JPS61244087A - Integrated semiconductor laser - Google Patents

Abstract

PURPOSE:To stabilize modulation operation and reduce a magnitude of frequency chirping by a method wherein the first guide layer is formed in series (to the direction of the light propagation) with an activation layer and the second guide layer is formed closely above or below the first guide layer and a P-N junction is formed in one of the guide layers. CONSTITUTION:A diffraction grating 6 is formed on the part of a semiconductor substrate 5 and a guide layer 7, an activation layer 8 and a P-type InP layer 9 are successively laminated on the substrate. Then the laminated layers are removed by etching as far as the guide layer 7 except the parts above the diffraction grating 6 and then the non-doped first guide layer 3, a P-type InP layer 9, the P-type second guide layer 4 and a P-type InP layer 9 are successively laminated. Moreover, after mesa-etching and burying growth, a groove 10 is formed at a part of the center by etching and an etching end surface 12 is formed. Finally, an electrode 11 and an AR coating film 13 are formed on the respective output end surfaces. With this constitution, a light output intensity can be modulated by varying the coupling condition of the lightwave in accordance with the variation of an applied current to the side of a modulator so that the operation at the time of modulation can be stabilized and the magnitude of frequency chirping can be reduced.

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to an integrated lid single-axis mode semiconductor laser with a built-in modulator or switching element.

(Prior art and its problems) Distributed feedback (DFB) semiconductor laser that stably oscillates in a single axis mode even during high-speed modulation, distributed Bragg reflection @ (DBR)
) Semiconductor lasers are seen as promising light sources for long-distance, high-capacity optical fiber communications. Experiments have been carried out on optical fiber transmission using these single-axis mode semiconductor lasers, for example, 2Gb/1g.

-It has become possible to realize the above transmissions. However, when trying to further extend the transmission distance and increase the capacity, the spectrum width (chirping) during modulation of the semiconductor laser becomes a problem. This is caused by carrier fluctuations when modulating the semiconductor laser, which causes the refractive index to change and the oscillation wavelength to fluctuate over time. For example, in the 1.55 μm band where the transmission loss of silica-based optical fiber is the minimum, it is 18 pa/km*
Dispersion on the order of nanometers increases, which greatly limits the transmission band, so it is desirable that the chirping of the light source be as small as possible. In a normal DFB-LD or DBR-LD, when directly modulated at a speed of about IGb/s, the IA
This results in some degree of chirping.

In order to reduce such chirping of the light source, it is effective to use a DFB-LD with a built-in loss modulator. A DF with a loss modulator as reported by Mr. Yamaguchi et al. at the S59 Autumn National Conference of the Optical and Radio Division of the Institute of Electronics and Communication Engineers 272.
Developed B-LD. The structural schematic diagram of the second rI4IC
show. A guide layer 7 partially having a diffraction grating 6 is formed on the active layer 8, and the part having the diffraction grating is formed into a DFB-LD.
I. The flat guide layer 70 is operated as the modulator 2.

An AR coating pattern 13 is formed on the end face of the modulator 2, and a DFB-LDIK current is injected to cause laser oscillation, and the modulation current is transferred to the modulator 2 while the DC bias current is flowing there.
It is possible to change the loss of the laser beam by applying it to the laser beam, thereby making it possible to modulate the intensity of the laser beam.

However, with this method, the phase condition of the reflected light to the DFB-LDI changes due to reflection from the end face of the modulator 2 due to changes in the modulation current, and the oscillation wavelength may change slightly by one or two people. Ta. It is thought that such wavelength fluctuations can be eliminated if the electrical insulation between the two regions is good and the AR coat end face is completely non-reflective, but normally the reflectance of the AR coat end face is 2. It has been difficult to suppress the above-mentioned wavelength instability to only a small degree, and it has been difficult to completely prevent the above-mentioned wavelength instability.

(Specific Means for Solving the Problems) From the above-mentioned viewpoint, the present invention aims to provide an integrated lid single-axis mode semiconductor laser in which the modulation operation is stable and the amount of frequency chirping is small. A laminated structure having a layer and a diffraction grating is provided on a semiconductor substrate, and a first guide layer K is formed in series with the active layer (with respect to the propagation direction of light) in the laminated structure, and the first guide layer is formed in series with the active layer in the laminated structure. At least a second guide layer is formed above or below the layers, and a pn junction is formed in at least one of the guide layers.

(First principle of operation of the invention) The present invention will be explained in detail below using drawings showing embodiments. To suppress chirping during modulation, for example, a method can be considered in which a constant bias current is passed through the active layer portion and the light is modulated using a modulator. - For example, as shown in FIG. 1, it is preferable to form a coupled waveguide type modulator 2 in series with the DFB-LDI. In the example shown in the figure, the modulator 2 has first and second guide layers 3, 4, one of which has a p-n junction formed therein. Therefore, by passing current through the modulator 2, its refractive index can be changed, and the output of the light wave coupled to the two guide layers 3, 4 can be changed between the upper and lower guide eyebrows. At the end face, the laser beam is output to either the upper or lower guide layer, but if one end face of the guide layer is etched diagonally as shown in the figure, the laser light will be output to the lower guide layer end face. Laser light can be extracted to the outside only when a proper coupling state is achieved. DFB-LD
I is driven with direct current to oscillate, and the amount of change in the modulation current flowing to the modulator side can be made small, and therefore the amount of frequency chirping can be made smaller than in the case of direct modulation.

(Embodiment) FIG. 1 shows an embodiment of the integrated lid DFB-LD according to the present invention. To obtain such an element, first an n-InP substrate 5 is prepared.
A diffraction grating 6 is partially formed thereon, and n-In whose emission wavelength corresponds to 1.3 μm is further formed. . -〇aoas A8
o4t PaJe guide layer 7, non-dawg Inox* GAa4r ASaa corresponding to emission wavelength 1.554 m
b. A pHJ6 active layer 8 and a P-InP layer 9 are sequentially stacked. The thickness of the diffraction grating active layer 8 was approximately 0.1 μm. Next, the portion other than the diffraction grating 6 is etched and removed up to the guide layer 7, and the non-doped first guide layer 3, p-
InP layer 9, P-type second guide layer 4, p-InP layer 9
were sequentially stacked. Both of the two guide layers 3 and 4 had a crystal composition corresponding to an emission wavelength of 1.3 μm. The p-InP layer 9 between the two guide layers had a thickness of 1.5 μm. Furthermore, after performing mesa etching and buried growth using a normal process, a groove 10 is etched in a part of the central part.
, and an etched end surface 12 is formed. Finally, the electrode 11 is formed and the AR coating film 13 is formed on the output end face to obtain the desired integrated lid DFB-LD. In the integrated lid DFB-LD produced as described above, the length of the DFB-LDI was cut out to 150 μm and the length of the modulator 2 was cut out to 400 μm, and the characteristics were evaluated. As a result, the oscillation end current at room temperature cw operation is 20 mA, the differential quantum efficiency is 25%, and the maximum is 40 mW.
, a device exhibiting stable single-axis mode oscillation up to a maximum temperature of 100° C. or higher was obtained with extremely good reproducibility.

In addition, the element was mounted on a diamond heat sink, and
When Gb/s NRZ random pulse modulation was performed, the amount of frequency chirping at that time was 0.3Xs degrees, which was reduced to 1/a to 1/4 compared to the conventional direct modulation method.

Although DFB-LDl was used as a light source in the embodiment of the present invention, it is of course possible to use DBR-LD as a light source. The guide layer on the modulator 2 side is shown as having two configurations; however, it is of course possible to configure it with three or more guide layers. Of course, a single-axis mode LD with variable oscillation wavelength should be used as the light source. In the examples, the materials used are InP for the substrate and I
Although the active layer is made of nGaAap, the active layer is not limited to this.
There is no problem in using other semiconductor materials such as / I nAJAa series.

(Effects of the Invention) A feature of the present invention is that a modulator or a switch element having a plurality of guide layers is formed in series with a single-axis mode semiconductor laser having a diffraction grating.

As a result, it is possible to modulate the optical output intensity by changing the coupling state of light waves by changing the current injected into the modulator side, and compared to the conventional example, the operation during modulation is stable and the amount of frequency chirping is small. We were able to realize an integrated lid semiconductor laser.

[Brief explanation of drawings]

FIG. 1 shows a schematic cross-sectional view of an integrated lid DFB-LD, which is an embodiment of the present invention. FIG. 2 shows a schematic diagram of a conventional semiconductor laser. In the figure, l is the DFB-LD, 2 is the modulator, 3 is the first guide layer, 4 is the second guide layer, and 5 is n-1np.
A substrate, 6 a diffraction grating, 7 a guide layer, 8 an active layer, 9 a p-InP layer, 10 a groove, 11 an electrode, 12 an etched end surface, and 13 an AR coat film are respectively shown. Pavilion 1 Figure 4, Pavilion 2. Uku 7'id 1

Claims (1)

[Claims] In a semiconductor laser with an integrated lid including a laminated structure having at least an active layer and a diffraction grating on a semiconductor substrate, a first guide layer is formed in series with the active layer (with respect to the propagation direction of light), An integrated semiconductor laser characterized in that at least a second guide layer is formed above or below the first guide layer, and a pn junction is formed in at least one of the guide layers.