A scheme of multiwavelength picosecond pulses generator using time lens by cascading Intensity Modulator (IM), Phase Modulator (PM) and Single-Mode Fiber (SMF) is proposed and experimentally demonstrated. In the experiment, single wavelength pulse with Full Width at Half-Maximum (FWHM) of about 14ps at 5.2GHz are obtained, four wavelength interleaved pulse trains with time intervals between adjacent wavelengths is about 48ps at 20.8GHZ and eight wavelength interleaved pulse trains with time intervals between adjacent wavelengths is about 24ps at 41.6GHz are obtained by using Tunable Delay Line (TDL) and a Variable Optical Attenuator (VOA) combined Dense Wavelength Division Multi-plexing (DWDM). This scheme has flexibility and tunability because the repetition rate, and time-interval can be readily controlled.
Denoising is significant in many fields, especially for computational imaging. Coherent diffraction imaging and speckle correlation imaging are regarded as the most promising computational imaging techniques. The above two imaging techniques can be classified as phase-retrieval-based imaging due to the phase-retrieval is a vital procedure for object reconstruction. However, the acquisition process would generate unavoidable noise and participate in the iteration process of phase-retrieval. Hence, it is necessary to denoising after obtained the original reconstruction image. Here, a denoising method that based on connected domain is proposed for phase-retrieval method. We experimentally demonstrate the denoising results and quantitatively analyze the effect. Comparison of the classical median filter, wiener filter and bilateral filter, our method shows a satisfactory denoising effect. Our results prove that connected domain denoising is useful and promising, which provides a new post-processing denoising method for phase-retrieval-based imaging.
Imaging objects hidden behind opaque layers is significant in many fields, with applications ranging from biomedical imaging to defense security. Techniques based on memory-effect scattering imaging have been developed in the past decade. The existing memory-effect-based scattering imaging techniques can be divided into two categories based on the working principle of light sources. In these methods, phase-retrieval algorithm is used to reconstruct object from the power spectrum diffraction patterns as the last step. Although both of them achieve single-shot scattering imaging, the experimental set-up is quite different. It is noted that the coherent diffraction imaging is introduced to the scattering imaging field using the visible coherent light. The principle and setup of the aforementioned two methods are analyzed and summarized respectively. We experimentally demonstrate the reconstruction and evaluate the Peak Signal-to-Noise Ratio (PSNR) and Structural Similarity Image Measurement (SSIM). As these technologies are limited to short range and memory effect range, the potential to imaging with wide field of view and long distance requires further exploration.
The mutual interference method is introduced to detect vortex beams. For the coaxial interference between l1-order and l2-order vortex beams, the intensity distribution is spirally fan-shaped. The partition number N=|l2-l1|, and the spiral direction can distinguish the sign of topological charge with larger absolute value between |l1| and |l2|. Fork-shaped fringes appear in the center for the small-angle interference between vortex beams with incident angle β1 and β2. The forking number between two fringes agrees with N=|l2-l1|, and the forks face upward when l1<l2 & β1<β2, or l1<l2 & β1<β2, and face downward when l1<l2 & β1<β2, or l1<l2 & β1<β2. Especially, when one of the beams is a Gaussian beam, such as l1=0, the value and sign of the topological charge l2 of the other vortex beam can be simply detected. The mutual interference method can conveniently detect the value and sign of vortex beams without borrowing redundant devices.
We analyzed the light spectrum after passing through the encoding template element. Comparing the influence of the ideal coding template elements and coding template elements with rounded errors on the far-field spectrum. The far-field spectrum has a red offset. With the changing of the aperture error value r, the deviation of the far-field spectrum relative to the light source spectrum is slightly different, and the closer the aperture is to the circle, the smaller the deviation of the spectrum, that is, the closer the light source spectrum. Five different constituent units from the two-dimensional random coding template is found, and these five constituent units are randomly distributed. The far-field spectral distribution when the beam passes through two units at the same time is numerically calculated, and the analysis shows that the spectral deviation after passing through different types of coding units are obviously different. The analysis result will provide prior information for the target recovery of compressed-sampling hyperspectral imaging, and make the target recovery more accurate.
As a fundamental components for the integrated microwave photonic links, the nonlinear loss of the Silicon waveguides will significantly affect the links’ performance. We study the effects of the effective mode area (Aeff), two-photon absorption (TPA), free-carriers absorption (FCA), and linear propagation loss on the insertion loss in silicon waveguides. According to our simulations, the results show that it should be an efficient way to reduce the insertion loss of the silicon by combining the large mode area, small linear propagation loss and carriers sweep out techniques. And, we can also know that when the nonlinear loss will dominate with the coupled power becoming larger. Thus, the results can provide guidances on the gain, loss, and linear dynamic range of analog photonics links based on silicon waveguide.
By using the finite difference method, the nonlinear effects of high repetition rate femtosecond pulse trains in silicon nanowire waveguides were analyzed. By numerically modeling the propagation of femtosecond pulse in silicon nanowire waveguides with the generalized nonlinear Schrödinger equation, the temporal and spectral properties of femtosecond pulses propagating are discussed, and the physical mechanisms of pulse evolution are demonstrated. The simulation results indicate that, owing to the remarkable nonlinear effect, the carriers in the silicon waveguide are rapidly excited with the increase of the input laser power, subsequently have significant modulation effects on the high repetition rate pulses train. For various repetition rate and power of the laser pulses train, the output pulsestrain will get different temporal compression and broadening under the dominance of different nonlinear effects. Furthermore, the results demonstrate that the spectrum evolution of pulse train with different transmission distances is similar to the calculated results of single pulse transmission. The results will provide an important reference for the design of optical sampling clock, microwave photonic radar system and the sweep of carriers in waveguide.
The encoding aperture errors with different types and different degrees occurred during the process of encoding aperture by micro-Nano technology. The encoding aperture is a key component of the CSSI, and the analysis of errors in encoding aperture processing provides an important evidence for the CSSI. In this paper, based on the error occurring in the process of encoding aperture, the simulation is established by commercial software FDTD by which the optical field modulation of incident light in the CSSI system is analyzed by comparing the ideal encoding aperture and the error encoding aperture. The simulation results show that there is a significant difference in the optical intensity distribution of incident light modulated by a single error aperture and a single ideal aperture, the optical intensity distribution modulated by the ideal aperture has two distinct peaks at the aperture surface, and the optical intensity distribution modulated by the error aperture is approximately twice as large as by the ideal aperture; the optical intensity distribution modulated by the two type aperture has obvious peaks while leaving the aperture surface, and the optical intensity distribution modulated by the ideal aperture is approximately twice as large as by the error aperture; changing the number of pixels of the encoding aperture, the ideal encoding aperture and the error encoding aperture have little difference in modulation of the incident light; comparing the ideal aperture, as the increasing of the rounded radius of error aperture, the influence of the optical field distribution modulation becomes more obvious.
By iteratively stitching together the series of low-resolution (LR) images captured by either various small-aperture illuminations or angle-varied illuminations, the Fourier ptychography (FP) can recover large space-bandwidth- product (SBP) and high-resolution (HR) object images. The FP has been considered to be promising in various computational imaging fields. However, the illumination-based FP is limited by strict requirements of the objects which must be thin and satisfy the one-to-one mapping relationship in the Fourier plane, and the aperture-scanning Fourier ptychography is also limited by the long-time scanning and stable scanning mechanical structures requirements even though it can achieve super-resolution macroscopic imaging. Furthermore, the position and shape of the scanning aperture must be accurately modeled for the reconstruction, otherwise false object images may be output. Herein, based on the 4-f optical correlator structure, we proposed a novel method, termed variable-aperture Fourier ptychography, for reconstructing HR images from series of LR images. The numerical simulations illustrated that the variable-aperture Fourier ptychography can use a small number of LR images to reconstruct the object images, The experiments demonstrated that a high-quality object image with better resolution and contrast than other schemes, include direct imaging based on 4-f system and aperture scanning FP, can be obtained by our method. Two additional experiments proved that it is almost unaffected by the position and shape of the apertures.
Under coherent light illumination, several approaches need either angle scanning or diffuser rotating to reconstruct the image through opaque scattering media. We propose a linear model to restore the hidden object through the actual power spectrum with disturbance of the scattering layer. The experimental results confirm that, the algorithm quickly converge to the only correct reconstruction solution with the accuracy power spectrum pattern of Fourier transform, and the method can reconstruct the high accuracy image of the object hidden by the scattering media with one-shot power spectrum.
This article depicts a experiment of utilizing multi-spectral image(MSI) system, which can benefit from compressed sensing to reduce data acquisition demands, with the employment of a dispersal prism and push-broom compressive sampling system, to realize image super-resolution both in spatial and in spectral.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.