1. Field of the Invention
The present invention relates to a planar lightwave circuit (PLC) which can decrease the coupling loss between a planar lightwave circuit and an optical fiber or between planar lightwave circuits.
2. Description of the Related Art
It is predicted that the planar lightwave circuits will be used more and more as main parts which have important functions such as routing of an optical signal in superfast large-capacity optical communication systems from now on. Especially, it is required to construct a larger optical communication system as capacity required for communication increases. In order to realize the enlargement of the optical communication system, it is necessary to downsize the planar lightwave circuit and to allow connection between many planar lightwave circuits.
When an optical signal is entered into the planar lightwave circuit 110 from the input waveguide 112, the optical signal is entered into the arrayed waveguides 114 via the slab waveguide 113 and polarization dependence is dissolved by the half waveplate 115. In addition, the optical signal is demultiplexed into signals of various wavelengths in the slab waveguide 116 due to delay line of the arrayed waveguides 114 so that demultiplexed signals are output from the output waveguides 117.
In order to downsize the planar lightwave circuit 110, it is very effective to adopt a waveguide (which will be called a superhigh- waveguide) in which relative refractive index difference is a high value which is larger than 1% where relative refractive index difference is the ratio of difference between the refractive index ncore of the core and refractive index nclad of the cladding to the refractive index ncore of the core as represented by the following equation (1). The reason is that the higher the relative refractive index difference is, the more completely the light is confined in the waveguide so that the waveguide can be used even when it is bent by a small bending radius.
=(ncore−nclad)/ncore (1)
However, there is a problem in that the coupling loss of the superhigh- waveguide is very large.
As shown in
In the planar lightwave circuit 110 used in the optical communication system, downsizing and decreasing of the coupling loss are mutually contradictory. That is, although the circuit can be downsized by increasing , the coupling loss increases. Therefore, construction of a practical system has limitations That is, it becomes difficult to enlarge capacity of transmission lines unless the coupling loss of the superhigh- waveguide is decreased, so that functions and scale of the optical communication system may be limited.
As a method for decreasing the coupling loss between the superhigh- waveguide and the optical fiber, use of a spotsize converter in which core width is narrowed toward an end face of a substrate is known as shown in
There is an region in which a spotsize is widened when the core width is narrowed to some extent. Then, it becomes possible to decrease the coupling loss by adjusting the widened field distribution with that of an optical fiber.
However, it is known that the coupling loss for the narrow taper spotsize converter largely changes due to slight fabrication error of core width, and the like. Thus, the narrow taper spotsize converter has not been in practical use.
It is an object of the present invention to provide a planar lightwave circuit which can suppress the coupling loss while downsizing is realized.
More particularly, it is an object of the present invention to provide a planar lightwave circuit and an optical circuit which use a narrow taper spotsize converter which has large fabrication tolerance.
The above object of the present invention is achieved by a planar lightwave circuit in which an input waveguide and an output waveguide are formed on a substrate wherein each of the input waveguide and the output waveguide are formed by a core and a cladding which covers the core, and refractive index of the core is higher than refractive index of the cladding, wherein:
In the planar lightwave circuit, a taper part is formed in the core in each of the input end side of the input waveguide and the output end side of the output waveguide, and a taper angle of the taper part is larger than 0° and equal to or smaller than 5°.
In the planar lightwave circuit, steps are formed in the core in each of the input end side of the input waveguide and the output end side of the output waveguide.
In the planar lightwave circuit, height between adjacent steps in the steps is larger than 0 μm and equal to or smaller than 5 μm.
In the planar lightwave circuit, taper parts and straight parts are formed alternately in the core in each of the input end side of the input waveguide and the output end side of the output waveguide, core width of each of the taper parts changes gradually toward an end face of the substrate and core width of each of the straight parts is constant.
In the planar lightwave circuit, length of each of the straight parts is equal to or larger than 1 μm.
In the planar lightwave circuit, a marker is provided for indicating a cutting position of the input waveguide or the output waveguide, or indicating a position where the core width changes.
The planar lightwave circuit may include a monitor waveguide in which an input end of the monitor waveguide is formed in an end face side of the substrate which is different from end face sides in which the input end of the input waveguide and the output end of the output waveguide are provided, wherein the monitor waveguide includes a core which is formed such that core width changes toward an end face of the substrate.
In addition, the planar lightwave circuit may include a monitor waveguide, wherein an input end of the monitor waveguide is formed in an end face side of the substrate in which the input end of the input waveguide is located, and
an output end of the monitor waveguide is formed in an end face side of the substrate in which the output end of the output waveguide is located, wherein shapes of an input end side and an output end side of the monitor waveguide are similar to the input end side of the input waveguide and the output end side of the output waveguide respectively.
In the planar lightwave circuit, the substrate is made of silicon and the input waveguide and the output waveguide are made of silica-based glass
The object of the present invention is also achieved by an optical circuit which includes a waveguide and a spotsize converter which is a part of the waveguide, wherein a core is embedded in a cladding in the waveguide, and the spotsize converter is located near an end face of a substrate on which the optical circuit is formed, the spotsize converter including:
alternating taper parts and straight parts;
wherein core width of each of the taper parts decreases toward an end face of the substrate and core width of each of the straight parts is constant.
In the optical circuit; an optimized taper is used as a shape of the taper part.
In addition, the object of the present invention is achieved by an optical circuit which includes a waveguide and a spotsize converter which is a part of the waveguide, wherein a core is embedded in a cladding in the waveguide, and the spotsize converter is located near an end face of a substrate on which the optical circuit is formed, the spotsize converter including:
a plurality of straight parts via steps, core width of each straight part being constant;
wherein core width of the spotsize converter is minimum at an end face of the substrate, and a height of the step is larger than 0 μm and equal to or smaller than 5 μm.
In the optical circuit, a length of the straight part is equal to or larger than 1 μm.
In the optical circuit, a mean taper angle of the spotsize converter is larger than 0° and equal to or smaller than 5°.
The object of the present invention is also achieved by an optical circuit which includes a waveguide and a spotsize converter which is a part of the waveguide, wherein a core is embedded in a cladding in the waveguide, and the spotsize converter is located near an end face of a substrate on which the optical circuit is formed, the spotsize converter including:
a core width fine-tuning part in an end face side of the substrate; and
a core width converting part which follows the core width fine-tuning part;
wherein core width of said spotsize converter is minimum at an end face of said substrate, a mean taper angle θ1 of the core width fine-tuning part is larger than 0° and smaller than a mean taper angle θ2 of the core width converting part.
In the optical circuit, the core width fine-tuning part may include a plurality of taper parts.
In the optical circuit, the core width fine-tuning part may include alternating taper parts and straight parts, core width of each straight part being constant.
In the optical circuit, the core width fine-tuning part may include:
a plurality of straight parts via steps, core width of each straight part being constant;
wherein a height of the step is larger than 0 μm and equal to or smaller than 5 μm.
In the optical circuit, an optimized taper is used as a shape of the core width converting part.
In the optical circuit, a mean taper angle θ1 of the core width fine-tuning part is larger than 0° and equal to or smaller than 0.04°, and a mean taper angle θ2 of the core width converting part is larger than 0.04° and equal to or smaller than 5°.
In the optical circuit, a marker for forming an end face of the substrate is provided in the optical circuit.
In the optical circuit, the marker is provided in a location corresponding to a location in which a shape of the core width fine-tuning part changes.
In the optical circuit, a monitor waveguide is provided on the substrate, the monitor waveguide including a second spotsize converter including:
a second core width fine-tuning part in an end face side of the substrate; and
a second core width converting part which follows the second core width fine-tuning part;
wherein core width of said second spotsize converter is minimum at an end face of said substrate, a mean taper angle θ1 of the second core width fine-tuning part is larger than 0° and smaller than a mean taper angle θ2 of the second core width converting part.
The optical circuit includes a plurality of the monitor waveguides, spotsize converters of the monitor waveguides are shifted to each other by a predetermined distance in the direction of the length of the monitor waveguides.
In addition, the optical circuit may include a first monitor waveguide and a second monitor waveguide;
wherein the first monitor waveguide includes a first spotsize converter in an end face side of the substrate which is different from end face sides corresponding to an input end or an output end of the waveguide, the first spotsize converter including:
a first core width fine-tuning part in an end face side of the substrate;
a first core width converting part which follows the first core width fine-tuning part;
wherein core width of said first spotsize converter is minimum at an end face of said substrate, a mean taper angle θ1 of the first core width fine-tuning part is larger than 0° and smaller than a mean taper angle θ2 of the first core width converting part;
wherein the second monitor waveguide includes a second spotsize converter in an end face side of the substrate where an input end or an output end of the waveguide is located, the second spotsize converter including:
a second core width fine-tuning part in an end face side of the substrate;
a second core width converting part which follows the second core width fine-tuning part;
wherein core width of said second spotsize converter is minimum at an end face of said substrate, a mean taper angle θ1 of the second core width fine-tuning part is larger than 0° and smaller than a mean taper angle θ2 of the second core width converting part.
In addition, the object of the present invention is also achieved by an optical circuit which includes input ports and output ports, each of the input ports and the output ports including:
a waveguide and a spotsize converter which is a part of the waveguide, wherein a core is embedded in a cladding in the waveguide, and the spotsize converter is located near an end face of a substrate on which the waveguide is formed, the spotsize converter including;
a core width fine-tuning part in an end face side of the substrate; and
a core width converting part which follows the core width fine-tuning part;
wherein a mean taper angle θ1 of the core width fine-tuning part is larger than 0° and smaller than a mean taper angle θ2 of the core width converting part.
Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings, in which:
As described in the related art, as for the spotsize converter which uses the narrow taper, fabrication tolerance of core width is very narrow for minimizing the coupling loss between the planar. lightwave circuit and the optical fiber. That is, an optimum value of the core width changes due to fabrication conditions of the relative refractive index difference between the core and the cladding, core thickness and the like. According to the present invention, the core width of the input waveguide is narrowed toward the end face of the substrate to allow the core width to be fine-tuned so that the optimum core width can be obtained. By adjusting the position of the end face, the optimum core width can be obtained with high reproducibility.
In the following, although each embodiment of the present invention will be described, the present invention is not limited to the embodiments.
[First Embodiment]
The first example of the first embodiment of the planar lightwave circuit of the present invention will be described with reference to
As shown in
In each embodiment, the part of the waveguide in which the core width decreases gradually from a part near the end face of the substrate toward the end face of the substrate will be called a spotsize converter. For example, the taper part shown in
As shown in
Output waveguides 17 made of silica-based glass formed on the substrate 11 are connected to the slab waveguide 16. In the same way as the input wave guide 12, the core 17a of the output waveguide 17 has a taper part 17aa in which the core width decreases gradually toward the output end which is located in another end face side of the substrate 11 as shown in FIG. 5.
The waveguide 12, 17 of the planar lightwave circuit can be fabricated in the following way.
First, undercladding glass soot mainly made of SiO2 is deposited on the substrate 11 made of silicon by a flame hydrolysis deposition (FHD) method. Then, core glass soot in which GeO2 is doped to SiO2 is deposited on the undercladding glass soot by the flame hydrolysis deposition method. After that, high temperature heat-treatment (larger than 1000° C.) is carried out for the glass soot such that the glass soot becomes transparent. Accordingly, an undercladding glass 12ba and a core glass 12a are formed on the substrate 11 (FIG. 6A). Thickness is adjusted such that thickness of the undercladding glass 12ba and the core glass 12a become proper when depositing the glass soot by the flame hydrolysis deposition method.
Next, etching masks 100 are formed on the core glass 12a using photolithography such that each etching mask 100 becomes tapered structure, that is, width of each etching mask 100 decreases toward the end face of the substrate 11 (FIG. 6B). After that, patterning of the core glass 12a is performed (FIG. 6C), and the etching masks 100 are removed (FIG. 6D).
Finally, overcladding glass 12bb mainly made of SiO2 is deposited on the undercladding glass 12ba and the core glass 12a by the flame hydrolysis deposition method so that the overcladding glass 12bb also spreads into a narrow spacing between the adjacent core glasses, wherein dopant such as B2O3 and P2O5 is doped in the overcladding glass 12ba so that glass transition temperature is lowered (FIG. 6E). Then, the waveguide 12, 17 can be formed on the substrate 11.
In the planar lightwave circuit 10, when an optical signal in which lights of a plurality of different wavelengths are multiplexed is entered in the input waveguide 12, the optical signal is entered in the arrayed waveguides 14 via the slab waveguide 13, and polarization dependence is dissolved by the half waveplate 15. In addition, the optical signal is demultiplexed into optical signals of the wavelengths in the slab waveguide 16 due to delay line of the arrayed waveguides 14. Then, the optical signals are output from the output waveguides 17.
As shown in
Thus, the taper part 12aa, 17aa is provided in the core 12a, 17a of the waveguide 12, 17 at the end face side of the substrate 11 in the planar lightwave circuit 10 of the first example in this embodiment. Accordingly, the coupling loss is decreased while satisfying propagation conditions of the single-mode light.
As mentioned above, the coupling loss increases rapidly when the core width deviates from 1.2 μm even slightly. Thus, there is a possibility in that the coupling loss may increase due to deviation from optimum width caused by dicing error of the planar lightwave circuit 10.
As shown in
a=x·tan θ (2)
For example, when θ is 1.5° and x becomes 5 μm (which is normal size of dicing error), a becomes 0.13 μm. Therefore, deviation amount of both side 2a a becomes 0.26 μm. Therefore, the core width becomes 1.2±0.26 μm. Thus, as shown in
Therefore, if error occurs when dicing the planar lightwave circuit 10, the error does not largely affect the coupling loss so that the planar lightwave circuit 10 of low coupling loss can be always fabricated easily.
It is desirable that the taper angle θ of the taper part 12aa, 17aa of the core 12a, 17a of the waveguide 12, 17 is larger than 0° and equal to or smaller than 5°. Because, if the taper angle θ is 0°, the effect of the present invention can not be obtained, and, if the taper angle is larger than 5°, the deviation amount a of the core width due to dicing error becomes too large so that the coupling loss becomes too large.
In the above-mentioned planar lightwave circuit 10, silica-based waveguides 11˜17 are formed on the silicon substrate 11. However, materials are not limited to these. The waveguides 11˜17 which are made of polyimide, silicon, semiconductor, LiNbO3 and the like can be formed on the substrate 11 which is made of various materials.
Instead of providing a simple taper shown in
If the number of the steps are increased so as to decrease the height difference b between adjacent steps (in other words, height of perpendicular section of the step), the shape of the core 32a, 37a becomes closer to a taper shape so that the effect of decreasing the coupling loss can be increased. Therefore, it is desirable that the steps 32aa, 37aa are provided as many as possible in consideration of the dicing error x .
That is, when low coupling loss can not be obtained at a dicing position, the waveguide can be used after cutting the substrate at a different position, since the core width becomes smaller toward the input end or the output end by using the steps 32aa, 37aa. Therefore, even when an accurate optimum core width is not known and only an estimated value of an analytic result is obtained, the optimum core width can be searched for by changing the cutting position.
Therefore, by applying the core 32a, 37a, a proper core width can be easily realized even when the dicing error x occurs.
It is desirable that the height difference between the adjacent steps b is larger than 0 μm and equal to or smaller than 5 μm. Because, when b is equal to 0 μm, the effect of the present invention can not be obtained. When b exceeds 5 μm, the propagation condition of the single-mode light can not be satisfied.
In the example shown in
In addition, as shown in
By applying the core 42a, 47a, the coupling loss can be decreased while the propagation condition of the single-mode light is satisfied. In addition, the dicing error can be absorbed by cutting the substrate at the straight part 42ab, 47ab. Therefore, a proper core width can be realized easily.
It is desirable that the length s of the straight part 42ab, 47ab is equal to or larger than 1 μm. Because, when s is smaller than 1 μm, it becomes difficult to absorb dicing error.
As for the example shown in
For example, as shown in
[Second embodiment]
A first example of the second embodiment will be described with reference to
In this embodiment, the present invention is applied to an arrayed waveguide grating (AWG), which is one of planar lightwave circuits, which performs multiplexing of optical signals of a plurality of different wavelengths and demultiplexing in an wavelength division multiplexing communication system. AWG is an example of a waveguide type optical circuit.
As shown in
In addition, a plurality of output waveguides 17 are provided on the substrate 11. The core width of input end face of the taper part 17aaof the core 17a is different by each output waveguide as shown in FIG. 13.
The waveguide 12, 17 of the AWG 50 can be fabricated in the same way as the planar lightwave circuit 10 in the first embodiment basically. For example, as shown in
In the AWG 50 which has such structure, when an optical signal in which lights of a plurality of different wavelengths are multiplexed is entered in any one of input waveguides 12, the optical signal is entered in the arrayed waveguides 14 via the slab waveguide 13, and polarization dependence is dissolved by the half waveplate 15. In addition, the optical signal is demultiplexed into optical signals of the wavelengths in the slab waveguide 16 due to delay line of the arrayed waveguides 14. Then, the optical signals are output from the output waveguides 17.
According to the AWG 50, since the core width of the taper part 12a, 17a at the end face of input or output is different for each other of the waveguides, increase of the coupling loss due to fabrication error can be resolved. The reason will be described in the following.
The multiplexed optical signal entered from an input port (which is not shown in the figure) which is connected to the input waveguide 12 is demultiplexed into signals having different wavelengths and the demultiplexed signals are output from output ports (which is not shown in the figure) connected to the output waveguides 17. The coupling loss varies from output port to output port since the core width varies from output port to output port due to dicing error.
Thus, a plurality of input waveguides 12 in which the core width is different from each other are provided and an input port is connected to each input waveguides 12. As a result, an input port to decrease the coupling loss can be selected for each output port. In addition, since the sum of the coupling losses of an input port and an output port can be selected to be constant, value of the coupling loss can be rendered equal for each port.
It is also possible to apply the core 32a, 37a of the second example of the first embodiment to this embodiment, in which a plurality of steps 32aa, 37aa are formed such that the core width decreases gradually toward the end side of input or output.
In addition, it is also possible to apply the core 42a, 47a of the third example of the first embodiment to this embodiment, in which alternating taper parts 42aa, 47aa and straight parts 42ab, 47ab are provided at the input end side or the output end side located in the end face side of the substrate 11, wherein the core width becomes smaller toward the input or output end as for the taper part, and the core width is fixed at a constant width as for the straight part which is formed along the axis of the core.
In the first example of this embodiment, an input port is selected among input ports connected to the input waveguides 12 such that the coupling loss becomes smallest. In addition, when it is necessary to use every input waveguide 12, a configuration shown in
[Third Embodiment]
The third embodiment of the planar lightwave circuit of the present invention will be described with reference to FIG. 17.
As shown in
As for the second monitor waveguides 69, structures of the input ends 69a and the output ends 69b are the same as those of the input waveguides 12 and the output waveguides 17 respectively. That is, the input ends 69a are located in an end face side of the substrate 11 where the input ends of the input waveguides 12 are located. In addition, each of the input end sides 69a are formed as taper such that the core width becomes smaller toward the input end, and, the core widths of the input ends 69a are different from each other. The output ends 69b are located in an end face side of the substrate 11 where the output ends of the output waveguides 17 are located. In addition, each of the output end sides 69b are formed as taper such that the core width becomes smaller toward the output end, and, the core widths of the output ends 69b are different from each other.
According to the AWG 60 on which the monitor waveguides 68 and 69 are formed, the core widths of the input end face of the input waveguides 12 and the core widths of the output end face of the output waveguides 17 can be set as proper sizes in the following way.
The input ends 68a of the monitor waveguides 68 on the substrate 11 are cut and the coupling loss of each monitor waveguide 68 is measured repeatedly so that the dependence of the coupling loss on the core width is checked. As a result, an optimum core width is obtained. After that, the end sides of the input waveguides 12 and the output waveguides 17 are cut such that the optimum core width is realized.
In addition, by measuring the coupling losses of the monitor waveguides 69, dicing error of the input waveguides 12 and the output waveguides 17 can be checked.
According to the AWG 60 of this embodiment, dicing error which occurs for each individual substrate 11 can be monitored, and optimum core width can be formed for the individual substrate 11.
Although examples in which the spotsize converter is applied to the AWG have been described in the above-mentioned second and third embodiments, it is not limited to the AWG. The present invention can be applied to any planar lightwave circuit and to any optical circuit by providing input and output waveguides where the core widths are different and selecting an optimum port when using the planar lightwave circuit. As a result, the coupling loss can be decreased irrespective of fabrication error.
[Fourth Embodiment]
Next, the fourth embodiment of the present invention will be described with reference to
In this embodiment, a spotsize converter 21 shown in
As shown in
In the following, design parameters of the core width fine-tuning part 21 and the core width converting part 22 will be described in detail.
As mentioned so far, according to the present invention, the input/output waveguide is formed as a taper shape such that optimum core width can be obtained with reliability by adjusting end face position. However, since the end face position of the waveguide is realized with accuracy of only about ±100 μm, the taper angle 2θ1 is set to be 0.057° in order to obtain ±0.1 μm accuracy of the core width in this embodiment.
Generally, the waveguide and the optical fiber is connected and fixed by an adhesive. Since the refractive index of the adhesive is subtly different from that of the glass, light reflections occur on a connection surface. To prevent the reflected light from reentering the optical fiber or the optical waveguide, the end surfaces of an optical waveguide and an optical fiber are generally angle polished by 5°-10°. In the current state that the input/output end face position is obtained by the angle polishing, it is difficult to obtain the input/output end face position with high accuracy. The accuracy of the end face position obtained by experiment was ±100 μm.
Therefore, the taper angle for fine-tuning part should be as small as possible to provide a higher degree of tolerance for angle polishing. Thus, as mentioned above, according to this embodiment, the taper angle 2θ1 is set to be 0.057° in order to obtain ±0.1 μm accuracy for finally obtained core width.
In this case, taper length of 4.2 mm is required when a simple taper is adopted where the core width is narrowed from 5 μm to 0.8 μm. Such a long taper is not desirable considering that the object of adopting the superhigh- waveguide is to downsize the planar lightwave circuit.
Therefore, according to the present invention, the spotsize converter 21 is divided into two sections which are the core width converting part 22 in which the core width is decreased sharply to the extent that loss does not occur and the core width fine-tuning part 21 in which the taper angle is set to be small in consideration of error of the end face forming position.
It is desirable that the taper angle 2θ2 of the core width converting part is large to the extent that the excess loss does not occur. As shown in the relationship of the taper angle and the excess loss in
As for the core width fine-tuning part, as mentioned above, the taper angle 2θ1 is set to be 0.057° so that the core width decreases from 1.5 μm to 0.8 μm in order that accuracy for forming the optimum core width becomes ±0.1 μm. In this case, the length of the core width fine-tuning part is 700 μm.
As a result, the sum of the lengths of the core width fine-tuning part and the core width converting part becomes 900 μm, which is about one-fifth of 4.2 mm of the case when using the simple taper.
It is desirable that the taper angle 2θ2 of the core width converting part is larger than 0.08° and equal to or smaller than 10°. Because, when the taper angle 2θ2 is equal to or smaller than 0.08°, the length of the core width converting part becomes too long so that downsizing can not be realized. When the taper angle 2θ2 is larger than 10°, the excess loss becomes too large.
In addition, the taper angle of the core width fine-tuning part is larger than 0° and equal to or smaller than 0.08°. Because, when the taper angle 2θ1 is larger than 0.08°, the length of taper part becomes too short so that adequate accuracy is not obtained due to mechanical polishing error.
The spotsize converter 20 shown in
In this case, the spotsize converter of the present invention is provided in the input end side of the AWG 70 in which the core width decreases toward the input end, and the spotsize converter of the present invention is provided in the output end side of the AWG 70 in which the core width decreases toward the output end.
In addition, in the same way as the second embodiment, the AWG can be formed such that the core widths of the end faces are different for each spotsize converter. In order to form the AWG like this, the spotsize converters in the input end and the output end are formed such that the taper angles θ1 are different from each other, or, the positions of the spotsize converters are shifted to each other. Then, the substrate is cut straightly for obtaining a proper core width.
In addition, dicing positions of the end faces can be determined by using the markers shown in FIG. 18 and FIG. 20. As shown in
The above-mentioned waveguide can be fabricated in the same way as described in the above-mentioned embodiments. The waveguides can be made of polyimide, silicon, semiconductor, LiNbO3 and the like in addition to silica-based glass.
This embodiment can be also applied to the input/output ports which were described by FIG. 16. In addition, although the arrayed waveguide grating (AWG) has been adopted as an example of the planar lightwave circuit in this embodiment, application of the present invention is not limited to the AWG since the point of the present invention is in the input/output waveguide including the spotsize converter so that the application of the present invention does not depend upon the kind of optical circuits.
[Fifth Embodiment]
A spotsize converter 75 of the fifth embodiment of the present invention is shown in
This embodiment is almost the same as the fourth embodiment where a difference is in the core width fine-tuning part 76. As shown in
For example, the core width fine-tuning part may be formed by alternately connecting tapered waveguides 82 and straight waveguides 81. In addition, the core width fine-tuning part may be formed by steps of straight waveguides as shown in FIG. 23. In this example, since the end face of the waveguide is in the straight waveguide instead of the tapered waveguide, the coupling loss between the waveguide and an optical fiber decreases.
A mean value (which will be called a mean taper angle) of the taper angle 2θ1 is defined by the following equation wherein the core width at an end which connects to the optical fiber is W1 and the core width at an end which connects to the core width converting part is W2, the length of the core width fine-tuning part is L as shown in FIG. 24.
For example, when the core width fine-tuning part is configured such that the mean taper angle 2θ1 is 0.057° and the straight waveguide is repeated seven times where the length of a straight waveguide is 200 μm, the core width can be decreased from 1.5 μm to 0.8 μm. θ1 instead of 2θ1 may be also called a mean taper angle. In addition, θ2 instead of 2θ2 may be also called a mean taper angle,
The above definition of the mean taper angle also can be used for the core width converting part. In this case, W2 in
In addition, the definition of the above-mentioned mean taper angle can be used for the spotsize converter of the first embodiment which does not have the core width converting part. In this case, a core width of the waveguide other than the spotsize converter part can be used as W2 in the equation (3) and the length of the spotsize converter can be used as L in the equation (3).
Also in this embodiment, the configurations shown in FIG. 16 and
[Sixth Embodiment]
Next, a planar lightwave circuit will be described which allows to realize optimum core width even when several conditions vary depending on process conditions with reference to
In this embodiment, in the same way as the third embodiment, monitor waveguides each of which has the spotsize converter of the present invention are provided separately from the planar lightwave circuit on a substrate on which the planar lightwave circuit is formed.
In the configuration shown in
This embodiment also can be configured like the configuration shown in FIG. 17.
The planar lightwave circuit which has the monitor waveguides and the planar lightwave circuit which is intended to be fabricated may be provided separately.
[Seventh Embodiment]
In the following, various embodiments of the markers which indicate end face forming position will be described.
In order to implement the core width which is obtained by using the monitor waveguides shown in
By properly providing the monitor waveguides and the markers, the planar lightwave circuit can be configured, for example, such that when the coupling loss is lowest in the fifth monitor waveguide, the coupling loss can be minimized by processing the end face such that the position of the fifth marker becomes the end face.
The markers can be provided in various forms. For example, markers shown in
In the spotsize converter of the present invention, a curve shape such as an exponential and a parabola can be used as the taper part in addition to the shape where the core width changes linearly. For example, an optimized taper which is proposed in “Soon Ryong Park and Beom-hoan, “Novel Design Concept of Waveguide Mode Adapter for Low-Loss Mode Conversion”, IEEE PHOTONICS TECHNOLOGY LETTERS, VOL.13, NO.7, JULY 2001, pp.675-677” can be used as the taper shape of the core width converting part shown in
Although the embodiments of the present invention have been described by taking the planar lightwave circuit as an example, application of the spotsize converter of the present invention is not limited to the planar lightwave circuit. For example, the spotsize converter can be applied to any optical circuit such as an optical circuit in which optical circuits or waveguides are multilayered. The “optical circuit” in this specification is used for meaning general optical circuit which is not limited to the planar lightwave circuit or the waveguide type optical circuit like AWG.
Although the main object of the present invention is to decrease the coupling loss between an optical waveguide and an optical fiber, the coupling loss also can be decreased when an optical component which is formed by a waveguide type optical circuit such as semiconductor laser is connected to the optical fiber or the planar lightwave circuit by using the optimum core width. In addition, the present invention can be used when different optical circuits are connected with each other.
According to the planar lightwave circuit of the present invention, the coupling loss of the superhigh- waveguide can be decreased while downsizing the planar lightwave circuit. In addition, dicing error which may occur when dicing the substrate can be dissolved. In addition, even when fabrication error occurs, low coupling loss can always be obtained by selecting and using a port which has the optimum core width. Therefore, the planar lightwave circuits, especially, low loss and highly integrated planar lightwave circuits can be applied to an optical communication system efficiently. Thus, a large capacity optical communication system which is in increasing demand can be constructed.
The present invention is not limited to the specifically disclosed embodiments, and variations and modifications may be made without departing from the scope of the invention.
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