Superluminescent Light-emitting Diodes Research Articles

Energy Efficiency Analysis of GaN-Based Blue Light Emitters

GaN-based light sources are in high demand for lighting, displays, medical equipment and other applications. InGaN/GaN blue light-emitting diodes (LEDs) reach an electrical-to-optical power conversion efficiency of more than 80% but less than 10% are reported for blue superluminescent light-emitting diodes (SLEDs) and less than 50% for blue laser diodes (LDs). We here analyze the physical mechanisms behind this surprising discrepancy in peak energy efficiency of GaN-based light emitters. Our study reveals that the Mg-doping of group-III-nitride layers, which was pioneered by Isamu Akasaki and collaborators, plays a key role in understanding this efficiency difference.

High power surface emitting InGaN superluminescent light-emitting diodes

A high power InGaN superluminescent light-emitting diode emitting normal to the substrate is demonstrated. The device uses a structure in which a monolithically integrated turning mirror reflects the light at both ends of the in-plane waveguide to direct amplified spontaneous emission downward through the transparent GaN substrate. Record optical peak powers of >2 W (both outputs) are reported under pulsed operation at 1% duty cycle. A broad, smooth emission spectrum with a FWHM of 6 nm centered at 416 nm is measured at peak output and ascribed to very low feedback associated with the turning mirror and antireflection coating.

Zastosowanie terapii fotodynamicznej z użyciem pulsacyjnej superluminescencyjnej lampy sLED w rogowaceniu słonecznym

Zastosowanie terapii fotodynamicznej z użyciem pulsacyjnej superluminescencyjnej lampy sLED w rogowaceniu słonecznym

Abnormal Stranski-Krastanov Mode Growth of Green InGaN Quantum Dots: Morphology, Optical Properties, and Applications in Light-Emitting Devices.

Stranski-Krastanov (SK) growth mode is widely adopted for the self-assembled growth of semiconductor quantum dots (QDs), wherein a relatively large critical thickness is essential and a thick wetting layer (WL) is formed beneath the QD layer. In this paper, we report the metal organic vapor phase epitaxy of green InGaN QDs, employing a growth interruption method to decrease the critical thickness and improve the morphology of QDs. The QDs exhibit similar photoluminescence properties with those grown by conventional SK mode, implying the existence of a WL. We experimentally verify that the formation of QDs, whether based on the SK mode or the growth interruption method, conforms to the phase separation theory. However, the density of QDs grown by the interruption method exhibits abnormal dependence on the strain when a quantum well (QW) is inserted beneath the QD layer. Furthermore, the underlying QW not only influences the morphology of the QDs but also plays as a reservoir of electrons, which helps enhance the photoluminescence and the electroluminescence of the QDs. The method of QD growth with improved morphology and luminescence by introducing the QW-QD coupled nanostructure is universally applicable to similar material systems. Furthermore, a 550 nm green light-emitting diode (LED) and a 526 nm superluminescent LED based on the nanostructure are demonstrated.

Single-transverse-mode broadband InAs quantum dot superluminescent light emitting diodes by parity-time symmetry.

Parity-time (PT) symmetry breaking in counterintuitive gain/loss coupled waveguide designs is numerically and theoretically investigated. The PT symmetry mode selection conditions are determined theoretically. Single-transverse-mode broadband InAs quantum dot (QD) superluminescent light emitting diodes (SLEDs) are fabricated and characterized; the PT symmetric broad-area SLEDs contain laterally coupled gain and loss PT- symmetric waveguides. Single-transverse-mode operation is achieved by parity-time symmetry breaking. The broadband SLEDs exhibit a uniform Gaussian-like emission spectrum with the 3-dB bandwidth of 110 nm. Far-field characteristics of the coupled waveguide SLEDs exhibit a single-lobe far-field pattern when the gain and loss waveguides are biased at the injection current of 600 mA and 60 mA, respectively.

High-performance GaAs-based superluminescent diode with 292-nm emission bandwidth using simple dot-in-a-well structures

We report a simultaneous amplified emission from InAs-based self-assembled quantum dot and quantum well in a multistack dot-in-a-well superluminescent light-emitting diode (SLD) for application in broadband sources. A combination of atomic force microscopy, photoluminescence of the test structures, and optoelectronic characterization of SLD is used to obtain an emission bandwidth of ∼292 nm covering O–S communication band (including 850-nm band) and a maximum continuous power of ∼1.33 mW at room temperature.

Optical Fiber Demodulation System with High Performance for Assessing Fretting Damage of Steam Generator Tubes.

In order to access the fretting damage of the steam generator tube (SGT), a fast fiber Fabry-Perot (F-P) non-scanning correlation demodulation system based on a super luminescent light emitting diode (SLED) was performed. By demodulating the light signal coming out from the F-P force sensor, the radial collision force between the SGT and the tube support plate (TSP) was interrogated. For higher demodulation accuracy, the effects of the center wavelength, bandwidth, and spectrum noise of SLED were discussed in detail. Specially, a piezoelectric ceramic transducer (PZT) modulation method was developed to get rid of the interference of mode coupling induced by different types of fiber optics in the demodulation system. The reflectivity of optical wedge and F-P sensor was optimized. Finally, the demodulation system worked well in a 1:1 steam generator test loop and successfully demodulated a force signal of 32 N with a collision time of 2 ms.

Ytterbium-Doped Fiber Amplifiers Seeded With Superluminescent Light Emitting Diode

We demonstrate multi-stage ytterbium-doped fiber amplifiers (YDFAs) seeded with a superluminescent light emitting diode (SLED). Laser pulses with four pulse durations, such as 350-ps, 6-ns, 55-ns, and 183-ns (full width half maximum), have been studied. The peak powers reach 332, 95, 119, and 92 kW for the four types of laser pulses, respectively. The 350-ps laser pulses are generated through gain switching. Thanks to the broadband optical spectrum of the seed laser from the SLED, the stimulated Brillouin scattering is avoided. The configuration of such YDFAs seeded by an SLED with adjustable laser pulse durations (from picosecond to nanosecond) is desirable for many industrial applications.

Compact quantum random number generator based on superluminescent light-emitting diodes.

By measuring the amplified spontaneous emission (ASE) noise of the superluminescent light emitting diodes, we propose and realize a quantum random number generator (QRNG) featured with practicability. In the QRNG, after the detection and amplification of the ASE noise, the data acquisition and randomness extraction which is integrated in a field programmable gate array (FPGA) are both implemented in real-time, and the final random bit sequences are delivered to a host computer with a real-time generation rate of 1.2 Gbps. Further, to achieve compactness, all the components of the QRNG are integrated on three independent printed circuit boards with a compact design, and the QRNG is packed in a small enclosure sized 140 mm × 120 mm × 25 mm. The final random bit sequences can pass all the NIST-STS and DIEHARD tests.

Gallium Nitride Superluminescent Light Emitting Diodes for Optical Coherence Tomography Applications

Optical coherence tomography (OCT) exploits the coherent properties of light to permit noninvasive and in situ imaging of biological tissues. By expanding the range of OCT light sources from the traditional telecoms wavelengths to include ~400 nm gallium nitride (GaN) based superluminescent light emitting diodes (SLEDs) subcellular axial and lateral resolution could be achieved, provided enhanced bandwidth is also achieved. Due to the focus on high-power applications for GaN SLEDs, there has been limited work on increasing the source bandwidth. In this paper, we demonstrate for the first time a ~400 nm GaN SLED with >10 nm bandwidth employed within an OCT system, where an axial resolution of ~7 μm is achieved. Bespoke GaN SLEDs suggest that <;4 μm axial resolution imaging is imminent for short wavelength devices.

Monolithically Integrated Electrically Pumped Continuous-Wave III-V Quantum Dot Light Sources on Silicon

In this paper, we report monolithically integrated III-V quantum dot (QD) light-emitting sources on silicon substrates for silicon photonics. We describe the first practical InAs/GaAs QD lasers monolithically grown on an offcut silicon (001) substrate due to the realization of high quality III-V epilayers on silicon with low defect density, indicating that the large material dissimilarity between III-Vs and silicon is no longer a fundamental barrier limiting monolithic growth of III-V lasers on Si substrates. Although the use of offcut silicon substrates overcomes the antiphase boundary (APB) problem, it has the disadvantage of not being readily compatible with standard microelectronics fabrication, where wafers with on-axis silicon (001) substrates are used. We therefore report, to the best of our knowledge, the first electrically pumped continuous-wave (c.w.) InAs/GaAs QD lasers fabricated on on-axis GaAs/Si (001) substrates without any intermediate buffer layers. Based on the achievements described above, we move on to report the first study of post-fabrication and prototyping of various Si-based light emitting sources by utilizing the focused ion beam (FIB) technique, with the intention of expediting the progress toward large-scale and low-cost photonic integrated circuits monolithically integrated on a silicon platform. We compare two Si-based QD lasers with as-cleaved and FIB-made facets, and prove that FIB is a powerful tool to fabricate integrated lasers on silicon substrates. Using angled facet structures, which effectively reduce facet reflectivity, we demonstrate Si-based InAs/GaAs QD superluminescent light emitting diodes (SLDs) operating under c.w. conditions at room temperature for the first time. The work described represents significant advances towards the realization of a comprehensive silicon photonics technology.

Large-aperture ground glass surface profile measurement using coherence scanning interferometry.

We present a coherence scanning interferometer configured to deal with rough glass surfaces exhibiting very low reflectance due to severe sub-surface light scattering. A compound light source is prepared by combining a superluminescent light-emitting diode with an ytterbium-doped fiber amplifier. The light source is attuned to offer a short temporal coherence length of 15 μm but with high spatial coherence to secure an adequate correlogram contrast by delivering strongly unbalanced optical power to the low reflectance target. In addition, the infrared spectral range of the light source is shifted close to the visible side at a 1,038 nm center wavelength, so a digital camera of multi-mega pixels available for industrial machine vision can be used to improve the correlogram contrast further with better lateral image resolutions. Experimental results obtained from a ground Zerodur mirror of 200 mm aperture size and 0.9 μm rms roughness are discussed to validate the proposed interferometer system.

Broadband Chirped InAs Quantum-Dot Superluminescent Light-Emitting Diodes With InxAl1-xAs Strain-Reducing Layers

In this paper, broadband InAs quantum-dot (QD) superluminescent light-emitting diodes (SLEDs) are grown by molecular beam epitaxy, fabricated, and then characterized. In order to achieve broadband and uniform emission spectra, the active regions contain a combination of chirped InAs QDs with different InxAl1-xAs strain-reducing layers (SRLs). It has been shown that the InxAl1-xAs SRLs can effectively enlarge the QD emission energy separation between the ground and the excited states. In this paper, QDs with increased energy separation are utilized to enable a broadband QD ensemble by adding additional QD layers with the ground state emission wavelength tuned to fill the gap in emission. In addition, we employed a short postgrowth annealing process of 30 s to further even out the emission spectra. Characterizations of the emission spectra of the as-grown QDs and fabricated QD SLEDs are performed by room-temperature photoluminescence and electroluminescence under continuous-wave (c-w) operation, respectively. In the SLED devices, a broad and uniform spectrum with a linewidth of 100 nm at 3 dB is realized at an injection current level of 100 mA, and no significant spectrum dip is observed in the entire injection current window ranging from 50 $\mu\text{A}$ to 100 mA.

Non-contact reflectometric readout of disposable microfluidic devices by near infra-red low-coherence interferometry

We are here demonstrating the functionality of infra-red low-coherence reflectometry for the spot optical readout of solution concentrations in commercially available microfluidic devices. Disposable polymeric microfluidic devices composed by 100-µm-deep channels were connected to an external fluidic path that allowed flow-through of water-glucose solutions at different concentrations. Measurements were performed with near-infrared low-power sources, namely a tungsten lamp and a Superluminescent Light Emitting Diode (SLED), allowing the read-out in a wavelength region of minimum invasiveness for biological fluids. The selected optical scheme based on an all-fiber Michelson configuration is well suited for non-contact, remote investigations of the fluids flowing in plastic microfluidic devices, with arbitrary layout and thickness. For the first time, using the SLED, we exploited the double round trip of light in the fluid channel for doubling the sensitivity with respect to the standard single pass set-up, previously demonstrated.

GaAs-Based Superluminescent Light-Emitting Diodes with 290-nm Emission Bandwidth by Using Hybrid Quantum Well/Quantum Dot Structures.

A high-performance superluminescent light-emitting diode (SLD) based upon a hybrid quantum well (QW)/quantum dot (QD) active element is reported and is assessed with regard to the resolution obtainable in an optical coherence tomography system. We report on the appearance of strong emission from higher order optical transition from the QW in a hybrid QW/QD structure. This additional emission broadening method contributes significantly to obtaining a 3-dB linewidth of 290 nm centered at 1200 nm, with 2.4 mW at room temperature.

Long-Wavelength InAs/GaAs Quantum-Dot Light Emitting Sources Monolithically Grown on Si Substrate

Direct integration of III–V light emitting sources on Si substrates has attracted significant interest for addressing the growing limitations for Si-based electronics and allowing the realization of complex optoelectronics circuits. However, the high density of threading dislocations introduced by large lattice mismatch and incompatible thermal expansion coefficient between III–V materials and Si substrates have fundamentally limited monolithic epitaxy of III–V devices on Si substrates. Here, by using the InAlAs/GaAs strained layer superlattices (SLSs) as dislocation filter layers (DFLs) to reduce the density of threading dislocations. We firstly demonstrate a Si-based 1.3 µm InAs/GaAs quantum dot (QD) laser that lases up to 111 °C, with a low threshold current density of 200 A/cm2 and high output power over 100 mW at room temperature. We then demonstrate the operation of InAs/GaAs QD superluminescent light emitting diodes (SLDs) monolithically grown on Si substrates. The fabricated two-section SLD exhibits a 3 dB linewidth of 114 nm, centered at ～1255 nm with a corresponding output power of 2.6 mW at room temperature. Our work complements hybrid integration using wafer bonding and represents a significant milestone for direct monolithic integration of III–V light emitters on Si substrates.

Long-range surface plasmon amplification with current injection on a one-dimensional photonic crystal surface.

A one-dimensional (1D) semiconductor photonic crystal (PC) structure with a terminal metal nanofilm, supporting propagation of long-range surface plasmons (LRSPs), is considered as an LRSP amplifier with current pumping. Current is injected to an active region through the metal nanofilm from one side and doped semiconductor layers from the other side. The propagation length of LRSP waves in such 1D PC structures reaches several millimeters, and therefore, a gain as low as 10 cm(-1) is enough to compensate for attenuation and amplify LRSPs. A unique advantage of this structure is that the refractive index of LRSP wave is very close to unity. As a result, no return reflection to semiconductor occurs during the edge-emission of LRSP to air, and this enhances the light extraction efficiency from semiconductor light sources such as edge-emitting superluminescent diodes and light-emitting diodes (LEDs). Optical feedback may be incorporated in this LRSP amplifier by grating deposition on the external side of the metal nanofilm, and LRSP lasing (i.e., long-range SPASER) may be realized without the use of complicated "etch-and-regrow" processes.

Experimental demonstration of binary shaped pupil mask coronagraphs for telescopes with obscured pupils

Abstract We present the fabrication and experimental demonstration of three free-standing binary shaped pupil mask coronagraphs, which are applicable for telescopes with partially obscured pupils. Three masks, designed to be complementary (labeled Mask-A, Mask-B, and Mask-C), were formed in 5 μm thick nickel. The design of Mask-A is based on a one-dimensional barcode mask. The design principle of Mask-B is similar, but has a smaller inner working angle and a lower contrast than Mask-A. Mask-C is based on a concentric ring mask and provides the widest dark region and a symmetric point spread function. Mask-A and Mask-C were both designed to produce a flexibly tailored dark region (i.e., non-uniform contrast). The contrast was evaluated using a light source comprising a broadband super-luminescent light-emitting diode with a center wavelength of 650 nm, and the measurements were carried out in a large vacuum chamber. Active wavefront control was not applied in this work. The coronagraphic images obtained by experiment were mostly consistent with the designs. The contrast of Mask-A within the ranges 3.3–8 λ/D and 8–12 λ/D was ∼ 10−4–10−7 and ∼ 10−7, respectively, where λ is the wavelength and D is the pupil diameter. The contrast of Mask-B was ∼ 10−4 and that of Mask-C over an extended field of view (5–25 λ/D) was ∼ 10−5–10−6. The effect of tilting the masks was investigated, and found to be irrelevant at the ∼ 10−7 contrast level. Therefore the masks can be tilted to avoid ghosting. These high-contrast free-standing masks have the potential to enable coronagraphic imaging over a wide wavelength range using both ground-based and space-borne general-purpose telescopes with pupil structures not specifically designed for coronagraphy.

光纤陀螺用超辐射发光二极管启动模型研究

In order to realize the quick start-up of fiber optic gyroscope,the start-up model of the superluminescent light emitting diodes( SLD) was established by analyzing the change principle of drive current and temperature in SLD after power on,and the factors affecting the start-up time of SLD were got. By using high-speed data acquisition card,the start-up time of SLD was measured to be 3- 4 s at room temperature,the power fluctuation error was 4. 5%,and the wavelength drift was0. 92 nm caused by the temperature control system. The experiment results were consistent with the theoretical model established. The methods to reduce the start-up time of SLD and realize the quick start-up of fiber optic gyroscope were proposed in theoretically.

Heterogeneously integrated III-V-on-silicon multibandgap superluminescent light-emitting diode with 290 nm optical bandwidth.

A broadband superluminescent III-V-on-silicon light-emitting diode (LED) was realized. To achieve the large bandwidth, quantum well intermixing and multiple die bonding of InP on a silicon photonic waveguide circuit were combined for the first time, to the best of our knowledge. The device consists of four sections with different bandgaps, centered around 1300, 1380, 1460, and 1540 nm. The fabricated LEDs were connected on-chip in a serial way, where the light generated in the smaller bandgap sections travels through the larger bandgap sections. By balancing the pump current in the four LEDs, we achieved 292 nm of 3 dB bandwidth and an on-chip power of -8 dBm.