JPS62121407A - Optical filter and wavelength multiplex transmission device using the optical filter - Google Patents

Abstract

PURPOSE:To prepare an optical filter by a process for forming a semiconductor light emitting element or a light receiving element by forming plural numbers of groove having deeper depth than the thickness of a waveguide with a desired spacing of period and a desired width along the propagation direction of light, and embedding film comprising a material having a different refractive index from the refractive index of the waveguide layer in the groove. CONSTITUTION:A substrate 1 comprises a semiconductor, ferroelectric body, magnetic body, or glass, and a waveguide layer 3 is formed interposing a clad layer 2. The refractive index of the clad layer 2 is smaller than the refractive index of the waveguide layer 3. Layers 4-1-4-m having smaller refractive indices than the waveguide 3 are formed with ca. n/2 wavelength spacings. In order to reduce radiation loss at the respective parts, the refractive indices of the layers 4-1-4-m are preferred to be larger than the refractive index of the clad layer. The width of the layers 4-1-4-m are regulated to ca. n/4 of the wavelength.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an optical filter having wavelength selectivity and a wavelength multiplexing transmission device using the optical filter.

[Background of the invention]

Optical wavelength division multiplexing transmission technology in optical fiber communications is important for economicalization of communication systems, and optical multiplexers and demultiplexers are essential devices in the above-mentioned optical wavelength division multiplexing transmission.

Conventionally, an interference film filter is used as one of the optical multiplexers/demultiplexers. An optical multiplexer/demultiplexer using this interference film filter has good characteristics in terms of passband, stopband loss characteristics, and passband width, and is about to be widely used. However, in the above configuration, the interference film filter is vapor-deposited on a glass flat plate, and the glass flat plate with the interference film filter is attached to the glass block with adhesive, which requires precise optical axis alignment when pasting with adhesive. The angle of attaching the flat glass plate to the glass block changes depending on the thickness of the agent, so it is necessary to precisely adjust the position and angle while exciting the light. Furthermore, it takes too much time to assemble, making it difficult to reduce costs. Furthermore, the glass block is mirror polished to improve dimensional accuracy.
Since angle accuracy must be increased, it becomes extremely expensive and difficult to mass-produce. Furthermore, when attempting to configure a hybrid optical module for bidirectional transmission by combining a semiconductor light-emitting element and a light-receiving element with the optical multiplexer/demultiplexer described above, since the optical multiplexer/demultiplexer is a combination of individual parts, assembly processing and optical axis adjustment may be required. The problem was that it was time consuming, very expensive, and difficult to mass produce (Nasoi, Optical Communication Handbook,
Published by Asakura Shoten, p.

324-I), 331. 1982).

[Purpose of the invention]

The present invention provides a one-chip monolithic optical filter that is simpler and more economical by using conventional processes for forming semiconductor light-emitting devices and light-receiving devices. The purpose is to obtain a wavelength division multiplexing transmission device.

[Summary of the invention]

The optical filter according to the present invention and the wavelength division multiplexing transmission device using the optical filter propagate light through a groove in a waveguide layer of a slab or a three-dimensional optical waveguide with a desired periodic interval and a desired width and which is deeper than the thickness of the waveguide layer. Form multiple pieces along the direction,
An optical filter is formed by embedding a film made of a material having a refractive index different from that of the waveguide layer in the groove, and at least one optical filter is provided in the optical waveguide, and an optical signal transmitted through the optical filter is formed. A wavelength multiplexing transmission device is constructed by arranging either a semiconductor light-emitting element or a light-receiving element, or both, on the side and the side of the optical signal reflected by the optical filter and forming a monolithic structure.

The optical filter according to the present invention employs a well-known interference film filter structure, as shown in FIG. In other words, the interference film filter has a layer with a high refractive index (for example, n
2+ n4. n6...) and a layer with a low refractive index (
For example, n3+n5. n7...) alternately with a width of approximately n/4 wavelength (n=1.3......) (in this case, d2゜d3...dn-1). It was formed. In contrast to the above-mentioned interference film filter, the optical filter according to the present invention has a plurality of grooves each having a width of approximately n/4 wavelength at approximately n/2 wavelength intervals in a waveguide layer having a high (or low) refractive index. However, a film made of a material having a low (or high) refractive index is embedded in the groove. and,
Depending on the wavelength characteristics of the optical filter, there may be a
forming at least one groove having a width approximately n/2 wavelengths;
This allows a film with a low (or high) refractive index to be embedded in the groove. That is, a cavity layer is provided to form an optical film of a short wavelength pass type, a long wavelength pass type, a band pass type, or a band rejection type. 1 is 3
It is formed of a dimensional waveguide type.

[Embodiments of the invention]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing the structure of an embodiment of the optical film according to the present invention, in which (a) is a plan view, (b) is a cross-sectional view, and FIG. 2 shows the calculation results of wavelength characteristics of the above embodiment. Figure, 3rd figure (a+
, (b) and (CL) (d) are diagrams showing the manufacturing process of the optical film, respectively, and FIG. 4 is a wavelength multiplex transmission according to the present invention.

1 is a diagram illustrating a first embodiment of a feeding device, in which (a) is a front view;
(b) is a side view, FIG. 5 is a diagram showing a second embodiment of the wavelength division multiplex transmission device, (a) is a front view, (bl is a side view, and FIG. 6 is a diagram showing the wavelength division multiplex transmission device). The third fruit of Denokuisu 1
FIG. 7 is a front view showing a fourth embodiment of the wavelength multiplexing transmission device, and FIG. 8 is a front view showing a fifth embodiment of the wavelength multiplexing transmission device.

The optical filter shown in FIG. 1 is a slab waveguide type optical filter, in which the substrate 1 is made of a semiconductor, ferroelectric material, magnetic material, or glass, and a waveguide layer 3 is formed with a clad layer 2 interposed therebetween. ing. The Clasode layer 2 has a lower refractive index than the waveguide layer 3. 4-1 to 4-m are lower than the refractive index of the waveguide 3, and 1 refractive index is set to approximately n/47 length. In the above embodiment, the substrate 1 is InP, the buffer layer 2 is I
nP, waveguide layer 3 using InGaAsP, 4-
An oxide film doped with 5 tOz of TiO was used as the 1 to 4-m low refractive index layer. The refractive index of the waveguide layer 3 is 3.2, the refractive index of the low refractive index layers 4-1 to 4-m is 1°8, the number of layers m is 23, and a cavity layer with a high refractive index is provided in the middle. FIG. 2 shows the calculation results when two cavity layers with a low refractive index are provided. As you can see from Figure 2, the wavelengths are 1.2 μm, 1.3 μm, and 1.55 μm.
A passband filter has been realized.

FIGS. 3(a) to 3(fd) are diagrams showing the manufacturing process of the above-mentioned optical film, and FIG. 3(a) shows the substrate 1! In the process of forming the cladding layer 2 and the waveguide layer 3, the figure (
b) shows the process of machining m5-i to m5-5 by dry etching, and the groove machining accuracy by dry etching in this case is currently 0.05 μm per 1 μm width.
For example, if the groove width is set to 3/4 wavelength and the groove interval is set to 3/2 wavelength, optical filter characteristics as shown in FIG. 2 can be achieved. FIG. 5C shows a step of filling the trenches 5-1 to 5-5 with a carbon dioxide film 6 (in this case, a film containing Si 02 and Ti 04 ). In the same figure (dl is the step of etching the oxide film 6 on the waveguide layer 3. The oxide film 6 on the waveguide layer 3 is used to prevent characteristic fluctuations due to humidity of the optical filter and to prevent surface contamination. In order to prevent absorption and scattering loss, it may be left as is without etching.

However, the oxide film formed on the waveguide layer 3 is as follows:
It is important that the refractive index is lower than that of the low refractive index layers 4-1 to 4-5 in order to reduce radiation loss in the waveguide. In addition, in the optical filter of the present invention, if a semiconductor material is used for the substrate 1 and a glass such as 8102 is used for the low refractive index layer 6, the refractive index difference can be increased, so that the passband width of the bandpass filter can be increased. It has the characteristics that it is possible to widen the optical filter and to have a large attenuation in the stopband.Therefore, the number of layers (m) may be half or less than that of a conventional optical filter.

FIG. 4 shows a first embodiment of a wavelength division multiplexing transmission device according to the present invention, in which (a) is a front view and (b) is a side view. A cladding layer 2 is formed on a substrate l, a slab waveguide layer 3 having a refractive index higher than that of the cladding layer 2 is formed thereon, and the optical filter 7.8 according to the present invention is formed on the slab waveguide layer 3.
was formed.

Lenses 13, 14, 15, 16 in FIG. 4(a) are formed by recessing a part of the slab waveguide layer 3 into a concave shape, and convert the light emitted from the optical fiber 17 into parallel light. It also converts light emitted from a semiconductor light emitting element into parallel light, or focuses light on a light receiving element. Semiconductor light emitting device or light receiving device 9.10.1
1.12 are attached to the side ends 20 and 21 of the slab waveguide layer 3, respectively. Next, the operation of the wavelength multiplexing transmission device shown in the first embodiment will be explained. The semiconductor light emitting device 9 uses a semiconductor laser with a wavelength λ1 (1.55 μm in this case), and the light receiving device 11 uses a Ge-APD (germanium PD) for receiving an optical signal with a wavelength of 1.2 μm.
An avalanche photodiode) was used for the light receiving element 12, and a Ge-APD for receiving an optical signal with a wavelength of 1.3 μm was used. The optical filter 7 has a wavelength of 1.3 μm, 1.55
A long wavelength pass filter is used that passes an optical signal with a wavelength of 1.2 μm but reflects an optical signal with a wavelength of 1.2 μm, and the optical filter 8 has a wavelength of 1.2 μm.

A band rejection filter was used that passes an optical signal with a wavelength of 1.55/jm but reflects an optical signal with a wavelength of 1.3 μm. Then, a 1.55 μm optical signal is propagated in the direction of arrow 19 within the optical fiber 17, and optical signals with wavelengths of 1.2 μm and 1.3 μm propagated from the direction of arrow 18 are received by the light receiving elements 11 and 12. Note that 10 is a light receiving element for monitoring the output light signal of the semiconductor light emitting element 9. The semiconductor light emitting device and the light receiving device may be formed by liquid phase growth on the substrate 1, or the devices may be externally attached.

FIG. 5 is a diagram showing a wavelength division multiplexing transmission device according to a second embodiment of the present invention, in which (a) shows a front view and (b) shows a side view. The second embodiment is a device having a three-dimensional waveguide structure, and those having the same numbers as those of the first embodiment shown in FIG. 4 have the same functions. In Figure 5, 2
2 is a waveguide layer, and although an embankment-shaped structure is used in this embodiment, a ridge-shaped, diffused-type, etc. may also be used. 23 and 24 are band-pass filters, 23 passing only an optical signal with a wavelength of 1.2 μm, and 24 passing only an optical signal having a wavelength of 1.3 μm. 6 Figure 6 shows a wavelength division multiplexing transmission device of the present invention. This is a diagram showing a third embodiment of the present invention, in which tapered portions 25 and 26 are provided in the waveguide layer in front of the light receiving elements 11 and 12 to suppress unnecessary optical signals. The above tapered part 25.2
The second embodiment is the same as the second embodiment shown in FIG. 5 above, except that 6 is provided.

FIG. 7 is a diagram showing a fourth embodiment of the wavelength division multiplexing transmission device of the present invention. In this embodiment, the semiconductor light emitting device 9 has a wavelength of 1
．． A 3-μm semiconductor laser was used, the light-receiving element 11 was a light-receiving element that received an optical signal with a wavelength of 1.2 μm, and the light-receiving element 12 was a light-receiving element that received an optical signal with a wavelength of 1.55 μm. For the optical filters 27, 28 and 29, band-pass filters shown in FIG. 2 were used, respectively. That is, in FIG. 2, the optical filter 27 has a thickness of 1.3 μm.
A 1 and 3 μm bandpass filter (B
PF), a 1.2 μm bandpass filter was used as the optical filter 28, and a 1.55 μm bandpass filter was used as the optical filter 29.

FIG. 8 is a diagram showing a fifth embodiment of the wavelength division multiplexing transmission device of the present invention. In this example, 1.2 μm in the direction of arrow 38,
Transmit an optical signal of 1.3 μm, and arrow 39 in the opposite direction
An example of a so-called three-wavelength multiplexing transmission device is shown in which a 1.55 μm optical signal is transmitted from the direction of . In FIG. 8, 31° and 32 are semiconductor lasers with wavelengths of 1.2 μm and 1.3 μm, respectively.
33 and 34 are light receiving elements for monitoring the emitted light from the semiconductor lasers 31 and 32, respectively. 30
is a combining element that combines 1.2 μm and 1.3 μm laser beams, and the optical filter 36 has 1.2 μm and 1.3 μm laser beams.
It is a short wavelength pass type or band rejection type filter that allows optical signals of 1.55 μm to pass through and reflects optical signals of 1.55 μm. The optical filter 37 is a long-wavelength passing filter that passes a 1.55 μm optical signal and reflects 1.2 μm and 1.3 μm optical signals.

The present invention is not limited to the above embodiments. First, the number of wavelengths to be multiplexed is not limited to three as in the above embodiment, but can be extended to any number of wavelengths greater than or equal to two. The semiconductor light emitting device may be a semiconductor laser or a light emitting diode. Further, the first embodiment shown in FIG. 4 may be a surface emitting type laser in which the semiconductor laser emits laser light perpendicularly to the substrate. Ge-A is used for the light receiving element.
In addition to PD, InGaAs-APD or InG
It may also be an aAs-PINPD (PIN photodiode). The film 6 buried in the grooves 5-1 to 5-5 has a composition of TiO2゜GeO2, PeOs, Zn, in addition to the simple composition of SiO2.
It may also contain a dopant that controls the refractive index, such as O or A1203. Furthermore, InGaAsP, AtG
Semiconductor materials such as aAs and GaAs, ferroelectric materials, magnetic materials, etc. may be used. The optical transmission system may be an optical multiplexing device or an optical demultiplexing device for unidirectional transmission in addition to bidirectional transmission.

That is, these can be achieved by using only semiconductor light-emitting elements or only light-receiving elements as optical elements. In addition, in FIG. 2, if Si is used as the substrate 1 and a high refractive index film containing B2O3 in S+Oz is formed as the cladding layer 2, a glass waveguide type optical filter can be constructed. can. In the case of the above-mentioned optical filter, characteristics with extremely low loss can be realized compared to the case where a semiconductor material is used. Processing methods for the grooves 5-1 to 5-5 shown in FIG. 3(b) include ion beam etching, high frequency sputter etching, reactive high frequency sputter etching,
Dry etching such as plasma etching, ion irradiation accelerated etching, or similar etching techniques can be used.

〔Effect of the invention〕

As described above, the optical filter according to the present invention and the wavelength division multiplexing transmission device using the optical filter can be applied to a slab or three wavelength multiplexing transmission device.
In the waveguide layer of the dimensional optical waveguide, a plurality of grooves having a desired periodic interval and a desired width and deeper than the thickness of the waveguide layer are formed along the light propagation direction, and the grooves have a refractive index different from that of the waveguide layer. an optical filter is formed by embedding a film made of a material having a refractive index, and either a semiconductor light emitting element or a light receiving element is provided on the side of the optical signal transmitted through the optical filter and the side of the optical signal reflected by the optical filter, Alternatively, by arranging both and forming them monolithically, it is possible to form an optical filter with a new configuration using the process of forming conventional semiconductor light emitting elements and light receiving elements, and using the above optical filter, It is possible to realize a simpler and more economical wavelength division multiplexing transmission device.

[Brief explanation of drawings]

FIG. 1 is a structural diagram showing an embodiment of an optical filter according to the present invention, in which (a) is a plan view, (b) is a cross-sectional view, and FIG. 2 is a diagram showing the wavelength characteristic calculation results of the above embodiment. Figure 3 (al,
(bl, (C1, and (d) are diagrams showing the manufacturing process of the above embodiments, respectively; FIG. 4 is a diagram showing the first embodiment of the wavelength division multiplexing transmission device according to the present invention; (a) is a front view;
bl is a side view, FIG. 5 is a diagram showing a second embodiment of the above device, (a) is a front view, (b) is a side view, and FIG. 6 is a front view showing a third embodiment of the above device. , FIG. 7 is a front view showing a fourth embodiment of the above device, FIG. 8 is a front view showing a fifth embodiment of the above device, and FIG. 9 is a diagram showing the configuration of a conventional interference film filter. 3.22... Optical waveguide 4-1.4-2 to 4-m, 5-1.5-2 to 5-5
...Groove 6...Membrane

Claims (9)

[Claims] (1) In the waveguide layer of a slab or three-dimensional optical waveguide, a plurality of grooves are formed along the light propagation direction at desired periodic intervals and with a desired width, and the grooves are deeper than the thickness of the waveguide layer, and the waveguide is formed in the grooves. An optical filter embedded with a film made of a material that has a refractive index different from that of the layer. (2) The grooves have a periodic interval of about n/2 wavelength (n=1, 3
, 5...), and the groove width is approximately n/4 wavelength. (3) The groove is characterized in that at least one groove with a width of about n/2 wavelength is provided in the middle of a plurality of grooves with a width of about n/4 wavelength. The optical filter described in Section 2. (4) The above-mentioned grooves are characterized in that at least one groove having an interval of approximately 3/4 wavelength is provided in the middle of a plurality of grooves having an interval of approximately n/2 wavelengths. The optical filter described in any of Item 3. (5) The optical filter according to any one of claims 1 to 4, wherein the embedded film covers the waveguide surface. (6) The optical filter according to any one of claims 1 to 5, wherein the material of the embedded film has a refractive index lower than the refractive index of the waveguide layer. (7) The waveguide is characterized in that the substrate constituting the waveguide is made of a semiconductor, a ferroelectric material, a magnetic material, or glass. The optical filter described in any of the above. (8) Form a plurality of grooves in the waveguide layer of a slab or three-dimensional optical waveguide at desired periodic intervals and with a desired width and deeper than the thickness of the waveguide layer along the light propagation direction, and insert the waveguide in the grooves. An optical filter is formed by embedding a film made of a material having a refractive index different from that of the layer, at least one optical filter is provided in an optical waveguide, and the optical signal side transmitted through the optical filter and the optical filter A wavelength multiplexing transmission device formed by arranging either a semiconductor light emitting element or a light receiving element, or both, on the side of the reflected optical signal. (9) The wavelength multiplexing transmission device according to claim 8, wherein the optical waveguide is provided with lenses on the incident side and the output side of the optical filter.