RU2091845C1 - Image converter - Google Patents

Abstract

FIELD: optoelectronics, serves for processing of video information, applicable in computer engineering as an optically controlled device for information input to a computer. SUBSTANCE: the image converter, having an input transparent conducting electrode, photosensitive semiconductor, interference filter, electrooptic crystal and an output transparent conducting electrode, uses also an active high-resistance resistive layer possessing a volt-ampere characteristic with a negative incremental resistance and positioned between the photosensitive semiconductor and the interference filter; a thin-film heater is introduced in the active high-resistance resistive layer. EFFECT: improved design. 2 cl, 3 dwg

Description

 The invention relates to optoelectronics and may find application in optical information processing devices and computer engineering.

 A known image converter, made in the form of a structure: an input transparent conductive electrode-dielectric-photosensitive semiconductor with an electro-optical effect, a dielectric-output transparent conductive electrode electrically connected to a high-voltage power supply unit (US patent N 3517206, publ. 1970). The principle of operation of the device is based on the conversion of optical radiation into an electrostatic charge relief at the semiconductor-dielectric interface, followed by its conversion into a visible image using polarized visible light due to the electro-optical effect in the semiconductor.

 The disadvantage of this device is the low sensitivity and low brightness of the image, especially at low levels of recording flare and the lack of the ability to control them.

 The closest in technical essence and the achieved result is an image converter containing an input transparent conductive electrode, a photosensitive semiconductor, an interference filter, an electro-optical (liquid) crystal, an output transparent conductive electrode electrically connected to a power source (collection Spatial light modulators, as amended by C .B. Gurevich, L. Nauka, 1977, p. 74-80). The principle of operation of this device is based on recording an image using a photosensitive semiconductor and converting it into visible using an electro-optical (liquid) crystal.

 Its disadvantages include a rather low sensitivity and low brightness of the recorded image at low levels of recording flare and the lack of the possibility of amplification. The change in the voltage drop across the liquid crystal during illumination corresponds to a decrease in the voltage drop across the semiconductor, and since the voltage across the semiconductor is small at low lighting levels, the voltage increment equal to it on the liquid crystal layer is also small, therefore, the modulation of the read light, and therefore , and the image registration will either be absent or very weakly manifested. Without changing the operating mode of the structure, it is not possible to enhance the brightness of the recorded image.

 The aim of the invention is to increase the sensitivity and brightness of the image converter.

 This goal is achieved by the fact that in the image converter containing an input transparent conductive electrode, a photosensitive semiconductor, an interference filter, an electro-optical crystal, an output transparent conductive electrode between the photosensitive semiconductor and an interference filter, an active high-resistance resistive layer having a current-voltage characteristic with negative differential resistance is introduced .

 In addition, a thin-film heater is introduced into the high-resistance resistive layer to control the range of sensitivity and brightness of the recorded image.

 In FIG. 1 is a diagram of an image converter; figure 2 its equivalent circuit; figure 3 volt-ampere characteristic of the active high-resistance resistive layer.

The image converter (figure 1) contains recording light with a wavelength of λ ₁ 1, transparency 2, transparent conductive electrodes 3, a photosensitive semiconductor 4, a high-resistance active resistive layer 5, a thin-film heater 6, an interference filter 7, an electro-optical crystal 8 that reads light 9 , a beam splitting element 10, an analyzer 11, a power source 12.

When voltage U _o 12 is applied to the current structure (Fig. 1), it drops on the layers of the semiconductor 4 U _f , electro-optical crystal 8 U _e , resistive 5 U _p U _f > U _e (voltage drop on other structural elements is negligible). Based on the equivalent image converter circuit (FIG. 2), U _{o is} defined as:
U _o U _f + U _e + U _p I (R _f + R _e + R _p ) (1)
where I is the flowing current. In this case, the voltage drop across the resistive layer U _p by selecting its design parameters and the magnitude of the external voltage U _o is set in the second section of the current-voltage characteristic (Fig. 3) at operating point A (U _p U _a ).

Image recording is carried out by light 1 active for photosensitive semiconductor 4 with a wavelength of λ ₁ when it passes through transparency 2, the input translucent conductive electrode 3 (Fig. 1) due to the generation of electron-hole pairs in the material 4 in accordance with the transparency of the transparency. This leads to a decrease in the resistance of the semiconductor layer by dR _f and a decrease in the voltage drop across the semiconductor dU _f .

On the other hand, a decrease in R _f under the action of recording backlight leads to an increase in current I through the structure and a shift of the operating point on the I – V characteristic of the active resistive layer 5 to point B (Fig. 3). This causes a decrease in the voltage on this layer by dU _p and its application also to the corresponding points of the electro-optical crystal 8. Thus, in the places where the recording illumination acts on the photosensitive semiconductor, an increase in the voltage on the electro-optical crystal is associated not only with a decrease in the voltage on semiconductor 4, but and with a decrease in the voltage drop across the active high-resistance resistive layer due to the displacement of the operating point in the CVC section with negative differential resistance.

где dU_эо приращение напряжения на электрооптическом кристалле для одинаковой подсветки при отсутствии в преобразователе изображения активного высокоомного резистивного слоя.The voltage increment on the electro-optical crystal layer dU _e due to voltage changes on other layers in the image converter under the action of illumination characterizes its sensitivity to radiation. The increase in the sensitivity of the converter with the introduction of an active high-resistance resistive layer 5 in comparison with a device in which these layers were absent is expressed by the coefficient γ corresponding to the ratio of the voltage increments on the electric crystal 8 for these cases:

wherein the voltage increment _eo dU in electrooptic crystal, for equal illumination in the absence of the image converter of the active high-ohmic resistance layer.

где (r отрицательное дифференциальное сопротивление на линейной части участка II ВАХ (фиг.3), а без него (R_p=0, r 0) в виде:

Тогда, согласно (2), коэффициент γ определится:

Увеличение чувствительности преобразователя изображения при введении активного высокоомного резистивного слоя по сравнению с прототипом выражается условием: γ > 1. Положив R_р/(R_э+R_ф)=n, получим

т. е. чувствительность преобразователя изображения растет с увеличением отрицательного дифференциального сопротивления r. Однако, при r=R_э+R_ф=R_p/n коэффициент γ равен бесконечности, что отражает возможность возникновения незатухающих колебаний тока в цепи преобразователя изображения.Based on (1), the voltage increment on the electro-optical crystal in the image converter in the presence of an active high-resistance resistive layer is written as (see the appendix):

where (r is the negative differential resistance on the linear part of section II of the CVC (Fig. 3), and without it (R _p = 0, r 0) in the form:

Then, according to (2), the coefficient γ is determined:

The increase in the sensitivity of the image converter with the introduction of an active high-resistance resistive layer in comparison with the prototype is expressed by the condition: γ> 1. Putting R _p / (R _e + R _f ) = n, we get

i.e., the sensitivity of the image converter increases with increasing negative differential resistance r. However, when r = R _e + R _f = R _p / n, the coefficient γ is equal to infinity, which reflects the possibility of the occurrence of undamped current oscillations in the image converter circuit.

а в частном случае при R_p=R_ф+R_э:0,5R_p < r < R_p.To eliminate self-excitation, it is necessary that

and in the particular case when R _p = R _f + R _e : 0.5R _p <r <R _p .

 An increase in the sensitivity of an image converter with an active resistive layer introduced compared to a device in the absence of this layer is manifested in an increase in the brightness of the recorded image at the same recording light intensity or in the possibility of recording the image at lower backlight intensities.

The introduction of a thin-film heater 6 into the active high-resistance resistive layer 5 makes it possible to control the values of R _p and r by changing the slope of the I – V characteristic in the region of negative differential resistance, and, consequently, the sensitivity of the image converter for the given design parameters of the layers of semiconductor 4 and electro-optical crystal 8.

Reading the recorded image is carried out by polarized visible light 9 with a wavelength of λ ₂ passing through the beam splitter 10, the output translucent conductive electrode 3 and the electro-optical crystal 8, which, reflected from the surface of the interference filter 7, is fed to the output of the image converter. Passing further through the analyzer 11, the polarization distribution at the output of the structure is converted into a distribution of the read light intensities, providing visualization of the recorded image.

Thus, the introduction of an active high-resistance resistive layer having a current-voltage characteristic with a region of negative differential resistance leads to an increase in the sensitivity of the device, especially at low light intensities, which allows image registration at lower light intensities compared with the absence of this layer. So, for example, for the case R _p = R _e + R _{f, the} choice of the material of the resistive layer with r 0.9 R _p according to (5) increases the sensitivity by 5 times, and at r 0.96 R _{p by} 12 times. Introducing an active high-resistance resistive layer with negative differential resistance r _ → R _p , you can increase the sensitivity and brightness of the recorded image by 100 or more times. By changing the temperature of the resistive layer using a heater, it is possible to change the range of brightness and sensitivity for a specific structure.

Claims (2)

 1. An image converter comprising an input transparent conductive electrode, a photosensitive semiconductor, an interference filter, an electro-optical crystal, an output transparent conductive electrode, characterized in that an active high-resistance resistive layer with a negative differential resistance between the photosensitive semiconductor and the interference filter is inserted into it.  2. The Converter according to claim 1, characterized in that a thin-film heater is introduced into the active high-resistance resistive layer.

Images