On-Demand Dynamic Terahertz Polarization Manipulation Based on Pneumatically Actuated Metamaterial.

In this paper, a new tuning strategy is proposed by incorporating a pneumatically actuated metamaterial to achieve on-demand polarization manipulation at THz frequencies. Through controlling the actuation pressure, the device function can be flexibly switched among three types of polarization conversion capabilities within the same operation frequency band, from 1.3 THz to 1.5 THz, in which the mutual conversion between linear polarization and circular polarization, such as a quarter-wave plate, and handedness inversion between circular polarizations as a helicity inverter as well as a helicity keeper, have been successfully achieved between the incidence and reflection. Moreover, the intrinsic tuning mechanism for the polarization manipulation is also discussed.

Silicon MMI-based power splitter for multi-band operation at the 1.55 and 2†µm wave bands.

Multimode interference (MMI)-based power splitters are fundamental building blocks for integrated photonic devices consisting of an interferometer structure. In order to forestall the 'capacity crunch' in optical communications, integrated devices capable of operating in multiple spectral bands (e.g., the conventional telecom window and the emerging 2 µm wave band) have been proposed and are attracting increasing interest. Here, we demonstrate for the first time, to the best of our knowledge, the realization of a dual-band MMI-based 3 dB power splitter operating at the 1.55 and 2 µm wave bands. The fabricated power splitter exhibits low excess losses of 0.21 dB and 0.32 dB with 1 dB bandwidths for 1500-1600 nm and 1979-2050 nm, respectively.

Ultra-low noise phase measurement of fiber optic sensors via weak value amplification.

The noise floor is a vital specification that determines the minimum detectable signal in the phase measurement. However, the noise floor in optical phase measurement conducted via conventional optical interferometry tends to approach the intrinsic limit. In this study, a low noise phase measurement of a fiber optic sensor conducted via weak value amplification is experimentally demonstrated. The system has a flat, wideband frequency response from 0.1 Hz to 10 kHz, as well as adequate linearity. The operating band is wider than the present sensor using the same mechanism. In particular, the system noise floor is measured to be -98 dB at 1 Hz and -155 dB at 1 kHz. The results indicate that the minimum detectable signal can reach as low as 5.6 × 10-6 rad at 1 Hz and 8 × 10-9 rad at 1 kHz. In addition, it is demonstrated that the noise result of the proposed system is two-order of magnitude lower than that of the typical interferometric fiber optic sensors through the comparison experiment. With the characteristic of low-noise, the system is promising in the field of weak signal detection such as underwater acoustic signal detection, seismic wave detection, and mineral resource exploration.

Design and Fabrication of a Tunable Optofluidic Microlens Driven by an Encircled Thermo-Pneumatic Actuator.

This paper presents the design, simulation, fabrication, assembly, and testing of a miniature thermo-pneumatic optofluidic lens. The device comprises two separate zones for air heating and fluid pressing on a flexible membrane. A buried three-dimensional spiral microchannel connects the two zones without pumps or valves. The three-dimensional microfluidic structure is realized using a high-resolution three-dimensional printing technique. Multi-physics finite element simulations are introduced to assess the optimized air chamber design and the low-temperature gradient of the optical liquid. The tunable lens can be operated using a direct-current power supply. The temperature change with time is measured using an infrared thermal imager. The focal length ranges from 5 to 23 mm under a maximum voltage of 6 V. Because of the small size and robust actuation scheme, the device can potentially be integrated into miniature micro-optics devices for the fine-tuning of focal lengths.

Single-step etched two-dimensional polarization splitting dual-band grating coupler for wavelength (de)multiplexing.

Diffractive periodic-structure-based grating couplers (GCs) are the most widely used devices for light coupling between optical fibers and integrated photonic devices. However, conventional GCs have limited wavelength operation and are polarization specific, which is due to the intrinsic radiation angle dependency on both wavelength and polarization. Here we propose and experimentally demonstrate a polarization-splitting dual-band grating coupler (PS-DBGC) for polarization diversity and wavelength division (de)multiplexing (WDM) operation. The four-port two-dimensional PS-DBGC is based on a periodically arranged structure with square holes, and requires only a single etch step in a 340-nm silicon-on-insulator platform. The simulation predicts that the maximum coupling efficiency (CE) of the proposed PS-DBGC is -2.8 dB and -4.6 dB for the O- and C-band, respectively. The measured peak CEs of the fabricated device are -4.7 dB at 1280 nm and -8.4 dB at 1522 nm. We anticipate that this PS-DBGC could potentially improve the performance of any future integrated WDM passive optical network.

Ultra-compact optical zoom endoscope using solid tunable lenses.

We report an ultra-compact optical zoom endoscope containing two tunable Alvarez lenses. The two tunable lenses are controlled synchronously by piezoelectric benders to move in directions perpendicular to the optical axis to achieve optical zoom while keeping images in clear focus without moving the scope. The piezoelectric benders are arranged circumferentially surrounding the endoscope optics with a diameter about 2 mm, which results in an ultra-compact form. The demonstrated endoscope is capable of optical zoom close to 3 × from field of view (FOV) 50° to 18° continuously with the required movements for its constituent optical elements less than 110 µm. Such optical zoom endoscopes may find their potential uses in healthcare and industrial inspection systems.

Solid electrically tunable dual-focus lens using freeform surfaces and microelectro-mechanical-systems actuator.

In this Letter, a miniature solid tunable dual-focus (DF) lens, which is designed using freeform optical surfaces and driven by one microelectro-mechanical-systems rotary actuator, is reported. Such a lens consists of two optical elements, each having a flat surface and one freeform surface optimized by ray-tracing technology. By changing the relative rotation angle of the two lens elements, the lens configuration can form double foci with corresponding focal lengths varied simultaneously, resulting in a tunable DF effect. Results show that one of the focal lengths is tuned from about 30 to 20 mm, while the other one is varied from about 30 to 60 mm, with a maximum rotation angle of about 8.2 deg.

Miniature adjustable-focus endoscope with a solid electrically tunable lens.

The design, fabrication and characterization of a miniature adjustable-focus endoscope are reported. Such an endoscope consists of a solid tunable lens for optical power tuning, two slender piezoelectric benders for laterally moving the lens elements perpendicular to the optical axis, and an image fiber bundle for image transmission. Both optical and mechanical designs are presented in this paper. Dynamic tuning of optical powers from about 135 diopters to about 205 diopters is experimentally achieved from the solid tunable lens, which contains two freeform surfaces governed by 6-degree polynomials and optimized by ray tracing studies. Results show that there is no obvious distortion or blurring in the images obtained, and the recorded resolution of the lens reaches about 30 line pairs per mm. Three test targets located at various object distances of 20 mm, 50 mm and 150 mm are focused individually by the endoscope by applying different driving DC voltages to demonstrate its adjustable-focus capability.