JP2021022684A - Wavelength sweeping type optical coherence tomography device and wavelength variable laser light source - Google Patents

Abstract

To allow for broadband laser oscillation in 1.1 μm band.SOLUTION: A wavelength sweeping type coherence tomography device includes a wavelength variable laser light source 11. The wavelength variable laser light source 11 includes a gain chip 21 emitting seed light generated by amplification natural light emission without laser oscillation by electric current impregnation, and an external resonator 22 configured to laser oscillating the light of wavelength selected from the seed light, and capable of controlling the wavelength of laser oscillation. The gain chip 21 has a quantum dot where the center wavelength of first between excitation level light emission ES1 exists in a range of 1 μm to 1.15 μm, the seed light includes at least the first between excitation level light emission ES1 having an optical intensity larger than the between ground level light emission GS, and the external resonator 22 is configured to control the wavelength of laser oscillation within a wavelength variable width, i.e., a range including the center wavelength of the first between excitation level light emission ES1.SELECTED DRAWING: Figure 2

Description

The present disclosure relates to a wavelength sweep type optical coherence tomography apparatus and a tunable laser light source.

Optical coherence tomography (OCT) is used for non-invasive medical tomography using light and the like. There are several image acquisition methods in OCT, but at present, wavelength sweep type OCT (SS-OCT) using a wavelength sweep laser light source (SS: Swept Source) that continuously changes the wavelength has become the mainstream. ing.

JP-A-2018-152573

In order to realize SS, for example, it is necessary to prepare an optical gain medium having a constant gain band capable of tunable laser oscillation. Further, in SS-OCT, the optical axis resolution of the obtained image is inversely proportional to the wavelength sweep width of the tunable laser that is the light source. Therefore, in order to obtain high optical axis resolution, a wide band laser wavelength variable Width is needed.

Further, a wavelength at which light absorption by hemoglobin or water, which is the main component of the biological sample, is minimized exists in the vicinity of 1.05 μm. Therefore, in SS-OCT, in order to achieve both high resolution and high invasion depth (image depth), a light source having a wide band wavelength tunable width centered around 1.05 μm, which has high in vivo transparency, is required. It becomes. That is, an optical gain medium capable of wideband laser oscillation in the 1.1 μm band (1.0 to 1.15 μm) is required.

If a semiconductor material can be used as the optical gain medium, a compact, lightweight, and inexpensive light source can be obtained. However, conventionally, there are few options for semiconductor materials having a wide band optical gain width in the 1.1 μm band, and it has been difficult to obtain a wide band laser oscillation.

One aspect of the present disclosure is an SS-OCT apparatus including a tunable laser light source. The disclosed wavelength variable laser light source uses a gain chip that emits seed light generated by wide-band amplified natural emission without laser oscillation by injecting a current, and a laser that emits light having a wavelength selected from the seed light. The gain chip includes an external resonator that is configured to oscillate and can control the wavelength of laser oscillation, and the gain chip has a central wavelength of emission between the first excited levels within a range of 1 μm to 1.15 μm. The seed light includes at least the first excitation level emission having a light intensity higher than that of the base level emission, and the external resonator emits light between the first excitation levels. It is configured to control the wavelength of laser oscillation within the wavelength variable width, which is the range including the central wavelength of.

Another aspect of the disclosure is a tunable laser light source. Further details will be described as embodiments described below.

FIG. 1 is a block diagram of a wavelength sweep type optical coherence tomography apparatus. FIG. 2 is a configuration diagram of a tunable laser light source. FIG. 3 is a cross-sectional view of the gain tip. FIG. 4 is an explanatory diagram of light emission between basis levels, light emission between first excited levels, and light emission between second excited levels. FIG. 5 is an EL spectrum of a gain chip having a linear ridge waveguide. FIG. 6 is an EL spectrum of a gain chip having a J-shaped ridge waveguide. FIG. 7 is a graph showing the relationship between the current and the light intensity in the emission between the basal levels, the emission between the first excited levels, and the emission between the second excited levels. FIG. 8 is a diagram showing a wavelength range of laser oscillation when the injection current is 350 mA. FIG. 9 is a diagram showing a wavelength range of laser oscillation when the injection current is 400 mA. FIG. 10 is a diagram showing a wavelength range of laser oscillation when the injection current is 500 mA. FIG. 11 is a diagram showing a wavelength range of laser oscillation when the injection current is 600 mA. FIG. 12 is a diagram showing a wavelength tunable width at which laser oscillation is possible for each injection current.

<1. Overview of wavelength sweep type optical coherence tomography equipment and tunable laser light source>

(1) The wavelength sweep type optical coherence tomography apparatus according to the embodiment includes a tunable laser light source. The wavelength-variable laser light source has a gain chip that emits seed light generated by amplified natural light emission without laser oscillation when a current is injected, and laser oscillation of light having a wavelength selected from the seed light. It includes an external resonator that is configured and can control the wavelength of laser oscillation.

The gain chip has quantum dots in the range of 1 μm to 1.15 μm in which the central wavelength of emission between the first excited levels exists. The seed light includes at least the first excited interlevel emission having a light intensity higher than that of the interbasal level emission. The external cavity is configured to control the wavelength of laser oscillation within a tunable wavelength range that includes the central wavelength of the first excitation level emission. With such a configuration, a wavelength sweep type optical coherence tomography apparatus suitable for biological use and medical use, in which the center of wavelength sweep is in the vicinity of 1.1 μm, can be obtained.

(2) The tunable wavelength is preferably in a range that does not include a longer wavelength side than the center wavelength of light emission between basis levels.

(3) The quantum dots are preferably configured such that the central wavelength of the interbasal level emission is on the longer wavelength side than 1.15 μm.

(4) The quantum dot is configured so that the center wavelength of the second excitation level emission is further present within the range of 1 μm to 1.15 μm, and the seed light is the second excitation interlevel emission. The wavelength variable width is preferably in a range further including the central wavelength of the second excitation level emission.

(5) In the seed light, the second excitation level emission preferably has a higher light intensity than the basis level emission.

(6) In the quantum dot, the center wavelength of the second excitation interlevel emission is further present in the range of 1 μm to 1.15 μm, and the center wavelength of the base level emission is from 1.15 μm. Also is configured to exist on the long wavelength side, and in the seed light, the second excited level emission has a higher light intensity than the base level emission, and the wavelength variable width has the base level. It is preferable that the range does not include the longer wavelength side than the central wavelength of the interposition emission and further includes the center wavelength of the second excited level emission.

(7) The wavelength-variable laser light source according to the embodiment has a gain chip that emits seed light generated by amplified natural light emission without laser oscillation when a current is injected, and a wavelength selected from the seed light. It includes an external resonator that is configured to oscillate an optical laser and can control the wavelength of the laser oscillation. The gain chip has quantum dots in the range of 1 μm to 1.15 μm in which the central wavelength of the first excited interlevel emission exists, and the seed light has a higher light intensity than the base level emission. The external resonator includes at least the emission between the first excitation levels having the wavelength, and the external resonator controls the wavelength of laser oscillation within a wavelength variable width range including the central wavelength of the emission between the first excitation levels. Has been done.

<2. Examples of wavelength sweep type optical coherence tomography equipment and tunable laser light source>

FIG. 1 shows a wavelength sweep type optical coherence tomography apparatus (hereinafter, “SS-OCT) 10. The SS-OCT includes a wavelength variable laser light source 11, a half mirror 12, a reference mirror 13, and a photodetector 15. The wavelength-variable laser light source 11 outputs laser light whose wavelength is continuously swept. The light output from the wavelength-variable laser light source 11 is a reference light traveling to the reference mirror 13 by the half mirror 12. , The signal light traveling to the sample 14 side. The reference light reflected from the reference mirror 13 and the signal light reflected from the sample 14 are combined in the half mirror 12 to become interference light. The interference light intensity is high. , The reflected light intensity distribution on the optical axis of the signal light can be obtained by Fourier transforming the time waveform of the interference light intensity detected by the photodetector 15.

FIG. 2 shows a tunable laser light source 11. The tunable laser light source 11 includes a gain chip 21 which is a gain medium and an external resonator 22. The gain tip 21 includes a ridge type waveguide 21A. Here, the waveguide 21A is configured as a J-shaped ridge waveguide in which one end surface 21B side of the waveguide 21A is inclined in a J-shape. The J-shaped inclination angle (inclination angle from the direction perpendicular to the end face) θ was set to 7 °. As shown in FIG. 2, the produced gain tip 21 has a rectangular shape in a plan view, a short side length of 2 mm, and a long side length of 6 mm. The gain chip 21 is not limited to the one that emits light from the end face, and may be one that emits light vertically from the gain chip 21.

The external resonator 22 includes a diffraction grating 22A and an optical fiber (lensed fiber) 23. The seed light emitted from the inclined end face 21B is guided to the diffraction grating 22A by the optical fiber 23. The diffraction grating 22A is arranged in a retrow type as an example. The diffraction grating 22A is configured so that the diffraction grating angle can be changed. By changing the diffraction grating angle, light of various wavelengths can be fed back to the gain chip 21. In addition to the diffraction grating 22A, a prism or a bandpass filter can be used as a method for feeding back light of a specific wavelength. It is also possible to use a polygon mirror, a galvano mirror, a MEMS element, an optical scanner, or the like in order to change the angle of light incident on the diffraction grating 22A. In the gain chip 21, laser oscillation is induced at the wavelength of the light returned from the external resonator 22.

The laser beam induced in the gain chip 21 is output from the end face 21C on the side opposite to the external resonator of the waveguide 21A. When measuring the output laser light, the laser light is guided by an optical fiber (lensed fiber) 24 from the end face 21C to the optical spectrum analyzer.

FIG. 3 shows a schematic cross-sectional view of the gain tip 21. The gain chip 21 is manufactured by forming a waveguide structure by semiconductor microfabrication technology and electrode vapor deposition on a crystal substrate formed by a molecular beam epitaxy method. In the gain chip 21, a plurality of InAs quantum dots (InAs-QD) are laminated in a p-in junction AlGaAs / GaAs. More specifically, the gain chip 21 includes a first electrode 31, a substrate 32, a contact layer 33, a clad layer 34, a waveguide layer 35, a clad layer 36, a contact layer 37, and a second electrode 39 from the bottom. .. An insulating layer 38 is provided between the second electrode 39 and the clad layer 36 in addition to the upper surface of the waveguide.

The waveguide layer 35 includes four active layers (InAs-QD layer) 35A. A capping layer 35B is formed on each active layer 35A. Quantum dots (InAs self-assembled quantum dots) are formed by supplying In · As, which is a raw material of quantum dots, onto a GaAs substrate in a molecular beam epitaxy apparatus.

Here, ordinary InAs-QD exhibits a wide band emission in the 1.2-1.3 μm band. The QD emits a wide band light because the QD has a size distribution and an In composition distribution. Since it has a wide emission band, QD is suitable as a wide band wavelength tunable light source. However, ordinary InAs-QD has a light emitting property in the 1.2-1.3 μm band and has a low transmittance for a biological sample containing water, so that it is not suitable for ОCT for ophthalmic applications and the like.

Therefore, in order to shift the emission wavelength of the QD to the short wavelength side, the present inventor controlled the growth conditions of the QD so that the size (height) of the QD becomes smaller than usual. As the size of the QD becomes smaller, the emission wavelength of the QD shifts to the shorter wavelength side.

Here, when forming a normal QD, an appropriate growth temperature for the growth of the QD is set. The appropriate growth temperature depends on other growth conditions, but is generally about 480 ° C. The growth temperature here is the temperature on the substrate on which the QD is formed. If the growth temperature is higher than the appropriate temperature, thermal diffusion of In is strongly generated and the QD structure is destroyed. For this reason, growth temperatures that are too high are generally undesirable.

On the other hand, the present inventor sets the growth temperature to a temperature (about 500 ° C. to 510 ° C.) slightly higher than the appropriate temperature (about 480 ° C.) to cause heat diffusion of In slightly stronger. It was. Since the thermal diffusion of In was generated slightly stronger, the QD structure could be slightly broken and the size of the QD could be reduced. Moreover, by not raising the growth temperature too high, a large collapse of the QD structure was prevented. Further, at the time of QD growth, the back pressure (As pressure (BEP)) necessary to prevent the collapse of the QD structure was applied to secure an appropriate growth rate.

Further, simply breaking the structure of the QD makes it easier for the QD to contain defects. That is, when a large non-equilibrium state is reached during the growth of QD, the diffusion of atoms becomes strong and defects in which atoms are not bonded are included. A QD containing a defect is not suitable for laser oscillation because a sufficient optical gain cannot be obtained due to carrier loss. Therefore, it is desired that the QD has few defects. Therefore, the growth conditions are controlled so that a laminated crystal in which single crystals are piled up is formed while appropriately diffusing so as not to include defects while causing thermal diffusion.

From the above viewpoint, the present inventor controls the growth temperature of the QD layer 35A and the capping layer 35B during growth, and the size is smaller than usual, there are few defects, the quality is high, and the gain is large enough to allow laser oscillation. Succeeded in producing a QD that can be obtained.

Further, the present inventor does not simply reduce the size of the QD, but the emission wavelengths of the emission between the first excitation level (ES1) and the emission between the second excitation levels (ES2) of the QD are 1 μm to 1. The size of the QD was controlled so that it was within the range of 15 μm. As a result, highly efficient laser oscillation in the vicinity of 1 μm to 1.15 μm can be obtained.

Here, a single QD has discrete electron levels in the conduction band and the valence band, respectively, due to the quantum confinement effect, and is discrete due to the recombination of electrons and holes between those levels. Shows light emission. When this becomes an aggregate of QDs with a constant size distribution, as shown in FIG. 4, discrete emission with a constant spread, that is, emission between basal levels (GS), emission between ES1, and ES2 Intermittent emission can occur. The emission energy of QD increases discretely in the order of GS, ES1, and ES2. Along with this, the emission wavelength of the QD is shortened in the order of GS, ES1, and ES2. Of these inter-level emission, the first excitation level and the second excitation level generally have a larger number of electron states than the base level, and are higher than the emission between base levels. The gain increases.

Therefore, highly efficient laser oscillation can be obtained by controlling the size of the QD so that the emission wavelengths between the levels of ES1 and ES2 exist in the band in which the laser oscillation is desired. That is, by allowing the emission wavelength between the ES1 and ES2 levels to exist in the range of 1 μm to 1.15 μm, highly efficient laser oscillation can be obtained in the vicinity of the range of 1 μm to 1.15 μm.

The growth conditions (examples) of QD adopted by the present inventor are as follows.
-QD growth rate: Approximately 0.2 M / s
-InAs supply during QD growth: Approximately 2.0 ML
-As pressure (BEP): 1.8 x ^10-5 Torr

Under the above conditions, the substrate temperature during growth of the QD layer 35A was set to about 500 ° C. to 510 ° C. This temperature is about 20 ° C. to 30 ° C. higher than the normal QD growth temperature of about 480 ° C.

Further, the substrate temperature during growth of the capping layer 35B was lowered from 450 ° C. to about 460 ° C. This temperature is about 10 ° C. to 20 ° C. higher than the normal capping layer growth temperature.

The growth conditions are not limited to the above, and from the above viewpoint, the growth conditions that can cause the thermal diffusion of In to be slightly stronger may be appropriately set.

FIG. 5 shows the electroluminescence (EL) spectra S2, S3, and S4 of the gain chip 21 produced according to the above, and the photoluminescence (PL) spectrum S1 of ordinary QD (Reg. InAs-QDs). There is. In FIG. 5, S2 is an EL spectrum when a current is injected at 5 mA, S3 is an EL spectrum when a current is injected at 3 mA, and S4 is an EL spectrum when a current is injected at 1 mA.

It can be seen that the wavelength of the emission peak between the GSs exists in the vicinity of 1160 nm (1.16 μm) at the time of low current injection of 1 mA to 5 mA. Since the wavelength of the emission peak between GS of normal QD (Reg. InAs-QDs) exists in the vicinity of 1250 nm (1.25 μm), the emission peak of the gain chip 21 is shifted to the short wavelength side by about 90 nm. doing.

FIG. 5 shows Fabry-Perot lasing with a gain tip 21 similar to the above, except that a linear ridge waveguide is formed instead of a J-shape, without using an external cavity 22. ) Are further shown in the EL spectra S11 and S12. In FIG. 5, S11 is an EL spectrum at the time of 110 mA injection, and S12 is an EL spectrum at the time of 100 mA injection.

As shown in FIG. 5, laser oscillation was observed at the wavelength of interbasal level emission (near 1160 nm) due to the injection current of 110 mA (S11). From the optical output vs. injection current characteristics, the laser oscillation threshold is estimated to be 106 mA, and at 100 mA (S12), laser oscillation does not occur. In the case of Fabry-Perot lasing without using the external resonator 22, the emission wavelength lacks variability, and the obtained emission wavelength is also about 1160 nm.

FIG. 6 shows an EL spectrum obtained from a gain chip 21 similar to the case of FIG. 5 except that the waveguide 21A is a J-shaped ridge waveguide. In this case as well, the external cavity 22 is not used. FIG. 6 shows the EL spectra when the injection current is 100 mA, 200 mA, 300 mA, 400 mA, and 500 mA.

In the case of the gain chip 21 provided with the linear ridge waveguide, as shown in FIG. 5, laser oscillation was induced by internal resonance when the injection current exceeded 106 mA. On the other hand, in the case of the gain chip 21 provided with the J-shaped ridge waveguide 21A, it can be seen that laser oscillation does not occur even if a large current exceeding 100 mA is injected.

By suppressing the laser oscillation inside the gain chip 21, amplified natural light emission can be obtained even if a large current exceeding 100 mA is injected. The injection current could be increased to, for example, about 650 mA.

If laser oscillation does not occur even if a large current is injected into the gain chip 21, the amplified natural light emission by the gain chip 21 can include not only light emission between GS but also light emission between ES1. If the injection current is made sufficiently large, the amplified natural emission by the gain chip 21 can further include the emission between ES2.

Here, when the current density supplied to the quantum dots is low, the light emission between GS is dominant. As the current density increases, the light emission between GS (center wavelength 1172 nm) is saturated, and the light emission between ES1 (center wavelength 1120 nm) begins to increase. Since ES1 has a larger number of states than GS, the gain of light emission between ES1 is larger than that of light emission between GS. For example, in FIG. 6, when the injection current is 100 mA, the light intensity of the light emission between ES1 is about the same as or slightly lower than that of the light emission between GS. However, in FIG. 6, when the injection current is 200 mA or more, the emission intensity between ES1 is larger than that between GS. According to the inventor's experiment, as shown in FIG. 7, when the injection current exceeds about 120 mA, the light intensity of the emission between ES1 becomes larger than that of the emission between GS.

When the current density is sufficiently increased, not only the light emission between ES1 but also the light emission between ES2 (center wavelength 1075 nm) increases. Since ES2 has a larger number of states than GS, the gain of light emission between ES2 can be made larger than that of light emission between GS. For example, in FIG. 6, when the injection current is 200 mA, the light intensity of the light emission between ES2 is about the same as or slightly lower than that of the light emission between GS. However, in FIG. 6, when the injection current is 300 mA or more, the light intensity of the light emission between ES2 is larger than that of the light emission between GS. According to the inventor's experiment, as shown in FIG. 7, when the injection current exceeds about 220 mA, the light intensity of the light emission between ES2 becomes larger than that of the light emission between GS.

In this way, by sufficiently increasing the injection current while suppressing the laser oscillation, it is possible to obtain the light emission between ES1 and ES2, which has a higher light intensity than the light emission between GS. Wide bandwidth can be ensured by utilizing both ES1 and ES2 light emission having different center wavelengths. In order to ensure wide bandwidth, it is preferable that the intensity of the light emission between ES2 is about the same as or higher than the light emission between ES1. As shown in FIG. 6, in order to make the intensity of the light emission between ES2 equal to or higher than that of the light emission between ES1, the injection current may be 300 mA or more, preferably 400 mA or more.

According to the EL spectrum of FIG. 6, when the injection current is 300 mA or more, light emission between ES1 and ES2 having discrete wavelengths is emitted in the vicinity of the 1100 nm band (1.1 μm band) desired in SS-OCT for living organisms. The wide bandwidth utilized can be secured. Moreover, the gain can be made larger than that of the inter-GS light emission. The wide bandwidth is also obtained by the size distribution of QD.

If the QD contains a defect due to a change in the growth condition accompanying the control of the emission wavelength of the QD, the emission between ES1 and ES2 as shown in FIG. 6 may not be obtained due to the carrier loss even if the injection current is increased. obtain. Therefore, it is preferable to appropriately control the growth conditions to reduce defects. Further, as the size of the growth substrate increases, the emission characteristics of the QD may change depending on the location on the substrate. Therefore, among the gain chips 21 manufactured in large quantities from the growth substrate, the emission of the QD such as intensity and band Those with desirable characteristics may be selected and used. That is, a current (for example, 300 mA or more) is injected into the manufactured gain chip 21 to measure the EL spectrum, and based on whether or not sufficiently large ES1 and ES2 emission is obtained in a desired wavelength band. , The gain chip 21 having more excellent QD light emission characteristics may be selected.

When the gain chip 21 (wavelength 21A is a J-shaped ridge waveguide) used in the case of FIG. 6 is used for the wavelength tunable laser light source 11 with the external resonator 22 shown in FIG. 2, laser oscillation is induced. Can be done. That is, the wideband amplified natural light emission (including the light emission between GS, the light emission between ES1 and the light emission between ES2) obtained from the gain chip 21 is used as the seed light, and the seed light is guided to the external resonator 22 by the diffraction grating 22A. Light of the selected specific wavelength returns to the gain chip 21 and oscillates by laser.

When the external resonator 22 was used, the laser oscillation was induced when the injection current was about 300 mA or more, and the laser oscillation was not induced when the injection current was less than 300 mA. That is, when the external resonator 22 was used, it was confirmed that the threshold value of laser oscillation was about 300 mA.

Since the threshold value of the laser oscillation was about 300 mA, it can be seen that the amplified natural light emission obtained in the cases of 100 mA and 200 mA shown in FIG. 6 is insufficient for the laser oscillation. In FIG. 6, the emission intensity at the wavelength of inter-GS emission (near 1172 nm) is saturated even if the injection current is increased to 300 mA or more, and an increase in the transition rate of carriers contributing to inter-GS emission cannot be expected. On the other hand, the intensity of light emission between ES1 and ES2 increases as the injection current is increased to 300 mA or more, indicating that the transition rate of carriers contributing to light emission increases. For this reason, in the gain chip 21, laser oscillation is possible by using ES1 and ES2 emission that can increase the emission intensity in response to an increase in injection current above the threshold value, without the GS emission contributing to laser oscillation. It becomes.

By changing the incident light angle of the diffraction grating 22A in the external resonator 22, light of various wavelengths can be fed back to the gain chip 21. 8 to 11 show the measurement results of the laser oscillation when the wavelength to be fed back is variously changed.

FIG. 8 shows a case where the injection current I into the gain tip 21 is 350 mA. In this case, the laser beam is generated in the range of wavelength λ _ECLpeak = 1092-1125 nm, and the tunable range Δλ is about 33 nm. From the wavelength range of laser oscillation, it can be seen that when the injection current I to the gain chip 21 is 350 mA, the emission between ES1 and the emission between ES2 are used for laser oscillation, and the emission between GS is not used for laser oscillation. ..

FIG. 9 shows a case where the injection current I into the gain tip 21 is 400 mA. In this case, the peak wavelength λ _ECLpeak of the laser beam is 1084 to 1135 nm, and the wavelength tunable range Δλ is about 51 nm. From the wavelength range of laser oscillation, it can be seen that even when the injection current I to the gain chip 21 is 400 mA, the emission between ES1 and ES2 is used for laser oscillation, and the emission between GS is not used for laser oscillation.

FIG. 10 shows a case where the injection current I into the gain tip 21 is 500 mA. In this case, the laser beam is generated in the wavelength range of λ _ECLpeak = 1078 to 1139 nm, and the tunable range Δλ is about 61 nm. From the wavelength range of laser oscillation, it can be seen that even when the injection current I to the gain chip 21 is 500 mA, the light emission between ES1 and ES2 is used for laser oscillation, and the light emission between GS is not used for laser oscillation.

FIG. 11 shows a case where the injection current I into the gain tip 21 is 600 mA. In this case, the laser beam is generated in the wavelength range of λ _ECLpeak = 1074 to 1139 nm, and the tunable range Δλ is about 65 nm. From the wavelength range of laser oscillation, it can be seen that even when the injection current I to the gain chip 21 is 600 mA, the emission between ES1 and ES2 is used for laser oscillation, and the emission between GS is not used for laser oscillation.

FIG. 12 is a graph showing the wavelength range of laser oscillation shown in FIGS. 8 to 11 with the horizontal axis representing the wavelength and the vertical axis representing the injection current. As is clear from FIG. 12, it can be seen that the larger the injection current, the wider the wavelength range in which the laser oscillates.

In particular, when the injection current I was 600 mA, a wide laser oscillating wavelength tunable width of 65 nm centered on about 1100 nm (1.1 μm) was obtained. Therefore, the SS-OCT including the wavelength tunable laser light source 11 having the gain chip 21 can sweep the wavelength in the 1.1 μm band, and can realize the OCT having high resolution and high depth of penetration.

<3. Addendum>
The present invention is not limited to the above embodiment, and various modifications are possible.

10: Wavelength sweep type optical coherence grating device 11: Wavelength variable laser light source 12: Half mirror 13: Reference mirror 14: Sample 15: Photodetector 21: Gain chip 21A: J-shaped ridge waveguide 21B: Inclined end face 21C: Opposite end face 22 : External resonator 22A: Diffraction grating 23: Optical fiber 24: Optical fiber 31: First electrode 32: Substrate 33: Contact layer 34: Clad layer 35: Wavelength layer 35A: Active layer (quantum dot layer)
35B: Capping layer 36: Clad layer 37: Contact layer 38: Insulation layer 39: Second electrode ES1: Emission between first excited levels ES2: Emission between second excited levels GS: Emission between levels

Claims (7)

A wavelength sweep type optical coherence tomography apparatus equipped with a tunable laser light source.
The tunable laser light source is
A gain chip that emits seed light generated by amplified natural light emission without laser oscillation by injecting an electric current.
An external resonator that is configured to oscillate light with a wavelength selected from the seed light and can control the wavelength of laser oscillation.
With
The gain chip has quantum dots in the range of 1 μm to 1.15 μm in which the central wavelength of emission between the first excited levels exists.
The seed light contains at least the first excited interlevel emission having a light intensity higher than that of the interbasal level emission.
The external resonator is a wavelength sweep type optical coherence stromography apparatus configured to control the wavelength of laser oscillation within a wavelength variable width within a range including the central wavelength of light emission between the first excitation levels. The wavelength sweep type optical coherence tomography apparatus according to claim 1, wherein the wavelength tunable width is a range not including a wavelength side longer than the center wavelength of light emission between base levels. The wavelength sweep type optical coherence tomography apparatus according to claim 2, wherein the quantum dots are configured such that the central wavelength of the inter-basal level emission is on a longer wavelength side than 1.15 μm. The quantum dots are configured such that the center wavelength of the second excitation level emission is further present within the range of 1 μm to 1.15 μm.
The seed light further includes the emission between the second excited levels.
The wavelength sweep type optical coherence tomography apparatus according to any one of claims 1 to 3, wherein the wavelength variable width is a range further including the central wavelength of the second excitation level emission. The wavelength sweep type optical coherence tomography apparatus according to claim 4, wherein in the seed light, the second excitation inter-level emission has a light intensity higher than that of the base inter-level emission. In the quantum dot, the center wavelength of the second excitation interlevel emission is further present in the range of 1 μm to 1.15 μm, and the center wavelength of the base level emission is longer than 1.15 μm. Configured to be on the side,
In the seed light, the inter-level emission between the second excitations has a higher light intensity than the emission between the basal levels.
The wavelength sweep according to claim 1, wherein the wavelength variable width does not include a wavelength side longer than the center wavelength of the base level emission, and further includes the center wavelength of the second excitation interlevel emission. Type optical coherence stromography device. A gain chip that emits seed light generated by amplified natural light emission without laser oscillation by injecting an electric current.
An external resonator that is configured to oscillate light with a wavelength selected from the seed light and can control the wavelength of laser oscillation.
With
The gain chip has quantum dots in the range of 1 μm to 1.15 μm in which the central wavelength of emission between the first excited levels exists.
The seed light contains at least the first excited interlevel emission having a light intensity higher than that of the interbasal level emission.
The external resonator is a tunable laser light source configured to control the wavelength of laser oscillation within a tunable width within a range including the central wavelength of the first excitation level emission.

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