JP2009049123A - Optical semiconductor device, wavelength tunable light source and optical tomographic image acquisition apparatus using the optical semiconductor device - Google Patents

Abstract

An optical semiconductor device is provided that is easy to manufacture and has a wide gain spectrum width.
In an optical semiconductor device 10 in which at least an InGaP lower cladding layer and an InGaAs active layer are stacked on an n-GaAs substrate 11 in which the resonance of light in the device is suppressed, the plane orientation as the n-GaAs substrate 11 is obtained. An n-GaAs substrate is used which is inclined at an angle of 2 degrees to 10 degrees from the (100) plane to the (111) B plane, for example, 3 degrees. Step bunching of the InGaP lower cladding layer is formed, and the thickness of the InGaAs active layer varies.
[Selection] Figure 2A

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 a fiber gyroscope and medical OCT (Optical Coherence Tomography). In the optical measurement field, the wider the wavelength band, the better the measurement resolution. Therefore, further widening of the wavelength band is required. The wavelength bandwidth of the SLD is determined by the gain spectrum width of the SLD.

  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. In recent years, a demand for a wavelength tunable light source having a wider wavelength tunable width has increased, and a wider gain spectrum width of the SOA has been desired.

As a method of widening the gain spectrum width of an optical semiconductor element such as SLD or SOA, a multilayer structure of quantum wells having different film thicknesses and compositions, that is, a method of forming a multiple quantum well layer (Patent Document 1), light propagation, etc. A method (Patent Document 2) for modulating the film thickness and composition of a quantum well in the direction is known. From the viewpoint of expanding the gain spectrum width, the latter can be expected to have a wider bandwidth. It is also possible to combine both methods.
JP-A-8-307014 JP-A-6-196809

  However, it is known that the method of modulating the film thickness / composition of the quantum well in the light propagation direction described in Patent Document 2 is very difficult to manufacture a device. Specifically, this method forms two stripe-like SiO2 masks parallel to each other at regular intervals, and by changing the mask width, an active layer grown in a region sandwiched between the masks is formed in the resonator axis direction. Although this is a method of changing the film thickness and composition, there are many technical problems in manufacturing the layer on the active layer, such as compositional modulation.

  In view of the above circumstances, an object of the present invention is to provide an optical semiconductor device that is easy to manufacture and has a wide gain spectrum width. It is another object of the present invention to provide a wavelength tunable light source and an optical tomographic image acquisition apparatus using the optical semiconductor element.

The optical semiconductor element of the present invention is an optical semiconductor element in which resonance of light in the element is suppressed,
On the GaAs substrate, at least an InGaP lower cladding layer and an InGaAs active layer are laminated,
The plane orientation of the GaAs substrate is inclined at an angle of 2 degrees or more and 10 degrees or less from the (100) plane to the (111) B plane direction.

  The inclination angle of the GaAs substrate may be not less than 2.5 degrees and not more than 7.5 degrees. The inclination angle of the GaAs substrate may be 4 degrees or more and 6 degrees or less.

  The InGaAs active layer may be an InGaAs quantum well layer. The InGaAs quantum well layer may be a single quantum well or a multiple quantum well structure.

  The InGaAs quantum well layer may be an InGaAs strained quantum well layer.

The center wavelength of the light emitted from the optical semiconductor element may be 0.9 μm or more and 1.2 μm or less. Further, the center wavelength of the emitted light may be 1.0 μm or more and 1.1 μm or less.

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.
In the optical amplifier, at least an InGaP lower cladding layer and an InGaAs active layer are stacked on a GaAs substrate whose plane orientation is inclined at an angle of 2 degrees to 10 degrees from the (100) plane to the (111) B plane direction. And an optical semiconductor element in which resonance of light in the element is suppressed.

Furthermore, 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,
The light source has at least an InGaP lower cladding layer and an InGaAs active layer stacked on a GaAs substrate whose plane orientation is inclined at an angle of not less than 2 degrees and not more than 10 degrees from the (100) plane to the (111) B plane direction, And it has the optical semiconductor element by which the resonance of the light in an element is suppressed, It is characterized by the above-mentioned.

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, at least an InGaP lower cladding layer and an InGaAs active layer are stacked on a GaAs substrate whose plane orientation is inclined at an angle of 2 degrees to 10 degrees from the (100) plane to the (111) B plane direction. And an optical semiconductor element in which resonance of light in the element is suppressed.

  In the process of earnestly studying to achieve the above-mentioned object, the inventor suppresses the resonance of light in an element such as SLD or SOA, and at least an InGaP lower cladding layer and an InGaAs active layer are stacked on a GaAs substrate. In the optical semiconductor device, the gain spectrum width depends on the crystal orientation of the main surface of the GaAs substrate, in particular, the surface orientation of the GaAs substrate is changed from the (100) plane to the (111) B plane direction by 2 degrees or more. It has been found that the gain spectrum width increases when tilted by a degree or less.

  The reason why the gain spectrum width is increased by slightly tilting the GaAs substrate is not clearly clarified, but can be estimated as follows. When growing a GaInP crystal, it is known that the characteristics including the band gap of the GaInP crystal vary greatly depending on the growth conditions. The cause is that when the GaInP crystal grows on the group III sublattice, the order of the arrangement of Ga and In changes. When a GaInP crystal is grown on a GaAs substrate whose plane orientation is inclined from 2 degrees to 10 degrees from the (100) plane to the (111) B plane direction, the formation of one variant of the natural superlattice is promoted, and the entire GaInP crystal The degree of order tends to increase.

  As a result of the increase in the degree of order of the GaInP crystal, step bunching due to the density of the atomic layer step spacing is likely to occur. When a thin layer such as an InGaAs quantum well active layer (emission wavelength: 0.9 to 1.2 μm) with a thickness of several nanometers is formed on top of the GaInP layer where step bunching occurs, the layer thickness fluctuates and the substrate surface Therefore, the thickness of the active layer varies. As described above, when the thickness of the active layer varies, the gain spectrum width of the optical semiconductor element increases. InGaAs, in particular, has a larger lattice constant than GaAs and GaInP. Therefore, when the thickness of the InGaAs thin film is thin, the InGaAs thin film is subjected to compressive strain and becomes a strained layer. The effect on is increased.

  That is, when producing a semiconductor laser or the like, it is important to suppress step punching in order to improve the light emission characteristics. However, the inventor of the present invention has an inclination angle that easily causes step punching. It has been found that the gain spectrum width can be widened by using a substrate.

  In view of this, the present inventor, in an optical semiconductor device in which an InGaP lower cladding layer and an InGaAs active layer are stacked on a GaAs substrate, the maximum self-emission spectrum reflecting the tilt angle of the substrate and the gain spectrum width of the semiconductor device. The relationship with width was examined in detail. FIG. 1 shows the result. As can be seen, when the tilt angle is 5 degrees, the widest gain spectrum width is obtained, and the gain spectrum width becomes narrower as the tilt angle is smaller than 5 degrees or larger than 5 degrees. Recognize. Based on this knowledge, the present invention sets the angle of 2 degrees or more and 10 degrees or less where the gain spectrum width is wider than the case where the substrate is not inclined as the upper and lower limits of the inclination angle. In particular, when the substrate tilt angle is 2.5 degrees or more and 7.5 degrees or less, it is possible to obtain a gain spectrum width that is clearly wider than when the substrate is not tilted, and when the substrate tilt angle is 4 degrees or more and 6 degrees or less. For example, it is clear from FIG. 1 that a wider gain spectrum width can be obtained.

  As described above, according to the present invention, step bunching is formed by using a GaAs substrate inclined at an angle of 2 degrees or more and 10 degrees or less from the (100) plane to the (111) B plane direction. A wide optical semiconductor element can be obtained. Further, when the substrate tilt angle is 2.5 degrees or more and 7.5 degrees or less, a wider gain spectrum width can be obtained, and when the substrate tilt angle is 4 degrees or more and 6 degrees or less, the bandwidth is further increased. Gain spectrum width is obtained.

  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. Thus, the wavelength of the emitted light can be easily changed over a wide band.

  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. The optical wavelength band can be broadened, and an optical tomographic image with high resolution can be acquired.

  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.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 2A is a schematic sectional elevation view showing the optical semiconductor device according to the first embodiment of the present invention, and FIG. 2B is a schematic sectional view. As shown in the figure, the optical semiconductor device 10 of this embodiment includes an n-GaAs substrate 11 whose plane orientation is inclined by 3 degrees from the (100) plane to the (111) B plane, and an n-GaAs buffer sequentially stacked thereon. Layer (0.2 μm thickness) 12, n-GaInP lower cladding layer (2.0 μm thickness) 13, GaAs light guide layer 14, InGaAs strained quantum well layer 15, GaAs light guide layer 16, p-GaInP upper cladding layer 17, GaAs etching A stop layer 18, a p-GaInP upper second cladding layer 19, an n-AlGaInP current blocking layer 20, a p-AlGaInP upper third cladding layer 21, and a p-GaAs contact layer 22 are provided. A p-electrode 23 is formed on the p-type GaAs contact layer 22, and an n-electrode 24 is formed on the back side of the n-type GaAs substrate 11. The quantum well structure is a single quantum well structure with an emission wavelength of 1.0 μm. The element length of the optical semiconductor element 10 is 1.5 mm.

When the semiconductor laser of this embodiment is manufactured, crystal growth is performed by a metal organic chemical vapor deposition (MOCVD) method as an example. TEG (triethylgallium), TMA (trimethylaluminum), TMI (trimethylindium), AsH3 (arsine), PH3 (phosphine) as source gas, SiH4 (silane) as n-type dopant, DEZ (diethylzinc) as p-type dopant or Cp ₂ Mg (biscyclopentadienyl magnesium) is used. Next, a specific method for manufacturing an optical semiconductor element will be described.

  First, an n-GaAs buffer layer (0.2 μm thickness) 12, n − is grown by crystal growth by MOCVD on an n-GaAs substrate 11 having an inclination angle of 5 degrees from the (100) plane to the (111) B plane. GaInP lower cladding layer (2.0 μm thick) 13, GaAs light guide layer 14, InGaAs strained quantum well layer 15, GaAs light guide layer 16, p-GaInP upper cladding layer 17, GaAs etching stop layer 18 and p-GaInP upper second The clad layer 19 is laminated in this order.

Next, a SiO ₂ selective growth mask serving as a dielectric mask is formed on the p-GaInP upper second cladding layer 19, and a part of the p-GaInP upper second cladding layer 19 is removed by etching. At this time, a GaAs etching stop layer 18 is buried between the p-GaInP upper cladding layer 17 and the p-GaInP upper second cladding layer 19 in order to control the etching range. Note that the portion of the InGaAs strained quantum well layer 15 below the p-GaInP upper second cladding layer 19 that has not been removed by etching functions as an optical waveguide.

Then, the n-AlGaInP current blocking layer 20 is embedded in the portion removed by etching by crystal growth by the second MOCVD method. Further, after removing the SiO ₂ mask, the upper portion of the p-AlGaInP so as to cover the entire optical waveguide portion (below the p-GaInP upper second cladding layer 19) and the buried layer portion (n-AlGaInP current blocking layer 20). A third cladding layer 21 is laminated, and a p-GaAs contact layer 22 is further laminated thereon. The optical waveguide can be formed by a photolithography technique using a SiO ₂ mask and an etching technique. Thereafter, the substrate is polished until the total thickness becomes about 100 μm, and finally the n-side electrode 24 is formed on the back surface of the substrate and the p-side electrode 23 is formed on the optical waveguide side by vapor deposition and heat treatment. The composition and film thickness of each layer are set to values that enable single mode waveguide. Here, the optical semiconductor element 10 having the buried ridge stripe structure is described as an example, but other structures such as an internal stripe structure may be used. The InGaAs strained quantum well layer 15 may have a single quantum well or a multiple quantum well structure.

  Further, the optical semiconductor element 10 has an AR coating applied to the end faces 25 and 26 from which the light L is emitted, as shown in FIG. Further, the InGaAs strained quantum well layer 15 which is a waveguide is inclined by 7 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.

  As apparent from the above description, the optical semiconductor element 10 of the present embodiment is formed using the GaAs substrate 11 whose plane orientation is inclined by 5 degrees from the (100) plane to the (111) B plane direction. Step bunching is formed, and the thickness of the InGaAs strained quantum well layer 15 varies, so that the gain spectrum width of the optical semiconductor element 10 is widened. In particular, when the thickness of the InGaAs strained quantum well layer 15 is small, the InGaAs strained quantum well layer 15 becomes a compressive strained layer, and the influence of the variation in the layer thickness on the gain spectrum width increases.

  In the above-described embodiment, a substrate having a plane orientation tilt angle of 5 degrees is used. However, for the reasons described above, this tilt angle can be freely selected within a range of 2 degrees to 10 degrees. In particular, when the substrate tilt angle is not less than 2.5 degrees and not more than 7.5 degrees, a gain spectrum width having a broad band can be obtained as compared with the case where the substrate is not tilted. If the tilt angle of the substrate is 4 degrees or more and 6 degrees or less, a wider gain spectrum width can be obtained.

  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 uses the optical semiconductor element 10 described in the first embodiment as an optical amplifier, and a Littman arrangement type external resonator type wavelength tunable using the diffraction grating 32 and the mirror 33 as wavelength selection means. FIG. 3 shows a schematic configuration diagram of the laser device.

  In the wavelength tunable laser device 30, a resonator is constituted by the mirror 33 and the output mirror 31 (transmittance ???%). The spontaneously emitted light emitted from the optical semiconductor element 10 toward the diffraction grating 32 is collected by the lens 34 a to become parallel light and enters the diffraction grating 32. Of the light wavelength-dispersed by the diffraction grating 32, light having a wavelength that is perpendicularly incident on the mirror 33 is reflected by the mirror 33 and enters the diffraction grating 32 as return light. This light resonates in the resonator composed of the mirror 33 and the output mirror 31, and is emitted as laser light L from the output mirror 31 to the optical isolator 36 side. The optical isolator 36 has a function of preventing 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 36 is condensed by the condenser lens 34b and enters the optical fiber FB1. In the Littman arrangement type wavelength selection means, the wavelength of the return light can be changed and the resonance light frequency (laser oscillation wavelength) can be changed by rotating the mirror 33. 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. In the wavelength tunable laser device 30 using the optical semiconductor element 10 stacked on the GaAs substrate 11 inclined at 3 degrees as an optical amplifier according to the present embodiment, the wavelength of the laser light is changed over the wavelength band of 80 nm. I was able to. On the other hand, for the purpose of comparison, the present inventor has proposed a wavelength tunable laser using an optical semiconductor device fabricated on a non-tilted GaAs substrate, except that the GaAs substrate is not tilted. A device was prepared and the wavelength variable range was measured in the same manner, and it was 50 nm.

  As is apparent from the above description, the wavelength tunable laser device 30 uses the optical semiconductor element 10 that is small, easy to handle, and has a wide gain spectrum width as an optical amplifier. The wavelength can be changed.

  Note that the wavelength variable width of the laser light described above is different in the structure of the present invention depending on the strain amount of the InGaAs strained quantum well layer 15, and the variable width is larger on the long wavelength side where the strain amount is large. There was a tendency to expand. However, as the wavelength approaches 1.2 μm, it is difficult to increase the wavelength and the characteristics tend to deteriorate, so the 1.0 to 1.1 μm band is the range in which the effect of the present invention can be obtained to the maximum.

  Here, a laser resonator is configured by the mirror 33 and the output mirror 31, but one end face of the optical semiconductor element 10 may be used instead of the output mirror 31. In this case, the optical waveguide of the optical semiconductor element 10 has an oblique waveguide configuration with respect to the normal direction at the end face on the diffraction grating side, and the normal line of the end face at the other end face that serves as the output mirror 31. What is necessary is just to comprise so that it may become a waveguide parallel to a direction.

  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 polygon mirror 41 is used instead of the mirror 33. As the polygon mirror 41 rotates, the oscillation wavelength of the laser light La emitted from the wavelength sweep laser device 40 is periodically swept.

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

  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. Note that the apparatus of this example has a mechanism for guiding the light obtained by dividing the interference light L4 into two by the optical fiber coupler 3 to the photodetectors 142a and 142b, and performing balance detection in the computing 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 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. The spectroscopic interference light L4 incident on the spectroscopic means 242 is split and emitted toward the light detecting means 244. 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.

  The operation of the optical tomographic image acquisition apparatus 200 having the above configuration will be described below. 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 into the body cavity and is irradiated onto the irradiation target S. At this time, the measurement light L1 emitted from the optical probe 130 scans the irradiation target S one-dimensionally. 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.

  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.

The figure which shows the relationship between the inclination-angle of a board | substrate and the maximum self-emission spectrum width 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 Optical semiconductor element 11 n-GaAs substrate 13 n-GaInP lower clad layer 15 InGaAs strained quantum well layers 25 and 26 End face 30 Wavelength variable laser device 32 Diffraction grating 33 Mirror 40 Wavelength sweep laser device 41 Polygon mirror 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 adjustment means 130 Probe 140, 240, 330 Interference light detection means
La Laser light Lb Low coherence light

Claims (10)

An optical semiconductor element in which resonance of light in the element is suppressed,
On the GaAs substrate, at least an InGaP lower cladding layer and an InGaAs active layer are laminated,
An optical semiconductor element, wherein the plane orientation of the GaAs substrate is inclined at an angle of 2 degrees to 10 degrees from the (100) plane to the (111) B plane direction.   2. The optical semiconductor element according to claim 1, wherein an inclination angle of the GaAs substrate is 2.5 degrees or more and 7.5 degrees or less.   3. The optical semiconductor element according to claim 2, wherein the inclination angle of the GaAs substrate is not less than 4 degrees and not more than 6 degrees.   4. The optical semiconductor device according to claim 1, wherein the InGaAs active layer is an InGaAs quantum well layer.   5. The optical semiconductor device according to claim 4, wherein the InGaAs quantum well layer is an InGaAs strained quantum well layer.   6. The optical semiconductor element according to claim 1, wherein the center wavelength of the emitted light is 0.9 μm or more and 1.2 μm or less.   7. The optical semiconductor element according to claim 6, wherein the center wavelength of the emitted light is 1.0 μm or more and 1.1 μm or less. 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,
In the optical amplifier, at least an InGaP lower cladding layer and an InGaAs active layer are stacked on a GaAs substrate whose plane orientation is inclined at an angle of 2 degrees to 10 degrees from the (100) plane to the (111) B plane direction. An optical semiconductor element in which resonance of light in the element is suppressed. 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,
The light source has at least an InGaP lower cladding layer and an InGaAs active layer stacked on a GaAs substrate whose plane orientation is inclined at an angle of not less than 2 degrees and not more than 10 degrees from the (100) plane to the (111) B plane direction, An optical tomographic image acquisition apparatus having an optical semiconductor element in which resonance of light in the element is suppressed. 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, at least an InGaP lower cladding layer and an InGaAs active layer are stacked on a GaAs substrate whose plane orientation is inclined at an angle of 2 degrees to 10 degrees from the (100) plane to the (111) B plane direction. An optical tomographic image acquisition apparatus comprising an optical semiconductor element in which resonance of light within the element is suppressed.

Images