POET Technologies demos optical engines, CPO LightBar based on proprietary optical interposer

Toronto-based POET Technologies used the virtual OFC 2021 conference and expo last week to demonstrate a pair of products based on the POET Optical Interposer, the company’s CMOS-based hybrid integration platform. The products, 100G and 200G CWDM4 optical engines and the O-Band LightBar applicable to co-packaged optics (CPO) applications, will reach the sampling stage in the next few months.

According to Chairman and CEO Suresh Venkatesan and President and General Manager Vivek Rajgarhia, the design of the POET Optical Interposer enables straightforward integration of photonic elements such as waveguides, filters, and gratings, as well as passive alignment of lasers for flip-chip bonding (see "POET Technologies optical interposer platform for electronic and optical component co-packaging in single MCM unveiled"). The interposer also features integrated spot-size converters designed to minimize coupling losses and increase laser power efficiency. The approach obviates the need for elements such as lenses, thereby decreasing package size and simplifying manufacture, say the executives.

For example, the 100G and 200G CWDM4 Optical Engines (which will come in transmit-only, receive-only, and transmit and receive versions) integrate an athermal multiplexer and demultiplexer, 28G detectors, monitor photodiodes, and bonding pads, with 28G DMLs of the company’s own design flip-chip attached. The transmit and receive single multi-chip engine will measure less than 60 mm square. Venkatesan and Rajgarhia emphasized the low-loss characteristics of the optical engines, saying the 100G CWDM4 transmit engines suffer only about 5 dB. In a demonstration conducted by Dan Meerovich, POET’s vice president – product engineering, the 100G transmit engine showed an eye margin of approximately 45%. Venkatesan stated later in response to a Lightwave query that the transmit engine offers 25% power coupling efficiency including multiplexer, whereas conventional TOSAs offer 25% efficiency before a multiplexer would be introduced to the transmission chain.

The optical engines are designed to support a transmission range of 500 m to 10 km under ambient operating temperatures of 0°C to 70°C. The POET executives said they expect to begin sampling the optical engines next month beginning with the transmitter/receiver combo device at 100G. The PAM4-based 200G optical engines should begin sampling two months later. Meanwhile, the company also has 400G DR4 and FR4 transmit and receive optical engines in the pipeline, with the receive engine scheduled for sampling in September and the transmit engine, which will feature high-power CW lasers and silicon photonic modulators, slated to follow in the fourth quarter of this year.

The initial version of the LightBar, meanwhile, features four CW DFB lasers flip-chip attached and passively aligned to the POET Optical Interposer; the company says the design will support up to 12 such lasers. Each lane will provide up to 17 dBm of optical output power, equivalent to 50mW per channel, over an operating temperature range of 0°C to 70°C. The four-laser version being demonstrated 4-dB loss. The LightBar’s channel spacing and output pitch can be customized, as can the multiplexing options. Venkatesan and Rajgarhia add that modulators could be added to the LightBar as well to create the 400G FR4 and DR4 optical engines; the company is talking to at least one customer about the possibility.

Samples of the device are expected to be shipped this September. Venkatesan and Rajgarhia say the LightBar could find application as an external laser source for co-packaged optics applications or, perhaps, as an engine in 400G FR4 applications with the aforementioned addition of modulators. They also foresee adding capabilities that could help the LightBar address requirements at 800G and above economically, including the integration of optical grating “slits” that could enable a single light source to generate eight wavelengths.

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