A development of microlenses achromatically corrected for near infrared range is reported. Internal nanostructurization of microlens allows to obtain an effective parabolic gradient index profile. A standard stack-and-draw method was used to fabricate the microlens. They have a nearly wavelength-independent working distance of 35 μm over the wavelength range of 600-1550 nm. The proposed achromatic microlens can be applied in micro imaging systems and for wavelength independent coupling into optical fibers.
Nanostructured GRIN components are optical elements which can have arbitrary refractive index profile while retaining flat-parallel entry and exit facets. They are composed of more than 9000 individually placed glass subwavelength rods made of two types of glass with different refractive indices. They are developed using a standard stack-and-draw method used for fibre drawing. The refractive index profile of the nanostructured GRIN element can be described by the effective refractive index theory when the diameter of the individual rods are sufficiently smaller than the wavelength. In this paper we show that use of glasses designed for high diffusion and high temperatures during drawing process allows to develop parabolic nanostructured GRIN microlenses with rod diameter larger than wavelength. In particular, we have developed a GRIN microlens with diameter of 115 μm composed of 115 rods on diagonal. Our GRIN microlens has a length of 200 μm and a working distance equal to 1.05 mm, with focal spot of 8.5 μm measured for the 658 nm wavelength. We experimentally verified its imaging properties. Image resolution higher than 3.25 μm was measured.
We report for the first time successful inscription of high reflectivity Bragg grating in nanostructured core active fiber. Nanostructurization of the fiber core allows to separate the active and photosensitive areas and to distribute them all over the core. As a result unfavorable clustering between germanium and ytterbium particles is avoided. The distribution of discrete glass areas with feature size smaller than λ/5 results in effectively continuous refractive index profile of the fiber core. We present a single-mode fiber with built-in Bragg grating for laser application with the core composed of ytterbium and germanium doped silica rods. The core structure is arranged as a regular lattice of 1320 doped with ytterbium and 439 doped with germanium silica glass rods. The average germanium doping level within the core of only 1.1% mol allowed efficient inscription of Bragg grating. The nanostructured core was 8.6 μm and the internal cladding was 112 μm in diameter coated with low index polymer to achieve the double-clad structure. In the first proof-of-concept in the laser setup we achieved 35 % of slope efficiency in relation to launched power for the fiber length of 18 m. The output was single-mode with spectrum width below 1 nm. The maximum output power limited by pumping diode was 2.3 W. The nanostructurization opens new opportunities for development of fibers with a core composed of two or more types of glasses. It allows to control simultaneously the refractive index distribution, the active dopants distribution and photosensitivity distribution in the fiber core.
Cost effective multi-wavelength light sources are key enablers for spectroscopic applications at Mid-IR wavelength range. Utilizing a novel Mid-IR Si-based photonic integrated circuit filter and wide-band Mid-IR SLEDs, we show the concept of a light source that covers 2.7…3.5 μm wavelength range with a resolution <1nm. The spectral bands are switchable and tunable and they can be modulated. The source allows for the fabrication of an affordable multi-band gas sensor with good selectivity and sensitivity. The unit price can be lowered in high volumes by utilizing tailored molded IR lens technology and automated packaging and assembling technologies.
The status of the development of the key components of the light source are reported. The Mid-IR PIC is based on the use of thick-SOI technology, SLED is based on AlGaInAsSb materials and the lenses are tailored single crystal, nonoxide glass and heavy metal oxide glasses fabricated by the use of hot-embossing. The packaging concept utilizing automated assembly tools are depicted.
In safety and security applications, the Mid-IR wavelength range covered by the source allows for the detection of several harmful gas components with a single sensor. At the moment, affordable sources are not available. The market impact is expected to be disruptive, since the devices currently in the market are either complicated, expensive and heavy instruments, or the applied measurement principles are inadequate in terms of stability and selectivity.
We study optical properties of the gradient index vortices obtained using effective medium approach. Vorteces with charge +1 has been was developed using two types of nanorods made of thermally matched low and high refractive index glasses. Their optical properties of vortices are analyzed in the context of glass refractive index and size of the components. Consequently vortex has been integrated with single mode optical fiber and such a system is analyzed.
We study optical properties of gradient index vortex masks based on an effective medium approach. We consider masks with single charge developed using two types of nanorods made of thermally matched low and high refractive index glasses. Optical performance of generated vortices are analyzed in terms of glass refractive index difference and spatial dimension of the components. A fabricated vortex mask has been combined with single mode optical fiber. Optical performance of the resulting fiber integrated vortex mask is characterized and discussed.
Cost effective multi-wavelength light sources are key enablers for wide-scale penetration of gas sensors at Mid-IR wavelength range. Utilizing novel Mid-IR Si-based photonic integrated circuits (PICs) filter and wide-band Mid-IR Super Luminescent Light Emitting Diodes (SLEDs), we show the concept of a light source that covers 2.5…3.5 μm wavelength range with a resolution of <1nm. The spectral bands are switchable and tunable and they can be modulated. The source allows for the fabrication of an affordable multi-band gas sensor with good selectivity and sensitivity. The unit price can be lowered in high volumes by utilizing tailored molded IR lens technology and automated packaging and assembling technologies. The status of the development of the key components of the light source are reported. The PIC is based on the use of micron-scale SOI technology, SLED is based on AlGaInAsSb materials and the lenses are tailored heavy metal oxide glasses fabricated by the use of hot-embossing. The packaging concept utilizing automated assembly tools is depicted. In safety and security applications, the Mid-IR wavelength range covered by the novel light source allows for detecting several harmful gas components with a single sensor. At the moment, affordable sources are not available. The market impact is expected to be disruptive, since the devices currently in the market are either complicated, expensive and heavy instruments, or the applied measurement principles are inadequate in terms of stability and selectivity.
In this paper we present a numerical study on the optimization of dispersion of a photonic crystal fiber infiltrated with water-ethanol mixtures. The advantage of such an approach stems from the fact that the dependence of the refractive index on temperature is larger in liquids than in solid materials. Here, we examine photonic crystal fibers with a regular, hexagonal lattice and with various geometrical and material parameters, such as different number of rings of holes, various lattice constants and the size of core and air-holes. Additionally, for the optimized structure with flat dispersion characteristics, we analyze the influence of temperature and concentration of the ethanol solution on the dispersion characteristic and the zero dispersion wavelength shift of the fundamental mode.
The main goal of this work was to examine the possibility of fabrication of glassy diffractive optical elements for application in the near-infrared and mid-infrared spectral ranges. In the paper we focused on fabrication of Fresnel lenses with use of the hot embossing process. Lead-bismuth-gallium oxide and tellurite glasses were used in the experiment. Both types of glasses possess high transmittance from the visible up to mid-infrared (0.4÷6.5μm). Fused silica element was used as the mold, which was fabricated with standard ion etching method. The elements presented in this work were fabricated in a static process with the use of low pressure. The quality of the fabricated elements was examined with white light interferometer.
To achieve high non-linearity in photonic crystal fibers a high nonlinear coefficient of the glass is required accompanied by high coupling efficiency and flat dispersion profile of the fiber with the specific zero dispersion wavelength. In this paper, we present a deterministic method that allow step-by-step design of photonic crystal fibers with desired zero dispersion wavelength, modality and coupling efficiency due to sequential engineering of geometrical parameters of microstructured fibers with nanostructured cores. The fiber consists of inclusions of low refractive index material, embedded in a host glass of higher refractive index, where a single central micro-rod is omitted. In its place an additional nano-inclusion is located of a given diameter. The choice of the glass determines the nonlinear coefficient of the fiber and fabrication possibilities as well. Zero dispersion wavelength is varied by the change of the lattice constant of the cladding. High filling factor in the cladding leads to a large number of propagating high order modes, which can be selectively cut off, when the filling factor of the outer part of the cladding is reduced. The diameter of the nano-inclusion in the core is responsible for the fundamental mode area, which influences directly the coupling efficiency. Several designed structures were modeled numerically and developed to confirm the design method.
We present a computer simulation and an experimental realization of an optical setup for automatic quality control of microlenses arrays. The method is based on a 4f correlator setup with an amplitude filter. The output intensity signal is simple to analyze and interpret because the intensity is proportional to the first derivative of the distortion of the input wavefront. This method is shift invariant, allows for the examination of single elements, or sets of micro-optical elements simultaneously, and is particularly suitable for assessing the quality of optical elements. However, combining the method with a more detailed analysis based on the Fourier modal method, allows for obtaining quantitative data. Although errors are within the 2-3% range, such an analysis enables a fast and relatively accurate comparison of numerous elements with each other and with the model. The combination has never been applied but allows for a fast and cost-effective analysis that can be used for industrial purposes. Both the methods give separate results for each lens or for all the lenses in the array, simultaneously. In the combination proposed, the analysis is computer-based and done on the basis of the initial single optical measurement.
The paper deals with a computer simulation and an experimental realization of an optical setup for automatic quality
control of microlenses arrays. The method is based on a 4f coherent light correlator setup with an amplitude filter placed
in the Fourier plane. The output intensity signal is simple to analyze and interpret because the intensity is proportional to
the first derivative of the distortion of the input wavefront. This method is shift invariant, so it allows for examination of
single elements or a set of micro-optical elements simultaneously. Such an analysis does not allow to obtain quantitative
data, however it can give the initial assessment of the quality of the elements to be analyzed. A more detailed analysis
can be carried out with the use of the Fourier-based modal method and Zernike polynomials expansion method. What is
important, the analysis is computer-based and is done on the basis of the initial single optical measurement. Moreover,
the whole resolution of the camera is used.
The paper deals with a computer simulation and an experimental realization of a new kind of an optical setup for simple
and fast control of the wavefront distortion. The method is based on a 4f coherent light correlator setup with a
semiderivative real filter placed in the Fourier plane. In the setup described the distorted wavefront passes through the
filter located in the frequency plane of the correlator. In the output plane a camera registers the intensity of light whose
gradient carries information about the shape of the wavefront distortion. The output image is simple to analyze and
interpret because the intensity is directly proportional to the first derivative of the distortion of the input wavefront.
The role of the computer simulations presented in the paper was, first of all, to check how the semiderivative real filter
deals with various kinds and levels of distortions. Secondly, it was to estimate how the technical limitations of the filter
and the setup can influence the quality of the results obtained.
The experiment checked the possibility of using the setup for examining the distortion of wavefront caused by hot air.
The experimental results obtained show that the method is suitable and effective for real-time monitoring of the
distortion of the wavefront, which allows for its use in adaptive optics and phase visualization. The method also allows
for measuring other phase objects where the gradient of the phase and the thickness of the object undergo abrupt
The article describes application of Level Set method for two different microfabrication processes. First is shape
evolution of during reflow of the glass structure. Investigated problem were approximated by viscous flow of
material thus kinetics of the process were known from physical model. Second problem is isotropic wet etching
of silicon. Which is much more complicated because dynamics of the shape evolution is strongly coupled with
time and geometry shapes history. In etching simulations Level Set method is coupled with Finite Element
Method (FEM) that is used for calculation of etching acid concentration that determine geometry evolution of
the structure. The problem arising from working with FEM with time varying boundaries was solved with the use
of the dynamic mesh technique employing the Level Set formalism of higher dimensional function for geometry
description. Isotropic etching was investigated in context of mico-lenses fabrication. Model was compared with
experimental data obtained in etching of the silicon moulds used for micro-lenses fabrication.
In this paper we present a numerical analysis of a planar or sub-structured metallic flat lens for mode coupling
between a pair of waveguides. The analysis of periodically sub-structured silver coupler is based on the finite
element model of the device. The uniform and infinite double layered silver coupler is also considered, and is
modelled with the transfer matrix method. The study is focused on minimising propagation losses and optimising
the coupling coefficient, which is calculated from the transfer properties of the lens for a Gaussian distribution
of the modal fields. The analysis reveals the importance of the periodic nanostructure of the silver layers for
reaching a coupling efficiency which is higher than could be obtained with uniform layers or with air.
One of the methods used for fabrication of microelements is ion track lithography, and especially deep proton lithography. Structural depth of the produced elements depends on the energy of the protons. Equally important are the deposited dose and the time of development. One type of element where the thicknesses or depths are important is channels, used in microfluidic setups or used as rectangular waveguides. The waveguides can be obtained both by filling in with a different material and by the change of the refraction index. The shape of the obtained channels is important in both applications. The advantage of deep proton lithography is the possibility of influencing the shape of the channels by controlling the parameters of the radiation process. When using deep proton lithography to fabricate channels, it is necessary to precisely measure the dose deposited inside the material. A new method of channel fabrication, where the deposited dose is measured in the plane before the target, is presented. This is done with the use of a novel deep proton lithography setup operating in air. Experimental results are presented for such a setup built for the tandem accelerator in Erlangen, Germany.
In this paper we present a novel concept of NxN switch with full reconfigurability. A rapid prototyping technique based on direct laser writing is considered as an implementation technology. As a first step towards an NxN switch, the experimentally properties of 2x2 switch are investigated. Several samples of the switch with different coupling lengths and distances between the waveguides are developed. Measurement results of coupling efficiency are presented.
Polymer display based on a movable membrane designed in MOEMS technology may be an alternative for other display
devices. The display consists of two plastic elements. The first one is a planar waveguide. It is coated in metal with
electric contacts etched in it. The second element is a metalized membrane with a matrix of pillars functioning as pixels.
The simplicity of the setup makes it cheap and easy for mass production. On the other hand, each size of the display has
to be optimized independently, which may be a problem. When deciding on the size of the matrix one has to optimize
several interconnected parameters, which decide on the functioning of the display. In this paper we describe the
modeling process for a 20×20 pixel matrix with an active display matrix area of 5×5 mm2.
We proposed a new kind of setup for the automatic control of the quality of micro lens array, which is based on semiderivative real filter. With the use of the 4f correlator setup with a semiderivative filter placed in the Fourier plane and connected with the camera, it is possible to examine phase objects. Such a setup is shift invariant, so it enables us to simultaneously examine a set of identical elements, such as a micro lens array. Additionally, the same setup allows for a simultaneous measurement of both thin and thick phase objects. It is also possible to measure a wide range of phase gradients.
The article presents the results of simulations where the semiderivative filter was used to measure phase objects such as cylindrical and spherical lenses. A special emphasis was placed upon checking how the proposed setup works for a number of similar phase optical elements, such as microlens arrays. The article also presents an analysis of how various technological limitations can influence the quality and the precision of the results obtained. Further on, it shows the initial results of the use of 3D lithography to produce semiderivative filters.
Tunable wavelength selective and band pass filters are widely used nowadays in transmission technology and light processing, with setups based on Acustooptic modulators, Fabry Perot filters, Mach Zehnder and Sagnac interferometers and fiber Bragg gratings (FBGs) with electro-optical, mechanical or thermal tuning mechanism. Multilayer structures like FBGs are used in the design of e.g. broad-band terminations of transmission lines1, narrow-band transmission filters for wavelength-division multiplexing (WDM)2 and in other fiber optics systems for signal processing3. One of the biggest advantages of dielectric mirrors is that they are characterized with very small losses, as compared with normal metallic mirrors. Apart from that, with the use of Bragg mirrors one can control bandwidth of the reflected light beam, as well as the angles for which the reflection is obtained. This opens up a possibility of building setups sensitive to such parameters as the lighting angle and the wavelength. Additionally, Bragg mirrors can be used for a wide spectrum of the electromagnetic waves from UV to FIR. In this paper we propose a new concept of MOEMS-based free-space tunable Bragg grating as a wavelength selective and band pass filter. The use of MEMS allows obtaining fast and reliable tuning with respect to other methods.
There are several technologies for cheap mass fabrication of microelements. One of them is deep proton lithography, used for the fabrication of elements of high structural depth. In this technology, accelerated protons are usually focused or formed by a mask to light a target. The energy of the proton beam is enough for all the protons to get through the target, losing only a part of their kinesthetic energy. Protons leaving the target are counted in various ways, thanks to which it is possible to estimate the energy deposed inside the target. In the next step chemical development is used to get rid of the radiated part of the target. With the use of this method, various 2D microelements can be obtained and the proton beam plays the role of a knife, cutting out the required shapes from the material. However, in order to make elements of modified surface (2.5D surface) it is necessary to change the energy of the proton beam or to change the dose deposed inside the material. The current article presents a proposal of creating simple 2.5D structures with the use of the method modifying the deposed does. This entails the modification of the deep proton lithography setup, which results moving the part for measuring the deposed dose of energy before the target. Additionally, the new deep proton lithography setup operates in the air. This article presents the results of simulations, as well as experimental results for such a setup built for the tandem
accelerator in Erlangen, Germany.
There are several technologies for cheap mass fabrication of microelements. When we need elements of high structural depth, one of the most important technologies is the LIGA process. Since this method is time- and cost-consuming, there are a few alternative methods to be used instead of the LIGA. One of them is the use of the ion track lithography, especially deep proton lithography. So far, all the deep lithography setups have operated in vacuum. Accelerated protons were focused or formed by a mask to light a target placed in vacuum. Such an approach limited the size of the target and lengthened the time needed to place a new the target in the setup. It also needed a relatively small steering setup, adapted to operate in vacuum. That is why a novel proton lithography setup operating in the air has been proposed. The setup, whose size is no longer limited, allows for a quick access to the target. However, the parameters of the proton beam moving from vacuum into the air change, which affects the way protons interact with the target. This enforces adding several new elements to the classical proton lithography setup. In spite of that, such a setup is cheaper and easier to use than the classical one, but it allows for obtaining microelements of similar quality.
We propose, what is to our knowledge, a new approach to the analysis of detection signals from optical sensors. The technique is based on the pattern recognition algorithms that belong to the family of composite linear filters. We focus on the information recovery from the reflectivity spectrum of a Bragg sensor measured with an optical spectrum analyzer. However the method is applicable to the extraction of information in other types of sensors, where in general the detection signal is multidimensional and includes data related to several measured parameters.
The proposed pixel matrix display consists of two plastic elements: a planar waveguide which plays the role of a light reservoir and a deformable thin membrane with a matrix of pillars. On the bottom side of the membrane that touches the light reservoir there is an electrode surrounding all pillars and leaving tops of pillars transparent. The light reservoir has a matrix of individual electrical contacts so that the display can be addressed pixel by pixel and switched on by applying a voltage to the electrical contacts on the light reservoir and the membrane electrode. The electrostatic force locally deforms the membrane and puts the pillars in contact with the light reservoir, therefore, coupling light into the membrane. A demonstrator of a polymer-based pixel matrix display is fabricated in MOEMS technology. The proof-of-principle experiment is made on a 20x20 pixel matrix with an active display matrix area of 5x5 mm2, a light emitting diode illumination and 80 V applied to address pixels.
The problem of crosstalk in the optical resonator neural network based on double correlator architecture is digitally analyzed. Minimum average correlation energy filter (MACE) reducing the crosstalk has been used as a first storing hologram. The comparison of the results obtained for nonorthonormalized pattern by using the MACE filter with those obtained by orthonormalization procedure and phase-only filter is presented.