Optical fiber coupling part
An optical fiber coupling part capable of reducing coupling loss while maintaining a large operating distance, and having a good module assembling property. AT least one GRIN lens having numerical aperture NA that is larger than numerical aperture NAs of a light-emitting source (such as a semiconductor laser) is fusion-spliced with one end of the optical fiber. All lights emitted from the light-emitting source can enter the GRIN lens, and the loss of the light can thereby be reduced. In addition, a second GRIN lens having numerical aperture NA 2 is fusion-spliced with one end of the optical fiber having numerical aperture NA f , and further a first GRIN lens having numerical aperture NA 1 , which is larger than numerical aperture NA 2 , is fusion-spliced with the other end of the second GRIN lens. Thereby, the light emitted from the light-emitting source can efficiently enter the optical fiber, and loss of the light can thereby be reduced. In this case, the formula expressed by NA f ≦NA 2 <NA s ≦NA 1 is desirable.
1. An optical fiber coupling part comprising:
an optical fiber; and
at least one GRIN lens having an unattached first end and having a second end fusion-spliced with an end of said optical fiber, said GRIN lens having a numerical aperture NA that is larger than a numerical aperture NA s of a light emitting source, wherein the numerical aperture NA is 0.43 or more, wherein said light emitting source comprises a semiconductor laser, and wherein a tip part of said unattached first end of said GRIN lens is flat.
2. The optical fiber coupling part according to claim 1 , wherein the GRIN lens has a coefficient of thermal expansion expressed by 15×10 −7 K −1 or less, and is formed by a sol-gel method.
3. The optical fiber coupling part according to claim 1 , wherein said unattached first end of said GRIN lens is arranged so as to directly receive light from said semiconductor laser.
4. An optical fiber coupling part comprising:
an optical fiber having a numerical aperture NA f ;
a first GRIN lens having a numerical aperture NA 1 , said first GRIN lens having an unattached first end; and
a second GRIN lens having a numerical aperture NA 2 , wherein a first end of said second GRIN lens is fusion spliced with a second end of said first GRIN lens and a second end of said second GRIN lens is fusion spliced with an end of said optical fiber,
wherein a tip part of said unattached first end of said first GRIN lens is flat, and wherein the numerical aperture NA f of the optical fiber, the numerical aperture NA 1 of the first GRIN lens, the numerical aperture NA 2 of the second GRIN lens, and a numerical aperture NA s of a light emitting source are selected to satisfy the formula expressed by:
NA f ≦NA 2 <NA s ≦NA 1 ,
wherein said light emitting source comprises a semiconductor laser.
5. The optical fiber coupling part according to claim 4 , wherein the numerical aperture NA 1 of said first GRIN is 0.43 or more.
6. The optical fiber coupling part according to claim 4 , wherein a length Z 1 of the first GRIN lens satisfies the formula expressed by:
Z 1 =( n 0 *d 1 /NA 1 )arctan( d 1 /( NA 1 *L )
wherein a refractive index of glass at a center part of the first GRIN lens is set at n o , a radius of the first GRIN lens is set at d 1 , and a distance between the lens and the semiconductor laser is set at L.
7. The optical fiber coupling part according to claim 4 , wherein said first GRIN lens and said second GRIN lens have a coefficient of thermal expansion expressed by 15×10 −7 K −1 or less, and at least the first GRIN lens is made by a sol-gel method.
8. The optical fiber coupling part according to claim 4 , wherein said unattached first end of said GRIN lens is arranged so as to directly receive light from said semiconductor laser.