Optical wavelength filter and optical demultiplexer

An optical demultiplexer having a first input port for receiving an input optical signal having a plurality of wavelength components, a first output port for outputting an optical signal having only a predetermined wavelength component from the input optical signal, a second output port for outputting an optical signal having wavelength components other than that of the predetermined wavelength component, and a plurality of optical wavelength filters serially connected and connected to another first input port corresponding to the second output port,

• the plurality of optical wavelength filters each comprising:
• a first coupler having a first port connected to the first input port, for receiving the input optical signal, third and fourth ports for dividing the input optical signal received from the first port into two halves and outputting the divided outputs, respectively, and a second port connected to the first output port, for outputting optical signals reflected from the optical signal output from the third and fourth ports;
• a first optical wavelength reflector having an input port for receiving the optical signal from the third port of the first coupler, and an output port for reflecting only an optical signal having the predetermined wavelength component from the optical signal received from the input port, outputting the reflected optical signal to the third port of the first coupler, and outputting an optical signal having the wavelength components other than that of the predetermined wavelength component;
• a second optical wavelength reflector having an input port for receiving the optical signal from the fourth port of the first coupler, and an output port for reflecting only an optical signal having the predetermined wavelength component of the optical signal received from the input port, outputting the reflected optical signal to the fourth port of the first coupler, and outputting an optical signal having wavelength components other than that of the predetermined wavelength component;
• and
• a second coupler having first and second ports for receiving the optical signals from the respective output ports of the first and second optical wavelength reflectors, and a third port connected to the second output port of the optical wavelength filter, for outputting the optical signals received from both the first and second ports, there being a −π/2 phase difference between the optical signals received by the first and second ports of the second coupler, said third port having an optical coupling area for causing a −π/2 phase shift to one of said optical signal such that said optical signals output from said third port have the same phase and are thus coupled;
• the optical signals received from the first output ports of the plurality of optical wavelength filters having predetermined wavelength components different from one another.