JPS6148695B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention particularly relates to an optical coupling device that allows selective optical coupling between a thin film optical waveguide and an optical fiber.

In general, optical fibers, which can transmit light with high efficiency, are seen as promising optical communication networks in optical communication systems. It is necessary to have a functional function.

Conventionally, in the case of simple optical coupling, a method has been used to mechanically join optical fibers by polishing their joint points, but such coupling means do not have any active function. Without,
In order to provide an active function, in addition to the optical fiber as a transmission line, for example, as shown in Figure 1, a dedicated thin-film optical waveguide 1 that is functionalized using the electro-optic effect or the acousto-optic effect is required. This is connected between optical fibers 2 and 3 using an element, and the optical waveguide 1
The controller 4 controls the excitation by voltage or ultrasonic waves as appropriate.

However, when trying to actually apply such a thin film optical waveguide 1 to a communication network using optical fibers,
It is necessary to efficiently receive and receive optical signals between it and the optical fibers 2 and 3, but the coupling conditions between the two are very strict, and in reality, light reflection at the joint becomes a problem, and a certain amount of It is becoming difficult to obtain binding conditions. In addition, in particular, the film thickness of the thin film optical waveguide 1 is usually only about μm, and there are extremely strict requirements for the alignment of the thin film and optical fiber for optical coupling and the flatness of their joints, making it highly reliable. There is a problem in that it is actually very difficult to perform optical coupling. Recently, so-called optical ICs have been developed in which multiple active elements such as optical modulators or simply non-active elements are integrated on the same substrate. The problem of optical coupling between thin-film optical waveguides and optical fibers has become a major hindrance.

The present invention has been made in consideration of the above points, and
An optical coupling device that can easily perform efficient optical coupling between a thin-film optical waveguide and an optical fiber, and also allows the coupling part to be used as an active optical coupler with active functions. This is what we provide.

The optical coupling device according to the present invention includes, on a thin film optical waveguide formed on the surface of a substrate, an optical fiber whose side cladding is polished until its core is exposed, in contact with or in close proximity to the optical fiber;
An ultrasonic transducer is attached directly to the substrate, and one end of the optical fiber is used as one optical input path of the optical coupler, and the propagation constant of the input light wave is changed by the ultrasonic signal to selectively connect it to the external transmission path. This allows optical coupling to occur.

Hereinafter, one embodiment of the present invention will be described in detail with reference to the accompanying drawings.

The optical coupling device according to the present invention is shown in FIGS.
As shown in the figure, impurities such as Cu and Ti are thermally diffused in a line shape onto a substrate 5 made of a crystalline material such as LiNbO ₃ or LiTaO ₃ to form a thin film optical guide with a refractive index slightly larger than that of the substrate 5. forming a wave path 6;
On the optical waveguide 6, there is an optical fiber 7 whose side cladding is polished until the core is partly exposed (in some cases, even a part of the core is polished).
It consists of an interdigital (comb-shaped) electrode 8 that is placed in contact with (or very close to) at the polishing location, and that can excite ultrasonic waves onto the optical waveguide 6 and send surface acoustic waves W thereto. It is constructed by providing an ultrasonic transducer. The optical fiber 7 may be a single or multimode fiber, or a step-in-disk type or a graded-in-disk type fiber, depending on the purpose of optical transmission.

In the optical coupling device configured in this way, an optical signal is input from one end A of the optical fiber 7, and at the same time, the electrode 8 is excited to propagate ultrasonic waves in the optical waveguide 6 in the same direction as the incident light wave. let At this time, the propagation constant of light in the optical waveguide 6 is β ₁
Then, by propagating the ultrasonic wave through the optical waveguide 6, the propagation constant of the light changes to β ₁ ±mK (K is the propagation constant of the ultrasonic wave, m is an integer). Therefore, if the optical propagation constant β ₂ in another optical waveguide 9 (or optical fiber) adjacent to this optical coupling device is β ₂ =β ₁ +mK, the optical phase matching condition between the two is perfectly obtained. The optical signal input from one end A of the optical fiber 7 can be transferred from one end B of the optical waveguide 6 to another optical waveguide 9 (for example, a part where another element is incorporated as an optical IC) without being reflected or attenuated in any way. It will be transmitted to. In this case, two optical transmission lines 7,
Transition of light between the transmission lines 9 and 9 is carried out periodically from one transmission line 7 to the other transmission line 9 at a certain predetermined interval, and at this time, the coupling constant between both transmission lines is defined as C.
Then, the coupling length L for performing 100% transmission of the optical signal is given by L=C/2π.

Thus, the optical coupling device according to the invention
By changing the magnitude m of the ultrasonic output or changing the output frequency to change the propagation constant K, the optical signal input from one optical fiber is perfectly matched and transmitted to the other transmission path. In addition, the degree of optical coupling between the two can be arbitrarily adjusted as necessary.

FIG. 4 shows another embodiment of the present invention, in which the end face of the optical waveguide 6 on the substrate 5 is
An ultrasonic transducer 10 made of a ZnO thin film or a LiNbO ₃ crystal thin plate is attached, and the operation and effect of the optical coupling device constructed in this way are no different from those of the embodiments described above.

Furthermore, FIG. 5 shows an ultrasonic transducer 10 made of a ZnO thin film or a LiNbO ₃ crystal thin plate on one end surface of an optical fiber 7 provided on an optical waveguide 6 formed on a substrate 5 by the same means as described above. Install the
It is configured so that ultrasonic waves are propagated through the optical fiber 7. In this case, the optical fiber 7
The light incident from the other end D is appropriately phase modulated by the ultrasonic wave sent from one end, and is sent to the other transmission line (not shown) via the optical waveguide 6, but the phase matching conditions If β ₃ is the propagation constant of light in the optical fiber 7 through which the ultrasonic wave is propagated, then it is given by β ₂ =β ₃ +mK as described above.

As described above, in the optical coupling device according to the present invention, the optical fiber is polished and cut by polishing the side cladding on the optical waveguide formed on the surface of the substrate of the thin film optical waveguide until a part of the core is exposed. In addition to contacting or being placed very close to each other at certain points,
An ultrasonic transducer is installed in the optical fiber or optical waveguide at the joint so that an ultrasonic signal can be sent in the propagation direction of the light incident from one end of the optical fiber. The optical waveguide can be connected to other transmission lines connected to one end of the optical waveguide by simply controlling the ultrasonic signal and arbitrarily changing the optical propagation constant without requiring high alignment at each joint. It has the advantage that optical coupling can be performed selectively and with high precision, and that it can be used as an optical coupler with a single active function and excellent coupling efficiency due to its simple structure.

[Brief explanation of the drawing]

FIG. 1 is a simplified configuration diagram showing an optical coupling device using a conventional thin film optical waveguide, FIG. 2 is a perspective view showing a schematic configuration of an optical coupling device according to an embodiment of the present invention, and FIG. 3 is a front cross section thereof. 4 and 5 are front sectional views showing other embodiments of the present invention, respectively. DESCRIPTION OF SYMBOLS 1, 6... Thin film optical waveguide, 2, 3, 7... Optical fiber, 4... Control device, 5... Substrate, 8... Electrode, 9... Other transmission path, 10... Ultrasonic transducer.

Claims (1)

[Claims] 1. On an optical waveguide formed on the surface of a substrate, an optical fiber whose side cladding is polished until its core is exposed is placed in contact with or very close to it at the polished location, and the optical fiber at the bonding location is An ultrasonic transducer is provided in the section or optical waveguide section so as to be able to send an ultrasonic signal in the propagation direction of the light incident from one end of the optical fiber, and the ultrasonic transducer is provided to control the ultrasonic signal to propagate the incident light. An optical coupling device characterized in that a constant is arbitrarily changed to achieve optical coupling with a transmission line on an output side.