JP2004311834A - Light receiving circuit, light quantity stabilizing circuit and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly responsive light receiving circuit where the selection of light receiving elements is not limited and a highly responsive light quantity stabilizing circuit where the stability of light quantity is improved, the fluctuation of light outputs is prevented, and any special circuit or the like is not necessary; and to improve picture quality by improving the light quantity stability of light outputs and the responsiveness of the light receiving elements. <P>SOLUTION: This light receiving circuit is provided with a light receiving element 16, a light diffusing member 14 arranged on the optical path of the front face of the light receiving element for diffusing incident lights, and a member 15 arranged between the light receiving element and the light diffusing member for stopping lights from the light diffusing member to the light receiving face of the light receiving element. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a light receiving circuit having improved responsiveness, a light quantity stabilizing circuit having improved light quantity stability and responsiveness, and an image forming apparatus.
[0002]
[Prior art]
2. Description of the Related Art In an image output apparatus in the medical and printing fields, a semiconductor laser (LD) or the like is used for image formation or the like, and a light amount stabilizing circuit is used to stabilize the light amount from this light source. An APC (Auto Power Control) circuit is often used as such a light amount stabilizing circuit (see Patent Document 1 below). The APC circuit is a method in which a light amount control signal is compared with a signal from a light receiving element such as a photodiode (PD) to control the light amount to be constant. Shooting and undershoot occur, which may cause damage to the semiconductor laser and adverse effects on images. In particular, an image output device that changes the density of an image according to the amount of light easily affects the image and may cause unevenness or the like. In addition, when the response of the photodiode deteriorates, a problem is likely to occur when measuring the amount of light at high speed.
[0003]
Further, in the APC circuit, it is required to prevent the optical output fluctuation caused by the mode hopping of the semiconductor laser. For this reason, Patent Document 1 described below discloses that a light diffusion plate is disposed in front of a light receiving surface of a photodiode to stabilize the light output of a semiconductor laser by preventing the detected light amount of a light receiving element from fluctuating. ing.
[0004]
Regarding photodiodes, it is known that the response speed is reduced due to carriers generated when light enters outside the PN junction plane of the semiconductor (outside the depletion layer around the PN junction) (see Patent Document 2 and Non-Patent Document 1).
[0005]
In order to suppress a decrease in the response speed of the photodiode, Patent Literature 2 below discloses that a short life region is provided in which the life of minority carriers contributing to a photocurrent causing a decrease in the response is shortened. Patent Document 3 discloses that a light-shielding film is formed on a light-receiving surface of a light-receiving element to prevent oblique incidence of external light and to prevent aging of electrical characteristics and a decrease in reliability.
[0006]
The countermeasures described in Patent Documents 2 and 3 are all based on the configuration of the light receiving element itself. For the light receiving element having no such configuration, another countermeasure is required. I will receive it.
[0007]
Patent Document 4 listed below discloses a laser driving device provided with a compensation circuit for performing frequency compensation and temperature compensation in a feedback unit in order to compensate for the effect of diffusion current of a photodiode and temperature characteristics and perform appropriate power control. ing. However, a special compensation circuit is required, and the APC circuit becomes complicated.
[0008]
[Patent Document 1]
JP-A-5-145163
[0009]
[Patent Document 2]
JP-A-5-13798
[0010]
[Patent Document 3]
JP-A-6-310697
[0011]
[Patent Document 4]
JP-A-5-121805
[0012]
[Non-patent document 1]
Catalog of photodiodes by Hamamatsu Photonics Co., Ltd.
[0013]
[Problems to be solved by the invention]
An object of the present invention is to provide a light receiving circuit capable of improving the responsiveness without being limited by the selection of the light receiving element in view of the above-mentioned problems of the related art.
[0014]
It is another object of the present invention to provide a light quantity stabilizing circuit that can improve the light quantity stability to prevent fluctuations in the light output, does not require a special circuit, and can improve the response.
[0015]
It is still another object of the present invention to provide an image forming apparatus capable of improving image quality by improving the stability of light quantity of light output and the response of light receiving elements.
[0016]
[Means for Solving the Problems]
In order to achieve the above object, a light receiving circuit according to the present invention includes a light receiving element, a light diffusing member disposed on an optical path in front of the light receiving element and diffusing incident light, the light receiving element and the light diffusing member. And a member disposed between the light-diffusing member and the light-diffusing member to restrict light from the light-diffusing member to a light-receiving surface of the light-receiving element.
[0017]
According to this light receiving circuit, by arranging the light diffusing member on the front surface of the light receiving element, it is possible to reduce the fluctuation in the amount of light due to the optical axis shift, thereby improving the assemblability of the light receiving circuit and reducing component costs. This is advantageous in cost. In addition, since the light diffusing member is arranged, even if light is obliquely incident on the light receiving surface, such a light incident can be limited by disposing a member for restricting the light between the light diffusing member and the light receiving element. Responsiveness can be improved. Therefore, the response can be improved without being limited by the selection of the light receiving element.
[0018]
In the light receiving circuit, the light receiving element and the member for stopping down the light may be integrally formed. Thus, the light receiving circuit can be made compact and the assemblability of the light receiving circuit can be improved.
[0019]
Further, the member for restricting the light can be constituted by a condenser lens or an aperture member having an aperture.
[0020]
In addition, the light receiving element has a region where current is generated by light irradiation, and the member that restricts the light restricts the incidence of light outside the region, so that the response of the light receiving element can be improved.
[0021]
It is preferable to use a PIN photodiode or a PN photodiode as the light receiving element. For example, a Schottky photodiode or an avalanche photodiode may be used.
[0022]
A light amount stabilizing circuit according to the present invention includes the light receiving circuit described above and a light source, wherein at least a part of the light amount from the light source is incident on a light receiving element of the light receiving circuit.
[0023]
According to this light amount stabilizing circuit, the light amount of the light source can be stabilized by making the light from the light source incident on the light receiving element, and the light diffusing member is arranged on the front surface of the light receiving element to assemble the light receiving circuit. In addition to improving the performance and cost, it is possible to prevent the light output from the light source from fluctuating. For example, when the light source is a semiconductor laser, it is possible to prevent the light output from fluctuating due to mode hopping. In addition, since the light diffusing member is arranged, even if the light tries to enter the light receiving surface obliquely, the light incident can be restricted by the member that restricts the light, so that the response of the light receiving element can be improved, and a special circuit is required. Since there is no light quantity stabilization circuit, the circuit does not become complicated.
[0024]
The light amount stabilizing circuit may include a beam splitter for directing a part of the light amount from the light source to the light receiving element. Although there is a possibility that interference occurs due to reflection on the front and back surfaces of the beam splitter, the influence of such interference can be prevented by disposing the light diffusing member.
[0025]
Further, it is preferable that a driving circuit for driving the light source is provided in accordance with a difference between an externally input light intensity command signal and an output signal from the light receiving circuit.
[0026]
By configuring the light source from a semiconductor laser, the light amount stabilizing circuit can be configured as a light amount stabilizing circuit of the semiconductor laser.
[0027]
An image forming apparatus according to the present invention includes the above-described light amount stabilizing circuit, and forms an image on a recording medium based on light from the light source. According to this image forming apparatus, the image quality can be improved by improving the light amount stability of the light output and the responsiveness of the light receiving element by the light amount stabilizing circuit described above.
[0028]
Another image forming apparatus according to the present invention has a light source, a light receiving element provided so that at least a part of the light amount from the light source is incident, and a light receiving surface of the light receiving element disposed on a front surface of the light receiving element. A light amount stabilizing circuit having a member for restricting light from the light source; and forming an image on a recording medium based on the light from the light source. According to this image forming apparatus, the image quality can be improved by improving the responsiveness of the light receiving element.
[0029]
In each of the above image forming apparatuses, the image density can be changed according to the amount of light from the light source. As described above, the light amount can be stabilized and the responsiveness can be improved, so that a change in image density due to a change in light amount can be prevented.
[0030]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, first to third embodiments of the present invention will be described with reference to the drawings.
[0031]
<First Embodiment>
[0032]
FIG. 1 is a diagram schematically showing a light receiving circuit according to the present embodiment. FIG. 2 is a diagram schematically showing another light receiving circuit according to the present embodiment.
[0033]
In the light receiving circuit of FIG. 1, light from a light source 11 such as a semiconductor laser enters a beam splitter 13 through a collimator lens 12, and a part of the incident light is reflected by the beam splitter 13 and enters a light diffusion member 14. The light diffused by the light diffusion member 14 is converged by the condenser lens 15 and then enters the light receiving surface 17 of the light receiving element 16.
[0034]
The light diffusing member 14 is a light diffusing plate or the like that diffuses incident light, and can be made of, for example, frosted glass, milky white glass, acrylic resin, or the like.
[0035]
The condenser lens 15 can be constituted by a convex lens or the like that focuses the incident light on the light receiving surface 17. Further, the condenser lens 15 may be formed integrally with the light receiving element 16.
[0036]
The light receiving element 16 is preferably composed of a PN photodiode or a PIN photodiode, but may be composed of various photodiodes such as a Schottky photodiode or an avalanche photodiode. Note that a photodiode is a light-receiving element in which current or voltage is generated by light incident on a PN junction (or PIN junction) of a semiconductor.
[0037]
In the light receiving circuit of FIG. 2, light from a light source 11 such as a semiconductor laser enters a beam splitter 13 through a collimating lens 12, and a part of the incident light is reflected by the beam splitter 13 and The light that is incident and diffused by the light diffusion member 14 is configured to be narrowed by the opening 18 a of the opening member 18 and then incident on the light receiving surface 17 of the light receiving element 16.
[0038]
The opening member 18 can be configured by forming an opening 18a in a member having no light transmission. Further, the opening member 18 may be formed integrally with the light receiving element 16.
[0039]
1 and 2, the light transmitted through the beam splitter 13 can be configured to be incident on a recording medium or the like for image formation, for example.
[0040]
According to the light receiving circuits of FIGS. 1 and 2, the following effects can be obtained by disposing the light diffusing member 14 on the optical path in front of the light receiving surface 17 of the light receiving element 16.
[0041]
(1) By arranging the light diffusing member, it is possible to reduce the fluctuation of the light amount with respect to the deviation of the optical axis. That is, even when the optical axis p is deviated from the center of the light receiving surface 17 of the light receiving element 16, the light amount fluctuation becomes very gentle by the light diffusing member 14, so that the light amount fluctuation due to the optical axis deviation can be reduced. Therefore, the adjustment at the time of assembling the light receiving circuit is simplified, and the assemblability of the light receiving circuit can be improved.
[0042]
(2) While interference may occur due to reflection on the front and back surfaces of the beam splitter 13, the arrangement of the light diffusing member 14 can prevent the influence of the interference.
[0043]
(3) When the light receiving circuit is applied to, for example, a light quantity stabilizing circuit (APC circuit) of a semiconductor laser as shown in FIG. 5 described later, it is possible to prevent a light output fluctuation when the semiconductor laser causes mode hopping.
[0044]
(4) An ND filter or the like can be used to reduce the light amount to an appropriate value. However, the light diffusion plate is cheaper and has a cost advantage because it does not require component costs.
[0045]
1 and 2, since the light diffusing member 14 is disposed, even if light is obliquely incident on the light receiving surface 17, the light diffusing member 14 is gathered as a member that restricts the light on the optical path between the light diffusing member 14 and the light receiving element 16. By arranging the optical lens 15 or the aperture member 18, such light incidence can be restricted, and the responsiveness of the light receiving element 16 can be improved. Therefore, since no countermeasures are taken for the internal configuration of the light receiving element, there is no need to select the light receiving element as in Patent Document 2 and the like when selecting the light receiving element, and there is no restriction.
[0046]
FIG. 3 shows an example of a layer configuration of a PN photodiode as the light receiving element 16. The PN photodiode shown in FIG. 3 includes an insulating layer 21, a P-type semiconductor layer 22, an N-type semiconductor layer 23, ⁺ The semiconductor layer 24 is formed in order, a PN junction surface 25 is formed between the P-type semiconductor layer 22 and the N-type semiconductor layer 23, and light enters from the light receiving surface 17 so that the PN junction surface 25 Can be taken out between the electrodes 20 and 27.
[0047]
When the light incident on the light receiving surface 17 of the photodiode reaches the PN junction surface 25, the light (photons) is immediately changed to a current (electrons and holes) at the PN junction surface 25. In FIG. 3, when light enters the PN junction surface 25 like light 31 in FIG. 3, the conversion from light to current is fast, but as shown in light 32, the PN junction surface 25 (exactly around the PN junction surface). It is considered that the response speed is reduced if the light is incident outside the depletion layer 26).
[0048]
Next, a description will be given of a decrease in the response of the photodiode as shown in FIG. 3 and an improvement thereof (see Non-Patent Document 1). The response speed of a photodiode is a value indicating how quickly generated carriers can be taken out as a current to an external circuit, and is usually expressed by a rise time (tr) or a cutoff frequency (fc). The rise time (tr) is a time when the output signal reaches 10% to 90%, and is determined mainly by the following elements (a) to (c).
[0049]
(A) Time constant (t1) of capacitance (Ct) between terminals of light receiving element and load resistance (RL)
(B) Diffusion time of carriers generated outside the depletion layer (t2)
(C) Carrier depletion layer running time (t3)
[0050]
Regarding the above (a), the inter-terminal capacitance (Ct) is the sum of the package capacitance and the photodiode junction capacitance Cj, and the time constant (t1) is expressed by the following equation (1).
[0051]
tl = 2.2 × Ct × RL (1)
[0052]
From the above equation (1), it can be seen that Ct or RL may be reduced to speed up t1. Cj is substantially proportional to the light receiving area A and inversely proportional to the square root to the cube root of the depletion layer width d. Since the depletion layer width d is proportional to the product of the reverse voltage VR and the specific resistance ρ of the substrate material, the following equation (2) holds.
[0053]
Cj {A} (VR + 0.5) × ρ} ^{−1/2 to − ／} ... (2)
[0054]
From the above equation (2), it can be seen that it is sufficient to apply a reverse voltage to a photodiode having a small A and a large ρ in order to speed up t1.
[0055]
Regarding the above (b), carriers generated outside the depletion layer are generated when incident light is absorbed around the chip deviating from the PN junction surface of the photodiode or at a substrate portion deeper than the depletion layer. The time (t2) required for these carriers to diffuse may be several μS or more.
[0056]
Regarding the above (c), the velocity vd at which the carrier travels in the depletion layer is expressed as vd = μE when represented by the mobility μ of the carrier and the electric field E in the depletion layer. The average electric field is E = VR / d (d: depletion layer width). Therefore, the time (t3) at which the carrier travels in the depletion layer can be approximated by the following equation (3).
[0057]
t3 = d / vd = d ² / (ΜVR) (3)
[0058]
From the above equation (3), it can be seen that it is necessary to shorten the traveling distance of the carrier or increase the reverse voltage in order to increase t3.
[0059]
The above elements (a), (b) and (c) determine the rise time (tr) of the photodiode, and the rise time (tr) can be approximated by the following equation (4).
[0060]
tr ≒ √ (t1 ² + T2 ² + T3 ² ) ・ ・ ・ (4)
[0061]
Further, the cut-off frequency (fc) is a frequency at which the output for a sine wave input from the semiconductor laser is attenuated by 3 dB from the output maintaining relatively 100%, and the rising time (tr) is expressed by the following equation (5). Can be approximated by
[0062]
tr ≒ 0.35 / fc (5)
[0063]
According to experiments and studies by the present inventor, when the incident light is narrowed down as shown in FIGS. 1 and 2 and when the incident light is incident as shown in FIG. It was confirmed that the response speed was reduced as shown in FIG. 4A when the light was expanded, and that the response speed was increased as shown in FIG. 4B when the incident light was narrowed as in the former case. The reason for this is that in FIG. 4A, light enters a portion other than the depletion layer near the PN junction surface around the chip of the light receiving element, and FIG. It is considered that the light incidence on the portion was restricted to make it difficult to enter.
[0064]
As described above, in the light receiving circuits of FIGS. 1 and 2, by disposing the condenser lens 15 or the aperture member 18 on the optical path between the light diffusing member 14 and the light receiving surface 17 of the light receiving element 16, FIG. In this case, it is possible to limit the oblique light incidence such as the light 32 that enters the outside of the depletion layer near the PN junction surface. For this reason, the light diffusion member 14 is arranged to obtain the above-described effects (1) to (4), and the light is diffused. , The response of the light receiving element 16 can be improved. Thus, the light amount can be measured at high speed by the light receiving element 16.
[0065]
As described above, by providing a member for focusing light on the front surface of the light receiving element, light is prevented from being incident on the outside of the depletion layer near the PN junction surface of the light receiving element 16, thereby improving the responsiveness of the light receiving element 16 and improving light diffusion. Providing the member 14 can improve light quantity stabilization.
[0066]
<Second embodiment>
[0067]
FIG. 5 is a basic circuit diagram of a light amount stabilizing circuit (APC circuit) of the semiconductor laser according to the present embodiment including the light receiving circuit of FIG. 1 or FIG.
[0068]
As shown in FIG. 5, the light quantity stabilizing circuit 40 of the semiconductor laser according to the present embodiment includes a light quantity command signal (modulation signal) S modulated based on an image signal and the like, and the light receiving element 16 of FIG. When the negative light receiving signal M fed back from is input to the adder / subtractor 41, the adder / subtracter 41 outputs a deviation signal indicating the deviation between them, and sends it to the drive current output circuit 42. The drive current output circuit 42 outputs a drive current I to the semiconductor laser 11 according to the increase or decrease of the light amount command signal, and drives the semiconductor laser 11 with the drive current I.
[0069]
Then, a part of the light emitted from the semiconductor laser 11 is incident on the light receiving surface 17 of the light receiving element 16 as shown in FIG. 1 or FIG. 2, and the received light signal M is sent to the adder / subtractor 41 to complete the closed loop.
[0070]
According to the semiconductor laser light quantity stabilizing circuit (APC circuit) as described above, when the light output of the semiconductor laser 11 fluctuates, the light receiving signal M increases or decreases according to the fluctuated light quantity, and the light quantity becomes constant. Since the deviation signal is output from the adder / subtractor 41 to the drive current output circuit 42, the amount of light output from the semiconductor laser 11 can be automatically stabilized.
[0071]
As described above, since the light quantity stabilizing circuit 40 of the semiconductor laser of FIG. 5 includes the light receiving circuit of FIG. 1 or 2, the light from the semiconductor laser 11 is made to enter the light receiving element 16 and the light from the light receiving element 16 is received. By feeding back the signal, the light amount of the semiconductor laser 11 can be stabilized. However, as described above, by disposing the light diffusing member 14 on the front surface of the light receiving element 16, the assemblability and cost of the light receiving circuit can be reduced. Since the light output from the light source can be prevented from fluctuating, the stability of the light amount can be improved.
[0072]
Further, since the oblique incidence of light on the light receiving surface can be restricted by the condenser lens 15 and the aperture member 18, the response of the light receiving element can be improved. As described above, since the light amount can be measured at high speed by the light receiving element, the feedback control based on the light receiving signal from the light receiving element in the light amount stabilizing circuit (APC circuit) 40 can be stably executed.
[0073]
Further, in Patent Document 4 described above, a compensation circuit such as frequency compensation is provided in the feedback unit. However, in FIG. 5, since the response can be improved without using such a special circuit, the light amount stabilization circuit is very simple. It is possible to adopt a simple configuration, and it is advantageous in terms of cost.
[0074]
<Third embodiment>
[0075]
FIG. 6 schematically shows an exposure unit of the image forming apparatus having the light quantity stabilizing circuit (APC circuit) of the semiconductor laser of FIG. 6, illustration of the light diffusion member 14 and the condenser lens 15 of FIG. 1 is omitted.
[0076]
The exposure unit 120 of the image forming apparatus shown in FIG. 6 includes the APC circuit 40 of the semiconductor laser shown in FIG. 5, and is provided with a semiconductor laser 11 driven based on a light amount command signal (image signal) S output from an image signal output device 45. The emitted laser light L of a predetermined wavelength is deflected by the rotating polygon mirror 113 to perform main scanning on the film F which is a sheet-shaped recording medium, and the film F is moved in the main scanning direction X with respect to the laser light L. The laser beam L is used to perform sub-scanning by relatively moving in a substantially perpendicular direction Y, and a latent image is formed on the film F using the laser beam L.
[0077]
6, a light amount command signal (image signal) S output from an image signal output device 45 is input to the APC circuit 40 in FIG. 5, and the semiconductor laser 11 is driven by a drive current I from the APC circuit 40. The laser beam L modulated by the image signal S from 11 is emitted. After passing through the collimating lens 12, a part of the laser light L is reflected by the beam splitter 13 and is incident on the light receiving surface 17 of the light receiving element 16, while passing through the beam splitter 13, and is only vertically transmitted by the cylindrical lens 115. The light is converged and is incident on the rotating polygon mirror 113 rotating in the direction of arrow A in FIG. 6 as a line image perpendicular to the drive shaft.
[0078]
The rotary polygon mirror 113 reflects and deflects the laser light L in the main scanning direction. After the deflected laser light L passes through an fθ lens 114 including a cylindrical lens formed by combining four lenses, the laser light L is focused on the optical path. The main scanning is repeated in the arrow X direction on the surface 117 to be scanned of the film F, which is reflected by the mirror 116 provided in the direction extending in the direction and conveyed in the arrow Y direction by the sub-scanning conveyance section 142 and is sub-scanned. Is done.
[0079]
As described above, the latent image based on the image signal S is formed on the film F by scanning the laser light L over substantially the entire surface to be scanned 117 on the film F. Thereafter, the latent image is visualized by subjecting the film F to a heat development process or a wet development process.
[0080]
According to the above-described image forming apparatus, since the light amount stabilizing circuit (APC circuit) 40 described above is included and the light amount stability of the light output of the laser light L and the responsiveness of the light receiving element can be improved, the film F The image quality of the formed image can be improved. Further, in the case of image formation in which the density of an image is changed in accordance with the amount of laser light, stabilization of the amount of light can be achieved and responsiveness can be improved as described above. .
[0081]
In particular, the responsiveness of light receiving elements such as photodiodes is improved, so that overshoot and undershoot are unlikely to occur, damage to the semiconductor laser and adverse effects on images can be prevented beforehand, and there is no effect on images and density unevenness. Can be prevented.
[0082]
Further, in an image forming apparatus in the field of medical and printing, a light amount fluctuation of several percent or less affects an image, and when the light amount changes, the image density fluctuates considerably. Therefore, stabilization of the light amount is very important. However, according to the image forming apparatus of FIG. 6, since the stabilization of the light amount can be reliably achieved, the image density fluctuation can be prevented by applying the image forming apparatus to the image forming apparatus in the medical and printing fields.
[0083]
For example, in the case of photosensitive materials (films, photographic papers, and the like) in the medical and printing fields, the light amount and the density are not proportional, and the light amount-density characteristic, which is the exposure characteristic of the photosensitive material, is generally linear as shown in FIG. It has a characteristic close to logarithm, and in the low light area and the high light area, the light quantity and the density have a relationship that the density does not change much even if the light quantity is changed, but in the medium light quantity area, the light quantity and the density are almost the same. Since there is a proportional relationship, the sensitivity of the density fluctuation to the light quantity fluctuation is high in the medium light quantity range. For this reason, if overshoot / undershoot that occurs when the response of the light receiving element is slow occurs in the medium light amount region, even a slight change in the light amount may cause a streak, image blur, or the like. Therefore, when forming an image on a photosensitive material (recording medium) such as a film or photographic paper having the exposure characteristics as shown in FIG. 8, it is essential to stabilize the amount of light and increase the response speed of the light receiving element. With this image forming apparatus, stable image formation is possible.
[0084]
Next, a modified example of the exposure unit of the image forming apparatus shown in FIGS. 5 and 6 will be described with reference to FIG. As shown in FIG. 7, in this example, the light diffusing member is omitted in the light receiving circuit of FIG. 1, and a condensing lens 15 is disposed in front of the light receiving element 16 as a member for restricting light. The light from the light source 11 is restricted. Note that an aperture member as shown in FIG. 2 may be provided instead of the condenser lens 15.
[0085]
By using the light amount stabilizing circuit (APC circuit) 40 of FIG. 5 to which the light receiving circuit of FIG. 7 is applied in the exposure unit of FIG. 6, the response of the light receiving element is improved. Is less likely to occur, and damage to the semiconductor laser and adverse effects on images can be prevented beforehand, and density unevenness can be prevented without affecting images.
[0086]
As described above, the present invention has been described with the embodiments, but the present invention is not limited to these, and various modifications can be made within the technical idea of the present invention. For example, in FIG. 2, the diffusion member and the opening member may be integrally formed.
[0087]
Also, the light receiving circuit as shown in FIGS. 1 and 2 can be applied to a light quantity measuring circuit for measuring the light quantity of a light source such as a semiconductor laser at a high speed. The image forming apparatus can also be applied to an apparatus that forms an image on a recording medium other than a film, such as paper or a sheet.
[0088]
【The invention's effect】
According to the present invention, it is possible to provide a light receiving circuit capable of improving responsiveness without being limited by selection of a light receiving element.
[0089]
In addition, it is possible to provide a light quantity stabilizing circuit that improves light quantity stability, prevents fluctuations in light output, does not require a special circuit, and can improve responsiveness.
[0090]
Further, it is possible to provide an image forming apparatus capable of improving the image quality by improving the stability of the light amount of the light output and the response of the light receiving element.
[Brief description of the drawings]
FIG. 1 is a diagram schematically showing a light receiving circuit according to a first embodiment.
FIG. 2 is a diagram schematically showing another light receiving circuit according to the first embodiment.
FIG. 3 is a diagram illustrating an example of a layer configuration of a PN photodiode as a light receiving element in FIGS. 1 and 2;
FIG. 4A is a diagram showing the response when the incident light is made incident on the photodiode as shown in FIG. 3 while being expanded, and the incident light is narrowed and made incident as shown in FIGS. 1 and 2; FIG. 7B is a diagram showing the response in the case.
FIG. 5 is a basic circuit diagram of a light quantity stabilizing circuit (APC circuit) of a semiconductor laser according to a second embodiment including the light receiving circuit of FIG. 1 or FIG.
6 is a diagram schematically showing an exposure unit of the image forming apparatus having the light quantity stabilizing circuit (APC circuit) of the semiconductor laser of FIG. 5;
FIG. 7 is a view for explaining a modification of the exposure unit of the image forming apparatus of FIG. 6;
FIG. 8 is a diagram schematically showing a light amount-density characteristic which is an exposure characteristic of a general photosensitive material.
[Explanation of symbols]
11 Light source, semiconductor laser
13 ... Beam splitter
14 ... light diffusion member
15 ... Condensing lens (member for restricting light)
16 ・ ・ ・ Light receiving element, photodiode
17 ... Light receiving surface
18 ··· Opening member (member for restricting light)
40: Light intensity stabilization circuit, APC (Auto Power Control) circuit
120 ・ ・ ・ Exposure unit

Claims (11)

A light receiving element, a light diffusing member disposed on an optical path in front of the light receiving element to diffuse incident light, and a light diffusing member disposed between the light receiving element and the light diffusing member with respect to a light receiving surface of the light receiving element. A light-receiving circuit, comprising: a member that restricts light from the diffusion member. The light receiving circuit according to claim 1, wherein the light receiving element and a member that restricts the light are integrally formed. The light receiving circuit according to claim 1, wherein the member that stops the light is a condenser lens. The light receiving circuit according to claim 1, wherein the member that restricts the light is an opening member having an opening. 5. The light-receiving element according to claim 1, wherein the light-receiving element has a region that generates a current by light irradiation, and the member that restricts the light restricts light incident outside the region. 6. Light receiving circuit. A light source, comprising: the light receiving circuit according to claim 1; and a light source, wherein at least a part of a light amount from the light source is incident on a light receiving element of the light receiving circuit. Light stabilization circuit. The light quantity stabilizing circuit according to claim 6, further comprising a beam splitter for directing a part of the light quantity from the light source to the light receiving element. 8. The light amount stabilizing circuit according to claim 6, further comprising a driving circuit that drives the light source in accordance with a difference between an externally input light amount command signal and an output signal from the light receiving circuit. An image forming apparatus comprising the light amount stabilizing circuit according to claim 6, wherein an image is formed on a recording medium based on light from the light source. A light source, a light receiving element provided so that at least a part of the light amount from the light source is incident thereon, and a member arranged on the front surface of the light receiving element and for narrowing light from the light source to a light receiving surface of the light receiving element, A light amount stabilizing circuit having
An image forming apparatus for forming an image on a recording medium based on light from the light source. The image forming apparatus according to claim 9, wherein a density of the image is changed according to a light amount from the light source.

Images