JP4239751B2 - Bit interleaved orthogonal polarization multiplexed signal light receiving method and apparatus - Google Patents

Description

  The present invention relates to an optical receiving method and apparatus in bit interleaved orthogonal polarization multiplexing transmission in which polarization is orthogonalized for each bit.

  In order to increase the capacity of the optical transmission system, the bit rate of the optical pulse signal may be increased. However, considering the generation of short optical pulses and the separation or identification of individual optical pulses in the receiving device, there is a limit to narrowing the optical pulse width.

  On the other hand, bit interleave polarization orthogonal multiplexing in which the polarization is orthogonalized between adjacent bits on the time axis has been proposed (see, for example, Patent Documents 1 and 2). In bit interleaved polarization orthogonal multiplexing, it is possible to allow overlapping of optical pulses between adjacent bits on the time axis, so that relatively long optical pulses can be used. As a result, the generation of light pulses is facilitated, and the bit rate is easily increased. However, the optical receiver needs a means for separating the optical pulse of each bit according to the polarization.

  Patent Document 1 describes the following bit interleaved polarization orthogonal multiplex transmission system. In other words, bit interleaved polarization orthogonal multiplexed signal light is input to the polarization beam splitter via the polarization controller. The polarization control device controls one polarization component signal light of the input light to be parallel to one polarization direction of the polarization beam splitter by feedback control described later. The signal light of each polarization separated by the polarization beam splitter is converted into an electric signal by the light receiving element and input to the electric receiving device. In order to control the polarization control device, there is a method of extracting a fundamental frequency component from the output of one light receiving element by an electric filter and controlling the polarization control device so that the amplitude of the fundamental frequency component becomes maximum. Are listed.

  In addition, when the signal bit rate exceeds 40 Gbps, photoelectric conversion becomes difficult. Therefore, the transmitter apparatus preliminarily modulates the intensity of one polarization signal light, and the optical receiver apparatus A configuration is also described in which one polarization component after wave separation is converted into an electric signal, and the polarization control device is controlled so that the amplitude of the intensity modulation of the electric signal is maximized.

  Further, in FIG. 7 of Patent Document 2, the following receiving apparatus is described. That is, the bit interleaved polarization orthogonal multiplexed signal light is separated into each polarization signal by the polarization beam splitter and then converted into an electric signal. Also, the clock is regenerated from the bit interleaved polarization orthogonal multiplexed signal light. Each electric signal is sampled by the high-speed sampling circuit by the reproduction clock. The phase of the recovered clock applied to the high-speed sampling circuit is controlled by the output of the high-speed sampling circuit.

Patent Document 3 describes a polarization multiplexed signal separation apparatus and method that uses an EO modulator instead of the high-speed sampling circuit of Patent Document 2.
JP 2002-344426 A US Patent Application Publication 2003/0020985 US Patent Application Publication 2002/0093993

  In the configuration described in Patent Document 1, a means for modulating the intensity of one polarized signal light is required in the optical transmission device. In addition, a third signal source having no or little correlation with the original signal must be prepared.

  In the configurations described in Patent Documents 2 and 3, the electric high-speed sampling circuit or the EO modulator uses a specific polarization signal output from the polarization beam splitter and follows a clock regenerated from the bit interleaved polarization orthogonal multiplexed signal light. Since a signal of a specific bit is sampled or separated, its transmission capability is limited to the response speed of a high-speed sampling circuit or EO modulator. That is, it cannot be applied to a high-speed optical transmission system that reaches 160 Gbps.

It is an object of the present invention to provide an optical reception method and apparatus in bit interleaved polarization orthogonal multiplex transmission that can be applied to high-speed optical transmission such as 160 Gbps.

An optical receiving method according to the present invention is a method of receiving bit interleaved orthogonal polarization multiplexed signal light in which linearly polarized first signal light and second signal light orthogonal to each other are time-division multiplexed with bit alternation. A polarization conversion step of converting the polarization direction of the bit interleaved orthogonal polarization multiplexed signal light by the polarization conversion device, and a first polarization of the polarization signal orthogonal to the output signal light of the polarization conversion device by the polarization separation device a polarization separation step of separating the polarization component and the second polarization component, and a clock reproducing step of reproducing a clock from the first polarization component, in accordance with reproduction clock reproduced in the clock reproducing step, said first polarized of the wave components, a first transmission step of transmitting a bit signal light corresponding to the first signal light, in accordance with the reproduction clock, of the said second polarization components, corresponding to the second signal light A second transmission step that transmits the bit signal light, a first photoelectric conversion step that photoelectrically converts the transmission light of the first transmission step, and a second photoelectric conversion step that photoelectrically converts the transmission light of the second transmission step. The polarization for controlling the polarization conversion in the polarization converter so that the optical power of the bit signal light transmitted in the first transmission step is increased according to the electrical signal generated in the first photoelectric conversion step. From a conversion control step, a first reception step of receiving a signal carried by the first signal light from the electric signal generated by the first photoelectric conversion step, according to the reproduction clock, and a second photoelectric conversion step And a second receiving step of receiving a signal carried by the second signal light from the generated electric signal according to the reproduction clock. And butterflies.

An optical receiving apparatus according to the present invention is an apparatus for receiving bit interleaved orthogonal polarization multiplexed signal light in which linearly polarized first signal light and second signal light orthogonal to each other are time-division multiplexed with bit alternation, A polarization conversion device that converts the polarization direction of the bit interleaved orthogonal polarization multiplexed signal light, and the output signal light of the polarization conversion device into a first polarization component and a second polarization component of polarization orthogonal to each other The first signal in the first polarization component according to the polarization separation device to be separated, the clock recovery device that recovers the clock from the first polarization component, and the recovered clock output from the clock recovery device a first optical gate for transmitting bit signal light corresponding to the light, in accordance with the reproduction clock, of the said second polarization component, and the second light gate which transmits a bit signal light corresponding to the second signal light The first light gauge A first photoelectric conversion means for converting the bets of the output light to the first electrical signal, a second photoelectric conversion means for converting the output light from the second optical gate to the second electrical signal, the output of the first photoelectric conversion means In accordance with the polarization conversion control device for controlling the polarization conversion in the polarization conversion device so that the output signal light power of the first optical gate increases , the first electrical signal is applied to the first electric signal in accordance with the reproduction clock. A first receiver for receiving a signal carried by signal light; and a second receiver for receiving a signal carried by the second signal light from the second electric signal according to the reproduction clock. Features.

  With the above-described configuration, in the present invention, an optical gate that removes crosstalk from the first polarization component after polarization separation is provided, and the polarization converter is controlled by the output of the optical gate. It is possible to separate the first and second signal lights multiplexed with mutually orthogonal polarizations of the bit interleaved orthogonal polarization multiplexed signal.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a schematic block diagram of an embodiment of the present invention. Bit interleaved orthogonal polarization multiplexed signal light 10 is input to the polarization converter 12 from an optical fiber transmission line (not shown). The even bits b0, b2,... Of the signal light 10 are carried by the first linear polarization, and the odd bits b1, b3,... Are orthogonal to the first linear polarization. It is conveyed by. The bit interleaved orthogonal polarization multiplexed signal light 10 is also a signal obtained by time-division multiplexing the first signal light of even bits b0, b2,... And the second signal light of odd bits b1, b3,. Even in this respect, the signal light 10 is time-division multiplexed and polarization multiplexed signal light.

  Even if the polarization of adjacent bits of the bit interleaved orthogonal polarization multiplexed signal light 10 is orthogonal during transmission, the polarization dependent transmission characteristics (polarization mode dispersion, polarization dependent loss, etc.) of the optical fiber transmission line can After transmission through the fiber transmission line, the polarization of the first signal light and the polarization of the second signal light are not completely orthogonal.

  The polarization converter 12 performs polarization control of the input signal light 10 so that the polarization of the odd-numbered bit or even-numbered bit of the input signal light 10 matches one polarization plane of the polarization beam splitter 14 by feedback control described later. Convert wave direction. This type of polarization converter 12 is known as a so-called polarization controller.

  The polarization beam splitter (PBS) 14 separates the output light of the polarization converter 12 into two polarization components (TE component and TM component) 14a and 14b orthogonal to each other. As described above, since the orthogonality of the polarization of the orthogonal polarization multiplexed signal light 10 is deteriorated, the polarization components 14a and 14b separated by the PBS 14 are crosstalk of signals included in other polarizations. including. That is, the polarization component 14a mainly including the bits b0 and b2 includes the weak light of the bits b1 and b3 as crosstalk, and the polarization component 14b mainly including the bits b1 and b3 is the crosstalk of the bits b0 and b2. Includes faint light.

  The optical demultiplexer 16 divides one polarization component 14 a from the PBS 16 into two parts, applies one to the clock recovery device 18, and applies the other to the optical gate 20. The clock regenerator 18 generates an electric clock (or optical clock) having the same frequency as the fundamental frequency of the input light. The optical gate 20 transmits optical pulses in time slots corresponding to even bits b0, b2,... From the output light of the branching filter 16 according to the clock output from the clock recovery device 18, and the other time slots. Block light pulses. The optical gate 20 can remove crosstalk of odd bits b1, b3,. Such an optical gate 20 can be realized by, for example, an electroabsorption (EA) type optical modulator.

  The light receiver 22 converts the output signal of the optical gate 20 into an electrical signal. The output signal of the light receiver 22 is input to the electric receiver 26 via the low-pass filter 24. The phase of the output clock of the clock regenerator 18 is adjusted by the phase adjuster 28 and applied to the electric receiver 26. The electric receiver 26 demodulates the signal carried by the even bits b0, b2,... From the output signal of the low-pass filter 24 according to the clock from the phase adjuster 28. The control device 30 controls the polarization conversion device 12 according to the output signal of the light receiver 22 so that the output of the light receiver 22 is maximized. As a result, the polarization converter 12 allows the input signal light 10 of the input signal light 10 so that the crosstalk components of the odd bits b1, b3,... Contained in the input light of the optical gate 20 are minimized and ideally 0. Convert polarization.

  In this embodiment, by providing the optical gate 20, the control device 30 can control the polarization converter 12 without being affected by the crosstalk of the odd bits b1, b3,. If the optical gate 20 is not provided, the influence of crosstalk from adjacent bits is increased, the time required for the control device 30 to control is increased, and the polarization conversion device 12 changes the input signal light 10 to an appropriate polarization direction. It takes a long time to convert to, and the reception characteristics during that time deteriorate.

  The other polarized wave component 14 b separated by the PBS 14, that is, the component 14 b mainly including odd bits b 1, b 3,. The light receiver 32 converts the input signal light into an electrical signal. The output signal of the light receiver 32 is input to the electric receiver 36 through the low pass filter 34. The phase of the output clock of the clock regenerator 18 is adjusted by the phase adjuster 38 and applied to the electric receiver 36. The electric receiver 36 demodulates the signal carried by the odd bits b1, b3,... From the output signal of the low-pass filter 34 according to the clock from the phase adjuster 38.

  FIG. 2 shows a schematic block diagram of the second embodiment of the present invention. An optical gate 40 having the same function as that of the optical gate 20 is disposed in front of the light receiver 32. An output clock of the clock regeneration device 18 is applied to the optical gate 40 via the phase adjustment device 42. The optical gate 40 transmits the optical pulse in the time slot corresponding to the odd bits b1, b3,... Among the other polarized wave components 14b separated by the PBS 14 in accordance with the output clock of the phase adjusting device 42. Blocks light pulses in other time slots.

  In the embodiment shown in FIG. 2, by adding the optical gate 40, the crosstalk of the even bits b0, b2,... Contained in the other polarization component 14b separated by the PBS 14 can be removed.

  In each embodiment shown in FIGS. 1 and 2, the polarization components 14a and 14b separated by the PBS 14 are converted into electric signals, but a TDM (time division multiplexing) signal light separation device is used as the light receivers 22 and 32. It may be arranged in the previous stage and separated into a plurality of lower-speed optical signals by the separation device, and then converted into electrical signals.

  In the embodiment shown in FIGS. 1 and 2, the optical gate 20 and the light receiver 22 are used in combination for signal reception and control of the polarization converter 12. However, the optical gate 20 and the light receiver 22, or means corresponding to the light receiver 22 may be provided separately from the signal reception for controlling the polarization converter 12.

It is a schematic block diagram of the first embodiment of the present invention. It is a schematic block diagram of the second embodiment of the present invention.

Explanation of symbols

10: Bit interleaved orthogonal polarization multiplexed signal light 12: Polarization converter 14: Polarization beam splitter (PBS)
14a, 14b: Component 16 separated by PBS 14: Optical demultiplexer 18: Clock recovery device 20: Optical gate 22: Light receiver 24: Low pass filter 26: Electric reception device 28: Phase adjustment device 30: Control device 32: Light reception Device 34: low-pass filter 36: electric receiving device 38: phase adjusting device 40: optical gate 42: phase adjusting device

Claims (2)

A method of receiving bit interleaved orthogonal polarization multiplexed signal light (10) in which the first signal light and the second signal light of linear polarization orthogonal to each other are time-division multiplexed in a bit alternating manner,
A polarization conversion step of converting the polarization direction of the bit interleaved orthogonal polarization multiplexed signal light (10) by the polarization converter (12);
Polarization separation for separating the output signal light of the polarization conversion device (12) into a first polarization component (14a) and a second polarization component (14b) of polarizations orthogonal to each other by the polarization separation device (14) Steps ,
A clock recovery step of recovering a clock from the first polarization component (14a);
A first transmission step for transmitting the bit signal light corresponding to the first signal light in the first polarization component (14a) according to the recovered clock recovered in the clock recovery step ;
A second transmission step of transmitting the bit signal light corresponding to the second signal light in the second polarization component (14b) according to the reproduction clock;
A first photoelectric conversion step for photoelectrically converting the transmitted light of the first transmission step;
A second photoelectric conversion step for photoelectrically converting the transmitted light of the second transmission step;
In accordance with the electrical signal generated in the first photoelectric conversion step, the polarization conversion in the polarization converter (12) is controlled so that the optical power of the bit signal light transmitted in the first transmission step is increased. A polarization conversion control step;
A first receiving step of receiving a signal carried by the first signal light from the electric signal generated by the first photoelectric conversion step according to the reproduction clock ;
An optical reception method comprising: a second reception step of receiving a signal carried by the second signal light from the electric signal generated by the second photoelectric conversion step according to the reproduction clock. A device for receiving bit-interleaved orthogonal polarization multiplexed signal light (10) in which the first signal light and the second signal light of linear polarization orthogonal to each other are time-division multiplexed with bit alternation,
A polarization converter (12) for converting the polarization direction of the bit interleaved orthogonal polarization multiplexed signal light (10);
A polarization separation device (14) that separates the output signal light of the polarization conversion device (12) into a first polarization component (14a) and a second polarization component (14b) that are orthogonal to each other;
A clock recovery device (18) for recovering a clock from the first polarization component (14a);
A first optical gate (20) that transmits bit signal light corresponding to the first signal light in the first polarization component (14a) in accordance with the recovered clock output from the clock recovery device (18); ,
A second optical gate (40) that transmits bit signal light corresponding to the second signal light in the second polarization component (14b) according to the reproduction clock;
First photoelectric conversion means (22) for converting the output light of the first optical gate into a first electrical signal;
Second photoelectric conversion means (32) for converting the output light of the second optical gate into a second electrical signal;
Polarization conversion control for controlling the polarization conversion in the polarization converter (12) so that the output signal light power of the first optical gate (20) is increased in accordance with the output of the first photoelectric conversion means (22). Devices (22, 30);
A first receiver (26) for receiving a signal carried by the first signal light from the first electric signal according to the reproduction clock;
A second receiver (36) for receiving a signal carried by the second signal light from the second electric signal according to the reproduction clock.
An optical receiver characterized by comprising:

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