JP3879320B2 - Optical transmitter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical transmitter for transmitting laser light using a multimode optical fiber, and more particularly to an optical transmitter for reducing and eliminating the influence of propagation delay between modes.
[0002]
[Prior art]
When long-distance transmission is performed with a multimode optical fiber (hereinafter referred to as MMF), if light that is focused on the center of the core enters, propagation delay between modes (hereinafter referred to as DMD) Due to this phenomenon, the characteristics may deteriorate. This is because an inappropriate refractive index distribution exists near the center of the MMF core. When light is incident on a position shifted from the center in any direction (eccentric or eccentric), avoiding the core center. 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.
[0004]
FIG. 5 shows a transmission system when 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 coupling adapter, 508 denotes one MMF connecting the connectors 511 and 512, and 510 denotes an MMF as a transmission medium.
[0005]
FIG. 7 is an enlarged view of the inside (only on the transmission side) of the fiber connection portion at the middle point of the special patch cord shown in FIG. 5, 705 and 706 are the SMF cladding and core, and 707 and 708 are respectively. The cladding and core of MMF are shown. In the case where the core diameter of the MMF 510 is 62.5 μm, the SMF core 706 is fused and displaced from the center of the MMF core 708 by about 10 μm at the fiber connection portion. By connecting the SMF 520 of the special patch cord having such a structure to the transmission side connector 511 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.
[0006]
As a method for solving the DMD problem without using a special patch cord, the present applicant has proposed an optical transmitter with a mode conditioner as shown in FIG. 6 (Japanese Patent Application No. 10-328233). . This is an optical transmitter that has a laser light source 601 and is connected to the MMF 610 and performs optical transmission, and is disposed on the optical axis of the laser light source 601, and a ferrule 602 that covers the MMF 610 is inserted partway from the emission side. The split sleeve 603, the capillary 604 inserted so as to be in contact with the MMF 610 on the incident side of the split sleeve 603, and inserted into the capillary 604, transmit light from the laser light source 601 to the MMF 610, and the core serves as the MMF 610. An eccentric single mode optical fiber (hereinafter referred to as an eccentric SMF) 640 that is deviated from the center of the optical fiber.
[0007]
[Problems to be solved by the invention]
In the special patch cord, when the core diameter of the MMF of the transmission medium is 62.5 μm, as a method of obtaining an eccentricity amount of about 20 μm, the method of fusing the SMF by shifting from the center of the MMF is adopted. In this case, separation occurs, and it takes a lot of work to obtain eccentricity with high accuracy. Furthermore, the inspection after fusion cannot be evaluated by simple measurement of passage loss or the like, and the manufacturing cost for the inspection work is increased.
[0008]
Further, in order to satisfy the IEEE Gigabit Ethernet Coupled Power Ratio (CPR) standard in the optical transmitter of FIG. 6, the length of the capillary 604 in which the eccentric SMF 640 is inserted must be larger than 2 cm. Is known by measurement. Here, the CPR is a value that serves as an indication of whether or not the optical transmitter shown in FIG. When the length of the capillary 604 is 2 cm or less, the light incident on the cladding of the eccentric SMF 640 is coupled to the MMF 610 without being attenuated, and is coupled near the center of the MMF. The board length of the optical transceiver 550 for Gigabit Ethernet is about 2 to 3 cm, and it is difficult to mount the optical transmitter having the shape of FIG. 6 on this board.
[0009]
Therefore, an object of the present invention is to provide an optical transmitter that solves the above-described problems and reduces and eliminates the influence of propagation delay between modes.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the present invention has a laser light source, uses a single mode optical fiber to inject laser light from the laser light source into the multimode optical fiber , and connects the laser light source and the multimode optical fiber. A capillary is provided in between, and the capillary and a ferrule sheathed on the end of the multimode optical fiber are brought into contact with each other in the split sleeve, and the center of the core of the single mode optical fiber and the multimode light in the split sleeve Light provided by penetrating the capillary through the single-mode optical fiber, which is shifted from the center of the fiber by 10 μm or more and makes the laser light from the laser light source enter a position shifted from the center of the multimode optical fiber. in the transmitter, the capillary has a hollow portion, of the single-mode optical fiber Bending light propagating Rudd is attenuated formed in the single-mode optical fiber at the hollow portion, the length of the capillary with the hollow portion is obtained by less than 2 cm.
[0011]
The capillary may be divided into a capillary disposed on the laser light source side and a capillary disposed on the multimode optical fiber side, and the single mode optical fiber may be bent between the two capillaries.
[0012]
A portion having an inner diameter that is twice or more the outer diameter of the single mode optical fiber may be formed in the hollow portion.
[0013]
The inner diameter of the hollow portion may be thickened at a position away from the end of the hollow portion on the multimode optical fiber side, and the inner diameter may be gradually reduced from this position to the end of the hollow portion on the multimode optical fiber side.
[0014]
The position where the single mode optical fiber penetrates the capillary is decentered from the center of the multimode optical fiber, and the amount of eccentricity of the penetrating position on the laser light source side is different from the amount of eccentricity of the penetrating position on the multimode optical fiber side. Also good.
[0015]
The laser light source side of the single mode optical fiber may be inclined with respect to the center line of the multimode optical fiber and penetrate the capillary.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.
[0017]
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 is connected to a multimode optical fiber (MMF) 110 for optical transmission. . A hollow cylindrical split sleeve 103 having both ends opened is provided with the laser light source 101 facing one opening, and is accommodated in a TX holder 106. A ferrule 102 that covers the MMF 110 is inserted into the exit side opening (opening far from the laser light source 101) of the split sleeve 103 in contact with the inner wall of the split sleeve 103 until the middle of the split sleeve 103, and the center of the MMF 110 is split. The sleeve 103 is held at the center (center line C). A capillary having a hollow part is provided between the laser light source 101 and the MMF 110. This capillary is inserted into the incident side opening of the split sleeve 103, is in contact with the inner wall of the split sleeve 103, and is in contact with the ferrule 102 in the split sleeve 103. The capillary is composed of an LD side capillary part 107 arranged on the laser light source side and an MMF side capillary part 108 arranged on the multimode optical fiber side. An eccentric single mode optical fiber (eccentric SMF) 170 for allowing laser light from the laser light source 101 to enter a position shifted by 10 μm from the center of the MMF 110 passes through the LD side capillary part 107 and the MMF side capillary part 108. The eccentric SMF 170 is bent and accommodated in the hollow portion of the capillary.
[0018]
The LD side capillary part 107 and the MMF side capillary part 108 may be provided apart from each other. However, in consideration of mass productivity, it is desirable that they are brought into contact with each other and bonded together. This is because when the LD side capillary part 107 and the MMF side capillary part 108 are in contact with each other, the size of the hollow part is made uniform, and a certain bending can be secured when the eccentric SMF 170 is inserted into this capillary.
[0019]
In order to penetrate the eccentric SMF 170, the LD side capillary part 107 and the MMF side capillary part 108 are each provided with a through hole having the same thickness as the eccentric SMF 170. The through hole of the LD side capillary 107 may or may not be parallel to the center line C of the MMF 110, but it is preferable that the through hole is not parallel. This is because the eccentric SMF 170 is bent more tightly when the through hole of the LD side capillary portion 107 is not parallel to the center line C of the MMF 110 but has an angle. When the eccentric SMF 170 is parallel to the center line C of the MMF 110, the position of the through hole of the LD side capillary part 107 needs to be decentered to a position different from the position of the through hole of the MMF side capillary part 108.
[0020]
The hollow portion formed by the MMF side capillary portion 108 has an inner diameter that is more than twice the outer diameter of the eccentric SMF 170 at a position away from the end of the MMF side hollow portion. The wall thickness increases so that the inner diameter gradually decreases to the through hole. The through hole of the MMF side capillary part 108 is at least 1 mm parallel to the center line C from the end of the hollow part on the MMF side, and the through hole outlet on the MMF side is on the center line C. By adopting such a structure, the eccentric SMF 170 inserted into the LD side capillary part 107 and the MMF side capillary part 108 is bent at a short distance. That is, the eccentric SMF 170 is inserted into the hollow portion inclining with respect to the center line C according to the through hole of the LD side capillary portion 107 and bent along the inner wall of the hollow portion where the inner diameter gradually decreases. 108 through holes are reached. In this structure, the bending of the eccentric SMF 170 can be tightened as the diameters of the LD side capillary part 107 and the MMF side capillary part 108 are larger.
[0021]
As described above, the capillary has a hollow portion, and a part of the through hole of the capillary is inclined with respect to the center line C, or the SMF that penetrates the capillary is bent by a structure in which the positions of the two through holes are different. be able to.
[0022]
In the optical transmitter of the present invention, the eccentric SMF 170 is accommodated in the hollow portion of the capillary. Since light propagating through the cladding is rapidly attenuated by bending, the light incident on the cladding of the eccentric SMF 170 from the laser light source 101 is attenuated before being coupled to the MMF 110. In the optical transmitter of FIG. 6, since the eccentric SMF 640 is accommodated straight in the capillary 604, attenuation of light propagating through the cladding could not be obtained. In contrast, in the optical transmitter of the present invention, light propagating through the cladding can be significantly attenuated.
[0023]
FIG. 2 is an enlarged view of the connecting portion between the eccentric SMF 170 and the MMF 110. 205 and 206 indicate the cladding and core of the eccentric SMF 170, respectively, and 207 and 208 indicate the cladding and core of the MMF 110, respectively. Both the eccentric SMF 170 and the MMF 110 are located on the center line C. The core 206 of the eccentric SMF 170 is displaced by 10 μm or more from the center of the eccentric SMF 170. 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.
[0024]
The eccentric SMF 170 has a refractive index at the outermost peripheral portion of the clad higher than that at the peripheral portion of the core. That is, in the clad 205 of the eccentric SMF 170, the refractive index of the outermost peripheral portion A is higher than the refractive index of the peripheral portion of the core, so that light incident on the clad 205 and having an angle away from the center is Absorbed without being reflected by the part A. As a result, it is possible to attenuate light propagating through the cladding as compared with the conventional eccentric SMF.
[0025]
Next, another embodiment of the present invention will be described.
[0026]
As shown in FIG. 3, the optical transmitter includes a laser light source 301, a ferrule 302, a split sleeve 303, a TX holder 306, an LD side capillary part 307, an MMF side eccentric capillary part 308, an MMF 310, and an SMF 360. This optical transmitter has the same structure as that of FIG. 1, except that the SMF is eccentric by an eccentric capillary. The MMF-side eccentric capillary section 308 has a through-hole end at a position that is eccentric by 10 μm or more in an arbitrary direction from the center line C. The SMF 360 is an SMF without eccentricity in which the refractive index of the outermost peripheral portion is higher than the refractive index of the core peripheral portion in the cladding. The through hole of the LD side capillary portion 307 may or may not be parallel to the center line C, but is preferably not parallel in terms of bending the SMF. When the through hole of the LD side capillary part 307 is parallel to the center line C, the through hole needs to be eccentric to a position different from the position of the through hole of the MMF side eccentric capillary part 308.
[0027]
FIG. 4 is an enlarged view of a connection portion between the SMF 360 and the MMF 310. Reference numerals 405 and 406 denote the cladding and core of the SMF 360, 407 and 408 denote the cladding and core of the MMF 310, respectively, and A denotes the outermost peripheral part having a refractive index higher than that of the core peripheral part.
[0028]
Although the eccentric form in FIG. 4 is different from the eccentric form in FIG. 2, the action of making light incident while avoiding the vicinity of the center of the MMF is equivalent.
[0029]
As described above, the eccentric SMF is arranged on the center line, or the SMF without the eccentricity is eccentric from the center line by the eccentric capillary, so that light is not almost completely combined near the center of the MMF. Accordingly, there is no light propagating in the vicinity of the center of the MMF with an inappropriate refractive index, and transmission characteristic deterioration due to band deterioration caused by DMD can be avoided. In addition, since the light propagating through the cladding can be significantly attenuated by bending of the SMF, the CPR problem can be solved without increasing the capillary length as compared with the prior art of FIG.
[0030]
The eccentric SMF is several centimeters per optical transmitter, and once the eccentric SMF is manufactured, it can be used for a very large amount of optical transmitters with the same accuracy. Therefore, the cost of the eccentric SMF per optical transmitter is reduced.
[0031]
By using the optical transmitter according to the present invention, it is possible to reduce the propagation delay (DMD) between modes at the time of long-distance multimode fiber transmission without using a special patch cord. Further, by bending the SMF which is an optical path in the capillary and further making the refractive index of the outermost peripheral portion of the clad higher than the refractive index of the core peripheral portion, the light propagating through the clad can be significantly attenuated. Therefore, CPR can be improved and the size can be reduced without increasing the capillary length to 2 cm or longer.
[0032]
【The invention's effect】
The present invention exhibits the following excellent effects.
[0033]
(1) Since a single mode optical fiber (SMF) for allowing laser light from a laser light source to enter a position shifted from the center of the multimode optical fiber (MMF) is provided, there is no propagation delay (DMD) between modes. .
[0034]
(2) The light propagating through the clad can be significantly attenuated by bending of the SMF.
[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 an enlarged view of a connection portion of an optical fiber of the optical transmitter of FIG. 1. FIG.
FIG. 3 is a cross-sectional view of an optical transmitter showing another embodiment of the present invention.
4 is an enlarged view of a connection portion of an optical fiber of the optical transmitter of FIG. 3;
FIG. 5 is a diagram showing a transmission system when MMF is used as a transmission medium in Gigabit Ethernet.
FIG. 6 is a cross-sectional view of an optical transmitter with a mode conditioner.
7 is an enlarged view of a connection portion of an optical fiber in the special patch cord of FIG.
[Explanation of symbols]
101, 301 Laser light source 102, 302 Ferrule 103, 303 Split sleeve 107, 307 LD side capillary part 108 MMF side capillary part 110, 310 Multimode optical fiber (MMF)
170 Eccentric single mode optical fiber (Eccentric SMF)
205, 207, 405, 407 Core 206, 208, 406, 408 Clad 308 MMF side eccentric capillary part 360 Single mode optical fiber (SMF)
A Outermost part C Center line

Claims (6)

A laser light source is provided, laser light from the laser light source is incident on the multimode optical fiber using a single mode optical fiber, a capillary is provided between the laser light source and the multimode optical fiber, and the capillary and the multimode optical fiber are provided. A ferrule coated on the end of the mode optical fiber is brought into contact with the split sleeve, and the center of the core of the single mode optical fiber and the center of the multimode optical fiber are shifted within the split sleeve by 10 μm or more. The optical transmitter in which the single-mode optical fiber for allowing the laser light from the laser light source to enter a position shifted from the center of the multi-mode optical fiber penetrates the capillary , and the capillary has a hollow portion. And bending that attenuates the light propagating through the cladding of the single mode optical fiber. Wherein at hollow portion is formed in the single-mode optical fiber, the optical transmitter is characterized in that shorter than 2cm lengths of capillary having a hollow portion. 2. The capillary according to claim 1, wherein the capillary is divided into a capillary disposed on a laser light source side and a capillary disposed on a multimode optical fiber side, and the single mode optical fiber is bent between the two capillaries. Optical transmitter. The optical transmitter according to claim 1, wherein a portion having an inner diameter that is twice or more an outer diameter of the single mode optical fiber is formed in the hollow portion. The inner diameter of the hollow portion is increased at a position away from the end of the hollow portion on the multimode optical fiber side, and the inner diameter is gradually reduced from this position to the end of the hollow portion on the multimode optical fiber side. The optical transmitter according to any one of? The position where the single mode optical fiber penetrates the capillary is decentered from the center of the multimode optical fiber, and the amount of eccentricity of the penetrating position on the laser light source side is different from the amount of eccentricity of the penetrating position on the multimode optical fiber side. The optical transmitter according to claim 1, wherein The optical transmitter according to any one of claims 1-4 in which the laser light source side is inclined with respect to a center line of the multimode optical fiber is characterized in that passed through the capillary of the single-mode optical fiber.

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