| 1. |
- Cao, Shun, et al.
(författare)
-
Enhancing single photon emission through quasi-bound states in the continuum of monolithic hexagonal boron nitride metasurface
- 2021
-
Ingår i: Journal of Physics. - : IOP Publishing. - 2515-7639. ; 4:3
-
Tidskriftsartikel (refereegranskat)abstract
- A patterned structure of monolithic hexagonal boron nitride (hBN) on a glass substrate, which can enhance the emission of the embedded single photon emitters (SPEs), is useful for onchip single-photon sources of high-quality. Here, we design and demonstrate a monolithic hBN metasurface with quasi-bound states in the continuum mode at emission wavelength with ultrahigh Q values to enhance fluorescence emission of SPEs in hBN. Because of ultrahigh electric field enhancement inside the proposed hBN metasurface, an ultrahigh Purcell factor (3.3 x 10(4)) is achieved. In addition, the Purcell factor can also be strongly enhanced in most part of the hBN structure, which makes the hBN metasurface suitable for e.g. monolithic quantum photonics.
|
|
| 2. |
- Cao, Shun, et al.
(författare)
-
High-temperature ultra-broad UV–MIR high-efficiency absorber based on double ring-shaped titanium nitride resonators
- 2021
-
Ingår i: Optics Communications. - : Elsevier B.V.. - 0030-4018 .- 1873-0310. ; 485
-
Tidskriftsartikel (refereegranskat)abstract
- An ultrabroad absorber based on double-ring-shaped titanium nitride (TiN) nanoresonators, which can work in high temperatures, is proposed and numerically studied. The absorber with some optimal parameters exhibits an averaged absorption of 94.6% in the range of 200–4000 nm (from ultraviolet to mid-infrared) and a band from 200–3518 nm having an absorption > 90%. We have demonstrated in detail the physical mechanisms of the ultra-broad absorption, including the dielectric lossy property of TiN material itself in shorter wavelengths and plasmonic resonances caused by the metallic property of TiN nano-resonators in longer wavelengths. In addition, the absorber shows polarization independent and wide-angle acceptance. Another absorber with double TiN nano-rings of different heights has flatter and higher absorption efficiency (more than 95% absorption) at 200–2860 nm waveband. These properties make the proposed absorbers based on TiN has great potentials in many applications, such as light trapping, photovoltaics, thermal emitters.
|
|
| 3. |
- Fu, J., et al.
(författare)
-
Enabling Ultrathin Metamaterial Absorbers with Narrow Slits
- 2020
-
Ingår i: Advanced Optical Materials. - : Wiley-VCH Verlag. - 2162-7568 .- 2195-1071. ; 8:16
-
Tidskriftsartikel (refereegranskat)abstract
- Metamaterial absorbers (MAs) consisting of subwavelength units offer flexible design freedom and prominent advantages over traditional absorbers. Here, it is found that narrow slits provide the MAs a significant passageway to control the absorption behavior and obtain an ultrasmall thickness. As narrowing the slits in an MA gradually, two effects appear in turn, of which the former is that the slits help the localized energy leak away from the resonant units to balance the material absorption and radiation leakage rates and sustain perfect absorption, and the latter is that acting as a capacitor, the slits red-shift the absorption peak. A record ultrathin microwave MA with a thickness of only 1/474 of the working wavelength is demonstrated. Colossal electric field is excited inside ultranarrow slits by the assistance of localized resonance in collecting the incident wave. The finding can be extended to other frequencies, and is fascinating for some areas requiring ultrathin absorption structures or strong interaction between waves and matters.
|
|
| 4. |
- He, Nan, et al.
(författare)
-
All-in-One Collimating Splitter Based on a Meta-Fiber Platform
- 2023
-
Ingår i: Applied Sciences. - : MDPI AG. - 2076-3417. ; 13:7
-
Tidskriftsartikel (refereegranskat)abstract
- The use of array generators has become ubiquitous in various applications such as laser fabrication, face identification, and motion sensing. The Dammann grating, a diffractive optical element, is the mainstream approach for generating uniform spot arrays. However, its limited capability and the contradiction between the performance and the complexity of fabrication hinder its application. To address this issue, an all-in-one collimating splitter based on metasurfaces is theoretically proposed by synthesizing the phase of an inverse-optimized Dammann grating and a collimating lens. Leveraging both the diffraction effect of Dammann grating and the Fourier transformation of the collimating lens, the number of spot arrays can be largely increased with a single lenslet. The proposed design shows a large field of view of 62 degrees x 62 degrees ffi and a high uniformity of 1.29% in generating a spot array of 3 x 3 on a single-fiber platform, confirmed by both the scalar and full-wave simulation. Further, a larger spot array up to 15 x 15 is also derived in the far field by integrating the proposed metasurface on a 5 x 5 fiber array platform, confirmed by the scalar simulation. Our design may be transplanted to the vertical-cavity surface-emitting laser platform, and shows great potential in various applications including face identification and motion sensing.
|
|
| 5. |
- He, Nan, et al.
(författare)
-
High-Speed Duplex Free Space Optical Communication System Assisted by a Wide-Field-of-View Metalens
- 2023
-
Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 10:9, s. 3052-3059
-
Tidskriftsartikel (refereegranskat)abstract
- Free space optical communication (FSO) has gained significant attention due to the growing demand for a high information capacity. For FSO between multiple or moving targets, a receiver with a wide angle of acquisition capability is necessary. Traditionally, gimbals and fast steering mirrors have been used, but they are often difficult to make both compact and wide-angle. Here, a novel duplex FSO system is demonstrated, which utilizes a highly compact fiber coupling metalens to receive and transmit signals in a large field of view up to 80°. High coupling efficiency up to 48.8% at a wavelength of 1550 nm is experimentally achieved. The small coupling loss enables the user to modulate and direct the downstream power from the base station back along the same path, saving energy and leaving only one source in the FSO system. The low bit error rate and the open and clear eye diagram results validate the excellent downlink/uplink communication performance of a 10 Gbps FSO system empowered by the metalens. The system exhibits a large field of view, high data rate, compact size, and low power consumption, which meets the size, weight, and power requirement of smart devices.
|
|
| 6. |
- He, N., et al.
(författare)
-
Highly Compact All-Solid-State Beam Steering Module Based on a Metafiber
- 2022
-
Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 9:9, s. 3094-3101
-
Tidskriftsartikel (refereegranskat)abstract
- Optical phased arrays occupy the predominant position in the solid-state light detection and ranging; however, their applications are limited by high insertion loss, complex control, and the need for tunable lasers. Here, by assembling a quadratic silicon metalens onto the end face of a single-mode fiber array to form a metafiber, we propose an all-solid-state beam steering module. With the introduction of the flat metalens, the module is highly compact, and the field of view may be extremely wide. A large field of view up to about 60° is testified experimentally based on a one-dimensional module. The application for parking space monitoring is also demonstrated based on a two-dimensional module. The beam steering module can be switched between the scanning mode and the flash mode compatibly and can also be extended to a larger scale with a higher scanning precision by increasing the size of the fiber array and scaling the metalens. The presented scheme featured with high compactness, high performance, and good compatibility provides a distinctive beam steering candidate for light detection and ranging or optical wireless communication applications.
|
|
| 7. |
- He, Wang, et al.
(författare)
-
Fast Power Density Assessment of 5G Mobile Handset Using Equivalent Currents Method
- 2021
-
Ingår i: IEEE Transactions on Antennas and Propagation. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-926X .- 1558-2221. ; 69:10, s. 6857-6869
-
Tidskriftsartikel (refereegranskat)abstract
- As the fifth-generation (5G) mobile communication is utilizing millimeter-wave (mmWave) frequency bands, electromagnetic field (EMF) exposure emitted from a 5G mmWave mobile handset should be evaluated and compliant with the relevant EMF exposure limits in terms of peak spatial-average incident power density (PD). In this work, a fast PD assessment method for a 5G mmWave mobile handset using the equivalent current (EQC) method is proposed. The EQC method utilizes the intermediate-field (IF) data collected by a spherical measurement system to reconstruct the EQCs over a reconstruction surface and then computes the PD in close proximity of the mobile handset with acceptable accuracy. The performance of the proposed method is evaluated using a mmWave mobile handset mock-up equipped with four quasi-Yagi antennas. The assessed PD results are compared with those computed using full-wave simulations and also those measured with a planar near-field (NF) scanning system. In addition, three influencing factors related to the accuracy of the EQC method, namely, the angular resolution, the phase error, and the handset position in the IF measurements, are also analyzed. The proposed method is a good candidate for fast PD assessment of EMF exposure compliance testing in the mmWave frequency range.
|
|
| 8. |
- He, Wang, et al.
(författare)
-
Implications of Incident Power Density Limits on Power and EIRP Levels of 5G Millimeter-Wave User Equipment
- 2020
-
Ingår i: IEEE Access. - : Institute of Electrical and Electronics Engineers (IEEE). - 2169-3536. ; 8, s. 148214-148225
-
Tidskriftsartikel (refereegranskat)abstract
- User equipment (UE) is required to comply with the relevant radio frequency (RF) electromagnetic field (EMF) exposure limits, which are of relevance to establish the maximum permissible transmitted power and the maximum equivalent isotropically radiated power (EIRP). Recently, international RF EMF exposure guidelines, such as those published by the International Commission on Non-Ionizing Radiation Protection (ICNIRP) as well as by the IEEE, have been updated. In this paper, the implications of the revised incident power density limits are investigated in terms of maximum permissible transmitted power and the maximum EIRP for devices operating in close proximity of the user. A similar analysis is conducted according to the US Federal Communications Commission (FCC) regulation on RF exposure. EMF compliance of UE is studied by means of numerical modelling of patch antenna arrays of different array sizes taking into consideration of possible beam-steering operations, at frequencies ranging from 10 GHz to 100 GHz. The results are compared with the 3rd Generation Partnership Project (3GPP) requirements on the total radiated power (TRP) and EIRP levels. The present implications of the incident power density limits for 5G millimeter-wave UE will give valuable insights to mobile equipment manufacturers, network operators, and standardization bodies.
|
|
| 9. |
- He, Xie, et al.
(författare)
-
Patterned few nanometer-thick silver films with high optical transparency and high electrical conductivity
- 2021
-
Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 11:19, s. 11481-11489
-
Tidskriftsartikel (refereegranskat)abstract
- Transparent conductive electrodes (TCEs) are experimentally demonstrated using patterned few nanometer-thick silver films on zinc oxide-coated rigid and flexible substrates. The grid lines are completely continuous, but only 8.4 nm thick. This is the thinnest metallic grid we are aware of. Owing to the high transparency of both the grid lines and spacing, our TCE with an opening ratio (OR) as small as 36% achieves an average optical transmittance up to similar to 90% in the visible regime, breaking the optical limits of both the unpatterned film counterpart and the thick grid counterpart (whose optical transmittance is determined by the OR). The small OR enables a low sheet resistance of similar to 21.5 omega sq(-1). The figure of merit up to similar to 17 k omega(-1) is superior to those of the unpatterned film counterpart, our fabricated 180 nm thick ITO, as well as most reported thick metal grid TCEs. Our ultrathin TCE, firmly attached to the substrate, is mechanically more flexible and more stable than the film counterpart and ITO. As a flexible transparent film heater, it achieves comparable or even superior heating performances with previously-reported heaters and performs well in a thermochromic test.
|
|
| 10. |
- He, Xie, et al.
(författare)
-
Visible-blind and flexible metal-semiconductor-metal ultraviolet photodetectors based on sub-10-nm thick silver interdigital electrodes
- 2021
-
Ingår i: Optics Letters. - : The Optical Society. - 0146-9592 .- 1539-4794. ; 46:18, s. 4666-4669
-
Tidskriftsartikel (refereegranskat)abstract
- We propose and experimentally demonstrate a distinct visible-blind and flexible metal-semiconductor-metal ultraviolet (UV) photodetector (PD) based on sub-10-nm thick silver interdigital electrodes. The transparent PD with 7-nm thick electrodes shows enhanced visible transmittance (80%) in average and achieves greatly improved responsivity (60.5 mA/W), and detectivity (1.75 x 10(10) Jones) at 5 V under 380-nm illumination, compared with its opaque counterpart. It is as fast as the opaquePDwith short rise and fall times (22.4 and 11.5 ms) and shows good flexibility. All the properties are comparable or superior to many reported transparent UV PDs, mainly attributed to the broad high UV-visible transmittance and the high conductivity of the ultrathin silver film.
|
|
