Coherent optical mixer circuit

Patent metadata

Field	Value
Publication number	US-10295744-B2
Application number	US-201615568610-A
Country	US
Kind code	B2
Filing date	May 27, 2016
Priority date	May 29, 2015
Publication date	May 21, 2019
Grant date	May 21, 2019

Abstract

A coherent optical mixer circuit is provided that can measure a phase error without requiring a step of cutting away a delay circuit. Odd-numbered or even-numbered two of four inputs of an 4-input-and-4-output multimode interference circuit are connected to an input mechanism. The four outputs of the multimode interference circuit are all connected to an output mechanism to the exterior. Other two inputs of the multimode interference circuit are connected to two monitor waveguides. One of the monitor waveguide is longer than the other to configure a light delay circuit. The monitor waveguides constituting the light delay circuit are connected to the respective outputs of a 2-branched light splitter. The 2-branched light splitter has an input connected to a monitor light input mechanism from the exterior via a monitor input waveguide.

First claim

The invention claimed is:

1. A coherent optical mixer circuit including a 4-input-and-4-output multimode interference circuit having a silicon waveguide in which the multimode interference circuit has two odd-numbered or even-numbered inputs that are connected to an input mechanism of externally-inputted signal light and reference light via input waveguides and the four outputs of the multimode interference circuit are all connected to an output mechanism to the exterior via output waveguides, wherein:
the other two inputs of the multimode interference circuit are connected to two monitor waveguides,
one of the monitor waveguide is longer than the other of the monitor waveguide to configure a light delay circuit,
the monitor waveguides constituting the light delay circuit are connected to respective outputs of a 2-branched light splitter, and
the 2-branched light splitter has an input connected to a monitor light input mechanism from the exterior via a monitor input waveguide;
wherein:
at least a part of the monitor waveguide is formed by a silicon waveguide,
the remaining portion of the monitor waveguide and the 2-branched light splitter connected to the monitor waveguide and the monitor input waveguide, and the monitor light input mechanism connected to the monitor input waveguide are formed by a light waveguide formed in another layer different from that of the silicon waveguide, and
a part of the monitor waveguide formed by the silicon waveguide and the light waveguide of another layer different from that of the silicon waveguide are interlayer-coupling, and
the interlayer-coupling is a structure comprising the part of the monitor waveguide formed by the silicon waveguide and the part of the light waveguide formed in another layer different from that of the silicon waveguide, wherein
each tips of the waveguides are formed in a tapered shape,
and the tips of the tapered shape are formed in the direction to face each other,
and the tips of the tapered shape are overlapping seen from a vertical direction to substrate.

2. The coherent optical mixer circuit according to claim 1 , wherein:
the output waveguides of the multimode interference circuit includes a waveguide intersection.

3. The coherent optical mixer circuit according to claim 1 , wherein:
at least one of the signal light and reference light input mechanism, the monitor light input mechanism, and the output mechanism comprises a grating coupler.

4. The coherent optical mixer circuit according to claim 1 , wherein:
the waveguides formed in another layer different from that of the silicon waveguide are made of a material having a refractive index between those of silicon and quartz.

5. The coherent optical mixer circuit according to claim 1 , wherein:
the output mechanism is connected to a photo detector.

6. The coherent optical mixer circuit according to claim 5 , wherein:
the photo detector has a subsequent stage including a grating coupler, and
light not absorbed by the photo detector is outputted from the grating coupler.

7. A polarization separation-type coherent optical mixer circuit including two coherent optical mixer circuits according to claim 1 of the invention, wherein:
the reference light inputted from the input mechanism is 2-branched by a light splitter and the resultant lights are inputted to two coherent optical mixer circuits, respectively,
the signal light inputted from the input mechanism is optical polarization-separated by a polarization beam splitter,
one polarized signal light obtained through the optical polarization-separation is inputted to a first coherent optical mixer circuit,
the other polarized signal light obtained through the optical polarization-separation is inputted to a second coherent optical mixer circuit via a polarization rotation circuit,
monitor lights are inputted from two monitor light input mechanism to two coherent optical mixer circuits, respectively, and
the polarization separation-type coherent optical mixer circuit has a coherent-type polarization diversity configuration.

Assignees

• Nippon Telegraph & Telephone

Inventors

• Kamei Shin
• Jizodo Makoto
• Fukuda Hiroshi
• Kikuchi Kiyofumi
• Tsuzuki Ken

Classifications

• G02B6/125 Primary

  Bends, branchings or intersections · CPC title

• G02F2/002 Primary

  using optical mixing · CPC title

• H04J14/06

  Polarisation multiplex systems · CPC title

• G02B6/126

  using polarisation effects {(G02B6/1226 takes precedence)} · CPC title

• G02F2/00

  Demodulating light; Transferring the modulation of modulated light; Frequency-changing of light (G02F1/35 takes precedence) · CPC title