Optical module and wavelength division multiplexing optical module

An optical module, comprising:

• a package in which a fiber, a ferrule, a first lens, a first wavelength selection filter, a second wavelength selection filter;
• and
• a first substrate, a second lens, a second substrate on which an optical element is mounted, and a pin are fastened respectively,
• wherein the module further includes a first optical system, a second optical system, and a third optical system;
• wherein the first optical system includes the fiber, the ferrule, and the first lens;
• wherein the fiber, the ferrule, and the first lens are fastened in this order or in the reverse order in the package so as to be connected optically to the wavelength selection filter of the second optical system;
• wherein the second optical system includes a first wavelength selection filter and a second wavelength selection filter;
• wherein the first and second wavelength selection filters are fastened in the package so that a light reflected from the first wavelength selection filter is connected optically to the second wavelength selection filter;
• wherein the third optical system includes a first substrate, a second lens, and a second substrate;
• wherein the first substrate, the second lens, and the second substrate are fastened in the package so that the wavelength selection filter, the first substrate, and the second lens are connected optically to the optical element mounted on the second substrate in this order or in the reverse order.
• wherein the module further includes a plurality of the third optical systems;
• wherein one of the plural third optical systems is connected optically to the first wavelength selection filter;
• and
• wherein the other two third optical systems are connected optically to the second wavelength selection filter.