Chengju Ma

Slow-light element for tunable time delay based on optical microcoil resonator

We propose a simple and compact slow-light element by use of an optical microcoil resonator (OMR) constituted by two microfiber coils. Based on the matrix exponential method, we solve the coupled-wave equations of the OMR with n turns of microfiber coils and obtain a general solution. Simulations indicate that a tunable slow-light propagation can be obtained by controlling the coupling coefficient between the two adjacent microfiber coils by means of regulating the voltage applied to the ferroelectric crystal. A slow-light time delay up to 62 ps with a bandwidth of 0.4 nm is performed at the wavelength around 1.5 μm.

Design and fabrication of tapered microfiber waveguide with good optical and mechanical performance

In this paper, the inherent dependence of optical and mechanical characteristics of tapered microfiber waveguide on its contour profile is studied. Both theoretical analysis and experimental investigation are given. In theory, the optimal profile parameters of the tapered microfiber are proposed to improve the microfiber performance, where it is better to make the tapered microfiber keep two longer than 5-mm-long transition regions which have a decaying exponential profile. And the uniform waist diameter of the tapered microfiber should be more than 600 nm and less than 1 μm. In this case, the microfiber indicates several favorable advantages, such as low loss, strong evanescent field and relatively shorter transition region. In experiment, according to the profile parameters we proposed, we successfully fabricated a tapered microfiber with a low loss of 0.05 dB in air and 0.8 dB on a MgF2 substrate at the wavelength of 1550 nm, and it has low surface roughness.

Wideband slow light in microfiber double-knot resonator with a parallel structure

The characteristics of slow light in the microfiber double-knot resonator with a parallel structure are investigated both theoretically and experimentally. It is predicted that a wide bandwidth of about 20 GHz and flat-top group delay of about 70 ps can be generated in this resonator by changing the coupling coefficient. In the experiment, such a resonator was fabricated and the slow-light effect was demonstrated. As a result, when a pulse with a bandwidth of 3.35 GHz (equivalent to the temporal width of 299 ps) was launched into the resonator, a large group delay, whose average value was about 69.4 ps with a flat-top wavelength bandwidth of about 190 pm, was achieved

Theoretical and experimental study of structural slow light in a microfiber coil resonator

In this paper, a compact slow-light microfiber coil resonator (MCR) is fabricated and the slow-light properties of it are analyzed and tested. Based on coupled-wave theory, a theoretical model for describing the slow-light propagation in the MCR is established. Experimentally, the MCR slow-light element is fabricated and its relative slow-light time delay is measured. The group velocity of the light pulse in the MCR slow-light element can be reduced to about 0.47c (c is the speed of light in vacuum) and the shape of the light pulse passing through the MCR is well preserved.

Wide-bandwidth zero-dispersion slow light in MKRs with a two-ring parallel connection structure based on an analogue of electromagnetically induced transparency

Based on an analog of electromagnetically induced transparency (EIT) in microfiber knot resonators with a two-ring parallel connection structure, a wide bandwidth and zero-dispersion slow-light waveguide is proposed. The EIT-like transmission spectrum with the variation of wavelengths for different coupling coefficients is numerical simulated. By appropriately adjusting the coupling coefficients of the two knot rings, a group time delay of about 72.4 ps with a flat wavelength bandwidth of about 82.7 pm and a full width at half-maximum of about 228 pm at one of the induced transparency windows is achieved theoretically. And the group time delay dispersion at the same induced transparency window nearly reaches to zero with a wavelength bandwidth of about 82.7 pm.

Wide-Range Continuously-Tunable Slow-Light Delay Line Based on Stimulated Brillouin Scattering

Through selectively controlling the stimulated Brillouin scattering in optical fibers with different lengths, a continuously tunable time-delay scheme enabling to work in a large range is proposed in this letter. This is realized by connecting a fixed long single-mode fiber (SMF) to one of the several selectable short SMFs that successively have an equal increment in length. These short-length fibers are, respectively, fixed to the different channels between two identical optical switches. Therefore, a wide-range and continuously tunable slow-light delay line can be constructed by changing the power of the pump beam, assisted by switching to different channels. In the experiment, a time delay from 0 to 201.29 ns is demonstrated for a five-channel configuration. A further large-range time delay can be expected if one adds the number of channels accordingly.

Slow light and fast light in microfiber double-knot resonator with a parallel structure

Based on the theoretical model of a microfiber double-knot resonator with a parallel structure, numerical simulations on the transmission spectrum, the phase, and the group time delay of the resonator as a function of wavelengths are given. We find that with this kind of resonator both slow light and fast light can be obtained at different resonant wavelengths. Experimentally, such a kind of microfiber resonator was fabricated successfully. The transmission spectrum of the fabricated resonator is well consistent with the theoretical simulation. A slow-light delay of about 38 ps and a fast-light advance of about 40 ps are demonstrated at different wavelengths, which might benefit the resonator to the applications in data delay lines, optical buffers, and optical memories.

Stability-improved slow light in polarization-maintaining fiber based on polarization-managed stimulated Brillouin scattering

With the idea of controlling the polarizations of the pump and Stokes beams in an optical fiber, a simple scheme is presented for enhancing the stability of the stimulated Brillouin scattering (SBS) interaction and thus that of the SBS-based slow light. For this purpose, a special slow-light element is constructed by fusing a polarization-maintaining circulator (its fast axis being blocked) to each terminal of the polarization-maintaining fiber (PMF). This configuration ensures that the pump and Stokes beams always have identical polarization in the whole fiber during the SBS interaction. An experimental setup is established accordingly. The SBS gain feature and the slow-light performance are studied. A tunable time delay with a slope of 0.82?ns?dB?1 is demonstrated for a Gaussian pulse with a width of 88.9?ns. The experimental results with and without polarization management are compared. It is found that such a polarization-managed scheme can improve both the stability of the Brillouin gain and that of the time delay of the Stokes pulse. Moreover, for the same pump power, the Brillouin gain is also enhanced.

Numerical study on propagation of the trapping pulse in high nonlinear silicon waveguides

Abstract. We numerically investigated the pulse trapping in high nonlinear silicon waveguides. The two orthogonally polarized components of the pulse can trap and copropagate as a unit in a silicon waveguide. Our numerical results show that the trapping pulse can stably propagate when the polarization mode dispersion is compensated by shifting the frequencies of two orthogonally polarized components. We also analyze the effects of the free-carrier absorption and initial polarization angles on the pulse propagation in a silicon waveguide. The proposed on-chip trapping pulse in the silicon waveguide exhibits compact configuration and can potentially have important applications in integrated optics.

Demonstration of a stable and uniform single-wavelength erbium-doped fiber laser based on microfiber knot resonator

Abstract. We propose and demonstrate an application of microfiber knot resonator (MKR) in the generation of a stable and uniform single-wavelength erbium-doped fiber laser (EDFL). An MKR was fabricated using a microfiber a few micrometers in diameter. By embedding the MKR to the ring cavity of the EDFL, a laser with a wavelength of 1558.818 nm and a 3-dB linewidth of 0.0149 nm is demonstrated. The side mode suppression ratio of the laser is about 30 dB, and the maximum power fluctuation is about 0.85 dB. The results demonstrate that the MKR can be employed as a high-performance comb filter to realize a stable and uniform fiber laser.