Exalos of Schlieren, Switzerland that makes quantum-well based light emitters the company calls Superluminescent LEDs (SLEDs), reported that the company has successfully created what the company is terming its first cyan-green SLED with an output wavelength of 495 nm. In the color spectrum the wavelength is of cyan is actually halfway between blue and green, and the company’s Cyan/Green SLED is really just a cyan color.
According to the company the new SLED that they are calling Cyan-Green (which is really just Cyan) represents an important step
toward a complete red-green-blue (RGB) SLED illumination source for micro-displays for augmented reality applications,
head-up display architectures, etc.
The company notes that SLEDs are broadband semiconductor devices that are closely related to their more commonly known relatives, laser diodes (LDs) and light-emitting diodes (LEDs). They employ quantum wells to achieve light emission.
Cyan/Green, a Step Towards Green
After the company’s successful demonstration of blue SLEDs, Exalos began a comprehensive program last year to develop green devices. The effort employed a number of the advances that had successfully yielded 450 nm GaN-based SLEDs and required increasing the indium concentration in the quantum well (QW) structures to achieve the longer wavelengths. After just six months, the company says it has attained a major milestone with the demonstration of the company’s first cyan-green (actually just Cyan) device at an optical output power of > 5 mW.
According to Exalos, the advance resulted from a combination of extensive modeling and simulation, iterative epitaxial designs, and improvements in the modal gain of the semiconductor structure. Exalos is now working to increase the power, enhance the wall plug efficiency, and extend the output to wavelengths beyond 500 nm (more into the green range of the spectrum).
The company points to the excitement about the potential of augmented and virtual reality (AR/VR) applications. Exalos says that this excitement has garnered significant interest into compact, high luminance displays for near-to-eye and pico-projector systems that offer a wide color gamut and operate with high overall efficiency.
The company contends that while laser diodes and LEDs have been the chosen illumination sources for such AR and VR displays, their deficiencies have been well documented. For example, Exalos asserts that that laser diodes feature a narrowband output which can comprise image quality with unwanted speckle and coherent artifacts.
Broader Spectrum Bandwidth of SLEDs can Reduce Spectral Noise
Exalos claims, that LEDs, on the other hand, operate as broad area emitters which result in low efficiency when they are coupled with waveguide architectures. SLEDs (the company’s quantum well-based light emitters), however, operate as directional light sources. And the company claims that SLEDs enable efficient coupling to micro-optical elements with a broader spectral bandwidth that results in greatly reduced speckle noise and improved image quality when utilized as illumination sources for holographic and MEMS-based scanning micro-displays.
In addition, Exalos says that its visible SLEDs can also offer benefits in applications including broad area illumination, sensing, spectroscopy, microscopy, or machine vision.
