JP2015187636A - Optical module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical module capable of improving mass productivity and cost saving.SOLUTION: The optical module is constituted of cores 11 and 12 which are waveguides through which light transmits in a single mode; and a clad formed around the cores 11 and 12. The optical module includes: a Mach-Zehnder interferometer employing a half coupling length 2 core coupling waveguide structure; and a phase control unit 11D that controls the phase of the light passing through either one of two arm waveguides 11B and 12B constituting the Mach-Zehnder interferometer.

Description

  The present invention relates to an optical module.

  When a planar optical waveguide optical system is assembled, light emitted by an active medium such as a laser (LD: Laser Diode) must be input from the outside. In this case, since the coupling efficiency of the LD to the waveguide core decreases as the overlap integral between the waveguide modes decreases, the device generally has a position tolerance of 1 μm or less with respect to the position in the plane perpendicular to the optical axis. High-precision mounting is required.

  In Patent Document 1 below, a lens position disposed between an LD and a waveguide is adjusted, and a stainless steel member that holds the lens is deformed by using a stress caused by YAG laser irradiation to move the lens slightly. A method is disclosed. Further, Patent Document 2 discloses a method in which a lens is finely moved using a micro electro mechanical system (MEMS) with respect to a system similar to Patent Document 1, and the position is fixed with solder. . Further, Non-Patent Document 1 discloses a method for improving the position tolerance of an LD by using a system in which an LD and a waveguide are butt-joined without using a lens, and an LD incident portion of the waveguide is a trident structure called a trident type. ing. Patent Document 3 discloses a method of relaxing the positional tolerance of an LD by setting a waveguide to a multimode (MM) instead of a single mode (SM).

JP 2013-231937 A US Patent Application Publication No. 2011/0013869 International Publication No. 2004/104662

N. Hatori et al., “A novel spot size convertor for hybrid integrated light sources on photonics-electronics convergence system”, in Proc. Group IV Photonics, ThB2 (2012).

  In the inventions described in Patent Documents 1 and 2, since the positional tolerance required for the lens is small, there is a problem in mass productivity. Further, the invention described in Patent Document 2 has a problem in terms of cost because it is incorporated in the module together with the mechanical system.

  In the invention described in Non-Patent Document 1, since the spot size of the waveguide can be increased by devising the shape of the LD incident portion of the waveguide, the position tolerance required for the LD can be reduced. However, the amount of relaxation is small, and the LD still requires a position tolerance of 1 μm or less, which causes a problem in mass productivity.

  In the invention described in Patent Document 3, not only the fundamental mode but also the higher order mode propagates in the waveguide as a compensation for expanding the position tolerance. Therefore, there has been a problem that the waveform of the modulation signal is distorted by the influence of mode dispersion. Further, the high-order mode does not contribute to coupling when another waveguide (optical fiber) arranged on the waveguide exit side is SM, so there is a problem that coupling loss increases.

  The present invention has been made in view of the above, and an object thereof is to obtain an optical module that realizes improvement in mass productivity and cost reduction.

  In order to solve the above-described problems and achieve the object, the present invention is composed of a core that is a waveguide that transmits light in a single mode and a clad formed around the core, and has two cores with a semi-coupling length. A Mach-Zehnder interferometer to which a coupled waveguide structure is applied, and a phase control unit that controls the phase of light passing through one of the two arm waveguides constituting the Mach-Zehnder interferometer. It is characterized by that.

  According to the present invention, there is an effect that it is possible to obtain an optical module capable of improving mass productivity and reducing costs.

FIG. 1 is a configuration diagram showing a configuration example of an optical module according to the present invention. FIG. 2 is a diagram illustrating an example of the structure of the optical waveguide. FIG. 3 is a diagram showing an example of the structure of the optical waveguide. FIG. 4 is a diagram showing an example of the structure of the optical waveguide. FIG. 5 is a diagram illustrating a main part of the optical waveguide. FIG. 6 is a diagram illustrating a main part of the optical waveguide. FIG. 7 is a diagram illustrating a main part of the optical waveguide. FIG. 8 is a diagram illustrating a relationship example between the coupling power and the LD-waveguide eccentricity when there is one SM input waveguide. FIG. 9 is a diagram illustrating an example of the relationship between the coupling power and the LD-waveguide eccentricity when the first embodiment is applied. FIG. 10 is a diagram illustrating a configuration example of the two-core coupled waveguide according to the third embodiment. FIG. 11 is a diagram illustrating a configuration example of the two-core coupled waveguide according to the fourth embodiment.

  Embodiments of an optical module according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 is a configuration diagram illustrating a configuration example of a first embodiment of an optical waveguide which is an optical module according to the present invention. As shown in FIG. 1, the optical waveguide has a plurality of cores (cores 11, 12, 21, 22, 31, 32, 41, 42) that guide light and around the cores. The formed cladding 5 and an optical multiplexing unit 6 that multiplexes a plurality of inputted lights are provided. Each core includes an input waveguide, an arm waveguide, and an output waveguide. That is, the core 11 is composed of an input waveguide 11A, an arm waveguide 11B, and an output waveguide 11C, and the core 12 is composed of an input waveguide 12A, an arm waveguide 12B, and an output waveguide 12C. The core 21 includes an input waveguide 21A, an arm waveguide 21B, and an output waveguide 21C, and the core 22 includes an input waveguide 22A, an arm waveguide 22B, and an output waveguide 22C. The core 31 includes an input waveguide 31A, an arm waveguide 31B, and an output waveguide 31C. The core 32 includes an input waveguide 32A, an arm waveguide 32B, and an output waveguide 32C. The core 41 includes an input waveguide 41A, an arm waveguide 41B, and an output waveguide 41C, and the core 42 includes an input waveguide 42A, an arm waveguide 42B, and an output waveguide 42C. The output waveguides 12C, 22C, 32C and 42C are connected to the optical multiplexing unit 6. Further, light emitted from an external LD (Laser Diode) 101 as a light source is incident on each corresponding core.

The lengths of the input waveguide and the output waveguide of each core are both L _c / 2. L _c is the bond length. That is, the cores 11 and 12, the cores 21 and 22, the cores 31 and 32, and the cores 41 and 42 respectively constitute a Mach-Zehnder interferometer that is a two-core coupling waveguide with a semi-coupling length (L _c / 2). doing. In the optical waveguide according to the present embodiment, each core (waveguide) is designed to transmit light in a single mode (SM).

  In addition, phase control units 11D, 21D, 31D, and 41D that change the phase of light passing therethrough are provided in the arm waveguides 11B, 21B, 31B, and 41B of the optical waveguide, respectively. The phase control units 11D, 21D, 31D, and 41D realize phase adjustment by, for example, irradiating the arm waveguide with ultraviolet (UV) light. Each phase control unit has the same configuration as the conventional structure, such as a silica-based waveguide, a polymer waveguide, a SiN waveguide, and a SiON waveguide. In the case of the Si waveguide, as shown in FIGS. 2 to 4, a structure using a polymer material such as polysilane for the upper clad (FIG. 2), a structure inserted into a groove provided in the waveguide (FIG. 3), Alternatively, a slot waveguide structure (FIG. 4) is adopted.

Next, the operation of the optical waveguide according to the first embodiment will be described. Even if eccentricity (positional deviation) occurs in the direction perpendicular to the optical axis with respect to the mounting positions of the LDs 101 to 104, if light enters one of the cores of the two-core coupled waveguide, after propagation of L _c / Light having different phases propagates. Therefore, if the phase control unit provided in one of the arm waveguides controls the phase, the direction in which the light is output after passing through the subsequent coupling region is the output waveguide side connected to the optical multiplexing unit 6. be able to. The phase control operation will be described in detail with reference to FIGS. 5 to 7 are diagrams showing a two-core coupled waveguide that is a main part of the optical waveguide according to the first embodiment. As an example, input waveguides 11A and 12A, arm waveguides 11B and 12B, a phase control unit 11D, and output waveguides 11C and 12C, which are two-core coupled waveguides configured by cores 11 and 12, are shown.

First, as shown in FIG. 5, when the LD emitted light is incident on the left core 11 (input waveguide 11 </ _b > A) with respect to the propagation direction, after the L _c / 2 propagation, Light having a phase shift of π / 2 with respect to the waveguide propagation light is propagated. In this case, if the phase control unit 11D irradiates the UV light so that the phase shift amount becomes 0, the light can be emitted to the output waveguide 12C connected to the optical multiplexing unit 6. In addition, as shown in FIG. 6, when the LD emitted light is incident on the right core 12 (input waveguide 12A), after propagation through L _c / 2, in the left core 11 with respect to the right waveguide propagation light. Thus, the light having a phase shift of π / 2 is propagated. In this case, if the phase control unit 11D irradiates the UV light so that the phase shift amount becomes π, the light can be emitted to the output waveguide 12C side. Also, as shown in FIG. 7, when the LD emitted light is incident on the center of the left core 11 and the right core 12, light having the same phase propagates in the left and right waveguides after L _c / 2 propagation. It will be in the state. In this case, if the phase control unit 11D irradiates the UV light so that the phase shift amount is π / 2, the light can be emitted to the output waveguide 12C side.

  Next, specific operations of the phase control units 11D, 21D, 31D, and 41D will be described. In the case of a silica-based waveguide, since the refractive index of a normal core is increased by doping Ge, the refractive index is changed by UV light irradiation, and the irradiation intensity of the UV light and the length of the waveguide to be irradiated are changed. By changing the phase, the phase can be controlled. Similarly, in the case of a polymer waveguide, SiN waveguide, and SiON waveguide, phase control can be performed by changing the refractive index of the core by UV light irradiation. In the case of a Si waveguide, since the refractive index of Si does not change by UV light irradiation, a polymer material such as polysilane whose refractive index changes by UV irradiation is used for the upper cladding in the phase control unit (FIG. 2), or By inserting a polymer material into a groove provided in the waveguide (FIG. 3) or a slot waveguide structure (FIG. 4), the effective refractive index of the propagation mode can be changed. Phase control can be realized.

  The effect when this embodiment is applied will be described. FIG. 8 is a diagram illustrating the concept of dependence of coupling power on LD-waveguide eccentricity (positional deviation) when there is one conventional SM input waveguide. FIG. 9 is a diagram showing a conceptual diagram of the dependence of coupling power on the LD-waveguide eccentricity when this embodiment is applied. When this embodiment is applied, it is only necessary that light is incident on one of the two cores of the coupled waveguide, so that the positional tolerance of the LD can be increased. Specifically, the required position tolerance of about 1 μm can be relaxed to 2 μm, which is about twice as much (the two conventional coupling power curves are shifted side by side and overlapped). It becomes a characteristic like this). Further, unlike the inventions described in Patent Documents 1 and 2, the optical waveguide according to the present embodiment corrects the LD eccentricity (position shift) not by the submicron physical position but by the phase. Therefore, it is excellent in mass productivity. In addition, unlike the invention described in Patent Document 2, since no mechanical system is used, the cost is excellent. In addition, unlike the invention described in Non-Patent Document 1, the required position tolerance can be greatly relaxed to about twice, which is excellent in mass productivity. Further, unlike the invention described in Patent Document 3, since it is realized by arranging two SM waveguides on the input side of the LD emitted light, propagation of higher-order modes does not occur in principle.

As described above, the optical waveguide according to the present embodiment includes a Mach-Zehnder interferometer that is a two-core coupled waveguide having a semi-coupling length (L _c / 2), and includes a phase control unit that changes the phase of light passing therethrough. One of the two arm waveguides of the Mach-Zehnder interferometer is provided, and each waveguide operates in a single mode. Thereby, it becomes possible to increase the position tolerance of the LD with respect to the optical waveguide, and the correction of the positional deviation of the LD is performed by phase control, so that the mass productivity of the optical waveguide can be improved. Further, cost reduction and performance improvement can be realized.

Embodiment 2. FIG.
The optical waveguide according to the second embodiment will be described. The overall configuration of the optical waveguide of the present embodiment is the same as that of the first embodiment (see FIG. 1). The optical waveguide of the present embodiment is constituted by a silica-based waveguide, and each phase control unit changes the refractive index by irradiating a femtosecond laser.

  In other words, in the optical waveguide of the present embodiment, the phase control unit irradiates the arm waveguide with a femtosecond laser, thereby realizing an instantaneous high temperature and high pressure state to generate a pressure wave and increase the refractive index. Control the phase.

  The technique for changing the refractive index by irradiating a femtosecond laser is described in, for example, the document “K. Miura et al.,“ Photowritten optical waveguides in various glasses with ultrashort pulse laser, ”Appl. Phys. Lett. 71, 3329 (1997). "

  Thus, in the case of a silica-based waveguide, phase control can be realized by irradiation with a femtosecond laser, and the same effect as in the first embodiment can be obtained.

Embodiment 3 FIG.
The optical waveguide according to the third embodiment will be described. The overall configuration of the optical waveguide of the present embodiment is the same as that of the first embodiment (see FIG. 1). FIG. 10 is a diagram illustrating a configuration example of the two-core coupled waveguide according to the third embodiment. As an example, a two-core coupled waveguide including the cores 11 and 12 is illustrated.

  As illustrated, the phase control unit 11D according to the present embodiment includes a heater, and performs phase control by heating the arm waveguide 11B using the heater.

When the heater is used, the refractive index of the material can be changed by the thermo-optic effect, and as a result, the phase can be controlled. The thermo-optic coefficient of the material is, for example, 1 × 10 ⁻⁶ / ° C. in the case of silica-based waveguides using quartz, 18 × 10 ⁻⁶ / ° C. in the case of silicon waveguides, and polymer waveguides (fluorine polyimide). In this case, it is about −100 × 10 ⁻⁶ / ° C.

  Even when this embodiment is applied, the same effects as those of the first embodiment can be obtained.

Embodiment 4 FIG.
The optical waveguide according to the fourth embodiment will be described. The overall configuration of the optical waveguide of the present embodiment is the same as that of the first embodiment (see FIG. 1). FIG. 11 is a diagram illustrating a configuration example of a two-core coupled waveguide according to the fourth embodiment. As an example, a two-core coupled waveguide including cores 11 and 12 is illustrated.

  As illustrated, the phase control unit 11D of the present embodiment includes an electrode. For example, in the case of a Si waveguide, when the phase controller 11D applies an electric field to the arm waveguide 11B, the refractive index can be changed by the carrier plasma effect, and phase control is possible. In the case of a polymer waveguide, when the phase controller 11D applies an electric field, the refractive index can be changed by the electro-optic effect, and phase control becomes possible.

  Even when this embodiment is applied, the same effects as those of the first embodiment can be obtained.

  As described above, the optical module according to the present invention is useful as an optical waveguide configured with a core that transmits light in a single mode.

  5 Clad, 6 Optical multiplexing part, 11, 12, 21, 22, 31, 32, 41, 42 Core, 11A, 12A, 21A, 22A, 31A, 32A, 41A, 42A Input waveguide, 11B, 12B, 21B, 22B, 31B, 32B, 41B, 42B Arm waveguide, 11C, 12C, 21C, 22C, 31C, 32C, 41C, 42C Output waveguide, 11D, 21D, 31D, 41D Phase control unit, 101, 102, 103, 104 LD (Laser Diode).

Claims (9)

A Mach-Zehnder interferometer, which is constituted by a core that is a waveguide that transmits light in a single mode and a clad formed around the core, and that employs a two-core coupled waveguide structure with a semi-coupling length;
A phase control unit for controlling the phase of light passing through one of the two arm waveguides constituting the Mach-Zehnder interferometer;
An optical module comprising:   The optical module according to claim 1, wherein the phase control unit changes the phase of light by UV light irradiation. The waveguide is a silica-based waveguide, a polymer waveguide, a SiN waveguide or a SiON waveguide,
The optical module according to claim 2, wherein the phase control unit adjusts the phase by changing an irradiation intensity and an irradiation range of the UV light applied to the waveguide. The waveguide is a Si waveguide, and the cladding is made of a polymer material,
The optical module according to claim 2, wherein the phase control unit adjusts the phase by irradiating the clad with UV light. The waveguide is a waveguide having a structure in which a polymer material is inserted in the middle of the Si waveguide,
The optical module according to claim 2, wherein the phase control unit adjusts the phase by irradiating the polymer material with UV light. The waveguide is a slot-type waveguide having a structure in which a polymer material is inserted into the slot region,
The optical module according to claim 2, wherein the phase control unit adjusts the phase by irradiating the polymer material with UV light. The waveguide is a silica-based waveguide,
The optical module according to claim 2, wherein the phase control unit adjusts the phase by irradiating the waveguide with a femtosecond laser. The waveguide is made of a material whose refractive index changes due to heat,
The optical module according to claim 2, wherein the phase control unit adjusts the phase by heating the waveguide. The waveguide is made of a material whose refractive index changes when an electric field is applied,
The optical module according to claim 2, wherein the phase control unit adjusts the phase by applying an electric field to the waveguide.

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