Control Of Group Velocity Dispersion Research Articles

Accurate modeling and measurement of pressure-induced group velocity dispersion variations in anti-resonant hollow-core fibers.

Precise control of group velocity dispersion (GVD) by pressure in a gas-filled hollow-core fiber (HCF) is of essential importance for many gas-based nonlinear optical applications. To accurately calculate the pressure-induced dispersion variations (∂β2/∂p) in anti-resonant types of HCF, an analytical model combining the contribution of the gas material, capillary waveguide, and cladding resonances is developed, with an insightful physical picture. Broadband (∼1000 nm) GVD measurements in a single-shot manner realize accuracy and precision as low as 0.1 ps2/km and 2 × 10-3 ps2/km, respectively, and validate our model. Consistent with our model, a pronounced negative ∂β2/∂p is observed experimentally for the first time, to our knowledge. Our model can also be extended to other HCFs with cladding resonances in predicting ∂β2/∂p, such as in photonic bandgap types of HCF.

Experimentally Validated Dispersion Tailoring in a Silicon Strip Waveguide With Alumina Thin-Film Coating

We propose a silicon strip waveguide structure with alumina thin-film coating in-between the core and the cladding for group-velocity dispersion tailoring. By carefully designing the core dimension and the coating thickness, a spectrally-flattened near-zero anomalous group-velocity dispersion within the telecom spectral range is obtained, which is predicted to significantly broaden the bandwidth of four-wave mixing. We validate this by characterizing the wavelength conversion in a waveguide sample by atomic layer deposition technology, which to our best knowledge is the first experimental demonstration of the proposed structure. Due to the alumina thin-film coating, the wavelength conversion bandwidth reaches $58\,\mathrm{nm}$, an increase by a factor of 1.3 compared to the corresponding structure without coating. This method can also be applied to other material platforms and applications requiring accurate group-velocity dispersion control.

Axial scanning with pulse shaping in temporal focusing two-photon microscopy for fast three-dimensional imaging

By integrating ultrafast laser pulse shaping into temporal focusing two-photon microscopy, a high-speed 3D imaging method is developed. This 3D imaging system requires neither laser beam steering nor sample mechanical scanning. The z scanning is achieved by shifting the temporal focal plane via applying different group velocity dispersions on the femtosecond laser spectrum in the temporal focusing two-photon microscope, and this group velocity dispersion control is done with the pulse shaping method by applying modulation functions on an acoustic optic modulator which diffracts the laser spectrum. The dependence of scanning depth on the applied electronic signals which can be tuned at kHz speed was characterized. Its high-speed 3D imaging capability was demonstrated by imaging fluorescence microspheres in a volume of 100 × 100 × 80 µm3.

Achieving comb formation over the entire lasing range of quantum cascade lasers.

Frequency combs based on quantum cascade lasers (QCLs) are finding promising applications in high-speed broadband spectroscopy in the terahertz regime, where many molecules have their "fingerprints." To form stable combs in QCLs, an effective control of group velocity dispersion plays a critical role. The dispersion of the QCL cavity has two main parts: a static part from the material and a dynamic part from the intersubband transitions. Unlike the gain, which is clamped to a fixed value above the lasing threshold, dispersion associated with the intersubband transitions changes with bias, even above the threshold, and this reduces the dynamic range of comb formation. Here, by incorporating tunability into the dispersion compensator, we demonstrate a QCL device exhibiting comb operation from Ith to Imax, which greatly expands the operation range of the frequency combs.

Fundamentally mode-locked, femtosecond waveguide oscillators with multi-gigahertz repetition frequencies up to 15 GHz

We demonstrate passively mode-locked Yb(3+)-doped glass waveguide lasers in a quasi-monolithic configuration with a maximum pulse repetition frequency up to 15.2 GHz. A semiconductor saturable absorber mirror (SESAM) is used to achieve stable mode-locking around 1050 nm with pulse durations as short as 811 fs and an average power up to 27 mW. Different waveguide samples are also employed to deliver pulses with repetition rates of 4.9 GHz, 10.4 GHz and 12 GHz with an average power of 32 mW, 60 mW and 45 mW, respectively. The group velocity dispersion control in the cavity is provided by changing the gap between the SESAM and the waveguide end-face to facilitate a soliton mode-locking regime.

All-optical control of group velocity dispersion in tellurite photonic crystal fibers

We demonstrate all-optical control of group velocity dispersion (GVD) via optical Kerr effect in highly nonlinear tellurite photonic crystal fibers. The redshift of the zero-dispersion wavelength is over 307nm, measured by soliton self-frequency shift cancellation, when the pump peak power of a 1.56μm femtosecond fiber laser is increased to 11.6kW. The all-optical control of GVD not only offers a new platform for constructing all-optical-control photonic devices but also promises a new class of experiments in nonlinear fiber optics and light-matter interactions.

Nonlinear Amplifying Loop-Mirror-Based Mode-Locked Thulium-Doped Fiber Laser

We present an SESAM mode-locked thulium-doped fiber laser incorporating nonlinear amplifying loop mirror with intracavity and external group velocity dispersion control, which generates sub-300-fs near-transform-limited pulses at 1920-nm wavelength, with 106-mW maximum average output power. The dispersion control was realized by implementing a low-loss highly doped germanium silica fiber.

Efficient non-linear optical fibres and their applications

There seem to be three possible approaches to achieve efficient non-linear optical effects in fibres: the increase of optical intensity in fibres, the control of group velocity dispersion in fibres and the use of efficient non-linear optical materials for fibres. From this viewpoint, high-numerical-aperture single-mode fibres with high optical intensity, single-mode fibres with extremely small dispersion at the operating wavelength and LiNbO3 single-crystal fibres with efficient non-linear effects, are now being investigated. This paper describes the fabrication of these optical fibres, and their non-linear optical applications.