JP2001326413A - Semiconductor laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor laser which enhances a high-speed modulation operation by eliminating a limitation by the capacitance on an element in the high-speed modulation operation. SOLUTION: A DFB semiconductor laser 4 and a semiconductor electric field absorption optical modulator 5 are provided on a semiinsulating semiconductor substrate 6. The electrode structure of the optical modulation part 5 is formed as a traveling wave-type electrode 3. It is desirable that the characteristic impedance of the electrode 3 has the same impedance as an external-voltage supply source in order to reduce the reflection of microwaves which are supplied from the outside.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a semiconductor laser used for optical communication and various kinds of optical signal processing, and more particularly to a semiconductor laser light source in which a semiconductor electroabsorption modulator is integrated.

[0002]

2. Description of the Related Art A semiconductor laser with a modulator is known as one of semiconductor lasers (LDs) used as a light source in an optical communication system. In recent years, an optical modulator integrated semiconductor laser in which an optical modulator and a semiconductor laser are integrally formed on a semiconductor substrate has been used. For example, JP-A-10-228005 and JP-A-11-186661 disclose a semiconductor laser in which a semiconductor electroabsorption modulator is integrated.

FIG. 3 is a perspective view of a conventional semiconductor electro-absorption modulator integrated laser, and FIG. 4 is a top view of FIG. In this semiconductor electro-absorption modulator integrated laser, a laser beam is generated by current driving using a laser electrode 12 formed on a distributed feedback (DFB) semiconductor laser unit 11, and the laser beam is converted to a DFB semiconductor. The light is emitted to the outside through the semiconductor electroabsorption modulator 13 on the emission side of the laser.

In this semiconductor laser, when the laser beam passes through the semiconductor electroabsorption modulator section 13, the intensity of the laser beam emitted by the voltage supplied from the semiconductor electroabsorption modulator electrode 14 can be modulated. Yes, it is widely used as a laser modulation light source. The operation of the semiconductor electro-absorption modulator section 13 is based on the Franz-Keldysh effect (Franz-Keldish effect) when the optical waveguide is formed of a bulk crystal.
Keldysh effect; When a strong electric field is applied to an insulator or a semiconductor, the state density at the edge of the valence band or conduction band changes,
The phenomenon that the light absorption spectrum changes near the fundamental absorption edge), and the quantum confined Stark effect (quantum-confined Stark effe
ct; the applied voltage called the Stark effect, which is generated when the wave functions and quantization levels of electrons and holes confined in the quantum well structure are changed by an electric field applied perpendicularly to the well layer from the outside. It utilizes the phenomenon that the absorption edge of the absorption spectrum shifts to the longer wavelength side in response, and is realized by controlling the light absorption amount of the optical waveguide.

[0005]

However, a conventional semiconductor electro-absorption modulator integrated laser has been put into practical use as a laser light source for 10 Gbps optical communication utilizing its high-speed operation. With the development of communication systems and optical signal processing technologies, there is a demand for realizing higher-speed modulation operations. However, the structure of the electroabsorption modulator electrode 4 in the conventional semiconductor electroabsorption modulator integrated laser is a lumped-constant electrode structure, and its operation speed is limited by the capacitance of the element. The capacitance of the element is determined by the capacitance between the mesa stripe portion 16 and the back electrode 15 of the electroabsorption modulator, the electrode pad portion 17 and the back electrode 1.
The capacitance is expressed by the sum of the capacitances between the electrodes 5, and the reduction of the element length of the semiconductor electroabsorption modulator section 13 and the reduction of the electrode pad section 17 are effective means. .

However, when the element length is shortened, the amount of light absorption in the optical waveguide portion becomes small and a sufficient extinction ratio (ON / OFF ratio of an optical signal) cannot be obtained. Is done. Further, the electrode pad portion 17 and the back surface electrode 15
Between the mesa stripe 16 and the back electrode 15
Since the capacitance is very small as compared with the capacitance between them, the element capacitance that can be reduced by reducing the electrode pad portion 17 is very small. Further, when the electrode pad portion 17 is made smaller, there is a problem in manufacturing that electric wiring becomes difficult. Therefore, it has been extremely difficult to reduce the capacitance of the element and realize a higher speed modulation operation of the semiconductor electroabsorption modulator integrated laser having the conventional structure.

The present invention has been made in view of such a problem, and an object of the present invention is to eliminate the limitation due to the capacitance of the element in the high-speed modulation operation and realize a dramatic improvement in the high-speed modulation operation. An object of the present invention is to provide a semiconductor laser in which a semiconductor electroabsorption modulator that can be integrated.

[0008]

According to the present invention, there is provided a semiconductor laser in which a semiconductor electroabsorption modulator is integrated. It is characterized by having an electrode structure.

Further, a semi-insulating semiconductor substrate, a distributed feedback semiconductor laser section provided on the semiconductor substrate, and a semiconductor electroabsorption modulator section provided on the semiconductor substrate have an integrated structure. The electrode structure of the semiconductor electro-absorption modulator is a traveling wave electrode structure.

Further, the characteristic impedance of the traveling-wave-type electrode structure is the same as that of an external voltage supply in order to reduce the reflection of microwaves supplied from the outside.

As described above, in the semiconductor laser, the introduction of the traveling wave electrode structure to the electrode structure of the semiconductor electroabsorption modulator can eliminate the limitation of the operation speed due to the element capacitance.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a perspective view showing an embodiment of a semiconductor laser in which a semiconductor electroabsorption modulator according to the present invention is integrated.
FIG. 2 is a top view of FIG.

A semiconductor laser in which a semiconductor electroabsorption modulator according to the present invention is integrated has a DF on a semi-insulating semiconductor substrate 6.
It has a B semiconductor laser section 4 and a semiconductor electroabsorption modulator section 5, and the electrode structure of the semiconductor electroabsorption modulator section 5 is a traveling wave electrode 3. At this time, the traveling wave type electrode 3
Is preferably the same impedance as the external voltage supply in order to reduce the reflection of the microwave supplied from the outside, and its value is generally 50Ω.
It is designed to be.

D formed on a semi-insulating semiconductor substrate 6
The driving p-electrode 1 of the FB semiconductor laser unit 4 is configured to be in contact with the contact layer of the semiconductor mesa stripe, and the n-electrode 2 is configured to be in contact with the n-contact layer 7 below the semiconductor mesa stripe.

The laser p-electrode 1 and the traveling-wave electrode (center conductor) 3 are made of, for example, AuZnNi + Au, and the n-electrode 2 is made of, for example, AuGeNi + Au. The semiconductor substrate 6 is made of, for example, a semi-insulating InP substrate doped with Fe, and the n-contact layer 7 is made of, for example, n-InP.
It is composed of layers.

In this semiconductor laser, by using the traveling wave type electrode 3 for the electroabsorption modulator 5, the high-speed modulation operation of the laser beam is not restricted by the capacitance of the element. On the other hand, by using the structure of the traveling wave type electrode 3, there is no factor that degrades other characteristics such as the extinction characteristic and the propagation loss of the electroabsorption modulator unit 5. as a result,
Only the high-speed modulation operation of the semiconductor electro-absorption modulator integrated laser can be dramatically improved.

The semiconductor laser unit 4 shown in FIG.
Although a DFB semiconductor laser structure that easily oscillates at a single wavelength is used, a waveguide type laser structure may be used, and the structure is not limited to the structure shown in the embodiment.

[0019]

As described above, according to the present invention, since the electrode structure of the semiconductor electroabsorption modulator is a traveling wave electrode structure, the high speed modulation operation of the semiconductor laser in which the semiconductor electroabsorption modulator is integrated is performed. , The limitation by the element capacitance is eliminated, and a dramatic improvement in the high-speed modulation operation can be realized.

[Brief description of the drawings]

FIG. 1 is a perspective view of a semiconductor laser in which a semiconductor electroabsorption modulator of the present invention is integrated.

FIG. 2 is a top view of FIG.

FIG. 3 is a perspective view of a semiconductor laser in which a conventional semiconductor electroabsorption modulator is integrated.

FIG. 4 is a top view of FIG. 3;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 p-electrode for laser 2 n-electrode 3 traveling-wave electrode for electro-absorption modulator 4 distributed feedback semiconductor laser section 5 electro-absorption modulator section 6 semiconductor substrate 7 n-contact layer 11 distributed feedback semiconductor laser section 12 distributed feedback semiconductor Electrode for laser 13 Electroabsorption modulator section 14 Electrode absorption modulator electrode (lumped constant electrode) 15 Back electrode 16 Mesa stripe section in electroabsorption modulator 17 Electrode pad section in electroabsorption modulator

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Hiroaki Takeuchi 2-3-1 Otemachi, Chiyoda-ku, Tokyo F-term (reference) 2H079 AA02 AA13 BA01 CA04 DA16 EA03 EA07 EA08 EB04 EB12 HA15 KA18 4M104 AA04 BB36 CC01 FF03 FF09 GG04 HH20 5F073 AA61 AA64 AB12 AB21 BA01 CA12 CB03 CB22 DA30 EA14

Claims (3)

[Claims] 1. A semiconductor laser in which a semiconductor electroabsorption modulator is integrated, wherein the electrode structure of the semiconductor electroabsorption modulator is a traveling wave electrode structure. 2. An integrated structure comprising a semi-insulating semiconductor substrate, a distributed feedback semiconductor laser unit provided on the semiconductor substrate, and a semiconductor electroabsorption modulator unit provided on the semiconductor substrate. A semiconductor laser wherein the electrode structure of the semiconductor electroabsorption modulator section is a traveling wave electrode structure. 3. The characteristic impedance of the traveling-wave-type electrode structure is set to be the same as that of an external voltage supply in order to reduce the reflection of microwaves supplied from the outside. A semiconductor laser as described in the above.