Waveguide Detector Research Articles

High-efficiency Ge-based waveguide photodetector integrated with a grating coupler on silicon-on-insulator.

We propose the design of a composite device structure with germanium-based (Ge-based) waveguide photodetectors integrated with grating couplers on a silicon-on-insulator platform. The finite-difference time-domain method is used to establish simulation models and optimize the design of the waveguide detector and grating coupler. For the grating coupler, by adjusting the size parameters to the optimal value and combining the advantages of the nonuniform grating and the Bragg reflector structure, the peak coupling efficiency reaches 85% at 1550nm and 75.5% at 2000nm, which is, respectively, 31.3% and 14.6% higher than that of uniform grating. For the waveguide detector, a germanium-tin (GeSn) alloy was introduced to replace Ge as the active absorption layer at 1550 and 2000nm, which not only broadened the detection range and significantly improved the light absorption of the detector but also realized the near-complete light absorption of the GeSn alloy when the device length was 10µm. These results make it possible to miniaturize the device structure of Ge-based waveguide photodetectors.

Picosecond timing planes for future collider detectors

We report experimental test-beam results on dielectric-loaded waveguide detectors that utilize microwave Cherenkov signals to time and characterize high energy particle showers. These results are used to validate models and produce high-fidelity simulations of timing plane systems which yield picosecond time tags and millimeter spatial coordinates for the shower centroid. These timing planes, based on the Askaryan effect in solid dielectrics, are most effective at the high center-of-momentum energies planned for the Future Circular Collider (FCC-hh), and are of particular interest in the forward region due to their high radiation immunity. We use our beam test results and GEANT4 simulations to validate a hybrid microwave detector model, which is used to simulate a reference timing plane design for the FCC forward calorimeters. Our results indicate that 0.5-3 ps particle timing is possible for a wide range of collision products in the reference FCC hadron collider detector, even with current technology.

Waveguide-coupled heterodyne terahertz detector based on AlGaN/GaN high-electron-mobility transistor

We report a room-temperature, low output impedance, broad intermediate-frequency (IF) bandwidth field-effect terahertz detector based on an AlGaN/GaN high-electron-mobility transistor (HEMT) integrated in a metal waveguide. The waveguide detector equips a pair of quasi-Yagi antenna probes that are used to couple the terahertz energy to the HEMT channel. The gate is configured as an asymmetric edge-coupled coplanar waveguide transmission line. This terahertz electric field is asymmetrically distributed in the channel along the edges of the transmission lines. The responsivity and noise for direct and heterodyne detections are characterized and analyzed at different local oscillator (LO) powers. The noise-equivalent power in direct detection is below 189 pW/Hz1/2. Operated in a heterodyne mode with a LO power of −3 dBm, the detector offers a conversion loss less than 55 dB in a frequency band of 320–340 GHz. The channel in a form of transmission line performs the broad IF bandwidth, which is increased to gigahertz range (3 GHz), and reduces the output impedance to 377 Ω which is about 20 times lower than previously reported. The transmission-line impedance could be optimized together with the distribution of the terahertz electric field in the gated channel to reduce the conversion loss.

Design of a Slab Tamm Plasmon Resonator Coupled to a Multistrip Array Waveguide for the Mid Infrared.

In this work, we present and analyze a design of an absorber–waveguide system combining a highly sensitive waveguide array concept with a resonant selective absorber. The waveguide part is composed of an array of coupled strip waveguides and is therefore called a coupled strip array (CSA). The CSA is then coupled to the end of a slab Tamm plasmon (STP-) resonator, which is composed of a quasicrystal-like reflector formed by the patterning of a silicon slab and an interfacing tungsten slab. The concept describes an emitter–waveguide or waveguide–detector system featuring selective plasmon-enhanced resonant absorption or emission. These are crucial properties for corresponding optical on-chip integrated devices in context with evanescent field absorption sensing in fluids or gases, for example. Thus, the concept comprises a valuable and more cost-effective alternative to quantum cascade lasers. We designed the lateral dimensions of the STP resonator via a simple quasi-crystal approach and achieved strong narrowband resonances (emittance and Q-factors up to 85% and 88, respectively) for different silicon thicknesses and substrate materials (air and silicon oxide). Moreover, we analyze and discuss the sensitivity of the complete emitter–waveguide system in dependence on the slab thickness. This reveals the crucial correlation between the expected sensitivity assigned to the absorber–waveguide system and field confinement within the silicon.

High-sensitivity transparent photoconductors in voltage-controlled silicon waveguides.

On-chip optical power monitors are essential elements to calibrate, stabilize, and reconfigure photonic integrated circuits. Many applications require in-line waveguide detectors, where a trade-off has to be found between large sensitivity and high transparency to the guided light. In this work, we demonstrate a transparent photoconductor integrated on standard low-doped silicon-on-insulator waveguides that reaches a photoconductive gain of more than 106 and an in-line sensitivity as high as -60 dBm. This performance is achieved by compensating the effect of electric charges in the cladding oxide through a bias voltage applied to the chip substrate or locally through a gate electrode on top of the waveguide, allowing one to tune on demand the conductivity of the core to the optimum level.

Understanding the Light Detection in an Integrated Novel Electrophotonic Wavesensor Photodetector

This work presents a novel integrable silicon photodetector which can only be conceived as part of a monolithic electrophotonic basic structure formed of a silicon light emitter, waveguide and light detector. That is, it cannot operate as a single electronic or photonic device. The detector presents current gain, and photons reach the depletion region straightforward, allowing the detection of low power light produced by silicon light sources currently in use, which is difficult for existing photodetectors. The waveguide core is made of silicon nitride, and it is simultaneously the insulator in a MOS-like device. The light detection unit is intended for novel seamless electrophotonic platforms, and it is called wavesensor. In spite that the device is a MOS-like structure, it is not a MOSFET neither a lateral bipolar transistor, and one of the main differences with the former is that this is a bulk device working in Punch-Through regime. Being a MOS-like structure, it is fully compatible with standard microelectronics technology. A development of the mathematics involved in its operation is carried out in order to understand the physics of the detector, showing a gain factor in the photocurrent. Computer simulations of the fabrication process and photoelectric response of the device confirmed photocurrent values higher than the expected for a photodiode with efficiency = 1, thus demonstrating a new integrable photodetector with gain, capable of detecting light in the range of nW for electrophotonic applications.

(Invited) Monolithic Ge Integration on the 3 μm SOI Platform for 40 GHz Photodiodes

Silicon photonics offers the possibility to integrate a large number of photonic components on a small Si chip in a similar fashion as microelectronic circuits have been realized for many decades. This enables low power consumption, small footprint and low-cost mass production. Application areas for Si photonics reach from optical communication and computing to optical sensing and imaging. Monolithic germanium PIN detectors are one of the key components in photonic integrated circuits (PICs) and convert light into electrical signals. Germanium is the preferred material for photodetectors in silicon photonics as it absorbs light in the datacom and telecom wavelength range (1.2-1.7 μm) due to its small bandgap. Germanium is also tolerated in the IC-clean manufacturing lines, unlike many other potential semiconductor materials. Electron and hole mobilities in germanium are high, enabling high-bandwidth detectors. Challenges in Ge integration on silicon-on-insulator (SOI) wafers include unintentional oxidization and etching in many of the standard silicon technology processing steps, fast diffusion of n-type dopants in Ge and relatively large lattice mismatch between Ge and Si.High refractive index contrast between silicon (3.5) and silicon dioxide (1.5) is the key to achieve ultra-dense photonics integration. Most of the silicon photonics research is carried out using submicron-thick SOI waveguides and latest microelectronics fabrication technologies that involve (and require) very small wafer topography. In this paper, we present Ge photodiode integration on a 3 µm SOI platform with 3 µm thick Si waveguides. Those offer ultra-low propagation losses (~0.1 dB/cm), ultra-dense integration (μm-scale bends), small polarization dependency (down-to-zero birefringence) and ability to tolerate relatively high optical powers (>1W). One major limitation on the 3 µm SOI platform has been the lack of as fast modulators and photodetectors as those integrated on sub-µm SOI platforms. In this work, we monolithically integrated a fast horizontal PIN photodiode on the 3 µm SOI platform. The 3 dB cutoff frequency was 40 GHz and the responsivity was 1.0 A/W at -1 V bias and 1.55 µm wavelength. This high bandwidth indicates that the detector is limited by the transit time of the carriers over the i-region, rather than the junction capacitance. The electric field in the i-region at -1 V is sufficient to keep the carrier drift speed close to the maximum carriers velocity in Ge.The design of the 40 GHz PD included analytical calculations and numerical simulations. Physical dimensions of the detector were chosen so that they are compatible with the 3 µm SOI process flow and meet the bandwidth and responsivity targets. Germanium was selectively grown into cavities in the 3 µm SOI layer, leading to very low amount of stress-induced crystal defects. The Ge waveguide detector and the Si waveguides were patterned with a common hard mask to achieve self-alignment between them. The n- and p-contacts were directly made into Ge using Ti/Al metallization. The vertical sidewalls of the Ge detector were implanted in order to create a horizontal PIN structure. Due to high confinement of light into the 3 µm thick SOI and Ge waveguides, the 3 µm thick and 1 µm wide Ge detector could be made as short as 9 µm. This led to small junction capacitances. The electrical output pulse shape was not distorted by the slow diffusion current of electrons and holes because the incoming light does not enter the doped regions. The development of 40 GHz PDs was an important step in improving the feasibility of the 3 µm SOI platform in high-bandwidth applications. Figure 1

(Invited) Monolithic Ge Integration on the 3 µm SOI Platform for 40 GHz Photodiodes

Ge photodiodes were integrated on the 3 µm SOI platform, where the 3 µm thick Si waveguides offer ultra-low propagation losses (~0.1 dB/cm), ultra-dense integration (μm-scale bends), small polarization dependency (down-to-zero birefringence) and the ability to tolerate relatively high optical powers (>1W). A horizontal Ge PIN photodiode was monolithically integrated on the 3 µm SOI platform. It reached a 3 dB cutoff frequency of 40 GHz and 1.0 A/W responsivity at -1 V bias and 1.55 µm wavelength. Germanium was selectively grown into cavities in the 3 µm SOI layer and the Ge waveguide detector was patterned with the same hard mask with the Si waveguides to achieve waveguide self-alignment. The development of 40 GHz PDs was an important step in improving the feasibility of the 3 µm SOI platform in high-bandwidth applications.

Silicon Waveguide Integrated with Germanium Photodetector for a Photonic-Integrated FBG Interrogator.

We report a vertically coupled germanium (Ge) waveguide detector integrated on silicon-on-insulator waveguides and an optimized device structure through the analysis of the optical field distribution and absorption efficiency of the device. The photodetector we designed is manufactured by IMEC, and the tests show that the device has good performance. This study theoretically and experimentally explains the structure of Ge PIN and the effect of the photodetector (PD) waveguide parameters on the performance of the device. Simulation and optimization of waveguide detectors with different structures are carried out. The device’s structure, quantum efficiency, spectral response, response current, changes with incident light strength, and dark current of PIN-type Ge waveguide detector are calculated. The test results show that approximately 90% of the light is absorbed by a Ge waveguide with 20 μm Ge length and 500 nm Ge thickness. The quantum efficiency of the PD can reach 90.63%. Under the reverse bias of 1 V, 2 V and 3 V, the detector’s average responsiveness in C-band reached 1.02 A/W, 1.09 A/W and 1.16 A/W and the response time is 200 ns. The dark current is only 3.7 nA at the reverse bias voltage of −1 V. The proposed silicon-based Ge PIN PD is beneficial to the integration of the detector array for photonic integrated arrayed waveguide grating (AWG)-based fiber Bragg grating (FBG) interrogators.

Characterization of integrated waveguides by atomic-force-microscopy-assisted mid-infrared imaging and spectroscopy.

A novel spectroscopy technique to enable the rapid characterization of discrete mid-infrared integrated photonic waveguides is demonstrated. The technique utilizes lithography patterned polymer blocks that absorb light strongly within the molecular fingerprint region. These act as integrated waveguide detectors when combined with an atomic force microscope that measures the photothermal expansion when infrared light is guided to the block. As a proof of concept, the technique is used to experimentally characterize propagation loss and grating coupler response of Ge-on-Si waveguides at wavelengths from 6 to 10 µm. In addition, when the microscope is operated in scanning mode at fixed wavelength, the guided mode exiting the output facet is imaged with a lateral resolution better than 500 nm i.e. below the diffraction limit. The characterization technique can be applied to any mid-infrared waveguide platform and can provide non-destructive in-situ testing of discrete waveguide components.

Photon-number-resolving segmented detectors based on single-photon avalanche-photodiodes.

We investigate the feasibility and performance of photon-number-resolved photodetection employing single-photon avalanche photodiodes (SPADs) with low dark counts. While the main idea, to split n photons into m detection modes with a vanishing probability of more than one photon per mode, is not new, we investigate here a important variant of this situation where SPADs are side-coupled to the same waveguide rather than terminally coupled to a propagation tree. This prevents the nonideal SPAD quantum efficiency from contributing to photon loss. We propose a concrete SPAD segmented waveguide detector based on a vertical directional coupler design, and characterize its performance by evaluating the purities of Positive-Operator-Valued Measures (POVMs) in terms of number of SPADs, photon loss, dark counts, and electrical cross-talk.

100 GHz Plasmonic Photodetector

Photodetectors compatible with CMOS technology have shown great potential in implementing active silicon photonics circuits, yet current technologies are facing fundamental bandwidth limitations. Here, we propose and experimentally demonstrate for the first time a plasmonic photodetector achieving simultaneously record-high bandwidth beyond 100 GHz, an internal quantum efficiency of 36% and low footprint. High-speed data reception at 72 Gbit/s is demonstrated. Such superior performance is attributed to the subwavelength confinement of the optical energy in a photoconductive based plasmonic-germanium waveguide detector that enables shortest drift paths for photogenerated carriers and a very small resistance-capacitance product. In addition, the combination of plasmonic structures with absorbing semiconductors enables efficient and highest-speed photodetection. The proposed scheme may pave the way for a cost-efficient CMOS compatible and low temperature fabricated photodetector solution for photodetection b...

A High-Sensitivity Terahertz Detector Based on a Low-Barrier Schottky Diode**Supported by the National Natural Science Foundation of China under Grant No 61434006, and the Basic Application Research of Sichuan Province under Grant No 2017JY0227.

A low-barrier Schottky barrier diode based on the InGaAs/InP material system is designed and fabricated with a new non-destructive dry over-etching process. By using this diode, a high-sensitivity waveguide detector is proposed. The measured maximum responsivity is over 2000 mV/mW at 630 GHz. The measured noise effective power (NEP) is less than 35 pW/Hz0.5 at 570–630 GHz. The minimum NEP is 14 pW/Hz0.5 at 630 GHz. The proposed high-sensitivity waveguide detector has the characteristics of simple structure, compact size, low cost and high performance, and can be used in a variety of applications such as imaging, molecular spectroscopy and atmospheric remote sensing.

Experimental Demonstration of a High-Efficiency Relativistic Magnetron With Diffraction Output With Spherical Cathode Endcap

A previous computational study of a relativistic magnetron with diffractive output at the University of New Mexico using the particle-in-cell code MAGIC achieved an efficiency of 70%. The research described in this paper aimed to achieve an experimental verification of 70% efficient operation of this design. Changes to the topology were necessary, such as the introduction of a Helmholtz-like magnetic coil pair and the use of a polished stainless steel endcap on the downstream end of the transparent cathode. These structures maintain a high degree of magnetic field uniformity in the anode–cathode gap interaction space and intercept leakage electrons that might otherwise impact the dielectric output window. The use of these structures stands in contrast to the modified magnetic fields used in the work of others to protect the window. An ethanol calorimeter and S-band waveguide detector were placed in the near-field to obtain radio frequency pulse shape and frequency and to infer peak power through a measurement of total energy radiated. A coaxial D-dot probe and self-integrating Rogowski coil were used to measure pulser voltage and total current, respectively, and showed that the tube operated at an efficiency of 63.5% until the endcap started emitting electrons, after which the efficiency was 40.4% in $\pi $ -mode. Images of radiated field pattern on a neon-bulb grid and of air breakdown outside of the 21-cm diameter output window were captured to confirm conversion of the $\pi $ -mode of operation to a TE31 circular radiated output mode.

A High Performance Terahertz Waveguide Detector Based on a Low-Barrier Diode**Supported by the National High-Technology Research and Development Program of China under Grant No 2011AA010203, the National Basic Research Program of China under Grant Nos 2011CB201704 and 2010CB327502, and the National Natural Science Foundation of China under Grant No 61434006.

A Schottky barrier diode with low-barrier is presented, based on which a terahertz waveguide detector working at 500–600 GHz is designed and fabricated. By using the InGaAs/InP material system, the feature of the low barrier is obtained which greatly improves the performance of the detector. The measured typical voltage responsivity is about 900 V/W at 500–560 GHz and is about 400 V/W at 560–600 GHz. The proposed broadband waveguide detector has the characteristics of simple structure, compact size, low cost and high performance, and can be used in a variety of applications such as imaging, molecular spectroscopy and atmospheric remote sensing.

Radar backscattering measurement of bare soil and vegetation covered soil using X-band and full polarization

Abstract. The objective of the study is to measure backscattered power of bare soil and vegetation covered soil using X-band scatterometer system with full polarization and various angles during monsoon season and relate backscattered power to the density of vegetation over soil. The measurement was conducted at an experimental field located in the campus of Assam Engineering College, Guwahati, India. The soil sample consists of Silt and Clay in higher proportions as compared to Sand. The scatterometer system consists of dual-polarimetric square horn antennas, Power meter, Klystron, coaxial cables, isolator and waveguide detector. The polarization of the horn antennas as well as the look angle can be changed in the set-up. The backscattering coefficients were calculated by applying a radar equation for the measured values at incident angles between 30° and 60° for full polarization (HH, VV, HV, VH), respectively, and compared with vegetation cover over soil for each scatterometer measurement simultaneously. The VH polarization and 60° look angle are found to be the most suitable combination of configuration of an X-band scatterometer for distinguishing the land cover targets such as bare soil and vegetation covered soil. From the analysis of the results, polarimetric scatterometer data appear to be promising to distinguish the land cover types such as bare soil and soil completely covered by vegetation. The results of this study will help the scientists working in the field of active microwave remote sensing.

MHD instability fluctuation measurement on the HL-2A tokamak by using the HCN laser interferometer

The multichannel HCN laser interferometer has been routinely used to measure the electron density (n e ) on the HL-2A tokamak for several years. In order to explore its capability for qualitatively evaluating the Magnetohydrodynamic (MHD) fluctuation in plasmas from the probing signal, we implemented two important modifications on the hardware of channel #3 (r = −10.5 cm): (1) application of the high-response Schottky diode waveguide detector, and (2) utilization of a preamplifier with a broad pass-band of up to 500 kHz so as not to filter the fluctuation component mixed with the intermediate frequency (IF). Many MHD fluctuation phenomena, such as tearing modes (TMs), fishbones, long lived modes (LLMs), have been successfully detected by using the modified channel #3 in the HL-2A experimental campaign, and the results were quite coincident with those derived from the magnetic probe and the soft X-ray systems. We propose to apply this novel approach to more channels of the HCN laser interferometer.

二维三角晶格光子晶体波导的辐射特性

A photonic crystal waveguide structure with two-dimensional triangular lattice photonic crystals is proposed,in which emission efficiency can be enhanced. The composite structure is composed by cascading a coupled waveguide arrays to a single waveguide. The emission characteristics of light are analyzed via the finite-difference time-domain( FDTD) method. The results show that the emission efficiency of the cascading composite structure is improved. The device has been optimized further. When the distance between the single waveguide and the waveguide arrays is 1. 8a,the horizontal and vertical period number of the waveguide arrays are 6 and 5,the emission efficiency is the best. The emission efficiency is over 20%,when the distance is 100 a between the waveguide output and detector. This type structure of photonic crystal has potential applications in near-field optics and integrated optics.

Thermal-sensitive superconducting coplanar waveguide resonator used for weak light detection

Since the last decades, superconducting single-photon technology has been extensively used in the quantum security communication and the linear-optic quantum computing fields. Especially, the device based on the coplanar waveguide resonator has attracted substantial interests due to its evident advantages, including the relatively simple structure, the sufficiently high detection efficiency, and the photon-resolving capability, etc. With the profound investigation in optimizing the depositing methods and the material selections, as well as the the development of the relevant theories, the technology of single photon detection based on the coplanar waveguide resonator has obtained a breakthrough. In this review paper we begin from the basic principle of the coplanar waveguide detector, then interpret the relevant theory and some design details of the devices. Finally, based on some of the recent experimental results measured with the low-temperature devices in our lab, we give a brief perspective on the future development of the superconducting coplanar waveguide single photon detectors.

Broadband Electromagnetic Emission from PZT Ferroelectric Ceramics after Shock Loading

It was experimentally registered pulsed electromagnetic (EM) radiation in frequency range higher than television one using wideband horns with coaxial and waveguide outputs. The EM radiation was received during shock loading of lead zirconate titanate (PZT) ceramics cylinders in conventional piezoelectric ignition mechanisms. Digital oscilloscope allows registering whole series of EM pulses and each pulse from the series transmitted from horn antenna of (1 – 18) GHz operating band frequencies. There is (1 – 4) ms delay between the shock and the first pulse of the series. Duration of the series is about (3 – 4) ms. The PZT cylinders were cleaved along their axes and the surfaces formed in the process were investigated by scanning electron microscope. It was concluded that from electrical point of view PZT ceramics contain interacting subsystems. It was found that EM radiation spectrum of pulse detected by waveguide detector heads has harmonics reaching 80 GHz. Presence of harmonics higher than 20 GHz indicates on radiation due to deceleration of electrons emitted during the switching. The EM pulses in the series appear randomly and have different amplitudes which partly confirmed thesis on independent switching dynamics of small volumes governed by a local electric field.DOI: http://dx.doi.org/10.5755/j01.ms.19.4.3137