JPH0426233B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical integrated circuit that can be used as a light emitting element used in optical communication transmitters, optical information processing equipment, and the like.

Prior Art Semiconductor lasers are used as important devices in optical communication systems, optical information processing systems, and the like. However, the light emitting characteristics of semiconductor lasers deteriorate quickly, in other words, their lifetime is short. Therefore, in order to ensure system reliability, optical communication systems, optical information processing systems, and the like are equipped with spare semiconductor lasers.

Specifically, as shown in FIG. 1, for example, in addition to the main semiconductor laser 12 provided with a light receiving element 10 for monitoring, there is also a preliminary semiconductor laser 16 provided with a light receiving element 14 for monitoring. A mirror 18 for optical path switching, which is provided separately, is positioned at the first position 18A, and the laser beam from the main semiconductor laser 12 is directed to the optical fiber 1.
As a result of monitoring by the light receiving element 10, if the main semiconductor laser 12 has deteriorated, the optical path switching mirror 18 is moved to the second position 18B, and the laser beam from the preliminary semiconductor laser 16 is transferred to the optical fiber 19. Please send it to

With the configuration as described above, the short life span of the semiconductor laser can be compensated for. However, the above-described apparatus not only requires an optical path switching mechanism, but also requires mechanical assembly of the optical path switching mechanism, a monitoring light receiving element, and a semiconductor laser. Therefore, the device has to be relatively large and heavy. Furthermore,
The price had to be high not only because of the price of the individual parts, but also because of the large number of manufacturing steps and the need for high-precision fine adjustment such as optical axis alignment. Furthermore, since the optical path switching mechanism is mechanical, the semiconductor laser cannot be switched instantaneously.

Purpose of the Invention Therefore, in view of the above-mentioned problems, the present invention has been made to
In order to realize a lightweight and compact device without the need for a mechanical optical path switching mechanism, we have developed a main light emitting element, a preliminary light emitting element, a photodetector for monitoring the output light of these light emitting elements, and an output of each light emitting element. The present invention aims to provide an optical integrated circuit in which an optical waveguide for outputting light from the same output section is monolithically formed on the same semiconductor substrate, and can be switched to a preliminary light emitting element as needed.

Configuration of the Invention That is, according to the present invention, at least two semiconductor lasers formed on one substrate;
An optical waveguide with a branched structure formed on the substrate guides the output light of each semiconductor laser and outputs it from the same output part, and an optical waveguide formed on the substrate for each semiconductor laser so as to detect the optical output of the semiconductor laser. a photodetecting element provided, the photodetecting element comprising:
The semiconductor laser is formed on the semiconductor laser, and the semiconductor laser and the photodetection element are formed to have a multilayer epitaxial structure, and the photodetection element is formed on the topmost layer of the semiconductor laser. a first layer which is of the same conductivity type as a layer of the cladding layer and is shared with the cap layer of the semiconductor laser formed on the topmost cladding layer of the semiconductor laser; A monolithic optical integrated circuit is provided, characterized in that it is a PN junction photodiode having a second layer formed thereon and having a conductivity type opposite to that of the first layer.

According to the monolithic optical integrated circuit as described above, all the laser beams from each light emitting element pass through the optical waveguide and are output from the same output section.
One light-emitting element is operated as the main light-emitting element, and the status of that light-emitting element is monitored by the photodetector attached to it, while the other light-emitting elements are used as preliminary light-emitting elements and are not used. You can leave it there. If it is determined that the light emitting element has deteriorated as a result of monitoring, for example, if the output of that light emitting element decreases or oscillation stops, another light emitting element set as a backup light emitting element is operated in its place. This allows instant switching.

In the embodiment of the present invention, each of the light emitting elements is a semiconductor laser, for example, a DBR type laser diode. In addition, in the case of a long wavelength band of λ≒0.9 to 1.7 μm, an InGaAsP quaternary mixed crystal semiconductor laser with an InP substrate can be used, and in the case of a short wavelength band of λ≒0.9 μm or less, a semiconductor laser with a GaAs substrate can be used. A GaAlAs-based ternary mixed crystal semiconductor laser can be used.

Further, the photodetecting element is formed on the uppermost cladding layer of the semiconductor laser, and includes a first layer having the same conductivity type as that of the uppermost cladding layer of the semiconductor laser, and a first layer having the same conductivity type as that of the uppermost cladding layer of the semiconductor laser. The photodiode is a PN junction type photodiode having a second layer formed on the layer and having a conductivity type opposite to the first layer, and detects an evanescent wave from a semiconductor laser. When there are two light emitting elements, the optical waveguide having a branch structure can be of a Y-branch type.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 2 is a schematic perspective view of a monolithic optical integrated circuit according to the present invention incorporating an InGaAsP/InP DBR type laser diode, and FIG.
FIG. 4 is a sectional view taken along line A-A in the figure;
FIG. 4 is a sectional view taken along line BB in FIG. 3; The illustrated monolithic optical integrated circuit includes two laser diodes 22 and 24 formed on a substrate 40. And those laser diodes 22 and 2
4 are provided with photodiodes 28 and 30 for optical output monitoring. An optical waveguide 32 having a Y-branch structure is formed on the opposite side of the laser diodes 22 and 24 from the photodiodes 28 and 30.

To explain in detail, as shown in Figure 3,
Laser diodes 22 and 24 each have an n-InP cladding layer 42 formed on an n-InP substrate 40. On the n-InP cladding layer 42,
An InGaAsP active layer 44 is formed.
A p-InP cladding layer 4 is formed on the InGaAsP active layer 44.
6 is formed. Further, on the p-InP cladding layer 46, a p-InP cap layer is formed to form a good ohmic contact.
An InGaAsP layer 48 is formed. An n-side electrode 50 is formed on the lower side of the substrate 40, while a p-side electrode 52 is formed on the upper side of the p-InGaAsP layer 48.

On the other hand, photodiodes 28 and 30 are connected to laser diode 2, as shown in FIGS.
A PN formed from a p-InGaAsP layer 48 shared with the cap layers 2 and 24, and an n-InGaAsP layer 54 formed on the upper side of the p-InGaAsP layer 48.
It is a junction photodiode. And p-
Electrodes 56 and 58 are formed on the InGaAsP layer 48 and the n-InGaAsP layer 54, respectively.

With this configuration, these photodiodes 28 and 30 allow the evanescent wave (seepage light) of the propagating light to pass through the p-InGaAsP layer 48 and generate p-
Upon reaching the PN junction between the InGaAsP layer 48 and the n-InGaAsP layer 54, a photocurrent is generated. The photocurrent is extracted from between the electrodes 56 and 58. In other words, photodiodes 28 and 30 are
Detects evanescent waves of propagating light.

Further, the optical waveguide 32 has an n-InGaAsP cladding layer 60 formed on the substrate 40,
On the n-InGaAsP cladding layer 60 is an n-InGaAsP cladding layer 60.
An InGaAsP waveguide layer 62 is formed, and its n
An n-InGaAsP cladding layer 64 is formed on the -InGaAsP waveguide layer 62.

The upper part of the n-InGaAsP cladding layer 64 near the coupling portion of the optical waveguide 32 with the laser diode is subjected to grating processing to form a Bragg reflector 66, while the end face 72 of the laser diode opposite to the Bragg reflector 66 is grating-processed. is made into a cleavage plane, making the laser diode a DBR type.
Note that instead of the cleavage plane 72, a Bragg reflector may be formed.

The surroundings of the laser diodes 22 and 24, the photodiodes 28 and 30, and the optical waveguide 32 are
As shown in the figure, p-InP layer 68 and n-InP layer 7
It is surrounded by a laminated part with 0 and has an embedded structure,
It traps light inside.

The monolithic optical integrated circuit as described above is manufactured, for example, as follows. That is, as shown in FIG. 5A, an n-InP cladding layer 42, an InGaAsP active layer 44, a p-InP cladding layer 46, a p-InGaAsP layer 48, and an n-InP cladding layer 42 are formed on an n-InP substrate 40, as shown in FIG. 5A.
InGaAsP layer 54 is grown epitaxially in this order. Next, as shown in FIG. 5B, the portions corresponding to the laser diode and photodiode are masked with a mask 80 made of, for example, SiO ₂ so that half of the device, that is, the right side of the surface 74 in FIG.
The substrate 40 is etched to the depth by photolithography to form a waveguide layer. Then, as shown in FIG. 5C, an n-InGaAsP cladding layer 60 and an n-
The optical waveguide 32 is formed by epitaxially growing an InGaAsP waveguide layer 62 and an n-InGaAsP cladding layer 64 in sequence. At this time, in order to guide the laser beam, the n-InGaAsP waveguide layer 62 has the same composition ratio as the active layer of the laser diode.
Furthermore, a portion of the n-InGaAsP layer 54 on the optical waveguide side is removed by etching to expose the p-InGaAsP layer 48.

Then, as shown in FIG. 5D, n-
The area near the junction of the InGaAsP cladding layer 64 with the laser diode is grating-processed using holographic exposure or electron beam exposure and photolithography to form a bragg reflector 66.
form. The grating period Λ is chosen so that Λ=λg/2N so that the light waves in the active layer are effectively blurred and reflected. Here, λg is the wavelength with respect to the energy gap of the active layer, and N is the effective refractive index (propagation constant β in the waveguide layer and propagation constant in vacuum k ₀
The ratio: N=β/k ₀ ).

Thereafter, as shown in FIG. 5E, in order to make the laser diode a buried structure and the optical waveguide a Y-branched structure, a Y-shaped photomask 82 was formed and mesa-etched using photolithography until it reached the substrate 40. Thereafter, as shown in FIG. 5F, a p-InP layer 68 and an n-InP layer 70 are epitaxially grown to embed a laser diode and an optical waveguide.

After that, the p-InGaAs layer 48 is formed on the lower side of the substrate 40.
Ohmic electrodes 50, 52, 5 are placed at two locations on the upper side and on the upper side of the n-InGaAsP layer 54, respectively.
6 and 58 are formed to produce optical integrated circuits as shown in FIGS. 2 to 4. Au-Zn or the like can be used as the P-type ohmic electrode, and An-Ge-Ni or the like can be used as the N-type ohmic electrode. Finally, cleavage is performed to form a mirror crystal plane 72 for laser resonance.

As a result, a DBR type laser diode having a mirror crystal surface of the laser, that is, a single-end mirror and a single-end grating is formed.

As can be seen from the above, the formation of a photodiode does not require any special epitaxial process, and a photodiode and a laser diode can be formed simultaneously by a single continuous multilayer epitaxial process.
The epitaxial growth process is simple. Note that the epitaxial multilayer method includes a liquid phase growth method, a vapor phase growth method, an organometallic vapor phase deposition method, and the like.

The monolithic optical integrated circuit having the above structure can be used as follows. That is, since all the laser beams from the respective laser diodes 22 and 24 pass through the optical waveguide 32 and are outputted from the same output section, one of the laser diodes 22, for example, is operated as the main light emitting element, and the attached The output state is monitored by one photodiode 28, and the other laser diode 24 is used as a preliminary light emitting element and is left unused. As a result of monitoring by the photodiode 28, the laser diode 2
If it is determined that the laser diode 22 has deteriorated, specifically, if the output of the laser diode 22 decreases or the oscillation stops, the laser diode 24 can be operated in its place to instantly switch over. can.

Although the above embodiment is a monolithic optical integrated circuit incorporating an InGaAsP/InP DBR type laser, a -V group ternary or quaternary alloy can be used as the semiconductor material of the laser. For example, if a GaAlAs/GaAs semiconductor laser is incorporated as an example of a ternary alloy, GaAs is used as the substrate 40, the cladding layer 42,
GaAlAs can be used for 46, 60, and 64, and GaAs can be used for active layer 44 and waveguide layer 62.

Although an example of an optical integrated circuit according to the present invention incorporating two laser diodes has been described above, it is obvious that an optical integrated circuit according to the present invention incorporating three or more laser diodes can be similarly realized. Probably.

Effects of the Invention As described above, the optical integrated circuit according to the present invention includes at least two light emitting elements formed on one substrate, and the output light of each light emitting element is guided and outputted from the same output section. The optical waveguide has a branched structure formed on the substrate, and a photodetector element is provided on the substrate for each light emitting element to detect the optical output of the light emitting element. It is small and lightweight, and can be mass-produced using conventional semiconductor device manufacturing methods, making it possible to reduce costs.

In addition, since the output light of each light emitting element is guided to the same light output part by the optical waveguide with a branch structure,
There is no need for optical axis adjustment, high reliability, and no mechanical device for switching light sources.

Furthermore, since the light emitting element can be switched to the backup light emitting element by electrical operation, a deteriorated light emitting element can be instantly switched to the backup light emitting element, and when the system performance deteriorates, it can be recovered in an extremely short time.

When forming a semiconductor laser as a light emitting element,
The structure and composition of the semiconductor laser, especially the active layer, can be made common to all semiconductor lasers, and the oscillation wavelength and mode of all semiconductor lasers can be made the same. Therefore, even if the main semiconductor laser fails and the backup semiconductor laser is used, it is easy to use. , there is no change in the emission characteristics.

Since the photodiode section and the laser diode section are formed to have a layered structure, the photodiode section and the laser diode section can be formed by performing multilayer epitaxial growth only once.
No epitaxial growth process is required just for photodiode formation. Therefore, the manufacturing process is simple and can be manufactured at low cost.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of a conventional light generating device having a backup light source, FIG. 2 is a perspective view of a first embodiment of an optical integrated circuit according to the present invention, and FIG. 3 is a line A in FIG. 2. 4 is a sectional view along the line B--B of FIG. 3, and FIGS. FIG. 1 is a diagram illustrating a method for manufacturing an optical integrated circuit according to the invention. (Main reference numbers), 10, 14... Light receiving element for monitor, 12... Main semiconductor laser, 16... Spare semiconductor laser, 18... Mirror for optical path switching, 1
9... Optical fiber, 40... Substrate, 22, 24...
...Laser diode, 28, 30...Photodiode, 32...Optical waveguide.

Claims (1)

[Scope of Claims] 1. At least two semiconductor lasers formed on one substrate, and a light guide with a branching structure formed on the substrate, which guides the output light of each semiconductor laser and outputs it from the same output section. a wave path, and a photodetection element provided on the substrate for each semiconductor laser to detect the optical output of the semiconductor laser, the photodetection element being formed on the semiconductor laser, The semiconductor laser and the photodetection element are formed to have a multilayer epitaxial structure, and the photodetection element is of the same conductivity type as the topmost cladding layer of the semiconductor laser. a first layer shared with the cap layer of the semiconductor laser formed on the topmost cladding layer of the semiconductor laser; and a first layer formed on the first layer and opposite to the first layer. has a second layer of conductivity type of
A monolithic optical integrated circuit characterized by being a PN junction photodiode. 2. Claim 1, wherein the semiconductor laser is a DBR type laser diode.
The monolithic optical integrated circuit described in Section 1. 3 The semiconductor laser uses InP as a substrate.
3. The monolithic optical integrated circuit according to claim 1, wherein the monolithic optical integrated circuit is an InGaAsP quaternary mixed crystal semiconductor laser. 4 The semiconductor laser uses GaAs as a substrate.
3. The monolithic optical integrated circuit according to claim 1, wherein the monolithic optical integrated circuit is a GaAlAs-based ternary mixed crystal semiconductor laser. 5. The monolithic optical integrated circuit according to claim 1, wherein the optical waveguide has a Y-branch structure.