Cheng Ren

High resolution three-port filter in two dimensional photonic crystal slabs

An in-plane, three-port filter consisting of input/output waveguides and two point-defect cavities in a 2D PC slab is designed and fabricated, where a new feedback method is introduced, and its transmission properties are measured. The measured minimum output wavelength spacing between two channels is 1.5 nm, which is realized by slightly adjusting the size of the resonant cavities. The measured resonant wavelengths of two cavities agree well with the calculated ones and the quality factors of the cavities are almost the same. It is believed that this kind of filter may be useful in optical integrated circuits with high density.

Multichannel filters with shape designing in two-dimensional photonic crystal slabs

We investigated the influence of the irregular shape of air holes on the optical characteristics of channel-drop filters built in a two-dimensional photonic crystal slab. Three differently shaped structures are tested by experiments and simulations to demonstrate the shape-tuning capability of the optical devices. A four-channel filter based on this shape design is presented. The photonic crystal consists of a triangular array of air holes fabricated by focused ion beam lithographic technology on a silicon slab with thickness of 260 nm. The filter contains a heterostructure with different lattice constants of 420 and 430 nm. In each channel, the filtering functionality is guaranteed by the indirect resonant coupling between waveguide and cavity. The elliptical air holes that surround the cavity have different parameters, and this leads to a fine tuning of the cavity’s resonant frequencies. The performance of the multichannel filter is found to be very encouraging.

Multichannel filters via Γ-M and Γ-K waveguide coupling in two-dimensional triangular-lattice photonic crystal slabs

We demonstrate the design, fabrication, and characterization of a multichannel filter in a two-dimensional triangular-lattice photonic crystal slab. The output signal channel, which directs in the Γ-M crystalline direction, is orthogonal to the input signal channel that directs in the Γ-K crystalline direction. In each channel, the filtering function is guaranteed by the indirect resonant coupling between the waveguide and the cavity. Four resonant cavities with different sizes provide the mechanism of finely tuning the output wavelength. Our experimental results are in good agreement with simulations.

Near-field observation of anomalous optical propagation in photonic crystal coupled-cavity waveguides

An air-bridged silicon-based photonic crystal coupled-cavity waveguide (PCCCW) connected with an input and output W1 PC waveguide (PCW) was designed and fabricated. We mapped its intensity distributions with a near-field scanning optical microscope (NSOM) at near-infrared wavelengths around 1550 nm. Surprisingly, the intensity distributions demonstrate that the second odd eigenmode dominates in such a PCCCW, even though it possesses a much slower group velocity of light than that of the first even one. Further considering the measured transmission spectrum, we find that the modal profile and impedance matching between the eigenmodes in the PCW and PCCCW plays an important role in the optical propagation efficiency. Mode conversion between the first even and the second odd eigenmode was also detected at the interfaces between the W1 PCW and PCCCW.

Optical improvement of photonic devices fabricated by Ga+ focused ion beam micromachining

The authors propose a novel post-focused-ion-beam (FIB) treatment method to improve the optical properties of photonic devices fabricated by the Ga+ FIB technique on the silicon substrate with low temperature liquid annealing process. A conventional micrometric ridge waveguide is first fabricated and then annealed to roughly detect the improvement of its optical properties. Then a nanometric 12-fold photonic quasicrystal waveguide is designed to further study its topography variation as well as the subtle influence on its optical properties with different post-FIB treatments. By comparing the experimental results with the theoretical results that are made by means of the three-dimensional finite-difference time-domain method, the authors find that the proposed low temperature liquid annealing method can efficiently improve the optical properties of photonic devices by decreasing Ga+ contamination, removing redeposited Si–SiO2 composites, and restoring damaged silicon lattice structures caused by Ga+ bomba...

Evolution of dislocation loops in He ion irradiated nickel under different temperature

The effect of temperature on the evolution of loops in nickel was investigated under 30 keV He+ irradiation. The size, Burgers vector, and nature of loops were analyzed by a transmission electron microscope (TEM). In addition, the Weibull statistical analysis was introduced to analyze the size distributions of the loops. The TEM results indicate that the sizes of loops increase with increasing irradiation temperature, where they are mainly in the range of 10–30, 20–50, and 30–80 nm at 300, 400, and 500 °C, respectively. In the irradiation temperature range of 300–500 °C, the size distributions of loops fit Weibull distribution very well, which suggests that the loops tend to grow larger and/or be merged. In addition, almost all the loops formed under He+ irradiation are the interstitial loops with Burgers vectors b =   a2⟨110⟩, which is ascribed to the assistance of the He atom on the formation process of loops.

TWO-DIMENSIONAL SILICON-BASED PHOTONIC CRYSTAL SLAB WITH PARTIAL AIR-BRIDGE

We describe a fabrication process of the near-infrared two-dimensional photonic crystal (PC) slab, which is sustained by part of the silica layer underneath the slab and forms a partly air-bridged type. The process involves focused ion beam (FIB) direct write following the selective wet etching of silicon on isolator (SOI) structures. By control the time of dissolving of silica layer in SOI, we successfully fabricated the sample and measured its transmittance spectrum. It is found that the observed spectrum is consistent with the theoretical band structure with FDTD method. For there is partly silica layer remained to support the air-bridge slab, the PC can be fabricated with a large area. If we change the support material under the slab, we might be able to fabricate PC laser with this kind of structure.

Y-TYPE PHOTONIC CRYSTAL WAVEGUIDE WITH MINIMUM BRANCHES SPACE

The abstract should summarize the context, content and conclusions of the paper in less than 200 words. We fabricated a two-dimensional Y-branch photonic crystal waveguide in the near infrared region by using focused ion beam etching and depositing system. The light guide characters of the waveguide were measured for three different spaces between branches. Field intensity distributions of TE polarized wave in the branches were simulated by using the transfer matrix method. Both the theoretical and experimental results show that the shortest space between branches of the photonic crystal waveguide is about 1.4 times wavelength of transmitted light. If the space became shorter, the light in the two branches would couple to each other seriously. This result might be helpful for the design of compact wave demultiplexer and all-optical integrated circuits.