JPH0779182B2 - Semiconductor laser device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device, and more particularly to a semiconductor laser device capable of changing an oscillation wavelength.

[Conventional technology]

Conventionally, in a general semiconductor laser device, its optical waveguide is usually formed in a linear shape. Thus, in the case of this type of semiconductor laser device, either a method of changing the temperature or a method of changing the refractive index of the optical waveguide is adopted as a means for changing the oscillation wavelength.

Here, the former method of changing the temperature is, for example, AlGa
In the case of an As-based so-called short-wavelength laser device, the Peltier element or the like is used to raise or lower the temperature of the active layer to change its oscillation wavelength to short-wavelength or long-wavelength side at a rate of about 3Å / degree. Alternatively, or by increasing or decreasing the injection current supplied to the active layer, the temperature of the active layer is similarly changed to change the oscillation wavelength. That is, in this case, the band gap of the active layer becomes narrower as the temperature rises, the oscillation wavelength shifts to the long wavelength side, and at the same time, the resonator length becomes slightly longer due to the thermal expansion. ， And the refractive index is also reduced by the lower part of the density,
The oscillation wavelength is lengthened while jumping one after another on the longitudinal modes determined by these competitions.

The latter method, which utilizes the Franz-Keldesh effect, which is one of the most effective methods of changing the refractive index, has a refractive index of about 10 ^-4 when a high electric field is applied to the active layer by reverse bias. The refractive index can be changed to about 10 ⁻³ by optimally selecting the carrier concentration and the bias condition.

[Problems to be solved by the invention]

However, in the case of the former method of changing the temperature among the above-mentioned conventional means, the speed is limited by the heat capacity, and the threshold value changes with the change of the wavelength. However, in the latter method of changing the refractive index, the active layer and the amplification region are electrically insulated from each other in order to effectively apply the reverse bias. However, there is a problem that the optical loss is large when the focus is placed on the electrical insulation, and conversely, the insulation becomes difficult when the optical loss is suppressed.

Accordingly, the object of the present invention is, in view of such a problem in the conventional device, a semiconductor laser device of this kind which can independently change the oscillation wavelength regardless of the temperature or the optical output. Is to provide.

[Means for solving problems]

In order to achieve the above-mentioned object, in the present invention, the optical waveguide in the semiconductor laser device is formed into a shape having at least two or more curved portions with different curvatures, instead of being linear as in the conventional device, The spatial distribution of carriers in the pn junction is changed depending on the magnitude of the injected current to change the path of light, thereby making it possible to change the oscillation wavelength independently.

The operating principle of the present invention will be described with reference to FIG.

Now, it is assumed that a pn junction having a curved portion with a radius R is formed between a pair of reflecting surfaces having a predetermined angle (radian) θ.

In this case, however, when the forward current I is applied, the path having the radius of curvature R becomes the maximum gain line a. By increasing the forward current by ΔI, the electron density is also increased. Therefore, in connection with this, this time, the maximum gain line b is the portion that is closer to the p side by ΔR.

Therefore, when the injection current has a constant value I, it follows an optical path having a length of Rθ and a wavelength λ N oscillates with an effective refractive index, and m is an integer representing the resonance longitudinal mode order. However, when this injection current increases by ΔI and the value becomes I + ΔI, this becomes (R + ΔI) θ
In order to follow the optical path of Become longer.

However, in this case, in practice, the effect of increasing the injection current density is to move the energy distribution of gain to the high energy side, and even if it is slight, the forbidden band width is narrowed by the temperature rise. In order to oscillate in the longitudinal mode order of the wavelength closest to the gain maximum wavelength determined by the synergistic effect of each effect with the effect of moving to the low energy side, the oscillation wavelength is shown by the thick line in Fig. 2 (a). As shown in (1), it generally changes continuously within a certain range, and then moves to another longitudinal mode order discontinuously (stepwise).

Further, by appropriately setting the radius of curvature R and the angle θ, the resonance longitudinal mode line can be made parallel to the maximum gain line,
It should be possible to obtain a continuous wavelength change in a wide current range, but as described above, the maximum gain line depends on the temperature and the current density, and is slightly different for each laser device. According to the invention, not only one curved portion having a radius of curvature R, but also a portion having a different radius of curvature such as a curved portion due to -R, or a linear portion if necessary, is provided to make the inclination of the resonance longitudinal mode line from the outside. The injection current can be changed by adjusting the injection current.

That is, the present invention provides a semiconductor laser device in which an optical waveguide for obtaining an optical gain by current injection is formed between at least a pair of reflectors or reflecting surfaces,
A semiconductor laser device characterized in that at least two curved portions having different curvatures are formed in the optical waveguide, and an injection current having a controlled value can be applied to each of these curved portions. is there.

[Action]

Therefore, in the present invention, the oscillation wavelength is controlled by applying an injection current of a controlled value to each of the at least two curved portions having different curvatures that form the optical waveguide. It can be changed independently of temperature and light output.

〔Example〕

An embodiment of a semiconductor laser device according to the present invention will be described in detail below with reference to FIGS. 3 and 4.

3 (a) and 3 (b) are a perspective view schematically showing a schematic configuration of a semiconductor laser device to which an embodiment of the present invention is applied, and a plan view schematically showing an active layer portion of the same as above. .

That is, in the configuration shown in FIGS. 3 (a) and 3 (b), reference numeral 1 is a semi-insulating GaAs substrate, and 2 is n-Al.
_X Ga _1-y As layer, 3 is an n-Al _y Ga _1-y As active layer having a thickness of about 0.1 μm, 4 is an n-Al _x Ga _1-x As layer, and 5 is an n-GaAs layer. Each of these layers is continuously grown by the liquid phase epitaxial growth (LPE) method, the molecular beam epitaxial growth (MBE) method, or the metalorganic pyrolysis deposition (MO-CVD) method. The value of is controlled to about 0.4 and the value of y is controlled to about 0.1.

In addition, in this embodiment, a Si ₃ M ₄ film or the like is separately used, and each of the above-mentioned region portions is composed of at least two first and second curved portions, that is, FIG. 1 (b). At the positive side, the radius of curvature R ₁ is 2000 μm (2 mm)
And a curved portion 51b curved with a radius of curvature R ₂ on the negative side of −2000 μm (−2 mm) to divide into a first region and a second region. Impurities using a ₃ N ₄ film as a mask, Zn is diffused here at a temperature of about 650 ° C., and then each of the regions is partially heated by heat treatment at a high temperature except for Zn as the impurity diffusion source. To p-type. Here, the first and second regions exchanged to the p ^{+ type} by this diffusion are shown by broken lines, and the pn junction formed by the heat treatment is shown by solid lines.

In the figure, 21, 31, 41 and 51 are p ^{+ due to the} diffusion.
The Al _X Ga _1-x As layer 2, the Al _y Ga _1-y As active layer 3, the Al _x Ga _1-x As layer 4, and the GaAs layer 5 respectively converted into the shape,
The n-GaAs layer 5 extending between the first and second p ^{+ type} regions 31a and 31b and the pn junction is removed by etching. Further, 6 is an electrode for the n-GaAs layer 5, and 7 and 8 are respective electrodes for the p-GaAs layer 51 corresponding to the first and second regions 31a and 31b.

Therefore, in the case of this embodiment, the electrode 6 is made negative,
When 7 and 8 are positively biased, a forward current flows in the pn junction, and this injection current is n-Al _y Ga _1-y As with the lowest diffusion potential.
It flows through the pn junction between the active layer 3 and the p-Al _y Ga _1-y As active layer 31, and is narrow (normally about 2 μm) surrounded by a solid line and a broken line due to the relationship between the free carrier density and the band gap. p ⁺ region 32
This p ⁺ region 32 because the refractive index of
Light is guided to the
The light is injected into the p ⁺ region 32 to emit light, and the current density thereof is increased to generate a population inversion, and the light is amplified and oscillates on both reflecting surfaces.

Also here, as described above, the first region 31a on the p ⁺ side
Is curved to the positive side with a radius of curvature R ₁ , 2000 μm (2 mm), and the second region 31 b is also curved with a radius of curvature R ₂ , −2000.
Although it is curved to the negative side by μm (−2 mm), these radii of curvature are values obtained from its refractive index distribution so that light is guided along the p ⁺ region 32. It does not matter if you increase the value.

In the case of the configuration of this embodiment, if the bending angle of the first region 31a is β and the bending angle of the second region 31b is α, α = β
= 5.625 °, the optical path length is about 392.5 μm. Then, when the value of y is set to about 0.1, the oscillation wavelength is about 850 nm, and the effective refractive index in this wavelength range is about 3.4. Therefore, the longitudinal mode order m is about
It is 3,140, and the wavelength difference from the m ± 1st order is 0.27 nm.

In this case, the threshold current for oscillation is about 70mA.
In order to obtain a light output of about 3mW, the injection current I is about 90m.
It is necessary to set A, and the injection current I is about 1mA in this current region.
If it is increased only by, the gain maximum position moves to the p ⁺ region side by about 0.1 nm. When the optical waveguide is curved in an arc shape as shown in FIG. 1, ΔR = 0.1 · θ
Therefore, in the configuration shown in FIG. 3 according to this embodiment,
Since θ is π / 32 radians (5.625 °), about the injection current I
Due to the increase of 1 mA, the optical path length of the first region 31a becomes
It becomes about 0.0982nm longer, and about 0.0982n in the second region 31b.
Shortened by m. Therefore, each of these first and second areas 31
If the injection current I is increased by the same value at a and 31b, the optical path length will be canceled and there will be no change.
The current value corresponding to the amount increased in the first area 31a is set to the second area 3
By reducing by 1b, the optical path length can be lengthened by about 0.1964 nm, which is almost double.

However, in practice, the change in the injection current I not only moves the gain maximum position, but also changes the effective refractive index, the bandgap energy, and thus the gain maximum wavelength. If the injection current I flowing in the first region 31a and the second region 31b in the configuration of this embodiment shown in FIG. 3 is adjusted and controlled by means such as passing through a differential amplifier circuit, the gain is increased. The change in maximum wavelength and the change in optical path length can be made to coincide with each other. That is, in the structure of this embodiment, the oscillation wavelength of this semiconductor laser device is controlled by controlling the injection current I flowing in the first region 31a and the second region 31b, as shown by the bold line in FIG. 2 (b). Can be continuously changed within a range of about 10 nm.

In the configuration of the embodiment, the values of the radii of curvature R1 and R2 are set to 200 μm and −2000 μm, respectively, but this | R1 | = |
R2 | does not necessarily have a significant meaning, and other values may be used. Further, although the optical waveguide is formed by two curved curved portions, as shown in FIGS. 4 (a), (b),
As shown in (c), this optical waveguide may be formed by combining two curved curved portions 101 and 102 with another linear portion 103. When such a linear portion 103 is included, At the time of manufacturing the element, the cleavage position has some arbitrariness, which facilitates its manufacture. In addition, the linear portion 103 is also provided with an independent electrode so that the injection current I can be controlled. For example, the oscillation wavelength and the optical output can be controlled independently, and the degree of freedom can be further improved. Furthermore, as an example of configuring a resonator,
Although the case where the cleavage plane of the crystal is used has been described, a so-called DBR type reflector may be used as shown in FIG. 4 (d). In addition, in this embodiment, the AlGaAs laser device has been described.
It is needless to say that the same action and effect can be obtained by applying to a laser device using other semiconductor material such as a system.

〔The invention's effect〕

As described in detail above, according to the present invention, in a semiconductor laser device in which an optical waveguide for obtaining an optical gain by current injection is formed between at least a pair of reflectors or reflecting surfaces, At least 2 with different curvatures in the waveguide
Since two curved portions are formed and an injection current having a controlled value can be applied to each of these curved portions, the oscillation wavelength can be continuously changed. Introducing an FM modulation method, or applying each to a light source for coherent transmission and a local oscillation light source for heterodyne detection. In the optical measurement field, spectroscopic measurement is used in solid-state laser excitation. The tunable excitation at the optimum wavelength becomes possible, which can greatly contribute to the development of these various fields.

[Brief description of drawings]

1 and 2 (a) and 2 (b) are explanatory views showing the operating principle and effect of the semiconductor laser device according to the present invention, respectively, and FIGS. 3 (a) and 3 (b). Is a perspective view schematically showing a schematic configuration according to an embodiment of the same semiconductor laser device, and a plan view schematically showing the active layer portion of the same as above. FIGS. 4A to 4D are the same semiconductor laser device. 3 is a schematic plan view showing each of the other embodiments. 1 ... Semi-insulating GaAs substrate, 2,21 ... n-Al _x Ga _1-x As layer, p-
Al _x Ga _1-x As layer, 3,31 …… n-Al _y Ga _1-y As active layer, p-Al _y Ga
_1-y As active layer, 31a, 31b ... first region, second region, 4,41 ...
… N-Al _x Ga _1-x As layer, p-Al _x Ga _1-x As layer, 5,51 …… n-GaAs
Layers, p-GaAs layer, 6 ... Electrodes for n-GaAs layer 5, 7, 8
... Each electrode for the p-GaAs layer 51 corresponding to the first and second regions 31a and 31b.

Claims (2)

[Claims] 1. A semiconductor laser device in which an optical waveguide for obtaining an optical gain by current injection is formed between at least a pair of reflectors or reflecting surfaces, and the optical waveguide has at least two different curvatures. A semiconductor laser device, wherein two curved portions are formed, and an injection current having a controlled value can be made to flow to each of these curved portions. 2. The semiconductor laser device according to claim 1, wherein the at least two curved portions having different curvatures forming the optical waveguide optionally include a linear portion.