An Integrated Pump-Controlled Variable Coupler Fabricated by Ultrafast Laser Writing.

The design and fabrication of a integrated symmetric directional coupler dependent o the pumping power and operating at a 1534 nm wavelength is reported. The twin-core waveguide was inscribed into Er3+/Yb3+ co-doped phosphate glass by a femtosecond laser direct writing technique. By optical pumping, the coupling ratio can be modulated due to the changes induced in the refractive index of the material. The experimental results demonstrated that the coupling ratio can be tuned continuously from 100/0 to 50/50 by increasing the pump's power from 0 to 350 mW. The developed twin-core coupler has promising applications for on-chip all-optical signal processing and communication systems.

Propagation Losses Estimation in a Cationic-Network-Based Hydrogel Waveguide.

A method based on the photographic recording of the power distribution laterally diffused by cationic-network (CN) hydrogel waveguides is first checked against the well-established cut-back method and then used to determine the different contributions to optical power attenuation along the hydrogel-based waveguide. Absorption and scattering loss coefficients are determined for 450 nm, 532 nm and 633 nm excitation. The excellent optical loss values obtained (0.32-1.95 dB/cm), similar to others previously described, indicate their potential application as waveguides in different fields, including soft robotic and light-based therapies.

Contribution to the Improvement of the Correlation Filter Method for Modal Analysis with a Spatial Light Modulator.

Modal decomposition of light is essential to study its propagation properties in waveguides and photonic devices. Modal analysis can be carried out by implementing a computer-generated hologram acting as a match filter in a spatial light modulator. In this work, a series of aspects to be taken into account in order to get the most out of this method are presented, aiming to provide useful operational procedures. First of all, a method for filter size adjustment based on the standard fiber LP-mode symmetry is presented. The influence of the mode normalization in the complex amplitude encoding-inherent noise is then investigated. Finally, a robust method to measure the phase difference between modes is proposed. These procedures are tested by wavefront reconstruction in a conventional few-mode fiber.

Misalignment and tilt effect on aspheric intraocular lens designs after a corneal refractive surgery.

PURPOSE: To numerically evaluate and compare the tolerance to misalignment and tilt of aspheric intraocular lenses (IOLs) designed for three eyes: with standard cornea and with simulated corneas after myopic and hyperopic laser ablation surgery. METHODS: Three aspheric IOLs of +20.00 diopter (D) with different spherical aberration (SA) ([Formula: see text]) values have been designed using a theoretical model eye. Drastic changes on the theoretical eye anterior corneal asphericity have been performed to simulate myopic and hyperopic refractive surgeries. The effect of IOL misalignment and tilt on the image quality has been evaluated using a commercial optical software design for the three eye models. Image quality was assessed from the modulation transfer function (MTF), root mean square (RMS) values of defocus, astigmatism, coma and spherical aberration ([Formula: see text]), and retinal images obtained from a visual simulator using an aleatory optotype of 0.00 LogMar visual acuity (VA). RESULTS: IOL misalignment and tilt reduced MTF values in general, and increased wavefront aberrations errors. Aberration-free IOLs maintained best the MTF values when misalignments were applied, together with good on-axis optical quality. IOLs with negative SA ([Formula: see text]) correction decreased the MTF value under 0.43 for misalignments values higher than 0.50 mm with the three corneas. The effect of misalignment on RMS astigmatism and coma was correlated with the IOL SA ([Formula: see text]) and with the three corneas. CONCLUSIONS: This theoretical study shows that the largest degradation in image quality arises for the IOL with the highest amount of spherical aberration ([Formula: see text]). Moreover, it has been found that the aspherical design has a more influential role in misalignment tolerance than in tilt tolerance.

Evaluation of the optical performance for aspheric intraocular lenses in relation with tilt and decenter errors.

PURPOSE: To evaluate and compare the effect of misalignment and tilt on the optical performance of different aspheric intraocular lens (IOL) designs. METHODS: Three aspheric IOLs with a different quantity of spherical aberration (SA) have been designed and the effect of IOL misalignment and tilt on the imaging quality of an eye model has been numerically assessed using a commercial optical design software. The prototypes have been manufactured by lathe turning and tested in vitro using the same optical bench (PMTF, Lambda-X) that complies with International Organization for Standardization standard 11979-2 requirements. Image quality was evaluated from the modulation transfer functions (MTFs), through-focus modulation transfer functions (TF-MTFs), root mean square (RMS) values of defocus, astigmatism and coma, and images of the United States Air Force (USAF) target were taken. A comparison with the optical performance of spherical IOLs has also been performed. RESULTS: Intraocular lens misalignment and tilt increased wavefront aberrations; the effect of misalignment on root mean square (RMS) astigmatism and coma was positively correlated with the spherical aberration of the IOL. Aberration-free IOLs showed the highest MTF for all misalignment values and for IOLs with negative SA correction the MTF decays below 0.43 when they are decentered 0.50 mm. CONCLUSIONS: Aspherical IOLs are more sensitive than spherical IOLs to misalignment or tilt, depending on their SA correction. The optical degradation caused by IOL misalignment had a greater effect on IOL designs with a higher amount of negative spherical aberration. In contrast, the effect of tilt on the optical performance was less sensitive to the IOL design.