KR20040085954A - Optical electronic integrated circuit - Google Patents

Abstract

PURPOSE: An optical electronic integrated circuit is provided to easily perform the optical alignment with the optical detector by making the planar optical waveguide device have a predetermined slope at one end thereof. CONSTITUTION: An optical electronic integrated circuit includes a semiconductor substrate(210), an optical detector(220), a planar optical waveguide device(240) and a refractive index junction layer(230). The semiconductor substrate(210) supports each elements to form the optical electronic integrated circuit. The optical detector(220) is provided with an active layer and formed on the semiconductor substrate(210). The planar optical waveguide device(240) is formed on the semiconductor substrate(210) with inclining at a predetermined angle with respect to the active layer in such a way that the light outputted from the output terminal is impinged on the bottom surface of the active layer through the reception surface of the optical detector(220). And, the refractive index junction layer(230) is coated to covers the output terminal of the planar optical waveguide device and the reception surface of the optical detector(220) to improve optical coupling efficiency between the planar optical waveguide device and optical detector.

Description

Photoelectric Integrated Circuits {OPTICAL ELECTRONIC INTEGRATED CIRCUIT}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optoelectronic integrated circuit formed on a semiconductor substrate, and more particularly, to a structure of an optoelectronic integrated circuit integrated by a heterogeneous coupling method for improving optical coupling efficiency between a photodetector and a planar optical waveguide device.

In general, an integrated circuit (IC) in which an optical element and a photoelectric conversion element are integrated on the same substrate by the above-described heterogeneous integration or the like is called an optical electronic integrated circuit. In addition, the monolithic circuit by the semiconductor manufacturing method includes one or more luminous elements or light receiving elements, an integrated circuit or the like for processing an electrical signal or a planar optical waveguide element. . The photoelectric integrated circuit described above generally means using a gallium arsenide (GaAs) substrate, and is mainly used as a photoelectric conversion integrated circuit for a transceiver and a repeater in an optical communication system.

Typically, a method of integrating a photoelectric conversion element and an optical element on the same substrate surface by a semiconductor manufacturing process, a planar optical waveguide element, and a light reception or light emission capable of converting an optical signal into an electrical signal and converting the electrical signal into an optical signal. BACKGROUND OF THE INVENTION A hybrid integration (HI) method in which photoelectric conversion elements having a function and the like are separately manufactured and then integrated on the same substrate is widely used.

The above-described optoelectronic integrated circuits must improve the optical axis alignment and coupling efficiency between devices in order to minimize optical loss and possible error factors that occur when converting an optical signal into an electrical signal and an electrical signal into an optical signal.

1 is a side view illustrating a structure of a photoreceptive photonic integrated circuit according to a conventional heterojunction method. Referring to FIG. 1, the photoreceptive photonic integrated circuit includes a planar optical waveguide device 130 that controls an optical signal, and a microcontroller that adjusts an optical path of the optical signal 133 output from the planar optical waveguide device 130. The mirror 120 and a photo detector 140 for detecting the optical signal 133 input from the micro mirror 120.

The planar optical waveguide device 130 is a basic component of an optoelectronic integrated circuit, and is formed on a substrate 110 made of silica by a semiconductor manufacturing process or the like, and outputs an optical signal in its cross section. Typically, the optical signal 133 output from the planar optical waveguide device 130 travels in parallel with the substrate 110. The planar optical waveguide device 130 should have a low transmission loss and a low coupling loss with an optical fiber or an optical device.

As shown in FIG. 1, the photodetector 140 places an optical waveguide-type photodiode or the like, which is separately manufactured, on the upper surface of the micromirror 120, thereby reflecting the optical signal 133 reflected from the micromirror 120. ) Is input to the active layer 141 to detect the intensity or convert the optical signal into an electrical signal. In addition, a heterogeneous bonding may be performed on the substrate 110 on which the planar optical waveguide device 130 is formed, or a photodetector specially designed to improve coupling efficiency with the planar optical waveguide device 130 may be used.

The micromirror 120 has an inclined plane having a predetermined slope so as to convert a path of the optical signal output from the planar optical waveguide device 130 to be incident on the photodetector 140. 121 is molded. The micromirror 120 has a thickness of about several tens of microns and is located below the photodetector 140. Typically, the micromirror 120 is made of thin silicon flakes, and the aforementioned silicon flakes have a problem in that handling and optical axis alignment are not easy.

In addition to the structure shown in FIG. 1, photoelectric conversion elements having a light emitting or receiving function by heterojunction techniques, planar optical waveguides having an active or passive function, and optical fiber blocks are integrated and optically aligned in the structure of an optical integrated circuit. As a related invention, U. S. Patent No. 5,577, 142 (" OPTICAL FIBER TRANSMITTING AND RECEIVING COMMUNICATION DEVICE "), issued by Muller et al., Discloses the construction of a photoelectric integrated circuit by a conventional heterojunction scheme.

However, the related arts have a problem in that optical coupling occurs between the photodetector and the optical waveguide device, resulting in optical loss upon receiving light. In addition, a device such as a micro mirror has a problem that it is not easy to manufacture and align the optical axis by using a material that is small and easily damaged. As a result, the burden of process and production costs increases.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to provide a structure of an opto-electronic integrated circuit which is easy to manufacture and excellent in optical coupling efficiency.

In order to achieve the above object, an optoelectronic integrated circuit according to the present invention,

A semiconductor substrate supporting each element constituting the photoelectric integrated circuit;

A photodetector including an active layer and formed on the semiconductor substrate;

The output terminal is spaced apart from the side of the photo detector by a predetermined distance, and the output terminal is inclined toward the active layer so that the light output from the output terminal is incident on the lower surface of the active layer through the side of the photo detector. A planar optical waveguide device formed on the semiconductor substrate;

And a refractive index matching layer having a predetermined refractive index applied to cover an output end of the planar optical waveguide device and a side surface of the photodetector to improve optical coupling efficiency between the planar optical waveguide device and the photodetector.

1 is a side view showing the structure of a photoreceptive photonic integrated circuit heterojunction by the prior art;

2 is a side view illustrating a structure of an optical integrated circuit having optical axes aligned between a photodetector and a planar optical waveguide device according to the present invention;

3 is an enlarged view of only a part of an optical axis aligned optical axis between the photodetector and the planar optical waveguide device shown in FIG.

FIG. 4 is a graph showing a correlation between the refractive index of the refractive index matching layer shown in FIG. 3 and the light receiving angle of the optical signal refracted in the photodetector according to the slope of the planar optical waveguide device output terminal. FIG.

Hereinafter, with reference to the accompanying drawings will be described an embodiment of the present invention; In describing the present invention, detailed descriptions of related well-known functions or configurations are omitted in order not to obscure the subject matter of the present invention.

2 is a side view illustrating a structure of an optical integrated circuit in which an optical detector and a planar optical waveguide device are optically coupled to each other according to the present invention. Referring to FIG. 2, the photoelectric integrated circuit detects light output from the semiconductor substrate 210, the planar optical waveguide device 240 formed on the semiconductor substrate 210, and the planar optical waveguide device 240. Photodetector 220 and a refractive index matching layer 230 having a predetermined refractive index.

The semiconductor substrate 210 serves to fix and support the elements constituting the optoelectronic integrated circuit. In particular, the planar optical waveguide device 240 is directly formed on the semiconductor substrate 210.

The photodetector 220 may use an active layer 221 for detecting light and a waveguide-type photodiode, which is a light receiving surface 222 on which one side of the active layer 221 perpendicular to the active layer 221 is input. . The photodetector 220 is positioned on the semiconductor substrate 210 such that the active layer 221 is parallel to the semiconductor substrate 210.

In the planar optical waveguide device 240, the output terminal 241 is spaced apart from the light receiving surface 222 of the photodetector 220 by a predetermined distance, and the light output from the output terminal 241 is transferred to the photodetector ( The output terminal 241 is formed on the semiconductor substrate 210 to be inclined toward the active layer 221 so that the light may be incident on the lower surface of the active layer 221 through the light receiving surface 222. . The planar optical waveguide device 240 forms the output terminal 241 to be inclined at a predetermined angle, thereby easily aligning an optical axis with the photodetector 220 and minimizing a loss of light input to the active layer.

The refractive index matching layer 230 is an output terminal 241 and the photodetector 220 of the planar optical waveguide device 240 to improve the coupling efficiency of the planar optical waveguide device 240 and the photodetector 220. Is applied to cover the light receiving surface 222, and has a predetermined refractive index.

Light incident on the photodetector 220 through the light receiving surface 222 is refracted at a predetermined angle toward the active layer 221. If there is light refracted at an angle out of the active layer 221, this becomes a light loss that the active layer 221 can not detect. The angle at which light incident to the photodetector 220 is refracted may be adjusted according to the refractive index of the refractive index matching layer 230 and the inclination angle of the output terminal 241 of the planar optical waveguide device 240.

As a result, the present invention can easily align the optical axis with any type of photodetector by adjusting the slope of the output terminal of the planar optical waveguide device and the refractive index of the refractive index matching layer, and also minimize the optical loss. have.

At the output end 241, which is an interface between the photodetector 220 and the refractive index matching layer 230, and the interface between the planar optical waveguide device 240 and the refractive index matching layer 230. The angle of refracted light is based on any normal perpendicular to each of the boundaries described above.

FIG. 3 is an enlarged view of only a part of an optical axis coupled between the photodetector and the planar optical waveguide device shown in FIG. 2. Referring to FIG. 3, an optical signal output from the planar optical waveguide device 240 is due to a difference in refractive index between the planar optical waveguide device 240, the refractive index matching layer 230, and the photodetector 220. The traveling path is refracted at a predetermined angle. The angle of the optical signal refracted at the interface between the media having different refractive indices is determined by the difference in refractive index between the media and the angle incident at the interface. The relationship between the geometrical path changes along the surface is called Snell's law. When this is applied to the optical signal traveling between the refractive index matching layer 230 and the planar optical waveguide device 230 according to the present invention, it can be expressed as Equation 1 below.

An arbitrary dotted line perpendicular to the output terminal 241 of the planar optical waveguide device 240 is called a normal line, and an angle at which an optical signal is refracted by Snell's law to be described below is based on an arbitrary normal line perpendicular to the boundary surface.

<Equation 1> is a formula derived from Snell's law, the angle at which the optical signal incident from the planar optical waveguide device 240 to the refractive index matching layer 230 is refracted. That is, the equation represents the angle of refraction of the optical signal that advances the medium having different refractive indices with respect to the output terminal 241.

An optical signal traveling in the planar optical waveguide device 240 is referred to as an incidence angle 90-θ _{1 at} the output terminal 241, and passes through the output terminal 241 to pass through the refractive index matching layer 230. The angle of the optical signal incident to the inside of the? In Equation 1, θ ₁ represents an angle of the output terminal 241 inclined toward the active layer, and n _c represents a refractive index of the refractive index matching layer 230. That is, θ1 means an angle between the semiconductor substrate 210 and the output terminal 241.

Equation 2 below represents an angle refracted by the light receiving surface 222 when an optical signal is incident from the refractive index matching layer 230 to the photodetector 220. That is, the equation represents an angle at which an optical signal for propagating a medium having different refractive indices to the light receiving surface 222 of the photodetector 220 is refracted.

In Equation 2, an angle at which the optical signal incident from the refractive index matching layer 230 to the photodetector 220 is refracted is called an incident angle θ 'and passes through the light receiving surface 222 to allow the light to pass through. The angle at which the optical signal incident into the detector is refracted is called the light receiving angle θ ₃ . n _p means the refractive index of the photodetector 220, n _c means the refractive index of the refractive index matching layer 230.

Each of the above-described light receiving angle θ ₃ and the incident angle θ ′ represents an angle between an arbitrary normal perpendicular to the light receiving surface 222 and an optical signal traveling through the light receiving surface 222, which is an interface between two media. .

Sin (θ ') of Equation ₂ may be expressed as sin (90−θ ₁ -θ ₂ ) of Equation 3 above. That is, the angle of incidence θ ′ of Equation 2 denotes an angle between a normal line perpendicular to the output terminal 241 and an optical signal, which corresponds to the normal line of the light receiving surface 222 and the light receiving surface 222. The angle between the incident optical signals. Therefore, the incidence angle θ 'of Equation ₂ is equal to the incidence angle 90-θ ₁ -θ ₂ of Equation 3.

The light receiving angle θ ₃ of Equations 2 and ₃ is determined according to the inclination angle θ ₁ of the output terminal 241 and the refractive index n _c of the refractive index matching layer 230. It is possible to change. Therefore, even when the optical waveguide device and the optical waveguide device are heterogeneously bonded to any type of photodetector or semiconductor laser, the optical axis can be easily aligned regardless of its size and shape.

That is, the angle θ ₁ of the output terminal 241 and the refractive index n _c of the refractive index matching layer may be variously applied according to the optical axis alignment conditions, and thus the optical axes of the optical detectors having various shapes and sizes may be applied. Easy to align The photoelectric integrated circuit having the structure of the present invention is applicable not only to heterojunction with a light receiving element such as a photodetector but also to optical axis alignment and heterojunction with a light emitting element such as a semiconductor laser.

FIG. 4 is a graph illustrating a correlation between a refractive index n _c of the refractive index matching layer 230 and a light receiving angle in which an optical signal incident inside the photodetector 220 is refracted. The x-axis of the graph represents the refractive index of the refractive index matching layer 230, the y-axis represents the light receiving angle (θ ₃ ) in which the optical signal incident inside the photodetector 220 is refracted, and the output end of the planar optical waveguide device 240 ( When the angle θ ₁ , which is the inclination of 241, is varied in various ways such as 30 °, 45 °, 60 °, and the like, the change in the received angle of the optical signal incident on the photodetector 220 is shown.

As a specific example according to the present invention, the graphs of FIG. 4 can be simulated from Equations 1 and 2, and in this case, n _p is 3.5 and n _s is 1.45 to fix the refractive index. In FIG. 4, when the angle of the inclined plane of the planar optical waveguide device is 45 ° and the refractive index of the refractive index matching layer 230 is 2.15, the light receiving angle of the optical signal incident inside the photodetector 220 is about 10 °. It can be seen that. The width (d) of the photodetector applied in this example is a photodiode of 100 µm and size of 1000 µm. In order to reach the active layer of the photodiode described above without losing the optical signal, a distance L of about 567 μm must be moved, which can be seen as inferred from Equation 4 below.

As described above, the light receiving angle at which the optical signal is refracted in the photodetector 220 includes the refractive index of the refractive index matching layer 230 and the inclination angle θ ₁ of the output terminal 241 of the planar optical waveguide device 240. Can be adjusted by adjusting.

For example, if the optical signal incident in the photodetector 220 is refracted at 20 °, the movement path of the optical signal is It can be seen that the distance is moved within the photodiode.

The present invention includes a planar optical waveguide device having an output end inclined at a predetermined angle and a refractive index matching layer using a medium having a predetermined refractive index, thereby easily fabricating an opto-electronic integrated circuit using a heterojunction method. In addition, by adjusting the inclination angle of one end of the planar optical waveguide element and the refractive index of the refractive index matching layer, there is an advantage that it is easily applicable to optical axis alignment with photodetectors of various sizes and shapes. In addition, optical axis alignment is possible without using elements such as a micro mirror for optical axis alignment, thereby reducing the process time and production cost.

The present invention is applicable not only to the heterojunction between the photodetector and the planar optical waveguide device but also to the heterojunction between the light emitting device and the planar optical waveguide device.

According to the present invention, one end of the planar optical waveguide device is molded to have a predetermined slope, so that the alignment of the optical axis with the photodetector is easy and the optical coupling efficiency is excellent. Further, by adjusting the inclination of one end of the planar optical waveguide element, the refractive index of the refractive index matching layer, the interval between the planar optical waveguide element and the photodetection period, and the like, the range of the acceptable light receiving angle is widened. That is, there is an advantage that it can be easily applied to photodetectors of various shapes and sizes. Moreover, optical axis alignment can be performed without using devices such as micro mirrors for optical axis alignment, and thus, there is an advantage of shortening process time and reducing production cost.

Claims (3)

In the photoelectric integrated circuit, A semiconductor substrate supporting each element constituting the photoelectric integrated circuit; A photodetector including an active layer and formed on the semiconductor substrate; The output terminal is spaced apart from the light receiving surface of the photodetector by a predetermined distance, and the output terminal is inclined toward the active layer so that the light output from the output terminal is incident on the lower surface of the active layer through the light receiving surface of the photodetector. A planar optical waveguide device formed on the semiconductor substrate in a structure; And a refractive index matching layer having a predetermined refractive index applied to cover the output end of the planar optical waveguide device and the light receiving surface of the photodetector to improve optical coupling efficiency between the planar optical waveguide device and the photodetector. Photoelectric integrated circuit. The method of claim 1, And adjusting the light receiving angle of the optical signal incident on the photodetector by adjusting the slope of the output terminal and the refractive index of the refractive index matching layer. The method of claim 1, wherein the photodetector, And a vertical photodiode positioned such that the active layer is parallel to the semiconductor substrate.