Energy Conversion Using Spatially Multiplexed Optical Inputs

In electrical systems the operation or testing of many electronic system components in a desired region of operability can be adversely affected by an undesirable unbalancing of the prevailing electromagnetic field of a region when electrical power cables are introduced into the area. To assure or enhance operation of these sensitive systems, low power can be delivered optically from a laser source across a sensitive region and into a system of interest or a controlled environment and subsequently using photovoltaic cells to convert this energy into electrical energy. However, photovoltaic cells produce very low voltage, approximately 0.5 to 1.0 volts per cell. Often a system's power requirements may be 30 times that voltage, and even more. To provide the required voltage under the environmental conditions noted requires a large, bulky arrangement of the cells. Other problems are created by the necessary series connection between such cells and the fact that the current produced by the series connection of the cells is limited to that of the cell producing the least amount of current. Thus, a system is needed that will not adversely affect the natural or established electromagnetic fields where the system is located and which can provide both intelligence signal and power without the inherent current limitations of prior art series connected cells.

A system and method of energy conversion is provided wherein spatially multiplexed optical energy is coupled through a region and then converted to electrical energy. A first laser light beam is directed through an optical fiber, exiting the fiber as a ring or annulus of laser light and is collected by a photovoltaic cell. One or more additional laser light beams are directed through the optical fiber at different angles of incidence of the impinging light entering the fiber. Upon exiting the fiber each beam is in the form of a ring or annulus of light leaving the fiber at a solid angle of rotation equal to the planar angle of incidence. Due to the angular separation of each annulus of light exiting the fiber the beams are collected by different photovoltaic cells. The electrical voltage output from the cells may then be transformed into useful electrical power and/or communication signals by, for example, coupling the energy to a step-up transformer for providing the required voltage for a systems operation and/or by coupling the energy to a signal processing circuit to filter and detect intelligence signals modulated into the energy.

FIG. 1 is a simplified, diagrammatic view of the energy conversion system coupled between a laser and load circuit.

FIG. 2 discloses the method of spatial light transmission within a single, multimode optical fiber.

FIG. 3 is a schematic showing the beam guiding optics of FIG. 1 in more detail.

FIGS. 4 and 5 are schematics showing the optical beam paths controlled by the output mirrors and the optical to electrical energy conversion circuit .

Referring now to the drawings wherein like numbers refer to like parts, FIG. 1 discloses a diagrammatic view of a preferred embodiment of the energy conversion system. A light source 10 for the system is comprised of a laser 12 and beam guiding optics 14 for directing a laser beam of light down more than one optical signal paths into a single, multimode optical fiber 16. By allowing the laser light to enter the fiber either alternately or sequentially at different angles of incidence and repeating the sequence, two or more beams of light are transmitted through the single fiber without interference between the beams of light. These light rays each exit fiber 16 as a ring or annulus of light and are directed to output mirrors 18 and 20 as separate rings of light 19 and 21. The vertex of each annulus or ring of light substantially defines a cone as it moves from its vertex at the output end of fiber 16 to impinge on mirror 18 or 20. The rings of light are reflected to respective photovoltaic cells 22 and 24. Photovoltaic cells 22 and 24 convert the optical input into output electrical energy as pulses of voltage which are directed to opposite sides of a step-up transformer 26 to provide an alternating current output according to well established procedures in the art and not discussed herein. The voltage may then be coupled directly to the system load 28 or be processed as by filtering (not shown) to provide smoother alternating or direct current outputs to the load according to standard practice. For communication purposes, typically, as shown in dashed lines, a modulator circuit 30 (such as a chopper wheel) may be coupled to laser 12 to modulate the output beam with intelligence signals. These signals can subsequently be picked off and the intelligence detected by communication signal processing circuits as is well known in the art. As shown also in dashed lines, this communication signal may be taken after the photovoltaic cell conversion. Alternatively, the communication signal may be taken by beam splitting optics in either one or both beams 19 and 21 before they reach the respective photocells and subsequently processed to remove the intelligence signals.

As shown more particularly in FIG. 2, laser light rays entering fiber 16 at an angle within the fiber's acceptance angle, will exit the fiber as a conical beam centered at the same angle to the fiber's axis, producing rings of light around the axis. The acceptance angle is the angle over which a fiber accepts light, depends on the refractive indexes of core and cladding of the fiber. Fiber 16 has a longitudinal central axis 17 which is central to the fiber at any cross sectional area regardless of curvature of the fiber. Thus a light beam 32 entering fiber 16 on axis is entering at zero degrees and exits the fiber as an axial beam 32A. A light beam 34 entering fiber 16 at an angle .theta..sub.1, with axis 17 exits the fiber as an annular ring of light 34A circumscribing an angle .theta..sub.11, around axis 17. Similarly, a light beam 36 entering the fiber at an angle .theta..sub.2 exits as an annular ring of light 36A circumscribing an angle .theta..sub.21 around the axis. For the particular embodiments shown, wherein two beams 34 and 36 are employed, .theta..sub.1 and .theta..sub.11 are equal to 12 degrees, while .theta..sub.2 and .theta..sub.21 are equal to 8 degrees. These angles are not limiting, however, except that for a particular beam, the exit angle circumscribed by the annular ring output is a solid angle equal to the entrance (planar) angle of the associated input beam.

The beam guiding optics 14 that determines the angle of incidence (.theta..sub.x) of respective beams 34 and 36 is shown in FIG. 3. The output light from laser 12 enters a pockel cell 40 or other medium for switching the direction of the beam. The pockel cell is cyclically switched by alternately applying an electric field to the medium and then removing the field. Before operation the beam is adjusted so that with pockel cell 40 turned on (activated by application of the field) the beam enters fiber 16 at angle .theta..sub.1 with respect to axis 17 at the point of entry. When the pockel cell is turned off (deactivated) the beam is at the angle .theta..sub.2. Mirrors, 42, 43, 44 are used merely to fold the path of optics 14 into a smaller physical space and are otherwise not required. Mirror 41 is polarization sensitive and its use is essential to the switching process. As shown the respective beams 34 and 36 are coupled alternately from pockel cell 40 to lens 45 and focused at the end 16A of fiber 16 at their respective angle of entry .theta..sub.1 and .theta..sub.2. Pockel cell 40 alternates polarization of the output signal therefrom, polarizer 41 responds to the alternating output to switch the beam between mirrors 42 and 44.

FIGS. 4 and 5 disclose the optical arrangement of the output mirrors 18 and 20 and the photovoltaic cell to receive beams 19 and 21 respectively and direct them to the respective photocells 22 and 24. Mirrors 18 and 20 are spherical mirrors having a common center line that coincides with axis 17 as it lies with respect to end 16B of optical fiber 16. The center point 48 of the two mirrors lies in an axis of tilt or rotation for the mirrors, allowing mirror 20 to be tilted forward to direct the impinging ring of light onto photocell 24 and allowing mirror 18 to be tilted to focus and direct the beam 19 onto photocell 22.

In operations of the system, with pockel cell 40 "off", the beam follows beam path 36 impinging fiber 16 at angle .theta..sub.2, passes through the fiber, exits as a ring (beam 21) at angle 1 .theta..sub.21, reflects from mirror 20 and impinges on photovoltaic cell 24 wherein it is converted to electrical energy and, as shown in solid lines is coupled to a transformer for providing power, and as shown in dashed lines can be sampled for intelligence signals riding on the voltage.

When the pockel cell is stressed "on" the beam then follows path 34, impinging the fiber end at angle .theta..sub.1, passes through the fiber and is reflected as a ring of light 19 from mirror 18 to photocell 22 and is processed in like manner as beam 21. Transformer 26 prepares the energy for use by the load.

The drawings disclose primarily the conveyance and processing of two optical annular rings of light for generation of power. Obviously more light beams can be processed, spaced apart angularly without exceeding the angle of acceptance of the fiber input end. More than one laser can be used, operating simultaneously or alternately, thereby providing more than one power source within a single system or providing sources to separate and distinct systems. Additionally the laser light can be modulated to provide both communication signals and power system requirements for a system or used solely for communication signals.

Other uses will readily suggest themselves to those practicing this form of energy conversion. Accordingly the scope of the invention is limited only by the claims appended hereto.