JP2012084627A - Semiconductor light-emitting element, and optical pulse tester using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor light-emitting element and an optical pulse tester using the same that can emit light having a plurality of wavelength bands, especially that can oscillate light having a plurality of different wavelength bands in a plurality of longitudinal modes respectively, that is high output, and that can be manufactured with high yield.SOLUTION: A first MQW (Multiple Quantum Well) active layer having an opening on a first light emission end surface, and having a first gain wavelength, a second MQW active layer having an opening on a second light emission end surface, and having a second gain wavelength, and a coupling waveguide layer coupling those optically, are coupled in a waveguide direction of light. An electrode above the coupling waveguide layer and a lower electrode are short-circuited. The first gain wavelength is longer than the second gain wavelength. A diffraction grating having a Bragg wavelength corresponding to the second gain wavelength is formed in the vicinity of the coupled waveguide layer. Light generated at the first MQW active layer is oscillated by a resonator consisting of the first light emission end surface and the second light emission end surface. Light generated at the second MQW active layer is oscillated by a resonator consisting of the diffraction grating and the second light emission end surface. Both are output from the second light emission end surface.

Description

  The present invention relates to a semiconductor light emitting device and an optical pulse tester using the same.

  In the field of optical communication, a system that outputs light of a plurality of wavelengths is used. For example, in the case of a system that outputs laser light of two wavelengths, two semiconductor lasers manufactured for each wavelength are prepared, and the output light from each semiconductor laser is combined and output ( For example, see Patent Document 1).

  In contrast, the applicant of the present application, as a two-wavelength laser light source configured without the need for such a complicated optical system, connected a plurality of active layers having greatly different gain wavelengths in series via a coupling waveguide layer, In addition, a semiconductor light-emitting element capable of emitting laser beams of a plurality of wavelengths from a single chip by arranging a diffraction grating in the vicinity of the coupling waveguide layer and realizing oscillation independently at each wavelength has been proposed (see Patent Document 2). .

JP 2008-209266 A Japanese Patent Application No. 2010-58610

  However, in the configuration disclosed in Patent Document 2, when a current is injected into the active layer on the long wave side and oscillated, leaked carriers flow into the adjacent coupled waveguide layer, which causes free carrier absorption. As a result, there was a problem that the output decreased.

  The present invention has been made to solve such a problem, and in a semiconductor light-emitting device in which a plurality of active layers having different gain wavelengths are connected in series via a coupling waveguide layer, long-wave activity is achieved. The light emitted and amplified in the layer is suppressed from being absorbed by carriers leaking from the long wave active layer when passing through the coupling waveguide layer, and the light output is reduced.

  The semiconductor light emitting device of the present invention has a first light emitting end face and a second light emitting end face formed by cleaving on a semiconductor substrate, and is open to the first light emitting end face and has a first gain. A first multiple quantum well active layer having a wavelength, a second multiple quantum well active layer having an opening at the second light emitting end face and having a second gain wavelength, and a coupled waveguide for optically coupling them A first electrode above the first multiple quantum well active layer, a second electrode above the second multiple quantum well active layer, A semiconductor light emitting device comprising a third electrode above the coupling waveguide layer and a fourth electrode short-circuited to the third electrode on a bottom surface of the semiconductor substrate, wherein the first gain wavelength Is longer than the second gain wavelength and corresponds to the second gain wavelength in the vicinity of the coupling waveguide layer. A diffraction grating having a lag wavelength is formed, and light generated in the first multiple quantum well active layer by energization between the first electrode and the fourth electrode is reflected on the first light emitting end face. The light generated in the second multiple quantum well active layer by oscillating in a resonator composed of the second light emitting end face and energized between the second electrode and the fourth electrode is Oscillation is caused by a resonator composed of the diffraction grating and the second light emitting end face, and both are emitted from the second light emitting end face.

  With this configuration, it is possible to prevent a part of current injected into the active layer on the long wave side from leaking to the adjacent coupled waveguide layer and absorbing the light emitted by the active layer on the long wave side to reduce the oscillation output. I can do it.

  Furthermore, the semiconductor light emitting device of the present invention may have a bulk structure in which the coupled waveguide layer has a composition wavelength that is the same as or shorter than the second gain wavelength.

  With this configuration, it can be manufactured with a high manufacturing yield.

  An optical pulse tester according to the present invention provides an optical pulse between any one of the semiconductor light emitting devices described above and either the first electrode or the second electrode of the semiconductor light emitting device and the fourth electrode. A light emitting element driving circuit that applies a pulsed driving current for emitting, and a light emitting unit that outputs the light pulse emitted from the second light emitting end face of the semiconductor light emitting element to the optical fiber to be measured; A light receiving unit that converts return light of the optical pulse from the optical fiber to be measured into an electric signal, and a signal processing unit that analyzes loss distribution characteristics of the optical fiber to be measured based on the electric signal converted by the light receiving unit And.

  With this configuration, the semiconductor light emitting device capable of oscillating light of a plurality of wavelength bands in a plurality of longitudinal modes with a high light output is provided, so that a small and high performance optical pulse tester can be realized.

  The present invention provides a semiconductor light emitting device capable of operating a semiconductor light emitting device capable of emitting light in a plurality of wavelength bands with high light output, and a small and high performance optical pulse tester using the semiconductor light emitting device. .

Sectional drawing which shows the semiconductor light-emitting device of the 1st Embodiment of this invention. The block diagram which shows the structure of the optical pulse tester of the 2nd Embodiment of this invention. The figure which shows the characteristic of the semiconductor light-emitting device of the 1st Embodiment of this invention.

  Embodiments of a semiconductor light emitting device and an optical pulse tester using the same according to the present invention will be described below with reference to the drawings.

(First embodiment)
FIG. 1 shows a first embodiment of a semiconductor light emitting device according to the present invention. This figure is a cross-sectional view of the semiconductor light emitting device 10 of the first embodiment cut along the light propagation direction.

As shown in FIG. 1, the semiconductor light emitting device 10 includes, for example, an n-type semiconductor substrate 11 made of n-type InP (indium / phosphorus), an n-type InP cladding layer 12, and an InGaAsP (indium / Pb) having a gain wavelength λ _1. A first gain region I having a first multiple quantum well type active layer 13a made of gallium, arsenic and phosphorus, and a second multiple quantum well type made of InGaAsP having a gain wavelength λ ₂ (<λ ₁ ). A second gain region II having an active layer 13b and a coupled waveguide region III having a bulk-type coupled waveguide layer 19 made of InGaAsP having a composition wavelength shorter than λ ₂ .

Here, the gain wavelength indicates a peak wavelength of a desired longitudinal mode among a plurality of longitudinal mode oscillation wavelengths described later. In this embodiment, gain wavelengths λ ₁ and λ ₂ will be described by taking wavelengths 1.55 μm and 1.3 μm used in an optical pulse tester as an example. The gain wavelengths λ ₁ and λ ₂ may be values within the ranges of 1.52 ≦ λ ₁ ≦ 1.58 and 1.28 ≦ λ ₂ ≦ 1.34, respectively.

Alternatively, any combination from each wavelength range of 1.28 to 1.34, 1.47 to 1.50, 1.52 to 1.55, 1.60 to 1.65 may be used (provided that λ ₁ > Λ ₂ , unit is μm, and so on)

  Further, the composition wavelength λj of the coupled waveguide layer 19 at that time may be 1.05 ≦ λj ≦ 1.27. The composition wavelength represents the band gap energy of the semiconductor mixed crystal in terms of the wavelength of light, and is one of the methods for expressing the mixed crystal composition.

  The first multiple quantum well type active layer 13a, the coupling waveguide layer 19 and the second multiple quantum well type active layer 13b are arranged along the light guiding direction and are optically coupled by a butt joint technique. Has been. The first multiple quantum well type active layer 13a and the second multiple quantum well type active layer 13b referred to here have a multiple quantum well (MQW) structure and an optical separation confinement (SCH) sandwiching them. : Separate Confinement Heterostructure) layer.

  In addition, a p-type InP cladding layer 14 and a p-type InGaAs (indium gallium. A contact layer 15 made of arsenic is laminated in this order.

  Further, on the contact layer, a first upper electrode 17a for the first gain region I, a second upper electrode 17b for the second gain region II, and a third upper electrode 17c for the coupling waveguide region III. The lower electrode (or fourth electrode) 16 is formed on the lower surface of the n-type semiconductor substrate 11 by vapor deposition.

  In FIG. 1, in order to improve the separation resistance between the upper electrodes, the contact layer is removed by etching leaving a lower portion of each upper electrode, and the first contact layer 15a is formed below the first upper electrode 17a. However, the second contact layer 15b is formed below the second upper electrode 17b, and the third contact layer 15c is formed below the third upper electrode, respectively.

  Further, the first multiple quantum well type active layer 13a and the second multiple quantum well type active layer 13b respectively have a first light emission end face 10a and a second light emission end face 10b formed by cleavage. . The first light exit end face 10a is provided with a high reflection (HR) coat 18a, and the second light exit end face 10b is provided with a low reflection (LR) coat 18b, and the light exits from the second light exit end face 10b. The reflectance with respect to the emitted light is lower than the reflectance with respect to the light emitted from the first light emitting end face 10a.

  Here, the reflectance on the first light emitting end face 10a side provided with the HR coat 18a is 90% or more, and the reflectance on the second light emitting end face 10b side provided with the LR coat 18b is about 1 to 10%. It is preferable that

Further, in the coupled waveguide region III of the n-type InP cladding layer 12, a diffraction grating 20 having a Bragg wavelength λ _{g of} 1.3 μm and a coupling coefficient κ of 100 cm ⁻¹ or more is formed in the vicinity of the coupled waveguide layer 19. Yes.

  The position where the diffraction grating 20 is formed may be below the coupled waveguide layer 19 as shown in FIG. 1, or within the p-type InP cladding layer 14 above the coupled waveguide layer 19. (Not shown). Further, a diffraction grating having a Bragg wavelength of 1.55 μm may be simultaneously formed in the vicinity of the first light emitting end face 10a of the first gain region I.

  A method for manufacturing a semiconductor light emitting device having such a structure is described in detail in Patent Document 2.

  Further, the third upper electrode 17c is electrically short-circuited with the lower electrode 16 by the wiring of the Au wire. Note that both electrodes may be grounded.

  Next, the operation of the semiconductor light emitting device 10 of the present embodiment configured as described above will be described.

  When a current is applied between the first upper electrode 17a and the lower electrode 16 for the first gain region I, the inside of the first multiple quantum well type active layer 13a enters a light emitting state. However, since the separation resistance between the first upper electrode 17a and the third upper electrode 17c is finite, part of the current leaks into the coupled waveguide region III.

  However, in the present invention, since the third upper electrode 17c in the coupled waveguide region III is electrically short-circuited with the lower electrode 16, the leakage current does not flow into the coupled waveguide layer 19, and the third upper electrode 17c. It flows to. As a result, light absorption by carriers caused by leakage current from the first gain region I flowing through the coupling waveguide region III and the second gain region II is suppressed, and laser light output by light emission from the first gain region I is suppressed. Will improve.

  As a result, as shown in FIG. 3, the saturation of the 1.55 μm light output is greatly improved especially at high currents, and a high output operation is realized. Since a chip output of 200 mW or more is obtained, when used in an optical time domain reflectometer, which is a typical example of an optical pulse tester, a high performance of 35 dB or more is obtained as a dynamic range.

  On the other hand, when a current is applied between the second upper electrode 17b and the lower electrode 16 for the second gain region II, the inside of the second multiple quantum well active layer 13b is in a light emitting state. Become.

The 1.3 μm band light generated in the second multiple quantum well active layer 13b propagates along the second active layer 13b. Since the 1.3 μm light is reflected by 90% or more by the diffraction grating 20 having a Bragg wavelength λ _{g of} 1.3 μm, the light in the first multiple quantum well active layer 13a having a gain wavelength of 1.55 μm. Absorption is suppressed.

  In this case, since the light in the 1.3 μm band generated by the second multiple quantum well active layer 13b hardly penetrates into the first multiple quantum well active layer 13a, as shown in FIG. The effect of shorting the upper electrode 17c of 3 is smaller than in the above case.

  As described above, in the semiconductor light emitting device of this embodiment, the upper electrode in the coupled waveguide layer region is short-circuited to the lower electrode, thereby suppressing the saturation of the light output and realizing a high light output. In particular, a great effect can be obtained when long-wave light is oscillated.

(Second Embodiment)
The semiconductor light emitting device 10 of the first embodiment capable of oscillating a plurality of light in different wavelength bands in a plurality of longitudinal modes can be used as a light source of an optical pulse tester. Hereinafter, an embodiment of an optical pulse tester including the semiconductor light emitting element 10 will be described with reference to the drawings.

  As shown in FIG. 2, the optical pulse tester according to the second embodiment has a semiconductor light emitting element 10 and a light emitting element driving circuit 2 that applies a pulsed driving current for emitting a light pulse to the semiconductor light emitting element 10. The light emitting unit 1 that outputs the light pulse emitted from the second light emitting end face 10b of the semiconductor light emitting element 10 to the optical fiber to be measured 3, and the return light of the light pulse from the optical fiber to be measured 3 as an electrical signal The light-receiving part 4 to convert and the signal processing part 5 which analyzes the loss distribution characteristic of the to-be-measured optical fiber 3 based on the electric signal converted by the light-receiving part 4 are provided.

  The signal processing unit 5 controls the timing at which the light emitting element driving circuit 2 applies a driving current to the semiconductor light emitting element 10.

  Furthermore, the optical pulse tester of the present embodiment outputs an optical pulse from the light emitting unit 1 to the bandpass filter (BPF) 6 and outputs an optical beam returned from the optical fiber 3 to be measured to the light receiving unit 4. 7, an optical connector 8 that is optically coupled to the optical fiber 3 to be measured, and a display unit 9 that displays a processing result of the signal processing unit 5.

  Next, the operation of the optical pulse tester of the present embodiment configured as described above will be described. In the following description, it is assumed that the optical pulse tester of this embodiment includes the semiconductor light emitting element 10.

  First, a pulsed driving current is applied to the first gain region I (or the second gain region II) of the semiconductor light emitting device 10 by the light emitting device driving circuit 2, and the third upper electrode 17 c is connected to the lower electrode 16. By being short-circuited, a light pulse of 1.55 μm band (or 1.3 μm band) is output from the light emitting unit 1.

  The optical pulse output from the light emitting unit 1 is incident on the measured optical fiber 3 through the optical coupler 7, the BPF 6, and the optical connector 8. The light pulse incident on the optical fiber 3 to be measured becomes return light and is received by the light receiving unit 4 through the optical coupler 7.

  The return light is converted into an electric signal by the light receiving unit 4 and input to the signal processing unit 5. Then, the loss distribution characteristic of the measured optical fiber 3 is calculated by the signal processing unit 5. The calculated loss distribution characteristic is displayed on the display unit 9.

  As described above, the optical pulse tester according to the present embodiment includes a semiconductor light emitting device capable of oscillating a plurality of light beams having different wavelength bands with a high optical output by using a single device, so that downsizing and high performance can be realized. .

DESCRIPTION OF SYMBOLS 1 Light emission part 2 Light emitting element drive circuit 3 Optical fiber to be measured 4 Light receiving part 5 Signal processing part 10 Semiconductor light emitting element 10a 1st light emission end surface 10b 2nd light emission end surface 13a 1st active layer 13b 2nd active layer 19 Coupling waveguide layer 20 Diffraction grating 17a First upper electrode (or first electrode)
17b Second upper electrode (or second electrode)
17c Third upper electrode (or third electrode)
16 Lower electrode (or fourth electrode)
18a High reflection (HR) coating 18b Low reflection (LR) coating 20 Diffraction grating

Claims (3)

On the semiconductor substrate,
A first multiple quantum well active layer having a first light emitting end face and a second light emitting end face formed by cleaving, having an opening at the first light emitting end face and having a first gain wavelength; A second multiple quantum well active layer having an opening at the second light emitting end face and having a second gain wavelength and a coupling waveguide layer for optically coupling them are coupled in a light guiding direction; A first electrode above the first multiple quantum well active layer, a second electrode above the second multiple quantum well active layer, and a third electrode above the coupled waveguide layer A semiconductor light emitting device comprising a fourth electrode short-circuited with the third electrode on the bottom surface of the semiconductor substrate,
The first gain wavelength is longer than the second gain wavelength;
A diffraction grating having a Bragg wavelength corresponding to the second gain wavelength is formed in the vicinity of the coupling waveguide layer,
The light generated in the first multiple quantum well active layer by energization between the first electrode and the fourth electrode is constituted by the first light emitting end face and the second light emitting end face. Light generated in the second multiple quantum well active layer by energization between the second electrode and the fourth electrode is emitted from the diffraction grating and the second light emission. A semiconductor light emitting device characterized in that it oscillates in a resonator composed of an end face and is emitted from the second light exit end face.   2. The semiconductor light emitting device according to claim 1, wherein the coupled waveguide layer has a bulk structure having a composition wavelength equal to or shorter than the second gain wavelength. 3. The semiconductor light emitting device according to claim 1 or 2, and a pulse for emitting a light pulse between any one of the first electrode or the second electrode of the semiconductor light emitting device and the fourth electrode. A light emitting element driving circuit for applying a driving current in the form of a light, and a light emitting unit for outputting the light pulse emitted from the second light emitting end face of the semiconductor light emitting element to the optical fiber to be measured;
A light receiving unit that converts the return light of the optical pulse from the optical fiber to be measured into an electrical signal;
An optical pulse tester comprising: a signal processing unit that analyzes a loss distribution characteristic of the optical fiber to be measured based on an electrical signal converted by the light receiving unit.

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