JP2012023325A - Light emitting module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light emitting module capable of suppressing a characteristic impedance mismatch.SOLUTION: A light emitting module 1 includes a multilayer ceramic package 2 having ceramic layers 3-5. The intermediate ceramic layer 4 comprises an opening 10 forming a recess section 11 to mount an optical device cooperating with an upper surface of the lower ceramic layer 3. The upper layer ceramic 5 is configured to have a side wall of the package so as to surround an area including the recess section 11. A sub-mount 14 is placed on a bottom surface of the recess section 11. A laser diode 16 is mounted on an upper surface of the sub-mount 14. An upper surface of the multilayer ceramic package 2 is bonded to a metal sleeve 31 via a holder 25 and a joint 28. A ferrule 34 holding an optical fiber 33 optically coupled to the laser diode 16 is put inside the metal sleeve 31.

Description

  The present invention relates to a light emitting module used in optical communication or the like.

  As a conventional light emitting module, for example, as described in Patent Document 1, a module including a ceramic package incorporating a VCSEL (light emitting element) and an optical coupler fixed to the ceramic package is known. .

U.S. Pat. No. 7,476,040

  However, in the above prior art, since the light emitting element is mounted on the upper surface of the ceramic package via the submount, when the wiring circuit pattern provided on the upper surface of the ceramic package and the light emitting element are connected by a wire, The wire length must be increased by the amount of the submount. For this reason, the influence of the parasitic inductance component of the wire increases, and mismatching of characteristic impedance occurs. As a result, good frequency characteristics cannot be obtained in high-speed transmission.

  The objective of this invention is providing the light emitting module which can suppress the mismatch of characteristic impedance.

  The light emitting module of the present invention includes a multilayer ceramic package containing a light emitting element, and a metal cylindrical member that is fixed to the upper surface of the multilayer ceramic package and accommodates an optical fiber that is optically coupled to the light emitting element. A first ceramic layer, a second ceramic layer laminated on the first ceramic layer, and having an opening for forming a recess for mounting the light emitting element in cooperation with the upper surface of the first ceramic layer; A third ceramic layer that is laminated on the ceramic layer and surrounds the region including the recess, the submount being disposed in the recess, and the light emitting element being mounted on the submount It is characterized by.

  As described above, in the light emitting module of the present invention, the submount is disposed in the concave portion formed by the cooperation of the upper surface of the first ceramic layer and the opening of the second ceramic layer in the multilayer ceramic package, and the submount emits light. By mounting the element, the wire length can be shortened when the wiring circuit pattern provided on the upper surface of the second ceramic layer and the light emitting element are connected by a wire. At this time, for example, when connecting a wire via a wiring circuit pattern provided on the upper surface of the submount, the upper surface height position of the second ceramic layer and the upper surface height position of the submount are matched, or the wire Is directly connected to the light emitting element, the upper surface height position of the submount is set lower than the upper surface height position of the second ceramic layer. Thus, the wire length can be sufficiently shortened by appropriately setting the height dimension of the submount in accordance with the connection form of the wires. Thereby, the influence of the parasitic inductance component of the wire can be reduced, and mismatching of the characteristic impedance can be suppressed.

  Preferably, a monitor light receiving element for monitoring the output light amount of the light emitting element is mounted on the bottom surface of the recess, and light emitted from the light emitting element is directed to the optical fiber between the light emitting element and the monitor light receiving element. And an optical member that transmits a part of the light toward the light receiving element for monitoring.

  The drive signal for driving the light emitting element is supplied from the rear side of the light emitting element, but the monitor light receiving element is arranged in front of the light emitting element (light emission side), so the weak output current of the monitor light receiving element. Becomes less susceptible to noise caused by the drive signal. Therefore, fluctuations in the output current of the monitoring light receiving element due to noise are suppressed, and as a result, the light emission output of the light emitting element can be kept stable.

  Preferably, the submount is formed of an insulating material having a higher thermal conductivity than the ceramic material forming the first to third ceramic layers. In this case, the heat generated by the light emitting element is sufficiently diffused by the submount. For this reason, the fall of the light emission output by the thermal expansion of a light emitting element can be suppressed.

  At this time, the submount is preferably formed of aluminum nitride. As an insulating material for forming the submount, it is most effective to use aluminum nitride having a sufficiently high thermal conductivity.

  ADVANTAGE OF THE INVENTION According to this invention, the mismatch of the characteristic impedance of a light emitting module can be suppressed. This makes it possible to obtain good frequency characteristics in high-speed transmission.

It is a perspective view which shows one Embodiment of the light emitting module concerning this invention. It is a perspective view including the partial cross section of the light emitting module shown in FIG. FIG. 3 is an enlarged view of a main part of FIG. 2. FIG. 3 is an enlarged cross-sectional view of a location including the multilayer ceramic package shown in FIG. 2. FIG. 3 is an enlarged perspective view showing the inside of the multilayer ceramic package shown in FIG. 2. It is sectional drawing which shows the direction of the light radiate | emitted from LD shown in FIG. It is sectional drawing which shows the optical transceiver provided with the light emitting module shown in FIG.

  Hereinafter, a preferred embodiment of a light emitting module according to the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a perspective view showing an embodiment of a light emitting module according to the present invention. 2 is a perspective view including a partial cross section of the light emitting module shown in FIG. 1, and FIG. 3 is an enlarged cross-sectional view of the main part of FIG. In each figure, the light emitting module 1 of this embodiment includes a multilayer ceramic package 2 in which optical devices and electronic components are arranged.

  The multilayer ceramic package 2 has a three-layer structure including a lower ceramic layer 3, an intermediate ceramic layer 4, and an upper ceramic layer 5. The intermediate ceramic layer 4 is laminated on the lower ceramic layer 3, and the upper ceramic layer 5 is laminated on the intermediate ceramic layer 4. These ceramic layers 3 to 5 are formed of alumina having excellent workability. The laminated ceramic package 2 is formed by performing sintering and dicing processing in a state where the ceramic layers 3 to 5 are positioned and laminated. In the state where the ceramic layers 3 to 5 are positioned and laminated, the ceramic layers 3 to 5 may be cut and subdivided using a blade and then sintered, and then the laminated ceramic package 2 may be formed. By cutting before sintering, the laminated ceramic layers 3 to 5 can be easily subdivided.

  The outer shape of the lower ceramic layer 3 is substantially rectangular. Metal circuit wiring patterns (metallized layers) 6 are respectively provided on the upper and lower surfaces of the lower ceramic layer 3. As shown in FIG. 4, a plurality of vias 7 that electrically connect the upper and lower circuit wiring patterns 6 are provided in the lower ceramic layer so as to penetrate the lower ceramic layer 3. An external connection terminal (not shown) for connecting to an external circuit is provided on the lower surface of the lower ceramic layer 3.

  The outer shape of the intermediate ceramic layer 4 is substantially rectangular like the lower ceramic layer 3. The thickness of the intermediate ceramic layer 4 is the same as that of the lower ceramic layer 3. Circuit wiring patterns 8 are respectively provided on the upper surface and the lower surface of the intermediate ceramic layer 4. As shown in FIG. 4, a plurality of vias 9 that electrically connect the upper and lower circuit wiring patterns 8 are provided in the intermediate ceramic layer 4 so as to penetrate the intermediate ceramic layer 4.

  An opening 10 is formed in the central portion of the intermediate ceramic layer 4. The opening 10 forms a rectangular recess 11 for mounting an optical device in cooperation with the upper surface of the lower ceramic layer 3.

  The upper ceramic layer 5 has a substantially rectangular ring shape so as to secure a space for mounting electronic components on the intermediate ceramic layer 4, and constitutes a side wall of the multilayer ceramic package 2. That is, the upper ceramic layer 5 is provided so as to surround a region including the recess 11. The thickness of the upper ceramic layer 5 is larger than the thickness of the intermediate ceramic layer 4. Alternatively, a plurality of upper ceramic layers 5 can be laminated with the thickness of the upper ceramic layer 5 equal to the thickness of the intermediate ceramic layer 4. By aligning the thicknesses of all the ceramic sheets (ceramic layers), the process of managing the thickness of the ceramic sheets can be unified, and the manufacturing process can be simplified.

  Circuit wiring patterns 12 are respectively provided on the upper and lower surfaces of the upper ceramic layer 5. However, the upper ceramic layer 5 is not provided with vias that electrically connect the upper and lower circuit wiring patterns 12 to each other. Therefore, the upper surface and the lower surface of the upper ceramic layer 5 are electrically insulated (separated) completely. A substantially rectangular metal ring 13 is fixed to a circuit wiring pattern (metallized layer) 12 on the upper surface of the upper ceramic layer 5 by brazing or the like.

  As shown in FIGS. 3 and 5, a rectangular parallelepiped submount 14 is placed on the bottom surface of the recess 11. The thickness of the submount 14 is equal to the thickness of the intermediate ceramic layer 4. That is, the upper surface of the submount 14 and the upper surface of the intermediate ceramic layer 4 are flush with each other.

  The submount 14 is formed of an insulating material having a higher thermal conductivity than alumina forming the ceramic layers 3 to 5. As such an insulating material, it is preferable to use aluminum nitride having a thermal conductivity 10 times or more that of alumina. As the insulating material, beryllium oxide (BeO), silicon carbide (SiC), sapphire, diamond, or the like can be used.

  A circuit wiring pattern 15 is provided on the upper surface of the submount 14. A laser diode (LD: light emitting element) 16 is mounted on the upper surface of the submount 14. The LD 16 is an edge-emitting LD and emits light in the lateral direction (the direction along the upper surface of the intermediate ceramic layer 4).

  At this time, since the submount 14 is formed of an insulating material having a high thermal conductivity, the heat generated by the LD 16 or the like is sufficiently diffused to the lower ceramic layer 3 via the submount 14. Heat is prevented from being trapped. Accordingly, a decrease in the light emission output due to the thermal expansion of the LD 16 is suppressed, so that the LD 16 operates well.

  As a base material constituting the LD 16, InP (indium phosphide) having a linear expansion coefficient of about 4.5 ppm / K is used. As an operation range of the light emitting module, −40 ° C. to 85 ° C. may be required. The LD 16 is mounted on the submount 14 via a bonding material such as solder. As the solder material, AuSn solder is desirable, but other than that, SuAgCu solder, AuGe solder or the like may be used. The solder has a higher thermal conductivity than the adhesive, and can efficiently conduct the heat generated in the LD 16 to the submount 14. When the LD 16 is mounted on the submount 14, if the linear expansion coefficient of the submount 14 is significantly different from the linear expansion coefficient of the LD 16, stress due to the difference in linear expansion coefficient is generated, which may cause distortion in the LD 16. Therefore, the material of the submount 14 is desirably a material having a thermal expansion coefficient and a linear expansion coefficient close to that of the LD 16. Aluminum nitride has a linear expansion coefficient of about 4.6 ppm / K and is very close to the linear expansion coefficient of LD 16. Therefore, it is desirable to use aluminum nitride as the material of the submount 14 as described above.

  As shown in FIG. 5, among the plurality of circuit wiring patterns 8 provided on the upper surface of the intermediate ceramic layer 4, two circuit wiring patterns located on both sides of the submount 14 become LD terminal connection patterns 8a. Yes. The LD terminal connection pattern 8 a is connected to a circuit wiring pattern (pad) 6 provided on the lower surface of the lower ceramic layer 3 through vias 9 and 7.

  The high frequency signal line of the LD terminal connection pattern 8 a and the high frequency signal line of the circuit wiring pattern 15 of the submount 14 are connected by a plurality of wires 17. At this time, since the height position of the upper surface of the intermediate ceramic layer 4 and the height position of the upper surface of the submount 14 coincide with each other, the length of the wire 17 can be minimized. The LD 16 and the high-frequency signal line of the circuit wiring pattern 15 are connected by a single wire 18. The ground line of the LD terminal connection pattern 8 a and the ground line of the circuit wiring pattern 15 are connected by a plurality of wires 19.

  Ribbon wires can also be used to connect the high-frequency signal lines of the LD terminal connection pattern 8a and the high-frequency signal lines of the circuit wiring pattern 15 of the submount 14. By using such a wide wire, the inductance component due to the wire can be reduced, and a more preferable design as a high-frequency line can be realized. In addition, when a ribbon wire is used, a wedge bond is used, so that the wire loop height can be further reduced and the wire length can be shortened.

  The high-frequency signal line inside the multilayer ceramic package 2 is designed to have a desired characteristic impedance, thereby reducing impedance variation in the line. In order to match the characteristic impedance, it is necessary to appropriately arrange the inductance component generated by the vias 7 and 9 and the conductance component generated by the coupling between the signal line and the ground line. By arranging the inductance component and the conductance component at short intervals with respect to the rise time of the high-frequency signal propagating through the signal line, the characteristic impedance can be matched.

特性インピーダンスＺ０が設計の狙いよりも高い場合は、伝送線路のインダクタンス成分Ｌが大きいため、コンダクタンス成分Ｃが大きくなるように伝送線路及び接地電位結合を高め、寄生容量を大きくする等の設計修正が必要となる。反対に特性インピーダンスＺ０が設計の狙いよりも低い場合は、伝送線路のインダクタンス成分Ｌを大きくする設計修正が必要となる。 The characteristic impedance Z0 is expressed by the following formula.

When the characteristic impedance Z0 is higher than the design target, since the inductance component L of the transmission line is large, design modifications such as increasing the transmission line and ground potential coupling and increasing the parasitic capacitance so that the conductance component C is increased. Necessary. On the other hand, when the characteristic impedance Z0 is lower than the design target, a design modification is required to increase the inductance component L of the transmission line.

  A monitoring photodiode (PD: light receiving element) 20 for monitoring the output light amount of the LD 16 is mounted on the bottom surface of the recess 11 located in front of the LD 16. Of the plurality of circuit wiring patterns 8 provided on the upper surface of the intermediate ceramic layer 4, two circuit wiring patterns located on both sides of the PD 20 are PD terminal connection patterns 8b. The output signal line of the PD terminal connection pattern 8b and the monitor PD 20 are connected by a wire 21. The ground line of the PD terminal connection pattern 8 b and the ground line of the circuit wiring pattern 6 are connected by a wire 22.

  An optical member 23 made of a mirror or a prism is disposed between the submount 14 and the monitoring PD 20 in the recess 11. As shown in FIG. 6, the optical member 23 reflects a part of the light emitted from the LD 16 vertically upward and transmits the remainder of the light, and the reflection / transmission surface 23a. And an exit surface 23b for emitting incident light toward the monitor PD 20. The reflection / transmission surface 23a is inclined at an angle of 45 degrees with respect to the upper surface of the intermediate ceramic layer 4, and has a predetermined reflectance.

  The shape of the optical member 23 may be a right triangle, a pentagon, or a planar shape as long as it has a reflection / transmission surface 23a and an emission surface 23b. Further, as the material of the optical member 23, a glass part or a resin material having a high transmittance with respect to the emission wavelength of the LD 16 can be used. On the reflection / transmission surface 23a, a reflection / transmission film may be formed by dielectric multilayer coating. In the dielectric multilayer film, the material and thickness of each layer are controlled so as to have a desired reflectance with respect to the emission wavelength of the LD 16.

Since the light transmitted through the optical member 23 is diffused light, the dependence on the mounting position of the monitor PD 20 is small. For this reason, it is not necessary to control the mounting position of the monitor PD 20 with high accuracy. Here, the reflectance R of the reflection / transmission surface 23a of the optical member 23, the optical power Po obtained from the LD 16, the optical power Pf coupled to the optical connector inserted into the metal sleeve 31 described later, and the lens 24 described later. The relationship with the coupling efficiency ηl by
Pf = Po × R × ηl
It becomes. Further, the monitor current IPD obtained by the monitoring PD 20, the optical power Pp (= Po × R) transmitted through the optical member 23, and the efficiency ηp for coupling the light transmitted through the optical member 23 to the light receiving surface of the monitoring PD 20. The relationship with the quantum efficiency ηi for converting the light received by the monitoring PD 20 into a current is:
IPD = Pp × ηp × ηi = Po × R × ηp × ηi
It becomes. Therefore, it is necessary to design the required reflectance R from the required specification of the optical power Pf coupled to the optical connector and the required specification of the monitor current IPD.

  When the optical power Po of the LD 16 is sufficiently higher than the optical power Pf required for the light emitting module, it is necessary to reduce the optical power. In general, the metal sleeve 31 (described later) is disposed at a position separated (distant) in the optical axis direction, and defocused so that the optical power is lower than the optimum coupling position by the lens 24 (described later). On the other hand, in the structure using the optical member 23, the reduction of the optical power due to defocusing can be minimized by designing the reflectance R to be small. Thereby, the amount of separating the metal sleeve 31 in the optical axis direction can be reduced, and the variation in the overall length of the light emitting module 1 can be designed to be small. In addition, when the light emitting module 1 is mounted on the optical transceiver 37 as described later, the distance variation between the light emitting module 1 and the circuit board 41 can be designed to be small, and the high-frequency line of the flexible board 42 and the circuit board 41 can be designed to be short. It becomes possible to design the optical transceiver 37 exhibiting good high frequency characteristics.

  In addition, the RIN resistance required for the light emitting module can be increased by designing the reflectance R to be small within a range in which the relationship between the light power Pf of the light emitting module and the light power Po of the LD 16 is established. When the reflected light quantity defined by the standard is returned to the light emitting module with respect to the light power Pf of the light emitting module, the light quantity obtained by multiplying the reflected light quantity by the reflectance R of the optical member 23 is transmitted to the LD 16. Therefore, if the reflectance R is designed to be sufficiently small, the amount of reflected light transmitted to the LD 16 is smaller than that of a general light emitting module, and RIN resistance can be improved. Depending on the design, the RIN resistance can be satisfied even without an isolator having a function of suppressing the amount of reflected light, and the component cost of the light emitting module can be reduced.

  A part of the light emitted from the LD 16 is reflected by the reflectance R at the reflection / transmission surface 23a of the optical member 23 and refracted in the vertical direction, and the other light is transmitted through the optical member 23 to the monitor PD 20 side. Emitted. At this time, the light from the LD 16 is refracted and transmitted according to Snell's law by the angle of 45 degrees of the reflection / transmission surface 23a and the material refractive index n of the optical member 23. Further, the horizontal light emitted from the LD 16 is refracted downward from the horizontal as shown by the dotted line in FIG. 6 when passing through the optical member 23. Here, when the light receiving surface of the monitoring PD 20 is the upper surface, the light emitted from the LD 16 and transmitted through the optical member 23 needs to be incident on the upper surface of the monitoring PD 20. As a result, it is necessary to design the upper surface (light receiving surface) of the monitoring PD 20 relatively lower than the active layer of the LD 16. In this structure, since the LD 16 is mounted on the upper surface of the submount 14 mounted on the recess 11 and the monitor PD 20 is mounted on the recess 11, the light transmitted through the optical member 23 is efficiently monitored. It can be received by the light receiving surface of the PD 20.

  Although not particularly illustrated, electronic parts such as an IC, a resistor, and a capacitor may be mounted on the upper surface of the intermediate ceramic layer 4. The circuit wiring pattern 8 and the electronic component are connected by bonding, wiring, or flip chip.

  Note that the LD 16, the monitoring PD 20, and the electronic components are mounted by soldering or an adhesive. For soldering, AuSn solder, SuAgCu solder or the like is used. As the adhesive, a conductive adhesive is used for bonding electronic components, and a non-conductive adhesive is used for bonding non-electronic components.

  A metal holder 25 that holds the lens 24 is fixed to the upper surface of the multilayer ceramic package 2 as described above. The lens 24 and the holder 25 are sealed using a sealing material made of low melting point glass or the like. At this time, the interior of the multilayer ceramic package 2 is hermetically sealed by welding the holder 25 to the upper surface of the metal ring 13 in an environment in which the interior of the multilayer ceramic package 2 is replaced with nitrogen.

  The holder 25 is mounted on a jig for positioning the lens 24 and is put into a high temperature furnace in a state where low melting point glass is supplied. And each part is sealed by cooling in the state which the low melting glass was familiar with the lens 24 and the holder 25. FIG. In general, when a compressive stress is applied to a glass material, cracks and the like hardly occur. As a material of the lens 24, a glass material having a refractive index of about 1.4 to 1.9 such as BK7 or TaF3 is used. Their linear expansion coefficient has a value of about 7 to 8 ppm / K. A material having a linear expansion coefficient equal to or larger than that of the lens 24 is used for the low melting point glass disposed on the outer peripheral portion of the lens 24. As a material of the holder 25 arranged further on the outer peripheral portion than the low melting glass, it is desirable to use an Fe—Ni alloy having a larger linear expansion coefficient than the low melting glass. In particular, 50 alloy (composed of Fe and Ni and the ratio is 50%) has a linear expansion coefficient of about 10 ppm / K, and is desirable as a material for the holder 25.

  In addition to using a seam seal, the holder 25 may be sealed by supplying a brazing material to the upper surface of the metal ring 13 in advance and dissolving the brazing material by heating. As a heating method, in addition to the whole heating by an oven or the like, the vicinity of the brazing material may be heated spot by laser beam.

  The holder 25 is joined to the metal ring 13, and has a lid part 26 that covers and closes the upper opening of the multilayer ceramic package 2, and a cylindrical part 27 that is integrated with the lid part 26. The axis of the cylindrical portion 27 is orthogonal to the upper and lower surfaces of the multilayer ceramic package 2. The lens 24 is sealed and fixed to an annular holding portion 27 a provided so as to protrude from the inner peripheral surface of the cylindrical portion 27. When such a holder 25 is fixed to the metal ring 13, the position of the holder 25 with respect to the metal ring 13 is adjusted so that the optical axis shift between the lens 24 and the LD 16 is reduced.

  In addition, you may comprise a lid part and a cylindrical part with another components. In this case, a flat window glass for transmitting light emitted from the LD 16 and securing airtightness of the multilayer ceramic package 2 is sealed and fixed to the lid portion. And a cylindrical part is fixed to the lid part. As both fixing methods, YAG welding, resin bonding, or the like is used.

  A metal joint 28 is fixed to the holder 25 by YAG welding. The joint 28 includes a base portion 29 having a through hole 29 a for allowing light to pass therethrough, and a cylindrical portion 30 integrated with the base portion 29. The inner peripheral surface of the cylindrical portion 30 is joined to the outer peripheral surface of the cylindrical portion 27 of the holder 25.

  A metal sleeve 31 is fixed to the base 29 of the joint 28 by YAG welding. A zirconia sleeve 32 is disposed inside the metal sleeve 31. On the side of the joint 28 in the zirconia sleeve 32, a ferrule 34 holding an optical fiber 33 optically coupled to the LD 16 is disposed. Further, inside the metal sleeve 31, a metal cylindrical body 35 that press-fits and fixes the ferrule 34 is disposed adjacent to the zirconia sleeve 32. A flange portion 36 having an annular holding groove 36 a is provided on the outer peripheral surface of the metal sleeve 31. When the metal sleeve 31 is fixed to the base portion 29 of the joint 28, the metal sleeve 31 is aligned with two or three axes so that the light emitted from the LD 16 can be coupled to the optical fiber 33 with high efficiency. .

  As a material for the joint 28 and the metal sleeve 31, it is desirable to use stainless steel that is compatible with YAG welding and hardly rusts even in a high temperature and high humidity environment. Among stainless steels, a ferritic stainless material having a linear expansion coefficient close to zirconia or 50 alloy is desirable. In particular, materials such as SUS430 and SF20T can be used. By using a stainless steel material whose linear expansion coefficient is close to zirconia or 50 alloy, it is possible to stabilize the internal stress generated during cooling after YAG welding and the stress state due to the difference in temperature environment with respect to the press-fit fixing part of stainless steel and zirconia.

  The fixing between the holder 25 and the joint 28 and the fixing between the joint 28 and the metal sleeve 31 may be performed by bonding using a UV curing adhesive or the like in addition to YAG welding. In this case, after temporarily fixing the UV curable adhesive by irradiating it with UV light, it is preferable to reinforce with a thermosetting adhesive so as not to deviate from the position.

  In the light emitting module 1 as described above, as shown in FIG. 6, the light emitted from the LD 16 is reflected upward by the reflection / transmission surface 23 a of the optical member 23 (see the solid line), and the lens 24 attached to the holder 25. Is condensed and coupled to the optical fiber 33. At this time, part of the light emitted from the LD 16 passes through the optical member 23 (see the broken line) and is received by the monitoring PD 20.

  The light emitting module 1 is incorporated in an optical transceiver 37 as shown in FIG. The optical transceiver 37 includes a housing 38, and a front end portion of the housing 38 forms a receptacle portion 39 that guides an optical connector (not shown) coupled to the light emitting module 1. The receptacle 39 is provided with a holding projection 39 a for holding the light emitting module 1. The holding projection 39 a is fitted in the holding groove 36 a of the metal sleeve 31 in the light emitting module 1, so that the light emitting module 1 is held in the housing 38.

  A circuit board 41 on which the electronic component 40 is mounted is disposed in the optical transceiver 37. The circuit board 41 is disposed so that the mounting surface 41 a is orthogonal to the bottom surface of the multilayer ceramic package 2. The external connection terminals on the bottom surface of the multilayer ceramic package 2 and the external connection terminals provided on the mounting surface 41 a of the circuit board 41 are connected via a flexible substrate 42. The signal line of the flexible board 42 is designed to match the characteristic impedance of the multilayer ceramic package 2 and the circuit board 41. For this reason, a high frequency signal can be propagated from the drive circuit of the circuit board 41 to the optical device such as the LD 16 and the electronic component so as to reduce the loss.

  The flexible substrate 42 and the multilayer ceramic package 2 are joined by solder. The wiring circuit pattern on the bottom surface of the multilayer ceramic package 2 includes a high-frequency signal pad, a DC signal pad, and a ground pattern other than these. Similarly, pads and a ground pattern are also formed on the flexible substrate 42. Both patterns are uniformly connected by solder. For this reason, the heat generated inside the multilayer ceramic package 2 is transmitted to the ground pattern of the flexible substrate 42 via the solder. Therefore, the heat in the multilayer ceramic package 2 can be diffused efficiently, and a favorable operation can be performed even in a high temperature environment.

  By the way, by matching the characteristic impedance of the high-frequency signal line that propagates the high-frequency signal in the multilayer ceramic package 2, signal deterioration due to reflection between the lines can be suppressed, and good high-frequency characteristics can be obtained. However, if the wire length of the high-frequency signal line is long, it is greatly affected by the parasitic inductance of the wire, which causes a mismatch in characteristic impedance.

  On the other hand, in the present embodiment, the submount 14 having the wiring circuit pattern 15 including the high frequency signal line formed on the upper surface is disposed in the concave portion 11 of the multilayer ceramic package 2, and the LD 16 is mounted on the upper surface of the submount 14. Thus, the length of the wire 17 that connects the high-frequency signal lines can be sufficiently shortened. Thereby, the mismatch of the characteristic impedance of the high frequency signal line can be minimized. As a result, good frequency characteristics can be obtained even when high-speed transmission exceeding 10 Gbps is performed, for example.

  Further, the monitor PD is generally arranged behind the LD so as to receive the backward outgoing light opposite to the outgoing surface of the LD. In this case, the high-speed signal line (high-frequency signal line) for driving the LD is formed behind the LD. In high-speed transmission applications, it is desirable that the high-speed signal line be as short as possible in order to suppress signal degradation. However, since the monitor PD is on the rear emission optical axis of the LD, it is necessary to form a high-speed signal line so as to bypass the monitor PD. It is also possible to form a high-speed signal line under the monitor PD by multilayer wiring. In this case, the output signal line through which the output current of the monitor PD flows faces or intersects with the high-speed signal line. Therefore, noise is generated in the weak output current of the monitor PD due to the drive signal passing through the high-speed signal line. If the output current of the monitor PD fluctuates due to noise, the output of the LD cannot be kept stable.

  On the other hand, in this embodiment, since the monitoring PD 20 is arranged in front of the LD 16, the output signal line through which the output current of the monitoring PD 20 flows does not face or intersect with the high-speed signal line, and the output of the monitoring PD 20 The current is less susceptible to noise from the drive signal. Thereby, since the fluctuation | variation of the output current of monitoring PD20 by noise is suppressed, the output of LD16 can be kept stable.

  The present invention is not limited to the above embodiment. For example, in the above embodiment, the upper surface height of the submount 14 and the upper surface height of the intermediate ceramic layer 4 are aligned in the multilayer ceramic package 2, but the configuration is not particularly limited. For example, the multilayer ceramic package 2 is mounted on the submount 14. The thickness (height) of the submount 14 may be set so that the upper surface height of the LD 16 and the upper surface height of the intermediate ceramic layer 4 are aligned. In short, the thickness of the submount 14 may be appropriately designed so that the total or average of the lengths of the plurality of wires connected to the high-frequency signal line is the shortest.

  In the above embodiment, the edge-emitting LD 16 is mounted on the upper surface of the submount 14. However, in order to emit light toward the optical fiber 33 above the multilayer ceramic package 2, edge emission is performed on the side surface of the submount 14. A mold LD may be mounted, or a surface emitting LD may be mounted on the upper surface of the submount 14.

  In the above embodiment, the multilayer ceramic package 2 has a three-layer structure, but the number of layers of the multilayer ceramic package 2 may be four or more.

  Furthermore, in the above-described embodiment, the bottom surface of the multilayer ceramic package 2 and the circuit board 41 of the optical transceiver 37 are connected by the flexible substrate 42. However, depending on the dimensions and arrangement location of the circuit board 41, the multilayer ceramic package 2 may be It may be directly bonded to the circuit board 41.

  Further, when the anode connection pad and the cathode connection pad of the LD 16 are on the same surface, the LD 16 may be flip-chip mounted on the submount 14 in order to suppress the characteristic impedance mismatch due to the wire 18. By flip-chip mounting the LD 16, an increase in inductance component due to wires can be eliminated, and the characteristic impedance of the transmission line can be designed to be more stable.

  Further, the mounting of the monitor PD 20 can also be a flip chip mounting. By doing so, the light receiving surface of the monitoring PD 20 becomes the lower surface, so that the monitor light can be received even if the LD 16 and the monitoring PD 20 are mounted on the same plane.

  DESCRIPTION OF SYMBOLS 1 ... Light emitting module, 2 ... Multilayer ceramic package, 3 ... Lower ceramic layer (1st ceramic layer), 4 ... Intermediate ceramic layer (2nd ceramic layer), 5 ... Upper ceramic layer (3rd ceramic layer), 10 ... Opening , 11 ... recess, 14 ... submount, 16 ... laser diode (light emitting element), 20 ... monitoring photodiode (monitoring light receiving element), 23 ... optical member, 25 ... holder (metal cylindrical member), 28 ... Joint (metal cylindrical member), 31 ... Metal sleeve (metal cylindrical member), 33 ... Optical fiber, 34 ... Ferrule.

Claims (4)

A multilayer ceramic package containing a light emitting element;
A metal cylindrical member that is fixed to the upper surface of the multilayer ceramic package and that contains an optical fiber that is optically coupled to the light emitting element;
The multilayer ceramic package includes a first ceramic layer and an opening that is stacked on the first ceramic layer and forms a recess for mounting the light emitting device in cooperation with an upper surface of the first ceramic layer. A second ceramic layer, and a third ceramic layer stacked on the second ceramic layer and provided so as to surround the region including the recess,
A submount is disposed in the recess,
The light emitting module, wherein the light emitting element is mounted on the submount. On the bottom surface of the recess, a light receiving element for monitoring that monitors the output light amount of the light emitting element is mounted,
An optical element that reflects light emitted from the light emitting element toward the optical fiber and transmits part of the light toward the monitor light receiving element between the light emitting element and the monitor light receiving element. The light emitting module according to claim 1, wherein a member is disposed.   3. The light emitting module according to claim 1, wherein the submount is formed of an insulating material having a higher thermal conductivity than a ceramic material forming the first to third ceramic layers. The light emitting module according to claim 3, wherein the submount is made of aluminum nitride.

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