A compact large-signal model for hydrogen-terminated (C-H) diamond metal-oxide field effect transistors (MOSFETs) is presented based on an improved quasi-physical zone division (QPZD) model. Unlike ...the conventional QPZD model for the AlGaN/GaN high-electron-mobility transistors (HEMTs), the linear-mode current-voltage (I-V) model of the diamond FET is analytically deduced with an improved velocity-electric field relation and temperature-dependent effective hole mobility <inline-formula> <tex-math notation="LaTeX">\mu _{\mathrm {eff}}(T) </tex-math></inline-formula>. The I-V model can directly demonstrate the relation between the negative <inline-formula> <tex-math notation="LaTeX">V_{\mathrm {ds}} </tex-math></inline-formula> and the negative <inline-formula> <tex-math notation="LaTeX">I_{\mathrm {ds}} </tex-math></inline-formula> of the p-type diamond FETs, which cannot be achieved by the conventional QPZD model. Finally, the proposed model has been verified by the on-wafer measurements of an in-house <inline-formula> <tex-math notation="LaTeX">2\times 500\,\,\mu \text{m} </tex-math></inline-formula> diamond FET. The good consistency shows that the presented compact large-signal model can accurately predict the DC I-V, multibias scattering-parameters (S-parameters), and large-signal performances. The results of this paper will be useful for the microwave diamond-based transistor and circuit designs.
The full-length nucleotide sequence of the foot-and-mouth disease virus O/BY/CHA/2010 strain, Mya-98 lineage of Southeast Asia (SEA) topotype, was determined and compared with O/HKN/20/2010 and other ...known FMDV strains. Homology analysis indicated >98.0% nucleotide identity between O/BY/CHA/2010 and the epidemic strains, O/HKN/20/2010, and O/VN/2009. However, with the exception of the VP4, 2A, and 3BCD regions, O/BY/CHA/2010 showed a lower similarity with SEA topotype strains, O/VN/2006, and HLJOC12/03. A comparison of O/BY/CHA/2010 with non-SEA topotype strains showed the highest level of homology (97.4–100%) with UKG/7B/2007, Akesu/58, and the PanAsia strains in the 2A, P2, and 3CD regions, which suggested the presence of similar characteristics among these strains. Phylogenetic analysis revealed that O/BY/CHA/2010 is clustered in the Mya-98 lineage of the SEA topotype and is linked to four other isolates: HKN/20/2010, O/VN/2009, O/VN/2006, and HLJOC12/03. The VP1-based phylogenetic tree was divided into distinct clusters according to the different topotypes, while other gene-based phylogenetic trees exhibited some degree of intercrossing among topotypes. Furthermore, sequence analysis of the Lpro gene revealed a single amino acid insertion in O/HKN/20/2010 and a single amino acid deletion in O/BY/CHA/2010, in addition to a 70-nucleotide deletion within the 5′-untranslated region of O/HKN/20/2010. The majority of strains were shown to be homologous in the pseudoknots region although some exceptions were noted. This study provides a comprehensive genetic characterization of a novel FMDV isolate of the Mya-98 lineage.
In biological fluorescence imaging, obtaining high spatial-temporal resolution volumetric images under low light conditions is one of the critical requirements. As a widely-used snapshot volumetric ...imaging modality, light field microscopy has the problem of impeded imaging performance caused by reconstruction artifacts, especially under low light conditions. Fortunately, low-rank prior-based approaches have recently shown great success in image, video and volume denoising. In this paper, we propose an approach based on the spatial-temporal low-rank prior combining weighted nuclear norm minimization (WNNM) denoising and phase-space 3D deconvolution to enhance the performance of light field microscopy (LFM) under low light conditions. We evaluated the method quantitatively through various numerical simulations. Experiments on fluorescence beads and Drosophila larvae were also conducted to show the effectiveness of our approach in biological applications.
High-speed actuation of laser frequency
is critical in applications using lasers and frequency combs
, and is a prerequisite for phase locking, frequency stabilization and stability transfer among ...optical carriers. For example, high-bandwidth feedback control of frequency combs is used in optical-frequency synthesis
, frequency division
and optical clocks
. Soliton microcombs
have emerged as chip-scale frequency comb sources, and have been used in system-level demonstrations
. Yet integrated microcombs using thermal heaters have limited actuation bandwidths
of up to 10 kilohertz. Consequently, megahertz-bandwidth actuation and locking of microcombs have only been achieved with off-chip bulk component modulators. Here we demonstrate high-speed soliton microcomb actuation using integrated piezoelectric components
. By monolithically integrating AlN actuators
on ultralow-loss Si
N
photonic circuits
, we demonstrate voltage-controlled soliton initiation, tuning and stabilization with megahertz bandwidth. The AlN actuators use 300 nanowatts of power and feature bidirectional tuning, high linearity and low hysteresis. They exhibit a flat actuation response up to 1 megahertz-substantially exceeding bulk piezo tuning bandwidth-that is extendable to higher frequencies by overcoming coupling to acoustic contour modes of the chip. Via synchronous tuning of the laser and the microresonator, we exploit this ability to frequency-shift the optical comb spectrum (that is, to change the comb's carrier-envelope offset frequency) and make excursions beyond the soliton existence range. This enables a massively parallel frequency-modulated engine
for lidar (light detection and ranging), with increased frequency excursion, lower power and elimination of channel distortions resulting from the soliton Raman self-frequency shift. Moreover, by modulating at a rate matching the frequency of high-overtone bulk acoustic resonances
, resonant build-up of bulk acoustic energy allows a 14-fold reduction of the required driving voltage, making it compatible with CMOS (complementary metal-oxide-semiconductor) electronics. Our approach endows soliton microcombs with integrated, ultralow-power and fast actuation, expanding the repertoire of technological applications of microcombs.
Optical frequency combs have a wide range of applications in science and technology
. An important development for miniature and integrated comb systems is the formation of dissipative Kerr solitons ...in coherently pumped high-quality-factor optical microresonators
. Such soliton microcombs
have been applied to spectroscopy
, the search for exoplanets
, optical frequency synthesis
, time keeping
and other areas
. In addition, the recent integration of microresonators with lasers has revealed the viability of fully chip-based soliton microcombs
. However, the operation of microcombs requires complex startup and feedback protocols that necessitate difficult-to-integrate optical and electrical components, and microcombs operating at rates that are compatible with electronic circuits-as is required in nearly all comb systems-have not yet been integrated with pump lasers because of their high power requirements. Here we experimentally demonstrate and theoretically describe a turnkey operation regime for soliton microcombs co-integrated with a pump laser. We show the appearance of an operating point at which solitons are immediately generated by turning the pump laser on, thereby eliminating the need for photonic and electronic control circuitry. These features are combined with high-quality-factor Si
N
resonators to provide microcombs with repetition frequencies as low as 15 gigahertz that are fully integrated into an industry standard (butterfly) package, thereby offering compelling advantages for high-volume production.
•End-to-end super-resolution method for facial images which can upscale the input image to a high resolution of up to 256 × 256•Training GAN with the in-the-wild facial dataset and generating ...realistic synthesis results with identifying information kept•A Flexible network structure which can process wide resolution range of input images with better performance compared to state of art algorithms
Image synthesis and super-resolution (SR) have always been a hot spot for computer vision and image processing research. Since the development of Deep Learning, especially after the Deep Convolutional Generative Adversarial Network (DC-GAN) methods, facial image synthesis and SR problem had been solved in many circumstances. But most of the existing works were focused on natural-looking of the synthesized result rather than keeping facial information of the original image. Our paper presented an end-to-end method of getting high-resolution photo-realistic facial images from low-resolution (LR) in-the-wild images without losing the facial identity details. The pipeline used a flexible stacked GAN structure for the SR process with different target image resolutions on different upscaling factors. To avoid getting blur or nonsensical image output and realize the flexibility, “U-Net” architecture and upsampling layers with residual learning blocks were stacked. The stacked network structure makes applying different loss functions in different parts of the network possible, which helps to solve the two problems of keeping identical facial details of the LR input image and generating high-quality output images simultaneously. By using 3 different loss functions in different positions of the stacked network separately, through experimental comparison, we found the best stacked residual block parameters which could get the best output image quality. Experimental results also explicated that the network had a good SR ability compare to state of the art methods in different resolution and upscaling factor.
The ability to amplify optical signals is of pivotal importance across science and technology typically using rare-earth-doped fibres or gain media based on III-V semiconductors. A different physical ...process to amplify optical signals is to use the Kerr nonlinearity of optical fibres through parametric interactions. Pioneering work demonstrated continuous-wave net-gain travelling-wave parametric amplification in fibres, enabling, for example, phase-sensitive (that is, noiseless) amplification, link span increase, signal regeneration and nonlinear phase noise mitigation6. Despite great progress all photonic integrated circuit-based demonstrations of net parametric gain have necessitated pulsed lasers, limiting their practical use. Until now, only bulk micromachined periodically poled lithium niobate (PPLN) waveguide chips have achieved continuous-wave gain, yet their integration with silicon-wafer-based photonic circuits has not been shown. Here we demonstrate a photonic-integrated-circuit-based travelling-wave optical parametric amplifier with net signal gain in the continuous-wave regime. Using ultralow-loss, dispersion-engineered, metre-long, Si3N4 photonic integrated circuits18 on a silicon chip of dimensions 5 × 5 mm2, we achieve a continuous parametric gain of 12 dB that exceeds both the on-chip optical propagation loss and fibre-chip-fibre coupling losses in the telecommunication C band. Our work demonstrates the potential of photonic-integrated-circuit-based parametric amplifiers that have lithographically controlled gain spectrum, compact footprint, resilience to optical feedback and quantum-limited performance, and can operate in the wavelength ranges from visible to mid-infrared and outside conventional rare-earth amplification bands.
Erbium-doped fiber amplifiers revolutionized long-haul optical communications and laser technology. Erbium ions could provide a basis for efficient optical amplification in photonic integrated ...circuits but their use remains impractical as a result of insufficient output power. We demonstrate a photonic integrated circuit–based erbium amplifier reaching 145 milliwatts of output power and more than 30 decibels of small-signal gain—on par with commercial fiber amplifiers and surpassing state-of-the-art III-V heterogeneously integrated semiconductor amplifiers. We apply ion implantation to ultralow–loss silicon nitride (Si
3
N
4
) photonic integrated circuits, which are able to increase the soliton microcomb output power by 100 times, achieving power requirements for low-noise photonic microwave generation and wavelength-division multiplexing optical communications. Endowing Si
3
N
4
photonic integrated circuits with gain enables the miniaturization of various fiber-based devices such as high–pulse-energy femtosecond mode-locked lasers.
On-chip optical amplification
The success of long-haul optical communications and our information society is largely due to the invention of the erbium-doped fiber amplifier. Because the need for faster chips is expected to see a shift from electronics- to photonics-based technologies, erbium ions could form the basis for amplification in optical integrated circuits. Liu
et al
. used an ultra-low-loss silicon nitride photonic integrated circuit with a waveguide length up to 0.5 meters and erbium ion implantation to fabricate an erbium-doped waveguide amplifier on a compact photonic chip (see the Perspective by Kim). Operating in the continuous-wave regime and providing large optical gain in the telecommunication bands, the results are promising for device applications. —ISO
An erbium-doped optical amplifier is fabricated on a silicon-nitride-based optical platform.
Integrated photonics enables signal synthesis, modulation and conversion using photonic integrated circuits (PICs). Many materials have been developed, among which silicon nitride (Si3N4) has emerged ...as a leading platform particularly for nonlinear photonics. Low-loss Si3N4 PICs have been widely used for frequency comb generation, narrow-linewidth lasers, microwave photonics and photonic computing networks. Yet, among all demonstrated functionalities for Si3N4 integrated photonics, optical non-reciprocal devices such as isolators and circulators have not been achieved. Conventionally, they are realized based on the Faraday effect of magneto-optic materials under an external magnetic field; however, it has been challenging to integrate magneto-optic materials that are not compatible with complementary metal–oxide–semiconductors and that require bulky external magnet. Here we demonstrate a magnetic-free optical isolator based on aluminium nitride (AlN) piezoelectric modulators monolithically integrated on low-loss Si3N4 PICs. The transmission reciprocity is broken by spatio-temporal modulation of a Si3N4 microring resonator with three AlN bulk acoustic wave resonators that are driven with a rotational phase. This design creates an effective rotating acoustic wave that allows indirect interband transition in only one direction among a pair of strongly coupled optical modes. A maximum of 10 dB isolation is achieved under 300 mW total radiofrequency power applied to three actuators, with minimum insertion loss of 0.1 dB. An isolation bandwidth of 700 MHz is obtained, determined by the optical resonance linewidth. The isolation remains constant over nearly 30 dB dynamic range of optical input power, showing excellent optical linearity. Our integrated, linear, magnetic-free, electrically driven optical isolator could be a key building block for integrated lasers and optical interfaces for superconducting circuits.An electrically driven, magnetic-free optical isolator is demonstrated. The device, based on aluminium nitride piezoelectric modulators and a silicon nitride microring resonator, may be useful for integrated lasers and other opto-electric systems.
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