Explore the vast range of titles available.

High spectral quality millimeter (MM) wave is desired for obtaining signal with high conversion efficiency and lesser nonlinear distortion. To enhance the spectral quality, the power of desired sidebands should be maximized and undesired sidebands should be completely suppressed. This paper reports the generation of tunable, high spectral purity and filterless high frequency MM wave with tunable sideband suppression ratio (SSR). Two Mach–Zehnder Modulators with gain in parallel configuration are utilized for obtaining spectrally pure fourth order sidebands. Beating of fourth order sidebands in the photodetector results a high frequency MM wave. Direction of polarization controller, phase shift relationship of local oscillator (LO) signal and appropriate value of gain is used to optimize the carrier suppression ratio. Cascaded erbium-doped fiber amplifier and dispersion compensation (DC) fiber is employed to compensate the nonlinear distortion for enhancing the system performance. 80 GHz MM wave with 59 dB optical sideband suppression ratio and 42 dB electrical sideband suppression ratio is realized from 10 GHz LO signal at a very low modulation index of 2.436. Variation of non-ideal factors such as extinction ratio and modulation index from their ideal value is examined for verifying the SSR optimization in the proposed radio over fiber (RoF) link. Sideband suppression ratio higher than 45 dB can be easily achieved at lower extinction ratio of 30 dB which goes to a maximum of 59 dB at higher extinction ratio. This shows a highly stable system with extinction ratio tolerance. Furthermore, the transmission effectiveness of the resulting MM wave with 10 Gbps non-return-to-zero data is analyzed by using with and without post-compensation technique through DC fiber. Transmission distance of 120 km through optical fiber and 20 km through DC fiber is reported with 6.65 Q factor, 3.8 dB power penalty and 1.45 e −11 BER by employing post-compensation technique. Proposed system offers longer transmission distance to high data rate RoF transmission system with lesser nonlinear distortion.

Extinction ratio is an extremely important parameter for generating a millimeter wave (MM wave) signal in optical domain. However, there are some practical limitations associated with this factor. Due to which generating a MM wave signal with extinction ratio insensitivity is a challenge. For addressing the problem that when the extinction ratio is relatively low the power of undesired sidebands and carrier is higher than the desired sidebands, a MM wave generation model is designed which is not dependent on MZM extinction ratio. Further, it is shown that by inserting an optimum phase shift between the arms of the modulator, the radio over fiber system could be made stable and conversion efficient. Simulation results have verified that optimum phase shift can make the powers of undesired sidebands equal to zero which results in better receiver sensitivity of system.

High conversion efficiency between electrical and optical power is highly desirable both for high peak and high average power radiation sources. In this paper we discuss a new mechanism based on stimulated superradiant emission in a strongly tapered undulator whereby a prebunched electron beam and focused laser are injected into an undulator with an optimal tapering calculated by dynamically matching the resonant energy variation to the ponderomotive decelerating gradient. The method has the potential to allow the extraction of a large fraction (∼50%) of power from a relativistic electron beam by converting it into coherent narrow-band tunable radiation, and shows a clear path to very high power radiation sources of EUV and hard x-rays for applications such as lithography and single molecule x-ray diffraction. Finally, we discuss a technique using chicane delays to suppress the sideband instability, improving radiation generation efficiencies for interaction lengths many synchrotron wavelengths long.

High-resolution magic angle spinning (HR-MAS) NMR is a powerful technique that can provide metabolic profiles and structural constraints on intact biological and environmental samples such as cells, tissues and living organisms. However, centripetal force from fast spinning can lead to a loss of sample integrity. In analyses focusing on structural organization, metabolite compartmentalization or in vivo studies, it is critical to keep the sample intact. As such, there is growing interest in slow spinning studies that preserve sample longevity. In this study, for example, reducing the spinning rate from 2500 to 500 Hz during the analysis of a living freshwater shrimp increased the 100% survivability threshold from ~14 to 40 h. Unfortunately, reducing spinning rate decreases the intensity of the isotropic signals and increases both the intensity and number of spinning sidebands, which mask spectral information. Interestingly, water suppression approaches such as excitation sculpting and W5 WATERGATE, which are effective at higher spinning rates, fail at lower spinning rates (<2500 Hz) while simpler approaches such as presaturation are not able to effectively suppress water when the ratio of water to biomass is very high, as is the case in vivo. As such there is a considerable gap in NMR approaches which can be used to suppress water signals and sidebands in biological samples at lower spinning rates. This research presents simple but practically important sequences that combine PURGE water suppression with both phase-adjusted spinning sidebands and an analogue of TOSS termed TOSS.243. The result is simple and effective water and sideband suppression even in extremely dilute samples in pure water down to ~100 Hz spinning rate. The approach is introduced, described and applied to a range of samples including, ex vivo worm tissue, Daphnia magna (water fleas), and in vivo Hyalella azteca (shrimp).

In this work, millimeter wave generation of sixtuple frequency scheme using dual parallel Mach–Zehnder modulator configuration has been investigated. The proposed scheme is mathematically analyzed and its performance is evaluated using software optisystem v.18. The vital parameters of both Mach–Zehnder modulator and phase of radio frequency local oscillator are properly adjusted for upconversion of 10 GHz radio frequency drive signal into 60 GHz mm wave. The impact of Mach–Zehnder modulator extinction ratio on radio frequency sideband suppression ratio, optical sideband suppression ratio and third sideband to carrier suppression ratio, is evaluated. An improved 63 dB third sideband to carrier suppression ratio is achieved at increased extinction ratio of Mach–Zehnder modulator. Impact of bias point drift and electrical phase shift on sideband suppression ratios are evaluated. Further, millimeter wave signal of 6–60 GHz tunability is realized by applying radio frequency local oscillator signal from 1 to 10 GHz.

To suppress the undesirable sideband transmission occurring in the conventional fibre Bragg grating based Fabry-Pérot filter, a fibre Fabry-Pérot interferometer that is composed of a single fibre Bragg grating and a broadband high-reflectance dielectric mirror coated on a fibre end surface is considered and its very narrow transmission bandwidth of 8.8 pm and high sideband suppression ratio of more than 20 is experimentally demonstrated in good conformity with the numerical simulation.

In this work, we investigate the influence of the second-order (20D) and third-order (30D) dispersion terms on chirp signal generation and transmission through RF photonic link without any optical filter. Dispersion equations are formalised using Taylor series and Bessel function to study the link performance. Our result (eye diagrams) shows that 20D+30D has a significant impact on chirp mm-wave propagation through fibres of different lengths. In this paper, chirp mm signal is controlled at photo detector by individual phase term of external modulators. Moreover, we experimentally demonstrate that the chirp rate can be significantly controlled by properly choosing the type of fibre in the experiments. We discuss the RF photonic link performance in terms of optical sideband suppression ratio (OPSSR), Radio Frequency Spurious Suppression Ratio (RFSSR), and Bit Error Rate (BER). Theoretical results are verified using MATLAB Software.

Optical single-sideband (SSB) modulation is theoretically realised by applying two modulation signals with a 90° phase difference to the dual-electrode type electro-optic (EO) modulator. A branch-line coupler (BC) as the microwave 90° hybrid was directly prepared on the EO modulator substrate, LiNbO3, to create two modulation signals from a single input signal. Output ports of the BC were connected to the modulation electrodes on the substrate. Thereby, an EO optical SSB modulator was realised with a single-tip and a small-sized configuration. The SSB modulator was designed and fabricated for around 10 GHz modulation frequency and 1550 nm light wavelength. The optical SSB modulation operation with a sideband suppression ratio of more than 20 dB was confirmed by the experiment.

In the nuclear magnetic resonance (NMR) test of coal, when the spinning frequency of magic‐angle spinning (MAS) is less than the frequency range of chemical shift anisotropy, serious aromatic carbon spinning sidebands will appear. Existing solutions to the sideband effect, such as changing the MAS frequency, inserting total suppression of sidebands (TOSS) pulse sequences, or simply defining the peak after chemical shift of 200 ppm as the sideband peaks generated by aromatic carbon peak, multipling the identified sideband integral by 2 and adding to the main peaks of protonated aromatic carbon and aromatic bridgehead carbon. None of these methods can reasonably correct for the sideband effect and cause errors to accurately quantifying the carbon structure parameters. Compared with 13C nuclear magnetic resonance (13C NMR) spectrum without sideband suppression (13C CP‐MAS NMR) and 13C NMR spectrum under sideband suppression conditions (13C CP‐MAS/TOSS NMR), according to the chemical shifts of the main peaks of four aromatic carbons, namely protonated aromatic carbon, aromatic bridgehead carbon, alkylated aromatic carbon and oxygen‐linked aromatic carbon, combined with the MAS frequency, the first‐ and second‐level sideband peaks generated by four types of aromatic carbons were accurately located and quantified, and they were added to the corresponding aromatic carbon main peaks in 13C CP‐MAS/TOSS NMR spectrum, thus realizing the accurate correction of sideband effect of the solid‐state 13C NMR spectrum of coal samples. The relative area of corrected aliphatic carbon, carbonyl (carboxyl) carbon, and various aromatic carbons were recalculated, and more accurate carbon structure parameters were obtained, which is significant for studying the coal structure from a microscopic perspective. The signal area of the sidebands that occur when the coal sample spinning frequency is less than the frequency range of chemical shift anisotropy is quantified. A correction method for the sideband effects is introduced. The application of this method to coals of different coal ranks is discussed.

At 2 µm wavelengths (149.9 THz), hollow-core photonics band gap fibers have higher light power damage thresholds, stable polarization states, and lower losses of 0.1 dB/km. Additionally, a thulium-doped fiber amplifier can provide a gain of >35 dB. Specifically, an indium-rich InGaAs photodetector shows a naturally higher photoresponsivity at 2 µm wavelengths than the C-band. Therefore, using tunable photo-generated microwave technology at 2 µm wavelengths could achieve higher photo-to-electric power conversion efficiencies for higher RF output power applications using the same method at the same frequency. Here, a double sideband with the carrier suppression modulation method was experimentally applied on 2 µm wavelengths to generate tunable and stable microwave carriers. Comparison experiments were also applied on the 1.55 µm (193.4 THz)/1.31 µm wavelengths (228.8 THz) based on the same indium-rich InGaAs photodetector. Through normalization on the wavelength-corresponded squared external quantum efficiency to visualize the photo-to-electric power conversion efficiency at different wavelengths under the same input optical signal power, the ratio between the results at 2 µm wavelengths and C/O-band is abstracted as 1.31/1.98, approaching theoretical estimations. This corresponds to a power conversion efficiency increasement of ~1.16 dB/~2.98 dB. To our knowledge, this is the first study on 2 micron wavelengths that proves the corresponding high efficiency power conversion property.