DE1589068A1 - Parametric device welding of circular ring seams - Google Patents

Description

WESTERN ELECTRIC COMPANY Incorporated C.K.N. Patel 10/11

χ New York, N. Y. 10007 USA

Parametric setup

The invention relates to parametric oscillators, parametric Amplifiers and other parametric devices for infrared wavelengths.

Recent proposals for optical communication systems relied on the well-known laser as sources of coherent radiation and on parametric devices as a means of providing for optical communications

usable frequency bands while maintaining the coherence of the (

To make radiation wider and more steady.

Parametric devices are devices that enhance their effectiveness derive from the fact that they are essentially non-

I.
respond linearly to an input signal. In particular, in the optical portion of the spectrum, including the infrared portion, parametric devices typically use a block of optical material that has a substantial coefficient of polarization

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second order. The input radiation or radiations are not guided through this block of material Propagated way. There is a wave-like shift of charge dipoles, i. H. a wave of polarization, the one Energy exchange between multiple input radiations produces or generates radiations of different frequencies under the influence of a simple input radiation. The first Kind of device is an amplifier for the radiation that extracts energy. The second type of facility can be a harmonic generator or, under changed conditions, a parametric oscillator. A parametric oscillator is particularly useful for broadening the frequency band that can be used for optical communication. Typically, a parametric oscillator has a resonator and a variable direction of propagation used in the material.

Although many attempts have been made with such optical parametric devices, their development has continued beyond the scientific interest because of the weakness of the achievable non-linear effects only very slowly. Among the better materials for such devices are lithium metaniobate and gallium arsenide.

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These materials can only be used with difficulty in the wavelength range of the "atmospheric window" from 8 η to 14 ju. Thus, it is desirable to find materials and methods that can be readily used in optical parametric devices that operate in this part of the infrared part of the spectrum.

The present invention is based on the discovery that surprisingly strong parametric effects are present in single crystal tellurium with a low hole concentration. Such a single crystal has been used in a phase-matched second harmonic pass generator. When the crystal was pumped with 170 mW of coherent radiation with steady waves from a carbon dioxide laser at 10, C <u, 10 mW of the second harmonic was obtained at 5, 3 u. The path length of the radiations within the crystal was 9 mm. The effect is therefore much stronger than it has been with other j

optical materials was achievable. In particular, the second order polarization coefficient (nonlinear coefficient) is describing the nonlinear interaction, at least 400 times the second order polarization coefficient of Lithium metaniobate, the best phase-adjustable nonlinear to date Material was.

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ORIGINAL tiMCif-

1569068

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The strength of the effect is all the more surprising as tellurium is an elementary crystal while so far the strongest parametric effects and other nonlinear effects in compound crystals have been achieved.

An investigation of the generator for second harmonic using tellurium shows that selenium is also strong non-

linear effects in a large part of the infrared portion would show the spectrum and ψ in the range of D, 8a st to 4 u preferable \ where tellurium gives a large attenuation.

Further advantages of the invention will become apparent from the following detailed explanation and the drawings.

Fig. 1 shows, partly schematically and partly as a block diagram, a preferred embodiment of the second harmonic generator according to the invention.

k Fig. 2 shows partially schematically and partially as

Block diagram of a preferred embodiment of a parametric oscillator according to the invention.

Fig. 3 shows partially schematically and partially as

Block diagram of a preferred embodiment of a parametric amplifier according to the invention.

Fig. 4 shows, partly pictorially and partly as a block diagram, an embodiment of an inventive device optical modulator.

0 0 9 8 1 3 / U 6 0 ^ ^{! G! NAL 1} ^ CTO

Fig. 5 is a graph showing the

Change of the generated second harmonic of the embodiment of FIG. 1 depending on the Angular deviation from the direction of the maximum second harmonic (phase matching direction) shows.

Fig. 6 shows partially pictorially and partially as a block diagram an embodiment of a Faraday modulator according to a further aspect of the invention.

FIG. 7 shows, partly pictorially and partly as a block diagram, an embodiment of a detector according to FIG a further aspect of the invention when used in a communication system.

In FIG. 1, the generator for second harmonics consists of the single crystal 11 of essentially intrinsically conductive tellurium and of the carbon dioxide laser 12, which sends a directed beam of coherent pump radiation to the tellurium crystal 11 at 10.6 η at an angle of about 14 10 'to the optical axis of the crystal 11 applies. Behind the exit surface of the crystal 11, the consumer device 13 is arranged, which can be, for example, a frequency-shifting stage in an optical receiver in which the 5, 3 u radiation is used in the manner of a local oscillator signal.

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Prior to incidence on the tellurium crystal 11 passes the 10, 6 "radiation from the laser 12 through the 1O ₁ 6 η bandpass filter 14 to eliminate unwanted fluorescence can also be emitted from the laser 12, further characterized by the damping means 15 and 16 to adjust the pump energy level, further through the 10, 6 u polarizer to polarize the laser radiation and finally to the concave focusing and reflective element 18 to ensure the correct concentration of the pump radiation in the crystal 11. On its way from tellurium crystal 11 to consumer device 13, the induced 5.3 tui radiation of the second harmonic goes through the 5.3 u polarizer 19, the focusing lens 20, the 10.6 u cut-off filter 21 and the 5, 3 u bandpass filters 22 and 23 All of these elements have a tendency to eliminate undesirable radiation and radiation components emanating from the tellurium crystal 11.

The tellurium crystal 11 was made from a commercially available crystal made with a nominal impurity level of less than 1 in 1 million. The contamination was preferential Copper, which is an acceptor in tellurium. So the load carriers were predominantly holes, flee hole concentration was

17 at room temperature less than 1x10 per ecm.

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It should be particularly noted that for each impurity concentration the effective hole concentration decreases rapidly with temperature. At lower temperatures the crystal 11 can have a much higher impurity content and still have a hole concentration of less than

17th
1x10 per ecm result. The crystal 11 was cut so that it has entry and exit surfaces for the radiation perpendicular to a direction which is at an angle of 14 10 ¹ to the optical axis. The normal distance between the entry and exit surfaces after polishing was 9 mm. The diameter of the crystal 11 in a plane perpendicular to the direction of propagation was about 7 mm.

The CO “laser 12 used had two concave mirrors a radius of curvature of 50 m, which had a distance of 300 cm. Although such reflectors are not confocal and show a spot size under normal conditions which is considerably smaller than the coupling hole of 15 mm diameter, The very effective cooling of the laser tube walls results in sufficient defocusing to expand the waveform and to maintain high-energy coherent shaft vibrations. Only a fraction of this available energy, namely 170 milliwatts were applied to the crystal 11 perpendicular to its entry and exit surfaces.

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If the crystal 11 consists of tellurium, the CO laser 12

Ci

can of course be replaced by another radiation source which emits coherent radiation with a wavelength of supplies more than 4aj of the band gap of tellurium. When the crystal 11 is a single crystal of selenium, the coherent radiation wave is said to be 12 provide coherent radiation with a wavelength greater than 0.8µ of the selenium band gap.

The 10, 6 ix band pass filter 14 consisted of pressed polycrystalline zinc sulfide coated with a dielectric. The attenuators 15 and 16 were 1 mm thick periclase (magnesium oxide) windows. The 10, 6 η polarizer 17 was a

18 single crystal of tellurium with more than 1x10 holes per ecm at room temperature, the larger surfaces of which were cut parallel to the optical axis and which was oriented perpendicular to the direction of propagation of the radiation. The reflector 18 was a spherically curved mirror which was coated with gold applied in a vacuum, so that it became opaque. The 5.3yU polarizer 19 consisted of several silver chloride plates with Brewster's angle. The focusing lens 20 was pressed polycrystalline zinc sulfide (IR-2) and had a focal length of 52 mm. The 10, 6 η ^ cfjf ^^ blocking filter was a 1 mm thick sapphire filter, while the 5, 3 "bandpass filters 22 and 23 consisted of germanium coated with a dielectric.

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When operating a device which was essentially the same as the device in FIG. 1, the spot size of the coherent radiation was 3.2 mm². 10 microwatts of coherent wave energy at 5.3 ai at the output of the last 5.3 η bandpass filter 23 were achieved. Figure 5 shows the change in the energy of the second harmonic (5, 3, u) when the angle of incidence of the pump jet

was changed to the optical axis, where 0, as stated above, was 14 ° 10 '.

The second order polarization coefficient d ₁₁ was calculated to be (1.27 + 0.2) χ 10 "ESE (electrostatic units), namely as 4000 times the d _ß of potassium dihydrogen phosphate

OD

and about 400 times d. by LiNbO.

Single crystal tellurium has sixfold symmetry about the c-axis. Thus there can be three equivalent groups of χ and y crystal axes can be defined if the c-axis is assumed to be the z-axis. It is assumed by agreement that a x-axis lies in one direction through opposite side corners of the crystal, the y-axis being perpendicular Has direction which happens to be perpendicular to opposite side surfaces of the hexagonal crystal.

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There are two possibilities for a phase-matched generation of second harmonics, that is to say that the phase velocity of the induced radiation is essentially the same as the phase velocity of the pump radiation. The first, which was used in this invention, is to propagate the Punip ray as an extraordinary wave in the yz plane with the phase matching angle 0 against the c-axis (optical axis) of the tellurium crystal. The electric field of the pump wave is predominantly polarized in the y-direction. In this case, the second harmonic eats an ordinary wave which is polarized along the x-axis and which is coupled to the pump wave with a strength related to the coefficient d. The pump wave and the second harmonic propagating at angle 0 are phase matched.

The other possibility for the generation of second harmonics is obtained by propagating the pump wave in such a way that it predominantly in the x-y-plane with essential χ and y-polarization components is polarized. The second harmonic is coupled to the pump wave with a strength equal to the Coefficient d is related, it is a.as ordinary Wave polarized in the y-direction. The corresponding phase matching angle 0 is approximately 52. Thus, the pump waves plant themselves and the second harmonic wave propagates at that angle to the optical axis.

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In particular, it should be noted that the above results were obtained for single passes through the tellurium crystal and that the output energy at the desired wavelength can be greatly increased by providing a resonator which is placed around the tellurium crystal.

An example of a parametric oscillator in which the tellurium crystal is arranged in a resonator is shown in FIG Execution of Figure 2.

In FIG. 2, the tellurium crystal 31 is provided with spherically curved, precisely confocal end faces 32 and 33, which result in a resonance axis at an angle to the optical axis of the crystal. The precisely confocal curved surfaces 32 and 33 are polished and dielectridch coated with suitable dielectric materials that are permeable in the infrared region, so that the dielectric coatings act as a matching transformer for the 10, 6u radiation and still have a high reflection in the range of give about 15 u to about 30 w. As in the embodiment of FIG. 1, the CO laser delivers 10.6 AJ radiation. In order to eliminate unwanted frequency components of the laser radiation and to effect an exact setting of the pump energy level, the output of the laser 12 is passed through the 10, 6n bandpass filter 14 and the attenuation devices 15 and 16.

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conducts, which are arranged in the radiation path in front of the crystal 31. Furthermore, a 10, 6 u polarizer 17 is in the way of the Laser radiation inserted in front of the crystal 31. The laser radiation is then through the focusing element 18 via the curved end face 33 focused on crystal 31 »the one over the other curved end face 32 of crystal 31 emitted radiation passes through the 10-3Ou polarizer 29 and is focused on the consumer device 34 by the focusing element 30. The unused 10, 6 u pump radiation

ι
is through the 10, 6 M blocking filter 21 from the consumer device

34 kept away.

The elements 14, 15, 16, 17, 18 and 21 are the same as described above in the embodiment of FIG. Of the Polarizer 29 is oriented so that it emits from the crystal 31 induced parametric oscillation with minimal Attenuation lets through. Typically, the polarization of the induced radiation at the exit of the crystal 31 is perpendicular for polarization of the unused pump radiation. The focusing reflector 30 is essentially the same as this focusing reflector 18, it focuses the parametric Vibration on the consumer device 34, the filter 21 is a Germanium window covered with a dielectric, which blocks the 10, 6 u pump radiation, but the undamped passage of the parametric 15-30Ji vibration signal of the tellurium

permitted.

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. As with the embodiment of Figure 1, the consumer device 34 can take many forms, but it is e.g. B. a device for determining the optical properties of crystals, it therefore does not need to be described in detail here. For example, the parametric radiation in the 10-30 a range can induce Raman spectra in a piezoelectric crystal which is arranged in the device 34.

In operation, the 10, 6 η pump radiation, insofar as it is not used up during the first passage through the crystal 31, repeatedly passes through the crystal until a large part of the pump radiation is used up. The result is accordingly a high conversion of the pump radiation into induced radiation. Furthermore, the presence of a resonator makes it possible for the induced radiations to be other than the radiation of the second harmonic insofar as other radiations can now be raised above the oscillation limit value, while the second harmonic is suppressed by the absence of phase matching. Two types of radiation are induced, called the signal wave and the secondary wave. The induced radiations have wavelengths which primarily depend on the angle between the pump radiation and the optical axis, as this is the case for the pump radiation. . and the induced radiation satisfies the phase matching conditions

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must be. That is, the phase velocity of each induced radiation is equal to the phase velocity of the pump radiation. From the signal wave and the auxiliary wave is one or both are extraordinary. The pump radiation is a decent wave.

are

Not equal to the second harmonic ^ s ⁷ I / the signal and secondary frequencies are both smaller than the second harmonic.

The signal and secondary frequencies can be changed in a wide range from the degenerate values on only by that the crystal 31 is rotated to change the angle between the direction of propagation and the c-axis. This Angle is the phase adjustment angle 0 for the new frequency group that is being created. In general, the useful ones lie induced radiations obtained from tellurium crystal 21 in the range of 10-30 Ji, during the propagation angle to the optical axis in one of the two ranges 0-12 and 16 ° - 90 ° Hegt.

As an extension of the foregoing, it is PrinziQs _{also possible to use tellurium as the nonlinear optical medium in a parametric amplifier with or without feedback. An amplifier of this type without feedback is shown in FIG.

00981 3/1 4SO

vs.

In Figure 3, the tellurium crystal 41 is through the coherent 10, 6m Radiation pumped by the CO_ laser 12 over the 10, 671 band

^£ I.

pass filter 14, the damping devices 15 and 16 slides the 10, 6 ix polarizer 17 and is focused on the crystal 41 by the concave focusing element 18. In addition, the polarized radiation passes through the partially transmissive and partially reflective element 44, which can be, for example, a potassium chloride (KCl) plate with partially transmissive dielectric coatings. The element 44 is arranged so that the polarization of the 10, 6 u pump radiation is oblique to its surface and is well transmissive with low reflection losses.

Likewise, the element 44 falls obliquely from its opposite side, polarized parallel to the surface of the element 44, so that it is easily reflected by it, a signal radiation from the source 45 with a wavelength of 13.7 u. the reflected signal radiation propagates in line with the pump radiation.

The tellurium crystal 41 is oriented in such a way that it receives the 10, 8 u pump radiation from the focussing element 18 at an angle to its optical axis, which enables a phase-matched propagation of the 10, 6 a and 13.7 ix radiation and the secondary radiation between the entrance and the Exit surfaces results. The entry and exit surfaces of the crystal 41 are

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cut so that they are perpendicular to the direction of propagation of the input radiation. These entry and exit surfaces are covered with anti-reflective material, e.g. B ₉ with selenium, cadmium sulfide or other suitable dielectrics. From the entrance surface of the crystal 41, the amplified signal radiation, the generated secondary radiation and the unused pump radiation go through the focusing lens 20 to the 10, 6u blocking filter 21. From there, the signal radiation goes through the 13, 7u bandpass filters 42 and 43 and falls on the receiver 48 where it is demodulated. The band pass filters 42 and 43 are dielectric coated pressed polycrystalline camidmium selenides.

The signal source 45 is, for example, a helium-neon laser that operates at 13, 7 η and an amplitude modulator that responds to a baseband information signal. The helium-neon laser is described in an article "Collision Processes Leading to Optical Masers in Gases" by CKN Patel in the book Atomic Collieion Processes, edited by MRC »McDowell, North Holland Publishing Company (1964). The receiver 46 consists, for example, of a photoconductor which * responds to infrared radiation and of suitable baseband amplifiers.

Other parts of Fig. 3 are the same as the parts in Fig. and 2, insofar as they are identified by the same numbers.

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When operating the embodiment of FIG. 3, one obtains a phase-matched gain as long as the angle between the common direction of propagation and the optical axis deB tellurium crystal 41 is the angle that the phase velocities for the signal wave, the auxiliary wave and the pump wave equal makes »Under these conditions, energy changes from a relatively high-energy pump wave to a relative one transmitted weak signal wave via the non-linear polarization wave in the crystal 41.

If the frequency source 45 is changed, so should the Angle between the common Fo rtpflanzungs direction and the optical axis of the crystal 41 can be changed to the Maintain phase match condition as described above for the parametric oscillator of FIG.

On the other hand, the design of Figure 3 can be modified so that that the sum or difference radiation generated in the nonlinear material is obtained. The sum or

Pump signal differential frequency radiation is made up of a strong and a weak,. generated signal to be detected. Again, phase matching is provided. The advantage of such a method is that z.3. can use a pump in 5 a and a weak signal 25 ii can determine, in 'which one instead the difference frequency or Nebenatrahlung

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found at 6, 25 η . The amplified secondary energy is proportional to the amplified signal energy. The detection of the 6, 25 α spurious is considerably easier than the detection of the amplified signal at 25 ii because good photoconductive detectors are available at 6, 25 η .

Furthermore, the embodiment of FIG. 3 can be modified so that the sum frequency radiation is determined at 4.16 η, in which case there is no amplification of the signal and both the pump wave and the signal wave are used to generate the 4.16 u radiation ν . The 4.16 η radiation is easier to determine than the 25 »signal using conventional methods.

With selenium as the non-linear material, a pump wave at iu and a signal fc _e i 13 ^ 7 _u can be used to produce a spurious wave at 1.07 ix -Has a noise ratio superior to that of a photoconductive detector at 13,711. The same argument applies if the sum frequency radiation is generated.

In broadband parametric devices it is extremely desirable to keep spurious resonances in the nonlinear material. For this purpose it is desirable to use Tellurium or QQ9813 / U6Q in all of the foregoing facilities

To use selenium in which the free charge concentration is not

17th
is significantly larger than 1.10 beams per cubic centimeter.

It is not necessary in a system like that shown in Fig. 3, To use photoconductors as detectors. The extraordinarily large second order polarization coefficients of tellurium and selenium are of the order of magnitude that single crystals of these materials act as square detectors for Makes amplitude modulation useful, which are performed by infrared radiation.

In FIG. 4, which shows a modulator circuit, the CO_-Laeer 112, the 10.6 a polarizer 113, the tellurium or selenium modulator 114 and the 1O ₄ 6 "polarizer 115 are connected in this order crossed with the axis of the polarizer 113, the modulator 114 being coupled to a source 116 of a modulated high frequency signal representing the modulation that is to be imposed on the 10, 8 Ii radiation.

For example, the 10, 6yu polarizers 113 and 115 are single crystals made of tellurium, the large areas of which are cut in such a way that they lie parallel to their optical axes and the hole concentrations (positive free charge carriers) are greater

18th
than 1.10 holes per cubic centimeter. The larger surfaces are oriented so that they are perpendicular to the direction of propagation of the 10.6u radiation.

00981 3/1460

The modulator 114 consists of a single crystal 117, for example made of tellurium, the optical axis of which is essentially parallel to the direction of propagation of the radiation and to the electrodes 118 and 119, which lie in planes that are essentially are parallel to the optical axis. The crystal 117 is oriented so that the direction of the optical axis induced by the electrical modulation field generated by the electrodes 118 and 119 arises, at an angle of 45 to the directions the polarization axes of the polarizers 113 and 115 lies. The induced optical axis lies on a main crystal axis (x or y). The tellurium crystal 117 is processed by known processes so that it is as intrinsic as possible is, in particular that it has a hole concentration (positive

17th

free charge carriers) that is less than 1.10 per cubic centimeter at the operating temperature. This serves to keep the unwanted "desired resonance absorption small. The hole concentration is typically the result of either copper traces or by lattice defects. As is known, the effective hole concentration can be _t by reducing the temperature reduced. The crystal 117, for example, has a length of about one Centimeters, its diameter perpendicular to the direction of propagation is, for example, 1 cm.The electrodes 118 and 119 consist, for example, of gold applied in a vacuum.

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The source 116 may include, for example, a microphone through which a speech signal is delivered, as well as a conventional one High frequency energy source and a conventional high frequency modulator which is set up to control the high frequency

j quente energy amplitude-modulated with the speech signal.

During operation, the laser 112 generates coherent radiation at 10.6 Ji _{1 and} the polarizer 113 polarizes this radiation, unless it is already polarized by the laser 112, in such a way that its electric field strength is vector parallel to a so-called crystalline y-axis of the crystal 117 lies. Finally, the modulator 114 changes the relative propagation speed of 45 polarization components of the radiation in such a way that, in general, an elliptical polarization with variable ellipticity is generated at the exit surface of the crystal 117. A portion of this radiation with variable amplitude then passes through the crossed polarizer 115.

In particular, the electrical modulation field is applied in the crystal 117 along a so-called crystalline x- axis and induces an optical axis perpendicular to the direction of propagation of the 10, 6 ju radiation and at an angle of 45 to the x and y axes. The component of the radiation with a polarization parallel to this induced optical axis propagates at a speed that

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is different from the speed of the radiation component, which has a polarization perpendicular to it. the The difference in propagation speeds is directly related to the strength of the electrical modulation field. the Modulation can also be viewed from the standpoint of the relative phase shift of the waves that the two Form components. This relative phase shift is commonly called a relative phase lag. if the. relative phase delay becomes 180, the resulting Polarization of the radiation that passes through the crystal 117 is rotated 90 and easily passes through the polarizer 115. At a beam with a lower amplitude, a smaller part of the radiation passes through the polarizer 115 Output of the polarizer 115 is an amplitude modulated Signal representing the modulation carried by the source 116 signal.

It is interesting to note that although the electrodes are arranged on the side 118 and 119, the crystal structure of tellurium is such that the linear electro-optic (Fockels) effect is used »I

A modulation index of 100% (180 relative phase delay) with a voltage of about 100 V applied between the electrodes 118 and 119 in the case of a tellurium crystal

009113/148 0

while the same index requires 7000 V applied to a crystal of potassium dihydrogen phosphate or about 5000 V _{1 applied} to a crystal of lithium metaniobate that is one centimeter long and three millimeters thick in the electric field direction when using one T rager radiation with an optimal wavelength for this facility assumes.

If the tellurium crystal 117 by a single crystal of selenium of comparable size and purity and with the same Replacing electrodes, one can use a modulation index of 100% (180 ° relative phase delay) vender 10, δ ai radiation with a voltage of about 800 V applied between the electrodes.

Furthermore, compared to previous modulators according to the invention Modulators with the use of tellurium and selenium have the particular advantage that they are suitable for a T rager radiation with a Wavelength in the range of the atmospheric window of 8 ii - 14 χι are relatively transparent. Selenium is also in the windows mkt shorter wavelength, e.g. in the 3, 5ai Window, permeable

A mixed single crystal of tellurium and selenium can be known through Process will be made, he will in general Have properties that are between the properties of the elements

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(i.e. band gap and second order polarization coefficient) »Through such a mixed crystal, optimal properties for operation in the 3, 5 ii window result.

Almost all modulation effects known to be useful in large optical crystals can be used to produce a modulation of infrared radiation in tellurium or selenium. A summary these effects can be found in Chapter 29 of Jenkins and White, "Fundamental of Optics", 3rd edition, McGraw-HiU (1957); she include the Zeeman effect and the reverse Zeeman effect, the magneto-optic Voight, Cotton-Mouton, Faraday and Kerr effects, the strong effect and the reverse strong effect, the electro-optical birefringence, the electro-optical Pockel effect and the electro-optical Kerre effect.

An embodiment of the invention using the Faraday effect is shown in FIG. 6. There the CO laser 112, the 10, 6 u polarizer 113, the tellurium modulator 124 and the 10, 6 ix polarizer 115 are connected in series in this order. The polarization axis of the polarizer 115 is crossed with the axis of the polarizer 113. The modulator 124 is coupled to a source 116 for a modulated high frequency signal, which is the modulation that is to be impressed on the 10, 6 a radiation.

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»Β

The devices 112, 113, 115 and 116 are the same as described above for the embodiment of FIG.

The modulator 124 consists, for example, of a single crystal 127 of tellurium, the optical axis of which is essentially parallel to the Direction of propagation of the radiation supplied by the laser 112 lies. The coil 128, which the magnetic modulation field has an axis that is substantially parallel to the optical. Axis de «; Crystal 127 lies. The orientation of the the crystalline axis of the crystal 127 is not critical except for the optical axis.

In this application, the Tellurium crystal 127 passes through the Methods known to semiconductor technology either by doping with copper or by introducing lattice defects are treated in such a way that at the operating temperature there is a hole concentration

18 19

tration in the range between 1.10 per ecm and ^ * Μψηαλ l. ok

18 holes per ecm, preferably about 1.5.10 holes per ecm having. For the latter concentration, for example, the crystal 127 is about 1 cm long, its diameter being perpendicular to the direction of propagation z »B. about 1 cm.

The coil 128 is e.g. an induction coil which is wound in such a way that that it forms a continuous cylinder which extends sufficiently far over each end d of the crystal 127 to be in the crystal to create a uniform field

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In operation, the laser 112 generates coherent radiation at 10, 6 a, the polarizer 113 polarizes this radiation to the extent that it has not already been polarized in this way by the laser 112 furthermore, the modulator 124 rotates the polarization direction of the 10, Su radiation by an amount which is in direct relation is related to the strength of the applied magnetic field as a result of Faraday's law, while the polarization is linear remain. The crossed polarizer 115 then transmits a portion of the variable amplitude radiation.

■ I Q

A modulation index of 100% (90 rotation of polarization) can be obtained with a magnetic field strength of about 1000 Gauss, while the same index typically has a field of

Requires IQ kilograms of gauss in indium antimonide (InSb) and chromium tribromide. Other materials that have heretofore shown promise for such use.

Even if demodulators or detectors of the previous ones

Kind can be used around the, as with the designs demodulate the modulation generated in FIGS. 4 and 6,

so tellurium and selenium have such large polarization coefficients second order, that it is advantageous, e.g. from the standpoint of reducing the equilibrium noise, Use single crystals of these materials as square detectors for the modulated IQ, 8 u radiation ζμ.

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Such a detector is shown in Fig. 7, where it is shown in a receiver 141 is used which is separated from a transmitter 140 by a transmission medium such as the atmosphere is. The transmitter 140 includes, for example, devices 112, 112, 114 and 115 related to execution of Fig. 4 have been described.

The receiver 141 contains the single crystal 147 made of tellurium, the optical axis of which is at a very small angle θ to the direction of propagation of the radiation is oriented with its electrodes 148 and 149 in planes which are substantially are parallel to the direction of propagation. The receiver output circuit 150 is also between the electrodes 148 and send 149 your eyes.

For this application, the tellurium crystal 147 is treated in the manner described above, so that it is

17 ^x temperature a hole concentration between 1.10 holes each

19th
ecm and 1.10 holes each ecm, preferably about

18th
10 holes each ecm.

The small angle 9 is used to enable phase adjustment to make it optimally has a size that is directly related to the modulation frequency, especially for modulation frequencies in the microwave range. Also for modulation

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copy,;

frequencies in the high microwave range (wavelength longer than, but close to 1 mm), the angle 0 can preferably have a size smaller than 10 »

For example, electrodes 148 and 149 are vacuum deposited Gold, they are both perpendicular to an x-axis of crystal 147, being the direction of the electric field being received Radiation lies parallel to a y-axis.

The receiver output circuit 150 consists of, for example, cascaded Voltage amplifiers, which include one or more power amplifiers and a loudspeaker or a another consumer device follows.

In operation, the second order polarization coefficient (nonlinear coefficient) d of the crystal 147, which corresponds to (1, 27

-5
+0, 2) χ 10 ~ ESE (electrostatic units) was measured to respond to the received amplitude-modulated radiation in the manner of a square detector. Since this effect can be traced back to the non-linear properties of the polarization wave, ie to a movement of charge dipoles that is not in resonance, it is inherently a very broadband effect. The upper limit of its frequency range is primarily determined by its time constant and is inversely related to it, the time constant being the product of the capacitance between the electrodes

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148 and 149 and the effective ohmic resistance between them. The increase in the concentration of holes in the crystal 147 is one way to decrease this resistance and increase the upper limit of the frequency range. Generally supposed the time constant can be much less than a quarter of the shortest period of the amplitude modulation, that of the infrared Radiation leads.

In particular, the polarization nonlinear wave typically has a component of motion which would be a fixed value in the absence of modulation and which, in the presence of modulation, changes in accordance with the modulation. A corresponding induced electromagnetic field with the modulation frequency is associated with this modulated component. Since this field would have the tendency to propagate along the optical axis of the crystal 147. at a speed which is different from the speed of the 10.6 η radiation, creating destructive interference effects on the electrodes 148 and 149, the provision of the Angle 0 a phase adjustment when used in the parametric oscillator and the second harmonic generator. An interaction with a traveling wave occurs, which appears as a constructive interference effect at the modulation frequency at the electrodes 148 and 149.

009813/1460

Claims (17)

The conversion efficiency of the detector, which consists of the crystal 147 and the electrodes 148 and 149, is, for example, about 1.10 V per watt of the 100% modulated input radiation when the crystal 147 has the preferred doping level. The conversion efficiency is essentially independent of the hole concentration as long as the 10.6 W radiation is lost as a result of absorption in the crystal. A very low noise level is associated with the above conversion efficiency, which is based on the low inherent impedance of the detector, so that the signal-to-noise ratio is very satisfactory for most infrared rectification requirements. As in the previous embodiments of the invention, a selenium single crystal can be used in place of the tellurium crystal 147 in order to provide an analogous effect which extends up to a wavelength of 0.8 η. Similarly, a mixed crystal of tellurium and selenium can be used to obtain properties in between. 009813/1460 PATENT CLAIMS 1. Parametric device using a crystal to produce parametric effects with running waves, the generation of second harmonics with running waves, optical demodulation or of Modulation effects in the infrared part of the electromagnetic spectrum, characterized in that the crystal (e.g. 11) is a single crystal which contains at least one element of the group consisting of tellurium and selenium and which is suitable transmit infrared radiation. 2. Device according to claim 1, characterized in that means are provided to polarized by the crystal to conduct coherent infrared pump radiation in order to induce another radiation of different wavelengths, whereby the pump radiation has a first wavelength which is longer than the wavelength of the ribbon pieces of the material and which is directed to the optical axis of the material at an angle which is a phase velocity for the pump radiation results, which is substantially equal to the phase velocity of the induced radiation. 009813 / U60 -3X- 3. Device according to claim 2, characterized in that that the angle is an angle that allows the induced radiation to be predominantly second harmonic radiation is. 4. Device according to claim 2, characterized in that a resonator is arranged around the crystal, which with
of the induced radiation is in resonance and in which the
Angle lies in the range which allows the induced radiation to occur predominantly at two frequencies, the sum of which is equal to the frequency of the directed radiation. 5. Device according to claim 2, characterized in that the single crystal is tellurium, the opposite surfaces of which are cut perpendicular to a direction which form an angle of 14 ° 10 * + 30 ¹ with the optical axis of the crystal and in which the angle of directed radiation to the optical axis 14 is 10 * + 30 ', so that the induced
Radiation is predominantly the second harmonic. 6. Device according to claim 2, characterized in that the opposite surfaces of the crystal are spherical
are curved, with tangents perpendicular to the
Direction of propagation and exactly convocal for one between 009813 / U60 radiation reflected from them, the opposite surfaces being provided with a dielectric coating, • so that a large internal reflection occurs for radiation which has a wavelength in the range from 15 u to 30 u, while the impedance matching for the coherent infrared beam is improved when the beam passes through the opposite one Surfaces goes. 7. Device according to claim 6, characterized in that that the dielectric coating is selected from the group consisting of selenium and cadmium sulfide. 8. Device according to claim 2, characterized in that the means for directing the pump radiation contains a laser which delivers the pump radiation with a wavelength which is in the atmospheric window from 8 ii to 14 η , that the single crystal is a tellurium crystal of the opposite faces which lie perpendicular to the direction of the pump radiation, that the angle which this direction forms with the optical axis lies in one of the ranges 0 to 12 and 16 to 90 in order to enable the induced radiation to occur predominantly at two frequencies, the Sum is equal to the frequency of the directed radiation, this combination being a signal radiation source with one of the Ü09813 / U60 contains both frequencies, furthermore a means of keeping the signal radiation in line with the pump radiation towards the crystal, the other frequency of the induced radiation being the secondary frequency. 9. Device according to claim 1, characterized in that means are provided around the crystal with coherent To illuminate infrared radiation and that means are connected to the crystal to transmit a signal in Regarding the infrared radiation. 10. Device according to claim 9, characterized in that the signal transmission means consists of two electrodes, which are attached to the crystal and which are oriented so that they lie in planes substantially parallel to the optical axis of the crystal, so that the device can be used as an electro-optical modulator. 11. Device according to claim 9, characterized in that that the signal transmission means is assisted by a device for generating a magnetic field which is so oriented is that it directs a magnetic field in the direction of the optical axis of the device, so that the device as Faraday modulator can be used. 009813/1460 -as · - 12. Device according to claim 9, characterized in that that the signal transmission means consists of two electrodes, which are attached to the crystal and which are oriented so that they are parallel to a direction which is an angle of forms less than 10 to the optical axis of the crystal, so that the device acts as a square detector for amplitude-modulated infrared radiation can be used. 13. Parametric device according to claim I ₁ characterized characterized in that the crystal material has a hole concentration 17 has tration, which is less than 1x10 holes per cubic centimeter and that means are provided to a modulated electrical To create a field on the crystal. 14. Parametric device according to claim I _1, characterized in that the crystal material has a hole concentration between 1x10 and 1x10 holes per ecm and that means are provided to apply a magnetic modulation field to the crystal. 15. Parametric device according to claim 1, characterized characterized in that the crystal material has a hole concentration 17 19 tration between 1x10 and 1x10 holes per ecm and that ° an electrode means a signal under the influence of the amplitude - »modulation decreases, the crystal with its optical axis ^ at an angle to the received modulated infrared beam ⁰ ^ ment oriented, so that a phase adjustment of the modulated * Radiation and the field of the signal is created, which is picked up by the electrode means.