Abstract:
The present invention is intended to realize a spectrometer which improves the wavelength resolution without being affected by the pitch of the photodiode array. The present invention is characterized by a spectrometer which comprises a wavelength dispersion device spectrally dividing the measured light beam and a photodiode array composed of a plurality of photodiodes that detect the spectrally divided light beams by the wavelength dispersion device and output photocurrents, and performs measurement using the outputs of the photodiode array; providing a deflecting means that deflects the measured light beams and changes the position where the measured light beams are detected by the above photodiode array, and measuring the characteristics of the measured light beam from the measured results for different deflection amounts.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a spectrometer in which the wavelength resolution is improved without being affected by the pitch of a photodiode array.  
           [0003]    2. Description of the Prior Art  
           [0004]    Wavelength Division Multiplexing (WDM) communication is one type of optical communication systems which transmit optical signals by using optical fibers. This WDM communication is a communication system which transmits multiple optical signals of different wavelengths using a single optical fiber. Multiple optical signals of different wavelengths are also called WDM signals. In many cases, each optical signal in WDM signals is counted, for example, in ascending order of wavelength (that is, starting at the shortest wavelength) as channel  1 , channel  2 , etc.  
           [0005]    The spectrometer is a measuring equipment that obtains the wavelength spectrum of the light being measured (hereafter called ‘measured light beam’) using a wavelength dispersion device, determines the optical power existing in an arbitrary wavelength band, and measures the characteristics of the measured light beam using this determined optical power. This spectrometer is used for measuring WDM signals very frequently, and obtains the wavelength spectrum of input WDM signals and determines optical signal levels and wavelengths and the like for each channel using the optical power determined.  
           [0006]    [0006]FIG. 1 is a configuration drawing indicating an embodiment of spectrometers that measure such WDM signals. In FIG. 1, spectroscope  10  is called a polychromator system into which WDM signals, the measured light beams, are input and which sends out the output corresponding to an optical power existing in an arbitrary wavelength band as a measured signal.  
           [0007]    Spectroscope  10  is composed of optical fiber  11 , collimating lens  12 , grating  13  that is a wavelength dispersion device, focusing lens  14 , mirror  15 , and photodiode array module  16  (hereafter abbreviated as “PDM”).  
           [0008]    Optical fiber  11  is a transmission line for making the measured light beam incident to spectroscope  10 . Collimating lens  12  is installed counter to the optical output window of optical fiber  11  and emits measured light beam  100  output from optical fiber  11  after collimating it.  
           [0009]    Grating  13  is installed oblique to collimating lens  12  to diffract the emitted light beam from collimating lens  12  by a desired angle. Then, grating  13  emits measured light beam  100  into a spectrum deflecting the light beam to different angles for every wavelength. Focusing lens  14  is provided on the optical path of emitted light from grating  13  and focuses the emitted light. Mirror  15  is installed to reflect the emitted light from focusing lens  14  in the desired direction.  
           [0010]    PDM  16  is placed in the position at which measured light beam  100  reflected from mirror  15  focuses. On PDM  16 , a PD array is formed, in which a plurality of strip-type or spot-type photodiodes (hereafter abbreviated as “PD”) is arranged. Each of these PDs generates a current (photocurrent) corresponding to the optical power of incident measured light beam  100  and outputs these photocurrents as measured signals of spectroscope  10 .  
           [0011]    In addition, a wavelength is assigned to each PD in advance. The assignment of wavelength corresponds to each position at which measured light beam  100  is deflected for each wavelength by grating  13  and focused on the PD array.  
           [0012]    Control unit  20  comprises driving means  21 , memorizing means  22 , and calculating means  23 . Driving means  21  changes over connections to each PD of PDM  16  in turn, reads measured signals from each PD in turn, for example, in ascending order of wavelength from the shortest one, and outputs each measured signal after converting them to the desired signals. Memorizing means  22  stores signals output from driving means  21  in turn. Calculating means  23  reads signals stored in memorizing means  22 , determines the optical signal levels, wavelengths, or the like of measured light beam  100 , and outputs the calculated results.  
           [0013]    Operation of the spectrometer shown in FIG. 1 will now be described. Assume that different wavelengths of wavelength A and wavelength B are multiplexed in measured light beam  100 . Measured light beam  100  emitted from optical fiber  11  is collimated with collimating lens  12 . Measured light beam  100  transmitted through collimating lens  12  is incident to grating  13 , and is spectrally divided into measured light beams  100 A and  100 B for each wavelength of λA and λB with this grating  13 . Although measured light beams  100 A and  100 B spectrally divided with grating  13  are focused on the PD array of PDM  16  by focusing lens  14  and mirror  15 , the positions of focusing the optical spot are shifted corresponding to wavelengths λA and λB of measured light beams  100 A and  100 B. Photocurrents are output from each PD respectively. As described above, spectroscope  10  does not contain mechanical moving parts and can operate stably for a long time.  
           [0014]    Driving means  21  changes over connections to each PD of PDM  16  in turn, reads photocurrents generated in each PD in turn starting at the shortest wavelength, and converts these read photocurrents to voltages. In addition, since the signals converted to voltages are analog signals, driving means  21  converts these analog signals to digital signals and stores them in memorizing means  22  in the order of reading from each PD. Calculating means  23  determines the optical signal levels and peak wavelengths of each channel using digital signals stored in memorizing means  22  and wavelengths assigned to each PD, and outputs these calculation results. The output unit not shown displays the calculation results output from calculating means  23 , for example, on the screen of the display unit or outputs them to external equipment not shown.  
           [0015]    Subsequently, the action of calculating means  23  for determining the optical signal levels and peak wavelengths of each channel will now be described in detail. FIG. 2 schematically shows that part of the PD array is irradiated with measured light beam  100 A. In FIG. 2, PD 16   a  to PD 16   e  are arranged in the direction in which measured light beam  100  is spectrally divided for wavelengths λA and λB by grating  13 . Wavelengths of λ a  to λ e  λ a &lt;λ b &lt;. . . &lt;λ e ) are assigned to each PD of 16a to 16e respectively.  
           [0016]    In addition, the PD array is not formed such that PD 16   a  to PD 16   e  that generate photocurrents are arranged without gaps in the direction of arrangement, but is formed such that PD 16   a  of width Δp, a dead zone of width Δq, PD 16   b  of width Δp . . . are arranged in this order in the direction of arrangement. Therefore, the width of one pitch is the sum of the width Δp of each PD of PD 16   a  to PD 16   e  and the width of dead zone Δq. Although each of PD 16   a  to PD 16   e  has the width Δp, the center positions of each PD in the direction of arrangement are generally made to correspond to assigned wavelengths λ a  to λ e  respectively.  
           [0017]    From one side or both sides of each of PD 16   a  to PD 16   e , photocurrents are output by signal wires not shown.  
           [0018]    If measured light beam  100 A has a line spectrum such as laser light, the optical spot of measured light beam  100 A formed on the PD array takes the shape of an ellipse or circle, whose optical power shows a Gaussian distribution. In this case, it is assumed that the center of measured light beam  100 A is in the vicinity of PD 16   c . FIG. 3 indicates the outputs of each of PD 16   a  to PD 16   e  stored in memorizing means  22 . The abscissa shows wavelengths λ a  to λ e  assigned to each of PD 16   a  to PD 16   e , and the ordinate shows the relative outputs of PD 16   a  to PD 16   e . The outputs of PD 16   a  to PD 16   e  are represented by P a  to P e . Since the center of measured light beam  100 A exists in the vicinity of PD 16   c , it is apparent that the output P c  from PD 16   c  is larger than any of the other outputs P a , P b , P d , and P e . In addition, Δλ shows a value in wavelength converted from the width of one pitch of the PD array.  
           [0019]    The response of spectroscope  10  to a line spectrum input to it is approximated as a Gaussian distribution and the peak wavelength λ peak  of measured light beam  100 A can be expressed by equation (1).  
           λ peak= λ 0 +δλ  )1)  
           [0020]    where λ 0  is the wavelength λ c  assigned to PD 16   c  whose optical power is closest to the peak optical power and δλ represents the difference between the peak wavelength λ peak  and the wavelength λ c  assigned to PD 16   c  whose optical power is closest to the peak optical power. The value δλ can also be expressed from equation (2) using the distance δx between the center of PD 16   c  and the center of the optical spot of measured light beam  100 A in FIG. 2, and the ratios of the output of PD 16   c  nearest to the center of the optical spot of measured light beam  100 A to each output of PD 16   b  and PD 16   d  both adjacent to PD 16   c .  
                     δ                 λ     =            δ                 x        Δλ       (       Δ                 p     +     Δ                 q       )     )                     =                Δ                 λ     2     ·       ln        (       P     +   1         P     -   1         )         ln        (         P   0     ·     P   0           P     -   1       ·     P     +   1           )                         (   2   )                               
 
           [0021]    where P 0  corresponds to the output P c  of PD 16   c  nearest to the peak optical power, and P −1  and P +1  correspond to P b  and P d  respectively.  
           [0022]    The optical signal level P sig  of measured light beam  100 A can be determined as shown in equation (3) using the integral of the spectrum spread over the PD array, or the sum of output values P b , P c , and P d  from three PDs, that is, PD 16   b , PD 16   c , and PD 16   d  near the peak optical power:  
             P   sig =α(δx)·( P   −1   +P   0   +P   +1 )   (3)  
           [0023]    where α(δx) is a function taking the distance between the center of the optical spot and the center of PD 16   c  as a variable. This is because the value to be added differs depending on the distance between the center of the optical spot and the center of PD 16   c . This is a function determined by the diameter of the optical spot and the width of one pitch of the PD array.  
           [0024]    Since operations in which calculating means  23  determines the optical signal level and peak wavelength of measured light beam  100 B in the other channel are similar to the above, description of them will be omitted.  
           [0025]    The wavelength resolution of spectroscope  10  depends on the size of the optical spot formed on the PD array. To improve the wavelength resolution, it is sufficient to make the optical spot size smaller (to sharpen the response spectrum) and focus it to one pitch of the PD array or less.  
           [0026]    [0026]FIG. 4 shows the outputs of PD 16   a  to PD 16   e , P a  to P e , in the case of, for example, improving the wavelength resolution by taking the optical spot size to about one pitch of PD 16   a  to PD 16   e . The wavelength resolution represents the performance that can identify channels if each channel is brought near. In FIG. 4, the same objects as those in FIG. 3 are given the same signs and so description of them is omitted.  
           [0027]    [0027]FIG. 4 ( a ) indicates the case where the peak optical power of measured light beam  100 A exists close to the center of PD 16   c . In FIG. 4 ( a ), outputs P b  and P d  that can be detected with PD 16   b  and PD 16   d  both adjacent to PD 16   c  which is nearest to the peak become extremely small. For this reason, these are easily subjected to influences of noise and it is hard to determine the optical signal level and the peak wavelength accurately.  
           [0028]    Also, FIG. 4 ( b ) indicates the case where the peak optical power of measured light beam  100 A exists at about the mid point between PD 16   c  and PD 16   d  (dead zone). In FIG. 4 ( b ), since the major part of the optical power is concentrated in the dead zone, PD 16   c  and PD 16   d , the output P b  that can be detected with PD 16   b  becomes extremely small. For this reason, the output P b  is easily subjected to influences of noise and it is hard to determine the optical signal level and the peak wavelength accurately.  
           [0029]    As described above, when the optical spot is made small to improve the wavelength resolution, the outputs of PDs to be used for calculation become small and are easily subjected to influences of noise. Accordingly, it becomes difficult to measure the optical signal level and the peak wavelength accurately. To reduce the influences of noise, it is sufficient to make the pitch of the PD array small. However, the types of generally available PD arrays are limited and it is not easy to change the shape such as changing the pitch of a PD array.  
         SUMMARY OF THE INVENTION  
         [0030]    The purpose of the present invention is to realize a spectrometer in which the wavelength resolution is improved without being affected by the pitch of a photodiode array. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0031]    [0031]FIG. 1 is a configuration drawing indicating an embodiment of the conventional spectrometer.  
         [0032]    [0032]FIG. 2 is a schematic drawing showing part of a photodiode array.  
         [0033]    [0033]FIG. 3 is a graph showing an output characteristic indicating an example of the relationship between a photodiode array and photodiode outputs.  
         [0034]    [0034]FIG. 4 shows graphs representing output characteristics indicating examples of the relationship between a photodiode array and photodiode outputs in the case where the optical spot of measured light beam  100 A is small.  
         [0035]    [0035]FIG. 5 is a configuration drawing indicating a first embodiment of the present invention.  
         [0036]    [0036]FIG. 6 shows graphs representing output characteristics indicating examples of the relationship between a photodiode array and photodiode outputs, in one of which calculating means  45  in a spectrometer shown in FIG. 5 carries out the sorting of the data of groups  1  and  2  in the order of the wavelength values.  
         [0037]    [0037]FIG. 7 is a configuration drawing indicating a second embodiment of the present invention.  
         [0038]    [0038]FIG. 8 is a configuration drawing indicating a third embodiment of the present invention.  
         [0039]    [0039]FIG. 9 is a configuration drawing indicating a fourth embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0040]    The embodiments of the present invention will now be described below with reference to the drawings.  
         [0041]    [0041]FIG. 5 is a configuration drawing indicating a first embodiment of the present invention. In FIG. 5, the same objects as those in FIG. 1 are given the same signs and so description of them is omitted. In FIG. 5, spectroscope  30  is provided instead of spectroscope  10  and electro-optic beam deflector  31 , which is one type of deflecting means that deflects measured light beams  100 A and  100 B, is newly installed between mirror  15  and PDM  16 .  
         [0042]    Electro-optic beam deflector  31  is a light deflector using the effect that the refractive index of a medium varies with an applied DC or applied electric field whose frequency is sufficiently lower than the optical frequency (electro-optic effect) by receiving a current or a voltage from outside. For example, deflection can be performed by changing the emitting direction of a prism by changing its refractive index or forming a linear phase distribution in a cross sectional plane orthogonal to the light wave propagating direction by refractive index changes generated in a medium by the electro-optic effect.  
         [0043]    Control unit  40  is provided instead of control unit  20  and is composed of synchronizing means  41 , driver  42 , driving means  43 , memorizing means  44  and calculating means  45 . Synchronizing means  41  outputs the synchronizing signals. Driver  42  applies a desired voltage to electro-optic beam deflector  31  according to synchronizing signals of synchronizing means  41 . Driving means  43  changes over connections with each PD of PDM  16  in turn according to synchronizing signals of synchronizing means  41 , reads the measuring signals of each PD in turn, for example, starting at the shortest wavelength, and outputs the measured signals after converting them to the desired signals. Memorizing means  44  stores the signals output from driving means  43  in turn and can hold the signals output from driving means  43  for an amount of up to several times of output. Calculating means  45  reads the signals stored in memorizing means  44  for an amount of up to several times of output, determines the optical signal level, the wavelengths, and the like of measured light beam  100  based on these read-out signals, and outputs the calculated results.  
         [0044]    Operation of the spectrometer shown in FIG. 5 will now be described. Synchronizing means  41  outputs the first time synchronizing signal to driver  42  and driving means  43 . Driver  42  deflects measured light beams  100 A and  100 B reflected by mirror  15  by the desired amount in the arranging direction of the PD array in PDM  16 , by applying a voltage V a  to electro-optic beam deflector  31  based on the synchronizing signal. Here, it is assumed that the centers of the optical spots of measured light beams  100 A and  100 B irradiate the same positions on the PD array of the spectroscope shown in FIG. 1. The deflected measured light beams  100 A and  100 B focus on the PD array respectively and photocurrents are output from each PD as the measuring signals.  
         [0045]    Driving means  43  changes over the connection of each PD of PDM  16  based on the synchronizing signal and reads photocurrents generated in each PD in ascending order of wavelength starting at the shortest wavelength. Driving means  43  further converts these photocurrents to voltages, converts the analog signals converted to voltages to digital signals, and stores them in memorizing means  44 . Digital signals stored in memorizing means  44  by the first time synchronizing signal are collected as the group  1  data.  
         [0046]    Subsequently, synchronizing means  41  outputs the second time synchronizing signal to driver  42  and driving means  43  again. Driver  42  applies voltage V b  to electro-optic beam deflector  31  based on this synchronizing signal and deflects measured light beams  100 A and  100 B reflected by mirror  15  by the desired amount in the arranging direction of the PD array. However, measured light beams  100 A and  100 B are deflected so that they irradiate the position deflected by a ½ pitch toward longer wavelengths from the position on the PD array irradiated with measured light beams  100 A and  100 B by the first time synchronizing signal. Deflected measured light beams  100 A and  100 B focus on the PD array respectively and photocurrents are output from each PD as the measured signals.  
         [0047]    Driving means  43  changes over the connection of each PD of PDM  16  based on the synchronizing signal and reads the photocurrents generated in each PD in ascending order of wavelength starting at the shortest wavelength. Driving means  43  further converts these photocurrents to voltages, converts the analog signals converted to voltages to digital signals, and stores them in memorizing means  44 . In this case, these signals are stored in a region other than that for group  1  data stored in memorizing means  44  based on the first time synchronizing signal. Digital signals stored in memorizing means  44  by the second time synchronizing signal are collected as the group  2  data.  
         [0048]    Calculating means  45  reads the group  1  and group  2  data from memorizing means  44  and carries out sorting of the group  1  and group  2  data in the order of the wavelength values. Through this operation, the group  1  and group  2  data become the data for interpolating each other and thus measured signals similar to those in the case of measurement with a ½ pitch on the PD array of PDM  16  are obtained.  
         [0049]    [0049]FIG. 6 shows graphs indicating the outputs of each of group  1  and group  2  data and outputs of the interpolated data in the spectrometer shown in FIG. 5. In FIG. 6, the same objects as those in FIG. 3 are given the same signs and so description of them is omitted. However, in FIG. 6, only the data for PD 16   b  to PD 16   d  in the vicinity of the peak are shown. Since, for the group  2  data, the position of measured light beam  100 A irradiation is deflected by a ½ pitch toward the longer wavelength, the wavelengths assigned to each of PD 16   b  to PD 16   d  are shifted toward the shorter wavelength by a ½ pitch respectively. In FIG. 6, for the group  1  data, the outputs corresponding to PD 16   b  to PD 16   d  are given the signs P 1   b  to P 1   d  respectively and represented with symbols •; and for the group  2  data, the outputs corresponding to PD 16   b  to PD 16   d  are given the signs P 2   b  to P 2   d  respectively and represented with symbols x.  
         [0050]    Calculating means  45  determines the optical signal level and peak wavelength of measured light beam  100 A using equations (1) to (3) from the values of wavelengths in the vicinity of peak λ c -Δλ/2, λ c , and λ d -Δλ/2 and the outputs corresponding to these wavelengths P 2   c , P 1   c  and P 2   d  based on the interpolated data. However, the first term of the second line of equation (2) becomes Δλ/4 because measured light beam  100 A is deflected by a ½ pitch and the pitch of the PD array is reduced to ½.  
         [0051]    Since the operations for determining the optical signal level and the peak wavelength of measured light beam  100 B are identical to the above, description of them is omitted. In addition, since other operations in the spectrometer shown in FIG. 5 are similar to those in the spectrometer shown in FIG. 1, description of them is also omitted.  
         [0052]    As described above, the measurement of measured light beams  100 A and  100 B is carried out by deflecting measured light beams  100 A and  100 B in the arranging direction of the PD array on PDM 16 with electro-optic beam deflector  31 , performing a series of operations in which measured signals are acquired by driving means  43  two or more times, and sorting these signals in order of wavelength values. This enables measured signals obtained by sorting to be acquired equivalent to the measurement with a pitch smaller than one pitch, and thus measurement can be performed even if the optical spot size of measured light beams  100 A and  100 B is made smaller because the data whose detecting outputs are small and which are easily subjected to influences of noise are not used. Consequently, the optical signal level and the peak wavelength can be measured with improved wavelength resolution.  
         [0053]    Further, since electro-optic beam deflector  31  employs the electro-optic effect without having mechanically moving parts, spectroscope  30  can be operated stably for a long time.  
         [0054]    [0054]FIG. 7 is a configuration drawing indicating a second embodiment of the present invention. In FIG. 7, the same objects as those in FIG. 5 are given the same signs and so description of them and indication in the drawing are both omitted. In FIG. 7, spectroscope  50  is provided instead of spectroscope  30  and mirror  51  instead of mirror  15 . In addition, piezoelectric actuator  52  is mounted instead of a deflecting means, electro-optic beam deflector  31 , so that the actuator mechanically shifts the position of mirror  51  to compose a deflecting means using piezoelectric actuator  52  and mirror  51 . A voltage is applied to piezoelectric actuator  52  from driver  42 . Piezoelectric actuator  52  generates a mechanical stress, such as expansion or contraction, if a voltage is applied.  
         [0055]    Operations of the spectrometer shown in FIG. 7 will now be described. Driver  42  applies voltage Vc to piezoelectric actuator  52  based on the first time synchronizing signal, shifts piezoelectric actuator  52  by the desired amount, and deflects measured light beams  100 A and  100 B reflected by mirror  51  in the arranging direction of the PD array on PDM  16 . Here, it is assumed that the center of the optical spot of measured light beams  100 A and  100 B irradiates the same position as that on the PD array of the spectrometer shown in FIG. 5. Further, driver  42  applies voltage Vd to piezoelectric actuator  52  based on the second time synchronizing signal, shifts piezoelectric actuator  52  by the desired amount, and deflects measured light beams  100 A and  100 B reflected by mirror  51  in the arranging direction of the PD array. However, measured light beams  100 A and  100 B are deflected so that their irradiating position on the PD array is shifted by a ½ pitch towards the longer wavelength from the position at which measured light beams  100 A and  100 B irradiate on the PD array based on the first time synchronizing signal.  
         [0056]    Here, since operations other than applying voltages Vc and Vd to piezoelectric actuator  52  based on the synchronizing signals and deflecting reflected light from mirror  51  by the desired amount are the same as those in the spectrometer shown in FIG. 5, description of them is omitted.  
         [0057]    As described above, measured light beams  100 A and  100 B are measured by deflecting measured light beams  100 A and  100 B in the arranging direction of the PD array on PDM  16  using mirror  51  and piezoelectric actuator  52 , performing a series of operations, in which driving means  43  acquires measuring signals two or more times, and sorting these signals in order of wavelength values. This enables measured signals obtained by sorting to be acquired similar to the measurement with smaller pitch than one pitch, and thus measurement can be performed even if the optical spot size of measured light beams  100 A and  100 B is made smaller because the data whose detecting outputs are small and which are easily subjected to influences of noise are not used. Consequently, the optical signal level and the peak wavelength can be measured with improved wavelength. resolution.  
         [0058]    [0058]FIG. 8 is a configuration drawing indicating a third embodiment of the present invention. In FIG. 8, the same objects as those in FIG. 5 are given the same signs and so description of them and indication in the drawing are both omitted. In FIG. 8, spectroscope  60  is provided instead of spectroscope  30 . Spectroscope  60  also has optical fiber  11 , fiber grating  61  as the wavelength dispersion device, lens  62 , PDM  16  and piezoelectric actuator  63  as a driving means. Fiber grating  61  includes a grating area formed by changing the periodical refractive index in the longitudinal direction of the optical fiber core.  
         [0059]    Fiber grating  61  is connected with the emission end of optical fiber  11  by, for example, fusion welding and measured light beam  100  is incident. Fiber grating  61  spectrally divides the incident light to measured light beams  100 A and  100 B for each of wavelengths λA and λB at grating area  61   a  in which the grating is formed and emits them at different angles to the space from fiber grating  61  itself for every wavelength of λA and λB. Lens  62  is installed in the optical path of emitted light from fiber grating  61  and focuses the emitted light. PDM 16 is mounted so that its position is where measured light beams  100 A and  100 B are focused by lens  62 , and outputs photocurrents generated in each PD. Piezoelectric actuator  63  is mounted by aligning its direction of expansion or contraction with the longitudinal direction of grating area  61   a . In addition, a voltage is applied to piezoelectric actuator  63  from driver  42 .  
         [0060]    Operations of the spectrometer shown in FIG. 8 will now be described. Driver  42  applies voltage Ve to piezoelectric actuator  63  based on the first time synchronizing signal and expands or contracts piezoelectric actuator  63  by the desired amount. This also expands or contracts grating area  61   a  to which piezoelectric actuator  63  is attached in the longitudinal direction. For this reason, the period of the refractive index, which is provided for grating area  61   a  to vary periodically, changes and so measured light beams  100 A and  100 B emitted from grating area  61   a  are deflected in the arranging direction of the PD array on PDM  16 . Here, it is assumed that the center of the optical spot of measured light beams  100 A and  100 B irradiates the same position as that on the PD array of the spectrometer shown in FIG. 5. Further, driver  42  applies voltage Vf to piezoelectric actuator  63  based on the second time synchronizing signal, expands or contracts piezoelectric actuator  63  by the desired amount, and deflects measured light beams  100 A and  100 B in the arranging direction of the PD array in a similar manner. However, measured light beams  100 A and  100 B are deflected so that their irradiating position on the PD array is shifted by a ½ pitch towards the longer wavelength from the position at which measured light beams  100 A and  100 B irradiate on the PD array based on the first time synchronizing signal.  
         [0061]    Here, since operations other than applying voltages Ve and Vf by driver  42  to piezoelectric actuator  63  based on the synchronizing signals and deflecting measured light beams  100 A and  100 B emitted from grating area  61   a , are the same as those in the spectrometer shown in FIG. 5, so description of them is omitted.  
         [0062]    As described above, measured light beams  100 A and  100 B are measured by deflecting measured light beams  100 A and  100 B in the arranging direction of the PD array on PDM  16  using piezoelectric actuator  63 , performing a series of operations, in which driving means  43  acquires measuring signals two or more times, and sorting these signals in order of wavelength. This enables measured signals to be acquired similar to the measurement with smaller pitch than one pitch, and thus measurement can be performed even if the optical spot size of measured light beams  100 A and  100 B is made smaller because the data whose detecting outputs are small and which are easily subjected to influences of noise are not used. Consequently, the optical signal level and the peak wavelength can be measured with improved wavelength resolution.  
         [0063]    [0063]FIG. 9 is a configuration drawing indicating a fourth embodiment of the present invention. In FIG. 9, the same objects as those in FIG. 5 are given the same signs and so description of them and indication in the drawing are both omitted. In FIG. 9, spectroscope  70  is provided instead of spectroscope  30 . Spectroscope  70  also includes optical fiber  11 , waveguide grating  71  as the wavelength dispersion device, lens  72 , PDM  16  and electrodes  73   a  and  73   b  as a deflecting means. Waveguide grating  71  includes a grating area where the periodical refractive index change is mechanically formed in the longitudinal direction of the optical waveguide. The optical waveguide is composed of a medium having the electro-optical effect, such as lithium niobate or the like.  
         [0064]    Optical fiber  11  is a transmission line that makes measured light beam  100  be incident to spectroscope  70 . Measured light beam  100  emitted from the emission end of optical fiber  11  is incident to waveguide grating  71 . In this case, a lens or matching oil or the like may be provided between optical fiber  11  and waveguide grating  71  to enable measured light beam  100  to be incident to waveguide grating  71  efficiently.  
         [0065]    Waveguide grating  71  spectrally divides the incident light to measured light beams  100 A and  100 B for each of wavelengths λA and λB at grating area  71   a  in which the grating is formed, and emits them at different angles to the space from waveguide grating  71  itself for every wavelength of λA and λB. Lens  72  is installed in the optical path of the light emitted from waveguide grating  71  and focuses the emitted light. PDM  16  is mounted so that its position is where measured light beams  100 A and  100 B are focused by lens  72 , and outputs photocurrents generated in each PD. Electrodes  73   a  and  73   b  are mounted counter to each other on both sides of grating area  71   a . The shape of electrodes  73   a  and  73   b  should be that of a comb. Voltages are applied to electrodes  73   a  and  73   b  from driver  42  respectively.  
         [0066]    Operations of the spectrometer shown in FIG. 9 will now be described. Driver  42  applies voltage Vg to electrodes  73   a  and  73   b  based on the first time synchronizing signal, changes the refractive index of grating area  71   a  using the electro-optic effect, and deflects measured light beams  100 A and  100 B emitted from grating area  71   a  in the arranging direction of the PD array of PDM  16  by the desired amount. Here, it is assumed that the center of the optical spot of measured light beams  100 A and  100 B irradiates the same position as that on the PD array of the spectrometer shown in FIG. 5. Further, driver  42  applies voltage Vh to electrodes  73   a  and  73   b  based on the second time synchronizing signal, changes the refractive index of grating area  71   a  using the electro-optic effect, and deflects measured light beams  100 A and  100 B emitted from grating area  71   a  in the arranging direction of the PD array by the desired amount. However, measured light beams  100 A and  100 B are deflected so that their irradiating position on the PD array is shifted by a ½ pitch towards the longer wavelength from the position at which measured light beams  100 A and  100 B irradiate on the PD array based on the first time synchronizing signal.  
         [0067]    Here, since operations other than applying voltages Vg and Vh by driver  42  to electrodes  73   a  and  73   b  based on the synchronizing signals and deflecting measured light beams  100 A and  100 B emitted from grating area  71   a  are the same as those in the spectrometer shown in FIG. 5, description of them is omitted.  
         [0068]    As described above, measured light beams  100 A and  100 B are measured by deflecting measured light beams  100 A and  100 B in the arranging direction of the PD array on PDM  16  using voltages Vg and Vh applied to electrodes  73   a  and  73   b , performing a series of operations, in which driving means  43  acquires measuring signals two or more times, and sorting these signals in order of wavelength values. This enables measured signals to be acquired similar to the measurement with a pitch smaller than one pitch, and thus measurement can be performed even if the optical spot size of measured light beams  100 A and  100 B is made smaller because the data whose detecting outputs are small and which are easily subjected to influences of noise are not used. Consequently, the optical signal level and the peak wavelength can be measured with improved wavelength resolution.  
         [0069]    Further, the electro-optic effect brought by applying a voltage to electrodes of waveguide grating  71  is adopted for deflection of measured light beams  100 A and  100 B. Since the above deflecting means has no moving parts, spectroscope  70  can be operated stably for a long time.  
         [0070]    Note that the present invention is not restricted to the configurations mentioned above; the configurations shown below may also be employed.  
         [0071]    Although an example is shown in which measured light beam  100  is multiplexed in two channels of wavelengths λA and λB, any number of channels may be multiplexed.  
         [0072]    In FIG. 5, although electro-optic beam deflector  31  is provided between mirror  15  and PDM  16 , the deflector may be installed anywhere if the installing place exists before measured light beam  100  is incident to PDM  16 , such as between optical fiber  11  and lens  12  or between lens  12  and grating  13 .  
         [0073]    Also in FIG. 5, although the configuration in which the light beam emitted from lens  14  is reflected by mirror  15  and detected by PDM  16 , a configuration in which mirror  15  is not provided and PDM  16  is installed in a position where the light beam emitted from lens  14  is focused may be employed. Electro-optic beam deflector  31  can be provided anywhere if the installing place exists before measured light beam  100  is incident to PDM  16 .  
         [0074]    The configuration in which grating  13  is used as the wavelength dispersion device in the spectrometers shown in FIG. 5 and FIG. 7 is indicated. However, that configuration may use a prism as the wavelength dispersion device or may use both a prism and grating  13 . The wavelength dispersion angles of a prism and grating  13  can be matched by using both a prism and grating  13 .  
         [0075]    In the spectrometers shown in FIG. 5 and FIG. 7, a plane type grating is used for grating  13 . However, a concave type grating can also be used. In addition, a configuration without using lens  12  and/or lens  14  may be adopted by using a concave type grating. This enables PDM  16  to detect measured light beam  100  without attenuation through lens  12  and/or lens  14 .  
         [0076]    In the spectrometers shown in FIG. 5 and FIG. 7 to FIG. 9, although a transmission type optical system using lens  12  and/or  14 , or  62  or  72  is shown, a reflection type optical system using a parabolic mirror can also be used. In the spectrometers shown in FIG. 5 and FIG. 7 to FIG. 9, a configuration, in which deflection of measured light beams  100 A and  100 B is carried out with the deflection amount of a ½ pitch towards longer wavelengths, is indicated. However, any deflection amount may be used if it is within one pitch and the beams can also be deflected towards shorter wavelengths.  
         [0077]    In addition, spectroscopes shown in FIG. 5 and FIG. 7 to FIG. 9 are presented as examples of the spectroscope. However, the present invention can be adapted to all spectroscopes that use a PD array system.  
         [0078]    Although, in the spectrometers shown in FIG. 5 and FIG. 7 to FIG. 9, a configuration in which driver  42  applies a voltage to a deflecting means based on the synchronizing signal of synchronizing means  41  and driving means  43  reads the measured signal from PDM  16 , a configuration without providing synchronizing means  41  may also be used. In the configuration without providing synchronizing means  41 , it is arranged such that signals are exchanged between driver  42  and driving means  43 . For example, driver  42  applies a voltage to a deflecting means, deflects measured light beams  100 A and  100 B by a desired amount, and then outputs a signal to driving means  43 . Driving means  43  starts to read the measured signal from PDM  16  based on the signal output from driver  42 .  
         [0079]    In the spectrometer shown in FIG. 7, an example, in which piezoelectric actuator  52  is mounted so that it mechanically shifts mirror  51  and in which a deflecting means is composed of mirror  51  and piezoelectric actuator  52 , is shown. However, a configuration, in which piezoelectric actuator  52  is attached to PDM  16  as a moving means and the actuator moves PDM  16  in the arranging direction of PD array by a desired amount, may be adopted. In such a configuration, the moving means moves PDM  16  to change the position where PDM  16  detects measured light beams  100 A and  100 B.  
         [0080]    In the spectrometer shown in FIG. 8, a configuration in which piezoelectric actuator  63  is used as a deflecting means is shown, and in the spectrometer shown in FIG. 9, a configuration in which electrodes  73   a  and  73   b  are used as a deflecting means is shown. However, measured light beams  100 A and  100 B may be deflected by a deflecting means which is composed of mirror  51  and piezoelectric actuator  52  and placed in the optical path between grating area  61   a  or  71   a  that emits the light beams and PDM  16  to which these light beams are incident.  
         [0081]    Further, although in the spectrometer shown in FIG. 8, a configuration in which piezoelectric actuator  63  is used as a deflecting means is shown, and in the spectrometer shown in FIG. 9, a configuration in which electrodes  73   a  and  73   b  are used as a deflecting means is shown, measured light beams  100 A and  100 B may be deflected by electro-optic beam deflector  31  placed in the optical path between grating area  61   a  or  71   a  that emits the light beams and PDM  16  to which these light beams are incident. Particularly in FIG. 8, this enables spectroscope  60  to operate stably for a long time because mechanical moving parts are removed.  
         [0082]    According to the present invention, there are the following effects:  
         [0083]    Since a deflecting means deflects measured light beams and changes the position where they are detected with a photodiode array, measured signals equivalent to those obtained by measurement using smaller pitch can be obtained without actually making the photodiode pitch smaller. This enables the optical spot size of measured light beams to be made smaller without using the data whose detecting outputs are small and which are easily subjected to influences of noise, and measurement can be performed with improved wavelength resolution without being affected by the photodiode pitch.  
         [0084]    Since the deflecting means employs an electro-optic effect, the spectroscope can be configured without including mechanical moving parts. This enables the spectrometer to be operated stably for a long time.  
         [0085]    Since a moving means moves the photodiode array in the direction in which obtaining the measured light beam spectrum is progressed and changes the position where the beam is detected with the photodiode array, measured signals equivalent to those obtained by measurement using smaller pitch can be obtained without actually making the photodiode pitch smaller. This enables the optical spot size of measured light beams to be made smaller without using the data whose detecting outputs are small and which are easily subjected to influences of noise, and measurement can be performed with improved wavelength resolution without being affected by the photodiode pitch.