Real-time monitoring and gradient feedback enable accurate trimming of ion-implanted silicon photonic devices

On-chip silicon electro-optical modulator with ultra-high extinction ratio for fiber-optic distributed acoustic sensing

Ultra-high extinction ratio (ER) optical modulation is crucial for achieving high-performance fiber-optic distributed acoustic sensing (DAS) for various applications. Bulky acousto-optical modulators (AOM) as one of the key devices in DAS have been used for many years, but their relatively large volume and high power consumption are becoming the bottlenecks to hinder the development of ultra-compact and energy-efficient DAS systems that are highly demanded in practice. Here, an on-chip silicon electro-optical modulator (EOM) based on multiple coupled microrings is demonstrated with ultra-high ER of up to 68 dB while the device size and power consumption are only 260 × 185 μm2 and 3.6 mW, respectively, which are at least two orders of magnitude lower than those of a typical AOM. Such an on-chip EOM is successfully applied to DAS with an ultra-high sensitivity of -71.2 dB rad2/Hz (4 pε/√Hz) and a low spatial crosstalk noise of -68.1 dB rad2/Hz, which are very similar to those using an AOM. This work may pave the way for realization of next-generation ultra-compact DAS systems by integration of on-chip opto-electronic devices and modules with the capability of mass-production.

Post-Processing Trimming of Silicon Photonic Devices Using Femtosecond Laser

Fabrication errors inevitably occur in device manufacturing owing to the limited processing accuracy of commercial silicon photonic processes. For silicon photonic devices, which are mostly processing-sensitive, their performances usually deteriorate significantly. This remains an unsolved issue for mass production, particularly for passive devices, because they cannot be adjusted once fixed in processes. This study presents a post-processing trimming method to compensate for fabrication errors by changing the cladding equivalent refractive indices of devices with femtosecond lasers. The experimental results show that the resonant wavelengths of micro-ring resonators can be regularly shifted within their free spectral range via tuning the illuminating area, focusing position, emitting power, and scanning speed of the trimming femtosecond laser with an acceptable loss increase. These experiments, as well as the trimming experiments in improving the phase balance of Mach-Zehnder interferometer switches, indicate that the femtosecond laser trimming method is an effective and fast method for silicon photonic devices.

Ge Ion Implanted Photonic Devices and Annealing for Emerging Applications

Germanium (Ge) ion implantation into silicon waveguides will induce lattice defects in the silicon, which can eventually change the crystal silicon into amorphous silicon and increase the refractive index from 3.48 to 3.96. A subsequent annealing process, either by using an external laser or integrated thermal heaters can partially or completely remove those lattice defects and gradually change the amorphous silicon back into the crystalline form and, therefore, reduce the material’s refractive index. Utilising this change in optical properties, we successfully demonstrated various erasable photonic devices. Those devices can be used to implement a flexible and commercially viable wafer-scale testing method for a silicon photonics fabrication line, which is a key technology to reduce the cost and increase the yield in production. In addition, Ge ion implantation and annealing are also demonstrated to enable post-fabrication trimming of ring resonators and Mach–Zehnder interferometers and to implement nonvolatile programmable photonic circuits.

Silicon erasable waveguides and directional couplers by germanium ion implantation for configurable photonic circuits

A novel technique for realization of configurable/one-time programmable (OTP) silicon photonic circuits is presented. Once the proposed photonic circuit is programmed, its signal routing is retained without the need for additional power consumption. This technology can potentially enable a multi-purpose design of photonic chips for a range of different applications and performance requirements, as it can be programmed for each specific application after chip fabrication. Therefore, the production costs per chip can be reduced because of the increase in production volume, and rapid prototyping of new photonic circuits is enabled. Essential building blocks for the configurable circuits in the form of erasable directional couplers (DCs) were designed and fabricated, using ion implanted waveguides. We demonstrate permanent switching of optical signals between the drop port and through the port of the DCs using a localized post-fabrication laser annealing process. Proof-of-principle demonstrators in the form of generic 1×4 and 2×2 programmable switching circuits were fabricated and subsequently programmed.