An apparatus for coupling a laser and an optical fiber, comprising: an optical signal transmission part, which comprises a laser fixing part and an optical fiber fixing part, which are respectively disposed at two ends of the optical signal transmission part, wherein the laser fixing part is configured to be coupled with the laser, and the optical fiber fixing part is configured to be coupled with the optical fiber; and wherein a refractive index of the optical signal transmission part changes gradually, the refractive index becomes higher at a position closer to a principal axis, and the optical signal transmission part is configured to: converge optical signals incident from the laser coupled to the laser fixing part or diverge an optical signal incident from the laser coupled to the laser fixing part, and then emit a converged optical signal or diverge optical signals into the optical fiber coupled to the optical fiber fixing part; wherein the optical signal transmission part comprises a third subpart and a fourth subpart, wherein the fourth subpart is connected to the third subpart at a position, from which an optical signal is emitted, of the third subpart; and a refractive index of the optical signal transmission part becomes higher at a position closer to a centre in any cross-section of the third subpart, a refractive index of the fourth subpart is constant, and the refractive index of the fourth subpart is equal to a refractive index at a principal axis of the third subpart; wherein if a length of the third subpart is greater than a threshold, the third subpart is configured to perform optical signal convergence, and a longer length of the third subpart indicates a higher degree of optical signal convergence; and if a length of the third subpart is less than a threshold, the third subpart is configured to perform optical signal divergence, and a shorter length of the third subpart indicates a higher degree of optical signal divergence. an optical signal transmission part, which comprises a laser fixing part and an optical fiber fixing part, which are respectively disposed at two ends of the optical signal transmission part, wherein the laser fixing part is configured to be coupled with the laser, and the optical fiber fixing part is configured to be coupled with the optical fiber; and wherein a refractive index of the optical signal transmission part changes gradually, the refractive index becomes higher at a position closer to a principal axis, and the optical signal transmission part is configured to: converge optical signals incident from the laser coupled to the laser fixing part or diverge an optical signal incident from the laser coupled to the laser fixing part, and then emit a converged optical signal or diverge optical signals into the optical fiber coupled to the optical fiber fixing part; wherein the optical signal transmission part comprises a third subpart and a fourth subpart, wherein the fourth subpart is connected to the third subpart at a position, from which an optical signal is emitted, of the third subpart; and a refractive index of the optical signal transmission part becomes higher at a position closer to a centre in any cross-section of the third subpart, a refractive index of the fourth subpart is constant, and the refractive index of the fourth subpart is equal to a refractive index at a principal axis of the third subpart; wherein if a length of the third subpart is greater than a threshold, the third subpart is configured to perform optical signal convergence, and a longer length of the third subpart indicates a higher degree of optical signal convergence; and if a length of the third subpart is less than a threshold, the third subpart is configured to perform optical signal divergence, and a shorter length of the third subpart indicates a higher degree of optical signal divergence.