We report a time-domain optical coherence tomography (TD-OCT) system operating in the 2 µm spectral region, enabled by a GaSb-based superluminescent diode (SLD). The spectrum emitted by the SLD exhibits a full-width half-maximum (FWHM) of ∼80 nm centered near 2.1 µm. For OCT operation, stable amplified spontaneous emission with low spectral ripple (<20%) is maintained at drive currents below 150 mA. The SLD is fiber coupled and integrated into a fiber-based Michelson interferometer. In the OCT system, the measured coherence envelope yields an axial resolution of approximately 300 µm in air and enables depth-resolved imaging of scattering paint-based coating samples. In contrast to OCT implementations at 2 µm wavelength region that commonly rely on supercontinuum sources, the use of GaSb-based SLDs offers a compact, practical alternative, leveraging the maturity and scalability of electrically driven semiconductor light sources packaged in a standard "butterfly" module. This report represents the first demonstration of TD-OCT imaging at 2 µm using a GaSb-based SLD source and establishes its suitability for compact and scalable mid-IR OCT instrumentation targeting non-biological, low-water-content materials.

The paper refers to advancements in the production of en-face optical coherence tomography (OCT) images from different depths in a sample in real time, using Downconversion Leader-Follower optical coherence tomography method. So far, for a sample placed in an interferometer (Follower), all previous Downconversion Leader-Follower reports employed an interferometer (Leader) to determine the depth where the OCT signal is selected from. In this paper, for the first time, the Leader interferometer is replaced by an arbitrary waveform generator, i.e. optical generation of the reference signal to perform downconversion is replaced by electrical synthesis. In this way, en face images from different depths are presented in real time, without recurring to a second interferometer. Avenues opened by electrical synthesis of signals otherwise provided by interferometers are discussed, with potential to be adopted in signal processing, manipulation and presentation of high resolution images in orthogonal orientations to serve better diagnosis.

We present a fully automated large-area OCT imaging procedure with real-time refocusing integrated with a combined OCT-Raman system. Scanning along the x-axis is achieved using a single galvanometer paired with a telecentric lens. Scanning along the y-axis is accomplished by translating a sample with a motorised horizontal stage over a much larger lateral size. The same translation stage is also moved along the y-axis to repeat the scanning over connecting columns. Automated refocusing at equidistant intervals along the y-axis is performed using a motorised vertical stage, which carries the combined OCT-Raman imaging head. We also perform spatial calibration between the OCT and Raman optics to enable automated focusing of the Raman optics onto the sample surface. The procedure is validated on a large 5 cm x 5 cm biological sample, with assessment of scanning time and other imaging parameters. A surface map is generated to guide the subsequent Raman measurements, and a targeted Raman measurement is performed on selected sites on the sample. This combined OCT-Raman system is designed for fully automated intraoperative breast cancer diagnosis, integrating OCT imaging, ML-based classification, and Raman spectroscopy.

The adaptation of a Raspberry Pi and low-cost camera into a full-field OCT system is demonstrated. Challenges in utilising the low-cost components are discussed. Promise is shown for a compact and cost-effective OCT solution. (c) 2025 The Author(s)

In this paper, a technique is presented for determining the sweeping direction of any swept source without recurring to optical spectrum measurements but using elements of the OCT system only. (c) 2025 The Author(s)

By combining a galvo scanner with a motorised XY-stage, we propose stripelike raster scanning for large-area OCT. We provide calculations for lateral dimensions, and test the technique on an 8 cm x 5 cm sample. (c) 2025 The Author(s)

In this study, a comprehensive theoretical model for the multi-harmonic dispersion-tuned mode-locking (DTML) regime for swept-source OCT (SS-OCT) is presented for the first time. The principle of wavelength tuning in this regime is described in detail, along with a derivation of the tuning bandwidth formula and scaling guidelines that predict the trade-offs between the tuning bandwidth and coherence performance. A comparison of the optical fields stored inside a conventional single-harmonic DTML cavity, a multi-harmonic DTML cavity, and an FDML cavity is also presented. As experimental validation of the multi-harmonic concept, OCT images of a finger tip and the retina of a volunteer are captured at a sweep rate close to 1 MHz with a 30 nm tuning bandwidth.

This paper comprehensively demonstrates the efficiency of balanced detection in a visible optical coherence tomography instrument employing a low-noise supercontinuum laser. By using an innovative technique for digitally aligning camera pixels, we achieved a noise floor reduction of up to 12.8 dB across the entire imaging depth range, particularly near the zero optical path difference between the interferometer arms. The instrument presented here operates at a central wavelength of 590 nm. It delivers high-resolution images with a sensitivity of up to 74 dB in a single spectrometer configuration and 92.8 dB in a balanced configuration. The enhancement in image contrast is exemplified through images of an optical phantom and in-vivo images of a human thumb and nail.

Can OCT-TL effectively help visualise non-invasively cellular dynamics during embryo development? OCT-TL offers a non-invasive, 3D visualization technique for detailed embryo imaging and dynamics interpretation, enhancing developmental biology research with high-resolution perspectives. Time-lapse imaging in IVF has depth visualization limitations. To overcome this, Optical Coherence Tomography (OCT) offers an advanced alternative by enabling non-invasive 3D embryo imaging with sectional depth visualization. This technique can potentially track embryonic movement and elasticity across 4-5 dimensions while using a low-power light source. Here, we visualised in-depth mouse embryos throughout their development to investigate their morphokinetics. A basic study was performed between January to March 2024. A total of six mouse zygotes were investigated for their morphology and movement through the different embryo development stages. To achieve this, two different Time Lapse (TL) systems were used: Geri (Genea Biomedx) and our custom-based OCT-TL system. Cryopreserved mouse zygotes (C57BL/6N) were obtained from Charles River Laboratories (France) and thawed according to the producer’s recommended protocol. Thawed zygotes were either placed in a Geri TL system or a custom-based OCT-TL system in an incubator for 96-100 hours at 37ºC. To visualise all the embryo stages, images were taken every 5 minutes (Geri) or 30 minutes (OCT-TL), and later manually annotated. Embryo development was successfully imaged in both systems, allowing the identification of the different embryo development stages. With our custom-based OCT-TL system, as per predefinition, images are taken at different depths throughout the sample, we could create a 3D image from several embryo development stages. Moreover, we could also detect the dynamic level across the embryo development as well as, when the embryo suffered an arrest. This allowed us to obtain non-invasively more information from the embryo development, while maintaining it under optimal conditions, providing the future utility of OCT-TL for embryo imaging. All images obtained were in the format of a pilot study using a novel OCT-TL system that was developed and placed in the incubator. Future imaging sessions would help to obtain more data points. Although in the present study, OCT was applied in mouse samples, this novel approach can also be employed for Human IVF or Livestock IVP procedures to overcome the current time-lapse limitations, providing more information on the embryo’s development quality. No

This work presents a technique designed to correct laser-induced phase variations in Swept-Source optical coherence tomography (SS-OCT) instruments. Conventionally, data resampling is achieved by using an external k-clock module, and the signal generated by taping some of the light and diverting it through a fibre Bragg grating is used to trigger the acquisition and stabilise the phase. Instead, in this work, the nonlinearities in the imaging interferometer output are computed from data generated by a reference interferometer block in synchronism with data collected by the imaging interferometer. Phase-stabilised digital channelled spectra are obtained by monitoring the number of cycles in the output signal of the reference interferometer. Our preliminary results show a significant improvement in the stabilisation of the phase, from an initial 3.6 radians to less than 0.1 radians when using our approach.

Loss of focus in depth due to the mismatch between the coherence gate and the focus gate is a limiting factor in the achievable high lateral resolution in optical coherence tomography (OCT). This work adapts a simplified dynamic focus method, utilising only one mechanical element to a full-field OCT configuration, and demonstrates the capability to maintain the alignment of the coherence gate and the depth of the focus gates, at sample depths of up to 4 mm while using a high numerical aperture objective lens (NA = 0.5).

This work presents a method that accurately senses the absolute positions of highly reflective layers without requiring resampling of the interferometric chirped signals or compensating for unbalanced dispersion. Our approach is based on the observation that, for a given position.. of a reflector, the number of cycles in the channelled spectrum does not depend on how the frequencies are distributed within the interferometer output. The technique was used to infer the positions of a mirror (while collecting channelled spectra), which are required for accurate compensation for the non-linearities of the channelled spectra. En-face images of a coin and thumb obtained using the proposed approach are also presented. (c) 2025 The Authors.

This paper evaluates the application of common path optical coherence tomography (OCT) in three applications: distance sensing, handheld imaging and dynamic OCT.

Akinetic swept-sources are essential for high-speed optical coherence tomography (OCT) imaging. Time-stretched supercontinuum (TSSC) lasers have proven to be efficient for multi-MHz swept-sources. However, lack of low-noise broadband lasers and of large dispersion devices in the water low-absorption band at 1060 nm have limited the biomedical applications of TSSC lasers. In this letter, an approach to tune the wavelength around 1050 nm over 90 nm with low-noise at 10 MHz is presented. This is based on all-normal dispersion (ANDi) supercontinuum dynamics, and employs a long chirped fiber Bragg grating (CFBG) to time-stretch a broadband pulse with a duty cycle of 93% . Retinal images are demonstrated, with a sensitivity of 84 dB - approaching the shot noise limit. We believe this high-speed low-noise swept-source will greatly promote the development of OCT techniques for biomedical applications.

RESEARCH QUESTION:Does exposure to near-infra-red optical coherence tomography (OCT) laser radiation induce phototoxic effects in porcine and human spermatozoa? DESIGN:Computer-assisted sperm analysis (CASA) was used to determine whether OCT laser illumination at or above levels typically used for imaging alters sperm motility. Flow cytometry was used to determine the impact of irradiation on sperm acrosome reaction status, DNA fragmentation, and membrane integrity. Additionally, in-vitro time-lapse OCT imaging of a porcine cumulus-oocyte complex with irradiated spermatozoa was performed to determine whether irradiated spermatozoa interact with and penetrate the cumulus oophorus. Finally, human spermatozoa were irradiated and analysed using CASA and flow cytometric techniques. RESULTS:All irradiated samples showed no significant difference in sperm DNA damage or CASA sperm motility parameters, including average path velocity, straight line velocity or curvilinear velocity, compared with their matched manipulation control, suggesting that sample irradiation did not compromise sperm viability, even when using an optical power of more than one order of magnitude greater than that typically required to image embryos. Proof-of-concept OCT imaging suggested that motility of irradiated spermatozoa during cumulus interaction was not affected by radiation. CONCLUSIONS:No significant effect on the kinetics of boar and human spermatozoa was observed following near-infra-red OCT laser radiation. Future work will investigate the fertilization process and embryo development following near-infra-red OCT laser radiation.

Common-path low-coherence interferometry enables high-resolution distance measurements to be made via thin fiber-optic probes. This is particularly advantageous for applications such as ophthalmic vitreoretinal microsurgery, where the probes can be used to precisely locate the position of surgical tools relative to the retinal surface, but could also have a wide range of other medical and industrial applications. The performance of the fiber probes depends critically on the fabrication of a focusing lens at the distal tip and on creating a medium-independent partial reflection that is used for common-path interferometry. These are complex multi-step procedures that are not fully described in the literature. In this note, we detail a procedure to manufacture probes by fusing coreless and gradient index sections of fiber to single-mode fiber and to apply a thin gold coating to act as a partial reflector. We also explain how quality control of the fabrication can be performed, demonstrate how the probes can be coupled to a common-path swept-source interferometer, and describe algorithms to convert raw data to distance measurements. These procedures are intended to aid researchers in developing their own customized probes and develop new applications for distance sensors.