JP2008268763A - Light reflecting circuit, half-mirror circuit, optical resonance circuit, laser oscillator, and optical function circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light reflecting circuit which need not have high manufacturing precision and has small loss. <P>SOLUTION: The light reflecting circuit 10 is composed of a single-mode waveguide 11, a Y-branch waveguide 12, and a circulation waveguide 13. Light made incident on the single-mode waveguide 11 branches off through the Y-branch waveguide 12 to be demultiplexed into clockwise propagated light and counterclockwise propagated light in the circulation waveguide 13, which are multiplexed through the Y-branch waveguide 12 to be projected from the single-mode waveguide 11. Since the light beams propagated in the opposite directions through the circulation waveguide 13 are propagated in the same waveguide, they are incident on the Y-branch waveguide 12 again in an in-phase state, and they are coupled and output nearly without any loss in principle. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a light reflection circuit that does not require high manufacturing accuracy and has little loss, and an optical resonance circuit, a half mirror circuit, a laser oscillator, and an optical functional circuit that use the light reflection circuit.

  A conventional light reflection circuit is formed by forming a groove in an optical waveguide and laminating a mirror such as a metal on the side surface (see, for example, Patent Document 1).

FIG. 10 is a diagram showing a configuration of a conventional light reflection circuit. FIG. 10A is an upper sectional view, and FIG. 10B is a side sectional view. The light reflection circuit 110 is formed by forming a groove 113 at the end of an optical waveguide composed of a core 111 and a clad 112 and laminating a mirror 114 made of metal or the like on the side surface.
WO02 / 054120 pamphlet

  However, the metal mirror 114 has an absorption loss. It is difficult to make the side surface of the groove 113 perpendicular to the light propagation direction, and when it is tilted, the reflection loss suddenly increases. In addition, in a multi-layered semiconductor waveguide, smooth etching is difficult, and the reflection surface has scattering loss. Therefore, the conventional light reflecting circuit is required to have high manufacturing accuracy, and even if manufactured with a considerably high accuracy, the loss is still large.

  In view of the above problems, the present invention provides an optical reflection circuit that does not require high manufacturing accuracy and has little loss, and an optical resonance circuit, a half mirror circuit, a laser oscillator, and an optical functional circuit that use the optical reflection circuit. With the goal.

  The light reflection circuit of the present invention includes a single-mode waveguide into which input light is incident, a Y-branch waveguide that divides the light emitted from the single-mode waveguide into two branches, and a branch by the Y-branch waveguide And a circular waveguide having a substantially arc shape in which light emitted from the two waveguides is incident on the other waveguide.

  In addition, the light reflection circuit of the present invention includes a single mode waveguide into which input light is incident and a multimode interference type one-to-two branch waveguide in which light emitted from the single mode waveguide is incident and branched into two. And a circular waveguide having a substantially arc shape in which light emitted from the two waveguides branched by the branching waveguide is incident on the other waveguide.

  In addition, the light reflection circuit of the present invention includes a single mode waveguide into which input light is incident, a directional coupling type branch waveguide that divides the light emitted from the single mode waveguide into two, and And a circular waveguide having a substantially arc shape in which light emitted from two waveguides branched by the branching waveguide is incident on the other waveguide.

  Further, the half mirror circuit of the present invention includes two light reflection circuits, and light emitted from the two waveguides of the circular waveguide of the first light reflection circuit is provided in the middle of each of the circular waveguides. 2: 2 optical coupling circuit which injects into the 1st input and the 1st output, and the 2nd 2 optical coupling circuit is used as the 2nd light reflection circuit for the outgoing light from the 2nd input and 2nd output of this 2 to 2 optical coupling circuit Are incident on the two waveguides of the circular waveguide, and a part of the incident light from the single mode waveguide of the first light reflection circuit is reflected, and the rest is single-ended by the second light reflection circuit. The light is transmitted through a single mode waveguide.

  Further, the optical resonance circuit of the present invention includes two of the above-described light reflection circuits or a plurality of the above-described half mirror circuits, and forms the optical resonance circuit by entering, reflecting, and emitting the reflected light of the other party. It is characterized by doing.

  The laser oscillator of the present invention is characterized in that a gain waveguide is provided in a part of the waveguide of the optical resonance circuit.

  In addition, the optical functional circuit of the present invention is characterized in that the above-described light reflecting circuit is arranged in the center of an optical functional circuit that is originally symmetric and is configured on only one side of the optical functional circuit that is originally symmetric. To do.

A typical effect obtained by the present invention will be briefly described as follows.
Since the light reflection circuit is configured without using elements that require high manufacturing accuracy, the light reflection circuit is easy to manufacture and has little loss.
-An optical reflector having little wavelength dependency can be configured by using an element having almost no wavelength dependency.
-By using an element having almost no polarization dependence, a light reflector with little polarization dependence can be configured.
-By using an element having almost no temperature dependence, an optical reflector with little temperature dependence can be configured.
-An optical resonant circuit and a composite optical resonant circuit can be configured.
・ Laser oscillator can be configured.
-A reflective optical functional circuit can be configured. Further, since the light reflector can be configured at an arbitrary position, the size is reduced.

  The best mode for carrying out the present invention will be described below in detail with reference to the accompanying drawings. In all the drawings, components having the same function are denoted by the same reference numerals, and repeated description thereof is omitted. The embodiment will be described on the assumption that a structure having a large relative refractive index difference is used for the optical waveguide.

  FIG. 1 is a diagram illustrating a configuration of a light reflection circuit according to a first embodiment of the present invention. The light reflecting circuit 10 according to the first embodiment includes a single mode waveguide 11, a Y branch waveguide 12, and a circular waveguide 13. The circular waveguide 13 has a substantially arc shape, and light emitted from the two waveguides branched by the Y-branch waveguide 12 enters the other waveguide. The light incident on the single mode waveguide 11 is branched by the Y-branch waveguide 12 to become clockwise propagation light and counterclockwise propagation light in the circular waveguide 13, and further combined by the Y-branch waveguide 12. And is emitted from the single mode waveguide 11. In the first embodiment, light propagating in the reverse direction in the circular waveguide 13 propagates through the same waveguide, and therefore enters the Y-branch waveguide 12 again at an equal phase. Combined and output.

  For example, if a waveguide consisting of a semiconductor core and a dielectric or air clad having a relative refractive index difference of around 40% is used, the bending radius of the circular waveguide 13 can be reduced to about 3 μm. The entire circuit 10 can be configured with a dimension of about 10 μm. Further, if a waveguide made of a dielectric core and a low refractive index resin or air clad having a relative refractive index difference of about 10% is used, the bending radius of the circular waveguide 13 can be set to about 200 μm. Can be configured with dimensions of about 500 μm.

  The loss of the light reflection circuit 10 according to the first embodiment is mainly caused by the branch loss of the Y branch waveguide 12. Further, the wavelength dependence and polarization dependence of the branching loss are very slight for incident light satisfying the single mode condition. As a result, the wavelength dependence and polarization of the reflectance of the light reflection circuit 10 of the first embodiment are as follows. The dependency is small.

  Note that the propagation constant for TE light and TM light may be different in the circular waveguide 13. In order to reduce the phase fluctuation of the reflected light due to this influence, it is effective to make the difference between the optical path lengths of the TE light and the TM light an integral multiple of the design wavelength.

  FIG. 2 is a diagram showing a configuration of a light reflection circuit according to the second embodiment of the present invention. The light reflecting circuit 20 of the second embodiment includes a single mode waveguide 11, a multimode interference type 1: 2 branching waveguide 22, and a circular waveguide 13.

  The operation principle is the same as that of the first embodiment, but the multimode interference type 1: 2 branching waveguide 22 has a lower loss than the Y branching waveguide 12, so that the light reflection circuit 20 also has a lower loss. Dimensions are slightly larger. The multi-mode interference type 1: 2 branch waveguide 22 is easy to manufacture because there is no sharp etching portion at the Y branch intersection as compared with the Y branch waveguide 12.

  FIG. 3 is a diagram showing the configuration of the light reflection circuit according to the third embodiment of the present invention. The light reflecting circuit 30 according to the third embodiment includes a single mode waveguide 31, a directional coupling type 2: 2 branch waveguide 32, and a circular waveguide 13.

  The operating principle is the same as in the first and second embodiments, but the directional coupling type 2: 2 branch waveguide 32 has a lower loss than the multimode interference type 1: 2 branch waveguide 22 when the fabrication accuracy is high. Therefore, the light reflection circuit 30 also has a low loss.

  FIG. 4 is a diagram showing a configuration of an optical resonant circuit according to the fourth embodiment of the present invention. FIG. 4A is a diagram showing the overall configuration of the optical resonant circuit, and FIG. 4B is an enlarged view of the periphery of the 2: 2 optical coupler 42a. The optical resonant circuit 40 of the fourth embodiment includes a single mode waveguide 11, a light reflection circuit 41a, 2: 2 optical coupler 42a, a light reflection circuit 41b, a single mode waveguide 43, a light reflection circuit 41c, 2: The two-optical coupler 42b, the light reflection circuit 41d, and the single mode waveguide 11 are connected in order.

  The light reflection circuit 41a and the light reflection circuit 41b are coupled via a 2: 2 optical coupler 42a. The light reflection circuit 41a is connected to one input and one output of the 2: 2 optical coupler 42a, and the light reflection circuit 41b is connected to the other input and the other output of the 2: 2 optical coupler 42a. The intensity branching ratio of the 2: 2 optical coupler 42a is k: 1-k. In this case, the portion composed of the light reflection circuit 41a, the light reflection circuit 41b, and the 2: 2 optical coupler 42a functions as a half mirror having a reflectance k and a transmittance 1-k. For this reason, the light incident on the optical resonant circuit 40 reciprocates between the two mirrors to form an optical resonant circuit. It is possible to adjust the resonance frequency by controlling the optical path length of the single mode waveguide 43.

  FIG. 5 is a diagram showing a configuration of a composite optical resonance circuit according to Embodiment 5 of the present invention. The composite optical resonance circuit 50 according to the fifth embodiment is configured by configuring the optical resonance circuit according to the fourth embodiment in multiple stages.

  The fifth embodiment is for the case where the optical resonant circuit is used as a frequency filter. By making the optical resonant circuit multi-stage, it is possible to make the filter characteristics steep, thin out the resonance peak, and realize complex wavelength characteristics. It becomes.

  FIG. 6 is a diagram showing a configuration of an optical resonant circuit according to the sixth embodiment of the present invention. The optical resonant circuit 60 of the sixth embodiment includes a single mode waveguide 11, light reflecting circuits 10 a and 10 b, and a 2: 2 optical coupler 61.

  The sixth embodiment is an optical resonant circuit, and has a configuration in which a 2: 2 optical coupler 61 performs optical input / output with the outside of the resonator. The sixth embodiment operates on the same principle as the fourth embodiment and has the same effect, but can be configured more compactly.

  FIG. 7 is a diagram showing a configuration of a laser oscillator according to a seventh embodiment of the present invention. The laser oscillator 70 of the seventh embodiment is configured by including a gain waveguide 72 in a part of the single mode waveguide 43 of the fourth embodiment (single mode waveguide 71 of the seventh embodiment).

  The gain waveguide 72 is a waveguide having an optical amplification function such as a semiconductor optical amplifier or a rare earth element-doped waveguide. When gain is provided by current injection in the case of a semiconductor optical amplifier and by optical pumping in the case of a rare earth element doped waveguide, the seventh embodiment operates as a laser oscillator 70. Conventionally, a waveguide type laser oscillator uses a cleaved mirror, an etched mirror, a distributed reflection type mirror, or the like, all of which require an advanced manufacturing process. In the seventh embodiment, since the mirror is formed by a normal waveguide forming process, there is an advantage that the manufacturing process becomes easy.

  FIG. 8 is a diagram showing a configuration of a reflective arrayed waveguide diffraction grating according to the eighth embodiment of the present invention. The reflective arrayed waveguide diffraction grating 80 of the eighth embodiment includes an input / output waveguide 81, a slab waveguide 82, and a waveguide array 83. A light reflection circuit 84 is connected to the end of the waveguide array 83.

  This configuration takes advantage of the advantage that the light reflecting circuit 84 can be arranged at an arbitrary position in the waveguide array 83. This is an effective layout when the waveguide array 83 is long. In general, a symmetrical optical functional circuit such as an arrayed waveguide diffraction grating can be configured as a reflective optical functional circuit by disposing an optical reflector in the center of the symmetrical circuit. Thus, the reflection type configuration has an advantage that the element size can be halved by the same function as compared with the transmission type. In addition to the arrayed waveguide diffraction grating shown in the eighth embodiment, various light functional circuits can be configured in a reflective type by applying the light reflecting circuit 84.

  FIG. 9 is a diagram showing a configuration of a reflective arrayed waveguide diffraction grating according to the ninth embodiment of the present invention. The reflection type arrayed waveguide diffraction grating 90 of the ninth embodiment is topologically the same as the configuration of the reflection type arrayed waveguide diffraction grating 80 of the eighth embodiment, but the waveguide array 83 is arranged in a spiral shape. It has a more compact structure.

  The present invention is not limited to the above embodiment.

It is a figure which shows the structure of the light reflection circuit by Example 1 of this invention. It is a figure which shows the structure of the light reflection circuit by Example 2 of this invention. It is a figure which shows the structure of the light reflection circuit by Example 3 of this invention. It is a figure which shows the structure of the optical resonant circuit by Example 4 of this invention. It is a figure which shows the structure of the composite optical resonance circuit by Example 5 of this invention. It is a figure which shows the structure of the optical resonant circuit by Example 6 of this invention. It is a figure which shows the structure of the laser oscillator by Example 7 of this invention. It is a figure which shows the structure of the reflection type | mold array waveguide diffraction grating by Example 8 of this invention. It is a figure which shows the structure of the reflection type | mold array waveguide diffraction grating by Example 9 of this invention. It is a figure which shows the structure of the conventional light reflection circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10, 10a, 10b Light reflection circuit 11 Single mode waveguide 12 Y branch waveguide 13 Circulation waveguide 20 Light reflection circuit 22 Multimode interference type 1: 2 branch waveguide 30 Light reflection circuit 31 Single mode waveguide 32 Direction Sexual coupling type 2: 2-branch waveguide 40 Optical resonant circuit 41a to 41d Optical reflecting circuit 42a, 42b 2: 2 optical coupler 43 Single mode waveguide 50 Compound optical resonant circuit 60 Optical resonant circuit 61 2: 2 optical coupler Reference Signs List 70 Laser oscillator 71 Single mode waveguide 72 Gain waveguide 80 Reflective array waveguide diffraction grating 81 Input / output waveguide 82 Slab waveguide 83 Waveguide array 84 Optical reflection circuit 90 Reflective array waveguide diffraction grating 110 Optical reflection circuit 111 Core 112 Clad 113 Groove 114 Mirror

Claims (7)

A single mode waveguide into which the input light is incident;
A Y-branch waveguide that divides the light emitted from the single-mode waveguide into two branches;
A light reflection circuit comprising: a circular waveguide having a substantially arc shape in which light emitted from two waveguides branched by the Y branch waveguide is incident on the other waveguide. A single mode waveguide into which the input light is incident;
A multimode interference type one-to-two branching waveguide that splits the light emitted from the single-mode waveguide into two branches;
An optical reflection circuit comprising: a circular waveguide having a substantially arc shape in which light emitted from two waveguides branched by the branching waveguide is incident on the other waveguide. A single mode waveguide into which the input light is incident;
A directional coupling type branched waveguide that divides the light emitted from the single mode waveguide into two branches;
An optical reflection circuit comprising: a circular waveguide having a substantially arc shape in which light emitted from two waveguides branched by the branching waveguide is incident on the other waveguide. 2. The two light reflection circuits according to claim 1 are provided, and light emitted from the two waveguides of the circular waveguide of the first light reflection circuit is provided in the middle of each of the circular waveguides. A two-to-two optical coupling circuit incident on the first input and the first output;
Light emitted from the second input and the second output of the two-to-two optical coupling circuit is incident on the two waveguides of the circular waveguide of the second light reflecting circuit, and the first light reflection is performed. A half mirror circuit, wherein a part of incident light from a single mode waveguide of the circuit is reflected and the rest is transmitted to the single mode waveguide of the second light reflection circuit.   It comprises two light reflection circuits according to any one of claims 1 to 3 or a plurality of half mirror circuits according to claim 4, and each of them reflects, reflects and emits the reflected light of the other party, and optical resonance An optical resonant circuit comprising a circuit.   A laser oscillator comprising a gain waveguide in a part of the waveguide of the optical resonant circuit according to claim 5. The light reflecting circuit according to any one of claims 1 to 3 is arranged in the center of an optical functional circuit that is originally symmetric, and is configured only on one side of the optical functional circuit that is originally symmetric. Optical functional circuit.

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