Second-order coherence properties of amplified spontaneous emission from a high-power tapered superluminescent diode

TL;DR

This study investigates the second-order coherence properties of a high-power tapered superluminescent diode, revealing how coherence varies with operation mode and providing insights into its potential applications in imaging.

Contribution

First detailed analysis of second-order coherence in a high-power tapered superluminescent diode, combining experimental results with semi-classical theory.

Findings

Coherence approaches thermal levels in free-running mode.

External cavity operation increases coherence, approaching near-laser levels.

High output power with good beam quality achieved while maintaining partial coherence.

Abstract

We study the degree of second-order coherence of the emission of a high-power multi-quantum well superluminescent diode with a lateral tapered amplifier section with and without feedback. When operated in an external cavity, the degree of second-order coherence changed from the almost thermal case of g$^{(2)}$(0)$\approx$1.9 towards the mostly coherent case of g$^{(2)}$(0)$\approx$1.2 when the injection current at the tapered section was increased. We found good agreement with semi-classical laser theory near and below threshold while above laser threshold a slightly higher g$^{(2)}$(0) was observed. As a free running device, the superluminescent diode yielded more than 400 mW of optical output power with good spatial beam quality of $M^2_{slow} < 1.6$. In this case, the DSOC dropped only slightly from 1.9 at low powers to 1.6 at the maximum output power. To our knowledge, this is the first investigation of a high-power tapered superluminescent diode concerning the degree of second-order coherence. Such a device might be useful for real-world applications probing the second order coherence function, such as ghost imaging.