Abstract:
A zigzag wavelength division multiplexer. The zigzag wavelength division multiplexer reduces the wavelength shift in the center of a frequency band caused by temperature changes. The zigzag wavelength division multiplexer includes an intermediate block, an input end and a plurality of output ends. The input end has a first sleeve and an optical collimator disposed in the first sleeve. Each of the output ends has a second sleeve, a wave filter and an optical collimator. The optical collimator and the wave filter are disposed in the second sleeve. The zigzag wavelength division multiplexer reduces use of the GRIN lens and glass ferrule, and thereby manufacturing costs.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a zigzag wavelength division multiplexer, and in particular to a zigzag wavelength division multiplexer reducing the wavelength shift in the center of a frequency band resulting from temperature changes. 
     2. Description of the Related Art 
     FIG. 1A is a schematic perspective view showing a conventional zigzag wavelength division multiplexer. The conventional zigzag wavelength division multiplexer (U.S. Pat. No. 5,859,717) includes a housing  1 . A support  2 , a first collimator  3 , a second collimator  4 , a third collimator  5 , a fourth collimator  6 , a fifth collimator  7  and a sixth collimator  8  are disposed in the housing  1 . A first wave filter  9 , a second wave filter  10 , a third wave filter  11  and a fourth wave filter  12  are disposed in the support  2 . The first collimator  3  outputs multi-channel collimated light to the first wave filter  9  at an incident angle. Generally speaking, the incident angle is between 5° and 9°. Preferably, the incident angle is 7°. Specifically, the wavelength of light passing through the wave filter is changed whenever the incident angle is changed by 0.15°. Furthermore, the higher the incident angle, the higher the polarization dependent loss (PDL). 
     In the conventional zigzag wavelength division multiplexer (U.S. Pat. No. 5,859,717), spacers  13  are used to fix the collimators, as shown in FIG.  1 B. The spacers  13  can only prevent length change of the collimator resulting from thermal expansion and contraction, but not tilt angle between the collimator and the wave filter. Thus, the adhesive  14  causes tilt angle between the collimator and the wave filter resulting from thermal expansion and contraction, and the tilt angle causes wavelength shift in a frequency band and subsequent light loss. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide a zigzag wavelength division multiplexer. The zigzag wavelength division multiplexer comprises an intermediate block, an input end and a plurality of output ends. The input end is disposed on one side of the intermediate block and has a first sleeve and an optical collimator. The first sleeve has a first fixing portion having a hole. The axis of the first sleeve is tilted to the plane of the opening of the first sleeve at a first angle. The optical collimator is disposed in the first sleeve and fixed to the first fixing portion. The output ends are disposed on two sides of the intermediate block. Each of the output ends has a second sleeve, a GRIN lens, a first pad, a glass ferrule, a second pad and a wave filter. The second sleeve has a first portion, a second portion and a second fixing portion having a hole. The axis of the first portion is coaxial to that of the second portion. The axis of the second portion is tilted to the plane of the opening of the second portion at a second angle. The GRIN lens is disposed in the first portion and fixed to the second fixing portion. The first pad is disposed on one end of the GRIN lens. The glass ferrule is disposed on the first pad. The second pad is disposed on the opening of the second portion of the second sleeve and the side of the intermediate block. The wave filter is disposed in the second portion and on the second pad. After multi-channel light enters the intermediate block via the input end, the output ends output corresponding channel light, respectively. 
     The invention has the following advantages. The invention uses sleeves to fix the optical collimators and the wave filters, thus preventing a tilt angle between the optical collimator and the wave filter. In addition, the invention reduces the wavelength shift in the center of a frequency band resulting from temperature changes. Furthermore, the invention uses the sleeves to fix the optical collimators and the wave filters, thus reducing light loss. 
     A detailed description is given in the following embodiments with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
     FIG. 1A is a schematic perspective view showing a conventional zigzag wavelength division multiplexer; 
     FIG. 1B is a schematic view showing the conventional zigzag wavelength division multiplexer using spacers to fix the collimator; 
     FIG. 2 is a schematic top view showing the zigzag wavelength division multiplexer of the invention; 
     FIG. 3A is a schematic perspective view showing an optical collimator; 
     FIG. 3B is a schematic perspective view showing the input end of the zigzag wavelength division multiplexer of the invention; 
     FIG. 4A is a schematic perspective view showing an output end of the zigzag wavelength division multiplexer of the invention; 
     FIG. 4B is a schematic perspective view showing another output end of the zigzag wavelength division multiplexer of the invention; 
     FIG. 4C is a schematic enlarged view showing the second sleeve according to FIG. 4B; 
     FIG. 5 shows the pad of the zigzag wavelength division multiplexer of the invention; and 
     FIG. 6 is a schematic view showing the configurations of the pad. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 2, the zigzag wavelength division multiplexer includes an intermediate block  20 , an input end  30  and a plurality of output ends  40   a,    40   b,    40   c  and  40   d.  The input end  30  and the plurality of output ends  40   a,    40   b,    40   c  and  40   d  are disposed on two sides  20   a  and  20   b  of the intermediate block  20 . After multi-channel light enters the intermediate block  20  via the input end  30 , the first output end  40   a  outputs a first channel beam λ 1 , the second output end  40   b  outputs a second channel beam λ 2 , the third output end  40   c  outputs a third channel beam λ 3 , and the fourth output end  40   d  outputs a residual channel beam λ 4 . 
     Referring to FIG. 3A, the optical collimator  50  includes at least a GRIN lens  51  and a glass ferrule  52 . An optical fiber  53  is disposed in the glass ferrule  52 . The optical collimator  50  further includes a glass tube  54  to fix the GRIN lens  51  and the glass ferrule  52 . 
     Referring to FIG. 3B, the input end  30  has the optical collimator  50  and a first sleeve  60 . A fixing portion  61  having a hole  62  is formed on the inner wall of the first sleeve  60 . The optical collimator  50  is disposed in the first sleeve  60  and fixed to the fixing portion  61  by hot solidified resin. The axis of the first sleeve  60  is tilted to the plane of the opening of the first sleeve  60  at a predetermined angle θ. Preferably, the angle θ is between 75° and 90°. 
     Referring to FIG. 4A, the output end  40  has a GRIN lens  41 , a glass ferrule  42 , a wave filter  43 , a first pad  44 , a second pad  45  and a second sleeve  80 . The second sleeve  80  has a first portion  81 , a second portion  82  and a fixing portion  83 . The fixing portion  83  has a hole  84  connected between the first portion  81  and the second portion  82 . In the second sleeve  80 , the axis of the first portion  81  is coaxial to that of the second portion  82 . The axis of the second portion  82  is tilted to the plane of the opening of the second portion  82  at the predetermined angle θ. Preferably, the angle θ is between 75° and 90°. The wave filter  43  is disposed in the second portion  82  and fixed to the second pad  45  by hot solidified resin  70 , and the opening of the second portion  82  is fixed to the second pad  45  by hot solidified resin  70 . The GRIN lens  41  is disposed in the first portion  81  and fixed to the fixing portion  83  by hot solidified resin  70 . The first pad  44  is fixed to an end  41   a  of the GRIN lens  41  by hot solidified resin  70 . The glass ferrule  42  is fixed to the first pad  44  by hot solidified resin  70 . 
     As described above, an optical collimator  46  having the first pad  44  is disposed in the first portion  81  and fixed to the fixing portion  83  of the second sleeve  80  by hot solidified resin  70 . The second sleeve  80  and the wave filter  43  are fixed to the second pad  45  by hot solidified resin  70 . Thus, the output end of the present zigzag wavelength division multiplexer is constructed. As shown in FIG. 4A, the output end of the present zigzag wavelength division multiplexer is disposed on one side of the intermediate block  20  by hot solidified resin  70 . 
     Referring to FIG.  4 B and FIG. 4C, another output end of the present zigzag wavelength division multiplexer includes a GRIN lens  41 , a glass ferrule  42 , a wave filter  43 , a first pad  44  and a second sleeve  80 . The second sleeve  80  has a first portion  81 , a second portion  82  and a fixing portion  83 . The fixing portion  83  has a hole  84  connected between the first portion  81  and the second portion  82 . In the second sleeve  80 , the axis L 1  of the first portion  81  is tilted to the axis L 2  of the second portion  82  at a predetermined angle θ′. The axis L 2  of the second portion  82  is perpendicular to the plane of the opening of the second portion  82 . As shown in FIG. 4B, the wave filter  43  is disposed in the second portion  82  and fixed to the fixing portion  83  by hot solidified resin  70 . Because of the predetermined angle θ′ between the axis L 1  of the first portion  81  and the axis L 2  of the second portion  82 , the wave filter  43  is substantially parallel to the side of the intermediate block  20 . The GRIN lens  41  is disposed in the first portion  81  and fixed to the fixing portion  83  by hot solidified resin  70 . The first pad  44  is fixed to an end  41   a  of the GRIN lens  41  by hot solidified resin  70 . The glass ferrule  42  is fixed to the first pad  44  by hot solidified resin  70 . Thus, the glass ferrule  42 , the first pad  44  and the GRIN lens  41  construct the optical collimator  46  having the pad. 
     As described above, an optical collimator  46  having the first pad  44  is disposed in the first portion  81  and fixed to the fixing portion  83  of the second sleeve  80  by hot solidified resin  70 . In addition, the optical collimator  46  having the first pad  44 , the second sleeve  80  and the wave filter  43  construct the other output end of the present zigzag wavelength division multiplexer. As shown in FIG. 4B, the other output end of the present zigzag wavelength division multiplexer is fixed to the intermediate block  20  by hot solidified resin  70 . 
     FIG. 5 shows the pad of the zigzag wavelength division multiplexer of the invention. As shown in FIG. 4A, FIG.  4 B and FIG. 5, there is no effect on light penetration when the thickness t of the pad  45  is changed. On the other hand, light penetration is affected when the thickness t of the pad  44  is changed. 
     FIG. 6 is a schematic view showing the configurations of the pad. The pad is hollow and has circular, rectangular and polygonal configurations. Additionally, the pad is made of metal, glass or other materials not deformed at temperatures over 200° C. 
     The intermediate block is made of a transparent material such as glass or quartz. Additionally, the intermediate block can be a hollow metal block. 
     In addition, the length of the first sleeve of the input end is substantially equal to that of the optical collimator. Furthermore, the depth of the first portion of the second sleeve of the output end is smaller than or equal to the length of the GRIN lens. 
     While the invention has been described by way of example and in terms of the preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.