JP4405952B2 - Refractive index adjusting device and refractive index adjusting method for planar optical circuit - Google Patents

Description

  The present invention relates to an apparatus for manufacturing a planar optical circuit element. More specifically, the present invention relates to a refractive index adjusting device and a refractive index adjusting method for an optical waveguide in a planar optical circuit element.

  In recent years, research and development of a planar lightwave circuit (PLC) composed of a silica-based glass optical waveguide formed on a silicon substrate or a quartz substrate has been actively conducted. Functional elements such as an arrayed waveguide type wavelength multiplexer / demultiplexer (AWG), a Mach-Zehnder interferometer, a directional coupler, and a thermo-optic switch have been developed, and their performance has been improved. Furthermore, various highly functional devices are realized by combining a plurality of functional elements.

  The optical circuit realizes various functions by using an optical interference phenomenon. In an optical circuit, propagating light is made to interfere by branching the propagating light into a plurality, controlling the phase of each propagating light with high accuracy, and combining them again. The phase control described above is performed by adjusting the length of the optical waveguide through which the branched light propagates, and is realized by appropriately setting the length of each optical waveguide. At this time, for adjusting the length of the optical waveguide, a very high accuracy of several nm to several tens of nm is required. However, in the actual optical circuit manufacturing process, it is very difficult to realize such high manufacturing accuracy, and a manufacturing error occurs in the length of the manufactured optical waveguide. Such a manufacturing error significantly deteriorates the performance of the optical circuit.

  Such manufacturing errors can be adjusted by irradiation with ultraviolet light (Non-Patent Document 1). When the core layer to which Ge is added is irradiated with ultraviolet light, the refractive index of the core layer can be increased. When phase control of propagating light is performed by the length of the optical waveguide, the phase amount given by the optical waveguide is determined by the product of the optical waveguide length and the refractive index of the optical waveguide. Therefore, even if the actual optical waveguide length deviates from the desired optical waveguide length due to errors that occur in the optical circuit manufacturing process, the optical waveguide can be adjusted by adjusting the refractive index of the optical waveguide after the optical circuit manufacturing process. The phase amount given by can be adjusted to a desired value.

  In the refractive index adjustment using ultraviolet light, it is necessary to irradiate the center of an optical waveguide having a size of several μm with ultraviolet light condensed to a size of several μm. In a refractive index adjusting device that irradiates a single optical waveguide such as an optical fiber with ultraviolet light, by measuring the intensity of the fluorescence generated by ultraviolet light irradiation in the core of the optical fiber at the end face of the optical fiber, Ultraviolet light can be collected at the center of the core of the optical fiber. In the case of an optical fiber, the fluorescence is refracted due to the cylindrical structure of the core. Accordingly, the shape of the emitted fluorescence changes depending on the emission location of the fluorescence. Therefore, by observing the shape of the fluorescence observed on the end face of the optical fiber, the irradiation position of the ultraviolet light can be grasped, and the center of the core of the optical fiber can be irradiated with the ultraviolet light (patent) Reference 1).

JP-A-8-286066 Control of defects in optical fibers-a study using cathode luminescence spectroscopy "Journal of Lightwave Technology, 1993, vol.11, 1793-1801

  However, the above-described refractive index adjustment method cannot be used in a planar lightwave circuit that is two-dimensionally complicated, not a one-dimensional optical waveguide such as an optical fiber. The planar optical circuit is composed of a plurality of optical waveguides, and a linear optical waveguide and a curved optical waveguide are mixed. Further, since the plurality of optical waveguides are branched and coupled, it is difficult to directly monitor the fluorescence generated at the irradiation position of the ultraviolet light from the end face of the optical waveguide. Further, since the optical waveguide of the planar optical circuit does not have a coaxial symmetry structure like an optical fiber, the irradiation position of ultraviolet light cannot be controlled by the shape of fluorescence.

  Refractive index adjustment by ultraviolet light in a planar lightwave circuit may reduce the optical circuit performance by a method used in a conventional optical fiber. When the condensed ultraviolet light is irradiated to a position deviated from the center of the optical waveguide, the polarization axis of the optical waveguide rotates, and the optical circuit performance deteriorates such as polarization crosstalk degradation and optical waveguide loss increase. Occurs. Furthermore, in the conventional method, it is necessary to estimate the amount of change in refractive index by constantly monitoring the change in characteristics of the entire optical circuit. Therefore, it is very difficult to control the refractive index, and the configuration of the refractive index adjusting device is very complicated. In addition, for monitoring the optical circuit surface where the refractive index is adjusted, a mechanism that controls the spot diameter of the ultraviolet light to be irradiated at the same time as focusing on the optical circuit in the visible light was not considered. .

  When adjusting the refractive index of the optical waveguide in a planar optical circuit, it is also necessary to control the spot diameter at the irradiated portion of ultraviolet light. This is because the birefringence state of the refractive index induced in the optical waveguide changes depending on the spot diameter of the ultraviolet light applied to the optical waveguide. Such birefringence is not a problem in adjusting the refractive index of an optical fiber having a coaxially symmetric structure, but is a problem peculiar to a planar lightwave circuit.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and is a simple configuration device that efficiently irradiates the center of the core portion with ultraviolet light focused to an appropriate spot diameter on the optical waveguide of a planar optical circuit. Accordingly, an object of the present invention is to provide a refractive index adjusting device capable of adjusting the refractive index and controlling the amount of birefringence.

In order to achieve such an object, the invention according to claim 1 is characterized in that the substrate is formed on a core layer of an optical waveguide of a planar optical circuit made of silica-based glass formed on the substrate. A refractive index adjusting device that changes the refractive index of the core layer by irradiating ultraviolet light from a vertical direction or an oblique direction of the light source, and is optically connected to the ultraviolet light source that generates ultraviolet light. An ultraviolet light beam control unit for controlling a beam diameter and a beam divergence angle of the ultraviolet light, and condensing ultraviolet light from the ultraviolet light beam control unit on the core layer, and from the core layer at an ultraviolet light condensing point Ultraviolet light condensing capable of collecting the generated fluorescence and focusing the visible light on the circuit configuration surface of the planar optical circuit to monitor the core layer near the ultraviolet light condensing point And the planar light The road is fixed, monitoring and possible optical circuit fixing 3D stage movement in three-dimensional directions, on the optical path axis of the visible light of the ultraviolet light condensing section, a core layer in the vicinity of the ultraviolet light condensing point A monitor unit, and a spectroscopic unit that measures the spectrum of the fluorescence generated from the core layer at the ultraviolet light condensing point and collected by the ultraviolet light condensing unit, and according to the measured fluorescence spectrum The core of the optical waveguide is irradiated with the ultraviolet light while controlling the position of the three-dimensional stage for fixing the optical circuit in a direction perpendicular to the optical axis direction of the optical waveguide near the ultraviolet light focusing point. Then, the refractive index of the core layer of the optical waveguide is adjusted .

  According to a second aspect of the present invention, in the first aspect of the invention, the spectroscopic unit includes a demultiplexing unit that branches fluorescence having a wavelength of 600 nm or less and fluorescence having a wavelength of 600 nm or more, and a wavelength of 600 nm branched by the demultiplexing unit. A first light receiving unit that measures the intensity of the following fluorescence and a second light receiving unit that measures the intensity of the fluorescence having a wavelength of 600 nm or more branched by the branching unit are provided.

  According to a third aspect of the present invention, in the invention according to the first or second aspect, the ultraviolet light condensing unit is a condensing lens capable of transmitting light having a wavelength of at least 200 nm to 600 nm. And

According to a fourth aspect of the present invention, by irradiating the core layer of the optical waveguide of a planar optical circuit made of quartz glass formed on the substrate with ultraviolet light from a vertical direction or an oblique direction to the substrate. An ultraviolet light source that generates ultraviolet light based on changing a refractive index of the core layer, and an ultraviolet light beam that is optically connected to the ultraviolet light source and controls a beam diameter and a beam divergence angle of the ultraviolet light The ultraviolet light from the control unit and the ultraviolet light beam control unit is collected on the core layer, the fluorescence generated from the core layer is collected at the ultraviolet light condensing point, and near the ultraviolet light condensing point by visible light In order to monitor the core layer, an ultraviolet light condensing unit capable of focusing on the circuit configuration surface of the planar optical circuit with respect to visible light, and the planar optical circuit are fixed and moved in a three-dimensional direction. optical circuit for fixed that can be And Dimension stage, a monitor unit that monitors the core layer in the vicinity of the ultraviolet light condensing point in the optical path on the axis of the visible light of the ultraviolet light condensing part, the result from the core layer in the ultraviolet light condensing point A method for adjusting a refractive index in a refractive index adjusting apparatus comprising a spectroscopic unit that measures a spectrum of the fluorescence collected by an ultraviolet light condensing unit , wherein the spectroscopic unit has a fluorescence intensity near a wavelength of 420 nm. Measuring the fluorescence intensity in the vicinity of the wavelength of 650 nm, determining the ratio of the fluorescence intensity in the vicinity of the wavelength of 420 nm and the fluorescence intensity in the vicinity of the wavelength of 650 nm, and the ultraviolet light focusing point so that the ratio is maximized. The core layer of the optical waveguide is irradiated with the ultraviolet light while controlling the position of the optical circuit fixing three-dimensional stage in a direction perpendicular to the optical axis direction of the optical waveguide in the vicinity of the optical waveguide. Characterized by comprising the step of adjusting the refractive index of the waveguide core layer.

  According to the refractive index adjusting device of the present invention, it is possible to realize downsizing of the device optical system and simplification of control. Furthermore, by controlling the beam diameter and the beam divergence angle by the ultraviolet light beam control unit, it is possible to control the spot diameter of the ultraviolet light at the position of the optical waveguide core part and control the amount of birefringence generated.

  When the core layer made of quartz glass is irradiated with ultraviolet light, fluorescence is generated. (Non-patent document 1) The spectrum of this fluorescence varies depending on the type of dopant added to the glass. Therefore, different fluorescence spectra are generated in the core layer to which Ge is added and the cladding layer to which Ge is not added. When the core layer is irradiated with ultraviolet light, fluorescence around 400 nm and two fluorescence spectra around 560 nm are observed. On the other hand, when the cladding layer is irradiated with ultraviolet light, only a fluorescence spectrum near 560 nm is observed.

  Therefore, it is possible to determine whether the center of the waveguide is irradiated with ultraviolet light by measuring the fluorescence spectrum level near 400 nm and the two fluorescence spectrum levels near 560 nm with the spectroscopic unit. That is, the optimal irradiation position is the position where the fluorescence spectrum level at 400 nm is the maximum and the fluorescence spectrum level at 560 nm is the minimum, and the planar optical circuit is fixed so that such a fluorescence spectrum is observed. The position of the optical circuit fixing stage is controlled.

  The fluorescence of 400 nm decreases with the lapse of the irradiation time when irradiated with ultraviolet light. On the other hand, the fluorescence at 560 nm tends to increase when irradiated with ultraviolet light. It is possible to estimate the amount of change in the refractive index generated in the optical waveguide irradiated with ultraviolet light by measuring the amount of decrease or increase in fluorescence in the spectroscopic unit.

  By combining such ultraviolet light condensing, fluorescent light collecting, and condensing position monitoring with a single condensing lens, the optical system of the refractive index adjusting device can be reduced in size and simplified in control. be able to. Furthermore, the spot diameter of the ultraviolet light at the position of the optical waveguide core can be controlled by controlling the beam diameter and the beam divergence angle by the ultraviolet light beam controller. It is possible to control the occurrence of birefringence.

[Example 1]
FIG. 1 is a diagram showing a configuration of a refractive index adjusting apparatus according to the present invention. A continuous wave ultraviolet laser having a wavelength of 244 nm is used as the ultraviolet light source 4 to adjust the refractive index of the optical waveguide 1 in the planar optical circuit 2. The ultraviolet light source 4 is optically connected to the ultraviolet light beam control unit 11. Ultraviolet light The ultraviolet light emitted from the ultraviolet light beam control unit 11 is further bent through the dichroic mirror 8 by 90 degrees and input to the condensing lens 3. An optical circuit fixing three-dimensional stage 10 is disposed opposite to the condensing lens 3. On the optical circuit fixing three-dimensional stage 10, the planar optical circuit 2 to be subjected to refractive index adjustment is fixed. Two half mirrors 9 b and 9 a are arranged on the optical axis of the condensing lens 3 on the opposite side of the dichroic mirror 8 from the condensing lens 3. An illumination lamp 5 that illuminates the planar optical circuit 2 is disposed in a direction perpendicular to the optical axis of the half mirror 9b. In addition, in the direction perpendicular to the optical axis of the half mirror 9a, a spectroscopic unit 6 for measuring the fluorescence generated in the planar optical circuit 2 is disposed. A monitor unit 7 is disposed on the optical axis further extended from the half mirror 9a. The monitor unit 7 includes a CCD that detects an image in the vicinity of the optical waveguide 1 of the planar optical circuit 2 to be subjected to refractive index adjustment.

  In the present invention, collection of ultraviolet light from the ultraviolet light source 4, monitoring of a refractive index adjustment state by visible light in a portion where the ultraviolet light is collected on the planar optical circuit 2, and fluorescence emitted from the optical waveguide 1 There is a great feature in that the collection of the light is performed by one condensing lens 3. With the configuration of such an optical system, the refractive index adjusting device can be reduced in size and simplified.

  With such a configuration of the optical system, only the fluorescence from the optical waveguide generated at the condensing point of the ultraviolet light in the spectroscopic unit 6 can be collected. The planar optical circuit 2 is fixed to the optical circuit fixing three-dimensional stage 10 and the image of the optical waveguide 1 of the planar optical circuit 2 recognized by the monitor unit 7 is confirmed, while the condensing lens 3 is visible in visible light. Adjust the focus. The ultraviolet light condensing position and the spot diameter are controlled by the ultraviolet light beam control unit 11 independently after determining the position of the condensing lens 3 with respect to visible light as described above.

  Hereinafter, a spot diameter control method for ultraviolet light applied to an optical waveguide, which is one of the characteristic parts of the present invention, will be described. When irradiating the optical waveguide 1 with ultraviolet light, it is necessary to observe the optical waveguide 1 through the condensing lens 3 by the monitor unit 7 in order to accurately grasp the position of the optical waveguide 1. For this reason, the distance between the condensing lens 3 and the optical waveguide 1 needs to coincide with the focus distance of visible light. That is, it is necessary to control the spot diameter of the ultraviolet light in the optical waveguide 1 while keeping the distance between the condensing lens 3 and the optical waveguide 1 constant. The spot diameter is controlled by the ultraviolet light beam control unit 11.

  FIG. 2 is a diagram illustrating a specific configuration of the ultraviolet light beam control unit. The ultraviolet light beam control unit 11 includes a pinhole 22 disposed between the two convex lenses 21a and 21b and the two convex lenses 21a and 21b. By changing the distance between the convex lens 21a on the ultraviolet light source 4 side and the convex lens 21b on the dichroic mirror 8 side, the spread angle of the ultraviolet light beam is changed, and the focal length of the ultraviolet light in the condensing lens 3 is controlled. The beam diameter of the ultraviolet light can also be controlled by arranging the pinhole 22 between the two convex lenses 21a and 21b.

  FIG. 3 is a diagram showing a calculation result of an optical path of ultraviolet light propagating through two convex lenses and a condensing lens. The focus distances of the two convex lenses 21a and 21b are 100 mm, and the focus distance of the condensing lens 3 is 10 mm. The diameter of the pinhole 22 was 5 μm. The distance between the two convex lenses 21a and 21b indicates a case where the solid line in FIG. 3 is 300 mm, the dotted line is 310 mm, and the broken line is 290 mm.

  FIG. 4 is an enlarged view of the calculation result of the optical path of the ultraviolet light near the focal point of the condensing lens. It can be seen that the focal point of the ultraviolet light can be changed back and forth in the optical axis direction by changing the distance between the two convex lenses 21a and 21b. In other words, the ultraviolet light beam control unit 11 can independently change the focus distance of the ultraviolet light in the condensing lens 3. Therefore, it is possible to change the spot diameter of the ultraviolet light irradiated to the optical waveguide 1 without moving the position of the condensing lens 3 while keeping the focus on the visible light coincident with the optical waveguide 1.

  FIG. 5 is a diagram for explaining how the ultraviolet light condensing point is controlled by the ultraviolet light beam control unit. Each figure of FIG. 5 shows a state in which ultraviolet light is condensed on the cross section of the condensing lens 3 and the planar optical circuit 2. In FIG. 5 a, the focal point of the ultraviolet light coincides with the position of the core part 51. On the other hand, in FIG. 5 b, the condensing point is located on the condensing lens 3 side above the core 51. The condensing point is controlled to a position shifted from the core unit 51 by a distance indicated by defocus in the optical axis direction. As understood from FIGS. 5a and 5b, the spot diameter of the ultraviolet light in the core 51 on the optical axis of the condensing lens 3 can be controlled by changing the position of the condensing point.

FIG. 6 is a diagram showing an ultraviolet light beam profile when the spot diameter is controlled. The ultraviolet light beam profile at the waveguide position is measured by the knife edge method. The focus distance of the two convex lenses 21a and 21b was 100 mm, the focus distance of the condensing lens 3 was 10 mm, and the diameter of the pinhole was 5 μm. In the beam profile of FIG. 6, the width of two points where the amplitude is 1 / e ² (13.533%) of the peak value was defined as the spot diameter. FIG. 6A shows a case where defocus = 0 μm, that is, the spot diameter is minimum, and the spot diameter at this time is 8 μm. FIG. 6b shows a case where defocus = 200 μm, and the spot shape at this time was 30 μm.

  As described above in detail, the ultraviolet light beam control unit 11 can control the condensing point of the ultraviolet light while the condensing lens 3 is fixed, and the core unit 51 of the planar optical circuit 2. The spot diameter can also be controlled. On the other hand, the condensing lens 3 can determine the position of the focus distance of visible light so that the monitor 7 can observe the image of the optical waveguide 1. Condensation of ultraviolet light, collection of fluorescence, and a visible light monitor at the adjustment position at the condensing position are used together with one condensing lens 3 to reduce the size and simplification of the optical system of the refractive index adjusting device. Can be realized.

  In the configuration of the optical system of the present invention, the optical axis of the condensing lens 3 is not perpendicular to the planar optical circuit 2 but is tilted several degrees from the vertical axis so that the rear surface of the substrate of the planar optical circuit 2 or the optical waveguide 1 is obtained. It is possible to prevent the fluorescence generated by other than the above or the reflected light of ultraviolet light from being collected in the spectroscopic unit 6. Thereby, it becomes possible to reduce a noise component, and the controllability of refractive index adjustment improves. Furthermore, by tilting several degrees from the vertical axis, the ultraviolet light incident on the planar optical circuit 2 interferes with the ultraviolet light reflected inside the substrate of the planar optical circuit 2, and thus near the core portion. It can also prevent the uniformity of the ultraviolet light intensity from deteriorating.

  The condensing lens 3 needs to transmit three types of light: ultraviolet light (244 nm), fluorescence (near 500 nm and 640 nm), and monitor light (visible light 450 nm to 750 nm). At least the wavelengths of the monitor light and the fluorescence may overlap, and it is necessary to use a condensing lens that can transmit ultraviolet light and fluorescence at a minimum.

  Next, a method for reliably capturing the center portion of the optical waveguide and adjusting the refractive index while irradiating the optical waveguide with ultraviolet light will be described. As described above, in order to prevent the deterioration of the performance of the optical circuit such as the deterioration of the polarization crosstalk and the increase of the optical waveguide loss, the collected ultraviolet light is passed along the center of the optical waveguide. Irradiation is necessary. Unlike an optical fiber, a planar lightwave circuit is composed of a straight optical waveguide or a curved optical waveguide, and they branch or merge. Therefore, it is necessary to irradiate ultraviolet light accurately along the center of the optical waveguide while following the layout of the optical waveguide. This can be executed by spectrally analyzing the fluorescence from the optical waveguide collected by the condensing lens 3 by the spectroscopic unit 6.

  FIG. 7 shows a fluorescence spectrum when an optical waveguide of a planar optical circuit is irradiated with ultraviolet light. As shown in FIG. 7a, when the central core portion of the optical waveguide is irradiated with ultraviolet light, a high level of fluorescence is generated in the vicinity of a wavelength of 420 nm. On the other hand, as shown in FIG. 7b, if the core part is not irradiated with ultraviolet light at all from the core part of the optical waveguide, fluorescence near the wavelength of 420 nm does not occur, and the fluorescence level near 650 nm increases. When the ultraviolet light is slightly deviated from the central core portion, the spectrum is in an intermediate state between FIGS. 7a and 7b. Therefore, when the ratio between the fluorescence peak level near the wavelength of 420 nm and the fluorescence peak level near the wavelength of 650 nm is maximized, the ultraviolet light is irradiated at the exact center of the optical waveguide core. In this way, whether or not the central core portion is irradiated with ultraviolet light is determined based on the spectral level observed by the spectroscopic portion 6, and the optical circuit fixing three-dimensional stage 7 to which the planar lightwave circuit 1 is fixed is moved. Let

  FIG. 8 is a diagram for explaining the control of the optical circuit fixing three-dimensional stage during irradiation with ultraviolet light. As described above, the optical waveguide 1 can be controlled while tracking the image recognized by the monitor unit 7. While irradiating ultraviolet light along the shape of the optical waveguide 1 (in the ultraviolet laser scanning direction in FIG. 8), the optical waveguide is such that the ratio between the fluorescence level near the wavelength of 420 nm and the fluorescence level near the wavelength of 650 nm is maximized. By further finely controlling the position of the optical circuit fixing three-dimensional stage in the axial direction perpendicular to the light traveling direction (the positional deviation adjusting direction in FIG. 8), errors in the ultraviolet light irradiation position are eliminated. Thereby, even in a complicated optical waveguide layout, it is possible to collect ultraviolet light while always capturing the center of the core portion.

  FIG. 9 is a block diagram showing an example of the entire refractive index adjusting apparatus of the present invention including the control unit. The refractive index adjusting apparatus 100 including the optical system unique to the present invention shown in FIG. 1 shows only the spectroscopic unit 6, the monitor unit 7, and the optical circuit fixing three-dimensional stage 10. The monitor unit 7 of the refractive index adjusting device 100 is connected to the optical waveguide capturing unit 103, and the spectroscopic unit 6 is connected to the positional deviation detecting unit 104. The waveguide capture detection unit 103 and the positional deviation detection unit 104 are connected to the control unit 102. Further, the control unit 102 is connected to the optical circuit fixing three-dimensional stage via the stage driving unit 101.

  Based on the image of the optical waveguide recognized by the monitor unit 7, an optical waveguide position information signal is supplied to the control unit 103 by the waveguide capture detection unit 103. Based on the spectral information from the spectroscopic unit 6, the positional deviation detection unit 104 supplies a position control signal to the control unit 103. In the control unit 103, a stage control signal for controlling the position of the optical circuit fixing three-dimensional stage 10 is supplied to the stage driving unit 101 based on the optical waveguide position information signal and the position control signal described above. Note that each block in FIG. 9 is illustrative, and is not limited to the above-described block configuration or function distribution of each control signal. Any block configuration and signal configuration may be used as long as the configuration can perform feedback control of the ultraviolet light irradiation position according to the spectrum level.

  Depending on the medium material of the optical circuit, the fluorescence level near the wavelength of 420 nm may be weak. In this case, the fluorescence level can be increased by storing the optical circuit under high pressure hydrogen of 1 to 200 atm for several hours to 10 days.

  FIG. 10 is a diagram showing a fluorescence spectrum from an optical circuit hydrogenated under high-pressure hydrogen. The optical circuit was stored in a hydrogen atmosphere at 100 atm for 7 days, and the fluorescence spectrum was measured. Although the peak wavelength of the fluorescence spectrum is slightly changed compared to the case where hydrogen is not added, the optical circuit is configured so that the ratio of the peak level of fluorescence near the wavelength of 420 nm to the peak level of fluorescence near the wavelength of 650 nm is maximized. While controlling the position of the fixing three-dimensional stage, the central core portion of the optical waveguide can be irradiated with ultraviolet light.

  As described above in detail, the refractive index adjustment device is simplified by the configuration of the optical system peculiar to the present invention, and the fluctuation of the fluorescence spectrum level is detected in real time by the spectroscopic unit. By controlling, the refractive index can be adjusted while aligning the ultraviolet light spot with the central core portion of the optical waveguide.

  FIG. 11 is a diagram showing a result of adjusting the refractive index by the refractive index adjusting device of the present invention. An optical waveguide section (core width 6 μm, section length 1 mm) of a certain length is subjected to ultraviolet light scanning by the refractive index adjusting device of the present invention, and the refractive index change when this scanning is repeated a plurality of times in the same section Show. One section scan takes 100 seconds and is repeated 20 times. The spot diameter in the core portion of the optical waveguide is controlled by the ultraviolet light beam control unit 11. FIG. 11a shows a case where the spot diameter at the core is 8 μm (corresponding to defocus = 50 μm in FIG. 5b), and FIG. 11b shows a case where the spot diameter is 20 μm (corresponding to defocus = 150 μm).

  Since the ultraviolet light is irradiated while capturing the center of the core portion of the optical waveguide, a sufficient change in the refractive index is obtained. 11A and 11B are compared, it can be seen that the amount of birefringence generated can be adjusted by changing the spot diameter of the ultraviolet light in the core portion. When the spot diameter in FIG. 11a is 8 μm, both the TE mode and TM mode lights have the same amount of refractive index increase. That is, no birefringence has occurred. On the other hand, when the spot diameter in FIG. 11b is 20 μm, the refractive index of the TE mode is greatly increased as compared with the TM mode. This indicates that birefringence occurs.

FIG. 12 is a diagram showing the relationship between the spot diameter of ultraviolet light in the core and the amount of birefringence generated. The horizontal axis in FIG. 12 actually indicates the distance between the optical waveguide and the focal point, and corresponds to the defocus distance shown in FIG. 5b. As described in FIG. 5, the spot diameter of the ultraviolet light in the core part can be controlled by changing the focus distance. The vertical axis shows the ratio between the refractive index change amount for the TE mode and the refractive index change amount for the TM mode. This ratio represents the value of the ratio when the average value of the TE mode refractive index variation and the TM mode refractive index variation is 1.0 × 10 ⁻³ .

  As can be seen from FIG. 12, when the spot diameter is about 40 μm, the value of the ratio is 1, and the amount of change in the refractive index does not depend on the polarization, and it can be seen that birefringence does not occur. Therefore, it can be seen that, in the present refractive index adjusting device, the occurrence of birefringence induced in the optical waveguide due to the refractive index adjustment can be controlled by appropriately setting the spot diameter. It is also possible to adjust the spot diameter to change to a desired birefringence. Note that the value of 40 μm in FIG. 12 varies depending on the type of medium having the core portion and the condensing lens in the optical waveguide of this embodiment. Therefore, it should be noted that the value is not uniquely limited to 40 μm, and an optimum value needs to be obtained according to the structure of the optical waveguide, the medium material, the refractive index value, the characteristics of the condenser lens, and the like.

  As described above, by controlling the ultraviolet light of the refractive index adjusting device of the present invention, the center of the core portion of the optical waveguide is always irradiated with ultraviolet light to adjust the refractive index and appropriately control the spot diameter in the core portion. Thus, the refractive index can be adjusted without generating birefringence.

[Example 2]
FIG. 13 is a diagram illustrating a configuration of a spectroscopic unit according to a simpler form of the present invention. The spectroscopic unit 6 in FIG. 1 has a simpler configuration. The fluorescence having a wavelength of 600 nm or more and the fluorescence having a wavelength of 600 nm or less are branched by the dichroic mirror 8, and the respective fluorescence levels are measured by PDs (photo detectors) 12a and 12b. There is a possibility that noise such as light other than fluorescence may be input, but without using an expensive measuring device such as a grating, a fluorescence level near a wavelength of 420 nm and a wavelength of 650 nm necessary for controlling the irradiation position of ultraviolet light are used. The ratio to the nearby fluorescence level can be measured. Even when the spectroscopic unit of FIG. 13 is used, the refractive index can be adjusted as in the first embodiment. In this case, there is a possibility that the PDs 12a and 12b receive light from the illumination lamp 5 used for monitoring the surface of the planar optical circuit. For this reason, the illumination lamp 5 is used for confirming the position of the waveguide before the irradiation with ultraviolet light, but the illumination lamp 5 was turned off during the irradiation with ultraviolet light.

  In the present invention, Ge has been described as an example of the additive material to the core layer. However, the refractive index can be adjusted by using other rare earth elements such as Er, Nd, and Ce. In this case, the wavelength of the generated fluorescence may be different, and is not limited to the control by the fluorescence of 420 and 650 nm of the present invention.

  As described above in detail, according to the refractive index adjusting device of the present invention, it is possible to reduce the size of the device optical system and simplify the control. Furthermore, the spot diameter of the ultraviolet light at the position of the optical waveguide core can be controlled by controlling the beam diameter and the beam divergence angle by the ultraviolet light beam controller. The amount of birefringence generated can be controlled.

It is a figure which shows the structure of the refractive index adjustment apparatus of this invention. It is a block diagram of an ultraviolet light beam control part. It is a figure which shows the calculation result of the optical path of the ultraviolet light which propagates two convex lenses and a condensing lens. It is the figure which expanded and showed the calculation result of the optical path of an ultraviolet light in the focus vicinity of the condensing lens. It is a figure explaining the mode of control of the condensing point of the ultraviolet light by an ultraviolet light beam control part. It is a figure which shows the ultraviolet light beam profile at the time of controlling a spot diameter. It is a figure which shows the fluorescence spectrum by a spectroscopic part at the time of irradiating the ultraviolet light to the optical waveguide of a planar optical circuit. It is a figure explaining control of the three-dimensional stage for optical circuit fixation at the time of ultraviolet light irradiation. It is a figure which shows the fluorescence spectrum from the optical circuit hydrogenated under high pressure hydrogen. It is a block diagram of the refractive index adjustment apparatus of this invention containing a control part. It is a figure which shows the characteristic of adjustment time and refractive index adjustment amount by the refractive index adjustment apparatus of this invention. It is a figure which shows the relationship between the spot diameter of the ultraviolet light in a core part, and the generation amount of birefringence. It is a figure which shows the structure of the spectroscopy part of the simpler form of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical waveguide 2 Planar type optical circuit 3 Condensing lens 4 Ultraviolet light source 5 Illumination lamp 6 Spectrometer part 7 Monitor part 8 Dichroic mirror 9a, 9b Half mirror 10 Three-dimensional stage for optical circuit fixation 11 Ultraviolet light beam control part 12a, 12b Photodetector (PD)
21a, 21b Convex lens 22 Pinhole 51 Core unit 100 Refractive index adjusting device 101 Three-dimensional stage driving unit for optical circuit fixation 102 Control unit 103 Position shift detection unit 104 Optical waveguide detection unit

Claims (4)

The refractive index of the core layer is changed by irradiating the core layer of the optical waveguide of the planar optical circuit made of quartz-based glass formed on the substrate with ultraviolet light from the vertical or oblique direction of the substrate. A refractive index adjusting device,
An ultraviolet light source that generates ultraviolet light;
An ultraviolet light beam control unit that is optically connected to the ultraviolet light source and controls a beam diameter and a beam divergence angle of the ultraviolet light;
Condensing ultraviolet light from the ultraviolet light beam control unit onto the core layer, collecting fluorescence generated from the core layer at an ultraviolet light condensing point, and the core layer near the ultraviolet light condensing point by visible light An ultraviolet light condensing unit capable of focusing on the circuit configuration surface of the planar optical circuit for visible light,
An optical circuit fixing three- dimensional stage that fixes the planar optical circuit and is movable in a three-dimensional direction;
On the optical path axis of visible light of the ultraviolet light condensing unit, a monitor unit for monitoring the core layer in the vicinity of the ultraviolet light condensing point;
A spectroscopic unit that measures the spectrum of the fluorescence generated from the core layer and collected by the ultraviolet light condensing unit at the ultraviolet light condensing point ;
While controlling the position of the three-dimensional stage for fixing the optical circuit in a direction perpendicular to the optical axis direction of the optical waveguide in the vicinity of the ultraviolet light condensing point according to the measured fluorescence spectrum, the ultraviolet light is controlled. Is applied to the core layer of the optical waveguide to adjust the refractive index of the core layer of the optical waveguide .   The spectroscopic unit includes a demultiplexing unit that branches fluorescence having a wavelength of 600 nm or less and fluorescence having a wavelength of 600 nm or more, a first light receiving unit that measures the intensity of fluorescence having a wavelength of 600 nm or less branched by the demultiplexing unit, The refractive index adjusting device according to claim 1, further comprising a second light receiving unit that measures the intensity of fluorescence having a wavelength of 600 nm or more branched by the branching unit.   The refractive index adjusting device according to claim 1, wherein the ultraviolet light condensing unit is a condensing lens capable of transmitting light having a wavelength of at least 200 nm to 600 nm. The refractive index of the core layer is changed by irradiating the core layer of the optical waveguide of the planar optical circuit made of quartz glass formed on the substrate with ultraviolet light from the vertical direction or the oblique direction to the substrate. An ultraviolet light source that generates ultraviolet light, an ultraviolet light beam control unit that is optically connected to the ultraviolet light source and controls a beam diameter and a beam divergence angle of the ultraviolet light, and the ultraviolet light beam control The ultraviolet light from the light is condensed on the core layer, the fluorescence generated from the core layer is collected at the ultraviolet light condensing point, and the core layer near the ultraviolet light condensing point is monitored by visible light. An ultraviolet light condensing unit capable of focusing on the circuit configuration surface of the planar optical circuit with respect to light, and a three- dimensional optical circuit fixing capable of moving in a three-dimensional direction by fixing the planar optical circuit. Stage and the purple A monitor unit that monitors the core layer in the vicinity of the ultraviolet light condensing point on the optical path axis of the visible light of the light condensing part, by the ultraviolet light condensing part originating from the core layer in the ultraviolet light condensing point In a refractive index adjusting device comprising a spectroscopic unit for measuring the spectrum of the collected fluorescence, a method for adjusting the refractive index,
Measuring the fluorescence intensity in the vicinity of a wavelength of 420 nm and the fluorescence intensity in the vicinity of a wavelength of 650 nm in the spectroscopic unit;
Obtaining a ratio of fluorescence intensity near the wavelength of 420 nm and fluorescence intensity near the wavelength of 650 nm;
While controlling the position of the three-dimensional stage for fixing the optical circuit in the direction perpendicular to the optical axis direction of the optical waveguide in the vicinity of the ultraviolet light condensing point, the ultraviolet light is And irradiating the core layer of the optical waveguide to adjust the refractive index of the core layer of the optical waveguide.

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