Abstract:
An uncooled, through-hole configured laser module adapted to receive and transmit RF signals to a laser at bandwidths from direct current (DC) to about ten gigahertz. The laser module incorporates an option for two pin-out configurations. One pin-out configuration has one ground pin and one signal pin for operation at about one gigabit/second or one gigahertz. The second high performance pin-out uses two ground pins and one signal pin for operation up to about ten gigabit/second or ten gigahertz.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a laser module, and more particular to an uncooled semiconductor laser module adapted for use in a fiber optics communication network. 
     BACKGROUND OF THE INVENTION 
     Laser module designs are useful for analog transmission, e.g., CATV, personal communication systems (PCS), cellular, and for low bit rate digital transmission at a bit rate of about one gigabit/second or below, and for high bit rate digital transmission, e.g., transmission at a bit rate greater than about one gigabit/second. 
     Some of the laser module designs are cooled. Such designs often utilize a thermal electric cooler (TEC) to provide cooling, or heating, depending upon the voltage polarity used, to the laser module. The presence of the TEC presents several disadvantages. One disadvantage is that the TEC increases the size of the laser module, making the module bulky. Another disadvantage is that the TEC adds to the cost of the laser module. Yet another disadvantage is that the presence of the TEC creates the need for a greater number of electrical connections which must be performed, adding further to the cost of the module. An example of such a laser module design is a cooled ILM (Isolated Laser Module) which is capable of use in analog CATV, analog personal communication systems (PCS), analog cellular and up to 2.5 gigabit/second digital transmissions. 
     Some laser module designs incorporate what is termed a butterfly configuration. The butterfly configuration is a configuration by which the laser module is electrically connected to a circuit board. In a butterfly configured design, the electrical leads are directly connected with the optical subassembly portion of the laser module. With such a design, the loss of bit speed due to signal degradation due to multiple reflections is lessened, and a transmission rate in excess of ten gigabits/second is achievable. A disadvantage to such a design is that it is prohibitively expensive to manufacture and/or test butterfly configured laser modules in high volume. 
     SUMMARY OF THE INVENTION 
     The disadvantages of the conventional laser module designs are overcome to a great extent by the present invention, which relates to an uncooled laser module adapted to receive and input radio frequency signals to a laser at direct current (DC) to ten gigahertz. This is accomplished through the inclusion of two pin configurations in a single laser module package. In a preferred embodiment of the laser module, there is included signal-ground circuitry matching an industry-wide standard capable of receiving and transmitting radio frequency (RF) signals to a laser at a bandwidth below about one gigahertz and ground-signal-ground circuitry for a high performance configuration capable of receiving and transmitting RF signals to a laser at a bandwidth up to ten gigahertz. 
     In an aspect of the present invention, the ground-signal-ground circuitry includes a signal pin, two ground pins, and a first characteristic line, such as a coplanar waveguide, in electrical connection with the ground and signal pins and with a metal pad, a second characteristic line, such as a microstrip, and a microstrip ground. The metal pad and microstrip ground act as grounds for an RF signal input from a driver to the signal pin, and transmitted therefrom through the coplanar waveguide and the microstrip and on to an optical subassembly including a laser. Further, the microstrip has a specific impedance and a specific electrical length. 
     In another aspect of the present invention, the signal-ground circuitry includes a signal pin, a ground pin, and a first characteristic line, such as a coplanar waveguide, in electrical connection with the signal pin, the ground pin, and two metal pads. One of the metal pads acts as a ground for an RF signal input from a driver to the signal pin, and transmitted therefrom through the coplanar waveguide and the other metal pad and on to an optical subassembly including a laser. 
     In another aspect of the present invention, the ground pin of the signal-ground circuitry is the signal pin of the ground-signal-ground circuitry. 
     The foregoing and other advantages and features of the invention will be more readily understood from the following detailed description of the invention, which is provided in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 a  is a top view of a preferred embodiment of the laser module constructed in accordance with the present invention. 
     FIG. 1 b  is a side view of the laser module of FIG. 1 a.    
     FIG. 1 c  is a front view of the laser module of FIG. 1 a.    
     FIG. 1 d  is an opposite side view of the laser module of FIG. 1 a.    
     FIG. 2 a  is a side view of the first ceramic layer of the laser module of FIG. 1 a.    
     FIG. 2 b  is a top view of the first ceramic layer of the laser module of FIG. 1 a.    
     FIG. 2 c  is an opposite side view of the first ceramic layer of the laser module of FIG. 1 a.    
     FIG. 2 d  is a front view of the first ceramic layer of the laser module of FIG. 1 a.    
     FIG. 3 a  is a side view of the second ceramic layer of the laser module of FIG. 1 a.    
     FIG. 3 b  is a top view of the second ceramic layer of the laser module of FIG. 1 a.    
     FIG. 3 c  is an opposite side view of the second ceramic layer of the laser module of FIG. 1 a.    
     FIG. 3 d  is a front view of the second ceramic layer of the laser module of FIG. 1 a.    
     FIG. 4 a  is a side view of the third ceramic layer of the laser module of FIG. 1 a.    
     FIG. 4 b  is a top view of the third ceramic layer of the laser module of FIG. 1 a.    
     FIG. 4 c  is an opposite side view of the third ceramic layer of the laser module of FIG. 1 a.    
     FIG. 4 d  is a front view of the third ceramic layer of the laser module of FIG. 1 a.    
     FIG. 5 a  is a side view of the fourth ceramic layer of the laser module of FIG. 1 a.    
     FIG. 5 b  is a top view of the fourth ceramic layer of the laser module of FIG. 1 a.    
     FIG. 5 c  is an opposite side view of the fourth ceramic layer of the laser module of FIG. 1 a.    
     FIG. 5 d  is a front view of the fourth ceramic layer of the laser module of FIG. 1 a.    
     FIG. 6 is a top view of the seal ring of the laser module of FIG. 1 a.    
     FIG. 7 is a cross-sectional view of the laser module of FIG. 1 a  taken along line VII—VII in FIG. 1 c.    
     FIG. 8 a  is a top view of the optical subassembly shown schematically in FIG.  7 . 
     FIG. 8 b  is a side view of the optical subassembly shown schematically in FIG.  7 . 
     FIG. 8 c  is a front view of the optical subassembly shown schematically in FIG.  7 . 
     FIG. 8 d  is a perspective view of the optical subassembly shown schematically in FIG.  7 . 
     FIG. 9 is an equivalent electrical circuit diagram of the ground-signal-ground signal path of the laser module of FIG. 1 a.    
     FIG. 10 is an equivalent electrical circuit diagram of the signal-ground signal path of the laser module of FIG. 1 a.   
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to FIGS. 1A-7, an uncooled universal laser module  10  is illustrated. With specific reference to FIGS. 1A-1D, the laser module  10  includes a package body  11  and a metal nose  254 . The package body  11  is comprised of a first ceramic layer  40 , a second ceramic layer  80 , a third ceramic layer  120 , a fourth ceramic layer  180 , and a seal ring  220 . Each of the ceramic layers  40 ,  80 ,  120 ,  180  has two long sides and two short sides, the long sides being generally parallel to one another and the short sides being generally parallel to one another. The ceramic layers  40 ,  80 ,  120 ,  180  are stacked one upon the other such that the long sides of the ceramic layers make up two long sides  16 ,  18  of the package body  11  and the short sides of the ceramic layers make up two short sides  12 ,  14  of the package body  11 . The short side  12  of the package body shall also be referred to herein as the front side  12  of the package body  11 . 
     More specifically, the ceramic layer  40  includes sides  40   a  and  40   c  (FIGS. 2 a - 2   c ), the ceramic layer  80  includes sides  80   a  and  80   c  (FIGS. 3 a - 3   c ), the ceramic layer  120  includes sides  120   a  and  120   c  (FIGS. 4 a - 4   c ), and the ceramic layer  180  includes sides  180   a  and  180   c  (FIGS. 5 a - 5   c ). Sides  40   a ,  80   a ,  120   a  and  180   a  make up the long side  18 , while sides  40   c ,  80   c ,  120   c  and  180   c  make up the long side  16 . As will be explained in greater detail below, the ceramic layers  40 ,  80 ,  120 ,  180  each has a front surface  46 ,  86 ,  126 ,  186 , respectively, which collectively make up the front side  12 . 
     Each of the ceramic layers  40 ,  80 ,  120 ,  180  includes both unmetallized ceramic portions and metallized ceramic portions. The metallized ceramic portions, as well as all the metallic portions in the layers  40 ,  80 ,  120 ,  180  include pre-metallized tungsten on ceramic with nickel, gold plating. 
     The first ceramic layer  40  includes an unmetallized ceramic portion  48 , metallized ceramic portions  50 ,  52 ,  54  and  56  on side  18 , metallized ceramic portions  58 ,  60 ,  62  and  64  on side  16 . Finally, the first ceramic layer  40  includes a metallized ceramic portion  66  on the front side  12 . 
     The second ceramic layer  80  has an unmetallized ceramic portion  89 . Further, the second ceramic layer  80  includes metallized ceramic portions  90 ,  92 ,  94  and  96  on side  18  and metallized ceramic portions  98 ,  100 ,  102  and  104  on side  16 . Finally, the second ceramic layer  80  includes metallized ceramic portions  106  on the front side  12 . 
     The third ceramic layer  120  includes an unmetallized ceramic portion  142 . The third ceramic layer  120  also includes metallized ceramic portions  144 ,  146 ,  148  and  150  on side  18  and metallized ceramic portions  152 ,  154 ,  156  and  158  on side  16 . Also, the third ceramic layer  120  includes metallized ceramic portions  160  on the front side  12 . 
     The fourth ceramic layer  180  includes an unmetallized ceramic portion  192 . The fourth ceramic layer  180  further includes metallized ceramic portions  194 ,  196 ,  198  and  200  on side  18  and metallized ceramic portions  202 ,  204 ,  206  and  208  on side  16 . The fourth ceramic layer  180  also includes a metallized ceramic portion  210  on the front side  12 . 
     Each of the ceramic layers  40 ,  80 ,  120  and  180 , as well as the seal ring  220 , includes a top surface and a base surface. Specifically, as best illustrated in FIGS. 2 a ,  2   b ,  2   c ,  2   d , the first ceramic layer  40  includes a base surface  42 , a top surface  44 , and a front surface  46 . The front surface  46  is coextensive with the front side  12  of the laser module  10 . The front surface  46  includes the metallized ceramic portion  66  and a cutout portion  70 . The top surface  44  of the first ceramic layer  40  includes an unmetallized ceramic portion  48  as well as a metal pad  68 . The metal pad  68  shall also be referred to herein as the optical subassembly (OSA) ground  68 . 
     The second ceramic layer  80 , best illustrated in FIGS. 3 a ,  3   b ,  3   c ,  3   d , has a base surface  82 , a top surface  84 , a surface  86  containing an opening  85 , a pair of opposing surface lips  88  and an inner surface  87 . The second ceramic layer  80  is roughly C-shaped when viewed from above. The base surface  82  of the second ceramic layer  80  is positioned above and contacts the top surface  44  of the first ceramic layer  40 . The top surface  84  of the second ceramic layer  80  includes an unmetallized portion  89 , and metallized portions including a microstrip ground  108 , and a positive-side monitor circuit (or P-side monitor circuit)  110 . The front surface  86  is coextensive with the front side  12  of the laser module  10 , and includes the metallized ceramic portions  106  positioned on either side of the opening  85 . 
     The third ceramic layer  120 , best illustrated in FIGS. 4 a ,  4   b ,  4   c ,  4   d , includes a base surface  122 , a top surface  124 , a front surface  126  containing an opening  125 , and an inner surface  127 . As with the second ceramic layer  80 , the configuration of the third ceramic layer  120  is roughly C-shaped when viewed from above. However, the inner surface  127  includes a first groove  130 , a second groove  132 , and a third groove  134 . Positioned between the first and second grooves  130 ,  132  is a first protrusion  136 . Positioned between the second and third grooves  132 ,  134  is a second protrusion  138 . Positioned adjacent to the third groove  134  is a third protrusion  140 . The third ceramic layer  120  further includes a pair of surface lips  128  positioned opposite one another and surrounding the opening  125 . The front surface  126  is coextensive with the front side  12  of the laser module  10 , and includes the metallized ceramic portions  160  on either side of the opening  125 . 
     The base surface  122  in the third ceramic layer  120  is positioned above and contacts the top surface  84  of the second ceramic layer  80 . The top surface  124  of the third ceramic layer  120  includes an unmetallized ceramic portion  142 . Further included on the top surface  124  are metal pads  162 ,  164 ,  166 ,  170 ,  174 , a negative-side monitor circuit (or N-side monitor circuit)  168  and a microstrip  172 . 
     The fourth ceramic layer  180 , best illustrated in FIGS. 5 a ,  5   b ,  5   c ,  5   d , includes a base surface  182 , a top surface  184  and a front surface  186 . The base surface  182  of the fourth ceramic layer  180  is positioned above and contacts the top surface  124  of the third ceramic layer  120 . The top surface  184  of the fourth ceramic layer  180  includes the unmetallized ceramic portion  192  and a top metal layer  188 . The front surface  186  is coextensive with the front side  12  of the laser module  10 , and includes the metallized ceramic portion  210  and a cutout  190 . The fourth ceramic layer  180  includes a rectangularly shaped opening  181  through the middle of the layer  180  such that one looking down upon the fourth ceramic layer  180  can see an optical subassembly  250  (described below) which will be contained within the laser module  10 . The seal ring  220  (FIGS. 6,  7 ) includes a base surface  222  which is positioned above and contacts the top surface  184  of the fourth ceramic layer  180 , and a top surface  224 . 
     The ceramic layers  40 ,  80 ,  120 ,  180  are formed into their final configurations by industry standard ceramic processing techniques. 
     Once properly positioned, the ceramic layers  40 ,  80 ,  120 ,  180  create an open area  258  (FIG. 7) within the package body  11 . The open area  258  is bounded by the cutouts  70 ,  190 , the openings  85 ,  125 ,  181  and the inner surfaces  87 ,  127 . Within this open area  258  is positioned the optical subassembly  250  (“OSA”) which is shown schematically in FIG.  7  and in greater detail in FIGS. 8A,  8 B,  8 C,  8 D. The ceramic layers  40 ,  80 ,  120 ,  180  form a housing for the optical subassembly  250 . 
     The OSA  250  includes a laser  282 , a backside monitor  264  and a collimating ball lens  286 . Because the open area  258  is sufficiently large, the area  258  may optionally include either an optical isolator or an optical double isolator, shown schematically in FIG. 8 a  as isolator  290 . In such a configuration, the OSA  250  is pushed up against a ledge  81  of the second ceramic pad  80  (FIG. 7) and the isolator  290  is positioned between the two ball lenses  286 ,  252 . The OSA  250  rests upon the OSA ground  68 , which is electrically connected to a Pin-two  22 , the case ground of the laser module  10  (described below). 
     With specific reference to FIG. 7, positioned forward of the OSA  250  is a focusing ball lens  252 . The ball lens  252  is seated within the cutouts  70 ,  190 , and fits within the openings  85 ,  125 . A metal nose  254  is positioned forward of the front side  12  of the laser module  10  and affixed thereto. Specifically, the metal nose  254 , which is formed of metal and is gold plated, is brazed to the metallized ceramic portions  66 ,  210  of, respectively, the first and fourth ceramic layers  40 ,  180 . 
     Physically affixed and electrically connected to the package body  11  are eight pins. Specifically, pins one through four (Pin-one, Pin-two, Pin-three, Pin-four)  20 ,  22 ,  24 ,  26  are affixed to side  18  of the package body  11 . Pins five through eight (Pin-five, Pin-six, Pin-seven, Pin-eight)  28 ,  30 ,  32 ,  34  are affixed to side  16  of the package body  11 . The pins Pin-one through Pin-eight  20 , 22 , 24 ,  26 ,  28 ,  30 ,  32 ,  34  are at one end affixed to legs, respectively,  21 ,  23 ,  25 ,  27 ,  29 ,  31 ,  33 ,  35 . Each of the legs  21 ,  23 ,  25 ,  27  ends at a tie-bar  36 . Each of the legs  29 ,  31 ,  33 ,  35  ends at a tie-bar  38 . The tie-bars  36 ,  38  are useful for shipping and assembly of the laser module  10 . Specifically, the tie-bars  36 ,  38  prevent shear forces from breaking the electrical and physical connection of the pins  20 ,  22 ,  24 ,  26 ,  28 ,  30 ,  32 ,  34  from the sides  16 ,  18  of the package body  11 . For testing and use of the laser module  10 , the tie-bars  36 ,  38  can be trimmed or clipped off, leaving the ends of the legs  21 ,  23 ,  25 ,  27 ,  29 ,  31 ,  33 ,  35  exposed. The legs  21 - 35  are then fit into a ZIF socket which provides clamp contacts to each of the legs  21 - 35 . 
     In actual use, the laser module  10  can be used in either a through-hole configuration or a gull wing configuration. If used in a through-hole configuration, the legs  21 - 35  each fit through a specific hole in the circuit board and are soldered thereto. If the gull wing configuration is used, each of the legs  21 - 35  is bent perpendicularly outwardly from the package body  11 . The bent legs  21 - 35  are then soldered onto the circuit board. A solder paste is utilized which includes small coagulated portions of metal solder within the paste. The paste is then heated, which thereby heats the resident metal solder, and in this way the pins  21 - 35  are soldered to the circuit board. 
     Each of the pins  20 - 34  is electrically connected to at least one metallized ceramic portion. With specific reference to FIG. 1 d , Pin-one  20  is physically connected to the metallized ceramic portion  50  and the metallized ceramic portion  90  of, respectively, the first and second ceramic layers  40 ,  80 . The Pin-two  22  is physically connected to the metallized ceramic portions  52 ,  92  of, respectively, the first and second ceramic layers  40 ,  80 . The Pin-three  24  is physically connected to the metallized ceramic portions  54 ,  94  of, respectively, the first and second ceramic layers  40 ,  80 . The Pin-four  26  is physically connected to the metallized ceramic portions  56 ,  96  of, respectively, the first and second ceramic layers  40 ,  80 . 
     With specific reference to FIG. 1 b , Pin-five  28  is physically connected to the metallized ceramic portions  58 ,  98  of, respectively, the first and second ceramic layers  40 ,  80 . The Pin-six  30  is physically connected to the metallized ceramic portions  60 ,  100  of, respectively, the first and second ceramic layers  40 ,  80 . The Pin-seven  32  is physically connected to the metallized ceramic portions  62 ,  102  of, respectively, the first and second ceramic layers  40 ,  80 . The Pin-eight  34  is physically connected to the metallized ceramic portions  64 ,  104  of, respectively, the first and second ceramic layers  40 ,  80 . Each of the pins  20 - 34  are affixed to the various metallized ceramic portions through the use of a metal braze. 
     With specific reference to FIGS. 1 b  and  1   d , it is noted that various metallized ceramic portions are in electrical connection with one another when the ceramic layers  40 ,  80 ,  120 ,  180  are stacked one upon another and fused together. Specifically, the metallized ceramic portions  50  and  90  (which are physically connected to Pin-one) are in electrical connection with the metallized portions  144 ,  194  and one another. Thus, these metallized portions  50 ,  90 ,  144 ,  194  are electrically connected to Pin-one  20 . The metallized ceramic portions  52  and  92  (which are physically connected to Pin-two) are in electrical connection with the metallized portions  146 ,  196  and one another. Thus, these metallized portions  52 ,  92 ,  146 ,  196  are electrically connected to Pin-two  22 . The metallized ceramic portions  54  and  94  (which are physically connected to Pin-three) are in electrical connection with the metallized portions  148 ,  198  and one another. Thus, these metallized portions  54 ,  94 ,  148 ,  198  are electrically connected to Pin-three  24 . The metallized ceramic portions  56  and  96  (which are physically connected to Pin-four) are in electrical connection with the metallized portions  150 ,  200  and one another. Thus, these metallized portions  56 ,  96 ,  150 ,  200  are electrically connected to Pin-four  26 . 
     With specific reference to FIG. 1 b , the metallized ceramic portions  58  and  98  (which are physically connected to Pin-five) are in electrical connection with the metallized portions  152 ,  202  and one another. Thus, these metallized portions  58 ,  98 ,  152 ,  202  are electrically connected to Pin-five  28 . The metallized ceramic portions  60  and  100  (which are physically connected to Pin-six) are in electrical connection with the metallized portions  154 ,  204  and one another. Thus, these metallized portions  60 ,  100 ,  154 ,  204  are electrically connected to Pin-six  30 . The metallized ceramic portions  62  and  102  (which are physically connected to Pin-seven) are in electrical connection with the metallized portions  156 ,  206  and one another. Thus, these metallized portions  62 ,  102 ,  156 ,  206  are electrically connected to Pin-seven  32 . The metallized ceramic portions  64  and  104  (which are physically connected to Pin-eight) are in electrical connection with the metallized portions  158 ,  208  and one another. Thus, these metallized portions  64 ,  104 ,  158 ,  208  are electrically connected to Pin-eight  34 . 
     With specific reference to FIGS. 1A-5D, it is further noted that the various groupings of metallized ceramic portions which are electrically connected to one another are further electrically connected with various metal pads. With specific reference to FIGS. 1D,  2 A and  2 B, the metallized ceramic portions  52 ,  92 ,  146 ,  196  are further electrically connected to the OSA ground  68 . Therefore, the OSA ground  68  is in electrical connection with the Pin-two  22 , which acts as the case ground for the laser module  10 . 
     With specific reference to FIGS. 1 b ,  3   b  and  3   c , the metallized portions  64 ,  104 ,  158 ,  208  are further electrically connected to the microstrip ground  108 . Therefore, the microstrip ground  108  is electrically connected with the Pin-eight  34 . Also with specific reference to FIGS. 1 b ,  3   b  and  3   c , the metallized ceramic portions  58 ,  98 ,  152 ,  202 , are further electrically connected with the P-side monitor circuit  110 . Therefore, the P-side monitor circuit  110  is electrically connected with the Pin-five  28 . 
     With specific reference to FIGS. 1 d ,  4   a  and  4   b , the metallized ceramic portions  50 ,  90 ,  144 ,  194  are electrically connected to the metal pad  162 . Therefore, the metal pad  162  is electrically connected to the Pin-one  22 . The metallized ceramic portions  52 ,  92 ,  146 ,  196  are in electrical connection with the metal pad  164 . Therefore, the metal pad  164  is in electrical connection with both the metal pad  68  (FIG. 2 b ) and the Pin-two  22 . 
     The metallized ceramic portions  54 ,  94 ,  148 ,  198  are in electrical is connection with the metal pad  166 . Therefore, the metal pad  166  is electrically connected with the Pin-three  24 . Finally, the metallized ceramic portions  56 ,  96 ,  150 ,  200  are in electrical connection with the negative-side (N-side) monitor circuit  168 . Therefore, the N-side monitor circuit  168  is electrically connected with the Pin-four  26 . 
     With specific references to FIGS. 1 b ,  4   b  and  4   c , the metallized ceramic portions  60 ,  100 ,  154 ,  204  are in electrical connection with the metal pad  170 . Therefore, the metal pad  170  is electrically connected with the Pin-six  30 . The metallized ceramic portions  62 ,  102 ,  156 ,  206  are in electrical connection with the microstrip  172 . Therefore, the microstrip  172  is electrically connected with the Pin-seven  32 . 
     With specific reference to FIGS. 1 d ,  5   a  and  5   b , the metallized ceramic portions  52 ,  92 ,  146 ,  196  are in electrical connection with the top metal layer  188 , which is further in electrical connection with the metallized ceramic portion  210 . Therefore, the metallized ceramic portion  210  and the top metal layer  188  are electrically connected with the Pin-two  22 , and thus, also electrically connected to the metal pads  68 ,  164 . 
     Next will be described the electrical circuitry of the laser module  10 . An important feature of the laser module  10  is that it is adapted to be flexible with regard to the type of signal to be transmitted from the laser  282 . More specifically, the laser module  10  is adapted to accept one ground pin and one signal pin for a low-bit rate and/or low frequency input signal to the laser  282  as well as two ground pins and one signal pin for a high-bit rate and/or high frequency input signal. By low-bit rate or low frequency, what is meant is a bit rate in the range of one gigabit or one gigahertz of bandwidth. With regard to high-bit rate or high frequency, what is meant is bit rates of up to ten gigabit/second, or approximately ten gigahertz of bandwidth. This flexibility is obtained through two discrete electrical signal path configurations within the laser module  10 . 
     Next will be described a signal-ground electrical signal path configuration which is utilized for low-bit rate signals and/or low frequencies, and which is illustrated equivalently in FIG. 10. A radio frequency (RF) signal is sent from a driver (not shown) through the circuit board (not shown) to Pin-six  30 . The RF signal can be any form of signal, namely a sine wave, a square wave or any signal wave therebetween. In the signal-ground electric configuration, Pin-six  30  is considered the input signal pin, and Pin-seven  32  is considered the ground. 
     In the signal-ground configuration, a characteristic line is created along the side wall  16 . Characteristic lines, or transmission lines, of which coplanar waveguides and microstrips are examples, allow for the transmission of an RF signal with little loss in bandwidth. More specifically, the metallized portions  60 ,  100 ,  154 ,  204  in electrical connection with Pin-six  30 , and the metallized portions  62 ,  102 ,  156 ,  206  in electrical connection with Pin-seven  32 , as well as the gap  302  positioned between each grouping of metallized ceramic portions make up a characteristic line, shown as the signal-ground coplanar waveguide  300 . The gap  302  of the coplanar waveguide  300  is thin enough to allow interaction of the RF signal between the metal portions in electrical connection with the signal (Pin-six  30 ) and the metal portions in electrical connection with the ground (Pin-seven  32 ) as the signal moves up the coplanar waveguide  300  along the side wall  16 . 
     The RF signal, having moved vertically up the coplanar waveguide  300 , now moves into the laser module  10 . As the signal moves into the laser module  10 , there is a large gap between metallized portions. This large gap halts the interaction of the signal between the signal (Pin-six  30 ) and the ground (Pin-seven  32 ), thereby breaking the waveguide  300 . This break results in a loss of bandwidth. More specifically, with reference to FIG. 4 b , the electrical signal moves into the laser module  10  through the metal pad  170  and the microstrip  172 . Please note, however, that the microstrip  172  does not act as a microstrip in the signal-ground configuration, but instead acts merely as a metal pad allowing the signal to move into the laser module  10 . A large gap  133  exists between the metal pads  170 ,  172 . Unlike the small gap  302  within the coplanar waveguide  300 , this large gap  133  is of great enough width to prevent the metal pads  170 ,  172  and the gap  133  from acting as a waveguide for the RF signals. Instead, the metal pad  170  acts as a signal pad and the metal pad  172  acts as a ground pad, thus allowing the signal to continue on into the interior of the package body  11 . The metal pads  170 ,  172  are wire bonded to a second characteristic line, shown as the coplanar waveguide  270  in the optical subassembly  250 . 
     The signal enters the optical subassembly coplanar waveguide  270  and then goes into the laser  282 , which emits modulated light. In a preferred embodiment, the laser  282  is a chip having a resistance of five ohms. Whether the RF signal is a digital signal, an analog signal, or any combination of the two, the laser  282  directly emits a corresponding optical signal. The modulated light signal exits the laser  282  as an optical signal and enters an optical fiber. 
     The signal-ground configuration is shown equivalently in FIG.  10 . As the signal moves up the sidewall  16 , the signal encounters inductors L 1 , Lt 12 , Lt 22 , Ltn 2 , L 3  and L 4  and capacitors C 1 , C 2 , C 3 , C a  and C 4 . The generally vertical line on the right-hand side of FIG. 10 denotes the conducting elements A-E of the coplanar waveguide  300 . The conducting elements A-E have varying lengths, and varying sizes of gaps therebetween. For example, the length of the conducting elements A, which run through the ceramic layer  40 , is 1.67 millimeters, while the size of the gap between the conducting elements A is 0.5 millimeters. The length of the conducting elements B, which run through the ceramic layers  80 ,  120  and into the ceramic layer  180 , is 0.87 millimeters, while the size of the gap between the conducting elements B is 0.5 millimeters. The lengths of the conducting elements C and D, which are on the ceramic layer  180 , are each 0.3 millimeters, while the sizes of the gaps between the conducting elements C and D are 0.5 millimeters. The length of the conducting elements E, which are on the ceramic layer  180 , is 0.95 millimeters, while the size of the gap between the conducting elements E is 0.3 millimeters. 
     As the signal goes from the signal-ground coplanar  300  into the package body  11 , the signal encounters an inductor L 5  prior to going to the OSA  250 . 
     It is to be understood that the signal-ground configuration illustrated in FIG. 10 is an exemplary embodiment and that the specific values described and illustrated (lengths and sizes of gaps) may be altered without departing from the invention. 
     Next will be described the ground-signal-ground electrical signal path configuration of the laser module  10 , which signal path is illustrated equivalently in FIG.  9 . In the ground-signal-ground electrical configuration, Pin-seven  32  is the input signal pin and Pin-six  30  and Pin-eight  34  are the grounds. Please note that in the ground-signal-ground electrical configuration, the signal pin (Pin-seven  32 ) is sandwiched between both grounds (Pin-six  30  and Pin-eight  34 ). As with the signal-ground configuration, a characteristic line is positioned on the side  16 . More specifically, a characteristic line, shown as a ground-signal-ground coplanar waveguide  310  is positioned along the side  16 . The ground-signal-ground coplanar waveguide  310  includes the metallized portions and the gap  302  of the signal-ground coplanar waveguide  300  as well as the metallized portions  64 ,  104 ,  158 ,  208  and the gap  312 . The ground-signal-ground coplanar waveguide  310  is a more efficient characteristic line, or transmission line, than the signal-ground coplanar waveguide  300  due to the placing of the input signal between two grounds. 
     Thus, for the ground-signal-ground electrical configuration, a high speed RF signal is received from a driver (not shown) through the circuit board (not shown) by Pin-seven  32 . The RF signal is then transmitted from the Pin-seven  32  to the ground-signal-ground coplanar waveguide  310 . The signal then moves to the interior of the laser module  10 . 
     More specifically, the RF signal comes through Pin-seven  32  through the ground-signal-ground coplanar waveguide  310  to a second characteristic line, shown as the microstrip  172 . In a preferred embodiment, the microstrip  172  has a characteristic impedance of twenty-five ohms and an electrical length of approximately one millimeter. The two grounds Pin-six  30  and Pin-eight  34  are connected in the interior of the laser module  10  by way of a wire bond from the metal pad  170  (FIG. 4 b ) and the microstrip ground  108  (FIG. 3 b ). The connection of grounds Pin-six and Pin-eight  30 ,  34  must be done on the interior of the laser module  10 . With specific reference to FIG. 3 b , the microstrip ground  108  is basically shaped as a backward L. There is a gap  109  along the long leg of the microstrip ground  108 . This gap  109  prevents the microstrip ground  108  from coming into connection with either Pin-six  30  or Pin-seven  32 . If the microstrip ground  108  was extended completely to the edge, namely to the side  16 , and no gap  109  was present, this configuration would short out Pin-six  30  and Pin-seven  32 . 
     In the ground-signal-ground configuration, the microstrip  172  adds unwanted inductance to the electrical signal path configuration. Hence, it is necessary to provide extra capacitance to the signal path. This is accomplished through the configuration of the microstrip  172 . With specific reference to FIG. 4 b , the microstrip  172  has a wide portion  173  and a thinner portion. The wide portion  173  provides added capacitance to the electrical configuration, thus balancing the inductance provided by the microstrip  172 . 
     The signal-ground configuration is shown equivalently in FIG.  9 . As the signal moves up the sidewall  16 , the signal encounters the inductors L 1 , Lt 12 , Lt 22 , Ltn 2 , L 3  and L 4 , as described previously regarding the signal-ground configuration. The signal also encounters capacitors C 1 ′, C 2 ′, C 3 ′, C a ′ and C 4 ′, which may have different values than the capacitors C 1 , C 2 , C 3 , Ca and C 4  shown in FIG.  10 . The conducting elements A-E have the same conducting element lengths and gap sizes between conducting elements as described with reference to FIG.  10 . 
     It is to be understood that the ground-signal-ground configuration illustrated in FIG. 9 is an exemplary embodiment and that the specific values described and illustrated (lengths and sizes of gaps) may be altered without departing from the invention. 
     As the signal goes from the coplanar waveguide  310  into the package body  11 , the signal encounters an inductor L 5 , a transmission line T 1  which is at about twenty-eight ohms, a step discontinuity S 1 , and a second transmission line T 2  at about twenty-five ohms. The signal then encounters a second step discontinuity S 2  prior to encountering the resistor  230  and going to the OSA  250 . 
     To minimize signal loss and reflections, it is preferred to match all input and output impedances in an electrical signal path. However, semiconductor lasers have become somewhat standardized in the industry at five ohms, while the resistance of printed circuit boards has become somewhat standardized at twenty-five ohms. Further, placing down five ohm lines on a printed wiring board would be prohibitively difficult. While no loss would be optimal, some loss is preferable in order to maintain a transmission line to the laser from the printed circuit board. 
     The ground-signal-ground coplanar waveguide  310  is preferably a forty-four ohm characteristic impedance waveguide. As shown in FIG. 9, however, the impedance fluctuates moving up the sidewall  16 . The variation is due to infinitesimal changes in inductance caused by variations in the length of wire and the gap between the metallization traces in the coplanar waveguide  310 . The microstrip  172  is preferably a twenty-five ohm characteristic impedance microstrip, and the OSA coplanar waveguide  270  is also preferably rated at a characteristic impedance of twenty-five ohms. Preferably, a matching twenty ohm wrap-around resistor  230  is positioned on the top of the microstrip  172  and wire bonded to the OSA coplanar waveguide  270 . In this way, the RF signal can move from the microstrip  172  through the OSA coplanar waveguide  270  to the five ohm laser  282 , allowing the laser  282  to transmit the light to an optical fiber. 
     Next will be described some of the components of the optical subassembly  250 . The OSA  250  includes both a laser  282  and a backside monitor  264 . The monitor  264  is provided in order to monitor the amount of continuous wave (CW) power from the laser  282 . The monitor  264  is connected to the Pin-four  26  through an N-side monitor pad  262  and to the Pin-five  28  through a P-side monitor pad  260 . The connection of the monitor pads  260 ,  262  to the Pin-four  26  and Pin-five  28  is through the P-side and N-side monitor circuits  110 ,  168 , respectively. With specific reference to FIG. 3 b  and FIG. 3 b , the P-side and N-side monitor circuits  110 ,  168  are kept well removed from the electrical circuitry utilized for the laser  282 , namely the microstrip ground  108 , the microstrip  172  and the metal pad  170 . If the monitor circuitry  110 ,  168  is placed too close to the laser circuitry, the monitor will pick up RF signal intended for the laser  282 . While picking up the RF signal will have no deleterious effect on the monitor  264 , it will, however, degrade the bandwidth of the input signal to the laser  282 . 
     The optical subassembly  250  may also include an isolator  290 . The isolator  290  is utilized for isolating the optical generator to the outside environment. Stated differently, the isolator  290  inhibits an optical signal from coming back from the fiber optic network. Optical signals which come back after being transmitted by the laser  282  will be picked up and retransmitted by the laser  282 . Due to the configuration of the laser module  10 , it is possible to place an isolator  290  within the optical subassembly  250 . A standard isolator provides forty decibels of isolation. Thus, for example, for a signal of one milliwatt, the isolator  290  would allow only one-tenth microwatt of a signal to come back. 
     The configuration of the laser module  10  allows for a double isolator  290   a  to be incorporated within the optical subassembly  250 . The double isolator  290   a  works the same as an isolator  290 ; however, standard double isolators  290   a  provide fifty decibels of isolation, which permits even less of a signal to come back. 
     The backside monitor  264  sits atop a backside monitor metal pad  266 . The metal pad  266  abuts with and is electrically connected to the N-side monitor pad  262 . Further, a ribbon bond  268  electrically connects the backside monitor  264  with the P-side monitor. Through this arrangement, continuity is provided with respect to the backside monitor  264  between the monitor pads  260 ,  262 . 
     The OSA coplanar waveguide  270  includes a first ground  272  and a second ground  274  on either side of a coplanar center conductor  276 . Between the first ground  272  and the conductor  276  is a first gap  278 , and between the second ground  274  and the conductor  276  is a second gap  280 . The two grounds  272 ,  274  extend underneath the laser  282 . A ribbon bond  284  provides electrical connection between the laser  282 , the center conductor  276  and a test pad  287 . The test pad  287  is used to test direct current (DC) power going to the laser  282 . 
     As described above, a preferred embodiment of the laser module of the present invention is capable of transmitting to a laser RF signals ranging from analog DC to 10 gigahertz and DC to approximately ten gigabits digital signals. The preferred embodiment accomplishes this through two discrete signal path configurations. 
     The above description and drawings are only illustrative of certain preferred versions which achieve the objects, features and advantages of the present invention. It is not intended that the present invention be limited to these versions. For example, while the laser module  10  is described as having eight pins, it is to be understood that more or less pins may be included in the module  10  to provide the desired result. Further, while the package body  11  is described as including four ceramic layers, the layers may be formed of any suitable insulating material, and the number of layers may be altered. Further, while the coplanar waveguides and the microstrip have been described with preferred characteristic impedances, these characteristic impedances may be altered.