JP2009204944A - Diffraction optical element, lighting system, and sensor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a diffraction optical element that is easily processed and hardly undergoes variation in characteristic dependently on the arrangement accuracy, and to provide a compact and inexpensive lighting system and sensor device. <P>SOLUTION: In a multi-stage diffraction optical element having condensing power and a plurality of diffraction zones, the number of condensing positions of primary light of each diffraction zone is at least two or more, and the diffraction efficiency of the primary light is the highest. The plurality of diffraction zones may have a concentric orbicular zone, or may have a linear lattice. The diffraction optical element 1 includes the same focal position, and the number of groups of one or more adjacent orbicular zones or zones is required to be at least larger than the number of condensing positions. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a diffractive optical element, an illuminating device, and a sensor device. For example, the present invention can be used for detecting a displacement of a measurement object in a digital copying machine or the like.

  There are many sensors that detect changes in the measurement target position by irradiating the measurement target position with a light beam and detecting the intensity and wavelength distribution of reflected light from the measurement target. For example, in a digital copying machine or a laser printer, the sensor is used to detect the position of a toner patch to be measured on an intermediate transfer belt in order to correct a color shift or magnification of an output image. In order to improve the position detection accuracy by such a sensor, or to allow a sufficient amount of light to reach the sensor, the illumination light is condensed near the measurement position, that is, the measurement target position, using an optical element such as a lens. Is often done.

  When condensing using a normal lens, a sharp light spot is obtained at the focal position. It spreads and the desired performance cannot be obtained. That is, a sufficient amount of illumination light cannot be irradiated to the measurement object.

  In order to solve such a problem, for example, it is conceivable to use a multifocal aspherical lens described in Patent Document 1. If this multifocal aspherical lens is used, the curvature of the lens, which is an optical element that collects and irradiates the illumination light on the measurement object, can be changed depending on the irradiation region, and the depth of focus can be increased.

  However, when a sensor is incorporated in a device such as a copying machine or a laser printer, it is described in Patent Document 1 in light of the current situation in which a reduction in size is required so that the sensor does not interfere with other mechanisms in the device. It is difficult to adopt technology. In particular, when the lens itself becomes small, for example, with a diameter of 1 mm or less, it becomes difficult to produce a desired aspherical shape.

  Further, as in the invention described in Patent Document 1, when the curvature of the lens is changed depending on the region to be irradiated, the range from the difficulty of processing to the extent of changing the curvature at the center and the periphery of the lens is at most realizable. . In this case, when the light distribution of the light source, that is, the direction of the maximum light amount and the emission angle characteristic of the light amount change, the characteristic after passing through the lens changes.

In order to solve these problems, it is conceivable to use a multifocal diffractive lens described in Patent Document 2 instead of an ordinary lens or an aspherical lens described in Patent Document 1. The multifocal diffractive lens described in Patent Document 2 is characterized in that a diffractive surface is provided with a number of optical heights and lows. If the multifocal diffractive lens described in Patent Document 2 is used, the focal depth is increased by utilizing the difference in focal length due to the difference in diffraction order, and a sufficient amount of illumination light is irradiated over the entire illumination light irradiation area of the measurement target. There is a possibility that you can.
However, the difference in focal length due to the difference in diffraction order is too large in the case of low-order diffracted light, and the focal point is formed at a completely different position for each diffraction order, so that the depth of focus cannot be increased. .

A possible solution to this problem is to use higher-order diffraction orders, but in this case, it is not possible to achieve efficiency unless a multi-stage diffraction grating is used. This is a trade-off with securing.
The difficulty of processing can be alleviated by reducing the power of the diffraction grating, but as the power decreases, the focal length increases and the size of the apparatus increases.
Although it is possible to supplement the power of the diffraction grating by providing a lens on the surface opposite to the diffractive optical element, there arises a processing problem that both surfaces of the lens must be processed with high accuracy.

Japanese translation of PCT publication No. 2002-522803 Japanese Laid-Open Patent Publication No. 7-198909

  The present invention has been made in view of these problems of the prior art, and aims to realize a diffractive optical element that is compact, easy to process, and whose characteristics do not easily change depending on placement accuracy, a compact, low-cost illumination device, and sensor device. And

The present invention is a multi-stage diffractive optical element having a condensing power and having a plurality of diffraction bands, wherein the primary light condensing positions of each diffraction band are at least two or more positions, and the primary light The most important feature is that the diffraction efficiency of each is the highest.
The multistage diffractive optical element may have a concentric annular zone as a plurality of diffraction zones.
The multistage diffractive optical element may have a linear grating as a plurality of diffraction bands.

  The diffractive optical element may have the same focal position, and one or more adjacent annular bands or groups of bands may be at least more than the number of condensing positions.

  An illuminating device according to the present invention includes a light source including a semiconductor laser or a light emitting diode and the diffractive optical element.

  The sensor device according to the present invention includes a detection member positioned within a range of a plurality of light collection positions of the illumination device, and a detection element that detects reflected light from the detection member. .

According to the present invention, in the multistage diffractive optical element, the primary light in each diffraction band is condensed at least at two or more positions, and the diffraction efficiency of the primary light is maximized, so that processing is easy. Thus, it is possible to obtain a diffractive optical element whose characteristics hardly change depending on the element arrangement.
According to the multistage diffractive optical element having concentric ring zones as a plurality of diffraction bands, a point-like condensing optical element can be obtained.
According to a multistage diffractive optical element having a linear grating as a plurality of diffraction bands, a linear converging diffractive optical element can be obtained.

  According to the diffractive optical element having the same focal position and having one or more adjacent annular bands or groups of bands at least more than the number of converging positions, the focal position given by the incident position of the light beam is dispersed, and the incident light flux Thus, it is possible to obtain an optical element in which the characteristic of the emitted light beam is not easily changed by the change in the light distribution (the direction of the maximum light quantity, the emission angle characteristic of the light quantity). The most prominent example of this configuration is a configuration in which the focal lengths of adjacent annular zones or bands are all different.

According to the illuminating device including the light source composed of the semiconductor laser or the light emitting diode and the diffractive optical element according to the present invention, a small and low-cost light source device whose characteristics are hardly changed by the arrangement of each element can be obtained.
According to the sensor device of the present invention, since the illumination device, the detected member within the range of the plurality of condensing positions of the illumination device, and the detection element that detects the reflected light from the detected member are included. Thus, it is possible to obtain a small and low-cost sensor whose characteristics hardly change depending on the element arrangement.

Embodiments of a diffractive optical element, an illumination device, and a sensor device according to the present invention will be described below with reference to the drawings.
FIG. 1 is a cross-sectional view of an embodiment of a diffractive optical element according to the present invention, and is an enlarged view in the vicinity of an axis of symmetry O. FIG. The diffractive optical element 1 according to this embodiment is configured so as to form phase irregularities on a transparent substrate and apply phase modulation to the light beam. More specifically, the diffractive optical element 1 is a multistage diffractive optical element having a condensing power and a diffraction grating surface having a plurality of diffraction bands.

  As an example, a multi-stage diffractive optical element having concentric ring zones as a plurality of diffraction bands can be configured by rotating the cross-sectional shape shown in FIG. 1 around the symmetry axis O. . According to this multistage diffractive optical element, incident light can be collected at a point.

  As another example, a multistage diffractive optical element having a linear grating as a plurality of diffraction bands can be obtained by extending the cross-sectional shape shown in FIG. According to this multistage diffractive optical element, incident light can be condensed linearly.

The diffractive grating surface of the diffractive optical element 1 shown in FIG. 1 has a four-step relief diffractive optical element in which the unevenness constituting each diffraction band is formed in four stages. The thickness d of the relief is given by assuming that the refractive index of the element is n and the wavelength of the light beam is λ.
λ / (n-1)
It is.

In the illustrated embodiment, the light is phase-modulated by forming irregularities on the transparent substrate, but phase modulation may be applied by means such as giving a refractive index distribution to the substrate itself.
As the number of stages of phase modulation increases, the light collection efficiency increases. However, since the processing becomes difficult as the number of stages increases, an arbitrary number of stages can be selected from the required light quantity and cost.

In the example of the diffractive optical element shown in FIG. 1, symbols R1, R2, and R3 represent one cycle of each diffraction band. Also,
R1, R3,..., R2j + 1 are focal lengths f1 (= f3,..., F2j + 1),
R2, R4,..., R2j are focal lengths f2 (= f4,..., F2j)
That is, it is configured to have two focal lengths and two condensing positions. However, the target focal length may be three or more, and the order of the target focal lengths may be changed. Further, in FIG. 1, the hatched portion indicates the target light collection state of each diffraction band.

また、幾何学的関係から式（２）が得られる。
式２

The design method of the diffractive optical element according to the above structure is as follows.
Assuming that the −1st order diffracted light is collected, Expression (1) is obtained from the lattice equation.
Formula 1

Moreover, Formula (2) is obtained from geometric relationship.
Formula 2

式（３）をｉ＝１から順次解くことにより、ｈｉを求めることができる。
また、同心円状の輪帯または直線状の格子からなる上記回折帯の一周期内の構造は−１次光の回折効率が最大となるように適宜設計すればよい。 Equation (3) is obtained from Equation (1) and Equation (2).
Formula 3

By solving Equation (3) sequentially from i = 1, hi can be obtained.
Further, the structure within one period of the diffraction band composed of concentric circular zones or linear gratings may be appropriately designed so that the diffraction efficiency of the −1st order light is maximized.

FIG. 4 shows a simulation result of a change in light quantity with respect to defocus, normalized by the light quantity at 0 mm defocus (corresponding to a distance of 5 mm from the element) of the multistage diffractive optical element according to the above example. The amount of light is the amount of light collected in a square area of 2.5 mm on a side with the focal point as the center. The simulation conditions here are as follows.
Light source wavelength: 733 nm
Refractive index of substrate: 1.457
Diameter of diffractive optical element: 1 mm
Focal length of normal diffractive optical element: 5mm
Focal length of the diffractive optical element according to the present invention: 4.7 mm, 5.3 mm

  As is apparent from FIG. 4, it can be seen that the change in the amount of light is small even when defocusing is performed, according to the diffractive optical element of the present invention, compared to a normal diffractive optical element.

  FIG. 2 shows an embodiment of a light source device using a diffractive optical element according to the present invention. In FIG. 2, a light emitting element 2 and a measurement surface 3 that is a light receiving surface of the light receiving element are arranged with the diffractive optical element 1 interposed therebetween. A measurement surface 3 is disposed on the diffraction grating surface side of the diffractive optical element 1. As the light emitting element 2, it is desirable to use a small-sized LED or a semiconductor laser having a narrow wavelength range of light rays. Since the diffractive optical element 1 configured as described above has a wide depth of focus, an illuminating device having a small change in light amount over the entire illumination light irradiation region even when the positional relationship between the diffractive optical element 1 and the measurement surface 3 is shifted is obtained. Can do.

  FIG. 3 shows an embodiment of a light detection sensor using the illumination device according to the present invention. The light detection sensor according to this embodiment is a toner detection sensor 9 that detects the position of a toner patch to be measured on an intermediate transfer belt in order to correct color shift and magnification of an output image in a digital copying machine or a laser printer. Is configured. In FIG. 3, it is desirable to use an LED or a semiconductor laser that is small and has a narrow wavelength range of light rays as the light emitting element 2. The diffractive optical element 1 having a diameter of about several millimeters is engraved on a transparent substrate 4 such as glass or resin in order to collect light from the light source 2 at a measurement position. The diffractive optical element 1 is a light source side diffractive optical element in the embodiment of the light detection sensor. A sensor-side diffractive optical element 8 that condenses the reflected light from the measurement position on the optical sensor 5 is engraved on the transparent substrate 4. The sensor-side diffractive optical element 8 may have the same shape as the light-source-side diffractive optical element 1, or may be a normal single-focus diffractive optical element or a spherical or aspherical lens shape.

  In FIG. 3, reference numeral 6 denotes a sheet-like image forming body on which a toner image 7 is formed. This image forming body 6 is a toner from an image carrier such as a photoconductor in a copying machine or a printer to a transfer paper. It may be an intermediate transfer member that conveys the toner or the transfer paper itself. The image forming body 6 is disposed so as to pass through the measurement surface by the light detection sensor. When the toner image 7 placed on the image forming body 6 moves to the measurement position along with the movement of the image forming body 6, the light reflected by the toner image 7 is transmitted through the sensor side diffractive optical element 8. The light enters the optical sensor 5. The light is condensed on the light receiving surface of the optical sensor 5 by passing through the diffractive optical element 8. When the toner image 7 moves to the measurement position, the amount of light felt by the optical sensor 5 changes, and the position of the toner image 7 is known by this change.

  According to the embodiment of the light detection sensor, since the diffractive optical element 1 is used as the light source side diffractive optical element, the image forming body 6 fluctuates in the vertical direction or the toner detection sensor 9 is ideally attached. Even if it is deviated from, the optical sensor 5 can sufficiently obtain light necessary for detection.

It is an expanded sectional view which shows the Example of the diffractive optical element concerning this invention. It is an optical arrangement | positioning figure which shows the Example of the light source device using the diffractive optical element concerning this invention. It is an optical arrangement | positioning figure which shows the Example of the photon detection sensor using the light source device concerning this invention. It is a graph which shows the simulation result of the light quantity change with respect to the defocus of the multistage diffractive optical element concerning an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Diffractive optical element 2 Light emitting element 3 Measurement surface 4 Transparent substrate 5 Optical sensor 6 Image forming body 7 Toner image 8 Sensor side diffractive optical element

Claims (6)

A multistage diffractive optical element having a condensing power and having a plurality of diffraction bands,
A diffractive optical element, wherein the primary light in each diffraction band has at least two condensing positions, and the primary light has the highest diffraction efficiency. A multistage diffractive optical element having condensing power and having concentric annular zones as a plurality of diffraction bands,
1. A diffractive optical element characterized in that at least two or more positions of primary light condensing positions in each annular zone are the highest and diffraction efficiency of primary light is the highest. A multistage diffractive optical element having a focusing power and having a linear grating as a plurality of diffraction bands,
A diffractive optical element, wherein the primary light in each diffraction band has at least two condensing positions, and the primary light has the highest diffraction efficiency.   4. The diffractive optical element according to claim 2, wherein the number of adjacent one or more annular zones or groups of bands having the same focal position is at least greater than the number of light collecting positions.   An illumination apparatus comprising: a light source comprising a semiconductor laser or a light emitting diode; and the diffractive optical element according to claim 1. The illuminating device according to claim 5, and a member to be detected that is positioned within a range of a plurality of condensing positions by the illuminating device,
A sensor device comprising a detection element for detecting reflected light from the detected member.

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