RU2690718C1 - Optical radiation receiver - Google Patents

Abstract

FIELD: physics.SUBSTANCE: invention relates to reception of optical radiation and to a receiver of optical radiation. Receiver includes a photosensitive element, a signal processing circuit and an optical shutter. Optical gate is made in the form of a shutter with two working positions. Proposed device comprises shutter drive consisting of current source and bimorph element composed of two-layer flat spring. One of the layers of the bimorph element is electrically conductive, the opposite ends of which are connected to the output of the current source. Second layer is made from transparent material having lower coefficient of temperature expansion. One end of the bimorph element is rigidly fixed on the body of the receiver, and the other end is twisted relative to it by 90 degrees around the longitudinal axis. Current-conducting layer is applied on the lower part of the bimorph element prior to twisting, and the upper part is a curtain with a semitransparent coating, which is arranged so that when the bimorph element is deformed under the action of the flowing current, the photosensitive element is opened.EFFECT: technical result consists in ensuring the device operability under active and passive laser counteracting conditions with minimum dimensions and maximum sensitivity at low signal level.3 cl, 4 dwg, 2 tbl

Description

The invention relates to the technique of receiving pulsed optical radiation, mainly to receivers of pulsed laser range finders and other light-emitting devices.

Known receivers of optical radiation [1] for systems of pulsed laser location, designed to convert into electrical signals reflected by remote objects of the probe pulses of laser radiation and the timing of electrical pulses to determine their delay τ relative to the moment of radiation of the laser probe pulse. This delay is used to judge the distance R to a reflecting object using the formula R = cτ / 2, where c is the speed of light. Optical receivers [2-3] are constructed in a similar way, containing a photosensitive element and a signal processing circuit. These devices have a limited dynamic range that prevents the use of such receivers in range meters and other equipment with increased accuracy requirements. There are a number of technical solutions aimed at expanding the dynamic range and improving the accuracy of temporal fixation of received signals [4-5]. However, these solutions do not ensure the efficiency of the FPU if the energy of the input radiation exceeds the level of radiation resistance of the photosensitive element.

The closest in technical essence of the present invention is a receiver containing a photosensitive element, a signal processing circuit, a beam splitter, a photo sensor, a delay device and an optical shutter mounted in front of the photosensitive element [6]. In this receiver, the optical shutter does not open if the signal from the photo sensor exceeds the threshold value corresponding to the input radiation level exceeding the radiation resistance threshold of the photosensitive element. Otherwise, the shutter opens and the input radiation enters the photosensitive element. The delay time of the signal in the delay line must exceed the response time of the gate to the control pulse from the photo sensor. Thus, the operation of the device is ensured not only in the working dynamic range of the reflected signals, but also beyond its limits - in conditions of active or passive counteraction.

The disadvantage of the receiver [6] is the radiation losses in the beam splitter, the delay device and the optical shutter, as well as the shutter speed limitations, which increase the signal delay in the delay device. This, in turn, leads to losses in the receiving path, distortion of the shape of the received signal, an increase in the dimensions of the device, especially due to the beam splitter, the delay device and the optical shutter.

The objective of the invention is to ensure the operability of the device in the conditions of active and passive laser counteraction with minimum dimensions and maximum sensitivity of the laser receiver for weak input signals.

This problem is solved due to the fact that in a known laser receiver containing a photosensitive element, a signal processing circuit and an optical shutter installed in front of the photosensitive element, the optical shutter is designed as a shutter with two working positions, and the shutter drive consisting of from a current source and a bimorph element in the form of a two-layer flat spring, one of the layers of the bimorph element is made conductive, the opposite ends of which are connected via a key to the output current point, and the second layer is made of optically transparent material having a lower coefficient of thermal expansion compared to the first layer, one end of the bimorph element is fixedly mounted on the receiver body, and the second end is twisted relative to it by 90 degrees around the longitudinal axis of the bimorph element, and the conductive layer is applied only to the lower part of the bimorph element to the twist, and the upper part is a curtain with a translucent coating, placed so that in the first working position when the power source is turned off shutter overlaps the aperture of the photosensitive member, while the deformation of the bimorph element under the action of current flowing opened photosensitive member, the photosensitive member moving parallel at a distance

where r is the radius of the arc formed by the bimorph element in the second working position; L is the length of the bimorph element with a conductive coating; h is the length of the upper portion of the bimorph element from the end of the conductive coating to the axis of the photosensitive element; d _FCE - diameter of the working area of the photosensitive element; a is the distance from the shutter to the surface of the photosensitive element; α is the angle of view of the photosensitive element; Δ is the error of fixing the lateral position of the shutter in the absence of a control signal at the drive input; b - the thickness of the rim of the curtain.

где E_фпу - энергетическая чувствительность оптического приемника; E_мин и Е_макс - нижняя и верхняя границы диапазона энергий перегрузочного сигнала; Е_пду - предельно допустимый уровень энергии сигнала, поступающего на фоточувствительный элемент оптического приемника.The transmittance of the semitransparent cover of the shutter τ, can meet the condition

where E _fpu is the energy sensitivity of the optical receiver; E _min and E _max - the lower and upper limits of the energy range of the overload signal; E _{remote control} - the maximum allowable energy level of the signal supplied to the photosensitive element of the optical receiver.

The conductive layer of the bimorph element can be made in the form of a chain of two or more parallel strips connected in series so that the beginning and end of the conductive circuit are on the fixed side of the bimorph element.

In FIG. 1 shows a functional diagram of the receiver. FIG. 2 illustrates a shutter drive device in its first position. FIG. 3 explains the calculated ratios for the second curtain position. FIG. 4 shows the variants of the conductive layer.

The laser receiver (Fig. 1) consists of a photosensitive element 1 (for example, a photodiode) and a signal processing circuit 2, which includes a preamplifier 3, an amplifier 4 and a driver of the output signal 5, the output of which is the output of the device. In front of the photosensitive element is a translucent shutter 6 with a drive 7, controlled by the output of the logic module 8, one of the inputs of which is connected to the output of the signal processing circuit, and the second is its control input. The optical receiver is placed in a sealed enclosure 9 with an optical window 10, through which the received radiation enters the photosensitive element 1. The shutter drive (Fig. 2) consists of a bimorph element 11 and a current source 12, through a switch 13 connected to the conducting layer of the bimorph element. The bimorph element 11 is a curved flat spring in the form of a composition of two layers - a conductive layer 14 and a second layer (substrate) 15 (Fig. 2).

The stroke of the shutter ΔC between its two fixed positions (Fig. 3) is determined from the condition of a fully closed and fully open photosensitive element in two working positions of the shutter. The physical model of the deformation of the bimorph element - FIG. 3a). Geometric model - FIG. 3b).

Depending on the technological features of the production, the conductive layer may be deposited on the substrate in the form of a single strip (Fig. 4a), two bands (Fig. 4b) or four bands (Fig. 4c).

The device works as follows.

In the initial state, a translucent curtain 6 with a transmittance τ is in front of the working platform of the photosensitive element 1, attenuating the signals arriving at it 1 / τ times. If a radiation source is in the field of view of the photosensitive element, creating a light on the photosensitive element 1 that exceeds the sensitivity threshold of the signal processing circuit 2, the key 13 remains open, the shutter remains in its original position, and the optical receiver works in a protected mode.

In the absence of a signal at the output of the device and at the input of the logic module 8, the latter sends a signal for closing the key 13, and the current source 12 is connected to the conductive layer of the bimorph element 11. Under the action of the flowing current, this layer heats up and the bimorph element is bent. Under the action of the force created by the bimorph element, the shutter moves a distance ΔC (Fig. 3).

When the conductive layer is heated by the current flowing through it, the curvature k of the bimorph element, that is, the reciprocal of the bend radius of the rod, changes according to [7]

Where:

ε = (α ₁ -α ₂ ) ΔT;

E ₁ and E ₂ are the elastic moduli of the materials of the first and second layers;

h ₁ and h ₂ - the thickness of the layers of the bimorph element (Fig. 3);

α ₁ and α ₂ - coefficients of thermal expansion of the materials of the layers;

ΔT is the temperature difference before and after heating the bimorph element.

When the conductive layer is rapidly heated by pulsed current, the second layer does not have time to warm up during the pulse, and the curvature of the bimorph element increases even more compared to the value obtained from expression (1).

The arrow of the arc formed during the deformation of the bimorph element (Fig. 3b) is determined by the formula

Where

r = 1 / k;

θ = kL;

L is the length of the conductive layer.

The additional shift of the shutter C _h is due to the inclination of the shoulder h by the angle α (Fig. 2b).

Curtain stroke

Example 1

The bimorph element is a metal-glass ribbon (Pyrex + Nichrome) with characteristics.

In brackets - shortened version L = 5 mm, h = l mm.

According to (1) k = 6.58 (α ₂ -α ₁ ) ΔT = 98.6ΔТ10 ^-6 . r = 1 / k.

If the shutter is made translucent, in its initial position, the receiver can receive signals exceeding the nominal sensitivity level of the receiver by 1 / τ times or more without damage to the photosensitive element.

Of the indications in FIG. 1 it can be seen that to cover the working platform of the photosensitive element with a curtain, the condition

where d _pcs - the working diameter of the translucent portion of the curtain; d _FCE - diameter of the working area of the photosensitive element; a is the distance from the shutter to the surface of the photosensitive element; α is the angle of view of the photosensitive element; Δ is the error of fixing the initial position of the shutter. The value of Δ includes both the alignment errors and the temperature drift in the ambient temperature range.

The working offset of the shutter ΔС must be at least d _pcs .

Example 2

Equivalent dimensions of the moving part of the bimorph element 2 × 0.5 × 0.2 = 0.2 mm ³ = 2⋅10 ^-4 cm ³ . With a glass density of 2.5 g / cm ^{3, the} mass is m ~ 5⋅10 ^-4 g = 5⋅10 ^-7 kg.

The impact force of the bimorph element on the curtain F = 0.001 N.

Acceleration a = F / m = 0.001 / 5⋅10 ^-7 ~ 2000 m / s ² .

Offset S = 0.3 mm = 3⋅10 ^-4 m.

Time to open the curtain in working position

Example 3

A conductive layer (nichrome) with a length of 20 mm and a cross section of 0.1 × 0.1 mm (Fig. 4c).

Density ρ _t = 7.94 g / cm ³ ; heat capacity β = 0.57 J / kgK.

The volume of the conductive layer V _T = 2⋅10 ^-4 cm ³ . Its mass is m = ρ _T V _T = 1.6⋅10 ^-6 kg.

Energy for heating the conductive layer at 300 °

Е _Т = βmΔТ = 0.57⋅1.6⋅10 ^-6 ⋅300 = 0.000273 J = 0.273 mJ.

Characteristics of the power source.

Power consumption of conductive layer

P _T = E _T / t, where t is the pulse duration.

For the example in question

Р _Т = Е _Т / t = 0.273 mJ / 0.5 ms ~ 0.55 W.

Conductive layer resistance

R _T = ρ _R L _T / S _t ~ 10 ^-6 ⋅2⋅10 ^-2 / (0.1⋅0.1) ⋅10 ^-6 = 2 Ohm,

where ρ _R ~ 1 µOhm⋅m - the resistivity of nichrome, L _T = 0.02 m - the length of the conductive layer; S _T - the cross-sectional area of the thread.

The power released in the conductor resistance R _T

Р _T = I _T ² ⋅R _T , from where the consumed current

I _T = (P _T / R _T ) ^0.5 = (0.55 / 2) ^0.5 = 0.51 A.

Source voltage

U _T = P _T / I _T = 0.55 / 0.51 ~ 1 V.

The shutter attenuation coefficient τ is determined by the expected level of laser illumination from an external source, which is dangerous for the photosensitive element in the given operating conditions of the receiver of pulsed optical signals as part of the equipment for which this receiver is intended. In this case, the shutter may be in the form of a transparent plane-parallel plate with a translucent coating applied, for example, by metallization. The thickness of this coating determines the value of τ while maintaining the overall-connecting parameters.

The described technical solution ensures the safe use of an optical radiation receiver as part of any equipment and in any operating conditions. At the same time, the dimensions and mass of the curtain with a drive, as well as the volume of the logic module, allow these nodes to be embedded into existing miniature receivers without changing their sizes. The placement of the protection elements of the receiver as part of its sealed enclosure ensures their reliability, durability and maximum service life.

Thus, the proposed technical solution ensures the operability of the device in the conditions of active and passive laser counteraction with minimum dimensions and maximum sensitivity of the receiver of pulsed optical signals with a low signal level.

Information sources

1. V.A. Volokhatyuk and others. "Questions of optical location." - M .: Soviet Radio, M, 1971. - p. 213.

2. V.G. Vilner et al. Analysis of the input circuit of a photodetector with an avalanche photodiode and noise-reduction correction. "Optical-mechanical industry". No. 9, 1981 - with. 593.

3. V.A. Afanasyev et al. Sensitivity threshold of a pulsed optical radiation receiver with high input impedance. Electronic equipment. Series 11. "Laser technology and optoelectronics." 1988, c. 3. - s. 78-83.

4. V.G. Vilner et al. Receiver of pulsed optical signals. The patent of the Russian Federation №2 506 547.

5. P.M. Borovkov et al. Peculiarities of circuit design of pulsed threshold FPU with a short sensitivity recovery time after exposure to an overload pulse. Applied Physics, No. 1, 2015 - p. 61-65.

6. Radiation receiver with active optical protection system. USpatentNo6,548,807 - prototype.

7. Clyne T.W. InterFacial debonding. KeyEngineeringMaterials (Switzerland) .Vol. 116-117, 1996, pp. 307-330.

Claims (5)

1. Receiver of optical radiation containing a photosensitive element, a signal processing circuit and an optical shutter installed in front of the photosensitive element, characterized in that the optical shutter is made in the form of a shutter with two working positions, and a shutter drive consisting of a current source and bimorph element in the form of a two-layer flat spring, one of the layers of the bimorph element is made conductive, the opposite ends of which are connected via a key to the output of the current source, and the second oh is made of optically transparent material having a lower coefficient of thermal expansion compared to the first layer, one end of the bimorph element is fixedly mounted on the receiver body, and the second end is twisted relative to it by 90 degrees around the longitudinal axis of the bimorph element, and the conductive layer is applied only on the lower part of the bimorph element to the twist, and the upper part is a curtain with a translucent coating, placed so that in the first working position with the power off regular enrollment current aperture overlaps the blind photosensitive member, while the deformation of the bimorph element under the action of current flowing opened photosensitive member, the photosensitive member moving parallel at a distance

where r is the radius of the arc formed by the bimorph element in the second working position; L is the length of the bimorph element with a conductive coating; h is the length of the upper portion of the bimorph element from the end of the conductive coating to the axis of the photosensitive element; d _FCE - diameter of the working area of the photosensitive element; a is the distance from the shutter to the surface of the photosensitive element; α is the angle of view of the photosensitive element; Δ is the error of fixing the lateral position of the shutter in the absence of a control signal at the drive input; b - the thickness of the rim of the curtain. 2. Receiver according to claim 1, characterized in that the transmittance of the semitransparent shutter cover τ meets the condition

where E _fpu is the energy sensitivity of the optical receiver; E _min and E _max - the lower and upper limits of the energy range of the overload signal; E _{remote control} - the maximum allowable energy level of the signal supplied to the photosensitive element of the optical receiver. 3. The receiver according to claim 1, characterized in that the conductive layer of the bimorph element is made in the form of a chain of two or more parallel strips connected in series so that the beginning and end of the conductive circuit are on the fixed side of the bimorph element.

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