JP2010081210A - Optical signal generator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To generate a high-speed optical pattern signal reduced in pattern dependency jitter and reduced in the deterioration of a waveform. <P>SOLUTION: In an optical signal generator 20 having: an optical pattern signal generator 21 which generates an optical pattern signal Pa of an NRZ form synchronized with a clock signal C; and a data form conversion part 30 which reduces the pattern dependency jitter by punching out the optical pattern signal Pa by a clock pulse synchronized with the clock signal C converted into an optical pattern signal Pb of an RZ form, the data form conversion part 30 is constituted of: an optical clock pulse generator 31 which generates an optical clock pulse Pc with a width narrower than one bit width of the optical pattern signal Pa synchronized with the clock signal C; and an EA modulator 32 which receives the optical pattern signal Pa and the optical clock pulse Pc and passes the optical pattern signal Pa only during the optical clock pulse Pc is made incident. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention is a technique for reducing pattern-dependent jitter by punching out an optical pattern signal output in NRZ format in synchronization with a clock signal with a clock pulse in synchronization with the clock signal and converting it into an RZ format optical pattern signal. The present invention relates to a technique for reducing waveform deterioration.

  In various optical signal devices that handle optical signals, evaluation of pattern-dependent jitter and random jitter generated by an E / O conversion unit that converts an electrical signal into an optical signal is an essential measurement item. Therefore, in order to separate and evaluate the pattern-dependent jitter and random jitter generated in the E / O conversion unit, a technique for generating an optical signal with extremely small pattern-dependent jitter is required.

  As a technique for realizing this, in Patent Document 1, as shown in FIG. 6, an optical pattern signal generator 11 generates an optical pattern signal Pa in NRZ format synchronized with an electrical clock signal C to generate an optical modulator 12. The optical signal is applied to the optical modulator 12, and the optical pattern signal is sampled (ie, binary reading process) to generate an RZ-format optical pattern signal Pb with reduced pattern-dependent jitter. Thus, a technique for expanding the pulse width by the pulse stretcher 13 and returning it to the optical pattern signal Pa ′ in the NRZ format is disclosed.

JP 2004-201327 A

  However, the bit rate of optical signals has been increased year by year, and in recent years, optical pattern signals exceeding 40G are required. On the other hand, in the method of sampling by inputting the electrical clock signal C to the optical modulator 12 as described above, the clock waveform is greatly degraded due to a slight mismatch of impedance, and as a result, the RZ format obtained. There is a problem that the waveform of the waveform is greatly deteriorated and the jitter suppression effect is lowered.

  An object of the present invention is to solve this problem and provide an optical signal generator capable of generating a high-speed optical pattern signal with little pattern-dependent jitter and little waveform deterioration.

In order to achieve the above object, an optical signal generator according to claim 1 of the present invention comprises:
An optical pattern signal generator (21) for generating an optical pattern signal in NRZ format synchronized with an electrical clock signal;
An optical signal generator having a data format conversion unit (30) that reduces the pattern-dependent jitter by punching out the optical pattern signal with a clock pulse synchronized with the clock signal and converting it to an RZ-format optical pattern signal In
The data format conversion unit is
An optical clock pulse generator (31) that generates an optical clock pulse having a width narrower than one bit width of the optical pattern signal in synchronization with the clock signal;
An optical pattern signal in NRZ format emitted from the optical pattern signal generator and an optical clock pulse emitted from the optical clock pulse generator are received, and the optical pattern signal is received only while the optical clock pulse is incident. And an EA modulator (32) that passes through.

An optical signal generator according to claim 2 of the present invention is the optical signal generator according to claim 1,
The optical pattern signal is incident on one optical terminal of the EA modulator,
The optical clock signal is incident on the other optical terminal on the other optical terminal side of the EA modulator, and an optical pattern signal component emitted from the other optical terminal when the optical clock pulse is incident Is provided with a coupler (33) for emitting the light to an optical path different from the incident optical path of the optical clock pulse.

An optical signal generator according to claim 3 of the present invention is the optical signal generator according to claim 1,
The wavelength of the optical clock pulse is different from the wavelength of the optical pattern signal;
A combiner (36) for combining the optical clock pulse and the optical pattern signal to enter one optical terminal of the EA modulator;
It has a wavelength filter (37) for selectively emitting only the wavelength component of the optical pattern signal among the light emitted from the other optical terminal of the EA modulator.

Moreover, the optical signal generator of Claim 4 of this invention is an optical signal generator in any one of Claims 1-3,
It has means for varying the power and pulse width of the optical clock pulse incident on the EA modulator.

Moreover, the optical signal generator of Claim 5 of this invention is an optical signal generator in any one of Claims 1-4,
It has a pulse stretcher (40) which expands the pulse width of the optical pattern signal in the RZ format emitted from the EA modulator and converts it into the NRZ format.

Moreover, the optical signal generator of Claim 6 of this invention is an optical signal generator in any one of Claims 1-5,
The optical clock pulse generator is a reproduction mode-locked fiber laser.

  As described above, in the present invention, the optical clock pulse is applied to the EA modulator that receives the optical pattern signal to reduce the optical loss inside the EA modulator (this is referred to as a mutual absorption modulation effect), and the sampling of the optical pattern signal is performed. Therefore, waveform deterioration due to impedance mismatching such as an electric signal does not occur, and a high-speed optical pattern signal with less pattern-dependent jitter can be generated.

  Further, if the optical pattern signal is incident on one optical terminal of the EA modulator and the optical pulse signal is incident on the other optical terminal, the passing directions of the optical pattern signal and the optical pulse signal are opposite to each other. Even if both wavelengths are equal, they can be used, and there is no restriction by wavelength.

  Further, when the optical pattern signal and the optical pulse signal are used in the same passing direction, it can be dealt with by extracting the optical pattern signal from the output of the EA modulator with a wavelength filter.

  Also, by providing means for varying the power and pulse width of the optical pulse signal incident on the EA modulator, the output and pulse width of the optical pattern signal emitted from the EA modulator can be varied.

  If the optical pulse generator is composed of a reproduction mode-locked fiber laser, not only pattern jitter but also random jitter can be suppressed.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a configuration of an optical signal generator 20 to which the present invention is applied.

  The optical signal generator 20 includes an optical pattern signal generator 21, a clock signal generator 25, a data format conversion unit 30, and a pulse stretcher 40.

  The optical pattern signal generator 21 includes a laser light source 22 that emits laser light P0 having a predetermined wavelength and a substantially constant intensity, and a predetermined frequency of electricity (for example, as shown in FIG. 2A) by the clock signal generator 25. The pattern signal generator 23 for generating the pattern signal A in the NRZ format synchronized with the clock signal C of 40 GHz) and the intensity of the laser beam P0 emitted from the laser light source 22 are modulated with the pattern signal A, and the waveform (b) of FIG. ), And an optical modulator 24 that generates an optical pattern signal Pa in the NRZ format.

  The NRZ optical pattern signal Pa emitted from the optical modulator 24 includes jitter (phase fluctuation) generated depending on the pattern of the pattern signal A, as shown in FIG. ing. In this example, the clock signal generator 25 is included. However, the clock signal C input from the outside may be used.

  The data format conversion unit 30 receives this light pattern signal Pa, performs a punching process (sampling process of binary data) with a clock pulse synchronized with the clock signal C, and converts it into an RZ format signal, thereby converting the light pattern signal Pa. The pattern-dependent jitter included in is reduced.

  The data format conversion unit 30 synchronizes with the clock signal C, and generates an optical clock pulse generator 31 that generates an optical clock pulse Pc having a width narrower than one bit width of the optical pattern signal Pa as shown in FIG. And an EA (Electoro Absorption) modulator 32 that receives the optical pattern signal Pa and the optical clock pulse Pc and passes (punches) the optical pattern signal Pa only while the optical clock pulse Pc is incident. .

  Although the configuration example of the optical clock pulse generator 31 is not specifically described, for example, the optical pattern signal generator 21 may use the clock signal C instead of the pattern signal A for the optical modulator. In this case, since modulation is performed using the clock signal C, pattern dependent jitter does not occur in principle.

  However, when the clock signal C has random jitter, the emitted optical clock pulse Pc also includes random jitter. When the random jitter becomes a problem, the optical clock pulse generator 31 having an effect of suppressing the random jitter is used. For example, by using a reproduction mode-locked fiber laser, even if the random jitter of the clock signal is about 0.5 ps, the optical clock pulse Pc with the random jitter suppressed to about 0.1 to 0.01 ps is emitted. be able to.

  The reproduction mode-locked fiber laser is a known one described in, for example, Non-Patent Document 1 below, and details thereof will not be described here.

IEEE PHOTONICS TECNOLOGY LETTERS, VOL.11, NO.5, MAY 1999'Measurement of Timing Jitter and Pulse Energy Fluctuation of a PLLRegeneratively Mode-Locked Fiber Laser '

  The EA modulator 32 generally modulates the intensity of the input light using an electroabsorption effect in which the optical loss changes according to the electric field strength of the applied electric signal. A mutual absorption modulation effect is used in which the optical loss changes according to the intensity of the input light (in this case, an optical clock pulse).

  Note that when the mutual absorption modulation effect of the EA modulator 32 as described above is used, in a period in which the optical clock pulse Pc is not incident, the loss due to light absorption is large, and the optical pattern signal Pa is not passed. During the period in which the clock pulse Pc is incident, the bias voltage Vb is set at the operating point where the loss due to light absorption is reduced and the optical pattern signal Pa is passed. Since the above principle is used, the peak intensity of the optical clock pulse Pc is necessarily greater than the intensity of the optical pattern signal Pa.

  Further, as the method of incidence of the optical clock pulse Pc on the EA modulator 32, as shown in the example of FIG. 1, the other optical terminal 32b opposite to the one optical terminal 32a on which the optical pattern signal Pa is incident. Can be considered to be incident on the optical terminal through which the optical pattern signal Pa is incident.

  As shown in FIG. 1, when the optical pattern signal Pa is incident on one optical terminal 32a and the optical clock pulse Pc is incident on the other optical terminal 32b via the coupler 33, the optical clock pulse Pc and the optical pattern signal Pa. Since the optical clock pulses Pc are opposite to each other and there is no fear that the optical clock pulse Pc is emitted in the direction of the pulse stretcher 40, any wavelength can be used as the optical clock pulse Pc. However, in consideration of the effect that the component of the optical clock pulse Pc emitted from the optical terminal 32a is incident on the optical pattern signal generator 21 side, a coupler 34 is also inserted on the optical terminal 32a side, so that the optical pattern signal Pa is incident on the optical terminal 32a, and the component of the optical clock pulse Pc emitted from the optical terminal 32a is applied to the optical absorber 35 to be absorbed.

  By making the optical clock pulse Pc incident on the EA modulator 32 in this way, as shown in FIG. 2D, each bit data of the NRZ format optical pattern signal Pa (here, a pattern following 10100...). Sampling is performed to obtain an RZ-format optical pattern signal Pb.

  It is assumed that the phase of the optical clock pulse Pc with respect to the optical pattern signal Pa is adjusted by a delay unit (not shown) or the like so that the peak of the optical clock pulse Pc is aligned with the center of each bit of the optical pattern signal Pa.

  The RZ optical pattern signal Pb thus obtained is incident on the pulse stretcher 40, and the width of each pulse corresponding to the data 1 is expanded to a width equal to the clock cycle as shown in FIG. Thus, an optical pattern signal Pa ′ in the NRZ format is obtained.

As the pulse stretcher 40 used here, as disclosed in the above-mentioned Patent Document 1, the optical pattern signal Pb is incident with linearly polarized light having an angle with respect to two orthogonal principal axes F and S of the polarization maintaining fiber. Thus, a technique for expanding the pulse width by combining the component along the main axis F (high-speed axis) and the component along the main axis S (low-speed axis) on the emission end side can be adopted.
Alternatively, the incident light may be divided into two paths and multiplexed through different optical path lengths.

  As described above, in the optical signal generation device 20 according to the embodiment, the optical clock pulse Pc is given to the EA modulator 32 on which the optical pattern signal Pa is incident to reduce the optical loss inside the EA modulator 32 (this is mutually reduced). Since sampling is performed on the optical pattern signal Pa by the absorption modulation effect), waveform deterioration due to impedance mismatch such as an electric signal does not occur, and a high-speed optical pattern signal with little pattern-dependent jitter can be generated. it can.

  Here, the pulse stretcher 40 is used to obtain the optical pattern signal Pa ′ in the NRZ format, but the pulse stretcher 40 is omitted when the output required as the apparatus may be the optical pattern signal Pb in the RZ format. it can.

  In the data format conversion unit 30 of the above embodiment, the optical terminals for inputting the optical pattern signal Pa and the optical clock pulse Pc to the EA modulator 32 are reversed, but as shown in FIG. The pattern signal Pa and the optical clock pulse Pc may be combined by the multiplexer 36 and may be incident on one optical terminal 32 a of the EA modulator 32. However, in this case, the optical pattern signal Pa and the optical clock pulse Pc are simultaneously emitted to the other optical terminal 32b, and the two lights cannot be distinguished. Therefore, there is also a configuration in which the wavelength of the optical clock pulse Pc is changed with respect to the optical pattern signal Pa, and the wavelength component of the optical pattern signal Pa is extracted by the wavelength filter 37 from the light emitted from the other optical terminal 32b. Can be adopted.

  Further, simply, as shown in FIGS. 4A and 4B, the coupler is configured such that the incident angle of the optical clock pulse Pc with respect to the EA modulator 32 is inclined with respect to the incident angle of the optical pattern signal Pa. The optical pattern signal Pc can be sampled without using 33, 34, the multiplexer 36, the wavelength filter 37, and the like.

  When the optical pattern signal Pa is sampled by applying the optical clock pulse Pc to the EA modulator 32, the intensity and pulse width of the optical pattern signal Pb emitted in the RZ format are the same as the intensity and pulse width of the optical clock pulse Pc. Therefore, when it is necessary to vary the intensity and pulse width of the optical pattern signal Pb, the pulse width varying means 38 and the power varying means 39 may be provided as shown in FIG. By controlling the pulse width varying means 38 and the power varying means 39, the output of the optical pattern signal Pb emitted from the EA modulator 32 and the pulse width can be varied within a predetermined range.

Configuration diagram of an embodiment of the present invention Operation explanatory diagram of the embodiment The figure which shows another structural example of the principal part of embodiment The figure which shows another structural example of the principal part of embodiment The figure which shows another structural example of the principal part of embodiment Configuration diagram of conventional equipment

Explanation of symbols

  21 …… Optical pattern signal generator, 22 …… Laser light source, 23 …… Pattern signal generator, 24 …… Optical modulator, 25 …… Clock signal generator, 30 …… Data format converter, 31 …… Optical Clock pulse generator, 32... EA modulator, 33, 34... Coupler, 35... Optical absorber, 36 .. multiplexer, 37 .. wavelength filter, 38. Power variable means, 40 ... Pulse stretcher

Claims (6)

An optical pattern signal generator (21) for generating an optical pattern signal in NRZ format synchronized with an electrical clock signal;
An optical signal generator having a data format conversion unit (30) that reduces the pattern-dependent jitter by punching out the optical pattern signal with a clock pulse synchronized with the clock signal and converting it to an RZ-format optical pattern signal In
The data format conversion unit is
An optical clock pulse generator (31) that generates an optical clock pulse having a width narrower than one bit width of the optical pattern signal in synchronization with the clock signal;
An optical pattern signal in NRZ format emitted from the optical pattern signal generator and an optical clock pulse emitted from the optical clock pulse generator are received, and the optical pattern signal is received only while the optical clock pulse is incident. And an EA modulator (32) that passes the light. The optical pattern signal is incident on one optical terminal of the EA modulator,
On the other optical terminal side of the EA modulator, the optical clock pulse is incident on the other optical terminal, and an optical pattern signal component emitted from the other optical terminal when the optical clock pulse is incident 2. An optical signal generator according to claim 1, further comprising a coupler (33) for emitting the light to an optical path different from the optical path of the optical clock pulse. The wavelength of the optical clock pulse is different from the wavelength of the optical pattern signal;
A combiner (36) for combining the optical clock pulse and the optical pattern signal to enter one optical terminal of the EA modulator;
2. A wavelength filter (37) that selectively emits only the wavelength component of the optical pattern signal out of the light emitted from the other optical terminal of the EA modulator. The optical signal generator described.   4. The optical signal generator according to claim 1, further comprising means for varying the power and pulse width of an optical clock pulse incident on the EA modulator.   5. The pulse stretcher (40) according to any one of claims 1 to 4, further comprising: a pulse stretcher (40) for widening a pulse width of an RZ-format optical pattern signal emitted from the EA modulator and converting it into an NRZ format. The optical signal generator described.   6. The optical signal generator according to claim 1, wherein the optical clock pulse generator is a reproduction mode-locked fiber laser.

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