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Researchers demonstrate organic laser diodes

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The high electrical current required to achieve the lasing process has made it difficult to create organic laser diodes up until now

Researchers from Japan have demonstrated that a laser diode based on organic semiconductors is possible, paving the way for the further expansion of lasers in applications such as biosensing, displays, healthcare, and optical communication.

An organic laser diode emitting blue laser light. Credit: Atula Sandanayaka

Long considered a ‘holy grail’ in the area of light-emitting devices, organic laser diodes use carbon-based organic materials to emit light instead of the inorganic semiconductors, such as gallium arsenide and gallium nitride, used in traditional devices.

The lasers are in many ways similar to organic light-emitting diodes (OLEDs), in which a thin layer of organic molecules emits light when electricity is applied. OLEDs have become a popular choice for smartphone displays because of their high efficiency and vibrant colours, which can easily be changed by designing new organic molecules.

OLEDs produce a much purer light, the researchers say, but require currents that are magnitudes higher than those used in OLEDs to achieve the lasing process. These extreme conditions caused previous devices to break down well before lasing could be observed.

Further complicating progress, previous claims of electrically generated lasing from organic materials turned out to be false on several occasions, with other phenomena being mistaken for lasing because of insufficient characterisation.

Scientists from the Center for Organic Photonics and Electronics Research (OPERA) at Kyushu University, Japan reported in the journal Applied Physics Express that they have enough data to demonstrate that organic semiconductor laser diodes can be developed.

A critical step in lasing is the injection of a large amount of electrical current into the organic layers to achieve a condition called population inversion. However, the high resistance to electricity of many organic materials makes it difficult to get enough electrical charges in the materials before they heat up and burn out.

In addition, a variety of loss processes inherent to most organic materials and devices operating under high currents lowers efficiency, pushing the required current up even higher.

To overcome these obstacles, the research group led by Professor Chihaya Adachi used a highly efficient organic light-emitting material (BSBCz) with a relatively low resistance to electricity and a low amount of losses – even when injected with large amounts of electricity. But having the right material alone was not enough.

Schematic representation of an organic semiconductor laser diode producing blue laser emission under electrical excitation. Credit: Center for Organic Photonics and Electronics Research, Kyushu University

They also designed a device structure with a grid of insulating material on top of one of the electrodes used to inject electricity into the organic thin films. Such grids – called distributed feedback structures – are known to produce the optical effects required for lasing, but the researchers took it one step further.

‘By optimising these grids, we could not only obtain the desired optical properties but also control the flow of electricity in the devices and minimise the amount of electricity required to observe lasing from the organic thin film,’ said Adachi.

The researchers are so confident in the promise of these new devices that they founded the startup company KOALA Tech – short for Kyushu Organic Laser Technology – in March 2019 to accelerate research and overcome the final obstacles remaining for using the organic laser diodes in commercial applications.

The founding members are now working to improve the performance of their organic laser diodes to bring this most advanced organic light-emitting technology to real-world applications. 

 

Diode lasers enter new markets

The evolution of diode laser price and performance is rapidly opening new markets, according to recent analysis by technology consulting firm IDTechEx.

During the past three decades, the average power of laser diodes increased significantly, while their average price per watt has decreased exponentially. Consequently, laser diodes are displacing some established laser and non-laser technologies, while enabling entirely novel optical technologies. Mature applications of laser diodes are data storage, data communication and the optical pumping of solid-state lasers. In contrast, material processing and optical sensing are examples of rapidly evolving market segments with many emerging applications. 

Dramatic improvements in beam quality have revealed DDLs as important tools for processing metals in addition to plastics and composites. DDLs and HPDDLs are emerging as major global trends in industrial manufacturing. Recent innovations include the development of blue diode lasers for welding and 3D printing copper.

The global market for laser diodes and direct diode lasers will be $14 billion by 2029, where laser diodes account for almost $12 billion and direct diode lasers account for $2 billion.

  • These findings are from a recent report by IDTechEx analyst Dr Nilushi Wijeyasinghe, titled ‘Laser Diodes and Direct Diode Lasers 2019-2029: Technologies, Markets and Forecasts’

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