Dichromated Gelatin Research Articles

High-sensitivity optical sensing of temperature based on side-polished fiber with polymer nanoporous cladding

We demonstrated temperature sensing of a side-polished fiber with polymer nanoporous film cladding, which was constructed by dehydrating dichromate gelatin film on the polished surface. Due to intermodal interference of core mode and cladding mode, two main transmission valleys were observed at 1219.2 and 1373.2 nm. The modulation amplitudes are ∼8 and 12 dB, respectively. These two transmission valleys show significant sensitivity to the temperature. At the wavelength of 1373.2 nm, the position of transmission valley blueshifted 114 nm while the temperature changes from 30°C to 90°C, and the sensitivity of temperature was up to 1.92 nm/°C. The linear correlation coefficient was 98.67%. The temperature sensing characteristics of nanoporous cladding fiber was successfully demonstrated, and it shows a high potential in photonics applications.

Off-axis holographic lens spectrum-splitting photovoltaic system for direct and diffuse solar energy conversion.

This paper describes a high-efficiency, spectrum-splitting photovoltaic module that uses an off-axis volume holographic lens to focus and disperse incident solar illumination to a rectangular shaped high-bandgap indium gallium phosphide cell surrounded by strips of silicon cells. The holographic lens design allows efficient collection of both direct and diffuse illumination to maximize energy yield. We modeled the volume diffraction characteristics using rigorous coupled-wave analysis, and simulated system performance using nonsequential ray tracing and PV cell data from the literature. Under AM 1.5 illumination conditions the simulated module obtained a 30.6% conversion efficiency. This efficiency is a 19.7% relative improvement compared to the more efficient cell in the system (silicon). The module was also simulated under a typical meteorological year of direct and diffuse irradiance in Tucson, Arizona, and Seattle, Washington. Compared to a flat panel silicon module, the holographic spectrum splitting module obtained a relative improvement in energy yield of 17.1% in Tucson and 14.0% in Seattle. An experimental proof-of-concept volume holographic lens was also fabricated in dichromated gelatin to verify the main characteristics of the system. The lens obtained an average first-order diffraction efficiency of 85.4% across the aperture at 532 nm.

An experimental distribution of analog and digital information in a hybrid wireless visible light communication system based on acousto-optic modulation and sinusoidal gratings

In this paper we propose a photonic architecture as an alternative tool to distribute point to multipoint analog and digital information over a hybrid wireless visible optical communication system. The experimental set-up is composed of a red laser pointer, an acousto-optic modulator, a sinusoidal grating and a photo-detector array. By using a simple and variable interferometric system, diffraction gratings with different spatial frequencies are generated and recorded on a photoemulsion which is composed of vanilla with dichromate gelatin. Analog video and digital information are first transmitted and recovered over a wireless communication system using a microwave carrier at 4.52 GHz which is generated by distributed feedback lasers operating in the low laser threshold current region. Separately, the recovered video information and digital data are combined with a radio frequency signal of 80 MHz, obtaining a subcarrier of information that is imposed on the optical carrier of the pointer laser using an acousto-optic modulator which is operated with an angle of incident light that satisfies the Bragg condition. The modulated optical carrier is sent to a sinusoidal grating, the diffraction pattern is photo-detected using an array of PIN photo-detectors. The use of sinusoidal gratings with acousto-optic modulators allows that number of channels to be increased when both components are placed in cascade.

Measurement of temperature and temperature profile of candle flame using holo-shear lens and Fourier fringe analysis technique

Holo-shear lens made on dichromated gelatin (DCG) is used as a lateral shear interferometer for measurement of temperature and temperature profile of an axi-symmetric gaseous flame. By using a Fourier fringe analysis technique, high-frequency speckle noise can be filtered out and disturbances of a nonspectral component may also be compensated for. The method is simple and easy to implement.

Novel cone lasing emission in a non-uniform one-dimensional photonic crystal

Novel cone lasing emission is observed from a photonic crystal (PC) with graded layers, which is fabricated by two-beam holographic interference in dichromated gelatin. The cone lasing is composed of one lasing spot and one concentric lasing ring. The good agreement between the experimental results and a numerical simulation performed using the transfer matrix method demonstrates that this lasing ring is induced by the coupling between the band edge and minigap, which is represented as some oscillations near the band edge in the passband of the reflection spectrum. The cone lasing may be useful for multi-wavelength fluorescence detection since the dual-colour directional enhanced fluorescence can be achieved without the mutual interference of lasing modes. Moreover, this readily observable cone lasing provides a direct visualization of the dispersion relation of non-uniform PCs.

Spectral interference in multiplexed volume Bragg gratings: theoretical calculations and experimental verification.

Multiplexed volume Bragg gratings can be applied to many types of broad- and narrowband spectral systems. However, there are often deleterious side effects to combining several gratings into a single holographic optical element, including loss of efficiency in diffracted waves of interest and the introduction of spurious waves. Design of these spectral systems requires analysis methods that are flexible and efficient and that take these side effects into account. We present a matrix-based algorithm for determining diffraction efficiencies of significant coupled waves in these multiplexed grating Holographic optical elements (HOEs). Several carefully constructed experiments with spectrally multiplexed gratings in dichromated gelatin verify our conclusions.

Study on measuring refractive index modulation of volume phase holographic gratings

In this paper, we present an approach to measure the refractive index modulation of volume phase holographic gratings (VPHG) by use of its angular selectivity, with the advantage of avoiding the diffraction efficiency errors induced by noise. Based on Kogelnik's coupled wave theory for volume holographic gratings, the wave vectors matching relationship for reflective VPHG at different readout wavelengths is deduced and the diffraction efficiency as a function of readout angle is also obtained. Then an all-fiber experimental system is designed to measure corresponding diffraction efficiency with different readout angles for VPHG recorded in dichromate gelatin. By seeking the Bragg angle where diffraction efficiency is maximum and the blank angle where diffraction efficiency drops to the minimum value, the refractive index modulation can be calculated. The experiment results proves the feasibility of the method.

Distributed feedback lasers based on dichromated poly(vinyl alcohol) reusable surface-relief gratings

A simple, low-cost and versatile holographic method to produce reusable surface-relief gratings on dichromated poly(vinyl alcohol) (DCPVA) films, with periods Λ ≥ 270 nm and modulation depths up to 300 nm, is reported. DCPVA presents processing advantages with respect to other photoresists, such as dichromated gelatine, i.e. higher light sensitivity, simpler fabrication process and better batch to batch reproducibility. The successful use of these DCPVA relief gratings as distributed feedback (DFB) laser resonators is demonstrated. Second-order DFB devices emitting in the wavelength range 577-614 nm have been easily prepared by coating a dye-doped polymer film on top of the resonators.

Perylenediimide-based distributed feedback lasers with holographic relief gratings on dichromated gelatine

One dimensional second-order distributed feedback (DFB) lasers consisting of polystyrene (PS) films doped with a perylenediimide laser dye, deposited over dichromated gelatine (DCG) photoresist layers with solvent resistant relief gratings recorded by holographic lithography, are reported. The advantage of using the grating on DCG in the final device is that the fabrication process is simplified and the grating pattern better preserved, since no etching methods to transfer the grating to another substrate are needed. A very simple model, proposed to explain the experimental waveguide properties, has allowed identifying the waveguide mode at which DFB emission appears, which was the key to optimize the device performance. In the frame of this model, the thickness of the PS and DCG films could be adjusted in order to minimize the laser threshold and to control its wavelength tuneability. The performance of these lasers is comparable to that of recently reported devices based on the same active material, but deposited over high-quality DFB gratings engraved on SiO2 by nanoimprint lithography.

Spectrum-splitting photovoltaic system using transmission holographic lenses

The optical efficiency of a holographic spectrum-splitting optical system with transmission holographic lenses is investigated. Spectrum-splitting is a promising approach to improve the efficiency of photovoltaic (PV) systems. By removing the lattice-matching constraints, it is possible to utilize low-cost thin-film PV materials and fabrication techniques. Transmission holograms are fabricated with the recording of the interference patterns of two or more coherent beams. It is also possible to use converging construction wavefronts to record holographic gratings that are matched to the focusing beam from the primary concentrator optics. Experimental holograms are fabricated in dichromated gelatin, and high diffraction efficiency is obtained. A single holographic lens is used to divide a broad spectrum into two types of PV cells. The position and orientation of the PV cells are chosen to match the dispersion properties of the holographic lens. The optical transfer efficiency of the holographic lens is measured to be ∼90% at the peak with fast transitions between the high diffraction efficiency and the high transmission spectral regions. With a GaAs solar cell and a 2.1-eV bandgap solar cell, the system efficiency is 31.0% under one-sun which is improved by 11.9% over the best single PV cell. The achievable system efficiency with the prototype filter is 96% compared to that of the ideal system.

Lasing in dye-doped photonic crystals at the edge of fluorescence band gaps

Based on holographic lithography, layered dye-doped photonic crystals are fabricated in dichromated gelatin emulsions. Under pumping of 532 nm pulse laser, fluorescence spectrums of samples show up remarkable band gaps, and lasing is achieved at the edge of fluorescence band gap with pumping energy increasing. Furthermore, the effects on lasing of matching between the edge of band gap and the peak of fluorescence are studied. Lasing threshold becomes lower as the edge of band gap is closer to the peak of fluorescence. Otherwise, it is difficult for lasing. The study provides new idea and method for the development of super low-threshold photonic crystal laser.

Defect modes in silver-doped photonic crystals made by holography using dichromated gelatin

The defect mode in silver-doped photonic crystals is investigated. 1D and 3D photonic crystals were made by holography using dichromated gelatin mixed with silver nitrate. By controlling the concentration of the silver nitrate, the defect mode was observed in the bandgaps of the holographic photonic crystals. The numerical simulations were made, and the results showed the consistency with the experimental observations.

Graded photonic crystals by optical interference holography

We report on the fabrication of graded photonic crystals in dye doped dichromate gelatin emulsions using an optical interference holographic technique. The gradedness is achieved by imposing a gradient form factor in the interference intensity resulting from the absorption of the dye in the dichromate gelatin. Wider and deeper photonic bandgaps are observed for the dyed samples as compared to the un-dyed samples. Our method could open up a new direction in fabricating graded photonic crystals which cannot be achieved easily using other techniques.

Ultra light-trapping filters with broadband reflection holograms

Significant optical absorption enhancement can be achieved by incorporating optical diffusers in the thin-film silicon photovoltaic (PV) cells. Absorption can be increased further by angular and spectral selective filters. In this work the properties of volume reflection holograms are examined for realizing ultra light-trapping filters for thin film silicon photovoltaic cell applications. The filter properties of reflection volume hologram are evaluated for this application. It is found that variation in the refractive index profile as a function of depth is an important factor. The optimized design is implemented in dichromated gelatin holograms and found to be in good agreement with predicted performance. The enhancement to the conversion efficiency of silicon PV cells are predicted with the PC-1D simulation tool and is found to be similar to that with an optimized Rugate filter. The simulated short circuit current density enhancement was found to be 8.2% for a 50 µm thick silicon PV cell and 15.8% for a 10 µm thick silicon PV cell.

Visible range lasing in dye-doped doubly periodic layered structures in dichromate gelatin emulsions

We have fabricated dye-doped doubly periodic layered structures exhibiting multiple bandgaps in the visible range in dichromate gelatin emulsions by a double-exposure holographic interference method. More importantly, optically pumped lasing with higher efficiency and lower threshold compared to that of singly periodic layered structures was observed in the dye-doped doubly periodic gelatin samples. This efficient lasing could be explained by the enhancement of the density of states at the overlapping bandgaps of two singly periodic layered structures.

Compensation of second-order dispersion in femtosecond pulses after filamentation using volume holographic transmission gratings recorded in dichromated gelatin

We have designed and developed a pulse compressor with volume transmission holographic gratings to be implemented in post-compression experiments based on filamentation in gases. Pulse compression down to 13 fs has been demonstrated. The gratings have been recorded in commercial PFG-04 dichromated gelatin emulsions with a recording wavelength of 532 nm, attaining sufficient index modulation to achieve high efficiency when they are illuminated by an 800-nm laser.

Control of the spectral position of dichromated gelatin reflection holograms

Dichromated gelatin (DCG) is one of the best light-sensitive materials for holographic recording. However, strict technological control should be observed during deposition, gelation, and drying of DCG plates and the chemical processing of the recorded structures. Usually, for reflection holograms the gelatin layer should be sealed in order to protect it from ambient humidity, which affects the value and position of the reflection maximum. Herein we give three different recipes for tuning the reflection maximum from 430 to 700 nm by swelling the hologram thickness with a filler material that is commercially available. The mechanism of the hologram swelling, which changes the period of the recorded holographic structure, is also briefly discussed.

The parameters effect on the holographic optical elements

In this work we fabrication holographic optical element diffraction grating thickness 40?m and mirror90?m by using dichromated gelatin,to perform that we have to use the Nd-yaG laser doubling frequency of wavelenght (532)nm and its powers of (80)mWatt.we have studyed the thickness and concentration dichromat effect in mirror reflaction ,effect of angle of reconstruction beam in band width and diffraction efficiency ,study effect gelatin hardener of the diffraction efficiency.

The parameters effect on the holographic optical elements

In this work we fabrication holographic optical element diffraction grating thickness 40?m and mirror90?m by using dichromated gelatin,to perform that we have to use the Nd-yaG laser doubling frequency of wavelenght (532)nm and its powers of (80)mWatt.we have studyed the thickness and concentration dichromat effect in mirror reflaction ,effect of angle of reconstruction beam in band width and diffraction efficiency ,study effect gelatin hardener of the diffraction efficiency.

Band-edge lasing in Rh6G-doped dichromated gelatin at different excitations

One-dimensional photonic crystal band-edge lasing at different excitations was studiedexperimentally by altering the excitation angle. We considered almost every conditionincluding in-band, out-of-band and near the band edge while keeping the density of statesunchanged. Holographic rhodamin 6G-doped dichromated gelatin was used for creatinglow-threshold photonic band-edge lasing (PBEL). Lasing actions excited near thehigh-energy and low-energy band edges were observed simultaneously, and their full widthsat half maximum were different. The results show that the PBEL intensity and pumpefficiency are sensitive to the excitation angle, enhanced obviously at the excitation nearthe band edge and suppressed distinctly in the band which agreed well with thetheoretical prediction. We also demonstrated for the first time that active mattersexist not only in the air voids but also in the high-index regions of the gelatin.