DE3604571A1 - HF PHASE SHIFT, REALIZED AS AN INTEGRATED-OPTICAL COMPONENT - Google Patents

Description

M.C.Bone 6-1

HF phase shifter, implemented as an integrated optical

Build ement

The invention relates to an RF phase shifter as a \ / \ / integrated optical device is realized. Such RF phase shifters are used, among other things, for microwell devices such as e.g. B. phased antennas required. Phase-controlled antennas are used, for example, in radar devices. The concept of phased antennas has been known for some time and its advantages have been thoroughly discussed. Nevertheless, it is used with relatively few radars. A major reason for the low enforcement is that the size, weight and cost of the programmable microwave phase shifters are very high. This is because microwave phase shifters are necessary for each element of an antenna array. These phase shifters must switch a large amount of RF power precisely and the loss must only be very small. Another and similarly weighty reason is weight

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and the awkward handling of coaxial cables that only may have a small loss, and which are necessary to the RF transmitter with the individual phase shifters connect to.

Lately the use of optical components has increased with phased antennas too. The starting point was to replace the coaxial cables with optical fibers. This was done to save weight. Furthermore, the benefits of the optical components, in particular the optical transmission lines, made use of, namely low loss, large bandwidth, electrical isolation, no EM radiation, no crosstalk, great reliability (due to the use of of several light redundant signal paths). is Once the step towards optics has been made, the transition to optical control of the microwave phase and the Modulation of optical waves with signals in the microwave range not only possible but very desirable. Then the way is clear for eliminating the microwave phase shifters from the antenna head. As a result, a large proportion of weight is saved and continues to be achieved one that the antenna positioning can be done more precisely and that the stability through the use is increased by more bits per phase adjustment.

The most common methods of generating microwave modulation on the optical carrier is the direct amplitude modulation via the laser control circuit or a external amplitude modulation, e.g. B. a LiNbO, Mach-Zehnder modulator. If amplitude modulation is used then the microwave modulation is not through a change in the phase of the optical carrier can be changed

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(which would be the case if single sideband modulation was used would be) and therefore other means must be used will.

The invention provides a solution with which it is possible to carry out phase control in a simple and elegant way.

The HF phase shifter implemented as an integrated optical component contains a body made of a highly birefringent electro-optical material. There is one in it Optical fiber implemented. On the surface of the body an electrode is arranged at one end in the vicinity of the optical waveguide, which is called a TEtr ^ TM mode converter serves. The length of the optical fiber, measured from the electrode is chosen so that the modulation components of two mutually orthogonally polarized Light waves that are uncoupled in the light source propagate with different phase velocities, at the point where they come out of the fiber optic cable are coupled out, are in phase quadrature to one another. In the further processing of these components takes place a vector addition. This will set the modulation frequency, which is impressed on the light beam, phase-shifted by the desired value.

The invention is based on the drawings at spi e Lswei se explained in more detail. It shows:

Fig. 1 is a schematic representation of the HF-Phasenschi ebe rs,

Fig. 2 shows an embodiment with one polarization walk r,

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3a and 3b a tunable polarization converter,

Fig. 4 is a schematic representation for an optical Phase shifter, and

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5 and 6 diagrams to explain how it works

The exemplary embodiment according to FIG. 1 is first referred to referred to. The RF phase shifter that has been implemented as an integrated optical component, consists of one Body 1 from a strongly birefringent electro-optic lens Material, e.g. B. Lithium Niobate (LiNbO,). Near the PLANAR SURFACE 2 is a single mode fiber optic cable intended. This waveguide 3 can thereby be generated be that you can get titanium into the flat surface of the body 1 diffused. OVER THE LIGHT WAVE GUIDE an electrode 4 is applied to the planar surface, by means of which it is possible to electro-optically generate a TE ^ t ^ TM mode wall lung perform. This electrode is arranged in the vicinity of one end of the component.

The ends of the component 1 are for connection to a Optical fiber prepared. From one side of the building element off the fiber optic cable is connected 3 with a modulated laser 5 and from the other end there is a connection of a photodetector 6 to the one mentioned Fiber optic cable 3. The mode of operation is like follows: monochromatic light, amplitude modulated with the frequency f, emerges from the laser 5 and is in the Optical fiber 3 coupled. The TEiIJTM mode converter

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is then used to bring the light from the TE into the To convert TM mode or vice versa, in such a way that the relationship between the power with the TE polarization to the power with the TM polarization is equal to R. if the wave propagation in the component takes place in the Y-direction, then the lithium niobate crystal a 11 must either be in the Be cut in the X or Z direction. If the wave propagates in the X-direction, then the lithium niobate must be cut in either the Y or the Z direction.

Then the two mutually orthogonally polarized waves (TE and TM) propagate uncoupled and with different phase velocities (V _n and V). The phase velocities are determined by the refractive indices (n _n and η) of the strongly birefringent lithium niobate crystal a I Is. If the length of the crystal is L, then the relative time delay (T) between the originally coincident points on the TE and TM modes given by:

T = with AV = (Vn-V ₆ )

For a given modulation frequency f, this is temporal Delay equivalent to a phase delay of 2 1Tf T radians. When the two orthogonal modes are in a photodetector 6 are processed at the same time, then the modulation components are vectorially added. Then - if for example 2 ITf TT equal - »is - the two modulation components in Phase quadrature and then the phase of the processed Modulation signal simply equals tan (R); see fig. 5. If 2 T f T 9 is greater than - ^ -, then the vector relation as shown in FIG. Therefore reduced

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the regulation of the phase of f is based on the regulation of R, which in turn is determined by a G light voltage excitation I voltage for the TE ^ p ^ TM mode converter.

The main advantages of this arrangement are the low optical quality OS insertion loss (due to the simple implementation straight waveguide) and efficient use optical signals and the integrated realization that it makes possible numerous components from a single wafer to manufacture. It is also not necessary, as in other realizations, two path lengths with one exactly to have predetermined path length difference. Therefore it is not necessary to cut and polish the Perform fibers with extreme accuracy; a factor which is particularly advantageous when the usual modulation frequencies are moving more and more into the millimeter wave range move.

Assuming an optical wavelength of 0.85 ^ m, then it is possible with a shaft length conductor length of 60 mm, to carry out a phase control from 0 to 90 at f = 50 GHz. Enable shorter shaft conductor lengths operation at frequencies above 50 GHz. It is possible to extend the micro wave frequency range below 50 GHz when using (a) larger substrates or (b) suitable lengths of strong birefringent ones 5 (polarization maintaining) optical fibers. To connect the device to a remote photodetector (What about controlling phased radar antennas the case) is a greater length of an ordinary one Single mode optical fiber provided. This has in general a very low birefringence and typically adds no more than 0.15 phase shift at 15 GHz added per 100 tn.

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In the general case where the component supplied optical wave has a given but not given specific polarization, is the I - 0 phase shifter 7 (Fig. 4) is necessary before the TEi ± TM mode converter to enable the entire Area of 100% for polarization control available stands.

To make the TE5p * TM mode converter match to a special Ha Ib ladder läserque I Ie is a tunable Mode converter provided as shown in FIG. The optical waveguide 3 is now partially superimposed from a ground electrode 10. Parallel to this is on on one side a tuning electrode 11 and on the other Side the transducer electrode 12 arranged. The dominant one electric field E is the mode wall le rfe Id,

that is controlled by a DC voltage V .. The secondary Field E is the voting field. It is to be noted that the voting field has only a minor effect and this is necessary so that no precise matching of the component to a special laser source is required is. It is possible, for example, that the component is designed for a wavelength of 820 nm, during the Laser coupled to this component can have a wavelength of 821 nm.

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Claims (4)

in t> & - o 'V _ ft ffi Q "3Β0457Ί INTERNATIONAL STANDARD ELECTRIC CORPORATION, NEW YORK M.C.Bone-G.R.Adams 6-1 patent claims 1. HF phase shifter, implemented as an integrated optical component , by g e k e η η ζ e i c h η e t that a monocrystalline, strongly birefringent body (1) made of electro-optical Material is provided that in it a Honomodelichtwe I lenLeiter (3) is realized that this near and parallel to a flat surface (2) this body is arranged so that the spatial orientation of this optical waveguide in a predetermined Direction is in relation to the crystal axes, that an electrode (4) is arranged on the planar surface in the vicinity of one end of the optical waveguide is that a G light voltage control voltage is applied to the electrode is created, and that as a result, for a mono- ZT / Pi-Sm / R, January 29, 1986
P242A chromatic light beam, which runs through the optical waveguide, starting from the end at which the electrode is arranged, a τ p4 ^ ^- M mode wall lung can be carried out, and that the length of the optical waveguide from the electrode in the direction of propagation of the light beam is dimensioned so that a desired phase relationship occurs between the TE and TM modes of the light beam when it is decoupled from the wave guide of the RF phase shifter. 2. RF phase shifter according to claim 1, characterized in that the shape of the electrode and its control are chosen so that there is an optical phase shift for the light beam before a TE »- * TM mode conversion lung he follows" 3. RF phase shifter according to claim 1 or 2, characterized in that that part of the birefringent waveguide is realized as an optical fiber. 4. RF phase shifter according to one of claims 1 to 3, characterized in that the mode converter additionally has tuning electrodes (11) with which a vote to desired optical wavelengths is possible. ZT / Pi-Sm / R, January 29, 1986
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