JPS6325604A - Optical circuit device - Google Patents

Abstract

PURPOSE:To reduce crosstalk without increasing the number of parts by arranging a pair of interference film filters out of plural ones for transmitting light with a prescribed wavelength and reflecting and attenuating other light beams at an angle of + or -alpha from an optical path. CONSTITUTION:The interference filters 51-54 constituted of alternate layers of TiO2 and SiO2 films have their transmitting areas and attenuation area respectively in 1,300nm and 1,200nm wavelength for light beams with 15 deg. incident light. On the x-y surface, the filters 51, 52 are arranged with -15 deg. and +15 deg. inclination from the (x) axis, and on the x-z surface filters 53, 54 are arranged with +15 and -15 inclination from the (z) axis. Light with 1,200nm wavelength radiated from a semiconductor laser 1 is sent to a fiber 3 and light with 1,300nm obtained from the fiber 3 is made incident on a Ge-APD 2 through a filter. Light with 1,200nm reflected by a node or the like in the optical path or its stray light is intensely reflected by the filter. Thereby, the crosstalk can be reduced without increasing the number of parts.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical circuit device used in optical wavelength division multiplexing communication for transmitting different optical signals for each wavelength in optical communication.

[Conventional technology]

In order to perform optical wavelength multiplexing, an optical circuit (hereinafter referred to as an optical demultiplexing circuit) that separates light into different wavelengths is required. There are methods to separate light into wavelengths, such as using interference filters, gratings, and prisms, but the most commonly used methods are:
This method uses an interference filter. For example, in Figure 4,
1985 IEICE General National Conference Lecture No. 262
1 is a configuration diagram of the conventional optical demultiplexing circuit shown in FIG.
is a semiconductor laser with wavelength λA, (2) is Ge-APD
, +31 is an optical fiber, (4) is an interference film filter that transmits light of two wavelengths and reflects light of wavelength λB, ls+l
, f'Ji2 An interference film filter that reflects light with wavelength λ9 and transmits light with wavelength λB, and the filter normal to the optical path is 1.
They are inserted to form a fifth degree. +61. (71,+
81 is a lens for collimating or condensing light;
+91. (1111 is a prism, αB is a mirror. In addition, solid lines and broken lines with arrows in the figure indicate optical paths. Next, the operation will be explained. The light with wavelength λA emitted from the semiconductor laser (1) is passed through the lens (6). It is converted into a parallel light beam, passes through an interference film filter (4), travels straight, and is sent out to a fiber (31) by a lens (7).
) is converted into a parallel beam by the lens (7), reflected by the interference film filter (91), propagates in one direction within the prism 0α, reflected by the mirror αυ, and passes through the tangent filter film filter i5j+, +521
G eAP D (21
The light is focused onto H'M. In this way, this optical circuit
It functions to send out the light with wavelength λA to the fiber and guide the light with wavelength λ8 from the fiber to the Ge-APD, thereby enabling bidirectional transmission of two-wavelength multiplexing. G here
Interference film filter +5+ inserted in front of e-APD
1. (521 is.

For example, when light with a wavelength λ9 emitted from the semiconductor laser (1) enters this filter due to reflection, scattering, etc.

It is inserted to remove this, and is selected so that it is transparent for the wavelength λB and reflective for the wavelength λ9.

[Problems that the invention attempts to solve]

However, since the conventional device was configured as described above, it had the following problems. That is, an interference film filter 1511 that transmits the wavelength λ8 and reflects the wavelength λA;
Due to some miscellaneous factors, light of wavelength λA was detected on f52+.

Filter (511, [
521, the filter (511, fs21
In some cases, it was not removed sufficiently.

? Figure 1'S5 is a diagram to explain the situation during this time, and the filter (s+I, 1s21, TiO2 and Sio shown in the paper in Applied Optics Vol. 22, No.
Transmission range wavelength 130 consisting of 23 alternating layers in total of 2 films
The attenuation characteristics for scattered light with a wavelength of 1200 μm when a 0 nm bandpass filter is used. The angle with respect to the optical path of the scattered light is the axis, and the vertical axis is the calculated value of the amount of attenuation of the scattered light received by the filter (511, +521). The broken line in the figure indicates the filter (511 or (52).
) Attenuation characteristic by single filter The solid line is the attenuation characteristic by two filters. As mentioned above, this filter is designed to transmit light with a wavelength of 13Q Onm along the optical path at an incident angle of 15 degrees, and attenuate light with a wavelength of 1200 nm. Every time)
, each filter attenuates the signal by 30 dB, resulting in an attenuation of 60 dB with the two filters.

As is clear from the figure, the angle is 110 degrees to -2 degrees relative to the optical path.
There is almost no attenuation characteristic for light with a wavelength of 1.2 μm that enters the filter at an angle of 0 degrees (arrowed part in the figure).
. In other words, it is clear from Figure 9 that the means used in conventional devices to obtain attenuation by stacking many filters is completely ineffective against such light.On the other hand, due to the reasons mentioned above, Stray light generated in an optical circuit is close to a type of scattered light and has a wide angular component including an angular range of 110 degrees to -20 degrees with respect to the optical path.For this reason, conventional filter configurations It was not possible to attenuate specific angular components of the scattered light, resulting in crosstalk deterioration.

Although we have shown an example in which a specific type of filter is used, this phenomenon is actually based on the operating principle of an interference film filter.

This occurs no matter what kind of interference film filter is used. In other words, in an interference film filter, the transmission and attenuation wavelength characteristics occur when the reflected light from the interface of the films forming each layer interferes with each other according to the optical path difference. Therefore, when the angle of incidence on the filter changes, Accordingly, the optical path difference changes and its transmission/attenuation characteristics change. For example, a filter that transmits light of wavelength λA at an angle of incidence αA is
It also exhibits transmission characteristics for light having an incident angle αB and wavelength λ8 that causes the same optical path difference. The relational expression between α person, αB, λA, and λB is given by (Equation 31).

λA = 130C1 nm, λB = f2(lon
m, θ is 15°, then θB = 27°, and if the filter is tilted at 15° with respect to the optical path, the wavelength 1200 that is incident on the optical path at θ - θB, that is, 112 degrees.
It also exhibits transmission characteristics for nm light, which can explain the characteristics shown in FIG. 5. In this way, when using a filter that has transmission characteristics at an incident angle of 0 for a specific wavelength λA in an optical circuit that performs wavelength multiplexing, equation (3) must be satisfied for other wavelengths λB as well. For an incident angle θBI, the filter exhibits transmission characteristics.

This is because conventional optical circuits do not take any stray light into consideration within the optical circuit.

No consideration was given to the light source entering the filter at an angle different from the designed optical path as described above, which caused crosstalk. Especially in recent years.

With the miniaturization of optical circuits, there is an increasing demand for circuits in which semiconductor optical devices are directly incorporated into optical circuits, as shown in Figure 4. Since the emitted light generally has an extremely wide radiation angle, the intensity of stray light generated within the optical circuit described above increases, and as a result, in conventional optical circuits, crosstalk due to the causes described above greatly deteriorates the performance of the optical circuit. Ta.

Of course (as is clear from equation 31, the wavelength λA and the wavelength λ8
Although such a problem can be avoided to a large extent by increasing the interval between t and t, it is clear that such a countermeasure against t is not desirable from the viewpoint of information density.

The present invention was made to solve the above-mentioned problems, and an object of the present invention is to obtain an optical circuit device with small crosstalk while using almost the same parts as conventional devices.

[Failure to solve the problem]

In the optical circuit device according to the present invention, a set includes two filters that allow light with a predetermined wavelength λA to pass through and attenuate light with another wavelength λ8, and an angle between the normal line of the two filters and the optical path. are inserted into the optical path so that they are equal and the directions of the normals to the optical path are symmetrical.

[For production]

In the optical circuit device according to the eighth aspect of the present invention, a plurality of filters are inserted in different directions with respect to the optical path so that the angles with the optical path are equal, so that the light with the wavelength λ3 to be attenuated is Even if stray light enters a filter at a non-zero angle with respect to the optical path, the angle of incidence to each of the multiple filters is different, so at least one of the filters will inevitably experience large attenuation and crosstalk deterioration. do not have.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an example of an optical circuit device according to the present invention, in which (1) is a semiconductor laser that emits light with a wavelength of 12 GO nm;
2) is Ge-A for receiving light with a wavelength of 1300 nm.
PD, +31 is optical fiber, (4) is wavelength 200nm
an interference film filter that transmits light with a wavelength of 1300 nm and reflects light with a wavelength of 1300 nm, +61. +71. +81 is a lens for collimating or condensing light, +91(l[l
is prism, full is Mi5+, 1st), 15
21.1531. f5411:! Each of the above-mentioned SitaTiO
This is a 23-layer filter consisting of alternating layers of 2 and 5i02 films.
It shows a transmission range for light with a wavelength of 300 nm and an attenuation range for light with a wavelength of 1200 nm. Figure 2 shows filter +5
jl, 1521.1531. It shows the insertion angle of +541 into the optical path, and shows the insertion angle of filter 1511 and (
52j is x −y −Z shown in Fig. 1 or 2
In the axis coordinates, the normal line of the filter is in the x-y plane, and the angle between the normal line and the X axis (optical path) is -15 degrees and +
It is inserted so that the angle is 15 degrees. Also filter (53)
and (54), the normal line of the filter is in the x-z plane and is inserted at +15 degrees and -15 angles with respect to the X axis (optical path).

Next, the present invention will be explained in detail with reference to FIG.

Light with a wavelength f2 (lonm) emitted from the semiconductor laser (1) is converted into a parallel beam by a lens (6), passes through an interference filter (4), is focused by a lens (7), and is sent to a fiber (3). On the other hand, light with a wavelength of 1300 nm that enters the fiber (31) is converted into a parallel beam by the lens (7), reflected by the interference filter (4), travels upward in the prism αG, is reflected by the mirror αυ, and goes along the optical path (X axis). along the interference filter (511, (s21. +53
1. (Sequentially incident on 541. Since the angle of incidence of this light on the filters is 15 degrees, the light of this wavelength passes through these filters and enters the lens (Ge-A
The light is focused onto the PD (21). Also, the light with a wavelength of 120 [1 nm is reflected by a connection point in the fiber transmission line, and passes through the same optical path as the light with a wavelength of 13 QOnm, and then passes through the interference filter t.
The component incident on 5tl, lzl, (矧, +541 is the filter (s+l, (simplified, +531.1541
is this optical path (for light with an incident angle along this path, the wavelength is 13
Since it transmits wavelengths of 1,200 nm and reflects wavelengths of 1,200 nm, it is strongly attenuated by the four filters. These characteristics are exactly the same as those of conventional optical circuit devices.

Next, the light with a wavelength of 1200 nm emitted from the semiconductor laser (1), which caused crosstalk in the conventional optical circuit device, is scattered by some reason such as the edge of the prism rLl and becomes stray light within this optical circuit device. Consider components that enter the filter (511) at wide angles with respect to the optical axis.

For the sake of simplicity, we will first describe the case where such a light ray is incident on the x-y plane at an angle θin with respect to the optical axis, as shown in FIG. 2+a+. This light enters the filter (51) at an angle of θin+15, and then filters (51) at an angle of θin+15.
21 at an angle of θ1n-15.

As a result, the two filters (51) and (52) receive different attenuation. Figure 3 shows the calculated values of the attenuation characteristics that stray light with a wavelength of 1200 nm undergoes when it passes through filters (511 and (521).
The horizontal axis represents the angle to
The solid line represents the attenuation characteristics experienced by each of the filters (5
1) and l52) are shown.

For example, the stray light incident on the filter (511) at an angle of +15 degrees to the optical axis is
This is because this light ray satisfies the relationship of Equation 31, which is a phenomenon that causes crosstalk deterioration in conventional optical circuit devices. However, the optical circuit device according to the present invention As shown in Figure 3, the stray light is strongly attenuated by nearly 30 dB and removed by the second-order filter (521). This is strongly attenuated by a filter configuration like this.Compare this with the fact that in conventional optical circuit devices, stray light could only be removed within the range of 15° to 35° relative to the optical path (Figure 5). It can be seen that the effect of the invention is extremely large.By the way, until now we have considered that stray light is incident at a wide angle with respect to the optical path in the x-y plane, but in general, t
Similar stray light can be considered even if there are 8 in the -y plane.It is clear from the operating principle described above that filters (53) and (54) have the same effect on such stray light. .

Furthermore, as is clear from the operating principle described above.

Filter +511. (The insertion angle of 521 into the optical path is such that the maximum effect can be obtained by having the other filter give the maximum amount of attenuation for the incident angle at which the light of the wavelength to be attenuated is transmitted to one filter. is clear.

Here, let the angle between the normal of the filter and the optical path be α,
If the wavelength to be transmitted is λB and the wavelength to be attenuated is λ8, then
The incident angle θB to the filter at which the filter has a transmission range for the wavelength λB is given by equation (3) as follows.

The angle θm at which the light of wavelength λB that has passed through one filter at the angle θ8 given by equation (4) is incident on the other paired filter is the angle θm where the two filters form an angle of 2α. Therefore, it is given by the following equation.

θ −2α−θB (5) Therefore, the wavelength λ of the filter at the angle of incidence given by equation (5)
The effect of this invention can be maximized by giving the maximum amount of attenuation to light in 8. In the actual example described in 6, the insertion angle of the filter is set so as to meet the conditions as described above. .

Generally, the maximum attenuation range of a filter differs depending on the membrane configuration of the filter, so it is necessary to design each filter individually.

Now, as mentioned above, although the present invention can be constructed from almost the same parts as the conventional optical circuit device, it is possible to make the conventional optical circuit device can significantly improve the shortcomings of

In other words, it has the advantage of being able to use the same components as conventional optical circuit devices and using almost the same assembly method, and yet provides superior effects.

In the above embodiment, four filters are inserted into fX2+, but in order to obtain an even larger amount of attenuation, each filter may be provided with a plurality of filters. Furthermore, since optical circuit devices are generally not axially symmetrical with respect to the optical path as shown in FIG. 1, stray light does not necessarily have an angular component that is axially symmetrical with respect to the optical path. For example, in Figure 1, if the stray light has a wide angle to the optical path only in the x-7 plane, the filter +5
31. (The same effect can be obtained even if 541 is omitted.Also, in the above practical example, the case where a semiconductor optical device is incorporated in an optical circuit device is described, but an optical fiber may be placed in place of the semiconductor optical device. Although the case where the same filter is used in the actual case has been shown, the same effect can be expected even if different filters are used, as is clear from the fact that the formula +11 holds true for filters in general.

However, one of the advantages of the present invention is that it can produce excellent effects using the same filter, and it goes without saying that this method is superior in mass production and manufacturability.

〔Effect of the invention〕

As described above, according to the present invention, since the filters are inserted in tandem at the same angle to the optical path but facing different directions, it is possible to use the same components and manufacturing methods as conventional optical circuit devices, and to achieve extremely low crosstalk. There is an effect that can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a top view of an example of an optical circuit device according to the present invention, FIG. 2 is a sectional view illustrating the insertion angle of the filter of the optical circuit device according to the present invention into the optical path, and FIG. 3 is a cross-sectional view of the optical circuit device according to the present invention. FIG. 4 is a top view showing an example of a conventional optical circuit device, and FIG. 5 is a characteristic diagram illustrating the cause of crosstalk in the conventional optical circuit device. (1) is a semiconductor laser with a wavelength of 1200 nm, (2) is a G
e-APD, +31 is fiber, (4) is filter,
+61°+71. +81 is the lens, +91. Qf
l is a prism and α0 is a mirror. (51, (sz, f531+) (54 is an interference film filter. Note that in the drawings, the same reference numerals indicate the same - or corresponding parts.

Claims (1)

[Claims] 1. In an optical circuit device in which a plurality of interference film filters are inserted in an optical path for the purpose of transmitting light of a predetermined wavelength λ_A and reflecting or attenuating light of other wavelengths, the above-mentioned At least one pair of the interference film filters is inserted with its normal at a non-zero angle α with respect to the optical path, and the pair of interference film filters are at an angle of 2α to each other.
An optical circuit device characterized by comprising: 2. In an optical circuit device in which a plurality of interference film filters are inserted in an optical path for the purpose of transmitting light of a predetermined wavelength λ_A and reflecting or attenuating light of other wavelengths, at least A pair of interference film filters and their normals are inserted at a non-zero angle α with respect to the optical path, and the pair of interference film filters form an angle 2α with each other, and the interference film filters of the other pair make an angle 2α with respect to the optical path. The filter is 1 above
An optical circuit device characterized in that a pair of interference film filters are inserted at an angle rotated by 90 degrees about an optical path as a central axis. 3. Allows light of a predetermined wavelength λ_A to pass through, and transmits light of other wavelengths λ_
In an optical circuit device in which a plurality of interference film filters are inserted in the optical path for the purpose of reflecting or attenuating the B light,
Let α be the angle between the normal line of the interference film filter and the optical path, and let θ_ be the angle of incidence of the light of wavelength λ_B on the interference film filter at which the interference film filter gives the maximum amount of attenuation for the light of wavelength λ_B.
The optical circuit device according to claim 1 or 2, wherein the relationship of equation (1) is established between θ_m and α, where m is the value of θ_m. θ_m=2_α−θ_B(1) where θ_B=cos＾−＾1{(λ_B/λ_A)c
osα} (2).