Jiangbing Du

Coupling in dual-core photonic bandgap fibers: theory and experiment

We have theoretically and experimentally investigated dual-core photonic bandgap fibers (PBGFs), which consist of a cladding with an array of high-index rods and two cores formed by omitting two nearby rods. We find novel features in their coupling characteristics such as maxima and minima in coupling length, complete decoupling of the cores, and an inversion of the usual ordering of supermodes so that the odd supermode has the higher propagation constant. This behavior is understood by considering the field distribution in the rods between the cores.

Electrically tunable Sagnac filter based on a photonic bandgap fiber with liquid crystal infused

We demonstrate an electrically tunable Sagnac filter based on a photonic bandgap fiber that is realized by infusing liquid crystal into a solid-core air-hole photonic crystal fiber. The filter enables an electrical tuning with a range of about 26 nm for one single interference minimum in the transmission bandgap from 1330 to 1650 nm wavelength. The tuning efficiency is averaged to 0.53 nm/V.

Photonic crystal fiber based Mach-Zehnder interferometer for DPSK signal demodulation

We demonstrate a novel fiber-based in-line DPSK demodulator using an in-fiber Mach-Zehnder interferometer (MZI). The device is fabricated by mismatch splicing of a photonic crystal fiber (PCF) with standard single mode fibers. The spectral characteristics at different PCF lengths are analyzed. The envelope of the interference fringes show a period that is inversely proportional to the PCF length, and is attributed to the periodic coupling between the core mode and the cladding mode. Error free demodulations of 10-Gb/s RZ- and NRZ-DPSK signals have been demonstrated using the in-fiber PCF-MZI demodulator with only 3-m PCF to introduce 91-ps delay. Wideband DPSK demodulation has also been achieved.

Liquid crystal photonic bandgap fiber: different bandgap transmissions at different temperature ranges

The temperature tuning properties of a liquid crystal (LC) photonic bandgap fibers bandgap transmission was investigated in this study. Because of the special temperature responses of the LCs indices and its phase transition property, the bandgap transmission was found to have different temperature responses at different temperature ranges below the LCs clearing point temperature. At temperatures lower or higher than the LCs clearing point, the bandgap transmissions are quite different, which permits switching with an extinction ratio as large as 45 dB. At temperatures around the LCs clearing point, the bandgap transmission was depressed.

All-Optical RZ-to-NRZ and NRZ-to-PRZ Format Conversions Based on Delay-Asymmetric Nonlinear Loop Mirror

We perform all-optical return-to-zero (RZ) to nonreturn-to-zero (NRZ) and NRZ to pseudoreturn-to-zero (PRZ) format conversions at tunable bit rates, both by using the same delay-asymmetric nonlinear loop mirror. The temporal and spectral characteristics of the input and output signals are analyzed. Bit-error-rate measurements of RZ-to-NRZ conversion at 10 and 12.5 Gb/s show error-free performance with power penalties less than 3 dB with reference to the input RZ signals.

Sensitivity enhanced strain and temperature measurements based on FBG and frequency chirp magnification.

In this work, highly sensitive measurements of strain and temperature have been demonstrated using a fiber Bragg grating (FBG) sensor with significantly enhance sensitivity by all-optical signal processing. The sensitivity enhancement is achieved by degenerated Four Wave Mixing (FWM) for frequency chirp magnification (FCM), which can be used for magnifying the wavelength drift of the FBG sensor induced by strain and temperature change. Highly sensitive measurements of static strain and temperature have been experimentally demonstrated with strain sensitivity of 5.36 pm/με and temperature sensitivity of 54.09 pm/°C. The sensitivity has been enhanced by a factor of five based on a 4-order FWM in a highly nonlinear fiber (HNLF).

Multiband Three-Dimensional Carrierless Amplitude Phase Modulation for Short Reach Optical Communications

Multi-dimensional carrierless amplitude phase (CAP) modulation attracts a lot interest in recent optical communications as an advanced modulation format with improved performance. In this paper, we have demonstrated a multiband three-dimensional CAP (3D-CAP) modulation scheme and investigated its applications in short reach optical communication systems. Corresponding digital filters are designed by minimax algorithm with additional linear constraint to avoid the coding intersymbol interference. The performance of the digital filters is analyzed for optical fiber links with data rate over 100 Gb/s based on simulations. Similar to discrete multitone technique, several independent bands can be loaded with different 3D-CAP signals in the proposed multiband 3D-CAP system, offering improved tolerance to non-flat channels. 2-km single mode fiber transmission at total bit rate of 112.5 Gb/s is investigated through simulations and the results indicate better performance of multiband 3D-CAP compared with conventional 3D-CAP in short reach optical communication.

Ultrawideband monocycle pulse generation based on delayed interference ofπ/2 phase-shift keying signal

We propose a scheme to generate ultrawideband (UWB) monocycle pulses using delayed interference of a π/2 phase-shift keying (PSK) signal. The PSK signal is generated with an optical phase modulator. A fiber-based delay interferometer is used to provide the delay together with a ±π/2 phase shift between the signals in its two arms before the interference. The two opposite phase shifts correspond to the generation of a pair of polarity-reversed UWB monocycle pulses. The full width at half maximum of the pulses is ~68 ps and the 10 dB fractional bandwidth is 168%.

Cascaded and Multisection Sagnac Interferometers for Scalable and Tunable All-Optical OFDM DEMUX

With cascaded and multisection Sagnac interferometers, all-optical fast Fourier transform (FFT) has been demonstrated for optical demultiplexing (DEMUX) of orthogonal frequency division multiplexing (OFDM) signals. The transmission characteristics of the interferometers have been investigated theoretically and experimentally. The scalability and tunability of the all-optical OFDM DEMUX are analyzed and demonstrated for 5-channel OFDM signals.

Reconfigurable two-channel demultiplexing using a single baseband control pulse train in a dispersion asymmetric NOLM.

We demonstrate a unique solution to use a one-pulse control to achieve simultaneous two-channel all-optical demultiplexing that usually requires a two-pulse control or a two-step operation based on the conventional approaches. By applying a dispersion asymmetric nonlinear optical loop mirror (DA-NOLM) to introduce cross phase modulation (XPM) in both the clockwise (CW) and the counter clockwise (CCW) propagating branches, we have demonstrated reconfigurable, error-free 40-to-10 Gb/s two-channel demultiplexing (DEMUX) for OTDM OOK signals. Switchable operation between two-channel and single-channel DEMUX is also realized based on the proposed all-optical DEMUX configuration.