Optically modulated scatterer and array thereof

[0001] (A) Field of the Invention

[0002] The present invention relates to an optically modulated scatterer and array thereof, and more particularly, to an optically modulated scatterer and array thereof for measuring a spatial distribution of an electromagnetic signal without interference. The optically modulated scatterer and array thereof is an important tool for measuring the spatial distribution of the electromagnetic field.

[0003] (B) Description of the Related Art

[0004] Since a wireless communication system uses an antenna to transmit and receive an electromagnetic signal, how to make the electromagnetic field emitted by the antenna to comply with the specifications is an important subject for improving the antenna quality. In addition, the intensity of the electromagnetic wave emitted by the wireless communication product must be lower than the specific absorption rate (SAR) specified by the international safety standard to come into the market, therefore the SAR measurement technique is very important for the development of the cell phone. Presently, there are many electromagnetic wave measurement techniques; one of them utilizes the modulated scatterer to measure the distribution of the electromagnetic field.

[0005] The conventional technique uses a modulated scatterer array to measure the electromagnetic field, wherein an electrical modulating signal is transmitted by a conductive wire to modulate a diode inside the scatterer and incorporates fast scanning to measure the electromagnetic field. The bias voltage applied to the diode inside the scatterer is transmitted through the conductive wire; however, the conductive wire will irradiate electromagnetic waves, which interfere with the electromagnetic signal to be measured. U.S. Pat. No. 4,305,153 discloses an electromagnetic field measurement technique using a light beam incorporating a chopper to modulate the diode inside the scatterer, wherein the bias voltage is supplied by a solar cell. In addition, G. Hygate et al. disclose an electromagnetic field measurement technique without electrical interference, which uses a phototransistor to produce an optically modulated scatterer, i.e., uses optical device rather than the conductive wire to modulate the scatter (SEE: Measuring microwave fields directly with an optically modulated scatterer, 1990, Meas. Sci. Technol., and A Probe for Making Near-Field Measurements with Minimal Disturbance: The Optically Modulated Scatterer). However, G. Hygate et al. only disclose the utilization of the optically modulated scatterer in the electromagnetic signal sensing system, the detailed structure of the optically modulated scatterer is not disclosed. Under this situation, it is difficult for one skilled in the art to overcome the shortcomings of the prior art using the disclosure by G. Hygate et al.

[0006] The objective of the present invention is to provide an optically modulated scatterer and array thereof for measuring the spatial distribution of an electromagnetic signal without interference.

[0007] In order to achieve the above-mentioned objective, and avoid the problems of the prior art, the present optically modulated scatterer comprises a substrate, an antenna positioned on the substrate, an optical switch connected to the antenna, and an optical waveguide connected to the optical switch. The antenna includes a first conductive line and a second conductive line, the optical switch electrically connects the first conductive line and the second conductive line, and the optical waveguide can transmit an optical modulating signal to the optical switch. In addition, the antenna can be a loop-shaped antenna with two free ends, and the optical switch electrically connects the two free ends. The optically modulated scatter array of the present invention comprises a first substrate and a plurality of optically modulated scatterers positioned on the surface of the first substrate in a one-dimensional or a two-dimensional array manner.

[0020] FIG. 1 illustrates an optically modulated scatterer 10 according to the first embodiment of the present invention. As shown in FIG. 1, the optically modulated scatterer 10 comprises a substrate 12, an antenna 20 positioned on the bottom surface of the substrate 12, an optical switch 30 electrically connected to the antenna 20, an optical waveguide 40 for transmitting an optical modulating signal to the optical switch 30, and a sheath 42 for fixing the optical waveguide 40 on the upper surface of the substrate 12. The antenna 20 includes a first conductive line 22 and a second conductive line 24 positioned on the bottom surface of the substrate 12, while the optical switch 30 can electrically connect the first conductive line 22 and the second conductive line 24.

[0021] FIG. 2 is a schematic diagram of the optical switch 30 according to the present invention. As shown in FIG. 2, the optical switch 30 comprises an intrinsic GaAs (gallium arsenide) substrate 31a, a highly-doped GaAs substrate 31b, a first interdigital electrode 32 and a second interdigital electrode 34 positioned on the highly-doped GaAs substrate 31b. The first interdigital electrode 32 and the second interdigital electrode 34 are electrically connected to the first conductive line 22 and the second conductive line 24 of the antenna 20, respectively. The optical waveguide 40 is aimed at an interdigital region between the first interdigital electrode 32 and the second interdigital electrode 34 of the optical switch 30. In addition, the highly-doped GaAs substrate 31b can be P-type or N-type, and forms an ohmic contact with the first interdigital electrode 32 and the second interdigital electrode 34.

[0022] When a light beam with appropriate energy irradiates the interdigital region of the optical switch 30, conductive electrons and holes are generated to reduce the resistance between the first interdigital electrode 32 and the second interdigital electrode 34 of the optical switch 30 so that the first interdigital electrode 32 and the second interdigital electrode 34 become conductive to couple the first conductive line 22 and the second conductive line 24 into a relatively longer metallic scattering body. In this way, the overall scattering cross-section is increased to enhance a modulated scattering signal emitted from the optically modulated scatterer 10, wherein the enhanced modulated scattering signal is in proportion or in square proportion to the electromagnetic field where the optically modulated scatterer 10 is positioned.

[0023] Referring to FIG. 1, the optical modulating signal transmitted by the optical waveguide 40 penetrates the substrate 12 to irradiate the interdigital region of the optical switch 30. Therefore, the substrate 12 is preferably formed of insulatvie material without absorbing the optical modulating signal to avoid signal decay on penetrating the substrate 12. Preferably, the substrate 12 is a mica substrate.

[0024] FIG. 3 illustrates an optically modulated scatterer 100 according the second embodiment of the present invention. As shown in FIG. 3, the substrate 12 further comprises an opening 14 positioned between the first conductive line 22 and the second conductive line 24, and the optical switch 30 and the optical waveguide 40 are aimed at the opening 14, wherein the substrate 12 can be made of microcrystal glass. Consequently, the optical waveguide 40 can transmit the optical modulating signal through the opening 14 directly to the optical switch 30, without any concern of the signal decay originating from the penetration of the substrate 12. The optically modulated scatterer 100 can be set up on a moving platform to perform a spatial scanning to measure spatial amplitude and phase distribution of an electromagnetic field.

[0025] FIG. 4 illustrates an optically modulated scatterer 110 according the third embodiment of the present invention. Compared with the optically modulated scatterer 10 in FIG. 1, the optically modulated scatterer 110 in FIG. 4 uses a loop-shaped antenna 120 with two free ends 122, 124. When the optical switch 30 electronically connect the two free ends 122 and 124, the loop-shaped antenna 120 can function to scatter a magnetic field to be measured.

[0026] FIG. 5 illustrates an optically modulated scatterer array 50 according to the first embodiment of the present invention. As shown in FIG. 5, the optically modulated scatterer array 50 comprises a substrate 52, a plurality of openings 54 positioned on the substrate 52 and a plurality of optically modulated scatterers 10. The diameter of the opening 54 is preferably slightly larger than the diameter of the sheath 42 so that the sheath 42 can be fixed inside the opening 54. The plurality of optically modulated scatterers 10 are positioned on the substrate 52 in a one-dimensional array manner, i.e., positioned along one direction the substrate 52, which can be used to measure the one-dimensional distribution of the electromagnetic field to be measured. The substrate 12 of the optically modulated scatterer 10 has an opening 14, and the optical waveguide 40 transmits the optical modulating signal to the optical switch 30 through the opening 14.

[0027] FIG. 6 illustrates an optically modulated scatterer array 60 according to the second embodiment of the present invention. As shown in FIG. 6, the optically modulated scatterer array 60 comprises a substrate 62, a plurality of antennas 20 positioned on the substrate 62, a plurality of optical switches 30 for controlling the antenna 20, and a plurality of optical waveguides 40 for transmitting the optical modulating signal to the optical switch 30. Compared with the optically modulated scatterer array 50 shown in FIG. 5, the plurality of antennas 20 of the optically modulated scatterer array 60 are formed directly on the surface of the substrate 62. In addition, there is an opening 64 positioned between the first conductive line 22 and the second conductive line 24, and the optical waveguide 40 transmits the optical modulating signal through the opening 64 to irradiate the optical switch 30.

[0028] FIG. 7 illustrates an optically modulated scatterer array 70 according to the third embodiment of the present invention, wherein only the antenna 20 is shown for the sake of clarity and the optical switch 30 and the optical waveguide 40 corresponding to each antenna 20 are not shown in the figure. As shown in FIG. 7, the optically modulated scatterer array 70 comprises a substrate 72 and a plurality of optically modulated scatterer 10 positioned in a two-dimensional array manner for measuring the two-dimensional distribution of the electromagnetic field.

[0029] FIG. 8 illustrates an optically modulated scatterer array 80 according to the fourth embodiment of the present invention, wherein only the antenna 20 is shown for the sake of clarity and the optical switch 30 and the optical waveguide 40 corresponding to each antenna 20 are not shown in the figure. As shown in FIG. 8, the optically modulated scatterer array 80 comprises three substrates 82 substantially perpendicular to each other, and each substrate 82 includes a plurality of scattering antennas 20 positioned in a two-dimensional array manner. The optically modulated scatterer array 80 can be used to measure the spatial distribution of the electromagnetic field.

[0030] FIG. 9 illustrates an optically modulated scatterer array 90 according to the fifth embodiment of the present invention. Compared with the optically modulated scatterer array 80 in FIG. 8, the optically modulated scatterer array 90 uses the loop-shaped antenna 120 rather than the antenna 20. Through switching and controlling the optical switches 30 (not shown in FIG. 9) that connects the plurality of loop-shaped antennas 120, the optically modulated scatterer array 90 can be used to measure the one-dimensional, two-dimensional or three-dimensional distribution of the electromagnetic field.

[0031] FIG. 10 illustrates an optically modulated scatterer array 130 according to the sixth embodiment of the present invention, wherein only the antenna 20 of each optically modulated scatterer 10 is illustratively shown for the sake of clarity, and the corresponding optical switch 30 and the optical waveguide 40 are not shown. As shown in FIG. 10, the optically modulated scatterer array 130 comprises a substrate 132 including a plurality of optically modulated scatterers 10 positioned in a two-dimensional array manner. The antenna 20 of each optically modulated scatterer 10 is positioned on the substrate 132 in a substantially perpendicular manner for measuring the spatial distribution of the electromagnetic field. In the other words, the antennas can be grouped into a plurality of sets 134 with two antennas 20 substantially perpendicular to each other.

[0032] FIG. 11 illustrates an optically modulated scatterer array 140 according to the seventh embodiment of the present invention. As shown in FIG. 11, the optically modulated scatterer array 140 comprises a substrate 142 and two optically modulated scatterers 10. The two optically modulated scatterers 10 are positioned on the upper and bottom surface of the substrate 142, respectively, and the two antennas 20 are substantially perpendicular to each other for measuring the spatial distribution of the electromagnetic field.

[0033] Compared with the scatterer modulated directly by the electrical signal according to the prior art, the present invention uses the optical waveguide 40 to transmit the optical modulating signal for modulating the optically modulated scatterer 10. Consequently, the present invention will not interfere with the electromagnetic signal to be measured on modulating the optically modulated scatterer 10. In addition, the present optically modulated scatterer 10 possesses high precision, high resolution and high fidelity to be applied to measure the spatial distribution of the electromagnetic field such as antenna near field, SAR distribution, electromagnetic wave propagation and electromagnetic compatibility analysis.

[0034] The above-described embodiments of the present invention are intended to be illustrative only. Numerous alternative embodiments may be devised by those skilled in the art without departing from the scope of the following claims.