Modal liquid crystal microaxicon array

Abstract

A novel tunable liquid crystal microaxicon array is proposed and experimentally demonstrated. The proposed structure is capable of generating tunable axicons [thousands of elements) of micrometric size, with simple control [four control voltages) and low voltage, and is totally reconfigurable. Depending on the applied voltages, control over the diameter, as well as the effective wedge angle, can be achieved. Controls over the diameter ranging from 107 to 77 \aa have been demonstrated. In addition, a control over the phase profile tunability, from 12» to 24» radians, has been demonstrated. This result modifies the effective cone angle. The diameter tunability, as well the effective cone angle, results in a control over the nondiffractive Bessel beam distance. The RMS wavefront deviation from the ideal axicon is only A/3. The proposed device has several advantages over the existing microaxicon arrays, including being simple having a low cost. The device could contribute to developing new applications and to reducing the fabrication costs of current devices. limitations on the axicon profile height and thus the axicon angle. To overcome these drawbacks, another technique based on using a multistep micromolding process [21] has been recently proposed. In general, the proposed ideas use complex fabricating processes. Moreover, a reconfiguration of the final device is not possible.The parameters defining an axicon are the aperture diameter (d) and the wedge angle (j). In order to increase the nondiffractive distance of a Bessel beam (« max ), one of these parameters has to be modified (_z msK ~ d/y). Until now, these parameters were modified in the fabrication process. As commented above, the fabrication processes proposed until now produce limitations in the microaxicon parameters. One solution is the use of liquid-crystal-on-silicon spatial light modulators (LCoSSLMs) [22]. Despite this, the main problem is the low phase shift achieved by this device (usually 2n) and the price. Another drawback could be the characteristic structure, based on pixels surrounded by opaque areas, causing losses of light efficiency and possible aliasing in the case of micro-optical systems. To solve this problem some manufacturers use a special anti-reflection coating to ensure that the influence of the pixellated structure is minimized and thus the diffraction losses. In addition, LCoS-SLMs have residual phase distortions and a limited resolution [22]. Another option has been reported [23], In this work a tunable MEMS axicon mirror array is proposed. It shows a high tunability by controlling the wedge angle with temperature changes. The required temperature control could complicate the final device.In this Letter, a microaxicon array with high tunability and simple control is proposed. A control over the aperture and effective wedge angle is experimentally demonstrated. This device is simple and reconfigurable with low voltage signals. The proposed structure is capable of generating tunable axicons (thousands of elements) of micrometric...

Multifrequency Driven Nematics

“…This dependence gives raise to the possibility of designing liquid crystal mixtures with very low relaxation frequencies of electric permittivity parallel ε∥, which is useful for many applications [16]. Apart from traditional SLM, the unique properties of this LC mixture can be used in all kind of optical phase modulators recently reported, e.g., adaptive lenses [17], beam steering [18], correction of aberrations [19], 3D vision applications [19][20][21][22], novel aberrations correctors for rectangular apertures [23], microaxicon arrays [24], multioptical elements [25], hole-patterned microlenses [26], multifocal microlenses [27], high fill-factor microlenses [28], frequency controlled [29] microlenses, optical vortices [30], lensacons, and logarithmic axicons [31]. The LC mixtures used in this work have been designed by mixing three different families of LC compounds to meet the requirements of the LC to be controlled by low frequencies of the electrical applied voltage.…”

Liquid Crystal Focusing Device

“…Due to the use of new resistive coating and alteration of geometry the decrease of focal distance of liquid crystal lenses was achieved [10]. Use of two high-resistive layers and six contact electrodes allows implementing two-dimensional array of modal LC lenses -micro-axicons, parameters of which can be controlled on the basis of applied voltage, to the authors [11,12]. In the paper [13] it is shown that the structure based on LC and high-resistance layer can be used as the spiral phase plate for generation of vortex light fields.…”

“…За счет использования нового резистив-ного покрытия и изменения геометрии удалось добиться уменьшения фокусного расстояния жид-кокристаллических линз [10]. Использование двух высокорезистивных слоев и шести контактных электродов позволило авторам [11,12] реализовать двумерную матрицу модальных ЖК линз -микро-аксиконов, параметрами которых можно управ-лять в зависимости от прикладываемого напря-жения. В [13] показано, что структура на основе ЖК и высокоомного слоя может использоваться в качестве спиральной фазовой пластики для фор-мирования вихревых световых полей.…”

Liquid Crystal Temperature Sensor Based on Three Electrodes and a High-Resistivity Layer

“…Thanks to this, the structure produces a high voltage output that does not need any type of amplification circuitry. Several materials can be employed, depending on the necessary sheet resistance (R sq ), for instance, Titanium Oxide (TiO 2 ) [17], PEDOT [18], thin films of ITO [19] or Nickel [20], etc. The resistivity of these materials ranges from 0.1 to 10 M /sq.…”