JP2010192528A - Semiconductor optical element and wavelength sweeping light source using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor optical element high in response speed of deflection of outgoing light; and to provide a wavelength sweeping light source including the semiconductor optical element and capable of suppressing mode hop in wavelength sweeping in real time. <P>SOLUTION: The semiconductor optical element includes: an n-type semiconductor substrate 21; a light-emitting region 22 formed on the n-type semiconductor substrate 21, emitting light and having an active layer 24 for transmitting the light; and a refractive index adjustment region 23 optically-coupled to the active layer 24 of the light-emitting region 22, having a waveguide layer 26 for transmitting light transmitted from the active layer 24, and adjusting an equivalent refractive index of the waveguide layer 26 in response to an injected refractive index adjustment region injection current I<SB>r</SB>; wherein the intersection angle &theta;<SB>1</SB>between an emission end face 20a on the refractive index adjustment region 23 side and the optical axis of the waveguide layer 26 is a non-right angle, an equivalent refractive index n<SB>1</SB>of the waveguide layer 26 is adjusted by the refractive index adjustment region injection current I<SB>r</SB>, and thereby an emission angle &theta;<SB>2</SB>of light emitted from the emission end face 20a with respect to the emission end face 20a is varied. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a semiconductor optical device, and more particularly to a semiconductor optical device capable of deflecting emitted light and a wavelength swept light source using the same.

  In the fields of frequency domain interferometry such as optical coherence tomography (OCT), and spectroscopic analysis using optical fiber sensing, gas sensors, and the like, a wavelength swept light source capable of broadband wavelength sweeping is used. The light source usually requires single-mode, mode-hop-free and high-speed wavelength sweep in order to perform high-sensitivity and high-speed measurement.

  High-precision optical axis adjustment is necessary to realize a high-speed and mode-hop-free light source. For this reason, a correction mechanism for readjusting the optical axis of each optical component constituting the light source after assembly is generally used for the light source. For example, a method is used in which the position of an optical component such as a lens or a diffraction grating constituting an external resonator is changed using a piezoelectric element to correct an optical axis shift.

  However, the addition of such mechanical parts complicates the structure of the light source and causes deterioration in assembly accuracy. In addition, such a mechanical mechanism is easily affected by environment such as vibration and temperature, and once the optical axis is corrected, the optical axis is shifted again if the arrangement of the optical components fluctuates with time. There was also a problem.

  In view of this, a semiconductor optical device that can finely adjust the optical axis without using a mechanical mechanism has been proposed (see, for example, Patent Document 1).

The semiconductor optical device disclosed in Patent Document 1 is composed of a metal thin film resistor in the vicinity of an oblique end surface where the normal of the emission end surface formed by cleavage and the active layer constituting the waveguide intersect at an angle θ _1. Provided with partial heating means. And the deflection | deviation of the light radiate | emitted from a semiconductor optical element is implement | achieved by changing the refractive index of the oblique end surface vicinity with the heat from a partial heating means.

  Also, if this semiconductor optical device is used as an external resonator-type wavelength-swept light source, the light emitted from the semiconductor optical device is deflected to correct the optical axis shift and realize a mode-hop-free wavelength-swept light source can do.

JP 2007-273549 A ([0027] to [0032], FIG. 1)

  However, the semiconductor optical device disclosed in Patent Document 1 has a problem that the response speed of the polarized light of the emitted light is slow because the refractive index is changed by heat. Therefore, even if this element is used as a wavelength swept light source that sweeps wavelengths at high speed, it is difficult to suppress mode hops during wavelength sweeping in real time.

  The present invention has been made in order to solve such a conventional problem, and provides a semiconductor optical device with a high response speed of deflection of emitted light, and also includes the semiconductor optical device described above, during wavelength sweeping. It is an object of the present invention to provide a wavelength-swept light source that can suppress the mode hop in real time.

  The semiconductor optical device of the present invention includes an n-type semiconductor substrate, an active layer formed on the n-type semiconductor substrate, emitting light and propagating the light, and the active layer optically on the n-type semiconductor substrate. In a semiconductor optical device comprising a waveguide layer that is coupled and propagates light propagated from the active layer, a light emitting region having the active layer, a refractive index adjustment region having the waveguide layer and injected A refractive index adjustment region for adjusting an equivalent refractive index of the waveguide layer with respect to light propagated from the active layer according to an injection current, and adjusting the refractive index to emit the light propagated through the waveguide layer. The intersection angle between the region-side emission end face and the optical axis of the waveguide layer is non-right angle, and the equivalent refractive index of the waveguide layer is adjusted by the refractive index adjustment region injection current. The emitted light with respect to the exit end face It has a structure of changing the elevation angle.

  With this configuration, by providing a refractive index adjustment region that adjusts the equivalent refractive index of the waveguide layer according to the injected current, the response speed of the deflection of the emitted light can be increased.

  Further, in the semiconductor optical device of the present invention, the light emitting region has a first p-type cladding layer laminated on the active layer, and the refractive index adjustment region is laminated on the waveguide layer. A second p-type cladding layer having a doping concentration in the thickness direction of the second p-type cladding layer in contact with the waveguide layer in the refractive index adjustment region is a maximum value within a predetermined distance from the upper end of the waveguide layer. It has the structure formed so that it may have.

  With this configuration, the doping concentration in the thickness direction of the second p-type cladding layer in contact with the waveguide layer in the phase adjustment region is maximized within a predetermined distance from the waveguide layer. Electron overflow caused by a small conduction band discontinuity ΔEc with the 2p-type cladding layer can be suppressed, and thereby the maximum phase adjustment amount can be increased.

  The semiconductor optical device of the present invention has a configuration in which the range of the predetermined distance is 25 to 150 nm.

  With this configuration, since the doping concentration in the thickness direction of the second p-type cladding layer has a maximum value in a range of 25 to 150 nm from the waveguide layer, electrons overflowing from the waveguide layer can be effectively blocked. The maximum phase adjustment amount can be greatly expanded.

  In the semiconductor optical device of the present invention, a third p-type cladding layer is formed on the first p-type cladding layer in the light emitting region and the second p-type cladding layer in the refractive index adjustment region, and the third p-type cladding layer is formed. A separation groove having a predetermined width is formed at a boundary portion between the light emitting region and the refractive index adjustment region of the layer.

  With this configuration, since the separation groove is provided at the boundary between the light emitting region and the phase adjustment region of the third p-type cladding layer, the separation resistance between the regions can be increased, and leakage from the light emission region to the phase adjustment region can be achieved. The current can be greatly reduced.

In the semiconductor optical device of the present invention, the doping concentration at the end point in the thickness direction of the third p-type cladding layer is larger than the doping concentration at the start point in the thickness direction, and 1.0 × 10 ¹⁸ (/ cm ³ ) to It has the structure set to the range of 2.5 * 10 < ¹⁸ > (/ cm < ³ >).

With this configuration, the doping concentration at the end point in the thickness direction of the third p-type cladding layer (the upper layer side far from the active layer and the waveguide layer) is doped at the start point in the thickness direction (the lower layer side close to the active layer and the waveguide layer). Since it is larger than the concentration and is set in the range of 1.0 × 10 ¹⁸ (/ cm ³ ) to 2.5 × 10 ¹⁸ (/ cm ³ ), it can be conducted without increasing the series resistance in the thickness direction. Waveguide loss can be reduced.

  The wavelength swept light source of the present invention reflects any one of the semiconductor optical elements described above, a diffraction grating that diffracts light emitted from the emission end face of the semiconductor optical element, and light diffracted by the diffraction grating. A rotatable mirror that re-enters the diffraction grating in a reverse optical path, and the diffraction grating diffracts the re-incident light and feeds it back to the emission end face of the semiconductor optical device. A Litman-type wavelength sweeping light source that sweeps the wavelength of light emitted from the emitting end face by rotating a moving mirror, and supplies a light emitting region injection current for emitting light to the light emitting region of the semiconductor optical device. A light emitting region current supply unit; a refractive index adjustment region current supply unit that supplies the refractive index adjustment region injection current for adjusting the refractive index of the waveguide layer to the refractive index adjustment region of the semiconductor optical device; Semiconductor light An output detection unit that detects the output of light emitted from the child, and based on the output detected by the output detection unit, detects a discontinuous point of the output caused by the mode hop, and eliminates the discontinuous point And a controller for controlling the refractive index adjustment region injection current.

  With this configuration, since the semiconductor optical device having a high response speed of outgoing light deflection is provided, mode hops during wavelength sweeping can be suppressed in real time.

  Further, in the wavelength swept light source of the present invention, the control unit calculates a time differential value of the output detected by the output detection unit, and controls the refractive index adjustment region injection current based on the time differential value. have.

  With this configuration, the occurrence of a mode hop can be detected.

  Further, in the wavelength swept light source of the present invention, the control unit detects the discontinuous point caused by the mode hop, so that the time differential value of the output detected by the output detection unit is sequentially calculated, and the time differential When the absolute value of the value is equal to or greater than a predetermined mode hop threshold, the refractive index adjustment region injection current is continuously increased or decreased, and the absolute value of the time differential value is less than a predetermined mode hop threshold. When this happens, the increase / decrease of the refractive index adjustment region injection current is stopped.

With this configuration, the emission angle θ ₂ of the emitted light of the semiconductor optical device continuously changes according to the continuous increase / decrease of the refractive index adjustment region injection current, so that the deviation of the optical axis can be corrected.

  The wavelength swept light source of the present invention converts the light emitted from the emission end face of the semiconductor optical device into parallel light, and emits the parallel light to the diffraction grating, and the reflection of the rotating mirror. A space sandwiched between a plane extending the surface and a plane extending the diffraction surface of the diffraction grating toward the rotation center position of the rotation mirror, and the predetermined incident position of the diffraction grating and the rotation of the rotation mirror A fixed mirror that is disposed at a position between the center position and reflects the parallel light emitted from the collimating lens toward a predetermined incident position of the diffraction grating, wherein the semiconductor optical element and the collimating lens are The optical path from the semiconductor optical element to the diffraction grating is disposed on the space side including the diffraction grating in two spaces separated by a plane obtained by extending the reflection surface of the rotation mirror. A distance r from the rotation center position to a predetermined incident position of the diffraction surface of the diffraction grating, and a distance from the rotation center position to a plane extending the reflection surface of the rotation mirror. L2, an optical path length L3 from the effective resonance end face of the semiconductor optical element to the fixed mirror, an optical path length L4 from the fixed mirror to a predetermined incident position of the diffraction plane of the diffraction grating, and a diffraction plane of the diffraction grating from the fixed mirror Between the light incident angle α and the light incident angle α, a relationship r = (L3 + L4−L2) / sin α is established.

  With this configuration, since the optical path from the semiconductor optical element to the diffraction grating does not cross the rotating mirror, high-speed wavelength sweep can be performed.

  The present invention provides a semiconductor optical device having a fast response speed of outgoing light deflection, and a wavelength-swept light source that includes the semiconductor optical device and can suppress a mode hop at the time of wavelength sweep in real time.

1 is a perspective view, a top view, and a cross-sectional view showing a configuration of a semiconductor optical device according to a first embodiment of the present invention. Doping concentration distribution diagram of second p-type cladding layer in refractive index adjustment region Doping concentration distribution diagram of the third p-type cladding layer in the refractive index adjustment region A top view for explaining deflection of emitted light of the semiconductor optical device of the first embodiment Graph showing the relationship between the refractive index adjustment region injection current I _r and the equivalent refractive index n ₁ Graph showing the relationship between the refractive index adjustment region injection current I _r and the emission angle theta ₂ A graph schematically showing the relationship between the reverse bias voltage V _b and the emission angle θ ₂ The perspective view which shows a part of manufacturing process of the semiconductor optical element of 1st Embodiment. The perspective view which shows a part of manufacturing process of the semiconductor optical element of 1st Embodiment. The top view which shows the structure of the wavelength sweep light source of the 2nd Embodiment of this invention. The schematic diagram for demonstrating the conditions for the wavelength sweep light source of 2nd Embodiment to sweep a wavelength continuously. Schematic graph explaining the mechanism by which mode hops occur The perspective view which shows the structure of the wavelength swept light source of the 3rd Embodiment of this invention. The schematic diagram for demonstrating the conditions for the wavelength swept light source of 3rd Embodiment to sweep a wavelength continuously The disassembled perspective view of the rotation mirror of the wavelength sweep light source of 3rd Embodiment

  Hereinafter, embodiments of a semiconductor optical device according to the present invention and a wavelength swept light source using the same will be described with reference to the drawings.

(First embodiment)
FIG. 1 shows a first embodiment of a semiconductor optical device according to the present invention. 1A is a perspective view of the semiconductor optical device 10, FIG. 1B is a top view, and FIG. 1C is a cross-sectional view taken along line AA of FIG. 1B.

  That is, the semiconductor optical device 10 is formed on the n-type semiconductor substrate 21, the active layer 24 that emits light and propagates the light, and the active layer 24 and the optical layer on the n-type semiconductor substrate 21. And a waveguide layer 26 that propagates light propagated from the active layer 24.

Further, the semiconductor optical device 10 includes a light emitting region 22 including an active layer 24, a waveguide layer 26, guide for light propagating from the active layer 24 depending on the implanted refractive index adjustment region injection current I _r And a refractive index adjustment region 23 for adjusting the equivalent refractive index of the waveguide layer 26.

In the semiconductor optical device 10, the intersection angle θ ₁ between the emission end face 20 a on the refractive index adjustment region 23 side that emits the light propagated through the waveguide layer 26 and the optical axis of the waveguide layer 26 is non-right angle. By equivalent refractive index n ₁ of the waveguide layer 26 is adjusted by the refractive index adjustment region injection current I _r, the emission angle theta ₂ is changed with respect to the emitting end face 20a of the light emitted from the emitting end face 20a.

Hereinafter, the configuration of the semiconductor optical device 10 will be described in more detail.
The semiconductor optical device 10 has an n-type semiconductor substrate 21 (hereinafter simply referred to as the substrate 21) made of InP (indium / phosphorus). The substrate 21 has a substantially constant doping concentration (for example, 1 × 10 ¹⁸ / cm ³ ).

  A light emitting region 22 is formed on one end side of the substrate 21 (right end side in FIGS. 1B and 1C) and refracted on the other end side (left end side in FIGS. 1B and 1C). A rate adjustment region 23 is formed.

  The active layer 24 is made of InGaAsP (indium, gallium, arsenic, phosphorus) and is formed in the center on the substrate 21 with a substantially constant width (for example, 5 μm). A first p-type cladding layer 25 made of InP is formed on the active layer 24 with a predetermined thickness (for example, 250 nm). The active layer 24 referred to here includes a multiple quantum well layer (MQW) and a light separation confinement (SCH) layer sandwiching the multiple quantum well layer (MQW).

  On the other hand, a waveguide layer 26 made of InGaAsP is formed in the center on the substrate 21 on the refractive index adjustment region 23 side so as to be optically coupled to the active layer 24. Here, the active layer 24 has a gain with respect to light in a certain wavelength range, and is formed so as to guide light in the length direction. On the other hand, the waveguide layer 26 mainly has a waveguide function for the light, but may have a gain for the light.

Waveguide layer 26, the carriers are injected by the application of the refractive index adjustment region injection current I _r from an external current source, the refractive index by the plasma effect is reduced.

  The energy gap of the waveguide layer 26 is set to be larger than the energy of the light generated in the active layer 24, and the light absorption in the waveguide layer does not occur.

  A second p-type cladding layer 27 is formed on the waveguide layer 26 so as to be continuous with substantially the same thickness as the first p-type cladding layer 25. The connection position of the active layer 24 and the waveguide layer 26 and the connection position of the first p-type cladding layer 25 and the second p-type cladding layer 27 are the same.

  A third p-type cladding layer 28 made of InP is formed on and on the first p-type cladding layer 25 and the second p-type cladding layer 27. A buried layer 29 made of p-type InP is formed on the substrate 21 on the side of the active layer 24, and a buried layer 30 made of n-type InP is formed on the buried layer 29. .

  The boundary portion between the light emitting region 22 and the refractive index adjustment region 23 of the third p-type cladding layer 28 is a bridge portion 31 where the active layer 24 and the waveguide layer 26 are optically coupled, and the left and right sides thereof. It is comprised from the isolation | separation groove | channels 32 and 33 provided in the area | region. The bridge portion 31 has, for example, a length of 50 μm, a width of 15 μm, and a depth of about 7.5 μm with respect to the size of the semiconductor optical device 10 (for example, a length of 1000 μm, a width of 400 μm, and a thickness of 100 μm).

  The separation grooves 32 and 33 are formed not only by the third p-type cladding layer 28 but also by performing an etching process deeper than the interface between the buried layers 29 and 30 and the substrate 21.

  The length of the bridging portion 31 in the element length direction is advantageously longer in order to obtain a high isolation resistance, but the emission intensity is reduced when the length of the active layer 24 is reduced, so that the range is from 25 μm to 100 μm. It is preferable.

  Further, the narrower the width of the bridging portion 31 is, the higher the separation resistance is. However, it is necessary to provide a margin for the width of the active layer 24 and the waveguide layer 26 (for example, 2 μm), and the light spot size is large. In consideration of the above, it is preferable to set the range of 10 μm to 20 μm. The depth is preferably in the range of 5 μm to 10 μm because etching of holes deeper than the interface between the substrate 21 and the buried layers 29 and 30 can be restricted.

  A contact layer 34 made of InGaAs (indium gallium arsenide) is formed on the third p-type cladding layer 28 on the light emitting region 22 side with the separation grooves 32 and 33 as a boundary, and the second layer on the refractive index adjusting region 23 side. Similarly, a contact layer 35 made of InGaAs is formed on the 3p-type cladding layer 28.

  A first upper electrode 36 and a second upper electrode 37 made of gold (Au), platinum (Pt), and titanium (Ti) are formed on the contact layers 34 and 35 by vapor deposition. A lower electrode 38 made of gold (Au), germanium (Ge), and platinum (Pt) is formed on the entire lower surface of the substrate 21 by vapor deposition.

  By the way, in the conventional semiconductor optical device having the refractive index adjustment region, since the conduction band discontinuity ΔEc between the waveguide layer and the p-type cladding layer in the refractive index adjustment region is small, an overflow of electrons easily occurs. As a result, the maximum refractive index adjustment amount is limited.

  As a result of conducting various experiments on the semiconductor optical device 10 having the above structure, the applicant of the present invention has a characteristic distribution in the doping concentration of the second p-type cladding layer 27 on the waveguide layer 26 in the refractive index adjustment region 23, that is, It has been found that by providing a distribution having a maximum within a predetermined distance from the waveguide layer 26, it is possible to suppress the overflow in the refractive index adjustment region 23 and expand the maximum refractive index adjustment range without flowing a wasteful current.

  FIG. 2 shows this configuration. As a result of various experiments, the doping concentration in the thickness direction of the second p-type cladding layer 27 in contact with the waveguide layer 26 in the refractive index adjustment region 23 as in the characteristic F is within a predetermined range from the upper end of the waveguide layer 26, particularly By forming so as to have a maximum value in the range of 25 to 150 nm, the effect of suppressing the overflow of injected carriers in the refractive index adjustment region 23 is enhanced, and it is not necessary to flow a useless current that does not contribute to the refractive index change. As a result, it was found that high efficiency of the entire device can be realized. The characteristic F ′ is an example of an actual doping concentration distribution.

  Thus, it has been found that setting the maximum position relatively close to the waveguide layer 26 is effective in blocking carriers (electrons) that diffuse as reactive currents. In particular, improvement in efficiency in the high implantation region was confirmed.

  The doping profile of the third p-type cladding layer 28 is important for determining the series resistance and the waveguide loss.

If the series resistance in the film thickness direction of the light emitting region 22 is high, a mode hop is likely to occur when the semiconductor optical device 10 is used as an external resonator type laser light source. This is a phenomenon that occurs because the refractive index changes due to Joule heat generated by current injection, resulting in a long wave. Although referred to as a current difference mode hopping current from mode to change the mode of the next [Delta] I _hop in the injected current Fabry-Perot modes, the higher the mode hopping current [Delta] I _hop, stable operation in one mode This is preferable because the range is wide.

That is, in order to increase the mode hop current ΔI _hop , it is desirable to set the doping concentration high and lower the series resistance. On the other hand, if the doping concentration in the lower layer region (starting point portion in the thickness direction) close to the active layer 24 and the waveguide layer 26 is set high, the light absorption loss in the vicinity of the active layer 24 and the waveguide layer 26 increases.

  Therefore, the doping profile of the third p-type cladding layer 28 is such that the series resistance of the entire third p-type cladding layer 28 becomes a predetermined value that does not cause mode hops, and the lower layer region close to the active layer 24 and the waveguide layer 26. It is necessary to make it low at (starting point portion in the thickness direction).

The characteristic of one of the doping profiles is shown in FIG. In this characteristic H, the doping concentration is changed from the lower layer region (starting portion in the thickness direction) close to the active layer 24 and the waveguide layer 26 to the active layer 24 and the upper layer region far from the waveguide layer 26 (end portion in the thickness direction). Toward, it is gradually increased to 3.0 × 10 ¹⁷ , 8.5 × 10 ¹⁷ , and 1.8 × 10 ¹⁸ (/ cm ³ ). As a result, a series resistance value of 0.5Ω is obtained. Empirically speaking, the series resistance is preferably 0.7Ω or less. For this purpose, the doping concentration at the end point in the thickness direction is set to 1.0 × 10 ¹⁸ (/ cm ³ ) to 2.5 × 10 ¹⁸ ( / Cm ³ ) has been confirmed.

  Furthermore, by limiting the layer thickness t to a range of 2 μm to 3.2 μm, the separation resistance from the light emitting region 22 to the refractive index adjusting region 23 is set to 1 kΩ while reducing the loss near the waveguide layer 26. I was able to. Note that if the layer thickness t of the third p-type cladding layer 28 is made smaller, the separation resistance can be further increased, but it becomes smaller than the spot size of the emission end face, resulting in increased loss and inability to guide. Also, if the layer thickness is larger than 3.2 μm, the resistance of the third p-type cladding layer 28 decreases and the isolation resistance between the regions decreases, so the above-mentioned layer thickness range is preferable.

  Although FIG. 3 shows an example in which the doping concentration is increased in three steps, the number of change steps may be two steps or four or more steps, or may be increased linearly. Changes may be used in combination.

Next, deflection of outgoing light from the outgoing end face 20a of the semiconductor optical device 10 will be described with reference to FIG.
The optical axis of the normal to the waveguide layer 26 of the light emitting face 20a of the refractive index adjustment region 23 side and forms a crossing angle theta _1, light emitted from the emitting end face 20a in accordance with Snell's law below, exit An outgoing angle θ ₂ is formed with respect to the normal line of the end face 20a.
n ₁ sin θ ₁ = n ₂ sin θ ₂ (1)

Here, n ₁ is an equivalent refractive index in the vicinity of the emission end face 20a of the waveguide layer 26, and n ₂ is a refractive index of air. The crossing angle θ ₁ is 0 ° <θ ₁ <18 ° so that the normal line of the emission end face 20a and the optical axis of the waveguide layer 26 are not parallel to each other and the emission light is not totally reflected by the emission end face 20a. Take the value.

According to Expression (1), the emission angle θ ₂ depends on the equivalent refractive index n ₁ in the vicinity of the emission end face 20 a of the waveguide layer 26. Therefore, the carrier concentration by applying a refractive index adjustment region injection current I _r of the refractive index adjustment region 23 is changed, since n ₁ is changed, it is possible to change the emission angle theta _2.

Here, when the refractive index adjustment region injection current I _r (forward bias) is applied via the second upper electrode 37 and the lower electrode 38 of the refractive index adjustment region 23, the equivalent refractive index n ₁ is lowered. The emission angle θ ₂ decreases. On the other hand, when the reverse bias voltage V _b is applied to the refractive index adjustment region 23, the equivalent refractive index n ₁ increases, and the emission angle θ ₂ increases.

The semiconductor optical device of the present embodiment configured as described above, in response to an applied refractive index adjustment region injection current I _r or reverse bias voltage V _b, the response speed of the deflection output angle theta ₂ below the order of microseconds Can be.

However, the applicant has carried out the calculation of the equivalent refractive index n ₁ and output angle theta ₂ of the variation to the refractive index adjustment region injection current I _r which is applied to the refractive index adjustment region 23. In the following, the center wavelength of the light emitted from the emission end face 20a is 1550 nm, the composition wavelength of the waveguide layer 26 in the refractive index adjustment region 23 is 1450 nm, the thickness is 0.17 μm, the width is 2 μm, the length is 100 μm, and the crossing angle θ. The result when ₁ is 6 ° is shown.

Figure 5 is a graph showing the relationship between the effective refractive index n ₁ of the refractive index adjustment region injection current I _r and the exit end surface 20a near to be applied to the refractive index adjustment region 23. The equivalent refractive index n ₁ of the light emitting face 20a near the waveguide layer 26 when applying no refractive index adjustment region injection current I _r of the refractive index adjustment region 23 becomes 3.21. The refractive index adjustment region injection current I _r is applied to the refractive index adjustment region 23, the carrier concentration of the waveguide layer 26 increasing the current until 35mA becomes 3.19 lower the effective refractive index n ₁ rises.

6 is a graph showing the relationship between the refractive index adjustment region injection current I _r and exit angle theta ₂ of the light applied to the refractive index adjustment region 23. At a current value of 0, the light emission angle θ ₂ is 19.62 °. The refractive index adjustment region injection current I _r is applied to the refractive index adjustment region 23, the emission angle theta ₂ and increasing the current value to 35mA it is possible to deflect the next 19.47 °, 0.15 °.

Further, by applying a reverse bias voltage _Vb to the refractive index adjustment region 23, the carrier concentration can be increased. In this case, since the equivalent refractive index n ₁ increases, it is possible to deflect the emission angle θ ₂ in the opposite direction as shown in FIG.

The change in the equivalent refractive index n ₁ of the waveguide layer 26 may be only in the very vicinity of the emission end face 20a, and the length of the refractive index adjustment region 23 is preferably shorter in consideration of efficient confinement of carriers. However, since the emission end face 20a is formed by cleavage, the length of the refractive index adjustment region 23 is preferably 50 μm to 100 μm in consideration of errors in the cleavage process.

  Hereinafter, an example of a method for manufacturing the semiconductor optical device 10 will be described with reference to the drawings. 8 and 9 are perspective views showing a part of the manufacturing process of the semiconductor optical device 10.

First, an n-type InP substrate 121 having a doping concentration of 1 × 10 ¹⁸ (/ cm ³ ) is prepared, and an active layer 122 made of InGaAsP is grown thereon by MOVPE. Further, a first p-type cladding layer 123 made of InP is laminated thereon. The active layer 122 referred to here includes an MQW and an SCH layer sandwiching the MQW.

  In addition, the thickness of the first p-type cladding layer 123 is, for example, 250 nm, and the distribution of the doping concentration in the thickness direction may be constant, but as described above, the distribution is maximized within a certain range. Thus, a structure that prevents carrier leakage at the time of supplying current may be used.

Next, an insulating film 125 made of SiO ₂ or SiNx is deposited on the first p-type cladding layer 123 by a plasma CVD method or the like, and a resist 126 is applied thereon (FIG. 8A).

  Subsequently, the resist 126 in the portion where the refractive index adjustment region 23 is formed is removed by photolithography, and the insulating film 125 in the region not covered with the resist 126 ′ is removed by etching (FIG. 8B).

  Further, the remaining resist 126 ′ is stripped, and the first p-type cladding layer 123 and the active layer 122 in the region not covered with the insulating film 125 ′ are removed by etching using the insulating film 125 ′ as a mask ( FIG. 8 (c)). Here, the InP of the first p-type cladding layer 123 is etched using, for example, a hydrochloric acid phosphoric acid etchant, and the active layer 122 is etched using hydrochloric acid, hydrogen peroxide, and water.

  Next, a waveguide layer 131 made of InGaAsP is grown on the portion of the substrate 121 etched as described above so as to be continuous with the active layer 122 ', and a second p-type made of InP is formed thereon. The clad layer 132 is laminated so as to have substantially the same height as the first p-type clad layer 123 ′.

  Next, after the remaining insulating film 125 'is peeled off, a new insulating film 140 is deposited on the entire surface, and a resist 141 is applied thereon (FIG. 8D).

  Then, in order to produce a mesa structure, the central portion of the resist 141 is left by photolithography, and both sides thereof are removed. Further, using the resist 141 ′ that remains in a line having a constant width and having a curved portion as a mask, both sides of the insulating film 140 are removed by etching (FIG. 9A).

  Subsequently, the remaining resist 141 'is stripped and removed, and etching is performed using the insulating film 140' as a mask, and the active layer 122 'whose section is substantially trapezoidal (mesa structure) as shown in FIG. 9B. (24), a waveguide layer 131 ′ (26), and a first p-type cladding layer 123 ′ (25) and a second p-type cladding layer 132 ′ (27) which are continuous in a trapezoidal shape are formed thereon.

  Next, a buried layer 142 (29) made of p-type InP and a buried layer 143 (30) made of n-type InP are formed on both sides of the active layer 24 and the waveguide layer 26 (FIG. 9B).

  Then, after peeling off the insulating film 140 ′, a third p-type cladding layer 145 (28) made of InP is grown on the buried layer 143 (30) and the second p-type cladding layer 132 ′ (27). Further, a contact layer 146 made of InGaAs is formed thereon (FIG. 9C).

  Then, the first upper electrode 36 made of Au, Ti, and Pt is vapor-deposited on the portion where the light emitting region 22 is formed on the contact layer 146, and Au, Ti, A second upper electrode 37 made of Pt is vapor-deposited, and further, the lower surface side of the substrate 121 is polished to vapor-deposit a lower electrode 38 made of Au, Ge, and Pt (FIG. 9D).

  Finally, an etching process for forming the bridging portion 31 and the separation grooves 32 and 33 is performed. Here, the InGaAs of the contact layer 146 is etched using, for example, a sulfuric acid-based etchant (selective etchant) and using the third p-type cladding layer (InP) 145 (28) as an etch stop layer. The third p-type cladding layer 145, the buried layers 142 and 143, and the substrate 121 are etched using, for example, a hydrochloric acid phosphoric acid etchant. Thereby, the semiconductor optical device 10 having a length of 1000 μm, a width of 400 μm, and a thickness of 100 μm is completed (FIG. 1A).

  As described above, the semiconductor optical device of this embodiment includes the refractive index adjustment region that adjusts the equivalent refractive index of the waveguide layer according to the applied refractive index adjustment region injection current, thereby deflecting the outgoing light. Response speed can be reduced to the order of microseconds or less.

  Further, since it is not necessary to apply heat to the semiconductor optical element in order to deflect the emitted light, the power consumption can be reduced as compared with the prior art.

(Second Embodiment)
An embodiment of a wavelength swept light source according to the present invention will be described with reference to the drawings. That is, as shown in FIG. 10, the wavelength swept light source of the second embodiment converts the light emitted from the semiconductor optical element 10 of the first embodiment and the emission end face 20a of the semiconductor optical element 10 into parallel light. The collimating lens 11, the diffraction grating 12 that diffracts the parallel light emitted from the collimating lens 11, and a rotatable rotation that reflects the light diffracted by the diffraction grating 12 and re-enters the diffraction grating 12 through the reverse optical path. A moving mirror 13, and the diffraction grating 12 diffracts the re-incident light and feeds it back to the emission end face 20 a of the semiconductor optical device 10, and the light emitted from the emission end face 20 a by the rotation of the turning mirror 13. The structure of a Littman-type wavelength swept light source that sweeps the wavelength of the light source.

  The rotation mirror 13 is supported by an arm 15 that is rotatable about a rotation center position O. The arm 15 is rotated by a spring 16 and a driving device 17.

Further, the wavelength swept light source of the present embodiment includes a light emitting region current supply unit 41 that supplies a light emitting region injection current I _e for emitting light to the light emitting region 22 of the semiconductor optical device 10, and a refractive index adjustment of the semiconductor optical device 10. the refractive index adjustment region current supply unit 42 supplies the refractive index adjustment region injection current I _r for aligning equivalent refractive index n ₁ of the waveguide layer 26 in the area 23, detects the output of light emitted from the end face 20b and an output detection unit 43, a control unit 44 for controlling the refractive index adjustment region injection current I _r on the basis of the detected by the output detector 43 output, the.

  The output detection unit 43 detects the light intensity P of the emitted light from the end surface 20b of the semiconductor optical device 10 by using, for example, a light receiving element (not shown).

  In the wavelength swept light source having this structure, out of the wavelength components of the light emitted from the semiconductor optical device 10 and diffracted by the diffraction surface 12a of the diffraction grating 12, the specific wavelength orthogonal to the reflection surface 13a of the rotating mirror 13 and the vicinity thereof Only the wavelength component returns to the semiconductor optical device 10. This causes stimulated emission of light having the specific wavelength and a wavelength in the vicinity thereof in the semiconductor optical device 10, so that only light of those wavelengths (hereinafter referred to as the sweep wavelength) resonates and is output. .

  This sweep wavelength depends on the angle formed by the diffraction surface 12 a of the diffraction grating 12 and the reflection surface 13 a of the rotating mirror 13, the incident angle of the incident light on the diffraction grating 12, the number of engravings of the diffraction grating 12, and the semiconductor optical device 10. It is defined by the optical path length from the diffraction grating 12 to the rotating mirror 13, and can be changed by adjusting the angle (or distance) of the reflection surface 13a with respect to the diffraction surface 12a.

  As will be described below, the wavelength sweep light source of the present embodiment can perform continuous wavelength sweep while suppressing mode hopping. Here, as shown in FIG. 11, the plane obtained by extending the diffraction surface 12a of the diffraction grating 12 is H1, the plane obtained by extending the effective resonance end surface 20c of the semiconductor optical device 10 is H2, and the reflection surface 13a of the rotating mirror 13 is extended. The obtained plane is designated as H3.

  The rotation center position O of the rotation mirror 13 is included in the plane H1, and is provided on the diffraction grating 12 side from the position where the plane H1 and the plane H2 intersect. The plane H1 and the plane H3 are set so as to intersect between the rotation center position O of the rotation mirror 13 and the diffraction grating 12.

  Here, when the distance from the predetermined incident position P to the emission end face 20a of the semiconductor optical device 10 is D1, and the optical path length from the emission end face 20a of the semiconductor optical element 10 to the effective resonance end face 20c is D2, the effective distance from the predetermined incident position P is effective. The effective optical path length L1 to the resonance end face 20c is represented by L1 = D1 + D2.

In order to perform continuous wavelength sweep while suppressing mode hopping, the distance r from the rotation center position O of the rotation mirror 13 to the predetermined incident position P of light incident on the diffraction grating 12, the above-mentioned effective optical path length L1, It is necessary to set each part so that the relationship between the distance L2 from the rotation center position O of the rotation mirror 13 to the plane H3 and the incident angle α of the light with respect to the diffraction grating 12 satisfies the following expression.
r = (L1-L2) / sin α (2)

However, in order to actually suppress the mode hop in the wavelength swept light source of this embodiment, it is necessary to match the rotation center position O with submicron order accuracy so as to satisfy the above equation. For this reason, in a general external resonator having a very large optical path length on the order of millimeters compared to that, a slight deviation of the outgoing angle θ ₂ of the outgoing light from the outgoing end face 20a of the semiconductor optical device 10 is a mode hop. Cause. In addition, the deviation of the optical axis due to temperature, change with time, and the like also causes mode hops.

  Here, the mechanism by which the mode hop occurs will be described with reference to FIG. FIG. 12A schematically shows the longitudinal mode of the semiconductor optical device 10 and the transmittance characteristics of the diffraction grating 12 when mode hops are not generated, and FIG. It is a graph. Here, the case where the sweep wavelength is further increased from the certain sweep wavelength (upper part of the figure) (lower part of the figure) is shown.

  When Expression (2) is satisfied (when no mode hop occurs), the longitudinal mode m is always selected by changing the peak of the transmittance characteristic in accordance with the change of one specific longitudinal mode m. (FIG. 12A). The relationship between the sweep time t (corresponding to the sweep wavelength) and the light intensity P of the emitted light from the wavelength sweep light source at this time draws a smooth curve as shown in FIG. The reason why the light intensity P is dependent on the sweep time t is that the characteristics of the optical components constituting the wavelength swept light source are wavelength dependent.

  On the other hand, when Equation (2) is not satisfied due to a shift of the optical axis or the like (when a mode hop occurs), the change in the peak of the transmittance characteristic does not correspond to the change in one specific longitudinal mode m, The selected vertical mode jumps to the next mode m ′ (FIG. 12B). Further, as can be seen from the figure, the light intensity P at this time is suddenly smaller or larger than the case of FIG. 12C in which the wavelength of a specific longitudinal mode and the peak of the transmittance characteristic coincide ( (Not shown). Accordingly, the relationship between the sweep time t and the light intensity P at this time has a discontinuous jump as shown in FIG.

  In order to suppress the occurrence of such mode hops, the wavelength swept light source of the present embodiment includes a control unit 44 described below.

When the absolute value | dP / dt | of the time differential value of the light intensity P detected by the output detection unit 43 becomes equal to or greater than a predetermined mode hop threshold, the control unit 44 adjusts the refractive index adjustment region injection current I. _r continuously increases, the absolute value of the time differential value | dP / dt | if is less than a mode hop threshold, maintains the refractive index adjustment region injection current I _r at that time.

  Here, the mode hop threshold value is a value that can be regarded as a mode hop when the absolute value | dP / dt | of the time differential value is equal to or greater than that value. On the other hand, if the absolute value | dP / dt | of the time differential value is less than that value, it can be considered that no mode hop has occurred.

  Note that the mode hop threshold value may take a different value for each sweep wavelength (or sweep time t).

In the above, the absolute value of the time differential value | dP / dt | when it becomes that the mode hopping threshold value above a predetermined, an example in which the control unit 44 increases the refractive index adjustment region injection current I _r continuously However, conversely, it may be as follows.

That is, the control unit 44, the time differential value of the absolute value | dP / dt | when it becomes that the mode hopping threshold value than the predetermined, the refractive index adjustment region injection current I _r decreases continuously, time differential absolute value | dP / dt | if is less than a mode hop threshold may be one which maintains the refractive index adjustment region injection current I _r at that time. The mode hop threshold value may be determined based on the change width | ΔP | of the light intensity P, and the occurrence of the mode hop may be detected using these.

  The wavelength swept light source according to the present embodiment configured as described above includes a semiconductor optical device having a response speed of the deflection of the emitted light of the order of microseconds or less. The generated mode hop can be suppressed in real time.

Next, the operation of the wavelength swept light source of the present embodiment configured as described above will be described.
First, a light emitting region injection current I _e (several hundred mA to 1 A) is applied between the first upper electrode 36 and the lower electrode 38 on the light emitting region 22 side of the semiconductor optical device 10 by the light emitting region current supply unit 41. As a result, the inside of the active layer 24 enters a light emitting state. Here, the light emitting region current supply unit 41 is controlled independently of the refractive index adjustment region current supply unit 42, and the light emitting region injection current _Ie is constant in the following description.

  The light generated in the active layer 24 propagates along the active layer 24 and the waveguide layer 26, and in the resonator composed of the end face 20 b, the diffraction grating 12, and the rotating mirror 13, the active layer 24 and the waveguide layer. 26, the effective optical path length determined by the refractive index of the diffraction grating 26, the angle formed by the diffraction surface 12a of the diffraction grating 12 and the reflection surface 13a of the rotating mirror 13, the incident angle of incident light on the diffraction grating 12, and the diffraction grating 12 Oscillates at a sweep wavelength λ corresponding to the number of engraved lines.

  Note that the reflectance of the emission end face 20a on the refractive index adjustment region 23 side is lower than the reflectance of the end face 20b on the light emission region 22 side.

  The light of wavelength λ output from the end face 20 b of the semiconductor optical device 10 is distributed into two by the half mirror 18 as shown in FIG. 10, and one is incident on the output detection unit 43. The output of the light incident on the output detection unit 43 is detected by the output detection unit 43.

Next, the absolute value | dP / dt | of the time differential value of the light intensity P detected by the output detection unit 43 is sequentially calculated by the control unit 44. When | dP / dt | that is equal to or greater than a predetermined mode hop threshold value is calculated, the refractive index adjustment region injection current I supplied from the refractive index adjustment region current supply unit 42 to the refractive index adjustment region 23 by the control unit 44. _r is continuously increased. At this time, as shown in FIG. 6, the emission angle theta ₂ of the light emitted from the emitting end face 20a of the semiconductor optical device 10 continuously decreases in accordance with the continuous increase of the refractive index adjustment region injection current I _r .

Then, not more than the upper limit of the refractive index adjustment region injection current I _r, | maintained if is less than a mode hop threshold, the refractive index adjustment region injection current I _r is the control unit 44 at that time | dP / dt As a result, the emission angle θ ₂ is fixed.

Meanwhile, more than the upper limit of the refractive index adjustment region injection current I _r, | dP / dt | if does not reach below the mode hopping threshold value, | by the control unit 44 until less than mode hopping threshold | dP / dt refractive index adjustment region injection current I _r is reduced continuously. In this case, as shown in FIG. 6, continuously increased emission angle theta ₂ of the light emitted from the emitting end face 20a of the semiconductor optical device 10 in accordance with the continuous reduction of the refractive index adjustment region injection current I _r and, | dP / dt | by being maintained by the refractive index adjustment region injection current I _r is the control unit 44 when the is less than the mode hopping threshold value, the emission angle theta ₂ is fixed.

The value of the refractive index adjustment region injection current I _r is also reduced to zero lower limit | dP / dt | if does not become less than the mode hopping threshold value, the control unit 44, the refractive index adjustment region current supply unit 42 A reverse bias voltage V _b is supplied to the refractive index adjustment region 23. At this time, as shown in FIG. 7, the emission angle θ ₂ can be further decreased continuously according to the continuous increase of the reverse bias voltage V _b .

(Third embodiment)
A third embodiment of the wavelength swept light source according to the present invention will be described with reference to the drawings. The description of the same configuration and operation as in the second embodiment is omitted. FIG. 13 is a perspective view showing the configuration of the wavelength swept light source of this embodiment, and FIG. 14 is a schematic diagram showing the main part of the configuration of the wavelength swept light source of this embodiment.

  The wavelength swept light source of the present embodiment is a Littman-type external resonance type wavelength swept light source using, for example, a MEMS (Micro Electro Mechanical Systems) scanner, and on the base 51, the semiconductor optical device 10 of the first embodiment and A collimator lens 52 that converts light emitted from the emission end face 20a, which is a low reflection end face of the semiconductor optical device 10, into parallel light, and a parallel light emitted from the collimator lens 52 on a diffraction surface 54a of a diffraction grating 54 described later. The fixed mirror 53 reflecting toward the predetermined incident position G, the diffraction grating 54 for diffracting the light reflected from the fixed mirror 53, and only the wavelength component of the diffracted light diffracted by the diffraction grating 54 vertically incident. The rotating mirror 60 includes a reflecting plate 62 that reflects light to the diffraction grating 54 through a reverse optical path.

  Here, as shown in FIG. 14, H1 is a plane obtained by extending the diffraction surface 54a of the diffraction grating 54, H2 is a plane obtained by extending the effective resonance end face 20c in consideration of the refractive index inside the semiconductor optical device 10, and a reflector 62 A plane obtained by extending the reflective surface 62a is denoted by H3.

  The fixed mirror 53 is disposed in a space between the plane H3 and the plane H1 and between the rotation center position O and the predetermined incident position G of the diffractive surface 54a. In addition, the semiconductor optical device 10 and the collimating lens 52 are arranged in a space including the diffraction grating 54 out of the two spaces separated by the plane H3. The optical path from the semiconductor optical element 10 to the diffraction grating 54 is non-intersecting with respect to the rotating mirror 60.

  As shown in the exploded perspective view of FIG. 15, the rotating mirror 60 is formed by etching or the like on a conductive substrate (for example, a silicon substrate), and includes an upper plate 61a, a lower plate 61b, and horizontal plates 61c and 61d. A frame 61 formed in the shape of a horizontally-long rectangular frame, a horizontally-long rectangular reflecting plate 62 arranged concentrically inside the frame 61 and having a reflecting surface 62a for reflecting light on at least one surface side, and the frame 61 The upper plate 61a and the lower plate 61b of the frame 61 extend in a straight line from the center of the inner edges of the upper plate 61a and the lower plate 61b facing each other to the center of the upper and lower edges of the reflecting plate 62, and are reflected from the upper and lower plates 61a and 61b of the frame 61. It has a pair of connection parts 63 and 64 which connect between the plates 62 and rotate the reflection plate 62 by twisting deformation.

  Further, electrode plates 65 and 66 for applying an external force to the reflecting plate 62 are insulated on both surfaces of one of the horizontal plates 61c and 61d (here, the horizontal plate 61c) of the frame 61 of the rotating mirror 60. It is attached via a spacer 67 having a property. The electrode plates 65 and 66 are overlapped with a gap corresponding to the thickness of the spacer 67 on both surfaces on one end side (here, the left end side) of the reflection plate 62.

  Further, the rotation mirror 60 applies an external force to the reflection plate 62 and drives the reflection plate 62 to reciprocate within a predetermined angle range with a line connecting the centers of the pair of connecting portions 63 and 64 as a rotation center position O. Have the device.

  The drive device (not shown) applies drive signals V1 and V2 whose phases are shifted by 180 °, for example, to the two electrode plates 65 and 66 using the frame 61 of the rotating mirror 60 as a reference potential, and the electrode plates An electrostatic attraction force is alternately generated between 65 and 66 and the end of the reflecting plate 62, and the reflecting plate 62 is reciprocally rotated.

  The frequencies of the drive signals V1 and V2 are set to be equal to the natural frequency of the reflecting plate 62 determined by the shape and weight of the reflecting plate 62 of the rotating mirror 60 and the torsion spring constant of the connecting portions 63 and 64. Therefore, the reflecting plate 62 can be reciprocated at a large angle with a small driving power.

  The reciprocating rotation of the reflection plate 62 changes the effective optical path length in the wavelength sweep light source of the present embodiment and the angle of the reflection surface 62a of the reflection plate 62 with respect to the diffraction surface 54a of the diffraction grating 54. The wavelength of the laser beam output from the wavelength swept light source changes continuously and periodically.

  Here, when the distance from the fixed mirror 53 to the emission end face 20a of the semiconductor optical element 10 is D1, and the effective optical path length from the emission end face 20a of the semiconductor optical element 10 to the effective resonance end face 20c is D2, the effective resonance from the fixed mirror 53 is effective. An effective optical path length L3 to the end face 20c is represented by L3 = D1 + D2.

The above-mentioned effective optical path length L3, the optical path length L4 from the fixed mirror 53 to the predetermined incident position G, the distance L2 from the rotation center position O to the plane H3 of the reflection plate 62 of the rotation mirror 60, and the rotation center position By setting each part so that the relationship between the distance r from O to the predetermined incident position G of the diffraction grating 54 and the incident angle α of the light with respect to the diffraction grating 54 satisfies the following formula, continuous wavelength sweep is performed in a mode-hop-free manner. Can be performed.
r = (L3 + L4-L2) / sin α (3)

  In addition, since the wavelength swept light source of the present embodiment has a configuration in which light is incident on the diffraction grating 54 via the fixed mirror 53 and the reflecting plate 62 and the optical path are not crossed, the reflecting plate 62 has a hole for passing light. It is not necessary to provide such as and the like, and deformation due to the reduction in rigidity does not occur, and stable and high-speed wavelength sweep can be performed.

  Therefore, the wavelength swept light source of the present embodiment configured in this way can perform a very fast wavelength sweep, and can sweep a wavelength range of 100 nm in about 1 millisecond, for example. That is, in order to suppress the mode hop, it is necessary to adjust the optical axis on the order of microseconds.

To suppress the even mode hopping at a wavelength swept light source of the present embodiment, as in the second embodiment, the optical axis adjustment is performed by controlling the refractive index adjustment region injection current I _r.

In the wavelength swept light source of the present embodiment, all members are fixed on the base 51, and the relative positions of the optical components are stored. Further, since the torsion spring mechanism is used for the rotating shaft of the rotating mirror, the shaft position is stable. For this reason, the reproducibility of the fluctuation of the optical path in the external resonator accompanying the rotation of the rotating mirror is very good. Therefore, even wavelength sweep is a very fast, simply increasing or decreasing the I _r, can be suppressed easily mode hopping.

  As described above, the wavelength swept light source according to the present embodiment also includes a semiconductor optical device having a response speed of the deflection of the emitted light of the order of microseconds or less. The generated mode hop can be suppressed in real time.

DESCRIPTION OF SYMBOLS 10 Semiconductor optical element 11, 52 Collimating lens 12, 54 Diffraction grating 12a, 54a Diffraction surface 13, 60 Rotating mirror 13a Reflecting surface 20a Output end surface 20b End surface 20c Effective resonance end surface 21 N-type semiconductor substrate (substrate)
22 Light emitting region 23 Refractive index adjusting region 24 Active layer 25 First p-type cladding layer 26 Waveguide layer 27 Second p-type cladding layer 28 Third p-type cladding layer 32, 33 Separation groove 41 Light emitting region current supply part 42 Refractive index adjusting region current Supply unit 43 Output detection unit 44 Control unit 53 Fixed mirror

Claims (9)

an n-type semiconductor substrate (21);
An active layer (24) formed on the n-type semiconductor substrate for emitting light and propagating the light;
A semiconductor optical device comprising: a waveguide layer (26) optically coupled to the active layer on the n-type semiconductor substrate and propagating light propagated from the active layer;
A light emitting region (22) having the active layer;
A refractive index adjustment region (23) having the waveguide layer and adjusting an equivalent refractive index of the waveguide layer with respect to light propagated from the active layer according to an injected current of the refractive index adjustment region injected; Prepared,
The intersection angle (θ ₁ ) between the exit end face (20a) on the refractive index adjustment region side for emitting the light propagated through the waveguide layer and the optical axis of the waveguide layer is non-right angle,
The exit angle (θ ₂ ) of the light emitted from the exit end face with respect to the exit end face is changed by adjusting an equivalent refractive index of the waveguide layer by the refractive index adjustment region injection current. Semiconductor optical device. The light emitting region has a first p-type cladding layer (25) laminated on the active layer;
The refractive index adjusting region has a second p-type cladding layer (27) laminated on the waveguide layer;
The doping concentration in the thickness direction of the second p-type cladding layer in contact with the waveguide layer in the refractive index adjustment region is formed to have a maximum value within a predetermined distance from the upper end of the waveguide layer. 2. The semiconductor optical device according to claim 1, wherein   3. The semiconductor optical device according to claim 2, wherein the range of the predetermined distance is 25 to 150 nm.   A third p-type cladding layer (28) is formed on the first p-type cladding layer in the light-emitting region and the second p-type cladding layer in the refractive index adjustment region, and the light-emitting region of the third p-type cladding layer and the 4. The semiconductor optical device according to claim 2, wherein a separation groove (32, 33) having a predetermined width is formed at a boundary portion with the refractive index adjustment region. The doping concentration at the end point in the thickness direction of the third p-type cladding layer is larger than the doping concentration at the start point in the thickness direction, and 1.0 × 10 ¹⁸ (/ cm ³ ) to 2.5 × 10 ¹⁸ (/ cm ^3). The semiconductor optical device according to claim 4, which is set in a range of The semiconductor optical device according to any one of claims 1 to 5,
A diffraction grating (12, 54) for diffracting light emitted from the emission end face of the semiconductor optical element;
A rotatable rotating mirror (13, 60) that reflects the light diffracted by the diffraction grating and re-enters the diffraction grating through a reverse optical path, and the light that the diffraction grating re-enters. A Littman-type wavelength sweeping light source that diffracts and feeds back to the emission end face of the semiconductor optical element, and sweeps the wavelength of light emitted from the emission end face by rotation of the rotating mirror,
A light emitting region current supply unit (41) for supplying a light emitting region injection current for emitting light to the light emitting region of the semiconductor optical device;
A refractive index adjustment region current supply unit (42) for supplying the refractive index adjustment region injection current for adjusting the refractive index of the waveguide layer to the refractive index adjustment region of the semiconductor optical device;
An output detector (43) for detecting the output of the light emitted from the semiconductor optical element;
Based on the output detected by the output detection unit, a control unit (44) detects a discontinuous point of the output due to the mode hop and controls the refractive index adjustment region injection current so as to eliminate the discontinuous point. And a wavelength-swept light source.   The said control part calculates the time differential value of the output detected by the said output detection part, and controls the said refractive index adjustment area | region injection current based on this time differential value. Wavelength swept light source.   The control unit sequentially calculates the time differential value of the output detected by the output detection unit in order to detect the discontinuous point caused by the mode hop, and the absolute value of the time differential value is determined in advance. When the hop threshold value is exceeded, the refractive index adjustment region injection current is continuously increased or decreased, and the refractive index adjustment region injection is performed when the absolute value of the time differential value is less than a predetermined mode hop threshold value. The wavelength-swept light source according to claim 7, wherein the current increase / decrease is stopped. A collimating lens (52) for converting light emitted from the emission end face of the semiconductor optical element into parallel light, and emitting the parallel light to the diffraction grating;
A space sandwiched between a plane extending the reflecting surface of the rotating mirror and a plane extending the diffraction surface of the diffraction grating toward the rotating center position of the rotating mirror, and a predetermined incident position of the diffraction grating and the A fixed mirror (53) that is arranged at a position between the rotation center position of the rotation mirror and reflects parallel light emitted from the collimating lens toward a predetermined incident position of the diffraction grating;
The semiconductor optical element and the collimating lens are arranged on the space side including the diffraction grating in two spaces separated by a plane obtained by extending the reflection surface of the rotating mirror,
The optical path from the semiconductor optical element to the diffraction grating is non-intersecting with the rotating mirror;
A distance r from the rotation center position to a predetermined incident position of the diffraction surface of the diffraction grating, a distance L2 from the rotation center position to a plane obtained by extending the reflection surface of the rotation mirror, and effective resonance of the semiconductor optical device Between the optical path length L3 from the end face to the fixed mirror, the optical path length L4 from the fixed mirror to a predetermined incident position of the diffraction surface of the diffraction grating, and the light incident angle α from the fixed mirror to the diffraction surface of the diffraction grating In addition,
r = (L3 + L4-L2) / sin α
The wavelength swept light source according to any one of claims 6 to 8, wherein the following relationship is established.

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