Superluminescent Diode Research Articles

Application of a super-luminescent diode coupled with an interference filter for mixed gas sensing

Laser-based spectroscopic techniques are very attractive methods for trace gas, environmental and industrial monitoring. By employing narrow spectral-width tunable coherent light sources, a single absorption line of the substance to be analyzed can be probed with a laser, avoiding interference signals from other species. Here we report a difference frequency generation (DFG) source in mid-infrared region using a tunable laser (825 – 870nm) and a fixed wavelength diode laser (1060nm) in combination with a PPLN having single period. Application of the approach for carbon dioxide (CO2) monitoring in air was studied. Many gas sensing applications do not require extreme sensitivities up to ppb order and in this case, super-luminescent diodes (SLD) are also of great interest. They are commonly produced in the spectral range of optical fibers telecommunications (1.3 – 1.7 m), where overtone vibration bands of many gas molecules of interest. As a typical example, measurements of ammonia (NH3) trace gas were studied for combustion measurement applications. A novel approach of using fiber-coupled SLD along with an interference filter can also be considered for such application to avoid influence of water vapor (H2O). The interest of this system consists in the possibility to detect several species with a single instrument.

High-power quantum dot superluminescent diode with integrated optical amplifier section

A 1.1 µm high-power quantum dot superluminescent diode has been fabricated by using a two-section device structure which consists of a superluminescent section and an optical amplifier section. The device exhibits 380 mW output power with 50 nm bandwidth or 260 mW output power with 66 nm bandwidth.

Influence and compensation of autocorrelation terms in depth-resolved spectroscopic Fourier-domain optical coherence tomography

We demonstrate depth-resolved spectral absorption measurements in the wavelength range from 750 to 850 nm using a broadband light source consisting of three spectrally shifted superluminescent light-emitting diode modules and a low-cost spectrometer-based Fourier-domain optical coherence tomography system. We present the theoretical model and experimental verification of interferences between autocorrelation terms and the signal carrying cross-correlation terms, strongly affecting the absorption measurements. A simple background subtraction, minimizing the artifacts caused by the interferences of autocorrelation and cross-correlation terms, is presented.

Multi-color quantum dot ensembles grown in selective-areas for shape-controlled broadband light source

Multi-color quantum dot (QD) ensembles were grown by selective-area growth method to realize a shape-controlled broadband light source. By using a metal-mask, QD ensembles and strain reducing layer (SRL) were formed in selective areas on a wafer. The SRL thickness was varied to achieve appropriate shifts in the peak wavelength of the QD emission spectrum up to 90nm. A summation of PL spectra obtained from the multi-color QD ensembles shows a broadband emission spectrum with a width of approximately 120nm, even though this spectrum is attributed to the ground state emissions of these QD ensembles. A current-induced broadband light source such as a superluminescent diode (SLD) based on the multi-color QD ensembles is expected to have an emission spectrum with a width of more than 120nm owing to the combination of excited state emissions. Furthermore, a desired shape of the SLD spectrum can be obtained by controlling the injection current applied to each QD ensemble. This approach is promising for a shape-controlled broadband SLD, and it is particularly applicable to optical coherence tomography (OCT).

Broadband light sources using InAs quantum dots with InGaAs strain‐reducing layers

AbstractWe fabricated broadband superluminescent diodes (SLDs) for optical coherence tomography (OCT). We used three kinds of quantum dot (QD) layers with different emission peak wavelengths in the active region of SLD. The emission wavelength was controlled by reducing the strain in QDs; by using the In0.1Ga0.9 As strain‐reducing layer, the peak wavelength shifted toward the longer‐wavelength side, and the photoluminescence peak intensity becomes strong in contrast to QDs on GaAs.By stacking these strain‐controlled QD layers, the SLD device shows a broad electroluminescence spectrum with the center wavelength of 1130 nm and the spectral linewidth of approximately 240 nm at the injection of 1A caused by the increased emission intensity from the excited states. This corresponds to an resolution of 2.3 μm in OCT. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Structure and properties of InAs/AlAs quantum dots for broadband emission

The InAs quantum dots (QDs) on an AlAs layer are grown on GaAs substrates by molecular beam epitaxy technique. The properties of materials and optics of such QD structures have been investigated by cross sectional transmission electron microscopy and photoluminescence (PL) techniques. It is discovered that the inhomogeneous strain filed mainly exists below InAs QDs layers in the case of no wetting layer. The full width at half maximums (FWHMs) and intensities of PL emission peaks of InAs QDs are found to be closely related to the thickness of the thin AlAs layers. The InAs QDs on an eight monolayer AlAs layer, with wide FWHMs and large integral intensity of PL emission peaks, are favorable for producing broadband QD superluminescent diodes, external-cavity QD laser with large tuning range.

Optimized Dipole-Surface Plasmon Waveguide Coupling for Enhancement of SLD Performance

A five-layer surface plasmon waveguide (SPWG) is proposed to be used in a superluminescent diode. It is shown that the generated light by the proposed device has higher power and broader spectrum compared with a conventional device in which a dielectric waveguide has been used. The effect of SPWG parameters on loss and spontaneous emission coupling factor is addressed, and design guidelines have been given for two cases where emphasis is on high output power or high power-spectral width product.

Interobserver variability for retreatment indications after Ranibizumab loading doses in neovascular age-related macular degeneration

To assess the interobserver variability (IOV) in indicating retreatment for neovascular Age-related macular degeneration 4 weeks after three Ranibizumab loading doses using spectral domain OCT (SD-OCT) as the primary objective diagnostic tool. Four observers decided for or against 4th Ranibizumab injection in 108 patients by six different rating rounds (RR) based on the SD-OCT findings after the loading doses. Postoperative OCT images were supplemented consecutively with information from a chart review as the 'patients subjective estimation of vision (SE)', the course of best-corrected visual acuity (BCVA) and the preoperative OCT as well as all information collectively. Agreement rates (AR) and Kappa statistics were calculated. Based on post-treatment OCT findings only (RR1), mean reinjection rate of all observers was 37.5%. Adding supplementary information, mean reinjection rate decreased to 20% when all information was available reflecting the 'real' situation (RR 6). Interobserver agreement rates varied from 66.7% to 90.7% depending on rating rounds and interobserver pairs. Mean AR and Kappa values (KV) were as following: AR 81.6%, KV 0.61 (RR1: 'only post-OP OCT'); AR 76.7%, KV 0.33 (RR2: post-OP OCT + SE); AR 80.3%, KV 0.45 (RR3: post-OP OCT + BCVA); AR 80.7%, KV 0.46 (RR4: pre- and post-OP OCT); AR 82.2%, KV 0.49 (RR5: post-OP OCT + SE + BCVA); and finally AR 83.6%, KV 0.47 (RR6: pre- and post-OP OCT + SE + BCVA). The overall mean agreement rate was 80.9% with a Kappa of 0.47. IOV for indicating retreatment after three Ranibizumab loading doses reveals only moderate agreement in Kappa statistics, which seems to be too low considering the high costs for retreatments. More concise guidelines based on the post-treatment OCT scans as the presumably most sensitive and noninvasive objective tool to follow choroidal neovascularization activity by judging the course of sub- and intraretinal fluid are necessary.

Statically scanned single and tandem low-coherence interferometers

Statically scanned single and tandem Michelson interferometer configurations are compared for the remote measurement of thermally induced group delay change in optically dispersive glass samples. A broadband tungsten filament bulb was used to illuminate the single interferometer, and a much narrower spectral bandwidth superluminescent diode (SLD) was used to illuminate the tandem interferometer. For a BK7 glass sample, measurements of thermally induced group delay changes were made with <0.5 fs root mean square error for optical path delay (OPD) scan lengths of only 260 µm when applied to low-coherence interferograms with signal-to-noise ratios as low as 6.5 dB. These results demonstrate the power of dispersive Fourier transform spectrometry (DFTS) applied to noisy, dispersion distorted low-coherence interferograms captured with non-mechanical, short path length scans. Further, following experimentally observed source bandwidth-induced measurement resolution limitations between the different illuminating sources, simulations were performed to examine this feature.

Characterization and Analysis of Relative Intensity Noise in Broadband Optical Sources for Optical Coherence Tomography

Relative intensity noise (RIN) is one of the most significant factors limiting the sensitivity of an optical coherence tomography (OCT) system. The existing and prevalent theory being used for estimating RIN for various light sources in OCT is questionable, and cannot be applied uniformly for different types of sources. The origin of noise in various sources differs significantly, owing to the different physical nature of photon generation. In this study, we characterize and compare RIN of several OCT light sources including superluminescent diodes (SLDs), an erbium-doped fiber amplifier, multiplexed SLDs, and a continuous-wave laser. We also report a method for reduction of RIN by amplifying the SLD light output by using a gain-saturated semiconductor optical amplifier.

Quantum Dot Superluminescent Diodes for Optical Coherence Tomography: Skin Imaging

We present a high-power (18 mW continuous wave exiting a single-mode fiber and 35 mW exiting the facet), broadband (85 nm full-width at half-maximum) quantum dot-based superluminescent diode, and apply it to a time-domain optical coherence tomography (OCT) setup. First, we test its performance with increasing optical feedback. Then we demonstrate its imaging properties on tissue-engineered (TE) skin and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in vivo</i> skin. OCT allows the tracking of epidermal development in TE skin, while the higher power source allows better sensitivity and depth penetration for imaging of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in vivo</i> skin layers.

Quantum Dot Superluminescent Diodes for Optical Coherence Tomography: Device Engineering

We present a 18 mW fiber-coupled single-mode superluminescent diode with 85 nm bandwidth for application in optical coherence tomography (OCT). First, we describe the effect of quantum dot (QD) growth temperature on optical spectrum and gain, highlighting the need for the optimization of epitaxy for broadband applications. Then, by incorporating this improved material into a multicontact device, we show how bandwidth and power can be controlled. We then go on to show how the spectral shape influences the autocorrelation function, which exhibits a coherence length of <;11 μm, and relative noise is found to be 10 dB lower than that of a thermal source. Finally, we apply the optimum device to OCT of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in vivo</i> skin and show the improvement that can be made with higher power, wider bandwidth, and lower noise, respectively.

Endoscopic Functional Fourier Domain Common-Path Optical Coherence Tomography for Microsurgery

A single-arm interferometer based optical coherence tomography (OCT) system known as common-path OCT (CPOCT) is rapidly progressing towards practical application. Due in part to the simplicity and robustness of its design, Fourier Domain CPOCT (FD-CP-OCT) offers advantages in many endoscopic sensing and imaging applications. FD-CP-OCT uses simple, interchangeable fiber optic probes that are easily integrated into small and delicate surgical tools. The system is capable of providing not only high resolution imaging but also optical sensing. Here, we report progress towards practical application of FD-CP-OCT in the setting of delicate microsurgical procedures such as intraocular retinal surgery. To meet the challenges presented by the microsurgical requirements of these procedures, we have developed and initiated the validation of applicable fiber optic probes. By integrating these probes into our developing imaging system, we have obtained high resolution OCT images and have also completed a demonstration of their potential sensing capabilities. Specifically, we utilize multiple SLEDs to demonstrate sub 3-micron axial resolution in water; we propose a technique to quantitatively evaluate the spatial distribution of oxygen saturation levels in tissue; and we present evidence supportive of the technology's surface sensing and tool guidance potential by demonstrating topological and motion compensation capabilities.

L-band tunable external cavity laser based on 158 μm superluminescent diode integrated with spot-size converter

We report a 1.58 μm superluminescent diode (SLD) with a spot-size converter (SSC) designed and fabricated as a light source for a tunable external cavity laser (T-ECL). The active section of the SLD is fabricated by using a planar buried heterostructure (PBH) for low-threshold current and high-output power operation at a low injection current. The SSC structure of the SLD is designed to possess a buried deep-ridge waveguide (BD-RWG) and show a beam of less divergence. The full-width at half maximum (FWHM) of the horizontal and vertical far-field patterns (FFPs), due to the beam of the less divergence, are 14° and 13°, respectively. We also confirm that an L-band T-ECL employing the SSC SLD operates well enough to prove the characteristics of high performance.

GaAs-Based Transverse Junction Superluminescent Diodes With Strain-Compensated InGaAs–GaAsP Multiple-Quantum-Wells at 1.1-$\mu$m Wavelength

In this study, we demonstrate a transverse junction superluminescent diode (TJ-SLD) with an engagement of chirped In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> As-GaAs <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.9</sub> P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.1</sub> strain-compensated multiple-quantum-wells (SC MQWs) at 1.1-μm wavelength. The problem relative to inhomogeneous carrier distribution in each QW, which is a problem in traditional vertical junction SLDs (VJ-SLDs), can be effectively minimized by utilizing the benefit of lateral carrier injection in TJ devices. Our demonstrated device offers significant improvements in threshold current, output power, and optical bandwidths compared to TJ-SLD without SC MQWs. Furthermore, compared with the high-performance ~1-μm VJ-SLDs, this novel device exhibits a comparable output power and 3-dB bandwidth performance with a more stable electroluminescence spectrum, which varies only negligibly under a wide range of bias current.

High-Power ($&gt; 110$ mW) Superluminescent Diodes by Using Active Multimode Interferometer

We have designed and fabricated, for the first time to our knowledge, novel superluminescent diodes by using active multimode interferometers that emit at a wavelength of 1.55 ¿ m. An output power as high as 115 mW was obtained with a wide 3-dB bandwidth of 50 nm and low spectral ripple of 0.03 dB. In addition, they showed stable single-transverse-mode outputs up to the maximum output power.

InGaAs Quantum Well Grown on High-Index Surfaces for Superluminescent Diode Applications

The morphological and optical properties of In0.2Ga0.8As/GaAs quantum wells grown on various substrates are investigated for possible application to superluminescent diodes. The In0.2Ga0.8As/GaAs quantum wells are grown by molecular beam epitaxy on GaAs (100), (210), (311), and (731) substrates. A broad photoluminescence emission peak (~950 nm) with a full width at half maximum (FWHM) of 48 nm is obtained from the sample grown on (210) substrate at room temperature, which is over four times wider than the quantum well simultaneously grown on (100) substrate. On the other hand, a very narrow photoluminescence spectrum is observed from the sample grown on (311) with FWHM = 7.8 nm. The results presented in this article demonstrate the potential of high-index GaAs substrates for superluminescent diode applications.

Flexible polymer waveguide tunable lasers

A flexible polymeric Bragg reflector is fabricated for the purpose of demonstrating widely tunable lasers with a compact simple structure. The external feedback of the Bragg reflected light into a superluminescent laser diode produces the lasing of a certain resonance wavelength. The highly elastic polymer device enables the direct tuning of the Bragg wavelength by controlling the imposed strain and provides a much wider tuning range than silica fiber Bragg gratings or thermo-optic tuned polymer devices. Both compressive and tensile strains are applied within the range from -36000 microepsilon to 35000 microepsilon, so as to accomplish the continuous tuning of the Bragg reflection wavelength over a range of up to 100 nm. The external feedback laser with the tunable Bragg reflector exhibits a repetitive wavelength tuning range of 80 nm with a side mode suppression ratio of 35 dB.

Three-dimensional shape measurement of micro-lens arrays using full-field swept-source optical coherence tomography

We report three-dimensional (3D) shape measurement of refracting samples using full field swept-source optical coherence tomographic (FF-SS-OCT) system. The optical arrangement of FF-SS-OCT consists of a swept-source system containing super-luminescent diode as low coherence light source and an acousto-optic tunable filter as electronically controlled frequency tuning device, a compact Michelson interferometer and an area detector. Refracting samples, such as, cylindrical lens and micro-lens arrays were used as object. By means of sweeping the frequency of the light source, multiple interferograms were recorded and both amplitude and phase map of the interference fringe signal were then reconstructed. Experimental results of optically sectioned images (tomography) of the cylindrical lens and micro-lens arrays obtained by means of selective Fourier filtering and 3D-surface profile retrieved from the phase-map are demonstrated. The proposed system does not require any mechanical scanning. In addition, a common optical path enables this proposed technique to be highly stable.

Comprehensive Modeling of Superluminescent Light-Emitting Diodes

We present a self-consistent electric and optic model for superluminescent light-emitting diodes (SLED) using 3D finite-element method. The carrier transport is calculated by the drift-diffusion method, which is coupled with the radiative recombination obtained from the solution of Shrodinger-Poison equations self-consistently. The spontaneous emission noise is described by the fundamental theory using the Green's function method. Our model allows 2D treatment of the carrier dynamics and optical confinement on the transverse plane, along with the electronic and optical variation on the longitudinal axis. The theoretical model has been benchmarked with an InP-based edge-emitting SLED. The device has nonidentical quantum wells with broad bandwidth from 1300 to 1600 nm. The results show the importance of 3D effects and demonstrate the validity of the model.