Dielectric slot-coupled half-Maxwell fisheye lens as octave-bandwidth beam expander for terahertz-range applications

Abstract

We present a paradigm for integrated photonic devices based on broadband slab-confined collimated beams that are launched with half-Maxwell fisheye lenses. Although it is challenging to match to the low-index focus of the lens while maintaining adequate field confinement for a close approximation of a point source, integrated dielectric slot waveguides prove highly suitable, yielding collimators of 90% efficiency and bandwidth greater than one octave. Terahertz technology will benefit from such broadband slab-confined beams to replace free-space optics toward compact, mass-producible systems that do not require manual optical alignment. We present two prototype systems to demonstrate the versatility of this concept, namely, a diagonally set distributed Bragg reflector as a frequency-division diplexer for terahertz communications and an attenuated total reflection-based liquid sensor. Both are enabled by oblique in-slab reflections that are collected at a location other than the originating lens, which is not attainable using ordinary single-mode channel waveguides.

300-GHz-Band Diplexer for Frequency-Division Multiplexed Wireless Communication

“…For dielectric unclad waveguides, bending loss is frequencydependent due to the delocalization of modal fields at lower frequencies. When the waveguide bends, the radiation of weakly-confined low frequencies is increased, and this effect can be exploited to realize a convenient high-pass filter [11]. Here, we employ two such narrowed bends to enhance roll-off and isolation.…”

3D‐Printed Photonic Crystal Sub‐Terahertz Leaky‐Wave Antenna

“…[34] Although various configurations of 2D photonic crystal slabs have been reported in the THz region , [34][35][36][37][38] there have been relatively few studies that focus on the detailed design of antennas based on photonic crystals. [39] Antennas are crucial for coupling guided waves into free space, which is a key challenge for realizing THz wireless communications. In this work, we propose an alternative photonic crystal design that enables free-space coupling using a leaky-wave mechanism.…”

Double-layer geodesic and gradient-index lenses

“…Graded index devices have been widely implemented using effective-medium techniques 10 , 14 – 21 . For instance, all-dielectric solutions have been employed for lensing from the microwave 10 , 15 to terahertz 16 , 17 and optical bands 18 , 19 , and they also prove viable for both lensing and cloaking in quasi-conformal transformation optics 18 – 20 . Such devices are usually realized by a dielectric slab (such as alumina or silicon) patterned with subwavelength structures like pillars or air holes.…”