Patent Publication Number: US-2022221391-A1

Title: Optical measuring device and optical measuring system

Description:
FIELD 
     The present disclosure relates to an optical measuring device and an optical measuring system. 
     BACKGROUND 
     Flow cytometry has conventionally been known as a method for analyzing proteins of biologically relevant microparticles such as cells, microorganisms, and liposomes. A device used for the flow cytometry is referred to as a flow cytometer (FCM). In the flow cytometer, microparticles flowing in a flow path in a line are irradiated with laser light having a specific wavelength, light such as a fluorescent ray, a forward scattered ray, or a side scattered ray emitted from each of the microparticles is converted into an electrical signal by a photodetector to be quantified, and a result thereof is statistically analyzed, thereby determining the type, size, structure, and the like of each of the microparticles. 
     In addition, in recent years, a so-called multispot type flow cytometer has been developed which emits excitation rays having different wavelengths to different positions on a flow path through which a specimen flows and observes a fluorescent ray emitted due to each of the excitation rays. 
     Furthermore, in recent years, a flow cytometer using an image sensor has also been developed instead of a photomultiplier. 
     Furthermore, in recent years, a flow cytometer capable of multicolor analysis using a plurality of fluorescent dyes has been developed on the basis of requirements of basic medicine and clinical fields. As the flow cytometer capable of multicolor analysis, a multi-channel type or spectral type flow cytometer exists. In the multi-channel type or spectral type flow cytometer, a fluorescent ray emitted from a specimen in a specific direction is spectrally dispersed by a spectroscopic optical system and is incident on an array-shaped photodetector. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature 1: JP 2017-58361 A 
       
    
     SUMMARY 
     Technical Problem 
     Here, in a general multispot type flow cytometer, irradiation spots irradiated with excitation rays are set at equal intervals at a plurality of locations in a linear flow path in the gravity direction. Therefore, for example, when an array direction of the irradiation spots coincides with a spectral direction of the spectroscopic optical system, dispersed rays of fluorescent rays emitted from the irradiation spots overlap each other and are incident on a photodetector. This makes accurate specimen analysis difficult disadvantageously. 
     On the other hand, the fluorescent rays emitted from the irradiation spots each have a beam cross-section spreading in a direction in which a specimen flows, that is, in a direction orthogonal to the array direction of the irradiation spots. Therefore, when the spectral direction of the spectroscopic optical system is set to a direction orthogonal to the array direction of the irradiation spots, a fluorescent ray is spectrally dispersed in a long axis direction of the beam cross-section. As a result, wavelength resolution is lowered, and accurate specimen analysis is difficult disadvantageously. 
     Therefore, the present disclosure proposes an optical measuring device and an optical measuring system that make more accurate specimen analysis possible. 
     Solution to Problem 
     To solve the above-described problem, an optical measuring device according to one aspect of the present disclosure comprises: a spectroscopic optical system that spectrally disperses a fluorescent ray emitted from a specimen that passes through each of a plurality of irradiation spots arrayed in a first direction in a second direction included in a plane parallel to the first direction; and an image sensor that receives the fluorescent ray spectrally dispersed by the spectroscopic optical system and generates image data, wherein the second direction is inclined with respect to a plane vertical to the first direction. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic diagram illustrating an example of a schematic configuration of a flow cytometer as an optical measuring device or an optical measuring system according to a first embodiment. 
         FIG. 2  is a schematic diagram illustrating an example of a spectroscopic optical system in  FIG. 1 . 
         FIG. 3  is a block diagram illustrating an example of a schematic configuration of an image sensor according to the first embodiment. 
         FIG. 4  is a diagram illustrating an example of a connection relationship between a pixel and a detection circuit in  FIG. 3 . 
         FIG. 5  is a circuit diagram illustrating an example of a circuit configuration of a pixel according to the first embodiment. 
         FIG. 6  is a timing chart illustrating an example of an operation of the pixel according to the first embodiment. 
         FIG. 7  is a timing chart illustrating an example of an operation of a pixel according to a modification of the first embodiment. 
         FIG. 8  is a timing chart for explaining an example of an operation of pulsed light detection in the flow cytometer according to the first embodiment. 
         FIG. 9  is a diagram for explaining an example of a region on which a fluorescent ray (dispersed ray) is incident in the image sensor according to the first embodiment. 
         FIG. 10  is a diagram for explaining pixels constituting the same channel when an inclination in a row direction of a pixel array unit with respect to an array direction of irradiation spots is 45° in the first embodiment. 
         FIG. 11  is a diagram for explaining pixels constituting the same channel when the inclination in the row direction of the pixel array unit with respect to the array direction of the irradiation spots is 30° in the first embodiment. 
         FIG. 12  is a diagram for explaining pixels constituting the same channel when the inclination in the row direction of the pixel array unit with respect to the array direction of the irradiation spots is 60° in the first embodiment. 
         FIG. 13  is a diagram illustrating an example of area division of a pixel array unit according to a second embodiment. 
         FIG. 14  is a diagram illustrating an example of a connection relationship between a pixel and a detection circuit according to the second embodiment. 
         FIG. 15  is a circuit diagram illustrating an example of a circuit configuration of a pixel according to the second embodiment. 
         FIG. 16  is a timing chart illustrating an example of an operation of the pixel according to the second embodiment. 
         FIG. 17  is a timing chart illustrating an example of a schematic operation of a multispot type flow cytometer according to the second embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, an embodiment of the present disclosure will be described in detail with reference to the drawings. Note that, in the following embodiments, the same parts are denoted by the same reference numerals, and redundant description will be omitted. 
     In addition, the present disclosure will be described according to the following item order.
         1. First Embodiment   1.1 Example of schematic configuration of flow cytometer   1.2 Example of configuration of image sensor   1.3 Example of circuit configuration of pixel   1.4 Example of operation of pixel   1.4.1 Modification of pixel operation   1.5 Example of operation of pulsed light detection   1.6 Example of relationship among array direction of irradiation spots, spectral direction, and inclination of image sensor   1.7 Action and effect   2. Second Embodiment   2.1 Example of connection relationship between pixel and detection circuit   2.2 Example of circuit configuration of pixel   2.3 Example of basic operation of pixel   2.4 Example of schematic operation of flow cytometer   2.5 Action and effect       

     1. First Embodiment 
     First, an optical measuring device and an optical measuring system according to a first embodiment will be described in detail with reference to the drawings. Note that a flow cytometer is classified into a cell analyzer type and a cell sorter type depending on whether or not the flow cytometer has a function of separating a specimen after examination, but a flow cytometer according to the present embodiment may be either of the cell analyzer type and the cell sorter type. In addition, when the flow cytometer is a cell sorter type, a method for supplying a specimen to an irradiation spot may be a droplet method in which liquid such as water containing a specimen is discharged in a droplet shape toward a predetermined flow path, or may be a chip method in which a chip containing a specimen is caused to flow along a predetermined flow path. In a case of the chip method, a chamber different from a chamber containing a specimen may be disposed in a chip, and the specimen may be separated into the chamber. 
     1.1 Example of Schematic Configuration of Flow Cytometer 
       FIG. 1  is a schematic diagram illustrating an example of a schematic configuration of a flow cytometer as the optical measuring device or the optical measuring system according to the first embodiment.  FIG. 2  is a schematic diagram illustrating an example of a spectroscopic optical system in  FIG. 1 . Note that, in the present description, a multispot type and droplet method spectrum type flow cytometer is exemplified. 
     As illustrated in  FIG. 1 , a flow cytometer  11  includes a flow cell  31 , a plurality of (five in this example) excitation light sources  32 A to  32 E, a photodiode  33 , a plurality of spectroscopic optical systems  37 A to  37 E, an individual imaging element (hereinafter, referred to as an image sensor)  34 , and condenser lenses  35  and  36 A to  36 E. 
     In the following description, when the excitation light sources  32 A to  32 E are not distinguished from each other, the excitation light sources  32 A to  32 E are denoted by ‘ 32 ’. Similarly, when the spectroscopic optical systems  37 A to  37 E are not distinguished from each other, the spectroscopic optical systems  37 A to  37 E are denoted by ‘ 37 ’, and when the condenser lenses  36 A to  36 E are not distinguished from each other, the condenser lenses  36 A to  36 E are denoted by ‘ 36 ’. In addition, similarly, when excitation rays  71 A to  71 E described later are not distinguished from each other, the excitation rays  71 A to  71 E are denoted by ‘ 71 ’, when irradiation spots  72 A to  72 E described later are not distinguished from each other, the irradiation spots  72 A to  72 E are denoted by ‘ 72 ’, when fluorescent rays  74 A to  74 E described later are not distinguished from each other, the fluorescent rays  74 A to  74 E are denoted by ‘ 74 ’, when dispersed rays  75 A to  75 E described later are not distinguished from each other, the dispersed rays  75 A to  75 E are denoted by ‘ 75 ’, and when fluorescence spots  76 A to  76 E described later are not distinguished from each other, the fluorescence spots  76 A to  76 E are denoted by ‘ 76 ’. 
     The cylindrical flow cell  31  is disposed in an upper portion of the drawing, and a sample tube  51  is inserted into the cylindrical flow cell  31  substantially coaxially. The flow cell  31  is a flow path through which a specimen  53  flows, and has a structure in which a sample flow  52  flows down in a downward direction in the drawing (Y direction in the drawing), and furthermore, the specimen  53  including a cell and the like is released from the sample tube  51 . The specimen  53  flows down in a line on the sample flow  52  in the flow cell  31 . 
     In the present description, the Y direction may be, for example, a gravity direction (also referred to as a vertical direction). In this case, the sample flow  52  flowing out of the flow cell  31  falls in the Y direction according to gravity. In addition, in the drawing, the Y direction and an X direction may be orthogonal to each other in a vertical plane. Meanwhile, the Y direction and the X direction may be orthogonal to each other in a horizontal plane, and the Y direction and a Z direction may be orthogonal to each other in a horizontal plane. 
     The excitation light sources  32 A to  32 E are, for example, laser light sources that emit excitation rays  71 A to  71 E each having a single wavelength, respectively, and irradiate the irradiation spots  72 A to  72 E set, for example, at equal intervals on a flow path through which the specimen  53  passes with the excitation rays  71 A to  71 E, respectively. For example, each excitation ray  71  may be incident on each irradiation spot  72  from the X direction. Each of the excitation rays  71 A to  71 E may be continuous light or pulsed light having a long time width to some extent. 
     When the specimen  53  is irradiated with the excitation ray  71  at the irradiation spot  72 , the excitation ray  71  is scattered by the specimen  53 , and the specimen  53 , a fluorescent marker attached thereto, or the like is excited. 
     In the present description, a component directed in a direction opposite to the excitation light source  32  across the irradiation spot  72  among scattered rays scattered by the specimen  53  is referred to as a forward scattered ray. A forward scattered ray  73  in  FIG. 1  is a forward scattered ray of the excitation ray  71 A. 
     The scattered ray also includes a component directed in a direction deviated from a straight line connecting the excitation light source  32  and the irradiation spot  72 , and a component directed from the irradiation spot  72  to the excitation light source  32 . In the present description, among the scattered rays, a component directed in a predetermined direction deviated from a straight line connecting the excitation light source  32  and the irradiation spot  72  (Z direction in the drawing, hereinafter, referred to as a side direction) is referred to as a side scattered ray, and a component directed from the irradiation spot  72  to the excitation light source  32  is referred to as a back scattered ray. 
     In addition, when the excited specimen  53 , the fluorescent marker, and the like are de-excited, fluorescent rays each having a wavelength unique to atoms and molecules constituting the excited specimen  53 , the fluorescent marker, and the like are emitted from the excited specimen  53 , the fluorescent marker, and the like. The fluorescent rays are emitted from the specimen  53 , the fluorescent marker, and the like in all directions. However, in the configuration illustrated in  FIG. 1 , among these fluorescent rays, a component emitted from the irradiation spot  72  in a specific direction (side direction) is defined as the fluorescent ray  74  to be analyzed. Note that the light emitted from the irradiation spot  72  in the side direction includes a side scattered ray and the like in addition to the fluorescent ray. However, in the following, light components and the like other than the fluorescent ray  74  are appropriately omitted for simplification of description. 
     The forward scattered ray  73  that has passed through the irradiation spot  72 A located on a most upstream side in the sample flow  52  is converted into parallel light by the condenser lens  35 , and then incident on the photodiode  33  disposed on the opposite side to the excitation light source  32 A across the irradiation spot  72 A. Meanwhile, the fluorescent ray  74 A emitted from the specimen  53  at the irradiation spot  72 A is converted into parallel light by the condenser lens  36 A and then incident on the spectroscopic optical system  37 A. 
     Similarly, the fluorescent rays  74 B to  74 E emitted from the irradiation spots  72 B to  72 E are converted into parallel light by the condenser lenses  36 B to  36 E, and then incident on the spectroscopic optical systems  37 B to  37 E, respectively. 
     Each of the condenser lenses  35  and  36  may include another optical element such as a filter that absorbs light having a specific wavelength or a prism that changes a traveling direction of light. For example, the condenser lens  36  may include an optical filter that reduces the side scattered ray out of the incident side scattered ray and the fluorescent ray  74 . 
     As illustrated in  FIG. 2 , the spectroscopic optical system  37  includes, for example, one or more optical elements  371  such as a prism and a diffraction grating, and spectrally disperses the incident fluorescent ray  74  into the dispersed rays  75  emitted at different angles depending on a wavelength. A direction in which the fluorescent ray  74  spreads by the spectroscopic optical system  37 , that is, a spectral direction, an array direction of the irradiation spots  72 A to  72 E, and an inclination of the image sensor  34  (for example, an inclination of a column direction V 1  of the image sensor  34  with respect to the spectral direction) will be described in detail later. 
     The dispersed rays  75  emitted from the spectroscopic optical systems  37  are incident on different regions on a light receiving surface of the image sensor  34 . Therefore, the dispersed rays  75  having different wavelengths depending on a position in a direction H 1  are incident on the image sensor  34 . 
     Here, while the forward scattered ray  73  is light having a large light amount, the side scattered ray and the fluorescent ray  74 A are weak pulsed light generated when the specimen  53  passes through the irradiation spot  72 A. Therefore, in the present embodiment, the forward scattered ray  73  is observed by the photodiode  33 , and a timing when the specimen  53  passes through the irradiation spot  72 A located on a most upstream side in the sample flow  52  is thereby detected. 
     For example, the photodiode  33  observes the forward scattered ray  73  emitted from the irradiation spot  72 A all the time. In this state, when the light amount detected by passage of the specimen  53  temporarily decreases, the photodiode  33  generates a trigger signal indicating passage of the specimen  53  at a timing when the light amount decreases, and inputs the trigger signal to the image sensor  34 . 
     The image sensor  34  is, for example, an imaging element including a plurality of pixels in which an analog to digital (AD) converter is built in the same semiconductor chip. Each pixel includes a photoelectric conversion element and an amplification element, and photoelectrically converted charges are accumulated in the pixel. A signal reflecting an accumulated charge amount (pixel signal, also referred to as a pixel value) is amplified and output via an amplifying element at a desired timing, and converted into a digital signal by the built-in AD converter. 
     Note that, in the present description, the case where the forward scattered ray  73  is used for generating the trigger signal has been exemplified. However, the present disclosure is not limited thereto, and for example, the trigger signal may be generated using the side scattered ray, the back scattered ray, the fluorescent ray  74 , or the like. 
     1.2 Example of Configuration of Image Sensor 
     Next, the image sensor  34  according to the first embodiment will be described.  FIG. 3  is a block diagram illustrating an example of a schematic configuration of a complementary metal-oxide-semiconductor (CMOS) type image sensor according to the first embodiment.  FIG. 4  is a diagram illustrating an example of a connection relationship between a pixel and a detection circuit in  FIG. 3 . 
     Here, the CMOS type image sensor is a solid-state imaging element (also referred to as a solid-state imaging device) formed by applying or partially using a CMOS process. The image sensor  34  according to the first embodiment may be a so-called back surface irradiation type in which an incident surface is on a side opposite to an element formation surface (hereinafter, referred to as a back surface) in a semiconductor substrate, or may be of a so-called front surface irradiation type in which the incident surface is on a front surface side. Note that the size, the number, the number of rows, the number of columns, and the like exemplified in the following description are merely examples, and can be variously changed. 
     As illustrated in  FIG. 3 , the image sensor  34  includes a pixel array unit  91 , a connection unit  92 , a detection circuit  93 , a pixel drive circuit  94 , a logic circuit  95 , and output circuit  96 . 
     The pixel array unit  91  includes, for example, a plurality of pixels  101  arrayed in a matrix (also referred to as a two-dimensional matrix). As described later, each pixel  101  includes a photoelectric conversion element (corresponding to a photodiode  111  described later) that photoelectrically converts incident light to generate a charge. Light incident surfaces of the photoelectric conversion elements in the pixels  101  are arrayed in a matrix on a light receiving surface of the pixel array unit  91 . 
     The pixel drive circuit  94  drives each pixel  101  to cause each pixel  101  to generate a pixel signal. The logic circuit  95  controls drive timings of the detection circuit  93  and the output circuit  96  in addition to the pixel drive circuit  94 . In addition, the logic circuit  95  and/or the pixel drive circuit  94  also functions as a control unit that controls readout of a pixel signal with respect to the pixel array unit  91  in accordance with passage of the specimen  53  through the irradiation spot  72 . 
     Note that the image sensor  34  may further include an amplifier circuit such as an operational amplifier that amplifies a pixel signal before AD conversion. 
     The fluorescent rays  74 A to  74 E emitted from the irradiation spots  72 A to  72 E in a side direction are collimated by the condenser lenses  36 A to  36 E, and then converted into the dispersed rays  75 A to  75 E by the spectroscopic optical systems  37 A to  37 E, respectively. Then, the dispersed rays  75 A to  75 E are incident on different regions on a light receiving surface on which the pixels  101  of the pixel array unit  91  are arrayed. 
     To each pixel  101  of the pixel array unit  91 , among the dispersed rays  75 , a wavelength component determined by a position in the row direction H 1  in the pixel array unit  91  is input. For example, in the positional relationship exemplified in  FIG. 2 , in the image sensor  34  in  FIG. 2 , light having a shorter wavelength is incident on a pixel  101  located on a more right side, and light having a longer wavelength is incident on a pixel  101  located on a more left side. 
     Each pixel  101  generates a pixel signal corresponding to an emitted light amount. The generated pixel signal is read out by, for example, the detection circuit  93  disposed on a one-to-one basis with respect to the pixel  101 . Each detection circuit  93  includes an AD converter, and converts the analog pixel signal that has been read out into a digital pixel signal. 
     Here, as illustrated in  FIG. 4 , for example, the plurality of detection circuits  93  may be arrayed so as to be divided into two groups (detection circuit arrays  93 A and  93 B) with respect to the pixel array unit  91 . One detection circuit array  93 A is disposed, for example, on an upper side of the pixel array unit  91  in a column direction, and the other detection circuit array  93 B is disposed, for example, on a lower side of the pixel array unit  91  in the column direction. In each of the detection circuit arrays  93 A and  93 B, the plurality of detection circuits  93  is arrayed in one row or a plurality of rows in a row direction. 
     For example, the detection circuits  93  of the detection circuit array  93 A disposed on an upper side of the pixel array unit  91  in the column direction may be connected to the pixels  101  in an upper half of the pixel array unit  91  in the column direction, and the detection circuits  93  of the detection circuit array  93 B disposed on a lower side in the column direction may be connected to the pixels  101  in a lower half of the pixel array unit  91  in the column direction. However, the present disclosure is not limited thereto, and various modifications may be made, for example, the detection circuits  93  of the detection circuit array  93 A may be connected to the pixels  101  in even number columns, and the detection circuits  93  of the detection circuit array  93 B may be connected to the pixels  101  in odd number columns. In addition, for example, the plurality of detection circuits  93  may be arrayed in one row or a plurality of rows on one side (for example, an upper side in the column direction) of the pixel array unit  91 . 
     In the present embodiment, it is assumed that a so-called global shutter method that executes readout operations for all the pixels  101  simultaneously in parallel is adopted for the image sensor  34 . In the global shutter method, each pixel  101  of the pixel array unit  91  is connected to the detection circuit  93  on a one-to-one basis. In this case, for example, if 100 pixels  101  are arrayed in the column direction V 1  in the pixel array unit  91 , it is necessary to arrange 100 detection circuits  93  for one column of pixels. 
     Therefore, as described above, when the detection circuits  93  are classified into two groups of the detection circuit arrays  93 A and  93 B and the number of rows of each of the groups is set to one, for 100 pixels  101  arranged in one column, it is only required to arrange 50 detection circuits  93  in each of the detection circuit arrays  93 A and  93 B. 
     Description will be made with reference to  FIG. 3  again. A pixel signal read out from each pixel  101  by the detection circuit  93  is converted into a digital pixel signal by the AD converter of each detection circuit  93 . Then, the digital pixel signal is output as image data for one frame (corresponding to fluorescence spectrum information, hereinafter, referred to as a spectral image) to an external signal acquisition system  1  via the output circuit  96 . 
     For example, the signal acquisition system (also referred to as a signal acquisition unit)  1  evaluates a spectral image input from the image sensor  34 , and inputs an evaluation value as a result thereof to an analysis system  2 . For example, the signal acquisition system  1  divides a spectral image into a plurality of regions (corresponding to channel regions described later) arrayed in the row direction H 1 , and adds up pixel values of pixels included in the regions to calculate an evaluation value of the spectral image (corresponding to multi-channel analysis described later). In addition, the signal acquisition system  1  may have a so-called virtual filter function of adding up pixel values of pixels included in one or more regions (corresponding to a virtual filter described later) set in advance or arbitrarily set by a user to calculate an evaluation value of a spectral image. 
     Such a signal acquisition system  1  may be a digital signal processor (DSP), a field-programmable gate array (FPGA), or the like disposed in the same chip as or outside the image sensor  34 , or may be an information processing device such as a personal computer connected to the image sensor  34  via a bus or a network. 
     The analysis system (also referred to as an analysis unit)  2  executes various analysis processes on the basis of an evaluation value input from the signal acquisition system  1 . For example, the analysis system  2  acquires information such as the type, size, and structure of the specimen  53  on the basis of the evaluation value. In addition, the analysis system  2  may display a spectral image and an evaluation value to a user and may also provide a user interface (UI) serving as an analysis tool. Such an analysis system  2  may be, for example, an information processing device such as a personal computer connected to the signal acquisition system  1  via a bus or a network. 
     1.3 Example of Circuit Configuration of Pixel 
     Next, an example of a circuit configuration of the pixel  101  according to the first embodiment will be described with reference to  FIG. 5 .  FIG. 5  is a circuit diagram illustrating an example of a circuit configuration of a pixel according to the first embodiment. 
     As illustrated in  FIG. 5 , the pixel  101  includes a photodiode (also referred to as a photoelectric conversion element)  111 , an accumulation node  112 , a transfer transistor  113 , an amplification transistor  114 , a selection transistor  115 , a reset transistor  116 , and a floating diffusion (FD)  117 . For example, an N-type metal-oxide-semiconductor (MOS) transistor may be used for each of the transfer transistor  113 , the amplification transistor  114 , the selection transistor  115 , and the reset transistor  116 . 
     A circuit including the photodiode  111 , the transfer transistor  113 , the amplification transistor  114 , the selection transistor  115 , the reset transistor  116 , and the floating diffusion  117  is also referred to as a pixel circuit. In addition, a configuration of the pixel circuit excluding the photodiode  111  is also referred to as a readout circuit. 
     The photodiode  111  converts a photon into a charge by photoelectric conversion. The photodiode  111  is connected to the transfer transistor  113  via the accumulation node  112 . The photodiode  111  generates a pair of an electron and a hole from a photon incident on a semiconductor substrate on which the photodiode  111  itself is formed, and accumulates the electron in the accumulation node  112  corresponding to a cathode. The photodiode  111  may be a so-called embedded type in which the accumulation node  112  is completely depleted at the time of charge discharge by resetting. 
     The transfer transistor  113  transfers a charge from the accumulation node  112  to the floating diffusion  117  under control of a row drive circuit  121 . The floating diffusion  117  accumulates charges from the transfer transistor  113  and generates a voltage having a voltage value corresponding to the amount of the accumulated charges. This voltage is applied to a gate of the amplification transistor  114 . 
     The reset transistor  116  releases the charges accumulated in the accumulation node  112  and the floating diffusion  117  to a power supply  118  and initializes the charge amounts of the accumulation node  112  and the floating diffusion  117 . A gate of the reset transistor  116  is connected to the row drive circuit  121 , a drain of the reset transistor  116  is connected to the power supply  118 , and a source of the reset transistor  116  is connected to the floating diffusion  117 . 
     For example, the row drive circuit  121  controls the reset transistor  116  and the transfer transistor  113  to be in an ON state to extract electrons accumulated in the accumulation node  112  to the power supply  118 , and initializes the pixel  101  to a dark state before accumulation, that is, a state in which light is not incident. In addition, the row drive circuit  121  controls only the reset transistor  116  to be in an ON state to extract charges accumulated in the floating diffusion  117  to the power supply  118 , and initializes the charge amount of the floating diffusion  117 . 
     The amplification transistor  114  amplifies a voltage applied to the gate and causes the voltage to appear at a drain. The gate of the amplification transistor  114  is connected to the floating diffusion  117 , a source of the amplification transistor  114  is connected to a power supply, and the drain of the amplification transistor  114  is connected to a source of the selection transistor  115 . 
     A gate of the selection transistor  115  is connected to the row drive circuit  121 , and a drain of the selection transistor  115  is connected to a vertical signal line  124 . The selection transistor  115  causes the voltage appearing in the drain of the amplification transistor  114  to appear in the vertical signal line  124  under control of the row drive circuit  121 . 
     The amplification transistor  114  and a constant current circuit  122  form a source follower circuit. The amplification transistor  114  amplifies a voltage of the floating diffusion  117  with a gain of less than 1, and causes the voltage to appear in the vertical signal line  124  via the selection transistor  115 . The voltage appearing in the vertical signal line  124  is read out as a pixel signal by the detection circuit  93  including an AD conversion circuit. 
     The pixel  101  having the above configuration accumulates charges generated by photoelectric conversion therein during a period from a time when the photodiode  111  is reset till a time when the pixel signal is read out. Then, when the pixel signal is read out, the pixel  101  causes a pixel signal corresponding to accumulated charges to appear in the vertical signal line  124 . 
     Note that the row drive circuit  121  in  FIG. 5  may be, for example, a part of the pixel drive circuit  94  in  FIG. 3 , and the detection circuit  93  and the constant current circuit  122  may be, for example, a part of the detection circuit  93  in  FIG. 3 . 
     1.4 Example of Operation of Pixel 
     Next, an example of an operation of the pixel  101  according to the first embodiment will be described with reference to a timing chart of  FIG. 6 .  FIG. 6  is a timing chart illustrating an example of an operation of a pixel according to the first embodiment. 
     As illustrated in  FIG. 6 , at timing T 41 , the row drive circuit  121  raises a transfer signal TRG to be applied to the gate of the transfer transistor  113  and a reset signal RST to be applied to the gate of the reset transistor  116  to a high level at a timing immediately before an accumulation period. As a result, both the transfer transistor  113  and the reset transistor  116  are put into an ON state, and charges accumulated in the accumulation node  112  between the photodiode  111  and the transfer transistor  113  are discharged to the power supply  118 . Hereinafter, this control is referred to as “PD reset”. 
     In addition, when the reset transistor  116  is put into an ON state, the floating diffusion  117  is also connected to the power supply  118  via the reset transistor  116 , and therefore charges accumulated in the floating diffusion  117  are also discharged to the power supply  118 . 
     Thereafter, the row drive circuit  121  causes the transfer signal TRG to fall to a low level to control the transfer transistor  113  to be in an OFF state. By this control, the accumulation node  112  is put into a floating state, and a new accumulation period starts. 
     In addition, the row drive circuit  121  sets the transfer transistor  113  to be in an OFF state and then causes the reset signal RST to fall to a low level to control the reset transistor  116  to be in an OFF state. By this control, the potential of the floating diffusion  117  is somewhat lowered from a reference potential due to coupling with the gate of the reset transistor  116 , and is put into a floating state. This control is hereinafter referred to as “FD reset”. 
     As described above, in the present example of an operation, the PD reset and the FD reset are continuously performed. 
     After the FD reset is executed, the voltage of the floating diffusion  117  in a reset state is amplified by the amplification transistor  114  and appears in the vertical signal line  124 . 
     The detection circuit  93  performs signal readout (hereinafter, referred to as sampling) one or more times (for example, four times) during one exposure period. In the sampling, the potential appearing in the vertical signal line  124  is read out by the detection circuit  93  as a signal in a state where the pixel  101  is reset (hereinafter, referred to as a reset signal), and converted into a digital signal. Multiple sampling of the reset signal is handled as first readout in correlated double sampling (CDS) described later. 
     Then, at timing T 42 , the row drive circuit  121  raises the transfer signal TRG to a high level immediately before the accumulation period ends, and controls the transfer transistor  113  to be in an ON state. By this control, charges accumulated in the accumulation node  112  are transferred to the floating diffusion  117 . At this time, if the potential of the floating diffusion  117  is sufficiently deep, all electrons accumulated in the accumulation node  112  are transferred to the floating diffusion  117 , and the accumulation node  112  is put into a completely depleted state. 
     In addition, when a predetermined pulse period has elapsed from timing T 42 , the row drive circuit  121  causes the transfer signal TRG to fall and controls the transfer transistor  113  to be in an OFF state. By this control, the potential of the floating diffusion  117  is lowered by the accumulated charge amount as compared with that before the transfer transistor  113  is driven (that is, the potential becomes shallower). 
     As described above, when the charges accumulated in the accumulation node  112  are transferred to the floating diffusion  117 , the voltage corresponding to the decrease is amplified by the amplification transistor  114  and appears in the vertical signal line  124 . 
     Similarly to the sampling of the reset signal, the detection circuit  93  samples the potential appearing in the vertical signal line  124  once or more times (for example, four times). In the sampling, the potential appearing in the vertical signal line  124  is read out by the detection circuit  93  as an accumulation signal of a voltage value corresponding to an incident photon amount and converted into a digital signal. The multiple sampling of the accumulation signal is handled as second readout in CDS. 
     The detection circuit  93  compares the sampled accumulation signal with the reset signal, and determines the incident photon amount on the basis of the comparison result. 
     For example, the detection circuit  93  adds all the plurality of accumulation signals and calculates an average value of the accumulation signals as necessary. Similarly, the detection circuit  93  adds all the plurality of reset signals and calculates an average value of the reset signals as necessary. 
     Then, the detection circuit  93  executes CDS that calculates a difference between an addition value (or an average value) of the accumulation signals and an addition value (or an average value) of the reset signals. By this CDS, kTC noise generated at the time of FD reset is canceled out, and a net pixel signal based on the light amount of the fluorescent ray  74  is determined. 
     The accumulation period of each pixel (pixel circuit)  101  is a period between the PD reset operation and the accumulation signal readout operation described above, and to be precise, a period from a time when the transfer signal TRG falls at the time of PD reset till a time when the transfer signal TRG falls again at the time of charge transfer. When a photon is incident on the photodiode  111  and a charge is generated during this accumulation period, the charge serves as a difference between the reset signal and the accumulation signal, and is acquired by the detection circuit  93  as the net pixel signal. 
     Note that, in the detection circuit  93 , by performing CDS between digital values that have passed through the AD converter, noise mixed in an AD conversion process can also be canceled out. 
     1.4.1 Modification of Pixel Operation 
     By the way, in the example of an operation using  FIG. 6 , a dead period in which accumulation is not performed is generated after a unit accumulation is completed and before a next accumulation starts, particularly, during a sampling period of the accumulation signal. Therefore, in particular, in order to cope with high-speed sampling, such a dead period may be removed. 
       FIG. 7  is a timing chart illustrating an example of an operation of a pixel according to a modification. In the example of  FIG. 7 , PD reset at timing T 41  performed in  FIG. 6  is omitted, and charge discharge of the photodiode  111  accompanying charge transfer at timing T 42 , which is a time of readout, is also used as the PD reset. 
     That is, at timing T 51  corresponding to timing T 41  in  FIG. 6 , only FD reset is performed, and subsequently, sampling at a reset level is performed. At this time, the transfer signal TRG remains at a low level, and accumulated charges of the photodiode  111  are held as they are. 
     Then, at timing T 52 , the transfer signal TRG is raised to a high level, and charges of the accumulation node  112  are transferred to the floating diffusion  117 , but this charge transfer is also used as the PD reset. In this case, a next accumulation period of the photodiode  111  starts immediately after the charge transfer is completed, that is, when the transfer signal TRG falls. As a result, the dead period during which no photon incident on the pixel  101  is detected is substantially zero. 
     Note that, in each of the examples of an operation in  FIGS. 6 and 7 , the shortest cycle of the unit accumulation can be defined by a total required time of sampling of the reset signal and sampling of the accumulation signal. 
     1.5 Example of Operation of Pulsed Light Detection 
     Next, an example of an operation of pulsed light detection in the flow cytometer  11  according to the first embodiment will be described with reference to a timing chart of  FIG. 8 .  FIG. 8  is a timing chart for explaining an example of an operation of pulsed light detection in the flow cytometer according to the first embodiment. Note that  FIG. 8  exemplifies an operation when the specimen  53  passes through the irradiation spot  72 A located on a most upstream side, in other words, an operation when pulsed light of the fluorescent ray  74 A emitted from the irradiation spot  72 A is detected. However, with respect to the fluorescent rays  74 B to  74 E emitted from the irradiation spots  72 B to  72 E on a downstream side, respectively, for example, a similar operation is executed at a predetermined time interval from a timing when passage of the specimen  53  through the irradiation spot  72 A is detected on the basis of the forward scattered ray  73  (for example, timing T 61  when an event signal S 0  is generated), and pulsed light of each of the fluorescent rays  74 B to  74 E can be thereby detected. Note that the predetermined time interval may be equal to a time interval at which the same specimen  53  passes through the irradiation spots  72 A to  72 E. 
     The light intensity of the fluorescent ray  74 A is drawn as a pulse waveform PL 1  as illustrated at an uppermost part of  FIG. 8  as the specimen  53  passes through the irradiation spot  72 A, and each pulse waveform PL 1  is a waveform corresponding to passage of one specimen  53 . At this time, the light intensity of the forward scattered ray  73  detected by the photodiode  33  illustrated in a middle part of  FIG. 8  is drawn as a pulse waveform PL 2  having a similar timing to the pulse waveform PL 1  in the upper part of  FIG. 8  and a large intensity attenuation ratio. 
     At timing T 61 , the photodiode  33  acquires a passage timing of the specimen  53  from comparison between the intensity of the pulse waveform PL 2  of the forward scattered ray and a threshold Thl, and generates the event signal S 0 . 
     Here, an end of the accumulation period and signal readout in the image sensor  34  are performed in synchronization with the event signal S 0  indicating that the specimen  53  has passed. An access sequence of the readout is a global shutter having almost no dead period in accordance with  FIG. 7 . 
     That is, the start and the end of the accumulation period are performed simultaneously for all the pixels. At this time, in-pixel transfer of charges is performed in synchronization with the event signal S 0  indicating passage of the specimen  53 , and the accumulation period ends all at once for all the pixels. Then, readout of the pixel signal starts. Furthermore, at this time, a next accumulation period starts all at once for all the pixels. 
     At timing T 62 , the image sensor  34  ends the accumulation period in the pixel, starts readout of the pixel signal, and further starts a next accumulation period. Here, timing T 62  is a timing after a certain delay time t 1  in consideration of the flow velocity and the size of the specimen  53  elapses from timing T 61  at which the event signal S 0  is acquired. 
     The readout of the pixel signal is performed with acquisition of a difference between the AD conversion value of the accumulation signal and the AD conversion value of the reset signal that has already been acquired, and a net pixel signal in which kTC noise or the like is canceled out is thereby derived. Furthermore, subsequently, acquisition and AD conversion of the reset signal in a next cycle are performed, and when the acquisition and the AD conversion are completed, the next accumulation period ends, and readout can be performed. That is, the shortest cycle of an event process is equal to the shortest cycle of the unit accumulation period, which is determined by a time required for acquisition and AD conversion of each of the accumulation signal and the reset signal. 
     A total value of the net pixel signals output from the plurality of pixels  101  in each event process corresponds to the total amount of photons received by the photodetector for each pulse. As a result, the intensity of the fluorescent ray  74 A for each specimen  53  is derived. That is, in the present embodiment, the pixel  101  accumulates photoelectrically converted charges therein, and incident light is thereby integrated in the pixel  101 . Therefore, the AD conversion for output from each pixel  101  only needs to be performed once, and it is not necessary to perform the AD conversion a plurality of times in time series. 
     For example, assuming that a total time of 10 μs is required for the AD conversion of the reset signal, the AD conversion of the accumulation signal, and CDS thereof, a minimum interval of events that can be handled is about 10 μs, and up to 100,000 events in one second, that is, passage of the specimen  53  through the irradiation spot  72 A can be evaluated. 
     Note that, in addition to the time for reading out the pixel signal from each pixel  101 , a time for outputting the pixel signal that has been read out via the output circuit  96  is also required. However, for example, by disposing a register in the detection circuit  93  and temporarily storing the pixel signal therein, AD conversion of the reset signal and the accumulation signal and output of the pixel signal can be executed in parallel by a pipeline method, and therefore the time required for outputting the pixel signal does not restrict the accumulation cycle. 
     In addition, in this example, the event signal S 0  indicating that the specimen  53  has passed is generated at downedge timing T 61  when the pulse waveform PL 2  falls below the threshold L 1 . However, the present disclosure is not limited thereto, and the event signal S 0  may be generated at upedge timing T 63  when the pulse waveform PL 2  exceeds the threshold L 1 . When the event signal S 0  is generated at upedge timing T 63 , it is easy to cope with a fluctuation in the size and flow rate of the specimen  53 . 
     In addition, the event signal S 0  may be generated using a detection result of the side scattered ray or the fluorescent ray  74 A (dispersed ray  75 A). In this case, light for event detection and light for specimen analysis may be spectrally dispersed, and the light for event detection may be incident on the photodiode  33 . 
     Furthermore, instead of the photodiode  33 , a light receiving element for event generation may be separately mounted in the image sensor  34 . 
     Furthermore, the delay time t 1  from the event signal S 0  is fixed here, but in general, the intensity attenuation amount of the pulse waveform PL 2  due to the forward scattered ray  73  is larger as the specimen  53  is larger. Therefore, the intensity of the pulse waveform PL 2  may be evaluated, for example, by the beginning of the pulse, and the length of the delay time t 1  may be set in accordance therewith. In this case, a longer delay time t 1  may be set for a large specimen  53 . 
     1.6 Example of Relationship Among Array Direction of Irradiation Spots, Spectral Direction, and Inclination of Image Sensor 
       FIG. 9  is a diagram for explaining an example of a region on which a fluorescent ray (dispersed ray) is incident in the image sensor according to the first embodiment. 
     When the condenser lenses  36 A to  36 E and the spectroscopic optical systems  37 A to  37 E in a conjugate relationship are configured to cause the dispersed rays  75 A to  75 E to be incident on the image sensor  34  with the array of the irradiation spots  72 A to  72 E as it is, respectively, the fluorescence spots  76 A to  76 E formed by the dispersed rays  75 A to  75 E incident on the pixel array unit  91  of the image sensor  34  are arrayed in the Y direction as illustrated in  FIG. 9 . 
     Here, in each fluorescence spot  76 , spread (beam cross-section) of light having the same wavelength has a shape in which the X direction is a longitudinal direction. Note that, in  FIG. 9 , for clarity, each fluorescent ray  74  is indicated as a set of rays having discrete wavelengths, and a spot SP formed by each of the rays having the wavelengths is indicated as an elliptical shape with a long axis in the X direction. However, actually, for example, when each fluorescent ray  74  is white light having a continuous and wide frequency spectrum, the fluorescence spot  76  formed by each fluorescent ray  74  has a shape spreading in a band shape. 
     Therefore, for example, when the spectral direction D 1  of the fluorescent ray  74  by the spectroscopic optical system  37  is the X direction, spots SP of rays having different wavelengths overlap with each other, and wavelength resolution is reduced. As a result, accurate specimen analysis is difficult. 
     On the other hand, for example, when the spectral direction D 1  of the fluorescent ray  74  by the spectroscopic optical system  37  is the Y direction, the fluorescence spots  76  of different fluorescent rays  74  overlap with each other, and accurate specimen analysis is difficult. In addition, suppressing spread of the dispersed ray  75  such that the fluorescence spots  76  of different fluorescent rays  74  do not overlap with each other means a decrease in wavelength resolution, leading to difficulty in accurate specimen analysis. 
     Therefore, in the present embodiment, as illustrated in  FIG. 9 , the spectral direction D 1  of the spectroscopic optical system  37  is set so as to be inclined by an angle θ with respect to the Y direction which is an array direction of the irradiation spots  72 A to  72 E. This makes it possible to enhance the wavelength resolution while avoiding overlapping of the fluorescence spots  76  of the different fluorescent rays  74 , and therefore more accurate specimen analysis is possible. 
     At this time, by setting a direction of an inclination of the row direction H 1  of the pixel array unit  91  with respect to the X direction to the same direction as a direction of an inclination of the spectral direction D 1  with respect to the X direction, the direction of spread of each fluorescence spot  76  and an outer edge of the pixel array unit  91  can be brought close to parallel, and therefore a necessary area of the pixel array unit  91  can be reduced. 
     Furthermore, by inclining the image sensor  34  such that the row direction H 1  of the pixel array unit  91  coincides with or substantially coincides with the spectral direction D 1 , the direction of spread of each fluorescence spot  76  and the outer edge of the pixel array unit  91  are parallel, and therefore a necessary area of the pixel array unit  91  can be further reduced. In addition, in this configuration, since the direction of spread of each fluorescence spot  76  and the row direction H 1  of the pixel array unit  91  coincide or substantially coincide with each other, complication of an evaluation process or the like executed by the signal acquisition system  1  on a spectral image of each fluorescence spot  76  can also be suppressed. 
     Note that an angle θ of the column direction V 1  of the pixel array unit  91  with respect to the Y direction that is the array direction of the irradiation spots  72 , in other words, the angle θ of the spectral direction D 1  and the row direction H 1  with respect to the X direction (for example, the horizontal direction) may be, for example, larger than 0° and smaller than 90°, and may be preferably in a range of about 30° or more and 60 or less. 
     For example, when the angle θ is set to 45°, as in the pixel  101  indicated by hatching in  FIG. 10 , by adding pixel values read out from the pixels  101  arrayed in an oblique direction in a region on the pixel array unit  91  in which the fluorescence spots  76  are formed as pixel values of the same channel, the intensity of light having the same wavelength can be calculated. Note that the same channel may be a set of pixels  101  on which light having the same wavelength or a wavelength that can be regarded as the same is incident in each of regions  91 A to  91 E. 
     In addition, when the angle θ is set to 30° or 60°, as in the pixel  101  indicated by hatching in  FIG. 11 or 12 , by adding pixel values read out from the pixels  101  on which light having the same wavelength is mainly incident in a region on the pixel array unit  91  in which the fluorescence spots  76  are formed as pixel values of the same channel, the intensity of light having the same wavelength can be calculated. 
     1.7 Action and Effect 
     As described above, according to the present embodiment, the spectral direction D 1  of the spectroscopic optical system  37  is set so as to be inclined by the angle θ with respect to the Y direction which is an array direction of the irradiation spots  72 A to  72 E. This makes it possible to enhance the wavelength resolution while avoiding overlapping of the fluorescence spots  76  of the different fluorescent rays  74 , and therefore more accurate specimen analysis is possible. 
     In addition, in the present embodiment, the image sensor  34  is inclined such that the row direction H 1  of the pixel array unit  91  coincides or substantially coincides with the spectral direction D 1 . As a result, since the direction of spread of each fluorescence spot  76  and the outer edge of the pixel array unit  91  are parallel, a necessary area of the pixel array unit  91  can be reduced. In addition, since the direction of spread of each fluorescence spot  76  and the row direction H 1  of the pixel array unit  91  coincide or substantially coincide with each other, complication of an evaluation process or the like executed by the signal acquisition system  1  on a spectral image of each fluorescence spot  76  can be suppressed. 
     Note that, in the first embodiment, the so-called global shutter method has been exemplified in which readout simultaneously starts for all the pixels  101  of the pixel array unit  91 , but the present disclosure is not limited thereto. For example, when one detection circuit  93  is connected to a plurality of pixels  101  in the same column, a so-called rolling shutter method can be adopted in which pixel signals are sequentially read out from the pixels  101  connected to the same detection circuit  93 . Note that, when the rolling shutter method is adopted, a selection transistor that controls connection between the drain of the amplification transistor  114  and the vertical signal line  124  according to a selection signal from the row drive circuit  121  is added to the drain of the amplification transistor  114  and the vertical signal line  124  in the pixel circuit of each pixel  101 . 
     2. Second Embodiment 
     Next, an optical measuring device and an optical measuring system according to a second embodiment according to the second embodiment will be described in detail with reference to the drawings. Note that, in the following description, a configuration similar to that of the first embodiment is cited, and redundant description thereof will be thereby omitted. 
     As described with reference to  FIG. 9  in the first embodiment, when the image sensor  34  is inclined such that the row direction H 1  of the pixel array unit  91  coincides with or substantially coincides with the spectral direction D 1 , the direction of spread of each fluorescence spot  76  and the outer edge of the pixel array unit  91  are parallel. 
     Therefore, in the second embodiment, as illustrated in  FIG. 13 , a pixel array unit  91  is divided into a plurality of (five in this example) regions  91 A to  91 E in which fluorescence spots  76 A to  76 E are formed, respectively, and a spectral image of a fluorescent ray  74  is read out for each of the regions  91 A to  91 E. 
     At this time, by making readout by the global shutter method possible for each of the regions  91 A to  91 E, frame data read out in one read operation can be reduced. Therefore, a readout time at one time and a subsequent processing time for frame data can be largely reduced. 
     2.1 Example of Connection Relationship Between Pixel and Detection Circuit 
       FIG. 14  is a diagram illustrating an example of a connection relationship between a pixel and a detection circuit according to the second embodiment. As illustrated in  FIG. 14 , in the second embodiment, one detection circuit  93  is connected to one pixel  101  in each of the regions  91 A to  91 E. Therefore, as exemplified in  FIG. 13 , when the pixel array unit  91  is divided into five regions  91 A to  91 E arrayed in the column direction V 1 , one detection circuit  93  is connected to five pixels  101  that are not adjacent to each other in the same column. 
     As described above, when one detection circuit  93  is connected to one pixel  101  in each of the regions  91 A to  91 E, readout by the global shutter method is possible in each of the regions  91 A to  91 E, and readout by the rolling shutter method is possible in a unit of the regions  91 A to  91 E. As a result, a spectral image can be read out from one of the regions  9 A 1  to  91 E by the global shutter method by one readout operation with respect to the pixel array unit  91 . 
     2.2 Example of Circuit Configuration of Pixel 
     Next, an example of a circuit configuration of the pixel  101  according to the second embodiment will be described with reference to  FIG. 15 .  FIG. 15  is a circuit diagram illustrating an example of a circuit configuration of a pixel according to the second embodiment. 
     As illustrated in  FIG. 15 , each pixel  101  according to the second embodiment has a configuration in which a selection transistor  115  is added to a configuration similar to the circuit configuration described with reference to  FIG. 5  in the first embodiment. A gate of the selection transistor  115  is connected to a selection drive line to which a selection signal SEL is supplied from a row drive circuit  121 , a source of the selection transistor  115  is connected to a drain of an amplification transistor  114 , and a drain of the selection transistor  115  is connected to a vertical signal line  124 . 
     In addition, one pixel  101  in each of the regions  91 A to  91 E is connected to one vertical signal line  124 . 
     2.3 Example of Basic Operation of Pixel 
     Next, an example of a basic operation of the pixel  101  according to the second embodiment will be described with reference to a timing chart of  FIG. 16 .  FIG. 16  is a timing chart illustrating an example of an operation of a pixel according to the second embodiment. 
     As illustrated in  FIG. 16 , in an operation of reading out a pixel signal from each pixel  101 , first, a reset signal RST supplied from the row drive circuit  121  to the gate of the reset transistor  116  and a transfer signal TRG supplied from the row drive circuit  121  to the gate of the transfer transistor  113  are set to a high level in a period of timings t 11  to t 12 . As a result, an accumulation node  112  corresponding to a cathode of the photodiode  111  is connected to a power supply  118  via the transfer transistor  113  and the reset transistor  116 , and charges accumulated in the accumulation node  112  are discharged (reset). In the following description, this period (t 11  to t 12 ) is referred to as photodiode (PD) reset. 
     At this time, since a floating diffusion  117  is also connected to the power supply  118  via the transfer transistor  113  and the reset transistor  116 , charges accumulated in the floating diffusion  117  are also discharged (reset). 
     The reset signal RST and the transfer signal TRG fall to a low level at timing t 12 . Therefore, a period from timing t 12  till timing t 15  at which the transfer signal TRG next rises is an accumulation period in which a charge generated in the photodiode  111  is accumulated in the accumulation node  112 . 
     Next, during a period of timings t 13  to t 17 , the selection signal SEL applied from the row drive circuit  121  to the gate of the selection transistor  125  is set to a high level. As a result, a pixel signal can be read out from the pixel  101  in which the selection signal SEL is set to a high level. 
     In addition, during the period of timings t 13  to t 14 , the reset signal RST is set to a high level. As a result, the floating diffusion  117  is connected to the power supply  118  via the transfer transistor  113  and the reset transistor  116 , and charges accumulated in the floating diffusion  117  are discharged (reset). In the following description, this period (t 13  to t 14 ) is referred to as FD reset. 
     After the FD reset, a voltage in a state where the floating diffusion  117  is reset, that is, in a state where a voltage applied to the gate of the amplification transistor  114  is reset (hereinafter, referred to as a reset level) appears in the vertical signal line  124 . Therefore, in the present operation, for the purpose of noise removal by correlated double sampling (CDS), by driving the detection circuit  93  during a period of timings t 14  to t 15  when the reset level appears in the vertical signal line  124 , a pixel signal at the reset level is read out and converted into a digital value. Note that, in the following description, readout of the pixel signal at the reset level is referred to as reset sampling. 
     Next, during a period of timings t 15  to t 16 , the transfer signal TRG supplied from the row drive circuit  121  to the gate of the transfer transistor  113  is set to a high level. As a result, charges accumulated in the accumulation node  112  during the accumulation period are transferred to the floating diffusion  117 . As a result, a voltage having a voltage value corresponding to the amount of charges accumulated in the floating diffusion  117  (hereinafter, referred to as a signal level) appears in the vertical signal line  124 . Not that, in the following description, the transfer of the charges accumulated in the accumulation node  112  to the floating diffusion  117  is referred to as data transfer. 
     As described above, when the signal level appears in the vertical signal line  124 , by driving the detection circuit  93  during a period of timings t 16  to t 17 , a pixel signal at the signal level is read out and converted into a digital value. Then, by executing a CDS process of subtracting the pixel signal at the reset level converted into a digital value from the pixel signal at the signal level similarly converted into a digital value, a pixel signal of a signal component corresponding to an exposure amount to the photodiode  111  is output from the detection circuit  93 . Note that, in the following description, readout of the pixel signal at the signal level is referred to as data sampling. 
     2.4 Example of Schematic Operation of Flow Cytometer 
     Next, a schematic operation of a flow cytometer according to the second embodiment will be described with an example.  FIG. 17  is a timing chart illustrating an example of a schematic operation of the multispot type flow cytometer according to the second embodiment. 
     Note that, in the timing chart illustrated in  FIG. 17 , a detection signal of the forward scattered ray  73  or the like output from the photodiode  33  or the like (hereinafter, referred to as a PD detection signal) is indicated at an uppermost part, an example of a trigger signal generated on the basis of the PD detection signal is indicated at a next highest part, examples of fluorescent rays  7474 A to  74 E (actually, dispersed rays  75 A to  75 E of the fluorescent rays  74 A to  74 E) incident on the regions  91 A to  91 E of the pixel array unit  91 , respectively, are indicated at a next highest part, and a drive example of the image sensor  34  or a drive example of each of the regions  91 A to  91 D of the image sensor  34  is indicated at a lowermost part. 
     In addition, in the present description, a case where the irradiation spots  72 A to  72 E are arranged at equal intervals along the sample flow  52 , and a time interval until the specimen  53  that has passed through an irradiation spot on an upstream side passes through a next irradiation spot is 16 μs will be exemplified. 
     As illustrated in  FIG. 17 , in the flow cytometer  11 , a reset signal S 1  (corresponding to the above-described reset signal RST and transfer signal TRG) that resets the photodiode  111  of the image sensor  34  is output at a predetermined cycle (for example, 10 to 100 μs (microseconds)) during a period in which the forward scattered ray  73  is not detected by the photodiode  33 . That is, during the period in which the forward scattered ray  73  is not detected by the photodiode  33 , the PD reset for each pixel  101  is periodically executed. 
     Thereafter, when the light amount of the forward scattered ray  73  incident on the photodiode  33  decreases due to passage of the specimen  53  through the irradiation spot  72 A, the photodiode  33  generates an on-edge trigger signal D 0  at a timing when a PD detection signal P 0  falls below a predetermined threshold Vt, and inputs the on-edge trigger signal D 0  to the image sensor  34 . 
     The image sensor  34  to which the on-edge trigger signal D 0  is input stops periodic supply of the reset signal S 1  to the pixel  101 , and in this state, waits until the PD detection signal P 0  detected by the photodiode  33  exceeds the predetermined threshold Vt. When the supply of the reset signal S 1  immediately before the stop is completed, a charge accumulation period starts in each pixel  101  of the image sensor  34 . Note that the threshold Vt may be the same as or different from the threshold Vt for generating the on-edge trigger signal D 0 . 
     Thereafter, the photodiode  33  generates an off-edge trigger signal U 0  at a timing when the PD detection signal P 0  exceeds the predetermined threshold Vt, and inputs the off-edge trigger signal U 0  to the image sensor  34 . 
     In addition, while the specimen  53  is passing through the irradiation spot  72 A, the dispersed ray  75 A of the fluorescent ray  74 A emitted from the specimen  53  passing through the irradiation spot  72 A is incident on the region  91 A of the image sensor  34  as a pulse P 1  together with the decrease in the light amount of the forward scattered ray  73 . Here, in the image sensor  34 , as described above, when the on-edge trigger signal D 0  preceding the off-edge trigger signal U 0  is input to the image sensor  34 , the supply of the reset signal S 1  is stopped, and the accumulation period starts. Therefore, while the specimen  53  is passing through the irradiation spot  72 A, charges corresponding to the light amount of the pulse P 1  are accumulated in the accumulation node  112  of each pixel  101  in the region  91 A. 
     When the off-edge trigger signal U 0  is input to the image sensor  34 , the image sensor  34  first sequentially executes FD reset S 11 , the reset sampling S 12 , data transfer S 13 , and data sampling S 14  for each pixel  101  in the region  91 A. As a result, a spectral image of the dispersed ray  75 A (that is, fluorescent ray  74 A) is read out from the region  91 A. Hereinafter, a series of operations from the FD reset to the data sampling is referred to as a readout operation. 
     In addition, the dispersed rays  75 B to  75 E are incident on the regions  91 B to  91 E of the image sensor  34  as pulses P 2  to P 5  in accordance with passage of the specimen  53  through the irradiation spots  72 B to  72 E, respectively. Here, according to the assumption described above, a time interval at which the same specimen  53  passes through the irradiation spots  72 A to  72 E is 16 μs. 
     Therefore, the image sensor  34  executes a readout operation (FD reset S 21  to data sampling S 24 ) on the pixel  101  in the region  91 B 16 μs after the timing when the FD reset S 11  starts for the pixel  101  in the region  91 A. 
     Similarly, the image sensor  34  executes a readout operation (FD reset S 31  to data sampling S 34 ) on the pixel  101  in the region  91 C 16 μs after the timing when the FD reset S 21  starts for the pixel  101  in the region  91 B, further executes a readout operation (FD reset S 41  to data sampling S 44 ) on the pixel  101  in the region  91 D 16 μs after the timing when the FD reset S 31  starts for the pixel  101  in the region  91 C, and further executes a readout operation (FD reset S 51  to data sampling S 54 ) on the pixel  101  in the region  91 E 16 μs after the timing when the FD reset S 41  starts for the pixel  101  in the region  91 D. 
     By the above operation, the spectral images of the fluorescent rays  74 B to  74 E are read out from the regions  91 A to  91 E at intervals of 16 μs, respectively. 
     Then, when the readout of the spectral image from the region  91 E is completed and the on-edge trigger signal D 0  due to passage of a next specimen  53  is not input, the image sensor  34  supplies the reset signal S 1  again and executes periodic PD reset. Meanwhile, when the on-edge trigger signal D 0  due to passage of the next specimen  53  is input before the readout of the spectral image from the region  91 E is completed, the image sensor  34  executes operations similar to those described above, and thereby reads out the spectral images of the fluorescent rays  74 A to  74 E from the regions  91 A to  91 E at intervals of 16 μs, respectively. 
     2.5 Action and Effect 
     As described above, in the present embodiment, the pixel array unit  91  is divided into the plurality of (five in the present example) regions  91 A to  91 E in which the fluorescence spots  76 A to  76 E are formed, respectively, and readout by the global shutter method for each of the regions  91 A to  91 E is possible. Therefore, frame data read out in one readout operation can be reduced. As a result, a readout time at one time and a subsequent processing time for frame data can be largely reduced. 
     Other configurations, operations, and effects may be similar to those of the above-described embodiment or modifications thereof, and therefore detailed description thereof is omitted here. 
     Although the embodiments of the present disclosure have been described above, the technical scope of the present disclosure is not limited to the above-described embodiments as they are, and various modifications can be made without departing from the gist of the present disclosure. In addition, components of different embodiments and modifications may be appropriately combined with each other. 
     In addition, the effects of the embodiments described here are merely examples and are not limited, and other effects may be provided. 
     Note that the present technology can also have the following configurations. 
     (1) 
     An optical measuring device comprising: 
     a spectroscopic optical system that spectrally disperses a fluorescent ray emitted from a specimen that passes through each of a plurality of irradiation spots arrayed in a first direction in a second direction included in a plane parallel to the first direction; and 
     an image sensor that receives the fluorescent ray spectrally dispersed by the spectroscopic optical system and generates image data, wherein 
     the second direction is inclined with respect to a plane vertical to the first direction. 
     (2) 
     The optical measuring device according to (1), wherein an inclination of the second direction with respect to the plane vertical to the first direction is 30° or more and 60° or less. 
     (3) 
     The optical measuring device according to (1) or (2), wherein 
     the image sensor includes a plurality of pixels arrayed in a matrix, and 
     a row direction in the array of the plurality of pixels is inclined with respect to the plane vertical to the first direction. 
     (4) 
     The optical measuring device according to (3), wherein a direction in which the row direction is inclined with respect to the plane vertical to the first direction is the same as a direction in which the second direction is inclined with respect to the plane vertical to the first direction. 
     (5) 
     The optical measuring device according to (4), wherein an inclination of the row direction with respect to the plane vertical to the first direction is the same as an inclination of the second direction with respect to the plane vertical to the first direction. 
     (6) 
     The optical measuring device according to any one of (1) to (5), further comprising a plurality of excitation light sources that irradiates the irradiation spots with an excitation ray having a predetermined wavelength, respectively. 
     (7) 
     The optical measuring device according to (6), further comprising a flow path through which the specimen moves in the first direction, wherein 
     the plurality of irradiation spots is set on the flow path. 
     (8) 
     The optical measuring device according to (1), wherein 
     the image sensor includes: 
     a pixel array unit including a plurality of pixels arrayed in a matrix; and 
     a plurality of detection circuits connected to the plurality of pixels on a one-to-one basis. 
     (9) 
     The optical measuring device according to (8), wherein 
     the image sensor includes: 
     a pixel array unit including a plurality of pixels arrayed in a matrix; and 
     a plurality of detection circuits connected to two or more pixels in the same column in the plurality of pixels, wherein 
     the pixel array unit is divided into a plurality of regions arrayed in a column direction of the matrix, and 
     the detection circuits are connected to the pixels on a one-to-one basis in each of the plurality of regions. 
     (10) 
     An optical measuring system including: 
     a spectroscopic optical system that spectrally disperses a fluorescent ray emitted from a specimen that passes through each of a plurality of irradiation spots arrayed in a first direction in a second direction; 
     an image sensor that receives the fluorescent ray spectrally dispersed by the spectroscopic optical system and generates image data; 
     a signal acquisition unit that evaluates the image data generated by the image sensor; and 
     an analysis unit that analyzes the specimen on a basis of an evaluation result of the image data by the signal acquisition unit, wherein 
     the second direction is inclined with respect to a plane vertical to the first direction. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  SIGNAL ACQUISITION SYSTEM 
               2  ANALYSIS SYSTEM 
               11  FLOW CYTOMETER 
               31  FLOW CELL 
               32 A to  32 E EXCITATION LIGHT SOURCE 
               33  PHOTODIODE 
               34  IMAGE SENSOR 
               35 ,  36 A to  36 E CONDENSER LENS 
               37 A to  37 E SPECTROSCOPIC OPTICAL SYSTEM 
               371  OPTICAL ELEMENT 
               51  SAMPLE TUBE 
               52  SAMPLE FLOW 
               53  SPECIMEN 
               71 A to  71 E EXCITATION RAY 
               72 A to  72 E IRRADIATION SPOT 
               73  FORWARD SCATTERED RAY 
               74 A to  74 E FLUORESCENT RAY 
               75 A to  75 E DISPERSED RAY 
               76 A to  76 E FLUORESCENCE SPOT 
               91  PIXEL ARRAY UNIT 
               92  CONNECTION UNIT 
               93  DETECTION CIRCUIT 
               93 A,  93 B DETECTION CIRCUIT ARRAY 
               94  PIXEL DRIVE CIRCUIT 
               95  LOGIC CIRCUIT 
               96  OUTPUT CIRCUIT 
               101  PIXEL 
               111  PHOTODIODE 
               112  ACCUMULATION NODE 
               113  TRANSFER TRANSISTOR 
               114  AMPLIFICATION TRANSISTOR 
               115  SELECTION TRANSISTOR 
               116  RESET TRANSISTOR 
               117  FLOATING DIFFUSION 
               118  POWER SUPPLY 
               121  ROW DRIVE CIRCUIT 
               122  CONSTANT CURRENT CIRCUIT 
               124  VERTICAL SIGNAL LINE