Tunable Hollow Waveguide Research Articles

Slow-light-assisted electrical tuning in hollow optical waveguide via carrier depletion in silicon and indium tin oxide subwavelength gratings

An electrically tunable hollow optical waveguide based on silicon-indium tin oxide (ITO) gratings is proposed to achieve phase modulation. The hollow waveguide consisting of Si-ITO gratings as top and bottom reflectors supports the propagation of slow-light mode with a high group index of 71 and a loss of 0.1 dB/cm in a narrow 1 µm thick air-core at 1550 nm. Carrier depletion in p -type Si and n -type ITO enables electrically controlled phase modulation of the guided slow-light mode. With the slow-light effect, 180° phase modulation is obtained in a short device length of 3 mm with a maximum reverse bias of − 5 volts and 3 dB modulation bandwidth of 63 GHz.

Investigation and Theoretical Analysis of Low-Loss Three-Dimensional Hollow Waveguides for Widely Tunable Optical Devices

A tunable hollow waveguide is a promising candidate for tunable photonic devices in various applications including photonic integrated circuits for dense wavelength division multiplexing networks. We propose two kinds of low-loss three-dimensional (3D) hollow waveguides; one with a simple 3D shape with a rectangular step of 200 nm depth and another with a curved air-core to realize low-loss, temperature-insensitive, and widely tunable photonic devices. Both 3D structures show strong confinement of light in three dimensions. The propagation characteristics of both 3D hollow waveguides have been discussed, and they demonstrate large tunability and low propagation loss. Both waveguides show polarization dependence small enough for use in practical devices and a widely tuned spot size that can be matched with that of a single mode optical fiber.

Beam steering and tilt coupling in tunable hollow waveguide

We present the new function of tunable hollow waveguides with a variable air core. We show a possibility of wide-angle beam steering from the hollow waveguide and efficient tilt-coupling in narrow air core hollow waveguides. Wide-angle beam steering was demonstrated by calculation and preliminary experiment. In addition, a possibility of an efficient optical coupling with a narrow air core was presented by the tilt-coupling scheme. Input and output coupling losses are 2.5dB and 1dB for 1µm air core, respectively. Wide tunability in sub-wavelength air cores enables us to realize new functions of tunable hollow waveguides and circuits.

Tunable hollow waveguide Bragg grating with low-temperature dependence

We demonstrate a tunable hollow waveguide Bragg grating with low-temperature dependence. We fabricated a distributed Bragg reflector consisting of a grating loaded slab semiconductor hollow waveguide with a variable air-core. A change in an air-core thickness enables us to achieve a tunable propagation constant of several percents resulting in a large shift of several tens of nanometers in Bragg wavelength. We demonstrate 10nm continuous wavelength tuning of a peak reflectivity. This value corresponds to a propagation constant change of 0.64%, which is larger than that of thermo-optic effects or electro-optic effects. The measured temperature sensitivity of the peak wavelength is as low as 0.016nm∕K, which is seven times smaller than that of conventional semiconductor waveguide devices.

Control of Group Delay and Chromatic Dispersion in Tunable Hollow Waveguide with Highly Reflective Mirrors

We propose the control of group delay and chromatic dispersion in a hollow waveguide with a variable air core and highly reflective mirrors. Both group delay and chromatic dispersion in a hollow optical waveguide increase markedly with decreasing air core. A wide tunability of group velocity and chromatic dispersion is predicted by reducing the air core to nearly half of wavelength. We discuss the potential applications of the proposed hollow waveguide for compact photonic integrated circuits including tunable optical delay lines, interferometers, chromatic dispersion compensators and dispersion slope compensators.

Tunable hollow waveguide distributed Bragg reflectors with variable air core

We demonstrate a tunable hollow waveguide distributed Bragg reflector consisting of a grating loaded slab hollow waveguide with a variable air-core. The modeling shows that a change in an air-core thickness enables a large shift of several tens of nanometers in Bragg wavelength due to a change of several percents in a propagation constant. We fabricated a slab hollow waveguide Bragg reflector with 620 mum long and, 190 nm deep 1st-order circular grating composed of SiO2, exhibiting strong Bragg reflection at 1558 nm with an air-core thickness of 10 mum for TM mode. The peak reflectivity is 65% including fiber coupling losses, the 3-dB bandwidth is 2.8 nm and the grating-induced loss is less than 0.5 dB. We demonstrate a 3 nm wavelength tuning of the fabricated hollow waveguide Bragg reflector by changing an air-core thickness from 10 mum to 7.9 mum.