JP4735097B2 - Optical module - Google Patents

Description

  The present invention relates to an optical module having an optical filter that demultiplexes light of a predetermined wavelength band, and more particularly to an optical module that can improve optical isolation and suppress optical crosstalk by an optical filter structure that suppresses the influence of stray light.

  In recent years, in the technical fields such as optical communication typified by regional networks and inter-city networks, and optical links within and between servers and routers, it is expected to realize small-sized optical modules at low cost. Yes. As optical modules used for these applications, optical modules for transmission, reception, and transmission / reception using multiplexed light using a plurality of signal light wavelengths are known.

  Conventionally, this type of optical module is provided with an optical transmitting unit on which a light emitting element is mounted and an optical receiving unit on which a light receiving element is mounted. In such an optical module, an optical filter for multiplexing and demultiplexing a plurality of signal lights is arranged in the middle of a path from the optical receiver to an optical fiber for connection to an external device. . Also in the optical subscriber system, an optical filter having a structure for demultiplexing multiplexed light is arranged in the middle of the optical path for the purpose of reducing the number of input / output fibers to one. In this case, the optical filter distributes the wavelength to the light emitting element and the light receiving element separately from the wavelength of the optical signal handled by the light emitting element and the light receiving element.

  However, even when the above optical filter is used, there is a problem in that the optical signal cannot be sufficiently demultiplexed and the optical isolation is poor (or the optical crosstalk is large). One possible cause is stray light. Stray light is light that enters the cladding without entering the core of the optical path at the joint between the optical fiber (or light emitting element) and the core of the optical path, or light that leaks without entering the cladding. . Such stray light enters the optical filter at various angles.

  Usually, when the incident angle of light to the optical filter changes, the wavelength characteristic of the light transmittance of the optical filter shifts. For example, in the case of an optical filter having the characteristic of transmitting light on the long wavelength side and blocking (reflecting) light on the short wavelength side, light in the blocking wavelength band close to the light in the transmitting wavelength band is light at a large incident angle. When entering the filter, the incident light tends to pass through the optical filter and tends to increase the light transmittance. When stray light is incident on such an optical filter at a small incident angle, such stray light is reflected by the optical filter and cut (does not become transmitted light), whereas when stray light is incident on the optical filter at a large incident angle, Such stray light is transmitted without being sufficiently reflected by the optical filter to increase the light transmittance. The optical isolation of the optical filter is deteriorated by the influence of such stray light. In order to improve optical isolation, it is necessary to suppress the transmission of stray light, and various means have been taken conventionally.

For example, in the optical module described in Patent Document 1, the outside of the optical waveguide is shielded by inserting a light shielding plate having a hole in the optical waveguide between the light emitting element and the light receiving element, and stray light is transmitted to the light receiving element side. It is restrained to do. In addition, in the optical module described in Patent Document 2, the stray light is prevented from being transmitted to the light receiving element side by arranging an optical filter with a pinhole covered with a metal film in front of the light receiving element. Yes.
JP 2001-249241 A (pages 3 to 4, FIG. 1 and FIG. 2) JP 2001-305365 A (page 3, FIG. 1)

  In the optical module described in Patent Document 1 or Patent Document 2, it is necessary to accurately adjust the optical filter so that the light shielding plate and the pinhole coincide with the optical waveguide portion. However, the precision required for such alignment adjustment is severe, and there is a problem that the mounting cost becomes high.

  The present invention has been made to solve the above-described problem, and an object of the present invention is to provide an optical module having a structure that can easily suppress transmission of stray light having a large incident angle to the light receiving element side. It is to provide.

The optical module of the present invention to solve the above problems, an optical module including an optical waveguide substrate having an optical waveguide formed in the cladding, and an optical filter provided at the end or in the middle of the optical waveguide, wherein as the light filter has a large angle of incidence, an optical filter whose transmittance of light is increased blocking wavelength region, high refractive index material having a refractive index higher than that of the cladding of the optical waveguide substrate, the said optical filter A light incident side from the optical waveguide is provided , a transmission side optical waveguide or an optical receiver is disposed on the transmitted light side of the optical filter, and light incident on the optical filter is disposed on the optical waveguide substrate. Are formed on the incident-side optical waveguide and the reflection-side optical waveguide of the light reflected by the optical filter, and these optical waveguides are merged in the optical waveguide substrate. Part Characterized in that provided in a portion except for the.

According to the present invention, the high refractive index material having a higher refractive index than the clad of the optical waveguide substrate is provided on the light incident side of the optical filter in which the transmittance of light in the blocking wavelength region increases as the incident angle increases. Therefore, the stray light that has propagated through the clad is refracted by the high refractive index material so that the incident angle becomes small, and then enters the optical filter. As a result, the stray light component reflected by the optical filter increases, and the optical isolation of the optical filter can be improved. Such an improvement in optical isolation is particularly effective when the transmission wavelength transmitted through the optical filter and the reflection wavelength reflected by the optical filter are close to each other. In the optical module of the present invention, when there is an optical transmitter, the optical filter structure reduces stray light due to the transmitted light, so that optical crosstalk can be suppressed. In addition, according to the present invention, since a high-refractive index material has a simple structure that is simply provided on the light incident side of the optical filter, high-precision alignment is not required for a light shielding plate or an optical filter with a pinhole. Becomes easy.
In addition, when an optical receiver is disposed on the transmitted light side of the optical filter, the optical receiver receives light that has passed through the optical filter. According to the present invention, stray light passes through the optical filter. As a result, it is possible to suppress reaching the optical receiving unit, so that it is possible to improve optical isolation in the optical filter and suppress optical crosstalk.
The optical waveguide substrate is formed with an incident-side optical waveguide for light incident on the optical filter and a reflective-side optical waveguide for light reflected by the optical filter, and these optical waveguides are within the optical waveguide substrate. It is preferable that the high refractive index material is provided in a portion excluding the joining portion. According to the present invention, the incident side optical waveguide and the reflection side optical waveguide are merged in the optical waveguide substrate, and the high refractive index material is provided in a portion other than the merged portion. Acts to cause stray light to enter the optical filter at a smaller incident angle. As a result, stray light that passes through the optical filter can be suppressed, optical isolation of the optical filter can be improved, and optical crosstalk can be suppressed.

  In the optical module of the present invention, the high refractive index material may be formed on a light incident surface of the optical filter, or may be formed on a surface of the optical waveguide substrate facing the optical filter. Good. According to any of these inventions, it is possible to easily provide a high refractive index material that exhibits the above effects.

  In the optical module of the present invention, the optical waveguide substrate is formed with a filling groove for arranging the high refractive index material, and the surface on the light incident side of the filling groove is other than the incident optical axis. It is preferable that the light scattering surface has a normal line. According to this invention, the light scattering surface having the normal line other than the incident optical axis acts so as to increase the light scattering effect on the stray light in the portion other than the optical waveguide. As a result, the amount of stray light transmitted through the optical filter can be reduced, optical isolation can be further improved, and optical crosstalk can be suppressed.

  In the optical module of the present invention, the optical waveguide substrate is provided with an optical waveguide on the side of the optical receiver that guides light to the optical receiver, and the optical waveguide is disposed on the transmitted light side of the optical filter. Preferably it is. According to this invention, since the optical waveguide substrate is disposed on the optical receiver side, the optical signal transmitted through the optical filter can be reliably guided to the optical receiver.

As described above, according to the optical module of the present invention, the stray light propagating through the optical waveguide substrate increases before entering the optical filter in which the transmittance of light in the blocking wavelength region increases as the incident angle increases. Since the refractive index material is refracted so that the incident angle becomes small, stray light is reflected by the optical filter, and a component that passes through the optical filter is reduced. As a result, the optical isolation of the optical filter can be improved. Such an improvement in optical isolation is particularly effective when the transmission wavelength that passes through the optical filter is close to the reflection wavelength that reflects the optical filter. The optical module of the present invention can suppress optical crosstalk because stray light due to transmission light is reduced due to the above structure.

  In addition, according to the optical module of the present invention, since it has a simple structure in which a high refractive index material is simply provided on the light incident side of the optical filter, high-precision alignment is not required for a light shielding plate or an optical filter with a pinhole. As a result, assembly becomes easy.

  Hereinafter, a plurality of embodiments of an optical module of the present invention will be described in detail with reference to the drawings. In the present application, “incident angle” is defined as the angle of incident light with respect to the normal of the incident surface of the optical filter.

(First embodiment)
1 and 2 are an overall perspective view and a plan view of an essential part showing an optical module according to a first embodiment of the present invention, and FIG. 3 shows an AA ′ line (wavelength λ ₀ of light having a wavelength λ ₀₎ in FIG. It is sectional drawing along a path | route.

  The optical module 1 is a module for optical reception or optical transmission / reception, and has a configuration in which an optical waveguide substrate 61 is mounted in a module package (not shown). On the optical waveguide substrate 61, an LD element (laser diode element) 7 that outputs light by light emission is mounted, and an optical fiber 8 is disposed in parallel with the LD element 7. The optical receiver 11 is disposed on the terminal side of the optical waveguide substrate 61 opposite to the LD element 7. In this case, an interface unit including an optical fiber or the like may be provided for output instead of the LD element 7.

  The optical receiver 11 is provided with a mounting substrate 10 (which can be manufactured simultaneously with the optical waveguide substrate 61) on which a PD element (photodiode element) 9 is surface-mounted. An optical filter 2 is provided between the optical receiver 11 and the optical waveguide substrate 61. The optical filter 2 is provided at the position described above by being attached to the end surface of the optical waveguide substrate 61, that is, the end surface on the optical receiver 11 side.

  As shown in FIG. 3, the optical waveguide substrate 61 includes a substrate 612, a clad 611 laminated on the substrate 612, and a core portion formed inside the clad 611 (referred to as “optical waveguide” in the present invention). ). The clad 611 is made of silicon, glass, polymer resin, or the like, and an optical waveguide (incident side optical waveguide) 62 that guides the light from the LD element 7 to the optical filter 2 and the light reflected by the optical filter 2 is an optical fiber 8. An optical waveguide (reflection-side optical waveguide) 63 is formed to guide the light.

The optical filter 2 is formed by, for example, a dielectric multilayer filter, and has a characteristic of transmitting light of a specific wavelength and reflecting light other than the specific wavelength among the multiplexed light propagating through the optical waveguide 62. is doing. In the embodiment shown in FIGS. 2 and 3, light having a wavelength λ ₀ on the long wavelength side is transmitted, and light having other wavelengths such as the wavelength λ ₁ on the short wavelength side is reflected.

  In this embodiment, a high refractive index material 5 is provided on the light incident side of the optical filter 2. The high refractive index material 5 has a higher refractive index than the clad 611 of the optical waveguide substrate 61. As a material having a refractive index higher than that of the clad 611, a light transmissive silicon resin, an ultraviolet curable epoxy resin, an acrylic resin, or the like can be selected. The high refractive index material 5 is formed by applying these materials to the light incident side surface of the optical filter 2 and curing or pasting them. As the application means, brushing or spraying may be performed on the light incident surface of the optical filter 2, or the light incident surface of the optical filter 2 may be immersed in the above-described material. Further, when the high refractive index material 5 is formed on the optical filter, it may be formed when the optical filter is formed (for example, when a dielectric multilayer filter is formed). The thickness of the high refractive index material 5 formed in this way is preferably about 10 to several tens of μm.

In the optical module 1 having the above structure, the incident signal light 71 having the long wavelength λ _{0 and} the incident signal light 73 having the short wavelength λ ₁ are propagated through the optical waveguide 62 as multiplexed light and propagated through the optical filter. 2 is reached. These signal light 71 and 73, by propagating through the optical waveguide 62, at an incident angle theta ₀ in the high refractive index material 5 (optical filter 2).

On the other hand, the stray light 41 in the clad 611 is incident on the high refractive index material 5 at various incident angles, but is cut by the filter characteristics of the optical filter 2 when incident at a small incident angle. The stray light 41 shown in FIG. 2 is light having a wavelength λ ₁ that is incident on the high refractive index material 5 at an incident angle θ ₁ (θ ₁ > θ ₀ ) that is larger than the incident angle θ ₀ of the incident signal lights 71 and 73.

In such an optical module 1, the signal light transmitted through the optical filter 2 enters the PD element 9 on the optical receiver 11 side as transmitted signal light 72 (wavelength λ ₀ ). On the other hand, the signal light reflected by the optical filter 2 becomes the reflected signal light 74 and propagates through the optical waveguide 63 of the clad 611 and is transmitted from the optical fiber 8. The stray light 41 reaching the high refractive index material 5 at an incident angle θ ₁ larger than θ ₀ is incident on the high refractive index material 5 and refracted, and then reaches the optical filter 2 to be reflected. Becomes smaller. Hereinafter, this operation will be described.

4 and 5 is for explaining the action of the high refractive index material 5, Figure 4 shows the variation of light transmittance with respect to wavelength, FIG. 5 is the light transmittance of the optical filter at the wavelength lambda ₁ of the light The incident angle dependency is shown.

In an optical filter that transmits long-wavelength light and reflects short-wavelength light, as shown in FIG. 4, the wavelength characteristic of light transmittance shifts to the short-wavelength side as the incident angle θ increases. Although it depends on the design of the optical filter, even when the transmittance of light with a wavelength λ ₀ is constant, the transmittance increases with an increase in the incident angle θ in the case of the wavelength λ ₁ . Accordingly, when the stray light 41 having the wavelength λ ₁ is directly incident on the optical filter 2 at a large angle (incident angle θ ₁ ), the transmission stray light 42 (see FIG. 2) is generated through the optical filter 2. Become.

On the other hand, in the optical module of the present invention, the high refractive index material 5 having a higher refractive index than that of the clad 611 is disposed on the light incident side of the optical filter 2. Thus, by arranging the high refractive index material 5 on the front side of the optical filter 2, the light having the wavelength λ ₁ (stray light 41) is refracted by the high refractive index material 5, so that the incident angle θ to the optical filter 2 is Get smaller. As a result, as shown in FIG. 5, the stray light 41 having the wavelength λ ₁ has a reduced transmittance of the optical filter 2, so that the component of the transmitted stray light 42 is decreased, and conversely, the component of the reflected stray light 43 is increased. Accordingly, it is possible to suppress the transmitted stray light 42 that is propagated to the optical receiver 11.

Then, if the refractive index of the medium of the optical waveguide 62 of the incident side (cladding 611) was n _1, for the refractive index n ₂ of the high refractive index material 5, it holds the Snell's law shown in Equation 1.

n ₁ × sin θ ₁ = n ₂ × sin θ ₀ (Expression 1)

At this time, the stray light 41 has the same incident angle θ ₀ as the incident signal light 73. Therefore, most components of the stray light 41 become reflected stray light 43, and the components of the transmitted stray light 42 approach zero. In this case, it is desirable to satisfy n ₂ of the formula 1, not limited thereto as stray light suppression. Thus, by providing the high refractive index material 5 on the light incident side of the optical filter 2, the incident angle θ ₀ of the stray light to the optical filter 2 is reduced, and the stray light can be reflected as the reflected stray light 43. Therefore, transmission of the stray light 41 through the optical filter 2 can be suppressed without changing the optical filter 2.

In such an embodiment, the stray light 42 propagating through the optical waveguide substrate 61 is refracted by the high refractive index material 5 before entering the optical filter 2, and the incident angle of the stray light with respect to the optical filter 2 becomes small. Enters the optical filter at a small angle. For this reason, the component of the stray light reflected by the optical filter 2 increases. Therefore, most of the light with the wavelength λ ₁ is reflected by the optical filter 2, whereas most of the light that passes through the optical filter 2 becomes the light with the wavelength λ ₀ , thereby improving the optical isolation of the optical filter 2. Can be made. This effect of improving optical isolation is particularly significant when the transmission wavelength transmitted through the optical filter 2 and the reflection wavelength reflected from the optical filter 2 are close to each other. Furthermore, the optical module 1 of this embodiment has a simple structure in which the high refractive index material 5 is simply provided on the light incident side of the optical filter 2, and high-precision alignment such as a light shielding plate or an optical filter with a pinhole is achieved. Since it becomes unnecessary, assembly becomes easy.

  As shown in FIG. 1, the optical receiver 11 has a structure in which a surface-type PD element 9 is surface-mounted on a mounting substrate 10 (which can be manufactured simultaneously with the optical waveguide substrate 61). For example, the end face on the optical filter side may be inclined so as to form a 45-degree mirror, for example, and the PD element 9 may receive the transmitted signal light 32 by converting the optical axis. The optical receiver 11 may have a structure in which a planar PD element 9 mounted on a subcarrier is close to the optical filter 2.

  The optical module of the present invention having such a configuration can suppress optical crosstalk because stray light due to transmission light is reduced. Needless to say, optical crosstalk occurs when light from the LD element on the transmission side is directly or indirectly optically coupled to the PD element on the light receiving side, and suppresses (or reduces) optical crosstalk. For example, to suppress stray light (light that is not coupled to the optical waveguide) generated when light from the LD element on the transmission side is guided to the optical waveguide 62 (core portion), or to reduce stray light that enters the PD element. In particular, in the present application, optical crosstalk can be suppressed by reducing stray light entering the PD element by the optical filter structure. Although FIG. 1 shows an optical transmission / reception module, stray light can be reduced by a similar optical filter structure even in an optical reception module without an optical transmission unit, and optical isolation can be improved.

In this embodiment, the dielectric multilayer optical filter 2 as a comparative example in which a high refractive index material is not attached, and the incident side surface is more refracted than the clad 611 (fluorinated polyimide, refractive index: 1.52). High-refractive index material 5 (acrylic or epoxy resin, refractive index: 1.67, thickness 20 μm) having a high refractive index is used as an example of dielectric multilayer optical filter 2 and these optical filters are used. 2, light having a wavelength of 1490 nm (wavelength λ ₁ ) and light having a wavelength of 1550 nm (wavelength λ ₀ ) were incident as incident signal lights 71 and 73. As a result, in both the comparative example and the example, the signal light 72 having a wavelength of 1550 nm out of the signal lights 71 and 73 passes through the optical filter 2 and becomes the transmitted signal light 72 and reaches the optical receiver 11. The signal light 73 having a wavelength of 1490 nm was reflected by the optical filter 2 to be reflected signal light 74 and transmitted to the optical fiber 8. In this case, the optical isolation of the comparative example was −30 dB, whereas the optical isolation of the example was −50 dB. This is because, in the comparative example, the amount of transmitted stray light 42 having a wavelength of 1490 nm is large, whereas in the example, the amount of reflected stray light 43 is increased by the high refractive index material 5 and the amount of transmitted stray light 42 is relatively decreased. Show.

(Second Embodiment)
6 and 7 are an overall perspective view and a plan view of an essential part showing a second embodiment of the optical module of the present invention, and FIG. 8 is an AA ′ line (wavelength λ ₀ light of wavelength λ ₀₎ in FIG. It is sectional drawing along a path | route.

  In the optical module 1A of this embodiment, the upper surface of the substrate 612 is separated into an optical waveguide substrate 61 on the optical transmission unit side and an optical waveguide substrate 65 on the optical reception unit 11 side. The optical waveguide substrate 61 and the optical waveguide substrate 65 are separated by forming an insertion groove 13 that crosses the boundary between the substrates 61 and 65, and the optical filter 2 is inserted and fixed in the insertion groove 13. The In such a structure, the optical filter 2 is provided in the middle of the entire optical waveguide substrate including the optical waveguide substrate 61 on the optical transmission unit side and the optical waveguide substrate 65 on the optical reception unit 11 side.

  A high refractive index material 5 is provided on the light incident surface of the optical filter 2. In this case, the high refractive index material 5 is not provided in the optical filter 2 but is highly refracted on the surface facing the optical filter 2 in the optical waveguide substrate 61 on the optical transmission unit side, that is, on the end surface on the optical transmission unit side in the insertion groove 13. It is also possible to provide the rate material 5 by pasting it.

  As shown in FIGS. 6 and 7, an optical waveguide 62 for propagating light from the LD element 7 to the optical filter 2 is formed in the clad 611 of the optical waveguide substrate 61 and reflected by the optical filter 2. An optical waveguide 63 that guides the reflected signal light 74 to the optical fiber 8 is formed. On the other hand, an optical waveguide 64 for guiding the transmitted signal 72 transmitted through the optical filter 2 to the PD element 9 is formed in the clad 613 of the optical waveguide substrate 65 on the optical receiver 11 side.

In this embodiment, a material having a higher refractive index than the clad 611 of the optical waveguide substrate 61 is used as the high refractive index material 5. In such a structure, the incident signal light 71 having the wavelength λ ₀ and the incident signal light 73 having the wavelength λ ₁ (λ ₀ > λ ₁ ) propagate through the optical waveguide (incident side optical waveguide) 62 at an incident angle θ ₀ . When reaching the optical filter 2, the incident signal light 71 having the long wavelength λ ₀ passes through the optical filter 2, propagates through the optical waveguide (transmission-side optical waveguide) 64, and reaches the PD element 9. On the other hand, the incident signal light 73 with the short wavelength λ ₁ is reflected by the high refractive index material 5 and the optical filter 2 to become reflected signal light 74, propagates through the optical waveguide 63 and reaches the optical fiber 8.

On the other hand, the stray light 41 having the short wavelength λ ₁ is incident on the high refractive index material 5 at an incident angle θ ₁ larger than the incident angle θ ₀ , but most of the stray light 41 is reflected as reflected stray light 43 as in the first embodiment. The transmitted stray light 42 transmitted to the light receiving unit 11 side is reduced. For this reason, optical isolation can be improved.

(Third embodiment)
FIGS. 9 and 10 are a plan view and a cross-sectional view taken along the line AA ′ showing an optical module according to a third embodiment of the present invention.

  This embodiment is substantially the same as the first embodiment shown in FIGS. 1 to 3, but the high refractive index material 5 is not formed on the optical filter 2 but is formed on the optical waveguide substrate 61. . The high refractive index material 5 is provided on the surface of the clad 611 of the optical waveguide substrate 61 facing the optical filter 2, specifically, on the end surface of the clad 611 on the light receiving unit side 11. That is, the high refractive index material 5 is provided by being attached or applied to the end surface of the clad 611 on the light receiving unit 11 side.

  Thus, in the structure in which the high refractive index material 5 is provided on the optical waveguide substrate 61 side, the refractive index of the high refractive index material 5 needs to be adjusted due to the dimensions of the optical waveguides 62 and 63 formed on the optical waveguide substrate 61. There is a merit that it can respond flexibly to the case.

(Fourth embodiment)
FIGS. 11 and 12 are a plan view and a cross-sectional view taken along line AA ′ showing an optical module according to a fourth embodiment of the present invention.

  In this embodiment, the incident-side optical waveguide 62 and the reflection-side optical waveguide 63 formed in the optical waveguide substrate 61 are merged in the substrate 61. These optical waveguides 62 and 63 are merged at the portion immediately before the optical filter 2 or at the surface (incident surface) thereof, and the high refractive index material 5 is not formed at the merged portion of the optical waveguide. That is, the high refractive index material 5 is provided on the light incident side surface of the optical filter 2 in a portion excluding the merged portions of the optical waveguides 62 and 63.

Thus, by forming the high refractive index material 5 so as not to overlap the optical waveguides 62 and 63, the incident signal lights 71 and 73 propagating through the optical waveguide 62 are reflected on the surface of the high refractive index material 5. Can be suppressed. As a result, the incident signal light 71 having the wavelength λ ₀ is transmitted through the optical filter 2 with high efficiency to become the transmitted signal light 32, and the incident signal light 73 having the wavelength λ ₁ is reflected by the optical filter 2 with high efficiency. Thus, the reflected signal light 74 is obtained.

  In the processing in this embodiment, when the optical waveguides 62 and 63 are formed in the clad 611, the filling groove is formed by RIE, laser processing, or the like. The filling groove is not formed in the joining portion of the optical waveguides 62 and 63, and the clad 611 is left in the joining portion. Then, by filling the filling groove with the high refractive index material 5, it is possible to make a structure in which the high refractive index material 5 is not disposed at the joining portion of the optical waveguides 62 and 63. In order to perform such processing, it is preferable to use a polymer material as the optical waveguides 62 and 63 and the high refractive index material 5.

  In addition to the above, in this embodiment, the surface on the optical waveguide 62 or 63 side (light incident side) in the filling groove is roughened or curved to give a surface other than the incident optical axis. The light scattering surface has a normal line. By setting it as such a light-scattering surface, the scattering effect with respect to the stray light of parts other than the optical waveguides 62 and 63 can be improved.

(Other forms)
FIG. 13 shows an optical module 1E of another form. In this embodiment, the optical module 1E is configured by forming the high refractive index material 5 on the light incident side surface of the optical filter 2. The incident signal light 31 having the wavelength λ ₀ and the incident signal light 33 having the wavelength λ ₁ are incident on the optical filter 2 at an incident angle θ ₀ as multiplexed light (λ ₀ > λ ₁ ). These signal lights may be collimator lights or may be focused beams. Further, stray light is incident on the high refractive index material 5 at various incident angles. Among these, stray light 41 shown in FIG. 13 is stray light incident on the high refractive index material 5 at an incident angle θ ₁ larger than the incident angle θ _0. It is. Since the signal lights 31 and 33 and the stray light 41 propagate in the space, the refractive index of the high refractive index material 5 is set to have a higher refractive index than the surrounding air or gas.

As described above, when the stray light 41 is incident on the high refractive index material 5 having a high refractive index at the incident angle θ ₁ , most of the components are reflected as the reflected stray light 43 and become the transmitted stray light 42. The amount that passes through 2 is reduced. Thereby, the optical isolation of the optical filter 2 can be improved.

1 is an overall perspective view showing a first embodiment of an optical module of the present invention. It is a top view of the principal part of 1st Embodiment of the optical module of this invention. It is sectional drawing along the AA 'line in FIG. It is a graph which shows the light transmittance with respect to the wavelength of an optical filter. It is a graph which shows the transmittance | permeability with respect to the incident angle of an optical filter. It is a whole perspective view which shows 2nd Embodiment of the optical module of this invention. It is a top view of the principal part of 2nd Embodiment of the optical module of this invention. It is sectional drawing along the AA 'line in FIG. It is a top view of the principal part of 3rd Embodiment of the optical module of this invention. It is sectional drawing along the AA 'line in FIG. It is a top view of the principal part of 4th Embodiment of the optical module of this invention. It is sectional drawing along the AA 'line in FIG. It is a top view of the principal part of the optical module of other forms.

Explanation of symbols

1, 1A, 1B, 1C, 1D, 1E Optical module 2 Optical filter 5 High refractive index material 7 LD element 8 Optical fiber 9 PD element 11 Receiver 13 Insertion groove 31, 33, 71, 73 Incident signal light 32, 72 Transmission Signal light
34, 74 Reflected signal light 41 Stray light 42 Transmitted stray light 43 Reflected stray light 61, 65 Optical waveguide substrate 62, 63, 64 Optical waveguide 611, 613 Cladding 612 substrate

Claims (5)

In an optical module comprising an optical waveguide substrate in which an optical waveguide is formed in a clad, and an optical filter provided at the end of or in the middle of the optical waveguide,
The optical filter is an optical filter that increases the transmittance of light in the blocking wavelength region as the incident angle increases.
A high refractive index material having a higher refractive index than the clad of the optical waveguide substrate is provided on the light incident side from the optical waveguide of the optical filter ;
On the transmitted light side of the optical filter, a transmission side optical waveguide or a light receiving unit is disposed,
The optical waveguide substrate is formed with an incident-side optical waveguide for light incident on the optical filter and a reflective-side optical waveguide for light reflected by the optical filter, and these optical waveguides merge in the optical waveguide substrate. An optical module , wherein the high refractive index material is provided in a portion excluding the joining portion .   The optical module according to claim 1, wherein the high refractive index material is formed on a light incident surface of the optical filter.   The optical module according to claim 1, wherein the high refractive index material is formed on a surface of the optical waveguide substrate facing the optical filter. The optical waveguide substrate is formed with a filling groove portion for arranging the high refractive index material, and the light incident side surface of the filling groove portion has a normal line other than the incident optical axis. the optical module according to any one of claims 1 to 3, characterized in that has a surface. The optical waveguide substrate is formed with an optical waveguide on the optical receiver side that guides light to the optical receiver, and the optical waveguide is disposed on the transmitted light side of the optical filter. Item 5. The optical module according to any one of Items 1 to 4 .

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