Advanced Photonics Research最新文献

Transparent amorphous germanium (a-Ge) has emerged as a promising material for engineering nanostructures and metasurfaces, offering significant potential for enhancing the performance of photonic devices in the short-wavelength infrared (SWIR) spectrum. Herein, the successful application of a-Ge metasurfaces with a truncated pyramid profile to enhance the external quantum efficiency (EQE) of a digital alloy Al_0.3InAsSb p–i–n photodiode across a broad-wavelength range in the SWIR is presented. The experimental findings demonstrate a broadband enhancement in EQE. Two metasurface samples are designed to emphasize different-wavelength ranges. Notably, 51% improvement in EQE at 1550 nm and 125% enhancement at 2000 nm is achieved. Finite-difference time domain simulations show that the observed EQE improvement originates from the reduction of reflection and electromagnetic field enhancement. This study underscores the promising role of a-Ge metasurfaces in advancing the capabilities of SWIR photodetectors. It lays the groundwork for further exploration in optoelectronic device enhancements.

Quantum Well Lasers

Benefitting from the interaction of the GaAs/GaAsP strained quantum well and InAlAs active region dislocation blocking layer, in article number 2300348, Jian Li and co-workers show that the threading dislocation penetration to the quantum well region of the silicon-based quantum well lasers can be bended and blocked. By the introduction of this strain compensate stress control structure, the 850 nm room temperature continuous wave emitting silicon-based quantum well laser exhibits a 94.2 mW power output, a 715 Acm^–2 threshold current density, and enhanced reliability.

Active Tunable Terahertz Metamaterials

Metamaterials give terahertz technology a broader application prospect. Active control ability of terahertz metamaterials is highly valuable and captivating. In article number 2300351, Kai Chen, Degang Xu, and co-workers categorize four basic types of tunable terahertz metamaterials based on external stimuli. Mechanical modulation offers simple yet efficient modulation, while electrical and magnetic modulation provide convenient adjustment. Moreover, optical modulation focuses on incorporating various materials to high-speed control.

Terahertz (THz) radiation is highly promising for various applications, from industrial inspections to medical diagnoses. Given the typically ultralow-level power of generated THz radiation, the achievement of high responsivity in THz detection stands as a critical imperative for its applications. Graphene-based detectors have become an attractive choice for THz detection due to the graphene unique 2D material structure, allowing a broad absorption spectrum and ultrafast response. Various plasmonic antenna arrays are also employed to couple with graphene, compensating for its modest optical absorption. However, the configuration of the plasmonic antenna arrays plays a crucial role in THz detection as it determines the graphene physical mechanisms of photodetection, directly impacting the final responsivity. Here, the key factors for achieving high responsivity are investigated and it is presented that reducing the gap size of the plasmonic antenna arrays to the nanoscale and implementing a series-connection configuration can result in a remarkable increase in responsivity, often by several orders of magnitude. Importantly, this approach effectively prevents short circuits and minimizes dark current, further enhancing the overall performance of the detection system.

Polymer-network liquid crystal (PNLC) possesses both advantages of low-molecular-weight liquid crystal (LMWLC) and liquid crystal (LC) polymer. Herein, a two-stage polymerization strategy for the formation of unique PNLC with oxygen-sensing properties is reported. The reaction mixture consists of 6% diacrylate RM257, 93.5% LMWLC 4-cyano-4′-pentylbiphenyl (5CB), and 0.5% photoinitiator dimethoxy-2-phenylacetophenone (DMPA). In the first stage, the mixture is exposed to UV light for 2 min to form a primary polymer network, which is highly uniform with a planar orientation. However, some free radicals are trapped inside the LC due to the short UV exposure time. Subsequently, the trapped free radicals are released by heating the PNLC sample into an isotropic state. Under this condition, the free radicals can move freely and react with surrounding monomers to form a secondary polymer network, which is highly disordered and scatters light strongly. Because oxygen can deactivate free radicals trapped inside the PNLC, the phenomenon to detect oxygen and monitor the diffusion of oxygen through the PNLC is exploited. The PNLC-based oxygen sensor is potentially useful for the detection of oxygen and monitoring the exposure time to oxygen.

In recent years, metasurfaces composed of lumped nonlinear circuits have been reported to exhibit the capability of detecting specific electromagnetic waves, even when the waves are of the same frequency, depending on their respective waveforms or, more precisely, their pulse widths. Herein, three types of metasurface absorbers (MSAs) are presented which are composed of a square-patch structure loaded with linear circuit components, including lumped resistors or resistors in parallel with capacitors/inductors, which can mimic the waveform-selective absorption behavior in the terahertz (THz) region. By judiciously selecting suitable values for the linear circuit components, these MSAs can achieve near-perfect absorption of incident continuous waves or longer pulses while exhibiting reduced absorption of short pulses at the same THz frequency. These linear circuit structures can be referred to as pseudo-waveform-selective MSAs because their waveform-selective absorption characteristics are primarily derived from the dispersion behavior of the resonator structures, as opposed to the frequency conversion commonly observed in nonlinear circuits. These outcomes and discoveries introduce an additional degree of freedom for waveform discrimination in the THz frequency range, potentially enabling a broader range of applications, including but not limited to detection, sensing, and wireless communication.

A silicon-based room temperature (RT) continuous wave (CW) operation quantum well (QW) laser emitting at 850 nm is reported in this article. By applying the dislocation filter superlattice, the threading dislocation density of the GaAs pseudosubstrate on Si is reduced to 1.8 × 10⁷ cm⁻². The metal-organic chemical vapor deposition-grown laser structure with GaAs/GaAsP QW and InAlAs active region dislocation blocking layer are fabricated into broad-stripe Fabry–Perot laser diodes. A typical threshold current and threshold current density of 286 mA and 715 Acm⁻² are obtained with 2 mm cavity length and 20 um stripe width samples. A 94.2 mW single-facet output power lasing around 854 nm and a 0.314 WA⁻¹ slope efficiency is measured under RT CW operation. After a 10-min aging process, the tested laser can operate stably under continuous operation conditions at RT and the lifetime can be approximated using an exponential fitting curve, indicating a good life reliability of this QW laser.