JP2751558B2 - Integrated optical semiconductor device and driving method thereof - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an integrated optical semiconductor device and a driving method thereof.

(Prior Art and Issues to be Solved) Optical communication technology has shown rapid progress in recent years, and high-speed systems of several Gb / s and long-distance and large-capacity systems exceeding 100 km have been reported. Among them, distributed feedback semiconductor laser (DFB-LD) and distributed Bragg reflection semiconductor laser (DBR
−LD) is used as a key device not only in a direct detection system but also in an application to, for example, an FSK coherent system. When a single DFB laser is used as a transmission light source of, for example, an FSK coherent system, a red shift FM in which a transmission frequency shifts to a longer wavelength due to an increase in modulation current due to a thermal effect in a low frequency region. In the high frequency region, the carrier effect causes a blue shift FM that shifts to a short wavelength due to an increase in the modulation current, and the dip frequency at the intersection is several hundred.
Occurs at kHz. Therefore, there is a problem that the waveform is deteriorated in transmission due to the phase inversion. Kotaki et al., Published in 1989, Electronics Letters, No. 25, aimed at eliminating such phase reversals.
Volume, pages 990 to 991, a λ / 4 shift DFB laser with a three-electrode structure was developed. By adjusting the injection current distribution ratio using such an element, a 19-mm wavelength tunable range, a spectral line width of 900 kHz or less, and an FM response characteristic without phase inversion at 20 mW optical output were realized. However, the FM modulation efficiency at the GHz level is about 0.5 GHz / mA, and higher FM modulation efficiency has been desired for high-speed FSK modulation. Further, it is desirable that the light output be as large as the local light source.

An object of the present invention is to provide an integrated single-wavelength semiconductor laser device having a high FM modulation efficiency and a large optical output based on the above-described viewpoint.

(Means for Solving the Problems) In an integrated optical semiconductor device according to the present invention, in an integrated optical semiconductor device having at least an active layer, a waveguide layer and a diffraction grating on a semiconductor substrate, two opposing end faces have high reflection. A film, a low-reflection film is formed, an electrode that applies a DC current to the low-reflection film side independently of the laser light resonance direction, and an electrode that applies a DC current and a modulation current to the high-reflection film side, The length of the electrode on the high reflection film side is shorter than the length of the electrode on the low reflection film side.

Further, according to the method of driving an integrated optical semiconductor device of the present invention, in an integrated optical semiconductor device having at least an active layer, a waveguide layer and a diffraction grating on a semiconductor substrate, a high reflection film and a low reflection film are provided on two opposing end faces. Are formed in the laser light resonance direction.
Two independent electrodes are formed, of the two electrodes
A DC current is applied to the low-reflection end face side electrode, and a DC current and a modulation current are applied to the high-reflection end face side electrode. The length of the electrode on the high reflection end face side is shorter than the length of the electrode on the low reflection end face side.

(Operation) The operation principle of the integrated device of the present invention will be described below. As shown in FIG. 1 (a), a DFB laser having a low-reflection and high-reflection end face structure is divided into two regions, and independent electrodes are formed on the respective regions. FIGS. 1B and 1C schematically show the electric field distribution and the carrier density distribution of light, respectively. When a laser is oscillated by injecting a current uniformly, a large amount of carriers are consumed because the light density is high on the high reflection end face side, and the carrier density is reduced there by the effect of spatial hole burning. This is indicated by broken lines in the figure. As in the present invention, by applying a larger amount of current to the high reflection end face side as an electrode division structure to suppress hole burning, a flat carrier density distribution can be obtained as shown by a solid line. Since the average value of the carrier density in the entire resonator is higher when the carrier density is non-uniform due to hole burning, the Bragg wavelength is shorter than when the carrier density is uniform. The degree of hole burning, that is, the oscillation wavelength, the spectral line width, and the like can be controlled by adjusting the current flowing to the high reflection end face side. Further, by applying a modulation current to the high reflection end face side, FM response characteristics of red shift can be realized. The principle of operation is the same as that of the three-electrode DFB laser by Kotaki et al. However, in the device of the present invention, the three-electrode structure device is divided at the center and a reflecting mirror is formed. It is expected that the modulation current value for causing the change is half, that is, the FM modulation efficiency is doubled. As shown in Fig. 2, the FM response characteristic is a superposition of the thermal effect and the carrier effect. However, the FM modulation efficiency due to the carrier effect in the high-frequency region increases, so that the FM response efficiency can be increased over a wider modulation frequency range compared to the conventional example. A flat FM response characteristic is obtained. Further, a significant improvement in light output can be expected, reflecting the low reflection and high reflection end face structures.

(Example) Hereinafter, the present invention will be described in more detail with reference to the drawings of the example. FIG. 1A is a schematic sectional view of an integrated optical semiconductor device according to one embodiment of the present invention. In order to obtain such an element, an emission wavelength of 1.3 nm is formed on the substrate 1 on which the diffraction grating 2 is formed.
An InGaAsP guide layer 3 corresponding to μm, an active layer 4 having a multiple quantum well (MQW) structure, and a cladding layer 5 are sequentially grown. The diffraction grating 2 has a period of 2400 A, the guide layer 3 has a thickness of 0.2 μm, the MQW active layer 4 has four 70-A thick InGaAs layers, and a 100-A thick 1.3-μm composition InGaAs.
Consists of a P barrier layer. After buried growth was performed by a normal process, a divided electrode 6 was formed, cut into individual elements, and a low reflection film and a high reflection film were formed on both end surfaces. The end face reflectivities were 0% and 95%, respectively. Coupling coefficient 20 cm ^-1 , element length 1 mm, low reflection end face side area length 600 μm, 25 separation grooves 8
The characteristics were evaluated with a μm and a high reflection end face region length of 375 μm. In such a device, a wavelength tunable range of 20 ° and a spectral line width operation of 1 MHz or less were obtained at a light output of 50 mW. FM modulation efficiency varies depending on injection current conditions, but 1.3GHz / mA when the injection current density ratio is 1: 0.8 on the low reflection and high reflection side
, And a very flat FM response with a variation of 2 dB or less over the modulation frequency range of 1 kHz to 15 GHz.

In the embodiment, an element having a wavelength of 1 μm using InP as a substrate has been described. However, the material used is not limited to this, and other materials such as GaAs may be used.

(Effects of the Invention) The feature of the present invention is that the DFB laser having a low reflection and high reflection end facet structure is divided into two in the direction of the cavity, thereby achieving a wavelength tunable operation at a high optical output, a high efficiency and a flat FM response characteristic. I realized it. Particularly effective for Gb / s level FSK coherent systems.

[Brief description of the drawings]

FIG. 1A is a sectional view of an integrated device according to an embodiment of the present invention, and FIGS. 1B and 1C are schematic diagrams showing a light intensity distribution and a carrier density distribution in a resonator direction, respectively. FIG. 2 shows an example of the FM response characteristic. 1: substrate, 2: diffraction grating, 3: waveguide layer, 4: active layer, 5: cladding layer, 6, 7: electrode, 8: separation groove, 9: low reflection film, 10: high reflection film.

Claims (3)

(57) [Claims] An integrated optical semiconductor device having at least an active layer, a waveguide layer, and a diffraction grating on a semiconductor substrate, a high reflection film and a low reflection film are formed on two opposing end faces, and are formed in a laser light resonance direction. An electrode for applying a direct current to the low reflection film side independently, and an electrode for applying a direct current and a modulation current to the high reflection film side, and the length of the electrode on the high reflection film side is low reflection film. An integrated optical semiconductor device, wherein the length is shorter than the length of the electrode on the side. 2. An integrated optical semiconductor device having at least an active layer, a waveguide layer and a diffraction grating on a semiconductor substrate, wherein a high reflection film and a low reflection film are formed on two opposing end faces, and Two independent electrodes are formed,
A method for driving an integrated optical semiconductor device, characterized in that a DC current is applied to a low-reflection end-face-side electrode and a DC current and a modulation current are applied to a high-reflection end-face side electrode. 3. The length of the electrode on the high reflection end face side is shorter than the length of the electrode on the low reflection end face side.
A driving method of the integrated optical semiconductor device according to the above.