We demonstrate the first broadband light source based on spectral combination of four superluminescent diodes (SLEDs) in the cyan-to-green wavelength range, suitable for high-resolution, visible optical coherence tomography (OCT). Two integrated combined-SLED sources, each comprising two wavelength-shifted green SLEDs, are realized through micro-optical module integration. Each of those two combined-SLED sources is delivering a highly polarized output spectrum at a polarization-maintaining (PM) fiber. The output of the two PM fibers is then spectrally combined with a free-space, micro-optical combiner module to a common, single-mode fiber output with a broadband output spectrum having a 10dB wavelength range from 481nm to 519nm, a 3dB bandwidth of 32nm and a coherence length of 4.5 microns in air.
We introduce an enhanced version of a full-color, RGB hybrid LD-SLED light source module for near-to-eye display systems, predominantly tailored for laser beam scanning (LBS) architectures. This light source module integrates blue and green semiconductor laser diodes (LD) emitting at wavelengths of 455 nm and 520 nm, respectively, along with a red superluminescent diode (SLED) operating at 638 nm. Besides the RGB emitter devices, this micro-RGB module includes collimation optics, wavelength-combining filters, and a prism pair to achieve circular output beams, all packaged with an innovative micro-optical, free-space bench architecture. With a compact footprint of 5.5 mm x 8.6 mm, this module produces collimated, circular, and collinearly aligned RGB beams with minimal divergence and large diameters of 1.0-1.3 mm at the module output. This third generation of an micro-RGB light source module delivers up to 50 mW of optical power per color at a total power dissipation of 1.2 W.
We report on the progress of our efforts to apply silicon nitride photonic integrated circuits (PIC) to the miniaturization of optical coherence tomography (OCT) with the goal of facilitating its widespread use in ophthalmology at the point of care. In particular, we highlight the design and optical characterization of photonic building blocks allowing the realization of a silicon nitride PIC-based multi-channel swept-source OCT system in the 1060 nm wavelength region. Apart from waveguide structures, these building blocks include 3D-printed microlenses on the PIC end facets for efficient light coupling to and from the PIC.
We present, to the best of our knowledge, the first compact, full-color, hybrid RGB LD-SLED light source module designed for near-to-eye display systems. This module integrates a blue and green semiconductor laser diode (LD) at a wavelength of 453 nm and 520 nm, respectively, and a red superluminescent diode (SLED) at 639 nm in combination with a novel micro-optical, free-space architecture. The light source module includes circularizing optics, wavelengthcombining filters, and a single aspheric collimation lens. The light source module has a compact footprint of 7.7 mm x 10.8 mm and generates collimated, circular and collinearly aligned RGB beams with low divergence and large diameters in the range of 1.7 mm to 2.2 mm at the optical output. The current generation of this light source module delivers up to 15 mW of optical power per color, with a total power dissipation value of only 430 mW.
We demonstrate, to our knowledge for the first time, an integrated light source module that emits broadband amplified spontaneous emission (ASE) light from two superluminescent diodes (SLEDs) through a single-mode fiber output simultaneously on two orthogonal polarizations. The dual-polarization SLED source is realized on a free-space, temperature-stabilized, micro-optical bench and integrated in a 14-pin butterfly module. The broadband light output from the single-mode fiber has twice the output power of a single-SLED source and achieves a polarization extinction ratio (PER) of 0 dB when the relative power levels of both SLED sources are carefully balanced.
The miniaturization of optical coherence tomography (OCT) systems could open up potential new markets, such as point-of-care application, home OCT to regularly monitor disease and treatment progress, and in low-resource settings. Photonic integrated circuits (PIC) are considered an attractive approach to miniaturize OCT. We present our recent achievements in in vivo retinal imaging with a PIC-based Mach-Zehnder interferometer integrated in a state-of-the-art ophthalmic OCT system. The system achieves 94 dB at 750 µW on the sample, running at 50 kHz. Preliminary results of a fully packaged 4-channel opto-electronic OCT engine further demonstrate the potential of PIC-based OCT.
We report on a swept-source OCT system based on a photonic-electronic integrated circuit. It enables a parallelization of data acquisition resulting in an effective A-scan rate of 4x100 kHz at a central wavelength of 840 nm.
The monolithic co-integration of photonic elements forming the multiplexed interferometers and the system electronics on one chip allows a very compact OCT engine in a photonic package. Integrated in an ophthalmic system, the maximum sensitivity was estimated to be 91 dB with an optical power of 4x520 µW at the model eye. An eye phantom was imaged at 400 kHz showing its layered structure.
Silicon nitride waveguide based photonic integrated circuits (PICs) are intensively investigated for a wide range of sensing applications in the visible to sub 1-µm near-infrared spectral region. The monolithic co-integration of silicon photodiodes and read-out electronics offers additional benefits in terms of performance and miniaturization. We discuss challenging aspects related to the efficient coupling and routing of light to, from, and within PICs and present interfacing photonic building blocks offering potential solutions. We demonstrate the suitability of these interfacing building blocks by using them for the realization of a PIC-based multi-channel optical coherence tomography concept at 840 nm.
We demonstrate a 1300-nm ultra-broadband and compact light source module with 180 nm FWHM optical bandwidth and 22 mW of output power, realized with four superluminescent diodes (SLEDs) that are integrated on a temperature-stabilized, free-space, micro-optical bench in a standard 14-pin Butterfly package. The light output of four SLED chips at 1220 nm, 1270 nm, 1310 nm and 1360 nm is collimated by micro-optical collimation lenses, spectrally combined through free-space dielectric edge filters and focused into a SMF-28 single-mode fiber. The combined broadband spectrum corresponds to a coherence length of 5.4 μm in air, suitable for ultra-high-resolution OCT systems at 1300 nm.
We demonstrate the first fiber-coupled, broadband master oscillator power amplifier (MOPA) module where amplified spontaneous emission (ASE) light from an 840-nm superluminescent diode (SLED) is amplified by a low-confinement,
broadband 840-nm semiconductor optical amplifier (SOA), generating power levels of more than 60 mW in single-mode fibers. The SLED and SOA are integrated, without an optical isolator in between, in a compact 14-pin Butterfly module on a temperature-stabilized optical bench. The highly-polarized ASE output has a polarization extinction ratio (PER) of more than 30 dB and a 10-dB bandwidth of more than 50 nm, resulting in a coherence length of 10 microns in air.
We demonstrate a miniaturized, full-color RGB light source module for near-to-eye display systems, incorporating three semiconductor laser diodes (LDs) that are integrated on a free-space, micro-optical bench together with collimation optics and wavelength filters. The ultra-compact package has a footprint of 4.4 mm x 4.15 mm with a height of 2.9 mm (0.053 cm3) and an optical output window for the collimated and collinearly aligned RGB beams. The light source module delivers up to 10 mW per color at low power dissipation values of 640 mW and provides low-divergent output beams having a high circularity and a diameter of 250-650 μm at a reference distance of 50 mm.
A novel lipid sensitive OCT setup is presented, using light source with a central wavelength of 1280 nm and a spectral tuning range of 201 nm. A cholesterol plaque located in the aorta was imaged post mortem. Different spectral bands were chosen in post processing. Analyzing the signal attenuation of the different spectral bands enables us to see a clear difference between the lipid absorption in the plaque between the bands. In the normal tissue no clear separation of the signal attenuation can be found. This enables us to visualize the plaque on a three dimensional level.
We demonstrate a novel light source for multi-modality imaging where three superluminescent diodes (SLEDs) are integrated on a free-space, temperature-stabilized, micro-optical bench in a standard 14-pin butterfly package. The light output of the three SLED chips is collimated by individual micro-optical collimation lenses and then spectrally and spatially combined in free space through dielectric edge filters before being coupled into a common HI-780 single-mode output fiber. The two SLEDs at 840 nm and 880 nm deliver a combined broadband spectrum with 120 nm bandwidth and 8.5 mW of output power for ultra-high-resolution optical coherence tomography (OCT) imaging with an axial resolution of ~4 microns in air. The third SLED at 750 nm is suitable for implementing eye tracking based on a scanning laser ophthalmoscope (SLO). Because of the free-space architecture, the polarization of all SLEDs is intrinsically aligned such that the UHR-OCT broadband source has a high PER of 20 dB across the entire spectrum.
We demonstrate, to our knowledge for the first time, an integrated broadband master oscillator power amplifier (MOPA) module where amplified spontaneous emission (ASE) light from an 840-nm superluminescent diode (SLED) is amplified by a low-confinement, broadband 840-nm semiconductor optical amplifier (SOA) in order to generate power levels of more than 100 mW in free space. The SLED-SOA MOPA architecture is realized on a free-space, temperaturestabilized, micro-optical bench and integrated in a 14-pin butterfly module with an optical window output. The highlypolarized ASE light from the SLED is intrinsically aligned to the polarization of the SOA, thereby providing high-power amplified ASE light with an extinction ratio of more than 20 dB and with an optical bandwidth of more than 35 nm FWHM. Optimization of the ASE input signal and of the booster SOA design may either increase the optical bandwidth of the amplified ASE output signal or may also increase the output power levels to a regime of 200-300 mW.
We demonstrate an 840-nm broadband and compact light source with 140 nm FWHM optical bandwidth and 8 mW of output power, realized with three superluminescent diodes (SLEDs) that are, to our knowledge for the first time, integrated on a free-space, micro-optical bench in a standard 14-pin butterfly package. The three SLED chips at 790 nm, 840 nm and 880 nm are mounted on a ceramic baseplate that is temperature-stabilized by a thermo-electric cooler. The light output of the SLEDs is collimated by micro-optical collimation lenses, spectrally combined through free-space dielectric edge filters and focused into a HI-780 single-mode fiber. The combined broadband spectrum corresponds to a coherence length of 2.9 μm in air, suitable for ultra-high-resolution OCT systems.
A swept source optical coherence tomography (SS-OCT) system with the interferometer engine being a photonic integrated circuit (PIC) has been developed. Furthermore, an Arrayed Waveguide Grating (AWG), representing a grating on a PIC, for spectral domain OCT (SD-OCT) has been integrated in a fiber-based OCT system. With measured sensitivities of ~87 dB (SS-OCT) and ~80 dB (SD-OCT), scattering tissue imaging becomes feasible for OCT-on-chip systems. In this study, we present two OCT-on-chip systems and first results of biological tissue imaging in-vivo and exvivo.
We present the first light source module that is realized with RGB superluminescent LEDs in a compact 14-pin butterfly housing for speckle-free display applications. The module provides a free-space output with collimated RGB beams that are colinearly aligned having 10 mW output power per color.
We show a broad range of swept source performances based on a highly-flexible external cavity laser architecture.
Specifically, we demonstrate a 40-kHz 1300-nm swept source with 10 mm coherence length realized in a compact
butterfly package. Fast wavelength sweeping is achieved through a 1D 20-kHz MEMS mirror in combination with an
advanced diffraction grating. The MEMS mirror is a resonant electrostatic mirror that performs harmonic oscillation only
within a narrow frequency range, resulting in low-jitter and long-term phase-stable sinusoidal bidirectional sweep
operation with an A-scan rate of 40 kHz. The source achieves a coherence length of 10 mm for both the up- and downsweep
and an OCT sensitivity of 105 dB.
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