Kaiyang Wang

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.

Plasmon resonance of silver micro–sphere in fiber taper

We have experimentally studied the plasmon resonance phenomenon of a silver micro-sphere with a diameter of 2.3 μm in cone-shaped air cavity of a hollow fiber taper. To take insight into the plasmon resonance phenomenon, we move the micro-sphere along the fiber and observe the significant shift of the resonance peak. We also explore the light response in both infrared and visible wavelength band by finite difference time domain method. The significant variations of the magnetic and power field distribution are observed. The interesting results imply that the configuration has great potential in optical sensors and color filters.

Reconfigurable dual-channel dropping filters based on a self-coupled resonator Sagnac interferometer

We report a reconfigurable dual-mode resonator-based dual-channel dropping filter. The dual dropping channels are generated within a free spectral range (FSR) via the interference between the electromagnetically induced transparency (EIT)-like and electromagnetically induced absorption (EIA)-like resonances despite only one resonator used. The reconfiguration of the dual channels enabling the truly on/off switching mechanism is realized, and the output modes resembling the add/drop/neutral states are provided. The compact, reliable, flexible, versatile, and extendable filter has profound implications for wavelength division multiplexing (WDM) applications in optical interconnection networks.

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.

Performance of a resonator-based interferometric fiber-optic gyroscope under the square wave phase bias modulation

We propose the modulation period and amplitude of the typical square wave phase bias modulation (SWPBM) applicable to a resonator-based interferometric fiber-optic gyroscope (R-IFOG) and theoretically study the performance of the R-IFOG under SWPBM. Under SWPBM of the proposed modulation period and amplitude, the R-IFOG possesses a performance distinct from that under the hypothetical time-independent phase bias. Also, the sensitivity of the R-IFOG with SWPBM to a slow rotation rate is boosted in comparison to that without phase bias, and the rotation direction can be indicated. Furthermore, the ultrahigh sensitivity can be attained by an R-IFOG of an extremely short fiber length when the R-IFOG with SWPBM consists of a high finesse resonator. Therefore, the SWPBM of the proposed modulation period and amplitude enables highly sensitive and compact integrated closed-loop R-IFOGs.

Experimental observations of the transition from fast light to slow light in a side-coupled ring resonator

We report the experimental observation of dispersion transition from abnormal dispersion (fast light) to normal dispersion (slow light) in a side-coupled ring resonator. We reveal that the transition from fast light to slow light can occur, when the tuned loss of the resonator results in the experience from the undercoupled regime to the overcoupled regime. Also, we experimentally fabricate the fiber side-coupled ring resonator, and measure the group delay of the resonator by coupling the resonator to a fiber Mach-Zehnder interferometer (MZI). The measured experimental results demonstrate the dispersion transition, and are in good agreement with the corresponding theoretical results. The sidecoupled resonator with the tunable dispersion (group delay) can exploited for optical storage devices, slow light Fourier transform (FT) interferometric spectrometers, white light cavities (WLCs), optical switches, optical routers, and optical sensors.

Observation of EIT like spectrum in the nested fiber ring resonator

We demonstrate the electromagnetically induced transparency like spectrum in the nested fiber ring resonator with the transfer matrix theory; the system consists of two rings and two waveguides which are connected by four couplers. The simulation results show that the tunable group delay can be realized by changing the coupling coefficients. At transmission window, the transmittance can achieve approximately 97.2% with the 0.05ns group delay. Through tuning the coupling coefficients, the group delay can vary from 0.05ns to -21.23ns and the bandwidth of the transparency window can vary from 37MHz to 15MHz.The ability for realizing such transparency resonance and for controlling the group delay or the bandwidth of such resonance is important for applications such as optical switching, as well as tunable bandwidth filter applications.

Improving the performance of Mach?Zehnder interferometer with the dispersion response of the add-drop ring resonator

We use the add-drop ring resonator (ADRR) to produce the normal and anomalous dispersion simultaneously and apply these two dispersion responses to enhance the sensitivity of the Mach–Zehnder interferometer (MZI). To estimate the sensing ability of the ADRR assisted MZI, the dispersion sensitivity of the structure is theoretically and experimentally demonstrated. For two equal amplitude coupling coefficients, a 19.2-fold increase in the dispersion sensitivity is experimentally achieved, a little lower than 19.5-fold predicted in theory. This value can be futher increased by minimizing the attenuation or by choosing different amplitude coupling coefficient settings at different coupling regions. To acquire better dispersion sensitivity, only output port one should be utilized at the over-coupling region, and two output ports should be adopted at the under-coupling region.

Fano resonance with tunablity in a single ring resonator based on add/drop interferometer

Theoretical investigation in a single resonator based add/drop on interferometer was made to achieve Fano resonance. The results show Fano resonance is tunable by controlling the coupling coefficients between the waveguide and ring resonator.