Optical probe system and method

This application is a National Stage Entry that claims the benefit of PCT/US2016/047703 that claims priority to U.S. Provisional Patent Application No. 62/210,012 filed on Aug. 26, 2015, which is hereby incorporated by reference in its entirety.

1. Field of the Invention

The present invention relates to fiber based electro-optic and magneto-optic sensing systems with a probe tip for measuring electric or magnetic fields.

2. Description of Related Art

Electro-optic and magneto-optic field mapping have been recognized as diagnostic measurement techniques for the microwave, millimeter-wave, and sub-millimeter-wave regimes. Due to the single micrometer spatial resolution, broad bandwidth, and low invasiveness, electro-optic and magneto-optic field mapping have been used for fault isolation of microwave integrated circuits, extreme near-field mapping and near-to-far field transition characterization of antenna elements, performance verification of active quasi-optical power-combining arrays, and performance testing of active and passive antennas.

FIGS. 1A-1N illustrate optical fiber-mounted electric field sensors;

FIGS. 2A-2N illustrate optical fiber-mounted magnetic field sensors;

FIGS. 3A-3H illustrate block diagrams of optical mainframes for use with the optical fiber-mounted electric field sensors of FIGS. 1A-1N and/or the optical fiber-mounted magnetic field sensors of FIGS. 2A-2N ; and

FIG. 4A illustrates the relative signal from the optical fiber-mounted field sensor of FIGS. 1A-1N and 2A-2N , while FIG. 4B illustrates the relative signal from the optical fiber-mounted field sensor of FIGS. 1A-1N and 2A-2N .

FIG. 1A illustrates an optical fiber-mounted electric field sensor 110 A utilizing a single optical fiber to guide a light beam both to and from the end of the sensor. An optical fiber-mounted electric field sensor as described in FIGS. 1A-1N can be utilized to measure an electric field at a location on a circuit board, in free space, or elsewhere. The optical fiber-mounted electric field sensor as described in FIGS. 1A-1N has the distinct advantage of allowing for nonintrusive, interference-free, reliable measurements with minimized noise.

Here, the sensor 110 A has an optical connector 112 A for connecting to an optical source, such as a laser or an optical mainframe, as will be described in FIGS. 3A-3H . Connected to the optical connector 112 A, is a fiber 114 A. The fiber 114 A may be polarization-maintaining fiber. The fiber 114 A is fed into a fiber guiding ferrule 116 A which functions to properly guide the fiber 114 A to the center of the face of a lens 120 A.

The sensor 110 A also includes an alignment sleeve 118 A for positioning the circular circumferential edge of the face of the ferrule 116 A so that it is aligned with the circular circumferential edge of a face of the lens 120 A. The lens 120 A may be a focusing lens, such as a graded-index (GRIN) lens. When connected as shown in FIG. 1A , an optical beam provided to the fiber 114 A is provided to the lens 120 A and is generally profiled by the dotted line 122 A.

The optical beam 122 A from the lens 120 A is then provided to a polarizer 124 A which functions to polarize the optical beam 122 A. Connected to the polarizer 124 A is a polarization manipulator 126 A. The polarization manipulator 126 A may be a wave plate or an optical rotator, and in either case, it functions to rotate the polarization of the optical beam 122 A.

Electro-optical material 128 A may be applied to the polarization manipulator 126 A. The electro-optical material 128 A may be made of any medium exhibiting the Pockels effect, such as gallium arsenide (GaAs), aluminum-gallium-arsenide (AlGaAs), indium phosphide (InP), cadmium telluride (CdTe), zinc selenide (ZnSe), zinc telluride (ZnTe), bismuth silicate (Bi 12 SiO 2 O), cadmium sulfide (CdS), cadmium selenide (CdSe), lithium tantalate (LiTaO 3 ), lithium niobate (LiNbO 3 ), composites thereof, and mixtures thereof. At the tip of the sensor 110 A, a high reflection coating 130 A may be applied. The high reflection coating 130 A may comprise of alternating dielectric layers such as ZnSe, MgF2, SiO2, SiO, Si3N4, or other various dielectric materials.

Referring to FIGS. 1B and 1C , the sensors 110 B and 110 C are similar to those described in FIG. 1A . As such, like reference numerals have been utilized to refer to like elements. However, the sensor 110 B of FIG. 1B has relocated the polarizer 124 B to be located between the lens 120 B and the ferrule 116 B. In FIG. 1C , the polarizer 124 C and the polarization manipulator 126 C are both located between the ferrule 116 C and the lens 120 C.

Referring to FIGS. 1D, 1E, and 1F , these figures are similar to FIGS. 1A, 1B, and 1C , respectively. However, the FIGS. 1D, 1E, and 1F have replaced the focusing lens 120 A, 120 B, 120 C, with a collimating lens, 120 D, 120 E, and 120 F. As a result, the optical beam profiles in the lenses 120 D, 120 E, and 120 F result not in a focusing profile but rather a collimating profile as shown in the dotted lines 122 D, 122 E, and 122 F.

Referring to FIG. 1G , the sensor 110 G is similar to the sensor described in FIG. 1A , however, in this embodiment, the sensor 110 G has removed the lens 120 A of FIG. 1A and the alignment sleeve 118 A of FIG. 1A . As such, the optical beam profile 122 G varies so that it is diverging, as it is no longer focused or collimated by a separate lens. Referring to FIG. 1H , the sensor 110 H is similar to the sensor 110 G, but in this case, there is a fiber splicing point 132 H. The fiber splicing point 132 H is connected to the polarization-maintaining fiber 114 H on one side and a different type of fiber 134 H on the other side. The different fiber 134 H may be a single mode fiber, gradient-index fiber or thermally expanded core fiber.

Referring to FIGS. 1I, 1J, and 1K , the sensors 110 I, 110 J, and 110 K are similar to the sensors 110 A, 110 B, and 110 C shown and described in FIGS. 1A, 1B, and 1C , respectively. However, the sensors 110 I, 110 J, and 110 K each additionally disclose the use of a right angle prism 136 I, 136 J, and 136 K being directly coupled to lens 120 I, 120 J, and 120 K, respectively. By so doing, the right angle prisms 136 I, 136 J, and 136 K have the advantage of allowing the tip of the sensors 110 I, 110 J, and 110 K to be bent at a 90-degree angle, potentially allowing access to a measurement area and/or an electric field polarization vector that may be inaccessible otherwise.

Referring to FIGS. 1L, 1M, and 1N , the sensors 110 L, 110 M, and 110 N are similar to those shown and described in FIGS. 1I, 1J, and 1K , respectively. However, the sensors 110 L, 110 M, and 110 N differ from those described above in that the focusing lenses 120 I, 120 J, and 120 K, have been replaced with the collimating lenses 120 L, 120 M, and 120 N, respectively.

FIG. 2A illustrates an optical fiber-mounted magnetic field sensor 210 A utilizing a single optical fiber to guide a light beam both to and from the end of the sensor. An optical fiber-mounted magnetic field sensor as described in FIGS. 2A-2N can be utilized to measure a magnetic field at a location on a circuit board, in free space, or elsewhere. The optical fiber-mounted magnetic field sensor as described in FIGS. 2A-2N has the distinct advantage of allowing for nonintrusive, interference-free, reliable measurements with minimized noise.

Here, the sensor 210 A has an optical connector 212 A for connecting to an optical source, such as a laser or an optical mainframe, as will be described in FIGS. 3A-3H . Connected to the optical connector 212 A, is a fiber 214 A. The fiber 214 A may be polarization-maintaining fiber. The fiber 214 A is fed into a fiber guiding ferrule 216 A which functions to properly guide the fiber 214 A to the center of the face of a lens 220 A.

The sensor 210 A also includes an alignment sleeve 218 A for positioning the circular circumferential edge of the face of a ferrule 216 A so that it is aligned with the circular circumferential edge of a face of a lens 220 A. The lens 220 A may be a focusing lens, such as a GRIN lens. When connected as shown in FIG. 2A , an optical beam provided to the fiber 214 A is provided to the lens 220 A and is generally profiled by the dotted line 222 A.

The optical beam 222 A from the lens 220 A is then provided to a polarizer 224 A which functions to polarize the optical beam 222 A. Connected to the polarizer 224 A is a polarization manipulator 226 A. The polarization manipulator 226 A may be a wave plate or an optical rotator, and in either case, it functions to rotate the polarization of the optical beam 222 A.

Magneto-optical material 228 A may be applied to the polarization manipulator 226 A. The magneto-optical material 228 A may be made of any medium exhibiting the Faraday effect, such as bismuth-substituted rare-earth iron garnet (commonly known as Bi:RIG), bismuth-substituted yttrium iron garnet, terbium gallium garnet, SF-29 glass, cadmium manganese telluride (CdMnTe), cadmium manganese mercury telluride (CdMnHgTe), cadmium manganese selenide (CdMnSe), fused silica, doped alumina silicate glass, silicon dioxide (SiO 2 ), composites thereof, and mixtures thereof.

Referring to FIGS. 2B and 2C , the sensors 210 B and 210 C are similar to those described in FIG. 2A . As such, like reference numerals have been utilized to refer to like elements. However, the sensor 210 B of FIG. 2B has relocated the polarizer 224 B to be located between the lens 220 B and the ferrule 216 B. In FIG. 2C , the polarizer 224 C and the polarization manipulator 226 C are both located between the ferrule 216 C and the lens 220 C.

Referring to FIGS. 2D, 2E, and 2F , these figures are similar to FIGS. 2A, 2B, and 2C , respectively. However, the FIGS. 2D, 2E, and 2F have replaced the focusing lens 220 A, 220 B, 220 C, with a collimating lens, 220 D, 220 E, and 220 F. As a result, the optical beam profiles in the lenses 220 D, 220 E, and 220 F result not in a focusing profile but rather a collimating profile as shown in the dotted lines 222 D, 222 E, and 222 F.

Referring to FIG. 2G , the sensor 210 G is similar to the sensor described in FIG. 2A , however, in this embodiment, the sensor 210 G has removed the lens 220 A of FIG. 2A and the alignment sleeve 218 A of FIG. 2A . As such, the optical beam profile 222 G varies so that it is diverging, as it is no longer focused or collimated by a separate lens. Referring to FIG. 2H , the sensor 210 H is similar to the sensor 210 G, but in this case, there is a fiber splicing point 232 H. The fiber splicing point 232 H is connected to the polarization-maintaining fiber 214 H on one side and a different type of fiber 234 H on the other side. The different fiber 234 H may be a single mode fiber, gradient-index fiber or thermally expanded core fiber.

Referring to FIGS. 2I, 2J, and 2K , the sensors 210 I, 210 J, and 210 K are similar to those sensors 210 A, 210 B, and 210 C shown and described in FIGS. 2A, 2B, and 2C , respectively. However, the sensors 210 I, 210 J, and 210 K each additionally disclose the use of a right angle prism 236 I, 236 J, and 236 K being directly coupled to lens 220 I, 220 J, and 220 K, respectively. By so doing, the right angle prisms 236 I, 236 J, and 236 K have the advantage of allowing the tip of the sensors 210 I, 210 J, and 210 K to be bent at a 90-degree angle, potentially allowing access to a measurement area and/or a magnetic-field polarization vector that may be inaccessible otherwise.

Referring to FIGS. 2L, 2M, and 2N , the sensors 210 L, 210 M, and 210 N are similar to those shown and described in FIGS. 2I, 2J, and 2K , respectively. However, the sensors 210 L, 210 M, and 210 N differ from those described above in that the focusing lenses 220 I, 220 J, and 220 K, have been replaced with the collimating lenses 220 L, 220 M, and 220 N, respectively.

Referring to FIG. 3A , an optical mainframe 310 A is shown. The optical mainframe 310 A functions to generate optical beams and send them to and receive them from the sensors described in FIGS. 1A-1N and FIGS. 2A-2N . The optical mainframe 310 A also processes the optical signals received from the sensors so that they can be interpreted. The optical mainframe 310 A includes a laser source 312 A. The laser source may be a continuous wave laser source such as a distributed-feedback laser diode or a continuous-wave fiber laser, or it may be a pulse modulated laser source such as a mode-locked solid-state (e.g., titanium-doped sapphire) or fiber (e.g., rare-earth-doped silica-glass fiber) laser. The laser source provides a continuous or pulsed laser beam to a hybrid circulator 316 A via a polarization-maintaining fiber 314 A.

The hybrid circulator 316 A functions to allow the optical beam provided by the laser source to be sent to the sensors, but also to allow any optical beam received from the sensors to be directed away from the laser source and to a photodetector, as will be explained later. Ports 1 and 2 of the hybrid circulator 316 A are connected with polarization-maintaining optical fiber, and Port 3 is connected with conventional single-mode optical fiber. The hybrid circulator 316 A has a polarization-maintaining path from its Port 1 input to its Port 2 output, with the polarization parallel to the fast axis of the PM fibers connecting Ports 1 and 2 being blocked within the circulator, while the circulator has a non-polarization-maintaining path between its Port 2 input to its Port 3 output, with the polarization parallel to the fast axis of the PM fiber 318 A connecting Port 2 not blocked within the hybrid circulator. Hence the complete intensity of the optical beam returning from the probe and entering the hybrid circulator 316 A via Port 2 is passed through to the photodetector. Optical beams provided to the sensors are sent to a fiber connector 320 A via polarization-maintaining fiber 318 A. From there, the sensors may be connected via polarization-maintaining fiber 322 A. Optical beams that are returned from the sensors are transmitted from the sensors through polarization-maintaining fibers 322 A and 318 A to the hybrid circulator 316 A. The hybrid circulator 316 A then redirects these beams to a photodiode 326 A via a fiber 324 A. In this situation, the fiber 324 A may be a single mode fiber. The photodiode 326 A converts the received optical beams to electrical signals that are provided to a read out instrument 330 A via an electrical cable 328 A.

Referring to FIG. 3B , the optical mainframe 310 B is similar to that shown above with regards to mainframe 310 A. However, the optical mainframe 310 B does not contain the fiber connector 320 A. Here, the sensor is directly connected or spliced to the polarization-maintaining fiber 322 B. As to the other components, the description applied above with regards to the optical mainframe 310 A is applicable.

Referring to FIG. 3C , the optical mainframe 310 C includes a laser source 312 C connected to a polarization controller 332 C via a polarization-maintaining fiber 314 C. Polarized optical beams from the polarization controller 332 C are provided to a non-polarization maintaining circulator 336 C via a single mode fiber 334 C. The non-polarization-maintaining circulator 336 C is interconnected via conventional single-mode optical fiber on all three of its ports, and the internal pathways between Ports 1 and 2 and between Ports 2 and 3 do not block any polarizations of light beams. These optical beams are provided to a fiber connector 320 C via a single mode fiber 340 C. From there, a polarization-maintaining fiber 322 C may be connected to the sensors described in FIGS. 1A-1N and FIGS. 2A-2N .

Optical beams received back from the sensor are provided to the non-polarization maintaining circulator 336 C via the single mode fiber 340 C. The non-polarization maintaining circulator 336 C functions to send these received optical beams to a photodiode 326 C via a single mode fiber 324 C. An electrical cable 328 C takes the electrical signals generated by the photodiode 326 C based on the received optical beams and provides them to a readout instrument 330 C.

Referring to FIG. 3D , the optical mainframe 310 D is similar to that described above in FIG. 3C , but this mainframe 310 D does not include a fiber connector 320 C. Here, the sensor is directly connected or spliced to the fiber 322 D in an unperturbed fashion.

Referring to FIG. 3E , the optical mainframe 310 E includes a laser source 312 E that is connected to an optical modulator 342 E via a polarization-maintaining fiber 314 E. The optical modulator 342 E functions to modulate the intensity of the optical beam at a local oscillator frequency that is separated from the signal frequency of the electric or magnetic field to be sensed by an intermediate frequency that falls within the radio-frequency spectrum. The optical modulator 342 E provides the intensity-modulated optical beam to a hybrid circulator 316 E via a polarization-maintaining fiber 318 E. From there, the beam is provided to a fiber connector 320 E via a polarization-maintaining fiber 319 E. The fiber connector 320 E allows the sensors described in FIGS. 1A-1N and FIGS. 2A-2N to be readily connected or disconnected from the optical mainframe 310 E. The signal frequency of the electric or magnetic field to be measured mixes with the intensity-modulated local-oscillator optical beam within the electro-optic or magneto-optic material of the sensors, yielding an additional intensity modulation on the optical beam at an intermediate frequency.

Optical beams returning from the sensors are provided to the hybrid circulator 316 E via the polarization-maintaining fiber 319 E. These beams are then provided to a photodiode 326 E via a single mode fiber 324 E. The photodiode 326 E functions to convert the optical beams into electrical signals at the radio-spectrum intermediate frequency, and these electrical signals are then provided to a read out instrument 330 E via electrical cable 328 E.

Referring to FIG. 3F , the optical mainframe 310 F is similar to that described above in FIG. 3E . However, in this embodiment, the fiber connector 320 E has been removed which allows the sensors to be directly connected or spliced to the optical mainframe 310 F via polarization-maintaining fiber 322 F.

Referring to FIG. 3G , an optical mainframe 310 G is shown. Here, the optical mainframe 310 G includes a laser source 312 G providing an optical beam to an optical modulator 342 G via a polarization-maintaining fiber 314 G. The optical modulator 342 G functions to modulate the intensity of the optical beam at a local oscillator frequency that is separated from the signal frequency of the electric or magnetic field to be sensed by an intermediate frequency that falls within the radio-frequency spectrum. The optical beam emanating from the optical modulator 342 G is provided to a polarization controller 332 G via a single mode fiber 344 G. The intensity-modulated optical beam is provided to a non-polarization-maintaining circulator 336 G via a single mode fiber 318 G. From there, the optical beam is provided to a fiber connector 320 G through single mode fiber 334 G so as to allow connection to the sensors described in FIGS. 1A-1N and FIGS. 2A-2N through their interconnecting fibers 322 G. The signal frequency of the electric or magnetic field to be measured mixes with the intensity-modulated local-oscillator optical beam within the electro-optic or magneto-optic material of the sensors, yielding an additional intensity modulation on the optical beam at an intermediate frequency.

The optical beam returning from the sensor is provided to the non-polarization-maintaining circulator 336 G, which then directs this returning beam into a photodiode 326 G via non-polarization maintaining fiber 324 G. The photodiode 326 G functions to convert the optical beams into electrical signals at the radio-spectrum intermediate frequency, and these electrical signals are then provided to a read out instrument 330 G via an electrical cable 328 G.

Referring to FIG. 3H , the optical mainframe 310 H is similar to that described above in FIG. 3G . However, the optical mainframe 310 H does not include the fiber connector 320 G. As such, the sensors must be connected or spliced to the optical mainframe 310 H directly via a single mode optical fiber 322 H.

As stated above, the optical fiber-mounted field sensors as described in FIGS. 1A-1N and 2A-2N have the distinct advantage of allowing for nonintrusive, interference-free, reliable measurements with minimized noise. Referring to FIGS. 4A and 4B , a comparison of the optical fiber-mounted field sensors as described in FIGS. 1A-1N and 2A-2N to a more traditional field sensor is shown.

Referring to FIG. 4A , line 402 shows the relative signal from the optical fiber-mounted field sensor as described in FIGS. 1A-1N and 2A-2N as it relates to the diameter of the interconnecting fiber when a section of it is formed into a loop. Line 404 shows a previous art optical fiber-mounted field sensor's relative signal as it relates to the diameter of the interconnecting fiber when a section of it is formed into a loop. As one can see from this graph, the optical fiber-mounted field sensor as described in FIGS. 1A-1N and 2A-2N can maintain a much steadier relative signal.

Referring to FIG. 4B , line 406 shows the relative signal from the optical fiber-mounted field sensor as described in FIGS. 1A-1N and 2A-2N as it relates to the temperature of the sensor's interconnecting optical fiber. Line 408 shows a previous art optical fiber-mounted field sensor's relative signal as it relates to the temperature of the sensor's interconnecting optical fiber. As one can see from this graph, the optical fiber-mounted field sensor as described in FIGS. 1A-1N and 2A-2N can maintain a much steadier relative signal.

As a person skilled in the art will readily appreciate, the above description is meant as an illustration of an implementation of the principles of this invention. This description is not intended to limit the scope or application of this invention in that the invention is susceptible to modification, variation, and change, without departing from the spirit of this invention, as defined in the following claims.