Kunhua Wen

Multiple Plasmon-Induced Transparency Responses in a Subwavelength Inclined Ring Resonators System

On the basis of single metal-insulator-metal (MIM) ring resonator (RR) structure, which acts as a band-stopped filter, a dual RR (DRR) system is proposed to obtain the plasmon-induced transparency (PIT) effect. By rotating the second RR an angle, double PIT windows are achieved due to the dual interference effects, which are attributed to different excitation pathways from the first RR to the second RR. In addition, triple PIT peaks are also achieved by adding an extra inclined RR to the DRR system. Phase shifts, which will occur at each transparency window, are also achieved and analyzed. These compact MIM waveguide structures may be used in the highly integrated optical circuits for biochemical sensors optical signal processing, and optical data storage.

Plasmonic-induced absorption in an end-coupled metal-insulator-metal resonator structure

An end-coupled composite-slot-cavity resonator (CSCR) is proposed based on the subwavelength metal-insulator-metal (MIM) waveguides. When compared with the perfect slot cavity, which acts as a Fabry–Perot resonator, plasmonic-induced absorption effect is achieved in the CSCR system. Single or dual absorption windows will arise at the former transmission peaks by arranging the position of vertical-slot cavity in the CSCR. According to the analyses on the phase responses, abnormal dispersions will be achieved inside the windows. Therefore, one can manipulate the fast-light applications in the nano-scale integrated circuits. Furthermore, based on the same interference effect, plasmonic-induced transparency response with normal dispersion is also obtained by changing the end-coupled CSCR system to a side-coupled one. The performances of the proposed structure are analyzed and investigated using the coupled mode theory and the finite-difference time-domain method, respectively.

Plasmonic-Induced Absorption and Transparency Based on a Compact Ring-Groove Joint MIM Waveguide Structure

Through adding a groove to an end-coupled perfect ring (PR) resonator, a ring-groove (RG) joint metal-insulator-metal (MIM) structure is proposed. Destructive interference for the expected surface plasmon mode will occur due to the phase differences between two optical paths, leading to the plasmonic-induced absorption response with abnormal dispersion, which is analogous to the electromagnetically induced absorption in the three-level atomic system. A transmission dip is achieved at the former-peak wavelength of the PR resonator, while two transmission peaks arise around the window. The proposed structure, which benefits from -0.3 ps group delay time, will be preferred in the ultrafast-light applications. Due to the same interference effect, plasmonic-induced transparency response with slow-light characteristic is also investigated by arranging the RG joint resonator to be a side-coupled configuration. Therefore, a new approach for on-chip light-speed control can be developed by using the proposed structures, whose performances are investigated by the finite-difference time-domain (FDTD) method and the coupled mode theory.

Fano Resonance Based on End-Coupled Cascaded-Ring MIM Waveguides Structure

Though adding a groove to a plasmonic end-coupled perfect ring (PR) resonator, two additional resonance modes, which can be controlled by the length of the groove, will arise in this proposed ring-groove (RG) joint metal-insulator-metal (MIM) waveguide. By further cascading, the PR resonator and the RG joint resonator, single and dual Fano resonances with asymmetric line shapes are obtained due to the interference effects between the dark modes and the bright modes. High figure of merit and high refractive-index sensitivity are achieved, and thus this structure is suitable for the biochemistry sensing area. Interestingly, normal and abnormal dispersions are also investigated for the Fano peaks and dips, respectively. The performances of the proposed structure are investigated by using the finite-difference time-domain method.

Tunable Multimode Plasmonic Filter Based on Side-Coupled Ring-Groove Joint Resonator

A tunable multimode plasmonic filter is proposed by using a side-coupled ring-groove joint resonator. In addition to the integer resonance modes of the perfect ring resonator (RR), extra non-integer resonance modes are excited by adding a groove on the RR. According to the simulations with finite difference time domain method, it is investigated that two integer and two non-integer modes are obtained. When the groove is placed on the antinodes of the magnetic fields, the effective resonance lengths for the corresponding modes will be changed by the groove. In this case, one can linearly manipulate the wavelengths by changing the length of the groove. On the contrary, the wavelengths of the specific modes will be always fixed when the groove locates at the nodes of the modes. Compared to those perfect structured Fabry-Pérot (FP) resonators, this compact device can provide more channels and manipulate the wavelengths flexibly. Therefore, it may find widely applications in the on-chip optical signal processing area.

Plasmonic Bidirectional/Unidirectional Wavelength Splitter Based on Metal-Dielectric-Metal Waveguides

A plasmonic bidirectional/unidirectional wavelength splitter based on asymmetric metal-dielectric-metal (MDM) waveguides is proposed. In the splitter, owing to the interference effects caused by the unequal phase delays from the two asymmetric arms of MDM waveguides, surface plasmon polaritons (SPPs) will only transmit through the output port that is close to the arm where constructive interference arises. The transmission wavelengths can be linearly modulated by changing the lengths of the arms. Since two different SPP modes are obtained in two output ports, respectively, the structure can act as a bidirectional wavelength splitter. Interestingly, both SPP modes can be manipulated to transmit through the same port by adding a notch in one arm. In this case, the notch must simultaneously locate at the anti-node and at the node of the magnetic fields of two SPP modes respectively. As a result, additional phase delay for the specific mode will be produced by the notch, but without any impact on the other mode. Then, the propagation directions of both modes will turn to be identical. High transmission and high cross-talk isolation are investigated for all the cases by using the finite-difference time-domain method.

Suppression of imaging crack caused by the gap between micromirrors in maskless lithography

Abstract. The digital micromirror device (DMD) is the key device in maskless lithography. However, because of the machinery manufacturing limit of DMDs, the gap between the micromirrors may destroy the continuity of the graphic. This work presents a simple way to fill the imaging crack by controlling the partial coherence factor σ of the light source. A crack can be regarded as the image of a dark space. By considering the resolving power for such cracks under partially coherent illumination, the images of such dark spaces can be covered, preventing them from being imaged on the substrate. By using mathematical derivations of the light intensity distribution exposed to the substrate, and by utilizing the diffraction effect induced by the finite aperture of the optical projection system, an appropriate σ value can be determined for eliminating the image of the crack in an actual scene. The numerical simulation results demonstrate that this method can ensure the continuity of the graphic at the critical partial coherence factor σc regardless of the shape of the target graphic.