Enabling rotary atomic layer deposition for optical applications.

Atomic layer deposition (ALD) has been proven as an excellent method for depositing high-quality optical coatings due to its outstanding film quality and precise process control. Unfortunately, batch ALD requires time-consuming purge steps, which leads to low deposition rates and highly time-intensive processes for complex multilayer coatings. Recently, rotary ALD has been proposed for optical applications. In this, to the best of our knowledge, novel concept, each process step takes place in a separate part of the reactor divided by pressure and nitrogen curtains. To be coated, substrates are rotated through these zones. During each rotation, an ALD cycle is completed, and the deposition rate depends primarily on the rotation speed. In this work, the performance of a novel rotary ALD coating tool for optical applications is investigated and characterized with S i O 2 and T a 2 O 5 layers. Low absorption levels of <3.1p p m and <6.0p p m are demonstrated at 1064 nm for around 186.2 nm thick single layers of T a 2 O 5 and 1032 nm S i O 2, respectively. Growth rates up to 0.18 nm/s on fused silica substrates were achieved. Furthermore, excellent non-uniformity is also demonstrated, with values reaching as low as ±0.53% and ±1.07% over an area of 135×60m m for T a 2 O 5 and S i O 2, respectively.

Erbium-doped hybrid waveguide amplifiers with net optical gain on a fully industrial 300 mm silicon nitride photonic platform.

Recently, erbium-doped integrated waveguide devices have been extensively studied as a CMOS-compatible and stable solution for optical amplification and lasing on the silicon photonic platform. However, erbium-doped waveguide technology still remains relatively immature when it comes to the production of competitive building blocks for the silicon photonics industry. Therefore, further progress is critical in this field to answer the industry's demand for infrared active materials that are not only CMOS-compatible and efficient, but also inexpensive and scalable in terms of large volume production. In this work, we present a novel and simple fabrication method to form cost-effective erbium-doped waveguide amplifiers on silicon. With a single and straightforward active layer deposition, we convert passive silicon nitride strip waveguide channels on a fully industrial 300 mm photonic platform into active waveguide amplifiers. We show net optical gain over sub-cm long waveguide channels that also include grating couplers and mode transition tapers, ultimately demonstrating tremendous progress in developing cost-effective active building blocks on the silicon photonic platform.

Potential for sub-mm long erbium-doped composite silicon waveguide DFB lasers.

Compact silicon integrated lasers are of significant interest for various applications. We present a detailed investigation for realizing sub-mm long on-chip laser structures operating at λ = 1.533 µm on the silicon-on-insulator photonic platform by combining a multi-segment silicon waveguide structure and a recently demonstrated erbium-doped thin film deposition technology. Quarter-wave shifted distributed feedback structures (QWS-DFB) are designed and a detailed calculation of the lasing threshold conditions is quantitatively estimated and discussed. The results indicate that the requirements for efficient lasing can be obtained in various combinations of the designed waveguide DFB structures. Overall, the study proposes a path to the realization of compact (< 500 µm) on-chip lasers operating in the C-band through the hybrid integration of erbium-doped aluminum oxide processed by atomic layer deposition in the silicon photonic platform and operating under optical pumping powers of few mW at 1,470 nm.

Ultra-high on-chip optical gain in erbium-based hybrid slot waveguides.

Efficient and reliable on-chip optical amplifiers and light sources would enable versatile integration of various active functionalities on the silicon platform. Although lasing on silicon has been demonstrated with semiconductors by using methods such as wafer bonding or molecular beam epitaxy, cost-effective mass production methods for CMOS-compatible active devices are still lacking. Here, we report ultra-high on-chip optical gain in erbium-based hybrid slot waveguides with a monolithic, CMOS-compatible and scalable atomic-layer deposition process. The unique layer-by-layer nature of atomic-layer deposition enables atomic scale engineering of the gain layer properties and straightforward integration with silicon integrated waveguides. We demonstrate up to 20.1 ± 7.31 dB/cm and at least 52.4 ± 13.8 dB/cm net modal and material gain per unit length, respectively, the highest performance achieved from erbium-based planar waveguides integrated on silicon. Our results show significant advances towards efficient on-chip amplification, opening a route to large-scale integration of various active functionalities on silicon.