Review—Review on Optimization and Current Status of (Al,In)GaN Superluminescent Diodes

Abstract

Superluminescent diodes represent a device type which can fill the gap between light emitting diodes (LEDs) and laser diodes. The light generation based on Amplified Spontaneous Emission promotes high brilliance of the light source (better than in case of LEDs), and by this efficient light harnessing e.g. coupling to optical fibers. At the same time the low time coherence of the light reduces the interference effects, unfavorable in applications such as Optical Coherence Tomography or in direct image projection. This article reviews the development process and the current status of nitride superluminescent diodes, from their first introduction in 2009 until present.

Single-Port Superluminescent-Diode Gain-Chip for Tunable Single-Wavelength and Dual-Wavelength Blue-Laser

“…The 12° angle of the front facet is optimized to avoid reflecting light back into the SLD's internal cavity which consequently prevents the lasing action. The modal reflectivity at different facet angles are found to be below 10 -5 with tilting angles greater than 6° in GaNbased devices [15], [16], [28]. This characteristic allows us to use the fabricated SLD without the need of adding an AR coating onto the tilted front facet nor designing a curved waveguide.…”

“…To address this issue, high-precision anti-reflective (AR) coatings have been developed to suppress the formation of the internal diode cavity and improve the control over the EClaser [13], [14]. An alternative to AR coatings is the use of a tilted facet or a tilted waveguide such as those found in superluminescent diodes (SLDs), leading to a modal reflectivity below 10 -5 via a single etching step [15], [16]. Previously, the implementation of tunable lasers based on SLDs in EC configurations focused on the near-infrared and red wavelength regime [17]- [21].…”

“…Nevertheless, combining InGaN-based SLDs with EC configurations has yet to be further explored for tunability and properties achieved herein. Besides, related research on InGaN-based SLDs has continued steadily with particular interests in lighting, displays, and biomedical instrumentation [16], [24]- [26]. These interests have been inspired because the SLD is emitting light in the amplified spontaneous emission (ASE) regime, showing droop-free performance, low temporal coherence, high-power density, and low etendue [16], [24], [26]- [30].…”

“…Besides, related research on InGaN-based SLDs has continued steadily with particular interests in lighting, displays, and biomedical instrumentation [16], [24]- [26]. These interests have been inspired because the SLD is emitting light in the amplified spontaneous emission (ASE) regime, showing droop-free performance, low temporal coherence, high-power density, and low etendue [16], [24], [26]- [30]. These unique optical properties, when implemented in an EC configuration, can offer a reconfigurable single-chip light source capable of emitting both time-incoherent light from the SLD and time-coherent laser light from the EC-SLD, appealing to a wide range of applications, including gas and liquid sensing [31], swept source optical coherence tomography [32], and coherenceconvertible light source [33].…”

3.8-Gbit/s visible light communication (VLC) based on 443-nm superluminescent diode and bit-loading discrete-multiple-tone (DMT) modulation scheme

“…This is because of the SLD's unique combination of high-power, droop-free operation, low etendue, low temporal coherence, among others. One of the important applications of SLDs 18 , is their application to dual illumination and communication 15 , hence, the further improvement and research of SLDs towards VLC and lighting are important for technology and commercial endeavors.…”