JP2007180563A - Laser light source - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser light source capable of reducing color density difference and color difference in the image. <P>SOLUTION: A laser array light source 40 is structured in such a manner that a sub-mount 44 is joined with an adhesive 46 on a heat sink 42 and a laser array chip 48 is mounted on the sub-mount 44 via a contact electrode 50. A trench 54 is formed between each of light-emitting points 52. In addition, a trench 58 is formed on each position corresponding to the trench 54 on the sub-mount 44. The trenches 54 and 58 make the thermal interference resistance between each laser higher than the thermal resistance between the laser array chip 48 and heat sink 42, thus improving the heat dissipation performance for reduction of light volume variations between each laser. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a laser array light source, and more particularly to a laser light source provided in an optical scanning device including a laser array, such as a laser printer or a copying machine.

  In recent years, color image forming apparatuses such as laser printers and copiers using semiconductor lasers have become more compact and less expensive in addition to high-speed and high-quality printing. High-speed and high-quality printing is achieved by increasing the speed by arranging a plurality of optical scanning devices with laser light sources for each color or using a laser array that emits a plurality of laser beams of each color from a single light source. This is achieved by increasing the density of scanning lines.

  FIG. 20 shows a so-called tandem type image forming apparatus in which a plurality of optical scanning devices are arranged for each color. An image forming apparatus 100 shown in FIG. 20 is arranged in parallel in the conveyance direction of the recording paper, and a photosensitive drum 104 that forms an electrostatic latent image on the surface by receiving a laser beam exposure by an optical scanning device described later. A charger 150 such as a corotron for charging the photosensitive drum 104 and Y (yellow) and M (magenta) obtained by performing predetermined processing on color data of R (red), G (green), and B (blue). ), C (cyan), K (black), an optical scanning device 102 that emits a laser beam modulated based on image data, and a cylindrical mirror that guides the laser beam emitted from the optical scanning device 102 to the photosensitive drum 104. 152, a developing unit 154 that develops the electrostatic latent image formed on the photosensitive drum 104 with toners of Y, M, C, and K, respectively, and a recording paper 156 that is a photosensitive member. A conveying belt 158 that conveys the toner images of the respective colors formed on the photosensitive drum 104 onto the recording paper 156, and a cleaner 160 that removes toner remaining on the photosensitive drum 104. And a fixing roll 162 for fixing the transfer image of the recording paper 156 after the transfer of each color is completed.

  However, as shown in FIG. 20, in the configuration in which the optical scanning device 102, the photosensitive member 104, the charger 150, the developing device 154, the cleaner 160, etc. are provided for each color, the distance L1 between the outermost photosensitive members 102 is as follows. There is a problem that the length of the image forming apparatus 100 increases and the size of the image forming apparatus 100 increases.

  FIG. 21 shows an image forming apparatus using a laser array that emits a plurality of laser beams of respective colors from a single light source. An image forming apparatus 107 shown in FIG. 21 includes a semiconductor laser array (not shown) that emits four laser beams 106 and a polygon mirror that reflects and deflects the four laser beams 106 emitted from the semiconductor laser array in common. 164, the reflecting mirror 166 for guiding the four deflected beams reflected and deflected by the polygon mirror 164 in a predetermined direction, and the four laser beams 106 reflected by the reflecting mirror 166 are respectively focused in the main scanning direction to be photosensitive drums. A combination of an fθ lens 168 that scans the exposure line 108 at a constant speed, a prism having four incident surfaces at different angles, and four mirrors, and four laser beams 106 that have passed through the fθ lens 168 are combined. A prism type reflecting mirror 170 that separates in a direction corresponding to the arrangement position of the photosensitive drums 108 and the prism type reflecting mirror 17. A reflection mirror 172 that guides the four laser beams 106 separated by 0 to the corresponding photosensitive drums 108 and a cylindrical lens 174 that focuses the four laser beams 106 reflected by the reflection mirror 172 in the sub-scanning direction, respectively. It is configured.

  However, as shown in FIG. 21, when a laser array light source that emits a plurality of laser beams 106 from a single light source (not shown) is used, a plurality of laser beams are optically allocated. There was a problem that the optical path design was complicated. Further, although not shown in the figure, related devices such as a cleaner and a developing device are arranged between the photosensitive drums 108, and therefore the distances between the photosensitive drums 108 are determined. Since the reflection mirror 172 is arranged in accordance with the position of the photosensitive drum 108, the distance L1 between the outermost reflection mirror 172 is the distance L2 between the outermost reflection mirror 172 and the imaging position of the photosensitive drum 108. There is a problem that the size of the optical scanning device 107 is increased.

  In order to prevent such an increase in the size of the image forming apparatus and an increase in the size of the optical scanning device, for example, Patent Document 1 proposes image forming apparatuses 101, 103, and 105 as shown in FIGS. Yes.

  An image forming apparatus 101 shown in FIG. 22 includes an optical scanning device 11 that emits four laser beams modulated based on Y, M, C, and K image data, and four optical beams emitted from the optical scanning device 11. And a photosensitive drum 32 that respectively forms an electrostatic latent image on the surface by exposure with the laser beam.

  The optical scanning device 11 includes a laser array light source 12 that emits four adjacent laser beams 13, a collimator lens 14 that converts the four diffusing laser beams emitted from the laser array light source 12 into parallel beams, and a collimator A cylindrical lens 16 that focuses the four laser beams that have passed through the lens 14 in the sub-scanning direction, a reflection mirror 18 that reflects the four laser beams that have passed through the cylindrical lens 16 in a predetermined direction, and a reflection mirror 18. The polygon mirror 20 that reflects and deflects the four reflected laser beams in a predetermined direction and the four laser beams reflected and deflected by the polygon mirror 20 are focused in the main scanning direction and the sub-scanning direction, respectively. The fθ lens 22 that scans the exposure line at a constant speed and the fθ lens 22 pass through. The four laser beams reflected in a predetermined direction and the four laser beams supported on the emission window support member 25 and reflected by the reflection mirror 24 in accordance with the arrangement position of the photosensitive drums 32 are reflected. A light separating polygon mirror 26 that separates in the direction and a final mirror (cylindrical mirror) 28 that guides the four laser beams separated by the light separating polygon mirror 26 to the corresponding photosensitive drums 32, respectively.

  The light separating polygonal mirror 26 passes through the centers of the four incident laser beams and is symmetric with respect to the plane parallel to the optical axis of these laser beams. Each of the two surfaces is arranged at an angle, and has a reflecting surface that reflects four incident laser beams in four different directions. The reflection angle of the reflection surface is set so that the optical path lengths from the laser array light source 12 to the photosensitive drum 32 are equal, including the position of the final mirror 28, according to the arrangement position of the photosensitive drums 32.

  The final mirror 28 passes through the centers of the four laser beams incident on the light separating polygon mirror 26, is symmetric with respect to a plane parallel to the optical axis of the laser beams, and is based on the arrangement position of the photosensitive drums 32. The optical path lengths from the laser array light source 12 to the photosensitive drum 32 including the relationship with the reflection angle of the reflection surface of the light separating polygon mirror 26 are arranged at positions set to be equal. Further, the distance L1 between the final mirrors 28 arranged on both outer sides is set to be smaller than twice the distance L2 between the final mirror 28 and the imaging position of the photosensitive drum 32.

  The photosensitive drums 32 are arranged with a small center-to-center distance L3 because the transfer efficiency to the transfer medium in the transfer part is designed to be 100%, and the cleaner and the waste toner storage part are unnecessary.

  Further, as shown in FIG. 22, the laser array light source 12 is controlled by the control device 15. Further, the control device 15 includes an APC circuit (not shown), and monitors the output (the amount of light of the laser beam) of a photodiode (not shown) for detecting the back beam of the laser beam 13 provided in the laser array light source 12. In addition, so-called APC (Auto Power Control) control can be performed to adjust the light amount so that the light amount becomes a predetermined light amount, and the on / off timing of each laser beam is controlled according to the input image signal. .

  Next, the image forming apparatus 103 shown in FIG. 23 will be described. The same parts as those in the image forming apparatus 101 shown in FIG.

  The image forming apparatus 103 includes a cylindrical lens 30 that uses the final mirror 28 as a reflection mirror and focuses the laser beam reflected by the final mirror 28 in the sub-scanning direction.

  Next, the image forming apparatus 105 shown in FIG. 24 will be described. The same parts as those in the image forming apparatus 101 shown in FIG.

  The image forming apparatus 105 has a configuration in which the photoreceptor 32 is disposed on the intermediate transfer drum 34 and the transfer roll 36 is disposed below the intermediate transfer drum 34.

  In these image forming apparatuses, each laser beam 13 from the laser array light source 12 that emits four laser beams is used for Y (yellow) color, M (magenta) color, C (cyan) color, K ( Black) is assigned to each color, and each laser beam is incident substantially parallel to the photosensitive member 32 provided for each color, whereby an image for four colors is formed by one optical scanning device. Further, in these image forming apparatuses, the toner images formed on the photoconductors 32 for the respective colors are sequentially superimposed on the intermediate transfer body and then transferred onto a sheet at a time. can do.

Further, in the above image forming apparatus, the distance L1 between the final mirrors 28 arranged on both outer sides is set to be smaller than twice the distance L2 between the final mirror 28 and the image forming position of the photosensitive drum 32. Therefore, the final mirror 28 and the like can be integrated with other scanning optical systems, and the optical scanning device can be miniaturized.
Japanese Patent Laid-Open No. 10-20608

  However, if a laser array light source with a large amount of light fluctuation due to thermal interference is used in these image forming apparatuses, or a laser emission light amount region with a large amount of light amount fluctuation is used, the density difference or color difference of each color in the sub-scanning direction. May occur. This point will be described with reference to FIG.

  FIG. 25 shows the laser lighting timing of each channel in the laser array light source 12 that emits four laser beams 13 and the light quantity of the laser beam irradiated to each photoconductor. The channel Ch1 is for M color, the channel Ch2 is for Y color, the channel Ch3 is for K color, and the channel Ch4 is for C color.

  As shown in FIG. 25, first, before image formation, the light is forcibly lit in order from the channel Ch1, and the light amount is adjusted by the APC control so that the light amount becomes the level of P1. When an SOS signal (scanning start signal) for each color is input, each laser beam is turned on / off according to the image signal for each color.

  Here, even if the amount of light of the laser beam is adjusted to the level of P1 by APC before image formation, the amount of light of each laser beam decreases due to thermal interference of the laser array as each laser beam is sequentially turned on. For example, the light amount of the laser beam from the channel Ch1 is caused by thermal interference as the laser beams from the channels Ch2 to Ch4 are turned on, and the light amount is reduced as shown in P21, P31, and P41 as shown in FIG. . This decrease in light amount (difference in light amount with respect to P1) appears as a density difference and a color difference.

  The present invention has been made in view of the above facts, and an object of the present invention is to provide a laser light source capable of suppressing the density difference and color difference of images.

  The inventor investigated the relationship between the light quantity fluctuation of the laser array and the density difference of each color and the color difference in the image forming apparatuses 101, 103, and 105 shown in FIGS. The result as shown in FIG.

  FIGS. 18 and 19 show the relationship between the light amount variation ΔP (%) of the laser array and the density difference ΔD and the relationship between the light amount variation ΔP and the color difference ΔEcmc in the M color, which has the highest human relative sensitivity. Yes. These experimental results are results obtained by adjusting the light amount fluctuation of the laser array in a plurality of stages (six stages in FIGS. 18 and 19), creating print samples, and measuring the colors. Each print sample was visually confirmed by 10 subjects and evaluated whether or not the density difference and color difference could be recognized. When the light amount fluctuation ΔP was about 9% (the density difference ΔD was about 0). In the case of .04), 50% of the people recognized that the difference in density occurred, but the result was that it was a level at which they did not care. When the light amount fluctuation ΔP becomes larger than this, a density difference and a color difference that can be detected with the naked eye are generated.

  Therefore, in order to achieve high image quality with the image forming apparatus as shown in FIGS. 22 to 24, it is necessary to suppress the light quantity fluctuation caused by the thermal interference of the laser array, and preferably the light quantity fluctuation ΔP is about 9% or less. It is necessary to suppress it.

  Accordingly, the laser array light source according to the first aspect of the present invention includes a plurality of light emitting regions that emit a plurality of laser beams and that are arranged along a predetermined direction intersecting with an emission direction of the laser beams. A laser array provided with a first groove in between, and a second groove provided at a position corresponding to the first groove provided so that at least a part of the laser array is in contact with a predetermined position in the predetermined direction. A heat sink for dissipating heat generated in the laser array via the provided submount, and the thermal resistance in the predetermined direction between the light emitting regions is from the light emitting region to the heat sink. It is characterized by being larger than the thermal resistance in the direction crossing the predetermined direction.

  According to this invention, the laser light source includes a plurality of light emitting regions that emit a plurality of laser beams and that are arranged along a predetermined direction intersecting the laser beam emitting direction, and the first groove between the light emitting regions. Is provided. That is, a plurality of laser beams are emitted from a single laser light source. In addition, the laser light source is provided via a submount in which at least a part of the laser array is in contact with a predetermined position in a predetermined direction and a second groove is provided at a position corresponding to the first groove. A heat sink for dissipating the heat generated in the heat sink is provided. The heat sink may be provided so as to be in contact with the laser array in a predetermined direction.

  And the thermal resistance of the predetermined direction between light emitting areas is larger than the thermal resistance of the direction which cross | intersects the predetermined direction in a heat sink from a light emitting area. This reduces the area between the light emitting regions by providing a first groove between the light emitting regions and providing a second groove at a position corresponding to the first groove of the submount provided on the heat sink, This can be realized by increasing the distance between the light emitting regions.

  Thus, since the thermal resistance between the light emitting regions is larger than the thermal resistance from the light emitting region to the heat sink, the heat generated by the laser beam emitted from the light emitting region can easily escape to the heat sink side, and the heat dissipation is improved. Thereby, the light quantity fluctuation | variation of each laser beam can be suppressed.

  As described above, according to the present invention, the image density difference and the color difference can be made inconspicuous, and the degree of freedom in designing the optical scanning device can be increased.

[First Embodiment]
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. First, a laser array suitable for an image forming apparatus that irradiates a corresponding photosensitive member with a plurality of laser beams emitted from a single laser light source such as the image forming apparatuses 101, 103, and 105 shown in FIGS. The light source will be described.

  FIG. 1A shows a plan view of a laser array light source 40 according to the present invention, and FIG. 1B shows a cross-sectional view of the laser array light source 40.

  In the laser array light source 40, as shown in FIG. 1B, a submount 44 is bonded on a heat sink 42 with an adhesive 46, and a laser array chip 48 is mounted on the submount 44 via a contact electrode 50. It has been configured.

  The laser array chip 48 has a configuration in which an n layer, an active layer, a p layer, and the like (not shown) are sequentially stacked from the top, and each light emitting point arranged along a predetermined direction intersecting the laser beam emission direction. Between 52, trenches (grooves) 54 extending from the p layer to the n layer are formed. In the submount 44, trenches 58 are formed at positions corresponding to the trenches 54, respectively. A p-electrode 56 is formed on the p-layer corresponding to each light emitting point 52, and the p-electrode 56 is connected to the contact electrode 50. Further, as shown in FIG. 1A, a lead pattern electrode 50 </ b> A is drawn from each contact electrode 50, and this is connected to an external electrode 62 by a connection wire 60. Further, an n-electrode 64 is formed on the surface opposite to the p-electrode 56, and the n-electrode 64 is connected to the heat sink 42 through a connection wire 60 as shown in FIG. .

  Next, conditions satisfied by the laser array light source 40 will be described. First, a description will be given of light amount fluctuation when attention is paid to an arbitrary laser of a general laser array light source.

  If the amount of heat generated during self-lighting of an arbitrary laser is ΔTi, ΔTi is expressed by the following equation.

ΔTi = Iopi × Vopi × α × Ri × (1-EXP (t / (Ri × Ci)) (1)
Here, Iopi is an operating current (mA) at an arbitrary light amount P, Vopi is an operating voltage (V) at an arbitrary light amount P, Ri is a thermal resistance (K / W), Ci is a heat capacity (J / K), and i Is a natural number (i = 1, 2, 3,... N) and indicates a laser number. For example, ΔT ₁ indicates the amount of heat generated when the first laser is turned on, and Iop1 indicates the operating current at the light amount P of the first laser. The thermal time constant τi of the laser is expressed as Ri × Ci. Α is a correction coefficient specific to the laser array depending on the number of lights. When multiple lasers are turned on at the same time, heat is more difficult to escape than when the lasers are turned on alone, and the thermal resistance increases. Therefore, when the thermal resistance when the laser is turned on alone is Ri, n lasers are turned on. The thermal resistance at this time can be expressed by n × Ri.

  Further, ΔTrj is expressed by the following equation, where ΔTrj is the amount of heat flowing from a laser lighted on the jth (j is a natural number, j = 1, 2, 3,..., N: i ≠ j) other than the i-th laser. .

ΔTrj = Iopj × Vopj × Rrj × (1-EXP (t / (Rrj × Crj)) (2)
Where Rrj is the thermal resistance (K / W) due to thermal interference, and Crj is the thermal capacity (J / K) due to thermal interference. The thermal time constant τrj is expressed as Rrj × Crj. When there are three or more lasers to be turned on, the amount of heat flowing into the i-th laser is the total heat amount obtained by adding up ΔTrj in the above equation (2), that is, the total amount of heat from all the lasers turned on other than the i-th laser. and it becomes a sum of the self-heating value, when the total amount of heat and [Delta] T _Iall, [Delta] T _Iall is expressed by the following equation.

ΔT _iall = ΔTi + ΣΔTrj (3)
For example, when there are four lasers, the total amount of heat flowing into the first laser is ΔT _1all = ΔT ₁ + ΔT _r2 + ΔT _r3 + ΔT _r4 .

  From the above, assuming that the light amount fluctuation of the i-th laser is ΔPldi, ΔPldi is expressed by the following equation.

ΔPldi = ηi × (Iopi−Ithi × Exp ((ΔTi + ΣΔTrj) / T0i)) (4)
However, ηi is slope efficiency (W / A), Ithi is threshold current (mA), and T0i is characteristic temperature (K).

  In the above formula (4), the case of i = 1 and n = 1 is a formula for fluctuation of light quantity when there is one laser, that is, a single laser. That is, the above equation (4) is an extended equation including the case of a single laser.

  From the above formulas (3) and (4), when each laser is turned on for a laser array having the same cavity structure as that of a single laser, the amount of light fluctuation is single due to the amount of heat ΔTij due to thermal interference from adjacent lasers. It must be larger than a laser. This reduces the light transmission design range of the optical scanning device designed in the range of the amount of light emitted from a single laser, and causes a change in the optical design and, in some cases, an increase in the cost of the optical scanning device.

  Further, when an image forming apparatus using such a laser array distributes each beam to Y color, M color, C color and K color as shown in FIG. Image density changes and color changes occur when increasing or decreasing. In particular, if the difference between the heat generation characteristics and the heat dissipation characteristics of each laser in the laser array is large, the difference in light quantity variation between the lasers increases, resulting in a problem that the color difference of the composite color is different.

  From the above, in the image forming apparatus shown in FIGS. 22 to 24, the ideal conditions for the laser array not to affect the image quality are that the heat generation amount of each beam is uniform and low, and the thermal interference is small. In addition, even if thermal interference occurs, the amount of change in the amount of heat between the beams is small.

  FIG. 2 shows a conventional four-beam laser array light source 110. 2A is a plan view of the laser array light source 110, and FIG. 2B is a cross-sectional view of the laser array light source 110.

  As shown in FIG. 2B, the laser array light source 110 has a configuration in which a submount 114 is bonded to a heat sink 112 with a conductive adhesive 116, and a laser array chip 118 is mounted on the submount 114. It has become.

  The laser array chip 118 has a configuration in which an n layer 120, an active layer 122, a p layer 124, and an insulating layer 126 are sequentially stacked on a submount 114. An insulating part 130 reaching the layer 120 is formed. Further, electrodes 132 are formed on the p layer 124 corresponding to each light emitting point 128, and a connection wire 134 is connected to each electrode 132 so that it can be connected to an external electrode. In addition, the dotted line part in the figure has a multilayer structure with an insulating layer interposed therebetween, and is configured such that the electrodes do not contact each other.

  The thermal resistance value of the laser array light source 110 has a certain range. This is because the ratio of the area in contact with the heat sink 112 that contributes to heat dissipation is small with respect to the heat generation amount that increases as the number of lasers turned on. Because it becomes. In addition, the thermal resistance R between objects is represented by the following formula.

R = (1 / k) × (L / S) (5)
Here, k is the thermal conductivity between the objects, L is the length between the objects, and S is the contact area between the objects.

  FIG. 11 shows the relationship between the laser emission light amount (mW) of the laser array light source 110 and the light amount fluctuation ΔP (%), and FIG. 12 shows the relationship between the number of laser lighting and the normalized light output ratio.

  Note that the light amount fluctuation ΔP shown in FIG. 11 is a pulse lighting with a frequency of 600 Hz and a duty of 10% and 90%, and when the laser array light source package temperature is about 60 ° C. Is the ratio of the amount of convergent light and the peak amount of light when it is lit at a duty of 10%.

  In addition, the normalized light quantity ratio shown in FIG. 12 indicates that when the package temperature of the laser array light source is about 25 ° C., the light quantity when the output light output of each laser is kept constant is 1, and the number of lighting is increased. It shows the ratio of the laser output light power when

  As can be seen from FIGS. 11 and 12, the light amount fluctuation ΔP increases in proportion to the number of lasers to be turned on, and the light amount fluctuation ΔP rapidly decreases as the emitted light amount of each laser increases.

  Next, the heat flow around the laser array chip of the laser array light source 110 will be described.

  As shown in FIG. 2, when a plurality of lasers are turned on, the heat flow components A are a heat flow component A flowing from the laser array chip 118 to the heat sink 112, a heat flow component (thermal interference) B between the lasers, and a heat flow component C flowing as an atmosphere to the outside. The heat flow component D flowing from the connection wire 134 to the external electrode can be classified.

The contribution ratio of the heat flow component C and the heat flow component D to the heat flow flowing in the laser array light source 110 can be obtained from the ratio of the heat resistance of the laser array light source 110 and the heat resistance of each main constituent material. When the calculation is performed assuming that the heat flow flowing in the laser array light source 110 is 100%, the heat flow component C is about 1.7% or less and the heat flow component D is about 1.5% or less. A specific calculation case is dry air, N ₂ gas, which is an enclosed gas in the confidential terminal package in which the laser array light source 110 is housed, and a gold wire having a diameter of 28 μm and a length of 1 mm for the connection wire 134.

  Thus, the heat flow components C and D are very small with respect to the heat flow flowing in the laser array light source 110, and it can be seen that the heat flow components A and B are dominant in the heat flow when the laser is turned on.

  FIG. 3 shows a simple thermal resistance equivalent circuit in the thermal saturation state obtained by using the relationship between the heat flow and the thermal resistances Ri and Rrj.

  As shown in FIG. 3, the thermal resistance simple equivalent circuit 140 includes heat sources Ch1 to Ch4 corresponding to the lasers, and heat flows I1 to I4 flow from the heat sources Ch1 to Ch4. Further, switches SW1 to SW4 are connected to the heat sources Ch1 to Ch4. The state where this switch is turned on corresponds to the state where the laser is turned on. Thermal switches R1 to R4 are connected to the switches SW1 to SW4, respectively, a thermal interference thermal resistance R12 is provided between the thermal resistance R1 and the thermal resistance R2, and a thermal resistance R2 is provided between the thermal resistance R2 and the thermal resistance R3. The interference thermal resistance R23 is connected between the thermal resistance R3 and the thermal resistance R4, respectively. Moreover, the thermal resistance Rs of the heat sink 112 is connected to each thermal resistance R1-R4. In FIG. 3, the heat flows flowing through the respective thermal resistances R1 to R4 are indicated by i1 to i4, the heat flows flowing through the respective thermal interference thermal resistances R12, R23, and R34 are indicated by i12, i23, i34, and the heat flows flowing through the heat sink 112 are indicated by is ing.

  When the calorific value of each laser is set to Q1, Q2, Q3, and Q4 from such a simple thermal resistance equivalent circuit 140, the necessary conditions for the ideal laser array light source described above are as follows.

  Condition 1: Heat generation of each laser is substantially uniform and small.

Q1 ≒ Q2 ≒ Q3 ≒ Q4 and Q1 → 0
Condition 2: The heat dissipation of each laser is substantially uniform and small.

R1≈R2≈R3≈R4 and R1 → 0
Condition 3: Thermal interference between lasers is small.

R12, R23, R34 → ∞
As prior art relating to the conditions 1 and 2, there are techniques described in Japanese Patent No. 2622029 and Japanese Patent No. 2677219. Further, in order to realize the ideal state of Condition 3, it is necessary to separate adjacent lasers with a gas such as gas, but it is extremely difficult to realize with a laser array in which the lasers are close to each other. This is because there is no inexpensive technique for placing chips with submicron accuracy for each laser.

The laser array light source according to the present invention has a laser structure that substantially satisfies the conditions 1 and 2, and the relationship between the conditions 2 and 3 is reviewed to newly satisfy the condition 4 shown below.
Condition 4: R1≈R2≈R3≈R4 <R12, R23, R34
However, the relationship between R12, R23, and R34 is arbitrary.

The condition 4 is a condition for increasing the heat flow flowing through the heat sink 112 and reducing the heat interference component than the heat flow flowing between the lasers. In addition, as shown below, the following conditions may be used as subordinate conditions of Condition 4.
Condition 4 ′: R1≈R2≈R3≈R4 <R12≈R23≈R34
Condition 4 ″: R1≈R2≈R3≈R4 <R12≈R34 <R23
Condition 4 ′ is a condition in which the heat flow flowing in the heat sink 112 is made larger than the heat flow flowing between the lasers to reduce the heat interference component, and the thermal interference thermal resistances are made substantially equal. Condition 4 ″ is that the heat flow flowing in the heat sink 112 is made larger than the heat flow flowing between the lasers to reduce the heat interference component, the heat interference heat resistances R12 and R34 are made substantially equal, and the heat interference heat resistance R23 This is a condition for reducing the thermal interference at the center side.

  In condition 4 ′, the difference in thermal resistance between the lasers is substantially uniform, so that variation in heat inflow when a large number of lasers are turned on can be suppressed. Therefore, the saturation temperature difference due to the lighting pattern decreases, and 2 in the image plane. The color difference between the secondary colors and the color difference between the tertiary colors can be reduced.

  This will be briefly described with reference to FIG. In FIG. 25, when the heat dissipation of the heat generated by lighting each laser is different, the light amount convergence values P21, P31, P41, P22, P32,. For example, in the conventional laser array light source 110 as shown in FIG. 2, the heat radiation balance between the lasers on both ends (Ch1 and Ch4) and the lasers on the center (Ch2 and Ch3) is different. P32-P22 is different, and the light amount fluctuation difference is divided into two states. In this state, Ch1 is set to M color, Ch2 is set to Y color, Ch4 is set to C color, and two lasers are turned on to create an RGB composite color. Then, R color (MY composite color) and G color (YC composite) B color (MC composite color) is formed at a density different from that of (color). In addition, when trying to form a uniform full-color image in a plane with three colors using laser arrays having different heat dissipation characteristics, the one-color lighting area, two-color lighting area, and three-color lighting area differ in the sub-scanning direction. In addition to the mixed light quantity fluctuation, the number of light quantity fluctuation states at the time of saturation of each laser increases, and the combined color difference in the sub-scanning direction becomes larger than the laser array with uniform heat dissipation. Moreover, in an actual color print image, the shades of various color image outputs are dealt with by the blinking operation of each laser, so the number of thermal light quantity fluctuation states of each laser constantly changes, resulting in a very large number of complicated light quantity fluctuation states. .

  In order to reduce such complicated fluctuations in the amount of light, it is necessary to use a laser array in which the heat dissipation of each laser is substantially uniform and the heat dissipation difference between the lasers is equal. In this case, adverse effects such as density difference and color difference with respect to the color image are reduced.

  That is, in the case of condition 4 ′, the relationship between the amounts of light in FIG. −P31.

  Condition 4 ″ is a further improvement in the balance of thermal interference than condition 4 ′. This is because there is a difference in the heat radiation of the laser on both ends and inside, and the influence of the thermal interference is smaller at the end laser. For example, when the thermal interference thermal resistance value is increased for every two beams, each laser approaches the heat radiation property of the laser at the end portion, so that the difference in light quantity fluctuation between lasers due to thermal interference can be reduced.

  In order to verify this, let us calculate the impedance for each Ch in the simplified thermal resistance equivalent circuit shown in FIG. In order to simplify the calculation, as shown in FIG. 4, the thermal resistance to the heat sink is all R1, and the thermal resistance between lasers is R2.

  For example, an equivalent circuit when Ch1 is turned on is shown in FIG. 4, and a combined impedance Zch1 of this circuit is shown by the following equation.

Zch1 = R1 (R2 + Z2) / (R1 + R2 + Z2) + Rs (6)
However, Z2 = R1 (R2 + Z2) / (R1 + R2 + Z2)
Z1 = R1 (R1 + R2) / (2R1 + R2)
An equivalent circuit when Ch2 is turned on is shown in FIG. 5, and a combined impedance Zch2 of this circuit is shown by the following equation.

Zch2 = R1 (R1 + R2) (R2 + Z1) / (R1 (R2 + Z1) + (R1 + R2) (R2 + Z1) + R1 (R1 + R2)) + Rs
... (7)
However, Z1 = R1 (R1 + R2) / (2R1 + R2)
FIG. 6 shows the relationship between R2 / R1 and Zch2 / Zch1 when the thermal resistance R1 is an input parameter. FIG. 27 shows the relationship between R2 / R1 and the light quantity variation ΔP. As shown in FIG. 27, it can be seen that the light quantity variation ΔP decreases as R2 / R1 increases, that is, as the thermal interference thermal resistance R2 becomes larger than the thermal resistance R1. Also, the closer Zch2 / Zch1 is to 1, the smaller the difference in the combined thermal resistance between the lasers, so that the light quantity fluctuation difference can be further suppressed, but as R2 / R1 becomes larger as shown in FIG. Zch2 / Zch1 approaches 1 and the light quantity fluctuation difference can be suppressed.

  As is apparent from FIG. 6, the change in Zch2 / Zch1 is large when R2 / R1 <1, that is, when the thermal interference thermal resistance R2 is smaller than the thermal resistance R1. This indicates that since the thermal resistance due to the thermal interference between the lasers is small, the temperature change due to the inflow of heat from the adjacent lasers becomes large, and the difference in light quantity fluctuation when each laser is turned on becomes large. The laser array light source in this region, that is, the laser array light source whose thermal interference thermal resistance R2 is smaller than the thermal resistance R1 causes a large light amount fluctuation difference even with a small thermal resistance change such as a variation in thermal resistance when the laser array chip is bonded. It is a thermally unstable structure. Therefore, the thermally stable region is a region where R2 / R1 is greater than 1, and the laser array light source having a structure in which the thermal interference thermal resistance R2 is greater than the thermal resistance R1 suppresses the difference in light amount fluctuation. be able to. Specifically, for example, the distance between the lasers is longer than the distance from the laser to the heat sink.

  Also, since Zch2 / Zch1 is a combined impedance ratio of thermal resistances, a structure in which Zch2 / Zch1 = 1 is obtained in order to obtain a laser array light source having a good heat dissipation balance with little change in the amount of heat between lasers. It is preferable to make it.

  From the above, in order to obtain a laser array light source with little fluctuation in light quantity, thermally stable, and good balance of heat dissipation, a structure in which R2 / R1 is 3 or more, for example, as shown in FIG. It is preferable.

  Although the above verification can be carried out using condition 4, it is cheaper to create a laser array of condition 4 ′, and since the heat radiation balance is better than a laser array satisfying condition 4, The effect of suppressing the density difference and color difference of the color print due to the pattern change is high, and the condition 4 ′ is more practical.

  Although the above case was a verification with a 4-beam laser array, if the heat generation characteristics of each laser are uniform and the heat dissipation characteristics of each laser are symmetrical, even if the number of lights that can be lit increases, If there is a relationship of R2> R1 between the lasers, the same kind of effect is brought about.

  The laser array light source 40 according to the present invention has a structure that substantially satisfies the conditions 1 to 3 and substantially satisfies the condition 4 '. That is, by reducing the contact area S between the lasers by the trenches 54 provided in the laser array chip 48 and the trenches 58 provided in the submount 44, the thermal interference between the lasers is reduced and the heat flows through the heat sink 42. In this structure, the heat flow is increased, and the distance L1 between the lasers is made substantially uniform, so that the heat interference resistance is made substantially uniform, thereby improving the heat dissipation.

  Such a laser array light source 40 is manufactured as follows. First, an AlGaAs buffer layer, an n-AlGaAs cladding layer, a Multi-Quantum-Well layer, and a p-AlGaAs cladding layer are epitaxially grown on an n-type GaAs substrate (all not shown), and then a laser emission region ( On the light emitting point 52) shown in FIG. 1B, p-AlGaAs stripes (not shown) corresponding to the number of light emission (4) are formed by photolithography, and an n-type AlGaAs current confinement layer and a p-type are formed by 2nd epitaxial growth. A cap layer (both not shown) is formed, and ohmic properties are further improved by diffusion of impurities such as Zn. Then, a p-electrode 56 is deposited so that current can be individually supplied to each laser by photolithography etching.

  The points to be noted here are that the properties of each laser as a heat source are substantially equal, and in order to satisfy the condition 1 as much as possible, the light emitting point interval L1 is constant, and the above formulas (1) and (4) are used. In order to make the parameters of Iopi, Vopi, ηi, Ithi, and T0i the same in each laser, the structure parameters and impurity setting parameters of the active layer and the stripe portion including the light emitting point are made common. Further, the laser light emission structure is configured such that the absolute value of the characteristic temperature T0 of each laser is adjusted to a band gap structure so that the absolute value becomes relatively large (for example, 150K or more), and the heat generation amount of each heat generation source is suppressed.

  Next, in order to electrically and optically separate the lasers (between the light emitting points), as shown in FIG. 1B, trenches 54 are formed between individually formed p electrodes 56. The trench 54 uses an anisotropic etching such as reactive ion etching when the distance L1 between light emitting points is relatively short, and uses a chemical etching method when the distance L1 between light emitting points is relatively long. Cut to a depth that reaches the GaAs substrate. The deeper the trench 54, the higher the thermal resistance between the lasers. However, in the subsequent back surface polishing, the substrate is cut in a range where the substrate is not damaged.

  After the trench 54 is formed, backside polishing is performed to reduce the thickness of the substrate to about 0.1 mm, for example, and an n-electrode 64 is formed on the polished backside, and the substrate is cleaved into a bar shape. Resonator mirrors (not shown) are deposited on both surfaces perpendicular to the laser oscillation direction of the laser, and the bar is cleaved to form each laser.

The submount 44 has moderate insulating properties and a material having higher thermal conductivity than GaAs (0.54 W / K · cm ² ), such as Si, AlN, Al ₂ O ₃ , BeO, SiC, SiC (including BeO), and the like. A substrate obtained by dividing a substrate whose main component is A is used. On the mounting surface side of the submount 44 with the laser array chip 48, a contact electrode (Au-based, Al-based) 50 having the same size as the p-electrode 56 of the laser array chip 48 is deposited. Then, a lead pattern electrode 50A drawn from the contact electrode 50 as shown in FIG. 1A is formed so that the contact electrode 50 and the external electrode 62 can be connected. The lead pattern electrode 50A is connected to the external electrode 62 by a connection wire 60 made of a gold wire.

  Note that a PbSn solder or the like (not shown) is further formed as a bonding layer on the contact electrode 50 on the submount 44 by electroplating, and the back mount is polished to a thickness equivalent to that of the laser array chip 48. In addition, as shown in FIG. 1B, a trench 58 is formed in the submount 44 in contact with the laser array so as to increase the thermal resistance between the lasers. Further, the thermal resistance between the lasers may be adjusted by making the size of the lead pattern electrode 50A formed on the submount 44 different between the lasers.

  The ohmic contact between the laser array chip 48 and the submount 44 aligns the p-electrode 56 of the laser array chip 48 and the PbSn solder portion (not shown) of the submount 44 by heat treatment by self-alignment.

  The submount 44 on which the laser array chip 48 thus manufactured is surface-mounted is bonded to the heat sink 42. The adhesive 46 is bonded by applying a heating adhesive to the heat sink 42 by potting and heating the submount 44 on which the laser array chip 48 is mounted. In addition, it is preferable to use a conductive material with low thermal resistance for the heating adhesive. As the heat sink 42, a one having a structure integral with the T0 tube type confidential package stem and a Kovar material (Cu material) was used.

  FIG. 7 shows an example of a general T0 tube type package 70. 7A shows a top sectional view of the T0 tube type package 70, and FIG. 7B shows a side view of the T0 tube type package 70 with the window cap 72 shown in FIG. 7A removed. It is shown.

  As shown in FIG. 7B, the T0 tube type package 70 has a configuration in which the laser array light source 40 is provided on a stem 74 and this is packaged by a window cap 72 as shown in FIG. 7A. ing. A window portion 76 is provided on the upper portion of the window cap 72, and a glass 78 is bonded to the inside of the window cap 72 corresponding to the window portion 76 with a sealing adhesive 80. The laser beam is emitted from the window 76.

  The stem 74 is mounted with a PiN silicon photodiode chip 82 for detecting the amount of the back beam of the laser beam emitted from the laser array chip 48. The submount 44 on which the laser array chip 48 is surface-mounted is mounted. After surface mounting on the heat sink 42, the lead pattern electrode 50A formed on the submount 44 and the external electrode 62, and the n electrode 64 of the laser array chip 48 and the ground electrode are electrically connected to each other by gold wire bonding.

  Finally, the window cap 72 is connected to the stem 74 by electric welding or heat welding, thereby completing the production of the laser array light source 40.

  As a structure satisfying the condition 4 ', a structure as shown in FIG. 8 may be used. The laser array light source 41 shown in FIG. 8 has no trench in the submount 44, and the depth of the trench 54 provided in the laser array chip 48 is the depth of the trench 54 of the laser array light source 40 shown in FIG. Although it is shallower than this, the distance L2 between the lasers is made longer than the distance L1 between the lasers of the laser array light source 40 shown in FIG. The heat radiation performance is improved by making the thermal interference resistance substantially equal by making the distance L2 between the lasers substantially equal.

  In this way, by increasing the distance L2 between the lasers, the distance H2 between the light emitting point 52 and the heat sink 42 is changed to the distance H1 between the light emitting point 52 and the heat sink 42 of the laser array light source 40 shown in FIG. Can be made smaller. In addition, since the submount 44 is not provided with a trench, it can be manufactured at low cost.

  Further, a structure satisfying the condition 4 ″ may be adopted. A laser array light source having such a structure is shown in FIGS.

  In the laser array light source 43 shown in FIG. 9, the depth of the central trench 54 is deeper than the depth of the trenches 54 on both sides. Others are the same as the laser array light source 40 shown in FIG. That is, the laser array light source 43 makes the central trench 54 deeper than the trenches 54 on both sides, thereby making the thermal interference thermal resistance between the two light emitting points on both sides substantially equal, and this thermal interference resistance. In this structure, the heat radiation is improved by increasing the thermal interference thermal resistance between the central light emitting points.

  The laser array light source 45 shown in FIG. 10 has no submount 44, the laser array chip 48 and the heat sink 42 are bonded by an insulating adhesive 46, and a trench 57 is formed at the center of the heat sink 42. Is provided.

  In the laser array light source shown in FIGS. 1, 8, and 9, there is an insulating submount 44 between the heat sink 42 and the laser array chip 48, and the groove processing is performed in the case where the submount 44 is grooved. In order to increase the thermal resistance between the lasers more than the thermal resistance between the laser array chip 48 and the heat sink 42 (thermal resistance in the direction crossing the predetermined direction), the above equation (5) is used. As can be seen from the above, the thermal conductivity K2 of the submount 44 may be made higher than the thermal conductivity K1 of the laser array chip 48. Further, the relationship between the distance L1 (or L2) between the lasers and the distance H1 (or H2) from the light emitting point 52 to the heat sink 42 is large because the effect of the magnitude relationship of the thermal conductivity ratio K2 / K1 is large (K2 / K1)> (H1 / L1) or (K2 / K1)> (H2 / L2) may be satisfied.

  FIG. 13 shows the relationship between the laser emission light quantity (mW) and the light quantity fluctuation ΔP (%) in the laser array light source according to the present invention, and FIG. 14 shows the number of lasers lit and the standard in the laser array light source according to the present invention. FIG. 15A shows the relationship between the laser output light ratio and the relationship between the light emission amount (mW) of Ch1 and the light amount fluctuation ΔP during the thermal interference of the laser array light source according to the present invention. ) Shows the relationship between the amount of laser emitted light (mW) of Ch2 and the amount of light fluctuation ΔP at the time of thermal interference of the laser array light source according to the present invention. 13 and 14 is the same as that shown in FIGS. 11 and 12.

  Further, the light amount variation ΔP shown in FIG. 15 is the peak light amount when the laser array light source is driven with a pulse whose duty is approximately 50% close to the operating condition of the image forming apparatus to which the laser array light source according to the present invention is applied. It is a ratio to the convergent light quantity. The reason for selecting Ch1 and Ch2 is that, in the case of a four-beam laser array light source, since the heat dissipation structure is symmetrical, Ch1 and Ch4 and Ch2 and Ch3 can be regarded as substantially the same, and Ch1 and Ch2 are selected sufficiently. That's why.

  As shown in FIG. 13, in the case of the laser array light source according to the present invention, the light amount fluctuation ΔP is reduced by about 50 to 60% compared with the conventional laser array light source shown in FIG. I can see that. That is, as shown in FIG. 26, it can be seen that ΔP is improved by about 50% when the laser emission light quantity is around 0.4 mW. Further, the difference in light amount fluctuation between the lasers (Ch) is about 8% at maximum (difference in ΔP when the laser emission light amount is around 0.4 mW) in the conventional laser array light source as shown in FIG. In the laser array light source according to the present invention, as shown in FIG. 13, the maximum is about 3% (the difference in ΔP in the amount of emitted laser light is about 1 mW), which is an improvement of about 5% compared to the conventional case. It was.

  Further, as shown in FIG. 14, the normalized light output ratio when four lasers are turned on with the laser array light source according to the present invention is about 40% compared with the conventional laser array light source shown in FIG. It can be seen that the light intensity fluctuation is greatly improved.

  In addition, the lower limit value Pmin of the laser emission light amount that causes the light amount variation ΔP to be about 9% or less when the adjacent laser is turned on is about 2.5 mW in the related art as shown in FIG. The laser array light source according to the present invention is expanded to about 1.2 mW as shown in FIG. Thereby, the design range of the light transmittance of the optical scanning device is expanded, and the degree of design freedom can be increased. Furthermore, as described above, since the difference in light quantity variation between the lasers is small, it can be seen that the heat dissipation balance of the laser array is also improved.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. In the second embodiment, a mode of suppressing light amount fluctuation on the photoconductor with a simple configuration will be described.

  As described above, in the conventional laser array light source, as shown in FIGS. 11 and 12, the light amount fluctuation increases in proportion to the number of lasers lit, and the light amount fluctuation ΔP increases as the emitted light amount of each laser increases. Decreases rapidly.

  On the other hand, the light amount range of the photosensitive member needs to be adjusted to about a specified value ± 10% or less in order to stabilize the image. For this reason, in an optical scanning device (see FIGS. 20 and 21) using a plurality of conventionally used single lasers (laser light sources that emit a single laser beam), each light transmittance (for example, laser In order to absorb the variation in the ratio of the amount of light emitted and the amount of light on the photoconductor, the injection current is changed for each laser, and adjustment is performed at the stage of assembling the optical scanning device so that the required light quantity range for the photoconductor is obtained. Was.

  Such an adjustment cannot be applied to a laser array light source that emits a plurality of lasers. That is, when a laser array light source that emits a plurality of lasers is applied to an optical scanning device with a relatively high light transmittance, the amount of light emitted from the laser array light source is larger than when applied to an optical scanning device with a relatively low light transmittance. Is set low. As described above, the laser array light source has a large variation in the amount of light, especially in the range where the amount of emitted light is low, compared to a single laser, so that the image density difference and color difference become conspicuous and the optical scanning device cannot be manufactured stably. It was a problem.

  Here, when the upper limit value of the laser emission light amount determined from the lifetime of the laser array light source is Pmax and the lower limit value of the laser emission light amount determined by the variation in the light transmittance of the optical scanning device is Pmin, the optical scanning device is designed safely. The light quantity range that can be produced is desirably a range that satisfies Pmax / Pmin> 5 or more. However, in the conventional laser array light source as shown in FIGS. 11 and 12, the light amount range is about 2 <Pmax / Pmin <4, which is not the light amount range in which the optical scanning device can be safely designed and produced.

  Therefore, in the present embodiment, an optical scanning device having a relatively low light transmittance is used, and the light amount of the laser beam emitted from the optical scanning device is attenuated by a filter that is a relatively inexpensive optical component. Thereby, since the emitted light quantity of a laser array light source is set high, the area | region which suppresses a light quantity fluctuation | variation can be used and generation | occurrence | production of the image density difference by the thermal interference of a laser array light source and a color difference can be suppressed. . The effect is the same as long as it is an optical component that adjusts the amount of light, and is not limited to a filter.

  FIG. 16 shows the image forming apparatus 10 according to the present embodiment. The same parts as those of the image forming apparatus 105 shown in FIG. 24 are denoted by the same reference numerals, and detailed description thereof is omitted.

  As shown in FIG. 16, in the image forming apparatus 10, the final mirror 28 is a cylindrical mirror, and a filter 27 as an attenuation unit is provided on the optical path of the laser beam 13 reflected from the final mirror 28. Each laser beam passes through this filter 27 and is irradiated to each photoconductor 32. As a result, the amount of light of each laser beam is attenuated by the filter 27.

  FIG. 17 is a development view in a plane including the optical axis of the scanning optical system of the optical scanning device 11. Here, FIG. 17A corresponds to a developed view in the sub-scanning direction. The laser beam emitted from the laser array light source 12 is focused on the polygon mirror 20 by the collimator lens 14 and the cylindrical lens 16, and then fθ. The light is focused on the reflecting surface of the light separating polygon mirror 26 by the lens 22 and further focused on the photosensitive drum 32 by the final mirror 28. That is, in the sub-scanning direction, the emission surface of the laser array light source 12 and the polygon mirror 20, the polygon mirror 20 and the light separating polygon mirror 26, and the light separating polygon mirror 26 and the drum surface of the photosensitive drum 32 are optically coupled. It is a conjugate relationship.

  On the other hand, FIG. 17B corresponds to a development view in the main scanning direction, and the laser beam emitted from the laser array light source 12 is collimated by the collimator lens 14 and then on the photosensitive drum 32 by the fθ lens 22. Imaged.

  In the above configuration, when four laser beams modulated based on the Y, M, C, and K image data are emitted from the laser array light source 12, the collimator lens 14 converts the laser beams into parallel beams, and then a cylindrical lens. 16 is focused in the sub-scanning direction, and further reflected and deflected by the polygon mirror 20. The four deflected deflected beams are focused in the main scanning direction and the sub-scanning direction by the fθ lens 22 and guided to the light separating polygonal mirror 26 by the reflecting mirror 24, where they correspond to the arrangement position of the photosensitive drums 32. It is separated in the direction. The four separated light beams are reflected by the final mirror 28 that leads to the corresponding photosensitive drum 32, and the photosensitive drum 32 that rotates by being charged in advance through the cylindrical lens 30 is exposed to expose the photosensitive drum 32. An electrostatic latent image is formed on the surface.

  In such an optical scanning device 11, each lens and mirror are configured so that the light transmittance is relatively low.

  As shown in FIG. 16, the laser array light source 12 is controlled by the control device 15. The control device 15 includes an APC circuit (not shown), and the control device 15 outputs an output of a photodiode (not shown) for detecting the back beam of the laser beam 13 provided in the laser array light source 12. The amount of light) can be monitored to perform APC control, and the on / off timing of each laser beam is controlled in accordance with the input image signal. Specifically, as described above, the lighting timing of the laser array light source 12 is controlled in a sequence as shown in FIG.

  Further, the light transmittance of the optical scanning device 11 and the light transmittance of the filter 27 are set so that the light amount fluctuation ΔP between the photosensitive members when a plurality of lasers are turned on is about 9% or less.

  In this way, by using an optical scanning device having a relatively low light transmittance and providing the filter 27, the amount of light emitted from the laser array light source is set high, so even when the conventional laser array light source 12 is used, Light intensity fluctuation can be suppressed with a simple configuration. Further, by setting the light transmittance of the optical scanning device 11 and the light transmittance of the filter 27 so that the light amount fluctuation ΔP between the photosensitive members when a plurality of lasers are turned on is about 9% or less, the human eye It is now possible to suppress the occurrence of density and color differences that can be detected with the.

  The filter 27 may be one that uniformly attenuates the amount of light of each laser beam, that is, one that has the same transmittance on all surfaces, but one that has a different attenuation for each laser beam, that is, each Those having different transmittances at positions where the laser passes may be used, or a plurality of filters having different transmittances may be used.

  Further, the laser array light source according to the present invention described in the first embodiment may be applied to the image forming apparatus 10 shown in FIG. Thereby, the light quantity fluctuation can be further suppressed. Further, the filter 27 has the same effect as described above even when applied to the image forming apparatus shown in FIGS.

[Third Embodiment]
Next, a third embodiment of the present invention will be described. In the present embodiment, for example, the light amount adjustment timing of the laser array light source 12 of the image forming apparatus illustrated in FIGS.

  The light amount stabilization time necessary for stabilizing the light amount of the laser beam emitted from the laser array light source 12 is the longest among the times determined by the thermal time constants τi and τrj in the above equations (1) and (2). It's time.

  Therefore, the energizing time for supplying current to each laser must be longer than the time determined by the maximum thermal time constant that is thermally stable. The maximum thermal time constant of each laser is about 5 msec, and it is known that the thermal time constant τi (thermal interference saturation time) at the time of thermal interference is longer.

  On the other hand, the adjustment of the laser light amount includes a step of adjusting the initial light amount by the optical scanning device and a step of adjusting by the APC circuit before image writing. The former is to adjust the injection current of each laser of the laser array light source sequentially when assembling the optical scanning device as before. Usually, this light amount adjustment time is performed in the assembly apparatus of the optical scanning device and requires several seconds. Therefore, the light amount adjustment time is longer than the thermal interference saturation time of the laser array light source, and a stable laser light amount is obtained.

  However, the light amount adjustment before image writing has only one light amount monitor (photodiode) built in the laser array light source, and the APC circuit forcibly turns on the laser sequentially in order to adjust the feedback. In order to converge the APC control within the forced lighting time, each forced lighting time must be longer than the time determined by the maximum thermal time constant at the time of thermal interference.

  In addition, the forced lighting time interval of each laser must be longer than the time determined by the maximum thermal interference time constant, and the laser array light source must be cooled. This light amount adjustment is normally performed for each job including continuous printing every time one sheet is printed. Also, the image writing interval for each color must be longer than the time determined by the maximum thermal time constant. This is because, even when the light quantity adjustment by APC control of each laser before image writing is performed over a time longer than the time determined by the maximum thermal time constant, the writing of the image of each color is thermally unstable. This is because the light amount adjustment accuracy by the APC control is lowered when the operation is started. Further, the period from the last color image writing timing to the end of the first color image formation needs to be longer than the time determined by the maximum thermal interference time constant.

  That is, the control device 15 controls the laser array light source 12 so as to satisfy the following conditions. Note that the maximum thermal interference time constant is τmax.

(1) Forced lighting time of each laser (light quantity adjustment period)> maximum thermal interference time constant That is, the control device 15 performs the lighting time of the laser of Ch1 (t2-t1) and the lighting time of the laser of Ch2 ( t4-t3), the laser array light source 12 is controlled so that the Ch3 laser lighting time (t6-t5) and the Ch4 laser lighting time (t8-t7) are longer than the maximum thermal interference time constant τmax.

(2) Forced lighting interval of each laser (light quantity adjustment interval)> Maximum thermal interference time constant That is, the controller 15 starts the forced lighting of the Ch2 laser after the forced lighting of the Ch1 laser shown in FIG. Time (t3-t2), the time from when the forced lighting of the Ch2 laser is finished until the forced lighting of the Ch3 laser is started (t5-t4), the forced lighting of the Ch3 laser is finished Then, the laser array light source 12 is controlled so that the time (t7-t6) from when the Ch4 laser is forcibly turned on becomes longer than the maximum thermal interference time constant τmax.

(3) Time from the end of the last forced lighting to the start of writing the first color image (the period from the end of the laser beam intensity adjustment corresponding to the last color image to the start of image formation of the first color image)> Maximum heat Interference time constant In other words, the controller 15 determines that the time (t9-t8) from the end of forced lighting of the Ch4 laser shown in FIG. 25 to the start of image writing by the Ch1 laser is the maximum thermal interference. The laser array light source 12 is controlled so as to be longer than the constant τmax.

(4) Time from the start of writing the first color image to the start of writing the second color image, time from the start of writing the second color image to the start of writing the third color image, start of writing the fourth color image from the start of writing the third color image Time until image formation start interval of color image> Maximum thermal interference time constant In other words, the controller 15 starts writing an image by the Ch2 laser after the image writing by the Ch1 laser shown in FIG. 25 is started. Time (t10-t9) until the start of image writing by the Ch2 laser until the start of image writing by the Ch3 laser (t11-t10), image writing by the Ch3 laser Is the maximum thermal interference time constant τmax from the start of image writing to the start of image writing by the Ch4 laser (t12-t11). The laser array light source 12 is controlled so as to be longer.

(5) Time from the start of writing the final image to the end of writing the first color image (period from the start of image formation of the last color image to the end of image formation of the first color image)> Maximum thermal interference time constant In the apparatus 15, the time from the start of image writing by the Ch4 laser shown in FIG. 25 until the end of image writing by the Ch1 laser (t13-t12) is longer than the maximum thermal interference time constant τmax. The laser array light source 12 is controlled.

  In this way, the control device 15 adjusts the light amount in a time longer than the maximum thermal interference time constant, that is, the thermal interference saturation time, and controls the writing timing of each image based on the thermal interference saturation time. Can be suppressed. At this time, it is preferable to control the light amount adjustment time and the writing timing of each image so that the light amount fluctuation is about 9% or less.

  The laser array light source 40 according to the first embodiment, the image forming apparatus 10 according to the second embodiment, and the control of the lighting timing of each laser by the control device 15 according to the third embodiment may be combined. Thereby, the light quantity fluctuation can be further suppressed.

(A) is a top view of the laser array light source which concerns on this invention, (B) is sectional drawing of (A). (A) is a top view of the laser array light source which concerns on a prior art example, (B) is sectional drawing of (A). It is a circuit diagram of a thermal resistance simple equivalent circuit. It is a circuit diagram of a thermal resistance simple equivalent circuit. It is a circuit diagram of a thermal resistance simple equivalent circuit. It is a diagram which shows the relationship between thermal resistance ratio R2 / R1 and thermal resistance impedance ratio Zch2 / Zch1. (A) is a top sectional view of the T0 tube type package, and (B) is a side view of the T0 tube type package with the window cap removed. (A) is a top view of the laser array light source which concerns on this invention, (B) is sectional drawing of (A). (A) is a top view of the laser array light source which concerns on this invention, (B) is sectional drawing of (A). (A) is a top view of the laser array light source which concerns on this invention, (B) is sectional drawing of (A). It is a diagram which shows the relationship between the laser emission light quantity of the conventional laser array light source, and light quantity fluctuation | variation. It is a diagram which shows the relationship between the lighting number of the laser of the conventional laser array light source, and the normalized light output ratio. It is a diagram which shows the relationship between the laser emission light quantity of the laser array light source which concerns on this invention, and light quantity fluctuation | variation. It is a diagram which shows the relationship between the number of laser lighting of the laser array light source which concerns on this invention, and a normalized light output ratio. (A) is a diagram showing the relationship between the amount of light emitted from the laser beam Ch1 at the time of thermal interference with the laser array light source according to the present invention and the variation in the amount of light, and (B) is at the time of thermal interference with the laser array light source according to the present invention. It is a diagram which shows the relationship between the laser emitted light quantity of Ch2, and a light quantity fluctuation | variation. 1 is a schematic configuration diagram of an image forming apparatus according to the present invention. (A) is a development view of the optical scanning device in the sub-scanning direction, and (B) is a development view of the optical scanning device in the main scanning direction. It is a diagram which shows the relationship between the light quantity fluctuation | variation of a laser array, and a density | concentration difference. It is a diagram which shows the relationship between light quantity fluctuation | variation and a color difference. It is a schematic block diagram of the conventional image forming apparatus. It is a schematic block diagram of the conventional image forming apparatus. 1 is a schematic configuration diagram illustrating an example of an image forming apparatus. 1 is a schematic configuration diagram illustrating an example of an image forming apparatus. 1 is a schematic configuration diagram illustrating an example of an image forming apparatus. It is a timing chart which shows the lighting timing of a laser. It is a diagram which shows the relationship between the laser emitted light quantity of the laser array light source which concerns on this invention, and a prior art example, and light quantity fluctuation | variation. It is a diagram which shows the relationship between thermal resistance ratio R2 / R1 and light quantity fluctuation | variation.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 11 Optical scanning device 12, 40 Laser array light source (laser light source)
15 Control Device 27 Filter 32 Photoconductor 42 Heat Sink 44 Submount 46 Adhesive 48 Laser Array Chip (Laser Array)
50 Contact electrode 52 Light emitting point 54 Trench 56, 58 Electrode 57 Trench 60 Connection wire 62 External electrode

Claims (1)

  A laser array that emits a plurality of laser beams and includes a plurality of light emitting regions arranged along a predetermined direction intersecting with an emission direction of the laser beams, and a first groove provided between the light emitting regions; Generated in the laser array through a submount provided so that at least a part of the laser array is in contact with a predetermined position in the predetermined direction and provided with a second groove at a position corresponding to the first groove A heat sink for dissipating heat, and the thermal resistance in the predetermined direction between the light emitting regions is larger than the thermal resistance in the direction intersecting the predetermined direction in the heat sink from the light emitting region. A featured laser light source.

Images