JP5141288B2 - Optical semiconductor package - Google Patents

Description

  The present invention relates to an optical semiconductor package that couples laser light from a semiconductor laser element such as a surface-emitting semiconductor laser (Vertical-Cavity Surface-Emitting Laser diode: hereinafter referred to as VCSEL) to an optical fiber. The present invention relates to a technique for suppressing a decrease in output.

  When a semiconductor laser element such as a VCSEL is used as a light source in the communication field, the semiconductor laser element is accommodated in a package in order to improve the reliability and stability of the light source. FIG. 10 is a schematic cross-sectional view showing a typical configuration of a conventional optical semiconductor package. The optical semiconductor package 200 shown in the figure has a receptacle 210 in which a housing 212 and a lens 214 are integrated. A can package 220 is coupled to one end of the housing 212, and an optical fiber 230 is inserted into the other end. As described above, the optical semiconductor package 200 in which the can package 220 and the receptacle 210 are fixed is called TOSA (Transmitter Optical Subassembly).

  The can package 220 includes a VCSEL 222 therein, and the laser light emitted from the VCSEL 222 is collected by the lens 214 and is incident on the core of the optical fiber 230, and the VCSEL 222 and the optical fiber 230 are optically coupled.

  In addition to this, technologies relating to an optical semiconductor package using a VCSEL are disclosed in several patent documents. Patent Document 1 includes a lens, a housing, and a photoelectric conversion element. One of the lenses has a function of collimating incident light, and the other is a technique related to a subassembly in which an optical fiber is coupled with intentional aberration. Is disclosed. By intentionally giving aberration in the Z direction and omitting alignment in the Z direction, the alignment process is simplified.

  Patent Document 2 discloses a technique related to a subassembly in which a lens and a housing are integrated and a space for storing an optical device is formed. This enables downsizing and cost reduction.

  Patent Document 3 discloses a manufacturing method of two-stage molding in which a primary molded piece in which a lens is insert-molded with a resin is manufactured, and then insert-molded to be secondarily molded into a housing shape. The cost is reduced by forming the lens and the housing from the same material.

US Pat. No. 5,537,504 US Pat. No. 6,302,596 JP-A-11-54849

  FIG. 11 is a graph showing the light output characteristics at room temperature of the VCSEL alone, and FIG. 12 is a graph showing the light output characteristics at room temperature after the VCSEL is packaged. When a VCSEL is packaged in a can (TO-can), TOSA, or the like, there is a problem that a thermal rollover point, that is, a driving current for obtaining a maximum light output is lowered. As shown in FIG. 11, the VCSEL alone has a maximum light output of 3.7 mW, but the drive current at that time is 21.5 mA, and the can-sealed package has a maximum light output of 0.98 mA. The drive current at that time is 22 mA. However, in TOSA, the drive current at the maximum optical output of 0.58 mW is reduced to 18 mA.

  When the VCSEL is driven at room temperature, the drive current is sufficiently smaller than the current value of the thermal rollover point. On the other hand, when the VCSEL is driven at a high temperature, the graphs of the optical output characteristics shown in FIGS. 11 and 12 shift to the right, and in order to obtain an optical output equivalent to that at room temperature, the drive current must be increased. I must. However, as shown in FIG. 12, when the VCSEL is packaged, there is a problem that even if the drive current is increased, the maximum light output does not reach the prescribed light output. This is because when the drive current of the VCSEL is increased, the spread angle of the laser light emitted from the VCSEL is increased, and the laser light is incident on the peripheral portion of the lens (for example, the lens 214 in FIG. 10). This is because the amount of light that is appropriately incident on the optical fiber is reduced due to the influence of aberration and the like. In particular, in the case of a multi-mode VCSEL, since the divergence angle is larger than that in the single mode, the loss of light amount is increased.

  The present invention solves such a problem, and an object thereof is to provide an optical semiconductor package in which a decrease in light output is suppressed in a wide temperature range.

  An optical semiconductor package according to the present invention is formed of a first resin having a first coefficient of thermal expansion, has a first end and a second end facing the first end, A housing in which first and second openings are formed in the first and second ends, respectively, and an internal space is formed between the first end and the second end; and a semiconductor laser A support member for supporting the element; and a light transmissive second resin having a second thermal expansion coefficient different from the first thermal expansion coefficient, and the inner part being in contact with a part of the inner wall of the housing. A lens member disposed in the space, and the support member is coupled to the first end so that the semiconductor laser element is located in the first opening, and is emitted from the semiconductor laser element The laser beam that has passed through the lens member is guided to the second opening.

The support member is, for example, a stem on which a semiconductor laser element is mounted. Further, the support member can include a cap for sealing the semiconductor laser element. The lens member may seal the semiconductor laser element on the support member. Preferably, the first resin is an epoxy resin and the second resin is a polycarbonate. Alternatively, the first resin is a silicone resin and the second resin is a polycarbonate. Preferably, a first thermal expansion coefficient of the first resin is larger than a second thermal expansion coefficient of the second resin, and the lens member is caused by a difference in thermal expansion coefficient between the housing and the lens member. When stress is applied, the refractive index of the second resin increases. Preferably, the second resin has a photoelastic coefficient of 30 × 10 ⁻¹² / Pa or more, and a change in refractive index is 0.003 or more.

  Preferably, the lens member includes an incident surface on which a laser beam from the semiconductor laser element is incident, an emission surface facing the incident surface, and an outer peripheral surface connecting the incident surface and the emission surface. Preferably, the outer peripheral surface is fixed to a part of the inner wall with an adhesive. Preferably, an optical fiber is coupled to the second opening. The semiconductor laser element is a surface emitting semiconductor laser that emits multimode laser light.

  According to the present invention, a lens member having a coefficient of thermal expansion different from that of the housing is provided in the housing, and stress caused by a difference between the two coefficients of thermal expansion is applied to the lens member at a high temperature so that the refractive index of the lens member is increased. To substantially increase the numerical aperture of the lens member. Thereby, the laser light emitted from the semiconductor laser element is effectively refracted by the lens member and guided to the second opening, and a decrease in light output at the second opening can be suppressed.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  FIG. 1A is a sectional view showing a schematic configuration of an optical semiconductor package according to the first embodiment of the present invention, and FIG. 1B is a sectional view of a housing. The optical semiconductor package 10 according to the first embodiment includes a can package 12 including a VCSEL, a housing 14 made of a cylindrical resin, and a lens member 16 accommodated in the housing 14.

  The housing 14 is formed by molding a resin such as epoxy, and as shown in FIG. 1B, the first end portion 14a and the second end portion facing the first end portion 14a. 14b. An internal space 14c is formed between the first end portion 14a and the second end portion 14b. A circular first opening 14d is formed at the first end portion 14a, and a second opening 14e having a smaller diameter than the first opening 14d is formed at the second end portion 14b. . The internal space 14c is connected to the first opening 14d and the second opening 14e, respectively, and has a step surface 14f at the boundary between them. Further, a locking portion 14g having a slightly smaller inner diameter is formed in the second opening 14e.

  The can package 12 includes a VCSEL 30 that emits laser light, a disc-shaped stem 32 on which the VCSEL 30 is mounted, a cup-shaped cap 34 that seals the VCSEL 30 on the stem 32, and a conductive member attached to the bottom surface side of the stem 32. And a plurality of lead terminals 36 made of a conductive metal. A circular opening window is formed in the center of the upper surface of the cap 34, and a flat glass 34a is attached to the opening window. The lead terminal 36 is inserted into the stem through a through hole (not shown), and is electrically connected to the electrode of the VCSEL 30. The stem 32 serves as a support member that supports the VCSEL 30, but not only the stem 32 but also a cap 34 that seals the VCSEL can be included as a support member of the VCSEL 30.

  The can package 12 is attached to the first end portion 14a so that the VCSEL 30 is located in the first opening 14d. For example, the peripheral portion of the stem 32 can be fixed to the first end portion 14a of the housing 14 using an adhesive or the like. At this time, it is preferable that the emission point of the VCSEL 30 coincides with substantially the center of the first opening 14d. A cylindrical ferrule 18 for holding the optical fiber 20 is inserted into the second opening 14e of the second end portion 14b. The ferrule 18 holds the core 20a of the optical fiber 20 in a through hole formed therein. The tip of the ferrule 18 is brought into contact with the locking portion 14g in the second opening 14e, and the core 20a is positioned substantially at the center of the second opening.

  FIG. 2 is a cross-sectional view showing a typical configuration of a VCSEL. The VCSEL 30 includes an n-side electrode 102 formed on the back surface of an n-type GaAs substrate 100, and a lower DBR in which n-type GaAs buffer layers 104 and n-type AlGaAs layers having different Al compositions are alternately stacked on the substrate 100. (Distributed Bragg Reflector) 106, active region 108, current confinement layer 110 made of p-type AlAs including an oxidized region on the periphery, and upper DBR 112 in which p-type AlGaAs layers having different Al compositions are alternately stacked. , A semiconductor layer including a p-type GaAs contact layer 114 is stacked. A cylindrical post (or mesa) P is formed by etching the stacked semiconductor layers.

  On the top of the post P, an annular p-side electrode 118 made of a conductive material such as Au / Ti connected to the contact layer 114 through the contact hole of the interlayer insulating film 116 is formed. The opening formed in the center of the p-side electrode 118 serves as a laser light emission window. By applying a forward bias current between the n-side electrode 102 and the p-side electrode 118, for example, multimode laser light in the vicinity of 850 nm is emitted from the emission window in the direction perpendicular to the substrate. The emitted laser light is incident on the lens member 16 through the flat glass 34 a of the cap 34. The can package 12 can also be mounted with a multi-spot type VCSEL in which a plurality of light emission spots are formed.

  The lens member 16 is configured by molding a resin different from the resin constituting the housing 14. The resin constituting the lens member 16 is light-transmissive, desirably has a thermal expansion coefficient smaller than the thermal expansion coefficient of the housing 14, and further has a photoelastic characteristic in which the refractive index changes when a stress is applied. have.

  As shown in FIG. 3, the lens member 16 includes a convex incident surface 40 on which light from the VCSEL 30 is incident, an annular flat surface 42 connected to the incident surface 40, and a substantially right angle from the flat surface 42. A first contact surface 44 extending; a second contact surface 46 extending substantially perpendicularly from the first contact surface 44 and opposite the flat surface 42; and a third contact surface extending substantially perpendicularly from the second contact surface 46. It has a contact surface 48 and a convex exit surface 50 connected to the third contact surface and facing the entrance surface 40.

  The optical axes of the entrance surface 40 and the exit surface 50 substantially coincide with the light emitting point of the VCSEL 30 and the center of the core 20a, respectively. The first contact surface 44 is in contact with the cylindrical inner wall 14h of the housing 14 as shown in FIG. 1A, and is preferably fixed in a state of surface contact with the inner wall by an epoxy adhesive or other methods. Has been. The second contact surface 46 is in surface contact with the stepped surface 14f of the internal space of the housing 14, and the third contact surface 48 is in surface contact with the inner wall 14i of the second opening at the second end. Preferably, at normal temperature (25 ° C.), no thermal stress is generated between the first, second, and third contact surfaces 44, 46, and 48 and the housing 14 due to a difference in thermal expansion coefficient. When the temperature in the package or the ambient temperature rises, the lens member and the housing are thermally expanded at their respective thermal expansion coefficients. However, since the first contact surface 44 is fixed to the inner wall 14h, the lens member 16 Thermal stress is received by 14h. When the thermal expansion coefficient of the resin constituting the housing 14 is larger than the thermal expansion coefficient of the resin constituting the lens member 16, the lens member is subjected to thermal stress that is pulled in the radial direction. Here, since the second and third contact surfaces 46 and 48 are in free contact with the step surface 14f and the inner wall 14i (that is, not fixed by an adhesive or the like), thermal stress is applied by the housing. I do not receive it. However, the second and third contact surfaces 46 and 48 may be fixed to the inner wall with an adhesive or the like. In this case, the second and third contact surfaces 46 and 48 are similarly subjected to thermal stress. become.

  Next, the operation of the optical semiconductor package at a high temperature will be described. When the semiconductor optical package is used at a high temperature such as 120 ° C., for example, as described above, thermal stress is applied to the lens member 16 due to the difference in thermal expansion coefficient between the housing and the lens member. FIG. 4B shows a state when the lens member 16 receives a thermal stress in the pulling direction. That is, a substantially uniform tensile force P acts in the radial direction around the optical axis C of the lens member 16.

  Since a material having a photoelastic effect is used for the lens member 16, the refractive index of the lens member 16 increases when thermal stress is applied to the lens member 16. If the refractive index of the lens member 16 can be increased, this is practically equivalent to increasing the numerical aperture of the lens member 16.

FIG. 5 is a graph showing the relationship between the photoelastic coefficient and the refractive index change. The horizontal axis is the photoelastic coefficient, and the vertical axis is the refractive index change. As shown in the figure, if the substance has a large photoelastic coefficient, the refractive index change Δn also becomes large due to the photoelastic effect. When the photoelastic coefficient is 30 × 10 ⁻¹² / Pa or more, the refractive index change Δn is 0.003 or more, and this change amount appears as a change in lens characteristics. Therefore, it is desirable that the material of the lens member 16 has a photoelastic coefficient of 30 × 10 ⁻¹² / Pa or more. The numerical aperture NA of the lens member can be derived from the following equation.

FIG. 6 shows a combination of the resin constituting the housing and the lens member of this embodiment. As shown in FIG. 6, as a preferred first specific example, an epoxy resin is used as a material for the housing, and polycarbonate is used as a material for the lens member 16. The thermal expansion coefficient of the epoxy resin is 30 × 10 ⁻⁵ / ° C., and the thermal expansion coefficient of the polycarbonate is 7 × 10 ⁻⁵ / ° C. Further, the polycarbonate has photoelastic characteristics, the photoelastic coefficient is 100 × 10 ⁻¹² / Pa, and the refractive index n when the stress is zero is 1.59. Referring to the graph of FIG. 5 described above, polycarbonate has a refractive index change Δn of about 0.011 due to photoelasticity. Therefore, when thermal stress is applied to the lens member 16, the refractive index n of the polycarbonate changes from 1.59 to 1.60.

As a preferred second specific example, a silicone resin can be used as the material of the housing, and a polycarbonate can be used as the material of the lens member 16. The thermal expansion coefficient of the silicone resin is 20 × 10 ⁻⁵ / ° C., and the thermal stress applied to the lens member 16 is somewhat smaller than that in the first specific example.

  FIG. 7 is a graph showing the optical characteristics of Specific Example 1, Specific Example 2 and Comparative Example shown in FIG. 6, where the horizontal axis indicates the temperature and the vertical axis indicates the change in the numerical aperture NA. The lens diameter D (incident surface diameter) when calculating the numerical aperture NA according to the equation (1) is 1.60 mm, and the laser beam diameter d is 1.66 mm. As is apparent from the graph of FIG. 7, in the specific example 1 and the specific example 2, when the package temperature or the ambient temperature rises, the numerical aperture change ΔNA increases in proportion thereto. When the package temperature reaches about 120 ° C., ΔNA increases to 0.014 in specific example 1, and ΔNA increases to 0.008 in specific example 2. On the other hand, the comparative example uses polyetherimide for the housing and the lens member, respectively, and it can be seen that the numerical aperture NA hardly changes regardless of the package temperature.

  When an optical semiconductor package is used at a high temperature, the VCSEL is driven with a larger driving current than at normal temperature in order to suppress a decrease in light output from the package. At this time, the spread angle of the laser light from the VCSEL is widened. However, since the refractive index of the lens member 16 increases due to the photoelastic effect and the numerical aperture NA increases, the laser light incident on the peripheral portion of the incident surface 40 (see FIG. 3) of the lens member 16 is a light beam. The light is further refracted in the axial direction, is further refracted by the exit surface 50, and is effectively incident on the core 20a of the optical fiber 20. As a result, the loss of the amount of light incident on the optical fiber is suppressed compared to the conventional case, the optical coupling efficiency between the VCSEL 30 and the optical fiber 20 can be improved, and the decrease in the optical output of the optical semiconductor package in a high temperature environment is suppressed. can do.

  In the first embodiment, the can package 12 in which the VCSEL 30 is sealed by the cap 34 is coupled to the housing 14, but the cap 34 is not necessarily required. For example, as shown in FIG. 4A, the stem from which the cap 34 is removed may be coupled to the first end portion 14 a of the housing 14. The can package 12 may include a light receiving element 31 for monitoring the output state of the VCSEL 30.

  The shape of the lens member 16 is not limited to the shape shown in FIG. 1, and can be changed as appropriate. For example, as shown in FIG. 4A, the entire surface is convex and a flat surface facing the entrance surface. A plano-convex lens 16 a having an exit surface can be used, or a lens shape such as a spherical lens or an aspherical lens can be used, and the side surface of such a lens can be joined to the inner wall of the housing 14. Further, the lens member is not necessarily inserted into the second opening 14e as shown in FIG.

  Further, in the above embodiment, the entire first contact surface 44 of the lens member 16 is brought into surface contact with the inner wall of the housing. For example, as shown in FIG. A plurality of protrusions 52 may be formed in the X direction and the Y direction, and these protrusions 52 may be joined to the inner wall of the housing. Alternatively, as shown in FIG. 4D, a plurality of protrusions 54 may be formed on the inner wall of the housing, and these protrusions 54 may be joined to the first contact portion 44 of the lens member. If the protrusions 52 and 54 are in a rotationally symmetric position at the center of the lens member, it is possible to apply a substantially uniform thermal stress to the lens member.

  Next, a second embodiment of the present invention will be described. FIG. 8 is a sectional view showing a schematic configuration of an optical semiconductor package according to the second embodiment of the present invention. In the optical semiconductor package 10A according to the second embodiment, the resin package 60 is coupled to the first end portion of the housing 14 instead of coupling the can package. The resin package 60 mounts the VCSEL 30 and the light receiving element 31 on a pedestal formed at the tip of one lead terminal via a die attach or the like, and seals the VCSEL 30 and the light receiving element 31 with a light transmissive resin 62. ing. The resin 62 has a smaller thermal expansion coefficient than that of the resin constituting the housing 14 and changes the refractive index due to photoelastic characteristics when an external force is applied. As the resin 62, for example, the polycarbonate shown in specific examples 1 and 2 as shown in FIG. 6 can be used.

  The resin 62 includes a convex emission surface 64 that emits laser light, and an outer peripheral surface 66 connected to the emission surface 64, and the outer peripheral surface 66 is in the first opening at the first end of the housing 14. Are bonded to each other by an adhesive or the like. For this reason, when the optical semiconductor package is used in a high temperature environment, the resin 62 is subjected to a thermal stress that is pulled in the outer peripheral direction, the refractive index of the resin 62 is increased, and the numerical aperture NA is increased. As a result, the spread angle of the laser light of the VCSEL 30 is increased, but the refractive index of the resin 62 is increased, so that the laser light emitted from the emission surface 64 is refracted more than at normal temperature, and as a result, the optical fiber. Is efficiently incident on the core 20a, and a decrease in light output at high temperatures is suppressed.

  FIG. 9 is a graph showing the relationship between the temperature change and the numerical aperture change of the optical semiconductor package according to the second embodiment. Also in the second example, as in the first example, it can be seen that the change in the numerical aperture NA of the resin 62 increases as the temperature rises. In the second embodiment, when the temperature in the optical semiconductor package is about 120 ° C., the numerical aperture NA increases by 0.008.

  As described above, according to this embodiment, the housing and the lens member are made of different materials, and stress due to the difference in thermal expansion coefficient between the lens member and the housing that holds the lens member at high temperatures is applied to the lens member. By increasing the refractive index by the photoelastic effect, it is possible to suppress a decrease in the coupling efficiency between the VCSEL and the optical fiber even under a high driving current. Therefore, even in a package such as TOSA, it is possible to suppress a decrease in the thermal rollover point at high temperatures, and as a result, good output characteristics can be obtained at high temperatures.

  The preferred embodiment of the present invention has been described in detail above, but the present invention is not limited to the specific embodiment, and various modifications can be made within the scope of the present invention described in the claims. Deformation / change is possible.

  In the above-described embodiment, the thermal stress in the direction in which the lens member is pulled is applied. On the contrary, if the resin has a photoelastic effect in which the refractive index increases due to the thermal stress in the compression direction, A combination in which the thermal expansion coefficient of the resin is larger than the thermal expansion coefficient of the resin of the housing may be used.

  The optical semiconductor package according to the present invention can be used in various fields such as optical information processing and optical high-speed data communication.

FIG. 1A is a sectional view showing a schematic configuration of an optical semiconductor package according to the first embodiment of the present invention, and FIG. 1B is a sectional view of a housing. It is sectional drawing which shows the typical structure of VCSEL. 3A is a plan view of the lens member, and FIG. 3B is a cross-sectional view taken along the line AA. 4A is a cross-sectional view showing the configuration of another optical semiconductor package of the first embodiment, FIG. 4B is a diagram for explaining the thermal stress of the lens member at a high temperature, and FIG. 4C. FIG. 4D is a diagram for explaining another joined state of the lens member. It is a graph which shows the relationship between a photoelastic coefficient and a refractive index change. It is a figure which shows the combination of the material each used for the housing and lens member in a 1st Example. It is a graph which shows the relationship between the change of the numerical aperture of the combination of the material shown in FIG. 6, and a temperature change. It is sectional drawing which shows schematic structure of the optical semiconductor package which concerns on the 2nd Example of this invention. It is a graph which shows the relationship between the change of the numerical aperture of the lens member by a 2nd Example, and a temperature change. It is a schematic side sectional view showing a conventional optical semiconductor package. It is a graph which shows the optical output characteristic of VCSEL single-piece | unit. It is a graph which shows the optical output characteristic of VCSEL after a package.

10: optical semiconductor package 12: can package 14: housing 14a: first end 14b: second end 14c: internal space 14d: first opening 14e: second opening 14f: step surface 14g: locking Portion 14h: Inner wall 14i: Inner wall 16: Lens member 18: Ferrule 20: Optical fiber 20a: Core 30: VCSEL 32: Stem 34: Cap 34a: Flat glass 36: Lead terminal 40: Incident surface 42: Flat surface 44: First 1 contact surface 46: second contact surface 48: third contact surface 50: exit surface 52, 54: protrusion 60: resin package 62: resin 64: exit surface 66: outer peripheral surface

Claims (8)

Formed from a first resin having a first coefficient of thermal expansion, having a first end and a second end opposite the first end, the first and second ends being Each having a first opening and a second opening, and an inner space formed between the first end and the second end; and
A support member for supporting the semiconductor laser element;
It has a smaller second coefficient of thermal expansion than the first thermal expansion coefficient, and is formed from a light transmitting second resin have a photoelastic properties, so as to contact a portion of the inner wall of the housing A lens member disposed in the internal space,
The support member is coupled to the first end so that the semiconductor laser element is located in the first opening,
Laser light emitted from the semiconductor laser element passes through a lens member and is guided to the second opening ,
When the lens member receives a thermal stress that is pulled in a radial direction of the lens member due to a difference between the first thermal expansion coefficient and the second thermal expansion coefficient, the lens member changes so as to increase a refractive index. Optical semiconductor package. The optical semiconductor package according to claim 1 , wherein the first resin is an epoxy resin, and the second resin is a polycarbonate. The optical semiconductor package according to claim 1 , wherein the first resin is a silicone resin, and the second resin is a polycarbonate. 4. The optical semiconductor package according to claim 1, wherein the second resin has a photoelastic coefficient of 30 × 10 ⁻¹² / Pa or more and a change in refractive index of 0.003 or more. The lens member includes an incident surface on which a laser beam from the semiconductor laser element is incident, an exit surface facing the incident surface, and an outer peripheral surface connecting the incident surface and the exit surface, and the outer peripheral surface. The optical semiconductor package according to claim 1, which contacts a part of the inner wall of the housing. The optical semiconductor package according to claim 5 , wherein the outer peripheral surface is fixed to a part of the inner wall with an adhesive. The optical semiconductor package according to claim 1, wherein an optical fiber is coupled to the second opening. The semiconductor laser device is a surface-emitting type semiconductor laser that emits a multi-mode laser light, an optical semiconductor package according to any one claims 1 to 7.

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