Abstract: An optical demultiplexer that separates, for each signal wavelength, signal light a plurality of wavelengths of which is multiplexed, the optical demultiplexer including: an antireflection film disposed at on an incident surface of a glass block; filters disposed on an emission surface of the glass block, the filters transmit light of a wavelength predetermined for each signal wavelength included in the signal light and reflect light of a wavelength other than the transmitting wavelength toward the incident surface; and a reflection film disposed on the incident surface of the glass block, wherein processing to reduce reflection of the reflection light into the glass block is applied on an optical path of the reflection light reflected by the filter disposed at an end away from the antireflection film.

Abstract: The photo module is provided with an incident light fiber guiding light, a gradient index lens having an optical axis different from the incident light fiber, having a period length larger than a ¼ period length and smaller than a ½ period length with respect to the wavelength of the incident light, joined to the incident light fiber on a surface forming a finite angle with a surface vertical to the optical axis, and having, as a light exit surface of emitting light, a surface substantially vertical to the optical axis, and a light receiving element disposed at a position where the emitting light is collected and measuring the strength of the emitting light.

Abstract: The present invention provides an array-type photo module including a filter, which, in each channel, transmits therethrough a portion of emitted light from an incident optical fiber on the opposite side of a gradient-index lens array and reflects another portion of the emitted light from the incident optical fiber toward the gradient-index lens array, and a light-shielding member which is arranged on the opposite side of the filter from the gradient-index lens array, so as to be spaced from the filter and, in each channel, has an opening passing therethrough transmitted light from the filter on the opposite side of the filter. The array-type photo module is easily and inexpensively manufactured, and may be used in a high-density array, with low crosstalk.

Abstract: A photo module which measures a signal strength in a transmission path, and this technique collects a signal light, guided to a photo module, on a light receiving element without increasing the number of manufacturing processes and the cost and, at the same time, prevents reflected light returned from the photo module from entering inside the transmission path again.