JP2011176374A - Semiconductor laser, and semiconductor optical integrated element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform stable single wavelength operation and low threshold operation even if an injection current value is increased to obtain a desired optical output, in a semiconductor laser. <P>SOLUTION: This semiconductor laser includes, on a semiconductor substrate, an optical waveguide capable of generating a gain by current injection, and a diffraction grating having a phase shift and provided along the optical waveguide over the overall length of the optical waveguide. The semiconductor laser is constituted so that Bragg wavelengths in regions in vicinities of both ends of the optical waveguide are set longer than that in a region in the vicinity of the phase shift while current injection is not performed to the optical waveguide. The phase shift is provided in one part, and the quantity of the phase shift is set to a 1/4 wavelength. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a semiconductor laser for a light source and a semiconductor optical integrated device used in, for example, optical communication.

A semiconductor laser for a light source used in optical communication is required to oscillate stably at a single wavelength. In addition, from the viewpoint of low power consumption, it is also required that the oscillation threshold current is small.
Conventionally, a distributed feedback (DFB) laser having a phase shift has been used as a semiconductor laser that stably oscillates at a single wavelength.

In the phase shift DFB laser, in order to realize a low threshold operation, the coupling coefficient (diffraction intensity) in the diffraction grating is increased so that a large feedback can be obtained.
However, as shown in FIG. 12A, when a phase shift (here, λ / 4 phase shift) 11 is provided in the center of the diffraction grating 10 of the DFB laser, if the coupling coefficient is increased, FIG. ), The light intensity (optical electric field intensity) is concentrated in the vicinity of the phase shift 11, the stimulated emission rate in the vicinity of the phase shift 11 is increased due to the large light intensity, and the number of electron-hole pairs (carriers) is reduced. .

As a result, as shown in FIG. 12C, the carrier density is low near the phase shift 11, and the carrier density is high at the end, resulting in non-uniform carrier density.
Here, the carrier density affects the refractive index (waveguide refractive index) of the semiconductor material constituting the optical waveguide of the laser due to the plasma effect.
For this reason, when the carrier density is nonuniform, the waveguide refractive index is nonuniform. That is, in the vicinity of the phase shift 11, since the carrier density is small, the waveguide refractive index is high, and in the end portion, the carrier density is high, and thus the waveguide refractive index is low.

  Such a difference in waveguide refractive index is equal to a difference in optical length (optical length) of the optical waveguide, and affects the Bragg wavelength. That is, as shown in FIG. 12D, the refractive index increases in the vicinity of the phase shift 11, so that the optical length becomes longer and the Bragg wavelength becomes longer, whereas the refractive index becomes lower at the end. The optical length is shortened and the Bragg wavelength is shortened.

As a result, the Bragg wavelengths do not match within the resonator, and the laser oscillation spectrum deteriorates as the injection current increases so that the desired optical output can be obtained. Operation (single wavelength operation) is not possible. Such a phenomenon is called spatial hole burning (see, for example, Non-Patent Document 1).
Here, in FIG. 13, each oscillation spectrum when the injection current value is increased to 7 mA, 10 mA, 20 mA, 40 mA, 60 mA, 80 mA, 100 mA, etc. Large).

As shown in FIG. 13, when the injection current value is increased so that a desired light output can be obtained, the light intensity increases and oscillation occurs in multiple modes, making it impossible to operate in a single mode. I understand that.
Incidentally, several methods have been proposed to avoid such a spatial hole burning phenomenon.

  For example, in Patent Document 1 (see, for example, FIGS. 1 and 2), the phase shift is not realized by a diffraction grating, but is realized by reducing the equivalent refractive index of the waveguide near the center of the resonator. A method for suppressing the spatial hole burning of the above has been proposed. In this method, compared with the case where the phase shift is realized by the diffraction grating, the concentration of the optical electric field intensity is moderated so that hole burning occurs but the wavelength stability is not greatly deteriorated.

  For example, Patent Document 2 (see, for example, FIG. 4) proposes a method of flattening the optical electric field intensity and suppressing hole burning by reducing the coupling coefficient of the diffraction grating near the center of the resonator. Yes.

Soda et al., "Stability in Single Longitudinal Mode Operation in GaInAsP / InP Phase-Adjusted DFB Lasers", IEEE Journal of Quantum Electronics, vol.QE-23, No.6, June 1987, pp. 804-814

JP-A-4-330793 Japanese Patent No. 2687526

However, in the method proposed in Patent Document 1 described above, the threshold value becomes higher compared to the ideal phase shift. In addition, it is necessary to optimize the manufacturing conditions so that the phase is reversed in the region where the equivalent refractive index near the center of the resonator is reduced. Setting and manufacturing the conditions are not easy.
Further, in the method proposed in Patent Document 2 described above, since the coupling coefficient is changed inside the resonator, a complicated process such as changing the depth of the diffraction grating and the ratio of line and space in the resonator is required. And In addition, since the coupling coefficient is lowered, the threshold value is increased.

  The present invention was devised in view of such problems, and can realize stable single wavelength operation and low threshold operation even when the injection current value is increased so as to obtain a desired light output. An object of the present invention is to provide a semiconductor laser and a semiconductor optical integrated device.

  Therefore, the semiconductor laser of the present invention includes an optical waveguide capable of generating a gain by current injection on a semiconductor substrate, a diffraction grating provided along the optical waveguide over the entire length of the optical waveguide, and a phase shift provided in the diffraction grating. In the state where current is not injected into the optical waveguide, the Bragg wavelength in the region near both ends is 0.025 to 0.100% than the Bragg wavelength in the region near the phase shift adjacent to the phase shift. It is configured to be long in the range, the phase shift is provided at one place, and the phase shift amount is ¼ wavelength.

  A semiconductor optical integrated device according to the present invention includes the semiconductor laser and an optical functional device that is provided on a semiconductor substrate on which the semiconductor laser is formed and is optically coupled to the semiconductor laser.

  Therefore, according to the semiconductor laser and the semiconductor optical integrated device of the present invention, stable single wavelength operation and low threshold operation can be realized even when the injection current value is increased so as to obtain a desired light output. There is an advantage.

1 is a schematic cross-sectional view showing a configuration of a semiconductor laser according to a first embodiment of the present invention. 1 is a schematic diagram showing a main part configuration of a semiconductor laser according to a first embodiment of the present invention. (A) is a figure which shows the Bragg wavelength of the state which is not performing the current injection of the semiconductor laser concerning 1st Embodiment of this invention, (B) is a figure which shows the Bragg wavelength of the state which performed the current injection It is. It is a figure which shows each oscillation spectrum for every injection current value of the semiconductor laser concerning 1st Embodiment of this invention. (A) is a figure for demonstrating the full length of the semiconductor laser concerning 1st Embodiment of this invention, and the length of the vicinity area | region of both ends, (B) is concerning 1st Embodiment of this invention. It is a figure which shows the relationship between the change rate of the Bragg wavelength of a semiconductor laser, and a side mode suppression ratio. It is a figure which shows the relationship between the change rate of the Bragg wavelength of the semiconductor laser concerning 1st Embodiment of this invention, and carrier density. It is a schematic diagram which shows the principal part structure of the semiconductor laser concerning 2nd Embodiment of this invention. It is a figure which shows the relationship between the waveguide width (mesa width) of the semiconductor laser concerning 2nd Embodiment of this invention, and the change rate of a Bragg wavelength. It is a typical sectional view showing the composition of the semiconductor laser concerning a 3rd embodiment of the present invention. It is a figure which shows the Bragg wavelength of the state which is not performing the current injection of the semiconductor laser concerning the modification of each embodiment of this invention. It is a typical sectional view showing composition of a semiconductor optical integrated device provided with a semiconductor laser concerning each embodiment of the present invention. (A)-(D) are the figures for demonstrating the subject of this invention. It is a figure for demonstrating the subject of this invention.

Hereinafter, a semiconductor laser and a semiconductor optical integrated device according to an embodiment of the present invention will be described with reference to the drawings.
[First Embodiment]
First, a semiconductor laser according to a first embodiment of the present invention will be described with reference to FIGS.

  The semiconductor laser (semiconductor device) according to the present embodiment has an optical waveguide (optical waveguide structure) capable of generating a gain by current injection on a semiconductor substrate (here, n-type InP substrate) 100 as shown in FIG. For example, a waveguide core layer having a GaInAsP multiple quantum well structure) 200 and a diffraction grating (a continuous diffraction grating structure that perturbs the optical waveguide 200) 300 provided along the optical waveguide 200 over the entire length of the optical waveguide 200. With. Further, an electrode 500 is provided above the optical waveguide 200, and an electrode 400 is provided below the semiconductor substrate 100.

Here, the diffraction grating 300 is provided with one phase shift (here, λ / 4 phase shift) 310 at the center (resonator center) position. That is, the diffraction grating 300 has a phase shift 310 at one central position, and the phase shift amount is ¼ wavelength. That is, this semiconductor laser is a distributed feedback laser (phase shift DFB laser) having a phase shift 310.
Then, in a state where current is not injected into the optical waveguide 200, a region (a desired length from the end portion) in the vicinity of both end portions (both end portions of the element; both end portions of the resonator) of the region where the diffraction grating 300 is provided. The Bragg wavelength of the region having (1) is longer than the Bragg wavelength of the region in the vicinity of the phase shift 310 (region adjacent to the phase shift 310).

In the present embodiment, the Bragg wavelength is configured to change stepwise in a state where current is not injected into the optical waveguide.
Specifically, as shown in FIG. 2, the period Λ 2 of the diffraction grating 300 provided in the vicinity region of both end portions is 0 than the period Λ 1 of the diffraction grating 300 provided in the vicinity region of the phase shift 310. .05% longer. The period Λ1 of the diffraction grating 300 provided in the vicinity region of the phase shift 310 is set according to a desired Bragg wavelength (here, 1550 nm).

  As a result, as shown in FIG. 3A, in the state where no current is injected into the optical waveguide 200, the Bragg wavelength in the vicinity of both ends (the configuration of the optical waveguide 200 and the diffraction grating 300 in the vicinity of both ends). Is 0.05% longer than the Bragg wavelength in the region near the phase shift 310 (determined by the configuration of the optical waveguide and diffraction grating in the region near the phase shift 310).

Here, the length of the entire laser (element length; resonator length) is 600 μm, and the length of the vicinity of both ends (here, the length of the region where the diffraction grating 300 is Λ2; the period of the diffraction grating 300) (Long region) is 100 μm from the end.
Here, FIG. 4 shows each oscillation spectrum when the injection current value is increased to 7 mA, 10 mA, 20 mA, 40 mA, 60 mA, 80 mA, and 100 mA in the semiconductor laser configured as described above (FIG. 4). 4, the upper one indicates a larger injection current value).

As shown in FIG. 4, even when the injection current value is increased and the light intensity is increased so that a desired light output can be obtained, stable single wavelength oscillation without oscillating in multiple modes. It can be seen that (single mode oscillation) is obtained. In this case, the threshold value is the same as that of a normal phase shift DFB laser, and a low threshold value operation can be realized.
Therefore, the semiconductor laser according to the present embodiment has an advantage that stable single wavelength operation and low threshold operation can be realized even when the injection current value is increased so as to obtain a desired light output. is there.

  That is, according to the present semiconductor laser, light intensity (optical electric field intensity) is concentrated in the vicinity of the phase shift [see FIG. 12B], and the Bragg wavelength in the vicinity of the phase shift becomes longer [see FIG. 12 (D)], as shown in FIG. 3A, the Bragg wavelengths in the vicinity of both ends are offset to the long wavelength side when no current is injected into the optical waveguide 200. As shown in (B), the Bragg wavelength becomes nearly constant over the entire length inside the resonator, and stable single wavelength operation is obtained. Further, since the threshold value is close to the minimum in the state where the Bragg wavelength is substantially uniform, a low threshold value operation can be obtained.

In the present embodiment, as described above, the element length is 600 μm and the length of the region where the period of the diffraction grating 300 is long (the region near both ends) is 100 μm. However, the present invention is not limited to this. Even if these lengths are different or the ratio of these lengths is different, the same effect can be obtained.
Here, FIG. 5B shows a case where the λ / 4 phase shift 310 is provided in the center, where the laser length (the total length of the region where the diffraction grating 300 is provided) is L, and the Bragg wavelength on one side is When the length of the region to be changed (region where the period of the diffraction grating 300 is long) is L ′ [see FIG. 5A], the Bragg wavelength change rate (%) and the higher-order mode suppression ratio (side mode suppression ratio) ) (DB). The higher-order mode suppression ratio represents single wavelength characteristics, and how much the light intensity of the higher-order mode (side mode) is suppressed with respect to the light intensity of the fundamental mode (optical electric field strength). Is shown.

FIG. 6 shows the relationship between the Bragg wavelength change rate (%) and the carrier density (threshold carrier density representing threshold current) (cm ⁻³ ). Here, the laser current values (injection current values) are 60 mA and 100 mA.
For example, as shown in FIGS. 5B and 6, the lengths of the regions near both ends (the region where the period of the diffraction grating 300 is long; the region where the Bragg wavelength is changed) are all the entire length ( If the length is in the range of 1/8 to 3/8 of the laser length (that is, the length of the region near one end is 1/8 to 3/8 of the entire length) If the length is within the range, a semiconductor laser having excellent single wavelength stability and low threshold can be realized. In other words, if the ratio L ′ / L of the length L ′ of the region for changing the Bragg wavelength on one side to the laser length L is in the range of 1/8 to 3/8, the single-wavelength stable operation is excellent and low. A threshold semiconductor laser can be realized. Here, the ratio L ′ / L of the length L ′ of the region for changing the Bragg wavelength on one side to the laser length L is 1/8, 1/4, and 3/8, respectively. ing.

  In the present embodiment, as described above, the period of the diffraction grating 300 is changed by 0.05% in the vicinity region of both end portions and the vicinity region of the phase shift 310, and the Bragg wavelength is changed by 0.05%. However, the present invention is not limited to this. For example, as shown in FIGS. 5B and 6, the Bragg wavelengths in the vicinity of both ends are phase-shifted when no current is injected into the optical waveguide 200. If it is longer in the range of 0.025 to 0.100% than the Bragg wavelength in the vicinity of 310 (if the rate of change of the Bragg wavelength is in the range of 0.025 to 0.100%), the side mode suppression ratio is A semiconductor laser having a desired value (for example, 40 dB or more), excellent single-wavelength stable operation, and a low threshold can be realized.

That is, the period Λ2 of the diffraction grating 300 provided in the region near both ends is in the range of 0.025 to 0.100% than the period Λ1 of the diffraction grating 300 provided in the region near the phase shift 310. If it is configured to be longer, the Bragg wavelength in the region near both ends is 0.025 to 0.100% than the Bragg wavelength in the region near the phase shift 310 in a state where no current is injected into the optical waveguide 200. Thus, a semiconductor laser having a side mode suppression ratio of a desired value (for example, 40 dB or more), excellent single-wavelength stable operation, and a low threshold can be realized.
[Second Embodiment]
Next, a semiconductor laser according to a second embodiment of the present invention will be described with reference to FIGS.

  In the semiconductor laser (semiconductor device) according to the present embodiment, the period of the diffraction grating 300 is changed stepwise in the vicinity of both end portions and the vicinity of the phase shift 310 in the first embodiment. On the other hand, the difference is that the width of the optical waveguide 200 is changed stepwise between the vicinity of both ends and the vicinity of the phase shift 310. In the present embodiment, the same reference numerals are used for the same components as those in the first embodiment (see FIG. 1).

That is, in this semiconductor laser, as shown in FIG. 7, the width d2 of the optical waveguide 200 provided in the vicinity region of both ends is greater than the width d1 of the optical waveguide 200 provided in the region near the phase shift 310. Is also getting wider.
Specifically, as shown in FIG. 7, the width (waveguide width) d2 of the optical waveguide 200 provided in the vicinity region of both ends is 1.7 μm, and is provided in the vicinity region of the phase shift 310. The width d1 of the optical waveguide 200 is 1.6 μm, and the waveguide width d2 is 0.1 μm wider than the waveguide width d1.

Here, the length of the entire laser (element length) is 600 μm, and the length of the vicinity of both ends (here, the length of the region where the width of the optical waveguide 200 is d2; the region where the width of the optical waveguide 200 is wide) Are 100 μm from the end.
As described above, when the waveguide width d2 is 0.1 μm wider than the waveguide width d1, the equivalent refractive index of the optical waveguide 200 provided in the region near both ends is in the region near the phase shift 310. It becomes 0.05% larger (equivalently larger) than the equivalent refractive index of the optical waveguide 200 provided. That is, in the state where current is not injected into the optical waveguide 200, the Bragg wavelength in the region (region having a desired length from the end) near both ends (both ends of the element; both ends of the resonator) is the phase. It is 0.05% longer (equivalently longer) than the Bragg wavelength in the region near the shift 310 (region adjacent to the phase shift 310).

  In the semiconductor laser configured as described above, as in the case of the first embodiment described above (see FIG. 4), the injection current value is increased and the light intensity is increased so that a desired light output can be obtained. Even when it becomes large, stable single wavelength oscillation (single mode oscillation) can be obtained without oscillating in multiple modes. In this case, the threshold value is the same as that of a normal phase shift DFB laser, and a low threshold value operation can be realized.

The details of the other configurations are the same as those of the first embodiment described above, and thus the description thereof is omitted here.
Therefore, according to the semiconductor laser according to the present embodiment, as in the first embodiment described above, even when the injection current value is increased so as to obtain a desired optical output, stable single wavelength operation is possible. And there is an advantage that low threshold operation can be realized.

In the present embodiment, as described above, the element length is 600 μm, and the length of the wide region of the optical waveguide 200 (region near both ends) is 100 μm. However, the present invention is not limited to this. Even if these lengths are different or the ratio of these lengths is different, the same effect can be obtained.
For example, the length of the region near both ends (the region where the width of the optical waveguide 200 is wide; the region where the Bragg wavelength is changed) is 1/8 to 3/8 of the entire length (laser length). (That is, if the length of the region near one end is within the range of 1/8 to 3/8 of the total length), A semiconductor laser having excellent single-wavelength stable operation and a low threshold value can be realized [see FIGS. 5B and 6].

  Further, in the present embodiment, as described above, the width of the optical waveguide 200 is changed by 0.1 μm in the vicinity region of both end portions and the vicinity region of the phase shift 310, and the Bragg wavelength is changed by 0.05%. However, the present invention is not limited to this, and as in the case of the first embodiment described above, the Bragg wavelength in the vicinity of both ends is set in the vicinity of the phase shift 310 in a state where current is not injected into the optical waveguide 200. If it is longer in the range of 0.025 to 0.100% than the Bragg wavelength in the region (if the rate of change of the Bragg wavelength is in the range of 0.025 to 0.100%), the single wavelength stable operation is excellent. A low threshold semiconductor laser can be realized [see FIGS. 5B and 6].

FIG. 8 shows the relationship between the Bragg wavelength change rate (%) and the width of the optical waveguide 200 (waveguide width; mesa width) (μm).
As shown in FIG. 8, when the waveguide width is changed in the range of 0.05 to 0.25 μm with an optical waveguide having a width of 1.6 μm as a reference, the rate of change of the Bragg wavelength is 0.025 to 0.100. % Range.

  For this reason, if the width of the optical waveguide 200 is changed in the range of 0.05 to 0.25 μm between the region near both ends and the region near the phase shift 310, no current is injected into the optical waveguide 200. The Bragg wavelength in the vicinity region of both ends can be made longer in the range of 0.025 to 0.100% than the Bragg wavelength in the vicinity region of the phase shift 310, thereby achieving excellent single wavelength stable operation. A low threshold semiconductor laser can be realized [see FIGS. 5B and 6].

That is, the width of the optical waveguide 200 provided in the vicinity region of both end portions is wider in the range of 0.05 to 0.25 μm than the width of the optical waveguide 200 provided in the region near the phase shift 310. With this configuration, the optical waveguide 200 provided with the equivalent refractive index of the optical waveguide 200 provided in the vicinity of both end portions in the vicinity of the phase shift 310 without current injection into the optical waveguide 200. It becomes larger in the range of 0.025 to 0.100% than the equivalent refractive index of 200. As a result, in a state where current is not injected into the optical waveguide 200, the Bragg wavelength in the region near both ends is made longer in the range of 0.025 to 0.100% than the Bragg wavelength in the region near the phase shift 310. As a result, a semiconductor laser having excellent single-wavelength stable operation and a low threshold value can be realized [see FIGS. 5B and 6].
[Third Embodiment]
Next, a semiconductor laser according to a third embodiment of the invention will be described with reference to FIG.

The semiconductor laser (semiconductor device) according to this embodiment is different from that of the first embodiment and the second embodiment described above in that it is a wavelength tunable laser capable of changing the oscillation wavelength of the laser.
That is, in the present semiconductor laser, as shown in FIG. 9, the optical waveguide 200 has a gain waveguide portion (for example, including a waveguide core layer having a GaInAsP multiple quantum well structure) capable of generating a gain by current injection. Wavelength control waveguide part that can control the oscillation wavelength of the laser by changing the refractive index by current injection (transparent waveguide part; waveguide core layer made of a semiconductor material whose refractive index changes by current injection such as GaInAsP 220) are alternately provided in the optical axis direction. That is, the optical waveguide 200 is configured as a gain waveguide section 210 and a wavelength control waveguide section 220 that are periodically arranged. Here, both end portions of the optical waveguide 200 are gain waveguide portions 210. In FIG. 9, the same components as those in the first embodiment (see FIG. 1) are denoted by the same reference numerals.

Here, the wavelength control waveguide section 220 is configured using a semiconductor material whose refractive index changes by current injection, such as GaInAsP, so that the refractive index changes by current injection.
Further, as shown in FIG. 9, an electrode 510 for injecting a current into the gain waveguide section 210 is provided on the upper portion of the gain waveguide section 210. Further, as shown in FIG. 9, an electrode 520 for injecting a current into the wavelength control waveguide section 220 is provided on the wavelength control waveguide section 220. Note that an electrode 400 is provided below the semiconductor substrate 100.

  In the present embodiment, the wavelength control waveguide unit 220 is configured such that the refractive index is changed by current injection. However, the present invention is not limited to this, and for example, the wavelength control waveguide unit 220 is reverse. You may comprise using the semiconductor material from which a refractive index changes by applying a reverse bias voltage (by voltage application) so that a refractive index may change by applying a bias voltage (by voltage application). In this case, since the amount of change in the refractive index is small, the amount of change in wavelength is small, but the oscillation wavelength can be changed at high speed.

Further, in the present embodiment, as in the case of the second embodiment described above (see FIG. 7), the width d2 of the optical waveguide 200 provided in the region near both ends is provided in the region near the phase shift 310. The optical waveguide 200 is wider than the width d1.
Specifically, as in the case of the second embodiment described above (see FIG. 7), the width (waveguide width) d2 of the optical waveguide 200 provided in the vicinity of both ends is 1.7 μm. The width d1 of the optical waveguide 200 provided in the region near the phase shift 310 is 1.6 μm, and the waveguide width d2 is 0.1 μm wider than the waveguide width d1.

Here, the length of the entire laser (element length) is 600 μm, and the length of the vicinity of both ends (here, the length of the region where the width of the optical waveguide 200 is d2; the region where the width of the optical waveguide 200 is wide) Are 100 μm from the end.
As described above, when the waveguide width d2 is 0.1 μm wider than the waveguide width d1, the equivalent refractive index of the optical waveguide 200 provided in the region near both ends is in the region near the phase shift 310. It becomes 0.05% larger (equivalently larger) than the equivalent refractive index of the optical waveguide 200 provided. That is, in the state where current is not injected into the optical waveguide 200, the Bragg wavelength in the region (region having a desired length from the end) near both ends (both ends of the element; both ends of the resonator) is the phase. It is 0.05% longer (equivalently longer) than the Bragg wavelength in the region near the shift 310 (region adjacent to the phase shift 310).

  In the semiconductor laser configured as described above, as in the case of the first embodiment described above (see FIG. 4), the injection current value is increased and the light intensity is increased so that a desired light output can be obtained. Even when it becomes large, stable single wavelength oscillation (single mode oscillation) can be obtained without oscillating in multiple modes. In this case, the threshold value is the same as that of a normal phase shift DFB laser, and a low threshold value operation can be realized.

The details of the other configurations and the like are the same as those of the first embodiment and the second embodiment described above, and thus the description thereof is omitted here.
Therefore, according to the semiconductor laser according to the present embodiment, as in the first embodiment described above, even when the injection current value is increased so as to obtain a desired optical output, stable single wavelength operation is possible. And there is an advantage that low threshold operation can be realized.

In the present embodiment, as described above, the element length is 600 μm, and the length of the wide region of the optical waveguide 200 (region near both ends) is 100 μm. However, the present invention is not limited to this. Even if these lengths are different or the ratio of these lengths is different, the same effect can be obtained.
For example, the length of the region near both ends (the region where the width of the optical waveguide 200 is wide; the region where the Bragg wavelength is changed) is 1/8 to 3/8 of the entire length (laser length). (That is, if the length of the region near one end is within the range of 1/8 to 3/8 of the total length), A semiconductor laser having excellent single-wavelength stable operation and a low threshold value can be realized [see FIGS. 5B and 6].

  Further, in the present embodiment, as described above, the width of the optical waveguide 200 is changed by 0.1 μm in the vicinity region of both end portions and the vicinity region of the phase shift 310, and the Bragg wavelength is changed by 0.05%. However, the present invention is not limited to this, and as in the case of the first embodiment described above, the Bragg wavelength in the vicinity of both ends is set in the vicinity of the phase shift 310 in a state where current is not injected into the optical waveguide 200. If it is longer in the range of 0.025 to 0.100% than the Bragg wavelength in the region (if the rate of change of the Bragg wavelength is in the range of 0.025 to 0.100%), the single wavelength stable operation is excellent. A low threshold semiconductor laser can be realized [see FIGS. 5B and 6].

As described with reference to FIG. 8 in the second embodiment, when the waveguide width is changed in the range of 0.05 to 0.25 μm with the optical waveguide having a width of 1.6 μm as a reference, the Bragg wavelength The rate of change is in the range of 0.025 to 0.100%.
For this reason, if the width of the optical waveguide 200 is changed in the range of 0.05 to 0.25 μm between the region near both ends and the region near the phase shift 310, no current is injected into the optical waveguide 200. The Bragg wavelength in the vicinity region of both ends can be made longer in the range of 0.025 to 0.100% than the Bragg wavelength in the vicinity region of the phase shift 310, thereby achieving excellent single wavelength stable operation. A low threshold semiconductor laser can be realized [see FIGS. 5B and 6].

That is, the width of the optical waveguide 200 provided in the vicinity region of both end portions is wider in the range of 0.05 to 0.25 μm than the width of the optical waveguide 200 provided in the region near the phase shift 310. With this configuration, the optical waveguide 200 provided with the equivalent refractive index of the optical waveguide 200 provided in the vicinity of both end portions in the vicinity of the phase shift 310 without current injection into the optical waveguide 200. It becomes larger in the range of 0.025 to 0.100% than the equivalent refractive index of 200. As a result, in a state where current is not injected into the optical waveguide 200, the Bragg wavelength in the region near both ends is made longer in the range of 0.025 to 0.100% than the Bragg wavelength in the region near the phase shift 310. As a result, a semiconductor laser having excellent single-wavelength stable operation and a low threshold value can be realized [see FIGS. 5B and 6].
[Others]
In each of the above embodiments, the semiconductor substrate 100 is an n-type InP substrate. However, the present invention is not limited to this. For example, a p-type InP substrate or a semi-insulating InP substrate (SI-InP substrate) may be used. For example, other semiconductor substrates such as GaAs and GaN may be used. However, a semiconductor laser that generates light in the wavelength band used for optical communication can be obtained by using an InP substrate, and a semiconductor laser that has excellent electrical characteristics and can be easily manufactured can be obtained by using an n-type substrate. It is done.

In each of the above-described embodiments, one λ / 4 phase shift 310 is provided at the center of the diffraction grating 300. However, the present invention is not limited to this. For example, the phase shift is performed at least at one location inside the diffraction grating. Should be provided.
In other words, the λ / 4 phase shift with the phase shift amount of ¼ wavelength is provided in one place, but the present invention is not limited to this. For example, a 3λ / 8 phase shift with a phase shift amount of 3/8 wavelength may be used, or phase shifts may be provided at a plurality of locations. However, by using a λ / 4 phase shift with a phase shift amount of ¼ wavelength, characteristics such as wavelength stability and threshold value are best.

Further, the phase shift does not necessarily have to be provided at the center. For example, the phase shift may be moved from the center position to the left and right within a limit of about 10% of the resonator length. In this case, the single wavelength stability is slightly degraded, but a larger light output can be obtained.
In such a case as well, in the same manner as in each of the above-described embodiments, in the state where current is not injected into the optical waveguide 200, the vicinity region (end portion) of both end portions (both end portions of the element; both end portions of the resonator) The region having a desired length from the Bragg wavelength may be longer than the Bragg wavelength in the region near the phase shift 310 (region adjacent to the phase shift 310). Whether a semiconductor laser has such a configuration can be determined by observing transmission and reflection spectra in the regions near both ends and the region near the phase shift.

  For example, when the phase shift is provided in two places (when the element length is L, each is provided at a position of L / 4 from the end), the diffraction grating is provided in a state where no current is injected into the optical waveguide. The region near both ends of the region (both ends of the element; both ends of the resonator) and the Bragg wavelength in the central portion and the vicinity thereof are configured to be longer than the Bragg wavelength in the region near the phase shift. Just do it.

  Further, in each of the above-described embodiments, the Bragg wavelength is changed by changing the period of the diffraction grating 300 and the width of the optical waveguide 200 in the vicinity of both ends and the vicinity of the phase shift 310. For example, the thickness and composition of the optical waveguide are changed (ie, the equivalent refractive index of the optical waveguide is changed) between the vicinity of both ends and the vicinity of the phase shift, and the Bragg wavelength is changed. In this case, the same effect can be obtained.

  In each of the above-described embodiments, the Bragg wavelength is changed stepwise in the vicinity of both ends and the vicinity of the phase shift 310 in a state where no current is injected into the optical waveguide 200. However, the present invention is not limited to this. For example, as shown in FIG. 10, the Bragg wavelength continuously changes from the vicinity of the phase shift toward both ends (element ends) (that is, gradually). In this case, the same effect can be obtained [see FIGS. 5B and 6].

  For example, in the state where current is not injected into the optical waveguide, the laser length (total length; resonator length; element length) of the region where the Bragg wavelength is changed in one region from the center to one end portion The product of the ratio to the length) and the average value of the rate of change of the Bragg wavelength in the region where the Bragg wavelength is changed may be within the range of 0.003125 to 0.037500%.

  Here, as described in each of the above-described embodiments, the length of the region near both ends is set to a length within the range of 1/8 to 3/8 of the laser length, It can be seen that if the Bragg wavelength is made longer in the range of 0.025 to 0.100% than the Bragg wavelength in the region near the phase shift, it is possible to realize a semiconductor laser with excellent single wavelength stability and low threshold. Therefore, if it is within the range of 0.025% × 1/8 to 0.100% × 3/8, that is, within the range of 0.003125 to 0.037500%, the single wavelength stable operation is excellent. The above numerical range is determined so that a low threshold semiconductor laser can be realized.

  Here, since the numerical range is determined based on the length of the vicinity region at both ends, it seems that the Bragg wavelength is continuously changed in the vicinity region at both ends, Even when the Bragg wavelength is continuously changed over the entire length of the laser (that is, over the entire length of one side from the center to one end), the one side from the center to one end is not limited to the above case. The product of the ratio of the length of the region in which the Bragg wavelength is changed to the laser length in the region of and the average value of the Bragg wavelength change rate in the region in which the Bragg wavelength is changed is 0.003125 to 0.037500%. When configured so as to fall within the range, a semiconductor laser having excellent single-wavelength stable operation and a low threshold value can be realized.

  In each of the above embodiments, a single semiconductor laser is described as an example. However, the present invention is not limited to this. For example, as shown in FIG. Also, other optical functional elements (for example, optical modulators and optical amplifiers) 700 can be integrated to form a semiconductor optical integrated element. In this case, the same effect can be obtained. That is, the semiconductor optical integrated device is mounted on the semiconductor substrate on which the semiconductor laser of each of the above-described embodiments is formed (on the same semiconductor substrate), and at least one optical functional device optically coupled to the semiconductor laser. It can also comprise as what is provided, and the same effect is acquired also in this case.

The present invention is not limited to the above-described embodiments and modifications thereof, and various modifications can be made without departing from the spirit of the present invention.
(Appendix 1)
On a semiconductor substrate, an optical waveguide capable of generating a gain by current injection, and a diffraction grating having a phase shift and provided along the optical waveguide over the entire length of the optical waveguide,
A semiconductor laser characterized in that a Bragg wavelength in a region near both ends is longer than a Bragg wavelength in a region near the phase shift when no current is injected into the optical waveguide. .

(Appendix 2)
The semiconductor laser according to appendix 1, wherein the Bragg wavelength is changed stepwise in a state where current is not injected into the optical waveguide.
(Appendix 3)
In a state where current is not injected into the optical waveguide, the Bragg wavelength in the vicinity region of the both ends is longer in the range of 0.025 to 0.100% than the Bragg wavelength in the vicinity region of the phase shift. The semiconductor laser as set forth in appendix 1 or 2, characterized by being configured.

(Appendix 4)
The period of the diffraction grating provided in the vicinity region of the both ends is longer in the range of 0.025 to 0.100% than the period of the diffraction grating provided in the vicinity region of the phase shift. The semiconductor laser according to any one of appendices 1 to 3, which is characterized in that
(Appendix 5)
The equivalent refractive index of the optical waveguide provided in the vicinity region of the both end portions is in a range of 0.025 to 0.100% than the equivalent refractive index of the optical waveguide provided in the vicinity region of the phase shift. The semiconductor laser according to any one of appendices 1 to 3, wherein the semiconductor laser is large.

(Appendix 6)
The width of the optical waveguide provided in the vicinity region of the both end portions is wider in the range of 0.05 to 0.25 μm than the width of the optical waveguide provided in the vicinity region of the phase shift. The semiconductor laser according to any one of appendices 1 to 5.
(Appendix 7)
Any one of Supplementary notes 1 to 6, wherein the length of the vicinity region of one end of the both end portions is a length within a range of 1/8 to 3/8 of the entire length. The semiconductor laser according to item.

(Appendix 8)
The semiconductor device according to appendix 1, wherein the Bragg wavelength is continuously changed from the vicinity of the phase shift toward both ends in a state where current is not injected into the optical waveguide. laser.
(Appendix 9)
In the state where current is not injected into the optical waveguide, the ratio of the length of the region where the Bragg wavelength is changed in the region on one side from the center to one end, and the region where the Bragg wavelength is changed 9. The semiconductor laser as set forth in appendix 8, wherein the product of the average value of the rate of change of the Bragg wavelength is within a range of 0.003125 to 0.037500%.

(Appendix 10)
10. The semiconductor laser according to any one of appendices 1 to 9, wherein the semiconductor substrate is an InP substrate.
(Appendix 11)
11. The semiconductor laser according to any one of appendices 1 to 10, wherein the phase shift is provided at one place and the phase shift amount is ¼ wavelength.

(Appendix 12)
The semiconductor laser as set forth in appendix 11, wherein the phase shift is provided at the center.
(Appendix 13)
The optical waveguide includes alternately a gain waveguide section capable of generating a gain by current injection and a wavelength control waveguide section capable of controlling an oscillation wavelength by current injection or voltage application in an optical axis direction. The semiconductor laser according to any one of appendices 1 to 12.

(Appendix 14)
14. The semiconductor laser as set forth in appendix 13, wherein the wavelength control waveguide portion is configured such that a refractive index is changed by current injection.
(Appendix 15)
14. The semiconductor laser according to appendix 13, wherein the wavelength control waveguide section is configured such that a refractive index changes by applying a reverse bias voltage.

(Appendix 16)
The semiconductor laser according to any one of appendices 1 to 15;
A semiconductor optical integrated device comprising: an optical functional device provided on a semiconductor substrate on which the semiconductor laser is formed and optically coupled to the semiconductor laser.

DESCRIPTION OF SYMBOLS 100 Semiconductor substrate 200 Optical waveguide 210 Gain waveguide part 220 Wavelength control waveguide part 300 Diffraction grating 310 Phase shift 400,500,510,520 Electrode

Claims (10)

An optical waveguide capable of generating gain by current injection on a semiconductor substrate, a diffraction grating provided along the optical waveguide over the entire length of the optical waveguide, and a phase shift provided in the diffraction grating;
In a state where current is not injected into the optical waveguide, the Bragg wavelength in the vicinity region of both ends is in the range of 0.025 to 0.100% than the Bragg wavelength in the vicinity region of the phase shift adjacent to the phase shift. Configured to be long,
The semiconductor laser according to claim 1, wherein the phase shift is provided at one place, and the phase shift amount is ¼ wavelength.   2. The semiconductor laser according to claim 1, wherein the phase shift is provided in the center.   The period of the diffraction grating provided in the vicinity region of the both ends is longer in the range of 0.025 to 0.100% than the period of the diffraction grating provided in the vicinity region of the phase shift. The semiconductor laser according to claim 1, wherein the semiconductor laser is characterized.   The equivalent refractive index of the optical waveguide provided in the vicinity region of the both end portions is in a range of 0.025 to 0.100% than the equivalent refractive index of the optical waveguide provided in the vicinity region of the phase shift. The semiconductor laser according to claim 1, wherein the semiconductor laser is large.   The width of the optical waveguide provided in the vicinity region of the both end portions is wider in the range of 0.05 to 0.25 μm than the width of the optical waveguide provided in the vicinity region of the phase shift. The semiconductor laser according to any one of claims 1 to 4.   The length of the vicinity region of one end of the both end portions is a length within a range of 1/8 to 3/8 of the entire length. 2. The semiconductor laser according to item 1.   The Bragg wavelength in the vicinity region of the both end portions is configured to be continuously longer toward the both end portions in the vicinity region of the both end portions in a state where current is not injected into the optical waveguide. The semiconductor laser according to claim 1, characterized in that:   In the state where current is not injected into the optical waveguide, the ratio of the length of the region where the Bragg wavelength is changed in the region on one side from the center to one end, and the region where the Bragg wavelength is changed 8. The semiconductor laser according to claim 7, wherein the product of the rate of change of the Bragg wavelength with an average value is within a range of 0.003125 to 0.037500%.   The optical waveguide includes alternately a gain waveguide section capable of generating a gain by current injection and a wavelength control waveguide section capable of controlling an oscillation wavelength by current injection or voltage application in an optical axis direction. The semiconductor laser according to any one of claims 1 to 8. A semiconductor laser according to any one of claims 1 to 9;
A semiconductor optical integrated device comprising: an optical functional device provided on a semiconductor substrate on which the semiconductor laser is formed and optically coupled to the semiconductor laser.

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