JP4249093B2 - CS-RZ output wavelength converter - Google Patents

Description

  The present invention relates to a wavelength conversion technique for high-density wavelength multiplexing when using an optical transmission code suitable for high-density wavelength multiplexing long-distance transmission, and more particularly to a CS-RZ output wavelength conversion apparatus.

  NRZ (Non return zero) code and RZ (Return to zero) code are generally known as coding techniques applicable to future ultra-high-speed backbone optical networks, but CS-RZ (carrier suppression RZ) is also known. ) Code, DCS-RZ (Duobinary CS-RZ) code, and the like. These encoding techniques perform band compression by inverting the phase of the optical pulse train for each bit in the optical pulse train generation process (Non-patent Document 1). Depending on the network environment, it may be necessary to convert not only the wavelength but also a normal RZ code or NRZ code into a CS-RZ code as described above, or a wavelength conversion technique between CS-RZ codes.

As a conventional example 1, FIG. 4 shows a configuration of a conventional RZ output wavelength converter that is normally used. The RZ output wavelength converter includes an optical multiplexer / demultiplexer 401, a clock regenerator 402 that regenerates clock light from input data light, and a differential phase modulation type wavelength converter 403. Here, the input signal light input to the optical demultiplexer 401, an RZ (return to zero) code at a wavelength lambda _1. One of the input data beams branched into two by the optical multiplexer / demultiplexer 401 is input to the wavelength converter 403 and the other is input to the clock regenerator 402. Examples of the clock regenerator 402 include a mode-locked laser diode (MLLD) (Non-Patent Document 2). Let λ ₂ be the wavelength of the clock light regenerated by the clock regenerator 402. When the data light (λ ₁ ) and the clock light (λ ₂ ) are input to the wavelength converter 403, the wavelength converter 403 performs a differential phase modulation type wavelength conversion operation, and the clock light (λ ₂ ) is converted into the data light (λ ₁ ) modulated by As a result, the RZ signal light having the wavelength λ ₂ is output from the wavelength converter 403.

As Conventional Example 2, FIG. 5 shows a configuration of a conventional CS-RZ output wavelength converter. This CS-RZ output wavelength converter has a configuration in which a phase modulator 504 is added to the configuration shown in FIG. Similar to the RZ output wavelength converter of Conventional Example 1, one of the input data light branched into two by the optical multiplexer / demultiplexer 501 is input to the wavelength converter 503 and the other is input to the clock regenerator 502. The thick line in the figure means an optical signal, and the thin line means an electric signal. The clock light (frequency f, wavelength λ ₂ ) extracted from the clock regenerator 502 is input to the wavelength converter 503 together with the data light (wavelength λ ₁ ) from the optical multiplexer / demultiplexer 501, and the same wavelength conversion as in Conventional Example 1 The operation is performed, and phase modulation of 0-π inversion is performed by the phase modulator 504 at the subsequent stage. The phase modulator 504 is driven by the electric clock signal (frequency f / 2, amplitude voltage 2Vπ) from the clock regenerator 502. As a result, the wavelength-converted signal light (wavelength λ ₂ ) of the CS-RZ code obtained by inverting the phase of the RZ signal light for each bit is output from the phase modulator 504.

As Conventional Example 3, FIG. 6 shows a configuration of a conventional CS-RZ output wavelength converter of the OE-EO type (photoelectric-electrical optical type). This CS-RZ output wavelength converter has a configuration in which a 3R receiver 601 and a CS-RZ transmission system are combined. The input signal light (wavelength λ ₁ ) of the CS-RZ code is input to the 3R receiver 601 and converted into an electrical data signal and an electrical clock signal. The electrical data signal output from the 3R receiver 601 is input to the modulator 602, and the electrical clock signal is input to the phase modulator 603. The input condition of the electric clock signal is the same as that of the conventional example 2. Light having a wavelength λ ₂ is also incident on the modulator 602 from the CW light source 604, and data (electrical data signal) is applied to the light having the wavelength λ _{2 by} the modulator 602. At 603, phase modulation with 0-π inversion is performed.

Y. Miyamoto et al, Electron. Lett., Vol. 35, pp. 2041-2042, 1999.) Y. Hashimoto et al., OFC′02 technical digest WV-5 S. Uokamura et al., OFC04 FD3, 2004)

  However, in the above-described conventional example 1, the CS-RZ code is not output. On the other hand, in the conventional examples 2 and 3, since a CS-RZ code is output, another phase modulator is required compared to the conventional example 1, and the configuration becomes complicated.

  The present invention has been made in view of the above points, and an object thereof is to provide a CS-RZ output wavelength converter capable of outputting a CS-RZ code without increasing the number of components.

  In order to achieve the above object, a CS-RZ output wavelength converter of the present invention includes a wavelength converter in which a phase modulator (CS-RZ optical pulse generator) and an intensity modulator (data application unit) are integrated, The phase change unit of the wavelength converter includes a non-linear medium that can be driven by a high-speed electric signal.

That is, the CS-RZ output wavelength converter according to the present invention includes an optical multiplexer / demultiplexer that divides input data light into two, and one of the data lights that is branched into two by the optical multiplexer / demultiplexer. A clock regenerator that generates an electrical signal, the other data light that is branched in two by the optical multiplexer / demultiplexer, and the clock light and the clock electrical signal output from the clock regenerator, A wavelength converter that simultaneously modulates the phase of the clock light by the input of the data light, and further undergoes phase modulation by the input of the clock electric signal, and the wavelength converter includes first to fifth lights. An optical interferometer composed of a coupler and an optical waveguide consists of a non-linear medium whose refractive index changes with light incidence and can be driven by an electric signal, and is driven by the clock electric signal. The data light and the clock light are incident on the optical interferometer, the first optical coupler splits the data light in two, and the second light The coupler splits the clock light into two, a delay unit having a delay time τ is connected to one output port of the first optical coupler, and the third optical coupler is connected to the data light output from the delay unit. The clock light output from one output port of the second optical coupler is combined and input to the first phase change unit, and the fourth optical coupler is the other of the first optical coupler. The data light output from the output port of the second optical coupler and the clock light output from the other output port of the second optical coupler are combined and input to the second phase change unit, The optical coupler includes an output of the first phase change unit and an output of the second phase change unit. And an output multiplexes, wherein together with first and said data light in the second phase change portion converts the wavelength of the data beam I Noriutsu the clock light, the optical clock phase by the data light differential phase modulation type wavelength converter der to be multiplexed by the fifth optical coupler with a time difference τ after being modulated is, the frequency of the electrical clock signal is half the frequency of the clock light, the The amplitude voltage of the clock electrical signal is 2Vπ, and Vπ is an input amplitude voltage necessary for the phase of the clock light passing through the phase change unit to change by π.

Further, the wavelength converter inputs the said optical clock of the input data optical wavelength lambda ₂ wavelength lambda _1, wherein the wavelength-converted light of the CS-RZ code having a wavelength lambda ₂ is output be able to.

According to the present invention, with the above-described configuration, a conventional wavelength conversion device in which an output is a CS-RZ code having a wavelength λ ₂ with respect to input data light having a wavelength λ ₁ of an NRZ, RZ, or CS-RZ code. There is an effect that it can be realized with a simple configuration without changing the number of components.

  Further, according to the present invention, since the phase modulator (CS-RZ optical pulse generation unit) and the intensity modulator (data application unit) are integrated, there is no need for a delay adjustment point between the wavelength converter and the phase modulator. The effect which becomes.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 shows a schematic configuration of a CS-RZ output wavelength converter according to an embodiment of the present invention. This CS-RZ output wavelength conversion device includes an optical coupler (optical multiplexer / demultiplexer) 101, a clock regenerator 102, and a CS-RZ wavelength converter 103. The input data light (wavelength λ ₁ , transmission speed B (Gb / s)) of the CS-RZ code is branched into two by the optical coupler 101, one being input to the clock regenerator 102 and the other being input to the wavelength converter 103. Both the clock light (frequency f, wavelength λ ₂ ) regenerated by the clock regenerator 102 and the clock signal (electricity) (frequency f / 2, amplitude voltage 2Vπ) are input to the wavelength converter 103.

When the data light of wavelength λ ₁ and the clock light of wavelength λ ₂ are incident on the wavelength converter 103, the clock light is modulated by the data light, so that the wavelength of the data light is converted from λ ₁ to λ ₂ . At this time, the phase changing units have a frequency f / 2 so that the phase is inverted by π for each bit with respect to the clock light passing through the phase changing units (203 and 204 in FIG. 2 described later) in the wavelength converter 103. , Modulated with an amplitude voltage of 2Vπ.

  FIG. 2 shows a configuration example of the CS-RZ wavelength converter 103 described above. The CS-RZ wavelength converter 103 shown in FIG. 2 is a differential phase modulation type wavelength converter, and a Mach-Zehnder type optical interferometer including an optical waveguide 202 and phase change units 203 and 204 is formed on a substrate 201. Yes. Reference numerals 205 to 209 denote optical couplers.

  When the clock light from the clock regenerator 102 enters from the port 210, the clock light is branched into two by the optical coupler 206, passes through the phase change units 203 and 204, is combined by the optical coupler 207, and is output to the port 211. .

  On the other hand, when the CS-RZ data light from the optical coupler 101 enters from the port 212, the CS-RZ data light is branched into two by the optical coupler 205, one is the port 214 via the delay unit 213, and the other is the port. Then, the light beams are incident on the phase change units 203 and 204 through the couplers 208 and 209, respectively.

  The adjusters of the phase change units 203 and 204 are 216 and 217, respectively. A clock signal (electricity) having a transmission rate B / 2 (GHz) is applied to the adjusters 216 and 217. Examples of the phase change units 203 and 204 include a nonlinear medium that can be driven by a high-speed electrical signal, for example, an electroabsorption modulator (EAM). When pulsed light as shown in FIG. 2 is incident on the phase change sections 203 and 204, the refractive index sharply decreases due to the saturable absorption effect, but a certain amount of relaxation time is required to return to the original state again. It becomes. For this reason, by shifting the data light by the delay time τ and entering the phase change portion, this slow phase change can be canceled out, and the phase change window opens sharply. At this timing, only when there is data light, the clock light output port is switched from the bar to the cross (port 211), so that the clock light is modulated.

Only the data light having the wavelength λ ₂ is cut out by the wavelength filter 218 at the rear stage of the port 211, and the CS-RZ data light (wavelength λ ₂ ) is output. At this time, both phase change sections 203 and 204 are modulated with the frequency f / 2 and the amplitude voltage 2Vπ.

  3 shows, from above, input data light incident on the optical coupler 101, input clock light incident on the port 210, input clock signals (electricity) to the phase change units 203 and 204, and output data light from the optical filter 218. The waveform change is shown.

In the clock regenerator 102, the clock is extracted from the CS-RZ data (1011) at the transmission rate B (Gb / s), the extracted clock light at the transmission rate B (GHz), and the transmission rate B / 2 (GHz). 2 is input to the wavelength converter 103 in FIG. 2, whereby CS-RZ data light having a wavelength λ ₂ is output.

  In the CS-RZ output wavelength converter of the present invention, it goes without saying that the output is CS-RZ even when the input optical signal is a normal RZ signal.

  Further, the 40 Gb / s-class NRZ wavelength conversion operation (Non-patent Document 3) can be performed using the differential phase modulation wavelength converter 103 as shown in FIG. 2 even when the input optical signal is an NRZ code. In the CS-RZ output wavelength conversion device of the present invention, such an input optical signal is considered applicable.

  The differential phase modulation wavelength converter 103 used in the present invention may be a monolithic type in which the phase change units 203 and 204 and the optical waveguide 202 are integrally formed on the same semiconductor substrate 201. It may be a hybrid type having a configuration in which a semiconductor optical amplifier is mounted on a planar lightwave circuit. Further, the same wavelength may be used as long as the data light and the clock light are incident on each other.

It is a block diagram which shows schematic structure of the CS-RZ output wavelength converter in one Embodiment of this invention. It is a block diagram which shows the structural example of the differential phase modulation type | mold wavelength converter of FIG. It is a wave form diagram which shows the input-output waveform in the CS-RZ output wavelength converter of this invention. It is a block diagram which shows the structural example of the RZ output wavelength converter of the prior art example 1. FIG. It is a block diagram which shows the structural example of the CS-RZ output wavelength converter of the prior art example 2. FIG. It is a block diagram which shows another structural example of the CS-RZ output wavelength converter of the prior art example 3. FIG.

Explanation of symbols

101 Optical coupler (optical multiplexer / demultiplexer)
102 Clock regenerator 103 CS-RZ wavelength converter 201 Substrate 202 Optical waveguide 203, 204 Phase change unit 205-209 Optical coupler 210, 211, 212 Port 213 Delay unit 214, 215 Port 215
216, 217 Adjuster 218 Wavelength filter 401, 501, 601 Optical multiplexer / demultiplexer 402, 502 Clock regenerator 403, 503 Wavelength converter 504, 603 Phase modulator 601 3R receiver 602 Modulator 604 CW light source

Claims (2)

An optical multiplexer / demultiplexer that splits the input data light in two;
A clock regenerator for inputting one of the data lights branched by the optical multiplexer / demultiplexer to generate a clock light and a clock electric signal;
The other data light branched into two by the optical multiplexer / demultiplexer, the clock light and the clock electric signal output from the clock regenerator are input, and the clock light is phased by the input of the data light. A wavelength converter that simultaneously modulates and further undergoes phase modulation by input of the clock electrical signal;
The wavelength converter is
An optical interferometer composed of first to fifth optical couplers and an optical waveguide includes a non-linear medium whose refractive index changes with light incidence and can be driven by an electric signal, and is driven by the clock electric signal. 1 and a second phase change unit,
The data light and the clock light are incident on the optical interferometer, the first optical coupler branches the data light in two, the second optical coupler splits the clock light in two, and the first optical coupler A delay unit having a delay time τ is connected to one output port of the optical coupler, and the third optical coupler is output from the data light output from the delay unit and one output port of the second optical coupler. The fourth optical coupler combines the clock light with the data light output from the other output port of the first optical coupler and the second optical coupler. The clock light output from the other output port of the optical coupler is combined and input to the second phase change unit, and the fifth optical coupler outputs the output of the first phase change unit and the output of the first phase change unit. Combine the output of the second phase change unit,
Wherein with the first and the data beam at the second phase change portion converts the wavelength of the data beam Noriutsu the clock light, the optical clock time difference after receiving a phase modulated by the data light τ differential phase modulation type wavelength converter der to be multiplexed by the fifth optical coupler with a is,
The frequency of the clock electric signal is ½ of the frequency of the clock light, the amplitude voltage of the clock electric signal is 2Vπ, and the phase of the clock light passing through the phase change unit changes by π. A CS-RZ output wavelength converter characterized by having an input amplitude voltage required for the above. Claim wherein the wavelength converter, which when entering the said optical clock of the input data optical wavelength lambda ₂ wavelength lambda _1, characterized in that the wavelength-converted light of CS-RZ code having a wavelength lambda ₂ is output The CS-RZ output wavelength converter according to any one of 1 to 3.

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