The first optical filter element transmits light of a wavelength longer than a first cutoff wavelength and reflects light of a wavelength shorter than the first cutoff wavelength.

Preferably, the cutoff wavelength is 900 nm or less.

The cabled fiber has a cutoff wavelength less than about 1300 nm.

The optical fiber (11) has a cutoff wavelength shorter than 1.53 μm.

Based on the measured cutoff wavelength, the target diameter of glass for acquiring the desired wavelength dispersion characteristic is determined.

N laser sources operate at a wavelength λn in a spectral absorption band separated by the cutoff wavelength for single-mode transmission.

The cabled HDSF fiber has cutoff wavelength of less than about 1500 nm.

The wavelength of cut is the wavelength C in lower part of which the fiber is not monomode any more.

The wavelength of cut is the wavelength C in lower part of which the fiber is not monomode any more.

The nanofibers have an average fiber diameter comparable in size to the cutoff wavelength.

The high-order mode cutoff wavelength of the single-mode optical fiber is shorter than the wavelength of the light propagating through the optical receptacle by 100 to 500 nm.

Since this configuration allows the specific wavelength to coincide with the cutoff wavelength of the second optical filter, the second optical filter can be manufactured easily.

Provided is an image pickup lens which is configured so that a shift amount of a cutoff wavelength toward a short wavelength is prevented from being larger.

The Cut-on wavelength is defined at 50% transmittance of maximum.

First, part of an optical fiber material is drawn to a fixed length, and the cutoff wavelength of the resulting optical fiber is measured.