Hybrid III-V/SOI resonant cavity enhanced photodetector

Plasmonic internal-photoemission-based Si photodetector design suitable for optical communication

We propose a high-performance plasmonic photodetector based on the internal photoemission (IPE) process for the C-band communication wavelength. This photodetector takes advantage of an embedded nanohole array in Schottky metal. Owing to localized surface plasmon resonance, the absorption of the active metal layer increases, which results in the generation of more hot carriers and subsequently compensates for the low efficiency of IPE-based photodetectors. Simulations show that for the proposed photodetector with 2-nm-thick Au, Cu, and Ag Schottky contacts, the absorptance dramatically enhances to 95.1%, 93.2%, and 98.2%, respectively, at the wavelength of 1.55 µm. For the detector based on Au, the highest external quantum efficiency of 25.3% and responsivity of 0.32 A/W are achieved at a reverse bias voltage of 1 V. Furthermore, the 3 dB bandwidth can exceed 369 GHz owing to the low capacitance of the structure and the fast transit time of carriers from the thin p-Si layer. Finally, by studying the current-voltage characteristics of the photodetector, it is shown that under the reverse bias voltage of 1 V, the dark current is 665 nA at room temperature, and by reducing the temperature to 200 K, it improves three orders of magnitude and decreases to 810 pA.

Metasurface Photodetectors

Photodetectors are the essential building blocks of a wide range of optical systems. Typical photodetectors only convert the intensity of light electrical output signals, leaving other electromagnetic parameters, such as the frequencies, phases, and polarization states unresolved. Metasurfaces are arrays of subwavelength structures that can manipulate the amplitude, phase, frequency, and polarization state of light. When combined with photodetectors, metasurfaces can enhance the light-matter interaction at the pixel level and also enable the detector pixels to resolve more electromagnetic parameters. In this paper, we review recent research efforts in merging metasurfaces with photodetectors towards improved detection performances and advanced detection schemes. The impacts of merging metasurfaces with photodetectors, on the architecture of optical systems, and potential applications are also discussed.

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.

Plasmons in ultra-thin gold slabs with quantum spill-out: Fourier modal method, perturbative approach, and analytical model

We numerically study the effect of the quantum spill-out (QSO) on the plasmon mode indices of an ultra-thin metallic slab, using the Fourier modal method (FMM). To improve the convergence of the FMM results, a novel nonlinear coordinate transformation is suggested and employed. Furthermore, we present a perturbative approach for incorporating the effects of QSO on the plasmon mode indices, which agrees very well with the full numerical results. The perturbative approach also provides additional physical insight, and is used to derive analytical expressions for the mode indices using a simple model for the dielectric function. The analytical expressions reproduce the results obtained from the numerically-challenging spill-out problem with much less effort and may be used for understanding the effects of QSO on other plasmonic structures.

All-Si Photodetectors with a Resonant Cavity for Near-Infrared Polarimetric Detection

This work developed an all-Si photodetector with a surface plasmonic resonator formed by a sub-wavelength Au grating on the top of a Si-nanowire array and the same one beside the wires. The Au/Si interface with a Schottky barrier allows the photo-electron detection in near-infrared wavelength based on the internal emission of hot electrons generated by the surface plasmons in the cavity. Meanwhile, the Au sub-wavelength grating on the Si nanowire array acts as a polarizer for polarimetric detection. Finite-difference time-domain method was applied in the design of the novel device and state-of-art nanofabrication based on electron beam lithography was carried out. The characterization of the photo-electronic properties as well as the polarimetric detection demonstrate that the fabricated detectors on the silicon substrate possesses great prospects for sensing technology on all-Si.

Resonant gratings with an etch-stop layer and a fabrication-error tolerant design

Sub-wavelength gratings (SWG) have shown much promise for applications such as lightweight high bandwidth reflectors, polarising filters and focusing lenses. Unfortunately, grating performance may be rapidly degraded through variability in grating dimensions. We demonstrate, in particular, how an error in depth of etch can be detrimental to the performance of zero contrast grating reflectors. We mitigate the impact of this fabrication error through the introduction of an etch stop layer and in so doing we experimentally realise a high bandwidth reflector based on this modified structure. Another common fabrication error is variation in the duty-cycle of fabricated gratings. This duty-cycle variation can weaken grating performance, however we demonstrate that grating designs that exhibit tolerance to duty-cycle fluctuation can be identified through simulation. Finally, we discuss the impact of lateral etching and the resulting sidewall concavity. We present our approach for numerically predicting the spectral response from such a grating and also for convenience we outline an approach for quickly approximating grating performance. Good agreement is observed between these numerical predictions and measurements made on a HCG with concave sidewalls.

Dynamical dispersion engineering in coupled vertical cavities employing a high-contrast grating

Photon’s effective mass is an important parameter of an optical cavity mode, which determines the strength of light-matter interaction. Here, we propose a novel method for controlling the photon’s effective mass by using coupled photonic cavities and designing the angular dependence of the coupling strength. This can be implemented by employing a high-contrast grating (HCG) as the coupling reflector in a system of two coupled vertical cavities, and engineering both the HCG reflection phase and amplitude response. Several examples of HCG-based coupled cavities with novel features are discussed, including a case capable of dynamically controlling the photon’s effective mass to a large extent while keeping the resonance frequency same. We believe that full-control and dynamical-tuning of the photon’s effective mass may enable new possibilities for cavity quantum electrodynamics studies or conventional/polariton laser applications. For instance, one can dynamically control the condensate formation in polariton lasers by modifying the polariton mass.