JPS61164289A - Integrated semiconductor laser - Google Patents

Abstract

PURPOSE:To eliminate the instability of the uniaxial mode operation of an integrated semiconductor laser, which is due to the leakage-in of carriers, by a method wherein, in the integrated uniaxial mode semiconductor laser, the mutually different operating regions are optically coupled together with an organic material such as a polyimide or an insulating material. CONSTITUTION:A diffraction grating 2 is partially formed on an N-type InP substrate 1. An N-type In0.72Ga0.28As0.61P0.39 guide layer 3 to correspond to a luminous wavelength of 1.33mum, for example, and a non-doped In0.59Ga0.41As0.90P0.10 active layer 4 to corre spond to a luminous wavelength of 1.55mum are respectively laminated thereon in a thickness of 0.1mum from the mountain of the diffraction grating 2 and in a thickness of 0.1mum, and moreover, a P-type InP clad layer 5 is laminated in order on the grating 2. After an electrode is formed thereon, a dry etching is performed using chlorine mixed gas, whereby a groove 8 of a depth of 10mum or thereabouts is formed in the central part between a DFB region 6 having the diffraction grating 2 and a modulator 7 having the falt guide layer 3. An SiO2 layer 9 is laminated on the bottom surface of the groove 8. Then, a spin coating is performed on the SiO2 layer 9 with a polyimide 10 to form the integrated semiconductor laser into a waveguide structure.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to an integrated single-axis mode semiconductor laser.

(Prior art) Distributed feedback (DFB) or distributed Bragg reflection type (D old semiconductor laser) is used as a semiconductor light source that exhibits stable single-axis mode oscillation even during high-speed modulation and can widen the transmission band in optical fiber communication. LD) is being developed.These semiconductor lasers have a wavelength selection mechanism using a diffraction grating with an appropriate pitch, and are stable at a single wavelength even when modulated at high speeds of Gb/s level. Furthermore, recently, the magazine [Electron
, Lett, ) j19(17), 65 of 1983
On page 6, there is an integrated type DBL't-LD as reported by Tomori et al., or a phase control type DFB-L.
With the development of D, it has become possible to control the emission wavelength, spectral linewidth, and stability of single-axis mode operation, such as axial mode selection ratio.

(Problems to be Solved by the Invention) In such an integrated DFB/DBR-LD, independent electrodes are formed in the active region and control region, but the insulation resistance between these electrodes is If it is not large enough, current leakage may occur.

FIG. 2 is a cross-sectional structural diagram of a conventional phase control type DFB-LD. This is a structure in which an active layer 4 and a guide layer 3 are laminated on an n-InP substrate 1, and a diffraction grating 2 is partially formed on the guide layer 3.

The portion where this diffraction grating 2 is formed is operated as a DFB region 14, and the portion where the flat guide layer 3 is formed is operated as a phase control region 15. By performing gear injection on the phase control region 15 side, the refractive index there can be changed, and the effective end face phase in the DFB-LD can be controlled through the change in the refractive index. By such phase control, the output/loss axis mode multiplier of the DFB-LD can be controlled; for example, in this case, +1 across the stop band
It is now possible to select the axis mode between mode and -1 mode.Independent electrodes 16 and 17 are formed in these DFB areas 14 and phase control areas 15, respectively, but the central part of these If they are separated by a normal insulation method such as etching, the resistance between them can only be a few hundred ohms at most, and electrical losstalk will occur between them. In this conventional example, 9. I) It is expected that stable single-axis mode oscillation will occur up to a high optical output level of several tens of mW by passing current through the FB region 14, but as mentioned above, if electrical insulation is insufficient, When a current is applied, it also flows into the phase control region 15 side, which causes the phase condition to deviate from the optimum, causing mode skipping and the like, making it impossible to obtain stable single-axis mode oscillation. .

(Objective of the Invention) The object of the present invention is to solve the above-mentioned problems, provide electrical insulation between the active region and the control region, and provide an integrated semiconductor laser that can operate sufficiently stably. It is about providing.

(Structure of the Invention) The structure of the present invention is an integrated semiconductor laser having, on a semiconductor substrate, at least an active layer and a light guide layer having a larger energy gap than the active layer and having a diffraction grating formed on one surface. A light emitting region including at least the active layer and having a first electrode in the direction of the laser resonance axis; and a control region controlling output light of the light emitting region and having a second electrode in a region different from the first electrode. It is characterized in that a groove into which an organic material or an insulating material is inserted into which light waves are coupled is provided in the boundary region of each region.

(Principle of the Invention) In the present invention, in order to obtain sufficient electrical insulation in the boundary region between the active layer region and the control region, a deep groove is formed between the two using a technique such as etching. There is.

In this case, it is important to have good optical coupling even if electrically insulated.

To achieve this, it is sufficient to conduct 5-waves between the two using an insulating medium that is transparent to light, such as an organic material such as polyimide.

(Example) The present invention will be described in detail below using the drawings.

FIG. 1 shows a schematic cross-sectional view of an embodiment of an integrated semiconductor laser according to the present invention in a direction parallel to the laser resonance axis direction. To obtain this element, first, a diffraction grating 2 is partially formed on an n-InP substrate 1, and then, for example, a diffraction grating 2 with an emission wavelength of 1.3
n-Ino, 7□Ga(1,21As6
．． 61 Fo, 39 guide layer 3 from the peak of the diffraction grating to a thickness of 018 m9, non-doped In corresponding to the emission wavelength of 1655 μm), 5 g Ga0041 As6. g(IF5.10
The active layer 4 has a thickness of 01 μm1, and the p-InP cladding layer 5 is sequentially laminated. The diffraction grating 2 was formed by laser interference exposure using a He-Ca gas laser and chemical etching, and had a period of 2400A. In order to partially form this diffraction grating 2, it is possible to mask other areas and perform interference exposure, or to partially expose a positive type resist in advance and continue to perform interference exposure. The portion other than the diffraction grating 2 may be etched flat. This Example 6-1 was produced using the latter.

Further etching was performed to form a mesa stripe, and buried growth was performed in a semiconductor laser having a normal buried structure. After forming an electrode on this, dry etching is performed using a chlorine-based mixed gas to form a 10 μm thick film in the center of the DFB region 6 having the diffraction grating 2 and the modulator 7 having a flat guide layer. 8102 layers 9 were laminated therein. Next, polyimide 10 was spin-coated to form a waveguide structure.

This SiO2 film 9 is deposited by the usual CVD method,
Its upper surface was positioned below active l1i4. 8
The refractive index of i02 is approximately 1.48. Polyimide had a refractive index of about 1.75. In this case, the groove 8 had a width of about 10 μm, and a light wave coupling of 80q6 or more was obtained even without depositing the 5 in 2 film 9. In order to improve the coupling of light waves, the top and bottom of the polyimide 10 may be covered with a material having a lower refractive index to form a waveguide structure.

An 8iNOAR coating film 11 was formed on the output end face of the integrated DFB-LD thus fabricated on the modulator 7 side. This is formed by the plasma CVD method, and a good AR coating film can be formed even at a relatively low temperature of about 150°C.

By injecting current into the DFB region 6 of this element to cause laser oscillation, and adjusting the current of the modulator 7 to change the optical loss in that part, the linewidth is zero even during high-speed modulation of p, lGb/s.
．． We were able to keep it sufficiently small at 5 A.

When a normal I)l"B-LD is modulated at high speed, the width of a single oscillation axis mode expands to about 1 to 2 due to the change in refractive index due to carrier fluctuation, which limits the transmission band of optical fiber communication. Was.

Furthermore, even in the case of integrated DFB-Li), if only the electrodes are formed independently, when current is applied to the modulator 7, it will flow into the DFB region 6, and the wavelength change during modulation will be large, resulting in a stable single axis. It was difficult to obtain mode oscillation.

On the other hand, in the embodiment of the present invention, the electrical crosstalk described above could be suppressed to a sufficiently low level, and stable operation with a narrow spectral linewidth could be achieved even during high-speed modulation.

If the coupling of light waves in the groove 8 portion is not sufficient, the DFB oscillation light may not be coupled to the modulator 7 and become scattered light.
Such scattered light poses no practical problem since there is no coupling port in the optical fiber. In order to further improve the coupling of light waves, it is also effective to increase the size of the waveguide of the modulator 7. Further, if a semi-insulating semiconductor substrate is used and the grooves 8 are formed so as to be late, the electrical insulation will be improved.

Note that in this example, InP is used as the substrate, and InGaAs is used as the substrate.
Although a semiconductor material with a wavelength of 1 μm in which P is used as an active layer is shown, the present invention is not limited to these, and includes GaAlAs/GaAs systems.

Other semiconductor materials such as InGaAs/InA7As may also be used. In addition, although this embodiment shows an integrated type DFB-LD in which the loss modulator 7 is integrated, the present invention is not limited to this, and it is not limited to a wavelength control type DBR-LD, and a reflective end face phase control type DIi''.
All integrated single-axis mode semiconductor lasers such as B-LDs are included. Furthermore, the organic/insulating material used is not limited to SiO□ and polyimide, and other materials may be used.

(Effects of the Invention) According to the present invention, by optically coupling different operating regions in an integrated single-axis mode semiconductor laser with an organic material such as polyimide or an insulating material,
Good electrical insulation and optical coupling could be obtained, and instability in single-axis mode operation caused by carrier leakage could be eliminated.

[Brief explanation of drawings]

Claims (1)

[Claims] In an integrated semiconductor laser having at least an active layer and a light guide layer having a larger energy gap than the active layer and having a diffraction grating formed on one surface on a semiconductor substrate, at least the active layer is disposed on a semiconductor substrate. A light emitting region including a layer and having a first electrode, and a control region having a second electrode in a region different from the first electrode for controlling the output light of the light emitting region, and a boundary region between these regions. An integrated semiconductor laser characterized by having a groove in which an organic material or an insulating material is inserted into which light waves are coupled.