The overall goal of the following experiment is to use microwave scale samples of dielectric solids to study the photonic properties of disordered photonic band gap materials. This is achieved by constructing test samples made with dielectric components inserted into a 3D printed base template with holes and slots arranged to form particular ordered or disordered patterns. As a second step, place the sample on a rotating stage between a pair of microwave horn antennas and take transmission measurements over a wide range of frequencies for different incident angles, which will allow determination of the band gap properties of the structure.
Next, modify the structure to form a functional defect and perform transmission measurements in order to study wave guiding and resonating properties of the modified structures. Results are obtained that show the frequency range and angular dependence of the structures band gap, as well as the performance of their functional defects based on analyzing the measured transmission spectrum. The main advantage of this technique of a numerical simulation and sub micron scale experimental method is that this technique avoids use of the enormous amount of competing resources and expensive sub-micron fabrication, so that one can quickly and inexpensively construct disorder, photonic band gap material, modify them with arbitrary defect design and characterize their photonic properties directly.
The implications of this technique extend toward any photonic system, including the visible light region and the infrared region. Because micro equations are scaling in variant, the exact same design and results can be applied to visible light when the zaper are shrunk 10, 000 times.Insights. This video begins after a two dimensional hyperuniform disordered dielectric structure has been designed and its base fabricated.
The base is made of a clear resin and has holes and slots on which the disordered structure will be assembled. A second square lattice base has also been made for comparison. Each base is two centimeters tall with these elements ready.
Turn attention to the building blocks that will be used to construct the structures. Obtain Illumina rods and thin walls that are at least a few wavelengths in height here, 10 centimeters. The diameter of all the rods is five millimeters, and the wall thickness is always 0.38 millimeters with varying widths.
Next, construct a defect-free test structure with a nearly circular boundary for band gap measurements. Do this by inserting the rods and walls into the base for the desired structure architecture. This is the hyperuniform disordered structure.
After construction produced the square lattice structure in the same manner. Here is the final result for the square lattice. Set up the experiment on a benchtop.
Use a synthesized sweeper microwave generator to provide radiation in the 45 megahertz to 50 gigahertz range with one hertz resolution. Connect this to an S parameter test set to measure transmission parameters to measure and process the signal from the S parameter test set. Connect a microwave vector network analyzer, then use high quality semi flexible coaxial cables to connect the S parameter test set ports with the input and output wave guides to ensure linear polarization of the E field.
Use rectangular single mode wave guides and adapters connected to parametal horn antennas. The antennas are on either side of a rotating stage where the structure will be placed. Next, set the instrument parameters for the experiment at the control panel.
For the vector network analyzer, select the frequency range for measurement here, seven gigahertz to 15 gigahertz. Then select an averaging factor to control noise. Finally, for this seven to 15 gigahertz measurement, choose the required number of data points to achieve a frequency resolution of 10 megahertz.
Arrange for a computer to automate measurements and data logging. Begin band gap measurements by calibrating the system. First, align the horns vertically and horizontally so they face one another at a distance of about 40 centimeters, roughly 15 times the average wavelength for the sweep with the setup as it will be for the measurements, but without a sample between the horns.
Start a microwave sweep to measure the transmission through free space. Once the sweep is done in one to two minutes, save the results as a calibration set in the vector network analyzer. Here is a typical plot of transmission through free space as a function of frequency.
First, be sure to zero the angle scale of the stage. Now center a defect-free structure with a nearly circular boundary on the rotating stage between the two horns. In this case, the hyperuniform disordered structure is used to prepare the vector network analyzer for the measurement.
Turn on the saved calibration set to allow the measurement of relative transmission through the sample. Start the microwave sweep to collect data when a sweep has been completed and the data saved. Arrange for the radiation to be incident on the structure from another direction.
To do this, rotate the stage two degrees counterclockwise in preparation for the next measurement with the saved calibration data on perform another measurement of the relative transmission. Once all measurements between zero and 180 degrees have been completed, remove the structure from between the antennas. Rotate each horn 90 degrees to achieve a different field polarization.
The polarization is being changed from transverse magnetic to transverse electric. Perform the calibration and the measurements with the structure. Again, after the band gap measurements, prepare the structure for wave guide measurements.
Make use of the modular design to quickly create a waveguide by removing elements. In this case, transform a defect-free hyperuniform structure into one with a channel through it. Change to smaller horn antennas for waveguide measurement.
Then move the antennas as close to the channel openings as possible. This arrangement of antennas with respect to the channel ensures good coupling turn off calibration in the vector network analyzer and start the microwave sweep. The vector network analyzer will show and record the raw transmission ratio of the detected power over the source power.
When the measurement is completed. Rotate both horns by 90 degrees. In order to allow characterization of the polarization, dependence of the structure, measure the transmission ratio in this new configuration.
This is the TE polarization transmission of a hyperuniform structure. At one angle, the vertical axis is in decibels. The horizontal axis is the frequency.
In gigahertz, a drop of more than two orders of magnitude between 8.5 gigaherz and 9.5 gigaherz indicates a stop band region. The drop off at about 13 gigahertz is due to antenna performance. These are polar plots of the transmission through a square lattice and a hyperuniform defect structure.
Along the radial direction is the frequency in units of the speed of light over the lattice spacing. The angle corresponds to the angle of incidents. Regions of low transmission are in blue for the square lattice stop bands due to brag, scattering appear along the square shaped BRI and boundaries.
In contrast, the hyperuniform defect structure, stop gap forms and isotropic photonic band gap. Here is a hyperuniform disordered sample with a straight channel wave guide. The width of the channel is twice the average inner rod spacing.
This is the measured ratio of detected power to source power for TM waves through the channel in units of the speed of light over the average inner rod spacing. The pink region is the TM band gap of the sample without the channel. With the introduction of the channel, a broadband is guided through the sample.
Once mastered, the design, construction and transmission measurement of the modular sample can be done in a few hours if it is performed properly after its development. This technique paved the way for researchers to explore the photonic properties of disordered materials and their possible applications.
