Method for connecting optical fibers

A method for connecting a first optical fiber to a second optical fiber having a W-shaped refractive index profile and a mode field diameter which is smaller than the mode field diameter of the first optical fiber, the method comprising the steps of:

• preparing a third optical fiber having a short length and a mode field diameter which is smaller than the mode field diameter of the first optical fiber and larger than the mode field diameter of the second optical fiber;
• connecting the first optical fiber to the third optical fiber;
• connecting the second optical fiber to the third optical fiber;
• and
• increasing at least one of the mode field diameter of a part of the third optical fiber near a portion connected to or to be connected to the first optical fiber and the mode field diameter of a part of the second optical fiber near a portion connected to or to be connected to the third optical fiber by heating.

A method for connecting a first optical fiber to a second optical fiber having a mode field diameter which is smaller than the mode field diameter of the first optical fiber, the method comprising the steps of:

• preparing a third optical fiber having a short length and a mode field diameter which is smaller than the mode field diameter of the first optical fiber;
• increasing the mode field diameter of a part of the third optical fiber near a portion to be connected to the first optical fiber by heating such part;
• and
• connecting the first optical fiber to the third optical fiber, and the second optical fiber to the third optical fiber.

A method for connecting a first optical fiber to a second optical fiber, having a W-shaped refractive index profile and a smaller mode field diameter than the mode field diameter of the first optical fiber, the method comprising the steps in the sequence of:

• preparing a third optical fiber having a short length and a mode field diameter which is smaller than the mode field diameter of the first optical fiber and approximately the same as the mode field diameter of the second optical fiber;
• increasing the mode field diameter of a part of the third optical fiber near a portion to be connected to the first optical fiber by heating such part;
• and
• connecting the first optical fiber to the third optical fiber, and the second optical fiber to the third optical fiber.