JPS61168980A - Semiconductor light-emitting element - Google Patents

Abstract

PURPOSE:To enable waveguide parts to be of lower loss and of high speed modulation by using an active layer of quantum well constitution and a light modulator of an electro-optical absorption type. CONSTITUTION:An InAlAs active layer 3 including a quantum well layer 4, an InAlAs optical waveguide path layer 5 and a P-type Inp clad layer 6 are formed. On an N-type Inp semiconductor substrate 2 and an electric insulated region 8, a diffraction lattice 10 and an SiN anti-reflection layer 11 are provided, then a common electrode 1, a laser electrode 9 and a modulated electrode 7 are formed. When the laser electrode 9 is impressed in forward direction and electric current injection is performed, a part, which forms a diffraction lattice 10, works as a distributed feedback type laser and oscillates. When bias in reverse direction and modulated voltage are impressed to the modulated electrode 7 a lower section of the electrode 7 works as an electric field optical absorption modulator. An oscillating light of the laser is subjected to do electric field optical absorption by the modulator, and the intensity of electric field optical absorption is varied by modulated voltage and optical output is modulated.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is capable of ultra-high-speed modulation of several GA/II or more,
Furthermore, the present invention relates to a semiconductor light emitting device in which the oscillation line width does not widen even during modulation.

[Conventional technology]

As a light source for long-distance, high-capacity optical communications, there is a need for a semiconductor light-emitting device whose oscillation linewidth does not widen even during high-speed modulation. So far, single-longitudinal mode lasers such as distributed feedback (DFB) and distributed reflection (RMT) type lasers that have a diffraction grating inside the laser have been developed, and the number of multi-longitudinal mode lasers whose linewidth during modulation is normal. It has been confirmed that - of ten minutes. However, even with these vertical AAA drapes, when direct modulation of ah/z or more is performed, the oscillation frequency changes (Chirpi%g) due to the change in the refractive index of the active layer, and the oscillation linewidth increases by several A. It will spread further. Therefore, when used as a light source for optical communication in the 1.5 μm band, transmission characteristics deteriorate due to wavelength dispersion of the optical 7-eyeper.

Furthermore, when a semiconductor laser is directly modulated, there is a resonant frequency determined by the lifetime of carriers and photons, which limits the upper limit of the modulation frequency. In the case of pulse modulation, due to the resonance effect caused by this, the modulation characteristics tend to change depending on the modulation pattern (Patter 7 effect).
This resulted in deterioration of transmission characteristics.

In order to solve this problem, an element in which a distributed feedback laser and a light absorption modulator are integrated as shown in FIG. 2 has been proposed. This element is formed of a distributed feedback laser formed on a semiconductor substrate 22, an electrically insulating region and a current injection optical modulator connected by an optical waveguide layer 25 and an active layer 23 common to the laser. It is an integrated optical device that reduces optical absorption and modulates optical output by injecting current into the modulator. In the figure, 2
1 is a common electrode, 26 is a beam 2 Rad layer, 27 is a modulation electrode, 2
9 is a laser electrode.

According to this configuration, since a distributed feedback structure is adopted for the semiconductor laser, there is no need for a reflective end face, and the laser and modulator can be directly coupled through the waveguide, thereby reducing the coupling loss between the two to almost zero. It can be done.

[Problem that the invention seeks to solve]

However, the above conventional element configuration has the following drawbacks as a light source for high-speed modulation.

■ Since the electrically insulating region includes the same active layer as the laser part, the loss as a waveguide is large. That is, since the active layer has a normal DH groove structure, the electrically insulating region where no current is injected exhibits strong light absorption. Therefore, sufficient electrical insulation cannot be ensured, and chirping (a phenomenon in which the oscillation frequency fluctuates when intensity modulation of light is applied) occurs due to the current flowing from the modulator to the laser.

■ Since the modulator is a carrier injection type element with forward bias (utilizing changes in optical absorption due to current injection), the modulation frequency band is narrow in the GA/8 region due to the carrier accumulation effect. is difficult to modulate. 400M
It can only be modulated to about h/g.

[Means for solving interlayer points]

In the present invention, the active layer of the device has a quantum well structure, and the optical modulator is an electro-optical absorption disk, thereby eliminating the drawbacks of the conventional device. A type laser is integrated with an electrically insulating region and an electro-optical absorption modulator connected by an active layer having a quantum well structure common to the laser.

〔Example〕

The device according to the embodiment of the present invention shown in FIG. 1 will be explained below.

Road layer 5. Each growth layer of the p-type 1nP cladding layer 6 is formed. Reference numeral 8 designates an electrically insulating region formed by removing a part of the shuffled layer by etching, 10 a diffraction grating formed in a part of the optical waveguide, and 11 an SiN antireflection film. Further, a common electrode 1 is formed on the n-type 1nP substrate/board 2, and a laser electrode 9 and a modulation electrode 7 are formed on the cladding layers 6 on the left and right sides of the electrically insulating region 8.

To operate this device, a headward (positive) voltage is applied to the laser electrode 9 to inject a current. As a result, the portion where the two-element diffraction grating 10 is formed operates as a distributed feedback laser and oscillates. On the other hand, by applying a reverse bias to the modulation electrode 7 and applying a modulation voltage thereto, the portion below the stain pole 7 operates as an electric field light absorption modulator. The oscillated light of the distributed feedback laser is subjected to electric field light absorption by the modulator. Since the intensity of electric field light absorption changes depending on the modulation voltage, the light output passing through the modulator is modulated. Anti-reflection film 11
is provided to prevent the light passing through the modulator from being reflected at the end face and affecting the distributed feedback laser.

This device is a type of device that integrates a semiconductor laser and an optical modulator, and by configuring it as described above, the following effects can be obtained.

By forming the active layer into a quantum well structure, it becomes possible to reduce the loss of the waveguide and increase the electro-optic absorption effect of the modulator.

It is known that the oscillation wavelength of a quantum well laser shifts to a longer wavelength side than the absorption band when no current is injected. Therefore, the waveguide used in the electrically insulating region and the modulator in this device is almost transparent to the laser light from the laser region, and is a low-loss waveguide.

In this device, the laser and modulator are connected through this low-loss waveguide, so the laser and modulator can be separated without increasing loss, allowing complete electrical isolation.

This makes it possible to eliminate electrical interference between the laser and the modulator, and it becomes possible to operate the laser with forward bias and the modulator with reverse bias, as in the present device.

In addition, in the quantum well structure, exciton absorption can be observed even at room temperature.
Therefore, it is known that the electro-optical absorption effect is more than ten times greater than that of ordinary semiconductors.

Therefore, by using an active layer having a quantum well structure as an electric field light absorption modulator, it is possible to obtain a sufficient degree of modulation with an electric field of about 10' V/am.

Modulators based on electric field light absorption are capable of high-speed modulation because they do not involve fluctuations in carrier density, and modulation results at 10 GA/a have also been reported. However, with ordinary semiconductors, the modulation rate is about 10' V/am. Since it requires a high electric field, there are few examples of practical use.This device uses a quantum well structure to realize a modulator that operates with a voltage of the number r.

In addition, by adopting a distributed feedback structure for the semiconductor laser in this embodiment as well, there is no need for a reflective end face, and the laser and modulator can be directly coupled via a waveguide. This element has the same effect as the element shown in FIG. 2 in that the coupling loss of the element can be reduced to almost zero.

In the embodiments shown above, the laser is of the distributed feedback type, but a distributed reflection type (DBR) laser may also be used. Further, the electrically insulating layer is formed by removing a part of the cladding layer by etching, but h.

Insulation by ion implantation of F- or the like may also be used.

If the active layer has a quantum well structure, the active layer has a single quantum well (SQ
W) or multiple quantum well CMQW). In addition, in the above embodiment, the end face of the laser part remains a hexagonal facet, but in order to increase the output, it may be coated with a highly reflective film such as gold, or it may be further connected with a waveguide to It may also be coupled to an output monitor or the like.

Further, as for the laser part, a phase shift grating type laser or the like may be used to improve performance.

〔Effect of the invention〕

As explained above, since the device of the present invention integrates an electro-optic absorption modulator capable of high-speed modulation and a distributed feedback laser that oscillates in a stable single longitudinal mode, it has the following effects. You can expect it.

(2) Since the electric field optical absorption modulator has no carrier accumulation effect, high-speed modulation of several tens of Gb/s is possible. Furthermore, unlike direct modulation of a semiconductor laser, there is no resonance effect, and no change in modulation characteristics due to pulse patterns (pattern effect) occurs, so it can be used as a light source for ultra-large capacity optical communications.

(2) In the device of the present invention, since the semiconductor laser operates continuously with a constant output, there is no broadening of the oscillation line width due to 'cNrpinl' even during modulation, making it a light source for optical communication.

When used for this purpose, the dispersion effect of fibers can be avoided.

(2) In the device of the present invention, since the laser is always in an oscillating state, it is less affected by reflected light from the outside. The magnitude of the influence of reflected light is determined by the ratio of the intensity of reflected light to the light intensity within the laser resonator. In the case of direct modulation, the strong light reflected during oscillation returns at the start of oscillation when the light intensity inside the resonator is weak, making it weak against reflection. In contrast, in the device of the present invention, since the laser is always in an oscillating state, it is resistant to reflected light and can operate stably without using an isolator.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an element according to an embodiment of the present invention, and FIG. 2 is a sectional view of a conventional element. 1, common electrode 2, n-type IP (semiconductor) substrate 3, (IPL including InGaAz quantum well layer, 47)
Active layer 4. GaAz quantum well layer 5, InAXAz optical waveguide layer 6, 13-type IP (semiconductor) cladding layer 7, modulation electrode 8, electrically insulating region 9, laser electrode 10, diffraction grating 11, (5 N) reflection prevention film

Claims (1)

[Claims] A grating feedback laser having an active layer with a quantum well structure, an electro-optical absorption modulator, and an electrically insulating region that optically couples the two and electrically isolates them are provided on a semiconductor substrate, and the electrical The optical absorption modulator and the electrically insulating region are
A semiconductor light emitting device, characterized in that the semiconductor light emitting device is coupled through an active layer having a quantum well structure common to the active layer having a quantum well structure of the diffraction grating feedback laser.