Patent Publication Number: US-2003235378-A1

Title: Optical transmitter/receiver module

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] This invention relates to an optical transmitter/receiver module capable of reducing an electrical noise in an optical receiver section with an optical detector device, which is caused by electromagnetic waves emitted from an optical transmitter section with an optical source device.  
       [0003] 2. Description of the Related Art  
       [0004] Recently, an asynchronous transfer mode based passing optical network (ATM-PON) system has been attracting a public attention as one of the networks which connect a plurality of subscribers and a station by optical fibers because it provides a low-cost and high-speed service. An optical transmitter/receiver module used by a subscriber receives an optical signal of 1.5 μm band from an optical fiber with the optical detector device of the optical receiver section, and transmits an optical signal of 1.3 μm band through the optical fiber, which is emitted by the optical source device of the optical transmitter section, thus providing a two-way communication. The optical source and detector devices are normally accommodated in the same package.  
       [0005] However, in the above conventional optical transmitter/receiver module, the optical transmitter and receiver sections are disposed so closely to each other that when both the sections simultaneously operate, an electrical noise caused in the optical receiver section by the electrical cross talk between the optical receiver and transmitter sections, reduces the minimum photo detecting sensitivity of the optical receiver section. If the optical transmitter and receiver sections are disposed at a remote distance for reducing the electrical cross talk, it is difficult to reduce the size of the optical transmitter and receiver module.  
       SUMMARY OF THE INVENTION  
       [0006] Accordingly, an object of the invention is to provide an optical transmitter and receiver module capable of reducing the electrical cross talk without increasing the distance between the optical transmitter and receiver sections.  
       [0007] According to one aspect of the invention, there is provided an optical transmitter/receiver module which comprises a package having an inside wall and a ground portion, an optical transmitter section provided in the package and having an optical source to convert an electrical signal to an optical signal, an optical receiver section provided in the package and having an optical detector to convert the optical signal to the electrical signal, and a metal wire provided over the optical transmitter or receiver section and having ends fixed to the inside wall of the package and connected to the ground portion of the package.  
       [0008] According to another aspect of the invention, an optical transmitter/receiver module comprises two metal wires; a first metal wire provided over the optical transmitter section and having ends which are fixed to the inside wall of the package and connected to the ground portion of the package, and a second metal wire provided over the optical receiver section and having ends fixed to the inside wall of the package and connected to the ground portion of the package.  
       [0009] According to still another aspect of the invention, an optical transmitter/receiver module comprises a plurality of metal wires provided in parallel to each other at a predetermined interval such that they pass over the optical transmitter and receiver sections, each metal wire having ends fixed to the inside wall of the package and connected to the ground portion of the package.  
       [0010] According to yet another aspect of the invention, an optical transmitter/receiver module comprises a metal plate covering the optical transmitter or receiver section and having an end fixed to the inside bottom of the package and connected to the ground portion of the package.  
       [0011] According to one aspect of the invention, an optical transmitter/receiver module comprises first and second metal plates covering over the optical transmitter and receiver sections, respectively, each metal plate having an end which is fixed to the inside bottom of the package and connected to the ground portion of the package.  
       [0012] According to another aspect of the invention, an optical transmitter/receiver module comprises a metal plate covering the optical transmitter and receiver sections and having ends bent in the same direction so as to be fixed to the inside bottom of the package and connected to the ground portion of the package.  
       [0013] According to still another aspect of the invention, an optical transmitter/receiver module comprises an electromagnetic wave absorbing member provided -in the vicinity of the optical transmitter section or the optical receiver section and having an end fixed to the inside bottom of the package.  
       [0014] According to yet another aspect of the invention, an optical transmitter/receiver module comprises first and second electromagnetic wave absorbing members provided in the vicinity of the optical transmitter section and the optical receiver section, respectively, and each absorbing member having an end fixed to the inside bottom of the package.  
       [0015] According to one aspect of the invention, an optical transmitter/receiver module comprises an electromagnetic wave absorbing member provided in the package so as to cover the optical transmitter and receiver sections. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0016]FIG. 1 is a block diagram of an optical transmitter/receiver module according to the invention.  
     [0017]FIG. 2 is a perspective view of the optical transmitter/receiver module of FIG. 1.  
     [0018]FIG. 3 is a top plan view of an optical transmitter/receiver module according to the first embodiment of the invention.  
     [0019]FIG. 4 is a sectional view taken along line  4 - 4  of FIG. 3.  
     [0020]FIG. 5 is a top plan view of an optical transmitter/receiver module according to the second embodiment of the invention.  
     [0021]FIG. 6 is a sectional view taken along line  6 - 6  of FIG. 5.  
     [0022]FIG. 7 is a top plan view of an optical transmitter/receiver module according to the fourth embodiment of the invention.  
     [0023]FIG. 8 is a sectional view of the optical transmitter/receiver module of FIG. 7 taken along the line  8 - 8 .  
     [0024]FIG. 9 is a top plan view of an optical transmitter/receiver module according to the fifth embodiment of the invention.  
     [0025]FIG. 10 is a sectional view taken along line  10 - 10  of FIG. 9.  
     [0026]FIG. 11 is a top plan view of an optical transmitter/receiver module according to the sixth embodiment of the invention.  
     [0027]FIG. 12 is a sectional view taken along line  1212  of FIG. 11.  
     [0028]FIG. 13 is a top plan view of an optical transmitter/receiver module according to the eighth embodiment of the invention.  
     [0029]FIG. 14 is a sectional view taken along line  14 - 14  of FIG. 13.  
     [0030]FIG. 15 is a top plan view of an optical transmitter/receiver module according to the ninth embodiment of the invention.  
     [0031]FIG. 16 is a sectional view taken along line  1616  of FIG. 15.  
     [0032]FIG. 17 is a top plan view of an optical transmitter/receiver module according to the tenth embodiment of the invention.  
     [0033]FIG. 18 is a sectional view taken along line  1818  of FIG. 17.  
     [0034]FIG. 19 is a top plan view of an optical transmitter/receiver module according to the twelfth embodiment of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
     [0035] Embodiments of the invention will now be described with reference to the accompanying drawings. In FIG. 1, an optical transmitter/receiver module according to the invention is composed of an optical transmitter section  12 , a wavelength division multiplex (WDM) optical circuit section  14 , an optical fiber  16 , and an optical receiver section  18 .  
     [0036] The optical transmitter section  12  includes an optical source device, such as a laser diode (LD), and transmits an optical signal  102  of 1.3 μm band which is modulated by an input signal  100 . The WDM optical circuit  14  multiplexes and demultiplexes optical signals of 1.3 μm band and 1.5 μm band by having a WDM filter inserted or using an optical wave path adhered to the end face thereof. The WDM optical circuit  14  reflects the optical signal  102  of 1.3 μm band supplied from the optical transmitter section  12  by the WDM filter and sends it to the optical fiber  16 , and sends the optical signal of 1.5 μm band supplied from the optical fiber  16  to the optical receiver section  18  through the WDM filter as an optical signal  104 .  
     [0037] The optical fiber  16  is an optical transmission path to connect subscribers and a station, which transmits the optical signal of 1.3 μm band from the subscribers to the station and the optical signal of 1.5 μm band from the station to the subscribers. The optical receiver section  18  converts the optical signal  104  supplied from the WDM optical circuit  14  to an electrical signal by an optical detector device, such as photo diode (PD), amplified it up to a predetermined level by a head amplifier, and outputs it as a signal  106 .  
     [0038] The operation of the optical transmitter/receiver module will be described briefly. The 1.5 μm band optical signal supplied from the optical fiber  16  is input to the WDM optical circuit  14  and sent to the optical receiver section  18  through the WDM filter of the WDM optical circuit  14  as the optical signal  104 . Then, it is converted to an electrical signal by the photo diode (PD) of the optical receiver section  18  and sent as the signal  106 . The signal  100  input to the optical transmitter section  12  is converted to the 1.3 μm band optical signal  102  by the laser diode (LD) and sent to the WDM optical circuit  14 . Then, it is reflected by the WDM filter of the WDM optical circuit  14  and sent to the optical fiber  16 .  
     [0039] In FIG. 2, reference number  22  is an insulative flat-mount type package made of an epoxy resin, and comprises an opening for receiving the optical fiber and a plurality of terminals to be connected to an external circuit. Silicon substrates  24  and  26  are provided on the interior bottom of the package  22  at a predetermined distance. The silicon substrates  24  and  26  are adhered to the interior bottom by a resin  28  (not shown).  
     [0040] The optical transmitter section  12  including the semiconductor laser (LD) for converting an electrical signal into an optical signal and the front end of the optical fiber  16  are mounted and fixed on the upper surface of the silicon substrate  24  at predetermined positions. The optical receiver section  18  including the photo diode (PD) for converting an optical signal to an electrical signal is mounted and fixed to the upper surface of the silicon substrate  26  at a predetermined position. The WDM optical circuit  14 , which is made by forming an optical wave path on a quartz substrate, is fixed between the silicon substrates  24  and  26 .  
     [0041] The optical transmitter section  12 , WDM optical circuit  14 , and optical receiver section  18  are fixed to the silicon substrates  24  and  26  by a flip-chip-dice bonder or the like after markers are precisely formed in an LD active layer of the optical transmitter section  12 , the optical wave path of the WDM optical circuit  14 , and a PD photo detective layer of the optical receiver section  18 , respectively, and aligned with, at the accuracy of a sub-micron order, V-shaped grooves having “V” cross sectional shapes, which are precisely formed by etching on the upper surfaces of the silicon substrates  24  and  26 .  
     [0042] The top portion of optical fiber  16  is mounted in a V-shaped groove precisely formed by etching on the upper surface of the silicon substrate  24  at a predetermined position and fixed on the V-shaped groove by UV adhesion. At this point, the top portion is pressed by a pressing plate  30  such that it is not lifted from the V-shaped groove. The pressing plate is also fixed on the V-shaped groove by the UV adhesive. A cap made of a resin is bonded on the package  22  at the final stage.  
     [0043] In addition, the optical transmitter/receiver module in FIG. 2 is provided with an electrical noise preventive measure to reduce the electrical cross talk between the optical transmitter section  12  and the optical receiver section  18  so that the electrical noise in the optical receiver section  18  is reduced.  
     [0044] In FIGS. 3 and 4, the optical transmitter/receiver module with the electrical noise preventive measure according to the first embodiment comprises a conductive wire, such as a metal wire  32  made of gold and having a diameter of25 μm, which is connected between points P1 and P2 on flat portions X1 and X2 formed on the inside walls of the package  22  such that the metal wire  32  crosses over the optical receiver section  18  mounted on the silicon substrate  26 . The ends of the metal wire  32  are not only bonded to the points P1 and P2 but also connected to a ground portion (GND) provided on the interior bottom of the package  22 . Accordingly, electromagnetic wave input to the optical receiver section  18  is weakened by the metal wire  32  so that the electrical cross talk from the optical transmitter section  12  to the optical receiver section  18  is reduced and the electrical noise in the optical receiver section  18  is reduced.  
     [0045] Experiments showed that when the photo output of the laser diode (LD) of the optical transmitter section  12  is 10 DBMS (minimum), photo detective sensitivity of the photo diode (PD) in the optical receiver section  18  is 0.8 A/W (minimum), the distance between the optical transmitter and receiver sections  12  and  18  is 5 mm, and the signal speed of transmitted signal (data) during the operation of the laser diode (LD) is 622.08 MHz, the minimum photo detective sensibility of the optical receiver section  18  during the operation of the laser diode (LD) was −28 dBm. The value meets the requirements under ITU-TG983.1 Class B. When the metal wire  32  was not provided, the minimum photo detective sensitivity was −26 dbms. Thus, the minimum photo detective sensitivity was increased by 3 dBm by providing the metal wire  32 .  
     [0046] In FIGS. 5 and 6, the optical transmitter/receiver module with the electrical noise preventive measure according to the second embodiment comprises a conductive wire, such as a metal wire  34  made of gold and having a diameter of 25 μm, which is connected between points P3 and P4 on flat portions X1 and X2 formed on the inside walls of the package  22  such that the metal wire  32  passes over the optical transmitter section  12  mounted on the silicon substrate  24 . The ends of the metal wire  32  are not only bonded to the points P3 and P4 but also connected to a ground portion (GND) provided on the interior bottom of the package  22 . According to the second embodiment, the same effects as those in the first embodiment are obtained.  
     [0047] In the optical transmitter/receiver module with the electrical noise preventive measure according to the third embodiment, the metal wire  32  passes over the optical receiver section  18  mounted on the silicon substrate  26  in the same way as that in the first embodiment and the metal wire  34  passes over the optical transmitter section  12  mounted on the silicon substrate  24  in the same way as that in the second embodiment. According to the third embodiment, the same effects as those in the first embodiment are obtained.  
     [0048] In FIGS. 7 and 8, the optical transmitter/receiver module with the electrical noise preventive measure according to the fourth embodiment comprises a plurality of metal wires  36  which pass over the optical transmitter section  12 , the WDM optical circuit  14 , and the optical receiver section  18 . That is, a plurality of the metal wires  36  having a diameter of  25  μmare connected between flat portions Y1 and Y2 formed on the inside walls of the package  22  at an interval of 500 μm such that the metal wires pass over the whole parts in the package  22 . The respective ends of the metal wires  36  are connected to the ground portion (GND) provided on the interior bottom of the package  22 . According to the fourth embodiment, the same effects as those in the first embodiment are obtained.  
     [0049] In FIGS. 9 and 10, the optical transmitter/receiver module with the electrical noise preventive measure according to the fifth embodiment comprises an L-shaped metal plate, such as a metal plate  38  made of a Copper-Nickel alloy and having a width of approximately 2.35 mm, which is bonded on the interior bottom of the package  22  in the vicinity of the optical receiver section  18  such that an end of the metal plate  38  covers the upper surface of the optical receiver section  18  on the silicon substrate  26 . The metal plate  38  is connected to the ground portion (GND) provided on the interior bottom of the package  22 . Accordingly to the fifth embodiment, the same effects as those in the first embodiment are obtained because the major part of electromagnetic wave input to the optical receiver section  18  is shielded by the metal plate  38 .  
     [0050] In FIGS. 11 and 12, the optical transmitter/receiver module with the electrical noise preventive measure according to the sixth embodiment comprises an L-shaped metal plate, such as a metal plate 4.0 made of a Copper-Nickel alloy and having a width of approximately 2.35 mm, which is bonded on the interior bottom of the package  22  in the vicinity of the optical transmitter section  12  such that an end of the metal plate  40  covers the upper surface of the optical transmitter section  12  in the silicon substrate  24 . The metal plate  40  is connected to the ground portion (GND) provided on the interior bottom of the package  22 . According to the sixth embodiment, the same effects as those in the fifth embodiment are obtained because the major part of electromagnetic wave emitted from the optical transmitter section  12  is shielded by the metal plate  40 .  
     [0051] According to the seventh embodiment, the metal plate  38  is bonded on the interior bottom of the package  22  in the vicinity of the optical receiver section  18  such that an end of the metal plate  38  covers over the upper surface of the optical receiver section  18  in the silicon substrate  26  in the same way as in the fifth embodiment, and the metal plate  40  is bonded on the interior bottom of the package  22  in the vicinity of the optical transmitter section  12  such that the end of the metal plate  40  covers over the upper surface of the optical transmitter section  12  in the silicon substrate  24  in the same way as in the sixth embodiment. The metal plates  38  and  40  are connected to the ground portion (GND) provided on the interior bottom of the package  22 . According to the seventh embodiment, at least the same-level of effects as those in the fifth and sixth embodiments are obtained because the major part of electromagnetic wave which is emitted from the optical transmitter section  12  and input to the optical receiver section  18  is shielded by the metal plates  40  and  38 , respectively.  
     [0052] In FIGS. 13 and 14, the optical transmitter/receiver module with the electrical noise preventive measure according to the eighth embodiment comprises a metal plate  42  made of a Copper-Nickel alloy and having a width of approximately 2.35 mm. Both ends of the metal plate  42  are bent in the same direction so as to be bonded to the interior bottom of the package  22  such that the metal plate  42  covers the upper surfaces of the optical transmitter section  12 , the WDM optical circuit  14 , and the optical receiver section  18 . Both the ends of the metal plate  40  are connected to the ground portion (GND) provided on the interior bottom of the package  22 . According to the eighth embodiment, the same effects as those in the fifth or sixth embodiment- are obtained because electromagnetic wave transmitted from the optical transmitter section  12  to the optical receiver section  18  is attenuated by the metal plate  40 .  
     [0053] In FIGS. 15 and 16, the optical transmitter/receiver module with the electrical noise preventive measure according to the ninth embodiment comprises an electromagnetic wave absorbing plate  44  which is bonded on the interior bottom of the package  22  in the vicinity of the optical receiver section  18  so as to absorb electromagnetic wave. According to the ninth embodiment, the same effects as those in the first embodiment are obtained because the major part of electromagnetic wave input to the optical receiver section  18  is absorbed by the absorbing plate  44  so that the electrical noise caused in the optical receiver section  18  is reduced.  
     [0054] In FIGS. 17 and 18, the optical transmitter/receiver module with the electrical noise preventive measure according to the tenth embodiment comprises an electromagnetic wave absorbing plate  46  which is bonded on the interior bottom of the package  22  in the vicinity of the optical transmitter section  12  so as to absorb electromagnetic wave. According to the tenth embodiment, the same effects as those in the ninth embodiment are obtained because the major part of electromagnetic wave transmitted from the optical transmitter section  12  is absorbed by the absorbing plate  46  so that the electrical noise caused in the optical receiver section  18  is reduced.  
     [0055] According to the eleventh embodiment, the electromagnetic wave absorbing plate  44  is bonded on the interior bottom of the package  22  in the vicinity of the optical receiver section  18  in the same way as in the ninth embodiment, and the electromagnetic wave absorbing plate  46  is bonded on the interior bottom of the package  22  in the vicinity of the optical transmitter section  12  in the same way as in the tenth embodiment. According to the eleventh embodiment, the same effects as those in the ninth or tenth embodiment are obtained because the major part of electromagnetic wave which is emitted from the optical transmitter section  12  and input to the optical receiver section  18  is absorbed by the absorbing metal plates  46  and  44 , respectively.  
     [0056] In FIG. 19, the optical transmitter/receiver module with the electrical noise preventive measure according to the twelfth embodiment comprises an electromagnetic wave absorbing plate  48 , which is bonded to the upper part of the inside wall of the package  22  and caps the package  22  so that the optical transmitter and receiver sections  12  and  18 , and the WDM optical circuit  14  are covered by the absorbing plate  48 . According to the twelfth embodiment, the same effects as those in the ninth embodiment are obtained because electromagnetic wave which is emitted from the optical transmitter&#39;section  12  to the optical receiver section  18  is absorbed by the absorbing metal plates  48  and the electrical noise caused in the optical receiver section  18  is reduced.  
     [0057] As has been described above, according to the invention, the electromagnetic wave, which is emitted from the optical transmitter section, transmitted from the optical transmitter section to the optical receiver section, or input to the optical receiver section, is decreased by the metal wire, metal plate, or electromagnetic wave absorbing plate so that the electrical noise which is produced in the optical receiver section is reduced and the minimum photo detective sensitivity is increased.