Quantifying the influence of Bessel beams on image quality in optical coherence tomography

Light scattered by turbid tissue is known to degrade optical coherence tomography (OCT) image contrast progressively with depth. Bessel beams have been proposed as an alternative to Gaussian beams to image deeper into turbid tissue. However, studies of turbid tissue comparing the image quality for different beam types are lacking. We present such a study, using numerically simulated beams and experimental OCT images formed by Bessel or Gaussian beams illuminating phantoms with optical properties spanning a range typical of soft tissue. We demonstrate that, for a given scattering parameter, the higher the scattering anisotropy the lower the OCT contrast, regardless of the beam type. When focusing both beams at the same depth in the sample, we show that, at focus and for equal input power and resolution, imaging with the Gaussian beam suffers less reduction of contrast. This suggests that, whilst Bessel beams offer extended depth of field in a single depth scan, for low numerical aperture (NA  0.95), superior contrast (by up to ~40%) may be obtained over an extended depth range by a Gaussian beam combined with dynamic focusing

Towards wafer-scale integration of high repetition rate passively mode-locked surface-emitting semiconductor lasers

One of the most application-relevant milestones that remain to be achieved in the field of passively mode-locked surface-emitting semiconductor lasers is the integration of the semiconductor absorber into the gain structure, enabling the realization of ultra-compact high-repetition-rate laser devices suitable for wafer-scale integration. We have recently succeeded in fabricating the key element in this concept, a quantum-dot-based saturable absorber with a very low saturation fluence, which for the first time allows stable mode locking of surface-emitting semiconductor lasers with the same mode areas on gain and absorber. Experimental results at high repetition rates of up to 30GHz are show

Deep tissue volume imaging of birefringence through fibre-optic needle probes for the delineation of breast tumour

Published online: 01 July 2016Identifying tumour margins during breast-conserving surgeries is a persistent challenge. We have previously developed miniature needle probes that could enable intraoperative volume imaging with optical coherence tomography. In many situations, however, scattering contrast alone is insufficient to clearly identify and delineate malignant regions. Additional polarization-sensitive measurements provide the means to assess birefringence, which is elevated in oriented collagen fibres and may offer an intrinsic biomarker to differentiate tumour from benign tissue. Here, we performed polarization-sensitive optical coherence tomography through miniature imaging needles and developed an algorithm to efficiently reconstruct images of the depth-resolved tissue birefringence free of artefacts. First ex vivo imaging of breast tumour samples revealed excellent contrast between lowly birefringent malignant regions, and stromal tissue, which is rich in oriented collagen and exhibits higher birefringence, as confirmed with co-located histology. The ability to clearly differentiate between tumour and uninvolved stroma based on intrinsic contrast could prove decisive for the intraoperative assessment of tumour margins.Martin Villiger, Dirk Lorenser, Robert A. McLaughlin, Bryden C. Quirk, Rodney W. Kirk, Brett E. Bouma and David D. Sampso

Multimodal imaging needle combining optical coherence tomography and fluorescence for imaging of live breast cancer cells labeled with a fluorescent analog of tamoxifen

Significance: Imaging needles consist of highly miniaturized focusing optics encased within a hypodermic needle. The needles may be inserted tens of millimeters into tissue and have the potential to visualize diseased cells well beyond the penetration depth of optical techniques applied externally. Multimodal imaging needles acquire multiple types of optical signals to differentiate cell types. However, their use has not previously been demonstrated with live cells.Aim: We demonstrate the ability of a multimodal imaging needle to differentiate cell types through simultaneous optical coherence tomography (OCT) and fluorescence imaging.Approach: We characterize the performance of a multimodal imaging needle. This is paired with a fluorescent analog of the therapeutic drug, tamoxifen, which enables cell-specific fluorescent labeling of estrogen receptor-positive (ER+) breast cancer cells. We perform simultaneous OCT and fluorescence in situ imaging on MCF-7 ER+ breast cancer cells and MDA-MB-231 ER-cells. Images are compared against unlabeled control samples and correlated with standard confocal microscopy images.Results: We establish the feasibility of imaging live cells with these miniaturized imaging probes by showing clear differentiation between cancerous cells.Conclusions: Imaging needles have the potential to aid in the detection of specific cancer cells within solid tissue

Vertical-external-cavity surface-emitting lasers and quantum dot lasers

The use of cavity to manipulate photon emission of quantum dots (QDs) has been opening unprecedented opportunities for realizing quantum functional nanophotonic devices and also quantum information devices. In particular, in the field of semiconductor lasers, QDs were introduced as a superior alternative to quantum wells to suppress the temperature dependence of the threshold current in vertical-external-cavity surface-emitting lasers (VECSELs). In this work, a review of properties and development of semiconductor VECSEL devices and QD laser devices is given. Based on the features of VECSEL devices, the main emphasis is put on the recent development of technological approach on semiconductor QD VECSELs. Then, from the viewpoint of both single QD nanolaser and cavity quantum electrodynamics (QED), a single-QD-cavity system resulting from the strong coupling of QD cavity is presented. A difference of this review from the other existing works on semiconductor VECSEL devices is that we will cover both the fundamental aspects and technological approaches of QD VECSEL devices. And lastly, the presented review here has provided a deep insight into useful guideline for the development of QD VECSEL technology and future quantum functional nanophotonic devices and monolithic photonic integrated circuits (MPhICs).Comment: 21 pages, 4 figures. arXiv admin note: text overlap with arXiv:0904.369

Waveguide optics for novel in situ biomedical imaging

Optical microscope-in-a-needle technology for 3D tissue micro-imaging will open up new avenues in diagnosis and treatment of disease. We describe innovations in guided-wave optical design for needle probes and demonstrate applications in tissues

Fiber-optic needle probes: Applications in deep tissue Imaging

Fiber-optic needle probes are highly miniaturized imaging devices that enable imaging deep inside the body. Utilizing optical coherence tomography (OCT), these devices replace the standard scanning mechanism of an OCT scanner with all-fiber focusing optics small enough to be encased within a hypodermic needle. We describe recent innovation in the design of these probes, including novel fiber-optic configurations to achieve extended depth of focus, and the use of double-clad fiber to enable the first dual-modality fiber-optic needle probe, simultaneously acquiring both OCT and fluorescence images

Accurate modeling and design of graded-index fiber probes for optical coherence tomography using the beam propagation method

Fiber-optic probes for sensing and biomedical imaging applications such as optical coherence tomography (OCT) frequently employ sections of graded-index (GRIN) fiber to re-focus the diverging light from the delivery fiber. Such GRIN fiber microlenses often possess aberrations that cause significant distortions of the focused output beam. Current design methods based on ABCD matrix transformations of Gaussian beams cannot model such effects and are therefore inadequate for the analysis and design of high-performance probes that require diffraction-limited output beams. We demonstrate use of the beam propagation method (BPM) to analyze beam distortion in GRIN-lensed fibers resulting from index profiles that exhibit a deviation from the ideal parabolic shape or artifacts such as ripples or a central dip. Furthermore, we demonstrate the power of this method for exploring novel probe designs that incorporate GRIN phase masks to generate wavefront-shaped output beams with extended depth-of-focus (DOF). We present results using our method that are in good agreement with experimental data. The BPM enables accurate simulation of fiber probes using non-ideal or custom-engineered GRIN fibers with arbitrary refractive index profiles, which is important in the design of high-performance fiber-based micro-imaging systems for biomedical applications