JP3820802B2 - Optical transmitter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical transmitter for performing optical transmission using a multimode optical fiber, and more particularly to an optical transmitter that reduces DMD and improves CPR.
[0002]
[Prior art]
When long-distance transmission is performed with a multimode optical fiber (hereinafter referred to as MMF), if light focused at the center of the core is coupled, a transmission delay between modes (hereinafter referred to as DMD) will be described. ), The characteristics may deteriorate. This is because there is an inappropriate refractive index distribution near the center of the MMF core. When light is incident on a position that is displaced in an arbitrary direction (eccentric) away from the center of the core, the DMD Can be reduced.
[0003]
Therefore, the IEEE Gigabit Ethernet standard requires the use of a special short length optical fiber (hereinafter referred to as a special patch cord) when using MMF as a transmission medium. FIG. 5 shows a transmission system using MMF as a transmission medium in Gigabit Ethernet. The special patch cord has a configuration in which two duplex connectors 511 and 512 are connected by an optical fiber cord, and has a joint 505 between a single mode optical fiber (hereinafter referred to as SMF) 520 and MMF 530 in the middle. Reference numeral 506 denotes an optical connector, 507 denotes an optical connector coupling adapter, 508 denotes one MMF connecting the connectors 511 and 512, and 510 denotes an MMF as a transmission medium.
[0004]
When the core diameter of the MMF 510 is 62.5 μm, the SMF core is shifted from the center of the MMF core by about 20 μm at the connection portion. By connecting the SMF 520 of the special patch cord having such a structure to the transmission-side duplex connector 551 of the optical transceiver 550 and connecting the MMF 530 to the MMF 510 of the transmission medium, light can be incident avoiding the vicinity of the center of the MMF 510.
[0005]
As a method for solving the DMD problem without using a special patch cord, an optical transmitter with a mode conditioner as shown in FIG. This is an optical transmitter that has a laser light source 601 and is connected to the MMF 610 for optical transmission. A ferrule 602 that is disposed on the optical axis of the laser light source 601 and covers the MMF 610 is inserted from the emission side to the middle. A split sleeve 603, a capillary 604 inserted in contact with the MMF 610 on the incident side of the split sleeve, and an eccentric core single mode optical fiber (hereinafter referred to as an eccentric core) inserted in the capillary 604 and having a core displaced from the center of the MMF 610. 640) (denoted as SMF). The eccentric SMF 640 faces the laser light source 601 with a space therebetween, and can transmit light from the laser light source 601 to the MMF 610.
[0006]
[Problems to be solved by the invention]
In the conventional special patch cord, when the core diameter of the MMF of the transmission medium is 62.5 μm, the eccentric amount of about 20 μm is obtained by the method of fusing by shifting the SMF from the center of the MMF. Deviation occurs, and it takes a lot of work to obtain eccentricity with high accuracy. Furthermore, the inspection after fusion cannot be evaluated by simple measurements such as passage loss, and the manufacturing cost for the inspection work increases.
[0007]
In order to satisfy the IEEE Gigabit Ethernet CPR (Coupled Power Ratio) standard with the method of FIG. 6, the length of the capillary 604 in which the eccentric SMF 640 is inserted must be larger than 2 cm. I know by measurement. Here, CPR is a difference in optical output obtained when MMF and SMF are inserted into the optical transmitter of FIG. 6, and is a measure of whether light is incident sufficiently avoiding the center of the transmission medium MMF. Value. If the length of the capillary 604 is 2 cm or less, the light incident on the clad of the eccentric SMF 640 is coupled to the MMF 610 without being attenuated, and is coupled near the center of the MMF. In the optical transmitter having the shape shown in FIG. 6, when the length of the capillary 604 is 2 cm or more, the length in the optical axis direction becomes long. On the other hand, the substrate length of the Gigabit Ethernet optical transceiver 550 is only about 2 to 3 cm, and it is difficult to mount the optical transmitter having the shape of FIG. 6 on this substrate.
[0008]
Accordingly, an object of the present invention is to provide an optical transmitter that solves the above problems, reduces DMD, and improves CPR.
[0009]
[Means for Solving the Problems]
To accomplish the above object, has a laser light source, in being connected to the multimode optical fiber optical transmitter performing optical transmission, 10 [mu] m core single-mode optical fiber from the center of the single-mode optical fiber connection or eccentricity is, the single-mode optical fiber described above eccentric provided coupled to said laser light source, a single-mode optical fiber described above eccentric to the multi-mode optical fiber that is not the eccentric and centered with one another By doing so, the laser beam is made incident at a position shifted by 10 μm or more from the center of the non - eccentric multimode optical fiber.
[0010]
The eccentric single-mode optical fiber is inserted into the center of the capillary, the non - eccentric multimode optical fiber is inserted into the center of the ferrule, and the capillary and the ferrule are butted together in a split sleeve, The center of the eccentric single-mode optical fiber and the non - eccentric multi-mode optical fiber may be aligned.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.
[0015]
As shown in FIG. 1, the optical transmitter according to the present invention has a laser light source composed of a laser diode (LD) 101, and can output an optical signal for transmission from the laser light source. Optical transmission can be performed by connecting this optical transmitter to a multimode optical fiber (MMF) 110 for transmission. This optical transmitter is provided with a hollow cylinder open at both ends called a TX holder 106, and a split sleeve 103 is accommodated in the TX holder 106. The terminal of the MMF 110 connected to the optical transmitter is inserted into the through hole of the ferrule 102 having a cylindrical shape and the through hole at the center, and the MMF 110 with the ferrule 102 is inserted into the split sleeve 103 in the TX holder 106 from one end. To connect. The other end of the TX holder 106 is opened facing the LD 101. One end of an eccentric single mode optical fiber (SMF) 170 is brought into contact with and coupled to the LD 101. The other end of the SMF 170 is inserted into the through hole of the capillary 104 that is cylindrical and has the through hole at the center. The capillary 104 is inserted into the split sleeve 103 in the TX holder 106. When the capillary 104 and the ferrule 102 are abutted in the split sleeve 103, the eccentric SMF 170 and the MMF 110 are connected.
[0016]
FIG. 2 shows an enlarged connection portion between the eccentric SMF 170 and the MMF 110. 205 indicates the cladding of the eccentric SMF 170, 206 indicates the core of the eccentric SMF 170, 207 indicates the cladding of the MMF 110, and 208 indicates the core of the MMF 110. As shown in the figure, the eccentric SMF 170 and the MMF 110 are connected with their centers aligned. Since the core 206 of the eccentric SMF 170 is arranged to be shifted by 10 μm or more from the center of the clad 205, it is displaced from the center line C by 10 μm or more. On the other hand, the core 208 of the MMF 110 is disposed at the center of the clad 207. Since the diameter of the core 208 is sufficiently larger than the diameter of the core 206, the core 206 is connected to the core 208.
[0017]
The light propagating through the core 206 is incident on a position shifted by 10 μm or more from the center of the MMF 110. Further, since the length of the eccentric SMF 170 is equal to the distance from the LD 101 to the split sleeve 103 (including bending), 2 cm or more is secured. Further, the eccentric SMF 170 can be bent from the LD 101 to just before the TX holder 106. This bending can increase the length. Thus, by providing the eccentric SMF 170 with a sufficient length, most of the light incident from the LD 101 to the clad 205 of the eccentric SMF 170 is significantly attenuated before being coupled to the MMF 110. Further, in the clad 205 of the eccentric SMF 170, as shown by A in the figure, the refractive index at the outermost periphery is higher than the refractive index around the core. For this reason, light incident on the clad 205 and having an angle in a direction away from the center is absorbed without being reflected by the portion having the highest refractive index at the outermost periphery. Therefore, the light propagating through the cladding is attenuated better than the conventional eccentric SMF.
[0018]
Next, another embodiment of the present invention will be described.
[0019]
The optical transmitter shown in FIG. 3 has substantially the same structure as that shown in FIG. 1, except that eccentricity is performed by an eccentric capillary (or ferrule). That is, this optical transmitter includes an LD 301, an SMF 360, a TX holder 306, a capillary 304, and a split sleeve 303, and an MMF 310 equipped with a ferrule 302 is inserted into the split sleeve 303 for connection. The capillary 304 is an eccentric capillary that is formed in a columnar shape and has a through hole at a position displaced by 10 μm or more in an arbitrary radial direction from the center thereof. The SMF 360 has a refractive index at the outermost periphery of the cladding that is refracted at the periphery of the core. The SMF is higher than the rate and has no eccentricity.
[0020]
FIG. 4 shows an enlarged connection between the SMF 360 and the MMF 310. Reference numeral 405 denotes an SMF 360 clad, 406 denotes an SMF 360 core, 407 denotes an MMF 310 clad, and 408 denotes an MMF 310 core. As shown in the figure, the SMF 360 and the MMF 310 are connected with their centers shifted from each other. Since the core 406 of the SMF 360 and the core 408 of the MMF 310 are disposed at the centers of the clads 405 and 407, respectively, the core 408 is located on the center line C, but the core 406 is displaced by 10 μm or more from the center line C. Yes. Further, as indicated by A in the figure, the clad 405 has a refractive index at the outermost periphery higher than that around the core.
[0021]
The form of this eccentricity is different from the form of FIG. 2, but is equivalent in that light can be incident while completely avoiding the vicinity of the center of the MMF 310. That is, no light is coupled in the vicinity of the center of the core of the MMF 310. Therefore, no light propagates in the vicinity of the center of the core of the MMF 310 having an inappropriate refractive index, and transmission characteristics are deteriorated due to band degradation caused by DMD. It can be avoided.
[0022]
In the present invention, since the laser light source and the TX holders 106 and 306 are connected by the SMF 170 and 360, the respective positions (for example, the distance and angle of the laser light source with respect to the TX holder) can be freely changed to some extent. For this reason, there is a degree of freedom in mounting on the substrate as compared with the prior art of FIG.
[0023]
Also, the amount of eccentric SMF used is several centimeters per optical transmitter, and once a long eccentric SMF is manufactured, it can be used with a very large amount of optical transmitters with the same accuracy. The cost per transmitter can be reduced.
[0024]
【The invention's effect】
The present invention exhibits the following excellent effects.
[0025]
(1) According to the present invention, an eccentric optical transceiver in which an eccentricity is given in advance to the MMF of the transmission medium can be realized. If this eccentric optical transceiver is used, DMD at the time of long-distance MMF transmission can be reduced without using a special patch cord.
[0026]
(2) The light transmission distance can be extended to 2 cm or more by bending the optical fiber without changing the distance between the laser light source and the TX holder.
[0027]
(3) Since the refractive index at the outermost periphery of the cladding is made higher than the refractive index at the periphery of the core, most of the light propagating through the cladding can be attenuated and CPR can be improved.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of an optical transmitter showing an embodiment of the present invention.
2 is a partially enlarged cross-sectional view of the optical transmitter of FIG.
FIG. 3 is a cross-sectional view of an optical transmitter showing another embodiment of the present invention.
4 is a partially enlarged cross-sectional view of the optical transmitter of FIG. 3;
FIG. 5 is a configuration diagram of a transmission system using a special patch cord of the prior art.
FIG. 6 is a cross-sectional view of a conventional optical transmitter.
[Explanation of symbols]
101, 301 Laser light source (LD)
102, 302 Ferrule 103, 303 Split sleeve 104 Capillary 106, 306 TX holder 110, 310 MMF
170 Eccentric SMF
304 Eccentric capillary 360 SMF

Claims (2)

In an optical transmitter having a laser light source and connected to a multimode optical fiber for optical transmission, the core of the single mode optical fiber is decentered by 10 μm or more from the center of the single mode optical fiber, and the eccentric single mode An optical fiber is coupled to the laser light source, and the eccentric single-mode optical fiber is connected to the non - decentered multi-mode optical fiber by aligning the centers thereof, thereby connecting the eccentric multi-mode optical fiber. An optical transmitter characterized in that a laser beam is incident on a position shifted by 10 μm or more from the center of the mode optical fiber. The eccentric single-mode optical fiber is inserted into the center of the capillary, the non - eccentric multimode optical fiber is inserted into the center of the ferrule, and the capillary and the ferrule are butted together in a split sleeve, The optical transmitter according to claim 1, wherein the center of the eccentric single-mode optical fiber and the non - eccentric multi-mode optical fiber are aligned with each other.

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