WO2025144319A1

WO2025144319A1 - Semi-active laser seeker head with proximity sensor for laser guided missile systems

Info

Publication number: WO2025144319A1
Application number: PCT/TR2024/051699
Authority: WO
Inventors: Selçuk Seyhun
Original assignee: Roketsan Roket Sanayi ve Ticaret AS
Current assignee: Roketsan Roket Sanayi ve Ticaret AS
Priority date: 2023-12-25
Filing date: 2024-12-24
Publication date: 2025-07-03
Anticipated expiration: 2026-06-25

Abstract

The invention relates to the production of a semi-active laser seeker that has a low volume and weight budget, can be used in miniature ammunition and has a laser proximity sensor.

Description

DESCRIPTION

SEMI-ACTIVE LASER SEEKER HEAD WITH PROXIMITY SENSOR FOR LASER GUIDED MISSILE SYSTEMS

Technical Field of the Invention

State of the Art

In laser guided missile systems, the detection of the target's position is provided by the laser seeker head section. This section consists of a combination of lenses, optical filters, sensors, electronic cards, mechanical bodies and connection elements. In some operational usage scenarios, it is desired for the munitions to be detonated in the air at a certain distance from the target. Thus, it is aimed to increase the effectiveness radius of the warhead. Proximity sensors are used so that laser guided missile systems can detonate in the air at a certain distance from the target without hitting it. In another common application, they are used to detect the target by the proximity sensor and detonate the munitions in case direct contact with air targets cannot be achieved. The most common types are RF proximity and laser proximity sensors. These are independent subsystems located in the same body as the seeker head.

Laser proximity sensors in the literature have separate optical and electronic components located in the seeker body. The laser proximity sensor is controlled as a separate system. Laser proximity sensors can fit into large and blunt nose seeker heads (diameter over 70 mm) due to their size, while they are used in sharp nose seeker heads by placing them next to the body and performing the detection in the direction of the missile's progress. There is no laser proximity sensor application directly located in the seeker nose area in miniature ammunition.

In the invention, which is the subject of the application numbered "WO2012158537" in the state of the art, techniques are explained for the detection of the position where laser signals are used and which comprises an electro-optic device, a detector array connected to one or more lenses to detect the signals, a Si photo detector and an avalanche photo detector (APD). The invention does not solve the problem of having a laser seeker and a laser range finder together.

The invention, which is the subject of the application numbered “WO2019032178” in the state of the art, is a laser range finder that can be used with guided bombs with or without laser seeker heads. As an independent system, it is aimed to increase the effectiveness of the bombs by detonating the bomb kits at a set height without hitting the ground.

The invention, which is the subject of the application numbered “WO2021251929” in the state of the art, is a product that meets the need for a seeker head that can be used in miniature ammunition with an outer diameter of 40 mm. The invention does not meet the need for the seeker head to perform both the laser seeker head and laser range finder functions within a limited volume using the same optical aperture.

The state of the art comprises a system that meets the need for a seeker head that can be used in miniature ammunition with an outer diameter of 40 mm. However, there is no system that allows adding a different detector to the laser seeker head, adding laser diodes, and reading the laser diodes and the new 5-slice sensor to measure distance without increasing the length of the seeker head, and its development is important.

As a result, due to the negativities described above and the inadequacy of existing solutions on the subject, a new technology is needed in the relevant technical field.

Brief Description and Aims of the Invention

The most important aim of the invention is to have the laser seeker head and laser proximity sensor in the same volume, and to use the same optics, the same sensor and electronic card set together. Another aim of the invention is to use the electronic, optical and sensor components of the laser seeker head to track the target marked with the laser marker, while also allowing the same components to be used as a proximity sensor.

Another aim of the invention is to enable this shared use of a special 5 (five) slice laser sensor and the optical components of the seeker head. Thus, target tracking and distance measurement are carried out through a single system.

Another aim of the invention is to provide the use of a semi-active laser seeker head with a laser proximity sensor that can be used in miniature missile systems up to 40 mm in diameter. Using a special sensor, reducing optical components, using electronic components together in target tracking and distance measurement, and reducing the number of mechanical parts also provide the advantages of reducing cost, integration time and total mass.

Description of Drawings

FIGURE-1 is the drawing showing the view of the sensor which is the subject of the invention.

FIGURE-2 is the drawing showing the graphical view of the radiation sensing of the seeker head which is the subject of the invention.

FIGURE-3 is the drawing showing the view of the seeker head which is the subject of the invention.

Reference Numbers

1. Laser diode

2. Laser diode window

3. Outgoing laser pulse

4. Reflected incoming laser beam

5. Lens

6. Filter

7. Sensor

7.1 silicon photodiode 7.2 avalanche photodiode

8. Preamplifier card

9. Gain control card

10. Digitisation, power management and control card module

T1. Intervals between laser pulses

T2. Window interval

TLD. Time taken by the laser proximity sensor for distance measurement

Detailed Description of the Invention

The invention is a product that emerged as a result of the need for an proximity sensor that can be used with a seeker head in a miniature laser guided missile system up to 40 mm in diameter. Instead of the four-slice sensor used in laser seeker heads, a unique sensor with a sensor surface containing 4 slices and 1 circular avalanche photodiode in the middle is used in this seeker head.

As seen in Figure 1 , the sensor (7) has silicon photodiodes (7.1 ) in the four slices of the seeker head and an avalanche photodiode (7.2) in the middle of these silicon photodiodes (7.1 ).

Semi-active laser seeker head with proximity sensor for laser guided missile systems comprises at least one laser diode (1 ) sending outgoing laser pulses (3) with a pulse width of 1 ns towards the front of the seeker; at least one sensor (7) comprising silicon photodiodes (7.1 ) in four slices of the seeker head onto which the incoming laser beam (4) reflected from the obstacle is focused by the seeker lens (5) and a circular avalanche photodiode (7.2) in the middle of these four slices, which enables the detection of the incoming signal with low energy; at least one laser diode window (2) that is located in front of the laser diodes (1 ), has a geometry compatible with the seeker head body, and through which the laser pulses pass; at least one lens (5) that determines the laser divergence and is integrated into the diode packages located in front of the laser diodes (1 ); at least one filter (6) that has special material and coating properties and transmits the radiation at the wavelength at which the laser marker and laser diodes operate, while absorbing other wavelengths; at least one preamplifier card (8) that enables amplification of the signals coming out of the four slices of the sensor (7); at least one gain control card (9) that is managed by the digitisation, control and power management card module (10) and comprises operational amplifiers (OPAMPs) that increase the gain when the signal level detected from the seeker is less than the lowest acceptable digitised level (The lowest acceptable level varies from application to application. When determining this level, it is a common practice to accept as the lowest level the condition that a signal is detected at least three times the level of electronic noise that the cards produce themselves when there is no detected signal. Another common practice is to accept a signal input that is 50% higher than the analogue signal input as the lowest level that the ADC accepts for digitisation) defined in the control card software, or decrease the gain when the signal is high (signal amplitudes that are 20% below the highest analogue input level that the ADC can accept are considered the highest acceptable level. For example, if the highest level voltage that the ADC accepts is 5V, reducing the gain when a voltage above 4.2V is reached); and at least one digitisation, control and power management card module (10) comprising the analogue-to-digital converter (ADC) required to convert the analogue electrical signals coming from the sensor (7), the preamplifier card (8) and the gain control card (9) into digital quantities, the controller that is required to drive all cards and process the data and transmit it to the flight computer, and the components that provide the power requirement at different voltage levels required to perform all these operations.

There is a laser diode (1 ) on each side of the seeker head. When the laser range sensor (7) is desired to be used, outgoing laser pulses (3) with a pulse width of ns (nanoseconds) are sent towards the front of the seeker. The laser pulses proceed by exiting from the flat laser diode windows (2) that are located just in front of the laser diodes (1 ) and have a geometry compatible with the seeker head body. The lenses (5) integrated into the diode packages located in front of the laser diodes (1 ) collect the radiations returning from the target and transmit them to the sensor. In this design, outgoing laser pulses (3) with a total divergence of 3 degrees are sent. The outgoing laser pulses (3) travel at the speed of light and are reflected back from the obstacle (target) that is in front of the seeker. The incoming beams are focused by the seeker optical elements and fall on the sensor (7). Since the incoming signal has low energy, its detection can only be carried out via the circular avalanche photodiode (7.2) that is located in the middle of the sensor (7). The time of flight (TOF) between the sending and detection of the laser pulse is multiplied by the speed of light to estimate the distance with cm precision. The seeker head produced within the scope of the invention can send and detect pulses at a frequency of 10Khz. This property allows the proximity steps to the target to be estimated mathematically with a resolution of approximately 3.5 cm in the case of the laser seeker head being placed on an ammunition flying at the speed of sound.

The avalanche photodiode (7.2) that is located in the middle of the laser sensor (7) constitutes approximately 1/50 of the total area of the sensor (7). In other words, the field loss on the side of the four-slice section used to detect the laser marker pulses and the resulting loss of the seeker head locking range are at a minimum level. The small physical surface area of the laser sensor avalanche photodiode (7.2) ensures that the rise and fall times (see rise/fall time of sensors) are proportionally low compared to large area sensor slices. Due to the low rise times, laser pulses with much narrower pulse widths can be detected. The laser diodes located on the seeker produce short but high peak energy pulses by emitting 1 ~1 ns wide laser. Such narrow pulses can be easily detected by the small area avalanche photodiode (7.2). These properties also allow the laser diodes (1 ) located on the laser seeker head to have lower pulse energy, thus being physically smaller, and to have a suitable volume budget on such a small seeker head.

In laser designators used with laser guided ammunition, laser pulses generally have pulse widths below 15-20ns. Depending on the marking code, there are intervals of approximately 50ms-100ms (T1 ) between laser pulses. Laser seekers open windows (T2) between 10us-20us while waiting for laser pulses, taking into account the laser marker timing errors. The remaining time is the time used by the laser proximity sensor for distance measurement (TLD).

In T2 times, the pulses coming from the laser marker to the laser are monitored, and in TLD times, the pulses sent from the laser diodes are detected and the approach distance is monitored. An ammunition flying at the speed of sound travels less than 1 cm in T2 time. As can be seen, this time for which the laser proximity sensor is not used is an insignificant time. Figure 2 shows the T2 and TLD time intervals, which are sequentially segmented and defined as fixed widths that do not change throughout the flight. After the laser seeker head starts to detect reflections from a target illuminated by a laser marker, the digitisation, power management and control card module (10) first checks whether the incoming laser pulses are sent at the expected frequency, i.e., with the required laser code. This period is defined as T1 . After that, since it knows when the next laser pulse should arrive, it waits for the next laser marker pulse within a certain time interval within an error interval window. This window interval is also defined as T2 in the time dimension. The T 1 -T2 period in between is used as the time allocated for laser distance measurement. This period is called the TLD period.

When the TLD time interval comes, a laser pulse is sent in the direction of the front of the seeker head with laser diodes (1 ). The moment the laser is sent is recorded by the controller as TO. If there is an obstacle in front of the transmitted laser pulse, it is reflected from there and returns at the speed of light and is detected by the avalanche photodiode (7.2). The time it takes for the laser to go back and forth from the moment TO is called TOF (time of flight). Since the light travels twice the distance to the target at the speed of light (C=3x108m) during TOF, the smallness of the target can be easily calculated with the equation D= (CxTOF)/2. The laser diodes (1 ) used are designed in such a way that the energy reflected from a target with approximately 20% reflectivity is detected by the Si avalanche photodiode located on the sensor and the target distance is measured. In this case, if there is a target at 50m away at most, a signal is expected to be detected within TOF=(2xD)/C=(2x50)/3x(10^A8)=0.33us. If no signal is detected, the remaining time for the TLD period is controlled by the digitisation, power management and control card module (10). If there is time, the measurement is taken again. If there is no time, the next TLD period is waited for.

In case of marking with 20Hz, the fastest code of laser markers, TLD periods are in the range of T1 -T2=50ms-20us=49.8ms. In other words, theoretically, 48.9x103us/0.33us = 149000 times time measurement can be performed in the TLD time interval. In reality, since the speed of the ammunition is very small compared to the speed of light, energy and processor load are saved by taking measurements at much lower frequencies. For example, if we measure the distance at 1 ms instead of 0.33us for an ammunition flying at the speed of sound (343m/s), the target distance can be measured at 34.3 cm resolution (intervals). With the distance measurements made one after the other at this resolution, the proximity to the target can be followed precisely and the munitions can be detonated at the appropriate location. In reality, the measurement frequency should be changed dynamically. If a problem-free measurement is achieved and gradually decreasing target distances are measured, the measurement frequency is not changed. However, if measurement problems occasionally give inconsistent results due to atmospheric backscattering or other physical obstacles, the measurement frequency is increased and erroneous measurement results are eliminated. In a successful measurement sequence, it is measured that the time between TO and TOF gradually decreases.

The working principle of the semi-active laser seeker head with proximity sensor for laser guided missile systems is as follows; the laser pulses emitted from the laser marker and reflected from the target reach the lens (5) and filter (6), which are the seeker optics. In addition, secondary laser pulses caused by scattering and reflection are detected by the four-slice sensor (7) by focusing and optically filtering (6) through optics. The signals coming out of the 4 slices (quadrant) of the sensor (7) reach the 4- channel collector circuit located in the preamplifier card (8) and the gain control card (9) respectively. Here, the 4-channel signal is converted into the TS total signal. TS is sent to the trigger circuit located in the gain control card (9). The trigger circuit generates a laser pulse observation signal if the TS signal is higher than a certain threshold level and transmits it to the digitisation, power management and control card module (10). The digitisation, power management and control card module (10) examines the magnitude of the detected laser pulses via the single-channel fast A/D. It decides that the largest signal in the pulse train is the target and operates the multichannel A/D to digitise the slice (quadrant) data one by one at the time the large pulse arrives. Using the incoming data, it finds the normalised orientations of the detected laser pulse with respect to the seeker head axis.

If there is no detected signal, the preamplifier card (8) is activated. If there is still no detected signal, the gain control card (9) is used to increase the gain level until the signal is detected. If the signal is still not detected, the highest gain level is waited until the signal is detected. The preamplifier and variable gain amplifier are used through the digitisation, power management and control card module (10). When the laser is locked on to the marker, the detected signal level increases as it approaches the target. The digitisation, power management and control card module (10) ensures that the lock on the target is maintained by closing the preamplifier card (8) and reducing the gain. The laser seeker head does not detect lasers between pulses, depending on the laser designator code it is locked to. During these periods, the digitisation, power management and control card module (10) sends laser pulses from the laser diode (1 ) located on both sides of the seeker. The laser pulses have pulse widths of 1 ns. The detection of the laser pulses is performed by the E sensor (7) section, which is an avalanche photodiode (7.2) located on the sensor. Since the laser pulses sent by the laser diodes (1 ) and reflected back from the obstacle in front of the seeker have very low energy, detection is performed at the highest gain level. The digitisation, power management and control card module (10) measures the time between the pulse sent from the laser diode (1 ) and the time it is detected. In the current embodiment, laser pulses that return longer than the time required to detect targets that are more than 50m away are not taken into account. Detections occurring under this period are monitored, and if measurements continue to show that there are no false detections and that there is a proximity, the flight computer of the ammunition is informed after the proximity to the specified distance is achieved.

Claims

1. Semi-active laser seeker head with proximity sensor for laser guided missile systems, comprising

- at least one laser diode (1 ) sending outgoing laser pulses (3) with a pulse width of 1 ns towards the front of the seeker;

- at least one sensor (7) comprising silicon photodiodes (7.1 ) in four slices of the seeker head onto which the incoming laser beam (4) reflected from the obstacle is focused by the seeker lens (5) and a circular avalanche photodiode (7.2) in the middle of these four slices, which enables the detection of the incoming signal with low energy;

- at least one laser diode window (2) that is located in front of the laser diodes (1 ), has a geometry compatible with the seeker head body, and through which the laser pulses pass;

- at least one lens (5) that determines the laser divergence and is integrated into the diode packages located in front of the laser diodes (1 );

- at least one filter (6) that has special material and coating properties and transmits the radiation at the wavelength at which the laser marker and laser diodes operate, while absorbing other wavelengths;

- at least one preamplifier card (8) that enables amplification of the signals coming out of the four slices of the sensor (7);

- at least one gain control card (9) that is managed by the digitisation, control and power management card module (10) and comprises operational amplifiers that increase the gain when the signal level detected from the seeker is less than the lowest acceptable digitised level defined in the control card software, or decrease the gain when the signal is high; and at least one digitisation, control and power management card module (10) comprising the analogue-to-digital converter required to convert the analogue electrical signals coming from the sensor (7), the preamplifier card (8) and the gain control card (9) into digital quantities, the controller that is required to drive all cards and process the data and transmit it to the flight computer, and the components that provide the power requirement at different voltage levels required to perform all these operations.

2. Semi-active laser seeker head with proximity sensor for laser guided missile systems according to Claim 1 , comprising the avalanche photodiode (7.2) located in the centre of the laser sensor (7), forming 1/50 of the total area of the sensor (7).