Whispering gallery mode microsphere resonator with microsphere-microsphere coupling

•We present a new type of whispering gallery mode microsphere resonator, which consists of two cascaded microspheres glued on the optical fiber tip for effective microsphere-microsphere coupling.•The incident light diverges in the first microsphere and part of light is coupled to the surface of the second microsphere and excites whispering gallery mode resonance when the angle between the connection line of the two microsphere centers and the fiber axis is appropriate.•The device is robust in structure, compact in size, and stable in operation.