Speckle reduction in laser illuminated endoscopy using adversarial deep learning

We propose and demonstrate a temporally and spatially incoherent spectrum-sliced light source for scintillation mitigation in free-space optical (FSO) communications. For the temporal incoherence, we utilize the spectrum-sliced incoherent light (SSIL) modulated by gain-saturated reflective semiconductor optical amplifiers for data modulation and the suppression of excess intensity noise inherent in a narrowband incoherent light source. We then employ offset launching from a single-mode fiber to a multi-mode fiber to add the spatial incoherence to the SSIL source. The experimental demonstration shows that this temporally and spatially incoherent light is effective in mitigating scintillation. For example, this light source reduces the transmitter power required to achieve a bit-error ratio of 10-3 by ∼6 dB in comparison with the laser source. This is an ∼3 dB larger reduction in the transmitter power than the reduction achieved by a temporally incoherent light source.

Phase imaging normally employs coherent a light source while an incoherent light source is not preferred due to its random wavefront. Another challenge for practical phase imaging is imaging through scattering media, which scatter the photons in a random manner and lead to seriously distorted images of speckles. Based on the convolutional neural network (CNN), this paper presents an approach for phase imaging through scattering media using an incoherent light source. A CNN was trained and utilized to reconstruct the target images from the captured images of speckles. Similarities of over 90% between the reconstructed images and their target images have been achieved. It was concluded that an incoherent light source can be used as an illumination source for scattering phase imaging with the assistance of deep learning technology. This phase imaging approach with an incoherent light source through scattering media can be used to record the refractive indices of transparent samples, which might lead to its application in biomedical imaging.

We propose and demonstrate a temporally and spatially incoherent spectrum-sliced light source for mitigating scintillation in free-space optical communications. The experimental results show this light source improves the receiver sensitivity by 5.9 dB, compared to EML.

Non-local means (NLM) filter is one of the state-of-the-art denoising filters. It exploits the presence of similar features in an image and averages those similar features to remove noise. However, a conventional NLM filter shows somewhat inferior performance of noise reduction around edges, suffering from low efficiency of collecting similar features to be averaged. In order to overcome this phenomenon, we propose a NLM filter with double Gaussian anisotropic kernels as a substitute for the conventional homogeneous kernel to effectively remove noise from OCT images corrupted by speckle noise. The proposed filter was evaluated by comparing with various denoising filters such as conventional NLM filter, median filter, bilateral filter, and Wiener filter. The fingertip OCT images, which were processed with the different denoising filters, indicated that the proposed NLM filter provides superior denoising performance, among the filters in terms of the contrast-to-noise ratio (CNR), the equivalent number of looks (ENL), and the speckle suppression index (SSI). A human retina OCT image was also used to compare and show the performances of noise reduction among different filters. In addition, the denoising performance with the proposed NLM filter was also investigated in the synthetic images for fair comparison among the filters by calculating the peak signal-to-noise ratio (PSNR). The proposed NLM filter outperformed the conventional NLM filter as well as the other filters.

Holographic display and imaging are usually implemented with coherent lasers, which usually suffer from speckles. Incoherent light sources have long been highly desired for holographic applications, but the corresponding spatial modulation scheme is still lacking. Here we demonstrate a hyperspectral complex field modulation based on a single spatial light modulator (SLM) for an incoherent white light-emitting diode (LED) with a 200 nm bandwidth. The technique encodes the complex fields of multiple wavelengths into a phase hologram. The hologram has an analytical expression and is the superposition of multiple fringe patterns with different frequencies. By tuning the local fringe frequency on the hologram, one can modulate the local output spectrum. The method is applied for sweeping wavelength and projecting color images, where tens of spectral channels are modulated independently. Moreover, the method can achieve complex modulation and is applied in multi-plane holographic projections.

Pointing, acquisition, and tracking (PAT) systems in spaceborne optical communications terminals can exploit inertial sensors and actuators to counter platform vibrations and maintain steady beam pointing. Interferometric fiber optic gyroscopes (IFOGs) can provide sensitive angle rate measurements down to very low (sub-milliHertz) mechanical frequencies, potentially reducing the required beacon power and facilitating acquisition for a spaceborne optical communications terminals. Incoherent broadband light sources are used in IFOGs to alleviate detrimental effects of optical nonlinearities, backscattering, and polarization non-reciprocity. But incoherent broadband sources have excess noise or relative intensity noise (RIN), caused by the beating of different spectral components on the photodetector. Unless RIN noise is suppressed, IFOG performance cannot be improved once the light on the photodetector exceeds one photon per coherence time (~microWatts). We propose a simple method to dramatically suppress the RIN of an incoherent light source and thereby reduce the angle random walk (ARW) of an IFOG using such a source. We demonstrate 20 dB RIN suppression of a broadband EDFA source, which we predict could improve the angle random walk (ARW) of an IFOG using this source by 12 dB.

Ion implantation of silicon in gallium arsenide: Damage and annealing characterizations

Light-emitting diodes (LEDs) are becoming increasingly important across various sectors of the lighting industry and are being used more frequently. In the field of symbolic projection, research is increasingly focusing on implementing light modulation using energy-efficient, incoherent LEDs rather than lasers. Since light modulation in micro- and nano-optics is typically achieved through phase modulation, Finite-Difference Time-Domain (FDTD) simulations are employed for analysis. The objective of this article is to investigate different approaches for approximating incoherent monochromatic light sources within FDTD simulations. To this end, two approaches based on dipole sources are considered, as well as a method involving plane waves with modulated wavefronts based on Cosine–Fourier functions and a method based on the superposition of Gaussian beams. These methods are evaluated in terms of their accuracy using a two-dimensional double-slit configuration and are compared against a fully incoherent analytical reference.

Speckle noise in Intravascular Ultrasound (IVUS) images poses a significant challenge, necessitating early elimination of these artifacts. In this study, two novel methods were designed: a denoising convolutional autoencoder and a modified non-local means algorithm using particle swarm optimization (PSO) for automatic parameter selection. This research delved into assessing the efficacy of various denoising models, encompassing spatial domain techniques (median filter, non-local means, optimized non-local means), transform domain methods (wavelet, curvelet), and deep learning approaches (denoising autoencoder). A wide array of data augmentation techniques was employed during the training of the autoencoder model. Evaluation was conducted using two key metrics: Structural Similarity Index Measure (SSIM) and Peak Signal-to-Noise Ratio (PSNR). The findings indicate the robustness of the autoencoder model with the proposed augmentation strategy across different speckle noise variances, highlighting its superiority over traditional methods. Moreover, the study underscores the enhanced performance of modified non-local means with particle swarm optimization (PSO) compared to manual non-local means.

Adjustable spatial coherence systems allow the possibility to make different intensity distributions using one source. Most common adjustable sources are based on the Collet-Wolf system. However, it is also possible to adjust the spatial coherence of the illumination field from white light sources by spatially filtering the source mutual intensity spectrum. We implement the Collet-Wolf source and the LED-based system to experimentally contrast a variety of partially coherent optical vortices that can be generated with spatial light modulation. We experimentally study the effects of changing the transverse coherence in partially coherent optical vortices, using a proposed metric of vortex contrast depth that quantifies the change of the vortex hollowness. To expand the analysis, we use a Michelson interferometer to reconstruct the spiral wavefronts using phase shifting. We found that the LED system at lower spatially correlated light produces truncated triangular distributions (a 50µm pinhole is used), and with higher correlated light, it produces partially coherent optical vortices (a 10µm pinhole is used). The Collet-Wolf system generates partially coherent optical vortices up to 0.5mm of focal shift in the diffuser. Our results provide an experimental understanding and instrumental methodology capable of steering the optical transverse coherence, producing adjustable partially coherent optical vortices that can be obtained using incoherent and coherent sources.

In this work, we report on the fabrication and photonic activation of a novel kind of photomobile polymer (PMP) film based mainly on a double layered asymmetric configuration. The PMP is cheap and extremely easy to make. It is made of PVC/isoprene tape with a layer of graphene-oxide (GO) attached. Under illumination at different intensities, and with coherent and incoherent light sources, the bending of the PMP film changes considerably. In particular, we noticed a more efficient bending effect when the film is directly exposed to high light intensities or to NIR radiation in the case of incoherent light sources. For the exposure times used in our experiments, the process is completely reversible when the light source is switched off. Additionally, if we paint the side of the PVC tape exposed to light black, the film is not able to return to its starting position and the bending results are permanent. This suggests that the presence of the GO-layer is responsible for the restoration of the position of the PMP film.

BACKGROUND: Ultraviolet‐B (UVB) light sources are widely used for the safe and effective treatment of inflammatory skin conditions. The recent commercial introduction of fiber‐coupled UVB phototherapy systems facilitates the selective exposure and treatment of localized psoriasis plaques while permitting the safe use of high‐dosage treatments.OBJECTIVE: In this study, the performance characteristics and clinical outcome of psoriasis treatments were assessed when using two technologically distinct sources of high‐intensity, fiber‐optically delivered therapeutic UVB.METHODS: A pulsed, monochromatic 308 nm excimer laser and a continuous‐wave, incoherent UVB light source were compared using photosensitive recording papers, images captured with a CCD camera, and on the healthy and lesional skin of ten psoriasis patients.RESULTS: Beam profile analyses and minimal erythema dose (MED) test spots revealed distinct energy distribution patterns from the two devices. The Guassian‐type laser beam energy distribution complicated MED determinations, whereas skin exposed to light from the incoherent UVB system developed a more uniform erythema. Both systems cleared the treated psoriasis plaques equivalently, requiring no more than two to five weeks of high‐dose treatments.CONCLUSION: When used at equally erythemogenic high doses, both systems produced rapid plaque clearance with minimal side effects. Unlike conventional phototherapy, localized UVB minimizes exposure to the healthy skin, making it suitable for patients with mild to moderate psoriasis, individuals with recalcitrant plaques and for the successful treatment of lesions occurring on most body sites.

We recorded a permanent phase transmission grating on a thin film made by using a recently developed holographic photomobile mixture. The recorded grating pitch falls in the visible range and can be optically manipulated by using an external coherent or incoherent low power light source. When the external light source illuminates the grating the entire structure bends and, as a consequence, the optical properties of the grating change. This peculiarity makes it possible to use the recorded periodic structure as an all-optically controlled free standing thin colour selector or light switch depending on the source used to illuminate the grating itself. Additionally, it could open up new possibilities for stretchable and reconfigurable holograms controlled by light as well as thin devices for optically reconfigurable dynamic communications and displays.

In the image handling process, effective interpretation or reconstruction of the original image is mandatory, since the post-processing of images relies upon this important pre-processing task. It is well recognised that the noise makes degradation in the quality of image, which in turn results poor interpretation of images. This paper targets to remove salt-and-pepper or fixed impulse noise from images by fusing two techniques, namely median and non-local means (MNLM) filtering, and exploits both filtering benefits altogether. In the first phase, median filtering has been applied along with new sorting algorithm instead of the conventional method of sorting in order to reduce computational and hardware complexity. Even though the non-linear median filter performs better for low-level noise density and best in edge preservation, it gives blurring effect in the case of high-level noise density. This paper tries to overcome this limitation by fusing NLM filter effectively during the second phase. This fusion approach has brought promising quantitative results such as higher PSNR (peak signal-to-noise ratio) and lower MSE (mean square error) when compared to other existing standard algorithms such as SMF (standard median filter) and NLM filtering approaches.

Since the first electrical integrated circuits (ICs), the level of integration has been increasing with the scaling down of transistors. Although it is possible to integrate a number of transistors in a single chip, however, the ICs suffers from a performance bottleneck. To eliminate the performance bottleneck, an on-chip optical interconnect system has been in the limelight. However, developments in on-chip interconnect system have been made slow progress due to the absence of efficient on-chip light sources. Germanium (Ge) is the promising material for the on-chip optical interconnect system. However, Ge is not suitable for light sources because of its poor light emission efficiency. Thus, an efficient light source is the only missing key for the on-chip optical interconnect system. Throughout this thesis, we discuss our achievements about the efficient Ge based light sources, which can pave the way towards the on-chip optical interconnect system.