DE19529497B4 - Optical switch for switching two or more optical wavelength bands - Google Patents

Abstract

Optical switch (1) for the simultaneous switching of optical input power (I0) on two or more different optical wavelength bands (Δλi, i = 1, 2, ... k ≥ 2), each with a different central wavelength (λi) from one input (10 ) of the switch (1) at least partially and optionally on one or the other of two outputs (11, 12) of the switch (1), consisting of - a Mach-Zehnder interferometer (11), which the the input (10) of Splits input power (I0) supplied to switch (1) into two power components (I01, I02) each having all wavelength bands (Δλ1), these two power components after passing through two optical paths (111 that differ from one another by a certain optical path length difference (Δ (nL)) , 112) superimposed on one another and the optical power resulting from this superimposition proportionately as two output powers (I1, I2), the two or more of which differ from one another en include optical wavelength bands (Δλi, i = 1, 2, ... k ≥ 2), distributed over the two outputs (11, 12) of the switch (1), ...

Description

To configure optical networks, space switches are needed that can distribute optical signals from one or more inputs to multiple outputs. In addition to electromagnetic fiber relays, optical waveguide switches are increasingly being developed which are based on current injection (see G. Müller, L. Stoll, G. Schulte-Roth, U. Wolff: Low current plasma effect optical switch to InP, Electronics Letters 26, 1990, Pp. 115-116), electro-optic effect (see M. Izutsu, Y. Yamane, T. Sueta: Broadband traveling-wave modulator using a LiNbO ₃ optical waveguide, IEEE j. Quantum Electronics, QE-13 (1977), p. 287-290) or thermo-optic detuning (see M. Okuno, K. Katho, Y. Ohmori, A. Himeno: Strictly nonblocking 16x16 matrix switch using silica-based planar liithgwave circuits, Proc. 20. ECOC, Florence 1994, Post deadline papers 83-86 and N. Keil, HH Yoa, C. Zawadzki, B. Strebel, C. Caspar: 4 × 4 polymer thermo-optic directional coupler switch at 1.55 μm, Optical Fiber Communication OFC 94, San Jose, California, 1994, PD 14, 1-4). These waveguide switches have the advantage over the electromagnetic switches of monolithic integration into more complex architectures, such as 16x16 switching arrays (see M. Okuno, K. Katho, Y. Ohmori, A. Himeno: Strictly Nonblocking 16x16 matrix switch using silica -based planar liithgwave circuits, proc. 20. ECOC, Florence 1994, Post deadline papers 83-86). However, because waveguide switches are based on optical interference, they have only a reduced optical bandwidth over the electromagnetic switches, ie, they only function in a narrow optical wavelength band.

In order to switch larger optical wavelength ranges, it has already been proposed to use electronic switches between optoelectronic and electro-optical converters, to use mechanical, in particular electromechanical, fiber relays and / or to optically filter different wavelength bands and switch them independently.

Walker, J. Urquhart, I. Bennion, A.C. Carter: 1.3 / 1.53 μm Mach-Zehnder wavelength duplexers for integrated optoelectronic transceiver modules. In: IEEE Proceedings Vol. 137, No. 1, 1990, pages 33-38, a passive filter is described which permanently separates two wavelengths and provides the separate, different wavelengths at two different outputs.

Takato, N. et al., "Silica-Based Integrated Optic Mach-Zehnder Multi / Demultiplexer Family with Channel Spacing of 0.01-250 nm", IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS Vol. 6 (1990), pp. 1120-1127 describes the use of a Mach-Zehnder interferometer in WDM applications. The Mach-Zehnder interferometer is used as a multiplexer / demultiplexer or frequency-selective switch. Optical signals are multiplexed and demultiplexed by a "family" of Mach-Zehnder interferometers. In this case, for example, optical signals of 16 frequency bands fed to the input and coupled out a selected frequency at the output or the signals of 8 frequency bands are fed to the input and distributed to 8 different outputs.

Takato, N. et al., "Silica-Based Single-Mode Waveguides to Silicon and their Application to Guided Wave Optical Interferometers", JOURNAL OF LIGHTWAVE TECHNOLOGY Vol. 6 (1988), pp. 1003-1010, the classical construction of a Mach-Zehnder interferometer and a multiplexing of optical signals with center frequencies or a demultiplexing is described.

The document US 4 900 112 A describes the use of a Mach-Zehnder interferometer as a demultiplexer. Two optical input signals with different frequencies are separated at two outputs.

The invention defined in claim 1 has the advantage that at least two optical wavelength bands can be switched simultaneously.

Preferred and advantageous embodiments of the invention will become apparent from the dependent claims.

The invention will be explained in more detail in the following description with reference to the figures by way of example. Show it:

1 a schematic representation of a switch according to the invention and

2a and 2 B in each case a graphical representation of the relative transmission of a switch according to the invention as a function of the optical wavelength, wherein 2a the unswitched and 2 B shows the switched state of the switch.

The in 1 illustrated inventive optical switch 1 for switching optical input power I ₀ to two or more optical wavelength bands Δλ _i with i = 1, 2, ... k ≥ 2, each having a different central wavelength λ _i from one input 10 of the switch 1 at least proportionately and optionally on one or the other of two exits 11 . 12 of the switch 1 consists of a Mach-Zehnder interferometer 11 and one Facility 12 for selectively changing a particular size of the interferometer 11 ,

The interferometer 11 divide the entrance 10 of the switch 1 fed and in the switch 1 coupled input power I ₀ in a power divider 110 in two power components I ₀₁ and I ₀₂ , each of which has all the wavelength bands Δλ _i .

One of the two power components I ₀₁ and I ₀₂ , for example the power component I ₀₁ , goes through an optical path 111 certain optical path length and the other power component 102 another optical path 112 certain optical path length. The optical path length is defined by the product nL of a refractive index n and a geometric length L of the relevant optical path 111 respectively. 112 ,

The optical path lengths of both optical paths 111 and 112 are different from each other and differ by a certain optical path length difference Δ (nL) from each other.

After passing through the two power components I ₀₁ and I ₀₂ through the two optical paths 111 and 112 they are in an optical overlay device 113 visually superimposed on each other and the optical power resulting from this superimposition in proportion to the two outputs 11 and 12 of the switch 1 distributed so that at an exit 11 an optical output I ₁ and at the other output 12 an optical output power I _{2 can be} coupled out. The ratio of the output powers I ₁ and I ₂ relative to each other depends on the switching state of the switch 1 which will be discussed later.

To define the switching state of the switch 1 is a facility 12 for selectively changing the determined optical path difference Δ (nL).

According to the invention, the different central wavelengths λ _{i of} the path length bands Δλ _i and the optical path length difference Δ (nL) are coordinated such that for each of the various central wavelengths λ _i the quotient Δ (nL) / λ _{i is} divided by the path length difference Δ (nL) Central wavelength λ _i is essentially an integer and changes only by a fraction of one in the optional change of the optical path length difference Δ (nL).

Preferably, two unchanged quotient Δ (nL) / λ _i and Δ (nL) / λ _{i + 1} belonging to adjacent central wavelengths λ _i , λ _{i + 1} differ essentially by one from one another. For two wavelength bands Δλ ₁ and Δλ ₂ with their central wavelengths λ ₁ and λ ₂ , this means, for example Δ (nL) / λ ₁ = m and Δ (nL) / λ ₂ = m + 1, where m is a predefinable integer and the equals sign ideally applies.

The fraction of one by which each quotient Δ (nL) / λ _i changes should, in view of a good switching behavior of the switch 1 be equal to 1/2.

For a better understanding of the invention, the case is considered that two wavelength bands Δλ ₁ and Δλ _{2 are} switched, wherein Δλ _1, the central wavelength λ ₁ and Δλ _2, the central wavelength λ ₂ .

In an ideal Mach-Zehnder interferometer 11 , no dispersion, no losses and an exactly wavelength-independent power splitter 10 with a power ratio I ₀₁ / I ₀₂ of 50% / 50% and an exactly wavelength-independent superposition device 13 also having a power ratio I ₀₁ / I ₀₂ of 50% / 50% and I ₁ / I ₂ of 50% / 50%: T _x = I ₂ / I ₀ = cos ² (Φ / 2) T _p = I ₁ / I ₀ = sin ² (Φ / 2), with Φ = 2π · Δ (nL / λ) = 2π · (Δn · L + n · ΔL) / λ, where Δn = | n1 - n2 | a refractive index difference amount between a refractive index n _{1 of} one of the two optical paths 111 and 112 for example the way 111 and a refractive index n _{2 of} the other optical path 112 , ΔL = | L ₁ - L ₂ | a long difference amount between a geometric length L _{1 of} the one optical path 111 and a geometric length L _{2 of} the other optical path 111 and λ is the wavelength at which the interferometer is operated.

The conditions for the two switching states of the switch 1 are ideally for a switching state in which I ₁ at an output 11 of the switch 1 equal to I ₀ and I ₂ at the other exit 12 of the switch 1 zero is equal _Tp = 1, and for a switching state in which I ₁ at an output 11 of the switch 1 zero and I ₂ at the other exit 12 of the switch 1 equal to I ₀ , equal T _x = 1.

From T _p = 1 follows Φ / 2 = mπ or Δ (nL / λ) = m, where m is an integer,
and
from T _x = 1 follows Φ / 2 = (m + 1/2) π or Δ (nL / λ) = m + 1/2.

The dependence of such a switch on the wavelength λ is given by dΦ / dλ = d / dλ (2π / λ · Δ (nL)) = - 1 / λ² · 2π · Δ (nL) = - Φ / λ.

In order to build a wideband switch, Φ must be as small as possible. In the case of the symmetrical Mach-Zehnder interferometer, in which the geometric length difference ΔL is zero, the condition for complete switching is m = 0 and thus Φ = n.

In the switch according to the invention 1 is the Mach-Zehnder interferometer 11 used so that two or more optical wavelength bands Δλ _i to be switched together lie in different orders, to which different integers m are assigned. In this case, orders are preferred that are adjacent, with adjacent orders being defined by two integers that are only around 1 differ from each other.

undFor two optical wavelength bands Δλ ₁ and Δλ ₂ with the central wavelengths λ ₁ and λ ₂ , this means, for example

and

A concrete embodiment of such a switch 1 according to the invention for the simultaneous switching of two optical wavelength bands Δλ ₁ , Δλ ₂ with the central wavelengths λ ₁ and λ ₂ is designed as follows:
λ ₁ = 1.3 μm
λ ₂ = 1.56 μm
m = 5
L = 5000 μm
ΔL = 5.57 μm
n = 1.4.

The device 12 for selectively changing the optical path length difference Δ (nL), this change is caused by a change in refractive index n by a refractive index difference δn = 1.4 × 10 ^-4 . The path length difference Δ (nL) itself is accordingly generated by the geometric length difference ΔL.

The switching behavior of this exemplary inventive switch 1 is in the 2a for the non-switched state and in the 2 B for the switched state, with the dashed curve for T _p and the solid curve for T _x . The switching range for 20 dB switching cancellation according to these figures for both T _p and T _{x is} just under 10 nm.

Claims (3)

Optical switch ( 1 ) for simultaneous switching of optical input power (I ₀ ) on two or more different optical wavelength bands (Δλ _i , i = 1, 2, ... k ≥ 2) each having a different central wavelength (λ _i ) from one input ( 10 ) of the switch ( 1 ) at least proportionately and optionally to one or the other of two outputs ( 11 . 12 ) of the switch ( 1 ), consisting of - a Mach-Zehnder interferometer ( 11 ), which is the entrance ( 10 ) of the switch ( 1 ) supplied input power (I ₀ ) in two each of all wavelength bands (Δλ ₁ ) having power components (I ₀₁ , I ₀₂ ) divides, these two power components after passing through two different by a certain optical path length difference (Δ (nL)) optical paths ( 111 . 112 superimposed on each other, and the optical power resulting from this superimposing as a proportion of two output powers (I ₁ , I ₂ ), each of the two or more different optical wavelength bands (Δλ _i , i = 1, 2, ... k ≥ 2) include, on the two outputs ( 11 . 12 ) of the switch ( 1 ), and - a switchable device ( 12 ) for selectively varying the path length difference (Δ (nL)), wherein - the ratio of the two output powers (I ₁ , I ₂ ) relative to each other from the switching state of the device ( 12 ) for selectively varying the path length difference (Δ (nL)), - when switching the device ( 12 ) the optical input power of both wavelength bands (Δλ _i , i = 1, 2, ... k ≥ 2) at least proportionally simultaneously to one or the other of the two outputs ( 11 . 12 ) of the switch ( 1 ), and - the different central wavelengths (λ _i ) and the path length difference (Δ (nL)) are matched to each other such that for each of the different central wavelengths (λ _i ) the quotient (Δ (nL) / λ _i ) is obtained from the The path-length difference (Δ (nL)) divided by these central wavelengths (λ _i ) is each substantially an integer and changes only by a fraction of one in the optional variation of the path-length difference (Δ (nL)). A switch as claimed in claim 1, wherein two adjacent central wavelengths (λ _i , λ _{i + 1} ) belonging unchanged quotients (Δ (nL) / λ _i , Δ (nL) / λ _i-1 ) differ substantially by one. A switch according to claim 1 and 2, wherein the fraction of one by which each quotient (Δ (nL) / λ _i ) changes on switching is substantially 1/2.

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