Monday, February 27, 2012

Semiconductor Laser's Golden Anniversary

(Above: First room temp. CW semiconductor nanolaser with subwavelngth cavity presented at CLEO 2011. From K. Ding et al, CTuG2, CLEO 2011.)

The year 2012 marks the impressive 50th anniversary of the invention of the prolific and ubiquitous semiconductor laser. Almost every household in the industrialized world owns at least one, be it in a DVD player (maybe two if it is a Blue-ray), CD player, optical mouse or depend on them indirectly for long-distance phone service, digital cable, or internet access. Besides making telecommunications a practical possibility, semiconductor lasers have paved the way for the development of silicon photonics and will be pivotal in the future of optical information storage and processing. Despite their primary use in mass consumer markets for communications, information processing, mutimedia, and teasing cats (you can even get semiconductor laser pointers with phase masks and lens attachments that project images mice or fish on the floor for your feline to chase), many subfields have profited from the low-cost and small-footprint of these robust laser sources. Take for example the handful of semiconductor sources offered commercially by Thorlabs for optical coherence tomography, or the inexpensive semiconductor laser diode sources used by the Ozcan group for field-portable, ultra-low footprint, holographic microscopes.

There are too many other technologies and subfields to name that have profited as well. All you need to do is think of the numerous optics applications that live at telecom wavelengths near 1300 nm or 1550 nm or DVD player wavelengths, 405 nm and 635 nm. Such lasers offer unbelievable device characteristics at such a low price that researchers and venture capitalists often build their technologies to fit these wavelengths instead of the other way around.

Amnon Yariv and Pochi Yeh write in their 2007 edition of the book Photonics that,

"The semiconductor laser invented in 1961 is the first laser to make the transition from a research topic and specialized applications to the mass consumer market...It is by economic standards and the degree of its applications, the most important of all lasers."

To celebrate the most important laser of lasers, CLEO will be hosting a special symposium with talks from pioneers of semiconductor laser technology. The list of speakers and subjects has been well-crafted to paint not only a historical picture but to address current research and trends on this ever-evolving technology.

From a fundamentals perspective Russel Dupuis from Georgia Tech will be talking about device materials. Nobel Laureate Herbert Kroemer of University of California Santa Barbara will discuss the double heterostructure which is still the basic framework for almost all semiconductor light sources and solar cells and which without there would be no continuous wave (CW) lasing in semiconductor devices at room temperature. To this end, Morton Panish, formerly of Bell Laboratories, will describe the development of the first room temperature semiconductor laser.

(Above: Evolution of threshold current. From Nobel Laureate Z. Alferov, IEEE J. Sel. Top. Quant. Elec. 6, 832, 2000.)

Charles Henry, formerly of Bell Laboratories, will discuss the quantum well structure which was pivotal in reducing active layer thickness and therefore significantly reducing threshold current, see the figure above. Yasuhiko Arakawa from the University of Tokyo will discuss quantum dot lasers which reduced threshold densities even further and remains a developing area of semiconductor laser physics research.

On the more practical side, Jack Jewell, of Green VCSEL will discuss the vertical cavity surface emitting laser (VCSEL) which among other important device attributes may be the best laser for high-yield production. VCSELs are grown, processed, and tested in wafer-form allowing parallel fabrication and testing, minimizing labor and maximizing yield. They also take up less space on a wafer- about three times less than edge emitters of similar power and can be made in 2-D arrays. Jewell will likely discuss the benefits of lower power consumption of VCSELs for use in short-reach, high-speed networks. My understanding is that the "green" in "Green VCSEL" refers to environmental considerations not wavelength.

There will also be talks discussing the semiconductor laser's role in telecommunications, quantum cascade lasers, integrated and hybrid optical circuits, high-power devices, as well progress in nano laser structures with subwavelength volume (see the figure at the top).

Whether to learn the history, fundamental principles, pay homage to the pioneers, or to learn new trends, be sure to mark your calendar for the 50th Anniversary of the Semiconductor Laser symposium to celebrate "the most important of all lasers."

1 comment:

  1. Wonderful blog & good post.Its really helpful for me, awaiting for more new post. Keep Blogging!

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