JPH03295289A - Integrated optical semiconductor device and driving method thereof - Google Patents

Abstract

PURPOSE:To enable an optical semiconductor device to be improved in FM modulation efficiency and optical output by a method wherein a DFB laser of low reflection and high reflection end face structure is divided into two parts in a direction of a resonator. CONSTITUTION:An InGaAsP guide layer 3 correspondent to the emitted light 1.3mum in wavelength, an active layer 4 of multi-quantum well structure, and a clad layer 5 are successively grown on a substrate 1 where a diffraction grating 2 has been formed. A buried layer is made to grow through a conventional process, then split electrodes 6 are provided, the substrate 1 is cut into unit elements, and a low reflection film 9 and a high reflection film 10 are provided to the end faces of the unit element respectively. The end faces are set to 0% and 95% in reflectivity respectively. Therefore, an integrated type optical semiconductor device which is high in optical output, variable in wavelength, high in efficiency, and flat in FM response property can be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an integrated optical semiconductor device and a method for driving the same.

(Conventional Technologies and Issues to be Solved) Optical communication technology has shown rapid progress in recent years, and systems with high speeds of several Gb/s, long distances exceeding 1100K, and long distances have been reported. Among these, distributed feedback semiconductor lasers (DFB-LD) and distributed Bragg reflection semiconductor lasers (DBR-LD) are used not only for direct detection systems but also for applications such as FSK coherent systems as a high-speed maintenance device. . When a single DFB laser is used, for example, as a transmission light source in an FSK coherent system, red-shifted FM occurs in which the transmission frequency shifts to longer wavelengths due to an increase in modulation current due to thermal effects in the low frequency region.

In the high frequency region, the modulation current increases due to the carrier effect, resulting in blue shift l-FM, which shifts the frequency to a shorter wavelength, and a dip frequency, which is the intersection point, occurs at several hundred kHz. There is a problem in that the phase is reversed, resulting in waveform deterioration during transmission. For the purpose of eliminating such phase reversal, Mr. Kotaki et al.
We have developed a λ/4 shift DFB laser with a three-electrode structure as reported in Volume 5, pages 990 to 991. By using such a device and adjusting the distribution ratio of the injected current, we achieved a wavelength tuning range of 19 people, a spectral linewidth of 900 kHz or less, and FM response characteristics without phase reversal at 20 mW optical output. However, with the same element, the FM modulation efficiency at the GHz level is only 0.5GHz/
mA, and higher FM modulation efficiency was desired for high-speed FSX modulation. Furthermore, the larger the optical output is, the more desirable it is for a local light source.

In view of the above, an object of the present invention is to provide an integrated single wavelength semiconductor laser device with high FM modulation efficiency and large optical output.

(Means for Solving the Problems) An integrated optical semiconductor device of the present invention includes an active layer on a semiconductor substrate,
An integrated optical semiconductor device having at least a waveguide layer and a diffraction grating is characterized in that two opposing end faces have different reflectances and two independent electrodes are formed in the laser beam resonance direction.

The driving method of the present invention is characterized in that, of the two electrodes, a DC current is applied to the electrode on the low reflection end face side, and a DC current and a modulation current are applied to the high reflection end face side electrode.

(Operation) The operating principle of the integrated device of the present invention is shown below. Figure 1 (a
) shows a cross-sectional structural diagram of the device, a DFB laser with a low-reflection and high-reflection end face structure is divided into two regions, and independent electrodes are formed in each region. Figure 1(b),
(C) schematically shows the electric field distribution and carrier density distribution of light, respectively. When a current is uniformly injected to cause laser oscillation, the optical density becomes stronger on the high-reflection end facet side, which consumes more carriers, and due to the effect of spatial hole burning,
There, the carrier density decreases. This situation is shown by the broken line in the figure. As in the present invention, a flat carrier density distribution can be achieved as shown by the solid line by suppressing hole burning by flowing more current to the high reflection end face side using a divided electrode structure. Since the average value of the carrier density in the entire resonator is higher when the carrier density becomes non-uniform due to hole burning, the Bragg wavelength becomes shorter than when the carrier density is uniform. By adjusting the current flowing to the high reflection end face, the degree of hole burning, and therefore the oscillation wavelength, spectral linewidth, etc., can be controlled.

Furthermore, by applying a modulation current to the high-reflection end face side, red-shifted FM response characteristics can be achieved. This operating principle is similar to the three-electrode structure DFB laser by Mr. Kotaki et al., but in the device of the present invention, the three-electrode structure element is divided in the center to form a reflecting mirror, so the same frequency The modulation current value to cause the change is half, that is, F
It is expected that the M modulation efficiency will double. As shown in Figure 2, the FM response characteristics are a combination of thermal effects and carrier effects.
By increasing the modulation efficiency, a flat FM response characteristic can be obtained over a wider modulation frequency range than in the conventional example. Furthermore, due to the low-reflection and high-reflection end face structure, a significant improvement in optical output can be expected.

(Example) The present invention will be described in more detail below with reference to drawings of examples. FIG. 1(a) is a schematic cross-sectional view of an integrated optical semiconductor device that is an embodiment of the present invention. To obtain such an element, a light emitting wavelength of 1.3 is placed on the substrate 1 on which the diffraction grating 2 is formed.
InGaAsP guide layer 3 equivalent to pm, multiple quantum well (
An active layer 4 and a crat layer 5 having a MQW) structure are sequentially grown. The diffraction grating 2 has a period of 240OA, and the guide layer 3 has a thickness of 0.
21Jm, MQW active layer 4 is 70A thick InGaAs
It consists of four layers, a 100A thick InGaAsP barrier layer with a composition of 1.3 pm. After performing buried growth using a normal process, divided electrodes 6 were formed and cut into individual elements, and a low reflection film and a high reflection film were formed on both end faces. The end face reflectance was 0% and 95%, respectively. Coupling coefficient 20cm'
The characteristics were evaluated with the overall element length of 1 mm, the length of the low reflection end face side region of 600 μm, the separation groove 8 of 25 pm, and the length of the high reflection end face region of 375 μm. In such a device, we obtained a wavelength tunable range of 20 people and a spectral linewidth operation below IMHz at 50 mW optical output. The FM modulation efficiency varies depending on the injection current conditions, but the ratio of injection current density is 1 on the low reflection side and the high reflection side.
:0.8, a high value of 1.3 GHz/mA was obtained, and an extremely flat FM response characteristic with a variation within 2 dB over the modulation frequency range of 1 kHz to 15 GHz was obtained.

In the embodiment, an element with a wavelength of 1 pm using InP as a substrate has been described, but the material system used is not limited to this, and other materials such as GaAs system may be used without any problem.

(Effects of the Invention) The feature of the present invention is that the DFB laser with a low-reflection and high-reflection edge structure is divided into two parts in the cavity direction, thereby achieving wavelength tunable operation with high optical output, high efficiency, and flat FM response characteristics. I was able to make it happen. It is particularly effectively used in FSK coherent systems at the Gb/s level.

[Brief explanation of drawings]

FIG. 1(a) is a cross-sectional view of an integrated device that is an embodiment of the present invention, and FIGS. 1(b) and 1(C) are schematic diagrams showing the light intensity distribution and carrier density distribution in the cavity direction, respectively. Figure 2 is FM
FIG. 3 is a diagram showing an example of response characteristics. substrate, 2: diffraction grating, 3: waveguide layer, 4: active layer, 5:
Land layer, 6.7: Electrode, 8: Separation groove, 9: Low reflection film, 1o: High reflection film.

Claims (2)

[Claims] (1) 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
An integrated optical semiconductor device characterized in that two end faces have different reflectances and two independent electrodes are formed in the laser beam resonance direction. (2) Of the two electrodes of the integrated optical semiconductor device according to claim 1, 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. A method for driving an integrated optical semiconductor device.