The amplified spontaneous emission from a superluminescent diode was frequency doubled in a periodically poled lithium niobate waveguide crystal.The temporally incoherent radiation of such a superluminescent diode is characterized by a relatively broad spectral bandwidth and thermallike photon statistics, as the measured degree of second order coherence, g (2) (0)=1.9±0.1, indicates.Despite the non-optimized scenario in the spectral domain, we achieve six orders of magnitude higher conversion efficiency than previously reported with truly incoherent light.This is possible by using single spatial mode radiation and quasi phase matched material with a waveguide architecture.This work is a principle step towards efficient frequency conversion of temporally incoherent radiation in one spatial mode to access wavelengths where no radiation from superluminescent diodes is available, especially with tailored quasi phase matched crystals.The frequency doubled light might find use in applications and quantum optics experiments.

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)≈1.9towards the mostly coherent case of g (2) (0)≈1.2when 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.

Amplified spontaneous emission from superluminescent diodes shows thermal like photon statistics, which has potential applications in precision metrology. We investigate the influence of operating parameters on the degree of second order coherence of the emission.

We report on utilizing the photon bunching effect in thermal light to enhance the efficiency of Two-Photon Excited Fluorescence (TPEF) under continuous wave illumination. This has potential applications in microscopy.