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Frequency modulated continuous wave laser ranging (FMCW LiDAR) enables distance mapping with simultaneous position and velocity information, is immune to stray light, can achieve long range, operate in the eye-safe region of 1550 nm and achieve high sensitivity. Despite its advantages, it is compounded by the simultaneous requirement of both narrow linewidth low noise lasers that can be precisely chirped. While integrated silicon-based lasers, compatible with wafer scale manufacturing in large volumes at low cost, have experienced major advances and are now employed on a commercial scale in data centers, and impressive progress has led to integrated lasers with (ultra) narrow sub-100 Hz-level intrinsic linewidth based on optical feedback from photonic circuits, these lasers presently lack fast nonthermal tuning, i.e. frequency agility as required for coherent ranging. Here, we demonstrate a hybrid photonic integrated laser that exhibits very narrow intrinsic linewidth of 25 Hz while offering linear, hysteresis-free, and mode-hop-free-tuning beyond 1 GHz with up to megahertz actuation bandwidth constituting 1.6 × 10 15 Hz/s tuning speed. Our approach uses foundry-based technologies - ultralow-loss (1 dB/m) Si 3 N 4 photonic microresonators, combined with aluminium nitride (AlN) or lead zirconium titanate (PZT) microelectromechanical systems (MEMS) based stress-optic actuation. Electrically driven low-phase-noise lasing is attained by self-injection locking of an Indium Phosphide (InP) laser chip and only limited by fundamental thermo-refractive noise at mid-range offsets. By utilizing difference-drive and apodization of the photonic chip to suppress mechanical vibrations of the chip, a flat actuation response up to 10 MHz is achieved. We leverage this capability to demonstrate a compact coherent LiDAR engine that can generate up to 800 kHz FMCW triangular optical chirp signals, requiring neither any active linearization nor predistortion compensation, and perform a 10 m optical ranging experiment, with a resolution of 12.5 cm. Our results constitute a photonic integrated laser system for scenarios where high compactness, fast frequency actuation, and high spectral purity are required. Stable and tunable integrated lasers are fundamental building blocks for applications from spectroscopy to imaging and communication. Here the authors present a narrow linewidth hybrid photonic integrated laser with low frequency noise and fast linear wavelength tuning. They then provide an efficient FMCW LIDAR demonstration.

Apodization weighted acquisition is a simple approach to enhance the sensitivity of multidimensional NMR spectra by scaling the number of scans during acquisition of the indirect dimension(s). The signal content of the resulting spectra is identical to conventionally sampled data, yet the spectra show improved signal-to-noise ratios. There are no special requirements for data acquisition and processing: the time-domain data can be transformed with the same schemes used for conventionally recorded spectra, including Fourier transformation. The method is of general use in multidimensional liquid and solid state NMR experiments if the number of recorded transients per sampling point is bigger than the minimum required phase cycle of the pulse sequence.

New apodization techniques are emerging rapidly to enhance the coronagraphs’ rejection capabilities and refine the optics for directly detecting exoplanets. One such technique, Interferometric Apodization by Homothety (IAH), involves splitting the incident Point Spread Function (PSF) into two using a 50 : 50 beamsplitter. One of the resulting PSFs has its amplitude reduced by a factor γ and its transverse dimension expanded by a factor ƞ . By combining these two PSFs, an apodized PSF is generated. In this study, we will use the standard values of γ and ƞ for both rectangular and circular apertures. We implement this approach in the laboratory using a Mach-Zehnder Interferometer with Cube Beamsplitters, chosen for their advantages over Plate Beamsplitters, including easy integration at a 0 ° angle of incidence and equal optical path lengths for reflected and transmitted light. This technique shows significant promise, achieving a contrast of approximately 5.10 −3 at small angular separations around 2.8 λ /D.

For two-dimensional forward-looking sonar imaging, high sidelobes significantly degrade the quality of sonar images. The cosine window function weighting method is often applied to suppress the sidelobe levels in the angular and range dimensions, at the expense of the main lobe resolutions. Therefore, an improved spatially variant apodization imaging method for forward-looking sonar is proposed, to reduce sidelobes without degrading the main lobe resolution in angular-range dimensions. The proposed method is a nonlinear postprocessing operation in which the raw complex-valued sonar image produced by a conventional beamformer and matched filter is weighted by a spatially variant coefficient. To enhance the robustness of the spatially variant apodization approach, the array magnitude and phase errors are calibrated to prevent the occurrence of beam sidelobe increase prior to beamforming operations. The analyzed results of numerical simulations and a lake experiment demonstrate that the proposed method can greatly reduce the sidelobes to approximately −40 dB, while the main lobe width remains unchanged. Moreover, this method has an extremely simple computational process.

To capture images of Earth-like planets orbiting distant stars, advanced instruments with exceptional contrast ratios are imperative. While coronagraphs play a crucial role, they often lack the capability to achieve the requisite contrast levels independently. Hence, supplementary apodization techniques are indispensable for augmenting their rejection capabilities. In this context, we introduce an innovative apodization method that harnesses interferometry, seamlessly integrating a deformable mirror into the Michelson interferometer setup. This sophisticated approach entails splitting the incident Point Spread Function (PSF) into two components, introducing an additional inhomgenious phase φ ( x , y ) to one of them via a deformable mirror, and subsequently recombining them to yield an apodized PSF. We illustrate, in particular, the influence of several parameters of the deformable mirror on the optimization of the additional phase profile.

This paper has deeply simulated the different configurations of pre, post, and symmetric dispersion compensation-based dispersion compensated fiber (DCF), Gaussian optic filter (GOF), and fiber Bragg grating. Output power, signal quality factor, and signal gain are the performance parameters in this study for the complete comparison for the proposed techniques for dispersion compensation. It is observed that FBG has presented the best performance parameters optimization in compared to other compensation techniques for different configurations of compensation. The FBG dispersion compensation technique is the key solution for dispersion compensation in compared with other compensation techniques that are comparatively as in previous section. It is observed that the FBG is the best dispersion compensation technique and change its location, and length, apodization, and chirp functions, to obtain the best performance of FBG and give the best quality factor, output power, and gain, FBG can be employed in different categories such as post compensation, pre compensation, and symmetric compensation with different FBG lengths, apodization, and chirp functions.

The study presents the basic apodization and chirp functions based fiber Bragg grating (FBG) for upgrading optical fiber performance efficiency. Variations of apodization and chirp functions are studied with grating length variations. Optical power after FBG, signal to noise ratio, maximum -factor, and output power are measured in the presence of the chirp functions. Gaussian apodization function has outlined good performance than other proposed apodization functions. As well as linear chirp function is better performance than other chirp functions. The optical system performance tested with/without chirp effects with high bit rates.

We investigate the formation of single and multiple optical bottle beams on the optical axis using a diffractive axicon with amplitude or phase apodization. The proposed approach allows one to control the location and the contrast of the boundaries of the generated dark intensity regions on the optical axis. Experimental results obtained using a spatial light modulator are in good agreement with numerically obtained ones. We successfully used the designed and experimentally formed set of three optical bottle beams for trapping light-absorbing agglomerations of carbon nanoparticles in air under the action of photophoretic forces. This confirms the efficiency of the proposed approach for optical manipulation applications.

In this paper, an energy regulation method based on the combination of a half-wave plate (HWP) and a polarization beam splitter (PBS) is proposed for the fabrication of apodized fiber gratings, which can effectively improve the side lobe suppression ratio of high-reflectivity fiber Bragg gratings (FBGs) fabricated by femtosecond laser. The apodized FBGs prepared by this method has good repeatability and flexibility. By inputting different types of apodization functions through the program, the rotation speed of the stepping motor can be adjusted synchronously, and then the position of the HWP can be accurately controlled so that the laser energy can be distributed as an apodization function along the axial direction of the fiber. By using the energy apodization method, the gratings with a reflectivity of 75% and a side lobe suppression ratio of 25 and 32 dB are fabricated in the fiber with a core diameter of 9 and 4.4 μm, respectively. The temperature and strain sensitivities of the energy-apodized fiber gratings with a core diameter of 4.4 μm are 10.36 pm/°C and 0.9 pm/με, respectively. The high-reflectivity gratings fabricated by this energy apodization method are expected to be used in high-power narrow-linewidth lasers and wavelength division multiplexing (WDM) systems.

This paper presents the high bandwidth profile based on fiber Bragg grating dispersion compensation systems for high bit rate optical communications with long distance links. We have studied the chirp, apodization functions and temperature variations effects on the operation performance efficiency of fiber Bragg grating sensors. The optimum values of fiber Bragg grating (FBG) devices such as power, and reflected signal power can be measured in the presence of Gauss, Tanh parameters variations at different ambient temperatures. FBG operation performance efficiency can be enhanced with the employment of user defined chirp function with user defined apodization function at room temperature in the presence of suitable value of Tanh parameter. It is observed that user defined apodization function has presented the highest FBG power and the lowest reflected signal power in compared with other apodization functions at different types of chirp functions. It is found that the dramatic negative effects of increasing ambient temperature on FGB power, reflected signal power, signal quality factor and bit error rate (BER) measurements.