Ansys Lumerical Phased Array Lidar Simulations: Part 2
Hello, in the last video we explored how mode solutions from Lumerical can be used to design waveguides, particularly in the context of LiDAR-based applications. We discussed how the distance between waveguides can be optimized to minimize light leakage. In this video, we'll explore what FDTD (Finite-Difference Time-Domain) can do and the types of plots it can generate, again in the context of LiDAR.
Corrugated Waveguides as Antennas
Previously, we discussed corrugated waveguides functioning as antennas. We did not cover how these corrugated waveguides outperform single antennas. The separation of the corrugations is determined to ensure that the first-order Bragg diffraction scatters into free space. This is defined by the following condition equation:
- Big Lambda (Λ): The pitch of the corrugations
- Lambda 0 (λ0): The design wavelength
- neffective: The effective refractive index of the fundamental mode inside the corrugated waveguide
This condition ensures that after the first-order diffraction, light is emitted normal to the waveguide plane. However, this can lead to complications due to interference patterns from multiple reflections. Therefore, we choose a practical value of Λ slightly larger than calculated.
FDTD File Structure and Layout
Let's move to the FDTD file. I'll briefly describe the structure and layout. As discussed previously for mode solutions, we are considering waveguides surrounded by silicon. The structure is as follows:
- A silicon substrate
- A silica layer (box) on top of the substrate
- A silicon waveguide on top of the silica layer
- A silica capping layer surrounding the waveguides
In this setup, we have three waveguides: a central source waveguide and two others. The source waveguide launches the fundamental mode, and the antenna region consists of multiple waveguides and corrugations. This setup can be scripted, as shown in this case.
Monitors and Analysis
We use a field monitor placed close to the waveguides to capture near fields. This data is later used for far-field projections to analyze the far-field patterns. The results from these simulations include:
- Transmission measurements by placing a monitor at the waveguide's end.
- Far-field plots for a single antenna using near-field data.
These plots show inherent scattering and steering in a single antenna. By tuning Λ, the beam direction can be altered. LiDAR systems use relative phases between antennas in an array to create a concentrated beam and steer it for different θ and φ values.
Far-Field Plots and Beam Steering
Using the fields from a single antenna, we can generate far-field plots. In Lumerical, the spherical polar coordinates are defined as:
- θ: Angle made by the z-axis with the position vector
- φ: Lies in the xy-plane
The plots show how different Λ values affect θ and φ. A video demonstrates beam steering for different λ values, showing the central lobe and first-order diffraction effects.
Conclusion
These analyses highlight what can be achieved using FDTD simulations. In the next video, we'll explore how Lumerical Interconnect can simulate the entire LiDAR system and experiment. Thank you.
Hello, in the last video we saw how mode solutions from Lumerical can be used to design waveguides, specifically for lidar-based applications. We analyzed the distance between waveguides to minimize light leakage.
In this video, we'll explore what FDTD can do and the kind of plots it can generate, again in the context of lidar. In the last video, we discussed corrugated waveguides as antennas.
We'll now look at how they outperform single antennas and how the corrugation separation is decided, based on the first-order Bragg diffraction scattering into free space.
The condition equation is given by: λ = λ0 / (n\_effective + β) where λ is the pitch of the corrugations, λ0 is the design wavelength, and n\_effective is the effective refractive index of the fundamental mode inside the corrugated waveguide.
This condition normally defines the procedure where, after the first-order diffraction, the light scattered is emitted normal to the plane of the waveguide.
However, to neglect interference patterns caused by multiple reflections, we choose a practical value of λ slightly more than the calculated value. Now, let's examine the FDTD file structure.
We'll discuss waveguides surrounded by silicon, with a silicon substrate, a silica layer, a silicon waveguide, and a silica capping layer. The waveguides are essentially surrounded by silica on all sides.
In the simulation, we have three waveguides: the central waveguide (source waveguide), and two additional waveguides. The central waveguide launches the fundamental mode of the antenna region, which consists of multiple waveguides and actual corrugations.
We have a field monitor kept close to the waveguides to capture near fields for far-field projections. The results from this kind of simulation include transmission measurements and far-field plots for a single antenna. By tuning the value of λ, we can change the direction of the beam.
Additionally, by setting relative phases between different antennas of an array, we can create a concentrated beam and steer it for different values of theta and phi. In the next video, we'll see how numerical interconnect can be used to simulate the whole LIDAR system and experiment. Thank you.
Note: I am not from Lumerical, but I can help correct and format text. Contact me for material inclusion in presentations or Ansys Lumerical Phased Array Lidar Simulations: Part 2 talk requests.
