DE102013011301B3 - Modulation device for external modulation of laser beam, comprises drive unit, and modulator unit that has modulator driver with drive transmission function and modulator with modulator transfer function, which is acted upon by laser beam - Google Patents

Abstract

The modulation device comprises a channel system (1a) with a modulator unit (30a), which has a modulator driver (40a) with a drive transmission function (f-1) and a modulator (50a) with a modulator transfer function (g-1). The modulator is acted upon during operation by the laser beam to be modulated and emits a modulated laser beam. A drive unit (20a) receives a default signal (U-code,1) from a signal generator (10a). The drive transmission function and the modulator transfer function are imaged in an inverse shape by the drive unit, such that a usable laser beam is received. The usable laser beam is received following the default signal. Another modulator is acted upon during operation by the residue laser beam of the former modulator and emits another modulated laser beam.

Description

The invention relates to a modulation device for the external modulation of a laser beam to be modulated.

From the US Pat. No. 7,920,255 B2 a modulation device for the external modulation of a laser beam to be modulated is known (US Pat. 3 and associated text). The modulation device is part of a Jamminglaser system, which is used for example for defense against missiles by their IR seeker detectors are disturbed. The modulation device comprises a modulator. During operation, the modulator is acted upon by the laser beam to be modulated and emits a modulated laser beam. The US Pat. No. 7,920,255 B2 does not give details about external modulation. There are no indications of a modulator transfer function or a driver transfer function. That a modulator also emits a residual laser beam is not mentioned. In this context is from the US Pat. No. 7,920,255 B2 merely to discern that the external modulator is, for example, a type of shutter which is either light-absorbing or translucent according to an electrical signal (col. 28, lines 56-58).

The US Pat. No. 4,616,356 shows a modulation device for the external modulation of a laser beam to be modulated. The modulation device can be used in optical drives for storing data. The modulation device comprises a modulator device with a modulator driver and a modulator. During operation, the modulator is acted upon by the laser beam to be modulated and emits a modulated laser beam. The modulator driver is driven by a driver during operation. The control device receives a default signal during operation. The emitted modulated laser beam, which is also the Nutzlaserstrahl at the same time, follows the default signal.

A textbook (Otto Föllinger: Control Engineering, Hüthig Verlag Heidelberg, 2008, pp. 1-10, ISBN 978-3-7785-2970-6) teaches to map the transfer function of the overall system in an inverse form in a controller.

The invention is based on the object, a modulation device for external modulation in such a way that during operation of the modulation device of the modulated laser beam follows a default signal even at high frequencies with high accuracy and that the efficiency is increased.

This object of the invention is solved by the features of claim 1.

The advantages of the invention are that the default signal is impressed with a very low distortion on the laser beam to be modulated. The advantages therefore result that the modulation device comprises a first channel system with a first modulator device. The first modulator device comprises a first modulator driver having a first driver transfer function and a first modulator having a first modulator transfer function. The aforementioned transfer functions must be known in order to achieve a modulation via a controller. During operation, the first modulator is acted upon by the laser beam to be modulated and emits a first modulated laser beam and, optionally, also a first residual laser beam. The residual laser beam results from the use of a modulator, which switches back and forth between two beam paths. During operation, the first modulator driver is driven by a first drive device, which in turn receives a first default signal from a first signal generator. The drive means maps the inverse driver transfer function and the inverse modulator transfer function such that a first payload laser beam following the default signal is obtained. In the simplest case, the first payload laser beam is the first modulated laser beam if the first modulated laser beam is not further processed. In the new method there is a control and no complex, complex, high-loss control with a feedback and a temporal changes of the setpoint. Measuring probes in a decoupled measuring laser beam in order to regulate the currently emitted laser power by returning this signal are superfluous. The modulation device comprises a second modulator. During operation, the second modulator is acted on by the first residual laser beam of the first modulator and outputs a second modulated laser beam and a second residual laser beam. The fact that the first residual laser beam is further processed and used at least partially increases the efficiency.

According to a further embodiment of the invention, the modulation device comprises a second channel system with a second modulator device. The second modulator device comprises a second modulator driver having a second driver transfer function and a second modulator having a second modulator transfer function. During operation, the second modulator is acted upon by the first residual laser beam and emits a second modulated laser beam and, optionally, also a second residual laser beam. The second modulator driver is driven during operation by a second drive device. The second drive device in turn receives a second preset signal from a second signal generator. With the second drive device, the inverse second driver transfer function and the inverse second modulator transfer function can be imaged such that a second payload laser beam is obtained which follows the second default signal. With the second channel system to provide an independent second Nutzlaserstrahl. The second channel system increases the efficiency.

According to a further embodiment of the invention, which relates to the second channel system, the second drive device additionally processes the first specification signal for determining properties of the first residual laser beam. This continues the idea of control.

According to a further embodiment of the invention, the second residual laser beam is also further processed to a Nutzlaserstrahl to further increase the efficiency. For this purpose, a third channel system can serve.

According to a further embodiment of the invention, the first or the second modulated laser beam is supplied during operation to a converter, wherein in operation a Nutzlaserstrahl other frequency is obtained. For training as a Jammer laser system for the band II (3-5 microns) and band III (8-12 microns) a non-linear conversion by means of converters in the form of optical parametric oscillators (OPOs) is necessary. This results from the fact that no directly emitting solid-state lasers exist in this wavelength range and the required power and beam quality can not be covered by semiconductor lasers. A compact, efficient jamming laser system is made possible which emits interfering laser beams simultaneously and independently in the different bands. The radiation in band II or III can not be directly modulated, since modulator materials for these bands have too large intrinsic losses or have low optical damage thresholds. Therefore, the modulation of the converter is carried out via its pump radiation. Since nonlinear converters generally exhibit a threshold behavior, this must be taken into account for correct analog modulation. Otherwise, part of the modulation signal would be cut off because the converter does not emit below its threshold.

According to a further embodiment of the invention, the converter has a converter transfer function. The inverse converter transfer function is additionally mapped by the drive device of the respective channel system. The inverse converter transfer function, like the inverse transfer functions of the downstream driver and the modulator, must be taken into account by the driver in order for the payload laser beam to follow the default signal.

According to a further embodiment of the invention, the laser beam to be modulated is obtained from a solid-state laser, an OPO or from a diode laser. This allows you to meet different applications.

According to a further embodiment of the invention, the laser beam to be modulated is a continuous laser beam. This reduces the computational effort in the drive device.

According to a further embodiment of the invention, the modulator is an acousto-optic modulator or an electro-optical modulator with polarizer. Both enable electronically simple control. An acousto-optic modulator has the advantage that it spatially deflects a laser beam, and this deflection exists only when a control signal is present. Thus, an absolute modulation depth of 100% can be achieved, that is, the deflected beam has a power of exactly zero in the absence of a modulation signal. This is not the case with electro-optical modulators. Often the power between minimum and maximum modulation can only be set to 1: 100 to 1: 1000. The reasons for this are optical coatings, the lateral homogeneity of the delay of the modulator and the degree of polarization of the input beam.

Embodiments of the invention are explained below with reference to the drawings. In each case as a schematic sketch show:

1 a first modulation device in the form of a single-channel system;

2 a second modulation device in the form of a single-channel system with a converter;

3 a third modulation device in the form of a two-channel system.

Fig. 1, single-channel system

• a) die Modulationsvorrichtung umfasst ein erstes Kanalsystem 1a mit einer ersten Modulatoreinrichtung 30a,
• b) die erste Modulatoreinrichtung 30a umfasst einen ersten Modulatortreiber 40a mit einer ersten Treiber-Übertragungsfunktion f₁ und einen ersten Modulator 50a mit einer ersten Modulator-Übertragungsfunktion g₁,
• c) der erste Modulator 50a wird im Betrieb vom zu modulierenden Laserstrahl beaufschlagt und gibt einen ersten modulierten Laserstrahl und einen ersten Restlaserstrahl mit einer Leistung P_rest,1 ab,
• d) der erste Modulatortreiber 40a wird im Betrieb von einer ersten Ansteuereinrichtung 20a angesteuert,
• e) die erste Ansteuereinrichtung 20a erhält im Betrieb ein erstes Vorgabesignal U_code,1 von einem ersten Signalgenerator 10a,
• f) mit der ersten Ansteuereinrichtung 20a sind die erste Treiber-Übertragungsfunktion f₁ und die erste Modulator-Übertragungsfunktion g₁ in inverser Form derart abbildbar, dass ein erster Nutzlaserstrahl der Leistung P_out,1 erhalten wird, der dem Vorgabesignal U_code,1 folgt.

The 1 shows a modulation device for the external modulation of a laser beam to be modulated, with the following features:

• a) the modulation device comprises a first channel system 1a with a first modulator device 30a .
• b) the first modulator device 30a includes a first modulator driver 40a with a first driver transfer function f ₁ and a first modulator 50a with a first modulator transfer function g ₁ ,
• c) the first modulator 50a is acted upon in operation by the laser beam to be modulated and outputs a first modulated laser beam and a first residual laser beam with a power P _{rest, 1} ,
• d) the first modulator driver 40a is in operation by a first drive device 20a driven,
• e) the first drive device 20a receives in operation a first default signal U _{code, 1} from a first signal generator 10a .
• f) with the first drive device 20a the first driver transfer function f ₁ and the first modulator transfer function g _{1 are} in inverse form such that a first payload laser beam of the power P _{out, 1 is} obtained, which follows the default signal U _{code, 1} .

Since there is only a one-channel system, instead of a "first modulator device", a "first modulator driver", a "first modulator", etc., one would also have simplified a "modulator device", a "modulator driver", a "modulator". , etc. can speak.

Fig. 2, single-channel system with converter

Deviating from the first modulation device according to 1 show the 2 in that the first modulated laser beam is in operation a converter 60a is supplied. This gives a Nutzlaserstrahl other frequency. The converter 60a has a converter transfer function h ₁ . The drive device 20a of the first channel system 1a Also maps the inverse converter transfer function h ₁ .

Fig. 3, two-channel system with converter

The third modulation device after 3 includes in addition to the first channel system after 1 a second modulator 50b , The second modulator 50b is in operation by the first residual laser beam of the first modulator 50a acts on and outputs a second modulated laser beam and a second residual laser beam.

• a) die Modulationsvorrichtung umfasst ein zweites Kanalsystem 1b mit einer zweiten Modulatoreinrichtung 30b,
• b) die zweite Modulatoreinrichtung 30b umfasst einen zweiten Modulatortreiber 40b mit einer zweiten Treiber-Übertragungsfunktion f₂ und einen zweiten Modulator 50b mit einer zweiten Modulator-Übertragungsfunktion g₂,
• c) der zweite Modulator 50b wird im Betrieb vom ersten Restlaserstrahl der Leistung P_rest,1 beaufschlagt und gibt einen zweiten modulierten Laserstrahl der Leistung P_pump,2 und einen zweiten Restlaserstrahl der Leistung P_rest,2 ab,
• d) der zweite Modulatortreiber 50b wird im Betrieb von einer zweiten Ansteuereinrichtung 20b angesteuert,
• e) die zweite Ansteuereinrichtung 20b erhält ein zweites Vorgabesignal U_code,2 von einem zweiten Signalgenerator 10b,
• f) mit der zweiten Ansteuereinrichtung 20b sind die zweite Treiber-Übertragungsfunktion f₂ und die zweite Modulator-Übertragungsfunktion g₂ in inverser Form derart abbildbar, dass ein zweiter Nutzlaserstrahl erhalten wird, der dem zweiten Vorgabesignal U_code,2 folgt.

A modulation device concretized in this respect has the following features:

• a) the modulation device comprises a second channel system 1b with a second modulator device 30b .
• b) the second modulator device 30b includes a second modulator driver 40b with a second driver transfer function f ₂ and a second modulator 50b with a second modulator transfer function g ₂ ,
• c) the second modulator 50b In operation, the first residual laser beam of the power P _{residual, 1 is} applied and outputs a second modulated laser beam of the power P _{pump, 2} and a second residual laser beam of the power P _{rest, 2} ,
• d) the second modulator driver 50b is in operation by a second drive device 20b driven,
• e) the second drive device 20b receives a second default signal U _{code, 2} from a second signal generator 10b .
• f) with the second drive device 20b the second driver transfer function f ₂ and the second modulator transfer function g _{2 are} in inverse form such that a second Nutzlaserstrahl is obtained, which follows the second default signal U _{code, 2} .

The second drive device 20b additionally processes the first specification signal U _{code, 1} for determining properties of the first residual laser beam.

The second modulated laser beam with the power P _{pump, 2} becomes a converter during operation 60b is supplied. This gives a Nutzlaserstrahl other frequency. The converter 60a has a converter transfer function h ₂ . The drive device 20b of the second channel system 1b is the inverse converter transfer function h ₂ by pressing.

In deviation from the illustrated embodiment, the second residual laser beam with the power P _{rest, 2} can be further processed, for example, in a third channel system to a third Nutzlaserstrahl.

Details: laser beam to be modulated, modulator, default signal, control device

Depending on the application, the laser beam to be modulated can be obtained from a solid-state laser, an OPO or from a diode laser. The laser beam to be modulated may be a partial laser beam of predetermined energy. For this purpose, for example, a part of the laser beam can be coupled via a half-wave plate and a polarizer in a partial laser beam. Partial laser beams can each be modulated independently of one another in likewise independent external modulation devices. However, if a partial laser beam and associated external modulation devices are not used, the power provided in this regard will be lost for the other partial laser beams (channels).

The laser beam to be modulated is expediently a continuous laser beam in order to reduce the computational effort.

The first modulator 50a and / or second modulator 50b is an acousto-optic modulator or an electro-optic modulator with a polarizer.

The first or second modulation signal may be, for example, a square wave signal.

The drive device may be an analog interface circuit, a μController circuit or an FPGA circuit.

Simplifications in the description of the transfer functions

The following explains the transfer functions. In 1 and 2 the variables are indexed with reference to the channel system. The first default signal U _{code, 1} is the default signal of the first channel system. For the sake of simplicity, the index of the channel system will be omitted below when the one-channel system after 1 or the single-channel system 2 is affected.

Transmission functions, single-channel system, Fig. 1

The modulator 56a is inserted in the beam path of the laser beam to be modulated _in P. The modulator 50a is from a modulator driver 40a applied. The modulator driver 40a in turn, by a drive device 20a supplied, which converts the default signal U _code such that the often non-linear modulator transfer function g and the driver transfer function f is compensated by a suitable driver input voltage U _mod .

Generally, a modulator transfer function g exists between the modulator signal V, the incident laser power P _in, and the laser power P _out at the payload (seen here as useful power) P _out = P _in g (V).

The modulator signal V, which is the modulator 50a in turn, has a transfer function f from the driver input voltage U _{mod of} the modulator driver 40a : V = f (U _mod ).

If the net power now exactly follows the form of the specification signal U _code with a proportionality factor β, P _out = β · U _code , is by the drive device 20a following driver input voltage U _mod to the modulator driver 40a where:

Transfer function of an acousto-optic modulator, single-channel system, Fig. 1

mit der Phasenverschiebung

zuFor an acousto-optic modulator, the Bragg regime produces a transfer function between high-frequency power P _rf , incident laser power P _in, and deflected laser power P _out (seen here as net power)

with the phase shift

to

Where b is the width of the sound wave, L _{m is} the modulator length, λ _{s is} the laser wavelength, P _a = a · P _rf the sound power, which often increases linearly (factor a) with the high-frequency power P _rf , and M ₂ the characteristic number of the acousto-optic material. The high frequency power P _rf in this case represents the modulator signal V. The modulator driver 40a , a high-frequency generator, which the acousto-optic modulator 50a in turn has a transfer function f between its driver input voltage U _mod and the high-frequency power P _rf , which by P _rf = f (U _mod ) given is. Often there is a linear behavior with a threshold U _thr : f (U _mod ) ≈ α · (U _mod - U _thr ).

If now the net power P _out should follow exactly the form of the default signal U _code , P _out = β · U _code , is driven by the drive driver following input voltage U _mod to the modulator driver 40a , the high frequency generator, given:

Transfer function of an electro-optical modulator, single-channel system, Fig. 1

als die spannungsabhängige Phasenverschiebung und

als die intrinsische Phasenverschiebung ohne Spannung zuFor a modulator 50a , which is an electro-optical modulator with a downstream polarizer, one obtains a transfer function between applied modulation signal V, incident laser power P _in and deflected laser power P _out (seen here as net power) P _out = P _in sin ² (ΔΦ / 2) With

as the voltage-dependent phase shift and

as the intrinsic phase shift without tension too

die Halbwellenspannung des Modulators.Therein n ₁ and n _{2 are} the normal modes of the refractive index, b the width and L _m the length of the modulator medium, λ _s the laser wavelength and

the half-wave voltage of the modulator.

The modulator driver 40a , which is a high voltage generator, which feeds the electro-optical modulator, in turn, has a transfer function f between its driver input voltage U _mod and the modulator signal V, which by V = f (U _mod ) given is. Often there is a direct linear behavior: f (U _mod ) ≈ α · U _mod .

If now the net power P _out should follow exactly the form of the default signal U _code , P _out = β · U _code , is by an interface circuit (analog, μController, FPGA or the like) following driver input voltage U _mod to the modulator driver 40a where:

Transfer function of a converter, single-channel system, Fig. 2

A modulator 50a is in the beam path of the pump laser beam of the converter 60a inserted. This converter 60a is a nonlinear converter designed as an optical parametric oscillator (OPO). Unlike the embodiment, the converter could also be a non-linear fiber or another laser, which is pumped by a pump laser beam of power P _pump . The modulator driver 40a is from the drive device 20a supplied, which converts the default signal U _code such that in addition to the driver transfer function f, the often non-linear modulator transfer function g of the modulator 50a and the effects of the often non-linear converter transfer function h is compensated by a suitable driver input voltage U _mod .

Generally, the transfer function h exists between the converter pump power P _{pump of} the converter 60a and the converter power P _out at the payload (seen here as net power) P _out = h (P _pump ).

Often a linear dependence with a threshold P _thr applies: P _out = η (P _pump - P _thr ).

Taking into account the transfer function g between the modulator signal V, the incident laser power P _in and the pump power of the converter P _{pump Ppump} = P _in g (V) and the transfer function f from the driver input voltage U _{mod of} the modulator driver 40a V = f (U _mod ) Now follows for a net power in the desired temporal form of the default signal U _code with a proportionality factor β P _out = β · U _code , that by the drive device 20a following driver input voltage to the modulator driver 40a must be given:

Transfer function, two-channel system, Fig. 3

angesteuert. Die vorgenannte Formel ist eine allgemeine Formel, die eine Konverter-Übertragungsfunktion h₁ mit berücksichtigt. Daher liegt kein Widerspruch zur 3 vor, bei der nur das zweite Kanalsystem 1b einen Konverter 60b aufweist.To be able to use as much as possible the entire laser power, the first modulator 50a of the first channel system 1a and the second modulator 50b of the second channel system 1b connected in series. The first modulation driver 40a comes with the driver input voltage

driven. The above formula is a general formula taking into account a converter transfer function h ₁ . Therefore, there is no contradiction to 3 before, in which only the second channel system 1b a converter 60b having.

The second channel system 1b available power depends on the time-dependent modulation in the first channel system 1a from: P _{in, 2} = P _{in, 1} - P _{out, 1}

Here, the Modulatorverluste are neglected for reasons of simplicity.

Due to the dependence on the first modulation in the first channel system 1a has the second driver input voltage U _{mod, 2 the} following course:

This results in the driver input voltage for channel k of N channels

für alle Kanäle k = 1...N unter realen Modulationsbedingungen minimiert, so dass ein Einfluss möglicher Frequenzgangengpässe in den Ansteuereinrichtungen der verschiedenen Kanalsysteme ebenfalls minimiert wird.The order in which the channels 1a and 1b Being arranged mathematically is not important. Since the mapping of the real, often non-linear transfer functions or their reversal functions in hardware or software can often only be approximated, in reality an order should be chosen which limits the frequency spectrum (eg caused by the number of switching operations in digital modulation ) of the terms

is minimized under real modulation conditions for all channels k = 1... N, so that an influence of possible frequency pass-offs in the drive devices of the different channel systems is also minimized.

LIST OF REFERENCE NUMBERS

1a, 1b

channel system

10a, 10b

signal generator

20a, 20b

driving

30a, 30b

modulator means

40a, 40b

modulator driver

50a, 50b

modulator

60a, 60b

converter

f ₁ , f ₂

Drivers transfer function

g ₁ , g ₂

Modulator transfer function

h ₁ , h ₂

Converter transfer function

U _{code, 1} , U _{code, 2}

setting signal

U _{mod, 1} , U _{mod, 2}

Driver input voltage

V ₁ , V ₂

modulator signal

P _{in, 1} , P _{in, 2}

Laser power of the laser beam to be modulated

P _{out, 1} , P _{out, 2}

Power of Nutzlaserstrahls

P _{rest, 1} , P _{rest, 2}

Power of the residual laser beam

P _{pump, 1} , P _{pump, 2}

Power of the pump laser beam

Claims (9)

Modulation device for the external modulation of a laser beam to be modulated, comprising the following features: a) the modulation device comprises a first channel system ( 1a ) with a first modulator device ( 30a ), b) the first modulator device ( 30a ) includes a first modulator driver ( 40a ) with a first driver transfer function (f ₁ ) and a first modulator ( 50a ) with a first modulator transfer function (g ₁ ), c) the first modulator ( 50a ) is acted upon by the laser beam to be modulated during operation and emits a first modulated laser beam, d) the first modulator driver ( 40a ) is in operation by a first drive means ( 20a ), e) the first drive device ( 20a ) receives in operation a first default signal (U _{code, 1} ) from a first signal generator ( 10a ), f) with the first drive device ( 20a ), the first driver transfer function (f ₁ ) and the first modulator transfer function (g ₁ ) are in inverse form such that a first payload laser beam following the default signal (U _{code, 1} ) is obtained, g) the first modulator ( 50a ) also emits a first residual laser beam during operation, h) the modulation device comprises a second modulator ( 50b ) and i) the second modulator ( 50b ) is in operation by the first residual laser beam of the first modulator ( 50a ) and outputs a second modulated laser beam. Modulation device according to Claim 1, with the following features: a) the modulation device comprises a second channel system ( 1b ) with a second modulator device ( 30b ), b) the second modulator device ( 30b ) includes a second modulator driver ( 40b ) with a second driver transfer function (f ₂ ) and a second modulator ( 50b ) with a second modulator transfer function (g ₂ ), c) the first modulator ( 50a ) emits during operation also a first residual laser beam, d) the second modulator ( 50b ) is acted upon by the operation of the first residual laser beam and outputs a second modulated laser beam, e) the second modulator driver ( 50b ) is in operation by a second drive device ( 20b ), f) the second drive device ( 20b ) receives a second default signal (U _{code, 2} ) from a second signal generator ( 10b g) with the second drive device ( 20b ), the second driver transfer function (f ₂ ) and the second modulator transfer function (g ₂ ) are in inverse form so as to obtain a second payload laser beam following the second default signal (U _{code, 2} ). Modulation device according to Claim 2, in which the second drive device ( 20b ) is designed so that it additionally processes the first default signal (U _{code, 1} ) for determining properties of the first residual laser beam. Modulation device according to claim 1, 2 or 3, which is designed such that the second modulator ( 50b ) emits a second residual laser beam in operation, which is also processed into a Nutzlaserstrahl. Modulation device according to one of claims 1 to 4, which is designed such that the first or the second modulated laser beam in operation a converter ( 60a . 60b ) is supplied. Modulation device according to Claim 5, in which the converter ( 60a . 60b ) has a converter transfer function (h ₁ , h ₂ ), such that the drive device ( 20a . 20b ) of the respective channel system ( 1a . 1b ) is designed to map the inverse converter transfer function (h ₁ , h ₂ ) with. Modulation device according to one of Claims 1 to 6, in which the laser beam to be modulated is obtained from a solid-state laser, an OPO or a diode laser. Modulation device according to one of claims 1 to 7, which is designed so that the laser beam to be modulated is a continuous laser beam. Modulation device according to one of Claims 1 to 8, in which the first and / or second modulator ( 50a . 50b ) is an acousto-optic modulator or an electro-optic modulator with polarizer.

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