JP2947142B2 - Tunable semiconductor laser - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength tunable semiconductor laser, and more particularly, to an integrated wavelength tunable semiconductor laser that performs wavelength tuning using a diffraction grating.

[0002]

2. Description of the Related Art High speed optical fiber communication has been rapidly progressing in recent years. At present, the transmission speed is being limited by the band of the electric circuit constituting the optical transmitter / receiver. Therefore, a wavelength division multiplexing (WDM) optical transmission system is attracting attention as a means that can easily increase the total transmission capacity without being restricted by an electrical speed with respect to the transmission speed, and can effectively utilize the broadband property of light. It is becoming.

[0003] Also related to this are wavelength-division multiplexing optical switching systems, wavelength cross-connect systems, and the like. In these systems, a semiconductor laser whose oscillation wavelength is variable in a wide wavelength range is regarded as important as a key device. The required wavelength variable width is desirably about 30 nm in consideration of fully utilizing the bandwidth of the optical fiber amplifier. Further, it is desirable that the wavelength variable laser can be controlled in wavelength by a single current or voltage from the side of using the variable wavelength laser. This is because if there are two or more control currents, complicated control is required to obtain a desired oscillation wavelength.

A typical example of a wide-band tunable semiconductor laser is an SSG (Super Structure Grating) semiconductor laser (for example, Y. Tohmori et al., IEEE Photonics Technology Letters Magazine, Vol. 5, No. 2, issued in 1993). 126-129). FIG. 7 shows a sectional view of this conventional example. As shown in FIG. 7, two diffraction gratings 33 are formed on the semiconductor substrate 31 and the light guide layer 3 is formed thereon.
2 are formed. The active layer 3 is formed on the light guide layer 32.
4 and a cladding layer 35 is formed thereon. The diffraction grating 33 is periodically modulated, so that SSG regions are formed on both sides of the active region. An electrode 36 is formed on the active layer 34, an electrode 37 is formed on the diffraction grating 33, and an electrode 38 is formed on the back surface of the substrate. The oscillation wavelength is controlled by injecting the main current Ia into the active region by these electrodes and injecting the control currents It ₁ and It ₂ into the SSG region.

In addition, a Y-branch semiconductor laser (M.
Kuznetsov et al., IEEE Photonics Tech, published in 1992.
nology Letters, Vol. 4, No. 10, pages 1093-10
95) and a sampled grating laser (V. Jay)
araman et al., Applied Phisics Letters published in 1992
Magazine, Vol. 60, No. 19, pp. 2321 to 2323) and the like are known as broadband tunable semiconductor lasers. Further, the laser beam is incident on a diffraction grating provided outside the semiconductor laser, and the laser beam is configured to receive the returned light (diffracted light). The oscillation wavelength may be changed by mechanically changing the angle of the diffraction grating. Are known.

[0006]

In the above-described SSG laser, two control currents It ₁ and It ₂ must be adjusted in order to obtain a laser having a desired wavelength. Therefore, there is a problem that the control circuit becomes complicated. This point is common to other broadband integrated tunable semiconductor lasers. In these conventional examples, it is necessary to supply two or more control currents, and the control becomes complicated. Was.

[0007] In the wavelength variable system in which a diffraction grating is provided outside the semiconductor laser and tuning is performed by using the diffraction grating, it takes a lot of time to align the semiconductor laser with an external element (diffraction grating), and the apparatus can be downsized. There was a disadvantage that it became difficult. Therefore, the object of the present invention is:
An object of the present invention is to provide a wavelength tunable semiconductor laser that can be integrated, requires only one control current or control voltage to obtain a desired wavelength, and can vary the wavelength over a wide band with a simple control circuit.

[0008]

Means for Solving the Problems] wavelength tunable semiconductor laser according to the present invention for achieving the above object, the current injection
An active stripe for generating more optical gain;
A reflector provided at one end of the tripe;
At the other end of the tripe, light in a horizontal plane
Light beam sweeper that can change the traveling direction electrically
A slab light guide for propagating light emitted from the light beam sweeper.
A waveguide and a diffraction grating provided at the tip of the slab optical waveguide.
And the reflector are integrated on a semiconductor substrate, and the reflecting mirror and the
Tunable semiconductor with resonator formed between diffraction grating
In the body laser, the light beam sweepers are arranged in parallel.
The plurality of optical waveguides and the output from the active stripe.
Light distribution means for distributing the emitted light to the plurality of optical waveguides;
The optical waveguides are asymmetrical in the direction perpendicular to the light propagation direction.
An electrode for injecting current or applying an electric field;
The part where the electrode is not formed on the optical waveguide is one side
From one to the other .

[0009]

Next, an embodiment of the present invention will be described. FIG. 1 is a conceptual diagram showing a schematic configuration of a wavelength tunable semiconductor laser according to the present invention. As shown in FIG. 1, a wavelength tunable semiconductor laser according to the present invention comprises an active stripe 2 having an optical gain generated by current injection, and a light beam sweeper 3 provided at one end thereof for adjusting an emission angle of a laser beam. And a lens 4 as a mechanism for collimating light and a diffraction grating 5 are integrated on a semiconductor substrate 1a. The laser resonator is formed between one end of the active stripe 2 (formed of a cleavage surface of a semiconductor or the like) and the diffraction grating 5. Then, the angle at which the laser light from the active stripe 2 is incident on the diffraction grating 5 is adjusted by changing the beam angle by the light beam sweeper 3.

Here, the pitch of the diffraction grating 5 is Λ, the angle between the axis perpendicular to the surface on which the diffraction grating 5 is formed and the extension axis of the active stripe 2 is φ, and the beam emitted from the light beam sweeper 3 is the angle between the extended line theta, when the equivalent refractive index of the slab waveguide (plate-shaped waveguides between the lenses 4 diffraction grating) and n _e, only the light of wavelength λ that satisfies the following equation (1) The light is selectively returned to the active stripe 2 by the diffraction grating 5, and as a result, the laser oscillates at the wavelength λ. λ = (2 / m) n e Λ sin (φ - θ) (1) (m is an integer) where changing the beam angle theta, it is possible to change the lasing wavelength than (1). The angle of the diffraction grating 5 is φ
= 53 degrees and a pitch of 0.3 μm (equivalent refractive index n
_e = 3.2, m = 1), for a center wavelength of 1.53 μm,
A wavelength control of about 20 nm can be realized by changing the beam angle by 1 degree.

The beam sweeper 3 guides the laser emission light to a plurality of parallel optical waveguides, and injects a current into the plurality of optical waveguides asymmetrically in a direction perpendicular to the light propagation direction or applies an electric field. It is to be . As a mechanism for collimating light, a combination of a concave mirror and a plane mirror (or a concave mirror) other than a lens can be used. Alternatively, instead of forming the diffraction grating 5 in a straight line, the diffraction grating 5 may be formed in a concave shape to have a collimating function. As the diffraction grating, a commonly used type can be appropriately used.

[0012]

Next, reference examples and embodiments of the present invention will be described with reference to the drawings. First Example] FIG. 2 is a first structural view from above of the wavelength tunable semiconductor laser of Example of the present invention. an active stripe 2 and a beam sweeper 3 connected thereto on an n-InP substrate 1;
A lens unit 4a for collimating the laser beam from the beam sweeper 3 and a diffraction grating 5 are integrated. The active stripe 2 and the beam sweeper 3 have electrodes 16 and 17 for current injection.

The distance between the beam sweeper 3 and the diffraction grating 5 is 1
mm, the pitch of the diffraction grating 5 was set to 0.3 μm, and the angle between the axis perpendicular to the surface on which the diffraction grating 5 was formed and the extension axis of the active stripe 2 was set to 53 degrees. The length of the active stripe 2 is 40
0 μm. The length of the beam sweeper 3 is 100 μm. The end of the active stripe 2 opposite to the beam sweeper 3 is terminated by a cleavage plane of the semiconductor crystal.

FIG. 3A is a sectional view taken along line AA 'in FIG. As shown in FIG. 3A, an n-InGaAsP light guide layer 11 (having a thickness of 0.1 μm) having a wavelength composition of 1.2 μm is formed on the n-InP substrate 1 in common with all regions.
Are formed. Furthermore, an active stripe 2
InGaAs having a wavelength composition of 1.55 μm in a region corresponding to
I consisting of P / InGaAsP multiple quantum well (MQW)
An nGaAsP active layer 12, an InGaAsP tuning layer 13 (0.2 μm in thickness) having a wavelength composition of 1.45 μm in a region of the beam sweeper 3, and a wavelength composition in a region between the lens portion 4 a and the diffraction grating 5. 1.2 μm InG
aAsP slab waveguide layers 14 (0.2 μm in thickness) are formed.

[0015] Then, p
-An InP cladding layer 15 (1.5 μm thick) is formed. In the lens portion 4a, a lens effect is provided by a difference in refractive index between a portion where the slab waveguide layer 14 is formed and a portion where the slab waveguide layer 14 is not formed and the shape of the boundary of the lens portion 4a having a convex curve. Electrodes 16 and 17 are provided on the active stripe 2 and the beam sweeper 3. n
An electrode 18 is formed on the back surface of the InP substrate 1.
The diffraction grating 5 is provided on a surface formed so as to vertically cut the slab waveguide layer 14 and the light guide layer 11 from the p-InP clad layer 15.

FIG. 3B is a sectional view taken along line BB 'of FIG. An optical guide layer 11 is provided on an n-InP substrate 1, on which an active layer 12 having a width of 1.5 μm and a cladding layer 15 surrounding the active layer 12 are formed. S on the semiconductor layer
An SiO ₂ film 19 is formed, and a window is provided in the SiO ₂ film 19 at a position corresponding to a position directly above the active layer, and an ohmic contact with the electrode 16 formed thereon is formed at this portion. Have been.

FIG. 3C is a sectional view taken along line CC 'of FIG. An optical guide layer 11 is formed on an n-InP substrate 1, and a tuning layer 13 having a width of 5.0 μm and a cladding layer 15 surrounding the tuning layer 13 are further formed thereon.
A groove is provided in the center of the cladding layer. The tuning layer 1 is provided on the SiO ₂ film 19 formed on the semiconductor layer.
A window is provided slightly offset from the center position of 3,
At that portion, an ohmic contact with the electrode 17 formed thereon is formed. As a result, current can be asymmetrically injected from the electrode 17 into the tuning layer 13.

By asymmetric current injection into the tuning layer 13, a laterally asymmetric refractive index distribution is formed inside the tuning layer 13. As a result, the beam emitted from the beam sweeper 3 is emitted at an angle θ with the axis of the active stripe 2.

Next, briefly described manufacturing method of the present embodiment element. Light guide layer 11 on n-InP substrate 1
Is grown over the entire surface. Subsequently, an active layer 12, a tuning layer 13, and a slab waveguide layer 14 are formed by a selective MOVPE (metal organic chemical vapor deposition) method. That is, first, an SiO ₂ film is formed on the light guide layer 11, then a window is opened in a portion of the SiO ₂ film corresponding to the active stripe 2, and the active layer 12 is selectively crystal-grown only in this window portion. .

Similarly, a window is opened in the SiO ₂ film in the region where the tuning layer 13 is to be formed, and the tuning layer is selectively grown. Subsequently, the window is opened in the SiO ₂ film in the region where the slab waveguide layer 14 is to be formed. To grow a slab waveguide layer. Thereafter, the window of the SiO ₂ film in each region is widened, and the cladding layer 15 is selectively grown so as to surround the active layer 12, the tuning layer 13, and the slab waveguide layer. Finally, by forming the SiO ₂ film 19 and the electrode 16, 17, 18 using a conventional electrode forming process, the wavelength tunable semiconductor laser of the present reference example is obtained.

The laser oscillation at an oscillation threshold 30mA by the current injected into the active stripe 2 of this reference example device has occurred. Further, by injecting a current of about 100 mA into the beam sweeper 3, control of the laser oscillation wavelength of 20 nm was realized with mode jump. In other words, the oscillation wavelength of 1.53 μm without injection of the control current was able to be oscillated at 1.55 μm by injection of 100 mA of current. In this reference example element is a diffraction grating from the beam sweeper 3 5
When viewed from the side, it is a kind of reflection type filter. The band of this filter is almost determined by the width of the opening of the beam sweeper 3 and the distance between the beam sweeper 3 and the diffraction grating 5. Is done. Here, since they are 5 μm and 1 mm, respectively, the half bandwidth of the filter is about 3 nm. This bandwidth is almost sufficient for the present laser to oscillate in a single mode, so that the present device can control the wavelength while always maintaining the single mode.

[0022] [Second Example] Fig. 4 is a structural view from above of the wavelength tunable semiconductor laser of the second reference example of the present invention. This reference example device basically operates on the same principle as the device of the first embodiment. But the first
In the element of the reference example, since the distance between the beam sweeper 3 and the diffraction grating 5 was as long as 1 mm, the device length was as extremely long as 1.5 mm or more. The element of this reference example has a feature that its device length can be shortened. In FIG. 4, an active stripe 2 and a beam sweeper 3 are provided on a semiconductor substrate 1.
Are formed, but these structures are the same as those of the first reference example.

[0023] In this reference example, as a means for collimating the laser beam, it is used concave mirror 21 instead of the lens. The light reflected by the mirror 21 is again reflected by the flat mirror 22 and enters the diffraction grating 5. The pitch and the formation angle of the diffraction grating 5 are the same as in the first reference example. Because the present reference example device utilizes a folded optical, physical distance between the diffraction grating 5 and the beam sweep device 3 is shortened, therefore the device length can be shortened. First participant
Device length to obtain the same wavelength control characteristics and considered examples could short to about 1 mm.

The mirrors 21 and 22 were vertically etched so as to reach the n-InP substrate 1 deeper than the optical waveguide 11 in order to obtain a high reflectance, thereby forming reflection surfaces. Further, high reflectance was realized by forming a metal on the etched surface. This method for obtaining a high reflectance is also effective for forming the diffraction grating 5. Substantially the same characteristics as elements of the first reference example is obtained in the reference example elements. That is, the wavelength control of about 20 nm was realized with the tuning current of the laser oscillation threshold current of 30 mA and 100 mA.

In the first and second reference examples, the electrode for current injection is formed only on one side of the beam sweeper 3 centering on the traveling direction of light, but the second electrode is also formed on the opposite side. By forming, the wavelength variable width can be doubled. That is, by injecting a current into one of the two electrodes, the beam can be swung in two directions. In the first and second reference examples, the lens portion 4a and the concave mirror 21 are used to collimate the beam. However, without using these, the diffraction grating 5 itself has a curved property, and the diffraction grating 5 It may be designed so that the light diffracted by is focused on the beam sweeper 3.

First Embodiment FIG. 5A is a top view of a wavelength tunable semiconductor laser according to a first embodiment of the present invention. An active stripe 2, a beam sweeper 3, and a diffraction grating 5 are formed on an n-InP substrate 1. First, compared to the second reference example, it does not require a mechanism for collimating the laser beam in this embodiment device. This is because the beam sweeper 3 has a function of beam collimation. The structure of the active stripe 2,
Pitch and form an angle of the diffraction grating 5 is the same as in the first embodiment.

The beam sweeper 3 includes a plurality of optical waveguides (here, ten optical waveguides) arranged in an array, a star coupler for branching the laser light from the active stripe 2 into these waveguides, and respective waveguides. And an electrode 17 for injecting a current or applying an electric field. The lengths of the electrode portions formed on the respective waveguides are different, and are shorter from the endmost optical waveguide toward the other.

FIG. 5B is a sectional view (DD 'section) taken along the active stripe 2 of the first embodiment. n-I
InGa having a wavelength composition of 1.2 μm is formed on the entire surface on the nP substrate 1.
An AsP light guide layer 11 is formed. An active layer 12 made of InGaAsP / InGaAsP · MQW having a wavelength composition of 1.55 μm is formed on a portion corresponding to the active stripe 2 thereon, and a 1.3 μm wavelength composition is formed on a portion corresponding to the arrayed optical waveguide of the beam sweeper 3. Tuning layer 13
Are formed selectively. And n-
An InP cladding layer 15 is formed, and electrodes 16 and 17 are formed on the active stripe 2 and the beam sweeper 3 thereon. The diffraction grating 5 is formed on a vertical plane formed by etching that reaches deeper than the light guide layer 11 and reaches the n-InP substrate 1.

FIG. 5C is a cross-sectional view (EE 'cross section) of the beam sweeper 3 of the first embodiment cut in the horizontal direction. An optical guide layer 11 is formed on an n-InP substrate 1, a tuning layer 13 that forms a plurality of (ten) waveguides thereon, and a cladding layer 15 is formed so as to surround them. Further, SiO formed on the semiconductor
_{The second} film 19 is provided with a window for injecting current into the tuning layer 13, and an ohmic contact with the electrode 17 formed thereon is formed in this window.

In the beam sweeper 3 of this embodiment, the light from the active stripe 2 is split into an array of optical waveguides by a star coupler. Then, the length and structure of each optical waveguide are optimized such that the phases of light at the emission ends of the optical waveguides are aligned in a state where no tuning current is injected. With this configuration, the light emitted from the beam sweeper 3 becomes a parallel beam without using an element such as a lens that collimates light.

Since the length of the electrode portion formed on the waveguide is changed for each waveguide so as to be reduced from one end to the other, the tuning current is reduced. The amount of phase change of the light that occurs when the light is injected slightly changes from the optical waveguide at one end to the other optical waveguide. As a result, the output beam maintains parallel light,
Since only the wavefront of the light is inclined, the light emitting direction can be changed. In the beam sweeper 3 of the device of this embodiment, the electrode length of the endmost waveguide is set to 100 μm, which is the longest, and the electrode length is set to zero in the opposite end of the waveguide.

The beam sweeper 3 of this embodiment has a length of 30.
0 μm, of which the star coupler is about half
Occupies 50 μm. The width of the optical waveguide after branching is 1.5 μm, the pitch of the waveguide is 5 μm, and the beam sweeper 3
Has a width of about 50 μm. Here the waveguide pitch P, the wavelength lambda, when the equivalent refractive index to n _e, maximum beam sweep angle of this type of beam sweep instrument given by Rael. θ = sin ⁻¹ (λ / _ne P) (2) From the above equation, it is possible to control the emission angle up to about 5 degrees in the device of this embodiment.

In the device of the present embodiment, of the light emitted from the beam sweeper 3 and diffracted by the diffraction grating 5 and returned, the return light (specific light) returned at the same angle as the light emitted from the beam sweeper 3 is returned. Only light having a wavelength is coupled back to the active stripe 2 and returns. The other return light, when light enters the star coupler from the plurality of optical waveguides, causes a phase mismatch of the light from each waveguide, and therefore does not return to the active stripe 2 by coupling. As a result, laser oscillation occurs at a specific wavelength λ. And the oscillation wavelength λ
Produces a wavelength change of about 20 nm for a change of the beam emission angle of 1 degree, similarly to the elements of the first and second reference examples.

[0034] In this embodiment elements, the band of the filter when viewed diffraction grating 5 side from the beam sweeper 3 is different from such elements of the first reference example, diffraction and beam sweeper 3 grating 5 Hardly depends on the distance between Therefore, this distance can be shortened, and the size of the element can be reduced. In the case of the device of this example, this distance was set to about 200 μm. The half bandwidth as a filter strongly depends on the number of waveguides of the beam sweeper 3. In our study, the number of waveguides was 10
In the case of a book, about 2.5 nm is obtained, and it is known that the value is almost sufficient for single mode oscillation.

The oscillation threshold current of the device of this embodiment is 40 m
A. Further, by injecting a current of about 100 mA into the beam sweeper 3, 30 nm is obtained while mode jumps occur.
The control of the laser oscillation wavelength was realized. The single mode operation was maintained even during the wavelength control, and a submode suppression ratio of 20 dB was obtained. In this embodiment, the number of the waveguides of the beam sweeper 3 is set to 10, but basically, it is sufficient if the number is two or more. However, in order to narrow the bandwidth as a filter and obtain more stable laser oscillation with a higher submode suppression ratio, the larger the number of waveguides, the better.

[ Second Embodiment] FIG. 6A is a structural view of a wavelength tunable semiconductor laser according to a second embodiment of the present invention as viewed from above. The structure and arrangement of the active stripe 2 and the beam sweeper 3 are the same as those of the element of the first embodiment. The difference is that in the first embodiment, the diffraction grating 5 is formed on a vertical semiconductor crystal plane, but in this embodiment, the diffraction grating 5 is formed on a horizontal plane. ₁ the angle φ formed by the extension direction and the active stripe 2 of the diffraction grating 5, the pitch lambda, the output angle of the beam theta, when the equivalent refractive index to n _e, the laser oscillation wavelength λ of the embodiment device following It is represented by the following equation. λ = 2ne _e / cos (φ ₁ −θ) (3) In the element of this embodiment, the pitch of the diffraction grating is 0.2 μm, and φ ₁ =
By setting the angle to 34 degrees, it is possible to realize an oscillation wavelength control of 18 nm for a change of the output angle of the beam with respect to the center wavelength of 1.55 μm.

FIG. 6B is a sectional structural view (F) of the device of the second embodiment along the active stripe 2 and its extension.
-F 'section). The diffraction grating is formed between the n-InP substrate 1 and the light guide layer 11. The oscillation threshold current of the device of this example was 40 mA, and a wavelength control of about 30 nm was realized with a tuning current of 100 mA. In the element of the present embodiment, the position where the diffraction grating 5 is formed may not be the position shown in the embodiment, but may be, for example, a periodic deep groove reaching from the cladding layer 15 to the optical n-InP substrate 1. You may.

In the first and second embodiments of the present invention, a tunable semiconductor laser having a wavelength band of 1.55 μm has been described. However, the present invention can of course be applied to lasers having other wavelength bands. In that case, the pitch Λ and the angle φ of the diffraction grating 5 may be appropriately adjusted. Further, since the maximum wavelength variable width also changes depending on the pitch Λ and the angle φ of the diffraction grating 5, even in the wavelength band of 1.55 μm, Λ and φ may be appropriately designed so as to obtain a desired wavelength variable width. . Further, the semiconductor material system is not limited to the InP / InGaAsP system shown here, but may be another material system. The active layer 12 does not have to have the MQW structure and may be a bulk semiconductor. Further, the tuning layer 13 may have an MQW structure. Further, in the embodiment of the present invention, the control current is injected into the beam sweeper 3, but a voltage (or an electric field) may be applied instead of the current injection.

In general, when a voltage is applied, sufficient wavelength control may not be obtained because the change in the refractive index of the semiconductor is smaller than that in the case of current injection, but in the case of the elements described in the first and second embodiments. Since the beam sweeper 3 does not require a large change in the refractive index, voltage application is also effective. Further, in the embodiment of the present invention, the end of the active stripe 2 on the side opposite to the beam sweeper 3 is constituted by a cleavage plane of the semiconductor crystal, but a diffraction grating is provided in this portion on the horizontal plane of the n-InP substrate 1. It may be formed to form a distributed reflection area. In this case, the distributed reflection area and the beam sweeper 3
Constitute a laser resonator with the diffraction grating 5 located at the end of the laser cavity.

Further, a modulator, a semiconductor optical amplifier, and the like can be integrated on the side opposite to the active stripe 2 with the distributed reflection region interposed therebetween. Further, the wavelength tunable semiconductor laser shown in the above embodiment can be operated as a wavelength tunable optical filter except for the active stripe portion 2. Further, even if an anti-reflection coating is applied to the cleaved surface at one end of the active stripe 2, it becomes a wavelength tunable filter. In this case, this portion functions as an optical amplifier by injecting current into the active stripe.

[0041]

As described above, the wavelength tunable semiconductor laser according to the present invention has an active stripe, a light beam sweeper, and a diffraction grating integrated on a semiconductor substrate. The wavelength can be controlled over a wide wavelength range of 30 nm by the current or the voltage. Being able to perform wavelength control with a single current or voltage has the effect of facilitating wavelength control in an actual system.
Therefore, according to the present invention, it is possible to provide a light source that is extremely useful for a wavelength multiplexing optical communication system, an optical switching system using wavelength switching, a cross connect system, and the like, and that is easily controlled. Further, the wavelength tunable width as wide as 30 nm sufficiently covers the wavelength band of the optical fiber amplifier. Therefore, according to the present invention, it is possible to realize wavelength multiplex communication that makes full use of the bandwidth of the optical fiber amplifier.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram illustrating an embodiment of the present invention.

FIG. 2 is a plan view showing a first reference example of the present invention.

3 is a line AA ', line BB' and line CC 'of FIG. 2;
Sectional view of the line.

FIG. 4 is a plan view of a second reference example of the present invention.

FIG. 5 is a plan view and a cross-sectional view of the first embodiment of the present invention.

FIG. 6 is a plan view and a cross-sectional view of a second embodiment of the present invention.

FIG. 7 is a sectional view of a conventional example.

[Explanation of symbols]

Reference Signs List 1 n-InP substrate 1a semiconductor substrate 2 active stripe 3 beam sweeper 4 lens 4a lens unit 5, 33 diffraction grating 11 InGaAsP light guide layer 12 InGaAsP active layer 13 InGaAsP tuning layer 14 InGaAsP slab waveguide layer 15 p-InP cladding layer 16, 17, 18, 36, 37, 38 Electrode 19 SiO ₂ film 21 Concave mirror 22 Mirror 31 Semiconductor substrate 32 Light guide layer 34 Active layer 35 Cladding layer

Claims (3)

(57) [Claims] 1. An active stripe in which an optical gain is generated by current injection, a reflecting mirror provided at one end of the active stripe, and a horizontal mirror provided at the other end of the active stripe. A light beam sweeper that can electrically change the traveling direction of the light, a slab optical waveguide that propagates light emitted from the light beam sweeper, and a diffraction grating provided at a tip end of the slab optical waveguide, Is integrated on a semiconductor substrate, in a wavelength-variable semiconductor laser in which a resonator is formed between the reflection mirror and the diffraction grating, the light beam sweeper, a plurality of optical waveguides arranged in parallel, A light distribution means for distributing light emitted from the active stripe to the plurality of optical waveguides, and an electrode for asymmetrically injecting a current or applying an electric field to the plurality of optical waveguides in a direction perpendicular to a light propagation direction; Said The electrodes on a plurality of optical waveguides are shaped
A wavelength tunable semiconductor laser characterized in that a portion not formed decreases from one side to the other side . 2. The semiconductor device according to claim 1, wherein the diffraction grating is formed at the end of the slab optical waveguide linearly on a surface perpendicular to a semiconductor substrate surface or in a concave shape so that diffracted light is focused. The tunable semiconductor laser according to claim 1. 3. The tunable semiconductor laser according to claim 1, wherein said diffraction grating is formed parallel to a semiconductor substrate surface along said slab optical waveguide.