JPS6089990A - Optical integrated circuit - Google Patents

Abstract

PURPOSE:To enable to switch to spare light emitting element as required by monolithically forming a main light emitting element, a spare light emitting element, a monitoring inspecting element and a light waveguide on the same semiconductor substrate. CONSTITUTION:Laser lights from laser diodes 22, 24 formed on a substrate 40 all pass the light waveguide 32 on the substrate 40 and are outputted from the same output unit. Thus, one diode 22 is operated as a main light emitting element, the photodiode 28 belonging thereto is used to monitor the output state, and the other diode 24 is not used as a spare light emitting element. As a result that the diode 28 is used to monitor, if the diode 22 is judged to be deteriorated, such as when the output of the diode 22 decreases or when the oscillation is stopped, the diode 24 is operated instead to instantaneously switch it.

Description

DETAILED DESCRIPTION OF THE INVENTION 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.

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 fR systems, optical information processing systems, and the like are equipped with spare semiconductor lasers.

Specifically, as shown in FIG. 1, for example, a main semiconductor laser 12 is provided with a light receiving element 10 for monitoring.
In addition, a preliminary semiconductor laser 16 similarly provided with a light-receiving element 14 for monitoring is separately provided, and an independently provided optical path switching mirror 18 is initially positioned at the first position 18A to The laser beam from the laser 12 is sent to the optical fiber 19, and as a result of monitoring by the light receiving element 10, if the main semiconductor laser 12 has deteriorated, the optical path switching mirror 1
8 to the second position 18B so that the laser beam from the preliminary semiconductor laser 16 is sent to the optical fiber 19.

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, not only the price of individual parts but also the large number of manufacturing steps and the necessity of high-precision fine adjustment such as optical axis alignment have forced the price to be high.

Furthermore, since the optical path switching mechanism is mechanical, the semiconductor laser cannot be switched instantaneously.

Therefore, in view of the problems that have been developed, the present invention has been developed by combining a main light emitting element and a preliminary light emitting element in order to realize a lightweight and compact device without requiring a mechanical optical path switching mechanism. , a photodetector element for monitoring the output light of these light emitting elements, and an optical waveguide for outputting the output light of each light emitting element from the same output part are monolithically formed on the same semiconductor substrate, and the optical waveguides are formed monolithically on the same semiconductor substrate. It is an object of the present invention to provide an optical integrated circuit that can be switched to a preliminary light emitting element.

That is, according to the present invention, at least two light emitting elements are formed on one substrate, and the light emitting elements formed on the substrate are guided to output light from the same output section. an optical waveguide having a branched structure, and a photodetecting element provided on the substrate for each light emitting element to detect the optical output of the light emitting element, and the photodetecting element is provided on the substrate. A monolithic optical integrated circuit is provided.

According to the monolithic optical integrated circuit as described above, all the laser light from each light emitting element passes through the optical waveguide and is output from the same output part, so one light emitting element is operated as the main light emitting element, The state of the light emitting element can be monitored by the attached photodetection element, while the other light emitting elements can be used as preliminary light emitting elements and left unused.

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 has decreased or the oscillation has stopped, another light emitting element that has been kept as a backup light emitting element can be used instead. By operating it, you can switch at once.

In an embodiment of the present invention, (:1) each of the light emitting elements is a semiconductor laser, for example, an I) T3 R type laser diode. In addition, in the case of a longer wavelength of λ#0.9 to 1.7 μm, InGaAsP system 4 using [In] as a substrate
If an original mixed crystal semiconductor laser can be used and the short wavelength band is λ#0.9μm or less, GaAlAs with a GaAs substrate can be used.
A 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 of the same conductivity type as a layer of the uppermost cladding layer of the semiconductor laser; The photodiode is a PN junction type photodiode having a second layer formed on the second layer of the first layer and having a conductivity type opposite to that of the first layer, and detects an evanescent wave from a semiconductor laser. When there are two light emitting elements, the leading waveguide of the branched structure can be of a Y-branched type.

fruit mouth The present invention will be described in detail below 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.
4 is a cross-sectional view along line A, and FIG. 4 is a cross-sectional view taken along line B-B in FIG.
FIG. The illustrated monolithic optical integrated circuit includes two laser diodes 2 formed on a substrate 40.
2 and 24.

Photodiodes 28 and 30 for monitoring optical output are provided above the laser diodes 22 and 24, respectively. A leading 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.

Specifically, as shown in FIG. 3, laser diodes 22 and 24 each have an n-1nP cladding layer 42 formed on an n4nP substrate 40.

An InGaAsP active layer 44 is formed on the n-1nP cladding layer 42, and a p-1nP cladding layer 46 is formed on the InGaAsP active layer 44. Further, on the p-1nP cladding layer 46, a p-InGaAsP layer 48 is formed which constitutes a cap layer for forming a good ohmic contact. 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 second side of the p-InGaAsP layer 48.

On the other hand, the photodiodes 2 and 30 have a p-InGaAsP layer 4, which is shared with the cap layer of the laser diodes 22 and 24, and a p-InGaAsP layer 4, as shown in FIGS. 3 and 4.
n-InG formed in one part of the InGaAsP layer 48
This is a PN junction photodiode formed from the aAsP layer 54. Then, the p-InGaAsP layer 48 and the n-
Electrodes 56 and 58 are formed on the InGaAsP layer 54, respectively.

With this configuration, these photodiodes 28 and 30 are configured so that when the laser diode oscillates, the evanescent wave (exuded light) of the propagating light is p=InGaA.
ζ through the sP layer 48, p-rnGaAsP layer 48 and n
- When reaching the PN junction surface with the TnGaAsP layer 54,
Generates a photocurrent. Then, the photocurrent is transmitted between the electrodes 56 and 5.
Take it out from the 8th room. In other words, photodiodes 2B and 30 detect evanescent waves of propagating light.

Further, the leading waveguide 32 is formed on the substrate 40''2.
It has a TnGaAsP cladding layer 60, and its n-
[n-InGaAs on the nGaAsP cladding layer 60
A P waveguide layer 62 is formed, and its n-InGaAs
An n4nGaAsP cladding layer 64 is formed on the P waveguide layer 62.

n- near the coupling part of the optical waveguide 32 with the laser diode
The upper part of the InGaAsP cladding layer 64 is grating processed to form a Bragg reflector 66, while the end face 7 of the laser diode opposite to the Bragg reflector 66
2 is made into a cleavage plane to DB the laser diode
It is an R type. Note that a Bragg reflector may be formed instead of the cleavage plane 72.

As shown in FIG. 4, the laser diodes 22 and 24, the photodiodes 28 and 30, and the guiding waveguide 32 are surrounded by a pJnP layer 68 and a seven-layer n-InP layer stack, forming a buried structure. This traps the light inside.

0 The monolithic optical integrated circuit as described above is manufactured, for example, as follows. That is, as shown in FIG. 5A, 11nP
On the substrate 40, an n-1nP crat" layer 42 and an InG
The aAsP active layer 44, the p-TnP Claso1' layer 46, the p4nGaAsr' layer 48, and the n-1n (iaAsP
A multilayer epitaxial growth is performed in a total of 54 layers. Next, as shown in FIG. 5B, the portions corresponding to the Raded diode and photodiode are masked with a mask 80 such as 5i02, so that half of the element, that is, the right side of the surface 74 in FIG. 3, is masked. is etched to the depth of the substrate 40 by photolithography to form a waveguide layer.

Then, as shown in FIG. 5C, the exposed substrate 40
On top of the n-TnGaAsr' cladding layer 60 and the n-
The InGaAsP waveguide layer 62 and the n-InGaAsP cladding layer 64 are epitaxially grown in sequence to form the guide waveguide 32.

At this time, in order to guide the laser light, n-InGa
The AsP waveguide layer 62 has the same composition ratio as the active layer of the laser diode. Furthermore, a part of the n-InGaAsP layer 54 on the optical waveguide side is removed by etching, and the p-InGaAsP layer 54 is removed by etching.
Expose the P layer for 4 days.

1. As shown in Figure 5, the vicinity of the coupling portion of the n-InGaAsP cladding layer 64 with the laser diode is processed into a grating by holography/7-dimensional exposure method or electron beam exposure method and photolithography to form a Bragg reflector. Form 66. The period A of the grating is chosen to be Δ=λg/2N so that the light waves in the active layer are effectively Bragg-reflected. Here, λg is the wavelength with respect to the energy gap of the active layer, and N is the effective refractive index (the ratio of the propagation constant β in the waveguide layer to the propagation constant kO in vacuum: N-β/
ko).

After that, as shown in FIG. 5, in order to make the laser diode a pitted structure and the optical waveguide a Y-branch structure, a 7-shaped photomask 82 is formed and the substrate 40 is reached by photolithography. After mesa etching up to
As shown in FIG. 5F, the p-1nP layer 68 and the n4nP layer 68
1i70 is grown epitaxially to embed a laser diode and an optical waveguide.

2 Thereafter, ohmic electrodes 50, 52, 56, and 58 are formed on the lower side of the substrate 40, on the upper side of the p-TnGaAs layer 48, and on the 1]2 side of the n-1nGaAsr' layer 54, respectively. Optical integrated circuits as shown in FIGS. 2 to 4 are produced. As a P-type ohmic electrode, Δu
- Zn etc. can be used, and A as an N-type ohmic electrode.
n-Ge-N+ etc. can be used. 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 the photodiode and laser diode can be formed simultaneously by one continuous multilayer epitaxial process. The 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 configured as described above can be used in the following three-order manner. That is, each laser diode 22
Since the laser beams from and 24 all pass through the optical waveguide 32 and are output from the same output section, one of them, for example, the laser diode 22, is operated as the main light emitting element.
The output state is monitored by the photodiode 28 attached thereto, and the other laser diode 24 is used as a preliminary light emitting element and left unused. As a result of monitoring by the photodiode 28, if it is determined that the laser diode 22 has deteriorated, specifically, if the output of the laser diode 22 decreases or oscillation stops, the laser diode 24 is By operating instead, it is possible to switch instantly.

The above embodiments are InGaAsP/InP based DBRs.
Although this is a monolithic optical integrated circuit incorporating a type laser, a ternary or quaternary alloy of the ■-■ group can be used as the semiconductor material of the laser. For example, in the case where a GaAlAs/GaAs semiconductor laser is incorporated as an example of a ternary alloy, the substrate 40 is made of GaAs.
The active layer 44 and the waveguide 1562 are
GaAs can be used as the material.

Although an example of an optical integrated circuit according to the present invention incorporating 1-1-12 laser diodes has been described below, an optical integrated circuit according to the present invention incorporating three or more laser diodes can also be similarly realized. It should be obvious that there is no need to explain what can be done.

As mentioned above, the optical integrated circuit according to the present invention includes at least two light emitting elements formed on one substrate,
An optical waveguide with a branched structure formed on the substrate guides the output light of each light emitting element and outputs it from the same output part; Since it is constructed monolithically with a photodetecting element provided therein, it is small and lightweight, and can be mass-produced using conventional semiconductor device manufacturing methods, resulting in lower costs.

In addition, since the output light of each light emitting element is guided to the same light output section 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 is required. Not necessary.

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, so that the main semiconductor laser can be prevented from failure. Even if you switch to the backup semiconductor laser, there is no change in the emission characteristics.

Since the photodiode section and the laser diode section are formed in a layered structure, the photodiode section and the laser diode section can be formed by performing multilayer epitaxial growth only once. There is no need for a single epitaxial growth process.Therefore, the manufacturing process is straightforward 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. - Along A...1
A top view, FIG. 4 is a sectional view taken along line B-B in FIG. 3,
FIGS. 5A to 5F are diagrams illustrating the method of manufacturing the optical integrated circuit according to the present invention shown in FIGS. 2 to 4. (Main reference numbers) 10.14... Light receiving element for monitor, 12... Main semiconductor laser, Ifi... Reserve semiconductor laser, 18...
・Mirror for optical path switching, I9...Optical fiber, 40...
・Substrate, 22.24...Laser diode, 28.3
0... Photodiode, 32... Leading waveguide Patent applicant... Sumitomo Electric Industries, Ltd. Agent... Patent attorney
New house sound stop 7 6 Figure 2 8 Ra 2 30 56 Af-, 66 β 32 1°＼ 70 66g 2

Claims (9)

[Claims] (1) at least two light emitting elements formed on one substrate; an optical waveguide having a branch structure formed on the substrate, which guides the output light of each light emitting element and outputs it from the same output section; Each light-emitting element includes a photo-detecting element provided on the substrate so as to detect the light output of the light-emitting element, and the photo-detecting element is formed on the light-emitting element. Monolithic optical integrated circuit. (2) The monolithic optical integrated circuit according to claim 1, wherein the light emitting element and the photodetecting element are formed to have a multilayer epitaxial structure. (3) The monolithic optical integrated circuit according to claim 1 or 2, wherein each of the light emitting elements is a semiconductor laser. (4) The monolithic optical integrated circuit according to claim 3, wherein the semiconductor laser is a DBR type laser diode. (5) The semiconductor laser is made of InG using InP as a substrate.
5. The monolithic optical integrated circuit according to claim 3, wherein the monolithic optical integrated circuit is an aAsP quaternary mixed crystal semiconductor laser. (6) The semiconductor laser has a GaAs substrate.
5. The monolithic optical integrated circuit according to claim 3, wherein the monolithic optical integrated circuit is an AlAs-based ternary mixed crystal semiconductor laser. (7) The photodetecting element is formed on the uppermost cladding layer of the semiconductor laser, and has a first layer of the same conductivity type as the uppermost cladding layer of the semiconductor laser. and a second layer formed on the first layer t- and having a conductivity type opposite to that of the first layer.
The monolithic optical integrated circuit according to any one of claims 3 to 6, characterized in that it is a PN junction type photodiode having a layer. (8) The monolithic optical integrated circuit according to claim 7, wherein the first layer of the photodiode is also used as a gap layer of the semiconductor laser. (9) The monolithic optical integrated circuit according to any one of claims 1 to 8, wherein the leading waveguide has a Y-branch structure. −