JP4116463B2 - Semiconductor laser device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor laser device that emits light generated in an active layer as main light from one end face and emits light as monitor light from the other end face.
[0002]
[Prior art]
In an optical measuring instrument that measures the characteristics of each optical communication device or optical transmission line incorporated in the optical communication system, a semiconductor laser device is used as a light source of an optical signal for measurement transmitted to the optical communication device or optical transmission line. Is incorporated. Since the signal level of the measurement optical signal needs to be strictly controlled, it is necessary to accurately control the light intensity of the light (main light) emitted from the semiconductor laser device as the light source.
[0003]
In order to accurately control the intensity of the light emitted from the semiconductor laser device (main light), as shown in FIG. 6, one end face 3a of the semiconductor laser device 1 in which the active layer 2 is formed is formed. The light intensity Pa of the main light 6 emitted from the optical fiber 5 and guided to the optical fiber 5 through the lens 4 and the light intensity Pb of the monitor light 8 emitted from the other end face 3b of the semiconductor laser device 1 are received by a light receiving element (PD). 7 to detect. A main light-side reflecting film 9 having a reflectance Ra set to about 2%, for example, is formed on the end face 3a from which the main light 6 is emitted, and a reflectance Rb is, for example, 95 at the end face 3b from which the monitor light 8 is emitted. The monitor light side reflective film 10 set to be equal to or greater than% is formed.
[0004]
Therefore, most of the light generated in the active layer 2 is emitted as the main light 6 from the end face 3a on which the main light side reflection film 9 is formed, and a part of the light generated in the active layer 2 is reflected on the monitor light side. The light is emitted as monitor light 8 from the end surface 3b on which the film 10 is formed.
[0005]
Since the ratio (Pb / Pa) between the light intensity Pa of the main light 6 and the light intensity Pb of the monitor light 8 is considered to be substantially constant, the light intensity Pb of the monitor light 8 detected by the light receiving element (PD) 7 The light intensity Pa of the main light 6 is controlled to the target light intensity Pa. Specifically, the current I supplied to the semiconductor laser device 1 is controlled.
[0006]
The monitor light-side reflection film 10 having a reflectance Rb set to 95% or higher, for example, includes an interference type wavelength filter as shown in FIG. As shown in FIG. 8, the monitor light side reflection film 10 constituted by this interference type wavelength filter reflects the wavelength λ of the light (incident light) 13 incident on the monitor light side reflection film 10. The rate Rb has a mountain-shaped characteristic. The wavelength of the incident light 13 that maximizes the reflectance Rb is λ _M.
[0007]
In the interference type wavelength filter in which the reflectance Rb is maximum at the wavelength λ _M , as shown in FIG. 7, the low refractive index layer 11 having the refractive index n ₁ of light and the high refractive index layer 12 having the refractive index n ₂ of light. Are alternately stacked (n ₂ > n ₁ ). As is well known, the thickness t _{1 of} each low refractive index layer 11 and the thickness t ₂ of each high refractive index layer 12 are set as follows.
[0008]
t ₁ = λ _M / 4n ₁
t ₂ = λ _M / 4n ₂
If the number of layers of the low refractive index layer 11 and the high refractive index layer 12 is increased, the reflectance Rb increases.
[0009]
In general, in order to use the monitor light side reflective film 10 with the maximum efficiency, the wavelength λ _M of the incident light 13 having the maximum reflectance Rb is matched with the wavelength (use wavelength) of the monitor light 8 (main light 6). I have to.
[0010]
A technique for attaching the interference type wavelength filter to one end face from which the light of the semiconductor laser device is emitted has already been reported in Patent Document 1.
[0011]
In this way, a part of the light generated in the active layer 2 is taken out as the monitor light 8 from the one end face 3b through the monitor light side reflection film 10, so that the other light intensity Pb of the monitor light 8 is used. It is possible to control the light intensity Pa of the main light 6 emitted from the end face 3a through the main light-side reflecting film 9.
[0012]
[Patent Document 1]
Japanese Patent Laid-Open No. 9-129799 [0013]
[Problems to be solved by the invention]
However, the semiconductor laser device 1 shown in FIG. 6 still has the following problems to be improved.
[0014]
Assuming that the intensity of light generated in the active layer 2 is constant, and the reflectance Ra of the main light side reflecting film 9 is constant, the reflectance Rb of the monitor light side reflecting film 10 changes. As shown in FIG. 9, the ratio Pb / Pa of the light intensity Pb of the monitor light 8 to the light intensity Pa of the main light 6 changes.
[0015]
On the other hand, if the current I supplied to the semiconductor laser device 1 is increased, the intensity of the light generated in the active layer 2 is increased. Therefore, as shown in FIG. The light intensity Pa of the main light 6 emitted through the light also increases.
[0016]
However, if the current I supplied to the semiconductor laser device 1 is increased, the temperature of the semiconductor laser device 1 rises. Therefore, as shown in FIG. The wavelength λ of the light changes to the long wavelength side.
[0017]
In recent years, improvement in the light intensity Pa of the main light 6 emitted from the semiconductor laser device 1 is required, and the light intensity Pa of the main light 6 is used in a wide light intensity range from a low light intensity Pa to a high light intensity Pa. . Accordingly, the use wavelength range (λ _{S to} λ _L ) of the wavelength λ of the monitor light 8 (main light 6) also covers a wide range from the use minimum wavelength λ _S to the use maximum wavelength λ _L as shown in FIG. It spans.
[0018]
The wavelength λ _M of the incident light 13 at which the reflectance Rb in the monitor light-side reflective film 10 is maximized is a used wavelength range that is a main used wavelength for obtaining a high output of the main light 6 as shown in FIG. The longest use wavelength λ _L of (λ _{S to} λ _L ) is set. In some cases, the wavelength is set longer than the longest wavelength λ _L used.
[0019]
However, when the wavelength λ _M of the incident light 13 having the maximum reflectance Rb is set to the longest wavelength λ _L of the used wavelength range (λ _{S to} λ _L ) or even longer, as described above, the monitor light side reflection film The reflectance Rb at 10 is an increasing function in the use wavelength range (λ _{S to} λ _L ). When the light intensity Pa of the main light 6 is increased, the ratio Pb / Pa of the light intensity Pb of the monitor light 8 to the light intensity Pa of the main light 6 decreases as shown in FIG. As a result, as shown in FIG. 12, even if the light intensity Pa of the main light 6 increases to the light intensity Pa corresponding to the longest wavelength λ _L used, the light intensity of the monitor light 8 transmitted through the monitor light side reflection film 10 Pb saturates without increasing corresponding to the increase in the light intensity Pa of the main light 6.
[0020]
In FIG. 12, the light intensity Pb of the monitor light 8 is enlarged and displayed for the sake of simplicity.
[0021]
Thus, if the light intensity Pb of the monitor light 8 does not increase corresponding to the increase of the light intensity Pa of the main light 6, the light intensity Pa of the main light 6 cannot be accurately controlled by the light intensity Pb of the monitor light 8.
[0022]
The present invention has been made in view of such circumstances, and the light intensity of the monitor light increases corresponding to the increase of the light intensity of the main light, and the light intensity of the main light is accurately determined by the light intensity of the monitor light. An object of the present invention is to provide a semiconductor laser device that can be controlled and can output light of high light intensity with high accuracy.
[0023]
[Means for Solving the Problems]
In the present invention, light generated in an active layer formed above a semiconductor substrate made of InP is emitted as main light from one end face and emitted as monitor light for monitoring the output characteristics of the main light from the other end face. In addition, a main light side reflection film is formed on the end face from which the main light is emitted, and a monitor light side reflection film having a higher reflectance than the main light side reflection film is formed and supplied to the end face from which the monitor light is emitted. As the current increases, the light intensity of the emitted main light increases and the temperature of the active layer rises. With this temperature rise, the wavelength of the light generated and emitted from the active layer moves to the longer wavelength side. The wavelength range of the emitted light changes and is applied to a semiconductor laser device whose range is 1450 nm which is the shortest use wavelength of the use wavelength range of the main light to 1480 nm which is the longest use wavelength .
Then, the reflectance of 95% or more of the light in the monitor light side reflective film changes depending on the wavelength of the incident light, and the wavelength of the incident light at which the light reflectance is maximum is the shortest use wavelength range of the main light. It is set shorter than the wavelength.
[0024]
In the semiconductor laser device configured as described above, the wavelength of the incident light having the maximum reflectance in the monitor light-side reflective film having a high reflectance formed on the end face from which the monitor light of the semiconductor laser device is emitted is the wavelength used. It is set shorter than the shortest usable wavelength in the range. Therefore, the reflectance of the monitor light side reflective film becomes a decreasing function with respect to an increase in wavelength within the wavelength range used.
[0025]
As a result, even if the light intensity of the main light increases and the wavelength becomes longer, the light intensity of the monitor light transmitted through the monitor light side reflective film does not decrease or saturate, and the light intensity of the main light increases. As you go up. Therefore, since the light intensity of the monitor light changes corresponding to the change in the light intensity of the main light within a wide use wavelength range, the light intensity of the main light can be accurately controlled by the light intensity of the monitor light.
[0026]
According to another invention, in the semiconductor laser device according to the invention described above, the monitor light-side reflection film has a wavelength of incident light that maximizes the light reflectance as λ _M , and the refractive index of the low refractive index layer as n _1. When the refractive index of the high refractive index layer is n ₂ , a plurality of low refractive index layers having a thickness of λ _M / 4n ₁ and high refractive index layers having a thickness of λ _M / 4n ₂ are alternately stacked. And an interference type wavelength filter.
[0027]
By adopting the interference type wavelength filter having such a configuration as the monitor light side reflection film, it is possible to set the wavelength λ _{M of the} incident light that maximizes the light reflectivity with high accuracy.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic diagram showing a schematic configuration of a semiconductor laser device according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view of the semiconductor laser device shown in FIG. 1 taken along the line AA ′. The same parts as those of the conventional semiconductor laser device shown in FIG.
[0029]
In this embodiment, a main light-side reflecting film 9 having a reflectance Ra set to about 2%, for example, is formed on one end face 3a of the semiconductor laser device 20 in which the active layer 2 is formed. The main light 6 having the light intensity Pa is emitted from the end face 3 a through the main light side reflection film 9 and guided to the optical fiber 5 through the lens 4. On the other end face 3b of the semiconductor laser device 20, a monitor light side reflective film 21 having a reflectance Rb set to, for example, 95% or more is formed. The monitor light 8 having the light intensity Pb is emitted from the end face 3b through the monitor reflection film 21 and is incident on the light receiving element (PD) 7.
[0030]
The light intensity Pa of the main light 6 is controlled to the target light intensity Pa by the light intensity Pb of the monitor light 8 detected by the light receiving element (PD) 7. Specifically, the current I supplied to the semiconductor laser device 1 is controlled.
[0031]
In the cross-sectional view of FIG. 2, a lower cladding layer 23 made of n-type InP and an active layer 2 made of InGaAsP are sequentially laminated on a semiconductor substrate 22 made of n-type InP. A part of the lower cladding layer 23 and the active layer 2 are formed in a mesa shape. A lower buried layer 25 made of p-type InP and an upper buried layer 26 made of n-type InP are formed on both sides of the mesa type.
[0032]
Further, an upper cladding layer 24 made of p-type InP is formed on the upper surface of the active layer 2 and the upper surface of the upper buried layer 26. A p-type contact layer 27 is formed on the upper surface of the upper cladding layer 24. A p-electrode 28 is attached to the upper surface of the p-type contact layer 9, and an n-electrode 29 is attached to the lower surface of the semiconductor substrate 22.
When a DC voltage is applied between the p electrode 28 and the n electrode 29, the active layer 2 generates light.
[0033]
As shown in FIG. 3, the monitor light side reflecting film 21 formed on the end face 3b of the semiconductor laser device 20 of this embodiment has a monitor light side formed on the end face 3b of the conventional semiconductor laser device 1 shown in FIG. Like the reflective film 10, it is composed of an interference wavelength filter.
[0034]
That is, when the reflectivity Rb is the wavelength lambda _M of the incident light 13 becomes the maximum, as shown in FIG. 3, the low refractive index layer with a refractive index n ₁ of the light 11 and the high refractive index of the refractive index n ₂ of the light A plurality of layers 12 are alternately stacked (n ₂ > n ₁ ). The thickness t _{1 of} each low refractive index layer 11 and the thickness t ₂ of each high refractive index layer 12 are set as follows.
[0035]
t ₁ = λ _M / 4n ₁
t ₂ = λ _M / 4n ₂
If the number of layers of the low refractive index layer 11 and the high refractive index layer 12 is increased, the reflectance Rb increases.
[0036]
In the semiconductor laser device 20, the wavelength λ _M of the incident light 13 at which the reflectance Rb in the monitor light side reflective film 21 is maximized is the main light 6 (emission from the semiconductor laser device 20 as shown in FIG. It is set shorter than the shortest usable wavelength λ _{S in} the usable wavelength range (λ _{S to} λ _L ) of the monitor light 8).
[0037]
In the semiconductor laser device 20 of this embodiment, the shortest usable wavelength λ _S in the usable wavelength range of the main light 6 (monitor light 8) is 1450 nm, the longest usable wavelength λ _L is 1480, and the reflection on the monitor light side reflecting film 21 is reflected. The wavelength λ _M of the incident light 13 that maximizes the rate Rb is set to 1430 nm.
[0038]
Since the reflectance Rb becomes maximum at the wavelength λ _M = 1430 nm of the incident light 13, in this embodiment, the low refractive index layer 11 is a silicon oxide having a refractive index n ₁ = 1.45 and a thickness t ₁ = 240 nm. (SiO ₂ ) is used, and titanium dioxide (TiO 2) having a refractive index n ₂ = 2.15 and a thickness t ₂ = 165 nm is used as the high refractive index layer 12. Then, as shown in FIG. 4, the number of layers of the low refractive index layer 11 and the high refractive index layer 12 is set so that the maximum reflectance Rb at the wavelength λ _M = 1430 nm is 98.5%. .
[0039]
Since the wavelength λ _M of the incident light 13 that maximizes the reflectance Rb is set to be shorter than the shortest usable wavelength λ _{S in the} usable wavelength range (λ _{S to} λ _L ), as shown in FIG. In the use wavelength range (λ _{S to} λ _L ) of the light 6 (monitor light 8), the reflectance Rb of the monitor light side reflective film 21 decreases as the wavelength λ increases. In this embodiment, when the wavelength λ increases from the shortest usable wavelength λ _S = (1450 nm) to the longest usable wavelength λ _L (= 1480), the reflectance Rb decreases from 98.45% to 98.30%.
[0040]
The main light-side reflection film 9 formed on the end face 3a from which the main light 6 is emitted is also an interference wavelength filter, similarly to the monitor reflection film 21 formed on the end face 3b from which the monitor light 8 is emitted. Although configured, the reflectance Ra is set to around 2%.
[0041]
In the semiconductor laser device 20 configured as described above, when the current I supplied to the semiconductor laser device 20 is increased, as shown in FIG. 5, the main light emitted from the end surface 3a through the main light side reflection film 9 The light intensity Pa of 6 also increases. When the current I is increased to increase the light intensity Pa of the main light 6, the wavelength λ of the main light 6 (monitor light 8) also moves to the longer wavelength side within the use wavelength range (λ _{S to} λ _L ). When the wavelength λ of the main light 6 (monitor light 8) moves to the longer wavelength side, the reflectivity Rb in the monitor light side reflective film 21 decreases as shown in FIG. When the reflectance Rb decreases, the light intensity Pb of the monitor light 8 increases.
[0042]
Therefore, as shown in FIG. 5, even if the light intensity Pa of the main light 6 increases and the wavelength λ becomes longer to the longest usable wavelength λ _L (= 1480) in the usable wavelength range (λ _{S to} λ _L ), The light intensity Pb of the monitor light 8 that passes through the monitor light-side reflecting film 21 does not decrease or saturate, but increases as the light intensity Pa of the main light 6 increases. Therefore, the light intensity Pb of the monitor light 8 changes corresponding to the light intensity change of the main light 6 within a wide wavelength range (λ _{S to} λ _L ). 6 can be accurately controlled.
[0043]
Since a known interference wavelength filter is employed as the monitor light side reflection film 21, the wavelength λ _M of the incident light 13 at which the reflectance Rb is maximized can be set with high accuracy.
[0044]
【The invention's effect】
As described above, in the semiconductor laser device of the present invention, the wavelength of incident light that maximizes the reflectance of light in the monitor light side reflective film is set to be shorter than the shortest usable wavelength in the usable wavelength range of the main light. . Therefore, the light intensity of the monitor light increases corresponding to the increase of the light intensity of the main light, the light intensity of the main light can be accurately controlled by the light intensity of the monitor light, and light with high light intensity can be output with high accuracy. .
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a schematic configuration of a semiconductor laser device according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing a schematic configuration of a semiconductor laser device according to the embodiment. FIG. 4 is a schematic configuration diagram of a monitor light side reflective film of the semiconductor laser device. FIG. 4 is a reflectance characteristic diagram of a monitor light side reflective film of the semiconductor laser device according to the embodiment. FIG. 6 is a characteristic diagram showing a relationship between the light intensity of light and the light intensity of monitor light. FIG. 6 is a schematic diagram showing a schematic configuration of a conventional semiconductor laser device. FIG. Schematic configuration diagram [FIG. 8] Reflectivity characteristic diagram of a general monitor light side reflection film [FIG. 9] A diagram showing the relationship between the reflectance of the monitor light side reflection film and the light intensity ratio [FIG. 10] Supply current and output The relationship between the light intensity and wavelength FIG. 11 is a reflectance characteristic diagram of the reflection light-side reflection film in the conventional semiconductor laser device. FIG. 12 shows the relationship between the light intensity of the main light and the light intensity of the monitor light in the conventional semiconductor laser device. Characteristics [Explanation of symbols]
DESCRIPTION OF SYMBOLS 1,20 ... Semiconductor laser device, 2 ... Active layer, 3a, 3b ... End face, 6 ... Main light, 8 ... Monitor light, 9 ... Main light side reflection film, 10, 21 ... Monitor reflection film, 11 ... Low refraction Index layer, 12 ... high refractive index layer, 22 ... semiconductor substrate, 23 ... lower cladding layer, 24 ... upper cladding layer, 25 ... lower buried layer, 26 ... upper buried layer, 27 ... p-type contact layer, 28 ... p electrode, 29 ... n electrode

Claims (2)

Light generated in the active layer (2) formed above the semiconductor substrate (22) made of InP is emitted as main light (6) from one end face (3a) and the main face from the other end face (3b). A main light-side reflecting film (9) is formed on the end face from which the main light is emitted and is emitted as monitor light (8) for monitoring the output characteristics of the light, and the main face is formed on the end face from which the monitor light is emitted. A monitor light side reflection film (21) having a higher reflectance than the light side reflection film is formed,
As the supplied current increases, the light intensity of the emitted main light increases and the temperature of the active layer rises. With this temperature rise, the wavelength of the light generated and emitted from the active layer In the semiconductor laser device (20), the wavelength range of the emitted light is in the range from 1450 nm which is the shortest use wavelength of the use wavelength range of the main light to 1480 nm which is the longest use wavelength . ,
The reflectance (Rb) of 95% or more of the light in the monitor light side reflective film varies depending on the wavelength (λ) of the incident light, and the wavelength (λ _M ) of the incident light that maximizes the reflectance of the light. Is set shorter than the shortest usable wavelength (λ _S ) in the usable wavelength range of the main light. The monitor light side reflective film (21) has a wavelength of incident light that maximizes the reflectance of the light as λ _M , a refractive index of the low refractive index layer (11) as n ₁ , and a high refractive index layer (12 the refractive index of) When n _2, interferometric wavelength are stacked high refractive index layers are alternately located in the low refractive index layer and the thickness of λ _M / 4n ₂ with a thickness of λ _M / 4n ₁ 2. The semiconductor laser device according to claim 1, wherein the semiconductor laser device is a filter.

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