Abstract:
A sensing system for detecting movement of an object is disclosed, including a laser source having a cavity emitting laser beams, a reflecting film, one side acting as a reflecting surface for the laser beams and the other side allowing the object to move thereover, with a plurality of pores having a distribution of a particular regulatory in area and/or density, an optical path focusing the laser beams onto the reflecting film, a measuring/converting module detecting variation in laser operation in the cavity induced by the laser beams reflected from the reflecting film and generating a corresponding electrical signal, and an analyzing circuit receiving and analyzing the electrical signal to determine the movement of the object.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to sensing systems, and in particular to a sensing system utilizing laser self-mixing effect. 
         [0003]    2. Description of the Related Art 
         [0004]    Input devices in conventional electronic devices acquire user information via mechanical means, such as mechanical mouse, mechanical keyboard and mechanical stick. Users activate a mechanical component (for example, a button of or ball of a mouse) such that the mechanical component activates a contact sensor, which generates a signal. Mechanical components tend to be covered and accumulate dust but are difficult to clean. Also, the press signal is one-by-one enabled. 
         [0005]    Conventional optical guiding technologies, unlike mechanical technologies, emit light to an object such as a desktop, a finger, and a virtual trace ball as disclosed in TW patent M256537, and determine movement of the object by sensing the displacement of reflected light from the object via a sensor. As disclosed in European Patent No. EP-0942282, laser beams are emitted to an object and diffracted partially by a raster. Diffracted laser beams are reflected into a sensor. The sensor then determines the movement of the object by interleaving the reflected laser beams. However, components of optical guiding devices require calibration and matching, increasing production complexity and costs. 
         [0006]    In view of these problems, U.S. Pat. No. 6,707,027 discloses a sensing system applied in input devices of electronic systems and applying laser self-mixing effect.  FIG. 1  is a cross-section of a sensing system  100  disclosed in the patent comprising a base plate  1  to carry a diode laser  3  and a sensor (such as a photo diode)  4 . The diode laser  3  emits laser beams  13 . An object  15  such as a finger to be detected moves on a transparent window  12 . A lens  10  is arranged between the diode laser  3  and the transparent window  12 , focusing the laser beams  13  on or near the transparent window  12 . The laser beams  13  are reflected by the object  15 , and some of the reflected laser beams are converged by the lens  10  to re-enter the cavity of the diode laser  3 . The radiation returning in the cavity interferes with radiation therein, referred to as self-mixing effect, further inducing variation in intensity of the laser radiation emitted by the diode laser  3 . The photo diode  4  receives and converts part of the laser radiation in the cavity to an electrical signal. A circuit  18  analyzes the movement of the object  15  according to the electrical signal. 
         [0007]      FIG. 2  shows waveforms of a driving current of the diode laser  3  and intensity of the laser radiation in the cavity, illustrating principle of the circuit analyzing the moving direction and speed of the object  15  according to the electrical signal. As shown, the laser diode  3  is driven by a triangular AC driving circuit. Due to Doppler and Laser self-mixing effects, when the object  15  moves towards and away from the object  3 , ripple component of the intensity of the laser radiation in the cavity exhibits waveforms  21  and  22  respectively. The circuit  18  determines the moving direction of the object by subtracting wave number in interval ½p(a) from that in interval ½p(2). Additionally, the difference between the wave numbers in intervals ½p(a) and ½p(b) increases with the speed of the object  15 . The circuit  18  thus determines the speed of the object  15  according to the difference between the wave numbers in intervals ½p(a) and ½p(b). 
         [0008]    Sensing system  100  in  FIG. 1  includes a diode laser  3  and a sensor  4  for one-dimensional movement detection of the object  15 . To achieve two or three dimensional movement detection of an object, two or three diode lasers and sensors are disposed in the sensing system. Additionally, if a DC current is used to drive the diode laser, the moving direction of the object cannot be determined. 
       BRIEF SUMMARY OF THE INVENTION 
       [0009]    The invention provides a sensing system comprising a reflecting film with a plurality of pores having predetermined distribution. The sensing system, with a single diode laser, is capable of determining one to two dimensional movement of an object. The invention further provides a sensing system with a flexible film, capable of determining two or three dimensional movement of an object. Additionally, the diode laser in the electronic system can be driven by not only AC driving current such as triangular wave but also DC driving current, thereby reducing complexity of driving current circuit and analyzing circuit. 
         [0010]    The invention provides a sensing system detecting movement of an object, comprising a laser source, a reflecting film, an optical path, a measuring/converting module, and an analyzing circuit. The laser source has a cavity emitting laser beams. The reflecting film, one side acting as a reflecting surface for the laser beams and the other side allowing the object to move thereover, comprises a plurality of pores with a predetermined distribution. The optical path focuses the laser beams onto the reflecting film. The measuring/converting module detects the variation in laser operation in the cavity and generates a corresponding electrical signal. The analyzing circuit receives and analyzes the electrical signal to determine the movement of the object. 
         [0011]    In an embodiment of the sensing system, the porosity of the reflecting film, defined as the total pore area per unit area of reflecting film, decreases in a predetermined direction. In another embodiment of the sensing system, the porosity of the reflecting film decreases along first and second directions at different rates. 
         [0012]    An embodiment of the analyzing steps performed by the analyzing circuit comprises detecting the amplitude variation of the ripple component of the electrical signal to determine the moving direction of the object. In another embodiment, the analyzing circuit analyzes the frequency of the ripple component of the electrical signal to determine the speed of the object. In another embodiment, the reflecting film is flexible, and the analyzing circuit detects whether the amplitude variation in the ripple component of the electrical signal is less than a predetermined amplitude to determine whether the object presses the reflecting film. 
         [0013]    The invention also provides an electronic system comprising an input device including the sensing system. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
           [0015]      FIG. 1  is a cross-section of a sensing system disclosed in U.S. Pat. No. 6,707,027; 
           [0016]      FIG. 2  shows waveforms of a driving current of a diode laser and intensity of laser radiation in a cavity of  FIG. 1 ; 
           [0017]      FIG. 3  is a block diagram of a sensing system in accordance with an embodiment of the invention; 
           [0018]      FIGS. 4A ,  4 C and  4 B,  4 D respectively show intensity of the laser radiation emitted from a cavity when an object stays stationary and moves with a constant velocity over first and second region of a reflecting film of  FIG. 1 , where a laser source is driven by DC and triangular driving currents respectively in  FIGS. 4A-4B  and  4 C- 4 D; 
           [0019]      FIGS. 5A-5C  are plan views of pore distributions of a reflecting film in accordance with embodiments of the invention; 
           [0020]      FIGS. 6A and 6B  show intensities of laser radiation emitted from a cavity when an object moves at different constant velocities over the same region of a reflecting film respectively when a laser source a is driven by DC and AC driving currents; 
           [0021]      FIGS. 7A and 7B  respectively show cross sections of a reflecting film when deforming and recovering in accordance with an embodiment of the invention; 
           [0022]      FIGS. 8A and 8B  show intensity of laser radiation emitted from a cavity in the embodiment of  FIGS. 7A and 7B  respectively when a laser source is driven by DC and AC driving currents; and 
           [0023]      FIGS. 9A and 9B  show application of the invention using a portable computer having a sensing system of the invention as an example; 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]      FIG. 3  is a block diagram of a sensing system  300  in accordance with an embodiment of the invention. The sensing system  300  comprises a laser source  30 , a reflecting film  31 , a optical path  32 , a measuring/converting module  33 , and an analyzing circuit  34 . As shown, the laser source  30 , a diode laser, comprises a cavity  30   1 , a front facet  30   2  and a rear facet  30   3 . The laser source  30  emits laser beam  35  through the front laser facet  30   2 . The optical path  32 , such as a convex lens, disposed between the laser source  30  and the reflecting film  31 , collimates and focuses the laser beam  35  on or near the reflecting film  31 . The laser beam  35  becomes substantially parallel after passing through the optical path  32 . 
         [0025]    The reflecting film  31  has a plurality of circular, square, elliptical or linear pores with a predetermined distribution of area and/or density. One side of the reflecting film  31  acts as a reflecting surface for the laser beam  35  to reflect part of the laser beam  35 , and the other side allows an object  36  (for example, a finger) to move thereover. It is noted that the object  36  is not required to closely contact the reflecting film  31  and is only required to move near thereto. Reflected part of the laser beam  35  is denoted by reference number  35  in the figure. Since the areas and/or densities of the pores on the reflecting film  31  are distributed regularly, when the object  36  moves over the reflecting film  31 , reflected beam  37  corresponding to the pore distribution is generated. 
         [0026]    Preferably, reflection coefficient of the reflecting film  31  is much less than that of the object  36 , such as a rough black surface with no tendency to reflect light. In this case, the laser beam  35  is reflected when reaching the object  36  and absorbed when reaching the surface of the reflecting film  31 . As such, when the object  36  moves in a region of higher porosity, the intensity of the reflected beam  37  is higher. In another preferable embodiment, reflection coefficient of the reflecting film  31  exceeds substantially that of the object  36 , such as a smooth surface with a high tendency to reflect light. In this case, the laser beam  35  is absorbed when reaching the object  36  and reflected when reaching the surface of the reflecting film  31 . As such, when the object  36  moves in a region of higher porosity, the intensity of the reflected beam  37  is lower. In these two embodiments, when the object moves over the surface of the reflecting film  31 , the intensity of the reflected beam  37  varies according to the distribution of the pores. While the following paragraphs references reflection coefficient of the reflecting film  31  being much less than that of the object  36 , those skilled in the art should be readily able to deduce the case where reflection coefficient of the reflecting film  31  exceeds substantially than that of the object  36 . 
         [0027]    The reflection beam  37  is further collimated and focused on the light source  30  by the optical path and reenters the cavity  30   1 , interfering with optical rays within the cavity  30 , and modulating the amplitude and frequency of rays emitted from the cavity  30   1 , creating a self-mixing effect. Since movement of the object  36  over the reflecting film  31  results in the reflected beam  37  corresponding to the pore distribution, when the reflection beam  37  enters the cavity  30   1  and interferes with the optical rays therein, variation of the optical radiation from the cavity  30   1  also corresponds to the cavity  30   1 . 
         [0028]    The measuring/converting module  33  detects variation in laser operation induced by the self-mixing effect within the cavity  30   1  and generates an electrical signal SE correspondingly. In an embodiment, the measuring/converting module  33  includes a photo diode. The photo diode absorbs part of the laser radiation from the cavity  30   1 , and converts the intensity of the laser radiation to the electrical signal SE. In another embodiment, the measuring/converting module  33  includes an impedance measuring device coupled to the cavity  30   1  to measure the impedance of the cavity  30   1 . Since the impedance of the cavity  30   1  is reversely proportional to the intensity of the laser radiation within the cavity  30   1 , the measured impedance can be converted to the electrical signal SE representing the intensity of the laser radiation. 
         [0029]    The measuring/converting module  33  then transmits the electrical signal SE to the analyzing circuit  34 . The analyzing circuit  34  sequentially makes an analysis of the electrical signal SE to detect movement of the object  36 . The analyzing circuit  34  is able to detect the movement of the object  36  via analysis of the variation in the electrical signal SE when the object  36  moves over the reflecting film  31  by variations in porosity. 
         [0030]      FIGS. 4A-4D ,  7 A- 7 B and  9 A- 9 B show intensities of the laser radiation emitted from the cavity  30 , of sensing system  300  with different motions of the object  36 , illustrating principle of the analyzing circuit  34  analyzing the electrical signal to detect the movement of the object  36 . 
         [0031]    In the following, the reflecting film  31  has different porosities, the amplitude of the intensity of the laser radiation within the cavity varies with the position of the object. 
         [0032]      FIGS. 4A and 4B  respectively show intensity of the laser radiation emitted from the cavity  30   1  when the object  36  stays stationary and moves with a constant velocity over first and second regions (with lower porosity than the first region) of the reflecting film  31 , where the laser source  30  is driven by a DC driving current. Referring to  FIG. 4A , the DC driving current is denoted by reference number  40   D , and the intensities of the laser radiation are represented by reference numbers  40   1  and  40   2  respectively when the object stays stationary in the first and second region. Since the first region has a higher porosity than the second region, reflected beam  37  has higher intensity when the object is located in the first region than in the second region, and accordingly, amplitude of the intensity of the laser radiation  41   1  exceeds that of the intensity of the laser radiation  41   2 . Referring to  FIG. 4   b , when the object moves with a constant velocity in the first and second regions, the intensity of the laser radiation are respectively represented by reference numbers  42   1  and  42   2 , and the intensities of the ripple component of the laser radiation are respectively represented by reference numbers  42 ′ 1  and  42 ′ 2  (difference in the heights relative to the transverse axis is for only illustration, not representing the difference of the amplitudes). Similarly, amplitude of the ripple component of the intensity of the laser radiation  42 ′ 1  exceeds that of the ripple component of the intensity of the laser radiation  42 ′ 2 . 
         [0033]      FIGS. 4C and 4D  respectively show intensity of the laser radiation emitted from the cavity  30   1  when object  36  stays stationary and moves with a constant velocity (towards the cavity  30   1 ) over first and second regions (with lower porosity than the first region) of the reflecting film  31 , where the laser source  30  is driven by a triangular AC driving current. In  FIG. 4C , the triangular AC driving current is denoted by reference number  40   A , and when the object stays stationary in the first and second regions, the intensity of the laser radiation is respectively represented by reference numbers  43   1  and  43   2 , and the intensities of the ripple of the laser radiation are respectively represented by reference numbers  43 ′ 1  and  43 ′ 2  (difference in the heights relative to the transverse axis is for only illustration, no representing the difference of the amplitudes). Since the first region has a higher porosity than the second region, reflected beam  37  has higher intensity when the object is located in the first region than in the second region, and accordingly, amplitude of the intensity of the laser radiation  41   1  exceeds that of the intensity of the laser radiation  41   2 . Referring to FIG.  4 D, when the object moves with a constant velocity in the first and second regions, the intensities of the laser radiation are respectively represented by reference numbers  44   1  and  44   2 , and the intensities of the ripple of the laser radiation are respectively represented by reference numbers  44 ′ 1  and  44 ′ 2 . Similarly, amplitude of the ripple component of the laser radiation  43 ′ 1  exceeds that of the intensity of the ripple component of the laser radiation  43 ′ 2 , and amplitude of the ripple component of the intensity of the laser radiation  44 ′ 1  exceeds that of the ripple component of the intensity of the laser radiation  44 ′ 2 . 
         [0034]    It is noted that  FIG. 4D  illustrates the case in which the object  36  moves towards the cavity  30   1 . In such a case, the frequency of the intensity of the laser radiation in rising period ½p(a) of the triangular AC driving current exceeds that in falling period ½p(b) of the triangular AC driving current. However, when the object  36  moves away from the cavity  301 , amplitude of the ripple component of the intensity of the laser radiation increases (decreases) with the increase (decrease) in the porosity of the region where the object is located, with the only difference being the frequency of the intensity of the laser radiation in rising period ½p(a) of the triangular AC driving current is less than that in falling period ½p(b) of the triangular AC driving current. 
         [0035]    As shown in  FIGS. 4A-4D , amplitude of the ripple component of the intensity of the laser radiation depends upon the porosity of the region where the object  36  is located. Accordingly, in an embodiment of the invention, the reflection film  31  has different porosity in different regions, and after the measuring/converting module  33  generates and passes a corresponding electrical signal SE to the analyzing circuit  34 , the analyzing circuit  34  determines the position of the object  36  by detecting the amplitude of the electrical signal SE. In another embodiment, the analyzing circuit  34  determines the moving direction of the object by detecting the variation in the amplitude of the ripple component of the electrical signal. When the amplitude of the ripple component of the electrical signal decreases, the object  36  moves from a region with higher porosity to another region with a lower porosity. 
         [0036]    It is noted that, when the laser source  30  is driven by a triangular AC current, the measuring/converting module generates a triangular electrical signal. For this reason, the analyzing circuits may include a filtering circuit to differentiate the triangular electrical signal into a square electrical signal in order to obtain the ripple component of the electrical signal for latter analysis. Further, in addition to the prementioned DC and triangular AC driving currents, driving currents of other shapes, such as square AC current, may also be applied to drive the laser source  30 . 
         [0037]    In an embodiment, the porosity of the reflecting film  31  is decreased along a predetermined direction for detection of one-dimensional movement of the object  36 .  FIGS. 5A and 5B  are plan views of distributions of pores of the reflecting film  31  in the embodiment. In  FIG. 5A , the spacing of the pores of the reflecting film  31  is constant while area of each pore decreases along a predetermined direction  51 . In  FIG. 5B , the spacing of the pores of the reflecting film is decreased along the predetermined direction  51  while area of each pore is constant. In both of the embodiments, the porosities of the reflecting film  31  are decreased along the predetermined direction  51 . It is noted that in addition to the distribution illustrated in  FIGS. 5A and 5B , spacing and area of each pore may have other distributions resulting in a decreased porosity along a predetermined direction. In the two embodiments, the analyzing circuit  34  determines whether the object  36  moves forwards or backwards along the predetermined direction  51  by detecting whether the variation of the amplitude in the ripple component of the electrical signal SE is negative or positive in a predetermined period. 
         [0038]    In another embodiment, the porosity of the reflecting film  31  is decreased along first and second predetermined directions with different decreasing rate for detection of two-dimensional movement of the object  36 .  FIG. 5C  is a plan view of distribution of pores of the reflecting film  31  in the embodiment. As shown, the spacing of the pores of the reflecting film  31  is constant while area of each pore is decreased along first and second predetermined directions  52  and  53 , where area differences between two neighboring pores are unequal along the two predetermined directions  52  and  53 . For example, in  FIG. 5C , the number for each pore denotes area of the pore (area of each pore drawn in the figure, however, is not procomponental to the real area of the pore for clear illustration). As shown, area differences between two neighboring pores are 1 and 3 respectively along the first and second predetermined directions  52  and  53 . In the embodiment, the analyzing circuit  34  determines whether the object  36  moves along the first predetermined direction  52  (or along the opposite direction thereto), the second predetermined direction  53  (or along the opposite direction thereto), third predetermined direction  54  (or along the opposite direction thereto), or fourth predetermined direction  55  (or along the opposite direction thereof), by detecting whether the variation in the amplitude of the ripple component of the electrical signal SE is −/+1, −/+3, −/+4 or −/+2 in a predetermined period. If the intervals between the times when the analyzing circuit  34  detects the electrical signal SE is T, the speed of the object  36  is V, the time the object  36  moves between two neighboring pores L/V is required to equal several times T to obtain an accurate determination result. The accuracy of the determination result may thus be judged by calculation of the speed V of the object  36  and comparison of L/V and T. 
         [0039]    Similarly, the two-dimensional moving direction of the object  36  can also be determined where area of each pore is constant while the spacing of the pores of the reflecting film  31  is decreased along first and second predetermined directions  52  and  53  with different decreasing rate. 
         [0040]    In the embodiments for detection of the moving direction of the object  36 , the shape of the reflecting film  31  can be flat, convex, or concave. The disposing angle θ can be set to 90° or other angles. Preferably, effects on the reflected beam  37  induced by the variation of incident angles of the laser beam  35  over the inflecting film  31  and distance between the cavity  30   1  and the reflecting film  31  are so much less than that induced by variation of porosity all over the reflecting film  31  to be ignored or filtered by a filtering circuit. 
         [0041]    In the following, as shown in  FIGS. 6A and 6B , shape or disposing angle of the reflecting film  31  are such that the incident angle of the laser beam  35  generated with the laser source  30  on the reflecting film is not 90°, the reflected beam  37  undergoes “Doppler effect” when the object  36  moves over the reflecting film  31 , causing frequency of the ripple component of the laser radiation within the cavity  301  to vary with the speed of the object  36 . 
         [0042]      FIG. 6A  shows intensity of the laser radiation emitted from the cavity  30   1  when the object  36  moves at constant velocities V 1  and V 2  (|V 1 |&gt;|V 2 |) over the same region of the reflecting film  31 , where the laser source  30  is driven by a DC driving current. In the figure, the DC driving current is denoted by reference number  60 D, and the intensity of the laser radiation is respectively represented by reference numbers  61   1  and  61   2 , and the intensities of the ripple of the laser radiation are respectively represented by reference numbers  61 ′ 1  and  61 ′ 2  respectively when the object  36  moves with velocities V 1  and V 2  (difference in the heights relative to the transverse axis is for only illustration, not representing the difference in amplitudes). As shown, frequency of the ripple component of the intensity of the laser radiation  61 ′ 1  exceeds that of ripple component of the intensity of the laser radiation  61 ′ 2 . 
         [0043]    Similarly,  FIG. 6B  shows intensity of the laser radiation emitted from the cavity  30   1  when object  36  moves at constant velocities V 1  and V 2  (|V 1 |&gt;|V 2 |, and both towards the cavity  30   1 ) over the same region of the reflecting film  31 , where the laser source  30  is driven by a triangular AC driving current. In the figure, the triangular AC driving current is denoted by reference number  60   A , and the intensity of the laser radiation are respectively represented by reference numbers  62   1  and  62   2 , and the intensities of the ripple of the laser radiation are respectively represented by reference numbers  62 ′ 1  and  62 ′ 2  respectively when the object  36  moves with velocities V 1  and V 2  (difference in the heights relative to the transverse axis is for only illustration, not representing the difference in amplitudes). As shown, in rising period ½p(a) of the triangular AC driving current, the frequency of the ripple component of the intensity of the laser radiation  62 ′ 1  exceeds that of the ripple component of the intensity of the laser radiation  62 ′ 2 ; in falling period ½p(b) of the triangular AC driving current, frequency of the ripple component of the intensity of the laser radiation  62 ′ 1  is less that that of the ripple component of the intensity of the laser radiation  62 ′ 2 . 
         [0044]    It is noted  FIG. 6B  illustrates the case in which the object  36  moves towards the cavity  30   1 . However, when the object  36  moves away from the cavity  301 , the only difference is that the frequency of the intensity of the laser radiation in rising period ½p(a) of the triangular AC driving current is less than that in falling period ½p(b) of the triangular AC driving current. When the object  36  moves with velocities V 1  and V 2 , in rising period ½p(a) of the triangular AC driving current, the frequency of the ripple component of the intensity of the laser radiation  62 ′ 1  is less than that of the ripple component of the intensity of the laser radiation  62 ′ 2 ; in falling period ½p(b) of the triangular AC driving current, frequency of the ripple component of the intensity of the laser radiation  62 ′ 1  exceeds of the ripple component of the intensity of the laser radiation  62 ′ 2 . 
         [0045]    As shown in  FIGS. 6A and 6B , frequency of the ripple component of the intensity of the laser radiation varies with the speed of the object  36 . Accordingly, after the measuring/converting module  33  generates and passes a corresponding electrical signal SE to the analyzing circuit  34 , the analyzing circuit  34  determines the speed of the object  36  by detecting the frequency of the ripple component of the electrical signal SE. It is also noted that, when the laser source  30  is driven by a triangular AC current, the measuring/converting module generates a triangular electrical signal. For this reason, the analyzing circuits may include a filtering circuit to differentiate the triangular electrical signal into a square electrical signal to obtain the ripple component of the electrical signal for latter analysis. Further, in addition to the prementioned DC and triangular AC driving currents, driving currents of other shapes, such as square AC current, may also be applied to drive the laser source  30 . 
         [0046]    In an embodiment of the invention, the analyzing circuit  34  obtains the velocity of the object  36  according to the speed and moving direction thereof, and obtains the position of the object by integrating the speed with time. 
         [0047]    In the embodiments for detection of the moving direction of the object  36 , the shape of the reflecting film  31  can be flat, convex, or concave. The disposing angle θ can be set to 90° or other angles. Preferably, effects on the reflected beam  37  induced by the variation of incident angles of the laser beam  35  over the inflecting film  31  and distance between the cavity  30   1  and the reflecting film  31  are so much less than that induced by variation of porosity all over the reflecting film  31  to be ignored or filtered by a filtering circuit. 
         [0048]    In another embodiment, the reflecting film is a flexible material so as to deform when being pressed by the object  36  and recover when the object  36  moves away, cross sections respectively shown in  FIGS. 7A and 7B . The analyzing circuit  30  thus determines whether the object presses the reflecting film  31  by detecting the variation in the electrical signal SE induced by the deformation of the reflecting film  31 . 
         [0049]    In the following, as shown in  FIGS. 8A and 8B  describes the ripple component of the laser radiation within the cavity  30   1  vanishes due to the deformation of the reflecting film  31  induced by the pressing with the object  36 . 
         [0050]      FIG. 8A  shows intensity of the laser radiation emitted from the cavity  30   1  when the object  36  presses and thereby deforms the reflecting film  31 , where the laser source  30  is driven by a DC driving current. In the figure, the DC driving current is denoted by reference number  80   D , and the intensity of the laser radiation is represented by reference number  81 , and the intensity of the ripple of the laser radiation is represented by reference number  81 ′ 1 . As shown, amplitude of the ripple component  81 ′ vanishes almost completely, since the laser beam  35  cannot focus precisely on the reflecting film  31  when the reflecting film  31  is pressed and hollowed. 
         [0051]      FIG. 8B  shows intensity of the laser radiation emitted from the cavity  30   1  when the object  36  presses and thereby deforms the reflecting film  31 , where the laser source  30  is driven by a triangular AC driving current. In the figure, the triangular AC driving current is denoted by reference number  80   A , and the intensity of the laser radiation is represented by reference number  82 , and the intensity of the ripple of the laser radiation is represented by reference number  82 ′ 1 . Similarly, amplitude of the ripple component  82 ′ vanishes almost completely. 
         [0052]    As illustrated in  FIGS. 8A and 8B , since amplitude of the ripple component of the intensity of the laser radiation within the cavity  30   1  vanishes almost completely, after the measuring/converting module  33  generates and passes a corresponding electrical signal SE to the analyzing circuit  34 , the analyzing circuit  34  determines whether the object  36  presses the reflecting film  36  by detecting whether the ripple component of the electrical signal SE falls below a predetermined amplitude. The analyzing circuit  34  may determine whether the object  36  presses the reflecting film  36  by detecting other variations in the electrical signal SE induced by the deformation of the reflecting film  31 . It is also noted that, when the laser source  30  is driven by a triangular AC current, the measuring/converting module generates a triangular electrical signal. For this reason, the analyzing circuits may include a filtering circuit to differentiate the triangular electrical signal into a square electrical signal to obtain the ripple component of the electrical signal for latter analysis. Further, in addition to the mentioned DC and triangular AC driving currents, driving currents of other shapes, such as square AC current, may also be applied to drive the laser source  30 . 
         [0053]    The sensing system of the invention can be disposed in an electronic system comprising an input device having the sensing system of  FIG. 3 . Users of the electronic system can provide information by moving an object since movement of the object thus can be sensed by the sensing system in the input device. The electronic system, for example, can be a desktop or portable computer, mobile set or other device. 
         [0054]      FIGS. 9A and 9B  show applications of the invention by using a portable computer  90  with a sensing system of the invention as an example. The sensing system  300  of  FIG. 3  acts as an input device of the portable computer  90 , where the reflection film  31  is disposed in an input region  92 . Users may move finger(s) over the reflection film  31  and a display region  93  generates display information accordingly.  FIG. 9B  is a logic block diagram of analyzing circuit  34  in the sensing system  300  in accordance with an embodiment of the invention. In Block  94 , the moving direction of the finger(s) is determined via analysis of variation in amplitude of the electrical signal SE, and an output signal  94 ′ is generated to control the moving direction of a pointer shown on the display region  93 . In Block  95 , the speed of the finger(s) is determined via analysis of the frequency of the electrical signal SE, and an output signal  95 ′ is generated to control the speed of the pointer shown on the display region  93 . The output signals  94  and  95  can control scrolling of the display region  93  in one dimension detection, and can control the position of the pointer shown on the display region  93 . In block  96 , whether the finger(s) presses the reflection film  31  is determined by detecting whether the amplitude of the electronic system disappears and an output signal  96 ′ is generated correspondingly to activate operation of “clicking”. It is noted that the analyzing circuit  34  is not required to include all of the blocks  94 ,  95 , and  96 . Different combinations of the blocks  94 ,  95 ,  96  are included in the analyzing circuit as required. For example, the analyzing circuit  34  includes only the blocks  94  and  95  to control the speed and moving direction of a pointer, but does not include the block  93  for recognizing clicking function. Alternatively, the analyzing circuit  34  includes only blocks  94  and  96  to control the moving direction of a pointer and recognize clicking function, but not block  95  to control the speed of the pointer. 
         [0055]    While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.