Patent Publication Number: US-2006006403-A1

Title: Optical module

Description:
CLAIM OF PRIORITY  
      The present application claims priority from Japanese patent application serial no. 2004-199346, filed on Jul. 6, 2004, the content of which is hereby incorporated by reference into this application.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an optical module, and more particularly, to a small optical module in which electrical wirings in a module package are simplified.  
      2. Description of the Related Art  
      As a demand of a marketplace in an optical communication system, there is miniaturization of size of an optical communication module. On the other hand, the optical communication module tends to be multi-functional and a plurality of wirings for electrically connecting various components to an outside of a package need to be provided. Accordingly, the number of leads in the module tends to be increased.  
      As a means for satisfying the above demand, there is a method of arranging leads included in the package of the optical communication module at a specific location. For example, if the leads are arranged at only one sidewall of a module package having a rectangular parallelepiped shape, the module can be arranged at an end of an optical transceiver when the optical module is mounted on the optical transceiver, thereby improving degree of freedom in arrangement of each component or degree of freedom in electrical wiring design. Also, since the leads exit from only one side thereof, it is advantageous in that the module size is reduced.  
      Japanese Patent Laid-Open No. 2003-060281 describes about a small light emitting element module capable of surface-mounting, and a method of manufacturing the same.  
      However, in a case of a package structure with leads formed at only one side, electrical wirings in the optical module package become complicated. Since optical and configurational restrictions have priorities in determining the arrangement of each functional component in the package, it is difficult to provide the electrical wirings in a simplified shape.  
      Particularly, in a case in which there are various electrodes at a side where leads do not exist with respect to an optical axis, it is necessary that they be connected by long bonding wires or a long relay board be formed. In this structure, the manufacturing process is complicated, and further there is a possibility that failure of the wirings is increased.  
     SUMMARY OF THE INVENTION  
      In order to solve the above-mentioned problems, in the present invention, a functional component is mounted on a substrate(functioning as a pedestal) in which inner wirings are formed and electrodes connected to the wirings are formed at a side where the functional component is mounted. The functional component and the electrodes provided at one ends of the wirings are connected to each other and one ends of the leads and the electrodes provided at the other ends of the wirings are connected to each other.  
      According to the invention, an optical module, having leads formed at only one side, of which manufacturing process is simple and in which there is little possibility of a failure such as wire disconnection. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Preferred embodiments of the present invention will now be described in conjunction with the accompanying drawings, in which;  
       FIG. 1  is a side view and a plan view of a light emitting element module according to a first embodiment of the present invention;  
       FIG. 2  is a side view and a plan view of a substrate according to the first embodiment of the present invention;  
       FIG. 3  is a side view and a plan view of a light emitting element module according to a second embodiment of the present invention;  
       FIG. 4  is a side view and a plan view of a light emitting element module according to a third embodiment of the present invention;  
       FIG. 5  is a side view and a plan view of a light emitting element module according to a fourth embodiment of the present invention; and  
       FIG. 6  is a plan view of a transceiver module according to a fifth embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.  
      First, a light emitting element module according to a first embodiment of the present invention will be described with reference to  FIGS. 1 and 2 . Here,  FIG. 1  shows the light emitting element module according to the first embodiment of the present invention, and  FIG. 1A  is a side view thereof and  FIG. 1B  is a plan view thereof. Also,  FIG. 2  show a substrate of the first embodiment,  FIG. 2A  is a side view thereof and  FIG. 2B  is a plan view thereof. Further, for simplicity of the figures, there are portions which are shown in the plan view but are not shown in the side view, and vice versa. This is the same in the other embodiments and what has been previously described will be omitted in the other embodiments.  
      In  FIG. 1 , a light emitting element  2  is an element for emitting a plurality of different wavelengths, which is called as a tunable laser diode. The light emitting element  2  has a plurality of waveguides (not shown) to emit light having a wide range of wavelength and two electrode groups  21  and  22  corresponding to each waveguide. The electrodes are formed at both sides with the waveguide therebetween. The plurality of waveguides is integrated into one waveguide (not shown) at a front emitting side in the light emitting element  2 .  
      A light beam emitted form the light emitting element  2  is focused by a lens  301  located ahead thereof, passes through an isolator  302  for suppressing light reflected toward the light emitting element  2 , and is coupled to an optical fiber  303  to be transmitted to an outside of the module.  
      A light emitting element module  100  is configured such that leads  11  for inputting electrical signals from an outside of a module package  1 , having a rectangular parallelepiped shape, to an inside thereof and for outputting the electrical signals from the inside to the outside thereof penetrates a wall  1   a  which is one side of the package  1 .  
      The light emitting element  2  is attached to a substrate  4  by soldering. Front and rear surfaces of the substrate  4  are formed with metallization layers, respectively (not shown). By using the metallization layers, the substrate  4  is mounted on a thermo-cooler  5  by the soldering connection and the thermo-cooler  5  is fixed to a bottom portion of the package  1  by soldering. Here, composition of the soldering (that is, melting point) is adequately selected by an order of the connection. The role of the thermo-cooler  5  is to cool the light emitting element  2  in which heat is generated due to the light emission and to control an oscillating wavelength by varying a temperature of the light emitting element  2 .  
      In other words, the substrate  4  mounted with the light emitting element  2  serves as a heat transfer path between the light emitting element  2  and the thermo-cooler  5 . Accordingly, it is preferable that a member having a low thermal resistance is used as the substrate  4  in order to efficiently emit the heat from the light emitting element  2 . In the present embodiment, a ceramic substrate mainly composed of AlN (aluminum nitride), which is an insulating material having a low thermal resistance, is used. The substrate  4  shown in  FIG. 2  includes electrical wirings  41  in which tungsten is used as a wiring material. Each electrode of an electrode group  42  is electrically connected to the corresponding electrode of an electrode group  43  through a via(also described as a via hole)  44  just below the electrode, an inner electrical wiring  41 , and a via  44  just below the electrode of the electrode group  43 . Also, the substrate  4  is provided with a step to match an optical axis of the light emitting element  2 , the lens  301  and the isolator  302 . This step is formed by laminating a ceramic sheet. Accordingly, if wirings are formed on the ceramic sheet, the wirings  41  can be formed only by adding a process of embedding the via in a process of manufacturing the substrate  4 .  
      Referring back to  FIG. 1 , by using the substrate  4 , the electrode group  21  at a lead side of the light emitting element  2  can be directly wire-bonded to leads  11  and the electrode group  22  at a non-lead side (a side where leads do not exit with respect to the optical axis) of the light emitting element  2  can be wire-bonded to the very near electrode group  43  of the substrate  4 . Since the electrode group  22  at the non-lead side of the light emitting element  2  is connected to the electrode group  44  of the substrate  4  closest to the leads  11  through the inner electrical wirings  41  of the substrate  4 , the electrode group  44  is wire-bonded to the leads  11 . Thereby, electrical connections can be made at a concentration portion of the bonding wires, without using long bonding wires. In addition, since the substrate for heat emission, which has been conventionally needed, can also perform a function of the electrical wirings, the number of components is not increased.  
      By wire-bonding a thermistor  12  formed on the light emitting element  2 , terminals of the thermo-cooler  5  and the leads  11 , the electrical wirings are completed. Here, it has been confirmed that, although bonding wires between the terminals of the thermo-cooler  5  and the leads  11  are long, there is no problem because interference with the other wires is little.  
      The light emitting element module  100  of the present invention is mounted with the light emitting element  2  having a plurality of the waveguides to correspond to a wide range of wavelength. Since the plurality of waveguides is provided with wirings, a waveguide can be selected from the outside to vary the wavelength in a wide range. Also, even by using only one waveguide, the wavelength can be varied in a narrow range by the thermistor  12 , the thermo-cooler  5  and an external controlling circuit. Accordingly, the light emitting element module  100  of the present invention can widely vary the wavelength with high precision.  
      According to the present invention, a small light emitting element module, in which leads exit from only one side of the package, can be obtained.  
      In addition, as a material of the substrate  4 , materials other than AlN may be used, but a material having a low thermal resistance is preferably used. As a suitable material substituting the AlN, there is SiC (silicon carbide), Si (silicon) or alumina. Also, with respect to an inner wiring material, materials other than Tungsten may be used if it does not have an extremely high electrical resistance.  
      Moreover, with respect to an optical structure, structures other than that of the embodiment may be used. For example, plural lenses may be used, or a light emitting element may be directly coupled to an optical fiber without using the lens. Further, an isolator may not be used if an effect due to reflected light can be avoided. In the present invention, a Peltier element is used as the thermo-cooler. The Peltier element becomes a thermo-heater in accordance with a direction of a flowing current, and is controlled to perform heating if a surrounding temperature is extremely low.  
      In the present embodiment, as a case of the light emitting element module, a metal wall type light emitting element module, in which leads pass through a hole formed in a side of a metal frame and which is hermetically sealed by glass, is used. However, the case is not limited to the metal wall type. For example, a field through type light emitting element module, in which a ceramic substrate formed with an electrical wiring is bonded to a metal frame, may be used. In this case, wirings formed on the ceramic substrate are leads. Modification of the above-mentioned embodiment is the same in the other embodiments.  
      Next, the light emitting element module according to a second embodiment of the present invention will be described with reference to  FIG. 3 . Here,  FIG. 3  shows the light emitting element module according to the second embodiment of the present invention, and  FIG. 3A  is a side view thereof and  FIG. 3B  is a plan view thereof.  
      In  FIG. 3 , the light emitting element  2  is attached to the substrate  4  through a sub-assembly substrate  3  by soldering. The substrate  4  is mounted on the thermo-cooler  5  by the soldering connection and the thermo-cooler  5  is fixed to a bottom portion of the package  1  by soldering.  
      The light emitting element module  100  of the second embodiment is configured to have leads  11  provided at one side  1   a  of the module package  1 . The light emitting element  2  of the present embodiment is a laser diode with a single wavelength. The light emitting element  2  is mounted on the sub-assembly substrate  3  to evaluate light emitting characteristic of the light emitting element  2  before it is mounted on the substrate  4 . There is a yield as an evaluating test item, and when there is a problem in the light emitting element  2 , the light emitting element  2  must be separated form the sub-assembly substrate  3 . On this account, the sub-assembly substrate  3  preferably has a low thermal resistance. Also, in consideration of a case in which the light emitting element  2  can not be separated from the sub-assembly substrate  3 , the sub-assembly substrate  3  is preferably low in price. Further, since the light emitting element  2  is mounted thereon, a thermal expansion coefficient of the sub-assembly substrate  3  should be close to that of the semiconductor. Accordingly, in the present embodiment, AlN is used as a material of the sub-assembly substrate  3 .  
      The sub-assembly substrate  3  is mounted with a thermistor  12  for monitoring a temperature of the light emitting element  2 . Furthermore, electrical wirings  112  for supplying electrical signals to the light emitting element  2  are provided. In order to efficiently arrange these components on the sub-assembly substrate  3 , it is preferable that they are symmetrically provided with respect to an optical axis of the light emitting element  2 . In the present embodiment, the thermistor  12  is arranged at a non-lead side.  
      As the substrate  4 , similarly to the first embodiment, a member mainly composed of AlN is used in order to efficiently emit the heat from the light emitting element  2 . Electrical wirings  41 , in which Tungsten is used as a wiring material, are provided in the substrate  4 . Electrodes of the electrode group  42  at a lead side and electrodes of the electrode group  43  at a non-lead side in the substrate  4  are electrically connected to each other through the electrical wirings  41  formed in the substrate  4 . The leads  11  and the electrode group  42  are electrically connected to each other by bonding wires  61 , and the electrode group  43  at a non-lead side of the substrate  4 , the electrode  113  for the thermistor  12  and the thermistor  12  are connected to one another by bonding wires  62 . Thereby, the electrode  113  for the thermistor  12  and the leads  11  of the package  1  can be electrically connected to each other.  
      According to the present embodiment, electrical connections can be made without employing a complicate form, such as using long bonding wires. In addition, since the substrate  4  for heat emission also performs a function of the electrical wirings, the number of components is not increased. Accordingly, a small light emitting element module, in which leads exit from only one side of the package, can be obtained.  
      Furthermore, although a component, in which electrical connections are made by using the inner wirings  41 , is used as the thermistor  12 , others may be used. For example, inner wirings may be used in the electrical wirings for supplying a current to the light emitting element  2 . Also, although an inner layer may be provided in the sub-assembly substrate  3 , it makes it difficult to separate the light emitting element  2 .  
      Moreover, a material of the sub-assembly substrate  3  is not limited to AlN. Specifically, SiC, Si (silicon) or alumina may be used.  
      Next, the light emitting element module according to a third embodiment of the present invention will be described with reference to  FIG. 4 . Here,  FIG. 4  shows the light emitting element module according to the third embodiment of the present invention, and  FIG. 4A  is a side view thereof and  FIG. 4B  is a plan view thereof. Further, as mentioned above, wiring at a vicinity of the light emitting element is not shown.  
      The light emitting element module  100  shown in  FIG. 4  includes a light emitting element  2  and a wavelength locker  7 . The wavelength locker  7  consists of two photodiodes and an etalon filter, and it is a component for monitoring a light intensity before and after the light emitted from the light emitting element  2  transmits the etalon filter to thereby stabilize a wavelength. A light beam emitted from the light emitting element  2  becomes collimated light by a lens  301  located ahead thereof and is incident on the wavelength locker  7  through an isolator  302 . The light beam transmitting through the wavelength locker  7  is focused by a lens  304  and is coupled to an optical fiber  303  to be delivered to an outside of the module.  
      The light emitting element module  100  is configured such that leads  11  are formed at a sidewall  1   a  of the module package  1 . An electrode group  71  of the photodiode constituting the wavelength locker  7  is arranged at a side (at a non-lead side) distant from the sidewall  1   a  through which the leads  11  penetrate. The wavelength locker  7  is attached to a substrate  8  by soldering, and the substrate  8  is mounted on a thermo-cooler  9  by soldering connection. Further, the thermo-cooler  9  is fixed to a bottom portion of the package  1  by soldering. Here, the thermo-cooler  9  controls a temperature of the wavelength locker  7  and a monitoring wavelength. An external controlling device (not shown) controls the temperature of the thermo-cooler  5  mounted with the light emitting element  2  so that the light intensity ratios before and after transmitting the etalon filter of the wavelength locker  7  can be constant.  
      The substrate  8  has inner electrical wirings  81  therein. In the present embodiment, alumina is used as an insulating material of the substrate  8  and tungsten is used as a material of the inner wirings. But, similarly to the first embodiment, other members may be used. Electrodes  82  at a lead side of the substrate  8  are electrically connected to electrodes  43  at a non-lead side through the electrical wirings  81  formed in the substrate  4 . The leads  11  and the electrodes  82  are electrically connected to each other by boding wires  91 , and electrodes  83  and electrodes  71  of the photodiode constituting the wavelength locker  7  are connected to each other by bonding wires  92 . Thereby, the electrodes  71  of the wavelength locker  7  and the leads  11  of the package  1  can be electrically connected to each other, and thus the electrical wirings can exit to an outside of the module package  1 .  
      In this specification, a light emitting element and a wavelength locker are called as functional components. Also, the functional component is not limited thereto, but it is a general term of components which have electric terminals and are placed on an optical axis. The functional component includes a light receiving element, and an optical modulator described below.  
      According to the present embodiment, electrical connections can be made without employing a complicate form, such as using long bonding wires. In addition, since the substrate for heat coupling with the thermo-cooler also performs a function of the electrical wirings, the number of components is not increased. Accordingly, a small light emitting element module, in which leads exit from only one side of the package, can be obtained.  
      With respect to an optical structure, structures other than the structure shown in the third embodiment may be used. For example, a structure in which convergence light is allowed to pass the wavelength locker  7  without using the lens  304  may be used. Furthermore, an isolator may not be used if an effect due to reflected light can be avoided. Also, although the wavelength locker  7  according to forward light of the light emitting element  2  is illustrated in the third embodiment, a wavelength locker according to backward light thereof may be used.  
      In the present embodiment, the Peltier element is used as a thermo-cooler. The Peltier element becomes a thermo-heater in accordance with a direction of a flowing current, and is controlled to perform heating in accordance with a wavelength to be monitored.  
      In addition, although the light emitting element and the wavelength locker are accommodated in the same case in the present embodiment, a structure in which they are accommodated in different cases and are coupled to each other using an optical fiber may be considered. In this case, a module accommodating the wavelength locker is called as a wavelength locker module. The light emitting element module and the wavelength locker module are generally called optical modules. Further, the optical module includes a light receiving element module and an optical modulator module, but it is not limited thereto.  
      Next, the light emitting element module according to a fourth embodiment of the present invention will be described with reference to  FIG. 5 . Here,  FIG. 5  shows the light emitting element module according to the fourth embodiment of the present invention, and  FIG. 5A  is a side view thereof and  FIG. 5B  is a plan view thereof.  
       FIG. 5  shows a light module  100  comprising a light emitting element  2 , a wavelength locker  7  and a Mach-Zehnder modulator  201  in a module package  1 . Light emitted from the light emitting element  2  becomes collimated light by a lens  301  and is incident on the wavelength locker  7  through an isolator  302 . Light beam transmitting through the wavelength locker  7  is focused by a lens  304  and is incident on the Mach-Zehnder modulator  201 . The light modulated by the Mach-Zehnder modulator  201  is transmitted to an outside of the module through an optical fiber  303 .  
      The light emitting element  2  is a tunable light source and comprises a plurality of waveguides so as to emit light having a wide range of wavelength and a plurality of electrodes  21  and  22  corresponding to each waveguide. The electrodes are formed at both sides of the waveguide. The waveguide locker  7  monitors a wavelength of the light emitted from the light emitting element  2  before and after transmitting an etalon filter, by using two photodiodes. The Mach-Zehnder modulator  200  has a function for modulating continuous light emitted form the light emitting element  2  into signal light, and the length of an optical axis thereof is several tens mm.  
      The module  100  is configured such that leads  11  for inputting electrical signals from an outside to an inside of the package  1  and for outputting the electrical signals from the inside to the outside are provided in a sidewall  1   a.    
      A mounting structure of the light emitting element  2  is that it is attached to the substrate  4  by soldering, similarly to the first embodiment. The substrate  4  is mounted on the thermo-cooler  5  by soldering connection and the thermo-cooler  5  is fixed to a bottom portion of the package  1  by soldering. Further, the light emitting element  2  may be mounted on the substrate  4  through the sub-assembly substrate, similarly to the second embodiment.  
      A ceramic substrate mainly composed of AlN (aluminum nitride) is used as a material of the substrate  4 , similarly to the first embodiment. The substrate  4  has inner electrical wirings  41  therein. As a material of the wiring, tungsten is used. Electrode group  42  at a lead side and electrode group  43  at a non-lead side of the package  1  of the substrate  4  are electrically connected to each other through the electrical wirings  41  formed at the inside in the substrate  4 .  
      Thereby, the leads  11  penetrating through a sidewall of the package and the electrode group  42  at the lead side are electrically connected to each other by bonding wires  61 , and the electrode group  43  at a non-lead side and the electrode group  22  at a non-lead side of the light emitting element  2  are connected to each other by bonding wires  62 . In this way, the electrodes  22  of the light emitting element  2  and the leads  11  of the package  1  can be electrically connected to each other, and thus the electrical wirings can exit to an outside of the module package  1 . The electrode group  21  of the light emitting element  2  at a lead side is directly connected to the leads  11  by wire bonding.  
      An electrode group  71  of the photodiode of the wavelength locker  7  is arranged at the non-lead side. The wavelength locker  7  is attached to the substrate  8  by soldering. The substrate  8  is mounted on the thermo-cooler  9  by soldering connection and the thermo-cooler  9  is fixed to the bottom portion of the package  1  by soldering.  
      The substrate  8  has inner electrical wirings  81  therein. In the present embodiment, alumina (aluminum oxide) is used as an insulating material of the substrate  8  and tungsten is used as a material of the inner wirings. An electrode group  82  at a lead side of the substrate  8  is electrically connected to an electrode group  43  at a non-lead side through electrical wirings  81  formed in the substrate  4 . The leads  11  penetrating through a sidewall of the package and the electrode group  82  at the lead side are electrically connected to each other by bonding wires  101 , and an electrode group  83  at the non-lead side of the substrate  8  and the electrode group  71  of the photodiode constituting the wavelength locker  7  are connected to each other by bonding wires  102 . Thereby, the electrode group  71  of the wavelength locker  7  and the leads  11  of the package  1  can be electrically connected to each other, and thus the electrical wirings can exit to an outside of the module package  1 .  
      The Mach-Zehnder modulator  200  is made of LiNbO 3  crystal and can modulate continuous light, having a wide range of wavelength, emitted from the tunable light source (the light emitting element  2 ) into an optical signal having a transmission rate of 10 Gbits/s, by using an electrical signal having a transmission rate of 10 Gbits/s from an outside (not shown).  
      In the present embodiment, electrical connections can be made without employing a complicate form, such as using long bonding wires. In addition, since the substrate for heat emission also performs a function of the electrical wiring, the number of the components is not increased. Accordingly, a small light emitting element module, in which leads exit from only one side of the package, can be obtained.  
      Furthermore, although the inner wirings are provided at both of the light emitting element  2  and the wavelength locker  7  in the present embodiment, a structure in which the inner wirings are provided at only one of them may be employed. Also, with respect to an optical structure, methods other than the embodiment may be used. For example, a method for coupling convergence light from the lens  304  to an optical fiber to transmit the light by directly connecting the optical fiber to the Mach-Zehnder modulator may be used.  
      Next, a transceiver module according to a fifth embodiment of the present invention will be described with reference to  FIG. 6 . Here,  FIG. 6  is a plan view of the transceiver module according to the fifth embodiment of the present invention.  
      An optical transceiver  1000  shown in  FIG. 6  consists of a light emitting element module  100  illustrated in the fourth embodiment, a light receiving element module  400  and peripheral circuits. Four electrical signals, each having a transmission rate of 2.4 Gbits/s, input from a connector  500  are multiplexed to a signal having a transmission rate of 10 Gbits/s at a multiplexing IC  130 , then is transmitted to the light emitting element module  100  through a driving IC  120  for outputting an modulated signal to the Mach-Zehnder modulator  200 , and then an optical signal having a transmission rate of 10 Gbits/s is transmitted to the optical fiber  303 .  
      An optical signal, having a transmission rate of 10 Gbits/s, transmitted from the optical fiber  305  is converted into an electrical signal in a light receiving element module  400 , then passes through an amplifying IC  420 , and then is divided into four signals, each having a transmission rate of 2.4 Gbits/s, in a demultiplexing IC  410  to be transmitted from the connector  500 .  
      In the optical transceiver of the present invention, since the light emitting element module  100 , in which leads are arranged at only one side of the package, is used, the light emitting element module  100  can be positioned at the end of the substrate  600  and thus the optical transceiver can be miniaturized.  
      Moreover, the package of the light receiving element, in which the leads are positioned at only one side thereof, may be used. Further, a light transmitter module, in which the light emitting element and the peripheral circuits are mounted on the substrate, may be used. Similarly, a light receiver module, in which the light receiving element having the leads provided at only one side of the package and the peripheral circuits are mounted on the substrate, may be used.  
      Here, the optical transceiver, the light transmitter module and the light receiver module all are optical modules.