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How to Increase Bandwidth Density in Photonics

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How to Increase Bandwidth Density in Photonics

In the past, optical transceivers were too bulky, too expensive, and not efficient enough, so they could only be used for long-haul telecom networks or data centers with massive bandwidth requirements. Electronic and photonic integration broke this paradigm, miniaturizing optical transceivers to the size of a large USB stick and reducing their cost. Through these advances, optical component manufacturers could pack exponentially more bandwidth into a smaller transceiver area within the last decade. Thanks to this exponential progress, component manufacturers managed to keep up with the exponentially-growing worldwide demand for data.

Figure 1: Exponential growth of bandwidth density over time through the evolution of types of transceiver module standards.

However, the next wave of innovative network services—autonomous vehicles, the Internet of Things, Industry 4.0—demands even more bandwidth and other requirements. Optical links that connect 5G controller units to the rest of the network must upscale from 10G to 100G. The links from metro networks to datacenters must upscale from 100G to 400G or 800G, and the links within datacenters must operate at Terabit speeds. These services require not only more bandwidth but also lower latencies and more reliability. Further electronic integration cannot keep up by itself; photonic integration must also continue pushing the envelope on bandwidth density.

In our previous articles and videos, we have already discussed one way to increase the bandwidth density through coherent transmission. Coherent technology can pack more bits into a laser signal because it encodes data in the laser light’s amplitude, phase, and polarization. The use of digital signal processing in these devices improves the reach and bandwidth of the signal even further. Coherent transmission allows network operators to reach higher bandwidths without upgrading their existing optical fiber infrastructure. Conserving and reusing existing fiber infrastructure is also a sustainability measure because it avoids spending additional energy and resources on manufacturing more fiber and laying it down on the roads.

However, another way to improve the bandwidth density is by moving to full photonic integration. Let’s use an analogy from electronics to explain what this means.

Figure 2: Example of integrating a laser to other photonic components through different integration approaches.

Before 2020, Apple made its computer processors with discrete components. In other words, electronic components were manufactured on separate chips, and then these chips were assembled into a single package. However, the interconnections between the different chips produced losses and incompatibilities that made the device less efficient. After 2020, starting with Apple’s M1 processor, they now fully integrate all components on a single chip, making the device more energy efficient and reducing its footprint.

Full photonic integration achieves something similar to Apple’s approach, but with optical components instead of electronic components. By integrating all optical elements required for optical transmission (lasers, detectors, modulators, etc.) into a single System-on-Chip (SoC), we can minimize the losses and reduce the chip’s footprint, transmitting more bits over the same chip area. Furthermore, as we discussed in a previous article, a fully integrated system-on-chip reduces materials wastage while at the same time ensuring increased energy efficiency of the manufacturing, packaging, and testing process.

Coherent transmission and full photonic integration approaches must synergize to achieve the highest possible bandwidth density. For example, EFFECT Photonics taped out a fully-integrated coherent optical System-on-Chip (SoC) last year. This device can push hundreds of Gigabits per second within a chip that fits inside your fingertip, and we want to turn this breakthrough into a world-class coherent product. We believe it is the next step in packing exponentially more data into optical chips, allowing the world to keep up with the exponential increase in data for years to come.

In the coming weeks, we will discuss more photonic integration and how to implement it in larger volumes to make coherent transmission more widespread around the world.

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