The waveguides are built by high quality silicon nitride, cladded in high quality silicon dioxide. Nitride thickness is fixed per batch and ranging from 150-1300nm depending on the application. Such high nitride thickness is enabled by LIGENTEC proprietary process, ensuring exceptional mode confinement, sharp bending radius and reduced device footprint. The high nitride thickness permits anomalous dispersion and a high damage threshold that is very important for LIDAR, quantum and nonlinear optical applications of these integrated devices.
LIGENTEC process offers a state of the art, cost-effective platform with superior critical dimension and thickness control. The process is accompanied by a validated design library, offering a rapid and low cost prototyping solution. The library developed with VLC Photonics includes integrated components for:
- spot converters
- ultra low loss spirals
- MZI, MMI
- ring resonators
To lower the entry cost to LIGENTEC processes a multi-project wafer run is available were the users share the process and engineering cost. For different target applications from the visible to mid-infrared we offer different waveguide thickness shown in the table below.
An unique feature of the thick waveguides is their anomalous dispersion and their high damage threshold that is important in a range of nonlinear optical applications, including integrated quantum communication, supercontinuum generation in waveguides from pulsed lasers, femtosecond pulse generation from CW lasers using soliton generation in microresonators. The high power threshold enables applications such as LIDAR to propagate Watts of power in the waveguides. In addition the transparency window in the visible renders silicon nitride planar photonic circuits attractive for microfluidics and bio-sensing applications.
The thick silicon nitride waveguides not only enable high damage threshold and low loss, but also a compact chip design as bending radii are very small. With a mode fully confined in the waveguide bends as small as a few tens of micrometers are possible without significant loss.
LIGENTEC enables with its silicon nitride technology products in different application areas.
Frequency comb generation
Silicon Nitride microresonators enable the generation of frequency combs from a single continuous wave laser source. Due to a balance of Kerr nonlinearity and the dispersion of the resonator equally spaced lines are generated through nonlinear processes, when the pump laser operates above a certain threshold. Dispersion engineering of the resonator is made easy due to the ability to shape height and width of the resonator through the fabrication process. The final repetition rate, i.e. the distance between two lines is given by the diameter of the resonator and can be customised from 20 GHz up to 1 THz.
Optical spectrum of a frequency comb generated with a microresonator. The diameter of around 670 μm provides a repetition rate of 50 GHz. (courtesy of LPQM, EPFL).