Víctor Navarro-Fuster

Highly photostable organic distributed feedback laser emitting at 573 nm

An efficient, low-cost, and highly photostable second-order distributed feedback (DFB) laser, fabricated by thermal nanoimprint lithography and based on a polymer active film containing a perylenediimide derivative, is reported. It shows a photostability half-life of 3.1×105 pump pulses (>8 h), when pumped at the same spot of the film. This value is the highest reported to date for organic DFB lasers measured under ambient conditions. The device emits at 573 nm, matching the second low-loss transmission window of poly(methylmethacrylate) (460–590 nm), thus offering potential for applications in data communications based on polymer optical fibers.

Improved performance of perylenediimide-based lasers

The aim of this work was to improve the laser performance, in terms of threshold and operational lifetime, of lasers based on polymer films doped with perylenediimide (PDI) derivatives as active media. For such purpose, we first investigated the amplified spontaneous emission (ASE) properties of perylene orange (PDI-O), when doped into polystyrene (PS) films. Lower ASE thresholds and larger photostabilities than those of similar films containing another PDI derivative (PDI-C6), recently reported in the literature, have been measured. Results have been interpreted in terms of the photoluminescence efficiency of the films, which depends on the type of molecular arrangement, inferred with the help of nuclear magnetic resonance experiments. We also show that PS films have a better ASE performance, i.e. lower thresholds and larger photostabilities, than those based on poly(methyl methacrylate), which was recently highlighted as one of the best matrixes for PDI-O. Finally, a one-dimensional second-order distributed feedback laser using PS doped with PDI-O was fabricated and characterized. This device has shown a threshold significantly lower (by around one order of magnitude) than that of a similar laser based on PDI-C6-doped PS.

Film thickness and grating depth variation in organic second-order distributed feedback lasers

We report on the preparation and characterization, under optical pump, of second-order one-dimensional distributed feedback (DFB) lasers based on polystyrene films doped with a perylenediimide derivative, as active media. The DFB gratings were engraved on the substrates (SiO2) by thermal nanoimprint lithography, followed by reactive ion etching. Laser emission wavelength was tuned from 554 to 583 nm by changing film thickness (h) between 240 and 1200 nm. The effect on the performance (emission wavelength, threshold, slope efficiency, number of modes, and spectral shape) of varying the grating depth (d) from 30 to 240 nm, for the whole range of h values, has been investigated. Although there is extensive work in the literature aiming to tune the emission wavelength of organic DFB lasers by h variation, the effect of changing d systematically has not been previously studied. Experimental results have been interpreted by models that take into account the presence of the grating by averaging either h or the effective refractive index. Single-mode emission (λ0) was observed for h   1000 nm, d affects significantly the losses associated with the TE1 mode, so single mode emission was achieved at λ0 or at λ1 for deep and shallow gratings, respectively. Finally, the shape of the emission spectra, both below and above threshold, has also been analyzed in order to clarify the physical mechanisms responsible for the existence of gain. Bragg dips were observed in the spectra below threshold only for devices with d/h larger than around 0.3 and their width increased with increasing d/h. In these cases, single-mode DFB emission appeared at the long-wavelength edge of the Bragg dip, indicating that index-coupling modulation contributes significantly to the gain process. On the other hand, for smaller d/h values, Bragg dips became too small to be detected, so gain coupling becomes the dominant mechanism accounting for the presence of gain.We report on the preparation and characterization, under optical pump, of second-order one-dimensional distributed feedback (DFB) lasers based on polystyrene films doped with a perylenediimide derivative, as active media. The DFB gratings were engraved on the substrates (SiO2) by thermal nanoimprint lithography, followed by reactive ion etching. Laser emission wavelength was tuned from 554 to 583 nm by changing film thickness (h) between 240 and 1200 nm. The effect on the performance (emission wavelength, threshold, slope efficiency, number of modes, and spectral shape) of varying the grating depth (d) from 30 to 240 nm, for the whole range of h values, has been investigated. Although there is extensive work in the literature aiming to tune the emission wavelength of organic DFB lasers by h variation, the effect of changing d systematically has not been previously studied. Experimental results have been interpreted by models that take into account the presence of the grating by averaging either h or the e...

Influence of the excitation area on the thresholds of organic second-order distributed feedback lasers

It is shown that the optical pump power (or energy) density thresholds required to obtain lasing from organic second-order distributed feedback lasers, increase when the excitation area (A) is smaller than a certain value (Acrit). So, in order to obtain the minimum possible thresholds and to ensure that they constitute adequate quantities for comparison purposes, the condition A > Acrit should be fulfilled. Results also indicate that when A < Acrit (Acrit ∼ 0.1 mm2 for the devices studied here), the operational device lifetime, which depends mainly on the pump power (or energy) density, becomes drastically reduced.

Diffractive lenses recorded in absorbent photopolymers.

Photopolymers can be appealing materials for diffractive optical elements fabrication. In this paper, we present the recording of diffractive lenses in PVA/AA (Polyvinyl alcohol acrylamide) based photopolymers using a liquid crystal device as a master. In addition, we study the viability of using a diffusion model to simulate the lens formation in the material and to study the influence of the different parameters that govern the diffractive formation in photopolymers. Once we control the influence of each parameter, we can fit an optimum recording schedule to record each different diffractive optical element with the optimum focalization power.

Blazed Gratings Recorded in Absorbent Photopolymers

Phase diffractive optical elements, which have many interesting applications, are usually fabricated using a photoresist. In this paper, they were made using a hybrid optic-digital system and a photopolymer as recording medium. We analyzed the characteristics of the input and recording light and then simulated the generation of blazed gratings with different spatial periods in different types of photopolymers using a diffusion model. Finally, we analyzed the output and diffraction efficiencies of the 0 and 1st order so as to compare the simulated values with those measured experimentally. We evaluated the effects of index matching in a standard PVA/AA photopolymer, and in a variation of Biophotopol, a more biocompatible photopolymer. Diffraction efficiencies near 70%, for a wavelength of 633 nm, were achieved for periods longer than 300 µm in this kind of materials.

Peristrophic multiplexed holograms recorded in a low toxicity photopolymer

Ministerio de Economia y Competitividad (Spain) (FIS2014-56100-C2-1-P and FIS2015-66570-P); Generalitat Valenciana (Spain) (PROMETEO II/2015/015).

Dimensional changes in slanted diffraction gratings recorded in photopolymers

This work was supported by the “Ministerio de Economia y Competitividad” (projects FIS2015-66570-P and FIS2014-56100-C2-1-P) and by the “Generalitat Valenciana” of Spain (projects PROMETEOII/2015/015 and ISIC/2012/013).

Holographic Lenses in an Environment-Friendly Photopolymer

In this paper, we theoretically and experimentally evaluated the quality of volume phase transmission lenses stored in an environmentally friendly photopolymer. Holographic lenses (HLs) were obtained using symmetrical and asymmetrical experimental setups with the same positive and negative focal length and pupil diameter. The image quality was evaluated from the calculation of the modulation transfer function (MTF) by capturing the point spread function (PSF) with a charge-coupled device (CCD). A maximum frequency of 14 L/mm, reaching an MTF value of 0.1, was obtained for a negative asymmetrically recorded HL, evaluated at 473 nm wavelength. A theoretical study of aberrations was carried out to qualitatively evaluate the experimental results obtained.

Efficient split field FDTD analysis of third-order nonlinear materials in two-dimensionally periodic media

In this work the split-field finite-difference time-domain method (SF-FDTD) has been extended for the analysis of two-dimensionally periodic structures with third-order nonlinear media. The accuracy of the method is verified by comparisons with the nonlinear Fourier Modal Method (FMM). Once the formalism has been validated, examples of one- and two-dimensional nonlinear gratings are analysed. Regarding the 2D case, the shifting in resonant waveguides is corroborated. Here, not only the scalar Kerr effect is considered, the tensorial nature of the third-order nonlinear susceptibility is also included. The consideration of nonlinear materials in this kind of devices permits to design tunable devices such as variable band filters. However, the third-order nonlinear susceptibility is usually small and high intensities are needed in order to trigger the nonlinear effect. Here, a one-dimensional CBG is analysed in both linear and nonlinear regime and the shifting of the resonance peaks in both TE and TM are achieved numerically. The application of a numerical method based on the finite- difference time-domain method permits to analyse this issue from the time domain, thus bistability curves are also computed by means of the numerical method. These curves show how the nonlinear effect modifies the properties of the structure as a function of variable input pump field. When taking the nonlinear behaviour into account, the estimation of the electric field components becomes more challenging. In this paper, we present a set of acceleration strategies based on parallel software and hardware solutions.