Generative Model Watermarking Based on Human Visual System

Intellectual property protection of deep neural networks is receiving attention from more and more researchers, and the latest research applies model watermarking to generative models for image processing. However, the existing watermarking methods designed for generative models do not take into account the effects of different channels of sample images on watermarking. As a result, the watermarking performance is still limited. To tackle this problem, in this paper, we first analyze the effects of embedding watermark information on different channels. Then, based on the characteristics of human visual system (HVS), we introduce two HVS-based generative model watermarking methods, which are realized in RGB color space and YUV color space respectively. In RGB color space, the watermark is embedded into the R and B channels based on the fact that HVS is more sensitive to G channel. In YUV color space, the watermark is embedded into the DCT domain of U and V channels based on the fact that HVS is more sensitive to brightness changes. Experimental results demonstrate the effectiveness of the proposed work, which improves the fidelity of the model to be protected and has good universality compared with previous methods.Comment: https://scholar.google.com/citations?user=IdiF7M0AAAAJ&hl=e

Simulation of high-efficiency resonant-cavity-enhanced GeSn single-photon avalanche photodiodes for sensing and optical quantum applications

A novel resonant-cavity-enhanced (RCE) GeSn single-photon avalanche photodiode (SPAD) detector is proposed and optimized for high-efficiency single-photon detection at 1,550 and 2,000 nm wavelength at room temperature for sensing and optical quantum applications. The corresponding fabrication methods based on direct epitaxy and wafer bonding are proposed as well. The RCE GeSn SPAD consists of a PIPIN GeSn/Si heterostructures embedded in an optical cavity form by a distributed Bragg reflector (DBR) and GeSn surface. The results show that high photon absorption efficiency and avalanche triggering probabilities can be achieved by careful design of DBR reflectors, GeSn absorber, doping concentrations of Si charge sheet layer and multiplication layer, which lead to a high single-photon detection efficiency (SPDE) of ~80%, which is promising for emerging quantum applications demanding high SPDE, such as linear optical quantum computing. The noise equivalent power (NEP) and dark count rate (DCR) as a function of threading dislocations density (TDD) are examined as well. It is found that the device could operate near room temperature with a similar DCR level to that of Ge SPAD operating at low temperature . A NEP of ~3x1015 W/Hz1/2 is observed from RCE GeSn SPAD for 1,550 nm wavelength at room temperature. This work shows that the proposed RCE GeSn SPADs are promising candidates for high-efficiency single-photon detection in short-wave infrared (SWIR) regime for sensing and optical quantum applications.Ministry of Education (MOE)National Research Foundation (NRF)Accepted versionThis research project is supported by the National Research Foundation, Singapore, under its Competitive Research Program (CRP Award NRF-CRP19-2017-01), and Ministry of Education Tier-1 Project under Grant 2019-T1-002-040

Transferable single-layer GeSn nanomembrane resonant-cavity-enhanced photodetectors for 2 μm band optical communication and multi-spectral short-wave infrared sensing

Semiconductor nanomembranes (NMs) have emerged as an attractive nanomaterial for advanced electronic and photonic devices with attractive features such as transferability and flexibility, enabling heterogeneous integration of multi-functional components. Here, we demonstrate the transferable single-layer GeSn NM resonant-cavity-enhanced photodetectors for 2 μm optical communication and multi-spectral short-wave infrared sensing/imaging applications. The single-layer strain-free GeSn NMs with Sn concentration of 10% are released from a high-quality GeSn-on-insulator (GSOI) substrate with the defective interface regions removed. By transferring the GeSn NMs onto a predesigned distribution Bragg reflector (DBR)/Si substrate, a vertical microcavity is integrated to the device to enhance the light-matter interaction in the GeSn NM. With the integrated cavity and high-quality single-layer GeSn NM, a record responsivity of 0.51 A/W at 2 μm wavelength at room temperature is obtained, which is more than two orders of magnitude higher than the reported values of the multiple-layer GeSn membrane photodetectors without cavities. The potential of the device for multi-spectral photodetection is demonstrated by tuning the responsivity spectrum with different NM thicknesses. Theoretical simulations are utilized to analyze and verify the mechanisms of responsivity enhancement. The approach can be applied to other GeSn-NM-based active devices, such as electro-absorption modulators or light emitters and present a new pathway towards heterogeneous group-IV photonic integrated circuits with miniaturized devices.Ministry of Education (MOE)National Research Foundation (NRF)Submitted/Accepted versionThis work was supported by National Research Foundation Singapore (NRF–CRP19–2017–01), Ministry of Education AcRF Tier 2 (T2EP50121-0001 (MOE-000180-01)) and Ministry of Education AcRF Tier 1 (2021-T1-002-031 (RG112/21))

High speed and ultra-low dark current Ge vertical p-i-n photodetectors on an oxygen-annealed Ge-on-insulator platform with GeOx surface passivation

Germanium (Ge) vertical p-i-n photodetectors were demonstrated with an ultra-low dark current of 0.57 mA/cm2 at -1 V. A germanium-on-insulator (GOI) platform with a 200-mm wafer scale was realized for photodetector fabrication via direct wafer bonding and layer transfer techniques, followed by oxygen annealing in finance. A thin germanium-oxide (GeOx) layer was formed on the sidewall of photodetectors by ozone oxidation to suppress surface leakage current. The responsivity of the vertical p-i-n annealed GOI photodetectors was revealed to be 0.42 and 0.28 A/W at 1,500 and 1,550 nm at -1 V, respectively. The photodetector characteristics are investigated in comparison with photodetectors with SiO2 surface passivation. The surface leakage current is reduced by a factor of 10 for photodetectors via ozone oxidation. The 3dB bandwidth of 1.72 GHz at -1 V for GeOx surface-passivated photodetectors is enhanced by approximately 2 times compared to the one for SiO2 surface-passivated photodetectors. The 3dB bandwidth is theoretically expected to further enhance to ∼70 GHz with a 5 µm mesa diameter.National Research Foundation (NRF)Published versionNational Research Foundation Singapore Competitive Research Programme (NRF-CRP19-2017- 01)

Ge-on-Si avalanche photodiodes with photon trapping nanostructures for sensing and optical quantum applications

High-sensitivity Ge/Si avalanche photodiodes (APDs) have recently gained attention for their application in sensing and optical communication due to their low cost and CMOS compatible process. However, compared to commercial III–V compound APDs, Ge/Si APDs usually suffer from the issue of relatively low primary responsivity. In this paper, we report Ge-on-Si separate absorption, charge, and multiplication avalanche photodiodes (SACM-APDs) with photon-trapping nanostructures to enhance light absorption. Besides, by optimizing the depth of the holes, the photon trapping structure could reduce the dark current without compromising the avalanche effect as confirmed by both simulations and experimental results. As a result, the responsivity of the photon trapping APDs increases by 20-50 % from that of control APDs at the 1,550 nm wavelength band. Furthermore, a quantum efficiency higher than 80% could be achieved at 1550 nm when the photon trapping Ge-on-Si APD is on Si-on-insulator (SOI) platforms as predicted by simulations. Our results demonstrate that the photon trapping Ge/Si APDs exhibit superior dark current, light absorption and gain than those of the control devices, which have the potential applications in sensing and optical quantum communications.Ministry of Education (MOE)National Research Foundation (NRF)Submitted/Accepted versionThis work was supported by the National Research Foundation, Singapore, under its Competitive Research Program (CRP Award NRF-CRP19-2017-01), Ministry of Education AcRF Tier 2 (T2EP50121-0001 (MOE-000180-01)) and Ministry of Education AcRF Tier 1 (2021-T1-002-031 (RG112/21 ))

Modulation of light absorption in flexible GeSn metal–semiconductor–metal photodetectors by mechanical bending

We have demonstrated flexible GeSn metal–semiconductor–metal (MSM) photodetectors (PDs) by exploring the effect of mechanical strain on their optoelectronic properties. The PDs were fabricated from transfer-printed GeSn nanomembranes on polyethylene terephthalate (PET) substrates. Strain was introduced into the GeSn PDs under bend-down (uniaxial tensile strain) and bend-up (uniaxial compressive strain) conditions and their values were measured by Raman spectroscopy. The applied strain can affect the band-structure of the GeSn alloys, leading to a modulation of the electrical and optical characteristics of the PDs. Accordingly, dark current characteristics show an increase from 8.1 to 10.3 μA under the bend-down conditions and a decrease to 7.2 μA under the bend-up conditions, respectively. The optical responsivity at a wavelength of 2 μm increased by 151% under bend-down conditions, while it decreases by 35% under bend-up conditions. A theoretical study was carried out to support the fact that the responsivity enhancement is attributed to the change in the absorption coefficient of the strained GeSn. The results offer a new pathway to modulate the optical properties of GeSn for flexible applications.Ministry of Education (MOE)Nanyang Technological UniversityNational Research Foundation (NRF)Accepted versionThe work was supported by the Nanyang Technological University (NTU) start-up grant (M4082289.040) and partly by the National Research Foundation, Singapore, under its Competitive Research Program (CRP Award NRF-CRP19-2017-01) and Ministry of Education, Singapore, under its Tier 2 (MOE2018-T2-1-137). The authors would like to thank Prof. Hong Wang at the NTU for providing a laser setup