JP2546366B2 - Semiconductor light emitting device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a semiconductor light emitting device that suppresses characteristic variations due to external semi-reflected light returning to a laser region.

(Prior Art) A semiconductor laser is widely used as a light source for optical communication or optical information processing. In semiconductor lasers, characteristic fluctuations occur due to the injection of external light such as reflection, and the operation becomes unstable. Therefore, it is important to prevent this in use. Therefore, various measures have been taken, such as coating the optical fiber on the side where light is incident with a non-reflective film. Among these measures, one of the effective methods performed on the light emitting device side is to dispose an isolator including a polarizer and a quarter wavelength plate on the laser emission surface.

(Problems to be Solved by the Invention) However, since the structure of the isolator becomes large, the distance between the laser and the optical fiber becomes large, and when entering the emitted light of the laser into the optical fiber, the lens used is limited. There are problems such as large insertion loss.

In the prior art, in the isolator region for propagating light in one direction, the quarter-wave plate that rotates the polarization plane of the light emitted from the laser is thick, so it is used for coupling to an optical fiber or the like through this. The lenses that can be used were limited. Even when the Faraday rotator is used instead of the quarter-wave plate, the rotator is still thick, and therefore the polarization plane rotating portion has been required to be small.

The output light from the laser has components of TE mode and TM mode, and only one mode component needs to be extracted. Generally, a polarizer is inserted to extract only the TE mode, but since the polarizer is an optical element, it could not be integrated with the laser.

As described above, conventionally, there has been a problem that, of the output light output from the laser, the light of a predetermined mode component cannot be efficiently introduced into an external medium such as an optical fiber.

The object of the present invention is to solve the above-mentioned problems of the prior art, and efficiently introduces the light of a predetermined mode component in the output light output from the laser into an external medium such as an optical fiber. Another object of the present invention is to provide a semiconductor light emitting device that can be manufactured.

(Means for Solving the Problem) A feature of the present invention is a semiconductor light emitting device having a laser region for outputting light and an optical waveguide layer arranged so as to be coupled to light emitted from the laser region, on the same semiconductor substrate. ,
A mode filter region configured to give a loss to a predetermined propagation mode of light propagating in the first optical waveguide layer arranged so as to be coupled to light emitted from the laser region, and the mode filter. An optical waveguide region having a second optical waveguide layer which is arranged so as to be coupled to the emitted light from the region and whose composition is determined so that the polarization plane of the propagating light is rotated; And a magnetic field applying means for applying a magnetic field having a component parallel to the traveling direction to the optical waveguide region.

(Embodiment 1) FIG. 1 is a cross-sectional view of a semiconductor element portion in an optical axis (light traveling) direction in a semiconductor light emitting device of a wavelength band of 0.6 μm according to the present invention, showing a laser region, a window region, a mode. It is composed of four regions, a filter region and an optical waveguide region. Of the four regions forming the semiconductor element portion, the regions characteristic of the present invention are the mode filter region and the semiconductor wave region. The magnetic field applying unit will be described later.

First, the structure of the laser region and the window region, which are the conventional structures, of the semiconductor light emitting device section will be described. 1 is a (100) plane n-Ga As substrate common to 4 regions, 2 is n-doped A1
InP lower cladding layer, 3 is an undoped Ga InP active layer, 4 is an undoped A1GaInP optical waveguide layer,
Reference numeral 5 is a cladding layer of P-A1InP forming the laser region and window region, 6 is a current blocking layer of n-A1InP forming the window region, and 7 is a cap of undoped Ga As forming the laser region and the window region. A layer, 15 is a Zn diffusion region, 16 is an insulating film, 17 is a p-side electrode, 18 is an n-side electrode common to each region, and these constitute a laser region and a window region.

Next, the mode filter region, which is one of the features of the present invention, includes a lower cladding layer 8 made of undoped A1InP and an undoped
Optical waveguide layer 9 (first optical waveguide layer) by A1Ga In P,
The buffer layer 10 is made of undoped A1 In P and the metal clad layer 11 is made of A1 or the like. Here, in order to give a loss to the TM mode and take out the TE mode, the metal clad layer 11 is arranged in a part of the optical waveguide in which the light is distributed (where it is close to the optical waveguide layer 9).

The optical waveguide region (or "polarization plane rotation region"), which is another feature of the present invention, is the same as the optical waveguide region of the "semiconductor light-emitting device" filed by the same inventors on the same day. The lower clad layer 1 made of Zn Mn SSe Te (wavelength corresponding to the forbidden band: λg = 0.40 μm).
2. Optical waveguide layer (second optical waveguide layer) 13 made of Zn Mn SSe Te (λg = 0.44 μm), Zn Mn SSe Te (λg = 0.40 μ)
It is composed of the upper clad layer 14 and the insulating film 16 according to m).

The second optical waveguide layer 13 is made of Zn _(1-w) Mn _w S _(1-pq) Se.
_It may be composed of a single layer of _p Te _q (0 ≦ p ≦ 1,0 ≦ q ≦ 1,0.05 ≦ w ≦ 0.5), or Zn _(1-w) Mn _w S _(1-pq) Se
_p Te _q (0 ≦ p ≦ 1,0 ≦ q ≦ 1,0.05 ≦ w ≦ 0.8) and Zn
_{(1-w ') Mn w} ' S (1-p'-q ') Se p' Te q '
A superlattice multilayer film of (0 ≦ p ′ ≦ 1,0 ≦ q ′ ≦ 1,0.05 ≦ w ′ ≦ 0.8) may be used.

That is, the present invention adds a mode filter region that gives a loss to a predetermined mode to the “semiconductor light emitting device” filed on the same day.

An optical waveguide is formed so that the laser light is emitted in the [011] direction, and has a refractive index waveguide structure for transverse mode control. A quarter wavelength shift diffraction grating 19 is formed on the surface of the optical waveguide layer 4 in the laser region. In addition, a mode filter region and an optical waveguide region (hereinafter, these two regions are collectively referred to as "optical isolator region").
Laser region facet on the side not in contact with, as the reflected light does not enter again the laser region, the window according to A1 _0.5 In _0.5 P layer 5, 6 having a forbidden band width larger made than the band gap of the active layer 3 A region is formed. The composition of each growth layer is selected so that lattice matching with the substrate 1 can be obtained.

Next, the configuration of the magnetic field applying unit will be described. The magnetic field applying unit B is also composed of a magnet or an electromagnet in order to rotate the polarization plane of the optical waveguide layer, as described in "Semiconductor Light Emitting Device" filed on the same day by the same applicant. Second
FIG. 6A is a diagram showing the relationship between the semiconductor element portion A and the magnetic field applying portion B, which is configured to apply a magnetic field component substantially parallel to the optical axis to the second optical waveguide layer in the optical waveguide region. FIG.
Is an example of adjusting the magnetic field strength in the case of a magnet, and the angle β may be changed. In the case of an electromagnet, the current may be changed.

Next, the operation of the semiconductor light emitting device according to the present invention will be described in which the semiconductor element portion A in which the laser region and the optical isolator region are integrated has the magnetic field applying portion B.

When a current is passed between the electrodes 16 and 17, laser oscillation occurs due to the 1/4 wavelength shift diffraction grating in the laser region. In this case, the oscillated light generally has both a TE mode and a TM mode. The propagation constant of the TE mode in the optical axis direction at this time is γ
And

In the mode filter region, the propagation constant for TE mode is γ
In addition, since the forbidden band width is larger than the forbidden band width corresponding to the wavelength of the incident light, no reflection occurs at the junction with the laser region and no internal absorption occurs. The light incident on the mode filter region is attenuated in the TM mode and propagated only in the TE mode without being attenuated due to the influence of the metal clad 11 arranged in the optical waveguide. By appropriately selecting the refractive index of the lower clad layer 8, the refractive index and the thickness of the optical waveguide layer 9 and the buffer layer 10,
Propagation loss for TE mode is less than 1 dB / mm, and the difference between TE mode and TM mode propagation loss can be several tens of dB / mm. Therefore, if the length of the mode filter region is about 500 μm, only the TE mode propagates in the mode filter region.

Therefore, only the TE mode is incident on the optical waveguide region.
In the optical waveguide region, the propagation constant for TE mode is γ, and the forbidden band width is larger than the forbidden band width corresponding to the wavelength of the incident light. Therefore, reflection does not occur at the junction with the mode filter region, and the internal absorption also occurs. Don't get up Light incident on the optical waveguide region corresponding to the polarization rotator is subjected to a magneto-optical effect (Mn) in the optical waveguide layer 13 by Zn Me SSe Te by applying a magnetic field having a component parallel to the optical axis. (Faraday effect) occurs and the plane of polarization rotates. The rotation angle θ is given by θ = V · 1 · B · cosβ ··· (1). Here, V is a constant, 1 is the optical waveguide length of the polarization plane rotator, B is the magnetic flux density of the applied magnetic field, and β is the angle between the optical axis and the direction of the magnetic field. V varies depending on the composition and the wavelength of incident light and is 0.1 to 0.5 deg / cm · gauss. Therefore, if B is about 3000 Gauss, the length of the optical waveguide region
The plane of polarization can be rotated 45 ° by about 1 mm.

For example, if reflection occurs at the end face of the optical waveguide region, the reflected light is rotated in the same direction to the left while the plane of polarization further rotates 45 ° in the same direction, and when it reaches the mode filter region, the TM mode is reached. It has become. Therefore, it is attenuated by the mode filter region and does not reach the laser region.
The same applies to light that is emitted from the semiconductor light emitting device, is reflected by the fiber incident surface, and is incident on the optical waveguide region again. The lower part of FIG. 1 schematically shows how each mode in each part propagates.

Although the distributed feedback laser having the 1/4 wavelength shaft diffraction grating is taken up in the description of the first embodiment, a normal distributed feedback laser may of course be used. Further, a reflectance control coating or the like may be used instead of the window structure. Although the mode filter region is a TE mode selection filter, it may be a TM mode selection filter by making the refractive index of the buffer layer 10 higher than that of the optical waveguide layer 9 and making it an appropriate thickness.

(Embodiment 2) In Embodiment 1, the mode filter region and the optical isolator region which is the optical waveguide region are provided on one emission side of the laser, but as shown in FIG. 3, the optical isolator regions are formed on both emission surfaces. You may. Also in this case, the reflected light does not reach the laser region due to both isolator regions, and does not affect the laser characteristics.

Normally, in a distributed feedback laser, the end face has a window structure or end face coating in order to eliminate the influence of the end face reflection, but in the case of a window structure, the spot of the emitted light spreads and the coupling loss is large. Has the drawback that
Further, the coating has a problem that the film thickness control is not easy. Therefore, by using the present invention, the laser light travels without spreading to the emission port due to the waveguide structure, so that the above-mentioned problem can be solved.

Although the left and right optical isolator regions have the same composition and structure in FIG. 3, they do not necessarily have the same composition and structure.

Example 3 In Examples 1 and 2, the case where the laser region has a normal double hetero structure has been described, but the present invention can also be applied to a case where the active layer 3 has a quantum well structure. In this case, the maximum gain of the TE mode in the laser region becomes considerably larger than the maximum gain of the TM mode. Therefore, the length of the mode filter region can be shortened as compared with the double hetero structure, and the TE mode loss in the mode filter region can be reduced. In addition,
Even if the cladding layer 5 has a superlattice structure, this tendency is not affected.

Further, the cladding layer 10 in the mode filter region and the optical waveguide layer / cladding layer 14 in the optical waveguide region may have a superlattice structure.

In the above description, the n-type substrate 1 is used, but of course p
There is no problem with a structure in which the shaped substrate is used and the conductivity type of the cladding layer 5 in the laser region is reversed. Regarding the optical waveguide structure,
Any optical waveguide structure of the refractive index waveguide type such as a buried structure may be used.

Any material may be used as long as it is a combination of semiconductors that can be grown in a lattice match with a semiconductor substrate. For example, as the substrate 1, Si, Ge, In P, Ga P, Ga As P, Zn Se, Zn S,
Any semiconductor of group IV, group III-V, group II-VI, chalcopyrite such as Cu Ga SSe may be used. The semiconductor in the laser region may be any semiconductor as long as it is substantially lattice-matched with the substrate 1.

Also, the semiconductor in the mode filter region may be any semiconductor as long as it is substantially lattice-matched with the substrate 1. Also for the semiconductor in the optical waveguide region, the substrate 1
However, the semiconductor does not have to be a specific semiconductor, although there is a requirement that it contains a transition metal element in its component and has a small absorption coefficient for laser light. Therefore,
A semiconductor other than Zn SSe Te-based semiconductor, for example, a material into which a transition metal such as Cd SSe Te-based is introduced may be used. Furthermore, for the transition metal element itself, instead of Mn described in the examples,
Fe, Co, Ni or the like may be used. Depending on the semiconductor or transition metal element used, the constant V in the equation (1) may be small. In this case, the dimension of the optical waveguide region may be lengthened or the magnitude of the magnetic field may be increased.

(Effects of the Invention) As described above, according to the present invention, by configuring the semiconductor light emitting device so as to have the mode filter region, the optical waveguide region and the magnetic field applying means, the predetermined propagation of the output light from the laser region can be achieved. Only the mode can be efficiently incident on the external medium.

The second optical waveguide layer 13 is composed of a semiconductor multilayer film that is substantially lattice-matched with the substrate 1, and is composed of a semiconductor layer in which a part of the group II element of the II-VI group compound semiconductor is replaced with a transition metal element. Thus, the polarization plane of the emitted light in the laser region can be rotated by the magnetic field from the magnetic field applying unit B.

The second optical waveguide layer 13 is Zn _(1-w) Mn _w S _(1-pq) Se _p Te
_{By configuring q} (0 ≦ p ≦ 1,0 ≦ q ≦ 1,0.05 ≦ w ≦ 0.5), the polarization plane of the emitted light in the laser region can be rotated by the magnetic field from the magnetic field applying unit B.

The second optical waveguide layer 13 is made of Zn _(1-w) Mn _w S _(1-pq) Se _p Te
_q (0 ≦ p ≦ 1,0 ≦ q ≦ 1,0.05 ≦ w ≦ 0.8) and Zn
_{(1-w ') Mn w} ' S (1-p'-q ') Se p' Te q '
By using a superlattice multilayer film of (0 ≦ p ′ ≦ 1,0 ≦ q ′ ≦ 1,0.05 ≦ w ′ ≦ 0.8), the polarization plane of the emitted light in the laser region is generated by the magnetic field from the magnetic field applying section B. Can be rotated.

By using Mn, Fe, Co, or Ni as the transition metal element, the optical waveguide layer 13 that is inexpensive and easy to manufacture can be configured.

The mode filter region can be integrated with the laser region and the optical waveguide region by forming the semiconductor multilayer film and the metal film, which are substantially lattice-matched with the semiconductor substrate.

[Brief description of drawings]

FIG. 1 shows a first embodiment according to the present invention, which is a sectional view of the semiconductor light emitting element section A in the optical axis direction, and FIGS. 2 (a) and 2 (b) show the semiconductor element section A according to the present invention and magnetic field application. FIG. 3 is a schematic view of a semiconductor light emitting device in combination with a portion B, and FIG. 3 is a second embodiment according to the present invention, which is a sectional view in the optical axis direction of a semiconductor light emitting element portion A having optical isolator regions on both sides of a laser region. Is. 1 …… (100) plane n−Ga As substrate 2 …… n−A1In P lower cladding layer 3 …… Ga In P active layer 4 …… A1Ga In P optical waveguide layer 5 …… p−A1In P upper cladding layer 6 …… n−A1In P current blocking layer 7 …… Ga As cap layer 8 …… A1In P lower cladding layer 9 …… A1Ga In P optical waveguide layer (first optical waveguide layer) 10 …… n−A1In P current blocking layer Layer 11 …… Metal clad layer 12 …… Zn Mn SSe Te Lower clad layer 13 …… Zn Mn SSe Te Optical waveguide layer (second optical waveguide layer) 14 …… Zn Mn SSe Te Upper clad layer 15 …… Zn Diffusion Region 16 ... Insulating layer 17 ... P-side electrode 18 ... N-side electrode 19 ... 1/4 wavelength shift diffraction grating

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-61-287186 (JP, A) JP-A-62-58689 (JP, A) JP-A-62-281386 (JP, A) JP-A-62- 36888 (JP, A) JP 60-235483 (JP, A) JP 51-62689 (JP, A) JP 60-198880 (JP, A) JP 2-122583 (JP, A)

Claims (6)

(57) [Claims] 1. A semiconductor light emitting device having, on the same semiconductor substrate, a laser region for outputting light and an optical waveguide layer arranged so as to couple emitted light from the laser region, the coupled light being emitted from the laser region. Of the light propagating in the first optical waveguide layer arranged so as to be coupled to a mode filter region configured to give a loss to a predetermined transport mode, and light emitted from the mode filter region. And a component parallel to the traveling direction of the emitted light in the laser region, and an optical waveguide region having a second optical waveguide layer whose composition is determined so that the plane of polarization of propagating light is rotated. A semiconductor light emitting device, comprising: a magnetic field applying unit that applies a magnetic field that is applied to the optical waveguide region. 2. The second waveguide layer is composed of a semiconductor multilayer film which is substantially lattice-matched with the semiconductor substrate, and II-VI.
The reaction light-emitting device according to claim 1, wherein part of the group II element of the group compound semiconductor is composed of a semiconductor layer substituted with a transition metal element. 3. The second optical waveguide layer comprises Zn _(1-w) Mn _w S
_{(1-pq) Se p Te} q (0 ≦ p ≦ 1,0 ≦ q ≦ 1,0.05 ≦ w ≦ 0.5)
2. The semiconductor light emitting device according to claim 1, wherein 4. The second optical waveguide layer is Zn _(1-w) Mn _w S
_{(1-pq) Se p Te} q (0 ≦ p ≦ 1,0 ≦ q ≦ 1,0.05 ≦ w ≦ 0.8)
And Zn _{(1-w ')} Mn _{w 'S (1-p'-q')} Se
_{p ′} Te _{q ′} (0 ≦ p ′ ≦ 1,0 ≦ q ′ ≦ 1,0.05 ≦ w ′ ≦ 0.
8. The semiconductor light emitting device according to claim 1, wherein the semiconductor light emitting device is formed of a superlattice multilayer film of 8). 5. The semiconductor light emitting device according to claim 1, wherein the transition metal element is Mn, Fe, Co, or Ni. 6. The semiconductor light emitting device according to claim 1, wherein the mode filter region is composed of a semiconductor multilayer and a metal film that are substantially lattice-matched with the semiconductor substrate.