Achromatic couplers, achromatic variable ratio couplers, and methods of making the same

A variable ratio coupler comprising:

• a glass tube having a refractive index n3 and comprising a passageway;
• a first optical waveguide and a second optical waveguide positioned within the passageway, each of the first optical waveguide and the second optical waveguide comprising a core surrounded by a cladding, and one or more airlines between one or more of the first optical waveguide and the second optical waveguide and an inner surface of the passageway wherein:
• the glass tube further comprises a tapered region having a taper length;
• a coupling region is present between the first optical waveguide and the second optical waveguide within the tapered region;
• a refractive index of the cladding is less than a refractive index of the core, and a lowest refractive index of the cladding of the first optical waveguide and the second optical waveguide is n2;
• n3 is lower than n2 such that a value of Δ2-3 is 0.07%≤Δ2-3≤0.125, where Δ2-3 equals (n22−n32)/2 n22;
• the first optical waveguide is fixed;
• and
• the second optical waveguide is configured to be deflected relative to the first optical waveguide to change a split ratio of the variable ratio coupler.

A method of fabricating a coupler, the method comprising:

• positioning a first optical waveguide and a second optical waveguide into a passageway of a glass tube, wherein:
• each of the first optical waveguide and the second optical waveguide comprising a core surrounded by a cladding, wherein:
• a refractive index of the cladding is less than a refractive index of the core, and a lowest refractive index of the cladding of the first optical waveguide and the second optical waveguide is n2;
• and
• n3 is lower than n2 such that a value of Δ2-3 is 0.07%≤Δ2-3≤0.125, where Δ2-3 equals (n22−n32)/2 n22;
• applying a vacuum seal to a first end and a second end of the glass tube;
• heating the glass tube using a gas having a methane to oxygen flow ratio of 0.42 slpm to 0.84 slpm wherein oxygen is less than 0.90 slpm;
• and
• pulling the glass tube to form a tapered region having a taper length, wherein:
• a coupling region is present between the first optical waveguide and the second optical waveguide within the tapered region;
• and
• one or more airlines are present between one or more of the first optical waveguide and the second optical waveguide and an inner surface of the passageway, wherein the coupler is configured to be deflected at the tapered region for changing a split ratio of the coupler and an optical loss of the coupler is about 0.08 dB or less at an optical wavelength of 1310 nanometers in the undeflected state.

A method of fabricating a coupler, the method comprising:

• applying a vacuum seal to a first end of a glass tube having a passageway and a tapered region where the passageway is tapered, wherein a first optical waveguide and a second optical waveguide are disposed within the passageway and a coupled region between the first optical waveguide and the second optical waveguide is present within the tapered region;
• applying an epoxy to a second end of the glass tube such that the epoxy flows a predetermined distance within the passageway;
• removing the vacuum seal from the first end;
• heating the second end with a heat source for a period of time;
• and
• removing the heat source after the period of time and applying the epoxy to the second end such that the epoxy flows within the passageway, and wherein the coupler is configured to be deflected at the tapered region for changing a split ratio of the coupler and an optical loss of the coupler is about 0.08 dB or less at an optical wavelength of 1310 nanometers in the undeflected state.