/s12200-023-00079-y

    The results of an optoelectronic system—frequency-shifted feedback (FSF) laser experimental examination are presented. The considered FSF laser is seeded only with optical amplifier spontaneous emission (ASE) and operates in the mode-locked regime, whereby the output radiation is sequence of short pulses with a repetition rate determined by the delay time in its optical feedback circuit. In the frequency domain, the spectrum of such a pulse sequence is an optical frequency comb (OFC). These OFCs we call initial. We consider the possibility of tunable acousto-optic (AO) dual and quad-comb frequency spacing downconversion in the FSF laser seeded with ASE and operating in the mode-locked regime. The examined system applies a single frequency shifting loop with single AO tunable filter as the frequency shifter that is fed with several radio frequency signals simultaneously. The initial OFCs with frequency spacing of about 6.5 MHz may be obtained in the wide spectral range and their width, envelope shape and position in the optical spectrum may be tuned. The dual-combs are obtained with a pair of initial OFCs aroused by two various ultrasound waves in the acousto-optic tunable filter (AOTF). The dual-combs frequency spacing is determined by the frequency difference of the signals applied to the AOTF piezoelectric transducer and can be tuned simply. The quad-combs are obtained with three initial OFCs, forming a pair of dual-combs, appearing when three ultrasound frequencies feed the AOTF transducer. The quad-combs frequency spacing is defined by the difference between the frequency spacing of dual-combs. Quad-combs with more than 5000 spectral lines and tunable frequency spacing are observed. The successive frequency downconversion gives the possibility to reduce the OFC frequency spacing form several MHz for initial OFC to tens of kHz for quad-combs.

  • RESEARCH ARTICLE
    Zhenzhu Xu, Li Mei, Yuhua Chong, Xudong Gao, Shoubao Han, Chengkun Yang, Lin Li
    Frontiers of Optoelectronics, 2023, 16(2): 11. https://doi.org/10.1007/s12200-023-00064-5

    An integrated microwave photonic mixer based on silicon photonic platforms is proposed, which consist of a dual-drive Mach–Zehnder modulator and a balanced photodetector. The modulated optical signals from microwave photonic links can be directly demodulated and down-converted to intermediate frequency (IF) signals by the photonic mixer. The converted signal is obtained by conducting off-chip subtraction of the outputs from the balanced photodetector, and subsequent filtering of the high frequency items by an electrical low-pass filter. Benefiting from balanced detection, the conversion gain of the IF signal is improved by 6 dB, and radio frequency leakage and common-mode noise are suppressed significantly. System-level simulations show that the frequency mixing system has a spurious-free dynamic range of 89 dB·Hz2/3, even with deteriorated linearity caused by the two cascaded modulators. The spur suppression ratio of the photonic mixer remains higher than 40 dB when the IF varies from 0.5 to 4 GHz. The electrical-electrical 3 dB bandwidth of frequency conversion is 11 GHz. The integrated frequency mixing approach is quite simple, requiring no extra optical filters or electrical 90° hybrid coupler, which makes the system more stable and with broader bandwidth so that it can meet the potential demand in practical applications.

  • RESEARCH ARTICLE
    Zixiong Li, Mingyu Li, Xinyi Hou, Lei Du, Lin Xiao, Tianshu Wang, Wanzhuo Ma
    Frontiers of Optoelectronics, 2023, 16(2): 12. https://doi.org/10.1007/s12200-023-00067-2

    This paper proposes a mode-locked fiber laser based on graphene-coated microfiber. The total length of the fiber laser resonant cavity is 31.34 m. Under the condition of stable output of bright-dark soliton pairs from the fiber laser, dual-wavelength tuning is realized by adjusting the polarization controller (PC), and the wavelength tuning range is 11 nm. Furthermore, the effects of polarization states on bright-dark solitons are studied. It is demonstrated that the mode-locking state can be switched between conventional solitons and bright-dark solitons in the graphene mode-locked fiber laser. Bright-dark soliton pairs with different shapes and nanosecond pulse width can be obtained by adjusting the PC and pump power.

  • RESEARCH ARTICLE
    Mengqiong Zhu, Yuanbo Zhang, Shuaicheng Lu, Zijun Wang, Junbing Zhou, Wenkai Ma, Ruinan Zhu, Guanyuan Chen, Jianbing Zhang, Liang Gao, Jiancan Yu, Pingqi Gao, Jiang Tang
    Frontiers of Optoelectronics, 2023, 16(2): 15. https://doi.org/10.1007/s12200-023-00069-0

    Infrared photovoltaic cells (IRPCs) have attracted considerable attention for potential applications in wireless optical power transfer (WOPT) systems. As an efficient fiber-integrated WOPT system typically uses a 1550 nm laser beam, it is essential to tune the peak conversion efficiency of IRPCs to this wavelength. However, IRPCs based on lead sulfide (PbS) colloidal quantum dots (CQDs) with an excitonic peak of 1550 nm exhibit low short circuit current (Jsc) due to insufficient absorption under monochromatic light illumination. Here, we propose comprehensive optical engineering to optimize the device structure of IRPCs based on PbS CQDs, for 1550 nm WOPT systems. The absorption by the device is enhanced by improving the transmittance of tin-doped indium oxide (ITO) in the infrared region and by utilizing the optical resonance effect in the device. Therefore, the optimized device exhibited a high short circuit current density of 37.65 mA/cm2 under 1 sun (AM 1.5G) solar illumination and 11.91 mA/cm2 under 1550 nm illumination 17.3 mW/cm2. Furthermore, the champion device achieved a record high power conversion efficiency (PCE) of 7.17% under 1 sun illumination and 10.29% under 1550 nm illumination. The PbS CQDs IRPCs under 1550 nm illumination can even light up a liquid crystal display (LCD), demonstrating application prospects in the future.

  • RESEARCH ARTICLE
    Baohao Xu, Zhiyuan Jin, Lie Shi, Huanian Zhang, Qi Liu, Peng Qin, Kai Jiang, Jing Wang, Wenjing Tang, Wei Xia
    Frontiers of Optoelectronics, 2023, 16(2): 13. https://doi.org/10.1007/s12200-023-00068-1

    As a member of Xenes family, germanene has excellent nonlinear saturable absorption characteristics. In this work, we prepared germanene nanosheets by liquid phase exfoliation and measured their saturation intensity as 0.6 GW/cm2 with a modulation depth of 8%. Then, conventional solitons with a pulse width of 946 fs and high-energy noise-like pulses with a pulse width of 784 fs were obtained by using germanene nanosheet as a saturable absorber for a mode-locked Erbium-doped fiber laser. The characteristics of the two types of pulses were investigated experimentally. The results reveal that germanene has great potential for modulation devices in ultrafast lasers and can be used as a material for creation of excellent nonlinear optical devices to explore richer applications in ultrafast photonics.

  • RESEARCH ARTICLE
    Yuting Ouyang, Jiayu Zhang, Wanggen Sun, Mengxiao Li, Tao Chen, Haikun Zhang, Wenjing Tang, Wei Xia
    Frontiers of Optoelectronics, 2023, 16(3): 19. https://doi.org/10.1007/s12200-023-00074-3

    Stable picosecond dissipative soliton pulses were observed in an ytterbium-doped fiber laser employing a high-quality mixture of BP/SnSe2-PVA saturable absorber (SA). The modulation depth, saturation intensity, and non-saturable loss of the mixture of BP/SnSe2-PVA SA were measured with values of 5.98%, 18.37 MW/cm2, and 33%, respectively. Within the pump power range of 150–270 mW, stable dissipative soliton pulses were obtained with an output power of 1.68–4 mW. When the minimum pulse duration is 1.28 ps, a repetition rate of 0.903 MHz, center wavelength of 1064.38 nm and 3 dB bandwidth of 2 nm were obtained. The maximum pulse energy of 4.43 nJ and the signal-to-noise ratio up to 72 dB were achieved at pump power of 270 mW. The results suggest that the BP/SnSe2-PVA mixture SA has outstanding nonlinear saturable absorption characteristics and broad ultrafast laser applications.

  • RESEARCH ARTICLE
    Semyachkina‑Glushkovskaya Oxana, Shirokov Alexander, Blokhina Inna, Fedosov Ivan, Terskov Andrey, Dubrovsky Alexander, Tsoy Maria, Elovenko Daria, Adushkina Viktoria, Evsukova Arina, Telnova Valeria, Tzven Anna, Krupnova Valeria, Manzhaeva Maria, Dmitrenko Alexander, Penzel Thomas, Kurths Jürgen
    Frontiers of Optoelectronics, 2023, 16(3): 22. https://doi.org/10.1007/s12200-023-00080-5

    With the increase in the aging population, the global number of people with Alzheimer’s disease (AD) progressively increased worldwide. The situation is aggravated by the fact that there is no the effective pharmacological therapy of AD. Photobiomodulation (PBM) is non-pharmacological approach that has shown very promising results in the therapy of AD in pilot clinical and animal studies. However, the mechanisms of therapeutic effects of PBM for AD are poorly understood. In this study on mice, we demonstrate that photodynamic effects of 5-aminolevulenic acid and laser 635 nm cause reduction of network of the meningeal lymphatic vessels (MLVs) leading to suppression of lymphatic removal of beta-amyloid (Aβ) from the right lateral ventricle and the hippocampus. Using the original protocol of PBM under electroencephalographic monitoring of wakefulness and sleep stages in non-anesthetized mice, we discover that the 7-day course of PBM during deep sleep vs. wakefulness provides better restoration of clearance of Aβ from the ventricular system of the brain and the hippocampus. Our results shed light on the mechanism of PBM and show the stimulating effects of PBM on the brain lymphatic drainage that promotes transport of Aβ via the lymphatic pathway. The effects of PBM on the brain lymphatics in sleeping brain open a new niche in the study of restorative functions of sleep as well as it is an important informative platform for the development of innovative smart sleep technologies for the therapy of AD.

  • RESEARCH ARTICLE
    Weilei Gou, Yuan Yu, Xinliang Zhang
    Frontiers of Optoelectronics, 2023, 16(3): 20. https://doi.org/10.1007/s12200-023-00075-2

    Optical beating is the usual approach to generation of microwave signals. However, the highest frequency achievable for microwave signals is limited by the bandwidths of optoelectronic devices. To maximize the microwave frequency with a limited bandwidth of a photodetector (PD) and relieve the bandwidth bottleneck, we propose to generate microwave signals with the single sideband (SSB) format by beating a continuous wave (CW) light with an optical SSB signal. By simply adjusting the frequency difference between the CW light and the carrier of the optical SSB signal, the frequency of the generated microwave SSB signal is changed correspondingly. In the experiment, amplitude shift keying (ASK) microwave signals with the SSB format are successfully generated with different carrier frequencies and coding bit rates, and the recovered coding information agrees well with the original pseudo random binary sequence (PRBS) of 27–1 bits. The proposed approach can significantly relieve the bandwidth restriction set by optoelectronic devices in high-speed microwave communication systems.

  • RESEARCH ARTICLE
    Liye Xu, Jiao Geng, Liping Shi, Weicheng Cui, Min Qiu
    Frontiers of Optoelectronics, 2023, 16(2): 16. https://doi.org/10.1007/s12200-023-00071-6

    We report self-organized periodic nanostructures on amorphous silicon thin films by femtosecond laser-induced oxidation. The dependence of structural periodicity on the thickness of silicon films and the substrate materials is investigated. The results reveal that when silicon film is 200 nm, the period of self-organized nanostructures is close to the laser wavelength and is insensitive to the substrates. In contrast, when the silicon film is 50 nm, the period of nanostructures is much shorter than the laser wavelength, and is dependent on the substrates. Furthermore, we demonstrate that, for the thick silicon films, quasi-cylindrical waves dominate the formation of periodic nanostructures, while for the thin silicon films, the formation originates from slab waveguide modes. Finite-difference time-domain method-based numerical simulations support the experimental discoveries.

  • RESEARCH ARTICLE
    Xinzhao Zhao, Mingyu Li, Tianjun Ma, Jun Yan, Gomaa Mohamed Gomaa Khalaf, Chao Chen, Hsien-Yi Hsu, Haisheng Song, Jiang Tang
    Frontiers of Optoelectronics, 2023, 16(3): 27. https://doi.org/10.1007/s12200-023-00085-0

    Infrared solar cells are more effective than normal bandgap solar cells at reducing the spectral loss in the near-infrared region, thus also at broadening the absorption spectra and improving power conversion efficiency. PbS colloidal quantum dots (QDs) with tunable bandgap are ideal infrared photovoltaic materials. However, QD solar cell production suffers from small-area-based spin-coating fabrication methods and unstable QD ink. Herein, the QD ink stability mechanism was fully investigated according to Lewis acid–base theory and colloid stability theory. We further studied a mixed solvent system using dimethylformamide and butylamine, compatible with the scalable manufacture of method-blade coating. Based on the ink system, 100 cm2 of uniform and dense near-infrared PbS QDs (∼ 0.96 eV) film was successfully prepared by blade coating. The average efficiencies of above absorber-based devices reached 11.14% under AM1.5G illumination, and the 800 nm-filtered efficiency achieved 4.28%. Both were the top values among blade coating method based devices. The newly developed ink showed excellent stability, and the device performance based on the ink stored for 7 h was similar to that of fresh ink. The matched solvent system for stable PbS QD ink represents a crucial step toward large area blade coating photoelectric devices.

  • Zheng Liu, Tianhua Xu, Ji Qi, Joshua Uduagbomen, Jian Zhao, Tiegen Liu
    Frontiers of Optoelectronics, 2023, 16(2): 17. https://doi.org/10.1007/s12200-023-00072-5

    Optical fiber communication networks play an important role in the global telecommunication network. However, nonlinear effects in the optical fiber and transceiver noise greatly limit the performance of fiber communication systems. In this paper, the product of mutual information (MI) and communication bandwidth is used as the metric of the achievable information rate (AIR). The MI loss caused by the transceiver is also considered in this work, and the bit-wise MI, generalized mutual information (GMI), is used to calculate the AIR. This loss is more significant in the use of higher-order modulation formats. The AIR analysis is carried out in the QPSK, 16QAM, 64QAM and 256QAM modulation formats for the communication systems with different communication bandwidths and transmission distances based on the enhanced Gaussian noise (EGN) model. The paper provides suggestions for the selection of the optimal modulation format in different transmission scenarios.

  • RESEARCH ARTICLE
    Qing Ye, Hui Kong, Jintian Bian, Jiyong Yao, Enlong Wang, Yunlong Wu, Haiping Xu, Kaihua Wen, Yihua Hu
    Frontiers of Optoelectronics, 2023, 16(3): 26. https://doi.org/10.1007/s12200-023-00077-0

    The widely tunable and high resolution mid-infrared laser based on a BaGa4Se7 (BGSe) optical parametric oscillator (OPO) was demonstrated. A wavelength tuning range of 2.76–4.64 μm and a wavelength tuning resolution of about 0.3 nm were obtained by a BGSe (56.3°, 0°) OPO, which was pumped by a 1064 nm laser. It is the narrowest reported wavelength tuning resolution for BGSe OPO, and was obtained by simultaneously controlling the angle and temperature of BGSe.

  • MINI REVIEW
    Xinxin Duan, Meng Zhang, Yu-Hui Zhang
    Frontiers of Optoelectronics, 2023, 16(4): 34. https://doi.org/10.1007/s12200-023-00090-3

    The development of super-resolution technology has made it possible to investigate the ultrastructure of intracellular organelles by fluorescence microscopy, which has greatly facilitated the development of life sciences and biomedicine. To realize super-resolution imaging of living cells, both advanced imaging systems and excellent fluorescent probes are required. Traditional fluorescent probes have good availability, but that is not the case for probes for live-cell super-resolution imaging. In this review, we first introduce the principles of various super-resolution technologies and their probe requirements, then summarize the existing designs and delivery strategies of super-resolution probes for live-cell imaging, and finally provide a brief conclusion and overview of the future.

  • RESEARCH ARTICLE
    Peixun Fan, Guochen Jiang, Xinyu Hu, Lizhong Wang, Hongjun Zhang, Minlin Zhong
    Frontiers of Optoelectronics, 2023, 16(4): 36. https://doi.org/10.1007/s12200-023-00092-1

    Controllable fabrication of surface micro/nano structures is the key to realizing surface functionalization for various applications. As a versatile approach, ultrafast laser ablation has been widely studied for surface micro/nano structuring. Increasing research efforts in this field have been devoted to gaining more control over the fabrication processes to meet the increasing need for creation of complex structures. In this paper, we focus on the in-situ deposition process following the plasma formation under ultrafast laser ablation. From an overview perspective, we firstly summarize the different roles that plasma plumes, from pulsed laser ablation of solids, play in different laser processing approaches. Then, the distinctive in-situ deposition process within surface micro/nano structuring is highlighted. Our experimental work demonstrated that the in-situ deposition during ultrafast laser surface structuring can be controlled as a localized micro-additive process to pile up secondary ordered structures, through which a unique kind of hierarchical structure with fort-like bodies sitting on top of micro cone arrays were fabricated as a showcase. The revealed laser-matter interaction mechanism can be inspiring for the development of new ultrafast laser fabrication approaches, adding a new dimension and more flexibility in controlling the fabrication of functional surface micro/nano structures.

  • RESEARCH ARTICLE
    Weinan Liu, Youmin Rong, Ranwu Yang, Congyi Wu, Guojun Zhang, Yu Huang
    Frontiers of Optoelectronics, 2023, 16(2): 14. https://doi.org/10.1007/s12200-023-00070-7

    The mechanisms of interaction between pulsed laser and materials are complex and indistinct, severely influencing the stability and quality of laser processing. This paper proposes an intelligent method based on the acoustic emission (AE) technique to monitor laser processing and explore the interaction mechanisms. The validation experiment is designed to perform nanosecond laser dotting on float glass. Processing parameters are set differently to generate various outcomes: ablated pits and irregular-shaped cracks. In the signal processing stage, we divide the AE signals into two bands, main and tail bands, according to the laser processing duration, to study the laser ablation and crack behavior, respectively. Characteristic parameters extracted by a method that combines framework and frame energy calculation of AE signals can effectively reveal the mechanisms of pulsed laser processing. The main band features evaluate the degree of laser ablation from the time and intensity scales, and the tail band characteristics demonstrate that the cracks occur after laser dotting. In addition, from the analysis of the parameters of the tail band very large cracks can be efficiently distinguished. The intelligent AE monitoring method was successfully applied in exploring the interaction mechanism of nanosecond laser dotting float glass and can be used in other pulsed laser processing fields.

  • RESEARCH ARTICLE
    Jungang He, You Ge, Ya Wang, Mohan Yuan, Hang Xia, Xingchen Zhang, Xiao Chen, Xia Wang, Xianchang Zhou, Kanghua Li, Chao Chen, Jiang Tang
    Frontiers of Optoelectronics, 2023, 16(3): 28. https://doi.org/10.1007/s12200-023-00082-3

    Lead selenide (PbSe) colloidal quantum dots (CQDs) are suitable for the development of the next-generation of photovoltaics (PVs) because of efficient multiple-exciton generation and strong charge coupling ability. To date, the reported high-efficient PbSe CQD PVs use spin-coated zinc oxide (ZnO) as the electron transport layer (ETL). However, it is found that the surface defects of ZnO present a difficulty in completion of passivation, and this impedes the continuous progress of devices. To address this disadvantage, fluoride (F) anions are employed for the surface passivation of ZnO through a chemical bath deposition method (CBD). The F-passivated ZnO ETL possesses decreased densities of oxygen vacancy and a favorable band alignment. Benefiting from these improvements, PbSe CQD PVs report an efficiency of 10.04%, comparatively 9.4% higher than that of devices using sol-gel (SG) ZnO as ETL. We are optimistic that this interface passivation strategy has great potential in the development of solution-processed CQD optoelectronic devices.

  • RESEARCH ARTICLE
    Xiaohua Xing, Die Zou, Xin Ding, Jianquan Yao, Liang Wu
    Frontiers of Optoelectronics, 2023, 16(4): 40. https://doi.org/10.1007/s12200-023-00098-9

    Polarization, a fundamental behavior of electromagnetic waves, holds immense potential across diverse domains such as environmental monitoring, biomedicine, and ocean exploration. However, achieving efficient modulation of terahertz waves with wide operational bandwidth poses significant challenges. Here, we introduce an all-silicon polarization converter designed specifically to operate in the terahertz range of the electromagnetic spectrum. Simulation results demonstrate that the average conversion efficiency of cross-linear waves exceeds 80% across a wide frequency range spanning from 1.00 to 2.32 THz, with the highest conversion efficiency peaking at an impressive 99.97%. Additionally, our proposed structure facilitates linear-to-circular polarization conversion with an ellipticity of 1 at 0.85 THz. Furthermore, by rotating the cross-shaped microstructure, active control over arbitrary polarization states can be achieved. To summarize, the proposed structure offers remarkable flexibility and ease of integration, providing a reliable and practical solution for achieving broadband and efficient polarization conversion of terahertz waves.

  • RESEARCH ARTICLE
    Wenbo Jia, Yi Jing, Han Zhang, Baoyan Tian, Huabo Huang, Changlei Wang, Ligang Xu
    Frontiers of Optoelectronics, 2023, 16(4): 47. https://doi.org/10.1007/s12200-023-00103-1

    Tin perovskites with exemplary optoelectronic properties offer potential application in lead-free perovskite solar cells. However, Sn vacancies and undercoordinated Sn ions on the tin perovskite surfaces can create deep-level traps, leading to non-radiative recombination and absorption of nucleophilic O2 molecules, impeding further device efficiency and stability. Here, in this study, a new additive of semicarbazide hydrochloride (SEM-HCl) with a N–C=O functional group was introduced into the perovskite precursor to fabricate high-quality films with a low concentration of deep-level trap densities. This, in turn, serves to prevent undesirable interaction between photogenerated carriers and adsorbed oxygen molecules in the device’s operational environment, ultimately reducing the proliferation of superoxide entities. As the result, the SEM-HCl-derived devices show a peak efficiency of 10.9% with improved device stability. These unencapsulated devices maintain almost 100% of their initial efficiencies after working for 100 h under continuous AM1.5 illumination conditions.

  • RESEARCH ARTICLE
    Yuqi Hu, Qingsong Bai, Xi Tang, Wei Xiong, Yilu Wu, Xin Zhang, Yanlan Xiao, Runchang Du, Leiji Liu, Guangqiong Xia, Zhengmao Wu, Junbo Yang, Heng Zhou, Jiagui Wu
    Frontiers of Optoelectronics, 2023, 16(3): 24. https://doi.org/10.1007/s12200-023-00081-4

    Ultrafast physical random bit (PRB) generators and integrated schemes have proven to be valuable in a broad range of scientific and technological applications. In this study, we experimentally demonstrated a PRB scheme with a chaotic microcomb using a chip-scale integrated resonator. A microcomb contained hundreds of chaotic channels, and each comb tooth functioned as an entropy source for the PRB. First, a 12 Gbits/s PRB signal was obtained for each tooth channel with proper post-processing and passed the NIST Special Publication 800-22 statistical tests. The chaotic microcomb covered a wavelength range from 1430 to 1675 nm with a free spectral range (FSR) of 100 GHz. Consequently, the combined random bit sequence could achieve an ultra-high rate of about 4 Tbits/s (12 Gbits/s × 294 = 3.528 Tbits/s), with 294 teeth in the experimental microcomb. Additionally, denser microcombs were experimentally realized using an integrated resonator with 33.6 GHz FSR. A total of 805 chaotic comb teeth were observed and covered the wavelength range from 1430 to 1670 nm. In each tooth channel, 12 Gbits/s random sequences was generated, which passed the NIST test. Consequently, the total rate of the PRB was approximately 10 Tbits/s (12 Gbits/s × 805 = 9.66 Tbits/s). These results could offer potential chip solutions of Pbits/s PRB with the features of low cost and a high degree of parallelism.