Patent Publication Number: US-2005123264-A1

Title: Stationary optical attenuator flange

Description:
FIELD OF THE INVENTION  
      The present invention relates generally to optical attenuators and, more particularly, to stationary optical attenuators having flanges for adhesively engaging capillaries.  
     PRIOR ART  
      A conventional stationary optical attenuator comprises a ferrule assembly that comprises a capillary having an attenuation fiber fixed along its center axis and a flange enclosing the capillary (see Patent Documents 1 and 2).  
      The attenuation fiber is coated with a certain material that effectively causes attenuation of the light beam traveling therein. The ferrule assembly is press-fitted in a split sleeve, and the so combined object is fixedly held in an associated plug frame. Then, the integral unit is so placed that it may be aligned with the optical axis of the whole system. Additionally, an inner housing may be integrally connected to the plug frame and the integral combination is accommodated in a plug housing. Usually the capillary is made of a ceramic material such as zirconium, whereas the flange is made of metal such as brass.  
      Patent Document 1: Japanese Patent Laid-Open No. 2002-258055 (see Paragraphs (0002) to (0009) and FIG. 4; and Paragraphs (0020) to (0024) and FIGS. 1-3)  
      Patent Document 2: Japanese Patent Laid-Open No. 2002-258104 (see Paragraphs (0002) to (0009) and FIG. 4; and Paragraphs (0021) to (0025) and FIGS. 1-3)  
     SUMMARY OF THE INVENTION  
      In such a conventional stationary optical attenuator, the capillary is press-fitted in and fastened to the flange. Otherwise, the capillary is bonded to the flange while being tentatively held by a jig in position; this is necessitated for aligning the capillary with the flange relative to their optical axis. The press-fitting, however, is apt to scar the outer surface of the capillary. Still disadvantageously, the capillary cannot be correctly positioned relative to the flange with ease. For these and other reasons, optical attenuators cannot be produced with efficiency.  
      One object of the present invention is to provide a stationary optical attenuator structure, which significantly contributes to efficient production. Another object of the present invention is to provide a flange for such stationary optical attenuator structure.  
      A stationary optical attenuator comprising: a ferrule assembly comprising a capillary having an attenuation fiber fixed along its center axis and a flange having the capillary press-fitted therein; a plug frame and an inner housing both fixedly holding the ferrule assembly in alignment with their optical axis, is improved according to the present invention in that the flange has slits made in its tubular section, the slits extending longitudinally from one end of the tubular section, and that the capillary is fixed to the flange by applying and filling the slits with adhesive agent.  
      A stationary optical attenuator, a flange structure, having a capillary press-fitted therein and the capillary having an attenuation fiber fixed along its center axis, is improved according to the present invention in that the flange has slits extending longitudinally from one end, and that the capillary is fixed to the flange by applying and filling the slits with adhesive agent.  
      In an exemplary stationary optical attenuator, the inner diameter of the flange is somewhat smaller than the outer diameter of the capillary at the one end, with the inner diameter of the flange gradually increasing toward the other end of the tubular section. This permits the capillary to be easily inserted from the other end into the flange without requiring any pushing force.  
      The slits may extend half the length of the flange. Furthermore, two slits may be included, where the slits are diametrically opposite to each other.  
      The flange may have a square collar formed at the other end, thereby allowing the ferrule assembly to be fitted in the plug frame at any of the predetermined rotary positions, which are 90 degrees apart from each other. The square collar may have four side planes, one selected side plane having a setting mark made therein.  
      The tubular section of the flange is longitudinally narrow-cut to provide the flange with resiliency, thereby facilitating insertion of the capillary into the flange without fear of scarring the capillary. The capillary is tentatively set in a first position, and then fastened to the flange by applying and filling the slits with liquid adhesive. The inner housing and plug frame used are separate parts. This contributes to the downsizing of the stationary optical attenuator, and at the same time, permits the selective four-directional orientation of the ferrule assembly relative to the plug frame.  
      With this arrangement, downsizing of the stationary optical attenuator as well as efficient production can be attained.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The present invention will now be described in detail with reference to the accompanying drawings, in which:  
       FIG. 1  is a perspective view showing how a ferrule assembly according to the present invention is nested within an inner housing;  
       FIG. 2  is a perspective view of a flange, which is one part of the ferrule assembly;  
       FIG. 3  is a side view of the flange;  
       FIG. 4  is an end view of the flange as viewed from the left side in  FIG. 3 ;  
       FIG. 5  is an end view of the flange as viewed from the right side in  FIG. 3 ;  
       FIG. 6  is a longitudinal section of the flange taken along the line  6 - 6  in  FIG. 3 ;  
       FIG. 7  is a perspective view of the ferrule assembly;  
       FIG. 8  is a side view of the ferrule assembly;  
       FIG. 9  is a longitudinal section of the ferrule assembly taken along the line  9 - 9  in  FIG. 8 ;  
       FIG. 10  illustrates how the ferrule assembly is provided, particularly how the capillary is inserted in the flange;  
       FIG. 11  illustrates how the capillary is fastened to the flange;  
       FIG. 12  illustrates how an attenuation fiber is fixedly inserted into the capillary;  
       FIG. 13  illustrates the ferrule assembly with the extra fiber lengths cut and removed from the opposite ends of the capillary;  
       FIG. 14  illustrates that the ferrule assembly is rotated 90 degrees about its optical axis;  
       FIG. 15  illustrates the ferrule assembly with a setting mark made in a selected side of the square collar:  
       FIG. 16  is a perspective view, showing how a plug frame is applied to the ferrule assembly-and-inner housing combination;  
       FIG. 17  is a perspective view, showing how a plug housing is applied to the triple combination of ferrule assembly, plug frame and inner housing;  
       FIG. 18  is a perspective view of the stationary optical attenuator;  
       FIG. 19  is a longitudinal section of the stationary optical attenuator; and  
       FIG. 20  is another longitudinal section of the stationary optical attenuator.  
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
      A stationary optical attenuator according to one preferred embodiment of the present invention is described below with reference to the accompanying drawings.  
       FIG. 1  shows how the ferrule assembly  20  with a slit sleeve  30  applied thereto is nested within the inner housing  40 . (see FIGS.  18  to  20 ) The ferrule assembly  20  includes capillary  21  and a flange  22 . The capillary  21  is a cylindrical object of zirconium, which has the attenuation fiber  23  along its center axis. The flange  22  is made of a metal or plastic material, comprising a hollow circular cylindrical or tubular section  22   c  and a square collar  222  formed on one end, as seen in FIGS.  2  to  6 .  
      The flange  22  is a hollow cylindrical object configured to accommodate the capillary  21  therein. It has one or more narrow long cuts or slits  221  longitudinally extending from the end  22   a  toward the square collar  222 . The slit  221  extends half the length of the flange  22 . If formed with two slits, each of the slits  221  is diametrically opposite the other.  
      The square collar  222  is integrally connected to the other end  22   b  of the flange  22 . The square collar  222  has four side flat surfaces or planes  223 .  
      The inner diameter “A” of the flange  22  at the end  22   a  is somewhat smaller than the outer diameter of the capillary  21 , gradually increasing toward the other end  22   b  (see  FIG. 6 ), thereby permitting the capillary  21  to be easily inserted from the other end  22   b  into the flange  22  without requiring any pushing force. For example, the diameter “A” is equal to 1.2 mm, whereas the diameter “B” is equal to 1.25 mm. As described above, the flange  22  is longitudinally cut to form plural slits  221 , thereby allowing the flange  22  to yieldingly expand in response to insertion of the capillary  21  from the end  22   a  of the flange  22  while resiliently gripping the capillary  21 . Thus, the capillary  21  can be tentatively held in a correct position relative to the flange  22   
      As shown in FIGS.  7  to  9 , after tentatively fastening the capillary  21  in the flange  22 , the capillary  21  is permanently fixed to the flange  22  by applying and filling the slits  221  with liquid adhesive  224 . Because of the resiliency imparted to the flange  22  by the long narrow slits  221 , the capillary  21  can be inserted into the flange  22  without applying any push to the capillary  21 . When the capillary  21  is put in the correct position, it is bonded to the flange  22  by filling the slits  221  with liquid adhesive. This reduces the danger of rubbing and scarring the surface of the capillary  21 . Advantageously, the parts still can be assembled at increased efficiency.  
      Referring to  FIG. 8 , a setting mark  225  is made on a selected side  223  of the square collar  222 .  
      FIGS.  10  to  16  show the sequential steps at which the capillary  21  is nested with the flange  22  to provide the ferrule assembly  20 , and the setting mark  225  is made in a selected side of the square collar  222 . Referring to  FIG. 10 , the capillary  21  is inserted from the square collar end into the flange  22  until the capillary  21  reaches the correct position in the flange  22 . Then, liquid adhesive  224  is applied to the slits  221 . The flange  22  is put in an oven with the square collar  222  down so that the liquid adhesive  224  is set. Thanks to the surface tension the liquid adhesive stops at the chamfered circumference  22   b  (see  FIG. 6 ). Thus, the capillary  21  is fixed to the flange  22  (see  FIG. 11 ).  
      Referring to  FIG. 12 , an attenuation fiber  23  is longer than the full length of the capillary  21 . Liquid adhesive is injected into the very small hole of the capillary  21 , and the attenuation fiber  23  is inserted into the capillary  21 . When the liquid adhesive is set, the attenuation fiber  23  is fixed to the capillary  21 . The extra fiber lengths projecting from the opposite ends of the flange  22  are then cut and removed. The flange  22  is optical-ground on its ends (see  FIG. 13 ).  
      Referring to  FIGS. 14 and 15 , the ferrule assembly  20  is oriented in the appropriate angular position relative to the attenuation fiber  23  to cause a required attenuation on the traveling beam of light. Such measurement is performed by using a light source  12  and a photo-sensor  14  (see  FIG. 14 ). These are aligned such that the beam of light from the light source  12  may fall on the photo-sensor  14  after passing through the attenuation fiber  23 . The ferrule assembly  20  is then rotated through angular increments of 90 degrees to determine the angular position at which the required attenuation may be caused on the traveling beam of light. A setting mark  225  is made on a selected side  223  of the square collar  222 . This assures that the ferrule assembly  20  is correctly arranged and nested within the inner housing  40  by referring to the setting mark  225  so that the required attenuation is caused on the beam of light traveling along the aligned optical axis of the ferrule assembly-and-inner housing combination. The setting mark  225 , therefore, can be made on either side of the square collar  222 , provided that the selected side of the square collar be fixedly related to a predetermined side of the inner housing  40 .  
      The square shape of the flange&#39;s collar  222  permits the incremental ninety-degree rotation of the ferrule assembly  20  to aid in determining the angular position in which the required attenuation is caused. Such incremental control is virtually fine enough to allow all optical attenuators thus calibrated to have their attenuation degrees remaining in the range of allowance.  
      As seen from  FIG. 1 , the ferrule assembly  20  has its rear capillary exposure inserted into a split sleeve  30 . The ferrule assembly-and-split sleeve combination is nested with the inner housing  40  by inserting it into the cylindrical extension  41  of the inner housing  40 . Referring to  FIG. 16 , the cylindrical extension  41  of the inner housing  40  is inserted in a plug frame  50 . The ferrule assembly  20  has its optical axis aligned with the optical axis L of the whole assembly.  
      Referring to  FIG. 17 , the integral combination of the ferrule assembly  20 , the inner housing  40  and the plug frame  50  is put in a plug housing  60 , providing a stationary optical attenuator  10  as shown in  FIG. 18 . The plug housing  60  may be formed of metal, and is strong enough to resist to the bending stress, which might be applied to the plug frame-and-inner housing combination. Thus, it is assured that the connection loss be reduced to possible minimum.  
      By way of example, the plug housing  60  is made of metal and the inner housing  40  and plug frame  50  are molded of a synthetic resin material. As seen from  FIGS. 1 and 19 , the cylindrical extension  41  of the inner housing  40  has recesses  43  made on two opposite sides  42 , thereby allowing the projections  52  of the overlying plug frame  50  (see  FIG. 17 ) to yieldingly withdraw when the inner housing-and-plug frame combination is inserted into the plug housing  60 .