JP2014199356A - Optical modulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical modulator in which a phase difference between signal light and monitor light of the optical modulator can be compensated and light-receiving sensitivity of a light-receiving element can be improved.SOLUTION: The optical modulator includes a substrate having an electro-optic effect, an optical waveguide including a Mach-Zehnder type optical waveguide formed on the substrate, a modulation electrode for modulating light waves propagating in the optical waveguide, and a waveguide for radiation light for guiding radiation light to either side of a waveguide for signal light which guides signal light from a multiplexing part of the Mach-Zehnder optical waveguide. The radiation light exiting from the waveguide for radiation light is guided to a single light-receiving element by use of different condensing means disposed in an exit part of the waveguide for radiation light.

Description

  The present invention relates to an optical modulator, and more particularly, to an optical modulator having a configuration in which radiated light from a Mach-Zehnder type optical waveguide is detected by a light receiving element.

  In the optical communication field and the optical measurement field, an optical modulator such as an intensity modulator having a Mach-Zehnder type optical waveguide is frequently used. In recent years, a polarization multiplexing optical modulator in which a plurality of Mach-Zehnder optical waveguides are formed on the same substrate has been proposed.

  In order to grasp the state of light modulation in each Mach-Zehnder type optical waveguide, radiation light emitted from a multiplexing part where two branching waveguides constituting the Mach-Zehnder type optical waveguide are combined is detected.

  FIG. 1 shows an optical modulator provided with two Mach-Zehnder type optical waveguides (which emit Xch and Ych signal light). Each Mach-Zehnder type optical waveguide is provided with a radiated light waveguide on both sides of the signal light waveguide, a light receiving element (PD) is disposed on one of the radiated light waveguides, and an evanescent wave is transmitted. It is configured to receive light.

  When a light receiving element (PD) is mounted on a lithium niobate (LN) substrate constituting an optical modulator, an arrangement space is required, and the substrate becomes large. Therefore, when a plurality of Mach-Zehnder type optical waveguides are formed, for example, as shown in FIG. 1, there is no space, so that there is no space, so that interference between the two radiated lights related to Xch and Ych is avoided. A light receiving element is arranged so as to monitor only the guided light emitted to the light.

  As shown in Patent Document 1, normally, the intensity of the radiated light to be monitored changes in the opposite phase to the signal light when only the off light is used, and the electric field amplitudes of the two radiated lights are opposite to each other. It becomes a state. However, if part of the light that causes conversion loss in the signal light (the same state as the signal light (on light)) is mixed with the emitted light, the light intensities of the two emitted lights are shifted in opposite directions to produce a phase difference. It will be. For this reason, when only one radiated light is detected as in the above configuration, a phase difference from the signal light occurs.

  Further, the light receiving element disposed on the substrate has a problem that the coupling efficiency between the emitted light and the light receiving element is low and the sensitivity is low in order to receive the emitted light.

Japanese Patent No. 4777789

  The problem to be solved by the present invention is to solve the problems described above, compensate for the phase difference between the signal light of the optical modulator and the monitor light, and improve the light receiving sensitivity of the light receiving element. Is to provide a vessel.

In order to solve the above problems, the optical modulator of the present invention has the following technical features.
(1) A substrate having an electro-optic effect, an optical waveguide including a Mach-Zehnder type optical waveguide formed on the substrate, a modulation electrode for modulating a light wave propagating through the optical waveguide, and the Mach-Zehnder type optical waveguide Radiation emitted from the radiated light waveguide in the optical modulator having the radiated light waveguide for guiding the radiated light on both sides of the signal light waveguide that guides the signal light from the combining portion The light is guided to one light receiving element by using different condensing means arranged at the emission part of the radiation waveguide.

(2) In the optical modulator according to (1), the condensing unit guides the emitted light to the light receiving element by adjusting an incident position or an incident angle of the emitted light.

(3) In the optical modulator according to the above (1) or (2), by adjusting the bending of the radiated light waveguide or the angle at the emission part of the radiated light waveguide, The incident position or the incident angle is adjusted, and the radiated light is guided to the light receiving element.

(4) In the optical modulator according to any one of (1) to (3), the traveling directions of the radiated light emitted from the different condensing means are substantially parallel to each other. .

(5) In the optical modulator described in any one of (1) to (4) above, the different condensing means is configured by an integrated lens in which a plurality of lenses are integrated. .

(6) In the optical modulator according to any one of (1) to (5), the optical waveguide includes a plurality of Mach-Zehnder optical waveguides, and is a Mach-Zehnder type that is a target that receives at least emitted light. One light receiving element is provided corresponding to the optical waveguide, and the different light condensing means is constituted by one integrated lens in which a plurality of lenses are integrated.

  According to the present invention, a substrate having an electrooptic effect, an optical waveguide including a Mach-Zehnder optical waveguide formed on the substrate, a modulation electrode for modulating a light wave propagating through the optical waveguide, and the Mach-Zehnder optical waveguide In an optical modulator having a radiated light waveguide for guiding radiated light on both sides of a signal light waveguide that guides signal light from a multiplexing portion of the waveguide, the light is emitted from the radiated light waveguide. Since the configuration is such that the radiated light is guided to one light receiving element by using different condensing means arranged in the emission part of the radiated light waveguide, two radiated lights are simultaneously incident on the light receiving element. Thus, since the radiated light detected by the light receiving element and the signal light are in a reverse phase state having no phase difference, more accurate monitoring can be performed. Moreover, since the two radiated lights are reliably incident on one light receiving element by a condensing means such as a lens, the light receiving sensitivity of the light receiving element can be improved.

It is a figure explaining the conventional optical modulator. It is a figure explaining the Example of the optical modulator of this invention. It is a figure explaining the other Example of the optical modulator of this invention.

Hereinafter, the present invention will be described in detail using preferred examples.
FIG. 2 shows an embodiment of the optical modulator of the present invention.
The present invention relates to a substrate having an electro-optic effect, an optical waveguide including a Mach-Zehnder type optical waveguide formed on the substrate, a modulation electrode for modulating a light wave propagating through the optical waveguide, and the Mach-Zehnder type optical waveguide In an optical modulator having a radiated light waveguide for guiding radiated light on both sides of a signal light waveguide that guides signal light from a multiplexing portion of the waveguide, the light is emitted from the radiated light waveguide. The radiated light is guided to one light receiving element by using different condensing means arranged at the emission part of the radiated light waveguide.

  As the substrate having an electro-optic effect, for example, a single crystal material such as lithium niobate, lithium tantalate, PLZT (lead lanthanum zirconate titanate), or a solid solution crystal material thereof can be used. Semiconductors and polymers can also be used as substrates having an electro-optic effect.

The optical waveguide can be formed, for example, by injecting or thermally diffusing a high refractive index material such as titanium into the substrate. It is also possible to form a ridge type or rib type optical waveguide by forming irregularities on the substrate. Although not shown in FIG. 2, in order to perform optical modulation, a modulation electrode (signal electrode and ground electrode) is formed in the vicinity of the optical waveguide. Further, when an electrode is formed immediately above the optical waveguide as in the case of using a Z-cut substrate, silicon oxide (SiO ₂ ) or the like is used to suppress absorption of the light wave propagating through the optical waveguide into the electrode layer. A buffer layer is formed on the optical waveguide or on the substrate.

  As shown in FIG. 2, in the optical modulator of the present invention, the radiated light waveguide extending from the multiplexing portion of the Mach-Zehnder type optical waveguide reaches the end of the LN substrate. Condensing means such as a lens is disposed at the end of the substrate, and a plurality of these are disposed corresponding to each of the radiation waveguides.

  The condensing means (lens) can appropriately guide the radiated light to the light receiving element (PD) by adjusting the incident position and the incident angle of the radiated light emitted from the radiated light waveguide and entering the condensing means. Is possible. Naturally, the condensing means also plays a role of adjusting so that the beam of signal light (Xch / Ych) comes to a predetermined position.

  As shown in FIG. 3, the method of adjusting the incident position or the incident angle to the condensing means is to adjust the bending of the radiated light waveguide, or the angle at the emission part of the radiated light waveguide. It is also possible to do. In particular, when a plurality of signal light and radiated light are emitted from the same end surface of the substrate, all the waveguides are parallel to each other in the vicinity of the substrate end surface in order to maintain a predetermined angle between all the waveguides and the substrate end surface. By doing so, the manufacturing process can be facilitated.

  In particular, it is preferable that the traveling directions of radiated light emitted from different condensing means are substantially parallel to each other as shown in FIG. This is to make it possible to easily adjust the light intensities of the two radiated lights incident on one light receiving element (PD) by adjusting the position of the condensing means or the light receiving element. In order to obtain a reverse phase state with respect to the signal light, it is necessary to make the light intensities of the two radiation lights to be detected the same.

  As shown in FIG. 2, the condensing means preferably uses an integrated lens in which a plurality of lenses are integrated. For example, by integrating four lenses into a four-unit type, it is possible to save time and effort for adjusting individual lenses, and to quickly and easily adjust the positions and angles of the lenses and light receiving elements.

  The optical modulator of the present invention can be suitably applied to one having a plurality of Mach-Zehnder type optical waveguides. FIG. 2 shows an example in which two Mach-Zehnder type optical waveguides are arranged in parallel, but even in the case of two or more, one by one corresponding to the Mach-Zehnder type optical waveguides that receive radiation light. By providing a light receiving element and different condensing means are constituted by one integrated lens in which a plurality of lenses are integrated, it is possible to efficiently introduce radiated light necessary for the light receiving element.

  The mounting position of the light receiving element (PD) is arranged on the outside (output side) of the LN substrate chip, and two radiated lights are simultaneously received using different condensing means, thereby improving the light receiving sensitivity of the light receiving element. Is possible. As a result, a general-purpose product can be used for the light receiving element, thereby reducing the cost.

  As described above, according to the optical modulator of the present invention, it is possible to compensate for the phase difference between the signal light of the optical modulator and the monitor light, and provide an optical modulator capable of improving the light receiving sensitivity of the light receiving element. It becomes possible to do.

Claims (6)

A substrate having an electro-optic effect;
An optical waveguide including a Mach-Zehnder type optical waveguide formed on the substrate;
A modulation electrode for modulating a light wave propagating through the optical waveguide;
In the optical modulator having a radiated light waveguide for guiding the radiated light on both sides of the signal light waveguide that guides the signal light from the multiplexing portion of the Mach-Zehnder optical waveguide,
An optical modulator characterized in that radiated light emitted from the radiated light waveguide is guided to one light receiving element by using different condensing means arranged at an output portion of the radiated light waveguide. The optical modulator according to claim 1.
The light condensing means guides the radiated light to the light receiving element by adjusting an incident position or an incident angle of the radiated light. The optical modulator according to claim 1 or 2,
By adjusting the bending of the radiated light waveguide or the angle at the emission part of the radiated light waveguide, the incident position or the incident angle to the light collecting means is adjusted, and the radiated light is guided to the light receiving element. An optical modulator characterized by. The optical modulator according to any one of claims 1 to 3,
An optical modulator characterized in that traveling directions of radiated light emitted from the different condensing means are substantially parallel to each other. The optical modulator according to any one of claims 1 to 4,
The different light condensing means is constituted by an integral lens in which a plurality of lenses are integrated. The optical modulator according to any one of claims 1 to 5,
The optical waveguide has a plurality of Mach-Zehnder optical waveguides,
At least one light-receiving element is provided corresponding to the Mach-Zehnder type optical waveguide that is the object to receive the radiated light,
The different light condensing means is constituted by a single integrated lens in which a plurality of lenses are integrated.

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