Single-mode Profile Research Articles

Single-mode light guiding in diamond waveguides directly written by a focused proton beam.

Ion-implanted waveguides were directly written in bulk single-crystal diamond by scanning a focused 2MeV proton beam. By controlling the fluence and the lateral size of the proton beam, a bright and near-circular single-mode profile was observed. Propagation loss and effective refractive index of the guided mode were measured by the Fabry-Pérot technique, confirming single-mode guiding. Micro-Raman maps of the waveguides were used to visualize damage profiles and defect distributions induced by the proton beam. The demonstration of single-mode light guiding in our waveguides shows that direct proton beam writing is a promising tool in the rapid manufacture of integrated optical circuits in bulk diamond.

Nodeless hollow-core fiber for the visible spectral range.

We report on a hollow-core fiber (HCF) whose fundamental transmission band covers almost the whole visible spectral window, starting at 440 nm. This HCF, in the form of a nodeless structure (NL-HCF), exhibits unprecedented optical performance in terms of low transmission attenuation of 80 dB/km at 532 nm, a broad transmission bandwidth from 440 to 1200 nm, a low bending loss of 0.2 dB/m at 532 nm under 8 cm bending radius, and single-mode profile. When launched to high-power picosecond laser systems at 532 nm, the fiber, exposed to ambient air, could easily deliver an 80 ps, 58 MHz, 32 W average power laser pulse with no damage and a 20 ps, 1 kHz high-energy laser pulse with a damage threshold in excess of 144 μJ at a fiber output. A proof-of-concept experiment on Raman spectroscopy in ambient air shows the significance of this broadband visible guiding HCF for interdisciplinary applications in nonlinear optics, ultrafast optics, lasers, spectroscopy, biophotonics, material processing, etc.

Optimal photon-pair single-mode coupling in narrow-band spontaneous parametric downconversion with arbitrary pump profile

A theoretical investigation of the performance of single-mode coupled spontaneous parametric downconversion sources is proposed, which only requires very few assumptions of practical interest: quasi-degenerate collinear generation and narrow bandwidth obtained through spectral filtering. Other assumptions, such as pump-beam spatial and temporal envelopes, target single-mode profile and size, and nonlinear susceptibility distribution, are only taken into account in the final step of the computation, thus making the theory general and flexible. Figures of merit for performance include absolute coupled brightness and conditional coupling efficiency. Their optimization is investigated using functions that only depend on dimensionless parameters, so that the results provide the best experimental configuration for a whole range of design choices (e.g., crystal length, pump power, etc.). A particular application of the theory is validated by an experimental optimization obtained under compatible assumptions. A comparison with other works and proposals for numerically implementing the theory under less stringent assumptions is also provided.

Abnormal wavelength dependence of the self-cleaning phenomenon during femtosecond-laser-pulse filamentation

Through investigating the laser beam patterns at various wavelengths of the filamentation supercontinuum, abnormal wavelength dependence of the beam profile self-cleaning phenomenon is reported. It is founded that only the Stokes light has a nice spatial profile, while the patterns at the anti-Stokes side and the fundamental wavelength are not smooth and regular. Furthermore, by numerical simulations, we propose that the intensity perturbation of the initial beam can be considered as high order spatial modes superpositioning on a fundamental mode. The fundamental mode self-focuses, first producing a single mode profile on the axis. The higher order modes undergo strong diffraction constituting the energy reservoir. That gives rise to the overall 'bad' spatial properties at the fundamental wavelength. On the other hand, the distortion of the beam patterns at the anti-Stokes side is due mainly to the interaction of the back part of the pulse with the plasma, which gives rise to anti-Stokes shifts. Finally, a possible application of our results to high beam quality tunable Ti: sapphire laser amplification is suggested.

Fabrication of large-cross-section single-mode reverse-ridge PLZT waveguides

We report the fabrication of new low-loss, large-cross-section single-mode PLZT (8.5/65/35) film reverse-ridge waveguides by depositing a PLZT film on an r-sapphire substrate with a patterned ITO spacer film. The single-mode profile and propagation losses were analyzed, and experimentally characterized at 0.633, 1.3, and 1.55 μm of light. ©1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 20: 121–124, 1999.