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 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 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 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.
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.
KEYWORDS: Signal processing, Field programmable gate arrays, Optical coherence tomography, Imaging systems, Visualization, Data processing, Signal to noise ratio, Data acquisition, Optical simulations, Computer simulations
We have developed a Swept-Source Optical Coherence Tomography (Ss-OCT) system with high-speed, real-time signal processing on a commercially available Data-Acquisition (DAQ) board with a Field-Programmable Gate Array (FPGA). The Ss-OCT system simultaneously acquires OCT and k-clock reference signals at 500MS/s. From the k-clock signal of each A-scan we extract a remap vector for the k-space linearization of the OCT signal. The linear but oversampled interpolation is followed by a 2048-point FFT, additional auxiliary computations, and a data transfer to a host computer for real-time, live-streaming of B-scan or volumetric C-scan OCT visualization. We achieve a 100 kHz A-scan rate by parallelization of our hardware algorithms, which run on standard and affordable, commercially available DAQ boards. Our main development tool for signal analysis as well as for hardware synthesis is MATLAB® with add-on toolboxes and 3rd-party tools.
KEYWORDS: Optical coherence tomography, Field programmable gate arrays, Signal processing, Fourier transforms, Computer simulations, Data acquisition, Digital signal processing, Convolution, Algorithm development, Imaging systems
We developed an FPGA-based engine for Fourier-domain OCT that performs real-time signal processing based on Non- Uniform Fast Fourier Transform (NUFFT). The basic NUFFT algorithm is discussed and compared with cubic-spline interpolation regarding efficient re-sampling in k-space with different phase nonlinearities of sinusoidal swept sources. The NUFFT algorithm was adapted for an implementation in an FPGA and its accuracy is analyzed and assessed using simulated numerical data. When implemented, the NUFFT algorithm allows a processing performance at a sampling rate of 100 MS/s. The real-time processing capability was tested with sinusoidal bi-directional swept sources with A-scan rates of 50 kHz.
We present a measurement method which is capable of measuring the instantaneous coherence length as a
function of the wavelength while the source is working at its full sweep rate. The measurement principle is based
on the dynamic decrease of fringe contrast as a function of the optical path difference. The measurement setup
consists of a free-space Mach-Zehnder interferometer with a variable optical path difference. We present results
for instantaneous coherence lengths in a range from 0 mm to 50 mm with a mean standard deviation of 0.42 mm
at sweep rates of up to 120 kHz.
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