Optical comb filter having first, second and third GT resonant cavities

1. An optical comb filter comprising:

an input/output collimator ( 50 ),

an output collimator ( 60 ),

a beam splitter ( 10 ),

a first GT resonant cavity ( 20 ),

a second GT resonant cavity ( 30 ), and

a third GT resonant cavity ( 40 ),

wherein the GT resonant cavity ( 20 ) comprises transparent solid blocks ( 201 , 202 ) coated with a first reflective membrane layer ( 201 f ) and a second reflective membrane layer ( 202 f ) and spacing parts ( 211 , 212 ), wherein the transparent solid block ( 202 ) has a through-hole ( 202 a ), the transparent solid blocks ( 201 , 202 ) and the spacing parts ( 211 , 212 ) form a hollow cavity ( 221 ), and the through-hole ( 202 a ) included in the first GT resonant cavity ( 20 ) connects with the hollow cavity ( 221 ) included in the first GT resonant cavity ( 20 ); the second GT resonant cavity ( 30 ) comprises a membrane layer transparent solid block ( 301 ) coated with a membrane layer ( 3010 f ), an antireflection membrane layer ( 100 f ) and spacing parts ( 311 , 312 ) coated on a surface of the beam splitter ( 10 ), wherein a through-hole ( 301 a ) is set on the transparent solid block ( 301 ), the transparent solid block ( 301 ), the beam splitter ( 10 ) and the spacing parts ( 311 , 312 ) form a hollow cavity ( 321 ), and the through-hole ( 301 a ) included in the second GT resonant cavity ( 30 ) connects with the hollow cavity ( 321 ) included in the second GT resonant cavity ( 30 ); the third GT resonant cavity ( 40 ) comprises a transparent solid block ( 402 ) coated with a reflective membrane layer ( 402 f ), reflective membrane layer ( 401 f ) coated on another surface of the transparent solid block ( 301 ) and spacing parts ( 411 , 412 ), wherein a through-hole ( 402 a ) is set on the transparent solid block ( 402 ), and the transparent solid blocks ( 301 , 402 ) and the spacing parts ( 411 , 412 ) form a hollow cavity ( 421 ), and the through-hole ( 402 a ) included in the third GT resonant cavity ( 40 ) connects with the hollow cavity ( 421 ) included in the third GT resonant cavity ( 40 );

wherein the transparent solid block ( 201 ) included in the first GT cavity ( 20 ) and the transparent solid block ( 301 ) included in the second GT resonant cavity ( 30 ) are of a same material and a same thickness in their respective optical path directions to realize temperature compensation;

gases are supplied and released to or from the hollow cavity ( 221 ) included in the first GT resonant cavity ( 20 ), the hollow cavity ( 321 ) included in the second GT resonant cavity ( 30 ) and the hollow cavity ( 421 ) included in the third GT resonant cavity ( 40 ) via the through-hole ( 202 a ) included in the first GT resonant cavity ( 20 ), the through-hole ( 301 a ) included in the second GT resonant cavity ( 30 ), and the through-hole ( 402 a ) included in the third GT resonant cavity ( 40 ) to adjust pressure in the first GT resonant cavity ( 20 ), the second GT resonant cavity ( 30 ) and the third GT resonant cavity ( 40 );

the second GT resonant cavity ( 30 ) and the third resonant cavity ( 40 ) form a composite GT cavity structure to realize appearance of an insertion loss curve as a rectangle.

2. The optical comb filter as claimed in claim 1 , wherein the second reflective membrane layer ( 202 f ) of the first GT cavity ( 20 ) is a highly reflective membrane layer, and the first reflective membrane layer ( 201 f ) is a partially reflective membrane layer.

3. The optical comb filter as claimed in claim 2 , wherein the antireflection membrane layer ( 100 f ) and the membrane layer ( 301 f ) of the second GT cavity ( 30 ) are both antireflection membrane layer.

4. The optical comb filter as claimed in claim 3 , wherein the reflective membrane layer ( 402 f ) of the third GT cavity ( 40 ) is a highly reflective membrane layer, and the reflective membrane layer ( 401 f ) of the third GT cavity ( 40 ) is a partially reflective membrane layer.

5. The optical comb filter as claimed in claim 1 , wherein the beam splitter is coated with a membrane layer with a splitting ratio of 50:50.

6. The optical comb filter as claimed in claim 1 , wherein the input/output collimator is a fiber collimator.

7. The optical comb filter as claimed in claim 6 , wherein the output collimator is a fiber collimator.

8. The optical comb filter as claimed in claim 1 , wherein a length of an optical path of the hollow cavity ( 421 ) included in the third GT cavity ( 40 ) and a length of an optical path of the hollow cavity ( 221 ) included in the first GT cavity ( 20 ) are equal, and both of the lengths of the optical paths are twice of a length of an optical path of the hollow cavity ( 312 ) included in the second GT cavity ( 30 ).

9. The optical comb filter as claimed in claim 8 , wherein when a channel spacing is selected as 100 GHz, the length of the optical path of the hollow cavity ( 421 ) included in the third GT cavity ( 40 ) and the length of the optical path of the hollow cavity ( 221 ) included in the first GT cavity ( 20 ) are both 3 mm, and the length of the optical path of the hollow cavity ( 312 ) of the second GT cavity ( 30 ) is 1.5 mm.

10. The optical comb filter as claimed in claim 1 , wherein the through-hole ( 202 a ) included in the first GT resonant cavity ( 20 ) is perpendicular to the hollow cavity ( 221 ) included in the first GT resonant cavity ( 20 ); a first portion of the through-hole ( 301 a ) included in the second GT resonant cavity ( 30 ) is perpendicular to the hollow cavity ( 321 ) included in the second GT resonant cavity ( 30 ); a second portion of the through-hole ( 301 a ) included in the second GT resonant cavity ( 30 ) is perpendicular to the first portion of the through-hole ( 301 a ) included in the second GT resonant cavity ( 30 ); and the through-hole ( 402 a ) included in the third GT resonant cavity ( 40 ) is perpendicular to the hollow cavity ( 421 ) included in the third GT resonant cavity ( 40 ).