Lumenge, I chuckled to myself when I  read that Richard Jones of Intel  was  presenting.

Richard Jones, Intel Corporation, USA
Overview and Future Challenges on III-V Laser Integration Technologies in Silicon Photonics Platform

In October at OIF Richard Jones presented a picture of Intel’s attempts  to provide a light source for Co-Packaged Optics which fell way short of industry needs tocouple light efficiently. Intel coupling loss is 4  times higher than the POET light bar solution.

Recall his presentation at OIF and my  comments as follows:

October 14, 2020 OIF Webinar - "Co-Packaged Optics - Why, What and How”

https://www.oiforum.com/meetings-events/oif-webinar-co-packaged-optics-why-what-and-how/

Representing Intel is Richard Jones, Senior Principal Engineer. He leads the laser development team at Intel’s Silicon Photonics Product Division.

https://on24static.akamaized.net/event/26/71/51/1/rt/1/documents/resourceList1602546460149/richardjones1602546458264.pdf

One of the key attributes that you need to connect your laser to silicon photonics die is to look at coupling loss. This is one of the challenges around the remote lasers. For integrated lasers at Intel we measure about .5dB coupling loss between the laser and the silicon photonic waveguide. For remote lasers we are estimating coupling loss to an optical fiber to be about 2dB with a similar coupling loss between the fiber and the silicon photonic chip.  You can tweak these numbers if you can improve the coupling there but you are about 4dB coupling loss for remote lasers which needs to be accounted for and minimized where possible.

So why would you actually do this? It has been mentioned before but thermal environment. So switches are getting hotter as the bandwidth increases independent of your choice of optics whether it is pluggable or co-packaged. The addition of Co-Packaged Optics drives different thermal decisions particularly around the thermal cross talk between the electrical and photonic chips.

Our internal assessment at Intel is that both fan cooled and liquid cooled are possible for next generation switches and that is applicable to ether CPO with integrated lasers or remote lasers.

The performance of lasers varies over temperature.

The lower temperature of the remote laser (Slide 7). The graph on the right shows measured laser bias required to emit different output power for different temperatures.  The grey bar shows estimated temperatures for remote and integrated lasers. So as you can see remote lasers can work at lower temperatures but the lower temperature does not compensate for the additional 4dB of loss as demonstrated by the circles on the graph.

Operating the lasers at lower temperature does not compensate for the additional 4dB of loss as demonstrated by the circles on the graph. So it is really key for remote lasers to reduce that coupling loss. Although operating the lasers at lower temperature does allow them to emit higher output powers.

For integrated lasers the real question is how hot the environment they are working under is. Pushing the laser at temperatures above 100’C will be challenging.

So looking at some of the laser reliability here I am assuming that the mature manufacturing process has been used weeding out premature failure with burn-in. So the focus will be on the random failures that occur during the operating life known as failure in time or FIT rate.

Refer to slide 8 and particularly to slide 9.

Remote laser

Field serviceability allows relaxation of acceptable failure rate.

Integrated laser

If the laser fails then the entire switch package needs to be replaced unless redundancy has been added.

Now let’s look at a recent news release by POET Technologies. As noted in the Intel presentation coupling loss of the remote laser is estimated at 4dB. POET’s coupling loss of their remote  laser solution is identified at less than 1dB.

POET Launches LightBar™ Solution for Data Centers

December 8th, 2020

Advanced Remote Laser Light Source for Transceivers and Data Center Switches

Management to Host “Beyond the Press Release” Interview to Discuss the LightBar Product

TORONTO, Ontario, December 8, 2020 – POET Technologies Inc. (“POET” or the “Company”) (TSX Venture: PTK; OTCQX: POETF) the designer and developer of the POET Optical Interposer™ and Photonic Integrated Circuits (PICs) for the data center and tele-communication markets, announced today that it has completed and tested its designs for a line of high-performance remote laser light source products for 400G FR4, 800G and Co-Packaged Optics (CPO) applications in Cloud Data Centers, named LightBar™.

For makers of conventional and Silicon Photonics-based optical transceivers, the LightBar product line offers a fully aligned, tested, and multiplexed laser light source attached to an output fiber, eliminating the difficult and costly step of four laser alignments in optical transceivers. For makers of next generation network switches that require the combination of switch components and optical components in a single package, commonly referred to as “Co-Packaged Optics” (CPO), using LightBar products will reduce heat generation within the package, which is a common cause of component failure.  When used as a remote laser source, POET’s LightBar is expected to improve overall system reliability for both transceiver and CPO applications by offering the ability to replace failed laser assemblies in the field, without disturbing other components and sub-assemblies.  Laser failures have proven to be the cause of a large majority of sub-assembly failures in both optical transceivers and co-packaged optics applications.

LightBar products are configured as a Transmit Optical Sub-Assembly (TOSA) incorporating four Continuous Wave (CW) lasers into the waveguide matrix of POET’s proprietary Optical Interposer, meeting the CWDM4 and FR4 technical specifications.  The 400G version is upgradeable to 800G with the incorporation of additional components. The LightBar is completely customizable and can support a wide range of output power from 15mW to 60mW depending on the application. In all cases, LightBar incorporates POET’s proprietary designs and assembly features that deliver an industry-leading laser coupling efficiency of >80% (power loss = <1.0dB), while maintaining wafer-scale integration capability.  These results are significantly better than the best results observed with competing integrated approaches. Better coupling efficiency allows the use of lower power, more reliable lasers to achieve the same output. POET will begin sampling the LightBar product line to customers beginning in Q1 2021.  Following qualification with customers, the Company expects to begin volume production in Q4 of 2021.

According to LightCounting, the market for 400G optical transceivers in all formats will grow to over $3 billion by 2025 from an estimated $0.5 billion in 2021. The market for optical connectivity, also known as chiplets in co-packaged optics, is forecast to be more than $4 billion in 2028.