In this study, we report a low-symmetric photonic crystal (PhC) structure that exhibits high coupling efficiency in a broadband frequency range with a tilted self-collimating capability. First, the analytical approach is implemented as a starting point, and the ideal configuration is chosen for the self-collimation effect, which is analytically supported by group velocity dispersion and third-order-dispersion calculations. Then, numerical analyses in both time and frequency domains are performed to the ideal PhC design, which possesses a strong self-collimating characteristic, even at huge incident angles within the operating frequencies. Later, experimental measurements are conducted in microwaves, and the existing self-collimation property is still preserved at longer wavelengths in the millimeter scale. The microwave experiment as well as numerical analyses indicate that the designed PhC self-collimator allows overcoming possible misalignment problems at the PhC-source interface and enables a strong broadband beam channeling with a high transmission.

We propose compact S-vector superprism providing broadband wavelength sensitivity within a/λ = 0.610–0.635, where “a” is the lattice constant, λ is the incident wavelength, and S denotes the Poynting vector. The reported configuration overcomes strong beam divergence and complex beam generation due to the self-collimation ability of the low symmetric primitive photonic crystal (PhC) cells. Analytical calculations of equi-frequency contours, photonic band structures, and group velocity dispersions are performed by solving Maxwell's equations and using the plane wave expansion method. Besides, finite-difference time-domain analyses are also conducted. The designed superprism induces large refracted angle variation for different frequencies when the incident angle is fixed: 4% change of incident frequencies results in approximately 40° deflected angle difference with a maximum 68.9° deflection angle inside the PhC. Meanwhile, for a fixed incident wavelength, a large output variation occurs if the incident angle is altered. Microwave experimental results are found to be in good agreement with the numerical analyses.

In this paper, we propose a microcavity supported by a designed photonic crystal (PhC) structure that supplies both tunability of cavity modes and cavity's quality factor. Low symmetric defect region provides a trigger effect for the frequency shifting by means of rotational manipulation of small symmetry elements. Deviation of effective filling ratio as a result of rotational modification within the defect region results in the emanation of cavity modes at different frequencies. Here, we numerically demonstrate the frequency shifting for each obtained mode with respect to defect region architecture. In addition to wavelength tunability, quality factor, mode volume, and Purcell factors are analyzed for the slightly modified structures. Also, electric field distributions of each mode that emerge at distinct frequencies have been also studied at adjusted frequency modes which are observed for all rotational modification scenarios as = [0°, 15°, 30°, 45°]. After the investigations in 2D of silicon material (ɛ = 12), 3D simulations are performed and the collected data is used for the stacking approximation of 3D structures to get the 2D, thus the crosschecking of the quality factor that acquired from the 2D simulation can be executed by comparison with 3D. Limited 3D results are projected to approximate 2D ones step by step and get an exponential trend which reaches in the limit to the ~10 8 value for Ԛ-factor. Besides, 2D and 3D simulations of alumina (ɛ = 9.61) in terms of mode analysis and quality factor have been repeated considering the microwave experiments. Therefore, experimental analysis is compared with the numerical results and good agreement between the two is found.

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We propose a perspective to the evaluation of the wide bandwidth phenomenon, by introducing the band tailoring and chiral band approximation on the self-collimation effect for low-symmetric photonic structures. In the case of the crossing of the bands, we claim the excitation of the lower mode can provide the utilization of the entire bandwidth by suppressing the intersection regions where the frequencies tend to mix. Thereby, we design broadband self-collimation capable, defect-free photonic structures and examine their performances. A fractional bandwidth of 0.35 ( = 0.429 − 0.607 ⁄ ) and 0.37 ( = 0.481 − 0.701 ⁄ ) are achieved for radii of = 0.25a and = 0.23a, respectively. We explore the full-range collimation using transmission and E-field intensity analysis in addition to band diagrams and group velocity dispersions. Moreover, we indicate all-angle collimation validity even for highly tilted sources up to an angle of 80°.