Zecen Zhang

Characteristics of ultraviolet photoluminescence from high quality tin oxide nanowires

We investigate the optical properties of ultraviolet range emission from high quality tin oxide nanowires prepared by vapor-liquid-solid growth technique. Temperature dependent photoluminescence (PL) measurement is performed between 10 and 300 K. At low temperatures, the PL originates from radiative recombination of excitons bound to neutral donors, donor-acceptor pair transition and their associated longitudinal optical (LO) phonon replicas. The LO-phonon replicas up to third order with Huang–Rhys factor of 0.34 are observed. Evolution of the peaks and the origin of PL thermal quenching at high temperatures are discussed in detail.

Rayleigh-instability-driven simultaneous morphological and compositional transformation from Co nanowires to CoO octahedra

Arrays of regularly distributed CoO nano-octahedra are obtained by annealing Co nanowires at high temperatures. Both the size and the separation distance of the nano-octahedra can be controlled by tuning the annealing temperature. These self-assembled linear arrays of CoO nanocrystals result from the synergetic combination of the morphological transformation due to the intrinsic Rayleigh instability and the phase transformation due to the cobalt oxidation.

Conversion between EIT and Fano spectra in a microring-Bragg grating coupled-resonator system

A conversion between the electromagnetically induced transparency (EIT) transmission and Fano transmission is theoretically and experimentally demonstrated in an all-pass microring-Bragg grating (APMR-BG) coupled-resonator system. In this work, the coupling between the two resonators (the microring resonator and the Fabry-Perot resonator formed by two Bragg gratings) gives rise to the EIT and Fano transmissions. The resonant status strongly depends on the round-trip attenuation of the microring and the coupling strength. By tuning the coupling strength, the EIT and Fano transmissions can be controlled and converted. The device performance has been theoretically calculated and analyzed with a specially developed numerical model based on the transfer matrix method. The APMR-BG coupled-resonator systems with different gap widths were designed, fabricated, and characterized on a silicon-on-insulator (SOI) platform. The conversion of resonance was experimentally observed and verified. In addition, this on-chip...

Low Loss SOI Waveguides and MMIs at the MIR Wavelength of

In this letter, we demonstrate high-performance waveguides and MMIs on an SOI platform at the fixed wavelength of 2 μm. The propagation loss demonstrated by the waveguides and the insertion loss of the MMIs are as low as 1 dB/cm and 0.29 dB, respectively, with TE polarization. To the best of our knowledge, this is the lowest loss for Si rib waveguides reported at a wavelength of 2 μm.

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An all-pass microring-Bragg gratings (APMR-BG) based coupling resonant system is proposed and experimentally demonstrated to generate electromagnetically induced transparency (EIT)-like transmission for the first time. The coupling between two light path ways in the micro-ring resonator and the Fabry-Pérot (F-P) resonator formed by two sections of Bragg gratings gives rise to the EIT-like spectrum. This system has the advantage of a small footprint consisting of only one microring resonator and one bus waveguide with Bragg gratings. It also has a large fabrication tolerance as the overlap requirement between the resonance wavelengths of the microring and the F-P resonator is more relaxed. The two most important properties of the EIT-like transmission namely the insertion loss (IL) and the full-width-at-half-maximum (FWHM) have been analytically investigated by utilizing the specially developed model based on the transfer matrix method. The APMR-BG based coupling resonant system was fabricated on a silicon-on-insulator (SOI) platform. The EIT-like transmission with an extinction ratio (ER) of 12 dB, a FWHM of 0.077 nm and a quality factor (Q factor) of 20200 was achieved, which agree well with the simulated results based on our numerical model. A slow light with a group delay of 38 ps was also obtained.

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Based on restricted interferences mechanism in a 1x2 MMI beam splitter, we theoretically investigate and experimentally demonstrate an ultra-compact MMI-based demultiplexer for the NIR/MIR wavelengths of 1.55 μm and 2 μm. The device is fabricated on 340 nm SOI platform, with a footprint of 293x6 μm2. It exhibits extremely low insertion losses of 0.14 dB and 1.2 dB at the wavelengths of 1.55 μm and 2 μm, respectively, with contrasts of approximately 20 dB for both wavelengths, and a cross-talk of 18.83 dB.

Electromagnetically induced transparency-like effect in microring-Bragg gratings based coupling resonant system.

The synthesis, morphology, and magneto-transport properties of nanostructure-engineered charge-ordered Pr0.5Ca0.5MnO3 grown on ZnO nanowires are reported. The stability of the charge-ordering can be tuned, but more interestingly, the sign of the magnetoresistance is inverted at low temperatures. Coexistence of ferromagnetic clusters on the surface and antiferromagnetic phase in the core of the grains were considered in order to understand these features. This work suggests that such a process of growing on nanowires (NW) network can be readily extended to other transition metal oxides and open doors towards tailoring their functionalities.

Ultra-compact MMI-based beam splitter demultiplexer for the NIR/MIR wavelengths of 1.55 μm and 2 μm

On-chip twisted light emitters are essential components of orbital angular momentum (OAM) communication devices1, 2. These devices address the growing demand for high-capacity communication systems by providing an additional degree of freedom for wavelength/frequency division multiplexing (WDM/FDM). Although whispering-gallery-mode-enabled OAM emitters have been shown to possess some advantages3, 4, 5, such as compactness and phase accuracy, their inherent narrow bandwidths prevent them from being compatible with WDM/FDM techniques. Here, we demonstrate an ultra-broadband multiplexed OAM emitter that utilizes a novel joint path-resonance phase control concept. The emitter has a micron-sized radius and nanometer-sized features. Coaxial OAM beams are emitted across the entire telecommunication band from 1,450 to 1,650 nm. We applied the emitter to an OAM communication with a data rate of 1.2 Tbit/s assisted by 30-channel optical frequency combs (OFCs). The emitter provides a new solution to further increase capacity in the OFC communication scenario.

Switching magnetoresistance in vertically interfaced Pr0.5Ca0.5MnO3 grown on ZnO nanowires

Compact all-pass and add-drop microring resonators (radius=10  μm) integrated with grating couplers working at 2 μm wavelength are designed, fabricated, and characterized on a commercial 340-nm-thick-top-silicon silicon-on-insulator platform. They are suitable for high-volume integrated optical circuits at 2 μm wavelength as the fabrication process involved are uncomplicated and complementary metal-oxide-semiconductor (CMOS)-process compatible, thus making them more convenient to be utilized. The performance of the grating couplers, based on four most important parameters, has been simulated and optimized. The simulation and experimental results of grating couplers show the lowest coupling loss of 4.5 dB and 6.5 Db, respectively. By utilizing the grating couplers to couple light in and out from the chip, the designed microring resonators have been tested. The experimental results of microring resonators show that an extinction ratio of 12 dB and a quality factor of 11,200 can be achieved. To the best of our knowledge, this is thus far the smallest microring resonator ever demonstrated at this wavelength.

Ultra-broadband on-chip twisted light emitter for optical communications

Silicon photonics has traditionally focused on near infrared wavelengths, with tremendous progress seen over the past decade. However, more recently, research has extended into mid infrared wavelengths of 2 μm and beyond. Optical modulators are a key component for silicon photonics interconnects at both the conventional communication wavelengths of 1.3 μm and 1.55 μm, and the emerging mid-infrared wavelengths. The mid-infrared wavelength range is particularly interesting for a number of applications, including sensing, healthcare and communications. The absorption band of conventional germanium photodetectors only extends to approximately 1.55 μm, so alternative methods of photodetection are required for the mid-infrared wavelengths. One possible CMOS compatible solution is a silicon defect detector. Here, we present our recent results in these areas. Modulation at the wavelength of 2 μm has been theoretically investigated, and photodetection above 25 Gb/s has been practically demonstrated.