Equivalent circuit model for multi-electrode semiconductor opticalamplifiers and analysis of inline photodetection in bidirectionaltransmissions

A rate equation model for static and dynamic behavior for bidirectional transmission in a multisection semiconductor optical amplifier (SOA) is presented. The rate equations for each section have been implemented on an electrical simulator. Here, we have used the model to study the inline photodetection in presence of bidirectional transmission. Small signal photodetection response in presence of co- and contrapropagating signals is given. The photodetection crosstalk expression in bidirectional transmission has also been reported. Simultaneous bidirectional photodetection experiments using a three-electrode SOA show good agreement between measured crosstalk and simulated results obtained by harmonic balance method. A photodetection response nearly free of crosstalk has been obtained for certain operating conditions due to the cross gain modulation between contrapropagating signals     

Narrow-core hollow optical waveguide with nanostructured SOI as ultra-low loss platform for efficient photodetection

A nanostructured hollow optical waveguide based on high-index contrast grating (HCG) embedded SOI is proposed. An ultra-low propagation loss of 1.22 dB/m even at narrow, 1-\(\upmu \)m thick, air-core is reported. A high-performance photodetection is realized by the introduction of hollow core in form of intrinsic region in the photodetection (PIN) layer within HCG-assisted narrow-core waveguide. A sufficiently high responsivity of 0.8 A/W and quantum efficiency of 64% are obtained at 1550-nm which is possible because of the presence of surface modes within HCG which get coupled in the photodetection layer leading to a strong optical confinement in that layer. High reflectivity, small penetration length and coupling of lateral surface modes in HCG make it possible to offer improved waveguiding and hence photodetection.     

Highly In-Plane Anisotropic 2D PdSe2 for Polarized Photodetection with Orientation Selectivity

Polarized photodetection based on anisotropic two-dimensional materials display promising prospects for practical application in optical communication and optoelectronic fields. However, most of the reported polarized photodetection are limited by the lack of valid tunable strategy and low linear dichroism ratio. A peculiar noble metal dichalcogenide—PdSe₂ with a puckered pentagonal structure and abnormal linear dichroism conversion—potentially removes these restrictions and is demonstrated in this study. Herein, azimuth-dependent reflectance difference microscopy combined with anisotropic electrical transport measurements indicate strong in-plane anisotropic optical and electrical properties of two-dimensional PdSe₂. Remarkably, the typical polarization-resolved photodetection exhibits anisotropic photodetection characteristics with a dichroic ratio up to ≈1.8 at 532 nm and ≈2.2 at 369 nm, and their dominant polarization orientation differs by 90° corresponding to the a-axis and b-axis, respectively. The unique orientation selection behavior in polarization-dependent photodetection can be attributed to the intrinsic linear dichroism conversion. The results make 2D PdSe₂ a promising platform for investigating anisotropic structure–property correlations and integrated optical applications for novel polarization-sensitive photodetection.     

CMOS integrated luminescence oxygen multi-sensor system

A miniaturised luminescence multi-sensor system is reported, which combines addressable micro-light emitting diodes (LEDs) for optical excitation, sol-gel derived xerogel recognition elements for encapsulation of luminophores, and a CMOS integrated circuit for photodetection and signal processing. As a prototype, three surface-mount type micro-LEDs coated with oxygen (O₂) sensitive xerogel thin films are presented. Each xerogel sensor operates satisfactorily over the entire range of O₂ concentrations but has a different sensitivity and response profile to O₂. The described integrated system establishes the viability for low-cost and low-power biochemical sensor systems with improved accuracy and certainty     

基于电光调制的毫米波辐射计研究

研究了一种通过电光调制将毫米波信号加载到光载波上进行处理的毫米波辐射计。天线接收的毫米波信号由电光调制器（EOM）调制加载到光载波的边带上,并通过光纤传输该信号;利用光纤布拉格光栅（FBG）滤波器滤掉载波分量,滤波后保留的边带分量信号由光电探测器（PD）探测。为提高探测灵敏度,使用锁相放大器对PD输出的信号进行检测。分...     

Plasmonic Charge Transfers in Large-Scale Metallic and Colloidal Photonic Crystal Slabs

The challenges in plasmonic charge transfer on a large-scale and low losses are systematically investigated by optical designs using 1D-plasmonic lattice structures. These plasmonic lattices are used as couplers to guide the energy in an underneath sub-wavelength titanium dioxide layer, resulting in the photonic crystal slabs. So far, photodetection is possible at energy levels close to the semiconductor bandgap; however, with the observed hybrid plasmonic–photonic modes, other wavelengths over the broad solar spectrum can be easily accessed for energy harvesting. The photo-enhanced current is measured locally with simple two-point contact on the centimeter-squared nanostructure by applying a bias voltage. As lattice couplers, interference lithographically fabricated conventional gold grating provides an advantage in fabrication; this optical concept is extended for the first time toward colloidal self-assembled nanoparticle chains to make the charge injection accessible for large-scale at reasonable costs with possibilities of photodetection by electric field vectors both along and perpendicular to the grating lines. To discuss the bottleneck of unavoidable isolating ligand shell of nanoparticles in contrast to the directly contacted nanobars, polarization-dependent ultrafast characterizations are carried out to study the charge injection processes in femtosecond resolution.     

Plasmon‐Induced Sub‐Bandgap Photodetection with Organic Schottky Diodes

Organic materials for near‐infrared (NIR) photodetection are in the focus for developing organic optical‐sensing devices. The choice of materials for bulk‐type organic photodetectors is limited due to effects like high nonradiative recombination rates for low‐gap materials. Here, an organic Schottky barrier photodetector with an integrated plasmonic nanohole electrode is proposed, enabling structure‐dependent, sub‐bandgap photodetection in the NIR. Photons are detected via internal photoemission (IPE) process over a metal/organic semiconductor Schottky barrier. The efficiency of IPE is improved by exciting localized surface plasmon resonances, which are further enhanced by coupling to an out‐of‐plane Fabry–Pérot cavity within the metal/organic/metal device configuration. The device allows large on/off ratio (>1000) and the selective control of individual pixels by modulating the Schottky barrier height. The concept opens up new design and application possibilities for organic NIR photodetectors.     

The performance of optical fiber direct-sequence spread-spectrummultiple-access communications systems

Because of the random nature of the photodetection process and the multiple-user interference, an exact analysis of avalanche photodiode (APD)-based optical code division multiple-access (CDMA) communications systems is intractable and quite often, Monte Carlo (MC) simulations which yield exact estimates of system performance in terms of bit error rates (BERs) require a prohibitive computational burden. A quick and accurate MC method for simulating APD-based optical CDMA systems is presented. In particular, a performance analysis of optical CDMA systems employing optical orthogonal and prime sequence codes is undertaken     

Effect of intermodulation in multichannel optical heterodyne systems

It is shown that large numbers of optical heterodyne channels may be frequency multiplexed over a single-mode optical fibre without the intermodulation byproducts of the photodetection process becoming a problem, provided the channels are spaced at five times their optical bandwidth, or greater.     

Analysis of the sign reversal of the photodetected signal responsein a multielectrode semiconductor optical amplifier

We present a theoretical analysis and experimental results for a two-electrode (200 μm×300 μm) 1.5-μm semiconductor optical amplifier (SOA) used in photodetection. The experimental results show that at a particular operating point regarding current and optical input power, a sign reversal of the photodetected signal response, and a frequency bandwidth shape modification are obtained at the SOA front contact. These results are confirmed by simulation and explained by the developed theoretical photodetection expression obtained by small signal analysis from the rate equation     

面向监视侦查的光电探测场景仿真系统总体设计

现有仿真设计软件功能还难以满足空天地一体化光电探测系统总体设计的需求,迫切需要开发一套光电探测场景仿真设计软件。通过对光电探测场景组成要素、探测链路与任务模式的分析,规划了仿真系统结构、功能与关键技术,设计了面向对象的数据结构属性方法与仿真计算流程,在VS2010+QT5.4环境下开发了光电探测场景仿真系统的基础版本。给出了美国STSS天基红外监视系统中段目标探测任务仿真实例计算结果和笔者团队的光电探测仿真技术主要应用成果。     

Demodulation Pixel Based on Static Drift Fields

A novel pixel architecture for two-dimensional pixel parallel demodulation of modulated light waves is introduced, enabling real-time three-dimensional (3-D) imaging. Applications for such methods can be found in the field of surveillance, robotics, automotive, and industry security applications. The pixel architecture is based on large areas of static drift fields and relatively small demodulation regions. The large area of static drift field forms the basic photodetection region. The constant drift field enables the very fast transport of photo-generated charges to the sampling region where demodulation of the light signal is performed. The main advantages compared to recently used demodulation pixels are lower power consumption and higher optical fill factor or sensitivity. The first implementation is a pixel of 40times40 mum ² size with 25% optical fill factor. Measurements prove the concept of transporting photo-generated charges within less than 1 ns to the demodulation node. The applicability of the pixel in 3-D imaging applications is highlighted by distance measurements achieving millimeter distance resolution     

Polarization‐Sensitive Ultraviolet Photodetection of Anisotropic 2D GeS2

Polarization‐sensitive photodetection in the UV region is highly indispensable in many military and civilian applications. UV‐polarized photodetection usually relies on the use of wide bandgap semiconductors with 1D nanostructures requiring complicated nanofabrication processes. Although the emerging anisotropic 2D semiconductors shed light on the detection of polarization with a simple device architecture, bandgaps of such reported 2D semiconductors are too small to be applied for visible–blind UV‐polarized photodetection. Here, germanium disulfide (GeS₂), the widest bandgap (>3 eV) in the family of in‐plane anisotropic 2D semiconductors explored to date, is introduced as an ideal candidate for UV‐polarized photodetection. The structural, vibrational, and optical anisotropies of GeS₂ are systematically investigated from theory to experiment. GeS₂‐based photodetectors show a strong polarization‐dependent photoresponse in the UV region. GeS₂ with a wide bandgap and high in‐plane anisotropy not only enriches the family of anisotropic 2D semiconductors but also expands the polarized photodetection from the current visible and near‐infrared to the brand‐new UV region.     

Strong Interlayer Transition in Few-Layer InSe/PdSe2 van der Waals Heterostructure for Near-Infrared Photodetection

Near infrared (NIR) photodetectors based on 2D materials are widely studied for their potential application in next generation sensing, thermal imaging, and optical communication. Construction of van der Waals (vdWs) heterostructure provides a tremendous degree of freedom to combine and extend the features of 2D materials, opening up new functionalities on photonic and optoelectronic devices. Herein, a type-II InSe/PdSe₂ vdWs heterostructure with strong interlayer transition for NIR photodetection is demonstrated. Strong interlayer transition between InSe and PdSe₂ is predicted via density functional theory calculation and confirmed by photoluminance spectroscopy and Kelvin probe force microscopy. The heterostructure exhibits highly sensitive photodetection in NIR region up to 1650 nm. The photoresponsivity, detectivity, and external quantum efficiency at this wavelength respectively reaches up to 58.8 A W⁻¹, 1 × 10¹⁰ Jones, and 4660%. The results suggest that the construction of vdWs heterostructure with strong interlayer transition is a promising strategy for infrared photodetection, and this work paves the way to developing high-performance optoelectronic devices based on 2D vdWs heterostructures.     

Code-selective frequency shifting by RF photonic mixing in a dual-electrode Mach-Zehnder modulator

Code-selective frequency shifting by RF photonic mixing that may be used to demultiplex direct sequence encoded CDMA signals in the optical domain has been demonstrated. The technique exploits the bipolar nature of the optical field without requiring an optical local oscillator, and spectrally isolates the desired channel before photodetection.     

High-speed photodetection characteristics of a Fabry-Perot laser amplifier under AM and FM formats

A comparison between the photodetection characteristics of an FP laser amplifier under AM and FM formats is reported. A 450 MHz photodetection bandwidth is obtained under the AM format using a Fabry-Perot laser amplifier, with two antireflection coated facets with 10/sup -5/ reflectivity. Using an FP laser amplifier with 10/sup -3/ reflectivity as an FM discriminator/photodetector, a photodetection bandwidth of up to 2.6 GHz was measured.<>     

Flexible Filter‐Free Narrowband Photodetector with High Gain and Customized Responsive Spectrum

Conventional narrowband photodetection is enabled by coupling broadband photodetectors with complex optical filters. The recently reported charge collection narrowing, an alternative filter‐free strategy, attains very narrowband photodetection at the sacrifice of sensitivity. Herein, a new strategy is proposed to customize the responsive spectrum with high gain by using dye molecules with intrinsically versatile and narrowband absorption. The device configuration is organic dye/Zn_0.9Mg_0.1O nanoparticles/graphene, where the organic dye serves as the narrowband absorber, graphene serves as the fast carrier transport channel, and Zn_0.9Mg_0.1O nanoparticles play a triple role of enhancing dye loading, suppressing dye aggregation and blocking charge back recombination. A high responsivity of 8 × 10³ A W^?1 is thus obtained at a 530 nm response peak with a 60 nm full‐width at half maximum, a four orders of magnitude increase in sensitivity compared to the best narrowband photodetectors reported to date under the comparable electric field. Organic dyes with dual‐band absorption to demonstrate narrowband photodetectors with customized responsive spectrum are further implemented. The approach opens the way to the realization of efficient flexible narrowband photodetection for electronic skin and wearable electronic applications.     

Optical technologies for signal processing in satellite repeaters

The evolution of modern communications satellites from the older cable-in-the-sky concept toward more intelligent architectures, exploiting onboard processing (OBP) techniques involving various technologies to improve the system performance and flexibility, is addressed. The key components in advanced communications satellite repeaters compatible with integrated optical device implementation are presented. The relevant device technologies and fabrication techniques are examined, and integrated optical circuit configurations that can be applied to OBP are described with reference to recent experimental data. Particular attention is given to optical beamforming networks. Areas for further research and development are suggested     

Semiconductor photodetection-active transmission line analog

Semiconductor detection of optical frequency (or less) signals makes use of the photoelectric effect and may be readily characterized by active transmission lines. This letter briefly describes the semiconductor photodetection analog.     

Two-dimensional spatial light modulators: a tutorial

Two-dimensional spatial light modulators (SLMs) modulate one of the properties of an optical wavefront (amplitude, phase, polarization) as a function of two spatial dimensions and time in response to information-bearing control signals that may be either optical or electrical. These devices form a critical part of optical information processing systems, serving as input transducers as well as performing several basic processing operations on optical wavefronts. A tutorial overview of the 2-D SLMs is given. their applications are outlined, a classification scheme for them is given, and major types of SLMs that are under active development are described