Optical circuit
The optical circuit of the present disclosure provides a new optical transmitter configuration that achieves both high output and high quality transmission characteristics regardless of variations at cleavage positions. The optical circuit of the present disclosure may be an optical transmitter having an AXEL configuration in which an EADFB laser and a semiconductor optical amplifier (SOA) are integrated. In a window structure portion of a chip emission edge face of the AXEL, a partially thickened bulk semiconductor layer is formed by a structure including a simulated mesa configured to be separated from an optical axis parallel to an optical axis of an emission optical waveguide.
1 . An optical circuit integrating a semiconductor laser and a semiconductor optical amplifier (SOA) on a substrate, the optical circuit comprising:
a waveguide being optically connected to the SOA and terminating inside of the substrate from an edge face; and
a window region through including a plurality of simulated mesas configured parallel to an optical axis from an end of the waveguide to the edge face and being buried by a bulk semiconductor except for the plurality of simulated mesas, each of the plurality of simulated mesas being separated from the optical axis by a distance M,
wherein
light emitted from the end of the waveguide propagates to the edge face,
the edge face is a cleavage surface,
the waveguide includes a bent waveguide portion having a bending angle θ wg toward the terminal end, and the optical axis is an extension line of an optical axis of the bent waveguide portion, and
the plurality of simulated mesas comprising:
two simulated waveguides that are arranged on both sides of the optical axis; and
a third simulated waveguide that is separated by a distance 2M from one simulated waveguide opposite to a bending of the bent waveguide portion of the two simulated waveguides and being parallel to the two simulated waveguides.
2 . The optical circuit according to claim 1 , wherein
each simulated mesa has a same layer structure as the waveguide.
3 . The optical circuit according to claim 1 , wherein each simulated mesa has a mesa structure with a width W.
4 . The optical circuit according to claim 1 , wherein
the light is incident on the edge face to be inclined by the bending angle θ wg from a direction perpendicular to the edge face.
5 . The optical circuit according to claim 1 , wherein
the semiconductor laser is a distributed feedback laser (DFB laser) in which an electric field absorption modulator is integrated,
the optical circuit is an optical transmitter, and
the waveguide is a passive waveguide including a core layer having a band gap wavelength shorter than an oscillation wavelength of the DFB laser.
6 . The optical circuit according to claim 5 , wherein,
the DFB laser, the electric field absorption modulator, and the SOA are formed on a surface (100) of an InP substrate, and
an optical axis of the DFB laser is parallel to a substrate crystal orientation [0 1 1] or [0 1 1 ].
7 . The optical circuit according to claim 1 , wherein
the distance M falls within a range of 2 μm<M<6 μm,
the width W of each simulated mesa falls within a range of 1 μm<W, and
a distance L between the terminal end and the edge face falls within a range of 5 μm<L<25 μm.