Double asymmetric optical fiber coupler

An optical fiber coupler comprising:

• a first optical fiber having a longitudinally extending multimode guiding region and a first fiber portion longitudinally extending between a first location and a second location of the first optical fiber;
• a second optical fiber having a longitudinally extending multimode guiding region and a second fiber portion longitudinally extending between a third location and a fourth location of the second optical fiber;
• and
• a coupling region where at least a portion of the first fiber portion is optically coupled to at least a portion of the second fiber portion, thereby defining a multimode injection direction extending from the third location of the second optical fiber to the first location of the first optical fiber, and a multimode extraction direction extending from the first location of the first optical fiber to the third location of the second optical fiber;
• wherein the coupling region is configured to allow propagation of a multimode signal having substantially fully-filled launching conditions both:
• along the multimode injection direction with a given multimodal injection ratio;
• and
• along the multimode extraction direction with a given multimodal extraction ratio.