Search

In this article, we propose an iterative receiver based on gridless variational Bayesian line spectra estimation (VALSE), named JCCD-VALSE, that jointly estimates the carrier frequency offset (CFO), the channel with high resolution and carries out data decoding. Based on a modularized point of view and motivated by the high resolution and low-complexity gridless VALSE algorithm, three modules named the VALSE module, the CFO estimation (CFO est.) module, and the decoder module are built. Soft information is exchanged between the modules to progressively improve the channel estimation and data decoding accuracy. Since the delays of multipath of the channel are treated as continuous parameters instead of on a grid, the leakage effect is avoided. Beside, the proposed approach is a more complete Bayesian approach as all the nuisance parameters, such as the noise variance, the parameters of the prior distribution of the channel, and the number of paths are automatically estimated. Numerical simulations and sea test data are utilized to demonstrate that the proposed approach performs better than the existing grid-based joint channel and data decoding approaches. Furthermore, it is also verified that joint processing, including CFO estimation, provides performance gain. [ABSTRACT FROM AUTHOR]

Erbium (Er)-doped fiber amplifier (EDFA) has achieved great success in modern optical communications for decades due to its outstanding gain performance in C-band. Nowadays, people are making efforts to make it monolithic integration due to the imperious demands from the advancement of high-performance and multi-function optoelectronic devices and chips. Except for the Er-doped waveguide amplifier, the other ion-doped on-chip waveguide amplifiers have also attracted much attention for multi-band optical communications, since they have own advantages in gain, bandwidth, selectivity of host materials, and integrability. Herein, we review the transmission characteristics of ion-doped on-chip waveguide amplifiers including gain and bandwidth, combining with the emission mechanisms and fabrication processes in applications of long-haul and short-reach optical communications. To facilitate the practical progress of the integrated waveguide amplifiers, from the perspective of gain medium, we also discuss the challenges and potential solutions for future technology roadmap. We expect that the bismuth (Bi)-doped waveguide amplifier would present impressive advantages in multi-band optical communications. [ABSTRACT FROM AUTHOR]

Spin-transfer torque (STT) magnetic random access memory (MRAM) is gaining commercial traction in low-density embedded and standalone memories, but the available market opportunities would grow exponentially if STT-MRAM could approach dynamic random access memory (DRAM) bit density. Of course, achieving DRAM density will require, among other things, demonstrating the ability to pattern MRAM bits at an extremely tight pitch. Here, an experimental demonstration of fabrication and electrical testing of a STT-MRAM bit array are reported. By optimizing the hard mask and ion beam etching (IBE) processes, MRAM bit arrays with a full pitch down to 50 nm are fabricated, in which the bits are individually tested using a novel bottom-point-contact method. [ABSTRACT FROM AUTHOR]

Performing effective medium access control (MAC) encounters great challenges for mobile underwater acoustic networks (UANs), because it suffers from low signal-to-noise ratio, Doppler shift, large communication latency, and so on. Multi-carrier code-division multiple access (MC-COMA) is a promising modulation technique appropriate for solving the above restrictions. In this article, we design a novel MC-COMA-based cross-layer MAC scheme for mobile UANs, called MCI-MAC, to achieve efficient high-concurrency communication. Specifically, this method allocates spread spectrum sequences dynamically on the basis of velocity, propagation distance, data size, and data grade to improve robustness and flexibility of communication. Moreover, we propose an ant-colony-based optimal channel selection algorithm to decrease inter-carrier interference and inter-symbol interference, which concurrently maximizes energy efficiency and network throughput. In addition, we further propose a solution to solve multihop networks' collisions. Simulation results show that MCI-MAC is more effective than the state-of-the-art methods in mobile UANs. [ABSTRACT FROM AUTHOR]

Conventional orthogonal matching pursuit (OMP) based channel estimation adopts discretized grids to represent path delays, which leads to energy leakage of off-grid paths. From the perspective of linear fitting, utilizing multiple atoms with fractional delays and shortening the distance between these atoms in the off-grid path reconstruction can reduce the energy leakage. To this end, an improved OMP channel estimation scheme is proposed in this letter for higher estimation accuracy. The proposed scheme utilizes trigonometric function based interpolation twice to estimate the delays of two atoms, which are adopted to reconstruct an off-grid path. Furthermore, a two-step search strategy is introduced to keep low computational complexity. The advantage of the proposed scheme is validated in simulations. [ABSTRACT FROM AUTHOR]

In this work, we report experimental characterizations of stimulated Brillouin scattering (SBS) in low-loss Ge25Sb10S65 (GeSbS) chalcogenide waveguides. A 7-cm-long spiral waveguide with a propagation loss as low as 0.2 dB/cm and a microring resonator with a high loaded quality factor of 1.34×106 are demonstrated. In addition, we use a high-resolution pump-probe measurement technique to investigate the SBS characteristics in the GeSbS waveguide. The measured Brillouin frequency shift and the intrinsic Brillouin linewidth are 7.443 GHz and 47.8 MHz, respectively. A Brillouin-gain coefficient of 338 m−1W−1 is obtained, which corresponds to an intrinsic Brillouin gain of 0.524×10-9 m/W, comparable to that of As2S3 chalcogenide. Moreover, a 17.6-dB probe gain is achieved with a continuous-wave pump of 200 mW, while nonlinear losses are not observed. The large Brillouin gain, together with the low linear propagation loss and the negligible nonlinear loss, make the GeSbS chalcogenide waveguides become a very promising arsenic-free integrated platform for on-chip Brillouin applications. [ABSTRACT FROM AUTHOR]

Use of magnetic fields (MFs) for underwater wireless communication is very promising nowadays due to its advantages such as low power, low cost, no multipath, no Doppler effect, and instant communication. Considering the importance and potential of MF communication for underwater wireless sensor networks, this article presents a review on the fundamental concepts and theory of MF communication by identifying the main blocks, describing the limitation of each block and mentioning the advancements being done. The three fundamental blocks identified are: 1) the transmit and receive coils; 2) the matching network; and 3) the channel characteristics of the MFs. The first block explains how a single-dimensional coil is used to establish a directional communication link between a transmitter and a receiver and then the method by which the directionality problem is solved using multidimensional coils and metamaterial coils. Furthermore, the matching network explains the difference between the induction and resonance phenomena and their effect on the range and capacity. In the third block, the factors affecting the MFs are mentioned, which are critical to underwater wireless communication with MFs. Finally, this article introduces the recent advancements at the physical, MAC, and network layers. [ABSTRACT FROM AUTHOR]

Optical resonator-based ultrasound detection plays a significant role in the modern ultrasonography. It consists of two steps including the optical readout of the acoustic wave signal and the electrical demodulation of the acoustic response. In this article, we conduct innovative researches on both of them for improved performance. High quality-factor (Q-factor) chalcogenide glass (ChG) microdisk and microring resonators as optical readout configurations are designed and fabricated. High-precision digital optical frequency comb (DOFC) technique is proposed to monitor the minor resonance frequency shift. The sensitivity up to 2.86 dB/Pa and noise equivalent pressure (NEP) down to 4 Pa are obtained under the 40 KHz ultrasound vibration using a 100-μm radius Ge11.5As24Se64.5 microdisk resonator with the Q-factor of 1.15 × 106. As a proof-of-concept, three cascaded SiNx microring resonators-based ultrasound detector is fabricated and characterized to further validate the versatility of DOFC in the arrayed microcavities. Successful realization of the 3-D ultrasound detection paves the way to the development of high-performance photoacoustic imaging. [ABSTRACT FROM AUTHOR]

On-chip waveguide-integrated suspended microcavity resonator as a good sensing element is constantly pursued combining with the advantages of an optical material to enhance device performance. In this work, low-loss waveguide-integrated suspended Ge11.5As24Se64.5 microdisk resonators have been successfully demonstrated using an optimized etching recipe. The realization of propagation loss down to 0.48 dB/cm verifies the low-loss characteristic of chalcogenide glass rectangular waveguide. An optical loaded quality factor of 1.1 × 106 for the no suspended microdisk resonator, approaching to the highest figure (1.2 × 106) so far reported in planar chalcogenide optical devices, is obtained experimentally to reveal the natural evolution of high quality chalcogenide glass membrane during the engineering of shallow suspension configuration. By comparing with the scattering loss of mode in no suspended case, the contributions of bottom roughness scattering to the optical losses increase exceeding 50% in the shallowly suspended counterparts. The optimization and optical losses analysis of the waveguide-integrated suspended chalcogenide microdisk resonators are helpful to further estimate its potentials in the emerging stress or strain sensors. [ABSTRACT FROM AUTHOR]