To enable operation under the environment over a wide temp. range by adopting the constitution having a negative light input/output characteristic to incident light in a specific temp. range where an element having the negative light input/output characteristic to the incident light is doped to a transparent preform.

The optical element having the negative light input/output characteristic to the incident light within the temp. range of at least -150 to 200°C at which the element having the negative light input/output characteristic to the incident light is doped to the transparent preform is used. This optical element has the negative light input/output characteristic to the incident light within the temp. range at which the element, such as rare earth erbium, having the negative light input/output characteristic to the incident light is doped to the transparent preform, such as ruthenium aluminum garnet. The negative light input/output characteristic refers to the characteristic that the intensity of the transmitted light through the optical element increases or decreases with the increase or decrease in the intensity of the incident light made incident on the optical element, i.e., the characteristic that the transmitted light intensity decreases with the incident light intensity increases and conversely that the transmitted light intensity increases when the incident light intensity decreases.