WO1996017417A1

WO1996017417A1 - Sender/receiver array for an optical duplex system

Info

Publication number: WO1996017417A1
Application number: PCT/DE1995/001757
Authority: WO
Inventors: Norbert Grote
Original assignee: HEINRICH-HERTZ-INSTITUT FüR NACHRICHTENTECHNIK BERLIN GMBH
Priority date: 1994-11-29
Filing date: 1995-11-29
Publication date: 1996-06-06
Also published as: DE4444470A1

Abstract

Sender-receiver arrays, with transmitting lasers (T) and receiving diodes (R) made from group III-V elements and arranged optically in series, must be easy to adjust and manufacture, have a high wafer surface yield, and facilitate on-wafer testing and completely polarisation-independent operation. The transceivers according to the invention have the form of two complementary types and have a vertical integration structure, i.e. transmitting lasers (Tμ1, Tμ2) and receiving diodes (Rμ2, Rμ1) constituted of layers of material which are aligned substantially vertically relative to the common optical axis, are located preferably on opposite faces of a common substrate (S) and have only one fibre/chip interface each. Splitting of the two operating wavelengths (μ1, μ2) is achieved by exploiting the different transmission and absorption characteristics of the group III-V materials with respect to the two operating wavelengths. Both types are identical in construction, so that all subscriber stations can be equipped with the one type and an associated switching point can be equipped with the other type.

Description

Transmitter / receiver arrangement for an optical duplex system

description

The invention relates to a transmitter / receiver arrangement, which is provided in the form of two complementary types for an optical duplex system with two operating wavelengths to be transmitted in opposite directions via an optical fiber and whose transmitting laser and receiving diode are optically in series and based on III -V materials with different transmission or absorption properties with respect to the two operating wavelengths are constructed.

Optical fibers, which are operated bidirectionally as optical connecting lines in the subscriber level, with a first light wavelength λ \ in one direction and a second light wavelength λ2 in the opposite direction, enable collision-free two-way communication traffic. For point-to-point connections, two transmitter and two receiver types are required, which are mutually assigned and each designed for one or the other light wavelength.

In the case of such optoelectronic systems, the endeavors to be able to provide cost-effective and functionally excellent solutions generally aim at the usability of integrated circuits (optoelectronic integrated circuit (OEIC); photonic integrated circuit - PIC). Here, too, micromechanical adjustments, particularly at the fiber / chip interfaces, require effort that should not be underestimated.

At the "Integrated Photonics Research (IPR)" conference, February 17-19, 1994, San Francisco, USA, R. Matz et al reported on "Development of a Photonic Integrated Transceiver Chip for WDM Transmission" (cf. Postdeadline Paper PD 1, pages 1 to 3). One form of the two complementary types required, for which details have been disclosed, contains the transmit laser for 1530 nm and a monitor diode assigned to it, a wavelength-selective directional coupler and the receive diode for 1300 nm. In comparison to hybrid micro-optical structures, such a chip offers through displacement A large part of the adjustment effort in the lithographic chip production, although considerable relief, but the area yield of wafers with chip dimensions of 4 mm x 0.6 mm is not particularly high, and the manufacturing cost of such a planar (= horizontal) ^OEIC's is considerably

The solutions presented by A C Carter at the same conference are a little different from the chip mentioned above (see Proc of IPR Paper # 26 / ThC 1, ThC 1/27 and

28 ThC 1-3) designed Although verbally briefly explained, it is represented in a graphically informative way in this publication a component of a

Subscriber circuit, which for a bidirectional telephone connection in the

Wavelength range 1300 nm (transmission direction between 1270 nm and 1300 nm, reception direction between 1310 nm and 1340 nm) and for receiving a

Broadband service in the 1530 nm wavelength range is the largest

With a chip length of the component of 3.75 mm, the optical waveguides with the couplers formed from them require space. The transmitter laser for 1300 nm with a monitor diode is located at one end of an optical waveguide. Five further waveguide ends form one of the network-side chip / fiber interfaces , two others lead to the receive diode components for 1300 nm and 1530 nm

Particularly taking into account the constraints to which such developments are generally subject, for example requirements regarding compatibility with components that have already been preserved, components that are in production, overarching conceptual ideas as well as subjective ideas of researchers and developers and the like, two development tendencies can be derived from the publications selected above as examples Recognize One is aimed at hybrid micro-optical structures, the other at integration in horizontal structures as far as possible

A further direction which forms the prior art from which the invention is based is known from "Proc Internat Semiconductor Laser Conf", DAVOS-CH (1990) K-4 pages 166/167. Line Bi-Directional 1 5 μm / 1 3 μm Transceivers "by TL Koch et al reports on exemplary photonic integrated circuits, the architecture of which is based on planar technology. The optical series connection used there of the components arranged next to one another in a horizontal integration structure (transmitting laser / receiving diode) and The III-V materials used with different amplification or vapor properties for different light wavelengths lead to considerable structural simplifications compared to PIC concepts, the interferometer and / or grating arrangements, couplers and other passive Need elements in addition to the transmit lasers and receive diodes. However, even with this prior art, complex chip production and high-precision micromechanical adjustments are still required at the chip / fiber interface.

Proceeding from this, the invention is based on the technical problem of reducing both the adjustment and the manufacturing outlay, further increasing the area yield of wafers, hybrid and integrated structures and testability of the chips already on the wafer and completely polarization-independent operation of the transmitters / Allow receiver arrangement.

The solution according to the invention for a transmitter-receiver arrangement of the type mentioned initially provides that the transmitter laser and the receiver diode consist of layers of material which are oriented essentially perpendicular to the common optical axis.

In such a vertical arrangement, the required structuring within the chip boundaries is considerably less complex than in horizontal arrangements and thus requires less manufacturing effort. The chip area is extremely small in terms of absolute space requirements, for example (0.3 x 0.3) mni ^* . All optical and electrical connections can be arranged on the top and bottom of the chips, so they are freely accessible at all times. Since the transmission and absorption properties of the material layers used for the transmitting laser and receiving diode are polarization-independent and an efficient fiber can be coupled in and small chip areas can be implemented, the transmitter / receiver arrangement according to the invention can be operated completely independently of the polarization.

The two operating wavelengths are separated without special optical filters due to the transparency of semiconductor layers above and the absorption below the band edge wavelength. With a wavelength difference of not significantly less than 250 nm in the wavelength range between 1.3 μm and 1.6 μm, values of greater than 40 dB can be achieved for the ratio of absorption and transmission.

The boundary condition that the channel spacing should not fall significantly below the 250 nm wavelength difference in the spectral range mentioned can be met without difficulty in an optical duplex system. Such transmitter / receiver chips are key components, can be produced at low cost due to the vertical integration structure in large numbers per wafer, for example 20,000 pieces per 2-inch wafer, and in principle with regard to the monomodal transmitter lasers with integrated electrical driver stage and with regard to the receiving diodes Equip photodiodes with a downstream electronic amplifier stage

Particularly advantageous embodiments of the invention result from the fact that the transmission laser is designed as a surface-emitting component. Because of the low divergence of the emitted light, the tolerance limits for an efficient fiber coupling in such a component are large.

In particular, in the case of embodiments of the invention, such surface-emitting transmission lasers can be formed with a vertical resonator whose mirror layers consist of material layers lying parallel to the laser layer.

The construction of transmitter / receiver arrangements according to the invention and their advantageous design forms mentioned above represents a basic concept for further modifications. For example, a medium that is transparent for both operating wavelengths can be arranged between the transmitting laser and the receiving diode. Such a medium represents e.g. Air, through which the operating temperature can be influenced as a cooling medium. Alternatively, the transmitting laser and the receiving diode can be monolithically integrated on a chip, whereby they are arranged on the same or on opposite sides of a common substrate.

For duplex traffic over a common optical fiber, it is expedient to use the operating wavelengths λ \ = 1300 nm and λ2 = 1550 nm and accordingly the two complementary types - a) T χ \ / Rχ2 ^m * ^t optical fiber connection at the transmission laser T and b): T χ2 ^ * λl ^rrι * - ^t optical fiber connection to be provided on the receiving diode R λ2 "These operating wavelengths are common both in conventional quartz-based optical fibers and in transmitting lasers and photodiodes as receiving diodes, especially in telecommunications applications. The channel spacing is 250 nm, so that the separation of and return channel in the transmitter / receiver arrangements can be brought about due to the different optical transmission or absorption properties of the materials in question for the transmission laser and the receiving diode. The 'high-pass' behavior of III-V materials leads to that in the complementary ones Types of transmitter / receiver arrangements are those components which are designed for the shorter operating wavelength, must be located at the fiber / chip interface and have to transmit the longer-wave light to the optically arranged components

Chip assemblies consist for example ^of one type in a) (T χι χ.2)

a laser diode for 1300 nm with a vertical resonator ("vertical cavity" - VC - laser) at the chip / fiber interface,

- The substrate made of InP and - A detector layer made of InGaAs for 1550 nm, in addition a filter layer with a cut-off wavelength between about 1350 nm and 1400 nm is provided directly on the top and / or bottom of the InP substrate for absorption of the rear residual light radiation of the laser can be, and with the other type b) (T λ2 ^/ ^ * λl) ^off - a laser diode for 1550 nm with a vertical resonator,

- The substrate made of InP and

- A detector layer made of InGaAsP or InGaAlAs for 1300 nm at the chip / fiber interface

In this context, reference should be made to the not yet completed technological development of providing long-wave VC lasers for the wavelength range from approx. 1.3 μm to 1.6 μm with usable optical output powers in continuous wave mode at room temperature. Highly reflective semiconductor Bragg mirrors are required for this in principle, different layer combinations from the material systems InGaAsP and InGaAlAs or also from non-III-V materials can be used is adapted to manufacture

The importance of the invention is also evident in the fact that for types of duplex systems, one type - a) or b) - for the equipment of all subscriber stations and the other type - b) or a) - of the transmitter / receiver arrangements for the equipment of one Switching point can be provided. The electrical signals with which the transmission lasers located in a chip are optically arranged in series or which deliver the receiving diodes are in the subscriber stations the relevant signal sources, e.g. microphone, camera, or signal sinks, e.g. speakers, Screen, assigned in the exchange these signals are fed from the relevant receiving diodes via a switching matrix to the transmission lasers, so that any point-to-point connections between two - or more - subscriber stations can be realized

In such a duplex system, identical transmitter / receiver chips of the one type are to be provided at all subscriber stations and also identical transmitter / receiver chips of the other, complementary type are to be provided in the switching center, each type of chip being required in terms of the number of subscriber stations

In the drawing, embodiments of the invention are shown schematically

1 shows a block diagram for optical wavelength duplex traffic over the same fiber between two stations which are equipped with complementary transmitter / receiver chips,

2 shows a block diagram of a duplex system for any number of subscriber stations, all subscriber stations being equipped with one type of identical transceiver chip and one switching center with another complementary type of identical transceiver chip, and

3 shows a cross-sectional representation - for an example of the invention - the designs of the two chip types of complementary, monolithically integrated transmitter / receiver arrangements in a vertical integration structure using "vertical cavity" laser diodes

The block diagram shown in FIG. 1 shows two types of complementary transmitter / receiver arrangements for optical wavelength duplex traffic, each of which has a transmitting laser T and a receiving diode R in optical series connection. The outgoing and return channels are implemented by means of two operating wavelengths λj, λ via an optical fiber

It can be seen from the block diagram of a wavelength duplex system shown in FIG. 2 that any number of subscriber stations are equipped with identical transmitter / receiver arrangements and are connected to one another by separate optical fibers

Exchange are connectable The exchange is complementary with the Type, also identical transmitter / receiver arrangements and built with a switching matrix E.

The electrical signals supplied by the receiving diodes R (χχ) reach the inputs of this switching matrix E and are switched through there to the output of the switching matrix E that leads to the transmission laser T (2) that is responsible for the selected connection. With regard to the signals in the electrical area, the structure and function of the switching center is independent of the signal transmission in the optical area between the individual subscriber stations and the switching center.

The subscriber stations send their optical signals in the channel with the operating wavelength λj to the exchange and receive from there the optical signals intended for them in the channel with the operating ^wavelength X2 * - * ^ιre transmitter / receiver chips accordingly contain receiving diodes R (χ2 ^und - - transmitting lasers T (j) in optical series connection.

It is readily possible, in embodiments of the invention, the transmitter / receiver chips of the subscriber stations with receive diodes R (χι) and transmit lasers Υ (χι) and in the exchange with receive diodes R (χ2) ^{un (} - 'transmit lasers T (χ _j ) The respective sense of direction of the two channels with the operating wavelengths X \ and λ in the optical fibers is then reversed compared to the example shown in FIG. 2.

3 illustrates the structure and mode of operation of the two complementary transmitter-receiver chip types for optical wavelength duplex traffic shown as an example for the invention.

In both chip types, the transmission lasers ^τ λl, ^τ λ2 (VCSEL yertical cavity surface emitting laser) are on the top of an InP substrate S and the ones on the bottom

Receive diodes R j ^. R χi with aligned vertical optical axes on the basis of mutually parallel material layers. Instead of the substrate S, any medium, including air, that is transparent for both operating wavelengths can be arranged.

The chip of one type - on the left in FIG. 3 - is based on the operating wavelength λ \ = 1.3 μm for the transmission channel and on the operating wavelength λ2 = 1.55 μm for the Receiving channel designed. The optical wave generated in the laser layer of the transmission laser Tχj initially spreads to both sides in the vertical direction, but is reflected in a mirror layer between the laser layer and the substrate. Another mirror layer above the laser layer is partially transparent, so that both the laser resonance conditions can be met and the radiation can be carried out with sufficient optical power for the application. The generated optical monomodal wave with the wavelength λj = 1.3 μm reaches the chip / fiber Interface in the optical fiber L.

The optical wave received by the optical fiber L with the

Operating wavelength λ2 = 1.55 μm occurs at the same chip / fiber interface, penetrates the latter and the InP substrate S due to the low absorption of longer-wave light in the material layers of the shorter-wave laser Tχ _j and reaches the InGaAs consisting of ternary material, the receiving diode Rχ2 forming layer is a prerequisite that the spectral reflection curves of

Mirror layers are so narrow that λ2 is not reflected This limits the

Material selection for the mirror layers

The chip of the other type - on the right in FIG. 3 - is designed for the operating wavelength λ2 (= 1.55 μm) for the transmission channel and for the operating wavelength X \ (= 1.3 μm) for the reception channel. Here, the transmission laser T 2 is open the top with a highly reflective layer and a partially transparent mirror layer between the laser layer and InP substrate S. The generated optical monomodal wave of wavelength λ (= 1.55 μm) penetrates the InP substrate S and a quaternary layer with a cut-off wavelength λg between approximately 1.35 μm and 1.4 μm and then reaches the chip / fiber located there Interface in the optical fiber L

The optical wave to be received by the transmitter / receiver chip of this type with the

Operating wavelength λl = 1.3 μm comes directly from the optical fiber L into the receiving diode Rχ2 formed from the quaternary layer and is absorbed there, i.e. optically / electrically converted. The thickness of the quaternary layer must be selected so that complete absorption is ensured

The function of the monomodal lasers of the transmitter / receiver arrangements are not influenced by light of the other operating wavelength

Comparatively broadband photodiodes, so that precautions must be taken to prevent their response to light from the other operating wavelength Transmitter / receiver chip with the operating wavelength λj = 1300 nm for the transmission laser Tχi can be directly on the top and / or bottom of the InP substrate S.

Filter layer F are provided, the cut-off wavelength of which is approximately between 1350 nm and 1400 nm. The high absorption below and the high transmission above this limit wavelength ensure that residual radiation from the "own" emitted optical wave of the operating wavelength λ \ = 1300 nm does not reach the receiving diode Rχ2 of the operating wavelength λ2 = 1550 nm. At the

Transmitter / receiver chip of the other type with the operating wavelength λ2 - 1550 nm for the transmitting laser T ^ 2, however, the quaternary layer for the receiving diode R χj has the corresponding cutoff wavelength of between approximately 1350 nm and

1400 nm so that only light of the operating wavelength λi = 1300 nm is detected and that of the "own" transmission laser Υ \ 2 is transmitted with the operating wavelength λ2 = 1550 nm.

It is not shown and also cannot be explained in more detail that, in embodiments of the invention, electrical driver stages for the transmission lasers T and amplifier stages for the receiving diodes R can be integrated. All connections, both the optical and the electrical ones, can be arranged in the vertical integration structure of these chips on their upper or lower side and thus enable the chips to be tested directly during and / or after completion on the wafer. The fiber / chip coupling does not require tight tolerances, so it can be done with little effort. Further advantages of the invention, in particular its complete insensitivity to polarization, are expressly mentioned in the present documents and can also be taken from the context.

Claims

claims

1 transmitter / receiver arrangement, which is in the form of two complementary types for an optical duplex system with two in opposite directions over one

Optical fiber to be transmitted operating wavelengths is provided and the transmission laser and receiving diode are optically in series and are built on the basis of III-V materials with different transmission or absorption properties with respect to the two operating wavelengths, characterized in that the transmission laser (T) and the receiving diode (R) consist of layers of material which are aligned substantially perpendicular to the common optical axis

2 transmitter / receiver arrangement according to claim 1, characterized in that the transmission laser (T) is designed as a surface-emitting component

3 transmitter / receiver arrangement according to claim 2, characterized in that the surface emitting transmission laser (T) is formed with a vertical resonator (VC)

4 transmitter / receiver arrangement according to one of claims 1 to 3, characterized in that between the transmission laser (T) and the receiving diode (R) a iar both operating wavelengths transparent medium is arranged

5 transmitter-receiver arrangement according to one of claims 1 to 4, characterized in that the transmitting laser (T) and the receiving diode (R) are monolithically integrated on a chip

6 transmitter / receiver arrangement according to one of claims 1 to 5, characterized in that the transmitting laser (T) and the receiving diode (R) are arranged on opposite sides of a common substrate

7. Transmitter / receiver arrangement according to one of claims 1 to 6, characterized in that the two in the duplex system

Operating wavelengths λ _] = 1300 nm and λ2 = 1550 nm and accordingly the complementary types: - a): (Tχι / Rχ2) ^m ^ ^t optical fiber connection on the transmission laser (χ \) and

- b): 0 2 / R * λl) mi optical fiber connection on the receiving diode (Rχi) are provided.

8. Transmitter / receiver arrangement according to claim 7, characterized in that the type a) (T, ι / Rλ2) - ^m optical path between the transmitter laser (Tχ \) and the receiving diode (Rχ2) ^e ' ^ne with respect to the emitted there Operating wavelengths (λ \) not transparent, but with respect to the operating wavelengths (λ2) to be received there is provided filter layer.

9. Transmitter / receiver arrangement according to one of claims 1 to 8, characterized in that in the duplex system of two complementary types

- all subscriber stations are equipped with one form, - an exchange with the other form.