Nippon Telegraph and Telephone Corporation

Akihiro Takagi

Masao Kawachi

Kaname Jinguji

Shin Kamei

Motohaya Ishii

Norio Takato

Takeshi Kitagawa

A practical optical waveguide circuit is provided which includes many intersections but is low loss. The width of a waveguide core is wat input and output terminal sections and wat an intersecting section, where w&#x3e;w. The core width of the intersecting section is made different from that of the input and output terminal sections, or the core height of the intersecting section is made different from that of the input and output terminal sections. The core width is smoothly varied between the intersecting section and the input and output terminal sections by a tapered section. When the number of the waveguides intersecting with the intersecting section is 100, the intersection loss is 5.8 dB for the conventional device where w=w=5 &#x3bc;m, but is 1.8 dB when w=12 &#x3bc;m, thereby being able to reduce the intersection loss sharply.

Optical waveguide circuit

A guided-wave optical branching device having optical waveguides disposed on a substrate. The waveguides are partially arranged to be close to each other to form a tapered directional coupler in which the waveguides are point symmetrical or line symmetrical. Alternatively, the waveguides are neither line symmetrical nor point symmetrical. The tapered directional coupler reduces the wavelength dependence of the coupling ratio of the output power derived from the branching device. The widths of the waveguides in the parallel coupling region, the length of the coupling region in the symmetrical or asymmetrical directional coupler, the asymmetrical parameters or the like are set at values determined in accordance with the wavelength range used, so that the wavelength dependence of the coupling ratio of the power between the input port and the output port is reduced in a desired wavelength range, for example, 1.2 .mu.m-1.8 .mu.m.

Guided-wave optical branching device

A guided-wave optical branching component is composed of a Mach-Zehnder interferometer having two or more directional couplers. A slight difference .DELTA.L in the optical-path length is provided in two or more optical waveguides connecting the two or more directional couplers. The difference of the optical-path length is less than the shortest wavelength in the operational wavelength region of the guided-wave optical branching component, and the coupling ratio of each of the two directional couplers monotonically increases with wavelength in the operational wavelength region. By using the optical branching components thus constructed (i.e., Mach-Zehnder interferometer type 3-dB optical coupler) in conjunction with a phase shifter, a Mach-Zehnder interferometer type optical switch can be achieved.

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Mito, Japan

Akihiro Takagi