Silicon on Insulator

Overview

Silicon Photonics (SiP) is the most mature and widely adopted photonic integrated circuits platform. It leverages the many advantages of integrated photonics by offering a high density of devices and mass producibility due to its compatibility with CMOS technology. By using the established infrastructure of the semiconductor industry, silicon photonics enables the integration of photonic and electronic components on a single chip, offering unmatched scalability and cost-effectiveness.

Characteristics

Silicon photonics leverages the mature silicon manufacturing infrastructure of the semiconductor industry. By itself, silicon cannot be used for light generation as it has an indirect band gap, but it can be used for other active optical components such as modulators and detectors when combined with other materials. When activated by doping silicon with germanium, it can be used to make both high-speed modulators and photodetectors operating at frequencies of 70 GHz and beyond.

Among the common PIC platforms, silicon has the highest refractive index contrast and the tightest fabrication tolerance. This enables unrivaled integration density with bending radii of a few micrometers and high yield. To connect optical fibers to SiP chips, grating couplers are often used, but also edge couplers become more and more available sometimes with additional silicon nitride layers. In silicon polarization control is relatively straightforward by implementing polarization splitters and then combiners. Thermo-optic phase shifters can switch as fast as 10s of kHz with a power consumption in the 10s of mW.

The typical operating wavelengths for SiP are 1310 nm and 1550 nm, but wavelengths between 1200 nm and 6500 nm are, in principle, accessible. Propagation losses are usually moderate, around 3 dB/cm or lower depending on the specific waveguide cross-section and wavelength. Due to its intrinsic two-photon absorption, silicon often cannot support higher optical powers of more than a few 10s of mW.

Because silicon cannot be used as a gain medium, lasers cannot be directly built within silicon. Therefore, external lasers or co-integrated gain materials must be used through hybrid or heterogeneous integration. However, when integrated with gain materials, SiP can be used for the feedback section of a hybrid integrated laser for improved performance.

Applications

Thanks to its scalability, integration density, and CMOS compatibility, Silicon Photonics (SiP) is a key enabler for a wide range of applications. SiP is especially common for transceivers, interconnects, and signal processing in telecom and datacom applications. It is also increasingly used in emerging quantum communication applications such as Quantum Key Distribution (QKD). In addition, silicon photonics has become the main platform for LiDAR thanks to its efficient grating couplers and small footprint, possibly in combination with silicon nitride for optical power handling.

The SiP technology is unique for (co-)integrating optical and electronic circuits on a single chip or substrate, reducing costs and power consumption. It is primarily used in data communication, sensors, and high-performance computing.

Bring your PIC project to life

At Epiphany Design, we work with all PIC material platforms and always advise our customers on the best choice for their particular applications. When it comes to silicon photonics, we know how to make the most of its strengths to create solutions across a wide range of use-cases. We specialize in PIC Design, but also provide support at all stages of PIC development when needed.