  We report the imaging of tendon, a connective tissue rich in collagen type I
proteins, with Interferometric Second Harmonic Generation (I-SHG) microscopy.
We observed that the noncentrosymmetric structural organization can be
maintained along the fibrillar axis over more than 150 {\mu}m, while in the
transverse direction it is ~1-15 {\mu}m. Those results are explained by
modeling tendon as a heterogeneous distribution of noncentrosymmetric
nanocylinders (collagen fibrils) oriented along the fibrillar axis. The
preservation of the noncentrosymmetric structural organization over multiple
tens of microns reveals that tendon is made of domains in which the fraction
occupied by fibrils oriented in one direction is larger than in the other.
