News

Improving the efficiency of lasers

Single-mode semiconductor laser delivers power with scalability

08.08.2022 - New approach to increase both size and power of a single-mode laser.

Berkeley engineers have created a new type of semi­conductor laser that accomplishes an elusive goal in the field of optics: the ability to maintain a single mode of emitted light while main­taining the ability to scale up in size and power. It is an achievement that means size does not have to come at the expense of coherence, enabling lasers to be more powerful and to cover longer distances for many appli­cations.

A research team led by Boubacar Kanté, showed that a semi­conductor membrane perforated with evenly spaced and same-sized holes functioned as a perfect scalable laser cavity. They demons­trated that the laser emits a consistent, single wavelength, regardless of the size of the cavity. “Increasing both size and power of a single-mode laser has been a challenge in optics since the first laser was built in 1960,” said Kanté. “Six decades later, we show that it is possible to achieve both these qualities in a laser. I consider this the most important paper my group has published to date.”

Despite the vast array of appli­cations ushered in by the invention of the laser – from surgical tools to barcode scanners to precision etching – there has been a persistent limit that researchers in optics have had to contend with. The coherent, single-wavelength direc­tional light that is a defining charac­teristic of a laser starts to break down as the size of the laser cavity increases. The standard workaround is to use external mechanisms, such as a waveguide, to amplify the beam.

“Using another medium to amplify laser light takes up a lot of space,” said Kanté. “By eliminating the need for external ampli­fication, we can shrink the size and increase the effi­ciency of computer chips and other components that rely upon lasers.” The study’s results are parti­cularly relevant to vertical-cavity surface-emitting lasers, or VCSELs, in which laser light is emitted vertically out of the chip. Such lasers are used in a wide range of appli­cations, including fiber optic communi­cations, computer mice, laser printers and biometric identi­fication systems.

VCSELs are typically tiny, measuring a few microns wide. The current strategy used to boost their power is to cluster hundreds of indi­vidual VCSELs together. Because the lasers are independent, their phase and wavelength differ, so their power does not combine coherently. “This can be tolerated for appli­cations like facial recognition, but it’s not acceptable when precision is critical, like in communi­cations or for surgery,” said Ph.D. student Rushin Contractor.

Kanté compares the extra effi­ciency and power enabled by BerkSEL’s single-mode lasing to a crowd of people getting a stalled bus to move. Multi-mode lasing is akin to people pushing in different directions, he said. It would not only be less effective, but it could also be counter­productive if people are pushing in opposite directions. Single-mode lasing in BerkSELs is comparable to each person in the crowd pushing the bus in the same direction. This is far more efficient than what is done in existing lasers where only part of the crowd contributes to pushing the bus.

The study found that the BerkSEL design enabled the single-mode light emission because of the physics of the light passing through the holes in the membrane, a 200-nanometer-thick layer of indium gallium arsenide phosphide, a semi­conductor commonly used in fiber optics and telecommuni­cations technology. The holes, which were etched using litho­graphy, had to be a fixed size, shape and distance apart.

The researchers explained that the periodic holes in the membrane became Dirac points, a topological feature of two-dimen­sional materials based on the linear dispersion of energy. They are named after English physicist and Nobel laureate Paul Dirac, known for his early contri­butions to quantum mechanics and quantum electro­dynamics.

The researchers point out that the phase of light that propagates from one point to the other is equal to the refractive index multiplied by the distance traveled. Because the refractive index is zero at the Dirac point, light emitted from different parts of the semi­conductor are exactly in phase and thus optically the same. “The membrane in our study had about 3000 holes, but theo­retically, it could have been 1 million or 1 billon holes, and the result would have been the same,” said postdoc Walid Redjem.

The researchers used a high-energy pulsed laser to opti­cally pump and provide energy to the BerkSEL devices. They measured the emission from each aperture using a confocal microscope optimized for near-infrared spectro­scopy. The semi­conductor material and the dimensions of the structure used in this study were selected to enable lasing at telecommuni­cations wavelength. The researchers noted that BerkSELs can emit different target wavelengths by adapting the design speci­fications, such as hole size and semi­conductor material. (Source: UC Berkeley)

Reference: R. Contractor et al.: Scalable single-mode surface emitting laser via open-Dirac singularities, Nature, online 29 June 2022; DOI: 10.1038/s41586-022-05021-4

Link: Kanté Lab, Dept. of Electrical Engineering and Computer Sciences, University of California, Berkeley, USA

 

Welding with Civan's Ultrafast CBC-Laser: Basics, Opportunities and Challenges

The first part of the webinar will provide an overview of the fundamentals and challenges of the welding process and the features of the CIVAN CBC laser. The second part of the webinar will discuss approaches to take advantage of fast, arbitrary beam shaping to control process problems.

Register now

Digital tools or software can ease your life as a photonics professional by either helping you with your system design or during the manufacturing process or when purchasing components. Check out our compilation:

Proceed to our dossier

Welding with Civan's Ultrafast CBC-Laser: Basics, Opportunities and Challenges

The first part of the webinar will provide an overview of the fundamentals and challenges of the welding process and the features of the CIVAN CBC laser. The second part of the webinar will discuss approaches to take advantage of fast, arbitrary beam shaping to control process problems.

Register now

Digital tools or software can ease your life as a photonics professional by either helping you with your system design or during the manufacturing process or when purchasing components. Check out our compilation:

Proceed to our dossier