Scarring alopecias are a group of inflammatory disorders resulting in irreversible hair loss and significant psychosocial burden. Standard therapies often yield incomplete responses, prompting exploration of alternative treatments. Laser-based therapies, including low-level laser therapy (LLLT), superluminescent diode (sLED) therapy, long-pulsed Nd:YAG, and excimer lasers, have emerged as potential options. This meta-analysis aims to evaluate the clinical effectiveness of laser-based interventions in treating scarring alopecias. A systematic search of PubMed, Cochrane CENTRAL, and Scopus was conducted, following PRISMA guidelines. Studies included were non-randomized clinical studies reporting outcomes after laser-based interventions for scarring alopecias. Data extraction and risk of bias assessment (ROBINS-I) were performed independently by two reviewers. Due to heterogeneity, descriptive synthesis and qualitative forest plots were generated. Seven studies involving 51 patients were included. Conditions studied included lichen planopilaris (LPP), frontal fibrosing alopecia (FFA), dissecting cellulitis (DCS), folliculitis decalvans (FD), and acne keloidalis nuchae (AKN). Laser interventions were associated with clinical or trichoscopic improvement in all studies. Two studies reported complete or near-complete disease remission. No significant adverse events were reported. Risk of bias was serious or critical in all studies, primarily due to small sample sizes and lack of controls. Laser-based therapies demonstrate promising clinical benefits in scarring alopecias, particularly in disease stabilization and symptom improvement. However, due to the high risk of bias and methodological limitations, high-quality randomized controlled trials are needed to confirm these findings.

Optical coherence tomography (OCT) is a non-invasive, high-resolution imaging technique widely used in medical diagnosis, biomedical research and other fields. It plays an important role in the early detection and accurate diagnosis of diseases. The superluminescent light-emitting diode (SLED) is the ideal light source for OCT systems, where the stability of its drive current and operating temperature directly determines the imaging quality of OCT. Existing driving and temperature control schemes for similar light sources predominantly rely on microcontrollers or field programmable gate arrays (FPGAs), a reliance which often results in complex system architectures and difficulties in balancing simplicity with control precision. To address these issues, a stable and compact SLED source driver module designed for OCT was developed in this study, integrating both a constant-current drive circuit and a temperature control circuit. The negative feedback control and improved current-limiting protection are employed in the constant-current drive circuit to maintain stable SLED operation and reduce the circuit footprint. A miniature dedicated temperature control chip is adopted in the temperature control circuit. The operating temperature of the SLED is acquired by linearizing the negative temperature coefficient (NTC) thermistor value and regulated through a proportional-integral-derivative (PID) compensation circuit. The size of the fabricated module (including casing) is less than 10 × 8 × 3 cm3. Experimental results show that the driver module achieves a drive current control accuracy of 0.1% and a temperature control accuracy of 0.01 °C. The output optical power fluctuation is less than 0.005 mW and the average axial resolution for OCT is 6.5992 μm with a standard deviation of 0.0107 μm. This light source driver module successfully balances control precision with structural simplicity, demonstrating excellent applicability in OCT systems.

A four-quadrant low-coherence envelope detection method was proposed for measuring the surface spacing of optical components, eliminating the requirement for precise control of the delay line scanning step to generate a π/2 phase shift. The method employs an orthogonal polarization Mach–Zehnder (MZ) fiber interferometer, illuminated by a broadband superluminescent diode (SLD), and a four-quadrant polarization-resolved detector to simultaneously acquire spatially phase-shifted interference signals carrying surface spacing information. The interference envelope is directly demodulated to extract surface spacing, thereby decoupling measurement accuracy from mechanical stepping constraints. To enable real-time, high-precision calibration of the delay line, two complementary schemes were implemented: wavelength division multiplexing (WDM)-based calibration and dual optical path calibration. Experimental results confirm that the dual-path scheme exhibits weak dependence on scanning velocity and remains stable across a wide speed range. Repeat measurements of the surface spacing of a 1 mm thick sapphire plate yielded a standard deviation (STD) of 1.3 μm. By relaxing the strict π/2 phase shift condition traditionally imposed on scanning step size, this method improves operational efficiency while maintaining measurement reliability—providing a robust and broadly applicable solution for metrology, including lens surface spacing and transparent plate thickness characterization.

Abstract Superluminescent diodes (SLDs) are promising devices for applications in which low coherence, high efficiency, small footprint and good optoelectronic integration are required. Blue emitting SLDs with good performances and easy fabrication process are sought for next generation solid state lighting devices, micro-projectors and displays. These devices are laser diodes (LDs) in which the optical feedback is inhibited and lasing action avoided. Conventional fabrication processes minimize optical feedback by ad hoc designs, e.g. anti-reflection coating, tilted waveguide or absorber sections, requiring specific fabrication steps. In this work, we propose and demonstrate the introduction of scattering defects in the device’s waveguide as a method for feedback inhibition. By performing pulsed laser ablation on a commercial 405 nm GaN LD we demonstrate a SLD, featuring a maximum output power of 1.8 mW and a spectral width of 5.9 nm.

A programmable ultrabroadband flying focus was produced using adaptive optics and an axiparabola with a continuous wave superluminescent diode. A deformable mirror and spatial light modulator were used to add a programmable amount of radial group delay, and an axiparabola was used to create an extended focus by imparting spherical aberration. Three different flying focus trajectories were measured using spectral interferometry, two with uniform velocity and one with an accelerating velocity. The temporal response function width of the flying focus optics alone was calculated to be 52 ± 6 fs, and the focal spot size was measured to be (1.2 ± 0.1) × larger than the diffraction-limited spot size through the extended focus.

In this work, we demonstrated the first ultraviolet (UV) superluminescent diodes (SLDs) with AlGaN/GaN-based multiple quantum wells (MQWs), emitting at 360 nm. The UV SLD samples were grown on the c-plane sapphire substrates using molecular beam epitaxy (MBE) and were processed into ridge waveguides with inclined facets. The epitaxial structure exhibits excellent crystalline quality with low dislocation density. Optical mode simulations reveal strong confinement within the QWs, with a confinement factor of 3.2%. Moreover, the fabricated UV SLDs achieve a maximum optical power of 8 mW and an external quantum efficiency (EQE) of 7.6% at a current density of 3.5 kA/cm2. These results represent a significant advancement in III-nitride light-emitting devices, paving the way for UV superluminescent light sources for applications such as UV optical communications, photolithography, and medical imaging.

In this study, InGaAs/GaAsSb Type‐II quantum wells (QWs) are investigated as promising broadband light sources for optical coherence tomography (OCT). OCT requires a wide spectral width for high axial resolution within the 700–1400 nm biological window. However, current superluminescent diodes (SLDs) using conventional materials have wavelength limitations. The GaAs‐based Type‐II QWs are promising for the 1.0–1.4 µm range, enabling wavelengths beyond 1.3 µm on GaAs substrates. Three QW structures (Type‐I, Type‐II W‐shaped, Type‐II) are fabricated on GaAs substrates via metal–organic vapor‐phase epitaxy (MOVPE), and their photoluminescence (PL) spectra are measured. Type‐II QWs consistently exhibit the widest broadband PL spectrum. Notably, the 5 nm well width Type‐II QW shows the broadest average PL full width at half maximum (FWHM), possibly because of narrower conduction‐band quantum level spacing. The SLD fabricated with 5 nm well width InGaAs/GaAsSb Type‐II QW as the active layer has a significant broadband electroluminescence (EL) spectrum. A maximum EL spectrum FWHM of approximately 180 nm is observed. This surpasses that of conventional Type‐I QW SLDs, highlighting InGaAs/GaAsSb Type‐II QWs on GaAs substrates as highly promising OCT broadband light sources.

A design strategy for achieving broadband optical gain in GaSb-based semiconductor heterostructures operating beyond 2 µm is presented. By employing asymmetric GaInSb/AlGaAsSb quantum wells (QWs) of varying thicknesses, a flat and wide gain spectrum is demonstrated. The approach leverages carrier density and transition energy tuning across QWs to access various energy levels at specific current densities. Simulations using "Harold" self-consistent environment predict a full-width at half-maximum (FWHM) gain bandwidth exceeding 340 nm for a structure comprising one 7 nm and three 13 nm-thick QWs. The modelling parameters were validated against experimental data, ensuring a robust framework for gain engineering in broadband amplifiers and superluminescent diodes for mid-infrared applications.

This is the first study to employ high-resolution anterior segment optical coherence tomography (HR-AS-OCT) for the evaluation of epithelial corneal disorders. The OCT REVO HR (Optopol Technology, Zawiercie Poland) uses a super luminescent diode as its signal source, operating at a central wavelength of 870 nm. The axial resolution of the device is 3 μm, with a transversal (lateral) optical resolution ideal at 12 μm and typically at 18 μm. We conducted a study involving patients with epithelial basement membrane dystrophy, Meesmann dystrophy and Thygeson keratitis to compare corneal epithelial disorders across these conditions. Each patient was examined with a slit lamp, HR-AS-OCT and In Vivo Confocal Microscopy (IVCM). Slit-lamp findings in epithelial basement membrane dystrophy (EBMD; also known as Cogan's dystrophy) are well characterized by its alternative name: map-dot-fingerprint dystrophy. Greyish borders and well-demarcated, continent-like patterns on the otherwise clear cornea represent the ‘map’ phenotype. The ‘dots’ correspond to small, irregular microcysts, whereas the ‘fingerprints’ are formed by parallel or spiral lines (Buffault et al., 2020). Meesmann dystrophy typically presents as numerous cystic lesions in the epithelial layer, extending from the central cornea to the mid-periphery (Patel et al., 2005). Thygeson superficial punctate keratitis usually manifests as small, scaly clusters of subepithelial deposits that do not stain with fluorescein. These deposits are slightly elevated, granular in appearance and have soft, feathery edges (Choe & Kim, 2023; Figure 1). In EBMD, IVCM typically reveals highly reflective extracellular deposits located in the superficial and basal epithelial layers as well as in Bowman's membrane. These deposits may appear as intercellular strands, microcysts or needle-like structures. Such features reflect the folding of a thickened epithelial basement membrane into the epithelium (Shukla et al., 2012). In Meesmann dystrophy, cystic lesions appear as hyporeflective areas within the basal epithelial layer. Hyperreflective material within these cysts corresponds to degenerated epithelial cells. Additionally, numerous isolated hyperreflective particles—unassociated with cystic structures—are seen (Javadi et al., 2010). In Thygeson keratitis, confocal imaging reveals irregular corneal nerve fibres, often obscured by marked haze. A diffuse stromal haze is also present in the anterior stroma, accompanied by areas of increased reflectivity, microdots and reflective deposits (Priyadarshini et al., 2021; Figure 2). In EBMD, high-resolution anterior segment optical coherence tomography (HR-AS-OCT) reveals irregular thickening of the epithelial basement membrane. Characteristic waviness and elevation of the corneal epithelium, along with its protrusion into the epithelial layer, are also observed. The observed imaging findings correspond to the map-like or fingerprint patterns that are often undetectable by slit-lamp examination but were previously only apparent using IVCM. Hyperreflective dots within the mid-epithelial layer correspond to the microcysts observed clinically (Eker et al., 2023). Precise assessment of structural alterations with HR-AS-OCT highlights areas prone to reduced epithelial–basement membrane adhesion and the development of secondary epithelial defects. Unlike lower longitudinal resolution OCT devices, such as the Zeiss Cirrus HD-OCT (5 μm) (Elhardt et al., 2019), the OCT REVO HR allows for the detection of hyperreflective cystic structures with posterior shadowing in both the epithelial and Bowman's layers in Meesmann dystrophy. In Thygeson keratitis, HR-AS-OCT reveals hyperreflective epithelial and subepithelial deposits that correspond to the clinically observed lesions. These deposits are distinctly elevated above the adjacent corneal surface, further supporting their identification on imaging. Even minimally elevated deposits are readily visualized on HR-AS-OCT as hyperreflective areas with indistinct margins. This further underscores the advantage of this device over others, as it enables the detection of flat lesions that may remain undetectable on slit-lamp examination (Figure 3). The recent introduction of HR-AS-OCT offers a powerful alternative, capable of producing detailed cross-sectional images of the epithelial corneal layer and accurate lesion localization, improving diagnostic precision by enabling clear identification of hyperreflective changes. The combined use of slit-lamp examination, HR-AS-OCT and IVCM provides clinicians with a comprehensive toolkit for the accurate diagnosis, monitoring and management of epithelial corneal disorders. HR-AS-OCT is particularly valuable in distinguishing subtle epithelial abnormalities and precisely localizing structural changes. This research received no external funding. The authors declare no conflicts of interest.

In this paper, a latest theoretical model for the performance optimization of the broad-sense quantum-well superluminescent diodes (SLDs) based on the concept of energy level divergence (ELD) is presented. The simulation results on the performance of such a kind of devices with GaAs/AlGaAs potential-well structures and ignorable residual facet-reflections show that the ELD concept is truly valid and necessary to be considered in the modelling. It is also found that, for a fixed output power, both the spectral ripple coefficient and the spectral bandwidth decrease monotonically as the well-thickness increases. Moreover, the simulation results are in a pretty good approximation with the experimental ones. Typically, for a 3 mm long and 10 μm wide (referring to the active-region width) device emitting a fixed power of 25 mW and being required to have a ripple-coefficient not larger than 5%, the experimentally determined optimum well-thickness is 90 nm and the simulation one is 87 nm. And, the corresponding spectral bandwidths are 15 nm and 14.8 nm, respectively. It is believed that such a theoretical model could be further improved and eventually worthy for practical use.

Luminescent nanostructures are gaining prominence as vital probes for detection and sensing due to the growing demand for advanced imaging techniques that require superior light sources. Although conventional lasers and superluminescent diodes offer high brightness, their high spatial coherence can result in speckle patterns that compromise image quality. In contrast, random lasers (RLs) leverage disordered media and multiple light scattering to produce low-coherence emissions. Among the materials used for RLs, ZnO nanostructures are particularly promising due to their strong light emission, high refractive index, and efficient light scattering properties, making them ideal candidates for advanced sensing and imaging applications. ZnO-based RLs are known for narrow emission lines and speckle-free output. Recent advances in multiphoton excitation (MPE) of ZnO RLs have enabled upconversion ultraviolet lasing using lower-energy, near-infrared light, which offers deeper tissue penetration. However, scalability, cost, and durability challenges must be addressed to support wider adoption. This review explores how RLs are engineered to achieve low spatial coherence and lower lasing thresholds, with emphasis on MPE mechanisms that allow emission at shorter wavelengths than the excitation source, thus enabling high-quality imaging. The benefits of these innovations for advanced bioimaging are highlighted, alongside the potential of ZnO nanostructures for bioimaging and biosensing, particularly when interfaced with biological tissues. Prospects include incorporating ZnO RLs into flexible fiber systems, which could promote their commercialization in medical diagnostics and other applications, with long-term photostability and device durability also discussed.

We report development of GaSb-based superluminescent diodes (SLDs) emitting around 2.1 μm wavelength for applications in sensing and non-destructive imaging benefitting from broad and smooth spectra with low modulation depth ripples. Record-large spectral bandwidth is reported by exploiting an asymmetric type-I double quantum well InGaSb/AlGaAsSb active region. Preventing lasing from such gain structures while enhancing the amplified stimulated emission and mitigating the spectral modulation is essential. To this end, we employ J-waveguide chip architecture and perform a systematic study of the influence of facet’s reflectivity orienting the SLD chip’s p-side in upward direction. Broad emission with a full width at half maximum spectrum of ≥140 nm [corresponds to ∼1 mW in continuous wave (CW) power] and minimal ripples is reported, which is a nearly twofold increase in emission bandwidth compared to the previous reports in this spectral region. We also report SLD devices that can deliver a maximum output power of 56 mW for a limited bandwidth of ∼45 nm at room temperature in CW operation.

Liquid crystal (LC) is a strong candidate material for nonmechanical beam‐steering devices, which are highly demanded in self‐driving vehicle applications. Conventional LC‐based approaches rely on the refractive index distribution resulting from the spatial distribution of LC alignments. This study proposes a new approach using three components: a superluminescent diode (SLD), an LC etalon, and a blazed grating. Broad‐spectrum light from the SLD passes through an electrically tunable LC etalon, which narrows the bandwidth and generates wavelength‐swept light. The swept light is introduced into the blazed grating for steering. The steering system achieves a large steering angle (≈7°) with an average switching time of 225 μs in the quasistatic modulation mode. Moreover, the system achieves a steering angle of 3.5° at a high steering speed of 1 kHz in the dynamic modulation mode.

Given the exceptional capabilities of femtosecond laser processing in achieving high-precision ablation for air-film cooling hole fabrication on turbine blades, it is imperative to develop an advanced monitoring methodology that enables real-time feedback control to automatically terminate the laser upon complete penetration detection, thereby effectively preventing backside damage. To tackle this issue, a spectrum-domain coherent imaging technique has been developed. This innovative approach adapts the fundamental principle of fiber-based Michelson interferometry by integrating the air-film hole into a sample arm configuration. A broadband super-luminescent diode with a 830 nm central wavelength and a 26 nm spectral bandwidth serves as the coherence-optimized illumination source. An optimal normalized reflectivity of 0.2 is established to maintain stable interference fringe visibility throughout the drilling process. The system achieves a depth resolution of 11.7 μm through Fourier transform analysis of dynamic interference patterns. With customized optical path design specifically engineered for through-hole-drilling applications, the technique demonstrates exceptional sensitivity, maintaining detection capability even under ultralow reflectivity conditions (0.001%) at the hole bottom. Plasma generation during laser processing is investigated, with plasma density measurements providing optical thickness data for real-time compensation of depth measurement deviations. The demonstrated system represents an advancement in non-destructive in-process monitoring for high-precision laser machining applications.

Superluminescent diodes are usually hard to fabricate and cannot switch to lasing operation. We demonstrate a practical approach for creating devices that can function as a laser as well as a superluminescent diode. The operation mode is controlled by a distinct contact that enables electrical switching between those modes. For the demonstration of this principle, we fabricated devices based on interband cascade gain media. The devices showed superluminescent power of up to 200 μW. The electrically switchable operation combines the good alignment capabilities of a laser with the broadband, low coherence properties of a superluminescent diode.

High-resolution optical coherence tomography (OCT) requires broadband, spatially coherent light sources. Today, the source of choice for visible light OCT, the supercontinuum (SC), is bulky, expensive, and prone to excess noise. Here we demonstrate high-resolution visible light OCT of the human retina with a combined superluminescent diode (SLD) source. The source is longer in wavelength than the high blue light hazard range but shorter in wavelength than the high photopic efficiency range, ensuring subject safety and comfort. We report an axial resolution of 3.2 µm in the retina. We find that Bruch's membrane is well-delineated in subjects without ocular pathology, even though the axial resolution is ∼3× coarser than SC visible light OCT.Imaging of intermediate age-related macular degeneration is also shown. Within the cyan-green wavelength range of the SLD, optical density spectra resemble those of macular pigments. While the combined SLD approach does not achieve the micrometer-scale resolution of the SC, it potentially reduces the cost and complexity of visible light OCT while providing novel disease-relevant biomarkers, to the best of our knowledge, in human retina.

Background/Objectives: The aim of this in vitro study was to determine the optimal combinations of wavelengths for short wavelength infrared (SWIR) multispectral transillumination and reflectance imaging of caries lesions on proximal and occlusal surfaces. Methods: The contrasts of (n = 76) caries lesions on the occlusal and proximal surfaces of extracted teeth were measured at 1050, 1300, and 1550 nm for occlusal transillumination and 1058, 1300, 1450, and 1675 nm for occlusal reflectance. All teeth were also imaged using radiography and microcomputed tomography (μCT) to verify lesion presence. A custom-fabricated handheld imaging probe suitable for clinical use and for the simultaneous acquisition of SWIR occlusal transillumination and reflectance (SWIR-OTR) images was used. Three high-power superluminescent diode lasers were used for transillumination, and a fiber-optic switch was used to switch between the transillumination wavelengths. Optical bandpass filters coupled with a tungsten halogen lamp were used for reflectance. All images were acquired at the same position and with the same field of view for comparison. Results: The highest contrasts in reflection were at 1450 and 1675 nm for occlusal and interproximal lesions, and the highest contrasts for transillumination were at 1050 and 1300 nm. Conclusions: This study suggests that the best wavelengths for SWIR-OTR are between 1000 and 1300 nm for transillumination and greater than 1400 nm for reflectance. Wavelengths beyond 1400 nm are advantageous for reflectance and yield significantly higher contrast. Wavelengths beyond 1300 nm are not promising for occlusal transillumination since internal water absorption leads to contrast inversion.

We demonstrate a new method to achieve high-power and wavelength flexible broadband light based on a random fiber laser (RFL)-pumped Raman amplifier seeded by a superluminescent diode (SLD). Benefiting from the wavelength flexibility of the RFL and the broadband Raman gain, the amplified broadband light with watt-level output power and continuously tunable central wavelength could be realized. As a verification, an in-house built cascaded RFL with a wavelength tuning range of 1210–1270 nm is employed as the pump source of the Raman amplifier, and a 1.3 μm broadband SLD source is used as seed light. As a result, the amplified broadband light with the 3 dB bandwidth of 13 nm, output power of 1 W and the tunable central wavelength in 1315–1340 nm is realized. Good temporal stability of the amplified broadband light is also demonstrated due to the use of low-noise Raman amplification in a backward pumping scheme. The method for further power scaling of the broadband light to 10-watt level is also numerically studied. The proposed method paves a new way for high-power and wavelength flexible broadband light amplification, which could be used as powerful sources to improve the system performances of optical coherence tomography, optical fiber communications, interferometric diffusing wave spectroscopy, fiber optic gyroscopes, etc.

We report on an investigation of InGaAs/GaAs quantum well-dot superluminescent diodes (SLDs) based on what we believe to be a novel and simple design of stripe waveguides. The design employing a chip side facet as a component of the SLD structure allows effective suppression of optical feedback, thus increasing the optical power. The test SLDs under study emitting in 950-1150 nm spectral range show CW optical power as high as 150 mW in combination with broad emission spectra of 20 nm full width at half maximum (FWHM).

Due to the high level of interest recently accorded to online surface measurement methods by academia and industry, engineers can now measure engineered surfaces rapidly and accurately. The present work involved illumination and individually examining a snapshot dispersive optical interferometer sensor with two different types of high-powered super-luminescent diodes (SLDs). Fringe pattern visibility is crucial to the effectiveness of this kind of interferometer. Two scenarios were introduced to examine the interference pattern visibility for the first-order (scanning range). Compared to the zero-order (reference beam), the first-order (diffraction/measurement beam) is less intense. Undesirable outcomes are generated by the dispersive line beam, like increased noise at a reduced intensity at the scanning range margin. Noise is among the parameters adversely impacting effective signal in all classes of optical measurement sensors; subsequently, sensor resolution measurement is influenced by any elevation in first-order intensity. The measurement noise peak to peak of the analyzed sample was developed from 28 to 20nm. Consequently, it is possible to apply the snapshot sensor to a next-generation snapshot fiber link interferometry sensor for surface inspection.