Highly efficient coupling between LD array and optical fiber array using Si microlens array

By using a Si microlens array, highly efficient coupling is realized between laser diode (LD) and optical-fiber arrays. The Si microlens is fabricated by transferring the lens shape of photoresist onto the Si surface using an etching process. For an optimal coupling scheme, a high-NA microlens with a diameter of 240 mu m and focal length of 190 mu m is designed and fabricated. The optical coupling efficiency for a four-channel system is -4.8+or-0.3 dB between an LD array with lasing wavelength of 1.55 mu m and a single-mode fiber array, which is the best data reported so far. Optical crosstalk exceeds -70 dB at the 250- mu m distant neighbor channel. >