JP2532484B2 - Method and apparatus for assembling hybrid optical integrated circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a hybrid optical system of a type in which a semiconductor optical device such as an optical gate device, a semiconductor laser, an optical modulation device, and an optical waveguide are combined and integrated on the same substrate. The present invention relates to a method of assembling an integrated circuit.

<Prior Art> In various optical circuits required in the fields of optical communication and optical information processing, an optical waveguide and various optical elements are combined and integrated on the same substrate for downsizing, high reliability, and cost reduction. Realization of a hybrid optical integrated circuit is expected.

In order to realize a hybrid optical integrated circuit, it is indispensable to align the optical element of the optical waveguide on the same substrate and optically couple as efficiently as possible.

The most common method for aligning an optical waveguide with a semiconductor optical device such as a semiconductor laser is a light emitting method for finding an optimum position by causing the semiconductor optical device to emit light and monitoring the optical output of the optical waveguide. However, since a semiconductor laser or the like cannot emit light under a high temperature environment, this method cannot be applied to the element fixing step that requires raising the temperature.

Therefore, there is a method of using a semiconductor optical device to be mounted as a photodetector (photodetector) as a method for position monitoring even in a high temperature environment (Yoshino et al., IEICE Tech.
-26). This photodetector method uses a light source with an oscillation wavelength in the wavelength region where the active layer of the semiconductor optical device absorbs light, excites the optical waveguide with the output light of this light source, and generates the photocurrent generated by the semiconductor optical device. Monitor and align to maximize photocurrent.

<Problems to be Solved by the Invention> However, in the latter method of using a semiconductor optical device as a photodetector, compared with the former method of emitting light from the semiconductor optical device, the change in the photocurrent with respect to the positional deviation is the characteristic of FIG. Since it has a relatively broad peak as shown by the curve A, it is difficult to determine the optimum position. When the semiconductor laser 11 and the optical waveguide 12 are arranged as shown in FIG. 7, the characteristic curve A in FIG. 6 shows the relationship between the positional deviation amount X between them and the photocurrent of the semiconductor laser 11 used as the photodetector. As shown, the positional deviation at which the photocurrent is reduced by 20% (1 dB) is ± 2 μm. On the other hand, the characteristic curve B in FIG. 6 shows the semiconductor laser 11 when the semiconductor laser 11 is made to emit light.
Shows the optical coupling efficiency between the and optical waveguide 12, and the optical coupling efficiency is 20%
The amount of positional deviation that decreases is ± 1 μm.

Further, in the method of using the semiconductor optical device as a photodetector, wire bonding is required in advance to the semiconductor optical device or the optical circuit board so that the electrodes of the semiconductor optical device can be taken out in order to perform the alignment. There is a problem that the assembly process of the optical integrated circuit becomes complicated.

It is an object of the present invention to provide a method for assembling a hybrid optical integrated circuit, which solves the above-mentioned problems of the prior art.

<Means for Solving the Problems> A method for assembling a hybrid optical integrated circuit according to the present invention is
A semiconductor optical device having an operating wavelength in a wavelength range in which a current is absorbed when a current is not applied and is transmitted when a current is applied in a gap for mounting an optical device provided in the middle of an optical waveguide formed on a substrate. At the time of mounting, as the monitor light, different from the operating wavelength of the semiconductor optical element, light in the wavelength range that is transmitted through the semiconductor optical element even when no current is flowing is used, and the monitor light is passed through the optical waveguide to Inputting to a semiconductor optical element, monitoring the output light from the optical waveguide that has passed through the semiconductor optical element, and aligning and fixing the semiconductor optical element at a position where the intensity of the output light of the optical waveguide is maximum. Is characterized by.

<Operation> In the conventional photodetector method, a semiconductor light device is operated as a photodetector by using a light source that outputs light in a wavelength region absorbed in the active layer of the semiconductor photodevice, whereas in the present invention, the semiconductor photodevice is operated. Since it is used as an optical monitor light in a wavelength range that becomes transparent even when no current flows, the semiconductor optical element operates as an optical waveguide. Therefore, the monitor light propagates in the order of the optical waveguide → semiconductor optical element → optical waveguide, and the optical coupling efficiency can be directly monitored, and the alignment accuracy is improved.

<Example> An example of the present invention will be described below with reference to FIGS. 1 to 5.

FIG. 1 shows a structural example of an assembling apparatus used for carrying out the method of the present invention. The assembling apparatus includes a sample stage 1 and a manipulator 2.
The light input means 3, the light output means 4, the light source 5 for outputting the monitor light, the light receiving section 6, and the control means 9 are the basic constituent elements.

The manipulator 2 includes an XY fine movement part 2D, a vertical (Z) fine movement part 2C provided on the XY fine movement part 2D, an arm 2B provided on the vertical fine movement part 2C, and a rotation angle (θ) fine movement part provided on the arm 2B. 2E and a chuck 2A for holding the semiconductor optical element 8 provided in the rotational angle fine movement unit 2E are main components, and the operation is controlled by the control means 9.

The semiconductor optical device 8 has an operating wavelength in a wavelength region in which it is absorbed in a state where no current is passed and is transmitted in a state where a current is passed.

The optical input means 3 is composed of a fiber holding base 3A and an input optical fiber 3B held by the fiber holding base 3A, and is installed near the sample base 1. The input end of the optical fiber 3B is optically coupled to the light source 5, and the output end is optically coupled to the optical waveguide 71 of the optical circuit board 7.

The light output means 4 comprises a fiber holding table 4A and an output optical fiber 4B held by the fiber holding table 4A, and is installed near the sample table 1. The input end of the optical fiber 4B is optically coupled to the optical waveguide 72 of the optical circuit board 7, and the output end thereof is optically coupled to the light receiving portion 6. The optical waveguides 71, 72 mount the semiconductor optical element 8 in the gap between them and optically couple them.

The light receiving section 6 gives a detection signal to the control means 9 via the connecting cable 10A, and the control means 9 gives a control signal to the manipulator 2 via the connecting cable 10B. The control means 9 is composed of a computer.

Unlike the operating wavelength of the semiconductor optical element 8, the light source 5 has an oscillating wavelength in a wavelength range that allows the semiconductor optical element 8 to pass through even when no current is flowing.
It is in the wavelength region longer than the operating wavelength of the semiconductor optical device 8 and also in the wavelength region shorter than the cutoff wavelength for the semiconductor optical device 8 to function as an optical waveguide.

 Next, the operation will be described.

The monitor light from the light source 5 is input to the optical waveguide 71 by the optical fiber 3B. This monitor light is guided through the active layer of the semiconductor optical device 8 placed on the substrate 7 while being held by the chuck 2A of the manipulator 2, and then propagated to the optical fiber 4B via the optical waveguide 72 and output. To do. This output light is received by the light receiving unit 6 and converted into an electric signal. This electric signal is transmitted to the control computer 9, and the computer 9 feeds back to the manipulator 2 the positions of X, Y and θ based on the electric signal from the light receiving unit 6,
The semiconductor optical element 8 is arranged at a position where the intensity of the output light from the optical waveguide 72 received by the light receiving section 6 is maximized. In this state, the position of the semiconductor optical device 8 is fixed by an appropriate means.

Next, as a specific example, the method of the present invention will be described in detail by taking as an example a case where an optical gate element which is a semiconductor optical element is mounted in an optical switch circuit.

FIG. 2 is an explanatory view of an optical switch circuit on which an optical gate element is mounted, FIG. 3 is a sectional view showing a structure of an optical waveguide, and FIG. 4 is a sectional view showing a structure near an active layer of the optical gate element.

In these figures, 7 is an optical circuit board made of a Si substrate, and 71 and 72 are quartz optical waveguides. Optical waveguide 71,72
Is composed of a core layer 72A, a clad layer 72B, and a buffer layer 72C. 73 is an electrode pattern, 8 is an optical gate element, 8A is its active layer, and 81 is a heat sink.

The optical gate element 8 is an optical waveguide formed on the optical circuit board 7.
It is mounted on the electrode pattern 73 between 71 and 72 in an upside down state with the active layer 8A facing downward. At this time, as shown in FIG. 3, the height from the bottom surface of the optical waveguide to the center of the core layer 72A and the height of the active layer 8A when the optical gate element 8 is mounted on the electrode pattern 73 are both made equal to l ₁ . Set it.

In the optical gate device 8 as shown in the structure of FIG.
The structure is such that light is confined across the three active layers 8A, the n-InGaAsP layer and the p-InGaAsP layer of the system. Therefore, these three layers as a whole function as the core layer 82 of the optical gate element.

Now, it is assumed that the optical gate element 8 operates in the wavelength band of 1.32 μm. That is, when no current is injected, the absorption edge of this optical gate element 8 is 1.32 μm. Also, by injecting a current, the absorption edge shifts to the short wavelength side, and the current value immediately before the oscillation threshold becomes 1.28 μm. Therefore,
When light of 1.30 μm is incident on the optical gate element 8, it is absorbed in a state where no current is passed (current off), but is transmitted in a state where current is passed (current off).

In the case of having the absorption edge as described above, when a semiconductor laser of 1.5 μm oscillation on the long wavelength side different from the operating wavelength of 1.30 μm of the optical gate element 8 is used as the light source 5, the optical gate element 8 is in a current off state. However, it becomes transparent to the monitor light. The monitor light of 1 h 5 μm is on the shorter wavelength side than the cutoff wavelength for the optical gate element 8 to function as an optical waveguide. Therefore, if the optical waveguides 71 and 72 and the optical gate element 8 are aligned with each other, 1.5 μm incident on the optical waveguide 71 is detected.
The monitoring light of 1) regards the optical gate element 8 simply as an optical waveguide, and propagates through the core layer 82 centering on the active layer 8A. This light is again coupled to the optical waveguide 72 and propagates.

Therefore, in FIG. 1, if a light source that oscillates at a wavelength of 1.5 μm is used as the light source 5, that is, if a monitor light of 1.5 μm is used, a position for mounting the optical gate element 8 on the optical switch circuit board 7 in FIG. Can be matched.

FIG. 5 shows the relationship between the optical waveguide output light intensity and the positional deviation in the configuration of the optical waveguide 71 → the optical gate element 8 → the optical waveguide 72 when the alignment is performed by the method described above.

From FIG. 5, the amount of positional deviation at which the output light intensity of the optical waveguide is reduced by 20% (IdB) is ± 1 μm.

This is about the same as the alignment accuracy in the method of emitting a semiconductor laser as shown by the characteristic curve B in FIG. 6, and it can be seen that the alignment can be achieved with higher accuracy than the method used as the photodetector.

In this case, since the monitor light having the wavelength that passes through the semiconductor element is used even when the current is not supplied, the output light intensity can be monitored in the state where the temperature is increased. Therefore, the semiconductor optical device 8
The semiconductor optical device 8 can be held at the optimum position while being fed back by using the assembling apparatus shown in FIG. 1 until the semiconductor device is fixed on the substrate 7, and a highly accurate hybrid optical integrated circuit is realized.

Further, since the monitor light having the wavelength that passes through the semiconductor optical element is used even when the current is not applied, it is not necessary to take out an electrode as in the conventional case where the semiconductor optical element is used as a photodetector.

<Effects of the Invention> According to the present invention, the optical coupling efficiency with the optical waveguide is directly monitored by guiding the monitor light in the wavelength region in which the semiconductor element is transparent even when no current flows, to the semiconductor optical element. Therefore, highly accurate alignment is possible. This can also be done by raising the temperature.

Moreover, since it is not necessary to take out the electrodes of the semiconductor optical device,
The complexity of hybrid integration can be reduced.

As described above, the present invention is extremely useful for manufacturing a hybrid optical integrated circuit such as an optical switch circuit in which a semiconductor optical device is mounted in a gap in the middle of an optical waveguide on an optical circuit board.

[Brief description of drawings]

FIG. 1 is a block diagram showing an example of an assembling apparatus used for carrying out the method of the present invention, FIG. 2 is an explanatory view of an optical switch circuit, FIG. 3 is a sectional view of an optical waveguide, and FIG. 4 is an optical gate element. FIG. 5 is a cross-sectional view near the active layer, FIG. 5 is a graph showing the alignment accuracy of the present invention, FIG. 6 is a graph showing the conventional alignment accuracy, and FIG. 7 is a schematic explanatory view of the conventional method. In the figure, 1 is a sample stage, 2 is a manipulator, 3 is light input means, 4 is light output means, 5 is a light source, 6 is a light receiving part, 7 is a substrate, 71 and 72 are optical waveguides, 8 is a semiconductor element, 8A is an active layer, 82 is a core layer, and 9 is a control computer.

Claims (2)

(57) [Claims] 1. An operating wavelength is set in a wavelength range in which a current is absorbed in a gap for mounting an optical element, which is provided in the middle of an optical waveguide formed on a substrate, and which is absorbed when a current is passed. When manufacturing a hybrid optical integrated circuit in which the semiconductor optical device having the semiconductor optical device is mounted, as a monitor light, a light in a wavelength range which is different from the operating wavelength of the semiconductor optical device and is transmitted through the semiconductor optical device even when no current is applied. The position where the intensity of the output light of the optical waveguide becomes maximum by inputting the monitor light to the semiconductor optical device via the optical waveguide and monitoring the output light from the optical waveguide via the semiconductor optical device. The method for assembling a hybrid optical integrated circuit, further comprising: aligning and fixing the semiconductor optical device. 2. The monitor light is in a wavelength region longer than the operating wavelength of the semiconductor optical device, and a wavelength shorter than a cutoff wavelength for the semiconductor optical device to function as an optical waveguide. The hybrid optical integrated circuit assembling method according to claim 1, wherein the hybrid optical integrated circuit is in the area.