DE102004037362A1 - Optical multiplexer transceiver, has several active photosensitive and light emitting units tuned in different wavelengths, where transceiver is developed as monolithically integrated optical semiconductor chip - Google Patents

Abstract

The transceiver has several active photosensitive and light emitting units tuned in different wavelengths. The transceiver is developed as monolithically integrated optical semiconductor chip. The transceiver is directly coupled to an optical wave guide. The multiplexer converts electrical signals into optical signals of specific wavelength, where the optical signals are coupled and decoupled via a single mode wave guide. Independent claims are also included for the following: (A) an optical semiconductor chip for multiplexer transceiver applications (B) a method for manufacturing an optical semiconductor chip.

Description

Field of the invention

The The invention relates generally to the field of integrated optics and in particular, an optical semiconductor chip having the function of Multiplexer transceivers for FTTx applications, in particular an optical triplexer transceiver.

The Demand for high-speed access for data transmission and so-called Tripleservices (Voice, data, video) is higher as before and FTTx networks are the key to these services. Currently These FTTx networks have already been introduced around the world. FTTx is an acronym for the applications "Fiber to the Home, Fiber to the Premises, Fiber to the Curb, or Fiber to the Building, etc. These terms stand for different "last mile "network access, in particular optical single-mode optical fiber networks. For example, is the FTTH technique like all other FTTx techniques include fiber optic connectivity the fiber from the local exchange to the house the subscriber terminal guided becomes. With this future-oriented connection technology can be all future, use interactive broadband distribution services.

It are several common Specifications and protocols for This technology (see for example: http://www.ftthcouncil.org/, and http://www.itu.int/home/index.html), although for single-mode waveguides based applications the most common technology for bidirectional Communication is used: 1490 nm data Rx, 1550 nm video Rx, 1310 nm data Tx; where Rx is for download (Provider → Home) and Tx for upload (Home → Provider) Data transfer is available. By means of so-called triplexer transceivers, those with the data transmitting monomoder fiber are coupled, can simultaneously signals to 1490 nm and 1550 nm wavelength receive and send to 1310 nm.

• a) einer Multiquantenwell Fabry Perot (MQW FP) Laserdiode als Transmitter mit 1310 nm Wellenlänge Ausgang
• b) einer 1490 nm InGaAs P-I-N Diode als digitalem Receiver
• c) einem in 45° montierten halbdurchlässigem Spiegel, der 1490 nm durchlässt und 1550 nm um 90° ablenkt, und
• d) einer 1550 nm InGaAs P-I-N Diode als digitalem Receiver.

Currently, triplexer transceivers are manufactured from discrete components that are housed together in a housing and look like in 1 :
The exemplified in this figure, currently commercially available, Txiplexer transceiver 1 consists:

• a) a multi-quantum well Fabry Perot (MQW FP) laser diode as a transmitter with 1310 nm wavelength output
• b) a 1490 nm InGaAs PIN diode as a digital receiver
• c) a 45 ° mounted semitransparent mirror which transmits 1490 nm and deflects 1550 nm by 90 °, and
• d) a 1550 nm InGaAs PIN diode as a digital receiver.

As one sees, here an external housing is absolutely necessary, there this case houses four different components. The entire triplexer Transceiver requires a corresponding installation effort and is relatively large. A Coupling to the single-mode optical fiber via a conventional Plug connection.

It is still to be mentioned that in the next Is remembered in other protocols the 1310 nm channel also as Rx channel and an additional one 1625 nm wavelength channel for mistakes To use detection. For this technique must then five-fold multiplexer Transceivers are developed and built. This complicates the structure in the conventional discrete construction in addition.

Disclosure of the invention

The The object of the invention is therefore a multiplex transceiver and to provide a method of making it, the smaller, cost-effective and more reliable is as the previous systems.

These The object is achieved by the Characteristics of the independent Claims solved.

preferred Embodiments and other advantageous features of the invention are in the subclaims specified.

According to the invention is a optical multiplexer transceiver described as monolithic integrated optical semiconductor chip is constructed and several, to different wavelengths coordinated active photosensitive and light-emitting elements includes.

Of the optical semiconductor chip is based on a semiconductor substrate, on the at least one first layer structure which is a photosensitive Element for light a first wavelength forms, and arranged on the first layer structure, further layer structure, which forms a light-emitting element for light of a further wavelength, are arranged. Between the photosensitive element and the light-emitting Element can one or more further photosensitive elements can be arranged.

According to the invention thus an integrated optical device in the form of a multiplexer transceiver, in particular a triplexer, created that can receive optical signals at wavelengths of preferably 1550 nm and 1490 nm and convert it into electrical signals by means of two photodetectors, and also electrical signals in optical signals of a wavelength of preferably 1310th nm converts and sends out. The optical signals are coupled in and out via a single-mode waveguide.

In contrast to the commercially available triplexer transceivers described at the beginning, according to the invention three optically active components are integrated on a semiconductor chip and are preferably connected directly to a single-mode waveguide. The components are:
A light-emitting component, preferably in the form of a 1310 nm laser diode, for example, designed as a vertical cavity surface emitting laser (VCSEL) or distributed feedback (DFB) laser, which radiates in the direction of surface normal,
a photosensitive component, preferably in the form of a 1490 nm photodiode, for example, by an InGaAs PIN diode feasible, and
another photosensitive component, preferably in the form of a 1550 nm photodiode, for example, also by an InGaAs PIN diode feasible.

The semiconductor chip comprises the different functionalities (photodiodes, lasers, etc.) realized in different epitaxial layers, wherein the layers are formed, for example, from In _x Ga _1-x As with different x content (doping content).

The Wavelength selectivity of the photodiodes is achieved by a clever arrangement (stratification) of the components in the vertical direction and additional lithographic steps (structuring) in the horizontal direction guaranteed. In particular, the individual optical elements are corresponding their assigned wavelength arranged on the substrate. The optical element with the longest wavelength becomes the next while arranged to the substrate the optical element with the shortest wavelength placed farthest from the substrate.

to Passivation of the wafer can be applied as a cover layer, a dielectric which is an oxide or oxynitride layer. The cover layer can the chip also completely enclose and be interrupted only by the electrical contacts.

One Another important feature is that the photosensitive and light-emitting Elements independent contacted and operable from each other.

In a particularly preferred embodiment of the invention, the the wafers supporting the photosensitive and light emitting elements divided into several adjacent columnar structures be, wherein the photosensitive and / or light-emitting elements each column structure also independent contacted and operable from each other.

In A further embodiment of the invention can be used to improve the signal-to-noise ratio one or more optical filter structures over the light-sensitive elements be attached, the unwanted Frequencies from the respectively photosensitive ones arranged underneath Keep elements away.

to Application of filter layers can be arranged at the top light-emitting elements are removed by e.g. the light-sensitive ones Elements are exposed by means of lithographic processes.

Provided the substrate a band gap greater than 0.9 eV corresponding to a wavelength of λ <1300 nm, the substrate be connected directly to an optical fiber. The single ones light-emitting and photosensitive elements are in this case arranged in reverse order on the substrate and send and receive the light to / from the waveguide through the transparent Substrate through.

A method for manufacturing an optical semiconductor chip for multiplexer transceiver applications is also provided. After the epitaxial production and the lithography steps, the semiconductor chips are cut, placed on carriers, electrically contacted and molded together with a waveguide (glass fiber) into a transparent mass (polymer or SiO ₂ ). The electronics for amplifying the signals can be implemented, for example, in Si technology; In principle, of course, would be possible, the amplifier electronics also z. B .: to perform in GaAs.

Brief description of the drawings

It shows:

1 : a conventional triplexer currently available on the market 1 with housing;

2 : a representation of the energy gap as a function of the lattice constant for III-V compounds;

3 FIG. 2: a basic diagram of an epitaxial layer sequence according to the invention, in which two Photodetectors and a laser on a common substrate (monolithic) are integrated;

4 : a plot of sensitivity and quantum efficiency as a function of wavelength for InGaAs, Si and Ge;

5 a top view and side view of a first embodiment of a lithographically structured component according to the invention;

6 a top view and side view of another embodiment of a lithographically structured component according to the invention;

7 a side view of the device according to 6 with glass fiber attached from above;

8th a side view of another embodiment of a lithographically structured device according to the invention with a transparent substrate and attached from below glass fiber;

9 an epitaxial layer sequence in which three photodetectors and a laser are integrated on a common substrate (monolithic);

10 a schematic representation of the layer structure of a PIN photodiode;

11 a schematic representation of the layer structure of a VCSEL laser diode.

Description of preferred Embodiments of the invention

1 shows a commercial triplexer 1 comprising a housing on which connections for a single-mode waveguide, two photodiodes and a laser diode are arranged.

2 is a representation of the energy gap as a function of the lattice constant for III-V compounds. This diagram shows with which lattice matched substrates direct III-V semiconductors can be generated at the interesting wavelengths of 1310 nm and 1550 nm. When using, for example, an InP substrate and its given lattice constant, the semiconductor materials InGaAs and GaAsSb are suitable for an energy gap of approximately 0.8 eV-0.95 eV, which corresponds to a wavelength range of approximately 1300-1550 nm.

In 3 is a schematic representation of the epitaxial layer structure of a possible embodiment of the invention indicated: On a semiconductor substrate 2 For example, an InP substrate, lattice is matched to a first photosensitive semiconductor layer 3 grown from In _x Ga _1-x As with x about 0.53. This first semiconductor layer 3 forms a photodetector in the form of a PIN (p-doped, intrinsic, n-doped) or avalanche diode whose structure is exemplified in 10 is shown. The one PIN photodiode 30 consists of a p-layer 31 , an n-layer 33 and an intervening intrinsic i-layer 32 (intrinsic layer). The light hits on the side of the p-layer. The p-layer 31 is preferably with an anti-reflective coating 34 Mistake. The p and n layers are with electrical contacts 35 Mistake. The resulting semiconductor has an energy gap of 0.79 eV, which corresponds to a first wavelength λ ₁ = 1550 nm (with λ wavelength in vacuum).

Directly over this first semiconductor layer 3 becomes a second photosensitive semiconductor layer 4 in the form of a photodetector, eg a PIN or avalanche diode, consisting of In _x Ga _1-x As grown to x approximately 0.49. The resulting semiconductor thus has an energy gap of 0.83 eV, which corresponds to a second wavelength λ ₂ = 1490 nm (with λ wavelength in vacuum).

This top, second semiconductor layer 4 absorbs radiation with λ ₂ = 1490 nm but allows other wavelengths, for example, λ ₁ = 1550 nm pass, and thus simultaneously serves as a filter for the lower PIN diode at λ ₁ = 1550 nm, so that this of the radiation with λ ₂ = 1490 nm is not affected.

• – einem unteren DBR 37, beispielsweise In_xAl_1-xAs/InP
• – einer aktiven lichtemittierenden Schicht 39 bei einer Wellenlänge von λ₃= 1310 nm, beispielsweise aus In_xGa_1-xAs mit x etwa 0,35; diese Schicht kann jedoch auch aus verzerrtem (engl. strained) Material bestehen, da auch Spannungen die Energie der Emission verschieben.
• – einem oberen DBR 38, beispielsweise In_xAl_1-xAs/InP, oder dieser könnte auch aus SiO₂/p-Si Schichten bestehen.

On the second semiconductor layer 4 now becomes a light-emitting third semiconductor layer 5 grown in the form of an InGaAs laser diode (VCSEL). VCSEL stands for Vertical Cavity Surface Emitting Laser, a special type of semiconductor laser: Unlike the edge emitter, the laser resonator is not formed from two gap edges of the semiconductor crystal, but from two distributed Bragg reflectors (DBRs), between which an active zone for the generation embedded in the laser light. A DBR is an alternating layer sequence of two semiconductor materials with different refractive indices, each with the thickness of half a wavelength of the laser light. In the range of this wavelength, the DBR reflects light almost completely. Two DBRs thus form a high-quality resonator. Part of the laser light is decoupled from the upper DBR and emitted. The structure of a VCSEL is in 10 shown schematically. The VCSEL 36 essentially comprises (in addition to the electrical contacts, not shown here) of three layer structures:

• - a lower DBR 37 , for example In _x Al _1-x As / InP
• An active light emitting layer 39 at a wavelength of λ ₃ = 1310 nm, for example, In _x Ga _1-x As with x about 0.35; However, this layer can also be strained Material exist, as even voltages shift the energy of the emission.
• - an upper DBR 38 , For example, In _x Al _1-x As / InP, or this could also consist of SiO ₂ / p-Si layers.

In _x Al _1-x As / InP (see 2 ) is used, for example, for the DBR layers 34 . 35 chosen, since this little or no lattice mismatch occurs and therefore no dislocations arise.

at Multiplexer is the order of the layer structures, that is the one above the other arranged optical elements, in the order of their assigned wavelength orderly. The elements with long working wavelength below and the elements with a short working wavelength above in the layer structure.

The last layer is a cover layer 29 from a dielectric.

The electrical contacting of the individual optical elements takes place in usual Techniques well known to a person skilled in the art. In the drawings Therefore, details of the electrical contact are not shown in detail.

4 shows a plot of sensitivity and quantum efficiency as a function of wavelength for InGaAs, Si and Ge. The material of choice for the detection of wavelengths between 1300 nm and 1625 nm is InGaAs, since it has a relatively high sensitivity and quantum efficiency for the mentioned wavelength range compared to Si or Ge. However, Ge would also be suitable for the purposes of the invention, but with lower quantum efficiency.

5 shows a plan view and side view of a lithographically structured component. After the epitaxial growth of the layers, as related to 3 was described by means of lithographic processes, the wafer is structured so that at least two, each z. B. about 5 microns × 5 microns wide columns 6 . 7 , on the substrate 2 stay standing. Each column consists of the in 3 described layer structure of the photosensitive elements 3 and 4 and a light-emitting element 5 ,

The active elements 3 . 4 and 5 both columns 6 . 7 can be contacted differently. In the left column 6 are the two photosensitive elements 3 and 4 electrically contacted while the light-emitting element 5 not contacted and therefore not active. In the right column 7 on the other hand, only the light-emitting element 5 electrically contacted while the photosensitive elements 3 and 4 not contacted and therefore not active. This different contacting serves to ensure that the photodetectors 3 . 4 not from the emitted signal of the laser diode 5 be controlled or disturbed. It should be emphasized that in this embodiment, no previously grown sub-component must be subsequently removed again (in comparison to 6 ).

To improve the signal to noise ratio in the photodetectors is in 6 an exemplary other variant of the layer structure shown.

By means of a lithographic process, the wafer is patterned so that four each z. B. about 5 microns × 5 microns wide columns 8th . 9 . 10 11 in a square arrangement on the substrate 2 stay standing. Every pillar 8th - 11 originally consisted of a first photosensitive layer 12 and a light-emitting layer 13 ,

So only one detector layer per column was used 12 applied epitaxially, being above the detectors 12 the left columns are the laser layers originally above 13 removed (etched) and through a selective filter layer 14 (eg Bragg reflector, Fabry Perot filter). On the right side was a laser layer 13 maintained.

The photosensitive layer 12 is designed for a long wavelength, eg 1550 nm, but also serves in this configuration for the detection of other wavelengths, eg 1490 nm and 1310 nm, wherein the respective frequency selection by the applied filter layers 14 he follows.

7 shows the arrangement 6 that coincide with the end of a waveguide 16 (Glass fiber) in a transparent mass 15 (For example, polymer or SiO ₂ ) was poured. This results in a good coupling of the semiconductor chip to the waveguide.

8th shows a side view of another embodiment of the invention with from below, so on the substrate 17 , plugged glass fiber 16 , This design requires that the substrate 17 is transparent in the required wavelength range. Here it should be noted that the arrangement of the layers within the two columns 18 . 19 on the substrate (compared to the arrangement according to FIG 6 ) must be reversed. First, a light emitting laser layer 20 and then a photosensitive detector layer 21 grown on the substrate. The detection and emission of the light takes place in the direction of the waveguide through the substrate 17 therethrough. On the waveguide 16 facing side of the substrate is a wavelength-selective filter layer 22 applied.

9 shows an epitaxial layer sequence again split into two adjacent vertical columns 23 . 24 wherein each column has three detector layers 25 . 26 . 27 and a laser layer 28 on a common substrate 2 includes (monolithic) integrated. In this figure, the scheme of a lithographically structured device is already shown.

In the left column 23 are only the photosensitive layers 25 - 27 electrically contacted while in the right column 24 only the storage layer 28 electrically contacted. Thus mutual interference between the detector layers and the laser layer is avoided.

1

Triplexers (Hours of technique)

2

substratum

3

First Semiconductor layer (photodetector)

4

Second Semiconductor layer (photodetector)

5

Further Semiconductor layer (laser diode)

6

pillar

7

pillar

8th

pillar

9

pillar

10

pillar

11

pillar

12

First Semiconductor layer (photodetector)

13

Further Semiconductor layer (laser diode)

14

filter layer

15

Polymer support or SiO _{2 support}

16

waveguides

17

substratum (transparent)

18

pillar

19

pillar

20

First Semiconductor layer (laser diode)

21

Further Semiconductor layer (photodetector)

22

filter layer

23

pillar

24

pillar

25

First Semiconductor layer (photodetector)

26

Second Semiconductor layer (photodetector)

27

third Semiconductor layer (photodetector)

28

Further Semiconductor layer (laser diode)

29

topcoat (Dielectric)

30

Pin photodiode

31

p-layer

32

i-layer

33

n-layer

34

anti Reflective layer

35

contact

36

VCSEL laser

37

DBR

38

DBR

39

laser Active layer

Claims (39)

Optical multiplexer transceiver, characterized in that it is constructed as a monolithically integrated optical semiconductor chip. An optical multiplexer transceiver according to claim 1, characterized in that the semiconductor chip comprises a plurality of independent, different wavelength tuned active photosensitive (30) and light emitting elements ( 36 ). An optical multiplexer transceiver according to claim 1 or 2, characterized in that it directly to a waveguide is coupled. Optical semiconductor chip, in particular for multiplexer transceiver applications, comprising: a semiconductor substrate ( 2 ); at least one first layer structure arranged on the semiconductor substrate ( 3 ) forming a photosensitive element for light of a first wavelength; and a further layer structure arranged on the first layer structure ( 5 ), which forms a light-emitting element for light of a further wavelength. Optical semiconductor chip according to claim 4, characterized in that between the first and the further layer structure at least one second layer structure ( 4 ) which forms a photosensitive element for light of a second wavelength. Optical semiconductor chip according to claim 4 or 5, characterized in that the first, second and the further layer structure ( 3 . 4 . 5 ) in reverse order ( 5 . 4 . 3 ) on the substrate ( 2 ) are arranged. Optical semiconductor chip according to one of Claims 4 to 6, characterized in that the layer structures ( 3 . 4 . 5 ) on the semiconductor substrate ( 2 ) grown epitaxial semiconductor layers. Optical semiconductor chip according to one of Claims 4 to 7, characterized in that the semiconductor substrate ( 2 ) consists of InP. Optical semiconductor chip according to one of Claims 4 to 8, characterized in that the layer structures ( 3 . 4 . 5 ) consist of In _x Ga _1-x As. Optical semiconductor chip according to one of claims 4 to 9, characterized in that the first layer structure ( 3 ) forms a photodetector. Optical semiconductor chip after one of the Claims 4 to 10, characterized in that the second layer structure ( 4 ) forms a photodetector. Optical semiconductor chip according to one of claims 4 to 11, characterized in that the further layer structure ( 5 ) forms a laser diode. Optical semiconductor chip according to one of claims 4 to 12, characterized in that the first wavelength λ ₁ = 1490 nm. Optical semiconductor chip according to one of claims 4 to 13, characterized in that the second wavelength λ ₂ = 1550 nm. Optical semiconductor chip according to one of claims 4 to 14, characterized in that the further wavelength λ ₃ = 1310 nm. Optical semiconductor chip according to one of Claims 4 to 15, characterized in that the second photosensitive element ( 4 ) over the first photosensitive element ( 3 ) is arranged. Optical semiconductor chip according to one of Claims 4 to 16, characterized in that the light-emitting element ( 5 ) in the beam direction of the emitted light as seen above the first and / or the second photosensitive element ( 3 . 4 ) is arranged. Optical semiconductor chip according to one of Claims 4 to 17, characterized in that the photosensitive ( 3 . 4 ) and light-emitting elements ( 5 ) are independently operable. Optical semiconductor chip according to one of Claims 4 to 18, characterized in that the respective photosensitive element ( 4 ) for the region of its associated wavelength as a filter for the underlying photosensitive element ( 3 ) serves. Optical semiconductor chip according to one of Claims 4 to 19, characterized in that the photosensitive and light-emitting elements ( 3 . 4 . 5 ) in descending order of their respective assigned wavelengths on the semiconductor substrate ( 2 ) are arranged. Optical semiconductor chip according to one of Claims 4 to 20, characterized in that the photosensitive and light-emitting elements ( 3 . 4 . 5 ) are electrically contacted, wherein the electrical contacts are guided on the back of the chip. Optical semiconductor chip according to one of Claims 4 to 21, characterized in that the photosensitive and light-emitting elements ( 3 . 4 . 5 ) carrying wafers into a plurality of adjacent columnar structures ( 6 . 7 ), wherein the photosensitive and / or light-emitting elements of each pillar structure are independently contacted and operable. Optical semiconductor chip according to one of claims 4 to 22, characterized in that for the passivation of the wafer as a cover layer ( 29 ) a dielectric is applied. Optical semiconductor chip according to one of Claims 4 to 23, characterized in that the cover layer ( 29 ) is an oxide or oxynitride layer. An optical semiconductor chip according to any one of claims 4 to 24, characterized in that the cover layer completely surrounds the chip and only by the electrical contacts is broken. Optical semiconductor chip according to one of Claims 4 to 25, characterized in that, to improve the signal-to-noise ratio, one or more optical filter structures ( 14 ) over the light-sensitive elements ( 12 ) are mounted. Optical semiconductor chip according to one of Claims 4 to 26, characterized in that the light-sensitive elements ( 12 ) are exposed by means of lithographic processes. Optical semiconductor chip according to one of Claims 4 to 27, characterized in that the substrate ( 17 ) has a band gap greater than 0.9 eV corresponding to a wavelength of λ <1300 nm and directly with an optical waveguide ( 16 ) connected is. Optical semiconductor chip according to one of claims 4 to 28, characterized in that on or between the individual layer structures ( 12 . 13 ) Filter layers ( 14 ) are arranged for at least one wavelength. Method for producing an optical semiconductor chip for multiplexer transceiver applications, comprising the steps of: providing a semiconductor substrate ( 2 ); Growing at least one first epitaxial layer structure ( 3 ) on the substrate, this first layer structure forming a photosensitive element for light of a first wavelength; and growing a further epitaxial layer structure ( 5 ) on the first layer structure, this further layer structure forming a light-emitting element for light of a further wavelength. Process for producing an optical Semiconductor chips for multiplexer transceiver applications, comprising the steps of: providing a semiconductor substrate ( 17 ); Growing at least one first epitaxial layer structure ( 20 ) on the substrate, said first layer structure forming a light emitting element for light of a first wavelength; and growing a further epitaxial layer structure ( 21 ) on the first layer structure ( 20 ), this further layer structure forming a photosensitive element for light of a further wavelength. A method according to claim 30 or 31, characterized in that prior to the growth of the further layer structure ( 21 ) a second epitaxial layer structure on the first layer structure ( 20 ), this second layer structure forming a photosensitive element for light of a second wavelength. Method according to one of claims 30 to 32, characterized in that a dielectric layer is applied as the uppermost covering layer becomes. Method according to one of claims 30 to 33, characterized that the optical chip completely surrounded by a dielectric layer. Method according to one of claims 30 to 34, characterized in that the wafer after the growth of the layer structures ( 3 . 4 . 5 ; 20 . 21 ) by means of lithographic methods in at least two adjacent columnar structures ( 6 . 7 ; 18 . 19 ), wherein the photosensitive and / or light-emitting elements of the individual columnar structures are electrically contacted and operated differently. Method according to one of claims 30 to 35, characterized in that after the formation of the column structures ( 8th . 9 ; 18 . 19 ) optionally one or more layer structures ( 13 ) are removed from either one or more columnar structures. Method according to one of Claims 30 to 36, characterized in that the photosensitive layers ( 12 ) acting as optical filter layers ( 14 ) are applied Method according to one of claims 30 to 37, characterized in that on the said first layer structure ( 20 ) opposite side of the substrate ( 17 ) acting as optical filter layers ( 22 ) are applied. Method according to one of claims 30 to 38, characterized in that in a further step, the semiconductor chips cut, placed on support, electrically contacted and connected to the end of a waveguide ( 16 ) together into a transparent mass ( 15 ) are poured.