JP4220421B2 - Waveguide type light source - Google Patents

Description

  The present invention relates to a waveguide type light source that is composed of an optical waveguide composed of a silicon fine wire core and emits light by excitation light.

  As an analysis method for knowing the characteristics of a substance, there is infrared spectroscopy that measures the infrared spectrum of the substance. One of the infrared spectroscopic methods is the total reflection absorption spectrum method (ATR method) using an ATR (Attenuated Total Reflection) crystal prism such as ZnSe. The ATR method uses light (evanescent light) that slightly oozes out of the prism in contact with the sample when infrared light is totally reflected inside the ATR crystal prism. This makes it possible to analyze the components inside with high sensitivity.

In the analysis by the ATR method, in order to further improve the sensitivity, it is configured so that multiple total reflections occur (see Non-Patent Document 1). In addition, an analysis system that simply measures the concentration of glucose in the blood of a human body without the need for blood sampling or embedding a sensor by the ATR method has been developed (see Patent Document 1).
On the other hand, instead of using the above-described ATR crystal prism, a technique has been proposed in which the same measurement is performed by exposing a part of the silicon core of the silicon optical waveguide. According to the analysis method using the silicon optical waveguide, a finer sensor can be configured.

  By the way, the above-described analysis requires a light source. Since silicon is an indirect transition semiconductor, it is not easy to realize a light-emitting element, but it has been confirmed that addition of rare earth elements causes photoluminescence and electroluminescence. Rare earth elements emit light by intra-shell transitions of 4f electrons, and thus are hardly affected by the base material, and are added to various semiconductor materials, and light emission has been confirmed.

In addition, when silicon is used as the base material, it has also been reported that the light emission intensity increases by adding light elements with high electronegativity such as oxygen, boron, fluorine, and carbon together with rare earth elements. (Refer nonpatent literature 2).
Therefore, it is possible to realize a sensor unit in which a light source and a sensor are monolithically integrated by using light emission by addition of rare earth elements.

The applicant has not yet found prior art documents related to the present invention by the time of filing other than the prior art documents specified by the prior art document information described in this specification.
Japanese Patent Publication No. 2002-527136 Practical spectroscopy series (4) Medical application of spectroscopy, published September 30, 1999, IPC Corporation J. Palm, et.al., "Electroluminescence of erbium-doped silicon", Phys. Rev. B, vol. 54, No. 24, pp. 17603-17615, 1996.

  However, when a silicon optical waveguide is used for an ATR type sensor, it is necessary to introduce infrared light having a bandwidth within a range in which a spectrum capable of identifying an analysis target can be measured into the silicon optical waveguide. As described above, in order to measure the absorption spectrum, a light source having a bandwidth that can identify the spectrum is required, and thus a single wavelength laser beam cannot be used. Further, the light emitting band of the light emitting diode is not in a state where a sufficient bandwidth can be obtained.

  The present invention has been made to solve the above-described problems, and is intended to enable introduction of a light source having a wider bandwidth to an ATR type sensor composed of a silicon optical waveguide. Objective.

Waveguide type light source according to the present invention is formed on the lower clad layer, a predetermined emission portion core length of single crystal silicon and oxygen and the rare earth element is added, so as to cover the light emitting portion core comprising an upper clad formed, the incident end provided on one end of the configured optical waveguide from the light emitting unit core excitation light is incident, and a light emitting exit end provided at the other end of the optical waveguide, the light emitting unit core Is formed in a thin wire type, and oxygen and rare earth elements are added so as to have a distribution in the central portion in the thickness direction of the light emitting core .
In this light source, when excitation light is incident from the incident end, the light emitting core made of silicon emits rare earth elements directly or indirectly through excitons due to light with a very high light intensity density that cannot be obtained under normal conditions. Excited to emit light.

  In the waveguide light source, the rare earth element may be at least one of erbium, thulium, holmium, ytterbium, neodymium, praseodymium, and dysprosium. In the waveguide type light source, the optical waveguide is a single mode optical waveguide, and the efficiency of optical coupling is improved by providing a spot size conversion unit on the incident end side for reducing the diameter of the input excitation light. Note that an excitation light emitting portion from which excitation light is emitted is optically coupled to the incident end of the optical waveguide.

  Also, in the above-described waveguide light source, a sensor unit core made of a silicon single crystal formed on the lower cladding layer and having at least a part of the surface exposed, and light incident on an optical waveguide composed of the sensor unit core An analysis unit that includes at least an end and a light output end of an optical waveguide and in which an analysis object contacts the exposed surface of the core optically couples the light input end of the analysis unit and the light emission output end of the waveguide light source Arranged in a state.

  As described above, in the present invention, since the optical waveguide is configured by the light emitting portion core made of silicon to which rare earth elements are added together with oxygen or the like, a wider band due to emission of rare earth elements by excitation light incident from the incident end. Light emission can be obtained. Therefore, according to the present invention, it is possible to obtain an excellent effect that a light source having a wider bandwidth can be introduced into an ATR type sensor constituted by a silicon optical waveguide.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a plan view showing a configuration example of a waveguide light source according to an embodiment of the present invention.
The configuration of this light source will be described. First, a V-shaped groove 101 to which the end of the optical fiber 200 on the incident side is fixed is provided, and the groove 101 is formed on the substrate part 111 of a generally available SOI substrate. Yes.

  A spot size conversion unit is disposed following the groove 101, and the spot size conversion unit includes a spot size conversion core 103 disposed on the incident side. The spot size conversion core 103 is made of, for example, silicon oxynitride. An optical fiber core 201 of an optical fiber 200 is connected to the spot size conversion core 103.

  A light emitting region is provided subsequent to the spot size conversion unit. In the light emitting region, a silicon fine wire core 105 and an upper cladding layer 106 formed so as to fill the silicon fine wire core 105 are formed, and an optical waveguide is configured. . In the light emitting region, erbium (Er), which is a rare earth element, and oxygen atoms are added to the silicon fine wire core 105. The silicon thin wire core 105 has a cross-sectional dimension of about 0.3 μm square. As shown in the cross-sectional view of FIG. 2, the silicon fine wire core 105 is disposed on the buried oxide layer 112 of the SOI substrate. 2 is a cross-sectional view taken along the line AA ′ of FIG.

  In the light emitting region, erbium and oxygen atoms are added to the silicon fine wire core 105. Note that an oxide film of about several nm to several tens of nm may be formed on the surface of the silicon fine wire core 105. As described above, since the silicon thin wire core 105 has a cross-sectional dimension of about 0.3 μm square, the optical waveguide propagates light having a wavelength of about 1.3 to 1.7 μm in a single mode. In other words, the silicon thin wire core 105 only needs to be formed in such a dimension that the optical waveguide formed thereby becomes a single mode.

  In addition, the optical waveguide composed of the silicon fine wire core 105 can change the waveguide direction with a very small curvature, ie, a minimum bending radius of about 15 μm or less. Accordingly, as shown in the plan view of FIG. 1, the silicon fine wire cores 105 can be reciprocated at a narrow interval, and the light emitting region can be made longer in the narrow region. In the waveguide type light source of the present embodiment shown in FIG. 1, the total length of the silicon fine wire core 105 is about 7.4 mm.

  As shown in FIGS. 1 and 2, the silicon fine wire core 105 is formed by processing a silicon layer of a substrate having an SOI structure. The silicon layer is disposed on the uppermost layer of the SOI structure substrate, and is formed on the buried oxide layer 112 on the substrate portion 111. A silicon fine wire core 105 is formed in the silicon layer by forming a groove penetrating to the buried oxide layer 112 so as to sandwich a region to be a core. The upper cladding layer 106 is formed by filling the groove with, for example, silicon oxide and covering the silicon thin wire core 105.

  One end of the silicon fine wire core 105 on the spot size conversion portion side has a tapered shape that becomes narrower toward the tip, and the upper and side portions are covered with the spot size conversion core 103 as shown in the cross-sectional view of FIG. It has been broken. The tapered portion of the silicon fine wire core 105 and the spot size converting core 103 that covers the tapered portion constitute a spot size converting portion. The spot size conversion unit is provided at the excitation light incident end of the optical waveguide constituted by the silicon fine wire core 105. The spot size conversion core 103 has dimensions of a height and a width from about half of the optical fiber core 201 to about the same.

  The spot size conversion part is covered with an upper clad layer 106 made of silicon oxide. Further, in the region where the end portion of the optical fiber 200 is fixed, as shown in the cross-sectional view of FIG. 4, the optical fiber 200 is fixed to the V-shaped groove 101 provided in the substrate portion 111 with, for example, an ultraviolet curable adhesive. ing. 3 shows a part of the BB ′ cross section of FIG. 1, FIG. 4 shows a part of the CC ′ cross section of FIG. 1, and FIG. 5 shows a part of the DD ′ cross section of FIG. Yes.

  In the spot size conversion section, “refractive index of silicon fine wire core 105> refractive index of spot size conversion core 103> refractive index of upper clad layer 106”. The spot size converter configured in this manner allows excitation light (for example, light having a wavelength of 1.48 μm) guided through the optical fiber 200 to be applied to one end of the silicon thin wire core 105 in a state where the spot size is converted with low loss. It can be combined. In this case, the optical fiber 200 serves as an excitation light emitting unit.

  Further, as shown in FIG. 5, the silicon fine wire core 105 has an oxide film 121 having a thickness of several nanometers to several tens of nanometers formed on the surface thereof, and erbium and oxygen atoms so as to have a distribution at the center in the thickness direction. And an addition region 122 to which are added. The added region 122 is distributed at a predetermined distance from the lower surface and the upper surface in contact with the buried oxide layer 112 serving as the lower cladding. The added region 122 may be distributed over the entire cross-sectional direction of the silicon fine wire core 105.

According to the waveguide light source shown in FIGS. 1 to 5, when a laser beam having a wavelength of 1.5 μm and an output of 3 mW is incident as excitation light, an emission spectrum as shown in FIG. 6 is obtained. The emission spectrum shown in FIG. 6 is a result of a waveguide type light source using a silicon thin wire core 105 having a total length of 7.4 mm into which erbium and oxygen are introduced under the following conditions. Conditions of introduction, an acceleration energy 310KeV, erbium a dose of 2 × 10 ¹⁴ cm ^-2 by ion implantation, oxygen ions are implanted at an acceleration energy 45 keV, a dose of 2 × 10 ¹⁵ cm ^-2, after ion implantation, Heat treatment is performed in a nitrogen atmosphere at 620 ° C. for 1 hour and 900 ° C. for 30 minutes.

  Here, the light emission in the light emitting region constituted by the silicon thin wire core 105 will be described. In order to emit light from the silicon fine wire core 105 doped with rare earth elements and oxygen, light having a wavelength shorter than the emission wavelength of the rare earth element added to the silicon fine wire core 105 is used as excitation light in the light emitting region. What is necessary is just to introduce. Here, the rare earth elements include, for example, erbium, thulium (Tm), holmium (Ho), ytterbium (Yb), neodymium (Nd), praseodymium (Pr), and dysprosium (Dy).

  There are two light emission mechanisms in the light emitting region: photoexcitation by excitation light and excitation caused by recombination of excitons (excitons) generated in the silicon crystal by excitation light at the rare earth element center. The optical waveguide composed of the silicon fine wire core 105 has a strong optical confinement effect because the difference in refractive index between the core and the clad is large. Therefore, in an optical waveguide using a silicon core, the light intensity at the core center reaches 1000 times that of a general optical fiber, and a very high light intensity density can be obtained. Therefore, even if the excitation light is infrared light having an energy smaller than the band gap energy of silicon, excitons can be generated by the two-photon absorption effect.

  By utilizing the two light emission mechanisms described above, the rare earth element added to the silicon fine wire core 105 can be directly or indirectly via excitons with light having a very high light intensity density that cannot be obtained under normal conditions. Luminescence can be obtained by excitation. Excitation using the above two emission mechanisms enables more efficient light emission than erbium-doped fiber (EDF) using direct excitation. Note that light having a wavelength longer than the emission wavelength of the rare earth element can be used as excitation light if the light emission mechanism is limited only to excitation by exciton. The wavelength that can be transmitted through the silicon core and exciton can be excited by two-photon absorption is about 1.1 to 2.2 μm.

  Excitation light may be input from the outside through the optical fiber 200 disposed so as to be optically coupled to the light input end of the optical waveguide composed of the silicon fine wire core 105. Further, instead of the optical fiber 200, a laser emitted from a semiconductor laser may be directly optically coupled and optically coupled through a spot size conversion region to improve the optical coupling efficiency. In this case, the semiconductor laser becomes the excitation light emitting part.

Next, a method for manufacturing the above-described waveguide light source will be briefly described.
First, an SOI (Silicon on Insulator) substrate is prepared. In the SOI substrate, the silicon layer (single crystal silicon layer) on the buried insulating layer (buried oxide layer) may be a high resistance p-type or a high resistance n-type. Further, the silicon layer may have a desired thickness by crystal growth of non-doped single crystal silicon on a high resistance p-type single crystal silicon layer thinner than the desired thickness. Similarly, the silicon layer may have a desired thickness by crystal growth of non-doped single crystal silicon on a high resistance n-type single crystal silicon layer thinner than the desired thickness.

  Once the SOI substrate as described above is prepared, the silicon layer is finely processed by a known lithography technique and etching technique, leaving a region that becomes the silicon fine wire core 105 in the light emitting region, and the silicon fine wire core in the spot size conversion unit. A pattern of the front end portion 105 is formed. As a result, the silicon fine wire core 105 is formed. In the fiber fixing region where the optical fiber 200 is fixed, the silicon layer is removed and the buried oxide layer 112 is exposed.

Next, as shown in FIG. 7A, an oxide film 121 having a thickness of several nanometers is formed on the surface of the silicon fine wire core 105 by a thermal oxidation method.
Next, a resist pattern in which a portion surrounded by the region 301 in FIG. Introduce erbium and oxygen.

  The implantation energy by ion implantation is such that the projected range of each ion is near the center in the thickness direction of the core, and the added region 122 is formed as shown in FIG. 7B. For example, when erbium is ion-implanted into the silicon fine wire core 105 having a core thickness of 0.3 μm, the implantation energy may be 300 to 400 keV. Moreover, when oxygen is ion-implanted, the implantation energy may be 40 to 60 keV. FIG. 8 is a distribution diagram showing the distribution in the depth (film thickness) direction of each ion when erbium and oxygen are ion-implanted under the above-described conditions.

After each ion implantation as described above, heat treatment is performed at 620 ° C. for 1 hour to restore crystallinity, and at 900 ° C. for 30 minutes to reduce defects and precipitate oxygen around erbium.
When erbium and oxygen are introduced by an ion implantation method, a single crystal region that is not damaged by ion implantation remains on the buried oxide layer 112 side of the silicon fine wire core 105 after ion implantation. By heat treatment after ion implantation, the entire silicon fine wire core 105 can be single-crystallized by solid phase epitaxial recovery using the remaining single crystal region as a seed.

  After each ion is implanted into the silicon fine wire core 105 as described above, the spot size conversion core 103 is formed from the silicon oxynitride film deposited by the ECR plasma CVD method. Further, a silicon oxide film is formed so as to cover the spot size conversion core 103 and the silicon fine wire core 105, and the upper clad layer 106 is formed. The silicon oxide film can also be formed by ECR plasma CVD.

  Next, a mask pattern that covers the light emitting region and the spot size conversion part is formed, and etching is performed using the formed mask pattern as a mask to form a vertical incident end face and an output end face of the spot size conversion part, and fiber fixing The buried oxide layer 112 in the region is selectively removed. In this etching, a dry etching technique having vertical anisotropy such as reactive ion etching may be used.

  Finally, a V-shaped groove 101 is formed in a predetermined region of the exposed substrate portion 111 in the fiber fixing region. The groove 101 can be formed, for example, by repeating selective etching with a plurality of mask patterns in which the interval between the openings is gradually widened. Further, if (100) plane single crystal silicon is used as the substrate portion 111, a V-shaped groove can be automatically formed by wet etching with an alkaline solution such as potassium hydroxide.

  In consideration of simplification of the manufacturing process, when the spot size conversion core 103 is formed by processing the silicon oxynitride film, the silicon oxynitride film may remain in the light emitting region. When the silicon oxynitride film is removed, damage to the silicon fine wire core 105 can be suppressed. Further, it is not so easy to increase the etching selection ratio between the silicon fine wire core 105 and the silicon oxynitride film, and the process can be simplified by leaving the silicon oxynitride film in the light emitting region.

  By the way, in the waveguide type light source of FIG. 1, the light is coupled by bringing the core end face of the optical fiber into contact, but the present invention is not limited to this. Microlenses may be provided between the end of the optical fiber 200 and the end of the spot size conversion core 103 of the spot size conversion unit to improve the optical coupling efficiency.

  Next, a configuration example of a sensor unit in which the above-described waveguide-type light source is combined with a sensor unit composed of a silicon optical waveguide will be described. As shown in FIG. 9, the sensor unit includes a groove 101 in which the optical fiber 200 is fixed on the same substrate unit 111, a spot size conversion core 103 disposed following the groove 101, and one end on the spot size conversion core 103. Are connected to the silicon core 105, the sensor core 905 connected to the silicon core 105, the spot size conversion core 903 connected to the other end (output end) of the sensor core 905, and the spot size conversion core 903. The groove 901 is formed monolithically.

  The silicon fine wire core 105 into which the rare earth and oxygen are introduced is covered with the upper clad 106, and the sensor core 905 is exposed on the buried oxide layer 112 serving as the lower clad. An optical fiber 200 into which excitation light is introduced is fixed in the groove 101, and an optical fiber 900 that propagates light that has passed through the optical waveguide formed by the sensor core 905 is fixed in the groove 901.

  Excitation light introduced from the optical fiber 200 is coupled to an optical waveguide composed of the silicon fine wire core 105 through a spot size conversion unit in which the spot size conversion core 103 is disposed. Due to the coupled excitation light, the light emitting region composed of the silicon fine wire core 105 emits light, and the light emitted from the light emitting region passes through the sensor region composed of the sensor core 905 and is emitted to the optical fiber 900.

  In the state described above, if the sample to be analyzed is in contact with the upper surface of the sensor unit core 905 exposed in the sensor region, the light that has exuded from the sensor unit core 905 is absorbed according to the characteristics of the sample. The intensity of the guided light decreases according to the intensity of the absorption. Therefore, for example, if the intensity of light guided through the optical waveguide (sensor region) configured from the sensor core 905 is measured with respect to a certain wavelength band, an absorption spectrum by the sample to be analyzed can be obtained.

  In the sensor region, the lower surface of the sensor core 905 is covered with the buried oxide layer 112 and the side surface and the upper surface are exposed. However, the present invention is not limited to this, and the lower surface and the side surface are covered with the cladding. Only the upper surface may be exposed. In the sensor region, it is only necessary that a part of the sensor core 905 is exposed and can be brought into contact with the sample.

  In the above description, erbium is added as a rare earth element to the silicon fine wire core 105. However, the present invention is not limited to this, and thulium or holmium may be added together with oxygen. When erbium is used, the center emission wavelength is around 1.54 μm, when thulium is used, the center emission wavelength is around 1.65 μm, and when holmium is used, the center emission wavelength is around 1.96 μm. Further, by adding these in combination, it becomes possible to widen the emission wavelength band and expand the analysis wavelength region. Further, any one of boron, fluorine, and carbon may be used instead of oxygen.

A case where three kinds of rare earth elements of erbium, thulium and holmium are added to the silicon wire core together with oxygen atoms in order to expand the analysis wavelength region will be described below. In this example, the silicon fine wire core constituting the light emitting region has a thickness of 0.2 μm and a width of 0.5 μm. Each rare earth element is introduced by an ion implantation method, and the ion implantation conditions are all 250 keV and 3 × 10 ¹³ cm ⁻² . The oxygen implantation conditions are 35 keV and 1 × 10 ¹⁵ cm ⁻² .

When ions are implanted under the above conditions, the distribution of each ion in the silicon fine wire core is as shown in FIG. Since the three rare earth elements have similar atomic numbers and mass numbers, they have the same distribution. Oxygen is implanted so as to be about 5 to 10 times the total amount of rare earth elements. However, if the amount of ion implantation is too large, recovery of damage becomes difficult.
As described above, by injecting three kinds of rare earth elements into the silicon fine wire core, a broadband light source in which the emission spectra from the rare earth elements are overlapped with the same excitation light source can be obtained. It becomes possible.

  In addition, as described above, by setting a state in which a broadband light source is obtained, the excitation target element is controlled by changing the wavelength of the excitation light to control the emission wavelength range, and the emission spectrum is changed to change the measurement target. It becomes possible to measure the absorption spectrum of a substance.

  In the above description, the three rare earth elements are added in the same manner, but the present invention is not limited to this. For example, a holmium-added region, a thulium-added region, and an erbium-added region from the excitation light incident direction and a region to which different rare earth elements are added may be provided in the optical waveguide direction of the silicon fine wire core in the light emitting region. Moreover, you may make it add in combination with another rare earth element.

It is a top view which shows the structural example of the waveguide type light source in embodiment of this invention. It is sectional drawing which shows the structural example of the waveguide type light source in embodiment of this invention. It is sectional drawing which shows the structural example of the waveguide type light source in embodiment of this invention. It is sectional drawing which shows the structural example of the waveguide type light source in embodiment of this invention. It is sectional drawing which shows the structural example of the waveguide type light source in embodiment of this invention. It is a characteristic view which shows the emission spectrum of the optical waveguide light source in this Embodiment. It is a partial process figure which shows the example of the manufacturing method of the waveguide type light source in embodiment of this invention. It is a distribution map which shows distribution of the addition element (ion) in the silicon | silicone thin wire | line core which comprises the optical waveguide light source in this Embodiment. It is a top view which shows the structural example of the sensor unit to which the waveguide type light source in embodiment of this invention is applied. It is a distribution map which shows distribution of the addition element (ion) in the silicon | silicone thin wire | line core which comprises the optical waveguide light source in this Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ... Groove, 103 ... Spot size conversion core, 105 ... Silicon fine wire core, 106 ... Upper clad layer, 111 ... Substrate part, 112 ... Embedded oxide layer, 121 ... Oxide film, 122 ... Addition area, 200 ... Optical fiber, 201 ... Optical fiber core.

Claims (5)

Is formed on the lower cladding layer, a light emitting unit core having a predetermined length of single crystal silicon and oxygen and the rare earth element is added,
An upper clad formed to cover the light emitting unit core;
An incident end provided at one end of a waveguide composed of the light emitting unit core and receiving excitation light;
Have a light-emitting exit end provided at the other end of said waveguide,
The light emitting core is formed in a thin line shape,
The waveguide-type light source, wherein the oxygen and the rare earth element are added so as to have a distribution in a central portion in the thickness direction of the light-emitting portion core . The waveguide light source according to claim 1, wherein
The waveguide type light source, wherein the rare earth element is at least one of erbium, thulium, holmium, ytterbium, neodymium, praseodymium, and dysprosium. The waveguide type light source according to claim 1 or 2,
The waveguide is a single mode waveguide,
A spot size converter that reduces the diameter of the input excitation light is provided on the incident end side. In the waveguide type light source according to any one of claims 1 to 3,
A waveguide-type light source comprising: an excitation light emitting portion that is optically coupled to the incident end and emits the excitation light. In the waveguide type light source according to any one of claims 1 to 4,
A sensor core made of a silicon single crystal formed on the lower cladding layer and having at least a part of the exposed surface, a light incident end of a waveguide composed of the sensor core, and a light emission of the waveguide And an analysis unit that includes at least an end and is in contact with an object to be exposed on the exposed surface of the core, wherein the light incident end and the light emitting end are optically coupled to each other. light source.

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