Abstract:
An optical comb filter, comprising an input/output collimator ( 50 ), an output collimator ( 60 ), a spectroscope ( 10 ), and first, second and third GT resonant cavities ( 20, 30, 40 ), wherein each GT resonant cavity comprises a transparent solid block coated with a membrane layer and a spacing part, a through hole is provided on the transparent solid block, and the transparent solid block and the spacing part form a hollow cavity; and rectangular orientation of an insertion loss curve is realized, and the bandwidth utilization rate is high.

Description:
TECHNICAL FIELD 
       [0001]    The present patent application relates to the technical field of optical communication devices, and more specifically, to the improvement to GT cavity interference-type filter used to filter optical signals. 
       BACKGROUND 
       [0002]    With the rapid development of the information communications technology, the exchange of voice, image and data information is increasing. Especially as the result of the widespread application of the Internet, people have higher requirements for broadband communication. In a bid to come up with a low-cost and high-quality system to meet people&#39;s requirements for broadband communication in the shortest possible time, the wavelength division multiplexing (WDM) technology is widely used. 
         [0003]    Another way of increasing the optical fiber transmission capacity is to further narrow the channel spacing. Currently, the channel spacings are all 100 Hz or 200 Hz, according to the provisions of the International Telecommunication Union (ITU). If people want to conduct low-cost capacity expansion of the original system, they prefer an optical comb filter that realizes the expansion by changing the channel spacing without altering the original equipment and system. The existing optical comb filter divides one-channel multi-wavelength optical signals into two channels, one of which have odd-channels of wavelengths and the other of which have even-channels of wavelengths, and the channel spacing becomes twice the original. Currently, a MGTI-type comb filter is widely used, thanks to its low cost and mature technology. However, the MGTI-type optical comb filter usually adopts a GT cavity structure to realize a flat top, but the channel bandwidth is small, so it sees low bandwidth utilization. 
       SUMMARY 
       [0004]    The present patent application provides an optical comb filter featuring the appearance of the insertion loss curve as a rectangle and high bandwidth utilization. 
         [0005]    To achieve the objective above, the present patent application provides an optical comb filter comprising an input/output collimator, an output collimator, a spectroscope, a first GT resonant cavity, a second GT resonant cavity and a third GT resonant cavity. The first GT resonant cavity comprises reflective films-coated transparent solid blocks and spacing parts. The transparent solid block has a through-hole. The transparent solid blocks and the spacing parts form a hollow cavity. The second GT resonant cavity comprises a reflective membrane layer-coated transparent solid block, a reflective membrane layer coated on the surface of the beam splitter and spacing parts. The transparent solid block has a through-hole. The transparent solid block, the beam splitter and the spacing parts form a hollow cavity ( 221 ). The third GT resonant cavity comprises a reflective membrane layer-coated transparent solid block, a reflective membrane layer coated on another surface of the transparent solid block and spacing parts. The transparent solid block has a through-hole. The transparent solid blocks and the spacing parts form a hollow cavity. 
         [0006]    Optionally, the beam splitter is coated with a membrane layer with a splitting ratio of 50:50. 
         [0007]    Optionally, the reflective membrane layer of the first GT cavity is a highly reflective membrane layer, and the reflective membrane layer is a partially reflective membrane layer. 
         [0008]    Optionally, both the films of the second GT cavity are antireflection films. 
         [0009]    Optionally, the membrane layer of the third GT cavity is a highly reflective membrane layer, and the membrane layer is a partially reflective membrane layer. 
         [0010]    Optionally, the input/output collimator is an optical fiber collimator. 
         [0011]    Optionally, the output collimator is an optical fiber collimator. 
         [0012]    Optionally, the optical path of the hollow cavity included in the third GT cavity and that of the hollow cavity included in the first GT cavity are equal, and both are twice the optical path of the hollow cavity included in the second GT cavity. 
         [0013]    Optionally, when a channel spacing is selected as 100 GHz, the optical path of the hollow cavity included in the third GT cavity and that of the hollow cavity included in the first GT cavity are both 3 mm, and the optical path of the hollow cavity of the second GT cavity is 1.5 mm. 
         [0014]    The optical comb filter of the present patent application has the following beneficial effects: 1. the transparent solid block and the transparent solid block are of the same material and thickness, which can realize temperature compensation; 2. by supplying and releasing gases to or from the cavities via the through-holes, it can conveniently adjust the pressure in the resonant cavity, to achieve the purpose of adjusting the optical path; 3. the second GT resonant cavity and the third resonant cavity form a composite GT cavity structure, realizing the appearance of the insertion loss curve as a rectangle high bandwidth utilization. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The structure of the present patent application is further detailed in combination with the drawings and embodiments hereinafter. 
           [0016]    The FIGURE is a diagram of the integral structure of the comb filter of the present patent application. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    The working principle of the low-dispersion optical comb filter is further detailed in combination with the drawings hereinafter. 
         [0018]    As shown in FIGURE, the present patent application provides an optical comb filter comprising a beam splitter  10 , a first GT resonant cavity  20 , a second GT resonant cavity  30 , a third GT resonant cavity  40 , an input/output collimator  50 , an output collimator  60   
         [0019]    The beam splitter  10  comprises a substrate of quartz or other optical glasses and a membrane layer coated thereof and with a splitting ratio of 50:50; 
         [0020]    The first GT resonant cavity  20  comprises transparent solid blocks  201 ,  202  and spacing parts  211  and  212  for separating the transparent solid blocks  201  and  202 , wherein the transparent solid blocks  201  and  202  and the spacing parts  211  and  212  form a hollow cavity  221 . 
         [0021]    The transparent solid block  202  has a through-hole  202   a.  The through-hole  202   a  connects with the hollow cavity  221  so that gases are supplied or released to or from the hollow cavity  221  via the through-hole  202   a  to control the gas pressure in the hollow cavity  221 . 
         [0022]    The transparent solid blocks  201 ,  202  are both coated with films  201   f  and  202   f  on the opposite surfaces. The membrane layer  201   f  is a partially reflective membrane layer, while the membrane layer  202   f  is a highly reflective membrane layer. Transparent solid blocks  201 ,  202 , for example, are glass blocks. 
         [0023]    The first GT cavity  20  is placed on the side of the beam splitter  10  of which light comes out. 
         [0024]    The second GT resonant cavity  30  comprises a transparent solid block  301  and spacing parts  311  and  312  for separating the transparent solid block  301  and the beam splitter  10 , wherein the transparent solid block  301  and the spacing parts  311  and  312  form a hollow cavity  321 . And the optical path of the hollow cavity  321  is half that of the hollow cavity  212 . 
         [0025]    The transparent solid block  301  has a through-hole  301   a.  The through-hole  301   a  connects with the hollow cavity  321  so that gases are supplied or released to or from the hollow cavity  321  via the through-hole  301   a  to control the gas pressure in the hollow cavity  321 . 
         [0026]    The beam splitter  10  and the transparent solid blocks  301  were both coated with films  100   f  and  301   f  on the opposite surfaces. The films  100   f  and  301   f  are both antireflection films. The transparent solid block  301 , for example, is a glass block, and the transparent solid block  301  and the transparent solid block  201  are of the same material and thickness. 
         [0027]    The second GT cavity  30  is placed on the side of the beam splitter  10  of which light comes out. 
         [0028]    The third GT resonant cavity  40  comprises transparent solid blocks  301 ,  402  and spacing parts  411  and  412  for separating transparent solid blocks  301  and  402 , wherein the transparent solid blocks  301  and  402  and the spacing parts  411  and  412  form a hollow cavity  421 . The optical path of the hollow cavity  421  and that of the hollow cavity  212  are equal, that is, both are twice the optical path of the hollow cavity  312 . 
         [0029]    The transparent solid block  402  has a through-hole  402   a.  The through-hole  402   a  connects with the hollow cavity  421  so that gases are supplied or released to or from the hollow cavity  421  via the through-hole  402   a  to control the gas pressure in the hollow cavity  421 . 
         [0030]    The transparent solid blocks  301 ,  402  were both coated with films  401   f  and  402   f  on the opposite surfaces. The membrane layer  401   f  is a partially reflective membrane layer, while the membrane layer  402   f  is a highly reflective membrane layer. The transparent solid block  301  and the transparent solid block  301  in the second GT cavity  30  is the same transparent solid block. The transparent solid block  402 , for example, is a glass block. 
         [0031]    The third GT cavity  40  is placed at the back of the second GT cavity  30 . 
         [0032]    Arranged on one side of the the beam splitter  10 , the input/output collimator  50  is used to collimate optical signals inputted in the optical path and then input them into the beam splitter  10 , or to collimate optical signals reflected back from the beam splitter  10  and then output optical signals with odd channels of wave lengths. The input/output collimator  50  is an optical fiber collimator. 
         [0033]    Arranged on the other side of the beam splitter  10 , the output collimator  60  is used to collimate optical signals output from the optical path and output optical signals with even channels of wavelengths. The output collimator  60  is a fiber collimator. 
         [0034]    When the channel spacing is selected as 100 GHz, the optical path of the hollow cavity  421  included in the third GT cavity  40  and that of the hollow cavity  212  included in the first GT cavity  20  may be both selected as 3 mm, and the optical path of the hollow cavity  312  of the second GT cavity  30  may be selected as 1.5 mm. 
         [0035]    The optical comb filter of the present patent application has the following beneficial effects: 1. the transparent solid block  201  and the transparent solid block  301  are of the same material and thickness, which can realize temperature compensation; 2. by supplying and releasing gases to or from the cavities  221 ,  321 ,  421  via the through-holes  201   a,    301   a,    402   a , it can conveniently adjust the pressure in the resonant cavity, to achieve the purpose of adjusting the optical path; 3. the second GT resonant cavity  30  and the third resonant cavity  40  form a composite GT cavity structure, realizing the appearance of the insertion loss curve as a rectangle and high bandwidth utilization. 
         [0036]    The foregoing is only the best embodiment of the present patent application and not intended to limit the scope of the present patent application. Any equivalent changes or modifications made based on the patent scope of the present patent application are all covered by the present patent application.