JP2008270585A - Optical semiconductor element, wavelength variable light source using same optical semiconductor element, and optical tomographic image acquisition device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical semiconductor element which is easy to manufacture, and has a wide-band gain spectrum width and emits light for a long time. <P>SOLUTION: The optical semiconductor element 10 has resonance in the element suppressed and also has a light emission layer, emitting light with a center wavelength λc of 0.9 μm to 1.2 μm, stacked on a GaAs substrate 11, the light emission layer being a multiple quantum dot layer including a first In<SB>x</SB>Ga<SB>1-x</SB>As quantum dot layers (0≤x≤1) emitting light with a first center wavelength of, for example, 1.06 μm and a second In<SB>x</SB>Ga<SB>1-x</SB>As quantum dot layer (0≤x≤1) emitting light with a second center wavelength of, for example, 1.09 μm different from the first center wavelength. Consequently, dislocation between the multiple quantum dot layers is avoided. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical semiconductor element that can be used as an SLD (Super Luminescent Diode), an SOA (Semiconductor Optical Amplifier), or the like, in which resonance in the element is suppressed. The present invention also relates to a wavelength tunable light source and an optical tomographic image acquisition apparatus using this optical semiconductor element.

  Among optical semiconductor elements, SLD (Super Luminescent Diode) and SOA (Semiconductor Optical Amplifier) are known as optical semiconductor elements capable of suppressing light in the element and emitting light in a wide wavelength band. Yes. These optical semiconductor elements have a structure close to that of a semiconductor laser, but various measures are taken so that light does not resonate within the element and laser light is not emitted. For example, the resonance in the element is suppressed by applying a non-reflective coating to the end face from which light is emitted or by tilting the optical waveguide by several degrees (about 3 to 12 degrees) from the normal direction of the element end face.

  In the SLD, spontaneous emission light generated by recombination of injected carriers is amplified with a high gain due to stimulated emission while traveling in the direction of the light emission end face, and is emitted from the light emission end face as in the semiconductor laser. An SLD is an optical semiconductor element that can obtain an optical output of up to several tens of mW like a semiconductor laser, and can emit light having a wide wavelength band incoherent like a normal light emitting diode. is there. For this reason, the SLD is mainly used as an incoherent light source in the field of optical measurement such as an optical tomographic image acquisition apparatus using fiber gyroscope or OCT (Optical Coherence Tomography) measurement.

  SOA (Semiconductor Optical Amplifier) is a device very similar to SLD, and has been studied as an optical amplifier for amplifying an optical signal in the field of optical communication. Application studies as a gain medium are actively conducted. As an example of a wavelength tunable light source, the light emitted from one end face of the SOA is converted into parallel light by a lens, the wavelength of this parallel light is dispersed by a diffraction grating, and then wavelength is selected by returning to the diffraction grating by a mirror. The laser is oscillated by feeding back to the SOA. An external resonator is configured by the output mirror installed outside the diffraction grating and the other end face of the SOA. Laser light emitted from the output mirror is converted into parallel light by a lens, passes through an optical isolator, and is transmitted to an external device such as an optical fiber. The wavelength of the laser beam can be changed by changing the angle of the mirror with respect to the diffraction grating, and the wavelength variable width is limited by the gain spectrum width of the SOA.

  On the other hand, the optical tomographic image acquisition apparatus using the above-described OCT measurement divides the light emitted from the light source into the measurement light and the reference light, and then from the measurement object when the measurement light is irradiated onto the measurement object. The reflected light and the reference light are combined, and an optical tomographic image is acquired based on the intensity of the interference light between the reflected light and the reference light.

  In such an optical tomographic image acquisition apparatus, by changing the optical path length of the reference light, the position in the depth direction with respect to the measurement target (hereinafter referred to as the depth position) is changed to obtain an optical tomographic image (TD-OCT). There is an apparatus that uses Time domain OCT) measurement.

  In recent years, an SD-OCT apparatus using SD-OCT (Spectral Domain OCT) measurement that acquires an optical tomographic image at high speed without changing the optical path length of the reference light described above has been proposed (Patent Document 1). ). This SD-OCT apparatus uses a Michelson interferometer or the like to divide broadband low-coherent light into measurement light and reference light, and then irradiates the measurement light with the measurement light, and then returns the reflected light. An optical tomographic image is constructed without scanning in the depth direction by performing Fourier transform on the channeled spectrum obtained by interfering the light with the reference light and decomposing the interference light into frequency components. .

  Further, an optical tomographic imaging apparatus based on SS-OCT (Swept source OCT) measurement has been proposed as an apparatus for acquiring an optical tomographic image at high speed without changing the optical path length of the reference light. This SS-OCT apparatus sweeps the frequency of laser light emitted from a light source, causes reflected light and reference light to interfere at each wavelength, and Fourier transforms the interference spectrum for a series of wavelengths, thereby measuring the depth of the object to be measured. The reflected light intensity at the vertical position is detected, and this is used to construct an optical tomographic image.

In such an optical tomographic image acquisition apparatus, it is known that the resolution is improved by using low-coherence light having a wide spectrum half width. In addition, the low coherence light in the band of the central wavelength of 0.9 μm to 1.2 μm has little absorption loss and scattering loss in the living body and is not easily affected by dispersion due to water, which is the main constituent material of the living body. It is known that low coherence light in a band of .9 μm to 1.2 μm is effective.
JP 11-325849 A

  Examples of the light source used in the optical tomographic image acquisition apparatus by OCT measurement described above include an SLD (super luminescent diode) using a compound optical semiconductor element and a wavelength sweep laser using the optical semiconductor element as an optical amplifier. However, wavelengths with a center wavelength of around 1.2 μm are close to the long-wave side limit of wavelengths that can be produced with devices that use InGaAs quantum well layers for the light-emitting layer, and devices with a crystallographically good light-emitting layer are produced. Difficult to do. Therefore, in this wavelength band, production of a semiconductor light emitting device that emits light stably for a long time required for OCT measurement has not been achieved.

  It has also been found that the light emission wavelength band (spectral width) of the light source needs to be increased in order to improve the measurement resolution in the optical tomographic image acquisition apparatus using OCT measurement. For example, Japanese Patent Application No. 2006-161045 discloses that it is desirable that λc2 / Δλ ≦ 15, where λc is the center wavelength of the emission wavelength band and Δλ is the full width at half maximum of the spectrum.

  In an optical semiconductor device having a quantum well structure, a method of expanding the emission wavelength band of the light emitting layer includes increasing the number of quantum wells in the light emitting layer and changing the composition, but this method further burdens the crystal of the light emitting layer. Therefore, it has been very difficult to produce an optical semiconductor element that has good quality crystals and emits light stably for a long time. In addition, a multi-quantum well layer type optical semiconductor element in which a light emitting layer is formed from a plurality of stacked quantum well layers is also known. For example, a quantum well layer having a different emission wavelength can be obtained by changing the composition. When stacked, dislocation occurs between the well layers, which makes it difficult to produce an optical semiconductor element that emits light stably for a long time.

  In view of the above circumstances, the present invention emits light with a wavelength in the range of a central wavelength of 0.9 μm or more and 1.2 μm or less, has a wide emission wavelength band, and can output up to several tens of mW and is stable for a long time. It is an object to realize an optical semiconductor element that emits light.

  It is another object of the present invention to provide a wavelength tunable light source and an optical tomographic image acquisition apparatus using the above optical semiconductor element.

The optical semiconductor element of the present invention is an optical semiconductor element in which resonance in the element is suppressed, and a light emitting layer emitting a central wavelength λc of 0.9 μm or more and 1.2 μm or less is laminated on a GaAs substrate.
The light-emitting layer, the first In _X Ga _1-X As quantum dot layer (0 ≦ x ≦ 1) and the first second center different from the center wavelength lambda ₁ that emits light at a first center wavelength lambda ₁ it is characterized in that a multiple quantum dot layers comprising second in _X Ga _1-X as quantum dot layer that emits light at a wavelength lambda ₂ and (0 ≦ x ≦ 1).

The first center wavelength λ ₁ and the second center wavelength λ ₂ may be separated by 30 nm or more. Further, the first center wavelength λ ₁ and the second center wavelength λ ₂ may be separated by 50 nm or more, or may be separated by 100 nm or more.

  The emission center wavelength λc of the light emitting layer may be 1.1 μm or more. Moreover, 1.15 micrometers or more may be sufficient.

When the full width at half maximum of the emission spectrum of the light emitting layer is Δλ,
λc ² / Δλ ≦ 15
It may be.

In the light emitting layer, the composition of the first In _X Ga _1-X As quantum dot layer and the composition of the second In _X Ga _1-X As quantum dot layer are substantially the same, and the first In _X the height of the dot of the Ga _1-X as quantum dot layer, and the height of the dot of the second in _X Ga _1-X as quantum dot layer may be different.

The height of the first In _X Ga _1-X As quantum dot layer and the height of the second In _X Ga _1-X As quantum dot layer are substantially the same, and the first In _X Ga _{1 -X} As quantum dot layer is substantially the same in height. the composition of _-X as quantum dot layer, and the composition of the second in _X Ga _1-X as quantum dot layer may be different.

The wavelength tunable light source of the present invention is an external resonator type tunable light source including an optical amplifier and wavelength selection means for selecting a wavelength of light amplified by the optical amplifier in the resonator.
Said optical amplifier, is resonance suppression in the element, the light emitting layer that emits light at more than 0.9μm on GaAs substrate and 1.2μm or less of the center wavelength lambda _c is laminated, the light emitting layer is a central emission wavelength is different first in _X Ga _1-X as quantum dot layer (0 ≦ x ≦ 1) and emit light at a different second center wavelength lambda ₂ is first center wavelength lambda ₁ that emits light at a first center wavelength lambda ₁ And an optical semiconductor element that is a multiple quantum dot layer including a second In _X Ga _1-X As quantum dot layer (0 ≦ x ≦ 1).

The optical tomographic image acquisition apparatus of the present invention includes a light source that emits low-coherence light,
A light splitting means for splitting the light emitted from the light source into measurement light and reference light;
Irradiating means for irradiating the measuring object with the measurement light;
Multiplexing means for superimposing the reflected light from the measurement object and the reference light when the measurement light is irradiated on the measurement object;
Interference light detection means for detecting interference light between the reflected light and the reference light multiplexed by the multiplexing means;
In an optical tomographic image acquisition apparatus comprising image acquisition means for acquiring a tomographic image of the measurement object from the interference light detected by the interference light detection means,
Said light source, is resonance suppression in the element, the light emitting layer that emits light at more than 0.9μm on a GaAs substrate and 1.2μm or less of the center wavelength lambda _c is laminated, the light emitting layer, the center emission wavelengths are different emitting at a different second center wavelength lambda ₂ and the first in _X Ga _1-X as quantum dot layer (0 ≦ x ≦ 1) and the first center wavelength lambda ₁ that emits light in one of the central wavelength lambda ₁ It has an optical semiconductor element which is a multiple quantum dot layer including a second In _X Ga _1-X As quantum dot layer (0 ≦ x ≦ 1).

Another optical tomographic image acquisition apparatus of the present invention includes a wavelength swept light source that emits laser light while sweeping the wavelength at a constant period;
A light splitting means for splitting the laser light emitted from the wavelength swept light source into measurement light and reference light;
Irradiating means for irradiating the measuring object with the measurement light;
Multiplexing means for superimposing the reflected light of the measurement light from the measurement object and the reference light;
Interference light detection means for detecting the intensity of the reflected light at each depth position of the measurement object based on the frequency and intensity of the interference light between the reflected light and the reference light superimposed by the multiplexing means; ,
In an optical tomographic image acquisition apparatus comprising: an image acquisition unit that acquires a tomographic image of the measurement object using the intensity of the reflected light at each depth position detected by the interference light detection unit;
The wavelength swept light source comprises an optical amplifier and wavelength sweeping means for sweeping the wavelength of light amplified by the optical amplifier,
In the optical amplifier, resonance in the device is suppressed, and a light emitting layer that emits light with a central wavelength λc of 0.9 μm or more and 1.2 μm or less is laminated on a GaAs substrate, and the light emitting layer has different central emission wavelengths. emitting at a different second center wavelength lambda ₂ and the first in _X Ga _1-X as quantum dot layer (0 ≦ x ≦ 1) and the first center wavelength lambda ₁ that emits light in one of the central wavelength lambda ₁ It has an optical semiconductor element which is a multiple quantum dot layer including a second In _X Ga _1-X As quantum dot layer (0 ≦ x ≦ 1).

In the optical semiconductor element of the present invention, resonance in the element is suppressed, and a light emitting layer emitting light having a center wavelength λc of 0.9 μm or more and 1.2 μm or less is laminated on a GaAs substrate, and the light emitting layer has a center emission wavelength. first in _X Ga _1-X as quantum dot layer (0 ≦ x ≦ 1) and the first center wavelength lambda ₁ second, different from the central wavelength lambda ₂ which emits light with a different first center wavelength lambda ₁ Since this is a multiple quantum dot layer comprising the second In _X Ga _1-X As quantum dot layer (0 ≦ x ≦ 1) that emits light at the center, it is possible to avoid the occurrence of dislocations, so that the center wavelength is 0.9 μm. An optical semiconductor element that emits light at a wavelength in the range of 1.2 μm or less and can output up to several tens of mW and emits light stably for a long time can be realized.

  Further, in the external resonator type tunable light source provided with an optical amplifier and a wavelength selection means for selecting the wavelength of light amplified by the optical amplifier in the resonator, the optical semiconductor element of the present invention is used as the optical amplifier. As a result, it is possible to realize a wavelength tunable light source that can easily change the wavelength of the emitted light over a wide band and operates stably for a long time.

  Further, in an optical tomographic image acquisition apparatus that acquires an optical tomographic image using light emitted from a light source that emits low coherence light, it is possible to easily achieve low coherence by using the light source having the optical semiconductor element of the present invention. Since the wavelength band of light can be broadened, an optical tomographic image with high resolution can be acquired. In addition, an optical tomographic image acquisition apparatus that operates stably for a long time can be realized.

  Furthermore, in an optical tomographic image acquisition apparatus for acquiring an optical tomographic image using light emitted from a wavelength swept light source that emits laser light while sweeping the wavelength at a constant period, the optical semiconductor element of the present invention is provided as a light source. By using one, the sweep wavelength band can be easily widened, and an optical tomographic image with high resolution can be acquired. In addition, an optical tomographic image acquisition apparatus that operates stably for a long time can be realized.

  An optical semiconductor element 10 according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an overall perspective view of the optical semiconductor element 10. The optical semiconductor element 10 is an optical semiconductor element having a buried ridge structure formed by crystal growth using a metal organic chemical vapor deposition (MOCVD) method.

As a raw material gas of metal organic chemical vapor deposition (MOCVD), TEG (triethyl gallium), TMA (trimethyl aluminum), TMI (trimethyl indium), is used AsH ₃ (arsine), PH ₃ (phosphine), or the like. Further, SiH ₄ (silane) and DEZ (diethyl zinc) are used as dopants.

First, the layer structure of the optical semiconductor element 10 will be described. The optical semiconductor element 10 includes an n-type GaAs buffer layer 12, an n-type In _0.49 Ga _0.51 P lower clad layer 13, a non-doped GaAs lower light guide layer 14, an In _x Ga _1-x As / GaAs on an n-type GaAs substrate 11. A multi-quantum dot light emitting layer 15, a non-doped GaAs upper light guide layer 16, a p-type In _0.49 Ga _0.51 P upper first cladding layer 17, and a p-type GaAs etching stop layer 18 are sequentially stacked.

A ridge-shaped p-type In _0.49 Ga _0.51 P upper second cladding layer 19 is formed on the p-type GaAs etching stop layer 18. This is the side of the ridge (p-type In _0.49 Ga _0.51 P upper second cladding layer 19) n-type InAlGaP current blocking layer 20 is formed, p-type In _0.49 yet the top surface of the ridge and the n-type InAlGaP current blocking layer 20 A Ga _0.51 P upper third cladding layer 21 and a p-type GaAs contact layer 22 are formed.

Hereinafter, a method for producing the optical semiconductor element 10 will be described. First, an n-type GaAs buffer layer (0.05 μm thick carrier concentration 7.0 × 10 ¹⁷ cm ⁻³ ) 12 is formed on an n-type GaAs substrate 11 under the conditions of a growth temperature of 600 ° C. and a growth temperature of 10.3 kPa by MOCVD. , N-type In _0.49 Ga _0.51 P lower cladding layer (2.0 μm thick carrier concentration 7.0 × 10 ¹⁷ cm ⁻³ ) 13, non-doped GaAs lower optical guide layer (0.034 μm thick) 14, and In _X A Ga _1-X As / GaAs multiple quantum dot layer 15 is grown. This layer has a self-formed InGaAs dot layer with a three-layer structure, and is grown while changing the In composition from 0.7 to 0.8. At this time, the heights of the multiple quantum dot layers are unified. In the photoluminescence measurement, the center emission wavelength is 1.06 μm, 1.09 μm, 1.12 μm for each layer, and the half-value width of the light emitted from the optical semiconductor element 10 is 150 nm. The composition is designed.

Then, non-doped GaAs upper optical guide layer (0.034 μm thickness) 16, p-type In _0.49 Ga _0.51 P upper first cladding layer (0.2 μm thickness, carrier concentration 7.0 × 10 ¹⁷ cm ⁻³ ) 17, p-type GaAs etching stop layer (100 mm thick, carrier concentration 7.0 × 10 ¹⁷ cm ⁻³ ) 18, In _0.49 Ga _0.51 P upper second cladding layer (0.5 μm thickness, carrier concentration 7.0 × 10 ¹⁷ cm ⁻³ ) 19 and a p-type GaAs cap layer (0.1 μm thick, carrier concentration 7.0 × 10 ¹⁷ cm ⁻³ ) are stacked in this order by the first growth.

Next, a dielectric film such as SiO ₂ is formed on the stripe, and the GaAs cap layer and the p-type In _0.49 Ga _0.51 P upper second cladding layer 19 are etched using the dielectric film as a mask to form a mesa stripe ridge. The structure is formed so that the width of the lower end is 3 μm and the inclination is 6 degrees with respect to the light emitting end face. Thereafter, an n-In _0.49 (Al _0.12 Ga _0.88 ) _0.51 P current blocking layer (0.5 μm thickness, carrier concentration) is formed on the p-GaAs etching stop layer 18 and excluding the stripes by selective growth. 1.0 × 10 ¹⁸ cm ⁻³ ) 20 is formed by a second crystal growth at a growth temperature of 600 ° C. Further, after removing the dielectric mask and the underlying GaAs cap layer, a p-type In _0.49 (Al _0.12 Ga _0.88 ) _0.51 P upper third cladding layer (1.3 μm) is formed on the entire surface of the stripe and current blocking layer. Thickness, carrier concentration 7.0 × 10 ¹⁷ cm ⁻³ ) 21, p-GaAs contact layer (0.5 μm thickness, carrier concentration 1.0 × 10 ¹⁹ cm ⁻³ ) 22 at the growth temperature of 600 ° C. for the third time Form by growth. Thereafter, the substrate is polished until the total thickness becomes about 100 μm, the n-side electrode 24 is deposited on the back surface of the substrate, the p-side electrode 23 is deposited on the contact layer, and further formed by heat treatment. Then, the optical semiconductor element bar is cut out by cleavage so that the resonator length becomes 0.7 mm, and an AR film (reflectance of 0.5% or less with respect to the emission wavelength from the element itself) is coated on the resonator surface. Ting. The chip is mounted on a heat sink with a pn junction part having a light emitting part facing down to enhance the heat dissipation effect, and the optical semiconductor element 10 is formed.

  As described above, the optical semiconductor element 10 has an AR coating on the end faces 25 and 26 from which the light L is emitted, as shown in FIG. Further, the mesa stripe-shaped ridge structure which is a waveguide is inclined 6 degrees from the normal direction of the end faces 25 and 26, thereby suppressing light resonance in the element. In this way, by suppressing the resonance of light in the optical semiconductor element, it is possible to prevent the optical semiconductor element 10 from lasing in the element. Since the resonance in the element is suppressed, the optical semiconductor element 10 can function as an SLD that emits spontaneous emission light or an SOA that amplifies an optical signal.

  In order to suppress the resonance of light in the element, various methods other than the above are possible. For example, irregularities are formed on the end face, the optical waveguide structure is lost near the end face, light is absorbed inside the element, or Resonance in the optical waveguide can also be suppressed by means such as providing a diffusion region.

  When the optical semiconductor element 10 thus fabricated was made to emit light as an SLD, the output was 30 mW, the emission center wavelength was 1.102 μm, and the emission spectrum full width at half maximum was 150 nm. When the device was continuously driven at room temperature to evaluate the device life, the output reached 90% of the initial value after about 13,000 hours.

In order to compare device performance, multiple quantum well light emission in which the portion other than the light emitting layer is exactly the same as described above, and the light emitting layer is made of InGaAs material and the well width is adjusted so that the center wavelength of the emitted light becomes 1.1 μm. An optical semiconductor element composed of layers was produced. The composition of the light emitting layer was In _0.2 Ga _0.8 As. When this optical semiconductor element was made to emit light as SLD, the full width at half maximum of the emission spectrum was 48 nm, and the output became 90% of the initial value after about 7000 hours.

  From the above description, the optical semiconductor element 10 in which the light emitting layer is formed of three InGaAs dot layers having different center wavelengths is prevented from generating dislocations between the respective dod layers, and thus stable for a long time. Can be seen to emit light. Further, it can be seen that the conventional light emitting layer structure emits light stably for a long time even when the center wavelength at which the device lifetime is shortened is 1.1 μm or more. In the modification of the above embodiment, the center wavelength of the light emitted from each quantum dod layer is changed by changing the In composition of each quantum dod layer forming the light emitting layer. The center wavelength of light emitted from each quantum dot layer can be changed by fixing the composition and changing the dot height of each quantum dot layer.

The present inventor fixed the In composition of the Ga _{1 -X} In _X As / GaAs multiple quantum dot layer 15 and changed the dot height of each layer from 2.8 ML to 3.5 ML. The optical semiconductor element 10 was produced by designing the height of the dod of each layer so that the half width of the emitted light was 150 nm, which was 06 μm, 1.09 μm, and 1.16 μm. . When the device was continuously driven at room temperature in order to evaluate the device life, it was about 9500 hours that the output became 90% of the initial value. Therefore, dislocation occurs between each dod layer even when the light emitting layer is formed by changing the center wavelength of the light emitted from each quantum dod layer by changing the dot height of each quantum dot layer. Therefore, it can be seen that light is emitted stably for a long time. Note that the center wavelength of the light emitted from each quantum dot layer may be changed by changing both the composition and the dot height of each quantum dot layer.

Furthermore, the present inventor has made the In composition of the Ga _1-X In _X As / GaAs multiple quantum dot layer 15 0.7 to 0.82 and uniformizes the height of each dot layer, and the center wavelength of the emitted light. Was designed to be 1.15 μm, and an optical semiconductor device 10 was produced. When this optical semiconductor element 10 was caused to emit light, the center wavelength was 1.153 μm, and the full width at half maximum of the emission spectrum was 160 nm. When the device was continuously driven at room temperature in order to evaluate the device lifetime, the output reached 90% of the initial value after about 10,000 hours.

In order to compare device performance, multiple quantum well light emission in which the portion other than the light emitting layer is exactly the same as the above, and the light emitting layer is made of InGaAs material and the well width is adjusted so that the center wavelength of the emitted light is 1.15 μm. An optical semiconductor element composed of layers was prepared. The composition of the light emitting layer was In _0.27 Ga _0.73 As. When the reliability was evaluated, the output reached 90% of the initial stage after about 3800 hours.

 From this, it can be seen that the conventional light emitting layer structure emits light stably for a long time even when the center wavelength at which the device lifetime is very short is 1.15 μm or more.

 In this embodiment, the MOCVD method is used as the crystal growth method, but the present invention is not limited to this, and other growth methods such as a molecular beam epitaxy method can also be used. In this embodiment, the material composition and layer thickness of the light guide layer, the material composition and layer thickness of the current blocking layer, and the material composition and layer thickness of the cladding layer are examples of conditions in which the emission wavelength is emitted in a single mode. The present invention is not limited to the above-described material composition and layer thickness. Although the optical semiconductor element having the buried ridge stripe structure has been described as an embodiment here, other structures such as an internal stripe structure may be used.

  Next, a wavelength tunable laser device 30 that is a second embodiment of the present invention will be described. The wavelength tunable laser device 30 is a Littrow arrangement type external resonator type wavelength tunable laser device using the optical semiconductor element 10 described in the first embodiment as an optical amplifier and the diffraction grating 32 as wavelength selection means. FIG. 3 shows a schematic configuration diagram thereof.

  In the wavelength tunable laser device 30, a resonator is constituted by the diffraction grating 32 and the output mirror 31 (transmittance 50%). Spontaneously emitted light emitted from the optical semiconductor element 10 toward the diffraction grating 32 is collected by the lens 33 to become parallel light and enters the diffraction grating 32. Of the light wavelength-dispersed by the diffraction grating 32, the light dispersed in the direction of the incident optical axis returns to the optical semiconductor element 10 as return light. This light resonates in the resonator composed of the diffraction grating 32 and the output mirror 31 and is emitted as laser light L from the output mirror 31 to the optical isolator 35 side. The optical isolator 35 has a function of preventing the reflected light at the far end from the optical fiber FB1 from being coupled to the optical semiconductor element 10. The laser light L that has passed through the optical isolator 35 is condensed by the condenser lens 34 and enters the optical fiber FB1. By rotating the diffraction grating 32, the wavelength of the return light can be changed, and the resonant light frequency (laser oscillation wavelength) can be changed. The wavelength tunable range of the laser light substantially matches the gain spectrum width of the optical semiconductor element 10 that is an optical amplifier.

The In composition of the In _X Ga _1-X As / GaAs multiple quantum dot layer 15 which is the light emitting layer of the optical semiconductor element 10 is 0.7 to 0.82, and the emission center wavelength when driven by current is 1. .15 μm and the full width at half maximum of the emission spectrum was designed to be 160 nm. The diffraction grating 32 was adjusted to an angle at which 1.15 μm light could be extracted.

  In order to evaluate the lifetime of the device, when it was continuously driven at room temperature with an output of 10 mW, the output became 90% of the initial value after about 28000 hours.

In order to compare the device performance, a similar tunable light source was prepared using an optical semiconductor device in which the light emitting layer was made of In _0.27 Ga _0.73 As (the emission wavelength when driven by current was 1.15 μm), and 10 mW at room temperature. With continuous output, the output reached 90% of the initial level after about 9000 hours.

From this, it was found that in the wavelength tunable light source, the reliability is improved when an optical semiconductor element in which the light emitting layer is formed of an In _X Ga _1-X As / GaAs multiple quantum dot layer is used as an amplifier. Such a wavelength tunable light source can easily change the wavelength of emitted light over a wide band and can operate stably for a long time.

  FIG. 4 shows a wavelength sweep laser apparatus 40 which is a modification of the present embodiment. In the wavelength sweep laser device 40, a wavelength sweep unit 41 that periodically changes the angle of the diffraction grating 32 is provided. As the angle of the diffraction grating 32 periodically changes, the oscillation wavelength of the laser light La emitted from the wavelength sweep laser device 40 is periodically swept.

  Furthermore, although the Littrow arrangement type wavelength variable laser has been described as an example of the wavelength variable laser in the above embodiment, the present invention is not limited to this, and a Littman arrangement type wavelength variable laser may be used.

  Next, a tunable ring laser apparatus 50 according to a third embodiment of the present invention will be described with reference to FIG. The wavelength tunable ring laser device 50 is a laser device having a resonator configuration in a ring shape. The optical semiconductor element 10 described in the first embodiment is used as an optical amplifier, and light composed of a multilayer dielectric film is used. The filter 51 is used as wavelength selection means. In the optical filter 51, the wavelength to be transmitted is determined by the angle of the multilayer dielectric film with respect to the optical axis, and the wavelength of the transmitted light can be changed by changing the angle of the optical filter 51.

  The spontaneously emitted light from the optical semiconductor element 10 is collimated by the lens 56, is incident on the optical filter 51, and transmits only a specific wavelength (oscillation wavelength). The light that has passed through the optical filter 51 is collected by the lens 56 and enters the optical fiber 53, further passes through the optical coupler 54, is collimated by the lens 58, passes through the optical isolator 52, and is collected by the lens 59. Then, the process returns to the optical semiconductor element 10. The optical isolator 52 determines the light circulation direction and contributes to the stable oscillation operation of the ring laser device 50. When the optical gain of the optical semiconductor element 10 exceeds the total loss of the ring laser resonator, laser oscillation occurs. As described above, since the oscillation wavelength is determined by the transmission center wavelength of the optical filter 54, the oscillation wavelength can be varied by changing the angle of the optical filter 54 with respect to the optical axis. The light in the wavelength tunable ring laser device 50 can be extracted by the optical coupler 56. Even in such a wavelength tunable light source, the wavelength of the emitted light can be easily changed over a wide band and can operate stably for a long time.

  FIG. 6 shows a wavelength swept ring laser device 60 which is a modification of the present embodiment. The wavelength sweep ring laser 60 includes an optical filter sweep unit 61 that is connected to the optical filter 54 and periodically changes the angle of the optical filter 54 with respect to the optical axis. The oscillation wavelength is periodically swept by changing the angle of the optical filter periodically.

  Hereinafter, an optical tomographic image acquisition apparatus for acquiring an optical tomographic image using a light source having an optical semiconductor element according to the present invention will be described. Conventionally, when an optical tomographic image of a living tissue is acquired, an optical tomographic image acquisition device using OCT measurement is sometimes used. This optical tomographic image acquisition apparatus divides low-coherent light emitted from a light source into measurement light and reference light, and then reflects reflected light and reference light from the measurement object when the measurement light is irradiated onto the measurement object. And an optical tomographic image is obtained based on the intensity of the interference light between the reflected light and the reference light.

  In the optical tomographic image acquisition apparatus as described above, by changing the optical path length of the reference light, the position in the depth direction with respect to the measurement target (hereinafter referred to as the depth position) is changed to acquire the optical tomographic image. There is an apparatus using (Time domain OCT) measurement.

  In recent years, an SD-OCT apparatus using SD-OCT (Spectral Domain OCT) measurement that acquires an optical tomographic image at high speed without changing the optical path length of the reference light described above has been proposed. This SD-OCT apparatus uses a Michelson interferometer or the like to divide broadband low-coherent light into measurement light and reference light, and then irradiates the measurement light with the measurement light, and then returns the reflected light. An optical tomographic image is constructed without scanning in the depth direction by performing Fourier transform on the channeled spectrum obtained by interfering the light with the reference light and decomposing the interference light into frequency components. .

  Further, an optical tomographic imaging apparatus based on SS-OCT (Swept source OCT) measurement has been proposed as an apparatus for acquiring an optical tomographic image at high speed without changing the optical path length of the reference light. This SS-OCT apparatus sweeps the frequency of laser light emitted from a light source, causes reflected light and reference light to interfere at each wavelength, and Fourier transforms the interference spectrum for a series of wavelengths, thereby measuring the depth of the object to be measured. The reflected light intensity at the vertical position is detected, and this is used to construct an optical tomographic image.

  An optical tomographic image acquisition apparatus 100 shown in FIG. 7 acquires a tomographic image by the so-called SS-OCT (Swept source OCT) described above, and has a constant period in a wavelength range of 80 nm with a central wavelength of 1.0 μm. The measurement light L1 is emitted to the measuring object S while sweeping the wavelength. Then, the optical tomographic image acquisition apparatus 100 generates a tomographic image based on the reflected light (backscattered light) Lr from the irradiation target S when the measurement light L1 is applied to the irradiation target, and displays the tomographic image on the display device 4. It is like that.

  As a light source in this apparatus, a wavelength sweep laser apparatus 40, which is a modification of the third embodiment, shown in FIG. 4 is used. From the wavelength sweep laser device 40, a laser beam Lb whose wavelength is swept at a constant period in a wavelength range of 80 nm with a center wavelength of 1.0 μm is emitted to the optical fiber FB1.

  The light splitting means 3 is composed of, for example, a 2 × 2 optical fiber coupler, and splits the light Lb guided from the wavelength swept laser device 40 through the optical fiber FB1 into the measurement light L1 and the reference light L2. The light splitting means 3 is optically connected to the two optical fibers FB2 and FB3, respectively. The measurement light L1 is guided through the optical fiber FB2, and the reference light L2 is guided through the optical fiber FB3. The light splitting means 3 in this example also functions as the multiplexing means 4.

  An optical probe 130 is optically connected to the optical fiber FB2, and the measurement light L1 is guided from the optical fiber FB2 to the optical probe 130. The optical probe 130 is inserted into a body cavity from a forceps port through a forceps channel, for example, and is detachably attached to the optical fiber FB2 by an optical connector 136.

  The optical probe 130 has a cylindrical probe outer tube 131 with a closed end, and one optical fiber 132 disposed in the inner space of the probe outer tube 131 so as to extend in the axial direction of the outer tube 131. A prism mirror 133 that deflects the measurement light L1 emitted from the tip of the optical fiber 132 in the circumferential direction of the probe outer cylinder 131, and the measurement light L1 emitted from the tip of the optical fiber 132 is arranged outwardly of the probe outer cylinder 131. A rod lens 134 that condenses light so as to converge on the measurement target S as the scanned body and a motor 135 that rotates the optical fiber 132 about the optical axis of the optical fiber 132 as a rotation axis. The rod lens 134 and the prism mirror 133 are arranged so as to rotate together with the optical fiber 132.

  On the other hand, optical path length adjusting means 120 is arranged on the side of the optical fiber FB3 from which the reference light L2 is emitted. The optical path length adjusting unit 120 changes the optical path length of the reference light L2 in order to adjust the position at which tomographic image acquisition is started, and reflects the reference light L2 emitted from the optical fiber FB3. 122, a first optical lens 121a disposed between the reflection mirror 122 and the optical fiber FB3, and a second optical lens 121b disposed between the first optical lens 121a and the reflection mirror 122. Yes.

  The first optical lens 121a has a function of converting the reference light L2 emitted from the core of the optical fiber FB3 into parallel light and condensing the reference light L2 reflected by the reflection mirror 122 onto the core of the optical fiber FB3. ing. Further, the second optical lens 121b condenses the reference light L2 converted into parallel light by the first optical lens 21a on the reflection mirror 122 and makes the reference light L2 reflected by the reflection mirror 122 into parallel light. have. That is, a confocal optical system is formed by the first optical lens 121a and the second optical lens 121b.

  Therefore, the reference light L2 emitted from the optical fiber FB3 becomes parallel light by the first optical lens 121a, and is condensed on the reflection mirror 122 by the second optical lens 121b. Thereafter, the reference light L2 reflected by the reflection mirror 122 becomes parallel light by the second optical lens 121b, and is condensed on the core of the optical fiber FB3 by the first optical lens 121a.

  Further, the optical path length adjusting means 120 has a base 123 to which the second optical lens 121b and the reflecting mirror 122 are fixed, and a mirror moving means 124 for moving the base 123 in the optical axis direction of the first optical lens 121a. is doing. Then, when the base 123 moves in the direction of arrow A, the optical path length of the reference light L2 can be changed.

  The multiplexing means 4 is composed of a 2 × 2 optical fiber coupler as described above, and the reference light L2 that has been subjected to frequency shift and change of the optical path length by the optical path length adjusting means 120 and the reflected light L3 from the irradiation target S. Are combined and emitted to the interference light detection means 140 side via the optical fiber FB4.

  The interference light detection unit 140 detects the interference light L4 between the reflected light L3 combined by the multiplexing unit 4 and the reference light L2. And the image acquisition means 150 detects the intensity | strength of the reflected light L3 in each depth position of the irradiation object S by Fourier-transforming the interference light L4 detected by the interference light detection means 140, and the tomography of the irradiation object S Get an image. The acquired tomographic image is displayed on the display device 160. The apparatus of this example has a mechanism that guides the light obtained by dividing the interference light L4 into two by the optical fiber coupler 3 to the photodetectors 142a and 142b, and performs balance detection in the calculation means 141. As described above, in this example, the interference light detection unit 140 is configured by the photodetectors 142 a and 142 b and the calculation unit 141.

  Here, the detection of the interference light L4 and the generation of the image in the interference light detection means 140 and the image acquisition means 150 will be briefly described. Details of this point are described in “Mitsuo Takeda,“ Optical Frequency Scanning Spectrum Interference Microscope ”, Optical Technology Contact, 2003, Vol. 41, No. 7, p426-p432”.

  The measurement light L1 is emitted from the optical probe 130 into the body cavity and irradiated to the measurement object S. At this time, the measurement light L1 emitted from the optical probe 130 scans the measurement object S one-dimensionally. Then, the reflected light L3 from the measuring object S is combined with the reference light L2 reflected by the reflecting mirror 122 of the optical path length adjusting unit 120, and the interference light L4 between the reflected light L3 and the reference light L2 is received by the interference light detecting unit 140. Detected.

Interference fringes with respect to each optical path length difference l when the reflected light L3 and the reference light L2 from the respective depths of the irradiation target S interfere with each other with various optical path length differences when the measurement light L1 is irradiated onto the irradiation target S. S (l) is the light intensity I (k) detected by the interference light detection means 140.
I (k) = ∫ ₀ ^∞ S (l) [1 + cos (kl)] dl
It is represented by Here, k is the wave number, and l is the optical path length difference. It can be considered that the above equation is given as an interferogram in the optical frequency domain with the wave number k = ω / c as a variable. For this reason, in the image acquisition means 150, the spectral interference fringes detected by the interference light detection means 140 are subjected to Fourier transform, and the light intensity S (l) of the interference light L4 is determined. Distance information and reflection intensity information can be acquired, and a tomographic image can be generated.

  Thus, in the optical tomographic image acquisition apparatus 100 that acquires an optical tomographic image using light emitted from a wavelength swept light source that emits laser light while sweeping the wavelength at a constant period, the optical semiconductor of the present invention is used as the light source. By using the wavelength swept laser device 40 having elements, the swept wavelength band can be easily widened, and an optical tomographic image with high resolution can be acquired. In addition, an optical tomographic image acquisition apparatus that operates stably for a long time can be realized.

  In the embodiment, the wavelength swept laser device 40 is used as the light source, but the wavelength swept ring laser 60 shown in FIG. 6 can also be used.

  Next, another example of the optical tomographic image acquisition apparatus using the optical semiconductor element according to the present invention as a light source will be described with reference to FIG. An optical tomographic image acquisition apparatus 200 shown in FIG. 8 acquires a tomographic image of a measurement target such as a living tissue or a cell in a body cavity by the above-described SD-OCT (Spectral Domain OCT) measurement. The difference from the optical tomographic image acquisition apparatus 1 of FIG. 7 is the configuration of the light source unit and the interference light detection means.

  A light source unit 210 that emits light Lb, a light splitting unit 3 that splits the light Lb emitted from the light source unit 210 into measurement light L1 and reference light L2, and an optical path of the reference light L2 split by the light splitting unit 3 An optical path length adjusting means 220 for adjusting the length, an optical probe 130 for irradiating the irradiation target S with the measurement light L1 divided by the light splitting means 3, and an irradiation target S when the irradiation target S is irradiated with the measurement light L1. And a light combining means 4 for combining the reflected light L3 reflected by the reference light L2 and the reference light L2, and an interference light detecting means 240 for detecting the interference light L4 between the combined reflected light L3 and the reference light L2. is doing.

  The light source unit 210 includes the optical semiconductor element 10 shown in FIG. 2 and an optical system 212 for causing the low coherence light Lb emitted from the optical semiconductor element 10 to enter the optical fiber FB1. The optical semiconductor element 10 functions as an SLD, and low optical coherence light Lb having a center wavelength of 1.0 μm and a spectral line width of 80 nm is emitted from the optical semiconductor element 10.

  On the other hand, the interference light detection means 240 detects the interference light L4 between the reflected light L3 combined by the multiplexing means 4 and the reference light L2, and uses the interference light L4 emitted from the optical fiber FB4 as parallel light. The collimator lens 241 to be converted, the spectroscopic means 242 for dispersing the interference light L4 having a plurality of wavelength bands for each wavelength band, and the light detection means 244 for detecting the interference light L4 of each wavelength band split by the spectroscopic means 242. And have.

  The spectroscopic means 242 is composed of, for example, a diffraction grating element or the like. Further, the light detection means 244 is composed of, for example, an element such as a CCD in which photosensors are arranged one-dimensionally or two-dimensionally, and each photosensor is configured to separate the interference light L4 that has been dispersed as described above for each wavelength band. It comes to detect.

  The light detection means 244 is connected to an image acquisition means 250 made up of a computer system such as a personal computer, for example, and the image acquisition means 250 is connected to a display device 160 made up of a CRT or a liquid crystal display device.

  Hereinafter, the operation of the optical tomographic image acquisition apparatus 200 having the above configuration will be described. When acquiring a tomographic image, the optical path length is adjusted so that the irradiation target S is positioned within the measurable region by first moving the base 123 in the direction of arrow A. Thereafter, the light Lb is emitted from the light source unit 210, and this light La is split into the measurement light L1 and the reference light L2 by the light splitting means 3. The measurement light L1 is emitted from the optical probe 130 toward the body cavity and irradiated on the irradiation target S. At this time, the measurement light L1 emitted from the optical probe 130 scans the irradiation target S in one dimension. Then, the reflected light L3 from the irradiation target S is combined with the reference light L2 reflected by the reflecting mirror 22, and the interference light L4 between the reflected light L3 and the reference light L2 is detected by the interference light detection means 240. The detected interference light L4 is subjected to appropriate waveform compensation and noise removal in the image acquisition means 250 and then subjected to Fourier transform, whereby reflected light intensity distribution information in the depth direction of the irradiation target S is obtained.

  Then, if the measurement light L1 is scanned on the irradiation target S by the optical probe 130 as described above, information in the depth direction of the irradiation target S is obtained at each portion along the scanning direction. A tomographic image of a tomographic plane including The tomographic image acquired in this way is displayed on the display device 160. For example, by moving the optical probe 130 in the left-right direction in FIG. 8 and causing the measurement light L1 to scan the irradiation target S in a second direction orthogonal to the scanning direction, this second It is also possible to obtain a tomographic image of a tomographic plane including the direction.

  As described above, in the optical tomographic image acquisition apparatus 200 that acquires the optical tomographic image using the light emitted from the light source that emits the low coherence light, the optical semiconductor element 10 of the present invention is used as the light source. The wavelength band of the coherence light can be widened, and an optical tomographic image with high resolution can be acquired. In addition, an optical tomographic image acquisition apparatus that operates stably for a long time can be realized.

  Next, still another example of the optical tomographic image acquisition apparatus using the optical semiconductor element according to the present invention as a light source will be described. An optical tomographic image acquisition apparatus 300 shown in FIG. 9 acquires a tomographic image to be measured by the above-described TD-OCT measurement, and is a light source including an optical semiconductor element 10 that emits laser light Lb and a condenser lens 121. The unit 210, the light splitting means 2 that splits the low-coherence light KLb that is emitted from the light source unit 210 and propagates through the optical fiber FB1, and the low-coherence light Lb that has passed therethrough is split into the measurement light L1 and the reference light L2. The light splitting means 3, the optical path length adjusting means 320 for adjusting the optical path length of the reference light L2 split by the light splitting means 3 and propagated through the optical fiber FB3, and the light splitting means 3 split and propagated through the optical fiber FB2 An optical probe 130 that irradiates the irradiation target S with the measurement light L1, and measurement when the measurement light L1 is irradiated from the optical probe 130 onto the irradiation target S. Interpolation between the reflected light L3 from the elephant and the reference light L2, and the interference between the reflected light L3 and the reference light L2 by the multiplexing means 4 (also serving as the light splitting means 3). Interference light detection means 330 for detecting the light L4.

  The optical path length adjusting means 320 is a mirror that is movable in the direction of arrow A in the figure so as to change the distance between the collimator lens 321 that collimates the reference light L2 emitted from the optical fiber FB3 and the collimator lens 321. 323 and mirror moving means 324 for moving the mirror 323, and has a function of changing the optical path length of the reference light L2 in order to change the measurement position in the irradiation target S in the depth direction. . Then, the reference light L 2 whose optical path length has been changed by the optical path length adjusting means 320 is guided to the multiplexing means 4.

  The interference light detection means 330 detects the light intensity of the interference light L4 that has propagated from the multiplexing means 4 through the optical fiber FB2. Specifically, when the difference between the total optical path length of the measuring light L1 and the reflected light L3 reflected or backscattered at a certain point of the irradiation target S and the optical path length of the reference light L2 is shorter than the coherence length of the light source Only an interference signal with an amplitude proportional to the amount of reflected light is detected. Further, by scanning the optical path length by the optical path length adjusting unit 320, the reflection point position (depth) of the irradiation target S from which the interference signal is obtained changes, and accordingly, the interference light detection unit 330 of the irradiation target S is changed. The reflectance signal at each measurement position is detected. The information on the measurement position is output from the optical path length adjustment unit 320 to the image acquisition unit. Then, based on the information on the measurement position in the mirror moving unit 324 and the signal detected by the interference light detection unit 330, the image acquisition unit 350 obtains the reflected light intensity distribution information in the depth direction of the irradiation target S.

  Then, if the measurement light L1 is scanned on the irradiation target S by the optical probe 130 as described above, information in the depth direction of the irradiation target S is obtained at each portion along the scanning direction. A tomographic image of a tomographic plane including The tomographic image acquired in this way is displayed on the display device 160. For example, by moving the optical probe 130 in the left-right direction in FIG. 9 and causing the measurement light L1 to scan the irradiation target S in a second direction orthogonal to the scanning direction, the second direction is changed. It is also possible to further acquire a tomographic image of the tomographic plane including it.

  Thus, in the optical tomographic image acquisition apparatus 300 that acquires an optical tomographic image using light emitted from a light source that emits low-coherence light, the optical semiconductor element 10 of the present invention is used as a light source. The wavelength band of the coherence light can be widened, and an optical tomographic image with high resolution can be acquired. In addition, an optical tomographic image acquisition apparatus that operates stably for a long time can be realized.

1 is a schematic sectional elevation view of an optical semiconductor device according to a first embodiment of the present invention. 1 is a schematic cross-sectional view of an optical semiconductor device according to a first embodiment of the present invention. Schematic configuration diagram of a wavelength tunable laser device according to a second embodiment of the present invention. Schematic configuration diagram of wavelength swept laser device Schematic configuration diagram of a wavelength tunable ring laser device according to a third embodiment of the present invention. Schematic configuration diagram of wavelength swept ring laser device Schematic configuration diagram showing an example of an optical tomographic image acquisition apparatus based on SS-OCT measurement Schematic configuration diagram showing an example of an optical tomographic image acquisition apparatus by SD-OCT measurement Schematic configuration diagram showing an example of an optical tomographic image acquisition apparatus based on TD-OCT measurement

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Opto-semiconductor element 11 n-type GaAs substrate 12 n-type GaAs buffer layer 13 n-type In _0.49 Ga _0.51 P lower cladding layer 14 non-doped GaAs lower light guide layer 15 InXGa1-XAs / GaAs multiple quantum dot light emitting layer 16 non-doped GaAs upper light guide Layer 17 p-type In0.49Ga0.51P upper first cladding layer 18 p-type GaAs etching stop layer 19 p-type In0.49Ga0.51P upper second cladding layer 20 n-type InAlGaP current blocking layer 21 p-type In0.49Ga0.51P upper Third cladding layer 22 p-type GaAs contact layer 23 p-side electrode 24 n-side electrodes 25 and 26 End face 30 Wavelength variable laser device 31 Output mirror 32 Diffraction grating 40 Wavelength sweep laser device 50 Wavelength variable ring laser device 51 Optical filter 60 Wavelength sweep Ring laser apparatus 100, 200, 300 Optical tomographic image acquisition apparatus 120, 320 Optical path length adjusting means 130 Probe 140, 240, 330 Wataruhikari detection means
La Laser light Lb Low coherence light

Claims (10)

In an optical semiconductor element in which resonance in the element is suppressed and a light emitting layer emitting a central wavelength λc of 0.9 μm or more and 1.2 μm or less is laminated on a GaAs substrate,
The light-emitting layer, the first In _X Ga _1-X As quantum dot layer (0 ≦ x ≦ 1) and the first second center different from the center wavelength lambda ₁ that emits light at a first center wavelength lambda ₁ An optical semiconductor element comprising a multiple quantum dot layer including a second In _X Ga _1-X As quantum dot layer (0 ≦ x ≦ 1) that emits light at a wavelength λ ₂ . _2. The optical semiconductor device according to claim 1, wherein the first center wavelength λ ₁ and the second center wavelength λ ₂ are separated by 30 nm or more.   3. The optical semiconductor element according to claim 1, wherein an emission center wavelength λc of the light emitting layer is 1.1 μm or more.   4. The optical semiconductor element according to claim 3, wherein an emission center wavelength [lambda] c of the light emitting layer is 1.15 [mu] m or more. When the full width at half maximum of the emission spectrum of the light emitting layer is Δλ,
λc ² / Δλ ≦ 15
The optical semiconductor device according to claim 1, wherein the optical semiconductor device is a semiconductor device. The composition of the first In _X Ga _{1 -X} As quantum dot layer and the composition of the second In _X Ga _{1 -X} As quantum dot layer are substantially the same, and the first In _X Ga _{1 -X} As quantum dot layer is substantially the same. 6. The dot height of the As quantum dot layer and a dot height of the second In _X Ga _1-X As quantum dot layer are different from each other. Optical semiconductor element. The height of the first In _X Ga _1-X As the height of the quantum dot layer and the second In _X Ga _1-X As quantum dot layer is substantially the same, the first In _X Ga _1-X 6. The optical semiconductor element according to claim 1, wherein the composition of the As quantum dot layer is different from the composition of the second In _X Ga _1-X As quantum dot layer. In an external resonator type tunable light source including an optical amplifier and wavelength selection means for selecting a wavelength of light amplified by the optical amplifier in the resonator,
Said optical amplifier, is resonance suppression in the element, the light emitting layer that emits light at more than 0.9μm on a GaAs substrate and 1.2μm or less of the center wavelength lambda _c is laminated, the light emitting layer is a central emission wavelength is different first in _X Ga _1-X as quantum dot layer (0 ≦ x ≦ 1) and emit light at a different second center wavelength lambda ₂ is first center wavelength lambda ₁ that emits light at a first center wavelength lambda ₁ A tunable light source comprising: an optical semiconductor element that is a multiple quantum dot layer including a second In _X Ga _1-X As quantum dot layer (0 ≦ x ≦ 1). A light source that emits low coherence light;
A light splitting means for splitting the light emitted from the light source into measurement light and reference light;
Irradiating means for irradiating the measuring object with the measurement light;
Multiplexing means for superimposing the reflected light from the measurement object and the reference light when the measurement light is irradiated on the measurement object;
Interference light detection means for detecting interference light between the reflected light and the reference light multiplexed by the multiplexing means;
In an optical tomographic image acquisition apparatus comprising image acquisition means for acquiring a tomographic image of the measurement object from the interference light detected by the interference light detection means,
Said light source, is resonance suppression in the element, the light emitting layer that emits light at more than 0.9μm on a GaAs substrate and 1.2μm or less of the center wavelength lambda _c is laminated, the light emitting layer, the center emission wavelengths are different emitting at a different second center wavelength lambda ₂ and the first in _X Ga _1-X as quantum dot layer (0 ≦ x ≦ 1) and the first center wavelength lambda ₁ that emits light in one of the central wavelength lambda ₁ An optical tomographic image acquisition apparatus comprising: an optical semiconductor element that is a multiple quantum dot layer including a second In _X Ga _1-X As quantum dot layer (0 ≦ x ≦ 1). A wavelength swept light source that emits laser light while sweeping the wavelength at a constant period;
A light splitting means for splitting the laser light emitted from the wavelength swept light source into measurement light and reference light;
Irradiating means for irradiating the measuring object with the measurement light;
Multiplexing means for superimposing the reflected light of the measurement light from the measurement object and the reference light;
Interference light detection means for detecting the intensity of the reflected light at each depth position of the measurement object based on the frequency and intensity of the interference light between the reflected light and the reference light superimposed by the multiplexing means; ,
In an optical tomographic image acquisition apparatus comprising: an image acquisition unit that acquires a tomographic image of the measurement object using the intensity of the reflected light at each depth position detected by the interference light detection unit;
The wavelength swept light source comprises an optical amplifier and wavelength sweeping means for sweeping the wavelength of light amplified by the optical amplifier,
Said optical amplifier, is resonance suppression in the element, the light emitting layer that emits light at more than 0.9μm on a GaAs substrate and 1.2μm or less of the center wavelength lambda _c is laminated, the light emitting layer is a central emission wavelength is different first in _X Ga _1-X as quantum dot layer (0 ≦ x ≦ 1) and emit light at a different second center wavelength lambda ₂ is first center wavelength lambda ₁ that emits light at a first center wavelength lambda ₁ An optical tomographic image acquisition apparatus comprising: an optical semiconductor element that is a multiple quantum dot layer including a second In _X Ga _1-X As quantum dot layer (0 ≦ x ≦ 1).

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