JP4617955B2 - OOK / PSK converter - Google Patents

Description

  The present invention relates to an apparatus for converting OOK (On-Off Keying) signal light into PSK (Phase Shift Keying) signal light.

  Conventionally, in optical fiber transmission, OOK signal light that transmits a signal depending on the presence or absence of an optical pulse has been used. However, the OOK signal light has a broad optical spectrum and is easily affected by chromatic dispersion and polarization mode dispersion, which makes it difficult to increase the bit rate.

PSK has no or less of the above-mentioned adverse effects because the optical spectrum does not spread compared to OOK. That is, PSK has better frequency utilization efficiency than OOK. DPSK (Differential Phase Shift Keying) signal light, which is a kind of PSK, has an advantage that it can be easily converted into OOK signal light by a 1-bit delay interferometer. Patent Documents 1 to 4 describe an apparatus configuration that generates DPSK signal light. Note that Patent Document 2 corresponds to Patent Document 1 and Patent Document 4 corresponds to Patent Document 3.
JP 2003-087201 A US Patent Application Publication No. 2003/2121 JP 2002-064574 A US Pat. No. 6,826,371

  In the apparatus configuration for generating the existing DPSK signal light, a data signal, which is an electrical signal, is encoded in advance by an encoding circuit, and an optical phase modulator is driven by an output signal of the encoding circuit. Not only is the encoding circuit complicated, but the tracking speed of the encoding circuit determines the final bit rate of the PSK signal light. That is, the bit rate of the PSK signal light is limited by the operation speed of the encoding circuit.

  A device configuration that generates OOK signal light and converts the OOK signal light into PSK signal light is more likely to achieve high-speed operation than directly generating a PSK signal.

  Accordingly, an object of the present invention is to provide an OOK / PSK conversion device that converts OOK signal light into PSK signal light.

The OOK / PSK conversion device according to the present invention is a device for converting an OOK signal light into a PSK signal light, and a logical inversion having a light intensity pattern indicating an inverted logical value of the OOK signal light from the OOK signal light. A logic inverter that generates data light, a probe light source that generates probe light, the OOK signal light, and the logic inverted data light output from the logic inverter are incident in opposite directions, and the probe light source The probe light output from the optical phase is incident in the same direction as one of the OOK signal light and the logically inverted data light, and an optical phase is applied to the probe light by the OOK signal light and the logically inverted data light. A modulator for the amount of optical phase shift given to the probe light with respect to the logical value “1” of the OOK signal light and the logical value “0” of the OOK signal light; And an optical phase modulator different in the amount of the optical phase shift given to the probe light by π .

The OOK / PSK conversion device according to the present invention is a device that converts an OOK signal light into a PSK signal light, and has a logical holding having a light intensity pattern indicating the same logical value as the OOK signal light from the OOK signal light. A logic holding light / logical inversion light generation device that outputs data inversion data light having a light intensity pattern indicating an inversion logic value of the OOK signal light, a probe light source that generates CW probe light, and the logic The logically held data light and the logically inverted data light output from the holding light / logically inverted light generating device are incident in opposite directions, and the probe light output from the probe light source is converted into the logically held data light and the logically inverted data light. incident at one and the same direction of the logic inversion data light, the logic holding data light and the logical by inverted data light gives an optical phase shift in the probe light phase A modulator, the logic and the amount of the light phase shift to be given to the probe light with respect to the logic value "1" of the data held light, the probe light with respect to the logic value "0" of the logical data held light And an optical phase modulator in which the amount of the optical phase shift given to is different by π .

  According to the present invention, the OOK signal light can be converted into the PSK signal light with all light. Since it can be converted from the OOK format to the PSK format in the state of light, it can also be applied to high-speed signal light.

  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. The laser diode (LD) 10 generates a continuous (CW) laser beam having a wavelength λ1. The light intensity modulator 12 modulates the light intensity of the laser beam output from the laser diode 10 according to the data D, and outputs an NRZ OOK signal light. The OOK / PSK converter 14 converts the OOK signal light output from the optical intensity modulator 12 to PSK signal light, for example, relative light phase to 0 for the pulse portion of the OOK signal light, and relative light to the space portion. Conversion to PSK signal light with a phase of π.

  The configuration and function of the OOK / PSK converter 14 will be described in detail. The optical demultiplexer 20 divides the output light of the light intensity modulator 12 into two and applies one to the wavelength conversion type logic inverter 22. The wavelength conversion type logic inverter 22 inverts the logic of the signal light having the wavelength λ1, that is, converts the mark portion into a space, converts the space portion into a mark portion, and converts the carrier wavelength from the wavelength λ1 to another wavelength λ3. .

  In the wavelength conversion type logic inverter 22, the laser diode 24 outputs a continuous (CW) laser beam having a wavelength λ 3 different from the wavelength λ 1. The laser light of wavelength λ3 output from the laser diode 24 acts as probe light for mutual gain modulation of a semiconductor optical amplifier (SOA) 28 described later. The optical multiplexer 26 combines the probe light having the wavelength λ 3 output from the laser diode 24 and the OOK signal light having the wavelength λ 1 from the optical demultiplexer 20, and applies the combined light to the semiconductor optical amplifier 28. The semiconductor optical amplifying element 28 modulates the intensity of the probe light having the wavelength λ3 by the mutual gain modulation effect by the signal light having the wavelength λ1. Here, the semiconductor optical amplifying element 28 reduces the gain with respect to the probe light with the wavelength λ3 at the mark portion of the signal light with the wavelength λ1, and increases the gain with respect to the probe light with the wavelength λ3 in the space portion with the signal light with the wavelength λ1. As shown, wavelengths λ1 and λ3 and their light intensities are preset.

  The output light of the semiconductor optical amplifying element 28 includes an OOK signal light having a wavelength λ1 amplified by the semiconductor optical amplifying element 28 and a probe light having a wavelength λ3 that has been intensity-modulated by the semiconductor optical amplifying element 28. The optical filter 30 transmits only the light component having the wavelength λ3 from the output light of the semiconductor optical amplifier 28. The output light of the optical filter 30 is a signal light obtained by inverting the logic of the OOK signal light having the wavelength λ1 output from the light intensity modulator 12 and converting the carrier wavelength from λ1 to λ3, that is, logically inverted data light. It has become.

  The output light of the optical filter 30, that is, the wavelength inversion data light, is applied to the optical multiplexer 32 via the variable attenuator 36. The variable attenuator 36 is provided to adjust the light intensity of the logically inverted light output from the optical filter 30. After the adjustment, the variable attenuator 36 is set to a constant attenuation value. The laser diode 34 outputs continuous laser light having a wavelength λ2 different from the wavelengths λ1 and λ3. The continuous laser light output from the laser diode 34 acts as probe light for cross-phase modulation in a semiconductor optical amplification element 38 to be described later. The optical multiplexer 32 multiplexes the output light of the optical filter 30 and the probe light having the wavelength λ 2 output from the laser diode 34.

  The other output light of the optical demultiplexer 20, that is, the logic-maintained data light having the wavelength λ 1, passes through the optical delay circuit 40 for timing adjustment and the optical coupler 42, and the probe light having the wavelength λ 2 of the semiconductor optical amplifier 38. The light is incident on the opposite end face of the logically inverted data light having the wavelength λ3. That is, in the semiconductor optical amplifying element 38, the probe light having the wavelength λ2, the logic inverted data light having the wavelength λ3, and the logic holding data light having the wavelength λ1 propagate in opposite directions. The delay time of the optical delay circuit 40 is set in advance so that the logically inverted data light having the wavelength λ3 and the logically held data light having the wavelength λ1 are incident on the semiconductor optical amplifier 38 at the same bit timing.

When the probe light and control light of different wavelengths are incident on the semiconductor optical amplifier in the same direction and when they are incident in the opposite direction, the phase shift received by the probe light even if the control light intensity is the same The amount is different. It is also possible to set the phase shift amount difference to π. FIG. 2 shows a light intensity change waveform of the probe light by the incidence of the control pulse. In FIG. 2 , the horizontal axis indicates time, and the vertical axis indicates the light intensity of the probe light. The incidence of the control pulse, the light intensity of the probe light decreases from I ₀ by [Delta] I _0, returns to the original light intensity I ₀ at a predetermined relaxation time. 3, the case where the semiconductor optical amplifying element and the probe light of the control light and the wavelength λ2 of the wavelength λ1 incident at the same direction, in a case where the incident in the reverse direction, the change in the phase shift amount probe light is subjected Show. In FIG. 3 , the horizontal axis represents the light intensity attenuation rate ΔI ₀ / I ₀ , and the vertical axis represents the optical phase change amount Δφ ₀ . In the vicinity of the broken line shown in FIG. 3 , even if the attenuation rate ΔI ₀ / I ₀ of the same light intensity, the optical phase shift amount in the case of reverse incidence is approximately π than that in the case of incidence in the same direction. About big. The PSK signal light can be generated by setting the wavelengths and light intensities of the probe light, the logic holding data light, and the logic inverted data light so that the difference between the optical phase shift amounts becomes π.

  The optical filter 44 that transmits the wavelength λ2 extracts the PSK signal light having the wavelength λ2 from the output light of the semiconductor optical amplifier 38. The output light of the optical filter 44 is output to, for example, an optical transmission line.

  FIG. 4 is a timing chart of the logic holding data light (wavelength λ1), the logic inverted data light (wavelength λ3), and the probe light (wavelength λ2) output from the semiconductor optical amplifier 38 with respect to the NRZ OOK signal light. Show. 4A shows the waveform of the logic holding data light, FIG. 4B shows the waveform of the logic inverted data light, and FIG. 4C shows the waveform of the probe light output from the semiconductor optical amplifier 38. . The horizontal axis indicates time, and the vertical axis indicates light intensity. The amount of shift of the optical phase is added to the probe light (FIG. 4C) having the wavelength λ2 output from the semiconductor optical amplifying element 38. The optical phase of the probe light having the wavelength λ2 is shifted by φ by the optical pulse portion of the logic holding data light (FIG. 4A), and the optical pulse portion (logic holding data) of the logic inverted data light (FIG. 4B). This corresponds to the space portion of light.) Is shifted by φ + π. Eventually, the relative phase of the probe light having the wavelength λ2 output from the SOA 38 becomes 0 for the optical pulse portion of the logic holding data light and becomes π for the space portion.

  In the embodiment shown in FIG. 1, logically inverted data light (wavelength λ3) is incident on the SOA 38 in the same direction as the probe light, and logical holding data light (wavelength λ1) is incident on the SOA 38 in the direction opposite to the probe light. Even if it is reverse, the same effect can be obtained.

  Further, in the embodiment shown in FIG. 1, the case of NRZ type OOK signal light is shown, but laser diodes 24 and 34 for generating wavelength conversion type logic inversion probe light and OOK / PSK converter probe light, respectively. Can be easily replaced by a light source that further branches the OOK signal light branched by the optical demultiplexer 20, extracts a clock by electrical or optical means, and generates an RZ pulse according to the extracted clock. It is possible to correspond to a form of OOK signal light.

  FIG. 5 shows a schematic block diagram of the second embodiment of the present invention.

  The laser diode (LD) 110 generates a continuous (CW) laser beam having a wavelength λ1. The light intensity modulator 112 modulates the light intensity of the output laser light from the laser diode 110 according to the data D, and outputs an NRZ OOK signal light. The OOK / PSK converter 114 converts the OOK signal light output from the light intensity modulator 112 into the PSK format and outputs the PSK signal light.

  The configuration and function of the OOK / PSK converter 114 will be described in detail. The logic holding / logic inversion signal light generator 116 has a logic holding data light having a light intensity pattern indicating the same logical value from the OOK signal light output from the light intensity modulator 112, that is, an optical pulse portion and a space portion. Logic holding data light having a light intensity pattern of the same arrangement and logic inverted data light indicating a light intensity pattern indicating an inverted logic value of the OOK signal light, that is, a light intensity pattern in which the light pulse portion and the space portion are inverted A logically inverted data light comprising: The logic holding / logic inversion signal light generator 116 is composed of a Mach-Zehnder interferometer in which semiconductor optical amplifying elements are arranged on two arms, and this function itself is known.

  Specifically, the laser diode 118 outputs continuous (CW) laser light having a wavelength λ3 called probe light. The wavelength λ3 is different from the wavelength λ1. The optical demultiplexer 120 divides the probe light output from the laser diode 118 into two, and applies one to the optical multiplexer 122 and the other to the semiconductor optical amplifier 126. The optical multiplexer 122 combines the OOK signal light from the optical intensity modulator 112 with the probe light having the wavelength λ 3 from the optical demultiplexer 120 and applies the combined light to the semiconductor optical amplifier 124. The semiconductor optical amplifying element 124 amplifies the probe light having the wavelength λ3 and, due to the cross-phase modulation effect, changes the optical phase shift that differs by π between the optical pulse portion and the space portion of the OOK signal light having the wavelength λ1 to the probe light having the wavelength λ3. To give.

  On the other hand, the semiconductor optical amplifier 126 amplifies the probe light having the wavelength λ3 from the optical demultiplexing 120 with a constant gain. The optical phase shift amount of the probe light in the semiconductor optical amplification device 126 is, for example, equal to the optical phase shift amount of the probe light in the mark portion of the OOK signal light by the semiconductor optical amplification device 124 and 126 is adjusted.

  The optical multiplexer / demultiplexer 128 multiplexes and demultiplexes the output light of the semiconductor optical amplification elements 124 and 126. Since the optical filters 130 and 132 in the subsequent stage extract only the probe light having the wavelength λ3, the optical multiplexer / demultiplexer 128 includes the phase-modulated probe light having the wavelength λ3 output from the semiconductor optical amplification element 124 and the semiconductor optical amplification element. 126 holds the probe light having the wavelength λ3 output from 126, and holds the logic holding data light 116a having the same light intensity pattern as the OOK signal light output from the light intensity modulator 112, and the inverted logic value The multiplexing / demultiplexing characteristics are set so as to output the logically inverted data light 116b having the light intensity pattern indicating. Such an operation itself is well known, and these two outputs are a so-called constructive output and a destructive output.

  The logically retained data light having the wavelength λ3 output from the optical filter 130 is applied to the optical multiplexer 134. The laser diode 136 generates a continuous (CW) laser beam having a wavelength λ2 different from the wavelength λ3. The wavelength λ2 may be equal to the wavelength λ1. The laser beam output from the laser diode 136 is a laser beam that is phase-modulated by a logic holding data beam and a logic inverted data beam in a semiconductor optical amplifying element 138, which will be described later. The optical multiplexer 134 combines the output light of the optical filter 130 and the output light of the laser diode 136, and applies the combined light to the semiconductor optical amplification element 138. The semiconductor optical amplifier 138 performs the same function as the semiconductor optical amplifier 38 of the embodiment shown in FIG.

  Further, the logically inverted data light having the wavelength λ3 output from the optical filter 132 passes through the variable attenuator 140 for adjusting the optical power, the optical delay circuit 142 for adjusting the time, and the optical coupler 144. Then, the light is incident on the end surface opposite to the incident end surface of the logic holding data light. That is, in the semiconductor optical amplifier 138, the logically inverted data light having the wavelength λ3 propagates in the opposite direction to the probe light having the wavelength λ2 and the logically held data light having the wavelength λ3. The delay time of the optical delay circuit 142 is set in advance so that the logically inverted data light of the wavelength λ3 and the logically held data light of the wavelength λ3 enter the semiconductor optical amplifier 138 at the same bit timing.

  Similar to the optical phase modulation function in the semiconductor optical amplifying element 38, the semiconductor optical amplifying element 138 also shifts the optical phase of the probe light having the wavelength λ2 in accordance with the logic inverted data light having the wavelength λ3 and the logic holding data light having the wavelength λ3. . At this time, the attenuation amount of the variable attenuator 140 and the light intensity of the probe light having the wavelength λ2 are adjusted so that the difference in optical phase shift amount between the optical pulse portion and the space portion of the logic holding data light becomes π. The Thereby, the PSK signal light that carries the data D is generated.

  The optical filter 146 that transmits the wavelength λ2 extracts the probe light having the wavelength λ2, which is phase-modulated by the semiconductor optical amplifier 138, that is, the PSK signal light. The output light of the optical filter 146 is output to, for example, an optical transmission line.

  Although the use incorporated in the optical transmission apparatus has been described, it is obvious that the OOK / PSK converter of the above-described embodiment can be used in other places where the PSK signal light is required. Since all light can be processed, high-speed OOK signal light can be converted into PSK signal light without being restricted by the limiting rate of the electric circuit.

  In the embodiment shown in FIG. 1, logically inverted data light (wavelength λ3) is incident on the semiconductor optical amplifying element 138 in the opposite direction to the probe light, and logically retained data light (wavelength λ3) is amplified in the same direction as the probe light. Although the light is incident on the element 138, the same operation and effect can be obtained even in the reverse case.

  Although the invention has been described with reference to specific illustrative embodiments, various modifications and alterations may be made to the above-described embodiments without departing from the scope of the invention as defined in the claims. This is obvious to an engineer in the field to which the present invention belongs, and such changes and modifications are also included in the technical scope of the present invention.

It is a schematic block diagram of the first embodiment of the present invention. Keru Contact the semiconductor optical amplifier device 38 is a waveform variation of the probe light. It is a figure which shows the change of the light intensity attenuation amount and optical phase shift amount in a semiconductor optical amplifier element by the same direction incidence and reverse direction incidence. FIG. 4 is a waveform example of logic holding data light, logic inversion data light, and probe light output from the semiconductor optical amplifying element 38, (a) shows the waveform of the logic holding data light, and (b) shows the waveform of the logic inversion data light. The waveform of the probe light output from the semiconductor optical amplifier 38 is shown. It is a schematic block diagram of the second embodiment of the present invention.

Explanation of symbols

10: Laser diode 12: Light intensity modulator 14: OOK / PSK converter 20: Optical demultiplexer 22: Wavelength conversion type logic inverter 24: Laser diode 26: Optical multiplexer 28: Semiconductor optical amplifier (SOA)
30: Optical filter 32: Optical multiplexer 34: Laser diode 36: Variable attenuator 38: Semiconductor optical amplifier (SOA)
40: optical delay circuit 42: optical coupler 44: optical filter 110: laser diode (LD)
112: Light intensity modulator 114: OOK / PSK converter 116: Logic holding / logical inversion signal light generator 116a: Logic holding data light 116b: Logic inversion data light 118: Laser diode 120: Optical demultiplexer 122: Optical multiplexing 124, 126: Semiconductor optical amplifier (SOA)
128: Optical multiplexer / demultiplexer 130, 132: Optical filter 134: Optical multiplexer 136: Laser diode 138: Semiconductor optical amplifier (SOA)
140: Variable attenuator 142: Optical delay circuit 144: Optical coupler 146: Optical filter

Claims (5)

An apparatus for converting OOK signal light into PSK signal light,
A logic inverter (22) for generating, from the OOK signal light, a logically inverted data light having a light intensity pattern indicating an inverted logical value of the OOK signal light;
A probe light source (34) for generating probe light;
The OOK signal light and the logic inverted data light output from the logic inverter are incident in opposite directions, and the probe light output from the probe light source is converted into the OOK signal light and the logic inverted data light. Is an optical phase modulator that applies an optical phase shift to the probe light by the OOK signal light and the logically inverted data light, and is applied to the logical value “1” of the OOK signal light . An optical phase modulator (38) in which the amount of the optical phase shift given to the probe light and the amount of the optical phase shift given to the probe light differ from the logical value “0” of the OOK signal light by π
And an OOK / PSK conversion device. 2. The OOK / PSK conversion device according to claim 1 , wherein the optical phase modulator comprises a semiconductor optical amplifying element (38). An apparatus for converting OOK signal light into PSK signal light,
From the OOK signal light, a logic holding data light having a light intensity pattern showing the same logical value as the OOK signal light and a logic inverted data light having a light intensity pattern showing an inverted logical value of the OOK signal light are output. A logic holding light / logic inversion light generating device (116),
A probe light source (136) for generating CW probe light;
The logic holding data light and the logic inversion data light output from the logic holding light / logical inversion light generation device (116) are incident in opposite directions, and the probe light output from the probe light source is An optical phase modulator that is incident in the same direction as one of the retained data light and the logically inverted data light and applies an optical phase shift to the probe light by the logically retained data light and the logically inverted data light. The amount of the optical phase shift given to the probe light with respect to the logical value “1” of the data light and the amount of the optical phase shift given to the probe light with respect to the logical value “0” of the logical holding data light Optical phase modulators differing by π (138)
And an OOK / PSK conversion device. 4. The OOK / PSK conversion apparatus according to claim 3 , wherein the optical phase modulator comprises a semiconductor optical amplifying element. The logical holding light / logical inversion light generation device (116)
A second probe light source (118) for generating second CW probe light;
An optical demultiplexer (120) that divides the second CW probe light into a first probe component and a second probe component;
A first optical phase modulation element (124) on which the first probe component and the OOK signal light are incident;
A second optical phase modulation element (126) on which the second probe component is incident;
A multiplexer / demultiplexer (128) that multiplexes and demultiplexes the output light of the first and second optical phase modulation elements and outputs the logical holding data light and the logical inversion data light
The OOK / PSK conversion apparatus according to claim 3 or 4 , characterized by comprising:

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