Dengke Zhang

Encoding and decoding of orbital angular momentum for wireless optical interconnects on chip

Beams carried orbital angular momentum (OAM) are proposed for wireless optical interconnects on chip and a full scheme of encoding and decoding of OAM at single frequency is demonstrated with numerical simulation. With proposed structure, beams with OAM order of -3 to 4 are generated and four orders of them (0 to 3) are used to encode and decode data so that the increased data density of two folds is achieved. According to such results, we believe that if OAM is utilized as an additional dimension in wireless optical interconnects, the data density can be significantly increased since the adopted orders of OAM could be infinite in principle. Moreover, such improvement could be easily applied to the existing architecture without any more complex technology.

Tunable and Reconfigurable Bandpass Microwave Photonic Filters Utilizing Integrated Optical Processor on Silicon-on-Insulator Substrate

A tunable and reconfigurable bandpass microwave photonic filter based on an integrated optical processor is proposed and experimentally demonstrated on a silicon-on-insulator substrate. The optical processor based on microrings, Mach-Zehnder interferometer, and Y-branches is utilized to produce two bandpass responses for separately processing optical carrier and sideband. Moreover, the microwave responses can be varied by thermal tuning the resonance of microrings. According to the experimental results, the operating frequency and -3-dB bandwidth can be tuned from 18 to 40 GHz and from 5 to 15 GHz, respectively.

Efficient single-active-layer organic light-emitting diodes with fluoropolymer buffer layers

In the present Letter, efficient organic light-emitting diodes (OLEDs) with tris(8-hydroxyquinolino) aluminum (Alq3) as a single-active layer have been prepared by using a series of fluoropolymer buffer layers. The OLEDs with a 10-nm-thick poly(tetrafluroethylene-perfluoroalkylvinylethers) (PFA) buffer layer had a current efficiency of 4.46cd∕A at a current density of 2000A∕m2, whereas conventional double-layer OLEDs with N,N′-bis-(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) and Alq3 showed a current efficiency of only 3.81cd∕A at the same condition in our experiment. The effect of the insulating fluoropolymer buffer layers could be interpreted to enhance hole injection and improve carrier balance.

Generating optical superimposed vortex beam with tunable orbital angular momentum using integrated devices.

An integrated device, which consists of a variable amplitude splitter and an orbital angular momentum (OAM) emitter, is proposed for the superposition of optical vortex beams. With fixed wavelength and power of incident beam, the OAM of the radiated optical superimposed vortex beam can be dynamically tuned. To verify the operating principle, the proposed device has been fabricated on the SOI substrate and experimentally measured. The experimental results confirm the tunability of superimposed vortex beams. Moreover, the ability of independently varying the OAM flux and the geometric distribution of intensity is illustrated and discussed with numerical simulation. We believe that this work would be promising in various applications.

Tunable and Reconfigurable Bandstop Microwave Photonic Filter Based on Integrated Microrings and Mach–Zehnder Interferometer

A bandstop microwave photonic filter is experimentally demonstrated with integrated optical processor fabricated on silicon-on-insulator substrate. The optical processor consists of microrings and a Mach-Zehnder interferometer so that two bandstop responses are produced for processing two sidebands separately. With such a structure, tunable and reconfigurable bandstop MPFs can be easily realized by thermally tuning the resonant wavelength of microrings. According to the experimental results, the operating frequency and 10-dB bandwidth can be tuned within the range of 7-34 GHz and 1.85-4.55 GHz, respectively.

Generating in-Plane Optical Orbital Angular Momentum Beams With Silicon Waveguides

A simple on-chip integrated structure is proposed to generate optical orbital angular momentum (OAM) beams, where only silicon waveguides and couplers are involved. The operating principle is based on mode converting and proper controlling the phase shift of second-order propagating mode so that OAM modes with charge numbers of 1 or -1 can be selectively generated with mode purity > 90%. The proposed device is very compact with footprint of <; 120 μm × 50 μm and can be easily fabricated with CMOS technology. Thus, such OAM mode generator is a promising candidate for applications ranging from optical tweezers and optical spanners to optical communications.

Compact Thermo-Optic Switch Based on Tapered W1 Photonic Crystal Waveguide

A compact thermo-optic switch based on the cutoff effect of slow-light mode of a tapered W1 photonic crystal waveguide (PCW) is demonstrated with an integrated microheater. Due to the low-group-index taper, the coupling loss of the slow-light PCW is reduced, and a high switching extinction ratio (ER) is attained. Moreover, three types of microheaters are evaluated for the power consumptions, heating transfer efficiency, and temperature uniformities, and an optimized slab microheater is utilized. As a result, low switching power of 8.9 mW and high ER of 23.5 dB are achieved experimentally, while the length of W1 PCW is only 16.8 μm.

Identifying Orbital Angular Momentum of Vectorial Vortices with Pancharatnam Phase and Stokes Parameters.

In this work, an explicit formula is deduced for identifying the orbital angular moment (OAM) of vectorial vortex with space-variant state of polarization (SOP). Different to scalar vortex, the OAM of vectorial vortex can be attributed to two parts: 1. the azimuthal gradient of Pancharatnam phase; 2. the product between the azimuthal gradient of orientation angle of SOP and relevant solid angle on the Poincaré sphere. With our formula, a geometrical description for OAM of light beams can be achieved under the framework of the traditional Poincaré sphere. Numerical simulations for two types of vectorial vortices have been carried on to confirm our presented formula as well as demonstrate the geometrical description of OAM. Furthermore, this work would pave the way for precise characterization of OAM charge of vectorial vortices.

Compact Optical Add-Drop Multiplexers With Parent-Sub Ring Resonators on SOI Substrates

A four-channel integrated optical add/drop multiplexer is experimentally demonstrated on a silicon-on-insulator substrate. With the help of a parent-sub microring resonator structure, compact footprint, large free spectral range, and uniform channel spacing are achieved simultaneously. Through controlling the resonance matching between the parent and sub-rings through thermo-optic effect, each channel can be switched independently between the states of dropping and passing through. The thermal tuning efficiency is as high as 0.27 nm/mW. Typically, for dropping state, all four channels can be de-multiplexed to the drop ports with 2 dB drop loss, 18 dB through port extinction, and less than -20 dB channel crosstalk.

Microring bio-chemical sensor with integrated low dark current Ge photodetector

An integrated Ge photodetector of very low dark current density is demonstrated in an optoelectronic integrated circuit label-free biosensing system. The sensor system consists of a microring for optical sensing and a monolithically integrated Ge detector. For point-of-care applications, integration of Ge detector increases the reliability of measurement by eliminating mechanical-optical alignment of output signals. Optimizing Ge detector performance will further enhance system signal-noise ratio and reliability. For homogeneous sensing, the system has a sensitivity of ∼18.8 nm/RIU and a detection limit of 3.50 × 10−5.