Optical multiplexer/demultiplexer module and prism using for the same

An optical multiplexer/demultiplexer module comprises: a plurality of prisms, each having an inclined surface that is formed by one of the four orthogonal corners of a transparent rectangular solid glass plate being cut and removed at a 45° angle with respect to the end surface; a frame for housing said plurality of prisms; and a plurality of collimator units that convert light having a different wavelength for each prism to collimated light, and inputs the light to the respective prism. When light a having different wavelength is input to a respective prism, the input light is reflected two times, by the inclined surface and a second end surface, after which the light is output from the respective prism. The light that is output from a previous stage prism of the plurality of prisms advances along the same optical path as the light that is output from a later stage prism, so the light that is output from each respective prism is sequentially multiplexed and wavelength multiplexed light is output from the third end surface of the final stage prism.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical multiplexer/demultiplexer module and prism using the same that are applied to an optical communication system and to the optical measurement field.

2. Description of the Related Art

Recently, with the rapid spread of broadband, study and research in order to increase the speed of optical transmission systems is actively being pursued. Optical multiplexer/demultiplexer modules are used in this kind of optical transmission system. The technology for this kind of optical multiplexer/demultiplexer module is known, such as disclosed in patent document 1. This conventional optical multiplexer/demultiplexer module has construction in which a filter is arranged between two collimating lenses. The filter reflects the λ1 signal light of the collimated light from one collimating lens, and lets the λ2 signal light of the collimated light from the other collimating lens pass through. The λ1 signal light that was reflected by the filter and the λ2 signal light that passed through the filter are optically coupled with an optic fiber by way of the collimating lenses.[Patent Document 1] Japanese patent Laid-open publication No. 2003-315611

However, in the conventional technology disclosed in patent document 1, in the case where the filter tilts at an angle θ due to change in the ambient temperature, the optical path of the transmitted light does not change, however, since the angle of the reflected light is 2θ, that reflected light is not optically coupled with the optic fiber by way of the collimating lenses.

SUMMARY OF THE INVENTION

The optical multiplexer/demultiplexer of one form of the present invention comprises: a plurality of prisms, each having an inclined surface that is formed by one of the four orthogonal corners of a transparent rectangular solid glass plate being cut and removed at a 45° angle with respect to the end surface; and a frame for housing the plurality of prisms; wherein each of the plurality of prisms has a first end surface through which a first light having a single wavelength that differs for each prism is input toward the inclined surface, or through which a first light that is reflected by the inclined surface is output; a second end surface that forms a filter having wavelength selectivity such that it reflects the first light and lets light having another wavelength pass through; and a third end surface through which wavelength multiplexed light, which is a multiplexed light having a plurality of different wavelengths, is output or input; and the plurality of prisms are arranged in a row so that when the first light is input from the first end surface of each of the plurality of prisms, that first light is reflected two times, by the inclined surface and the filter, after which the first light is multiplexed with a second light, which passes through the filter, and is output, and when the wavelength multiplexed light is input from the third end surface of one of the plurality of prisms, the first light that is included in that wavelength multiplexed light is reflected two times, by the filter and the inclined surface, and then output from the first end surface, while the light of other wavelengths passes through the filter.

With this kind of construction, even though the prisms may be tilted due to changes in the ambient temperature, that tilt is compensated for, so the light that is output from each prism is only shifted in the horizontal direction with respect to the output light in the case when there is no tilting, it becomes difficult for trouble to occur such as the output light not being able to be optically coupled with an optic fiber by way of a collimating lens, and it is possible to suppress a drop in optical coupling performance due to changes in ambient temperature. Furthermore, in each of the prisms, light is incident on the inclined surface from one of two end surfaces (first end surface) that faces the inclined surface, then the light that is reflected by that inclined surface is reflected by the other of the two end surfaces (second end surface), and that reflected light is output from an end surface (third end surface) that faces the second end surface.

Therefore, the incident angle at the first end surface or third end surface, and the incident angle at the second end surface are each small angles, so the anti-reflective film (AR coating) that is formed on the first end surface or the third end surface, and the polarization dependence of the filter such as a longwave pass filter (LWPF) that is formed on the second end surface are extremely good, and film design becomes simple.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the present invention will be explained in detail based on the accompanying drawings. In the explanations of the embodiments, the same reference numbers will be used for identical parts and any redundant explanations will be omitted.

Next, embodiments of the optical multiplexer/demultiplexer module of the present invention will be explained based on the drawings.

FIG. 1is a horizontal cross-sectional diagram of the optical multiplexer/demultiplexer module of a first embodiment of the invention, andFIG. 2is a vertical cross-sectional diagram of the optical multiplexer/demultiplexer module.FIG. 3is a top view of the optical multiplexer/demultiplexer module, andFIG. 4is a view as seen in the direction of arrow A inFIG. 3.FIG. 5is a top view of a prism that uses the optical multiplexer/demultiplexer module, andFIG. 6is a diagram for explaining the case in which the prism inFIG. 5is inclined.

As illustrated inFIG. 1andFIG. 5, the optical multiplexer/demultiplexer module10comprises a plurality of prisms, each having an inclined surface that is formed by one of the four orthogonal corners of a transparent rectangular solid glass plate being cut and removed at a 45° angle with respect to the end surface. Here, an example is given of an optical multiplexer/demultiplexer module10that comprises six prisms11to16, each having the same shape, as the plurality of prisms.

Moreover, as illustrated inFIG. 1toFIG. 4, the optical multiplexer/demultiplexer module10comprises: a frame17that houses the plurality of prisms11to16; a plurality of collimator units18to24, each having collimating lenses that respectively collimate light of differing wavelengths and cause that collimated light to enter into the prisms11to16; and a cover25.

The prisms11to16are identical prisms, so prism11will be explained based onFIG. 5. The prism11is a penta prism having an inclined surface27that is formed by one of the four orthogonal corners of a transparent rectangular solid glass plate being cut and removed at a 45° angle with respect to the end surface. The other prisms12to16also have a similar inclined surface27that is the same as the inclined surface27of prism11. The thickness of the prism11is, for example, 3 mm. The prisms11to16are not limited to being formed from a rectangular solid glass plate having an inclined surface, and could be formed from a cubic glass plate having an inclined surface.

Each of the plurality of prisms11to16comprises: a first end surface28through which a first light having a single wavelength that differs for each prism is input toward the inclined surface27, or through which a first light that is reflected by the inclined surface27is output; a second end surface29that forms a filter having wavelength selectivity such that it reflects the first light and lets light having other wavelengths pass through; and a third end surface30through which wavelength multiplexed light, which is multiplexed light comprising a plurality of different wavelengths, is output or input.

In this embodiment, as an example, light having a wavelength λ1 (λ1=405 nm) enters or leaves the first end surface28of prism11, light having a wavelength λ2 (λ1=445 nm) enters or leaves the first end surface28of prism12, light having a wavelength λ3 (λ3=488 nm) enters or leaves the first end surface28of prism13, light having a wavelength λ4 (λ4=515 nm) enters or leaves the first end surface28of prism14, light having a wavelength λ5 (λ5=555 nm) enters or leaves the first end surface28of prism15, and light having a wavelength λ6 (λ6=635 nm) enters or leaves the first end surface28of prism16(seeFIG. 1). Furthermore, light having a wavelength λ7 (λ7=660 nm) enters through the second end surface19of prism16as the first light.

There is also a longwave pass filter (LPF)50formed in the second end surface29of each of the prisms11to16, as a filter having wavelength selectivity of reflecting the first light and allowing light of other wavelengths to pass. This longwave pass filter is a dielectric multilayer film filter. The longwave pass filter that is formed on the second end surface29of prism11has wavelength selectivity that reflects the light having wavelength λ1 (405 nm), and allows light having longer wavelengths than λ1 (λ2 to λ7) to pass. The longwave pass filter that is formed on the second end surface29of prism12has wavelength selectivity that reflects the light having wavelength λ2 (445 nm), and allows light having longer wavelengths than λ2 (λ3 to λ7) to pass. The longwave pass filter that is formed on the second end surface29of prism13has wavelength selectivity that reflects the light having wavelength λ3 (448 nm), and allows light having longer wavelengths than λ3 (λ4 to λ7) to pass. The longwave pass filter that is formed on the second end surface29of prism14has wavelength selectivity that reflects the light having wavelength λ4 (515 nm), and allows light having longer wavelengths than λ4 (λ5 to λ7) to pass. The longwave pass filter that is formed on the second end surface29of prism15has wavelength selectivity that reflects the light having wavelength λ5 (555 nm), and allows light having longer wavelengths than λ5 (λ6, λ7) to pass. The longwave pass filter that is formed on the second end surface29of prism16has wavelength selectivity that reflects the light having wavelength λ6 (635 nm), and allows light having longer wavelengths than λ6 (λ7=660 nm) to pass.

In each of the prisms11to16, as shown inFIG. 5, in the case of multiplexing, collimated light (incident light31) enters from one of the two end surfaces (first end surface28) that faces the inclined surface27, which is formed by cutting at an angle that is 45° with respect to the end surface, and light that is reflected by the inclined surface27(reflected light32) is reflected by the other of the two surfaces (second end surface29) and that reflected light33is output from the third end surface30that faces the second end surface29.

Moreover, in each of the prisms11to16, as shown inFIG. 5, an antireflective film (AR coating)51is formed on the first end surface28that allows the incident light31to pass, a high reflecting film (HR film)52is formed on the inclined surface27, a longwave pass filter50described above is formed on the second end surface29, and an antireflective film53is formed on the third end surface30that faces the second end surface29.

The prisms11to16are arranged in a row such that they satisfy the following conditions.

(1) As illustrated inFIG. 1, when first light enters in from the first end surface28, the first light is reflected two times, by the inclined surface27and by the longwave pass filter50that is formed on the second end surface29, after which it is multiplexed with the second light that passes through the longwave pass filter50and is output from the third end surface30. Here, as was explained above, the first light is light having wavelength λ1 in prism11, is light having wavelength λ2 in prism12, is light having wavelength λ3 in prism13, is light having wavelength λ4 in prism14, is light having wavelength λ5 in prism15, and is light having wavelength λ6 in prism16.

(2) When wavelength multiplexed light comprising a plurality of light of differing wavelengths (λ1 to λ7) is input from the third end surface30of one (prism11) of the plurality of prisms11to16, the first light that is included in the wavelength multiplexed light is reflected two times, by the longwave pass filter50and the inclined surface27, after which that first light is output from the first end surface28and the light of other wavelengths is allowed pass through the longwave pass filter50.

Moreover, the prisms11to16are arranged in a row with the left and right alternately reversed such that the position of the inclined surface27of each prism is alternately changed between the left and right of adjacent prisms. In this embodiment, the prisms11to16are arranged such that the inclined surface27of prism11is positioned at the bottom right ofFIG. 1, the inclined surface27of prism12is positioned at the bottom left, the inclined surface27of prism13is positioned at the bottom right, the inclined surface27of prism14is positioned at the bottom left, the inclined surface27of prism15is positioned at the bottom right, and the inclined surface27of prism16is positioned at the bottom left.

The frame17, as illustrated inFIG. 1toFIG. 4, comprises a base section17ain which the prisms11to16are arranged as described above and fastened using adhesive or the like, and three wall sections17b,17c,17dthat are formed by the inner three sides of the four sides of the base section17a. There is no wall section formed in edge section of the one remaining side of the base section17a, and the side of one end of the frame17becomes an opening section17e. As illustrated inFIG. 1andFIG. 2, the prisms11to16are arranged on the top surface17fof the base section17in a row as described above and fastened with adhesive or the like.

An installation hole26for mounting three collimator units18,20,22are formed in the wall section17bof the frame17, an installation hole26for mounting a collimator unit24is formed in the wall section17c, and an installation hole26for mounting three collimator units19,21,23are formed in the wall section17d.

The collimator units18to24convert the light of wavelengths λ1 to λ7 that are respectively transmitted from single-mode optic fibers F1to F7to collimated light and then let the light enter into the respective prism11to16.

As illustrated inFIG. 1andFIG. 2, the collimator unit18comprises a ferrule40that holds the single-mode optic fiber F1, a collimating lens41, a sleeve42that holds the ferrule40and collimating lens41, and a spherical ring43that supports the sleeve42so that it can rotate freely. In the case of collimator unit18, by inserting part thereof into the installation hole26of the wall section17band moving the sleeve42back-and-forth with respect to the spherical ring43, the light having wavelength λ1 (405 nm) that is transmitted from the single-mode optic fiber F1is converted to collimated light and aligned such that it enters prism11at a specified incident angle. After this alignment, the spherical ring43and sleeve are fastened by welding, and the spherical ring43is further fastened to the outer surface of the wall section17bof the frame17by welding. The collimator units19,20,21,22and23all have the same construction as collimator unit18. InFIG. 1andFIG. 2, in order to avoid complexity of the figures, the reference numbers of the members that form the collimator units19to24have been omitted.

In the optical multiplexer/demultiplexer module10, light having a wavelength λ1 (405 nm) that has been converted to collimated light by the collimator unit18enters the prism11from the first end surface28. Light having a wavelength λ2 (445 nm) that has been converted to collimated light by the collimator unit19enters the prism12from the first end surface28. Light having a wavelength λ3 (488 nm) that has been converted to collimated light by the collimator unit20enters the prism13from the first end surface28. Light having a wavelength λ4 (515 nm) that has been converted to collimated light by the collimator unit21enters the prism14from the first end surface28. Light having a wavelength λ5 (555 nm) that has been converted to collimated light by the collimator unit22enters the prism15from the first end surface28. Light having a wavelength λ6 (635 nm) that has been converted to collimated light by the collimator unit23enters the prism16from the first end surface28. In addition, light having a wavelength λ7 (660 nm) that has been converted to collimated light by the collimator unit24enters the prism16from the second end surface29.

Moreover, the plurality of prisms11to16are arranged in a row so that light that is output from an adjacent prism and irradiated from the second end surface29, enters from the first end surface28and is reflected by the inclined surface27, and that reflected light (reflected light32inFIG. 1) takes the same path as the light (reflected light33inFIG. 1) that is reflected again by the second end surface29and is output. The operation of an optical multiplexer/demultiplexer module10having this kind of construction is explained.

First, multiplexing will be explained.

When light having differing wavelengths respectively enters the plurality of prisms11to16, each input light is reflected two times in the prism, by the inclined surface27and the second end surface29, after which the light is output from the prism. The light that is output from an earlier stage prism (for example the first stage prism16) of the plurality of prisms advances along the same optical path as light that is output from a later stage prism (second stage prism15), so the light that is output from each prism is sequentially multiplexed, and wavelength multiplexed light, in which light having wavelengths λ1 to λ7 is multiplexed, is output from the third end surface30of the final stage prism11. In other words, collimated light having wavelength λ6 that is input from the first end surface28of prism16is reflected by the inclined surface27and the second end surface29. This reflected light (reflected light33inFIG. 1) takes the same optical path as the collimated light having wavelength λ7 that is input from the second end surface29of prism16, and is output from the third end surface30.

This output light, that is, multiplexed light comprising collimated light having wavelength λ6 and collimated light having wavelength λ7, enters the second end surface29of the next stage prism15. This input light takes the same optical path as the collimated light having wavelength λ5 that is input from the first end surface28of prism15and reflected by the inclined surface27and second end surface29, and is output from the third end surface30.

This output light, or in other words the multiplexed light comprising collimated light having wavelengths λ5, λ6 and λ7, is input to the second end surface29of the next stage prism14. This input light takes the same optical path as the collimated light having wavelength λ4, which is input from the first end surface28of the prism14and reflected by the inclined surface27and the second end surface29, and is output from the third end surface30.

This output light, or in other words the multiplexed light comprising collimated light having wavelengths λ4, λ5, λ6 and λ7, is input to the second end surface29of the next stage prism13. This input light takes the same optical path as the collimated light having wavelength λ3, which is input from the first end surface28of the prism13and reflected by the inclined surface27and the second end surface29, and is output from the third end surface30.

This output light, or in other words the multiplexed light comprising collimated light having wavelengths λ3, λ4, λ5, λ6 and λ7, is input to the second end surface29of the next stage prism12. This input light takes the same optical path as the collimated light having wavelength λ2, which is input from the first end surface28of the prism12and reflected by the inclined surface27and the second end surface29, and is output from the third end surface30.

This output light, or in other words the multiplexed light comprising collimated light having wavelengths λ2, λ3, λ4, λ5, λ6 and λ7, is input to the second end surface29of the next stage prism11. This input light takes the same optical path as the collimated light having wavelength λ1, which is input from the first end surface28of the prism11and reflected by the inclined surface27and the second end surface29, and is output from the third end surface30. As illustrated inFIG. 1, wavelength multiplexed light comprising collimated light having wavelengths λ1 to λ7 is output. Multiplexing is performed in this way.

Next, demultiplexing will be explained.

When using the optical multiplexer/demultiplexer module10illustrated inFIG. 1for demultiplexing, wavelength multiplexed light comprising multiplexed light of wavelengths λ1 to λ7 is converted to collimated light by a collimator unit (not shown in the figure) and input. In this case, the light takes an optical path that is opposite that of the case of multiplexing described above, so the collimated light having wavelengths λ1 to λ5 are separately output from the respective prisms11to15, and collimated light having wavelengths λ6 and λ7 are respectively output from the first end surface28second end surface29.

The first embodiment that is constructed as described above has the following functional advantages.

When single wavelength first light of different wavelengths (λ1 to λ7) is respectively input to the prisms11to16, the wavelength multiplexed light comprising a plurality of multiplexed light of different wavelengths is output from the third end surface30of one of the prisms11to16(final stage prism11) that are arranged in a row, and multiplexed. By doing so, the wavelength multiplexed light comprising multiplexed light of wavelengths λ1 to λ7 can be optically coupled with a single-mode optic fiber (not shown in the figure) via a collimating lens (not shown in the figure).

When wavelength multiplexed light comprising multiplexed light of wavelengths λ1 to λ7 is input from the third end surface30of prism11(first stage) of the prisms11to16, by respectively outputting first light having different wavelengths (λ1 to λ7) for each prism from the first end surface28of each prism11to16, the light is demultiplexed. In this way, light of each wavelength λ1 to λ7 is optically coupled with single-mode optical fibers via the collimator lenses of the collimator units18to24.

In each prism11to16, the input light (first light that is input from the first end surface28, or wavelength multiplexed light that is input from the third end surface30) is reflected two times and output. In other words, in the case of multiplexing, first light that is input from the first end surface28is reflected two times, by the inclined surface27and the longwave pass filter50on the second end surface29, after which it is output. In the case of demultiplexing, wavelength multiplexed light that is input from the third end surface30is separated by the longwave pass filter50into first light and light having wavelengths longer than the first light, and the first light that is reflected by the longwave pass filter50is then reflected by the inclined surface and output from the first end surface28.

In this way, in each of the prisms11to16, the input light is reflected two times and then output. By doing so, even though the prisms11to16may be tilted due to changes in the ambient temperature, that tilt is compensated for, so the light that is output from each prism is only shifted in the horizontal direction with respect to the output light in the case when there is no tilting, and it is possible to suppress the occurrence of trouble such as the output light not being able to be optically coupled with an optic fiber by way of a collimating lens. Therefore, it is possible to suppress a drop in the optical coupling performance due to tilting of the prism (optical parts) caused by a change in ambient temperature. As illustrated inFIG. 6, when the prism11tilts by +1° or −1° as illustrated by the dashed line60or dashed-dotted line61, the light that is output from the third end surface30is shifted only in the horizontal direction by +0.15 mm or −0.15 mm with respect to light that is output when there is not tilting.

In each prism, light is input to the inclined surface27from one of the two end surfaces (first end surface28) that face the inclined surface27, then the light32that is reflected by the inclined surface27is also reflected by the other of the two end surfaces (second end surface29), and that reflected light33is output from the end surface (third end surface30) that faces the second end surface29. Therefore, the incident angle of the incident light on the inclined surface27and the reflection angle are about 37°, the incident angle at the first end surface28or third end surface30, and the incident angle at the second end surface29are each small angles of about 12°, so the anti-reflective film that is formed on the first end surface28or the third end surface30, and the polarization dependence of the filter such as a longwave pass filter that is formed on the second end surface29are extremely good, and film design becomes simple.

A plurality of collimator units18to24, having collimating lenses41that convert single-wavelength first light of different wavelengths for each prism to collimated light, are respectively mounted in the frame17for each of the plurality of prisms11to16, so it is possible to convert the light having different wavelengths for each prism to collimated light, then input the light.

The plurality of prisms11to16are arranged in a row such that they are alternately left-right reversed, so it is possible to alternately change the direction of input light to the prisms. By doing so, it is possible to arrange the collimator units18to24, having collimating lenses41that individually input light to the prisms11to16, in the frame17such that they are alternately left-right reversed, and thus it is possible to improve freedom of the design.

In each of the prisms11to16, an anti-reflective film51is formed on the first end surface28, a highly reflective film52is formed on the inclined surface27, and an anti-reflective film53is formed on the third end surface30, so it is possible to suppress loss at the first end surface28, inclined surface27and third end surface30in each of the prisms11to16.

Of the plurality of prisms11to16that are arranged in a row, light having a wavelength λ6 is input to the first end surface and light having wavelength λ7 is input to the second end surface of prism16, to which or from which wavelength multiplexed light that comprises a plurality of multiplexed light having different wavelengths (λ1 to λ7) is input or output and which is on the end opposite the prism11. In other words, light having different wavelengths is respectively input to the first end surface and the second end surface of one prism16to which or from which wavelength multiplexed light that comprises a plurality of multiplexed light having different wavelengths is input or output and which is on the end opposite the prism11. In this way, the optical multiplexer/demultiplexer module10illustrated inFIG. 1is constructed such that by using the second end surface29of prism16, which is located at the end of a plurality of prisms that are arranged in a row and to which no light that is output from another prism is input, light is input (in the case of multiplexing) or output (in the case of demultiplexing) from that end surface29as well. By doing so, it is possible to multiplex or demultiplex a number of lights that is one more than the number of prisms.

The optical multiplexer/demultiplexer module10has the advantage in that it uses light covering a wavelength band from 350 nm to 900 nm for each of the plurality of prisms11to16. The present invention can be changed and embodied as described below.

In the first embodiment described above, an example of an optical multiplexer/demultiplexer comprising six prisms11to16, and seven collimator units18to24was explained, however, the number of prisms is not limited to six and the number of collimator units is not limited to seven. For example, as illustrated inFIG. 7, the invention can also be applied to an optical multiplexer/demultiplexer module10A that comprises five prisms11to15and six collimator units18to23. In the optical multiplexer/demultiplexer module10A inFIG. 10A, the frame17that is shown inFIG. 1andFIG. 2is omitted.

In the first embodiment described above, identical prisms were used as the plurality of prisms11to16, however the present invention can be widely applied to optical multiplexer/demultiplexer modules that comprise a plurality of prisms that are arranged in a row so that the conditions described above are satisfied, and the prisms do not necessarily need to be identical.

It is preferred that the plurality of prisms11to16be arranged in a row such that they are alternately left-right inversed as in the first embodiment described above, however, the present invention can also be applied to an optical multiplexer/demultiplexer module that is constructed such that the left-right direction of all of the plurality of prisms is the same.

In the first embodiment described above, of the plurality of prisms11to16, light having wavelength λ6 is input to the first end surface and light having wavelength λ7 is input to the second end surface of the prism16that is located at the end opposite from prism11, however, the invention can also be applied to an optical multiplexer/demultiplexer module that is constructed such that light having wavelength λ7 is not input to that second end surface.

Although the invention has been described with respect to specific embodiments for a complete and clear disclosure, the appended claims are not to be thus limited, but are to be construed as embodying all modifications and alternative construction that may occur to one skilled in the art that falls within the basic teaching herein set forth.