Comb spectrum laser to drive WDM revolution

The InnoComb is the world's first diode laser to emit tens to hundreds of pure, low-noise colours (comb spectrum) from a single laser cavity.

Innolume is set to begin sampling its ground-breaking semiconductor laser, the InnoComb.

It is the world's first diode laser to emit tens to hundreds of pure, low-noise colours (comb spectrum) from a single laser cavity.

This new class of lasers will facilitate a wavelength-division multiplexing (WDM) revolution in short-reach high-bandwidth optical interconnects.

WDM was previously restricted to telecomms due to the costly laser arrays required.

Today, powered by a single InnoComb, WDM can finally be harnessed for low-cost, short-reach computer interconnects.

Following last year's demonstration of the first broad-spectrum Fabry-Perot (FP) laser, Innolume dramatically reduced relative intensity noise (RIN) of each spectral line, culminating in the diode comb laser as a practical computer communications source.

"This laser innovation offers increased integration and functionality at reduced sise and cost, ie using cavity resonance with QD gain behaviour to replace laser farms or integrated laser arrays", says Innolume's President and CEO, Jurgen Kurb.

He adds: "Space- and cost-efficient WDM systems are enabled for the first time, offering new datacom opportunities with respect to cost, power and reliability".

"Additionally, the comb laser simplifies system design by virtue of all channels moving in unison with shifting temperature".

InnoComb is a single FP laser emitting many lines/wavelengths/channels (longitudinal cavity modes) with nearly the same power on each.

Innolume has demonstrated 10mW of power per channel over 16 channels, and better than 1mW/channel over 100 channels.

Channel spacing is currently available from below 50 to 140GHz (less than 0.28 to 0.8nm) centred at any wavelength between 1250 and 1320nm.

For datacomms, the comb laser's channels are separated (demultiplexed), modulated externally at 10Gbit/s minimum, and multiplexed for single-fibre transmission.

External modulation on 16 comb channels was demonstrated by HHI, Berlin with error-free transmission (BER below 10e-13) due to exceptionally low RIN (0.1%) on each lasing line.

"The diode laser as a multiple-wavelength source in high speed communication systems has been something of a 'holy grail', but noisy longitudinal lasing modes in quantum well FP lasers made them a 'no-go'", says Dr Norbert Grote, Head of the Laser Group at Fraunhofer Heinrich-Hertz-Institut, Berlin.

"In contrast, the comb lasers we tested from Innolume show eye diagrams for each line comparable to the best single-frequency ECL lasers, thus opening great opportunities for efficient 1300nm WDM communication systems based on a single laser".

According to Prof Zhores Alferov, Ioffe Institute, St.Petersburg (2000 Nobel Laureate for the double heterostructure - the basis for diode lasers): "Ioffe graduates at Innolume have invented a new class of semiconductor lasers based on fundamental behaviours of quantum dots".

"With their enablement of comb laser diodes, quantum dots have found their key differentiator from conventional quantum wells, with huge potential for practical implementations".

"Integration has been a major driving force for the electronic industry, and now Quantum Dot technology puts us on the same road, making it possible to embody hundreds of CW lasers inside a single diode laser cavity".

"However great a technology is, it always comes down to cost", comments Innolume Senior Optical Engineer, Dongliang Yin.

"Our single InnoComb device relies on conventional FP edge emitter fabrication processes, providing a highly leveraged alternative to proposed arrays of 16, 32, or even 100 DFB lasers".

"Integrated DFBs can cost 10x more per laser than a single FP comb".

"The tradeoff is our need for an additional demultiplexer, an integrated AWG, instead of multiple lasers".

"Therefore, QD comb lasers provide an attractive light source for commodity applications including ubiquitous WDM for short-to-medium".

"In the long run it also brings the right economics to future chip-to-chip optical communication".

"As silicon photonics technology matures to the point of economically managing light between processor chips, a single comb laser 'power supply', either off-chip or bonded to the silicon, will drive the many optical channels necessary for terabyte-per-second interconnects".

In summary, conventional quantum well diode lasers with or without mode-locking remain too noisy to be practical comb lasers for high speed communication.

Innolume's quantum dot materials and laser designs overcome this deficiency for the first time, permitting novel and timely applications.

Now the industry can migrate the bandwidth advantages of WDM from expensive telecomms systems to very low-cost, short reach transceivers, alleviating cost, power, weight and volume issues with server and backplane interconnects.

Ultimately, the comb laser can drive high speed WDM interconnects in a photonics switching layer "under" future multicore computer processors.

According to architectural analyses by top-tier computer companies and academics, this offers a 100x power advantage over projected electronics performance.

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