JPS6159421A - Optical modulator with isolator - Google Patents

Abstract

PURPOSE:To obtain a small-sized optical modulated with an isolator which facilitates optical axis adjustment by providing a light guide for light incidence, light guide for optical transmission parallel to it, crossing light guide which crosses them, and branching light guide on the surface of a substrate. CONSTITUTION:The planar type light guide including the light guide 6 for light incidence coupled with a laser diode 1, light guide 7 for optical transmission which is arranged in parallel to it and coupled optically with an optical fiber 2 for transmission, crossing light guide 8 which crosses those light guides 6 and 7, and branching light guide 9 which branches from the light guide 7 for optical transmissioni near the coupling terminal with the light guide 2 is formed on a substrate of a dielectric or semiconductor material. Those light guides 6, 7, 8, and 9 constitute the isolator 5B. Electrodes 10 and 11 for optical modulation are formed near the coupling terminal of the light guide 6 for light incidence with the laser diode 1.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical transmitter, and particularly to an optical modulator with an isolator that has both the functions of an optical modulator and an isolator.

[Conventional technology]

An example of the configuration of a conventional optical transmitter is shown in FIG. 2 of the accompanying drawings. In the figure, numeral 1 indicates a semiconductor laser diode (LD) as a light source, and numeral 2 indicates an optical fiber for transmission.

In a conventional optical transmitter, the current flowing through the laser diode 1 is directly modulated. Further, an isolator 3 made of a material such as YIG is interposed between the light source and a condensing lens 4 on the optical fiber side to block the return light from the optical fiber 2.

[Problem that the invention seeks to solve]

A conventional configuration in which a laser diode is directly modulated has the disadvantage that the oscillation spectrum of the laser diode is broadened and that it is easily influenced by reflected and returned light, resulting in noise. Furthermore,
Direct modulation of several GHz or higher is difficult for radar diodes. Also, when using individual component isolators,
There are problems in that the structure is large and optical axis adjustment is complicated.

[Means for solving problems]

In order to solve the above-mentioned problems, the present invention provides a linear light guide for light introduction that is optically coupled to a light source on the surface of a dielectric or semiconductor substrate, and a straight light guide for light introduction that is arranged parallel to the light guide and that transmits light. a straight light transmission light guide optically coupled to the light transmission optical fiber; a straight cross light guide that intersects both the light introduction and light transmission light guides; ml branched near the bonding end with
The present invention provides an optical modulator with an isolator having a structure in which a planar light guide including a branch light guide of 1 is formed, and a light modulation electrode is formed in the vicinity of the coupling end with the light source of the light introduction light guide. It is.

[Effect]

In the optical modulator with isolator of the present invention, the optical modulator and the isolator are formed on one common substrate. That is, an optical modulator is constituted by the light guide for introducing light and the electrode for light modulation, and a light modulation function is obtained by modulating the current applied to the electrode. On the other hand, an isolator is constituted by a light guide for introducing light, a guide for transmitting light, a crossing light guide, and a branching light guide.

In addition, the TE polarized wave emitted from the laser diode repeatedly bends at the intersection of the light ids and is guided to the optical fiber, and conversely, the TE polarized wave of the reflected return light from the optical fiber and the
The M polarized waves are respectively annihilated by bending at the branching part of the light guide and going straight at the crossing part.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a schematic configuration diagram of an embodiment of an optical transmitter according to the present invention, in which reference numeral 1 indicates a semiconductor laser diode as a light source;
Reference numeral 2 indicates an optical fiber, and reference numeral 5 indicates an optical modulator with an isolator. The optical modulator 5 with an isolator is made of, for example, lithium niobate (LiNbO3) or quartz (Si0
2), planar light guides (hereinafter simply referred to as "light guides") 6, 7, 8.
9 and a pair of electrodes 10.11 to form the optical modulator 5A.
and isolator 5B are configured together. Incidentally, when the substrate is LiNbO3, the above-mentioned light guide is formed by thermally diffusing metal titanium (Ti) onto the surface of the substrate.

Now, the above-mentioned light guides 6#7F8#9 are all straight lines. The light guide 6 is for introducing light to be optically coupled to the radar diode 1, and the light guide 7 is for introducing the light to be optically coupled to the radar diode 1.
These light guides 6.7 are parallel to each other. The light guide 8 intersects with these light guides 6°7 at points P, , P, respectively, and the light guide 9 intersects with the light guide 7 for light transmission at points P, near the coupling end with the optical fiber 2. It's branching out. These light guides 6t7*8e9 constitute a shear isolator 5B.

On the other hand, electrodes 10.11 are formed near the coupling end of the light guide 6 for light introduction with the laser diode 1 so as to face each other with the light guide 6 in between, and constitute the optical modulator 5A.

According to the above configuration, the light emitted from the laser diode 1 is introduced into the light guide 6 from its end face. By applying a voltage between the electrodes 10 and 11 of the optical modulator 5A, the refractive index of the light guide 6 changes, and the light becomes 0N1.
0FF is made. Therefore, since it is sufficient to apply direct current to the laser diode 1, a stable oscillation spectrum can be obtained.The light emitted from the laser diode 1 is introduced into the isolator 5B, but the light emitted from the laser diode 1 is TE polarized (with a field in the horizontal direction). Therefore, by selecting the conditions for creating the light guide 7 as shown by the solid arrow TE in the figure, it is possible to repeat the bending at the intersection P1 * P@ of the light guide 6.7.8. It can be guided to fiber 2. Conversely, the reflected return light from the optical fiber 2 includes both TE and TM polarization, but the TE polarization bends and disappears at the branch point P3 of the optical guide 7.9, as shown by the dotted arrow TE in the figure. , and the 7M polarization is at the intersection P of the optical guide 7.8, as shown by the six-dot chain arrow TM in the figure.

Go straight and disappear. This makes it possible to completely eliminate the reflected return p'' light from the optical fiber 2 from entering the laser diode 1.

Note that the same effect can be obtained even when the branching light guide 9 is oriented in the opposite direction as shown by the imaginary line 9a.

〔Effect of the invention〕

The optical regulator with an isolator of the present invention is capable of obtaining a noise-free optical signal with a stable spectrum, and is also capable of optical modulation of several GHz or higher. In addition, Con A, which is composed of a planar light guide? The optical transmitter is easy to assemble because there are few points for optical axis adjustment between the light source and the optical fiber, and the optical transmitter can be made smaller.

[Brief explanation of drawings]

FIG. 1 is a schematic block diagram of an embodiment of an optical transmitter according to the present invention, and FIG. 2 is a schematic block diagram of an example of a conventional optical transmitter. 1... Light source (semiconductor laser diode), 2... Optical fiber, 5... Optical modulator with isolator, 5A.
... Optical modulator, 5B... Isolator, 6t7t8t
9... Planar light guide, 10.11... Electrode. 1st w

Claims (1)

[Claims] 1. On the surface of a dielectric or semiconductor substrate, a straight light guide for introducing light is optically coupled to a light source, and a straight light guide is arranged parallel to the light guide for introducing light and is optically coupled to a transmission optical fiber. A light guide for transmitting light, a straight intersecting light guide that intersects both the light guides for introducing light and transmitting light, and branching from the light guide for transmitting light at a position near the coupling end of the optical fiber. 1. An optical modulator with an isolator, characterized in that a planar light guide including a linear branched light guide is formed, and a light modulation electrode is formed near a coupling end of the light guide for light introduction with a light source.