JPH10282351A - Optical waveguide, and optoelectronic mixed substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical waveguide which is formed without needing any high-temperature process, and capable of sufficiently preventing the occurrence of the cross talk. SOLUTION: In an optical waveguide 12, a core part 6 is formed in a clad part 8, and the outer surface of the clad part 8 is covered with a metallic film 11. An optoelectronic mixed substrate comprises an optical waveguide on the substrate in which the core part is formed in the clad part and the outer surface of the clad part is covered with the metallic film, a photoelectric integrated circuit or an optical integrated circuit in which a photoelectronic conversion element and an electronic circuit are combined, and an integrated circuit or a high frequency electric circuit. The occurrence of the cross talk can be prevented in an approximately complete manner, the signal conversion and the optical transmission of excellent equality are possible, and the high- temperature process can be dispensed with, and various kinds of normal electric circuit substrates can be used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide used in an optical signal connection portion between electronic circuit boards of an optical communication system or a computer or an optical signal conversion area between elements in an electronic circuit board, and a photoelectric mixed substrate. It is.

[0002]

2. Description of the Related Art In response to demands for high-speed and large-capacity information processing in optical communication systems and computers, transmission of electric signals alone has limitations on transmission capacity and electromagnetic induction.
The use of optical signal transmission has been actively promoted for signal transmission between integrated circuit elements, between boards on which they are mounted, or between boards on which a plurality of circuit boards are integrated. in this case,
Since electronic components are responsible for processing transmitted signals, information processing using optical signal transmission requires signal conversion between optical signals and electrical signals.

[0003] In such a signal conversion region between an optical signal and an electric signal, a light transmission path composed of an optical fiber or an optical waveguide, an optoelectronic conversion element such as a laser diode or a photodiode, an optoelectronic conversion element and an electronic circuit are provided. Integrated optical devices (OEICs), optical integrated circuits (optical ICs) that process information only with optical signals, integrated circuit devices such as ICs and LSIs for controlling electronic devices and processing electrical signals, and electronic components. High-frequency electric circuits and the like for driving at high speed are mixed.

Conventionally, a module assembled from individual optical components and electronic components has been used in the signal conversion region of an optical signal and an electric signal. In order to achieve high-density mounting of components and high efficiency of optical connection, a photoelectric conversion element such as a light receiving / emitting element, and an optical waveguide on one substrate;
LSIs for controlling light receiving and emitting elements, OEIC, optical IC, OEIC
An opto-electronic multi-chip module (O / O) that includes integrated circuit elements such as control LSIs, high-frequency electric circuits, etc.
Research and development are proceeding toward the practical use of a photo-electron mixed substrate called E-MCM).

[0005]

In the case where a plurality of light receiving and emitting elements are mounted as photoelectric conversion elements on a photoelectric mixed substrate, a light emitting and receiving element is mounted at a high density and an optical circuit using an optical waveguide is densified. The problem of the occurrence of crosstalk due to the signal propagating as stray light in the substrate has been increasing. Such stray light includes, for example, scattered light caused by the roughness of the wall surface of the optical waveguide and fluctuation of the refractive index distribution, radiated light generated at the bent portion of the optical waveguide, and the light emitting element at the connection between the optical waveguide and the light emitting element. Light leaked due to the mismatch of the mode field diameter between the light emitted from the optical waveguide and the light propagating in the optical waveguide, and the leak light generated due to the mismatch in the mode field diameter of the light propagated at the connection between the optical waveguide and the optical fiber These may be coupled to and propagate with an optical waveguide other than the optical waveguide that should originally propagate, or may be incident on a light receiving element other than the light receiving element that should originally be incident, resulting in crosstalk.

On the other hand, for example, Japanese Unexamined Patent Publication No. 4-152396 discloses a core waveguide having a high refractive index (a SiO ₂ -TiO ₂ glass film having a refractive index about 0.3% higher than that of quartz glass as a substrate material). To a cladding layer having a low refractive index (SiO ₂ -P ₂ O ₅ -B having a refractive index about 0.3% lower than that of the core waveguide).
An optical waveguide type optical demultiplexing element consisting of the structure of an optical waveguide covered with ₂ O consists of ₃ type glass film), it is optically coupled to the optical transceiver Tanshirube waveguide at one end of the optical waveguide type optical demultiplexing element Optical fiber and a plurality of optical transmission / reception end waveguides at the other end of the optical waveguide type optical multiplexing / demultiplexing device.
In the optical transmission module having the semiconductor laser or the receiving photodiode coupled to the optical waveguide, the light having a higher refractive index than the cladding layer is provided outside the cladding layer covering the core waveguide of the optical waveguide type optical multiplexer / demultiplexer. Absorbing layer (SiO ₂ -T whose refractive index is about 0.3% higher than quartz glass
An optical transmission module provided with an iO ₂ -based glass) is disclosed.

According to this optical transmission module, the light absorption layer having a higher refractive index than the cladding layer provided outside the cladding layer of the optical waveguide absorbs extra light passing through the cladding layer and prevents its propagation. Due to the difference in near-field distribution between the optical waveguide and the receiving laser light emitted from the semiconductor laser or the optical fiber optically coupled to the optical transmitting and receiving end waveguide, the optical waveguide has a function. The cladding mode to be excited, the scattered light in the optical waveguide, and the radiated light generated in the bent portion of the optical waveguide are absorbed by the light absorbing layer, so that they re-leak into the optical waveguide, and the light receiving end waveguide. Leakage into the receiving photodiode that is optically coupled to is prevented, cross-talk degradation is suppressed, and high isolation between transmitted light and received light can be ensured. Is that.

However, according to the optical transmission module disclosed in Japanese Patent Application Laid-Open No. 4-152306, the light absorption layer utilizes the difference in the refractive index between the light absorption layer and the cladding layer, so that stray light or leakage to the outside is completely lost. There is a problem that light cannot be absorbed or blocked, and the occurrence of crosstalk cannot be completely prevented.

[0009] Further, in order to mix an optoelectronic conversion element, an integrated circuit element, a high-frequency electric circuit and the like with an optical waveguide, it is necessary to form an optical waveguide on a normal electric circuit board. Is required to be flat. Furthermore, when forming the optical waveguide, it is required not to damage the electric circuit board itself, electric wiring, opto-electronic conversion element, integrated circuit element, high-frequency electric circuit, and the like. It is necessary to consider the damage to the substrate and each component due to the processing of the stress and the waveguide core.

In the optical transmission module disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 4-152396, an optical waveguide and a light absorbing layer are formed of a silicate glass based optical material using quartz glass as a substrate, and the light absorbing layer is formed. Requires a high-temperature process, and thus cannot be applied to a photoelectric mixed substrate using various ordinary electric circuit boards.

The present invention has been devised in view of the above-mentioned problems of the prior art, and has an object to eliminate stray light and light leaking to the outside, and to reduce the occurrence of crosstalk almost completely. An object of the present invention is to provide an optical waveguide capable of high-quality signal conversion and optical signal transmission, which can prevent various problems and can use various electric circuit boards without requiring a high-temperature process for forming the optical waveguide.

Another object of the present invention is to eliminate stray light and light leakage to the outside in an optical waveguide, to almost completely prevent the occurrence of crosstalk, and to eliminate the need for a high-temperature process for forming the optical waveguide. It is an object of the present invention to provide an opto-electronic mixed substrate capable of utilizing various electric circuit boards and capable of high-quality signal conversion and optical signal transmission.

[0013]

An optical waveguide according to the present invention is characterized in that a core portion is formed in a cladding portion and an outer surface of the cladding portion is covered with a metal film.

The optical waveguide according to the present invention is characterized in that, in the optical waveguide having the above-mentioned structure, the metal film is made of a metal having a plasma frequency higher than a frequency of light transmitted through the core.

Further, the opto-electron mixed substrate of the present invention includes an optical waveguide having a core portion formed in a cladding portion on a substrate, an opto-electronic integrated circuit or an opto-integrated circuit formed by combining an opto-electronic conversion element and an electronic circuit. , An opto-electronic mixed substrate comprising an integrated circuit or a high-frequency electric circuit,
An outer surface of the clad portion of the optical waveguide is covered with a metal film.

Further, the photoelectric mixed substrate according to the present invention is characterized in that, in the photoelectric mixed substrate configured as described above, the metal film is made of a metal having a plasma frequency higher than the frequency of light transmitted through the core. is there.

According to the optical waveguide of the present invention, since the outer surface of the cladding constituting the optical waveguide is covered with the metal film, the leaked light from the optical waveguide to the outside and the stray light from the outside to the optical waveguide are reduced. Since the light is reflected or absorbed by these metal films and is blocked, stray light and leaked light are eliminated, and the occurrence of crosstalk can be almost completely prevented.

When the outer surface of the clad portion of the optical waveguide is covered with a metal film, the metal film can be formed by a thin film forming technique such as a vapor deposition method, a sputtering method or a CVD method. Since a high-temperature process using a glass-based optical material is not required unlike the light absorbing layer disclosed in Japanese Patent Application Laid-Open No. H10-115, the optical waveguide of the present invention can be formed on various ordinary electric circuit boards. Further, since the optical waveguide does not require such a high-temperature process, the use of the optical waveguide of the present invention makes it possible to realize an opto-electronic mixed substrate capable of high-quality signal conversion and optical signal transmission.

If the metal film is made of a metal having a plasma frequency higher than the frequency of light transmitted through the core, light having a frequency lower than the metal plasma frequency propagates through the metal. Is not reflected, the light is surely reflected on the metal surface and cannot enter the metal, so that light leaked from the optical waveguide to the outside and stray light from the outside to the optical waveguide are more effectively reflected or blocked. Therefore, the occurrence of crosstalk can be more completely prevented.

According to the photoelectron-mixed substrate of the present invention, since the outer surface of the clad portion of the optical waveguide formed on the substrate and composed of the clad portion and the core portion is covered with the metal film, the optical waveguide is connected to the external portion. The stray light to the optical waveguide and the stray light to the optical waveguide from the outside are reflected or absorbed by these metal films and cut off.Therefore, stray light and stray light are eliminated, crosstalk can be almost completely prevented, and high quality signal conversion and It is possible to realize a photoelectric mixed substrate capable of transmitting optical signals.

When the outer surface of the clad portion of the optical waveguide is coated with a metal film, the metal film can be formed by a thin film forming technique such as a vapor deposition method, a sputtering method, or a CVD method. Since a high-temperature process using a glass-based optical material is not required unlike the light absorbing layer disclosed in Japanese Patent Application Laid-Open No. H10-115, a photo-electron mixed substrate can be formed using various ordinary electric circuit boards.

When the metal film is made of a metal having a plasma frequency higher than the frequency of light transmitted through the core, light having a frequency lower than the metal plasma frequency propagates through the metal. Is not reflected, the light is surely reflected on the metal surface and cannot enter the metal, so that light leaked from the optical waveguide to the outside and stray light from the outside to the optical waveguide are more effectively reflected or blocked. Therefore, the occurrence of crosstalk can be more completely prevented, and an opto-electronic mixed substrate capable of high-quality signal conversion and optical signal transmission can be obtained.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. 1A to 1E are cross-sectional views illustrating an example of an embodiment of an optical waveguide according to the present invention for each step of a manufacturing process.

In FIG. 1 (a), 1 is a substrate, 2 is a metal film, 3 is a cladding layer serving as a cladding portion of an optical waveguide, 4 is a core layer serving as a core portion of the optical waveguide, and 5 is a patterning layer for the core layer 4. Is a mask metal film.

First, a metal film 2 made of, for example, aluminum (Al) is formed on a substrate 1 made of, for example, silicon (Si) or silica by sputtering or the like, and a desired optical waveguide is formed by photolithography. The metal film 2 is patterned so as to form a pattern. In addition, as the substrate 1, various electric circuit substrates such as a copper polyimide substrate, a ceramic substrate, a ceramic multilayer circuit substrate, a thin film multilayer circuit substrate, and a Si circuit substrate can be used.

Next, a clad layer 3 is formed on the metal film 2.
For example, by applying a siloxane polymer solution and heat-treating the siloxane polymer film (refractive index: 1.4405, λ = 1.
55 μm) to a thickness of about 15 μm.

Further, the core layer 4 serving as the core of the optical waveguide is coated on the cladding layer 3 by, for example, applying a mixed solution obtained by adding tetra-n-butoxytitanium to a siloxane polymer solution, and heat-treating the mixture. A siloxane polymer film (refractive index 1.4437, λ = 1.55 μm) is formed to a thickness of about 7 μm.

Further, a mask metal layer 5 is formed on the core layer 4.
For example, an Al film is formed by sputtering or the like. For the mask metal layer 5, a material other than Al is used as long as a sufficient selectivity can be obtained when the core layer 4 is etched by, for example, RIE (Reactive Ion Etching) using the layer 5 as a mask. You may.

Then, a resist pattern (not shown) serving as a core pattern is formed on the mask metal layer 5 by photolithography, and the mask metal layer 5 is patterned by wet etching or dry etching.

Next, after the resist pattern on the mask metal layer 5 is removed, the resist pattern is patterned as shown in FIG. 1B by, for example, the RIE method using a mixed gas of CF ₄ and O ₂ . The core layer 4 is etched using the mask metal layer 5 'as a mask to form the core 6 of the optical waveguide.

Next, the mask metal layer 5 'is removed, and FIG.
As shown in (c), a cladding layer 7 made of the same material as the cladding layer 3, for example, a siloxane polymer film (refractive index 1.4405, λ = 1.55 μm) is formed on the
It is formed so as to cover with a thickness of about m.

Next, a metal film made of the same material as that of the metal film 2, for example, Al is formed on the cladding layer 7, and patterned into a pattern to be an optical waveguide in the same manner as described above. The cladding layers 8 are formed by etching the cladding layers 7 and 3.

As a result, as shown in FIG. 1D, the height of the core 6 is 7 μm, and the refractive index of the core 6 is 1.4437 (λ).
= 1.55 μm), the upper, lower, left and right thicknesses of the cladding part 8 surrounding the core part 6 are each 15 μm, and the refractive index of the cladding part 8 is 1.
A buried optical waveguide of 4405 (λ = 1.55 μm) having a metal film 9 formed on the upper surface is formed.

Here, the optical signal transmitted by the optical waveguide is not completely confined in the core portion 6 but propagates by oozing into the cladding portion 8. If the thickness of the portion 8 is too thin, light is absorbed by the outer metal film 11 described later, and the propagation loss increases. In particular, in the case of the single mode, the influence is remarkable, so that the thickness of the clad portion 8 is desirably greater than the thickness of the core portion 6.

Finally, a metal film made of the same material as those, for example, Al, is formed on the side surface of the optical waveguide so as to be continuous with the metal films 2 and 9.
By forming 10, the optical waveguide 12 of the present invention in which the core 6 is formed in the clad 8 and the outer surface of the clad 8 is covered with the metal film 11 is obtained.

In the optical waveguide 12 of the present invention, the cladding 8
In addition to the above-mentioned Al, the metal film 11 covering the outer surface of the optical waveguide 12 has light in the range from visible light to near-infrared light used for optical communication as light for transmitting the core 6 of the optical waveguide 12. Various kinds of metal materials can be used as long as the metal material can reflect, absorb, and shield the outer surface of the clad portion 8 and form a coating film.

As such a metal material, for example, Al
Or Cu, Ti, Cr, Au, Pt, Mo, or alloys of these, and by using these metallic materials,
The clad portion 8 can be easily formed by forming the metal film 11 by various vapor deposition methods such as an electron beam vapor deposition method or a resistance heating vapor deposition method or a thin film forming method such as a sputtering method or a CVD method.

As a result, the leakage light from the optical waveguide 12 to the outside and the stray light from the outside to the optical waveguide 12 are reduced by the metal film 11.
Because the light is reflected or absorbed and cut off, there is no stray light or leaked light, and the optical waveguide 12 can almost completely prevent the occurrence of crosstalk.

When the metal film 11 is made of a metal having a plasma frequency higher than the frequency of the light transmitted through the core 6, the refractive index of the metal with respect to light having a frequency lower than the plasma frequency of the metal. Is a complex number and its imaginary part is related to the attenuation coefficient of the light wave.
It is totally reflected by the surface and cannot enter.

That is, in the case of a metal, it can be regarded as a medium composed of negative charges of conduction electrons and positive ions. The refractive index n felt by an electromagnetic wave having a frequency ω incident on the medium is given by ω _p being a plasma frequency. , N = ｛1- (ω _p ² /
ω ² )｝ ^1/2 . Here, if the frequency ω of the incident electromagnetic wave is smaller than the plasma frequency ω _p , ω _p > ω, so that n is an imaginary number, and the incident electromagnetic wave is e ^−mx
(Where e is the natural logarithm, m is the absolute value of n, and x is the distance at which the electromagnetic wave has entered the medium). That is, this electromagnetic wave cannot propagate through the medium and is totally reflected.

From such a phenomenon, the plasma frequency ω _p
Since light having a smaller frequency ω cannot propagate through the metal film 11, the leakage light from the optical waveguide 12 to the outside and the stray light from the outside to the optical waveguide 12 are more effectively reflected or blocked, so that the Talk can be more completely prevented from occurring.

Table 1 shows the calculated values of the plasma frequency ω _p and the corresponding plasma wavelength λ _p for various metals.

[0043]

[Table 1]

From Table 1, the plasma wavelength λ _p of the metal shown in Table 1 is shorter than the wavelength λ = 0.85 μm or 1.30 μm · 1.55 μm of the light used in optical communication.
It can be seen that the metal shown in FIG. 2 totally reflects light used in such optical communication.

The actual refractive index of the metal is a complex refractive index (n-ki, i is an imaginary unit).

For the main metals shown in Table 1, the wavelength λ of light used in optical communication is λ = 0.85 μm · 1.30 μm.
It shows the complex refractive index for m · 1.55 μm.

[0047]

[Table 2]

The thickness of the metal film 11 is such that a coating is formed on at least the entire outer surface of the clad portion 8 (generally, several tens of nm or more). Even if the light is incident on the metal and totally reflected, the incident light penetrates into the metal to some extent, and if the metal film thickness is not sufficient, the light may seep out to the opposite surface of the metal film. It is necessary to make the thickness such that there is no transmission due to light seeping. The thickness in consideration of such light seepage can be determined using the attenuation coefficient α of the incident light in the metal.

That is, the distance 1 in the metal having the attenuation coefficient α
When the light advances by / α, the light intensity becomes 1 / e ² (e is a natural logarithm). For example, when light having a wavelength of 1.3 μm travels in aluminum, the complex refractive index is 1.2-13.2i, the attenuation coefficient α is 63.8 μm ⁻¹ , and 1 / 63.8 μm is about 0.02 μm.
The light intensity becomes 1 / e ² with respect to the propagation distance. In this case, the light intensity becomes 0.01 at 0.04 μm which is twice the distance.
This is 5 times, which is equivalent to about -20 dB, which is a level sufficiently effective for preventing the occurrence of crosstalk.

As described above, the thickness of the metal film 11 is required to prevent the occurrence of crosstalk and the attenuation coefficient α of the metal used for the metal film 11 with respect to the light used for optical communication by transmitting the core. The required thickness can be obtained from the amount of attenuation, but in general, a thickness of 100 nm = 0.1 μm or more is sufficient.

On the other hand, as the upper limit of the thickness of the metal film 11, the patterning property (for example, pattern processing accuracy and time during wet etching and dry etching) of the metal film and peeling and cracking due to film stress when the thickness is increased are considered. In consideration of the fact that it is likely to occur, it is preferable that the thickness is not unnecessarily large. According to the experimental results of the inventor, for example, when Al is used for the metal film 11, the thickness is preferably set to about 2 μm or less.

As for the thickness of the metal film 11 made of Al, the frequency ω of the light transmitted through the core 6 is 1.4 × 10 ¹⁵ s
⁻¹ (λ = 1.3 μm), and the plasma frequency ω _{p of} Al used for the metal film 11 is 2.4 × 10 ¹⁶ s ⁻¹ (λ = 0.0786 μm)
Therefore, the thickness is set to 0.5 μm in consideration of the above-described attenuation effect and the step coverage of the optical waveguide pattern. At this time, the crosstalk was less than -40 dB, which is the measurement limit of the currently owned evaluation system.

If the thickness is within the above range, the metal film 11 can be easily formed by various vapor deposition methods such as an electron beam vapor deposition method or a resistance heating vapor deposition method or a thin film forming method such as a sputtering method or a CVD method. Thus, the clad portion 8 can be covered.

As the optical waveguide, in addition to the above-mentioned siloxane poly-based waveguide, other resin-based waveguides, for example, polyimide, PMMA, fluorine resin, etc., or GaAs, InP
Or a compound semiconductor waveguide or a quartz-based waveguide.

When a siloxane polymer waveguide is used as the optical waveguide, the solution for forming the siloxane polymer film used for the preparation may be, for example, a siloxane polymer having a phenyl group or a methyl group at a terminal group, a butyl group / propyl group, or the like. A siloxane polymer having a terminal group such as an alkyl group, an aryl group such as a phenyl group or a tolyl group, a functional group partially substituted with fluorine, a hydroxyl group, and the like; propylene glycol monomethyl ether;
It is preferable to use a mixed solution of butanol / ethylene glycol monobutyl ether and the like, and it is particularly preferable to use a mixed solution of a siloxane polymer having a phenyl group or a methyl group in a terminal group and propylene glycol monomethyl ether.

As the metal alkoxide to be added to the siloxane polymer film forming solution, for example, tetra-n-
There are butoxytitanium, tetramethoxytitanium, tetrapropoxytitanium, tetramethoxygermanium, tetraethoxygermanium, tetrapropoxygermanium, tetrabutoxygermanium and trimethoxyerbium.
The use of an alcoholate having a large number of (carbon) is preferable because the chemical stability is superior to that having a small number of C and gelation is less likely to occur during mixing and mixing can be easily performed.

The amount of the metal alkoxide to be added is determined in advance by measuring the refractive index of the polymer film with respect to the amount of the metal alkoxide added to the solution for forming a siloxane polymer film by each combination of the above-mentioned raw materials. Set the amount of addition.

The method of addition and the conditions are as follows:
For example, the alcoholate may be diluted with a sufficient amount of alcohol and mixed with the siloxane polymer film forming solution while refluxing. The alcohol used at this time preferably matches the alkoxylate of the alcoholate.

As described above, by adding the metal alkoxide to the siloxane polymer film forming solution, the metal alkoxide can be added and mixed at an arbitrary ratio to the siloxane polymer film forming solution to form a metal-containing siloxane polymer film. It becomes possible to precisely control the refractive index of the optical waveguide.

After the siloxane polymer film forming solution is applied onto a substrate by a coating method such as a spin coating method, a dip coating method, or a roller coating method, a heat treatment is performed by, for example, an oven or a hot plate to thermally polymerize. As a result, the crosslinking reaction of the siloxane bond proceeds, and a silica-based siloxane polymer film is obtained.

Here, the heat treatment temperature for thermal polymerization is about 270 ° C., and the decomposition temperature (typical value) of polyimide generally used as an insulating layer of a thin film circuit board for forming an optical waveguide according to the present invention. Is about 450 ° C.), so that the optical waveguide can be formed without damaging the underlying substrate such as the thin film circuit substrate by the heat treatment.

As described above, a copper polyimide substrate, a Si substrate, a ceramic substrate, a multilayer ceramic electric circuit substrate, a thin film multilayer circuit substrate,
Although there are i-circuit boards and the like, the state of the surface on which the optical waveguide is formed is such that irregularities and surface roughness are optically smooth and flat, and irregularities and surface roughness due to the underlying substrate cannot be ignored. Even so, since the shrinkage during thermosetting is small, the flatness is maintained when the siloxane polymer film forming solution is applied, so that an optical waveguide excellent in flatness can be formed irrespective of these.

Next, FIG. 2 shows a plan view of an example of an embodiment of a photoelectron mixed substrate of the present invention, and FIG. 3 shows a cross-sectional view.

In these figures, reference numeral 13 denotes a substrate. Here, an example is shown in which a ceramic multilayer circuit board in which a wiring conductor 15 such as a wiring conductor layer and a through conductor is formed in a plurality of ceramic dielectric layers 14 is used. I have. In addition, as the substrate 13, similarly to the substrate 1, various electric circuit boards such as a copper polyimide substrate, a Si substrate, a ceramic substrate, a thin film multilayer circuit substrate, and a Si circuit substrate can be used.

Reference numeral 16 denotes a light emitting element for transmitting an optical signal, 17 denotes a light receiving element for monitoring an optical output of the light emitting element 17 for transmitting an optical signal, and 18 denotes a light receiving element for receiving an optical signal. Diode, semiconductor laser) and LED
(Light emitting diode) and pnPD (pn
A light receiving element such as a photodiode (PD), pinPD (pin photodiode), and APD (avalanche photodiode) is used.

Reference numeral 19 denotes a semiconductor integrated circuit element (integrated circuit) such as an IC or LSI for driving and signal processing of the light receiving and emitting elements 16 to 18. These are mounted on the substrate 13 and (OEIC). In addition, in addition to these, a photoelectric integrated circuit (OEIC) element or an optical integrated circuit (optical IC) element may be mounted, or a high-frequency electric circuit may be further provided.

Reference numeral 20 denotes an optical waveguide according to the present invention, and reference numeral 21 denotes an optical fiber for transmitting and receiving an optical signal to and from an external circuit. The optical waveguide 20 is branched by an optical waveguide type multiplexing / demultiplexing optical circuit 22 into a transmitting optical waveguide 20a connected to the light emitting element 16 for transmitting an optical signal and a receiving optical waveguide 20b connected to the light receiving element 18 for receiving an optical signal. ing. Further, in this example, transmission / reception of optical signals to / from an external circuit is performed by using two systems of optical fibers 21.

In the optical waveguide 20 (20a, 20b), similarly to the optical waveguide 12, the core 24 is formed in the cladding 23 and the outer surface of the cladding 23 is covered with the metal film 25. It consists of

The optical waveguide 20 (20a, 20b) has the same structure in the optical waveguide type multiplexing / demultiplexing optical circuit 22, but here, the metal film 25 has a multiplexing / demultiplexing portion so as not to interrupt optical coupling. It is formed so as to cover the whole.

[0070]

EXAMPLES Specific examples of the comparative example and the optical waveguide of the present invention will be described below.

Example 1: Comparative Example The above-mentioned siloxane polymer was coated on a Si wafer and subjected to 85 ° C./30 minutes and 270 ° C./30 minutes.
Heat treatment for 15 minutes to form a cladding layer (refractive index
1.4405, λ = 1.3 μm).

Next, a 6 μm-thick core layer (refractive index: 1.4450, λ = 1.3 μm) was formed using a mixed solution of a siloxane polymer and tetra-n-butoxytitanium.

Subsequently, an Al film having a thickness of 0.5 μm serving as a mask at the time of processing the core portion is formed by a sputtering method.
A resist pattern having a line width of 6 μm serving as a pattern of the core portion was formed by photolithography. As shown in the plan view of FIG. 4, this pattern was composed of a branch optical waveguide 27 'and a linear optical waveguide 28' formed on a substrate 26 '.

Next, the Al film was etched with a mixed solution of phosphoric acid, acetic acid and nitric acid to obtain an Al pattern on which a resist pattern was transferred.

Next, after removing the resist, the core portion was patterned by RIE. Here RIE
The conditions were: O ₂ 60 sccm, pressure 5 Pa, output 600 W, and a substantially rectangular core section was formed.

Thereafter, the Al pattern was removed, and a clad layer (refractive index: 1.4405, λ = 1.3 μm) was formed in the same manner as described above.

As described above, the size of the core portion 30 having a cross section shown in FIG.
m × 6 μm, core part 30 has a refractive index of 1.4450, clad part 29
A buried optical waveguide of a comparative example having a refractive index of 1.4405 and a total thickness of the cladding portion 29 of 30 μm was manufactured.

Using this optical waveguide, crosstalk was evaluated as follows. First, power 10dBm,
Light from an LD having a wavelength of 1.3 μm was incident on the end face indicated by A of the branch optical waveguide 27 ′ in FIG. 4 through a single mode optical fiber and propagated through the branch optical waveguide 27 ′. Then, a single-mode optical fiber was optically connected to the end face indicated by B of the linear optical waveguide 28 ', and the intensity of light emitted was examined. As a result, the intensity of the light emitted from the end face B of the linear optical waveguide 28 ′ becomes −
23 dBm, and large crosstalk was observed.

[Example 2: Embodiment of the present invention] The above-mentioned siloxane polymer was applied onto a Si wafer having an Al film having a thickness of 0.5 μm formed by a sputtering method.
A heat treatment at 270 ° C. for 30 minutes was performed to form a 15 μm thick cladding layer (refractive index: 1.4405, λ = 1.3 μm).

Next, a 6 μm-thick core layer (refractive index: 1.4450, λ = 1.3 μm) was formed using a mixed solution of a siloxane polymer and tetra-n-butoxytitanium.

Subsequently, an Al film having a thickness of 0.5 μm serving as a mask at the time of processing the core portion is formed by a sputtering method.
A resist pattern having a line width of 6 μm serving as a pattern of the core portion was formed by photolithography. This pattern was composed of a branch optical waveguide 27 and a linear optical waveguide 28 formed on a substrate 26, as shown in a plan view in FIG.

Next, the Al film was etched with a mixed solution of phosphoric acid, acetic acid and nitric acid to obtain an Al pattern on which a resist pattern was transferred.

Next, after removing the resist, the core portion was patterned by RIE. Here RIE
The conditions were: O ₂ 60 sccm, pressure 5 Pa, output 600 W, and a substantially rectangular core section was formed.

Thereafter, the Al pattern was removed, and a clad layer (refractive index: 1.4405, λ = 1.3 μm) was formed in the same manner as described above.

Further, the optical waveguide pattern portion was etched in the same manner as the method of forming the core portion, and finally, an Al film was formed so as to cover the waveguide pattern by the sputtering method as described above.

As described above, the size of the core portion 32 having a cross section as shown in the cross section taken along line II ′ of FIG.
m × 6 μm, core part 32 has a refractive index of 1.4450, clad part 31
A buried optical waveguide of the present invention having a structure having a refractive index of 1.4405, a total thickness of the cladding portion 31 of 30 μm, and an outer surface of the cladding portion 31 covered with an Al film 33 having a thickness of 0.5 μm was manufactured.

Using this optical waveguide, crosstalk was evaluated in the same manner as in [Example 1]. First, power 10dBm,
Light from an LD having a wavelength of 1.3 μm was incident on the end face indicated by A of the branch optical waveguide 27 in FIG. 4 through a single mode optical fiber, and propagated through the branch optical waveguide 27. Then, a single mode optical fiber was optically connected to the end surface of the linear optical waveguide 28 indicated by B, and the intensity of the emitted light was examined. As a result, the intensity of light emitted from the end face B of the linear optical waveguide 28 is -40 dBm.
Or less (below the sensitivity of the detector), and no crosstalk was observed.

When a photoelectric mixed substrate using the optical waveguides 27 and 28 was manufactured, it was confirmed that the occurrence of crosstalk could be almost completely prevented, and high-quality signal conversion and optical signal transmission were possible. Was.

The present invention is not limited to the above-described embodiment, and various changes and improvements may be made without departing from the spirit of the present invention.

[0090]

According to the optical waveguide of the present invention, since the outer surface of the cladding constituting the optical waveguide having the core formed therein is covered with the metal film, the leakage from the optical waveguide to the outside is prevented. Light and stray light from the outside to the optical waveguide are reflected or absorbed by these metal films and cut off, so that stray light and leaked light were eliminated, and crosstalk was almost completely prevented.

According to the optical waveguide of the present invention, when the outer surface of the clad portion of the optical waveguide is covered with the metal film, the metal film is formed by a thin film forming method such as a vapor deposition method, a sputtering method, or a CVD method. The optical waveguide of the present invention can be formed on various kinds of ordinary electric circuit boards because it does not require a high-temperature process, and the optical waveguide of the present invention does not require such a high-temperature process. As a result, it was possible to provide an opto-electronic mixed substrate capable of high-quality signal conversion and optical signal transmission.

If the metal film is made of a metal having a plasma frequency higher than the frequency of light transmitted through the core, light having a frequency lower than the metal plasma frequency propagates through the metal. Is not reflected, the light is surely reflected on the metal surface and cannot enter the metal, so that light leaked from the optical waveguide to the outside and stray light from the outside to the optical waveguide are more effectively reflected or blocked. Therefore, the occurrence of crosstalk can be more completely prevented.

According to the photoelectric mixed substrate of the present invention,
Since the outer surface of the clad portion of the optical waveguide composed of the clad portion and the core portion formed on the substrate is covered with a metal film, light leaking from the optical waveguide to the outside and stray light from the outside to the optical waveguide are reduced. Provided is an opto-electron mixed substrate capable of almost completely preventing the occurrence of crosstalk, being able to almost completely prevent the occurrence of crosstalk, and being capable of high-quality signal conversion and optical signal transmission, because the light is reflected or absorbed and blocked by these metal films. Was completed.

According to the photoelectron-mixed substrate of the present invention, when the outer surface of the clad portion of the optical waveguide is covered with the metal film, the metal film is formed by a thin film forming method such as a vapor deposition method, a sputtering method, or a CVD method. Since a high-temperature process is not required, it is possible to configure a photoelectric mixed substrate using various kinds of ordinary electric circuit boards.

When the metal film is made of a metal having a plasma frequency higher than the frequency of light transmitted through the core, light having a frequency lower than the metal plasma frequency propagates through the metal. Is not reflected, the light is surely reflected on the metal surface and cannot enter the metal, so that light leaked from the optical waveguide to the outside and stray light from the outside to the optical waveguide are more effectively reflected or blocked. Therefore, the occurrence of crosstalk can be more completely prevented, and an opto-electronic mixed substrate capable of high-quality signal conversion and optical signal transmission can be obtained.

[Brief description of the drawings]

FIGS. 1A to 1E are cross-sectional views illustrating an example of an embodiment of an optical waveguide according to the present invention for each step of a manufacturing process.

FIG. 2 is a plan view showing an example of an embodiment of a photoelectric mixed substrate according to the present invention.

FIG. 3 is a cross-sectional view illustrating an example of an embodiment of a photoelectric mixed substrate according to the present invention.

FIG. 4 is a plan view showing an example of manufacturing an optical waveguide.

FIG. 5 is a cross-sectional view of the optical waveguide of the comparative example taken along line II ′ of FIG. 4;
It is a line sectional view.

FIG. 6 is a cross-sectional view of the optical waveguide of the present invention taken along line II ′ of FIG. 4;
It is a line sectional view.

[Explanation of symbols]

1, 13, 26 ... substrate 2, 9, 10, 11, 25, 33 ... metal film 6, 24, 32 ... core 8, 23, 31 ···················································································· ···························································································· / ..... Semiconductor integrated circuit device (integrated circuit)

Continuation of front page (72) Inventor Shigeo Tanahashi 3-5 Koikodai, Seika-cho, Soraku-gun, Kyoto Pref.

Claims (4)

[Claims] 1. An optical waveguide, wherein a core portion is formed in a cladding portion, and an outer surface of the cladding portion is covered with a metal film. 2. The optical waveguide according to claim 1, wherein said metal film is made of a metal having a plasma frequency higher than a frequency of light transmitted through said core. 3. An optical waveguide having a core portion formed in a clad portion on a substrate, an optoelectronic integrated circuit or an optical integrated circuit formed by combining an optoelectronic conversion element and an electronic circuit,
An opto-electronic mixed substrate comprising an integrated circuit or a high-frequency electric circuit, wherein an outer surface of a clad portion of the optical waveguide is covered with a metal film. 4. The optoelectronic mixed substrate according to claim 3, wherein said metal film is made of a metal having a plasma frequency higher than a frequency of light transmitted through said core.