Abstract:
A positioning system for an optical microstructure ( 64 ) in a devise ( 6 ) operating under the action of a control means includes a flexible element ( 63 ) supporting the optical microstructure and connected to the device. The orientation of the flexible element with respect to the device can be varied under the action of control means in order to put the optical microstructure ( 64 ) into at least one determined position. The flexible element is immobilized with respect to the device in order to hold the optical microstructure ( 64 ) in the determined position when the control means no longer act.

Description:
TECHNICAL DOMAIN 
     The invention relates to the domain of optical microstructures and microtechnologies. In particularly it relates to the domain of integrated optical switches. It also relates to the domain of optomechanical micro-devices, for example microdeflectors. 
     STATE OF PRIOR ART 
     Document FR-A-2 660 444 divulges an optical microstructure composed of an optical switch. It includes a description of the optical switch represented in FIG. 1 attached. This device receives an incident light beam I transported by fiber  2  and transmits a switched beam C either towards fiber  4  or towards fiber  6 . Switch  1  comprises a guide structure formed on a substrate  12  with an entry surface E and an exit surface S. It comprises an entry microguide  18  and two exit microguides  20  and  22 . In this example, microguides  18  and  20  are parallel to a direction x parallel to the largest surface  8   a  of the guide structure. Microguides  18  and  20  are laid out such that one continues on from the other and on each side of a recess  24  passing though the guide structure and extending into the substrate. 
     The exit microguide  22  located on the same side as the recess  24  and the microguide  20  and adjacent to this microguide, comprises a part  21  parallel to microguide  20  in this example on the exit side S of the switch, and a part  23  forming an elbow A with part  21 , on the side of the hollow part  24 . Thus the entry ends  20   a  and  22   a  of the exit microguides  20  and  22  respectively opening into hollow part  24 , are closer to each other than their exit ends, flush with the exit surface S of the guide structure. 
     Hollow part  24  defines a flexible beam  26  oriented at rest parallel to the x direction. This beam  26  can deform in hollow part  24  along a y direction, parallel to the surface  8   a  of the guide structure and perpendicular to the x direction. This beam  26  has a fixed end  28  fixed to the guide structure and substrate  12 , and a free end  30  capable of deforming in hollow part  24 . The beam  26  is defined in the guide structure and is provided with a central microguide  32  extending over its entire length and, at rest, oriented parallel to the x direction. This central microguide  32  is placed along the continuation of the entry microguide  18  such that their longitudinal axes parallel to the x direction are coincident. 
     The incident beam transported by the entry microguide  18  is switched towards the exit microguide  20  by bringing the free end  32   a  of the central microguide of the beam facing and coincident with the entry end  20   a  of the exit microguide  20 . Similarly, the incident beam transported by the entry microguide  18  is switched to the exit microguide  22  by bringing the free end  32   a  on the central microguide facing and coincident with the entry end  22   a  of the exit microguide  22 . This second configuration is shown in FIG.  1 . 
     For example, deformations of the beam to make end  32   a  of the central microguide coincide either with end  20   a  of the exit microguide  20 , or with end  22   a  of microguide  22 , are made using variable capacitors. This is done by applying metallizations  36  and  46  to each of the lateral surfaces of hollow part  24  on the guide structure  8  oriented along the x direction. Furthermore, metallizations  38  and  44  are applied to each of the lateral surfaces of the facing beam  26  oriented along the x direction when it is at rest. The facing metallizations  36  and  38  form the armatures of a first variable capacitor to which a voltage can be applied using an electrical power supply source  40  electrically connected to these armatures through conductors  42  placed on the surface  8   a  of the guide structure. Similarly, facing metallizations  44  and  46  form the armatures of a second variable capacitor to which a voltage can be applied using an electricity power supply source  48  connected using conducting wires  50  placed on the surface  8   a  of the guide structure. 
     Application of an appropriate voltage to the terminals of these capacitors creates an electrostatic force parallel to the y direction and causing deformation of the beam  26  along this y direction. 
     This type of optical switch may be made from a semi-conducting substrate using microelectronics methods. These methods can collectively obtain integrated optical switches. 
     At the present time, the problem of precise positioning of the optical switching microguide has been solved, either by controlling the control force on the moving beam or by bringing two etching planes into contact (in other words as a limit stop). The first solution makes it necessary to be able to apply a constant force and/or servocontrol the applied force as a function of a parameter representing the position. The second solution is sensitive to lateral under-etching and over-etching of the mechanical structure. 
     The optical switching microguide is only held in position by maintaining the force applied to the beam, which requires energy consumption to maintain this force. If an electrostatic force is applied, as in the case of the device shown in FIG. 1, once the capacitor has been charged it is still necessary to prevent it from becoming discharged in the long term. 
     DESCRIPTION OF THE INVENTION 
     The invention is designed to solve these problems by proposing a system for positioning an optical microstructure in a device under the action of control means, comprising an element supporting the optical microstructure and connected to the device, the orientation of the said element with respect to the device varying under the action of control means in order to put the optical microstructure in at least one determined position, mechanical means of fixing the said element in position with respect to the device being provided to hold the optical microstructure in the said determined position. 
     Advantageously, the mechanical immobilization means are designed to release the said element under the action of the control means. 
     Preferably, the mechanical immobilization means comprise a male part and a female part with a shape complementary to the male part, one of the said parts belonging to the said element and the other part belonging to the device, the microstructure being held in the said determined position by the male part penetrating into the female part. According to one preferred embodiment, the male part and the female part have axes of symmetry parallel to the optical axis of the optical microstructure. Thus, when the microstructure is immobilized, the axes of symmetry of the male and female parts are superposed and an over-etching or under-etching defect in the male or the female part has no incidence on the precise positioning of the microstructure. Operation is better if the male part has a pointed cross section, the female part being a housing with a complementary shape. The said element may comprise at least one beam, called the main beam, connected by one of its ends to the device and its other end being free. It may then comprise at least one secondary beam placed transversally with respect to the main beam and rigidly attached to the main beam, the secondary beam supporting one of the said parts of the mechanical immobilization means. Preferably, this secondary beam is located at the free end of the main beam. The secondary beam may be fixed by one of its ends to the main beam, its other end being free and comprising one of the said parts of the mechanical immobilization means, for example the male part. The secondary beam may be such that it does not deform during displacement of the microstructure under the action of the control means. 
     The control means may be capacitive devices developing an electrostatic force in response to an electrical control voltage. They may also be magnetic and/or piezoelectric means. They position the element in the determined position. 
     In some cases control means may also be used to cooperate with the mechanical means to hold the element in position. 
     The invention may be applied to the manufacture of an integrated optical switch, the optical microstructure being an optical microguide. It may also be applied to the manufacture of a device with a lens that can be oriented into at least one determined position, the optical microstructure being the said lens. It may also be applied to the manufacture of a device with an optical fiber orientable into at least one determined position, the optical microstructure being the said optical fiber. Finally, it may be applied to the manufacture of a device with a mirror orientable into at least one determined position, the optical microstructure being the said mirror. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     The invention will be better understood and other advantages and specific features will become apparent by reading the following description, given as a non-restrictive example, accompanied by the drawings in the appendix in which: 
     FIG. 1 is a perspective view of an integrated optical switch according to known art, 
     FIGS. 2 and 3 are top views of an integrated optical switch made according to this invention, and in different switching states, 
     FIG. 4 is an explanatory view showing operation of the positioning system according to this invention, 
     FIG. 5 is a top view of another variant of the integrated optical switch according to this invention, 
     FIG. 6 is a top view of yet another variant of the integrated optical switch made according to this invention, 
     FIG. 7 is a top view of a device with an orientable lens made according to this invention. 
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     FIGS. 2 and 3 show a top view of an optical switch according to the invention, in two different switching states. This switch is of the same type as that shown in FIG. 1, in other words it comprises an orientable beam and it is made using micro-electronics techniques. For example, its manufacturing process could be of the type that is described in document FR-A-2 660 444. FIGS. 2 and 3 show schematic representations of the invention, to facilitate understanding it. In particular, the dimensions and proportions of the various beams are not to scale. 
     The optical switch  60 , shown in FIGS. 2 and 3, comprises a recess  61  called the main recess, formed in the upper part  62  of the substrate on which the switch was formed. A beam  63 , called the main beam is attached by one of its ends to part  62 , and bends to move into the main recess  61 . The main beam  63  comprises an optical microguide  64  over its entire length. This optical microguide  64  is continuous with the optical microguide  65  in part  62 . The optical microguide  65  transports the optical signal to be switched to five possible outputs: optical microguides  71  to  75  formed in part  62  and in the plane of the microguides  64  and  65 . The microguide  71  is aligned with microguide  64 ; microguides  72  to  75  are offset from this alignment. 
     The free end of the main beam  63  extends transversely through a secondary beam  66 . Similarly, the main recess  61  extends along the center line of the secondary beam  66  into a secondary recess  67  into which the secondary beam  66  can fit. 
     The free end of the secondary beam  66  comprises a part  68  with a pointed cross section called the male part. The edge  69  of the secondary hollow part  67  facing the male part  68  is provided with recesses  70  called the female parts. The shape of the recesses  70  is complementary to the shape of the male part  68 . There is one recess  70  for each offset exit microguide. 
     The free end of the beam  63  moves under the action of a lateral force exerted on the main beam  63  in the direction of the secondary recess  67 , pulling the secondary beam  66  into the secondary recess  67 . The main beam  63  deflects more or less, as a function of the amplitude of the force applied on it. The lateral force is chosen such that the male part  68  engages in one of the female parts or recesses  70 . The separation between the recesses  70  corresponds with the separation between the optical exit guides  71  to  75  such that the exit from the optical microguide  64  on the main beam  63  is facing the entry to one of the microguides  72  to  75 . 
     Once the male and female parts are engaged, the main beam  63  remains in the deformed position. The applied lateral force may be eliminated. Another lateral force applied to the main beam enables switching to another optical exit microguide. 
     The lateral force may be an electrostatic force obtained by application of a voltage between electrodes as described in document FR-A-2 660 444. 
     FIG. 2 shows the switch according to the invention when the main beam is not deformed. In this case, the microguide  64  is aligned with microguide  71 . FIG. 3 shows the same switch when the main beam is deformed such that the microguide exit  64  is facing the entry to microguide  72 . In this case, the male part  68  is engaged in the first recess  70  of the edge  69  of the secondary recess  67 . 
     The main beam  63  may be moved by applying a force on this beam exceeding the sum of the elastic return force for the main beam and the sliding friction force of the male part  68  on the edge  69 . Possibly, a force may be applied in the x direction on the secondary beam  66  in order to reduce the coefficient of sliding friction between the male part  68  on the edge  69 . This force actually pulls the male part out of its recess, regardless of its shape. 
     The distribution of forces involved is shown in more detail in FIG.  4 . When the male part  68  is facing a recess  70 , all the applied forces can be canceled. The elasticity of beams  63  and  66  creates a return force F that can be broken down into a force F 1  in the y direction and force F 2  in the -x direction. The design of the two beams must be such that the sum of these two forces has a component F′ that exceeds the sliding friction force between the male part  68  and the local surface dS in the -y′ direction. This means that the top of the male part can remain in the recess  70  and move towards point P. It is held in place by the equilibrium of forces when the tip is at the bottom of its recess. The optical microguide  64  forming the microstructure is then in the required position, entirely determined by the etching mask that was used to make the switch. 
     In some cases, the support for the male part in its recess may be reinforced by the application of an additional force generated by the control means and applied to the secondary beam  66  in the -x direction. 
     The position of the main beam may be modified by adding an external force to forces F 1  and/or F 2  to modify the force ratio. 
     The tip of the cross section of the male part may be pointed, rounded or any other shape. A symmetric pointed cross section is the most advantageous. 
     The action of lateral under-etching or over-etching does not fundamentally change the state of equilibrium when the male part is in one of its recesses. In particular, the position of the male part along the y axis when in its recess remains the same. 
     So long as the mechanical surfaces remain in contact (male part in the recess), there is no variation in the coupling. The system should be less sensitive to vibrations. The optical microstructure remains in its position as long as the inertia forces generated by vibrations or any other cause do not modify the ratio of the forces. 
     For example, the dimensions of the various parts of the system according to the invention may be as follows: 
     for a beam  63  made of silica: width 50 μm and length 2 mm, 
     for beam  66 : width 75 μm and length 300 μm, 
     height of the male part: 15 μm, 
     angle of the symmetric pointed cross section for the male part: 45°. 
     angle of the cross-section of the symmetric recess: 9°. 
     spacing between recesses: 15 μm. 
     FIG. 5 shows another variant embodiment of an integrated optical switch according to the invention. The positioning system for this optical switch has the special feature that it is symmetric. The switch  80  has a main recess  81  that defines a main beam  82  comprising an optical microguide  83  continuous with the entry optical microguide  84 . This switch has three possible outputs, namely optical microguides  85 ,  86  and  87 . The exit microguide  86  is normally aligned with microguides  83  and  84  when no forces are applied to main beam  82 . Exit microguides  85  and  87  are located on each side of microguide  86 . Recess  81  is extended towards the free end of the main beam  82 , by two secondary recesses  88  and  89  with axes perpendicular to the axis of the main recess  81  located on each side of this main recess. Similarly, two secondary beams  91  and  92  extend perpendicular to the main beam  82 . Each secondary recess  88  and  89  has edges  93 ,  94  provided with recesses into which fit the male parts terminating secondary beams  91  and  92 . 
     When the secondary beams are made in the same part as the rest of the structure, the recesses into which the male parts fit when beam  82  is in its rest position must be widened so that male parts can be detached during their manufacture. 
     Capacitors may be made by metalizing the edges of beam  82  and the opposite edges of the recess  81 . It is thus possible to develop electrostatic forces on beam  82  by the application of an electric voltage, as described in document FR-A-2 660 444. 
     The variant embodiment of the optical switch shown in FIG. 6 is practically identical to that shown in FIGS. 2 and 3. Switch  100  comprises a main beam  101  defined by recess  102 , and a secondary beam  103 , the free end of which can move in the secondary recess  104 . If there is no force applied on the main beam  101 , the beam will be in the position shown as a chain dotted line. The solid line shows the main beam in a switched position. Note that the center line of the secondary beam  103  is not perpendicular to the center line of the main beam  101 . The secondary beam  103  was also designed so that it will not deform during movement of the main beam. This implies that the connection point between the two beams does not deform. This feature is useful to prevent deformation of the optical microstructure moved by the main beam. 
     The device shown in FIG. 7 was obtained by etching a substrate in the shape of a parallelepiped. The etching defined a part  110  acting as a support to which a central body  111 , two main beams  113  and  114 , a left extension  115  and a right extension  116  are connected. The etching also defined a cylindrical lens  112  connected by two symmetric arms  117  and  118  to the free ends of the main beams  113  and  114  respectively. The main beam  113  is extended by a secondary beam  119  along the center line of the arm  117 . The free end of the secondary beam  119  comprises a male part  120  in the shape of a point centered on an axis parallel to the main beam  113 . The male part  120  is engaged in one of the housings or female parts  121  with a shape corresponding to the male part  120  and etched in the terminal part of the left extension  115 . The housing corresponding to the rest position is wider than the other housings so that the male part can be made. 
     The device also comprises an electrostatic control comb  130 . The comb  130  comprises an arm  131  made during the etching and connected to the free end of the main beam  114 . The arm  131  is extended perpendicularly by electrode holders  132 . The right extension  116  is also terminated by electrode holders  133  alternating with electrode holders  132 . Electrodes  134 ,  135  are deposited on electrode holders  132 ,  133  respectively. These electrodes are connected to a control voltage. 
     The upper surface of the central body  111  is provided with a groove into which an optical fiber  138  fits. This central body was etched so that the exit end of the optical fiber is centered on lens  112  in the rest position. 
     As in the previous examples, it can be understood that under the effect of an electrostatic force applied through the control comb  130 , the optical microstructure composed of lens  112  can move relative to the exit from the optical fiber  138 .