JP3784483B2 - Semiconductor laser and its TE / TM polarization mode switching method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor laser and a TE / TM switching method thereof, and more particularly, to a TE / TM polarization mode switching method of a semiconductor laser using a difference in thermal expansion characteristics between a semiconductor laser element and a mounting material.
[0002]
[Prior art]
The semiconductor laser light is polarized into either a TE mode wave having an electric field component in the horizontal direction and a TM mode wave having a magnetic field component from the waveguide structure.
[0003]
In a general semiconductor laser, a laser beam polarized in the TE mode can be obtained from an interband structure in which an emission transition occurs, a loss in a waveguide and a reflection surface, and the like.
[0004]
However, only when a two-dimensional tensile strain is generated in the active layer, the TM mode polarization component becomes strong due to the band structure change in which the light emission transition occurs.
[0005]
As related literature concerning such technology, for example,
[Reference 1: H. Tanaka: “780 nm BAND ™ -MODE LASER OPERATION OF GaAsP / AlGaAs TENSILE-STRAINED QUANTUM-WELL LASTERS”, ELECTRONICS LETTERS 1993, Vol. 29, no. 18, pp 1611-1613]
[Reference 2: K.K. Magari, M .; Okamoto, H .; Yasaka, K .; Sato, Y .; Noguchi and O. Mikami: “Polarization Instinctive Traveling Wave Type Amplifier Using Strained Multiple Quantum Well Structure”, IEEE Photonics Tech. Letters. , 1990, Vol2, No. 8, pp 556-558].
[0006]
If the polarization mode of a single laser beam can be controlled, information can be transmitted in each mode by dividing the laser beam into two polarization components of TE / TM polarized light by a polarizing optical element or the like. It is possible to simply convey twice the amount of information as before with a single laser.
[0007]
Furthermore, since it can be switched by a single laser, it can be expected to be small and simple and to be applied to optical interconnection.
[0008]
[Problems to be solved by the invention]
However, it has only been reported that switching of TE / TM mode polarization from a single laser can be obtained by using a tensile strained quantum well laser and changing the cavity length [Reference 3: Hidetaka Tanaka, Junichi Shimada: "TE / TM mode control of GaAsP strained quantum well laser", Proceedings of the Japan Society of Applied Physics, 1992, No. 3, pp957].
[0009]
The present invention has been made in view of the above situation, and the mode gain switching of TE / TM polarized light in a semiconductor laser element can be easily and easily performed by changing the distortion amount of the semiconductor laser element. It is an object of the present invention to provide a semiconductor laser that can perform the same and a TE / TM polarization mode switching method thereof.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides
[ 1 ] This semiconductor laser element is obtained by utilizing the distortion caused by the difference in expansion coefficient between the mounting material and the semiconductor laser element, which is generated when the semiconductor laser is assembled and lowered from the bonding temperature, which is the melting point of the solder material, to the operating temperature. The semiconductor which switches the TE polarization mode and the TM polarization mode by changing the band structure of the active layer and switching the TE / TM polarization mode gain in the semiconductor laser element by changing the distortion amount of the semiconductor laser element A TE / TM polarization mode switching method of a laser, wherein the band structure of the active layer of the semiconductor laser element is changed by utilizing the strain exerted on the semiconductor laser element by the mounting material, and the TE · TM polarization mode gain is switched according to the amount of injected current. That.
[0011]
[ 2 ] A semiconductor laser that can be subjected to the TE / TM polarization mode switching method of the semiconductor laser according to [1].
[0012]
Since it comprised in this way, the TE * TM polarization mode switching of the semiconductor laser controlled by the mechanical strain can be performed. That is, by utilizing the tensile strain that the mounting material exerts on the semiconductor laser element, the switching of the TE / TM polarization mode gain in the waveguide and the reflecting surface in the semiconductor laser element, operating temperature, introduction of force to the mount, The TE / TM mode oscillation can be switched by a single semiconductor laser by changing the amount of injected current.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0014]
FIG. 1 is a sectional view showing the structure of a ridge type semiconductor laser according to an embodiment of the present invention, and FIG.
[0015]
In this figure, 1 is a heat sink mount material, 10 is a ridge type semiconductor laser device mounted on the heat sink mount material 1, and this ridge type semiconductor laser device 10 is mounted on the heat sink mount material 1 face down. That is, the ridge type semiconductor laser device 10 includes the SiN insulating film 11, the p-side Au electrode 12, the p-type GaAs cap layer 13, the p-type AlGaAs cladding layer 14, the GaAs active layer 15, the n-type AlGaAs cladding layer 16, and the n-type GaAs. The buffer layer 17, the n-type GaAs substrate 18, and the n-side Au electrode 19 are formed.
[0016]
Here, a single quantum well laser of a ridge type semiconductor laser having various GaAs active layer thicknesses was assembled using a SiC mount material having a smaller thermal expansion coefficient than GaAs.
[0017]
FIG. 3 shows the temperature dependence of the TE and TM mode polarization intensity ratios at the time of current injection that is twice the current threshold of these lasers.
[0018]
In the 200 and 600 lasers whose active layer is close to the bulk, the TE and TM mode ratios are reversed around 150 K, and the polarization mode of the oscillation light is switched.
[0019]
This is because the mounting material, SiC, has a smaller coefficient of thermal expansion than GaAs, which is the main material of the semiconductor laser, and as the operating temperature decreases, the laser undergoes a strong tensile strain, and the band structure changes, causing laser oscillation in the TM polarization mode. This is because of this.
[0020]
Such a phenomenon is also disclosed in the following documents.
[Reference 4: T.W. Ikegami: “Reflectivity of Mode at Facet and Oscillation Mode in Double-Heterostructure Injection Lasers”, IEEE Journal of Quantum Electronics. 1972, Vol. QE-8, no. 6, pp 470-476].
[0021]
In addition, the TE / TM ratio inversion does not occur in the laser having an active layer of 60 mm because the active layer is sufficiently quantized and the separation between the light hole and heavy hole subbands is large. This shows that no band structure change that would change the polarization mode occurred.
[0022]
This indicates that the band structure of the active layer of the semiconductor laser element changes due to the strain caused by the mounting material. By appropriately designing the amount of strain due to the semiconductor element structure and the mounting material, TE / TM It shows that a ratio reversal occurs. In addition to the ridge type semiconductor laser of this example, it was confirmed that the TE / TM ratio inversion occurred due to the change of the operating temperature in the semiconductor laser having the current confinement type structure.
[0023]
As described above, TE and TM polarization switching can be performed by using the difference in thermal expansion coefficient between the laser and the mounting material to change the distortion amount of the laser according to the operating temperature.
[0024]
Next, FIG. 4 shows the temperature dependence of the TE / TM intensity ratio when using SiC, GaAs, and Cu mount materials in which the laser during low-temperature operation has tensile strain, no strain, and compressive strain, respectively.
[0025]
The sample is a ridge type laser having a 200 mm thick GaAs active layer. TE / TM intensity ratio reversal occurs only with a SiC-mounted laser that causes tensile strain, and TE mode oscillation occurs mainly in lasers mounted on GaAs or Cu without TE / TM intensity ratio reversal. I understand that.
[0026]
As described above, since the strength ratio between the TE mode and the TM mode is reversed due to the shrinkage of the mounting material, it is understood that the polarization mode can be switched by controlling the laser distortion by applying an external force to the mounting material. .
[0027]
FIG. 5 shows the TE / TM intensity ratio with respect to the current injection amount in the vicinity of 150 K where the TE / TM intensity ratio of the laser mounted on SiC in FIG. 4 is reversed.
[0028]
At an operating temperature of 150 K, the intensity ratio of the TE / TM polarization mode of the laser beam is reversed by increasing the current injection amount. This is because the gain in the waveguide and the reflecting surface for TE / TM polarized light in the laser is reversed depending on the amount of current injection. This is because the mounting material is used to generate an appropriate tensile strain in the laser element, and by changing the current injection amount under the laser operating conditions in which the two polarization mode gains are approximately equal, the TE / TM of the laser is changed. It shows that mode switching is possible.
[0029]
If the polarization characteristics of the TE / TM mode of a single semiconductor laser can be controlled as an industry impact expected by the present invention, an increase in the amount of optical communication information due to the polarization mode component and the accompanying downsizing of the device In addition, a wide range of applications such as application to optical interconnection can be expected.
[0030]
In addition, this invention is not limited to the said Example, A various deformation | transformation is possible based on the meaning of this invention, and these are not excluded from the scope of the present invention.
[0031]
【The invention's effect】
As described above in detail, according to the present invention, switching of the mode gain of TE / TM polarized light in the semiconductor laser element can be easily and simply performed by changing the distortion amount of the semiconductor laser element. Can do.
[0032]
In this way, by controlling the TE / TM mode polarization characteristics of a single semiconductor laser, an increase in the amount of optical communication information due to the polarization mode component, the accompanying miniaturization of the device, and application to optical interconnection are achieved. be able to.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a configuration of a ridge type semiconductor laser showing an embodiment of the present invention.
FIG. 2 is a schematic diagram of electric field direction components during TE / TM polarization mode switching of a ridge type semiconductor laser device according to an embodiment of the present invention.
FIG. 3 is a diagram showing the temperature dependence of TE and TM mode polarization intensity ratios when a current injection of twice the current threshold of a ridge type semiconductor laser according to an embodiment of the present invention is injected.
FIG. 4 is a diagram showing the temperature dependence of the TE / TM intensity ratio when using SiC, GaAs, and Cu mount materials in which the laser during low-temperature operation has tensile strain, no strain, and compressive strain, respectively.
5 is a diagram showing the TE / TM intensity ratio with respect to the current injection amount in the vicinity of 150K where the TE / TM intensity ratio of the laser mounted on SiC in FIG. 4 is reversed. FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Heat sink mount material 10 Ridge type semiconductor laser element 11 SiN insulating film 12 p side Au electrode 13 p type GaAs cap layer 14 p type AlGaAs clad layer 15 GaAs active layer 16 n type AlGaAs clad layer 17 n type GaAs buffer layer 18 n type GaAs substrate 19 n-side Au electrode

Claims (2)

  When assembling the semiconductor laser, the distortion caused by the difference in expansion coefficient between the mounting material and the semiconductor laser element, which occurs when the operating temperature is lowered from the bonding temperature, which is the melting point of the solder material, A semiconductor laser that changes the TE / TM polarization mode gain in the semiconductor laser element by changing the band structure of the active layer, and switches the TE polarization mode and the TM polarization mode by changing the distortion amount of the semiconductor laser element. The TE / TM polarization mode switching method of the TE / TM in the semiconductor laser device by utilizing the strain that the mounting material exerts on the semiconductor laser device and changing the band structure of the active layer of the semiconductor laser device A semiconductor characterized in that the polarization mode gain is switched by the amount of injected current TE · TM switching method of polarization mode of Za. A semiconductor laser capable of being subjected to the TE / TM polarization mode switching method of the semiconductor laser according to claim 1.

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