Patent ID: 8266928

Claim:
A burner for manufacturing a porous glass base material, the burner comprising: a glass raw material gas ejection tube; a burnable gas ejection tube provided around and centered on the glass raw material gas ejection tube; and one or more sequences of auxiliary gas ejection tubes provided inside the burnable gas ejection tube, to be coaxial with respect to the glass raw material gas ejection tube, each of the auxiliary gas ejection tubes having an auxiliary gas ejection port at an end thereof whose perimeter is defined by the inner surface of the auxiliary gas ejection tube at the end of the auxiliary gas ejection tube, such that the auxiliary gas ejection tube has a front surface bounded on one side by the inner surface of the auxiliary gas ejection tube at the end of the auxiliary gas ejection tube and bounded on the other side by the outer surface of the auxiliary gas ejection tube at the end of the auxiliary gas ejection tube, wherein in each of the sequences, the auxiliary gas ejection ports have the same focal length as each other, and each of the auxiliary gas ejection tubes has a concave portion formed in the front surface so as to extend to a maximum depth H in the axial direction of the auxiliary gas ejection tube.