JPS61137388A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To obtain a sole vertical mode by forming a semiconductor multilayer film of n/4 (n is refractive index) wavelength on a semiconductor substrate, and forming a semiconductor laser of double-hetero structure including a P-N junction thereon. CONSTITUTION:A semiconductor multilayer film 2 in which InP layers of nL/4(NL is refractive index) wavelength and N type InGaPsP layers of nH/4(nH is refractive index) wavelength are alternately laminated is formed on an N type InP substrate, an InP layer 3, an N type InGaAsP active layer 4, a P type InP layer 6, a P type InGaAsP layer 6 are further sequentially grown, and ohmic electrodes 7, 8 are formed. Further, the both ends of the layer 4 are etched at approx. 45 deg.C, to form an Si/SiO2 reflecting film 9 (60% reflectivity) is formed. When the electrodes 7, 8 are energized, a laser oscillation is generated by a resonator made of the active layer 4, the film 9 and the film 2 to emit an oscillating light from the film 9. Thus, a single vertical mode is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to semiconductor lasers used as light sources in optical fiber communications.

Conventional technology Semiconductor lasers used as light sources in optical fiber communications are generally required to have single-transverse mode oscillation, low threshold current, good leading Kerr current characteristics, temperature characteristics, and no problems in life. In order to achieve long-distance, large-capacity transmission, single-longitudinal mode oscillation is required. Semiconductor lasers that have conventionally attempted to achieve a single longitudinal mode generally have a distributed feedback type structure. In this structure, a periodic diffraction grating is formed on a semiconductor substrate or an epitaxially grown layer to achieve single mode oscillation.

Problems to be Solved by the Invention Diffraction gratings as described above are made with a period of several thousand onguest σ-m and are generally made by exposing a photoresist to interference light from an ultraviolet laser. In particular, the depth has an extremely large effect on the oscillation threshold current, etc., and affects the reproducibility and yield of the characteristics of the laser itself, so that it has not been put into practical use at present.

Means for Solving the Problems In the present invention, in order to solve the above problems, it is possible to create a single longitudinal mode by the following method without using a distributed feedback type structure. That is, semiconductors having a thickness of about λ/4 (λ is the oscillation wavelength of the laser) having different refractive indexes in the growth direction are alternately grown and stacked. A general semiconductor laser, ie, a double heterostructure including a p-n junction, is grown on such a stack. A groove is formed at the edge of the active layer of such a wafer at an angle of about 45°, and a reflective film is provided in the groove, so that light emitted by the current injected into the active layer is guided to the semiconductor stack by the reflective film. If the higher refractive index of the stacked semiconductor layers is expressed as "H1" and the lower one is expressed as nL, then the reflectance R is expressed by the following equation.

Here, ns is the refractive index of the semiconductor substrate, and no is the refractive index of the first cladding layer in the double heterostructure.

Further, k is the number of layers. With such a semiconductor multilayer film, it is possible to obtain an extremely high reflectance at a desired wavelength, and it is also possible to provide an interference filter effect. The present invention provides strong selectivity to the oscillation wavelength by appropriately combining lnL.

Function: The light emitted from the active layer of the above-mentioned double heterostructure is reflected by the surface 450 provided with the reflective film and guided to the semiconductor multilayer film. This multilayer film is n Hn Ln Hn L"L"
H”l, nLnHnLnHnL (the thickness of each layer is equal to the wavelength)
That is, when na is sandwiched between nL having a thickness of % wavelength, or vice versa, there is sharp selectivity to the oscillation wavelength. Due to the correlation between the selectivity, the gain distribution, and the resonance condition, the extremely stable single-layer structure shown in FIG. 1 of the present invention (100
) shows a cross section of a semiconductor laser made using a substrate taken in the (011) direction. The active layer has a thickness of 0
．． 16μm.

It has a width of 2.6 μm and is embedded in n-InP. 1st
In the figure, n-InP/n-
Ten pairs of InGaAsP semiconductor multilayer films 2 are alternately provided with a thickness of about 990 layers, and further, n-InP3゜n-I
nGaAsP active layer 4, p-InP 5
, p-InGaAsP6 (this layer may be omitted) are successively grown. Ohmic electrodes 7 and 8 are attached to this, and both ends of the n-InGaAsP active layer 4 are etched to approximately 450 mm, and S 1 /S
Attach the iO2 reflective film 9. The reflectance of this Si/5iO29 is adjusted to be 80% for light with a wavelength of 1.3 μm. When electricity is applied to the ohmic electrode 7°8 having such a structure, the n-InGaAsP active layer 4 and
S1/SiO2 reflective film 9, and InP/InG
Laser oscillation is caused by the co-imager made of the aA+sP semiconductor multilayer film 2, and the oscillated light can be extracted from the S 1 /S iO2 reflective film. The oscillation spectrum is multimode as shown in FIG. In the structure shown in Fig. 1, n-1nP of n-InP/n-InGaAsP 9 [thickness %nL wavelength (nL is the refractive index of InP]) nLn-
InGaAsP [thickness%nH wavelength (nH is InGaAsP
refractive index of A s P)] In the above case, LHLHLHLHLHLHLHLHLH, but this can be changed to LHLHLHLHLLHLLHLHLHLH.
It was set as L. That is, the H layer has a thickness of 1/2n wavelength.
The structure is sandwiched between InP. In the above configuration, the reflectance has wavelength dependence with a peak at a wavelength of 1.3 μm.

Therefore, oscillation is possible under the highest reflectance among the resonance conditions determined by the cavity length. FIG. 3 shows the oscillation spectrum of the laser of the present invention having such a semiconductor multilayer film, and an extremely stable single-longitudinal mode was obtained.

Example 2 In the structure described in Example 1, layers corresponding to 1/2 nl of wavelength and an H layer sandwiched therebetween were inserted in duplicate.

That is, LHLHLHLH(LLHLL)HLHLH
A semiconductor multilayer film called LHL was inserted. In this case as well,
It becomes vertical mode.

However, LLHL that further increases such layers
L)3, single mode oscillation was not obtained. Therefore, up to two layers of LLHLL can be included.

Effects of the Invention As described above, the present invention provides a single-layer structure using a semiconductor multilayer film.
A longitudinal mode can be obtained, and production is extremely stable compared to conventional methods using diffraction gratings.

In the above embodiment, an InP/InGaAsP laser was described, but GaAs/GaAIAs
A similar effect can be obtained with a laser using

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a semiconductor laser according to an embodiment of the present invention, and FIGS. 2 and 3 are excavated spectra of the same semiconductor laser. 1... n-InP substrate, 2... semiconductor multilayer film, 4-=.n-I nGaAsP active layer, 9--
----- S i /S i O□ reflective film. Name of agent: Patent attorney Toshio Nakao and one other person vS
1 figure

Claims (2)

[Claims] (1) A semiconductor multilayer film with a wavelength of 1/4n (n is the refractive index) is formed on a semiconductor substrate, and a first cladding layer, an active layer, and a second cladding layer are sequentially formed on this to guide the wave of the active layer. The end face in the direction is processed at approximately 45°, a reflective film is formed on this face, the light emission from the active layer is guided to the semiconductor multilayer film, and the entire structure is made into a resonator structure.
A semiconductor laser characterized in that at least two layers each having a thickness of 1/2n wavelength are inserted into the semiconductor multilayer film. (2) The semiconductor laser according to claim 1, wherein the number of layers having a thickness of 1/2n wavelength is four at most.