JP2011040552A - Multi-beam semiconductor laser device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a beam-to-beam difference in a multi-beam semiconductor laser device. <P>SOLUTION: Auxiliary electrode patterns 13Sa and 13Sc are provided on a surface of a sub-mount 10 located in an optical path of backward light emitted from a laser chip 11. Accordingly, respective backward lights emitted from a plurality of light emission sections of the laser chip 11 are incident on a photodiode chip 14 independently from the surface condition of the sub-mount 10, thereby variations of current value caused by the surface condition of the sub-mount 10 is suppressed, and the current value can be monitored with high accuracy. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a multi-beam semiconductor laser device, and more particularly to a multi-beam semiconductor laser device including a photodiode element that receives a laser beam emitted from a semiconductor chip on which a laser diode element is formed and converts it into a current. is there.

  A laser diode (LD) element, which is widely used as a light source for an optical communication system and a light source for an information processing device, has a multilayer semiconductor layer made of AlGaInP, GaInP, GaAs, or the like on the main surface of a compound semiconductor substrate made of GaAs. Is epitaxially grown.

  A stripe-shaped active layer is provided in a part of the multilayer semiconductor layer, and one of the layers sandwiching the active layer is a first conductivity type (n-type) semiconductor layer, and the other is a second conductivity type ( By using a p-type semiconductor layer, a pn junction (pn junction) is formed. Various structures such as a ridge structure are employed to form a resonator (optical waveguide) for causing laser oscillation.

  The compound semiconductor substrate (chip) on which the laser diode element as described above is formed is a support substrate made of a material with good thermal conductivity called a submount (for example, AlN, SiC, CuW, etc.) disposed in the package. Used with soldering. Further, in order to efficiently dissipate the heat generated at the time of light emission of the laser diode element to the outside, it is mounted by a junction down method in which a pn junction serving as a heat generation source is fixed in the state of being close to the support substrate. Further, in order to control the light output emitted from the front of the laser diode element, a photodiode element is disposed behind the laser diode element, and the conversion current value is monitored.

  The multi-beam semiconductor laser device described in Patent Document 1 (Japanese Patent Laid-Open No. 2008-244440) discloses a structure that efficiently dissipates heat generated from each active region in a stripe shape. The semiconductor laser device is formed adjacent to the first surface in the vicinity of the plurality of stripe-shaped active regions, and electrically connected to each of the plurality of stripe-shaped laser electrodes of the laser element corresponding to each of the active regions. And a base on which a plurality of wirings connected to each other are formed, and current is injected into the active region from a plurality of connection points between each of the plurality of laser electrodes and the plurality of wirings. Yes. According to this structure, the heat generated from each stripe-like active region is efficiently radiated from the wiring and the base connected via each laser electrode. In addition, the current injected into each active region is uniformly injected from a connection point with a plurality of connected wirings.

JP 2008-244440 A

  As described above, the multi-beam semiconductor laser device is required to have a small characteristic difference between beams, that is, no variation in the characteristics of each beam. In particular, since the monitor current value of the photodiode is closely related to the light output control of the front light, it is particularly required to reduce the variation.

  FIG. 18A is a schematic plan view of a multi-beam semiconductor laser device for explaining this current value monitoring method. FIGS. 18B and 18C are respectively a BB line and a CC line of FIG. FIG. Here, a four-beam semiconductor laser device in which four laser diode elements are formed in a semiconductor chip will be described as an example.

  On the upper surface of the ceramic submount 10, a semiconductor chip (laser chip 11) on which a laser diode element is formed is mounted by a junction down method. A back electrode 12 is formed on the back surface (upper surface) of the laser chip 11. Further, four surface electrodes (not shown) corresponding to the four laser diode elements are formed on the surface (lower surface) of the laser chip 11 facing the submount 10.

  On the other hand, four electrode patterns 13 (13a, 13b, 13c, 13d) are formed on the upper surface of the submount 10. One end of each of the four electrode patterns 13 constitutes a bonding pad 13P for connecting wires, and the other end is a surface electrode of the laser chip 11 via Au-Sn solder (not shown) or the like. Is electrically connected. The electrode pattern 13 is composed of, for example, a multilayer metal film in which a Pt film and an Au film are sequentially stacked on a Ti film.

  On the extension line of the backward light emitted from the laser chip 11, a semiconductor chip (photodiode chip 14) in which a photodiode element that receives the backward light and converts it into an electric current is disposed.

  In the multi-beam semiconductor laser device, when controlling the light output of the forward light, the backward light emitted from each of the four laser diode elements (light emitting portions) formed on the laser chip 11 is individually and sequentially controlled. The chip 14 receives light and converts it into current, and monitors and compares the current values of the four light emitting units. Each current value is made equal.

  However, according to the study by the present inventor, in the current value monitoring method described above, even if the amount of the backward light emitted from the laser chip 11 is the same, it depends on the relative positions of the submount 10 and the backward light. It was found that the current value may fluctuate.

  In general, the light quantity of laser beams (front light and rear light) emitted from both end faces of a laser chip has an angular distribution that can be approximated to a normal distribution. As an example, the full width at half maximum in the horizontal direction is about 10 degrees. The full width at half maximum in the vertical direction is about 20 degrees.

  In the structure shown in FIG. 18, the height from the upper surface of the submount 10 to the light emitting point of the laser chip 11 is, for example, about several μm to 100 μm, and the rear end of the submount 10 from the light emitting point of the back light. It is smaller than the distance to the part (several hundred μm to several thousand μm). Therefore, a part of the backward light emitted from the laser chip 11 is reflected by the upper surface of the submount 10 and then enters the photodiode chip 14. That is, the light incident on the photodiode chip 14 is the sum of the light incident directly on the photodiode chip 14 from the laser chip 11 and the light incident on the photodiode chip 14 after being reflected by the upper surface of the submount 10. Accordingly, the amount of light incident on the photodiode chip 14 varies depending on the surface state of the submount 10, that is, the light reflectance of the upper surface of the submount 10 even if the amount of back light emitted from the laser chip 11 is the same. It will be.

  For example, as shown in FIG. 18B, the reflected light of the backward light emitted from the light emitting portion located near the center of the laser chip 11 is the reflected light that is mostly reflected by the surface of the electrode pattern 13b. . On the other hand, as shown in FIG. 18C, the reflected light of the backward light emitted from the light emitting part located in the vicinity of the peripheral part of the laser chip 11 is reflected by the corresponding part reflected by the surface of the submount 10. Light.

  As described above, the electrode pattern 13 is made of a metal material, while the submount 10 is made of a ceramic material having a light reflectance lower than that of the metal material. Therefore, the amount of light reflected on the surface of the electrode pattern 13 and incident on the photodiode chip 14 is larger than the amount of light reflected on the surface of the submount 10 and incident on the photodiode chip 14. As a result, even if the light quantity of the backward light emitted from the two light emitting parts is the same, the light quantity incident on the photodiode chip 14 is the backward light emitted from the light emitting part near the center part of the laser chip 11. The amount of light increases and the current value also increases.

  In the multi-beam semiconductor laser device, the electrode patterns 13 a, 13 b, 13 c, It is difficult to make the wiring length of 13d the same. Usually, the wiring lengths of the electrode patterns 13a and 13c connected to the light emitting portion near the peripheral portion of the laser chip 11 are connected to the light emitting portion near the central portion. It becomes shorter than the wiring length of the electrode patterns 13b and 13d. Therefore, as described above, the current value monitored by the photodiode chip 14 is emitted from the light emitting portion near the peripheral portion of the laser chip 11 rather than the back light emitted from the light emitting portion near the central portion of the laser chip 11. The rear light is smaller.

  As described above, in the above-described multi-beam semiconductor laser device, the amount of light reflected on the surface and incident on the photodiode varies depending on the surface state of the submount 10, and the conversion current value varies. There is a problem that it cannot be monitored with high accuracy.

  It is an object of the present invention to suppress a problem that the current value varies depending on the surface state of the submount on which the laser chip is mounted when the backward light emitted from the laser chip is received and the current value is monitored. To provide technology.

  The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

  Of the inventions disclosed in the present application, the outline of typical ones will be briefly described as follows.

  A preferred aspect of the present invention is a first semiconductor chip on which a plurality of laser diode elements are formed, a submount on which the first semiconductor chip is mounted, a chip mounting surface of the submount, and the plurality of the plurality of laser diode elements. A plurality of electrode patterns electrically connected to each of the laser diode elements, and a plurality of laser beams disposed near the submount and receiving a plurality of laser beams emitted from one end surface of the first semiconductor chip; A multi-beam semiconductor laser device including a second semiconductor chip on which a photodiode element for converting into current is formed, and is emitted from one end surface of the first semiconductor chip to the chip mounting surface of the submount. An auxiliary electrode pattern for making the reflectance of the plurality of laser beams uniform is formed.

  Another preferred aspect of the present invention is formed on a first semiconductor chip on which a plurality of laser diode elements are formed, a submount on which the first semiconductor chip is mounted, and a chip mounting surface of the submount, A plurality of electrode patterns electrically connected to each of the plurality of laser diode elements, and a plurality of laser beams disposed near the submount and emitted from one end surface of the first semiconductor chip are received. And a second semiconductor chip on which a photodiode element for converting into current is formed, and is emitted from one end surface of the first semiconductor chip to a part of the surface of the electrode pattern. A reflectance reduction film for uniformizing the reflectance of the plurality of laser beams thus formed is formed.

  Among the inventions disclosed in the present application, effects obtained by typical ones will be briefly described as follows.

  When a laser beam emitted from a first semiconductor chip on which a plurality of laser diode elements are formed is received by a photodiode element and the current value is monitored, the surface state of the submount on which the first semiconductor chip is mounted Therefore, it is possible to suppress the problem that the current value varies, so that the difference between beams of the multi-beam semiconductor laser device can be suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary perspective view showing an overall configuration of a 4-beam semiconductor laser device according to a first embodiment of the present invention. It is sectional drawing of the laser chip mounted in the submount. It is a perspective view which shows the chip mounting surface of a submount. FIG. 2 is an equivalent circuit diagram of the four-beam semiconductor laser device shown in FIG. 1. (A) is a schematic plan view showing the chip mounting surface of the submount, b) is a cross-sectional view taken along line DD in (a), and (c) is a cross-sectional view taken along line EE in (a). It is. It is a figure which shows the calculation model and calculation parameter of the electrode pattern dependence of the monitor current by a photodiode chip. It is a graph which shows the relationship between the electrode pattern length behind a laser chip, and the difference between monitor current beams. It is a graph which shows angle distribution of the incident light quantity in case the electrode pattern length of the back of a laser chip is 40 micrometers. It is a graph which shows angle distribution of the incident light quantity in case the electrode pattern length of the back of a laser chip is 630 micrometers. It is a graph which shows angle distribution of the incident light quantity at the time of applying this invention when the electrode pattern length of the back of a laser chip is 40 micrometers. It is a schematic plan view of the submount which shows another example of the layout of an auxiliary electrode pattern. It is a schematic plan view of the submount which shows the example which applied Embodiment 1 of this invention to the 8-beam semiconductor laser apparatus. It is a schematic plan view of the submount which shows the 4-beam semiconductor laser apparatus which is Embodiment 2 of this invention. It is a schematic plan view of the submount which shows the example which applied Embodiment 2 of this invention to the 8-beam semiconductor laser apparatus. It is a schematic plan view of the submount which shows the 8-beam semiconductor laser apparatus which is Embodiment 3 of this invention. It is a schematic plan view of the submount which shows the 4 beam semiconductor laser apparatus which is other embodiment of this invention. It is a schematic plan view of the submount which shows the 4 beam semiconductor laser apparatus which is other embodiment of this invention. (A) is a schematic plan view explaining the current value monitoring method of a multi-beam semiconductor laser device, (b) is a sectional view taken along line BB in (a), and (c) is CC in (a). It is sectional drawing along a line.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiment, and the repetitive description thereof will be omitted. Also, in the following embodiments, the description of the same or similar parts will not be repeated in principle unless particularly necessary. Further, in the drawings for explaining the following embodiments, hatching may be given even in a plan view for easy understanding of the configuration.

(Embodiment 1)
The present embodiment is applied to a four-beam semiconductor laser device having a convex ridge portion, and FIG. 1 is a fragmentary perspective view showing the entire configuration of the four-beam semiconductor laser device.

  The four-beam semiconductor laser device of the present embodiment includes a disc-shaped stem 30 made of an Fe alloy having a diameter of, for example, about 9.0 mm and a thickness of about 1.2 mm, and a cap 31 that covers the upper surface of the stem 30. It has a package (sealing container) provided. A flange portion 32 provided on the outer periphery of the bottom portion of the cap 31 is fixed to the upper surface of the stem 30. In addition, a circular hole 34 is provided at the center of the upper surface of the cap 31 to which a glass plate 33 that transmits a laser beam is bonded.

  Near the center of the upper surface of the stem 30 covered with the cap 31, a heat sink 35 made of a metal having good thermal conductivity such as Cu is mounted. The heat sink 35 is joined to the upper surface of the stem 30 via a brazing material (not shown), and the submount 10 is fixed to the one surface via solder (not shown).

  The submount 10 is made of ceramic such as AlN, SiC, or CuW, and a laser chip 11 on which four laser diode elements are formed is mounted on one surface by a junction down method. The submount 10 serves both as a heat sink for radiating heat generated when the laser diode element emits light to the outside of the laser chip 11 and a support substrate for supporting the laser chip 11.

  The laser chip 11 mounted on the submount 10 emits a laser beam from both end faces (upper end face and lower end face in FIG. 1). Therefore, the submount 10 that supports the laser chip 11 is fixed to the heat sink 35 so that the chip mounting surface faces a direction perpendicular to the upper surface of the stem 30. The laser beam (front light) emitted from the upper end surface of the laser chip 11 is emitted to the outside through the round hole 34 of the cap 31. Further, the laser beam (back light) emitted from the lower end surface of the laser chip 11 is received by the photodiode chip 14 mounted in the vicinity of the center portion of the upper surface of the stem 30 and converted into a current.

  FIG. 2 is a cross-sectional view of the laser chip 11 mounted on the submount 10. As shown in FIG. 2, a plurality of semiconductor layers are stacked on the main surface of the GaAs substrate 2. The semiconductor layer is composed of an n-type cladding layer 3, an active layer 4, a p-type first cladding layer 5, a p-type second cladding layer 6 and a p-type contact layer 7 deposited by, for example, metal organic chemical vapor deposition (MOCVD). Become. Of these semiconductor layers, the n-type cladding layer 3 is made of AlGaInP. The active layer 4 has a multi quantum well (MQW) structure in which barrier layers made of AlGaInP and well layers made of GaInP layers are alternately stacked. The p-type first cladding layer 5 and the p-type second cladding layer 6 are each made of AlGaInP, and the p-type contact layer 7 is made of GaAs.

  The p-type second cladding layer 6 is formed with four ridges (mesa stripes) 8 (8a, 8b, 8c, 8d) having a convex cross-sectional shape and extending in parallel with each other. . A p-type contact layer 7 is formed on each of the four ridge portions 8. A passivation film 9 made of silicon oxide is formed between the four ridge portions 8. The passivation film 9 is formed so as to cover the entire surface of the p-type second cladding layer 6 except for the surface (upper surface) of the p-type contact layer 7.

  A p-type surface electrode 15 ohmically connected to the p-type contact layer 7 is formed on the upper surface of the p-type contact layer 7 and the upper surface of the passivation film 9. Further, a heat radiating Au plating layer 16 is formed on the upper surface of the surface electrode 15. On the other hand, an n-type back electrode 12 is formed on the back surface of the GaAs substrate 2. Each of the front surface electrode 15 and the back surface electrode 12 is composed of, for example, a multilayer metal film in which a Pt film and an Au film are sequentially laminated on a Ti film.

  In the laser chip 11 configured as described above, when a predetermined voltage is applied to the front surface electrode 15 and the back surface electrode 12, in the active layer 4 (light emitting portion) below each of the four ridge portions 8, For example, a red laser beam having an oscillation wavelength of 650 nm oscillates. These red laser beams are emitted from both end faces of the laser chip 11 orthogonal to the extending direction of the ridge portion 8, and the forward light is emitted to the outside of the CAN package through the circular holes 34 of the cap 31 shown in FIG. The

  On the other hand, on the chip mounting surface of the submount 10, for example, four electrode patterns 13 (13a, 13b, 13c, 13d) made of a multilayer metal film in which a Pt film and an Au film are sequentially laminated on a Ti film are formed. ing. These electrode patterns 13 are arranged so as to face the ridge portions 8 (8a, 8b, 8c, 8d) of the laser chip 11 when the laser chip 11 is mounted on the submount 10, and are made of, for example, an Au—Sn alloy solder. The layer 22 and the Au plating layer 16 are electrically connected to the surface electrode 15 on the ridge portion 8. An insulating layer 17 made of silicon oxide or the like is formed between the electrode pattern 13 and the submount 10 in order to prevent a short circuit between the electrode patterns 13.

  FIG. 3 is a perspective view showing a chip mounting surface of the submount 10. Each of the chip mounting surfaces of the submount 10 is electrically connected to the surface electrode 15 on the ridge portion 8 (8a, 8b, 8c, 8d) of the laser chip 11 shown in FIG. The electrode patterns 13 (13a, 13b, 13c, 13d) and two auxiliary electrode patterns 13S (13Sa, 13Sc) that are electrically separated from these electrode patterns 13 are formed. The auxiliary electrode pattern 13 </ b> S is composed of the same multilayer metal film as the electrode pattern 13, and the light reflectance of the surface thereof is the same as that of the electrode pattern 13.

  The auxiliary electrode pattern 13Sa is disposed in a region between the electrode pattern 13a and the electrode pattern 13b. That is, the auxiliary electrode pattern 13Sa is located in the optical path of the backward light emitted from the laser diode element (the active layer 4 below the ridge portion 8a shown in FIG. 2) electrically connected to the electrode pattern 13a. Covers the top surface. On the other hand, the auxiliary electrode pattern 13Sc is disposed in a region between the electrode pattern 13c and the electrode pattern 13d. That is, the auxiliary electrode pattern 13Sc is located in the optical path of the backward light emitted from the laser diode element (the active layer 4 below the ridge portion 8c shown in FIG. 2) electrically connected to the electrode pattern 13c. Covering the surface.

  The other end of each of the four electrode patterns 13 (13a, 13b, 13c, 13d) constitutes a bonding pad 13P, and one end of an Au wire 36 is bonded to the surface thereof. As shown in FIG. 1, six leads 39a, 39b, 39c, 39d, 39e, and 39f are attached to the lower surface of the stem 30, and four Au wires connected to the four bonding pads 13P. Each other end of 36 is electrically connected to leads 39a, 39b, 39e, 39f. Of the remaining two leads 39c and 39d, the lead 39c is fixed to the lower surface of the stem 30 and is in an electrically equipotential state with respect to the stem 30. The lead 39d is electrically connected to the back electrode 12 of the photodiode chip 14 through the Au wire 38.

FIG. 4 is an equivalent circuit diagram of the above-described four-beam semiconductor laser device. Here, symbols LD ₁ , LD ₂ , LD ₃ , and LD ₄ indicate laser diode elements formed in the ridge portions 8a, 8b, 8c, and 8d of the laser chip 11 shown in FIG. 2, and PD is a photodiode. A photodiode element formed on the chip 14 is shown.

  FIG. 5A is a schematic plan view showing the chip mounting surface of the submount 10, and FIGS. 5B and 5C are cross-sectional views taken along the DD line and the EE line, respectively, of FIG. It is.

  The backward light emitted from the laser chip 11 and incident on the photodiode chip 14 is reflected by the light directly incident on the photodiode chip 14 from the laser chip 11 and the upper surface of the submount 10 and then incident on the photodiode chip 14. It is the sum of light.

As shown in FIG. 5B, most of the reflected light of the backward light emitted from the laser diode element (for example, the laser diode element LD _{2 in} FIG. 4) located near the center of the laser chip 11 is an electrode. After being reflected by the surface of the pattern 13 b, the light enters the photodiode chip 14. As shown in FIG. 5C, most of the reflected light of the backward light emitted from the laser diode element (for example, the laser diode element LD _{1 in} FIG. 4) located in the vicinity of the peripheral portion of the laser chip 11 Is reflected on the surface of the auxiliary electrode pattern 13Sa or the electrode pattern 13a, and then enters the photodiode chip 14.

  As described above, the light reflectance of the surface of the auxiliary electrode pattern 13 </ b> S is the same as that of the electrode pattern 13. Therefore, when the auxiliary electrode pattern 13S is provided on the surface of the submount 10 positioned in the optical path of the backward light emitted from the laser chip 11, each emitted from the four light emitting portions (laser diode elements) of the laser chip 11. Back light enters the photodiode chip 14 without depending on the surface state of the submount 10. Thereby, the variation in the current value due to the surface state of the submount 10 is suppressed, and the current value can be monitored with high accuracy.

In general, the arrangement and area of the auxiliary electrode pattern 13S are as follows: ΔP _ma = difference between beams before application of the present invention (without auxiliary electrode pattern), ΔP _mb = difference between beams after application of the present invention (with auxiliary electrode pattern) When it does, it designs so that the conditions shown in the following formula 1 may be satisfied.

ΔP _ma −ΔP _mb ≧ 1% (1)
Here, P _m is a light quantity weighted area corresponding to each beam position, and is defined by the following equation (1).

ΔP _m is the difference between beams in the light quantity weighted area shown in the following equation 2.
ΔP _m = {MAX (P _m ) −MIN (P _m )} / MAX (P _m ) × 100% (2)
However, MAX (P _m ) = maximum P _m in all beams, and MIN (P _m ) = minimum P _m in all beams.

  Next, calculation results performed on the electrode pattern dependency of the monitor current by the photodiode chip 14 will be described. FIG. 6 shows a calculation model and calculation parameters (Table 1).

  In the model, only the backward light in the vertical direction with respect to the upper surface (chip mounting surface) of the submount 10 was considered, and the backward light in the horizontal direction was ignored because it did not depend on the beam position. The angular distribution of the rear light quantity was a normal distribution with a standard deviation of 10 degrees (deg) (corresponding to about 20 degrees as the full width at half maximum in the vertical direction of the Far Field Pattern). The emitted light is emitted with a spread from a finite emission point height (here, the height of the light emission point (h) = 10 μm), and part of the downward direction (= the emission angle (θv) is negative) Is reflected by the upper surface of the submount 10 and enters the photodiode chip 14. Further, the upward direction directly enters the photodiode chip 14. On the upper surface of the submount 10, the reflectance (R1) of the region where the electrode pattern 13 exists was set to 1.0, and the reflectance (R2) of the region where the submount 10 was exposed was set to 0.83.

  In this model, the amount of light received (integrated value of all angles) incident on the photodiode chip 14 when the electrode pattern length (L1) behind the laser chip 11 was changed was obtained. FIG. 7 shows the difference between the monitor current beams when the electrode pattern length (L1) is changed. The difference between the beams was based on the monitor current value when the longest electrode length was 630 μm.

  According to this, when the electrode pattern length becomes shorter than about 100 μm, the increase in the difference between the beams of the monitor electrode becomes remarkable. This is because (1) tan θv = h / L1, so that the change in θ is large with respect to the decrease in L1, and (2) the angular distribution of the emitted light is a normal distribution, so the cumulative distribution is near the half value half angle. (L1 = 57 μm when h = 10 μm and θv = 10 deg).

  As an example, FIGS. 8 to 10 show the angular distribution of the incident light quantity when the present invention (the auxiliary electrode pattern 13S is arranged) is applied with L1 = 40 μm, 630 μm, and L1 = 40 μm. The gap between the electrode pattern 13 and the auxiliary electrode pattern 13S was 30 μm. The area of the hatched portion of the distribution graph is the amount of light received incident on the photodiode chip 14, and the monitor electrode is proportional to this. Further, the portion appearing as a depression with respect to the normal distribution corresponds to reflection in the exposed region of the submount 10. From the calculation results, it can be seen that the difference between the monitor current beams of L1 = 40 μm and 630 μm can be improved from 6.6% to 2.0% by applying the present invention.

  Since the auxiliary electrode pattern 13S (13Sa, 13Sc) may be formed at the same time in the step of forming the electrode pattern 13 on the chip mounting surface of the submount 10, the manufacturing process does not increase compared to the conventional structure. In addition, since the length of each of the electrode patterns 13a to 13d may be the same as that of the conventional structure, the electrical characteristics and high-frequency characteristics of the laser beam are not adversely affected.

  For example, as shown in FIG. 11, the auxiliary electrode pattern 13S (13Sa, 13Sc) may be disposed only in a region located in the optical path of the backward light emitted from the light emitting portion located in the vicinity of the peripheral portion of the laser chip 11. Good.

  FIG. 12 is an example applied to an 8-beam semiconductor laser device in which a laser chip 21 formed with 8 laser diode elements is mounted on a submount 10.

  On the chip mounting surface of the submount 10, eight electrode patterns 23 (23 a, 23 b, 23 c, 23 d, one end portion of which are electrically connected to eight laser diode elements formed on the laser chip 21. 23e, 23f, 23g, and 23h) are formed. Each other end of the electrode pattern 23 constitutes a bonding pad 23P to which one end of an Au wire (not shown) is bonded. In addition, two auxiliary electrode patterns 23 </ b> S that are electrically separated from the electrode pattern 23 are formed on the chip mounting surface of the submount 10.

  As shown in FIG. 12, the lengths of the eight electrode patterns 23 a to 23 h along the direction parallel to the optical path of the backward light emitted from the laser chip 21 are from the central part to the peripheral part of the laser chip 21. It is getting shorter. On the other hand, the length of the auxiliary electrode pattern 23S along the direction parallel to the optical path of the backward light becomes longer as it goes from the central part of the laser chip 21 toward the peripheral part.

  By forming the auxiliary electrode pattern 23S as described above on the chip mounting surface of the submount 10, each of the rear lights emitted from the eight light emitting portions (laser diode elements) of the laser chip 21 is the surface state of the submount 10. Therefore, the variation of the current value due to the surface state of the submount 10 is suppressed, and the current value can be monitored with high accuracy.

  Also in this case, the arrangement and area of the auxiliary electrode pattern 23S may be designed so as to satisfy the condition shown in the above formula 1.

(Embodiment 2)
FIG. 13 is a schematic plan view showing the chip mounting surface of the submount in the four-beam semiconductor laser device of the present embodiment.

  In the first embodiment, the auxiliary electrode pattern 13S having the same light reflectance as that of the electrode pattern 13 is formed on the chip mounting surface of the submount 10. However, in the present embodiment, the laser chip 11 is contrary to this. A reflectance reduction film 18 having a light reflectance comparable to that of the surface of the submount 10 is formed on a part of the surface of each of the electrode patterns 13b and 13d electrically connected to the laser diode element located in the vicinity of the center of Forming.

  By forming the reflectance reducing film 18 as described above on a part of the surface of each of the electrode patterns 13b and 13d, four electrodes along the direction parallel to the optical path of the backward light emitted from the laser chip 11 The same effect is obtained as when the lengths of the patterns 13a to 13d are the same. As a result, as in the first embodiment, each rear light emitted from the four laser diode elements of the laser chip 11 is incident on the photodiode chip 14 without depending on the surface state of the submount 10. Variation in the current value due to the surface state of the mount 10 is suppressed, and the current value can be monitored with high accuracy.

  The reflectance reduction film 18 can be formed, for example, by attaching a tape base material having a light reflectance comparable to that of the surface of the submount 10 to predetermined positions of the electrode patterns 13b and 13d. Alternatively, a base material having a light reflectivity comparable to that of the surface of the submount 10 can be formed by applying or printing on a predetermined surface of the electrode patterns 13b and 13d. Further, the solder layer pattern may be extended rearward of the laser chip along the electrode pattern. Since the solder surface has a lower reflectance than the electrode surface, it functions as a reflectance reduction film. Further, by reducing the smoothness of the surface of the predetermined portions of the electrode patterns 13b and 13d, the light reflectance of the region may be reduced to the same level as the surface of the submount 10.

  Also in the present embodiment, the arrangement and area of the reflectance reduction film 18 may be designed so as to satisfy the condition shown in the above-described Expression 1. In addition, since the length of each of the electrode patterns 13a to 13d may be the same as that of the conventional structure, the electrical characteristics and high-frequency characteristics of the laser beam are not adversely affected.

  FIG. 14 shows that eight of the eight patterns along the direction parallel to the optical path of the backward light emitted from the laser chip 21 by forming the reflectance reduction film 18 on a part of the electrode pattern 13 of the eight-beam semiconductor laser device. In this example, the same effect as that obtained when the lengths of the electrode patterns 23a to 23h are the same can be obtained.

(Embodiment 3)
FIG. 15 is a schematic plan view showing the chip mounting surface of the submount in the 8-beam semiconductor laser device of the present embodiment.

  In the present embodiment, of the reflected light of the backward light emitted from the laser chip 21, a region having a high ratio of incidence on the photodiode chip 14 (parallel to the optical path of the backward light from the rear end surface of the laser chip 21 shown in FIG. 15). The lengths of the eight electrode patterns 23a to 23h are made the same in the region up to the distance La in a certain direction.

  Here, La is a distance (unit: μm) defined by Equation 3 below.

La = 170 × h / θ _FWHM-V (3)
However, h (μm) = the height from the upper surface (chip mounting surface) of the submount to the light emitting point of the laser chip, and θ _FWHM-V (deg) = the full width at half maximum of the beam expansion in the vertical direction of the laser chip.

  According to the present embodiment, each rear light emitted from the eight light emitting portions (laser diode elements) of the laser chip 21 is incident on the photodiode chip 14 without depending on the surface state of the submount 10. As in the first and second embodiments, variation in current value due to the surface state of the submount 10 is suppressed, and the current value can be monitored with high accuracy.

  In the present embodiment, the auxiliary electrode pattern 13S is formed on the chip mounting surface of the submount 10 (Embodiment 1), or the reflectance reduction film 18 is formed on a part of the surface of the electrode pattern 13 ( Embodiment 2) It is not necessary to control the length of the electrode patterns 23a to 23h, and the wiring design is easy.

  As mentioned above, the invention made by the present inventor has been specifically described based on the embodiment. However, the present invention is not limited to the embodiment, and various modifications can be made without departing from the scope of the invention. Needless to say.

  In the first embodiment, the electrode pattern 13 and the auxiliary electrode pattern 13S are electrically separated. For example, as shown in FIG. 16, the electrode patterns 13a and 13c and the auxiliary electrode pattern 13S are integrally formed. Also good. For example, as shown in FIG. 17, the auxiliary electrode pattern 13 </ b> S may be formed by increasing the line width of a part of each of the electrode patterns 13 a and 13 c.

  In the above embodiment, the present invention is applied to the four-beam semiconductor laser device and the eight-beam semiconductor laser device. However, it is needless to say that the present invention is applicable to general multi-beam semiconductor laser devices.

  The present invention can be applied to a multi-beam semiconductor laser device.

2 GaAs substrate 3 n-type cladding layer 4 active layer 5 p-type first cladding layer 6 p-type second cladding layer 7 p-type contact layers 8, 8 a, 8 b, 8 c, 8 d Ridge portion (mesa stripe)
9 Passivation film 10 Submount 11 Laser chip 12 Back electrode 13, 13a, 13b, 13c, 13d Electrode pattern 13S, 13Sa, 13Sc Auxiliary electrode pattern 13P Bonding pad 14 Photodiode chip 15 Surface electrode 16 Au plating layer 17 Insulating layer 18 Reflection Rate reducing film 21 Laser chip 23, 23a-23h Electrode pattern 23P Bonding pad 23 Auxiliary electrode pattern 30 Stem 31 Cap 32 Flange portion 33 Glass plate 34 Round hole 35 Heat sink 36, 37, 38 Au wire 39, 39a, 39b, 39c, 39d, 39e, 39f lead _{LD 1, LD 2, LD 3} , LD 4 laser diode element PD photodiode elements

Claims (13)

A first semiconductor chip on which a plurality of laser diode elements are formed;
A submount on which the first semiconductor chip is mounted;
A plurality of electrode patterns formed on a chip mounting surface of the submount and electrically connected to each of the plurality of laser diode elements;
A multi-beam comprising: a second semiconductor chip disposed in the vicinity of the submount; and a second semiconductor chip on which a plurality of laser beams emitted from one end face of the first semiconductor chip are received and converted into a current. A semiconductor laser device,
An auxiliary electrode pattern for making the reflectance of the plurality of laser beams emitted from one end face of the first semiconductor chip uniform is formed on the chip mounting surface of the submount. Beam semiconductor laser device.   2. The multi-beam semiconductor laser device according to claim 1, wherein the auxiliary electrode pattern is made of the same material as the electrode pattern.   2. The multi-beam semiconductor laser device according to claim 1, wherein the auxiliary electrode pattern is electrically separated from the electrode pattern.   2. The multi-beam semiconductor laser device according to claim 1, wherein the auxiliary electrode pattern is formed integrally with the electrode pattern.   The multi-beam semiconductor laser device according to claim 1, wherein the first semiconductor chip is mounted on the chip mounting surface of the submount by a junction down method. The arrangement and area of the auxiliary electrode pattern are as follows: ΔP _ma = difference between beams when there is no auxiliary electrode pattern, ΔP _mb = difference between beams when there is the auxiliary electrode pattern, P _m = light quantity corresponding to each beam position When using the weighted area, the following formula 1
ΔP _ma −ΔP _mb ≧ 1% (1)
The multi-beam semiconductor laser device according to claim 1, wherein the conditions shown in FIG. A first semiconductor chip on which a plurality of laser diode elements are formed;
A submount on which the first semiconductor chip is mounted;
A plurality of electrode patterns formed on a chip mounting surface of the submount and electrically connected to each of the plurality of laser diode elements;
A multi-beam comprising: a second semiconductor chip disposed in the vicinity of the submount; and a second semiconductor chip on which a plurality of laser beams emitted from one end face of the first semiconductor chip are received and converted into a current. A semiconductor laser device,
A reflectance reduction film for uniformizing the reflectance of the plurality of laser beams emitted from one end face of the first semiconductor chip is formed on a part of the surface of the electrode pattern. Multi-beam semiconductor laser device.   8. The multi-beam semiconductor laser device according to claim 7, wherein the reflectance reduction film has a light reflectance comparable to that of the surface of the submount.   The multi-beam semiconductor laser device according to claim 7, wherein the first semiconductor chip is mounted on the chip mounting surface of the submount by a junction down method. The arrangement and area of the reflectance reduction film are as follows: ΔP _ma = difference between beams when there is no reflectance reduction film, ΔP _mb = difference between beams when there is the reflectance reduction film, and P _m = at each beam position. When the corresponding light quantity weighted area is used, the following formula 1
ΔP _ma −ΔP _mb ≧ 1% (1)
The multi-beam semiconductor laser device according to claim 7, wherein the condition shown in FIG. A first semiconductor chip on which a plurality of laser diode elements are formed;
A submount on which the first semiconductor chip is mounted;
A plurality of electrode patterns formed on a chip mounting surface of the submount and electrically connected to each of the plurality of laser diode elements;
A multi-beam comprising: a second semiconductor chip disposed in the vicinity of the submount; and a second semiconductor chip on which a plurality of laser beams emitted from one end face of the first semiconductor chip are received and converted into a current. A semiconductor laser device,
Of the laser beam emitted from one end surface of the first semiconductor chip and reflected by the surface of the submount, in a region having a high ratio of incidence on the second semiconductor chip, in a direction parallel to the optical path of the laser beam A multi-beam semiconductor laser device characterized in that the plurality of electrode patterns along the length have the same length. The region (La) having a high incidence rate to the second semiconductor chip is h = height from the chip mounting surface of the submount to the light emitting point of the first semiconductor chip (unit: μm), θ _FWHM-V When (deg) = full width at half maximum of the beam divergence in the vertical direction of the first semiconductor chip,
La (μm) = 170 × h / θ _FWHM-V (2)
The multi-beam semiconductor laser device according to claim 11, wherein the distance is defined by:   12. The multi-beam semiconductor laser device according to claim 11, wherein the first semiconductor chip is mounted on the chip mounting surface of the submount by a junction down method.

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