According to the present invention, there is provided a method of designing
a collimator array device which enables reduction of the insertion loss because
of the variation of the optical length. When the beam waist is positioned at the
intermediate position between the emitting side planar microlens and the receiving
side planar microlens (d1=L/2), the distance d0 between the emitting side
fiber array and the emitting side planar microlens can be used as the distance
between the receiving side fiber array and the receiving side planar microlens,
and thereby the design of the collimator array device can be simplified. The distance
d0 for satisfying d1=L/2 is calculated and two values d0-2 and d0-4 are
obtained. By selecting the smaller value d0-2, it is possible to reduce the insertion
loss because of the shift at the time of coupling.
