the present invention is directed to providing an environmentally stable , ultra - short pulse source . exemplary embodiments relate to passively modelocked ultra - short fiber lasers which are insensitive to temperature variations and which possess only negligible sensitivity to pressure variations . further , exemplary embodiments can be implemented in a cost - effective manner which render them commercially practical in unlimited applications . arbitrary fiber lengths can be used to provide an ultra - short pulse with a cost - effective architecture which is commercially practical .