Driving Innovation with Cutting-Edge Photonic Solutions

What is a transceiver?

Transceivers convert digital electrical signals generated by conventional electronic devices into light waves that can be transmitted over optical fibers with higher data density, lower loss and lower cost than copper wire.  In the reverse direction, the light waves are detected and converted back to digital electrical signals that can be transmitted using copper or another transmission medium.

Video-on-demand is the largest driver of mega data centers that are being built at an astonishing rate.  Such data centers are often referred to as the “cloud.” There are hundreds of thousands of transceivers in a hyper-scale data center, connecting acres of racks holding thousands of online memory storage devices and servers to switches and then to distant points for distribution to users. The cost of building a data center (including the transceivers) is very large, and any technology that promises to reduce cost has proven to catch the attention of the data center operators.  POET’s Optical Engines reduce the cost of transceivers. Under a different configuration, POET’s Optical Interposer also promises to allow a different architecture of the data center itself, by co-packaging network switching devices directly with optics, further reducing costs for data center operators.

What is an Optical Engine?

An Optical Engine (OE) includes only those parts of the transceiver module that convert the digital electrical signals into light signals, something that can only be done using certain types of compound semiconductor materials (e.g., Indium Phosphide, Gallium Arsenide). These materials are fabricated into so-called “active” devices (e.g., lasers, detectors, etc.). In addition, the OE includes waveguides that couple the light from the active devices and move it through “passive” devices (e.g., multiplexers and de-multiplexers, spot size converters) and eventually into the fiber. The reverse process of converting light signals back into electronic signals is also included in an OE.  The Optical Engine is not a complete transceiver, but it is the highest value part of the transceiver module, typically representing over 50% of the cost.

The POET Optical Engine consists of the POET Optical Interposer, lasers, photo detectors, laser monitoring diodes, waveguides, and filters integrated within the waveguides for multiplexing and de-multiplexing signals.  The green portion shows an electronic device, such as Trans-Impedance Amplifiers (TIAs) and Laser Drivers that are optional devices integrated on the Optical Engine. POET’s optical engines are available with and without these electronic devices to offer maximum implementation flexibility to transceiver makers. The TIA, laser driver and other electronic devices are mounted directly onto the Optical Interposer platform, utilizing the high-speed metal interconnects in the lower layers of the Optical Interposer platform for communication. The current design of the Optical Interposer includes both Copper (Cu) and Aluminum (Al) layers below the waveguide layer, providing excellent thermal conductivity.

How does the cost of building a POET Optical Interposer compare to more conventional approaches?

The costliest steps in the assembly of an optical engine are the placement of lasers, lenses, detectors, filters and fibers on the device.  Each time such a component is positioned, the optical alignment must be tested to ensure optimal transmission of light.  This can only be done one single placement and alignment at a time. Each time it is done and fails, production yield falls. There are several “yield points” associated with conventional approaches to transceiver design.

Conventional Approach Cost Drivers:

• Most companies utilize this conventional approach to transceiver design
• Active alignments of laser to waveguide is required
• Other incidental materials like carriers, base plates and, lenses, etc. are used
• Expensive CAPEX investment is needed to scale production
• And there are many yield points to manage that can lower yield and increase cost

In contrast to Conventional approaches, the POET approach:

• Eliminates active alignment of the laser to waveguide (huge savings)
• Minimizes expensive alignment equipment for scaling production
• Reduces number of yield points
• Utilizes a known-good OE die to increase final yield and lower cost

Wafer-level bonding and testing, passive alignment with embedded mux/de-mux, use of known good die - all reduce BOM cost, yield points, assembly and testing costs as well as required CAPEX investment.

Combined, all the features noted above and those shown below, enable the passive “pick-and-place” assembly of the POET Optical Interposer, eliminating the need for active optical alignment required by conventional approaches.

To retain its elegant design and to enable placement of devices without the costly procedure of active alignment with each device placement, lasers and other active devices are designed to be “flip-chipped” onto the surface of the POET Optical Interposer.  All passive components (mux – de-mux filters, gratings, spot-size converters, etc.) are built into the POET Optical Interposer waveguide layer. Any active device, including lasers, modulators, detectors, etc., can be coupled into the waveguide. Because loss from the waveguides is low across a wide energy spectrum, including visible and non-visible light, the POET Optical Interposer can be used to enable a wide variety of applications, providing a truly versatile platform technology.

An Optical Interposer-based Optical Engine for a 100G transceiver

From fabrication of an 8” POET Optical Interposer wafer, to the placement of active devices and fiber blocks onto the wafer using pick and place tools, to the testing of each Optical Engine, to the capping, sealing and singulation of the devices, the entire process is done at wafer scale, providing an across the board reduction in cost.

The power of wafer-scale fabrication, test and assembly – drives down cost with unlimited scalability.

A POET Optical Engine for a 400G transceiver – over 500 devices processed at the same time on a standard 8”silicon wafer.