Abstract:
An opto-isolator incorporating a MEMS device includes an optical signal source and an optical signal detector defining therebeween an optical path for communication of optical signals. A MEMS device having an actuator for controlling a moveable element is disposed between the source and detector for manipulating the optical signals. In one embodiment, the moveable element is a shutter which is operable to selectively allow optical signals to be received by the detector and prevent signals from being detected. In another embodiment, the moveable member is a MEMS tilt mirror for selectively directing optical signals to the detector.

Description:
RELATED APPLICATIONS 
     This application claims priority from provisional application Serial No. 60/164,457, filed Nov. 10, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention is related to optical isolators utilizing micro-electromechanical systems (MEMS). 
     2. Description of the Related Art 
     Electromechanical devices combine electrical and mechanical attributes as in motors and magnetic relays. There are also opto-electronic devices which combine light generation and/or light detection with electronics, such as in optical transmitters and receivers. Optical isolators (“opto-isolators”) are typically used in applications where a non-electrical connection in an electrical system is needed, such as to provide electrical isolation between components of a system. Such uses are widespread in biology, chemistry, physics, medicine and engineering. In medicine, for example, medical equipment may be interfaced with a patient through sensors or probes that are further connected to monitoring apparatus. For safety, the sensors/probes must be electrically isolated from the monitoring apparatus to protect against voltage surges and spikes that could injure or harm a patient. This isolation is accomplished by utilizing opto-isolators that convert an electrical signal to an optical signal for receipt by an optical detector. After receipt, the optical signal is typically re-converted to an electrical signal (i.e. a photo-current is generated) for analysis or processing. 
     MEMS is a technology that exploits lithographic mass fabrication techniques of the kind that are used by the semiconductor industry in the manufacture of silicon integrated circuits. Generally, the technology involves preparing a multilayer structure by sequentially depositing and shaping layers of a multilayer wafer that typically includes a plurality of polysilicon layers that are separated by layers of silicon oxide and silico nitride. The shaping of individual layers is commonly performed by etching, which is itself generally controlled by masks that are patterned by photolithographic techniques. The technology may also involve the etching of intermediate sacrificial layers of the wafer to release overlying layers for use as thin elements that can be easily-deformed or moved. 
     MEMS technology has proven highly versatile and has been used to form a wide variety of miniature devices varying in size from millimeters to microns. MEMS technology is discussed, for example, in a paper entitled “MEMS the Word for Optical Beam Manipulation”, published in  Circuits and Devices , Jul. 1997, pp. 11-18. 
     MEMS technology allows for the production of opto-isolators which are smaller and operate with lower power consumption than pre-existing designs. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an optical isolator for selectively conveying an optical signal along an optical path from a signal source to a detector spaced from the source. This functionality is accomplished by generating an optical signal from the signal source and directing it to a MEMS device positioned in the optical path between the source and detector. The MEMS device includes a moveable element which, when activated, will selectively direct the optical signal between the source and detector. 
     In one embodiment, the moveable element is a shutter which can be moved to a position directly in the optical path for preventing or limiting the detection of the optical signal by the detector, and out of the optical path for allowing detection of the optical signal. 
     In another embodiment, the moveable element is a MEMS tilt mirror operable for providing a variable optical signal attenuator. By selectively controlling an amount of tilt applied to the tilt mirror, the amount of light directed to the detector can be varied. 
     In yet another embodiment, aperture elements are used to configure the shape of the optical signal. A source aperture is disposed between a moveable MEMS element and an optical source for shaping the optical signal prior to receipt by the MEMS element. A detector aperture may also be included between the moveable MEMS element and the optical detector. 
     Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings, wherein like reference characters denote similar elements throughout the several views: 
     FIG. 1A is a top-plan schematic view of an opto-isolator in accordance with one embodiment of the present invention; 
     FIG. 1B is a side view of the opto-isolator of FIG. 1A; 
     FIG. 2 is a top-plan schematic view of a modified form of the device of FIGS. 1A and 1B; 
     FIG. 3 is a schematic representation of still another embodiment of the present invention; and 
     FIG. 4 is a diagrammatic illustration of the use of aperture elements in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1A depicts a MEMS opto-isolator  10  in accordance with a currently preferred embodiment of the invention. Isolator  10  includes an optical source  12  such as an LED or other optical signal generator for generating an optical signal, as is known in the art. An optical detector  14  is spaced at a distance from the source  12  and within the optical path of the generated optical signal for receiving or detecting the generated optical signal in accordance with the invention. The function and operation of detector  14  is well-known to those having ordinary skill in the art, and further description thereof is not deemed necessary. 
     A MEMS device  16  is included in isolator  10  for providing selective communication of the optical signal to detector  14 . Specifically, MEMS device  16  includes a moveable element  18  connected to and controlled by a moveable member such as an arm or beam  20  which, in turn, is controlled by an actuator  22  having control electrodes  24  and  26 . Moveable element  18  is a shutter-type blocking or masking element that is moveable between a first position and a second position along a path or direction shown by arrows  19  in FIG.  1 B. When in a first position, shutter  18  is disposed in the optical path to act upon the optical signal as it travels along the optical path. For example, and in accordance with one embodiment of the present invention in which shutter  18  is a blocking element, when shutter  18  is disposed in the first position light will be absorbed by the shutter and thereby be prevented from reaching detector  14 . In another embodiment, shutter  18  may be coated with a reflective material, such as aluminum, for reflecting the optical signal back toward or in the general direction of optical source  12  for receipt, for example, by a detector positioned in substantial alignment with the reflected optical signal. Shutter  18  may also be a masking element, as explained more fully below, wherein an aperture is formed therein for shaping the optical signal prior to receipt by the detector  14  when the shutter is in the first position. 
     When the MEMS device  16  is activated, shutter  18  is moved to its second position outside of the optical path to thus allow the optical signal to be conveyed uninhibited to the detector  14  for generating a photocurrent, as is known in the art. Alternatively, the shutter can be positioned outside of the optical path and moved into the optical path upon application of a voltage. When the shutter is outside of the optical path, the device may be a conventional optoisolator. The operation of MEMS shutter device  16  is more fully disclosed in commonly-owned and copending U.S. patent application Ser. No. 09/197,317, filed Nov. 20, 1998, the entire content of which is incorporated herein by reference. 
     The three components, i.e. MEMS device  16 , optical source  12  and optical detector  14 , can be assembled in a single package (as suggested the dashed line in FIG.  1 A), to create a 6-terminal MEMS opto-isolator. This packaging can be implemented, by way of example, in a standard miniDip carrier or a small outline (SOT) style package. The main electrical attribute of the MEMS opto-isolator is that there are now three pairs of electrically isolated terminals: those for the MEMS shutter, the light source, and the detector. The elements forming the device  10  can be readily expanded to include a number of MEMS shutters, sources and detectors, as a general matter of design choice, to produce MEMS opto-isolators of arbitrary complexity. 
     A significant property of the MEMS opto-isolator is the very high impedance and low capacitance of the MEMS shutter terminals. Typically, the dc resistance is in the hundred giga-ohms range and the capacitance is less than a picofarad. In contrast, the LED terminals of a conventional opto-isolator operate at milliamps current levels. 
     With the inventive MEMS opto-isolator, new approaches to circuit design, as for example ultra-low power electronics on the MEMS terminals, are now feasible. The MEMS shutter can be operated in a saturated mode with the shutter voltage being either zero or V max , and the opto-isolator can be then used as a simple digital switch. The shutter may also be operated in an analog mode with input and output signals being continuous functions. When such continuous function input-outputs are used, a linear transfer function between the input applied voltage and the output signal can be realized; this will allow many board-level applications, as well as uses as a high-impedance electrostatic probe for test instrumentation. 
     More complex analog functions are also within the intended scope and contemplation of the invention, utilizing properties of the MEMS shutter voltage response, the source intensity distribution, the shutter shape, source and detector aperturing, and the detector shape. A non-linear voltage response of the MEMS shutter motion may be used in special function blocks, such for example as logarithmic-amplifiers and square-root generators. 
     With reference now to FIG. 4, various geometries for the source detector  14  and optical source  12  can be selectively employed to predeterminately adjust or manipulate the shape of the optical signal in the MEMS opto-isolator transfer function. For example, a source aperture element  30  can be included between the optical source  12  and the shutter element  18  to manipulate the shape of the optical signal prior to receipt by the shutter  18 . In addition, or instead, a detector aperture element  34  may be included between the shutter element  18  and detector  14  for further or similar shaping of the optical signal. Also, and as explained above, the shutter element  18  can itself include or be formed with a selected sized aperture  32  for providing further optical signal manipulation. 
     Multi-mode or single-mode optical elements, such as optical waveguides or optical fibers, may be used to tailor the light transmission properties or spatially separate the source, detector or both from the main MEMS opto-isolator package. The MEMS opto-isolator can also function as a signal rectifier since the shutter displacement depends upon the magnitude of the voltage applied thereto and not the polarity. 
     A modification of the oscillator  10  of FIGS. 1A and 1B is shown in FIG.  2 . In the FIG. 2 embodiment, actuator  22  is replaced with actuator  22 ′ which has three separate actuator electrodes  24 ,  25  and  26  that can accommodate two separate voltage sources (V 1  and V 2 ). Voltage V 1  is shown applied between actuation electrodes  24  and  25 , and voltage V 2  between electrodes  24  and  26 . The use of actuator  22 ′ allows for shutter placement versatility in that the shutter placement is dictated by the difference in the potential applied between the actuation electrodes. By employing multiple actuation electrodes in this manner, a range of voltages can be applied to the actuator  22 ′ for selectively yielding a variety of predetermined shutter positions. 
     Turning now to FIG. 3, a further modification of the oscillator  10  is shown as oscillator  100  wherein the MEMS shutter element  18  is replaced by a MEMS tilt mirror  118  positioned in the optical path between the optical source  112  and optical detector  114 . The operation and construction of tilt mirror  118  is described in commonly-owned and copending U.S. patent application Ser. No. 09/415,178, filed Oct. 8, 1999, the entire content of which is incorporated by reference herein. As explained in the aforementioned patent application, tilt mirror  118  is variably tiltable about one or more axes based on a level of voltage applied to the actuating electrodes. By utilizing tilt mirror  118  in the inventive opto-isolator  100 , an optical signal can be received and selectively reflected by the mirror  118  in various directions, and to varying degrees, based on the voltage level applied to the electrodes. Thus, the optical signal can be reflected back to the optical source or reflected entirely to the optical detector, or a desired portion of the optical signal can be reflected to the optical detector. Moreover, when the tilt mirror  118  is used in conjunction with a shutter aperture element  32  and/or a detector aperture element  34 , optical signal shaping and thereby still further control of the signal passed to the detector can be realized. 
     Thus, while there have shown and described and pointed out fundamental novel features of the invention as applied to preferred embodiments thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.