Bin Sheng

Tunable guided-mode resonance filter with a gradient grating period fabricated by casting a stretched PDMS grating wedge

A compact, tunable guided-mode resonant filter (GMRF) is experimentally demonstrated whose spectral reflectance wavelength varies as a function of the illumination position on the device. The GMRF consists of a grating of gradient-varying period ranging from 402.5 to 466.6 nm, which is obtained by casting a stretched polydimethylsiloxane (PDMS) grating wedge. By spatially changing the illumination position on the GMRF over 11 mm, a spectral reflectance peak with low sidelobes varies from 596.8 to 684.1 nm. The influence on the resonance efficiency and the limitation of the wavelength tuning range are discussed in depth. The GMRF is a good candidate as a functional filtering component in wavelength selection and sensing applications.

Focal-length-tunable elastomer-based liquid-filled plano-convex mini lens.

A liquid plano-convex lens with focal length tuning is proposed, which is formed by sinking an oil droplet onto the bottom of an elastomer. A simple and low-cost fabrication method is presented. The lens aperture and initial focal length can be controlled during the fabrication. Furthermore, focal length tuning is demonstrated. The lens made of a 40 mg oil droplet can achieve the tuning range from 12 to 17 mm. The effective aperture of the lens is about 2.8 mm. In the demonstration of an imaging system, the lens assists in focusing and a clear image can be observed.

Tunable and Polarization-Independent Wedged Resonance Filter With 2D Crossed Grating

In this letter, a tunable and polarization-independent guided-mode resonance filter that has two-dimensional crossed grating on a wedged waveguide layer of Ta2O5 is fabricated and analysed for the communication band. The wedged waveguide layer is etched by the ion beam etching technique with a triangle-shaped mask, and the two-dimensional grating is made by holographic exposure technique. The measured spectra show that the filter can realize the property of polarization-independence at normal incidence. By the thickness gradient of the wedged layer, the filter is tunable in a range of 1599.9-1621.5 nm over a distance of 9 mm.

Ring Wrinkle Patterns with Continuously Changing Wavelength Produced Using a Controlled-Gradient Light Field

We report a facile method to prepare gradient wrinkles using a controlled-gradient light field. Because of the gradient distance between the ultraviolet (UV) lamp and polydimethylsiloxane (PDMS) substrate during UV/ozone treatment, the irradiance reaching the substrate continuously changed, which was transferred into the resulting SiOx film with a varying thickness. Therefore, wrinkles with continuously changing wavelength were fabricated using this approach. It was found that the wrinkle wavelength decreased as the distance increased. We fabricated 1-D wrinkle patterns and ring wrinkles with a gradient wavelength. The ring wrinkles were prepared using radial stresses, which were achieved by pulling the center of a freely hanging PDMS film. The resulting wrinkles with changing wavelength can be used in fluid handling systems, biological templates, and optical devices.

Spatial dispersion for diffraction grating based optical systems

Diffraction gratings are key components in many applications including pulse compression and stretch, optical imaging, spectral encoding and decoding and optical filtering. In this paper, spatial dispersion of two typical diffraction grating-based optical systems, single-grating system and grating-pair system, are thoroughly studied. The single-grating system consists of a diffraction grating to disperse the quasi-monochromatic lights and a convex lens to make the lights propagate in parallel and focused. In the grating–pair system, a pair of diffraction gratings is used to disperse the collimated lights in parallel. The spatial dispersion law for the two systems is developed and summarized. By investigating the spatial dispersion, the two systems are compared and discussed in detail.

Note: Measuring grating periods by diffraction method with a fore-end light path comprising fused fiber couplers and fiber port collimators

Based on the Littrow and Littman configurations for autocollimation, two methods are proposed herein with a fore-end light path comprising fused fiber couplers and fiber port collimators to measure the diffraction grating period. The experimental data from a uniform-line-spacing grating with a nominal value of 1200 lines/mm agreed well with theoretical values and with measurement errors of the Littrow and the Littman configurations of 1.05 × 10-4 and 4.99 × 10-5, respectively. Both methods were demonstrated to reduce the diameter of the laser spot and improve the alignment precision of the measurement system.Based on the Littrow and Littman configurations for autocollimation, two methods are proposed herein with a fore-end light path comprising fused fiber couplers and fiber port collimators to measure the diffraction grating period. The experimental data from a uniform-line-spacing grating with a nominal value of 1200 lines/mm agreed well with theoretical values and with measurement errors of the Littrow and the Littman configurations of 1.05 × 10−4 and 4.99 × 10−5, respectively. Both methods were demonstrated to reduce the diameter of the laser spot and improve the alignment precision of the measurement system.

Tailorable Elastomeric Grating With Tunable Groove Density Gradient

This paper describes a new method for fabrication of tailorable elastomeric gratings with tunable groove density gradients based on stretching of the grating sample in a direction perpendicular to the grating line within the grating surface. The advantage of this method is that the tunable groove density gradient can be achieved by tailoring of the shape of a grating sample with uniform thickness. The groove density gradient changes as a specific function of its spatial position on the tailored surface of the elastomeric grating. The resulting tailorable elastomeric gratings can be used in the fabrication of devices such as optical position sensors and tunable optical filters.

Photonic millimeter-wave-band ultra-wideband signal generation based on a dual-drive Mach-Zehnder modulator

A novel millimeter-wave (MMW) band ultra-wideband (UWB) signal generation scheme is proposed in this paper. A theoretical model is built to demonstrate the signal generation and to analyze the signal quality. The mechanism to suppress the residual local oscillation and low frequency components is investigated. The influence of the input signal over the bandwidth is studied. A 24 GHz-band MMW-UWB signal with the bandwidth of 8.1 GHz is generated at 25.5 GHz.