Abstract:
An optical switch ( 10 ) includes a light input ( 12   a ), a plurality of light outputs ( 12   b ) and at least one light pathway movable from a first position where a light communication path is formed between a light input ( 14   a ) and a first light output ( 14   b ) and a second position where a light communication path is formed between the light input and a plurality of light outputs. Multiple light pathways are configured within the switch and selectable by rotation of a switch housing part enabling sequential selection of light communication paths. The switch can be used on a surgical device to control illumination of the surgical field during a procedure.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to optical switches, especially those used with fibre optic cables. Moreover, the optical switch finds application in various fields, including surgical retractors with lights, for example that found in the disclosure of International Patent Application No PCT/GB2009/000097. 
       BACKGROUND OF THE INVENTION 
       [0002]    Fibre optics are used in a variety of industries including aerospace, telecommunications, lasers and medical devices. A common problem involves switching lights on or off and switching light between paths or combinations of paths. A variety of solutions have been developed to fulfill these requirements including (i) beam splitters, (ii) shuttles, (iii) optical shutters and (iv) variation of the shutter concept, the twisted-nematic liquid crystal shutter. 
         [0003]    A beam splitter in its most common form is a cube made from two triangular glass prisms, which are glued together at their base using Canada balsam. The thickness of the resin layer is adjusted such that for a certain wavelength half of the light incident through one “port” i.e. face of the cube is reflected and the other half is transmitted due to frustrated total internal reflection. 
         [0004]    A shuttle will usually include an input pipe which moves to align with one of the outputs. A key feature of this switch is that all outputs are exclusive, so it cannot select more than one at a time. Whilst it is possible to create an intermediate position for the shuttle such that it shines light into two outputs, considerable light will be lost at this junction owing to differences in the geometry of the input and outputs. As it stands, there is no “off” position. If one were needed separate from the light source itself, it would either have to separate, or include a dummy switch position. 
         [0005]    Common shutter mechanisms include a blade, which may be introduced into a light path to block the transmission of light or rotated out of the light path to allow transmission. The shutter may be spring loaded and attached to a driver such as a rotary solenoid such that the blade moves to the energized position when it receives an operating voltage and returns to its resting position when the voltage is removed. Alternatively, manual operation of the shutter is possible. 
         [0006]    The shutter mechanism relies entirely upon a simple mechanical beam blocking effect. It is inefficient as this light is “lost”. Furthermore, the “lost” light may be converted to heat, which is undesirable in some applications. Excessive local accumulation of heat can lead to burns in medical device applications where the device is in contact with the patient or user. 
         [0007]    Liquid crystal displays provide for another type of shutter: the Twisted-Nematic Liquid Crystal Shutter. 
         [0008]    The twisted nematic effect (TN-effect) is the breakthrough that made liquid crystal displays practical in portable devices and allowed them to replace technologies such as light emitting diodes and electroluminescence from most electronics. 
         [0009]    TN-cells do not require a current to flow for operation and use low operating voltages suitable for use with batteries. The twisted nematic effect is based on the precisely controlled realignment of liquid crystal molecules between different ordered molecular configurations under the action of an applied electric field. This is achieved with little power consumption and at low operating voltages. 
         [0010]    In one example, a TN-cell in the OFF state, i.e., when no electrical field is applied, a twisted configuration of nematic liquid crystal molecules is formed between two glass plates, which are usually separated by several spacers and coated with transparent electrodes. 
         [0011]    The electrodes themselves are coated with alignment layers that precisely twist the liquid crystal by 90° when no external field is present. When light shines on the front of the LCD, light with the proper polarization will pass through the first polarizer and into the liquid crystal, where it is rotated by a helical structure. The light is then properly polarized to pass through the second polarizer set at 90° to the first. The light then passes through the back of the cell and the image appears transparent. 
         [0012]    In the ON state, i.e., when a field is applied between the two electrodes, the crystal realigns itself with the external field. This “breaks” the careful twist in the crystal and fails to re-orient the polarized light passing through the crystal. In this case the light is blocked by the rear polarizer and the image appears opaque. 
         [0013]    The degree of opacity can be controlled by varying the voltage; at voltages near the threshold only some of the crystals will re-align, and the display will be partially transparent, but as the voltage is increased more of the crystals will re-align until it becomes completely “switched”. A voltage of about 1 V is required to make the crystal align itself with the field, and no current passes through the crystal itself. Thus the electrical power required for that action is very low. 
         [0014]    The obvious advantage such TN-cell shutters have is that they may be operated at very high switching speeds and with low operating voltage. For example switch speed of less than 0.3 milliseconds is typical at room temperature with an applied voltage of only 10V. 
         [0015]    Furthermore, activation or switching speed can be enhanced via use of higher operating voltages. 
         [0016]    However, the technology has several limitations. Notably, for unpolarised light with 500 nm wavelength (the approximate mid-point of the visible spectrum), transmission of light does not exceed 35% in the ON position, meaning that considerable light is lost. Furthermore, when the device is in the OFF position there is still some light transmitted. Even although the amount of light transmitted is typically less than 0.5% it is not completely blocked as with a purely mechanical shutter mechanism. 
         [0017]    Moreover, a long term DC component in the voltage will stimulate impurity ion migration and eventual failure of the device. Therefore such devices have a finite useful lifetime. 
         [0018]    Further, caution must be exercised in the handling and cleaning as it is easy to accidently damage the polariser surface or its components, by accidental scratching, use of inappropriate cleaning materials or even simple over-exposure to sunlight. 
       SUMMARY OF THE INVENTION 
       [0019]    According to a first aspect of the present invention there is provided an optical switch comprising a light input, a plurality of light outputs and at least one light pathway, and said light pathway may be selectively moved from a first position, where a light communication path is formed between the light input and a first light output and a second position where a light communication path is formed between the light input and a plurality of light outputs. 
         [0020]    Preferably said light pathway is selectively movable to further positions wherein it allows communication between said light input and at least one of said further light outputs. 
         [0021]    Preferably there is a plurality of light pathways, either separately or formed with common parts such as a branched arrangement. 
         [0022]    Preferably there is a plurality of light inputs, and more preferably said light pathway is selectively movable to further positions wherein it allows communication between at least one of said further light inputs and at least one of said further light outputs. 
         [0023]    Preferably said light pathway is selectively movable to an off position wherein light communication between at least one of said light inputs and all of said light outputs is prevented. 
         [0024]    Preferably said selective movement of said light pathway is performed by a rotational coupling. It will be appreciated that the light pathway way rotate, or the light pathway may be static and either said light input and/or light output may rotate, or preferably there is provided a rotatable mask between said light input or light output and said light pathway. 
         [0025]    Preferably said light pathway is deployed within a pathway housing, said pathway housing having a rotational coupling with respect to either said light input and/or light output. 
         [0026]    Preferably said rotational coupling is movable from a first extreme position to a second extreme position, and any point there between, rotation beyond said two extreme being resisted by a stopping mechanism. Preferably said stopping mechanism comprises a protrusion and semi-circular indentation arrangement. 
         [0027]    Preferably said rotational coupling includes a plurality of detents, said detents allowing rotation of the rotational coupling to progress in a controlled and step-wise fashion. 
         [0028]    Preferably sequential rotation of the rotational coupling results in a predetermined sequential selection of light communication paths being formed between one or more light inputs and one or more light outputs. 
         [0029]    Preferably said pathway housing is circular, and more preferably an exterior surface of said pathway housing includes one or more markings indicating the position of said light pathway at different rotational steps. 
         [0030]    Preferably said pathway housing is rotatably coupled with said rotatable mask, such that rotation of the pathway housing causes rotation of the rotatable mask. 
         [0031]    The rotational coupling may be manually actuated or actuated by some form of motorised actuation means or simply a motor. Programming means may also be included, such as a microchip or microcomputer, so that the optical switch may be programmed to perform a sequence of discrete rotational steps, for uniform or non-uniform time periods. 
         [0032]    According to a second aspect of the present invention there is provided a light source including an optical switch according to the first aspect of the present invention. 
         [0033]    According to a third aspect of the present invention there is provided a surgical retractor unit including either a light source according to the second aspect of the present invention or an optical switch according to the first aspect of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0034]    Reference will now be made, by way of example only, to the accompanying drawings, in which: 
           [0035]      FIG. 1  is an isometric view of an optical switch according to a first aspect of the present invention; 
           [0036]      FIG. 2  is an isometric view of the optical switch of  FIG. 1  with its housing removed; 
           [0037]      FIG. 3  is an isometric view of the optical switch of  FIG. 1  shown mounted on a retractor back assembly of a surgical retractor, according to the third aspect of the present invention; 
           [0038]      FIG. 4  is a rear isometric exploded view of the retractor back assembly of  FIG. 3 ; 
           [0039]      FIG. 5  is an isometric view of a base plate of the optical switch of  FIG. 1 ; 
           [0040]      FIGS. 6 &amp; 7  are two isometric views from either side of a light pathway plate of the optical switch of  FIG. 1 ; and 
           [0041]      FIGS. 8 &amp; 9  are two views of a housing of the optical switch of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0042]    An optical switch  10  according to a first aspect of the present invention is depicted in  FIG. 1 .  FIG. 3  shows the optical switch as a component part of a surgical retractor  100  according to a third aspect of the present invention. 
         [0043]    As can be best seen from  FIG. 4 , the optical switch  10  comprises a base plate  12 , a light pathway plate  14  and a housing  16 . These three “major” components are attached together via an axle  18  and fixing bolts  20 . 
         [0044]    The base plate  12  is generally circular, or to be more accurate is a cylinder with its facial diameter far exceeding its height. 
         [0045]    The base plate  12  has a number of bores running through it, and these bores define a light input  12   a  and a plurality of light outputs  12   b.  Although a single light input  12   a  is described in the present embodiment, it will be understood that a plurality of light inputs is a possibility, as is a singular light output  12   b,  or combinations thereof. 
         [0046]    There is a base plate central bore  12   c  which enables assembly and rotation. A further indentation  12   d  is provided at a location on the circumference of the base plate  12 . This allows for the proper orientation of base plate  12  when it cooperates with a corresponding feature on retractor back  104 . 
         [0047]    The light pathway plate  14  is of a generally similar formation to the base plate  12 , being a generally circular plate, and likewise includes various bores running through its depth. Four of these bores define light pathway inputs  14   a,  whereas several others define light pathway outlets  14   b . Further, there is a pathway central bore  14   c  and two bolt holes  14   d  which enable assembly and rotation. 
         [0048]    One surface of the light pathway plate  14  is a preferably polished smooth, and this surface forms a rotational mating surface with the corresponding surface of the base plate  12 . 
         [0049]    On the opposite surface is a plurality of light pathways  14   e.  The light pathways  14   e  are composed of several strands of fibre optic cable, each forming light pathways between one of the light pathway inputs  14   a  and one or more of the light pathway outputs  14   b.  Some light pathways  14   e  connect from a single light pathway input  14   a,  to a single light pathway output  14   b;  whereas some connect from a single light pathway input  14   a , to multiple light pathway outputs  14   b.  Collectively, the light pathways  14   e  form a pathway bundle  14   f.    
         [0050]    Although generally circular, the light pathway plate  14  is effectively two semi-circles of material, of two different radii: a smaller radius side  14   g  and a larger radius side  14   h.  The two junctions of these two sides around the circumference of the light pathway plate  14 , meet at stop lips  14   i . Effectively, a stop indentation  14   j  is formed around a portion of the circumference of the light pathway plate  14 . 
         [0051]    The stop lips  14   i  and stop indentation cooperate with a corresponding protrusion (not shown) on whatever member or substrate the optical switch is mounted to, which limits rotation. The corresponding protrusion is mounted through the stop indentation  14   j,  whereby rotation to the extent of the circumference of the stop indentation  14   j  is allowed as the protrusion and stop indentation  14   j  pass over one another. However, at either extreme of allowable rotation, the stop lips  14   i  interfere with the protrusion such that further rotation is resisted. These limits of rotation preferably correspond to OFF positions of the optical switch i.e. where light entering the device is not presented with a light pathway to move through the optical switch  10 . 
         [0052]    The housing  16  is cup-shaped and comprises an outer surface  16   a,  an inner surface  16   b  and two housing sockets  16   c.  The outer surface  16   a  is itself composed of two discrete surfaces: a fascia  16   d  and a side-wall  16   e . To aid operation, ergonomically knurled grips  16   f  are indented on the side-wall  16   e.  The distal edge of the side-wall  16   e  from the fascia  16   d  is formed in the pattern of multiple interconnecting chevrons, so that a “zig-zag” pattern is formed i.e. the relative height of the projection of the side-wall  16   e  away from the fascia  16   d  varies in a regular pattern from a minimum to a maximum. 
         [0053]    The fascia  16   d  includes an indented rim  16   g  adjacent the outer circumference of the fascia. Within the indented rim  16   g  are four indicator knobs  16   h.  The indicator knobs  16   h  act as gauges to determine the degree of rotation of the switch  10 , and act in conjunction with some form of corresponding pointer, in this case an arrow  102  provided on retractor back  104 . This provides a simple passive scale, but may be replaced with a more active device, such as lights or the like. 
         [0054]    The assembly of optical switch  10  can be best seen in  FIG. 4 . The light pathway plate  14  is sandwiched between the base plate  12  and the housing  16 . The axle  18  runs through the light pathway plate  14  and base plate  12 , whilst the bolts  20  connect the light pathway plate  14  to the housing  16 . Thus, the base plate  12  and the combination of light pathway plate  14  and housing  16  may rotate with respect to one another. 
         [0055]    The optical switch  10  is attached to a surgical retractor having lights, similar to that described in International Patent Application No. PCT/GB2009/000097. 
         [0056]    The surgical retractor has a main body  101  and a retractor back  104 . The retractor back  104  is a substantially plastic component which acts as a main structural component for the surgical retractor. The retractor back  104  includes within it a socket  106 . The socket  106  is adapted to receive the optical switch  10 , via the base plate  12 . The side-wall  106   a  of the socket  106  has a similar interconnecting chevron-like profile to that of the side-wall  16   e  of the housing  16 . These cooperating surfaces ensure that rotation of the light pathway plate  14 /housing  16  assembly (which are locked and therefore rotate together) relative to the base plate  12 /retractor back  104  proceeds in a controllable and step-wise fashion. 
         [0057]    The axle  18  connects through an aperture  108  which passes through the retractor back  104 . The axle is retained using a spring  110  and a locking clip  112 . 
         [0058]    A protrusion (not shown) projects from the retractor back  104  to limit rotation of the light pathway plate  14  by the mechanism described above. 
         [0059]    Optical fibres  114  are provided which channel light away from, the optical switch  10 . Light is provided by an external light source (not shown) via a light guide (not shown) which attaches to the top of the retractor back  104 . Prisms  116 , 118  and lenses  120 , 122  are also provided for further control of light that passes into and through the optical switch  10 , and out of the surgical retractor via optical fibres  114 . Inlet prism  118  receives light from the external light source (not shown) and bends this through 90° before entry into a light input  12   a.    
         [0060]    In use, light from an external source (not shown) is directed into the optical switch  10 , passing through the base plate  12  via a light input  12   a.  The optical switch  10  will have a particular setting, defined by the relative rotation of the light pathway plate  14 /housing  16  assembly with respect to the base plate  12 /retractor back  104 . 
         [0061]    Light continues through the optical switch  10  passing through a light pathway input  14   a,  into one or more light pathways  14   e  defined as part of a pathway bundle  14   f  to the light pathway output  14   b  and on through to a light output or light outputs  12   b.  Finally, the light passes back through one or more of the optical fibres  114  and out of the device and onto, for example, a lighting rig (not shown) for illuminating part of a patient (not shown). In this particular example, it will be assumed that the optical switch  10  is selected in a switching position to receive a single light input and provide a single light output, for example providing light to a single external light source. 
         [0062]    The user, who may be a surgeon or other medical professional in an operating theatre, may then rotate the light pathway plate  14 /housing  16  assembly with respect to the base plate  12 /retractor back  104  to a second switching position. 
         [0063]    In this situation, a different a light pathway input  14   a  is presented to the light input  12   a,  and consequently the light passes into a different light pathway  14   e  defined as a further part of the pathway bundle  14   f,  and onto a different light pathway output or outputs  14   b,  and further on through to a different light output or light outputs  12   b.    
         [0064]    In this second example, it will be assumed that the second light pathway branches into two separate light pathways on the fibre bundle  14   e,  and onto two light pathway outputs  14   b,  and further on through two light outputs  12   b.  Thus, two beams of light exit through to the optical fibres  114  and may be channelled, for example, to two separate external light sources. Thus the user may select to illuminate two separate portions of a patient, or simply provide a more diffuse light source over a greater area. It will be understood that further selections are possible, such as branching from one light source to three or more, or indeed from several light sources to a single, or indeed the same or different amounts of light outputs. For example, during an operation which comprises three or more steps, the specific lighting requirements may be set within three or more selections preselected within the optical switch. Thus, the user may start the operation with the first selection which, for example, may provide optical illumination for a first surgical task such as entering a chest cavity, moving to the second selection which, for example, may provide optical illumination for a second surgical task such as operating on a particular human organ or major blood vessel within the chest cavity, and onto the third selection which, for example, may provide optical illumination for a third surgical task such as operating inside a human organ or major blood vessel. 
         [0065]    Furthermore, programming means may be used to allow for controlled and automatic rotation of the optical switch  10  to different switch positions in a particular programmed sequence, or indeed there may be a remote control device, voice activation, ambient light sensor, or other form of control means adapted to move to different switching positions. 
         [0066]    Although described with respect to the medical field, it will be apparent that the optical switch  10  may find application in other fields. 
         [0067]    It should be further noted that various adjustments and reconfigurations are possible to the illustrated embodiment as described above within the scope of the invention as will be apparent to those skilled in the art.