JP2599276B2 - Optical integrated circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an optical integrated circuit, and particularly to transmitting a signal by transmitting TM (Transverse Magnetic) mode light in a slab waveguide. The present invention relates to a means for removing optical waves unnecessary for signal transmission and improving optical properties of an optical integrated circuit.

[Conventional technology]

The propagation loss of the guided light in the slab waveguide includes an absorption loss, a scattering loss, a mode conversion loss, and a radiation loss.
Among these propagation losses, in a dielectric waveguide including a slab waveguide, scattering loss is considered to be the main cause of the loss. (Nishihara, Haruna, Kashiwara, Optical Integrated Circuits, 1985)
Year, see Ohmsha, pages 249-251).

This scattering loss is generated because the light scattered in the slab waveguide changes its propagation direction and continues to propagate in the waveguide, and is an important cause for limiting device characteristics. . Therefore, when manufacturing a waveguide type device, it is necessary to eliminate the influence of scattered light in order to improve the optical performance.

In addition, among the light propagating in the waveguide, the light that may be a factor that restricts the characteristics of the device is not only the scattered light, but also the light reflected on the end face of the substrate, such as an acousto-optic device or a grating. Non-diffracted light and higher-order diffracted light in an element that uses diffraction, reflected light in a waveguide lens, and light source light propagating outside the collimating lens when parallel light is created by combining a light source and a collimating lens Leakage light is considered.

Furthermore, in addition to the light resulting from the light in the waveguide,
Light or the like caused by external light entering the waveguide or the photodetector can also be considered.

In this specification, light that may cause a restriction on device characteristics as described above is collectively referred to as unnecessary light,
Conversely, waveguide light required for the optical integrated circuit to exhibit its function will be referred to as signal light.

Conventionally, for example, the following three techniques have been proposed to remove unnecessary light.

A first technique is to form an aluminum film on a portion of the channel waveguide other than the waveguide and remove light leaked from the waveguide (Japanese Patent Laid-Open No. 59-198432).

The second is a technique for guiding the leaked light of the light beam emitted from the light source, which is not incident on the collimating lens, to the light absorbing portion by the lens or the reflecting portion (Japanese Patent Application Laid-Open No. 60-149006 or 60-149006). 254006).

Third, there is a technique in which undiffracted light that has not been diffracted by a surface acoustic wave is guided to a channel waveguide by a lens, and is absorbed by a light absorber or scattered by a minute groove (Japanese Patent Laid-Open No. 61-23119). Or JP-A-61-118704).

[Problems to be solved by the invention]

However, the above-mentioned prior arts disclose unnecessary light due to a specific cause in the slab waveguide, such as leaked light from the waveguide, leaked light not incident on the collimating lens, and undiffracted light that was desired to be diffracted into surface acoustic waves. It is effective for removing unnecessary light, but there is no consideration for removing unnecessary light due to other causes, and unnecessary light remaining in the slab waveguide without being removed is superimposed on the original signal light. As a result, there is a problem that the optical performance of the optical integrated circuit is deteriorated.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical integrated circuit in which unnecessary light in a slab waveguide is removed and optical performance is greatly improved.

[Means for solving the problem]

In order to achieve the above object, the present invention provides an optical integrated circuit that transmits a signal by transmitting TM mode light in a slab waveguide. An optical integrated circuit in which a complex dielectric material that absorbs light scattered in a slab waveguide is formed in a laminated structure.

A buffer layer may be interposed between the slab waveguide and the laminated structure of the complex dielectric material.

[Action]

If the signal light is set to the TM mode as long as the propagating portion of the light has no light-emitting property, the unnecessary light generated as a by-product also becomes the TM mode. In this case, the process of generating unnecessary light is scattering, diffraction (non-diffraction), refraction, deflection, reflection, and the like. Therefore, the method of transmitting unnecessary light is different from that of signal light.
The signal light propagates to the portion of the waveguide that does not propagate.

As means for removing the unnecessary light, for example, Japanese Unexamined Patent Publication No.
JP-19907 or JP-A-61-245134 proposes to provide a light absorbing layer over the entire length of the waveguide.

However, when the light absorption layer is provided over the entire length of the waveguide, the signal light transmission quality is degraded by absorbing even the originally required signal light.

Therefore, in the present invention, a complex dielectric material (a material having a complex dielectric constant) made of metal or conductive ceramics is formed in a laminated structure on a region other than a region for transmitting signal light in the slab waveguide. I made it. Since this complex dielectric material has a high complex permittivity (about -40 to -100 dB / cm), it can effectively absorb unnecessary light and remove unnecessary light from inside the waveguide. At that time, since the laminated structure of the complex dielectric material does not exist on the region of the slab waveguide where the signal light is propagated, the above-described JP-A-59-19907 or JP-A-61-245134 has been disclosed. Unlike the case, the signal light transmission quality can be maintained without absorbing the originally required signal light.

Further, if a buffer layer is interposed between the slab waveguide and the laminated structure of the complex dielectric material, the absorption of unnecessary light by the complex dielectric material can be optimized.

〔Example〕

Next, an embodiment of an optical integrated circuit according to the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing a cross section perpendicular to a waveguide of an optical integrated circuit according to the present invention, and (a) to (e) show examples of different structures. In FIG. 1, a waveguide 2 provided on a substrate 1 is divided into regions R, S, T, and U for convenience of explanation, and regions R and T are regions where unnecessary light propagates.
Regions S and U are regions where signal light propagates.

In the case of FIG. 1 (a), a complex dielectric material 5 is formed in a laminated structure on the surface of the waveguide 2 in the regions R and T,
Nothing is formed on the surface of the regions S and U, and the waveguide 2
Is exposed. Therefore, unnecessary light propagating in the regions R and T is effectively absorbed by the complex dielectric material. As a result, unnecessary light does not enter the regions S and T, and scattering of signal light due to unnecessary light is prevented in advance.

In the case of FIG. 1 (b), a complex dielectric material 5 is formed on the surface of the waveguide 2 in the regions S and U via the buffer layer 4b, and is formed on the surface of the waveguide 2 in the regions R and T. A complex dielectric material 5 is formed in close contact therewith. Note that the buffer layer 4b has a sufficient thickness so that signal light propagating in the regions S and U is not absorbed more than necessary. Therefore, the propagation loss of the signal light propagating in the regions S and U is small, and the unnecessary light generated as a by-product is absorbed in the regions R and T.

In the case of FIG. 1 (c), the complex dielectric material 5 is formed in a laminated structure on the surface of the waveguide 2 in the regions R and T via the buffer layer 4c.

In general, it is known that the absorptance of the complex dielectric material for the TM mode light changes depending on the thickness of the buffer layer, and the absorptance becomes maximum at a predetermined thickness. Therefore, the buffer layer 4c is set to a thickness such that the absorptance of the complex dielectric material 5 increases. Therefore, the unnecessary light is efficiently absorbed by the complex dielectric material 5 via the buffer layer 4c.

In the case of FIG. 1D, a buffer layer 4d is formed over the entire surface of the waveguide 2. This buffer layer 4d
The thickness is set to be the same as that of the above-described buffer layer 4c. In the regions R and T, the complex dielectric material 5 is formed on the buffer layer 4d in a laminated structure. Therefore, the signal light propagating in the regions S and U propagates without being absorbed by the buffer layer 4 d, but the unnecessary light is absorbed by the complex dielectric material 5.

In the case of FIG. 1E, a complex dielectric material 5 is formed on the entire surface of the waveguide 2 via a buffer layer 4e. However, the buffer layer 4e is set to the same thickness as the above-described buffer layer 4b in the regions S and U, and is set to the same thickness as the above-described buffer layer 4c in the regions R and T. For this reason, the signal light propagating in the regions S and U is
Unnecessary light that is propagated with low loss by the thick portion of 4e and generated as a by-product is absorbed by the complex dielectric material 5 in the regions R and T via the thin portion of the buffer layer 4e.

Next, an embodiment in which the present invention is applied to an optical integrated frequency analyzer will be described. FIG. 2 shows the manufacturing process of the integrated optical frequency analyzer of this embodiment in order.

In FIG. 2A, a waveguide type lens 3 is provided on a part of a waveguide 2 provided on a substrate 1 such as LiNbO ₃ .
As the waveguide type lens 3, a mode index lens, a geodesic lens, a diffraction type lens, or the like can be considered.

In FIG. 2B, a buffer layer 4 made of SiO ₂ or the like is provided in a region where signal light propagates in the waveguide 2 during operation of the present optical integrated circuit.

In FIG. 2 (c), a complex dielectric material 5 is provided in contact with the waveguide 2 and the buffer layer 4 in a region excluding a portion where SAW (surface acoustic wave) propagates, and an electrode for SAW generation is provided. 6 are formed. Further, a semiconductor laser 10 and a photodetector array 11 are mounted.

The operation of the optical integrated frequency analyzer thus configured will be described. As shown in FIG. 3, light emitted from the semiconductor laser 10 enters the waveguide 2 and is collimated by the waveguide lens 3 to become parallel light. This collimated light is
The light is diffracted by the SAW generated by the electric signal from the electrode 6 and propagated on the waveguide 2, and the propagation direction is changed. SAW
Is condensed by the waveguide lens 3 and enters the photodetector array 11. Based on the photodetection intensity distribution of the photodetector array, frequency analysis of the electric signal that has generated SAW can be performed.

The area BCHI shown in FIG. 3 is an area where SAW propagates, and the buffer layer 4 and the complex dielectric material 5 shown in FIG. 2 are not provided. The region LMNK and the region OEFP are regions where the signal light propagates, in which the buffer layer 4 and the complex dielectric 5 are provided. Further, the region ABML, the region CDEO, the region PFGH, and the region KNIJ are waveguide portions where signal light does not propagate, and only the complex dielectric material 5 is provided.
TM mode light is used as signal light, and the buffer layer 4
When the and the complex dielectric 5 are selectively provided, the signal light propagating through the waveguide will not be transmitted due to the presence of the buffer layer.
Unnecessary light, such as the undiffracted light 20 and the leaked lights 21 and 22, is not selectively affected by the light and is selectively removed from the waveguide. As described above, in this embodiment, the combination of the buffer layer 4 and the complex dielectric material 5 effectively works for removing unnecessary light.

In FIG. 3, the sides MN and OP may not cross the signal light at right angles. This is because the end faces of the buffer layer are on the sides MN and OP, and the equivalent refractive index of the waveguide may change abruptly at this portion to generate the reflected light 23. In order to distinguish the reflected light 23 from the signal light and to effectively remove the reflected light 23, the traveling direction of the reflected light 23 must be different from the signal light.

According to this embodiment, since the complex dielectric material 5 protects the waveguide 2, external light can be completely shielded. Further, since the complex dielectric material 5 can be formed simultaneously with the electrode 6, the manufacturing process is not so complicated.

FIG. 4 shows an embodiment in which the present invention is applied to another optical integrated frequency analyzer. In FIG. 4, light generated from a semiconductor laser 10 propagating through a waveguide 2 provided on a substrate 1 is diffracted by the effect of SAW generated from a waveguide lens 3 and an electrode 6, and collected by the waveguide lens 3. The light is emitted, and the light intensity distribution is detected by the photodetector array 11. In this embodiment, there is no buffer layer disposed in contact with the portion of the waveguide through which the signal light propagates as shown in FIG. 2 (b), and only the portion of the waveguide where the signal light and SAW do not propagate, A complex dielectric material 5 is provided. In this embodiment, since the buffer layer need not be formed, the manufacturing process is simplified.

FIG. 5 shows an embodiment in which the present invention is applied to an optical head for an optical integrated type optical disc. FIG. 5 shows two manufacturing processes of an optical head for an optical integrated type optical disk.
One is in the order of FIGS. 5 (a), (b) and (c) and the other is in the order of FIG.
Figures (a), (d) and (e) are in that order.

In FIG. 5 (a), SiO ₂ in contact with the substrate 30 such as Si
A buffer layer 31 is provided, and a thin film deposition type waveguide 32 is provided in contact with the buffer layer 31. TM to waveguide
The mode incident light 40 is converted into substantially parallel light by a waveguide lens 33 such as a mode index lens, a geodesic lens, and a diffractive lens. This light exits the waveguide surface by the action of the grating coupler 35 and is collected by the external lens 36. The light reflected from the optical disk surface at the focal point follows the same path, and enters the waveguide surface again by the grating coupler 35. Then, the light enters the light intensity detector 37 by the action of the beam splitter 34 and the waveguide lens 33. While reading information on the optical disk with an electric circuit (not shown),
A tracking error signal and a focus error signal are detected.

In FIG. 5 (b), a buffer layer 42 is provided in contact with the waveguide at the portion where the signal light propagates. Thereafter, in FIG. 5B, a complex dielectric material 43 is provided in contact with the waveguide 32 and the buffer layer. At this time, the complex dielectric material 43 is provided so that the light emitted from the grating coupler 35 is not blocked by the complex dielectric material 43. A semiconductor laser 45 serving as a light source is attached. This way,
Unnecessary light secondary to the signal light is removed by the complex dielectric material 43.

Also, after FIG. 5 (a), as shown in FIG. 5 (d),
The buffer layer 42 is provided in contact with not only the waveguide in the portion where the signal light propagates but also the grating coupler 35.
Then, as shown in FIG. 5 (e), a complex dielectric material 43 is provided so as not to block the light emitted from the grating coupler 35. Also in this case, unnecessary light generated as a secondary component from the signal light is removed by the complex dielectric material 43.

The complex dielectric material 43 installed in contact with the portion of the waveguide where signal light does not propagate may be installed directly on the waveguide, as shown in FIG. Fig. 1 (c)
As described above, a buffer layer having an appropriate thickness may be interposed.

With such a configuration, not only unnecessary light in the waveguide 32 can be removed, but also external light incident on the light intensity detector 37 can be shielded, or the light intensity detector 37 formed on the Si substrate or other light It can produce a magnetic shielding effect on an electric circuit or act as a protective film for the waveguide 32.

It is conceivable that the complex dielectric material 43 is dropped to ground or an appropriate potential is applied as necessary. By doing so, there is an effect that the magnetic shield effect by the complex dielectric material 43 can be improved.

FIG. 6 shows an embodiment in which the present invention is applied to an optical integrated fluid flow velocity detector. Light emitted from the semiconductor laser 10 is incident on the waveguide 2 provided on the substrate 1, and the TM mode light 51 is emitted.
To excite. The light 51 becomes the waveguide out-of-plane light 52 due to the action of the grating coupler 38 and is focused on the focal point 50. The scattered light 53 whose intensity is modulated by the particles passing through the focal point 50 on the flow of the fluid whose flow velocity is to be measured is turned into light 54 in the waveguide surface again by the action of the grating coupler 39, and is transmitted to the light intensity detector 12. Incident. The signal from the light intensity detector 12 is
It is converted into a flow velocity signal by an amplifier, counter or other electric processing circuit (not shown).

Here, the undiffracted light in the grating coupler 38
The light 55 is superimposed on the light 54 and is incident on the light intensity detector 12, causing deterioration of the optical performance of the device. This is particularly noticeable when the intensity of the light 54 is weak. In this embodiment, the complex dielectric material 5 is arranged in contact with the waveguide 2. Alternatively, they are arranged via a buffer layer as shown in FIG. This way,
The undiffracted light 55 is effectively absorbed, and the optical performance of the device is not deteriorated.

FIG. 7 is a diagram showing an embodiment in which the present invention is applied to a mechanism for obtaining parallel light in a slab waveguide and then diffracting the parallel light by SAW. In the waveguide 2 provided on the substrate 1, TM mode light is excited by the semiconductor laser 10. Part of this light is incident on the waveguide lens 3,
It becomes a predetermined parallel light. On the other hand, light that has not entered the waveguide lens 3 becomes unnecessary light, which may cause performance degradation of the optical integrated circuit.

Therefore, in the present embodiment, the complex dielectric material is disposed in contact with the waveguide or via the buffer layer to absorb unnecessary light. At this time, the complex dielectric material can be shared as an electrode for SAW generation. That is, as shown in FIG. 7, the complex dielectric material is disposed in contact with the waveguide at the portion where the unnecessary light propagates or via the buffer layer, and is formed into a shape that functions as an electrode. In FIG. 7, electrode portions 7 and 8 and unnecessary light absorbing portions 7 'and 8' of an object having a complex dielectric constant are formed simultaneously. In this way, the structure is simple and the manufacturing process is not complicated, so that the function of absorbing unnecessary light can be sufficiently exhibited. Further, there is an effect that the unnecessary light absorbing portion can be shared as a bonding pad.

Further, the present invention is applicable not only to a frequency analyzer and an optical disk optical head, but also to an arithmetic unit such as a correlator, an optical scanner, a multiplexer and a demultiplexer, and other optical integrated circuits using a slab waveguide. It can be implemented by a method.

Also, in any of the embodiments described above, any one of FIGS. 1A to 1E can be applied.

〔The invention's effect〕

ADVANTAGE OF THE INVENTION According to this invention, since the unnecessary light in a slab waveguide can be removed effectively, the optical performance of an optical integrated circuit can be improved significantly.

[Brief description of the drawings]

FIG. 1 is a sectional view of a plane perpendicular to a waveguide of an optical integrated circuit according to the present invention, FIG. 2 is a perspective view of an embodiment in which the present invention is applied to an optical integrated frequency analyzer, and FIG. 3 is FIG. FIG. 4 is a schematic view for explaining the operation of the embodiment, FIG. 4 is a perspective view of an embodiment in which the present invention is applied to an optical integrated type frequency analyzer, and FIG. 5 is an embodiment in which the present invention is applied to an optical integrated type optical disk optical head. Perspective view of embodiment, sixth
FIG. 7 is a perspective view of an embodiment in which the present invention is applied to a fluid flow velocity detector, and FIG. 7 is a view after the present invention obtains parallel light in a slab waveguide.
It is a perspective view of the example applied to the mechanism which makes it diffract by SAW. 1 ... substrate, 2 ... waveguide, 3 ... waveguide type lens, 4b ~
4e: buffer layer, 5: complex dielectric material, 6: electrode, 10
…… Semiconductor laser, 11 …… Photodetector array.

Claims (2)

(57) [Claims] 1. An optical integrated circuit for transmitting a signal by transmitting TM mode light in a slab waveguide, wherein the slab waveguide is provided on a region of the slab waveguide other than a region for transmitting the light. An optical integrated circuit characterized by forming a complex dielectric material that absorbs light scattered in a laminated structure. 2. The optical integrated circuit according to claim 1, wherein a buffer layer is interposed between the slab waveguide and the laminated structure of the complex dielectric material. circuit.