Optical amplifying device

An optical amplifying device comprising:

• an optical amplifier including
• an optical amplifying medium which optically amplifies to-be-amplified light, and
• a transparent medium configured to propagate the amplified light;
• and
• an energy supplier configured to supply excitation energy to the optical amplifying medium,
• wherein a plurality of components including the optical amplifying medium and the transparent medium of the optical amplifier are integrated,
• wherein the transparent medium has:
• a light input portion configured to input the amplified light;
• at least four inner faces configured to reflect the amplified light in the transparent medium;
• and
• a light output portion configured to output the amplified light, wherein the amplified light from the input portion travels in the transparent medium so as to circle at least two times in the transparent medium from being reflected by the at least four inner faces of the transparent medium.