Abstract:
An optical communication module being adapted to transmit a first optical signal to an optical transmitting device and receive a second optical signal is provided. The optical communication module includes a multi-mode distributed feedback laser diode (MM-DFB LD) and a receiver. The first optical signal is emitted by the MM-DFB LD and propagated by the optical transmitting device. The receiver is disposed at the propagating path of the second optical signal to receive the second optical signal propagated by the optical transmitting device. Moreover, another optical communication module having a lens with asymmetric numerical aperture (NA) is provided. Furthermore, an LD package includes a MM-DFB LD device with KL value ranged from 1.0 and 5.0 is further provided.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims the priority benefit of Taiwan application serial no. 94105561, filed on Feb. 24, 2005. All disclosure of the Taiwan application is incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of Invention  
         [0003]     The present invention relates to an optical communication module, more particularly to an optical communication module having a Multimode Distributed Feedback Laser Diode (MM-DFB LD) without using an optical isolator therein.  
         [0004]     2. Description of Related Art  
         [0005]     Nowadays, in accordance with the rapid development of the internet and various sorts of multimedia applications therein, the demand for more applicable bandwidth is increasing. The fiber optical communication techniques, which are previously more often applied in the field of long distance communication, are now likely to be used in short distance communication. In another hand, the field of fiber optical communication is closing to users to satisfy their requirements. The developing and manufacturing of optical communication modules play a key role in the field of optical communication. Conventional optical communication modules utilize laser diodes, such as Fabry-Perot laser diodes or distributed feedback laser diodes, as their light sources.  
         [0006]     Generally, conventional Fabry-Perot laser diodes are more often used in short-distance and low-speed optical communication modules known as Fiber To The Curb (FTTC). Such modules are most likely applied in the bandwidth about 1310 nm, due to their dispersion characteristic. In comparing the Fabry-Perot laser diode, DFB LDs have the advantage of being less limited by the dispersion, therefore optical communication modules having distributed feedback diodes are mainly used in the long-distance (&gt;10 km) high-speed optical communication. Remarkably, conventional DFB LDs are single mode distributed feedback laser diodes (SM-DFB LD). Such a conventional optical communication module is illustrated as follows.  
         [0007]      FIG. 1  schematically depicts a conventional optical communication module. A GE-PON ONU 1000 Based-PX20 is the example for descriptions. An optical communication module  100  includes a SM-DFB LD  110 , a PIN-TIA receiver  120 , a reflector  130 , an optical isolator  140 , and a housing  150 . The SM-DFB LD  110  is implemented in the housing  150 , for emitting optical signals to an optical fiber  160 , transmitting the optical signals thereby to the internet. The PIN-TIA receiver  120  and the reflector  130  are implemented in the housing  150 . When the optical signals transmit from the optical fiber  160  to the optical communication module  100 , the optical signals transmitted in the optical fiber are reflected to the PIN-TIA receiver  120  by the reflector  130 .  
         [0008]     Remarkably, since the SM-DFB LDs are relatively sensitive to lights and the reflection of unexpected lights (such as reflection from other optical nods) back from the optical fiber  160  occurs substantially often, an optical isolator is often employed between the SM-DFB LD  110  and the optical fiber  160  to prevent or reduce the interference caused by the reflected lights to the SM-DFB LD  110 .  
         [0009]      FIG. 2  is a cross-sectional view of a conventional SM-DFB LD. Referring to  FIGS. 1 and 2 , SM-DFB LD  110  includes a SM-DFB LD device  112 . It can be clearly seen from  FIG. 2 , the SM-DFB LD device  112  usually uses a technology of quarter wavelength shifted grating to improve the yield rate of the single mode, and the anti reflection (AR) layer  114  are formed on both sides of the laser diode. For this type of SM-DFB LD device  112 , the design of an grating layer  116  is adjusted to reduce the KL value, wherein K is the coupling coefficient, and L is the cavity length, so as to sustain a certain level for the laser outputting efficiency. Then, since the KL value is relatively lower, the SM-DFB LD device  112  is relatively sensitive to reflected lights. It should be noted that the cost of the SM DFB LD will be seriously affected by the yield of the side mode suppression ratio (SMSR).  
         [0010]     In view of the above, due to the expansive costs of the SM-DFB LDs  110  and the optical isolators  140 , the cost of manufacturing the optical communication modules  100  is hard to be further reduced.  
       SUMMARY OF THE INVENTION  
       [0011]     An objective of the present invention is to provide an optical communication module having a Multimode Distributed Feedback Laser Diode (MM-DFB LD) and needing no an optical isolator therein.  
         [0012]     Another objective of the present invention is to provide an optical communication module having a distributed feedback laser diode and a lens with asymmetric numerical aperture (NA).  
         [0013]     A further objective of the present invention is to provide a MM-DFB LD, which is insensitive to reflected lights or noise of lights.  
         [0014]     An optical communication module for transmitting a first optical signal to an optical transmitting device and receiving a second optical signal therefrom is provided in the present invention. The optical communication module includes a MM-DFB LD and a receiver, wherein the MM-DFB LD is suitable for emitting a first optical signal to an optical transmitting device and transmitting the optical signal thereby. The receiver is implemented on the path of the second optical signal to receive the second signal transmitted by the optical transmitting device.  
         [0015]     In an embodiment of the invention, the foregoing optical communication module further includes a lens, implemented between the MM-DFB LD and the optical transmitting device. In a preferred embodiment, the lens is integrated in the MM-DFB LD. In addition, one side of the lens adjacent to the MM-DFB LD has a first numerical aperture, and the side of the lens adjacent to the optical transmitting device has a second numerical aperture.  
         [0016]     In an embodiment of the invention, the optical communication module can further include a reflector, which is implemented between the optical transmitting device and the receiver, as well as on the transmitting path of the second optical signal.  
         [0017]     In an embodiment of the invention, the optical communication module can further include a housing, wherein the MM-DFB LD and the receiver are implemented within the housing.  
         [0018]     In an embodiment, the MM-DFB LD includes a supporter, a MM-DFB LD device and a cover. The MM-DFB LD device is implemented on and electrically connected to the supporter. The cover covers the MM-DFB LD device and at least a portion of the supporter. The MM-DFB LD comprises a substrate, a buffer layer, a first cladding layer, an active layer, a second cladding layer, a contacting layer and a grating layer, wherein the buffer layer is implemented on the substrate, the first cladding layer is implemented on the buffer layer, the active layer is implemented on the first cladding layer, the second cladding layer is implemented on the active layer, the contacting layer is implemented on the second cladding layer, and the grating layer is embedded between the first and the second cladding layers.  
         [0019]     In an embodiment of the invention, the KL value of the foregoing MM-DFB LD device is, for example, between 1.0 and 5.0.  
         [0020]     In an embodiment of the invention, the optical communication module device can further comprise an anti-reflection (AR) layer and a high reflection (HR) layer, the AR layer being implemented to the outputting surface, the HR layer being implemented to the opposite side of the AR coating.  
         [0021]     In an embodiment of the invention, the receiver is, for example, a PIN-TIA receiver.  
         [0022]     The present invention further provides an optical communication module, suitable for transmitting a first optical signal to an optical transmitting device and receiving a second optical signal from the optical transmitting device. The optical communication module comprises a DFB LD, a receiver, a lens. The DFB LD is adapted to emit a first optical signal to the optical transmitting device, and the optical transmitting device transmits the optical signal thereby. The DFB LD is, for example, a MM-DFB LD or a SM-DFB LD. The receiver is implemented on the transmitting path of the second optical signal to receive the second optical signal transmitted by the optical transmitting device. In addition, the lens is implemented between the DFB LD and the optical transmitting device. The lens has a first numerical aperture at the side towards the MM-DFB LD and a second numerical aperture at the side towards the optical transmitting device. The first numerical aperture is larger than the second.  
         [0023]     According to an embodiment of the present invention, the lens can be integrated to the optical communication module.  
         [0024]     In an embodiment of the present invention, the optical communication module can further comprise a reflector, which is implemented between the optical transmitting device and the receiver, as well as on the transmitting path of the second optical signal.  
         [0025]     In an embodiment of the present invention, the optical communication module can further comprise a housing, wherein the DFB LD and the receiver are implemented in side the housing.  
         [0026]     In an embodiment of the present invention, the DFB LD comprises a supporter, a DFB LD device and a cover. The DFB LD device is implemented on and electrically connected to the supporter. The cover covers the DFB LD and at least a part of the supporter.  
         [0027]     In an embodiment of the present invention, the KL value of the present invented DFB LD device is between 1.0 and 5.0.  
         [0028]     In an embodiment of the present invention, the DFB LD can further comprise an AR layer and a HR layer, the AR layer being implemented at the outputting surface, the HR layer being implemented at the opposite side of the AR layer.  
         [0029]     In an embodiment of the present invention, the receiver of the preferred embodiment of the present invention herein is a PIN-TIA receiver.  
         [0030]     The present invention further provides a MM-DFB LD, including a supporter, a MM-DFB LD device and a cover. The MM-DFB LD device is implemented on and electrically connected to the supporter. The MM-DFB LD device has an optical outputting surface. The KL value of the MM-DFB LD device is between 1.0 and 5.0. The cover covers the MM-DFB LD device and at least a part of the supporter.  
         [0031]     In an embodiment of the present invention, the MM-DFB LD device comprises a substrate, a buffer layer, a first cladding layer, an active layer, a second cladding layer, a contacting layer and a grating layer. Wherein, the buffer layer is implemented on the substrate, the first cladding layer is implemented on the buffer layer, the active layer is implemented on the first cladding layer, the second cladding layer is implemented on the active layer, the contacting layer is implemented on the second cladding layer, and the grating layer is embedded between the first and the second cladding layers.  
         [0032]     In an embodiment of the present invention, the optical communication module device can further include an AR layer and a HR layer, the AR layer being implemented to the outputting surface, the HR layer being implemented to the opposite side of the AR layer.  
         [0033]     In the present invention, an optical isolator is not necessarily needed in the present invention, because either a DFB LD having relatively low sensitivity to reflected light or a lens asymmetric numerical aperture is adopted in the present invention. Therefore the production cost can be cut down accordingly.  
         [0034]     Other objects and advantages of the present invention will become apparent from the following descriptions. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0035]     The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.  
         [0036]      FIG. 1  is a schematic diagram of a conventional optical communication module.  
         [0037]      FIG. 2  is a cross-sectional view of a conventional quarter wavelength shifted SM-DFB LD.  
         [0038]      FIG. 3  is a schematic diagram of an optical communication module according to an embodiment of the present invention.  
         [0039]      FIG. 4  is a spectrum diagram of a MM-DFB LD.  
         [0040]      FIG. 5  is a cross-sectional view of a MM-DFB LD device according to an embodiment of the present invention.  
         [0041]      FIG. 6  is a cross-sectional view of a MM-DFB LD TO Can according to an embodiment of the present invention.  
         [0042]      FIG. 7A  is a diagram of the relationship between the wavelength and the temperature of the MM-DFB LD.  
         [0043]      FIG. 7B  is a diagram of the relationship between the spectrum width and the temperature of the MM-DFB LD. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0044]     FIGS.  3  is a schematic diagram of an optical communication module according to an embodiment of the present invention. The optical communication module  200  of the present invention is adapted to transmit a first optical signal to an optical transmitting device  260 , and receive a second optical signal from the optical transmitting device  260 . In  FIG. 3 , the optical communication module  200  comprises a MM-DFB LD  210  and a receiver  220 , wherein the MM-DFB LD is adapted to emit a first optical signal to an optical transmitting device  260 , and transmit the first optical signal thereby to the internet. The receiver  220  is implemented on the transmitting path of the second optical signal to receive the second optical signal transmitted from the optical transmitting device  260 . In this preferred embodiment, the optical transmitting device  260  is, for example, one selected from the group consisting of optical fiber, optical waveguide and any other equivalent transmitting devices. Remarkably, in comparing with the conventional SM-DFB LD  110  (see  FIG. 1 ), the preferred embodiment adopts a MM-DFB LD  210  as a light source, which is insensitive to reflected lights, therefore the optical communication module  200  does not necessarily need an optical isolator therein, and then the production cost can be cut down accordingly.  
         [0045]     In an embodiment of the present invention, the optical communication module  200  can further comprise a reflector  230 . The reflector  230  is implemented between the optical communication device  260  and the receiver  220 , as well as on the transmitting path of the second optical signal. The purpose of implementing the reflector  230  therein is to reflect the second optical signal to the receiver  220  with a specific angle. However, in the present invention, the reflector  230  is not absolutely needed for the optical communication module. It should be noted that specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize that the reflector  230  is omissible by adjusting the positions of the MM-DFB LD  210  and the receiver  230 .  
         [0046]     Referring to  FIG. 3 , the optical communication module  200  of the embodiment can further include a housing  250  to adapt the MM-DFB LD  210 , the receiver  220  and the reflector  230  therein. Those skilled in the relevant art will recognize that the present invented MM-DFB LD  210  and receiver  220  can also be integrated inside any other optical products but not to this specific housing  250 .  
         [0047]     Still in  FIG. 3 , the optical communication module  200  of the embodiment can further include a lens  270 , wherein the lens  270  is implemented between the MM-DFB LD  210  and the optical transmitting device  260 . It is preferred to integrate the lens  270  onto the MM-DFB LD  210  (shown as  FIG. 3 ).  
         [0048]     Remarkably, the lens  270  can be either a lens with a single numerical aperture or a lens with an asymmetric numerical aperture. The lens with an asymmetric numerical aperture is taken as the example. The lens  270  has a first numerical aperture at the side towards the MM-DFB LD  210  and a second numerical aperture at the side towards the optical transmitting device  260 , the first numerical aperture is larger than the second numerical aperture. Such a design allows the MM-DFB LD  200  to be less interfered by the reflected lights. It is also to be noted that the shape, the quantity and the position of the lens  270  may vary according to the practical requirements.  
         [0049]      FIG. 4  is a spectrum diagram of a MM-DFB LD. Referring to  FIG. 4 , the spectrum of the MM-DFB LD in the embodiment has two peaks P 1  and P 2  (P 1 ≦P 2 ) near the position of 1310 nm with SMSR=|[−10*log (P 1 /P 2 )]|, wherein it satisfies the condition of SMSR=|[−10*log (P 1 /P 2 )]|&lt;30 dB. Accordingly, it is defined as MM-DFB LD by the present invention when the spectrum of the MM-DFB LD satisfies the condition of SMSR=|[−10*log (P 1 /P 2 )]|&lt;30 dB. Whereas, the present invention defines a DFB LD as a SM-DFB LD when the spectrum of the DFB LD satisfies the condition of SMSR=|[−10*log (P 1 /P 2 )]|&gt;30 dB.  
         [0050]     According to  FIG. 4 , the peaks P 1  and P 2  are only for example to illustrate the present invention, while the quantity of the peaks and the condition of P 1 &lt;P 2  should not be construed as a limitation thereof. In another words, when a spectrum of a DFB LD has two or more than two peaks P 1 , P 2 , . . . Pn, and the peaks satisfy the condition of SMSR=|[−10*log (Px/Py)]|&lt;30 dB, wherein 1&lt;x&lt;n, 1&lt;y&lt;n, and x≠y, then the DFB LD can be called a MM-DFB LD.  
         [0051]      FIG. 5  is a cross-sectional diagram of a MM-DFB LD device according to the present invention. Referring to  FIG. 5 , the preferred embodiment of the present invented MM-DFB LD device  212  includes, for example, a substrate  212   a,  a buffer layer  212   b,  a first cladding layer  212   c,  an active layer  212   d,  a grating layer  212   e,  a second cladding layer  212   f  and a contacting layer  212   g,  wherein the buffer layer  212   b  is implemented on the substrate  212   a,  the first cladding layer  212   c  is implemented on the buffer layer  212   b,  the active layer  212   d  is implemented on the first cover layer  212   c,  the second cladding layer  212   f  is implemented on the active layer  212   d,  the contacting layer  212   g  is implemented on the second cladding layer  212   f,  and the grating layer  212   d  is embedded between the first and the second cladding layers  212   c  and  212   f.  It is to be noted that the KL value of the MM-DFB LD device  212  in the embodiment is between 1.0 and 5.0.  
         [0052]     Referring to  FIG. 5 , the MM-DFB LD device  212  of the preferred embodiment can further include an AR layer  214  and a HR layer  214   a.  The AR layer  214  is disposed on the outputting surface, and the HR layer  214   a  is disposed at the opposite side of the AR layer  214 . Because it employs a design of an AR layer  214  and a HR layer  214   a  in the embodiment, and it has a KL value ranged from 1.0 to 5.0, the MM-DFB LD chip  212  of the present invention is insensitive to the reflected lights, and therefore an optical isolator is not necessary in the present invention.  
         [0053]      FIG. 6  is a cross-sectional diagram of a MM-DFB LD TO Can according to the present invention, wherein TO Can is a known as a packaging technology. Referring to  FIG. 6 , the MM-DFB LD  210  of the embodiment includes a supporter  216 , the MM-DFB LD device  212  and a cover  218 . The MM-DFB LD device  212  is implemented on and electrically connected to the supporter  216 . The cover  218  covers the MM-DFB LD device  212  and at least a part of the supporter  216 . The supporter  216  includes two parts of circuit board  216   a  and connection pin  216   b,  wherein the circuit board  216   a  is used to support the MM-DFB LD device  212  and/or other devices (such as detector) thereon, and the connection pin  216   b  is electrically connected with the MM-DFB LD device  212  and/or other devices through the circuit board  216   a.    
         [0054]      FIG. 7A  is a diagram of the relation between the wavelength and the temperature of the MM-DFB LD, while  FIG. 7B  is a diagram of the relation between the spectrum width and the temperature of the MM-DFB LD. Referring to  FIGS. 7A and 7B , when the MM-DFB LD is operated under the temperature ranged from 25 to 75 Celsius degrees, the wavelength of the lights emitted from the MM-DFB LD is ranged from 1306 nm to 1311 nm, and the spectrum width is about 0.72 nm. The relation between the ranges of the wavelength and the spectrum width can satisfy the standard of IEEE 802.3ah standard. It should be noted that the IEEE 802.3ah standard is specifically taken herein for illustrative purposes. The scope of the present invention should not be limited by above quotation, as those skilled in the relevant art will recognize that the present invention is also adapted to other optical communication standard such as ITU-T G.957 etc.  
                                         TABLE 1                                       RMS Frequency Bandwidth           Central Wavelength   (1000BASE-PX20-U Standard)           Unit(nm)   Unit(nm)                                        1260   0.72           1270   0.86           1280   1.07           1290   1.40           1300   2.00           1304   2.42           1305   2.55           1308   3.00           1317   3.00           1320   2.53           1321   2.41           1330   1.71           1340   1.29           1350   1.05           1360   0.88                        
         [0055]     It should be noted that deriving from the above disclosure to another optical communication module can be obtained. The optical communication module includes a DFB LD, a receiver and a lens, of which components the structure and the relation among the components have been previously described above and are not repeated. Specifically, in the invention, a MM-DFB LD or a SM-DFB LD can be implemented with a lens having an asymmetric numerical aperture. The interference of the reflected lights can therefore be reduced by employing such implementation in the optical communication module.  
         [0056]     In view of the above, because the present invention employs an above described MM-DFB LD having an AR layer implemented to one side and a HR layer to the other side, the optical output efficiency is therefore higher and thus the MM-DFB LD is able to adopt a grating having a larger KL value to reduce the sensitivity to the back reflection of the optical communication module. At the mean time, since a MM-DFB LD has a better output efficiency, an optical communication module having a MM-DFB LD can further reduce the interference of the reflected lights by reducing optical coupling efficiency. According to a combination of the above specific designs, the expensive optical isolator can be removed from the optical communication module.  
         [0057]     Further, since the MM-DFB LD in the invention includes a grating having a larger KL value, the resistance to back reflection is better, and the requirement of SMSR specification for the MM-DFB LD is relatively loose. And therefore, the fabrication yield can be improved, and the fabrication cost is reduced.  
         [0058]     In view of the above, the present invention has at least the advantages as follows.  
         [0059]     1. The optical transmitting module of the invention is designed without using the optical isolator, and the production cost can be reduced accordingly.  
         [0060]     2. The optical communication module of the invention can effectively prevent the DFB LD from being interfered by the reflected lights by employing a lens having an asymmetric numerical aperture.  
         [0061]     3. The MM-DFB LD of the invention in accordance with design uses an AR layer and a HR layer thereof, by which the laser outputting efficiency can be therefore increased.  
         [0062]     Other modifications and adaptations of the above-described preferred embodiment of the present invention may be made to meet particular requirements. This disclosure is intended to exemplify the invention without limiting its scope. All modifications that incorporate the invention disclosed in the preferred embodiment are to be construed as coming within the scope of the appended claims or the range of equivalents to which the claims are entitled.