JP2006193399A - Inorganic optical material, light source, michelson interferometer, optical coherent tomography device, and optical amplifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inorganic optical material which can generate a wideband fluorescence spectrum, while suppressing the background loss, and to provide a light source, a Michelson interferometer, an optical coherent tomography device, and an optical amplifier which can have a wide gain band. <P>SOLUTION: The inorganic optical material is characterized by containing at least one kind of rare earth elements, being colorless, and having a full width at half maximum of the fluorescence spectrum wider than 50 nm. Because the full width at half maximum of the fluorescence spectrum is so wider, a wideband fluorescence can be obtained by the inorganic optical material. Further, for example, when the wavelength at a peak of the fluorescence spectrum generated from the inorganic optical material is in the vicinity of the C band, a 20 μm or less resolution can be realized with an interference type optical sensor using a light source comprising the inorganic optical material. Further, because the inorganic optical material is colorless, it can suppress the background loss. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an inorganic optical material, a light source including the inorganic optical material, a Michelson interferometer including the light source, an optical coherent tomography apparatus using the Michelson interferometer, and an optical amplifier including the inorganic optical material. It is.

  An inorganic optical material containing at least a part of a rare earth element is brought into an excited state by supplying excitation light having a wavelength capable of exciting the rare earth element, and the rare earth element is changed from an excited state to a ground state. When spontaneous emission (fluorescence) occurs, the spontaneous emission light (fluorescence) is amplified to generate ASE light (Amplified Spontaneous Emission), or the signal light is amplified by stimulated emission. can do. Therefore, a light source, an optical sensor, or an optical amplifier can be realized by using such an inorganic optical material.

The resolution p of an optical sensor using interference such as an optical coherence tomography apparatus (hereinafter referred to as an OCT apparatus) (hereinafter referred to as an interference type optical sensor) is the wavelength (center wavelength) at the peak of the light source, λ _C When the line width is Δλ, the following equation (1) is given.
p = (2 · ln (2) · π) · (λ _C ² / Δλ) (1)

Therefore, in the interference type optical sensor, it is desirable to provide a light source including an inorganic optical material capable of generating broadband fluorescence in order to increase resolution. Therefore, various studies have been made in Non-Patent Documents 1 and 2 in order to obtain an inorganic optical material that generates a broadband fluorescence spectrum.
NTT Electronics Technical Document (May 2004) IEICE Transactions C, Vol.J83-C, No.4, pages 354-355

  However, in the inorganic optical material disclosed in Non-Patent Document 1, the obtained fluorescence band is as narrow as 20 nm. As a result, the resolution of the interference type optical sensor provided with the light source including the inorganic optical material becomes a low value of 37.3 μm. On the other hand, the inorganic optical material disclosed in Non-Patent Document 2 has a wide fluorescence band, and the resolution of an interference type optical sensor including a light source including this is high. However, since this optical material is reddish brown, when it is included in the light source, the background loss becomes large.

  Further, when optically amplifying signal light in an optical communication system or the like, it is desirable that a wide-band multi-wavelength signal light can be optically amplified using a small number of optical amplifiers. Therefore, it is desired that the gain band of the optical amplifier is wide.

  The present invention has been made to solve the above-described problems, and an inorganic optical material, a light source, a Michelson interferometer, and an optical coherence tomography apparatus that can generate a broadband fluorescence spectrum while suppressing background loss. An object of the present invention is to provide an optical amplifier that can have a wide gain band.

  In order to solve such an object, the inorganic optical material according to the present invention contains at least one kind of rare earth element, is colorless, and has a full width at half maximum of a fluorescence spectrum wider than 50 nm. In this inorganic optical material, since the full width at half maximum of the emitted fluorescence spectrum is wider than 50 nm, a broadband fluorescence spectrum can be obtained. For example, when the wavelength at the peak of the fluorescence spectrum emitted from this inorganic optical material is near the C band (1530 nm to 1565 nm), the interference type optical sensor using the light source including this inorganic optical material is as high as 20 μm or less. Resolution can be realized. Furthermore, since this inorganic optical material is colorless, background loss can be suppressed even when used as a light source.

  In particular, the full width at half maximum of the fluorescence spectrum is preferably 80 nm or more. When the wavelength at the peak of the fluorescence spectrum emitted from this inorganic optical material is, for example, near the C band (1530 nm to 1565 nm), the interference type optical sensor using the light source including this inorganic optical material achieves a resolution of 13 μm or less. can do.

  The full width at half maximum of the 980 nm band absorption spectrum is preferably 20 nm or more. This makes it possible to obtain a broadband fluorescence spectrum.

  More preferably, the shape of the fluorescence spectrum is substantially line symmetric with respect to the wavelength at the peak of the fluorescence spectrum. It can be considered that a fluorescence spectrum having a substantially line-symmetric shape is close to a Gauss function. Therefore, an interference type optical sensor using a light source including this inorganic optical material can realize high resolution.

  The center deviation, which is the difference between the wavelength at the peak of the fluorescence spectrum and the wavelength at the center of the full width at half maximum of the fluorescence spectrum, is preferably less than 9 nm, and the center deviation is particularly preferably less than 7 nm. If the center deviation is as small as this, the fluorescence spectrum can be considered close to a Gaussian function. Therefore, an interference type optical sensor using a light source including this inorganic optical material can realize high resolution.

  It is preferable that the fluorescence spectrum does not have a minimum. By using a light source including such an inorganic optical material, the interference optical sensor can achieve high resolution.

  The inorganic optical material is preferably an oxide system. If the inorganic optical material is an oxide system, the hydrogen resistance characteristics and the high power resistance characteristics are good, unlike the case of a fluoride system. Therefore, this inorganic optical material can have sufficient reliability.

  A light source according to the present invention includes the above-described inorganic optical material and excitation light supply means for supplying excitation light to the inorganic optical material, and fluorescence generated from a rare earth element in the inorganic optical material excited by the excitation light. Is amplified to output ASE light. By providing the inorganic optical material that generates broadband fluorescence, an interference optical sensor using this light source can achieve high resolution. Further, since this inorganic optical material is colorless, background loss in the light source can be suppressed. In particular, when the inorganic optical material contained in the light source is an oxide-based material, the inorganic optical material can have sufficient reliability in terms of hydrogen resistance and high power resistance.

  The Michelson interferometer according to the present invention is disposed on the optical path of the first split light, the beam splitter that splits the ASE light output from the light source into the first split light and the second split light, and the first split light. A mirror that is moved in parallel with the optical path of the split light and reflects the first split light in a direction along the optical path of the first split light, and the second split light is disposed on the optical path of the second split light. And a photodetector that detects interference light obtained by superimposing and interfering with the beam splitter the first divided light reflected by the mirror and the second divided light reflected by the reflector, It is characterized by providing. This Michelson interferometer can achieve high resolution by including the above-mentioned light source that generates broadband fluorescence. In particular, when the inorganic optical material contained in the light source included in the Michelson interferometer is an oxide, the inorganic optical material may have sufficient reliability in terms of hydrogen resistance and high power resistance. It becomes possible.

  An optical coherence tomography apparatus according to the present invention is characterized by measuring a three-dimensional tomographic image of a reflector using the Michelson interferometer. The interferometer included in the Michelson interferometer outputs broadband ASE light. Therefore, it is preferable to use the Michelson interferometer for an optical coherence tomography apparatus. In addition, this optical coherence tomography apparatus can achieve high resolution by using the Michelson interferometer. In particular, when the inorganic optical material included in the light source included in the optical coherence tomography apparatus is an oxide type, the inorganic optical material has sufficient reliability in terms of hydrogen resistance and high power resistance. Is possible.

  An optical amplifier according to the present invention is an optical amplifier that optically amplifies signal light input to an input end and outputs the signal light from an output end, and includes an amplification medium made of the above inorganic optical material that optically amplifies signal light, and an amplification medium And excitation light supply means for supplying excitation light. The signal light input to the input end is optically amplified in the amplification medium. Since the amplification medium is made of the above-described inorganic optical material, this optical amplifier can have a wide gain band.

  According to the present invention, a broadband fluorescence spectrum can be generated, or a wide gain band can be provided.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

  First, an embodiment of the inorganic optical material according to the present invention will be described. The inorganic optical material according to the present embodiment contains at least one kind of rare earth element, is colorless, and has a full width at half maximum of a fluorescence spectrum wider than 50 nm. As for the inorganic optical material which concerns on this embodiment, it is more suitable that the full width at half maximum of a fluorescence spectrum is 80 nm or more. As rare earth elements contained in this inorganic optical material, there are Pr element, Nd element, Tm element, Dy element, Er element, Yb element, etc., and Er element is particularly suitable. When Er element is contained, it is preferable when optically amplifying signal light in the 1500 nm to 1650 nm band, which is a wavelength generally used for optical communication.

  In addition, the inorganic optical material preferably has a fluorescence spectrum shape that is substantially line symmetric, that is, the fluorescence spectrum is line symmetric with respect to the wavelength at the peak. The conditions for being substantially line symmetric will be described with reference to FIG. FIG. 6 shows an arbitrary fluorescence spectrum, where the horizontal axis represents the wavelength and the vertical axis represents the normalized fluorescence intensity level when the peak time is 100%. When the normalized fluorescence intensity level is in the range of 20 to 100%, the case of being substantially line symmetric is the difference between the wavelength at the peak of fluorescence intensity and the center wavelength at each normalized fluorescence intensity level (hereinafter referred to as the center wavelength). This means that the absolute value of the difference is within 4 nm. The center wavelength at the normalized fluorescence intensity level refers to the wavelength at the center of two wavelengths (wavelength at the center of each wavelength range specified by the arrow in FIG. 6) showing the same normalized fluorescence intensity level value. .

  In particular, in this inorganic optical material, the center shift, which is the difference between the wavelength at the peak of the fluorescence spectrum and the wavelength at the center of the full width at half maximum of the fluorescence spectrum, is preferably less than 9 nm, more preferably less than 7 nm. preferable. The smaller the center deviation, the closer the shape of the fluorescence spectrum is to line symmetry. Moreover, it is preferable that this inorganic optical material does not have the minimum fluorescence spectrum.

Furthermore, the inorganic optical material is preferably an oxide system. In this case, the host material of the inorganic optical materials _{Al 2 O 3, SiO 2,} B 2 O 3, Ga 2 O 3, Y 2 O 3, Ta 2 O 5, GaTaO 4, Sb 2 O 3, Nd 2 O 5 And oxides such as La ₂ O ₃ and Yb ₂ O ₃ .

  Since the full width at half maximum of the fluorescence spectrum emitted from the inorganic optical material according to the present embodiment is wider than 50 nm, broadband fluorescence can be obtained by this inorganic optical material. Therefore, for example, when the wavelength at the peak of the fluorescence spectrum emitted from this inorganic optical material is in the vicinity of the C band (1530 nm to 1565 nm), the interference type optical sensor using the light source including this inorganic optical material is as high as 20 μm or less. It becomes possible to realize resolution. Moreover, since this inorganic optical material is colorless, background loss can be suppressed even when used as a light source. In particular, an interference optical sensor using a light source including an inorganic optical material whose full width at half maximum of the emitted fluorescence spectrum is 80 nm or more, for example, the wavelength at the peak is in the vicinity of the C band (1530 nm to 1565 nm) is as very small as 13 μm or less. High resolution can be realized.

  Further, when the shape is substantially line symmetric, the shape of the fluorescence spectrum is considered to be close to the shape of the Gauss function. Therefore, by using a light source including this inorganic optical material, the interference optical sensor can achieve high resolution.

  If the center shift in the fluorescence spectrum is as small as less than 9 nm, it can be considered that this fluorescence spectrum is close to the Gauss function. In particular, if the center shift is less than 7 nm, this fluorescence spectrum is considered to be closer to the Gauss function. Therefore, by using a light source including an inorganic optical material that generates a fluorescence spectrum with a small center deviation in this way, the interference type optical sensor can realize high resolution.

  In addition, even when the fluorescence spectrum of the inorganic optical material does not have a minimum, it is possible to achieve high resolution of an interference type optical sensor using a light source including the inorganic optical material.

  Further, if the inorganic optical material is an oxide system, the hydrogen resistance characteristics and the high power resistance characteristics are improved unlike the case of the fluoride system. Therefore, this inorganic optical material can have sufficient reliability.

Next, specific samples A to E of the inorganic optical material containing at least one kind of rare earth element will be described. Samples A to E are obtained by adding a rare earth element having a full width at half maximum of a fluorescence spectrum larger than 50 nm to an oxide-based inorganic optical material. Specifically, the host material of Sample A contains 95 mol% SiO ₂ and 5 mol% Ta ₂ O ₅ . The host material for sample B contains 95 mol% SiO ₂ and 5 mol% B ₂ O ₃ . The host material of sample C contains 95 mol% SiO ₂ and 5 mol% Al ₂ O ₃ . The host material for sample D contains 95 mol% SiO ₂ and 5 mol% Ga ₂ O ₃ . The host material for sample E contains 95 mol% SiO ₂ and 5 mol% GaTaO ₄ . The composition of the above host material represents the composition in the state before containing the rare earth element. Samples A to E all contain Er elements and Yb elements, which are rare earth elements. That is, each sample A~E is, 0.3 mol% of _Er 2 _{O 3,} and a 1 mol% of _Yb 2 _{O 3.} Each of these samples A to E is prepared by applying a reagent having the above composition ratio to a silica tube and heating it with a city gas burner at 1700 ° C. or higher for 10 minutes or more. Samples A to E thus prepared are all colorless. Sample C is vitrified, and the remaining samples A, B, D, and E are in a glass ceramic state.

  The fluorescence intensity was measured by irradiating each of these samples A to E with excitation light having a wavelength of 980 nm. FIG. 1 is a diagram illustrating fluorescence spectra of samples A to E. Graph A in FIG. 1 is the fluorescence spectrum of sample A, graph B is the fluorescence spectrum of sample B, graph C is the fluorescence spectrum of sample C, graph D is the fluorescence spectrum of sample D, and graph E is the fluorescence spectrum of sample E. Represents the spectrum. In FIG. 1, the horizontal axis represents the wavelength, and the vertical axis represents the intensity normalized by the fluorescence peak value. As shown in FIG. 1, among samples A to E, only samples A and E belong to the technical scope of the present invention. Samples A and E will be examined in detail below. Further, as understood from FIG. 1, each of the samples A and E can generate fluorescence in a wide wavelength band including the C band (1530 nm to 1565 nm).

  First, the fluorescence spectrum of sample A is examined. As shown in graph A of FIG. 1, the wavelength at the peak of sample A is 1533 nm, and the half-value wavelengths are 1489 nm and 1577 nm. Therefore, the full width at half maximum of this fluorescence spectrum is 88 nm, and the resolution of the interference type optical sensor using the light source including this sample A is about 12 μm from the equation (1). Further, as can be seen from FIG. 1, the graph A has no minimum.

The wavelength at the center of the full width at half maximum of the fluorescence spectrum represented by graph A is 1533 nm, which matches the wavelength of 1533 nm at the peak of graph A. Therefore, the center deviation is 0 nm. Further, only the graph A has a wide band in the peak portion. From the above, it can be said that the graph A has a shape close to the Gauss function f (λ) (λ is the wavelength). FIG. 2 shows the fluorescence spectrum and Gauss function of sample A for comparison. In the Gaussian function shown in FIG. 2, the peak wavelength (center wavelength) is matched with the peak wavelength in the fluorescence spectrum of sample A, and the dispersion value is 53. Graph A in FIG. 2 represents the fluorescence spectrum of sample A, and graph G represents the Gauss function. In FIG. 2, the horizontal axis represents the wavelength, and the vertical axis represents the intensity normalized by the peak value of fluorescence. Here, the Gauss function f (λ) represented by the graph G is represented by the following equation (2).
f (λ) = exp {- (λ-1533) 2/53 2} ... (2)

  Referring to FIG. 1 again, the fluorescence spectrum of sample E will be examined. As shown in FIG. 1, the wavelength at the peak of sample E is 1534 nm, and the half-value wavelengths are 1514 nm and 1566 nm. Therefore, the full width at half maximum of this fluorescence spectrum is about 50 nm, and the resolution of the interference type optical sensor using the light source including this sample E is about 20.1 μm from Equation (1), which is slightly over 20 μm. Further, as can be seen from FIG. 1, the graph E has no minimum.

  The wavelength at the center of the full width at half maximum of the fluorescence spectrum represented by graph E is 1541 nm, and the difference from the wavelength 1534 nm at the peak of graph E, that is, the center shift is 7 nm. Note that the wavelength at the peak of the fluorescence spectrum represented by the graph C is 1532 nm, and the half-value wavelengths are 1520 nm and 1562 nm. Therefore, the wavelength at the center of the full width at half maximum of sample C is 1541 nm, and the center deviation is 9 nm.

  Further, the line symmetry of the fluorescence spectra of samples A to E will be described in detail with reference to FIG. The horizontal axis of FIG. 7 represents the normalized fluorescence intensity level where 100% is 1, and the vertical axis represents the center wavelength difference at each normalized fluorescence intensity level. In FIG. 7, graph A represents sample A, graph B represents sample B, graph C represents sample C, graph D represents sample D, and graph E represents sample E. As understood from FIG. 7, in the sample A, the central wavelength difference is within the range of −2 nm to +4 nm, that is, the absolute value of the central wavelength difference is within 4 nm at the normalized fluorescence intensity level of 20% to 100%. Therefore, it can be said that the fluorescence spectrum represented by the graph A is substantially line symmetric. On the other hand, in Sample B or Sample D, the center wavelength difference is within a range of −5 nm to +7 nm at a normalized fluorescence intensity level of 20% to 100%.

  The sample described above is a Ta / Si based inorganic optical material co-added with an Er element, but the inorganic optical material according to the present invention is not limited to this specific composition, such as basicity and appropriate crystallization. If various conditions are met, different rare earth elements such as Tm element, Yb element, and Ho element may be added. Moreover, the composition ratio of the inorganic optical material in Samples A to E is an example, and is not limited to the composition ratio given here.

  In general, it is considered to achieve vitrification by adding an alkali element (for example, Li element, Na element, K element, Al element, etc.) to an inorganic optical material. When the Al element that vitrifies most stably among these alkali elements is added, that is, when the sample C is examined, the fluorescence spectrum becomes narrow as shown in the graph C of FIG. In general, glass forming ability and fluorescence broadening are trade-offs. That is, if the Er element and the Ta element are combined, the spectrum is widened, but on the other hand, the inorganic optical material to which these elements are added is easily crystallized. When an alkali element is added to an inorganic optical material, the Er element binds to these alkali elements (specifically, the Er element is present in the non-bridging oxygen region formed by the alkali element), so that the fluorescence spectrum band is alkaline. It tends to be the same as the fluorescence spectrum band in the inorganic optical material before the addition of the element. In particular, when the Al element is added, the Er element is bonded to the Al element and the spectrum tends to be almost the original band. In other words, basicity (K. Morinaga, et al., “Compositional dependence of absorption spectra of Ti in silicate, borate, and phosphate glasses”, J. Am. Ceram. Soc., Vol. 77, no. 12, p. As the basicity described in 3113, 1994) is higher, the fluorescence spectrum of the Er / Ta-codoped inorganic optical material tends to be narrower, and the basicity is preferably below a specific value. Further, there are a borate type and a gallate type as host materials which are easily vitrified.

FIG. 3 shows the fluorescence characteristics of ErTaO ₄ crystal and the fluorescence characteristics of the inorganic optical material of Sample A. Graph A in FIG. 3 represents the fluorescence spectrum of sample A, and graph H represents the fluorescence spectrum of ErTaO ₄ crystal. In FIG. 3, the horizontal axis represents the wavelength, and the vertical axis represents the intensity normalized with the peak value of fluorescence. As shown in FIG. 3, the graph H has a plurality of peaks. That is, in the inorganic optical material in the crystalline state, the fluorescence spectrum generates a plurality of peaks, which is preferable as a light source for an interference type optical sensor or as an optical amplifier for WDM optical transmission that collectively amplifies signals of a plurality of wavelengths. Absent.

In addition to the above samples A to E, specific samples P to R of the inorganic optical material containing at least one kind of rare earth element will be described. Specifically, the host material of sample P contains 53 mol% Bi ₂ O ₃ and 47 mol% B ₂ O ₃ . The host material for sample Q contains 100 mol% ZBLAN. The host material of sample R includes Ta ₂ O ₅ , Al ₂ O ₃ , and SiO ₂ . The composition of the above host material represents the composition in the state before containing the rare earth element. Each of the samples P to R contains an Er element that is a rare earth element. That is, samples P and R each contain 0.3 mol% Er ₂ O ₃ , and sample Q contains 0.5 mol% ErF ₃ .

  FIG. 8 shows the normalized absorption coefficient spectrum in the 980 nm band for each of normal EDF (Erbium Doped Fiber) to which these samples P to R and Al element are added. 1 is a normalized absorption coefficient spectrum of the sample P, a graph Q is a normalized absorption coefficient spectrum of the sample Q, a graph R is a normalized absorption coefficient spectrum of the sample R, and a graph X is a normal Al-added EDF ( Hereinafter, the normalized absorption coefficient spectrum of EDF) is represented. In FIG. 8, the horizontal axis represents the wavelength, and the vertical axis represents the absorption coefficient normalized by the peak value of the absorption coefficient spectrum.

  Comparing the full width at half maximum of these normalized absorption coefficient spectra, the EDF is 20 nm wider than the full width at half maximum of sample P, which is a Bi-based glass, which is generally referred to as a broad band from FIG. 8, and sample Q, which is ZBLAN glass. I understand. The full width at half maximum of the 980 nm band absorption coefficient spectrum and the full width at half maximum of the fluorescence and absorption coefficient spectrum of the 1530 nm band peak are determined only from the electric dipole size of Er ions. Therefore, in the samples P and Q, even if the 1530 nm band peak width is narrow, the difference between the bulge part in the 1540 to 1560 nm band determined by the magnetic dipole moment is small, and as a result, the full width at half maximum of the 980 nm band absorption coefficient spectrum is wide. It is considered that the full width at half maximum of the fluorescence and absorption coefficient spectrum of the 1530 nm band peak became a broad band. On the other hand, the sample R has a wide full width at half maximum of the absorption coefficient spectrum of 22 nm even when compared with the EDF, and also has a wide 1530 nm band peak. In addition, if the absorption spectrum in the 980 nm band is wide, the range of selection ranges of excitation wavelengths that can be used is widened, and it is possible to reduce the cost of devices such as light sources using inorganic optical materials.

Next, an embodiment of the OCT apparatus according to the present invention will be described with reference to FIG. FIG. 4 is a configuration diagram of the OCT apparatus 1 according to the present embodiment. The OCT apparatus 1 is a Michelson interferometer including a light source 10, a beam splitter 20, a mirror 30, and a photodetector 50, and obtains a three-dimensional tomographic image of the subject 40 based on the measurement principle of the Michelson interferometer. It is. The measurement principle by the OCT apparatus 1 will be briefly described. ASE light L _A emitted from the light source 10 is split into two by the beam splitter 20, each split beam is irradiated on the mirror 30 and the object 40, respectively. Two split light reflected respectively by mirrors 30 and the subject 40 is superimposed in the beam splitter 20, the interference light L _C is obtained. By tomographic image in a computer or the like the interference light L _C is detected by the photodetector 50, three-dimensional tomographic image of the subject 40 is obtained.

The light source 10 includes an optical waveguide 11 made of the above-described inorganic optical material, and excitation light supply means 13 that supplies excitation light L ₀ to the inorganic optical material in the optical waveguide 11. The light source 10 further includes a lens 12, a WDM filter 14, and an optical isolator 15. As shown in FIG. 4, the light source 10 is output in the reverse excitation method, that is, the ASE output from the same end surface as the end surface of the optical waveguide 11 on which the excitation light L ₀ is incident so as to travel in the opposite direction to the excitation light L _0. taking a method of the light L _a and the output light of the light source 10.

The excitation light source 13 is reflected by the WDM filter 14, and is supplied to the optical waveguide 11 with excitation light L ₀ having a wavelength (for example, 980 nm) that can be condensed on the incident end face of the optical waveguide 11 by the lens 12 to excite the rare earth element. To do. The rare earth element contained in the optical waveguide 11 is brought into an excited state when the excitation light L ₀ is supplied, and spontaneously emitted light (fluorescence) is generated when returning from the excited state to the ground state. Optical waveguide 11, and outputs the ASE light _{L A} The spontaneous emission light (fluorescence) and light amplification. Lens 12 collimates the ASE light _{L A} outputted from the optical waveguide 11. WDM filter 14 is transmitted through the ASE light _{L A} collimated. That is, the WDM filter 14 reflects the above-described excitation light L ₀ and transmits the ASE light L _A. The optical isolator 15 is to pass in the direction toward the ASE light L _A outputted from the optical waveguide 11 from the WDM filter 14 to the beam splitter 20 to be described later, the light does not pass in the opposite direction.

Beam splitter 20 is divided into two the ASE light _{L A} that has entered after the optical isolator 15 passes the first divided light _{L 1} and the second split light _{L 2.} Beam splitter 20 arranged on the optical path of the ASE light _{L A} is to reflect some of the ASE light _{L A,} and transmits the remaining. The ASE light _{L A} reflected by the beam splitter 20 and the first divided light _{L 1,} the transmission has been ASE light _{L A} and the second split light _{L 2.} The beam splitter 20 superimposes and interferes with first divided light L ₁ reflected by a mirror 30 described later and second divided light L ₂ reflected by a subject 40 described later.

Mirror 30 for reflecting the first split light L ₁ is located in the first divided light L ₁ of the optical path. The mirror 30 is arranged so that the first divided light L ₁ is reflected in the direction along the optical path of the incident first divided light L ₁ . The mirror 30 is held by a driving device so as to be movable in parallel (not shown) to the first optical path of the split light L _1.

On the other hand, the sample 40 is a reflector for reflecting the second divided light L ₂ is arranged on a second divided light L ₂ of the optical path.

Photodetector 50 detects the interference light L _C that is obtained by superimposing the first divided light L ₁ and the second split light L ₂ by a beam splitter 20. OCT apparatus 1 is provided with a computer (not shown) to tomographic imaging the detected interference light L _C, to obtain a three-dimensional tomographic image of the subject 40.

The operation of the OCT apparatus 1 will be described. The excitation light L ₀ output from the excitation light source 13 is supplied to the optical waveguide 11 through the WDM filter 14 and the lens 12. The excitation light L ₀ supplied to the optical waveguide 11 excites the rare earth element contained in the optical waveguide 11. Spontaneous emission light rare earth element is in the excited state occurs when returning to the ground state (fluorescence) is optically amplified in the optical waveguide 11, ASE light L _A is obtained. ASE light L _A generated in the optical waveguide 11 is output from the optical waveguide 11 along an incident light path of the excitation light L _0. ASE light _{L A} thus output is passed through then the lens 12, WDM filter 14, and an optical isolator 15, enters a beam splitter 20, is divided into two first divided light _{L 1} and the second split light _{L 2} .

The first split light L ₁ , which is ASE light reflected by the beam splitter 20, enters the mirror 30, where it is reflected in the direction along the optical path at the time of incidence and returned to the beam splitter 20. On the other hand, the subject 40 is irradiated with the second split light L ₂ that is ASE light that has passed through the beam splitter 20. Second divided light L irradiated ₂ propagates through the subject 40 while causing a forward and backward scattering. Of the scattered light propagating in the subject 40 in this way, the back scattered light is incident on the beam splitter 20 and is superposed on the first divided light L ₁ reflected by the mirror 30 there.

Interference light L _C that is obtained by the first division light L ₁ and the second split light L ₂ is interfered been superposed is detected by the photodetector 50. In the photodetector 50, only the backscattered light from the point in the subject 40 that is separated from the beam splitter 20 by a distance equal to the distance between the beam splitter 20 and the mirror 30 is selectively detected as an interference signal. Here, the mirror 30 is movable in a direction along the first optical path of the split light L _1. By moving the mirror 30, the selection of the scattering point which the interference signal is detected in the subject 40 can be performed with the second optical axis direction of the divided light L _2. That is, the measurement point in the depth direction of the subject 40 can be scanned by moving the mirror 30. The tomographic image of the subject 40 is obtained by processing the interference signal detected by the photodetector 50 with a computer or the like thereafter.

The light source 10 includes the inorganic optical material described above. Therefore, ASE light _{L A} emitted from the light source 10 is a broad band, is suitable as a light source of the OCT device. Furthermore, the OCT apparatus 1 obtains a three-dimensional tomographic image of the subject 40 using the measurement principle by the Michelson interferometer. Therefore, the Michelson interferometer using the light source 10 is very suitable for use in the OCT apparatus 1.

  In addition, the OCT apparatus 1 using the light source 10 that outputs broadband light in this way can achieve high resolution. Furthermore, since the inorganic optical material is colorless, background loss in the light source 10 can be suppressed. In particular, when the inorganic optical material contained in the light source 10 is an oxide, the inorganic optical material can have sufficient reliability in terms of hydrogen resistance and high power resistance.

  For example, when the optical waveguide 11 of the light source 10 includes an inorganic optical material that generates a fluorescence spectrum having a shape close to a Gaussian function as in the sample A, the optical waveguide 11 has a fluorescence that has only one autocorrelation peak. Has characteristics. Therefore, it is preferable to use such an inorganic optical material for an interference type optical sensor such as the OCT apparatus 1.

In the case where the optical waveguide 11 of the light source 10 is made of a glass ceramic inorganic optical material, the reverse excitation is preferable because the transmission loss is not always kept low. Further, in the configuration OCT apparatus 1, since the first divided light L ₁ reflected by the mirror 30 reverts inevitably light source 10, inserting the optical isolator 15 so that the output does not vary under the influence of the return light It is preferable to do.

  Next, an embodiment of an optical amplifier according to the present invention will be described with reference to FIG. FIG. 5 is a configuration diagram of the optical amplifier 60 according to the present embodiment. The optical amplifier 60 optically amplifies the signal light input to the input terminal 61 and outputs it from the output terminal 62.

  The optical amplifier 60 has a multi-stage configuration including a first optical amplification stage 70 and a second optical amplification stage 80, and an optical isolator 63, a first optical amplification stage 70, a gain equalizer 65, a second optical amplifier 60 are provided on the signal light path. An optical amplification stage 80 and an optical isolator 64 are sequentially provided.

  The first optical amplification stage 70 includes an optical coupler 71, an amplification optical waveguide 73, and an optical coupler 72 in this order on the signal light path, and the second optical amplification stage 80 includes an optical coupler 81 and an amplification on the signal light path. An optical waveguide 83 and an optical coupler 82 are sequentially provided.

  Each of the amplification optical waveguides 73 and 83 functioning as an amplification medium of the optical amplifier 60 is made of the above-described inorganic optical material, and can guide the excitation light and the signal light. It can be optically amplified. The amplification optical waveguides 73 and 83 are optically cascaded on the signal light propagation path. Each of the optical isolators 63 and 64 allows light to pass in the forward direction from the input end 61 toward the light output end 62, but does not allow light to pass in the reverse direction. The optical coupler 71 and the excitation light source 74, and the optical coupler 72 and the excitation light source 75 constitute excitation light supply means for supplying excitation light to the amplification optical waveguide 73, respectively. The optical coupler 81 and the excitation light source 84, and the optical coupler 82 and the excitation light source 85 constitute excitation light supply means for supplying excitation light to the amplification optical waveguide 83, respectively. The gain equalizer 65 has a loss spectrum having substantially the same shape as the gain spectrum of the amplification optical waveguides 73 and 83 in the gain band of the amplification optical waveguides 73 and 83, and equalizes the gain. .

  Next, the operation of the optical amplifier 60 will be described. In the first optical amplification stage 70, the excitation light output from the excitation light source 74 is supplied in the forward direction to the amplification optical waveguide 73 via the optical coupler 71. The pumping light output from the pumping light source 75 is supplied to the amplification optical waveguide 73 through the optical coupler 72 in the reverse direction.

  In the second optical amplification stage 80, the excitation light output from the excitation light source 84 is supplied to the amplification optical waveguide 83 through the optical coupler 81 in the forward direction. The pumping light output from the pumping light source 85 is supplied in the reverse direction to the amplification optical waveguide 83 via the optical coupler 82.

  The signal light input to the input terminal 61 is input to the amplification optical waveguide 73 through the optical isolator 63 and the optical coupler 71, and is optically amplified in the amplification optical waveguide 73. The signal light optically amplified in the amplification optical waveguide 73 is input to the gain equalizer 65 through the optical coupler 72. The signal light input to the gain equalizer 65 undergoes a loss corresponding to the wavelength in the gain equalizer 65, and then enters the amplification optical waveguide 83 through the optical coupler 81. Optically amplified. The signal light optically amplified in the amplification optical waveguide 83 is output from the output terminal 62 via the optical coupler 82 and the optical isolator 64.

  Since the amplification optical waveguides 73 and 83 of the optical amplifier 60 are made of the above-described inorganic optical material, the optical amplifier 60 can have a gain in a wide band.

  The optical amplifier according to the present embodiment has a two-stage multi-stage configuration, but is not limited to this, and may be, for example, three stages or more or one stage. However, among the above-mentioned inorganic optical materials, when the fluorescent spectrum is substantially line symmetric or the center deviation is less than 9 nm, the absorption cross-sectional area and the stimulated emission cross-sectional shape are very close to each other. Since it is difficult to obtain a net gain in a state where the inversion distribution is low, a multi-stage configuration is preferable. Furthermore, the host material is not necessarily glass, and background loss may be high, and it is considered that it is difficult to obtain a net gain. Therefore, a multi-stage configuration is preferable so as to keep the inversion distribution high. Further, as a use, a preamplifier that easily keeps the inversion distribution high is suitable.

  The inorganic optical material, light source, Michelson interferometer, optical coherent tomography apparatus, and optical amplifier according to the present invention are not limited to the above-described embodiments and configuration examples, and various modifications are possible.

It is a figure which shows the fluorescence spectrum of an inorganic optical material. It is a figure which shows the comparison with the fluorescence spectrum of an inorganic optical material, and a Gauss function. ErTaO ₄ shows a comparison between the fluorescence properties of the fluorescent properties and sample A of the crystal. It is a block diagram of the OCT apparatus which concerns on embodiment. It is a block diagram of the optical amplifier which concerns on embodiment. It is a figure for demonstrating a substantially line symmetrical fluorescence spectrum. It is a figure which shows the line symmetry of an inorganic optical material. It is a figure which shows the absorption coefficient spectrum of an inorganic optical material.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... OCT apparatus, 10 ... Light source, 11 ... Optical waveguide, 12 ... Lens, 13 ... Excitation light source, 14 ... WDM filter, 15 ... Optical isolator, 20 ... Beam splitter, 30 ... Mirror, 40 ... Subject, 50 ... Light Detector 60 ... Optical amplifier 61 ... Input end 62 ... Output end 63, 64 ... Optical isolator 65 ... Gain equalizer 70 ... First optical amplification stage 80 ... Second optical amplification stage 71 72, 81, 82 ... optical coupler, 73, 83 ... optical waveguide for amplification

Claims (12)

  An inorganic optical material containing at least one kind of rare earth element, colorless, and having a full width at half maximum of a fluorescence spectrum larger than 50 nm.   The inorganic optical material according to claim 1, wherein the full width at half maximum of the fluorescence spectrum is 80 nm or more.   3. The inorganic optical material according to claim 1, wherein the full width at half maximum of the 980 nm band absorption spectrum is 20 nm or more.   The inorganic optical material according to any one of claims 1 to 3, wherein the shape of the fluorescence spectrum is substantially line symmetrical with respect to the wavelength at the peak of the fluorescence spectrum.   The center shift that is the difference between the wavelength at the peak of the fluorescence spectrum and the wavelength at the center of the full width at half maximum of the fluorescence spectrum is less than 9 nm. Inorganic optical material.   The inorganic optical material according to claim 1, wherein the center deviation is less than 7 nm.   The inorganic optical material according to claim 1, wherein the fluorescence spectrum does not have a minimum.   The inorganic optical material according to claim 1, wherein the inorganic optical material is an oxide system. The inorganic optical material according to any one of claims 1 to 8,
An excitation light supply means for supplying excitation light to the inorganic optical material,
A light source characterized by optically amplifying fluorescence generated from the rare earth element in the inorganic optical material excited by the excitation light and outputting ASE light. A beam splitter that splits the ASE light output from the light source according to claim 9 into a first split light and a second split light;
A mirror disposed on the optical path of the first split light, moved in parallel with the optical path of the first split light, and reflecting the first split light in a direction along the optical path of the first split light When,
A reflector disposed on the optical path of the second split light and reflecting the second split light;
A photodetector for detecting interference light obtained by overlapping interference between the first split light reflected by the mirror and the second split light reflected by the reflector by the beam splitter;
A Michelson interferometer, comprising:   An optical coherence tomography apparatus that measures a three-dimensional tomographic image of the reflector using the Michelson interferometer according to claim 10. An optical amplifier that optically amplifies the signal light input to the input end and outputs from the output end,
An amplification medium made of the inorganic optical material according to any one of claims 1 to 8, which optically amplifies signal light;
Excitation light supply means for supplying excitation light to the amplification medium;
An optical amplifier comprising:

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