Jinkun Liao

A novel scheme for 1×N optical power splitter

A novel 1 × N optical power splitter has been proposed, to realize the desired specific optical power splitting, in which the asymmetric Y-branch waveguides based on total internal reflection have been introduced. The simulated results show that the arbitrary expected splitting can be achieved in the device. The device has been fabricated by using polymer materials, and it experimentally exhibits good uniformity at optical power output ports, which is consistent with the simulation prediction. The novel 1 × N optical power splitter has wide potential application in the integrated optical system.

Design and analysis of a novel tunable optical power splitter

A novel tunable optical power splitter, with a Y-branch waveguide based on the total internal reflection and a microprism with tunable index refraction, is presented. Numerical simulation of its optical performance shows that a high dynamic range, low optical loss, and relatively low wavelength-dependence can be achieved. This component offers numerous advantages such as ease for fabrication, low cost, and compact size, which are very useful for potential application in integrated optical devices.

Dark pulse generation in a dispersion-managed fiber laser

We report an experimental observation of dark pulse generation in a dispersion-managed erbium-doped fiber laser with net anomalous cavity group-velocity dispersion. It is found that apart from the bright soliton pulses, dark pulses with spectral sidebands could be obtained in the laser under appropriate operating conditions. The generation of dark pulses may be attributed to soliton shaping in the cavity.

Numerical simulation on spectral compression of frequency-shifting femtosecond pulses in photonic crystal fiber

We present a numerical investigation of nonlinear propagation of femtosecond pulses in photonic crystal fibers (PCFs) by solving the generalized nonlinear Schrodinger equation. The PCFs have a second-order dispersion of -48 ps2/km, nonlinear coefficient of 115 W-1km-1, and third-order dispersion (TOD) ranging from 0.1 ps3/km to 1 ps3/km at 1550-nm wavelength. The simulation results show that efficient spectral compression of ultrashort pulses can be induced in the regime of soliton self-frequency shift (SSFS) in PCFs when the input pulse parameters satisfy the condition 0.9 ≤N ≤ 1.2 for the soliton order N. It is found that the output spectral width is dependent on the peak power of input pulse and the PCF length. A spectral-compression factor up to 2.2 can be achieved for 50-fs, 1550-nm solitons propagating through 10-m PCF with a TOD of 0.5 ps3/km, where the soliton wavelength shifted from 1550 nm to 1698 nm. The effect of initial pulse chirp on output spectral width can be negligible for large PCF length. Greater spectral-compression factor can be obtained using PCF with larger TOD value. This SSFS-based spectral-compression scheme offers much promise for generation of narrow line-width tunable light sources in photonic applications.

Novel Approach for Controllable Polarization Beam Splitter: Design and Simulation

A novel controllable polarization beam splitter is designed by using the modified Y-branch waveguide structure, in which the nematic liquid crystal is introduced. The optical performance of the polarization beam splitter is numerically investigated by the beam propagation method. The results show that not only can high extinction ratio and low optical loss be easily achieved, but also the output ports for TE and TM modes can be dynamically interchangeable in our configuration. Moreover, the proposed polarization beam splitter has little wavelength dependence and large fabrication tolerance. This firstly proposed device provides a unique approach for the manipulation of polarization splitting, which has wide potential application in the photonic integrated circuits.

2×2 polymeric electro-optic MZI switch using multimode interference couplers

We present the design of a 2×2 photonic switch operating at 1.55-μm wavelength using electro-optic (EO) polymer waveguides. A Mach-Zehnder interferometer (MZI) is used to implement the proposed switch in which two identical 2×2 multimode interference (MMI) couplers are connected by two identical parallel single mode waveguides (two MZI arms). These two single-mode waveguides with electrodes allow modulating the phase difference between the two MZI arms based on the EO effect. In the proposed switch, the EO polymer, IPC-E/polysulfone, is used for the core layer of optical waveguides. UV15 and NOA61 are employed for the lower and upper cladding layers, respectively. The singlemode waveguide structure and 2×2 MMI coupler have been designed and analyzed for the EO switch. Device performance has been simulated using the beam propagation method. It is found that the switch performance is most sensitive to the MMI width and less sensitive to the MMI length. Optimized structure has been obtained for the 2×2 polymeric EO switch, which has a crosstalk level better than -25 dB and insertion loss lower than -1.8 dB. This performance makes the switch a potential candidate for practical use in photonic systems.

Passively mode-locked femtosecond fiber laser using a SESAM

We present an investigation of spectral dynamics of an ultrashort-pulse Er-doped fiber laser mode-locked by a semiconductor saturable absorber mirror (SESAM). The SESAM used has a saturable absorption modulation depth of 18%, a saturation fluence of 70 μJ/cm2 and a relaxation time of 10 ps at a wavelength of 1550 nm. Detailed pulse dynamics of the laser are measured at different pumping levels, and the laser operation is linked to the characteristics of the SESAM. It is observed that, as the pump power is increased, the laser operation changes from cw lasing, to self-Q switching, Q-switched mode-locking, and then cw mode-locking. Self-starting and stable mode-locking operation is achieved at a repetition rate of 12 MHz. The pulses with a width of 650 fs are produced at 1562-nm wavelength with a pump power of 80 mW, and the corresponding spectral width is about 5.0 nm (FWHM). Based on the complex Ginzburg-Landau equation, self-starting mode-locking process in the fiber laser is simulated, which confirms that ultrashort pulses can be achieved. The calculated spectral characteristics of the mode-locked pulses are consistent with the experimental observations.

Poling and characterization of a novel organic/polymer electro-optic material

Electro-optic organic/polymer material is important for the fabrication of polymer integrated optic-electronic devices and organic sensors. Recently, a novel organic high μβ value chromophore FFC have been synthesized by molecular design. The absorption spectrum in 400-4000 cm-1 is measured for the material, and the measurement result shows that the absorption loss is negligibly small. An organic/polymer high electro-optic activity material FFC/PSU is obtained by dissolving guest FFC (wt. 20%) and a host polysulfone (PSU) in a solvent. The resolvability of cyclohexanone for the material is satisfactory by comparison with other solvents experimentally, and the preparation of FFC/PSU thin film is ease relatively. The materiel is poled by electric field-assisted contact poling, and the near optimum poling condition is determined by adjusting poling parameters as pre-curing duration, poling temperature and poling voltage etc. The electro-optic coefficient of the material is measured as high as 130pm/V by using the widely accepted simple reflection technique. The investigation indicates that the FFC/PSU has excellent characteristics, such as high electro-optic coefficient, low absorption loss, good thermal stability and capability for withstanding the subsequent process techniques, suitable for the fabrication of high-performance integrated optic-electronic devices and sensors.

Three-photon absorption in MgO-doped LiNbO 3 crystal

Three-photon absorption in MgO-doped LiNbO3 crystal has been investigated using the Z-scan and pump-probe techniques with femtosecond pulses at 780-nm wavelength. The microscopic origin for the observed optical nonlinearity is discussed.

Analysis of Characteristic for Polymer Asymmetric Rib Waveguide

For organic polymer asymmetric rib waveguide, the fundamental mode cut-off conditions, the single-mode conditions and the polarization characteristics were studied systematically under different rib height, rib width, core height and the short side width of core slab by means of semi-vector finite-difference beam propagation method. The results showed that both fundamental mode cut-off area and the single-mode area increased with the reducing of rib height and rib width and the single-mode area decreased with the reducing of the short side width of core slab at a certain core height. The effect of core height was small on the fundamental mode cut-off and single-mode conditions at a certain rib height or rib width. In the asymmetric ridge waveguide the polarization characteristic had not been changed basically and the birefringence decreased with decreasing of the short side width of core slab. The results had great referential value for application of the organic polymer asymmetric rib waveguide.