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We present a reverse solving design approach to achieve accurate control over the response shapes and resonant peak positions of channel dropping filters implemented by coupled microring resonators. From performance to geometry, we obtain the geometric parameters based on the layout connecting multiple cells consisting of two straight waveguides and one microring in series to achieve the desired filter performance. We discuss the theoretical limit that the filters can reach and how to obtain the geometric parameters corresponding to the desired response reversely. Finally, the numerical simulations are carried out, and the results agree well with theoretical analysis, verifying the efficacy of our approach.

We present an approach to modify emission spectra of amplifiers by local density of states engineering with structured waveguides. More specifically, an inverse design algorithm is adopted to obtain the geometric parameters of the proposed structure that meets the local density of states target. The finite-difference time-domain numerical results indicate that the 3 dB bandwidth and the figure of merit on flatness in the structure we propose grow by over 22% and 32%, respectively, compared with the values of the typical reference baseline.

We propose theoretically a tunable circular Bragg microcavity to enhance the intensity of the emission band of interest in rare-earth-doped materials and to suppress the unwanted emission bands which produce noise and diminish the efficiency of the emission of interest. The surrounding of the microcavity comprises of alternating layers of high-index and low-index materials. The luminescent ions such as neodymium Nd3+ having different emission bands in different host materials are placed in the microcavity, and single emission band with stronger intensity can be observed, and other emission bands are suppressed. The wavelength of the single emission peak can be changed from one wavelength to other wavelengths by varying the refractive index, radius of the microcavity and thus modifying the local density of states of the microcavity. The fluorescence branching ratio of emission band of interest can be enhanced from 10% to 100% due to suppression of the unwanted emission bands.

Thermocrystals constitute a new type of periodic material that can be used to control heat flow. An important issue is how to widen the bandgap of thermocrystals to cover more of the thermal spectrum, and this is related to the efficiency of manipulating the transport of heat flow in a thermocrystal. In this letter, a one-dimensional supercrystal composed of multiple lattices is proposed, and the dispersion relation and heat flux transmittance of thermocrystals and thermo-supercrystals are simulated. The results show that supercrystals are effective for widening the bandgap of thermal phonons; thus, supercrystals are more efficient at preventing thermal phonons than are thermocrystals. As an example, the thermal conductivity is reduced by 37% in a supercrystal with five different lattice constants, compared to a reduction of only 19.6% in thermocrystals. This supercrystal can be used to achieve an effective thermal-conductivity barrier with general materials, which will be very important for manipulating heat conduction.

In this paper, we theoretically present a silicon photonic-crystal waveguide for waveband de-multiplexing. The waveguide is composed of three different microcavities, and three output ends. The three different microcavity waveguide branches allow the respective resonant wavelength channels go from the waveguide input end to the respective output end. The air hole and microcavity sizes are properly designed so that the microcavity waveguide can realize the respective transmission spectrum. With air-holes square array structure, the presented waveguide can apply to an optical window covering λ = 1.2–1.8 µm. The analytical techniques and numerical results indicate that the peak transmission at the three optical windows could reach 86.6%, 63.5% and 97.7%. This waveguide could provide a potential use as a building block of integrated photonic circuits. Keywords: Photonic crystal, Microcavity, De-multiplexer, Bandgap

We report the transmission and reflection properties of graphene-SiO2, graphene-Si interface with normal incidence. We analyze the real and imaginary parts of Graphene in a broad wavelength range 0.5–4.0 µm and use both Fresnel theory and Finite-difference Time-domain (FDTD) numerical simulations to calculate the transmittance and reflectance. The theoretical and numerical results show that the transmission and reflection on the interfaces mentioned above have a anormal phenomenon. The physical mechanism for anormal phenomenon is analyzed. Between 100 nm and 500 nm wavelength, the transmission and the reflection of graphene-SiO2 layer and graphene-Si layer have some sharp change. When the wavelength is more than 500 nm, the transmission and reflection of the two layers mentioned above have been a regular curve without sharp change. The transmission and reflection of the graphene layers is the order of 1.0, zero, respectively. These findings can pave new way for the active optoelectronic devices. Keywords: Graphene-dielectric interface, Broadband transmission, Optical property

We present a theoretical model to describe emission spectrum of an emitter in a micro-cavity. Our model proposes that the spectrum in a metal micro-cavity depends on the product of the emission spectrum in free space and the local density of states (LDOS) in the cavity which the emitter is placed in. Since Purcell effect can enhance LDOS of a micro-cavity, the emission intensity of an emitter is directly proportional to LDOS depending on the geometry of microcavity. Thus, the model predicts that the spectrum of an emitter can be modified as a narrow spectrum in microcavity possessing sharp LDOS spectrum, also can be modified as broadband spectrum with broadband LDOS spectrum. Finite-difference time-domain (FDTD) numerical simulations support our prediction. Keywords: Emission spectrum, Emitter, Microcavity, Local density of states