JP2002258086A - Optical waveguide and optical circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical waveguide which can be utilized as a waveguide type polarizer and is excellent in a transmission characteristic with less insertion loss, concerning an optical signal while being miniaturized and made low-profile and provides a high quenching rate and a wide usable band. SOLUTION: The optical waveguide is constituted by alternately and periodically connecting a first optical waveguide part consisting of a clad part 2 and a core part 1 to a second optical waveguide part having an effective refractive index being higher than that of the first optical waveguide part in a light propagating direction. When the effective refractive index is expressed as nE concerning the TE mode polarization of a propagation light and the effective refractive index is expressed as nM concerning TM mode polarization, |nE-nM|/nE or |nE-nM|/nM is >=1×10<-3> in at least one of the first and the second waveguide parts. Then the optical waveguide is utilized as the waveguide type polarizer and is excellent in the transmission characteristic with less insertion loss concerning the optical signal while being miniaturized and made low-profile, and provides the high quenching rate and the wide usable band.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide functioning as an optical waveguide polarizer suitable for forming an optical integrated circuit in which an optical waveguide is integrated, which is used for optical communication and optical information processing. And an optical circuit board using the same.

[0002]

2. Description of the Related Art An optical waveguide formed in a three-dimensional waveguide shape on a substrate is used as an important optical element constituting an optical integrated circuit used for optical communication and optical information processing. The functions required of this optical waveguide are:
There are wavelength selection, polarization selection, optical path selection, and optical isolation. Among these functions, the polarization selection function is an indispensable function for an optical isolator and a polarization independent device, and it is strongly required to realize these functions in an optical waveguide type.

As an example of a conventional waveguide polarizer, there is, for example, a metal-loaded polarizer. As shown in FIG. 9A, a metal layer 14 is provided near a core portion 11 of an optical waveguide formed on a substrate 13, for example, via a cladding portion 12, as shown in a perspective view of a main part in FIG. The polarizer function is realized by absorbing the TM mode polarized light of the propagating light by the metal layer 14.

As another example, there is an anisotropic Bragg grating type polarizer as shown in a perspective view of a main part in FIG. This is, for example, the cladding 12 on the substrate 13.
A refractive index increasing portion (high refractive index portion) 15 formed by irradiating light periodically in the propagation direction is provided in the core portion 11 formed thereon, thereby constituting a waveguide grating.

[0005]

However, although the conventional metal-loaded polarizer realizes the polarizer function by absorbing the TM mode polarized light, the absorption of the TE mode polarized light is not zero. There is a problem that an insertion loss becomes large to obtain a large extinction ratio, and a problem that a sufficiently small insertion loss and a sufficiently large extinction ratio required for the polarization selection function cannot be satisfied at the same time. was there.

A conventional anisotropic Bragg grating polarizer has a T.sub.1 of propagating light in a refractive index increasing portion (high refractive index portion) 15 which can be formed by irradiating the core portion 11 with light.
| N _E −n _M |, where n _{E is the} effective refractive index for E-mode polarized light and n _M is the effective refractive index for TM-mode polarized light.
/ N _E or | n _E −n _M | / n _M (hereinafter, this may be referred to as a specific effective refractive index difference) is at most about 10 ^{−3 at the} maximum, and a value of this degree is orthogonal to each other. A laser light source that has a very small half-value width and a low operating wavelength to suppress the fluctuation of the center wavelength because the difference between the resonance wavelengths of the gratings for TE-mode polarized light and TM-mode polarized light is only about 1 nm at most. However, it can be applied only to the transmission of light supplied from a computer, and there is a problem that the use is limited.

In recent years, research and development of a waveguide type or fiber type grating that modulates the refractive index utilizing interference of laser light has been advanced, and a polarizer utilizing this grating function and waveguide optical anisotropy has been proposed. (See JP-A-10-82923, JP-A-2000-56159, etc.).

However, these polarizers have a periodic structure of refractive index formed by ultraviolet-induced change in refractive index, and it is difficult to perform large refractive index modulation. Since it is necessary, miniaturization is difficult, and the wavelength range showing the polarization function is very narrow.

In recent years, a polarizer using a so-called photonic crystal in which one polarized light is blocked in a three-dimensional periodic structure has been studied, but its application to a waveguide type has not yet been sufficiently developed. It has not been.

The present invention has been made in view of the above-mentioned problems in the prior art, and has as its object to be used as a waveguide-type polarizer, and to reduce the insertion loss for an optical signal while reducing the size and thickness. It is an object of the present invention to provide an optical waveguide which is small, has excellent transmission characteristics, and can obtain a large extinction ratio and a wide usable band.

Another object of the present invention is to provide an optical waveguide of the present invention which can be used as such a waveguide polarizer.
It is an object of the present invention to provide an optical circuit board which can be manufactured by a simple process, can be miniaturized and highly integrated, and is suitable for an optical module used for optical communication and optical information processing.

[0012]

SUMMARY OF THE INVENTION An optical waveguide according to the present invention comprises a first cladding portion and a core portion in the cladding portion.
And a second optical waveguide having an effective refractive index higher than that of the first optical waveguide are alternately and periodically connected in the light propagation direction. When at least one of the optical waveguide portions of the above has the effective refractive index of propagating light for TE mode polarized light as n _E and the effective refractive index for TM mode polarized light as n _M , | n _E −n _M | / n _E or | n _E− n _M | / n _M is 1 × 10 ⁻³ or more.

[0013] In the above structure, the optical waveguide of the present invention may have an effective refractive index in at least one of the first and second optical waveguide portions with respect to TE mode polarized light or TM mode polarized light of the propagating light. The product of the length and the product of the effective refractive index and the length of the other optical waveguides is approximately one-fourth of the wavelength of the propagating light. It is a feature.

Further, in the optical waveguide according to the present invention, the product of the effective refractive index and the length of the three of the first and second optical waveguide portions is approximately one half of the wavelength of the propagating light. And the product of the effective refractive index and the length in the other optical waveguide portions is approximately one quarter of the wavelength of the propagating light.

Further, an optical circuit board according to the present invention is characterized in that it comprises an optical waveguide having each of the above-mentioned structures formed on the substrate, and a photoelectric conversion element mounting portion optically coupled to the optical waveguide. Things.

[0016]

According to the optical waveguide of the present invention, an optical waveguide having a relatively small refractive index difference composed of a clad portion and a core portion in the clad portion has a higher refractive index than the constituent material of the optical waveguide. Or by increasing the optical anisotropy by adding a low refractive index material and providing a height difference of the effective refractive index,
Since the first and second optical waveguide portions are connected alternately and periodically in the light propagation direction to form a periodic structure, the difference in resonance wavelength with respect to linearly polarized light (TE mode polarized light and TM mode polarized light) orthogonal to each other. By increasing
The extinction ratio of the waveguide-type polarizer can be increased while the insertion loss is reduced, and the extinction ratio is increased. Therefore, the number of connections can be reduced and the size can be reduced.

Further, according to the optical waveguide of the present invention, the product of the effective refractive index and the length of at least one of the first and second optical waveguide sections is determined for the TE mode polarized light or the TM mode polarized light of the propagating light. By setting the product of the effective refractive index and the length in the other optical waveguide portions to approximately one-fourth of the wavelength of the propagating light, the cutoff wavelength band of the wavelength selection characteristic is set to approximately one half of the wavelength of the propagating light. Can be suppressed, and a large extinction ratio can be obtained with the first and second optical waveguide portions having a small number of connections.

Further, according to the optical waveguide of the present invention, three of the first and second optical waveguides (three first optical waveguides, two first optical waveguides and one second optical waveguide) are provided. The product of the effective refractive index and the length in the waveguide section, one first optical waveguide section and two second optical waveguide sections, or three second optical waveguide sections) is calculated by dividing the product of the effective refractive index and the length by approximately half of the wavelength of the propagating light. 1, and the product of the effective refractive index and the length in the other optical waveguide portions is set to approximately one quarter of the wavelength of the propagating light, so that the maximum value of the transmittance in the transmission wavelength band is maintained and the ripple is reduced. Since the optical waveguide can be flattened to a minimum, the usable band of the waveguide type polarizer using the optical waveguide can be widened.

According to the optical circuit board of the present invention including the above-described optical waveguide formed on the substrate and the photoelectric conversion element mounting portion optically coupled to the optical waveguide, the optical waveguide Is an optical module used for optical communication and optical information processing, which is excellent in optical signal transmission characteristics, and can be miniaturized and highly integrated because it has low loss, high extinction ratio, and can be miniaturized. It becomes a suitable optical circuit board.

Hereinafter, the present invention will be described in detail with reference to the drawings. FIGS. 1A to 1C are perspective views each showing an example of an embodiment of the optical waveguide of the present invention.

In the example shown in FIG. 1A, an optical waveguide formed on a substrate 3 and formed of a clad 2 and a core 1 in the clad 2 is connected to the first optical waveguide by a first optical waveguide. As the optical waveguide portion, high refractive index portions 4 constituting a second optical waveguide portion having a higher effective refractive index than this are inserted alternately and periodically in the light propagation direction to form the first and second optical waveguides. The optical waveguide of the present invention in which the portions are alternately and periodically connected is configured.

In the example shown in FIG. 1B, an original optical waveguide is formed on a substrate 3 by an optical waveguide composed of a clad 2 and a core 1 in the clad 2. As a low-refractive-index portion 5 for forming a first optical waveguide portion having a lower effective refractive index than that of the optical waveguide portion, the cladding portions 2 are periodically and alternately deleted in the light propagation direction and air is inserted. Thus, the optical waveguide of the present invention in which the first and second optical waveguide portions are connected alternately and periodically is formed.

In the example shown in FIG. 1C, both the high refractive index portion 4 shown in FIG. 1A and the low refractive index portion 5 shown in FIG. An optical waveguide according to the present invention, in which a second optical waveguide having a higher effective refractive index than the second optical waveguide is alternately and periodically connected in the light propagation direction.

In the case where the optical waveguide of the present invention constitutes an optical circuit in which an optical waveguide and a light emitting / receiving portion of a photoelectric conversion element optically coupled to the optical waveguide are integrated on the same substrate, light receiving / emitting is performed. Since the semiconductor material constituting the portion generally has a high refractive index, and the present polarizer is made of the same material as the center, optical coupling with the photoelectric conversion element is facilitated. Therefore, the example shown in FIG. Is suitable.

In this case, since the material forming the core portion 1 and the cladding portion 2 constituting the first and second optical waveguides in the optical waveguide of the present invention is a material capable of receiving or emitting light, Silicon (Si) / GaAs
-AlGaAs, AlAs, InP, InGaAs, etc. are suitable.

In the case where the low refractive index portion 5 is formed as shown in FIGS. 1B and 1C to form the first optical waveguide, not only is air used, but also As the material, various optical materials having a refractive index smaller than that of the clad portion 2 can be used since the refractive index of the clad portion 2 formed of the above-mentioned material is as small as about 3 at a minimum.

When the optical waveguide of the present invention needs to be optically coupled to an optical fiber from outside the substrate 3,
Since the refractive index of quartz, which is an optical fiber constituent material, is about 1.4 to 1.5, and the present polarizer is also made of a similar material, optical coupling with an optical fiber becomes easy.
The example embodiment shown in FIG. 1 (c) is suitable.

In this case, the material for forming the core portion 1 and the cladding portion 2 constituting the first and second optical waveguides in the optical waveguide of the present invention has a similar refractive index to that of quartz. Glass, fluorinated polyimide, fluorinated acrylate, siloxane polymer or the like having a relatively close refractive index is suitable.

The material for forming the high refractive index portion 4 which is provided mainly to be inserted into the core portion 1 of the first optical waveguide portion and constitutes the second optical waveguide portion having a high effective refractive index is as follows. Since the refractive index is higher than that of the core 1, materials having a higher refractive index than the core 1, such as titanium oxide, tantalum oxide, zirconium oxide, aluminum oxide, germanium oxide, silicon nitride, and PMMA (polymethyl methacrylate), are used. Can be used. In order to make the effective refractive index of the first optical waveguide portion lower than that of the second optical waveguide portion, the material forming the low refractive index portion 5 may be air, magnesium fluoride, lithium fluoride, or the like. A material having a lower refractive index than that of the clad portion 2 such as a fluororesin can be used.

The substrate 3 comprises the cladding portion 2 and the core portion 1 in the cladding portion 2. An optical waveguide formed by alternately and periodically connecting the first and second optical waveguide portions in the light propagation direction is provided. It functions as a support substrate formed on the optical waveguide, and also as a support substrate on which an electric circuit and an opto-electric circuit including the optical waveguide are formed at the same time. As such a substrate 3, various substrates used as substrates for handling optical signals, such as an optical integrated circuit substrate and a photoelectric mixed substrate, such as a silicon substrate and a GaAs substrate.
An nP substrate, a glass substrate, an alumina substrate, a glass ceramic substrate, a multilayer ceramic substrate, a plastic electric wiring substrate, and the like can be used.

The substrate 3 may be made of an optical material having a low refractive index with respect to the core portion 1 and function as the clad portion 2 utilizing a difference in refractive index from the core portion 1. In that case, the same material as the core portion 1 and the clad portion 2 may be used, or different materials may be used.

Next, FIG. 2 is a top view of the example shown in FIG. 1C, and FIGS. 3A to 3C respectively show AA shown in FIG. 2 of the example shown in FIG. FIG. 3 is a cross-sectional view taken along a line, a line BB ′, and a line CC ′. In these figures, the width of the core portion 1 is W, the width of the high refractive index portion 4 is W _H , the length of the high refractive index portion 4 in the light propagation direction is d _H , and the width of the low refractive index portion 5 is W _{H L} , the length of the low refractive index portion 5 in the light propagation direction is denoted by d _L. The lengths d _H and d _L of the high refractive index portion 4 and the low refractive index portion 5 are usually the wavelengths λ of the propagating light.
Are set to approximately one-fourth of
4 copies may be displayed. Further, the high refractive index portion 4 or the low refractive index portion 5 includes a portion for setting the length of at least one of them to approximately one half of the wavelength λ of the propagating light. / 2 parts.

FIG. 3A is a sectional view taken along the line AA 'of FIG. 3 showing a second optical waveguide portion having a high effective refractive index by vertically penetrating the high refractive index portion 4 from the cladding portion 2 to the core portion 1. 3B is a cross-sectional view taken along line BB ′ of FIG. 3B. The low refractive index portion 5 is inserted into the cladding portions 2 on both sides of the core portion 1 to have a low effective refractive index. FIG. 3C is a cross-sectional view taken along line CC ′ of FIG. 3C.
On the other hand, a cross section of a portion of the original optical waveguide composed of only the original core portion 1 and the clad portion 2 is shown. In this example, the optical waveguide at the position of the cross section taken along the line CC ′ in FIG. 3C has no optical anisotropy, but the optical waveguide in the cross section taken along the line AA ′ shown in FIGS. The second optical waveguide portion at the location and the first optical waveguide portion at the location along the BB ′ line cross-sectional view are both perpendicular to the TE mode polarized light that is polarized horizontally with respect to the upper surface of the substrate 3. The effective refractive index is larger for the TM-mode polarized light that is polarized in the negative direction.

Here, the second optical waveguide shown in FIG.
The effective refractive index of the part is n_HE(TE mode polarization) and n
_HM(TM mode polarization), and the first optical waveguide shown in FIG.
The effective refractive index of the road is n_LE(TE mode polarization) and n_LM
(TM mode polarization), resonance wavelength is λ_E(TE mode bias
Light) and λ_M(TM mode polarized light). And each
Length d of λ / 4 part_HAnd d_LTo n_HE× d_H= Λ_E/ 4, n
_LE× d_L= Λ_E/ 4, n_HM× d_H= Λ_M/ 4, n_LM× d_L=
λ_M/ 4, the second optical waveguide
The relative effective refractive index difference in the road is (n_HM-N_HE) / N_HE=
(λ_M−λ_E) / Λ_EAnd (n _HM-N_HE) / N_HM= (Λ_M−
λ_E) / Λ_MAnd the specific effective bending in the first optical waveguide section.
The folding ratio difference is (n_LM-N_LE) / N_LE= (Λ_M−λ_E) / Λ_Eand
(n_LM-N_LE) / N_LM= (Λ _M−λ_E) / Λ_MBecomes this child
Means that the relative effective refractive index difference is the phase of the resonance wavelength due to the difference in polarization.
It is equal to the difference.

The laser light from a general DFB (distributed feedback) laser, which is a typical light source of the light propagating through the optical waveguide of the present invention, has a center wavelength fluctuation of about 0.1 nm / ° C. For example, assuming that the operating environment is 0 to 80 ° C., the center wavelength fluctuation is about 8 nm. In order to exhibit a sufficient function of the polarizer with respect to light from such a laser light source, it is necessary that λ _M −λ _E > 8 nm, and the width of the transmission wavelength band needs to be at least about 8 nm. . Also, λ
_M− λ _E is larger as the relative effective refractive index difference is larger, and the wavelength is 1.31.
In the case of μm, a specific effective refractive index difference larger than 6.1 × 10 ⁻³ is required. The width of the transmission wavelength band is wider as the ratio of the number of λ / 2 parts to the total number of the first and second optical waveguide portions is larger, and the ratio of the number of λ / 2 parts to the total number is the same. In this case, the case where the number of λ / 2 portions is three becomes the largest.

Next, FIGS. 4A and 4B are cross-sectional views of essential parts in each step showing an example of a manufacturing step of the optical waveguide of the present invention.

In the example shown in FIG. 4A, after the core 1 and the clad 2 are formed, the mask layer 6 having the pattern of the high refractive index as shown in FIG. And the core part 1 and the clad part 2 are etched as shown in FIG. Next, as shown in (3), a high refractive index portion 4 is formed by vapor deposition, sputtering, CVD, spin coating, dip coating or the like so as to fill this portion, and then the cladding portion 2 is formed as shown in (4). Excess high refractive index portion 4 above is removed together with mask layer 6 by polishing or etching. Further, a mask layer 6 having a pattern of the low refractive index portion 5 is newly formed thereon as shown in (5), and the core portion 1 and the clad portion 2 are etched as shown in (6). Do. Finally, the mask layer 6 is removed as shown in (7). Thereby, the optical waveguide of the present invention having the shape shown in FIG. 1C is obtained.

On the other hand, the example shown in FIG. 4B has a disadvantage that the number of steps is increased and the process is slightly complicated as compared with the example of the process shown in FIG. 4A, but the mask layer is drawn using a photomask or the like. There is an advantage that a very high accuracy is not required for the mask alignment accuracy in the case. Sub-micron-accuracy mask alignment is easy with an electron beam lithography apparatus, stepper, or the like, but sub-micron-accuracy mask alignment is difficult with an exposure machine using a normal photomask.
According to the process example shown in (b), when the latter is used for drawing a mask layer, it is very useful.

First, as shown in (1), a mask layer 7 having a pattern of a high refractive index portion 4 and a low refractive index portion 5 is drawn and formed by an electron beam exposure machine, an ultraviolet exposure machine or the like, and (2) As shown in FIG. 7, the pattern on the low refractive index portion 5 is covered with another mask layer 8. Next, after etching the core portion 1 and the cladding portion 2 as shown in (3), the high refractive index portion 4 is formed by vapor deposition, sputtering, CVD, spin coating or dip coating as shown in (4). After forming the film by using the above method, as shown in (5), the excess high refractive index portion 4 above the clad portion 2 is removed together with the mask layer 8 by polishing or etching. Further, the pattern of the high refractive index portion 4 is covered with a newly formed mask layer 8 as shown in (6), and the core portion 1 and the clad portion 2 are etched as shown in (7). Finally, the mask layer 7 and the mask layer 8 are removed as shown in (8). Thereby, the optical waveguide of the present invention having the shape shown in FIG. 1C is obtained.

Then, the optical waveguide of the present invention thus formed on the substrate, and a mounting portion of a photoelectric conversion element such as a light-emitting element, a light-receiving element, or an optical operation element optically coupled to the optical waveguide of the present invention. According to the optical circuit board of the present invention comprising: the optical signal of the optical signal between the photoelectric conversion element using the optical waveguide of the present invention, which is suitable for high integration that is low loss and can be reduced in size and thickness. The transmission and reception can be performed satisfactorily, and the optical circuit board is suitable for an optical circuit module used for optical communication and optical information processing.

As an example of the configuration of an optical circuit board in which the optical waveguide of the present invention and the photoelectric conversion element mounted on the photoelectric conversion element mounting section are optically coupled, a light receiving / emitting section and a wavelength filter are integrated. There is a substrate for an optical transceiver module for wavelength multiplexing communication, an optical operation circuit substrate on which an optical receiving / emitting unit and an optical switch are integrated.

[0042]

Next, specific examples of the optical waveguide and the optical circuit board of the present invention will be described.

FIGS. 5A and 5B respectively show FIGS.
It is a diagram which shows the effective refractive index and specific effective refractive index difference of the optical waveguide which has a cross-sectional structure shown to (a) and (b).

In FIG. 5A, the horizontal axis represents the width W _H (unit: μm) of the high refractive index portion 4, and the vertical axis represents the effective refractive index n _HE for the TE mode polarized light in the high refractive index portion 4. The effective refractive index n _HM for TM and TM mode polarized light is shown on the right, and the specific effective refractive index difference (n _HM −n _HE ) / n _HE and (n _HM −n _HE ) /
n _HM , and each plot and characteristic curve are represented by n _HE , n _HM and (n _HM) , respectively, as shown in FIG.
The graph shows how −n _HE ) / n _HE and (n _HM −n _HE ) / n _HM change. Note that the wavelength λ of the propagating light is 1.31 μm,
The refractive index of each part is 1.451 for the core part 1 and 1.4 for the clad part 2.
44, the high refractive index portion 4 is 2.11 (titanium oxide). As can be seen from the results shown in FIG. 5A, n _HM is larger than n _HE , and the relative effective refractive index difference is maximum when W _H = 0.25 μm. Further, it can be seen that the difference between the resonance wavelengths of the two polarized lights is maximum when the relative effective refractive index difference is maximum.

Further, in FIG. 5 (b), the width W _L (unit: [mu] m) on the abscissa low refractive index portion 5, the effective refractive index and the vertical axis on the left for the TE mode polarization in the low refractive index portion 5 n
_The effective refractive index n _LM for _LE and TM mode polarized light is shown on the right, and the specific effective refractive index difference (n _LM −n _LE ) / n _LE and (n _LM −
n _LE ) / n _LM , and the plots and characteristic curves are respectively n _LE · n _{LM as} shown in FIG.
_{· (N LM -n LE) /} n LE · (n LM -n LE) / n shows how the _LM changes. The refractive index of each part is 1.
451, the cladding part 2 is 1.444, and the low refractive index part 5 is 1.0 (air). As can be seen from the results shown in FIG. 5B, n _LM is larger than n _LE , as in FIG.
The relative effective refractive index difference is maximum when W _L = 0.35 μm. Further, it can be seen that the difference between the resonance wavelengths of the two polarized lights is maximum when the relative effective refractive index difference is maximum.

Next, FIG. 6 is a diagram showing a configuration example of a waveguide type polarizer using the optical waveguide of the present invention. In FIG. 6, the horizontal axis represents the direction of propagation of the propagating light in the optical waveguide, and the vertical axis represents the refractive index in the first and second optical waveguide portions. In the waveguide type polarizer in this example, the total number of λ / 4 parts of the first and second optical waveguide parts is 47.
And the number of λ / 2 parts is 3.

FIGS. 7 (a) and 7 (b) show FIG.
FIG. 7 is a diagram showing a transmittance of a waveguide polarizer having a configuration shown in FIG. 6 formed by an optical waveguide having a structure shown in FIG. In FIG. 7, the horizontal axis represents the wavelength (unit: μm) of the propagating light, and the vertical axis represents the transmittance T (unit: dB). Each plot and characteristic curve correspond to TE mode polarized light at a wavelength of 1.31 μm. The state of change of the transmittance with respect to the transmittance and the TM mode polarized light is shown.

In FIG. 7A, at the wavelength λ _E of the TE mode polarized light, λ _E = 1.31 μm, the transmittance T with respect to the wavelength of the propagating light of the waveguide polarizer that transmits the TE mode polarized light and blocks the TM mode polarized light is shown. 5 shows changes, and the refractive index of each part is the same as that of the example shown in FIG. The dimensions of each part are W _{H
= 0.45μm (n HE = 1.8233,} n HM = 1.9152), W L = 0.6
5 μm (n _LE = 1.2515, n _LM = 1.3143), d _H = λ _E / 4
n _HE , d _L = λ _E / 4n _LE . The relative effective refractive index difference of each part is 5 × 10 ⁻² and λ _M −λ _E = 65.5 nm (λ _M = 1.3755)
μm).

According to the results shown in FIG. 7A, the transmission wavelength band near the TE mode polarized light wavelength λ _E = 1.31 μm is 10 nm.
It can be seen that the extinction ratio at λ _E = 1.31 μm is 45 dB or more. With such a specification, it has sufficient performance as a light polarizer using a DFB laser as a light source without temperature control.

In FIG. 7B, at the wavelength of TM mode polarized light λ _M = 1.31 μm, the transmittance of the waveguide type polarizer that transmits TM mode polarized light and blocks TE mode polarized light with respect to the wavelength of propagating light is shown. And d _H = λ _M
The parameters other than / 4n _HM and d _L = λ _M / 4n _LM have the same values as in FIG.

According to the result shown in FIG. 7B, λ _E = 1.2
It is 445 μm, and it can be seen that the width of the transmission wavelength band and the extinction ratio at λ _M = 1.31 μm are similar to those in FIG. 7A.

FIG. 8 shows the TE around the wavelength of 1.31 μm.
Λ for transmission characteristics in transmission wavelength band for mode polarized light
The change with the number of / 2 parts is shown diagrammatically. 8, the horizontal axis and the vertical axis represent the wavelength (unit: μ) of the propagating light as in FIG.
m) and transmittance T (unit: dB). Further, in each plot and characteristic curve, the ratio of the number of λ / 2 parts to the total number of the first and second optical waveguide parts is made substantially constant, and the number of λ / 2 parts is 1 (the total number is 15) · 2. (All 31) ・ 3 (47 all) ・ 4 (63 all) ・ 5 (all
The state of the change in the case of 79) is shown. From this result,
It can be seen that when the number of λ / 2 parts is 3 (the total number is 47), the width of the transmission wavelength band is wide and the flatness of the transmittance T is the best.

It should be noted that the present invention is not limited to the above-described embodiments, and various changes can be made without departing from the gist of the present invention. For example, the first optical waveguide portion and the second optical waveguide portion are not limited to the above-described embodiment, and may have other structures as long as the waveguide has an effective refractive index anisotropy.

[0054]

According to the optical waveguide of the present invention, the optical waveguide composed of the cladding and the core in the cladding having a relatively small refractive index difference has a higher refractive index or a lower refractive index than the constituent material of the optical waveguide. The optical anisotropy is enhanced by adding a material having a refractive index to provide a height difference in the effective refractive index, and the first and second optical waveguide portions are connected alternately and periodically in the light propagation direction to form a periodic structure. Is formed, it is possible to increase the extinction ratio of the waveguide polarizer while reducing the insertion loss by increasing the difference between the resonance wavelengths with respect to linearly polarized light (TE mode polarized light and TM mode polarized light) orthogonal to each other. And the extinction ratio is large, so that the number of connections is small and the size can be reduced.

Further, according to the optical waveguide of the present invention, the product of the effective refractive index and the length of at least one of the first and second optical waveguide portions is determined for the TE mode polarized light or the TM mode polarized light of the propagating light. By setting the product of the effective refractive index and the length in the other optical waveguide portions to approximately one-fourth of the wavelength of the propagating light, the cutoff wavelength band of the wavelength selection characteristic is set to approximately one half of the wavelength of the propagating light. Can be suppressed, and a large extinction ratio can be obtained with the first and second optical waveguide portions having a small number of connections.

Further, according to the optical waveguide of the present invention, three of the first and second optical waveguide portions (three first optical waveguide portions, two first optical waveguide portions, and one second optical waveguide portion) are provided. The product of the effective refractive index and the length in the waveguide section, one first optical waveguide section and two second optical waveguide sections, or three second optical waveguide sections) is calculated by dividing the product of the effective refractive index and the length by approximately half of the wavelength of the propagating light. 1, and the product of the effective refractive index and the length in the other optical waveguide portions is set to approximately one quarter of the wavelength of the propagating light, so that the maximum value of the transmittance in the transmission wavelength band is maintained and the ripple is reduced. Since the optical waveguide can be flattened to a minimum, the usable band of the waveguide type polarizer using the optical waveguide can be widened.

According to the optical circuit board of the present invention including the optical waveguide of the present invention formed on the substrate and the photoelectric conversion element mounting portion optically coupled to the optical waveguide, the optical waveguide Is an optical module used for optical communication and optical information processing, which is excellent in optical signal transmission characteristics, and can be miniaturized and highly integrated because it has low loss, high extinction ratio, and can be miniaturized. It becomes a suitable optical circuit board.

[Brief description of the drawings]

FIGS. 1A to 1C are perspective views of a main part showing an example of an embodiment of an optical waveguide of the present invention.

FIG. 2 is a top view of the embodiment of the optical waveguide of the present invention shown in FIG. 1 (c).

FIGS. 3 (a) to 3 (c) are cross-sectional views taken along line AA ′, line BB ′ and FIG. 1 (c), respectively, showing an example of the embodiment of the optical waveguide of the present invention shown in FIG. 1 (c). It is CC 'sectional drawing.

FIGS. 4A and 4B are cross-sectional views of respective steps showing an example of a manufacturing step of an optical waveguide of the present invention.

FIGS. 5A and 5B are diagrams showing changes in the effective refractive index of the waveguide with respect to W _H or W _L in an optical waveguide according to an embodiment of the present invention, respectively.

FIG. 6 is a diagram showing a configuration example of a waveguide type modifier using an optical waveguide of the present invention.

FIGS. 7A and 7B are diagrams showing changes in transmittance with respect to a propagation light wavelength in an embodiment of the optical waveguide of the present invention.

FIG. 8 is a diagram showing a change in transmittance with respect to a propagation light wavelength in an embodiment of the optical waveguide of the present invention.

FIGS. 9A and 9B are perspective views of relevant parts showing an example of a conventional waveguide polarizer, respectively.

[Explanation of symbols]

 1 ... core part 2 ... clad part 3 ... substrate 4 ... high refractive index part 5 ... low refractive index part

Claims (4)

[The claims] 1. A cladding portion and a core in the cladding portion.
A first optical waveguide section comprising: a first optical waveguide section;
The second optical waveguide having a higher effective refractive index
Connected alternately in the carrying direction, and
At least one of the first and second optical waveguide portions is a
The effective refractive index for the TE mode polarization of light is n_E, TM
The effective index of refraction for_M| N_E−
n_M| / N _EOr | n_E-N_M| / N_MIs 1 × 10^-3that's all
An optical waveguide characterized by the following. 2. A TE mode polarized light or TM of the propagating light.
For mode polarized light, the product of the effective refractive index and the length in at least one of the first and second optical waveguide portions is approximately one half of the wavelength of the propagating light, and the other optical waveguide portions 2. The optical waveguide according to claim 1, wherein the product of the effective refractive index and the length is approximately one fourth of the wavelength of the propagating light. 3. The product of the effective refractive index and the length in three of the first and second optical waveguide sections is approximately one half of the wavelength of the propagating light, and the effective refractive index in the other optical waveguide sections is three. The product of the refractive index and the length is approximately one quarter of the wavelength of the propagating light.
The optical waveguide according to claim 2, wherein 4. An optical waveguide according to claim 1, formed on a substrate, and a photoelectric conversion element mounting portion optically coupled to the optical waveguide. Optical circuit board.