DE102017223197B3 - Method and device for frequency conversion - Google Patents

Abstract

The invention relates to a method for frequency conversion of electromagnetic radiation with the assistance of pump radiation (P). According to the invention, it is provided that the frequency conversion is carried out in a one-piece, optically nonlinear crystal (20), a first crystal section (A1) with an individually adjustable first tempering device (31) tempered to a first crystal temperature (T1) and operated as a first converter stage for frequency conversion is, and in the propagation direction of the pump radiation (P) - directly or separated by an intermediate crystal section (Az) - behind the first crystal section (A1) lying second crystal section (A2) with an individually adjustable second tempering device (32) to a second, of the temperature first different temperature, crystal temperature (T2) is controlled and operated as a second converter stage for frequency conversion.

Description

The invention relates to a method for frequency conversion of electromagnetic radiation with the assistance of pump radiation.

In non-linear mixing processes of the second order, the conservation of energy and the conservation of momentum, also called phase matching, must be fulfilled.

gilt. Dabei sind ω1, ω2, ω3 die Kreisfrequenzen der drei involvierten Photonen.In the case of a sum frequency generation (also called SFG for short), a photon with higher energy is generated from two other photons, whereby, because of the energy conservation $$\mathrm{\omega }1+\mathrm{\omega }2=\mathrm{\omega }3$$

applies. In this case, ω1, ω2, ω3 are the angular frequencies of the three photons involved.

wobei ki = ωi * ni/c (i=1...3) die Wellenvektoren der Photonen für die korrespondierenden Kreisfrequenzen ωi in einem Material mit dem dazugehörigen Brechungsindex ni bezeichnen.The phase adjustment for the sum frequency generation requires $$\text{k}1+\text{k}2=\text{k}\mathrm{3,}$$

where ki = ωi * ni / c (i = 1 ... 3) denote the wave vectors of the photons for the corresponding angular frequencies ωi in a material with the associated refractive index ni.

By changing the temperature, the refractive index in the material can be changed and a phase matching can be achieved. If the phase matching is not, or at least not sufficient, no mixture occurs or the conversion efficiency drops at least drastically.

$$\text{k}1+\text{k}2=\text{k}3\left(\text{wegen der Phasenanpassung}\right)$$

In addition to the sum frequency generation, there is also a difference frequency generation (also called DFG for short) in which the difference is generated from two photon frequencies, where: $$\mathrm{\omega }1+\mathrm{\omega }2=\mathrm{\omega }3\left(\text{because of the energy conservation}\right)$$

$$\text{k}1+\text{k}2=\text{k}3\left(\text{because of the phase matching}\right)$$

Differential frequency generation and sum frequency generation are often used, for example, to generate laser light of a wavelength that otherwise would not be easily generated.

It is known in the prior art to form a non-linear material with phase matching periodicity to allow conversion to more frequencies ("enhancement of second-harmonic generation in LiNb03 crystals with periodic laminar ferroelectric domains", Duan Feng et al., Applied Physics Letters 37, 607 (1980) ).

From the US patent US 5,768,302 A is also known a phase matching with different periodicities. The different periodicities are used to convert short laser pulses that are wide in the frequency domain.

The pamphlets DE 10 2014 017 931 B3 . DE 10 2016 112 343 B3 . DE 694 30 281 T2 . US 2002/0154663 A1 and WO 2017/062501 A1 also deal with nonlinear materials and methods based on them.

The publication US 5,898,718 A discloses a method and a frequency conversion device having the features according to the preamble of claims 1 and 8, respectively.

The invention has for its object to provide a method with which a frequency conversion is particularly efficient.

This object is achieved by a method having the features according to claim 1. Advantageous embodiments of the method according to the invention are specified in subclaims.

Thereafter, the invention provides that the first and second crystal sections have different crystal periods. In addition, it is provided that the first crystal section is tempered with the individually adjustable first temperature control to a first crystal temperature, in which the phase matching between the phases of the desired signal and the pump radiation for the signal input frequency and the pumping frequency is met, and working in the first converter stage first crystal section, the frequency of the useful signal is converted from the signal input frequency to a first intermediate frequency corresponding to the difference between the signal input frequency and the pumping frequency, and the second crystal section having the individually adjustable second temperature control means to a second, from the first temperature tempered different crystal temperature, wherein the phase matching between the phases of the first intermediate signal and the pump radiation for the first intermediate frequency and the pumping frequency is met, and in the second crystal step operating as a second converter stage, the frequency of the first intermediate signal is converted from the first intermediate frequency to a second intermediate frequency corresponding to the difference between the first intermediate frequency and the pumping frequency to form a second intermediate signal or an output signal.

A significant advantage of the method according to the invention is the fact that through the two or more converter stages, input signals can be converted several times in frequency over several stages and / or two or more input signals can be converted simultaneously in their frequency in different converter stages. Due to the one-piece nature of the optically non-linear crystal is only a minimal adjustment effort when coupling and decoupling the optical radiation and only a minimal effort in setting the system altogether necessary.

Since the first and second crystal sections according to the invention have different crystal periods, different converter stages can be realized with minimal heating or cooling capacity.

The intermediate crystal portion disposed between the first and second crystal portions preferably fully absorbs the temperature gradient between the first and second crystal temperatures in the propagation direction of the radiation, to a residual deviation of ± 5%, respectively.

The temperatures in the first and second crystal sections are preferably individually set in such a way that-seen in the propagation direction of the radiation-the temperature gradient is zero or at least less than 2K / cm.

In special time sections, the phase matching in the first and / or second crystal section can advantageously be destroyed by bringing the first crystal section to a temperature other than the first crystal temperature and / or the second crystal section to a temperature other than the second crystal temperature.

In the special time sections, the first and / or second tempering device is preferably switched off or switched over.

A three or more multi-stage conversion is preferably carried out with the aid of a third crystal section or even further crystal sections, which - viewed in the direction of propagation of the pump radiation - directly or in each case separated by further intermediate crystal sections - are cascaded behind the second crystal section and each form a converter stage.

By means of individual tempering devices, each converter stage is preferably tempered to a crystal temperature at which a phase adjustment for the pump radiation and the converted intermediate signal of a previous converter stage, in particular the immediately preceding converter stage, or a phase adjustment between an individually assigned electromagnetic useful signal, which is fed into the one-piece crystal , is achieved.

The pumping frequency is preferably smaller than the signal input frequency of the useful signal (s). In the crystal sections, the frequency is preferably converted in each case in the direction of lower frequencies.

The different crystal periods are preferably set by a polarity, in particular an application of one or more external electric fields.

The invention also relates to a frequency conversion device for frequency conversion of electromagnetic radiation having an input for feeding at least one useful electromagnetic signal having a signal input frequency, and pumping radiation having a different from the signal input frequency pumping frequency, wherein the frequency conversion means a one-piece, optically non-linear crystal and in the one-piece, optically non-linear crystal superimpose the at least one useful signal and the pump radiation, and wherein a first crystal section is equipped with an individually adjustable first temperature control and in the propagation direction of the pump radiation - directly or separated by an intermediate crystal section - lying behind second crystal section equipped with an individually adjustable second tempering device.

According to the invention, it is provided that the first and second crystal sections have different crystal periods and a control device of the frequency conversion device is connected to the first and second temperature control means and controls them in such a way that the first crystal section is tempered to a first crystal temperature with the individually adjustable first temperature control device the phase matching between the phases of the at least one useful signal and the pump radiation for the signal input frequency and the pumping frequency is satisfied, and in the operating as a first converter stage first crystal section, the frequency of the at least one useful signal from the signal input frequency is converted to form a first intermediate signal in a first intermediate frequency corresponding to the difference between the signal input frequency and the pumping frequency, and the second crystal section with the individually adjustable second tempering is tempered to a second, different from the first crystal temperature crystal temperature at which the phase matching between the phases of the first intermediate signal and the pump radiation for the first intermediate frequency and the pumping frequency is met, and in the second converter stage operating second crystal section the Frequency of the first intermediate signal from the first intermediate frequency is converted to form a second intermediate signal or an output signal in a second intermediate frequency, the difference between corresponds to the first intermediate frequency and the pumping frequency.

With regard to the advantages of the frequency conversion device according to the invention, reference is made to the above statements in connection with the method according to the invention.

• 1 ein Ausführungsbeispiel für eine erfindungsgemäße Frequenzumsetzeinrichtung, anhand derer beispielhaft ein Verfahren zur zweistufigen kaskadierten Frequenzumsetzung eines Nutzsignals erläutert wird,
• 2 den Temperaturverlauf über dem Ort in dem Kristall der Frequenzumsetzeinrichtung gemäß 1 während der Frequenzumsetzung,
• 3 beispielhaft die resultierende Amplitudenverteilung der Signale über der Frequenz,
• 4 ein Ausführungsbeispiel für eine erfindungsgemäße Frequenzumsetzeinrichtung, anhand derer beispielhaft ein Verfahren zur jeweils einstufigen Frequenzumsetzung bei zwei eingangsseitigen Nutzsignalen erläutert wird,
• 5 beispielhaft die resultierende Amplitudenverteilung der Signale über der Frequenz bei der Variante gemäß 4,
• 6 das Ausführungsbeispiel gemäß 4 bei einem Einsatz zur Frequenzumsetzung bei Photonenpaaren,
• 7 in einer dreidimensionalen Darstellung schräg von der Seite ein Ausführungsbeispiel für einen einteiligen, optisch nichtlinearen Kristall, der bei den Frequenzumsetzeinrichtungen gemäß den 1 bis 6 eingesetzt werden kann,
• 8 in einem Querschnitt den einteiligen Kristall gemäß 7 mit daran angebrachten Temperiereinrichtungen,
• 9 in einer dreidimensionalen Darstellung schräg von der Seite ein weiteres Ausführungsbeispiel für einen einteiligen, optisch nichtlinearen Kristall, der bei den Frequenzumsetzeinrichtungen gemäß den 1 bis 6 eingesetzt werden kann, und
• 10 in einem Querschnitt den einteiligen Kristall gemäß 9 mit daran angebrachten Temperiereinrichtungen.

The invention will be explained in more detail with reference to embodiments; thereby show by way of example

• 1 An exemplary embodiment of a frequency conversion device according to the invention, with reference to which a method for two-stage cascaded frequency conversion of a useful signal is explained by way of example,
• 2 the temperature profile over the location in the crystal of the Frequenzumsetzeinrichtung according to 1 during the frequency conversion,
• 3 exemplarily the resulting amplitude distribution of the signals over the frequency,
• 4 an embodiment of a frequency conversion device according to the invention, based on which by way of example a method for each single-stage frequency conversion is explained at two input-side payloads,
• 5 for example, the resulting amplitude distribution of the signals over the frequency in the variant according to 4 .
• 6 the embodiment according to 4 when used for frequency conversion in photon pairs,
• 7 in a three-dimensional representation obliquely from the side of an embodiment of a one-piece, optically nonlinear crystal, in the frequency conversion devices according to the 1 to 6 can be used
• 8th in a cross section the one-piece crystal according to 7 with tempering devices attached thereto,
• 9 in a three-dimensional representation obliquely from the side of a further embodiment of a one-piece, optically nonlinear crystal, in the frequency conversion devices according to the 1 to 6 can be used, and
• 10 in a cross section the one-piece crystal according to 9 with attached tempering.

For the sake of clarity, the same reference numbers are always used in the figures for identical or comparable components.

The 1 shows a frequency conversion device 10 for the frequency conversion of electromagnetic radiation. The frequency conversion device 10 comprises a one-piece, optically nonlinear crystal 20 , a first tempering device 31 , a second tempering device 32 , a control device 40 and a filter 50 ,

The first tempering device 31 is located in a first crystal section A1 of the nonlinear crystal 20 and the second tempering device 32 in one - in the operating direction or beam direction R the frequency conversion device 10 seen - behind it second crystal section A2 , The two crystal sections A1 and A2 are in the embodiment according to 1 through an intermediate crystal section az separated, for the thermal separation of the crystal sections A1 and A2 advantageous, but not mandatory.

The control device 40 is to the two tempering 31 and 32 connected and controls these individually with control signals ST1 and ST2 so that each of the two tempering 31 and 32 each forms an independent converter stage.

The filter 50 serves to suppress unwanted output frequencies in the output signal of the nonlinear crystal 20 ; this will be explained in more detail below.

The frequency conversion device 10 can for example be operated as follows:

At an entrance 21 of the nonlinear crystal 20 a sum signal N + P is irradiated, which has been formed by a superimposition of a useful signal N, which has a signal input frequency f1, and pump radiation P, which has a pump frequency fp differing from the signal input frequency f1 (frequency spectrum see FIG 3 ).

In the embodiment according to 1 is the useful signal N via a deflection mirror 15 and a beam splitter 30 to an entrance 21 of the nonlinear crystal 20 directed. The pump radiation P is also via the beam splitter 30 coupled, so that the beam splitter 30 for superposition or addition of the useful signal N and the Pump radiation P and the formation of said sum signal N + P is used.

The pump signal P is preferably of a in the 1 not shown laser generated. The useful signal N may be, for example, an optical data signal, as is customary in the telecommunications sector and that of a in the 1 not shown signal source comes.

In the following, it is assumed by way of example that the pumping frequency fp is smaller than the signal input frequency f1 and the nonlinear crystal 20 is to be used for two-stage conversion of the useful signal N in the direction of lower frequencies. For this purpose, the controller heats or cools 40 the first crystal section A1 up or down a first crystal temperature T1 and the second crystal section A2 to a different second crystal temperature T2 up or down; the temperature profile T is in the 2 shown above the location x. It can be seen that the intermediate crystal portion Az the thermal gradient between the crystal sections A1 and A2 receives.

und $$\text{kz}1=\text{k}1-\text{kp}$$

wobei fz1 die Frequenz eines bei der Mischung gebildeten ersten Zwischensignals Z1, kz1 den Wellenvektor des Zwischensignals Z1, k1 den Wellenvektor des Nutzsignals N und kp den Wellenvektor der Pumpstrahlung P bezeichnet.The first crystal temperature T1 is chosen such that in the first crystal section A1 to form a desired first intermediate signal Z1 with a first intermediate frequency fz1 (please refer 3 ) for a second-order non-linear mixing process, both the energy conservation and the momentum conservation or phase matching are fulfilled, and thus the following applies: $$\text{fz}1=\text{f}1-\text{fp}$$

and $$\text{concentration camp}1=\text{k}1-\text{kp}$$

in which fz1 the frequency of a first intermediate signal formed during the mixing Z1 . kz1 the wave vector of the intermediate signal Z1 , k1 denotes the wave vector of the useful signal N and kp denotes the wave vector of the pump radiation P.

$$\text{k}1=2*\mathrm{\pi }*\text{f}1-\text{n}\mathrm{1,}\text{ 1/c}$$

$$\text{kp}=2*\mathrm{\pi }*\text{fp}*\text{n}\mathrm{1,}\text{ p/c}$$

wobei n1,i (i=1,z1,p) die frequenz- bzw. wellenlängenabhängige Brechzahl im ersten Kristallabschnitt A1 und c die Vakuumlichtgeschwindigkeit bezeichnet.For the wave vectors, the first crystal segment is valid A1 : $$\text{concentration camp}1=2*\mathrm{\pi }*\text{fz}1*\text{n}\mathrm{1,}\text{z1 / c}$$

$$\text{k}1=2*\mathrm{\pi }*\text{f}1-\text{n}\mathrm{1,}\text{1 / c}$$

$$\text{kp}=2*\mathrm{\pi }*\text{fp}*\text{n}\mathrm{1,}\text{p / c}$$

where n1, i (i = 1, z1, p) the frequency or wavelength-dependent refractive index in the first crystal section A1 and c denotes the vacuum light velocity.

The 3 shows by way of example the resulting amplitude distribution A (f) over the frequency f.

und $$\text{kz}2=\text{k}1-\text{kp}=\text{k}1-2*\text{kp}$$

wobei fz2 die Frequenz eines bei der Mischung gebildeten zweiten Zwischensignals Z2 und kz2 den Wellenvektor des zweiten Zwischensignals Z2 bezeichnet.The second crystal temperature T2 is chosen such that for a non-linear mixing of the first intermediate frequency fz1 at the pumping frequency fp and to form a second intermediate signal Z2 both the conservation of energy as well as the momentum conservation or phase matching are fulfilled and thus the following applies: $$\text{fz}2=\text{fz}1-\text{fp}=\text{f}1-2*\text{fp}$$

and $$\text{concentration camp}2=\text{k}1-\text{kp}=\text{k}1-2*\text{kp}$$

in which fz2 the frequency of a second intermediate signal formed during the mixing Z2 and kz2 the wave vector of the second intermediate signal Z2 designated.

$$\text{kz}1=2*\mathrm{\pi }*\text{f}1*\text{n}\mathrm{2,}\text{ z1/c}$$

$$\text{kp}=2*\mathrm{\pi }*\text{fp}*\text{n}\mathrm{2,}\text{ p/c}$$

wobei n2,i (i=z1,z2,p) die frequenz- bzw. wellenlängenabhängige Brechzahl im zweiten Kristallabschnitt A2 bezeichnet.For the wave vectors applies in the second crystal section A2 : $$\text{concentration camp}2=2*\mathrm{\pi }*\text{fz}2*\text{n}\mathrm{2,}\text{z2 / c}$$

$$\text{concentration camp}1=2*\mathrm{\pi }*\text{f}1*\text{n}\mathrm{2,}\text{z1 / c}$$

$$\text{kp}=2*\mathrm{\pi }*\text{fp}*\text{n}\mathrm{2,}\text{p / c}$$

where n2, i (i = z1, z2, p), the frequency or wavelength-dependent refractive index in the second crystal section A2 designated.

The in the nonlinear crystal 20 irradiated pump radiation P and the useful signal N and that of the nonlinear crystal 20 intermediate signals formed by second order nonlinearity Z1 and Z2 leave the nonlinear crystal 20 at an exit 22 ,

The filter 50 is preferably adapted to the frequencies or wavelengths of the pump radiation P, the desired signal N and the first intermediate signal Z1 to attenuate or suppress and the output side only or primarily the second intermediate signal Z2 to let happen. The second intermediate signal Z2 , which was generated by a two-stage frequency conversion, thus forming the output of the frequency conversion device 10 according to 1 ,

The 4 shows an embodiment of a frequency conversion device 10 , with the exception of the design of the filter 50 the embodiment according to 1 can correspond. The filter 50 will be explained in more detail below.

The 4 shows the frequency conversion device 10 in an operation in which a first electromagnetic useful signal N1 that has a first signal input frequency fs1 has a second electromagnetic useful signal N2 that has a second signal input frequency fs2 and pumping radiation P having a pumping frequency fp different from the first and second signal input frequencies into the one-piece optically nonlinear crystal 20 is irradiated.

The first crystal section A1 comes with its individually adjustable first tempering device 31 to a first crystal temperature T1 tempered, in the in the first crystal section A1 for a second-order non-linear mixing process, both the conservation of energy and the conservation of momentum or phase matching between the phases of the first useful signal N1 and the pump radiation P for the first signal input frequency fs1 and the pumping frequency fp are met.

In the first crystal stage working as the first converter stage A1 becomes the signal input frequency fs1 of the first useful signal N1 thus forming a first intermediate signal Z1 in a first intermediate frequency fz1 converts the difference between the first signal input frequency fs1 and the pumping frequency fp, as related to the 1 has been explained above; the above statements apply accordingly.

The second crystal section A2 comes with its individually adjustable second tempering device 32 to a second crystal temperature T2 tempered, in which in the second crystal section A2 for a second-order nonlinear mixing process, both the conservation of energy and the conservation of momentum or phase matching between the phases of the second useful signal N2 and the pump radiation P for the second signal input frequency fs2 and the pumping frequency fp are met.

In the working as a second converter stage second crystal section A2 becomes the signal input frequency fs2 of the second useful signal N2 thus forming a second intermediate signal Z2 in a second intermediate frequency fz2 converts the difference between the second signal input frequency fs2 and the pumping frequency fp corresponds; the above statements in connection with the 1 apply here accordingly.

The in the nonlinear crystal 20 irradiated pump radiation P, the useful signals N1 and N2 as well as that of the nonlinear crystal 20 intermediate signals formed by second order nonlinearity Z1 and Z2 leave the nonlinear crystal 20 at an exit 22 ,

The 5 shows by way of example the resulting amplitude distribution A (f) over the frequency f.

The filter 50 is preferably adapted to the frequencies or wavelengths of the pump radiation P and the useful signals N1 and N2 to attenuate or suppress and on the output side only or primarily the first and second intermediate signal Z1 and Z2 to let happen. The two intermediate signals Z1 and Z2 , which have been generated independently of each other by mixing with the pump signal, thus form output signals of the frequency conversion device 10 according to 4 ,

To separate the two intermediate signals Z1 and Z2 can the frequency conversion device 10 according to 4 also a wavelength-selective element 60 exhibit.

The 6 shows the frequency conversion device 10 according to the 4 in a factory where in the one-piece crystal 20 an entangled photon pair PP or a sequence of such photon pairs is fed. A photon P1 of the photon pair PP has a first signal input frequency fs1 and forms a first electromagnetic useful signal N1 , The other photon P2 of the photon pair PP has a second signal input frequency fs2 and forms a second electromagnetic useful signal N2 ,

After the frequency conversion, as related to the 4 has been explained, the two frequency-converted photons P1 'and P2' of the photon pair PP by means of the wavelength-selective element 60 separated from each other.

The 7 shows in a three-dimensional representation obliquely from the side of an embodiment of a one-piece, optically nonlinear crystal 20 , which in the embodiments according to the 1 to 6 can be used.

In the one-piece crystal 20 according to 7 have the first crystal section A1 and the second crystal section A2 different crystal periods Λ1 or Λ2. The different crystal periods Λ1 or Λ2 are preferably set by a polarity, in particular an application of one or more external electric fields E.

The 8th shows in a cross section the one-piece crystal 20 according to 7 with attached tempering 31 and 32 , The tempering devices 31 and 32 For example, each have a high-resistance heating layer for heating 300 , an intermediate layer 310 , for example in the form of a metal layer, and a temperature sensor embedded therein or attached thereto 320 on.

Alternatively or in addition to the high-resistance heating layers 300 can the tempering 31 and 32 Have Peltier elements with which either heated or cooled.

The 9 shows in a three-dimensional representation obliquely from the side of another embodiment of a one-piece, optically non-linear crystal 20 , which in the embodiments according to the 1 to 6 can be used.

The 10 shows the crystal 20 according to 9 in cross-section with tempering devices attached thereto 33 that the temperature control equipment 31 and 32 in the embodiments according to the 1 to 8th can correspond. In the embodiment according to 9 are cascaded in the propagation direction R of the radiation four crystal segments A1 . A2 . A3 and A4 arranged one behind the other, which have different crystal periods Λ1 to Λ4 and each form a converter stage. Each converter stage is tempered to an individual crystal temperature at which a phase matching for the pump radiation and the converted intermediate signal of a previous converter stage, in particular the immediately preceding converter stage, or a phase matching between an individually assigned electromagnetic useful signal fed into the one-piece crystal, is achieved ,

The different crystal periods Λ1 to Λ4 are preferably set by a polarity, in particular an application of one or more external electric fields.

Claims (8)

Method for frequency conversion of electromagnetic radiation with the assistance of pump radiation (P), wherein - the frequency conversion is carried out in a one-piece, optically non-linear crystal (20), - a first crystal section (A1) with an individually adjustable first tempering device (31) to a first crystal temperature (T1) is tempered and operated as a first converter stage for frequency conversion, and - in the propagation direction of the pump radiation (P) - directly or separated by an intermediate crystal section (Az) - behind the first crystal section (A1) lying second crystal section (A2) with an individual adjustable second tempering device (32) is tempered to a second, different from the first temperature, crystal temperature (T2) and operated as a second converter stage for frequency conversion, - wherein an electromagnetic useful signal (N) having a signal input frequency, and pump radiation (P) , the a pump frequency which differs from the signal input frequency and is irradiated into the one-piece optically nonlinear crystal (20) in which the useful signal (N) and the pump radiation (P) are superimposed, characterized in that - the first and second crystal sections (A1 , A2) have different crystal periods, wherein - the first crystal section (A1) with the individually adjustable first tempering device (31) is heated to the first crystal temperature (T1) at which the phase matching between the phases of the useful signal (N) and the pump radiation ( P) is satisfied for the signal input frequency and the pump frequency, and in the operating as the first converter stage first crystal section (A1), the frequency of the useful signal (N) from the signal input frequency to form a first intermediate signal (Z1) is converted into a first intermediate frequency, the Corresponds to the difference between the signal input frequency and the pump frequency, and - the second crystal section (A2) is tempered with the individually adjustable second temperature control device (32) to the second crystal temperature (T2), wherein the phase matching between the phases of the first intermediate signal (Z1) and the pumping radiation (P) for the first intermediate frequency and the pumping frequency is satisfied, and in the second crystal section (A2) operating as the second converter stage, the frequency of the first intermediate signal (Z1) is converted from the first intermediate frequency to a second intermediate frequency forming the second intermediate signal (Z2) or an output signal Difference between the first intermediate frequency and the pumping frequency corresponds. Method according to Claim 1 , characterized in that - the intermediate crystal section (Az), which is arranged between the first and second crystal sections (A1, A2), completely absorbs the temperature gradient between the first and second crystal temperature (T1, T2) in the propagation direction of the radiation and / or the temperatures in the first and second crystal sections (A1, A2) are individually set in such a way that - viewed in the propagation direction of the radiation - the temperature gradient is zero or at least less than 2K / cm. Method according to one of the preceding claims, characterized in that during the process in special time periods, the phase matching in the first and / or second crystal section (A1, A2) is destroyed by the first crystal section (A1) to a different than the first crystal temperature (T1) and / or the second crystal section (A2) on a other than the second crystal temperature (T2) is brought. Method according to Claim 3 , characterized in that in the special time sections, the first and / or second temperature control device (31, 32) is switched off or switched. Method according to one of the preceding claims, characterized in that - a three-stage or more multi-stage conversion by means of a third crystal section or even further crystal sections (A3, A4) is performed, which - seen in the propagation direction of the pump radiation (P) - directly or respectively separated cascaded behind the second crystal section (A2) by cascading and forming a converter stage in each case, and tempering each converter stage to a crystal temperature by means of individual tempering means, in which a phase adaptation for the pump radiation (P) and the converted intermediate signal of a previous converter stage, especially the immediately preceding converter stage is reached. Method according to one of the preceding claims, characterized in that the pumping frequency is smaller than the signal input frequency of the useful signal (s) (N, N1, N2) and in the crystal sections the frequency is respectively converted in the direction of lower frequencies. Method according to one of the preceding claims, characterized in that the different crystal periods by a polarity, in particular an application of one or more external electric fields, is set. A frequency conversion device (10) for frequency converting electromagnetic radiation having an input for feeding at least one useful electromagnetic signal (N) having a signal input frequency and pump radiation (P) having a pumping frequency different from the signal input frequency, wherein the frequency conversion means (10) a one-piece, optically nonlinear crystal (20) and in the one-piece, optically non-linear crystal (20) the at least one useful signal (N) and the pump radiation (P) overlap, and - wherein a first crystal section (A1) with an individually adjustable first tempering device (31) is equipped and in the propagation direction of the pump radiation (P) - directly or separated by an intermediate crystal section (Az) - behind second crystal section (A2) with an individually adjustable second temperature control device (32) is provided, characterized in that he Ste and second crystal section (A1, A2) have different crystal periods, and a control device (40) of the frequency conversion device to the first and second temperature control (31, 32) is connected and controls them such that - the first crystal section (A1) with the individual adjustable first tempering device (31) is tempered to a first crystal temperature (T1), in which the phase matching between the phases of the at least one useful signal (N) and the pump radiation (P) for the signal input frequency and the pumping frequency is satisfied, and in the first Converter stage operating first crystal section (A1) the frequency of the at least one useful signal (N) from the signal input frequency is converted to form a first intermediate signal (Z1) in a first intermediate frequency corresponding to the difference between the signal input frequency and the pumping frequency, and - the second crystal section (A2) with the individual adj The second tempering device (32) is tempered to a second crystal temperature (T2) different from the first crystal temperature (T1), wherein the phase matching between the phases of the first intermediate signal (Z1) and the pumping radiation (P) for the first intermediate frequency and the In the second crystal section (A2) operating as a second converter stage, the frequency of the first intermediate signal (Z1) is converted from the first intermediate frequency to form a second intermediate signal (Z2) or an output signal to a second intermediate frequency equal to the difference between the first intermediate frequency and the pump frequency corresponds.

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