Changqiu Yu

Nested fiber ring resonator enhanced Mach–Zehnder interferometer for temperature sensing

We numerically investigate the properties of the nested fiber ring resonator coupled Mach-Zehnder interferometer as a sensor. By introducing the phase bias of 0.5π in the reference arm, the two output intensities exhibit sharp asymmetric line shapes around the resonance wavelength. Utilizing the intensity interrogation, we analyze the effect of parameters on the sensitivity and the detection limit. For the 30 dB signal-noise system, the sensitivity and the detection limit can achieve 4.0866/°C and 7.341×10(-3)°C, respectively; the results indicate that this structure is suitable for high-sensitivity measurements.

The lifetime of the triplet excited state and modulation characteristics of all-optical switching in phenoxy-phthalocyanines liquid

We present our experimental results on the measurements of excited state dynamics in 2, 9, 16, 23-phenoxy-phthalocyanine (Pc1) and 2, 9, 16, 23-phenoxy-phthalocyanine-zinc (Pc2) using the pump-probe experiment. The results show that the lifetime of the first triplet excited state of the Pc2 longer than Pc1. The lifetimes of the triplet excited state for Pc2 and Pc1 are 12.8 μs and 10.1 μs at the same intensity, respectively. Moreover, analysis of modulation characteristics of all-optical switching (A-OS) shows that the stronger the light intensity of the pump light is, the smaller the normalized transmittance is, and the lower the A-OS response time is. The consequences of such short lifetimes are also discussed in view of the strong A-OS properties of these molecules.

Tunable Fano resonance in a single-ring-resonator-based add/drop interferometer

We theoretically study a single-ring-resonator-based add/drop interferometer to achieve tunable Fano resonance. The Fano resonance results from the interference of two resonant beams propagating in the ring resonator. The line shapes of the Fano resonance are tunable by controlling the coupling coefficients between the waveguide and ring resonator. The spectra of the drop port and through port of the add/drop interferometer are horizontally mirror-symmetric. A box-like spectral response can be produced with the proper coupling coefficient owing to the double resonances. When the phase difference between the two light inputs to the add/drop interferometer is compensated, a doubled free spectral range can be obtained.

Electromagnetically induced-transparency-like spectrum in an add/drop interferometer

We propose a single-ring-resonator-based add/drop interferometer and theoretically investigate the transmission characteristics. Due to coherent interference of two resonant pathways, an electromagnetically induced-transparency (EIT)-like spectrum is produced and the line shapes of the transmission spectra are tunable by controlling the coupling coefficients between the waveguide and ring resonator. We observe the EIT-like behavior in a fiber system which agrees well with the theoretical analysis. The proposed configuration has potential applications in tunable delay lines.

A double-ring Mach?Zehnder interferometer sensor with high sensitivity

We theoretically proposed a cost-effective refractometer sensor, which includes an unbalanced two-ring Mach–Zehnder interferometer and can exhibit sharp asymmetric Fano lineshape. Our calculated results show this device has high sensitivity and can measure refractive index change in one of the resonators down to 10−9 refractive index units, which is two orders of magnitude higher than previous Fano lineshape based sensors.

Observation of EIT-like spectrum in the eye-like ring resonator

We theoretically analyze the electromagnetically induced transparency (EIT)-like spectrum in the Eye-like resonator configuration. The EIT-like spectrum results from the interference between the inner ring and the outer ring. In this paper, we obtain a tunable group delay and bandwidth of the transparency window through changing the coupling coefficients and the attenuation factors of the inner and the outer ring. The tunable group delay and the bandwidth will have potential application in optical switching or tunable delay lines and tunable bandwidth filter.

Tunable optical delay line based on micro-ring resonators

We theoretically investigate the series-coupled double micro-ring resonator as tunable optical delay line. Tunable optical delay line can be achieved by tunable self-coupling coefficient and attenuation factor of micro-ring waveguide. Through choosing suitable parameters of structure, the series-coupled double micro-ring resonator can obtain flat delay line that mitigates the deleterious effects of group delay dispersion.

Tunable Fano resonance based on add-drop ring resonator structure

We theoretically and experimentally study an add-drop ring resonator to achieve tunable Fano resonance. In this system, the Fano resonance results from the interference of two beams from add and through port. The line shapes of the Fano resonances are tunable through controlling the phase bias of the two beams from add and through port. At the same time, add-drop ring resonator structure enabling the truly on/off switching mechanism is realized when the phase bias is 0 or π. The experimental results well agree with the theoretical calculation.

Fano Resonances based on Nanoscale Plasmonic structure

The interaction between plasmonic resonances, sharp modes, and light in nanoscale plasmonic systems often leads to Fano interference effects. This occurs because the plasmonic excitations are usually spectrally broad and the characteristic narrow asymmetric Fano line-shape results upon interaction with spectrally sharper modes. We investigate a plasmonic waveguide system using the finite-difference time-domain (FDTD) method, which consists of a metal-insulator-metal waveguide coupled with a rectangle and a ring cavity. Numerical simulations results show that the sharp and asymmetric Fano-line shapes can be created in the waveguide. Fano resonance strongly depends on the structural parameters. This has important applications in highly sensitive and multiparameter sensing in the complicated environments.

Uniform flat-top interleaver consisting of a two-stage cascaded Mach-Zehnder interferometer

We theoretically investigate an all-fiber interleaver consisting of a two-stage cascaded Mach-Zehnder interferometer (MZI). The simulation results of the all-fiber interleaver presented symmetrical and asymmetrical output spectra and a uniform flat-top spectral response by changing the coupling coefficient of the couplers. In addition, the interleaver proposed can realize arbitrary passband width ratio between the two output ports by adjusting the coupling coefficient of the couplers involved. A near box-shaped spectral response can be generated through setting suitable parameters, at the same time, the passband and stopband of optical interleaver are improved significantly. This interleaver proposed should be useful to realize the deployment of flat-top all-fiber asymmetric interleaver in dense wavelength division multiplexing (DWDM) networks of high spectral efficiency.