Gallium nitride light sources for optical coherence tomography

Abstract

The advent of optical coherence tomography (OCT) has permitted high-resolution, non-invasive, in vivo imaging of the eye, skin and other biological tissue. The axial resolution is limited by source bandwidth and central wavelength. With the growing demand for short wavelength imaging, super-continuum sources and non-linear fibre-based light sources have been demonstrated in tissue imaging applications exploiting the near-UV and visible spectrum. Whilst the potential has been identified of using gallium nitride devices due to relative maturity of laser technology, there have been limited reports on using such low cost, robust devices in imaging systems.A GaN super-luminescent light emitting diode (SLED) was first reported in 2009, using tilted facets to suppress lasing, with the focus since on high power, low speckle and relatively low bandwidth applications. In this paper we discuss a method of producing a GaN based broadband source, including a passive absorber to suppress lasing. The merits of this passive absorber are then discussed with regards to broad-bandwidth applications, rather than power applications. For the first time in GaN devices, the performance of the light sources developed are assessed though the point spread function (PSF) (which describes an imaging systems response to a point source), calculated from the emission spectra. We show a sub-7µm resolution is possible without the use of special epitaxial techniques, ultimately outlining the suitability of these short wavelength, broadband, GaN devices for use in OCT applications.

Group-III-nitride and halide-perovskite semiconductor gain media for amplified spontaneous emission and lasing applications

“…In a different role, the integrated absorber section can be used to suppress lasing. This leads to the production of a superluminescent diode that operates in the ASE regime [204,234,[248][249][250][251]. In section 2.3, the InGaN-based superluminescent diode is discussed separately, and a review article is recommended for further reading.…”

A tutorial on laser-based lighting and visible light communications: device and technology [Invited]

“…Following these demonstrations, many studies on device optimization and system-level demonstrations have also been published. For instance, the design of waveguide structure [101,102], SLD on semipolar/non-polar substrates [47], SLD in solid-state lighting [97], optical coherence tomography [49,103], and optical communications [46] were demonstrated. Here, we summarize and discuss the key developments in SLD in both device-and system-level improvement, in particular, the practicality and feasibility in VLC.…”

The Atomic Rearrangement of GaN-Based Multiple Quantum Wells in H2/NH3 Mixed Gas for Improving Structural and Optical Properties

“…In recent years, InGaN/GaN multiple quantum wells (MQWs) have been extensively investigated due to its excellent application potentials in highly efficient optoelectronic devices operating in the whole visible spectral regions [1][2][3][4][5]. However, it is still challenging to grow high-quality MQW with higher indium composition for pure blue and green light emitting diodes (LEDs) and lasers diodes (LDs) via metal organic chemical vapor deposition (MOCVD).…”