JP6861775B2 - Optical waveguide element and optical axis adjustment method - Google Patents

Description

The present invention relates to an optical waveguide element and an optical axis adjusting method suitable for use in evaluating the characteristics of an optical waveguide device.

With the increase in the amount of information transmitted, optical wiring technology is drawing attention. In the optical wiring technology, an optical device using an optical fiber or an optical waveguide as a transmission medium is used to transmit information between racks, boards, chips, etc. in an information processing device by an optical signal. By using the optical wiring technology, it is possible to improve the band limitation due to the use of electrical wiring, which is a bottleneck in information processing equipment that requires high-speed signal processing.

Silicon (Si) as a light transmission medium is characterized by being transparent in the communication wavelength range and having a high refractive index as a waveguide core. In an optical waveguide element (Si waveguide element) made of Si, an optical waveguide core which is substantially an optical transmission path is formed of Si as a material. _{Then, a clad made of, for example, silicon oxide (SiO 2} ) having a refractive index lower than that of Si covers the periphery of the optical waveguide core.

In the Si waveguide configured by covering the periphery of the Si optical waveguide core with a SiO ₂ clad, a very large difference in the specific refractive index between the optical waveguide core and the clad is secured. Therefore, the equivalent refractive index of the propagation mode of the Si waveguide takes a value away from the refractive index of the cladding. As a result, light can be strongly confined inside the Si optical waveguide core. As described above, the strong confinement can suppress the radius of curvature of the bent waveguide and the minimum wiring pitch between the parallel waveguides to about several μm. Therefore, the layout size of the optical wiring can be reduced.

In addition, it is possible to finely process the Si waveguide by high-precision photolithography using a semiconductor manufacturing apparatus and etching technology. Furthermore, a modulator that applies a change in the refractive index (plasma carrier effect) associated with carrier amplification by applying a voltage to the PN-Si region formed by ion doping, and germanium (Ge), which has a narrower bandgap than Si, are placed on Si. Various functional devices such as a light receiving element (PD: Photodiode) that has been selectively grown can be monolithically integrated and formed on the same substrate, and mass production is easy. For this reason, the Si waveguide is regarded as a promising platform for realizing an optical module in a small size and at low cost, and various studies on this have been conducted (for example, Patent Document 1, Non-Patent Document 1 or Non-Patent Document). 2).

Generally, in the manufacturing process of an optical module, an optical waveguide device is formed on a substrate by a semiconductor manufacturing process, and then the substrate is diced to be individualized as a chip. The individualized chips include a TEG chip in which a TEG (Test Elemental Group) pattern for evaluating the characteristics of a single optical waveguide device is formed, and an integrated chip in which an integrated device for mounting on an optical module is formed. is there.

When evaluating the optical characteristics of optical waveguide devices for TEG chips and integrated chips, optical fibers are abutted against these chips from both ends, one optical fiber is used as a light source, and the other optical fiber is used as a spectrum analyzer or power meter. Optically connect with. The optical signal transmitted from the light source is received and evaluated by a spectrum analyzer or a power meter via an optical waveguide device on the chip.

In the integrated chip, the optical waveguide may be terminated by PD. In this case, the optical fiber connected to the light source is abutted against one end of the integrated chip, and the optical signal transmitted from the light source is photoelectrically converted by the PD on the chip and evaluated by a voltage / ammeter or the like. For example, an optical signal monitoring module for evaluating the polarization characteristics of an integrated chip has been proposed (see, for example, Patent Document 2).

Here, the Si waveguide has a small cross-sectional size of several hundred nm per side for satisfying the single mode transmission condition due to the large difference in the specific refractive index between the optical waveguide core and the cladding as described above. Even if a spot size converter (SSC: Spot Size Converter) is used, the mode field diameter (MFD: Mode Field Diameter) of light that can be expanded is limited to about 3 μm at most. Therefore, in the Si optical waveguide device composed of the Si optical waveguide, it is difficult to evaluate the optical characteristics requiring the optical axis adjustment as compared with other optical waveguide devices.

Further, the Si optical waveguide device is expected to be used mainly in the communication wavelength band (λ = 1.31 to 1.55 μm) in consideration of the absorption wavelength band of the material. The optical signal used for evaluating the optical characteristics is infrared light, and the fact that this infrared light cannot be visually confirmed also contributes to the difficulty of adjusting the optical axis.

The procedure for evaluating the optical characteristics of the conventional TEG chip will be described with reference to FIG.

In the evaluation of the TEG chip, as shown in FIG. 9, it is necessary to adjust the optical axes of the two optical fibers on the input side and the output side with respect to the TEG chip. Specifically, for example, the optical axis adjustment is performed in the following process.

First, the TEG chip 10 is placed on the sample stage 20. Then, with respect to the Si waveguide 40 formed on the TEG chip 10 including the optical waveguide device 30 to be evaluated, the CCD camera 50 installed above the TEG chip 10 is used to display the light on the TEG chip 10 and the input side. The optical fiber 60 on the input side is visually adjusted in the XZ plane while looking at the fiber 60. Here, the XZ plane refers to a plane parallel to the upper surface of the TEG chip 10. Further, the Y direction refers to a direction orthogonal to the XZ plane, that is, a direction orthogonal to the upper surface of the TEG chip 10.

Next, the infrared camera 55 is used from above the TEG chip 10 to adjust the position of the optical fiber 60 on the input side in the Y direction so that the intensity of scattered light from the Si waveguide 40 is maximized.

Next, with the optical fiber 60 on the input side fixed, the optical fiber 62 on the output side is adjusted in each of the X, Y, and Z directions so that the reception intensity of the spectrum analyzer or the power meter is maximized.

Japanese Unexamined Patent Publication No. 2011-77133 Japanese Unexamined Patent Publication No. 2004-361948

IEEE Journal of selected topics in quantum electronics, vol.11, No.1, January / February 2005 p.232-240 IEEE Journal of selected topics in quantum electronics, vol.12, No.6, November / December 2006 p.1371-1379 "Trends in standardization of next-generation optical access system (NG-PON2)" NTT Technical Journal 2015.1

In the conventional optical axis adjusting method described with reference to FIG. 9, an infrared camera is used for adjusting the optical axis of the optical fiber on the input side in the Y direction.

Here, what is monitored by the infrared camera is scattered light from the Si waveguide. In this case, if the light is completely confined in the Si waveguide, there is a problem in that the light that is not originally observed is used as a guide. In addition, in the case of light in the communication wavelength band, the scattered light from the Si waveguide is infrared light, and an expensive infrared camera of about one million yen is required for observing infrared light. It is an issue.

The present invention has been made in view of the above-mentioned problems. An object of the present invention is to provide an optical waveguide element and an optical axis adjustment method capable of adjusting the optical axis even when light is completely confined in the Si waveguide.

In order to achieve the above-mentioned object, the optical waveguide element of the present invention includes a support substrate, an optical waveguide core, and a clad formed on the support substrate including the optical waveguide core. The optical waveguide core is provided with a pattern for adjusting the optical axis. The optical axis adjusting pattern includes a probing filter unit and a radiation unit.

The probing filter unit transmits the signal light and extracts the verification light from the input light including the signal light and the verification light. The radiation unit radiates the verification light extracted by the probing filter unit in a direction orthogonal to the propagation direction of the input light in the probing filter unit and in a direction orthogonal to the end face of the optical waveguide element.

According to a preferred embodiment of the optical waveguide element of the present invention, the probing filter unit includes a grating and a mode conversion unit. In the grating, the Bragg wavelength is set to the wavelength of the verification light which is shorter than the wavelength of the signal light among the input lights, and the verification light which is a component of the 0th order mode is i (i is an integer of 1 or more). ) Convert to the next mode and reflect. The mode conversion unit converts the verification light of the i-order mode reflected by the grating into the 0th-order mode.

Further, according to a preferred embodiment of the optical waveguide element of the present invention, the radiating portion includes a tapered portion whose width continuously decreases as the distance from the probing filter portion increases. Further, the radiating portion may be provided with an extending portion having a constant width for connecting the end portion of the tapered portion opposite to the probing filter portion and the radiating end provided on the end surface of the optical waveguide element .

Further, the optical axis adjusting method of the present invention is a method of adjusting the optical axis between the above-mentioned optical waveguide element and an optical fiber, and is configured to include the following processes.

First, in the first process, the optical waveguide element and the optical fiber on the input side are aligned in a plane parallel to the upper surface of the optical waveguide element while looking at the upper surface of the optical waveguide element from the upper surface side of the optical waveguide element. I do. Next, in the second process, the infrared fluorescent sample is placed so as to face the radiating end of the radiating portion provided on the end face of the optical waveguide element. Next, in the third process, input light including verification light is input from the optical fiber on the input side, the infrared fluorescent sample is emitted by the verification light emitted from the radiation unit, and the optical waveguide element and the light emission are used as a guide. , Aligning with the optical fiber on the input side in the direction orthogonal to the upper surface of the optical waveguide element.

Further, according to a preferred embodiment of the optical axis adjusting method of the present invention, the fourth process and the fifth process, which are performed after the third process, are included.

In the fourth process, the optical waveguide element and the optical fiber on the output side are aligned in a plane parallel to the upper surface of the optical waveguide element while looking at the upper surface of the optical waveguide element from the upper surface side of the optical waveguide element.

In the fifth process, a light intensity measuring device is connected to the optical fiber on the output side, and the optical waveguide element and the optical fiber on the output side are optically connected so that the received light intensity of the light intensity measuring device is maximized. Align in the direction orthogonal to the upper surface of the waveguide element.

According to the optical waveguide element and the optical axis adjustment method of the present invention, after adjusting the position in a plane parallel to the upper surface of the optical waveguide element while using a CCD camera or the like, the intensity of the verification light emitted from the radiation portion is monitored. Then, the alignment in the direction orthogonal to the upper surface of the optical waveguide element can be performed. Therefore, the optical axis can be adjusted even when the light is completely confined in the Si waveguide. Further, even when the input light is infrared light, the optical axis can be adjusted without using an expensive infrared camera.

It is a schematic diagram which shows one structural example of the optical waveguide element of this invention. It is a schematic end view of an optical waveguide element. It is a schematic diagram for demonstrating the optical axis adjustment method in the TEG chip which formed the optical axis adjustment pattern. It is a schematic diagram of the integrated chip which has an optical axis adjustment pattern. It is a schematic diagram for demonstrating the optical axis adjustment method in the integrated chip which formed the optical axis adjustment pattern. It is a figure which shows the transmission spectrum and the reflection spectrum of a grating. It is a figure which shows the relationship between the radiation end width and the synchrotron radiation angle in SSC. It is a figure which shows the relationship between the radiation end width and the propagation loss per unit length in SSC. It is a schematic diagram of the optical characteristic evaluation of a conventional TEG chip.

Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the shape, size, and arrangement of each component are only schematically shown to the extent that the present invention can be understood. Further, although a preferable configuration example of the present invention will be described below, the material and numerical conditions of each component are merely suitable examples. Therefore, the present invention is not limited to the following embodiments, and many modifications or modifications can be made that can achieve the effects of the present invention without departing from the scope of the constitution of the present invention.

The optical waveguide device of the present invention will be described with reference to FIGS. 1 and 2. 1 and 2 are schematic views showing a configuration example of the optical waveguide device of the present invention. FIG. 1 shows only the optical waveguide core, omitting the support substrate and the cladding described later. FIG. 2 is a schematic end view of the radiation portion shown in FIG. 1 cut out along the line I-I.

The optical waveguide element 5 has an optical waveguide including a support substrate 110, a clad 120, and an optical waveguide core 130 as a basic structure.

The support substrate 110 is made of, for example, a flat plate made of single crystal Si as a material.

The clad 120 is provided on the support substrate 110. The clad 120 covers the upper surface of the support substrate 110 and is formed including the optical waveguide core 130. The clad 120 is formed of, for example, silicon oxide (SiO ₂ ) as a material.

The optical waveguide core 130 is formed of, for example, Si, which has a higher refractive index than the clad 120. As a result, the optical waveguide core 130 functions as a light transmission path, and the light input to the optical waveguide core 130 propagates in the propagation direction according to the planar shape of the optical waveguide core 130.

The optical waveguide element 5 includes a pattern 100 for adjusting the optical axis. The optical axis adjusting pattern 100 is configured according to the planar shape of the optical waveguide core 130. Here, an optical path determined according to the planar shape of the optical waveguide core 130 is also referred to as a Si waveguide.

The optical axis adjusting pattern 100 includes a probing filter unit 200 and a radiation spot size converter (SSC) 300 as a radiation unit. Further, depending on the design, the input waveguide 510 connected to the optical fiber on the input side, the routing waveguide 530 connecting the probing filter unit 200 and the SSC 300, and the output connected to the optical waveguide device to be evaluated. The optical waveguide 540 is provided.

In the optical waveguide element 5 provided with the optical axis adjustment pattern 100, the probing filter unit 200 selectively extracts the verification light contained in the light input through the optical fiber on the input side, and the extracted verification light is taken out by the SSC300. Radiate from. The optical axis is adjusted by monitoring the verification light emitted from the SSC 300. Here, the optical waveguide element 5 provided with the optical axis adjusting pattern 100 is also referred to as a chip. The optical axis adjusting pattern 100 described above is formed on a TEG chip on which a TEG pattern is formed, an integrated chip on which a light emitting element (LD: Laser Diode), a PD, or the like is mounted.

The probing filter unit 200 has a grating 210 and a mode filter 220. The grating 210 is configured by periodically forming a refractive index modulation region on the Si waveguide. The grating 210 converts propagating basic mode (0th mode) light into i-order mode (i> 0) light and reflects it with respect to light having a specific wavelength (Bragg wavelength). Here, the grating 210 has an all-through (total transmission) characteristic for an optical signal having a wavelength longer than the Bragg wavelength, and has a feature that it does not have an optical effect on the optical waveguide device in the subsequent stage. .. Therefore, it is preferable to set the Bragg wavelength of the grating 210 to a wavelength slightly shorter than the operating wavelength band of the optical waveguide device to be evaluated.

The mode filter 220 includes a main waveguide 221 and a sub waveguide 222. The main waveguide 221 and the sub waveguide 222 are arranged in parallel so as to be separated from each other so that light can be coupled to each other. The i-order mode light propagating in the main waveguide 221 is converted into the basic mode light propagating in the sub waveguide 222, and the path is switched.

The operation of the probing filter unit 200 will be described with i = 1.

The grating 210 and the main waveguide 221 included in the mode filter 220 are optically connected. The input light including the signal light and the verification light is input from the input waveguide 510 to the main waveguide of the mode filter 220. The input light propagating in the main waveguide 221 is
Sent to the grating 210. Of the input light, the signal light, which is a component of the basic mode having a wavelength longer than the Bragg wavelength of the grating 210, passes through the grating 210. On the other hand, of the input light, the verification light, which is a component of the basic mode having a wavelength shorter than the Bragg wavelength, is converted into the primary mode light by the grating 210 and reflected. The primary mode verification light reflected by the grating 210 is converted into basic mode light while propagating through the main waveguide 221 included in the mode filter 220, and is transferred to the sub waveguide 222 included in the mode filter 220. The sub waveguide 222 is optically connected to the SSC 300.

The SSC 300 has a tapered portion 310 in which the width dimension of the optical waveguide core is continuously reduced along the light propagation direction. The width of the tapered portion 310 on the side connected to the probing filter portion 200 is the width of the waveguide (routed waveguide) 530 that optically connects the probing filter portion 200 and the SSC 300. Further, the width (termination width) of the tapered portion 310 on the side opposite to that of the probing filter portion 200 is so small that a unique mode propagating in the Si waveguide cannot exist. That is, the end width of the tapered portion 310 satisfies the mode cutoff condition.

It is preferable that a stretched portion 320 having a constant width is connected to the terminal side of the tapered portion 310. The width of the stretched portion 320 is the same as the end width of the tapered portion 310. The stretched portion 320 stretches to the end face (chip end) of the optical waveguide element 5. If the stretched portion 320 is provided, it is possible to absorb an error in the cutting position at the time of chip fragmentation. Here, the width at the chip end of the SSC300 is also referred to as the radiation end width. The radial end width and the end width are the same size.

The SSC 300 radiates the verification light selectively taken out by the probing filter unit 200 from the radiation end to the outside of the optical waveguide element 5 (chip). The verification light (also referred to as synchrotron radiation) emitted from the SSC 300 irradiates the sample. As the sample, an infrared fluorescent sample (phosphor card) that emits visible light in the irradiated portion when irradiated with infrared light can be used. Here, an example of using a phosphor card as a sample will be described.

The larger the radiation end width of the SSC300, the larger the spread angle (FFP angle: Far Field Pattern) of the synchrotron radiation from the SSC300. If the FFP angle of the synchrotron radiation from the SSC300 is wide, the surface received by the phosphor card that detects the synchrotron radiation becomes large. In this case, since the intensity is dispersed, the emission intensity per unit area becomes weak. In addition, the phosphor card has a minimum detection sensitivity. Therefore, if the optical fiber on the input side and the optical axis of the input waveguide 510 of the optical axis adjustment pattern 100 do not almost completely match, the phosphor card is not exposed to light and the optical axis adjustment becomes difficult. That is, it is preferable that the FFP angle of the synchrotron radiation is narrow because the phosphor card can be locally and strongly irradiated.

On the other hand, if the radiation end width of the SSC 300 is made too small, the problem that the mode field diameter (MFD) of the light transmitting the SSC 300 becomes too wide arises. In the optical waveguide element 5, as shown in FIG. 2, the support substrate 110 exists below the optical waveguide core 130 at a finite distance. Therefore, the excessively spread light is transferred to the support substrate 110, which causes a transmission loss.

As described above, when the radiation end width is small, there is an advantage that the FFP angle is narrowed, but there is a disadvantage that the propagation loss is large. On the contrary, when the radiation end width is large, there is an advantage that the propagation loss is small, but there is a disadvantage that the FFP angle is wide. Therefore, it is preferable to set the radiation end width so that the propagation loss is small and the FFP angle is as small as possible.

The synchrotron radiation from the SSC300 is radiated in a direction orthogonal to the end face (side surface) of the chip in order to facilitate the visual recognition by the phosphor card and the adjustment of the optical axis of the synchrotron radiation from the SSC300. Is good. That is, the SSC 300 is preferably formed so as to extend in a direction orthogonal to the side surface of the chip.

Further, the SSC 300 is preferably provided so as to extend in a direction orthogonal to the light propagation direction of the probing filter unit 200. This is because the optical fiber on the input side and the optical fiber on the output side, which are connected in the light propagation direction of the probing filter unit 200, interfere with the arrangement of the phosphor card. Further, when the SSC 300 is provided on the output side of the probing filter unit 200, the light leakage intensity from the fiber is high when the optical axis of the optical fiber on the input side and the optical axis of the input waveguide 510 of the optical axis adjustment pattern 100 are not aligned. This is because the phosphor card receives the light and interferes with the adjustment of the optical axis.

The procedure of optical axis adjustment using this optical axis adjustment pattern will be described with reference to FIG. FIG. 3 is a schematic diagram for explaining an optical axis adjustment method in a TEG chip in which an optical axis adjustment pattern is formed. Hereinafter, FIG. 1 will be described with reference to the appropriate reference.

First, in the first process, while viewing the TEG chip 10 from the upper surface side with the CCD camera 50 installed above the TEG chip 10, the optical fiber 60 on the input side is placed in the XZ plane with respect to the TEG chip 10. Perform alignment. Here, the XZ plane refers to a plane parallel to the upper surface of the TEG chip 10. Further, the Y direction refers to a direction orthogonal to the XZ plane, that is, a direction orthogonal to the upper surface of the TEG chip 10.

Next, in the second process, the phosphor card 400 is installed at a position facing the radiation end of the SSC 300.

Next, in the third process, the transmission signal light generated by the light source is input to the optical axis adjustment pattern 100 of the TEG chip 10. Of the transmitted signal light, the verification light having the Bragg wavelength of the probing filter unit 200 is taken out by the probing filter unit 200 and sent to the SSC 300. The verification light sent to the SSC 300 is radiated from the radiation end and radiates to the phosphor card 400 as synchrotron radiation. As a result, since the phosphor card 400 emits light, it is possible to adjust the position, that is, the height of the optical fiber 60 on the input side in the Y direction with reference to this light emission (indicated by A in FIG. 3). .. In this way, the optical axis of the optical fiber 60 on the input side can be adjusted (aligned) with respect to the TEG chip 10.

Then, in the fourth process, the positions of the TEG chip 10 and the optical fiber 62 on the output side in a plane parallel to the upper surface of the TEG chip 10 while looking at the upper surface of the TEG chip 10 from the upper surface side of the TEG chip 10. Make a match. This fourth process is performed in the same manner as the first process.

Next, in the fifth process, a light intensity measuring device is connected to the optical fiber 62 on the output side, and the TEG chip 10 and the optical fiber 62 on the output side are connected so that the received light intensity of the light intensity measuring device is maximized. Is aligned in a direction orthogonal to the upper surface of the TEG chip 10. As the light intensity measuring instrument, for example, a spectrum analyzer or a power meter can be used.

In this way, the optical axis adjustment of the TEG chip 10 and the optical fiber 62 on the output side is performed in each of the X, Y, and Z directions.

In the above-mentioned optical axis adjustment method, the light emitted from the chip end face once passed through the Si waveguide is directly observed, as compared with the method using a conventional infrared camera that relies on the scattered light from the Si waveguide. It can be said that the alignment accuracy is high in that respect. In addition, the infrared camera, which has been required in the past and is expensive and relatively large in size, is no longer required. Therefore, the TEG chip can be evaluated more easily than the conventional optical axis adjustment method.

Next, an example of evaluating the integrated chip will be described with reference to FIGS. 4 and 5. FIG. 4 is a schematic diagram for explaining a configuration example of an integrated chip in which an optical axis adjustment pattern is formed. FIG. 5 is a schematic diagram for explaining an optical axis adjusting method in an integrated chip on which an optical axis adjusting pattern is formed.

Here, an example of a WDM chip used as an integrated chip 11 in a wavelength division multiplexing (WDM) system will be described.

The integrated chip 11, which is a WDM chip, integrates an input / output SSC600, a WDM filter 610, an LD620, and a PD630 as input interfaces.

The input / output SSC600 is used for input / output with an optical fiber for transmission. The WDM filter 610 separates the path according to the wavelength. The transmitted optical signal generated by the LD620 is transmitted through the WDM filter 610 and the input / output SSC600. On the other hand, the received optical signal input to the input / output SSC600 is sent to the PD 630 via the WDM filter 610 and received.

The optical axis adjusting pattern 100 is arranged between the input / output SSC 600 and the WDM filter 610. The optical axis adjustment is performed by the first to third steps as in the case of the TEG chip described above. At this time, for the grating 210 included in the probing filter unit 200 of the optical axis adjustment pattern 100, the Bragg wavelength is set to a shorter wavelength than the shortest wavelength optical signal used in WDM communication.

After that, the probe needle is dropped on the PD 630, and the current value photoelectrically converted by the PD 630 is monitored by the current / voltmeter 670 to evaluate the optical characteristics of the optical waveguide device.

In the evaluation of the conventional integrated chip, first, the optical fiber on the input side connected to the light source is visually adjusted in the XX direction with respect to the integrated chip while looking at the CCD camera installed above the integrated chip. For alignment in the height (Y) direction, the probe needle is dropped on the PD, and the current value photoelectrically converted by the PD is monitored by a current / voltmeter to align in the Y direction. In this conventional evaluation, it is necessary to always visually follow the photoelectric conversion value displayed on the current / voltmeter. Therefore, it is difficult to intuitively (visually) understand that the optical fiber and the integrated chip are aligned in the Y direction.

On the other hand, in the integrated chip 11 provided with the optical axis adjusting pattern 100 of the present invention, the state of light emission of the infrared sample (phosphor card) 400 is observed when the fiber is centered in the Y direction, as in the TEG chip 10. However, the alignment in the Y direction is possible. Therefore, it can be confirmed intuitively (visually) that the optical axes of the integrated chip 11 and the optical fiber 60 on the input side coincide with each other. As a result, it becomes possible to improve the alignment throughput of the fiber involved in the evaluation of the integrated chip 11.

As described above, according to the optical waveguide element and the optical axis adjustment method provided with the optical axis adjustment pattern of the present invention, the optical axis of the integrated chip and the fiber at the time of evaluating the optical characteristics of the TEG chip or in the assembly of the optical module. In the adjustment, it is possible to intuitively confirm that the optical axis of the optical fiber and the integrated chip are aligned with the easily available Phosphor card without using the infrared camera required in the conventional centering system. .. As a result, the mounting process related to the assembly of the optical module can be simplified.

Here, an example in which signal light is output via an optical waveguide device as a TEG chip has been described, and an example in which signal light is terminated by PD as an integrated chip has been described, but the present invention is not limited thereto. As a TEG chip, PD characteristics may be evaluated. In this case, the optical axis adjusting method described with reference to FIGS. 4 and 5 may be performed. Further, as an integrated chip, signal light may be output via an optical waveguide device. In this case, the optical axis adjusting method described with reference to FIG. 3 may be performed.

(Example)
As an example of an optical waveguide element provided with an optical axis adjustment pattern according to the present invention, a TWDM (Tmie Wavelength Division Multiplexing) -PON (Passive Optical Network) system represented by FTTH (Fiber To The Home) or the like. A configuration example will be described. Here, the TWDM-PON system is being standardized by ITU-T as a subscriber access network.

In TWDM-PON, a wavelength band of 1524-1544 nm is assigned as an uplink signal from a subscriber terminal (ONU: Optical Network Unit) to a communication base station (OLT: Optical Line Thermal). Further, a wavelength band of 1596 to 1604 nm is assigned as a downlink signal from the OLT to the ONU. Further, wavelength signals for 4 channels are superimposed on each of the uplink signal and the downlink signal at a frequency interval of 50 to 200 GHz (see, for example, Non-Patent Document 3).

Here, since the shortest wavelength in TWDM-PON is 1524 nm, the Bragg wavelength of the grating 210 included in the probing filter unit 200 may be set to a wavelength shorter than 1524 nm.

In the example shown here, the Bragg wavelength of the grating 210 was designed as 1500-1520 nm of TE (Transverse Electric) polarization. FIG. 6 is a diagram showing a transmission spectrum and a reflection spectrum of a grating 210 obtained by an FDTD (Finite Differential Time Domain) simulation. In FIG. 6, the horizontal axis represents the wavelength [unit: μm], and the vertical axis represents the output intensity [unit: dB] of the transmitted light and the reflected light of the grating 210.

Here, the input light is a basic mode light of TE polarization and TM (Transverse Magnetic) polarization. In FIG. 6, the reflected light in the primary mode of TE polarization is shown by a solid line I, and the transmitted light in the basic mode of TE polarization is shown by a broken line II.

Here, the thickness of the optical axis adjusting pattern 100 was set to 0.2 μm. Regarding the grating 210 of the probing filter unit 200, the grating period was set to 0.37 μm, and the amount of protrusion of the optical waveguide core to the left and right was set to 0.1 μm with respect to the linear optical waveguide core having a width of 0.52 μm. The protrusions to the left and right are provided so as to be antisymmetrically offset by 1/2 of the grating cycle.

Regarding the mode filter 220, the width of the end portion of the main waveguide 221 on the grating 210 side is 0.58 μm, the width of the opposite end portion is 0.46 μm, and the end portion of the sub waveguide 222 on the SSC300 side. The width of the above was 0.3 μm, and the width of the opposite end was 0.1 μm. Further, the length of the main waveguide 221 and the sub waveguide 222 was set to 80 μm, and the average interval was set to 0.3 μm.

As shown in FIG. 6, at the design wavelength of 1.5 to 1.52 μm, the basic mode of TE polarization is changed to the primary mode and reflected, and all long wavelength light of 1.52 μm or more is transmitted. Can be confirmed. The reason why the intensity of the primary mode reflected light of TE polarization does not reach 0 dB at the peak is that the calculation grating length could not be sufficiently secured due to the capacity limitation of the computer during the FDTD simulation. .. In the FDTD simulation, the length of the grating is calculated as about 200 μm, but in reality, the loss of the peak intensity is reduced by increasing the length of the grating 210, and the intensity of the reflected light is 0 dB or closer to the peak. It is thought that it can be a value. The primary mode reflected light of TE polarization transitions to the basic mode light of the sub-waveguide 222 by the mode filter 220 connected to the grating and is sent to the radiation SSC 300 as verification light.

Further, although not shown, the basic mode light shows a total transmission characteristic even for orthogonal TM polarized waves.

Next, an example of SSC300 will be described. FIG. 7 is a diagram showing the result of calculating the relationship between the radiation edge width Wtip and the synchrotron radiation (FFP) angle based on a BPM (Beam Propagation Method) simulation. In FIG. 7, the radiating end width Wtip [unit: nm] is shown on the horizontal axis, and the FFP angle [unit: degree] is shown on the vertical axis. The thickness of the Si waveguide core is 220 nm, which is equivalent to that of a general SOI (Si on Insulator) substrate. The FFP angle on the vertical axis is defined as the 1 / e full width value of the peak intensity of the electrolytic distribution of synchrotron radiation. In FIG. 8, the solid line I indicates the FFP angle in the X direction (width direction), and the broken line II indicates the FFP angle in the Y direction (thickness direction).

Further, FIG. 8 is a diagram showing propagation loss per 1 cm of waveguide length based on a BPM (Beam Propagation Method) simulation. In FIG. 8, the radiation end width Wtip [unit: nm] is shown on the horizontal axis, and the propagation loss [unit: dB / cm] is shown on the vertical axis.

Here, it is assumed that the support substrate (Si) exists at a position of 3 μm with the clad sandwiched under the Si waveguide core.

As shown in FIG. 8, the FFP angle tends to increase as the radiation end width Wtip increases. If the FFP angle is wide, the surface received by the phosphor card becomes large, but the intensity is dispersed, so that the emission intensity per unit area becomes weak. Since the phosphor card has a minimum detection sensitivity, the phosphor card is not exposed unless the optical axes of the light source side fiber and the Si waveguide are almost completely aligned. Therefore, if the FFP angle is large, it becomes difficult to align the center. That is, it is preferable that the radiation angle is small because the sample area can be strongly irradiated locally.

On the other hand, as shown in FIG. 8, the problem that the propagation loss increases as the radiation edge width Wtip becomes smaller arises. This is because when the radiation end width Wtip becomes small, the MFD becomes large and the excessively spread light is transferred to the support substrate.

Therefore, it is preferable to set the radiation end width Wtip so that the propagation loss is small and the FFP angle is as small as possible in consideration of the distance between the Si waveguide core and the support substrate. According to the examples shown in FIGS. 7 and 8, the optimum value of the radiation end width Wtip of the SSC can be set to around 160-180 nm.

5 Optical Waveguide Element 10 TEG Chip 11 Integrated Chip 20 Sample Stage 30 Optical Waveguide Device 40 Si Waveguide 50 CCD Camera 55 Infrared Camera 60, 62 Optical Fiber 100 Optical Axis Adjustment Pattern 200 Probing Filter Unit 210 Grating 220 Mode Filter 221 Main Guide Waveguide 222 Sub-waveguide 300 SSC
310 Taper part 320 Stretch part 400 Phosphor card 510 Input waveguide 530 Route routing waveguide 540 Output waveguide 600 Input / output SSC
610 WDM filter 620 LD
630 PD
670 current / voltmeter

Claims (5)

Support board and
Optical waveguide core and
With a clad formed on the support substrate including the optical waveguide core
It is an optical waveguide element provided with
The optical waveguide core is provided with a pattern for adjusting the optical axis.
In the pattern for adjusting the optical axis,
A probing filter unit that transmits the signal light and extracts the verification light from the input light including the signal light and the verification light.
A radiation unit that emits the verification light extracted by the probing filter unit in a direction orthogonal to the propagation direction of the input light in the probing filter unit and in a direction orthogonal to the end face of the optical waveguide element.
With
The probing filter unit
Of the input light, the verification light having a Bragg wavelength set to the wavelength of the verification light, which is shorter than the wavelength of the signal light, and which is a component of the 0th-order mode, i (i is an integer of 1 or more). ) Grating that converts to the next mode and reflects,
Optical waveguide device you; and a mode converter for converting the validation light of the i-th order mode that has been reflected by the grating, the zero-order mode. The radiating part
The optical waveguide element according to claim 1, further comprising a tapered portion whose width is continuously reduced as the distance from the probing filter portion is increased. The radiating part
The optical beam according to claim 2 , further comprising a stretched portion having a constant width for connecting an end portion of the tapered portion opposite to the probing filter portion and a radiation end provided on the end surface of the optical waveguide element. Waveguide element. In adjusting the optical axis between the optical waveguide element according to any one of claims 1 to 3 and the optical fiber.
While looking at the upper surface of the optical waveguide element from the upper surface side of the optical waveguide element, the optical waveguide element and the optical fiber on the input side are aligned in a plane parallel to the upper surface of the optical waveguide element. The first process and
The second process of arranging the infrared fluorescent sample so as to face the radiating end of the radiating portion provided on the end face of the optical waveguide element, and
Input light including verification light is input from the optical fiber on the input side, the infrared fluorescent sample is made to emit light by the verification light emitted from the radiation unit, and the optical waveguide element and the optical waveguide element and the said An optical axis adjusting method comprising a third process of aligning the optical fiber on the input side with the optical fiber in a direction orthogonal to the upper surface of the optical waveguide element. Performed after the third process,
While looking at the upper surface of the optical waveguide element from the upper surface side of the optical waveguide element, the optical waveguide element and the optical fiber on the output side are aligned in a plane parallel to the upper surface of the optical waveguide element. 4th process and
A light intensity measuring device is connected to the output side optical fiber, and the optical waveguide of the optical waveguide element and the output side optical fiber is connected so that the received light intensity of the light intensity measuring device is maximized. The optical axis adjusting method according to claim 4 , further comprising a fifth process of aligning in a direction orthogonal to the upper surface of the element.

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