CN103326782A - Method for improving multi-carrier light source carrier-to-noise ratios - Google Patents

Abstract

The invention discloses a method for improving multi-carrier light source carrier-to-noise ratios. The method includes the steps that S1, a time delay interferometer is arranged at the back of a light amplifier; S2, signals transmitted into the time delay interferometer are divided into two paths with the same strength, wherein one path is a time delay path used for adding time delay to the signals, and the other path is a phase modulation path and used for adding phase positions to the signals; S3, the time delay path and the phase modulation path are combined, and constructive interference at center frequency of all subcarriers and destructive interference at midpoint frequency between the adjacent subcarriers are achieved by selecting suitable time delay and phase shift. The method is suitable for multi-carrier light sources or optical frequency combs with a loop structure and is also suitable for multi-carrier light sources or optical frequency combs with a non-loop structure, the purpose of restraining amplified spontaneous emission noise produced by the light amplifier is achieved by using the time delay interferometer, the carrier-to-noise ratios can be improved by 10-15dB, and therefore technical support can be provided for practicability of network communication systems with higher speed rates.

Description

A kind of method that improves the multicarrier light source carrier-to-noise ratio

Technical field

The present invention relates to technical field of optical fiber communication, relate in particular to a kind of method that improves the multicarrier light source carrier-to-noise ratio.

Background technology

Along with increasing rapidly of global broadband services flow, particularly video class is professional such as SDTV(Standard Definition Television, the clear TV of SD), HDTV(High Definition Television, high definition television), Online Game(game on line), VOD(Video On Demand, video on demand techniques) etc. appearance has brought huge pressure to transport channel capacities.At present successful commercialization of 100Gb/s Ethernet system, the urgent task of next generation communication are exactly towards the too Ethernet transmission development of bit (Tb/s).At present in realizing the scheme of the high capacity transmission system of bit too, be a very competitive scheme based on the too bit transfer system of multicarrier light source.With WDM(Wavelength division multiplexing, wavelength division multiplexing) or DWDM(Dense Wavelength Division Multiplexing, dense wavelength division multiplexing system) compare, the laser that does not need usage quantity huge (hundreds of) based on the system of multicarrier light source, simultaneously, because the subcarrier of multicarrier light source all is to be produced by same seed light source, consistency of performance between the subcarrier is fine, there is not frequency drift between the carrier wave, the interval locks fully, can utilize these characteristics of multicarrier light source to realize super channel (super-channel) transmission, reach higher spectrum efficiency.

At present, being used for too, the Frequency Locking multicarrier light source implementation method of bit transfer system mainly contains: electrooptic modulator single depth modulation and circulation frequency shifter.Based on single MZM(Mach-Zehnder Modulator, Mach-Zehnder modulators), PM(Phase Modulator, phase-modulator) or the multicarrier light source that produces of the single depth modulation of the MZM+PM of cascade have good stability, and the frequency interval tunability between its subcarrier is good, but the number of sub carrier wave that utilizes this mode to produce is less, generally about 10, many can reach 30, and the carrier-to-noise ratio of light source is about 15～20dB.The circulation frequency shifter is based on IQM(I/Q Modulator, the IQ modulator), the circular modulating of the circulus of MZM or PM modulator formation, its advantage is not need high driving voltage, has the ability that produces the big figure subcarrier, can control simultaneously wavelet number and the centre frequency of output, flatness is better; But it need to be in loop comes energy loss in the compensation loop with image intensifer, so just inevitably can introduce ASE(amplified spontaneous emission, amplified spontaneous emission) noise, and the increase along with cycle-index, noise is accumulation constantly, causes the carrier-to-noise ratio of the final output of light source to reduce.

The carrier-to-noise ratio of the multicarrier light source that disclosed employing circulation frequency shifter produces in the document at present can only satisfy PDM(Polarization Division Multiplexing about 20dB, partially divide multiplexing)-QPSK(quarternary phase-shift keying (QPSK) signal) transmission requirement.Yet, in bit transfer system too, transmitting terminal generally need to adopt the PDM-16QAM(quadrature amplitude modulation) even the high order modulation pattern of PDM-64QAM form, respectively at 20dB and more than the 29dB, corresponding light source carrier-to-noise ratio is 27dB and 36dB to the requirement of light source light signal to noise ratio for they.

In sum, prior art still can't realize increasing substantially carrier-to-noise ratio, reduces simultaneously the ASE noise of introducing.

Summary of the invention

The technical problem that (one) will solve

For defects, the technical problem to be solved in the present invention is how in the amplified spontaneous emission noise that step-down amplifier is introduced, and increases substantially carrier-to-noise ratio.

(2) technical scheme

For addressing the above problem, the invention provides a kind of method that improves the multicarrier light source carrier-to-noise ratio, may further comprise the steps:

S1, the time delay interferometer is set after image intensifer;

S2, the signal that incides described time delay interferometer are divided into the identical two-way of intensity, and one the tunnel is the time delay road, are used for the signal additional time delay, and another road is the phase modulation road, are used for the signal additive phase;

S3, described time delay road and described phase modulation road merge, and realize that by selecting suitable time delay and phase shift interfering mutually between long and adjacent sub-carrier the midpoint frequency place to interfere to all subcarrier centre frequency places disappears mutually.

Further, described time delay interferometer is Mach-Zehnder structure.

Further, the light signal of described time delay road output is

Wherein E (ω) is the frequency domain components of incident optical signal, and ω is the angular frequency of light signal, and τ is the time delay size on time delay road described in the described time delay interferometer, and τ=1/f_s, f wherein_sBe the carrier frequency interval.

Further, the light signal of described phase modulation road output is

Wherein

Phase shift for described phase modulation road.

Further, the described condition of growing mutually in all subcarrier centre frequency places realization interference is

Wherein

Be the phase difference on described time-delay road and described phase modulation road, k is nonnegative integer.

Further, the described condition that the realization interference of midpoint frequency place disappears mutually between adjacent sub-carrier is

Further, described method is applicable to multicarrier light source or the frequency comb of loop structure.

Further, described method also is applicable to multicarrier light source or the frequency comb of non-loop structure.

(3) beneficial effect

The invention provides a kind of method that improves the multicarrier light source carrier-to-noise ratio, the method both had been applicable to multicarrier light source or the frequency comb of loop structure, also be applicable to multicarrier light source or the frequency comb of non-loop structure, use the time delay interferometer to reach the purpose of the amplified spontaneous emission noise that suppresses the image intensifer generation, improve carrier-to-noise ratio, can improve 10-15dB, thereby provide technical support for the network communicating system of higher rate is practical, and better network communication quality and better network reliability are provided.

Description of drawings

Fig. 1 is a kind of flow chart of steps that improves the method for multicarrier light source carrier-to-noise ratio of the present invention;

Fig. 2 is the multicarrier light source schematic diagram that method provided by the invention is applied in loop structure;

Fig. 3 is the multicarrier light source schematic diagram that method provided by the invention is applied in non-loop structure;

Fig. 4 is the spectrogram of exporting behind the broad spectrum light source process time delay interferometer;

The spectrogram of the multicarrier light source output of the circulation frequency shifter structure of the time delay interferometer that do not use the present embodiment and provide is provided Fig. 5;

The spectrogram of the multicarrier light source output of the circulation frequency shifter structure of the time delay interferometer that uses the present embodiment and provide is provided Fig. 6.

Embodiment

Below in conjunction with drawings and Examples, the specific embodiment of the present invention is described in further detail.Following examples are used for explanation the present invention, but are not used for limiting the scope of the invention.

A kind of method that improves the multicarrier light source carrier-to-noise ratio is provided in the embodiment of the invention, and idiographic flow may further comprise the steps as shown in Figure 1:

Step S1, the time delay interferometer is set after image intensifer, wherein the time delay interferometer is Mach-Zehnder structure.

The method that the present embodiment provides is not only applicable to multicarrier light source or the frequency comb of loop structure, also be applicable to multicarrier light source or the frequency comb of non-loop structure, shown in Fig. 2 and 3, wherein Fig. 2 is the multicarrier light source of loop structure, and Fig. 3 is the multicarrier light source of non-loop structure (being cascade structure).

Modulator group among Fig. 2 and Fig. 3 can be the cascade of an IQ modulator or N different modulating device.U_Bias1, U_Bias2U_BiasNBe the bias voltage of N different modulating device, U_RF1, U_RF2U_RFNRadio-frequency driven voltage for N different modulating.Generally all can use image intensifer to come the compensating signal Energy Damage and carrier wave is amplified, but in amplification process, can introduce the ASE noise.In the multicarrier light source generation scheme of Fig. 2 and two kinds of structures shown in Figure 3, all be after image intensifer, to place a MZ(Mach-Zehnder) the time delay interferometer of structure, suppress the ASE noise that image intensifer is introduced, this scheme can make the carrier-to-noise ratio of light source output have greatly improved, and its principle has been to utilize the frequency domain of wide spectrum light source to interfere.

Step S2, the signal that incides the time delay interferometer are divided into the identical two-way of intensity, and one the tunnel is the time delay road, are used for the signal additional time delay, and another road is the phase modulation road, are used for the signal additive phase.

In MZ time delay interferometer, signal is divided into two-way, wherein leads up to one section line of time delay, and its time delay size is the inverse at sub-carrier frequencies interval, and the phase place of signal is adjusted on another road by certain mode.In Fig. 2 and structure shown in Figure 3, U_DelayBe used for delay of control, U_PhaseBe used for adjusting phase shift, the two ways of optical signals through time delay and phase shift is combined again respectively.At last, the light signal of time delay interferometer output is

The signal light intensity at different frequency place is

Wherein the light signal of time delay road output is in the formula (1)

The light signal of phase modulation road output is

E (ω) is the frequency domain components of incident optical signal, and ω is the angular frequency of light signal, and τ is the time delay size on time delay road in the time delay interferometer, and τ=1/f_s, f wherein_sBe the carrier frequency interval, wherein

Phase shift for the phase modulation road.

Step S3, time delay road and phase modulation road merge, and realize that by selecting suitable time delay and phase shift interfering mutually between long and adjacent sub-carrier the midpoint frequency place to interfere to all subcarrier centre frequency places disappears mutually.

For the multicarrier light source that adds MZ time delay interferometer, at the phase difference of n sub-centre carrier frequency place two branch roads be

F wherein₀Be the centre frequency of seed light source, f_sBe the frequency of adding radiofrequency signal, i.e. difference on the frequency between adjacent sub-carrier.

If the phase difference on time-delay road and phase modulation road

Light at these frequency places will interfere longly mutually so, and satisfies

The light at ω place will interfere mutually and disappear.For the situation of broad spectrum light source incident, can produce periodic interference peaks on the output spectrum behind its process time delay interferometer, as shown in Figure 4.

By choosing suitable time delay τ and phase shift

Guarantee

Thereby the interference that can realize each subcarrier centre frequency place is long mutually, if choose τ=1/f_s, so

Only need to regulate the phase shift U of MZ interferometer_Phase, so that

(m is integer), the centre frequency place of each subcarrier will realize interfering long mutually so.

Accordingly, the Frequency point ω ' between two subcarriers=2 π f₀+ (2n+1) π f_sThe place has

Because before satisfied to arranging of phase shift

SoLocate to occur interfering disappearing mutually at ω '.Utilize this characteristic, can be used for comb-type light source is carried out filtering, suppress the ASE noise, and effect promoting is obvious.

Fig. 5 and Fig. 6 are the Contrast on effects of having verified the method that the present embodiment provides in the multicarrier light source based on circulation frequency shifter structure (multicarrier light source that belongs to loop structure), wherein the multicarrier light source output of the circulation frequency shifter structure of the time delay interferometer that do not use the present embodiment and provide is provided Fig. 5, and the multicarrier light source output of the circulation frequency shifter structure of the time delay interferometer that used the present embodiment and provide is provided Fig. 6.

To sum up, the method of the raising carrier-to-noise ratio that the present embodiment provides both had been applicable to multicarrier light source or the frequency comb of loop structure, also be applicable to multicarrier light source or the frequency comb of non-loop structure, use the time delay interferometer to reach the purpose of the amplified spontaneous emission noise that suppresses the image intensifer generation, improve carrier-to-noise ratio, can improve 10-15dB, thereby provide technical support for the network communicating system of higher rate is practical, and better network communication quality and better network reliability are provided.

Above execution mode only is used for explanation the present invention; and be not limitation of the present invention; the those of ordinary skill in relevant technologies field; in the situation that do not break away from the spirit and scope of the present invention; can also make a variety of changes and modification; therefore all technical schemes that are equal to also belong to category of the present invention, and scope of patent protection of the present invention should be defined by the claims.

Claims (8)

Translated fromChinese

1.一种提高多载波光源载噪比的方法，其特征在于，所述方法具体包括：1. A method for improving the carrier-to-noise ratio of a multi-carrier light source, characterized in that, the method specifically comprises:S1、在光放大器之后设置时延干涉仪；S1, setting a time-delay interferometer after the optical amplifier;S2、入射到所述时延干涉仪的信号被分成强度相同的两路，一路为时延路，用于对信号附加时延，另一路为调相路，用于对信号附加相位；S2. The signal incident to the time-delay interferometer is divided into two paths with the same intensity, one is a time-delay path for adding time delay to the signal, and the other path is a phase modulation path for adding phase to the signal;S3、所述时延路和所述调相路合并，通过选择合适的时延和相移实现对所有子载波中心频率处干涉相长和相邻子载波间中点频率处干涉相消。S3. The time delay circuit and the phase modulation circuit are combined, and the interference construct at the center frequency of all subcarriers and the interference cancellation at the midpoint frequency between adjacent subcarriers are realized by selecting an appropriate time delay and phase shift.2.如权利要求1所述的方法，其特征在于，所述时延干涉仪为马赫-曾德尔结构。2. The method according to claim 1, wherein the time-delay interferometer is a Mach-Zehnder structure.3.如权利要求1所述的方法，其特征在于，所述时延路输出的光信号为其中E(ω)为入射光信号的频域分量，ω为光信号的角频率，τ为所述时延干涉仪中所述时延路的时延大小，且τ＝1/f_s，其中f_s为载波频率间隔。3. The method according to claim 1, wherein the optical signal output by the time delay path is Where E(ω) is the frequency domain component of the incident optical signal, ω is the angular frequency of the optical signal, τ is the time delay of the time delay path in the time delay interferometer, and τ=1/f_s , where f_s is the carrier frequency interval.4.如权利要求1所述的方法，其特征在于，所述调相路输出的光信号为

其中

为所述调相路的相移。4. The method according to claim 1, wherein the optical signal output by the phase modulation circuit is

in

is the phase shift of the phase modulation circuit.5.如权利要求1所述的方法，其特征在于，所述步骤S3中选择合适的时延和相移具体包括：在所有子载波中心频率处实现干涉相长的条件是

其中

为所述延时路与所述调相路的相位差，k为非负整数。5. The method according to claim 1, characterized in that, selecting appropriate time delay and phase shift in the step S3 specifically comprises: the condition for realizing interferometric constructivity at all subcarrier center frequencies is

in

is the phase difference between the delay circuit and the phase modulation circuit, and k is a non-negative integer.6.如权利要求1所述的方法，其特征在于，所述步骤S3中选择合适的时延和相移具体包括：在相邻子载波中心频率处实现干涉相消的条件是

6. The method according to claim 1, wherein selecting an appropriate time delay and phase shift in the step S3 specifically comprises: the condition for realizing interference cancellation at the center frequency of adjacent subcarriers is

7.如权利要求1所述的方法，其特征在于，所述方法适用于环路结构的多载波光源或光频梳。7. The method according to claim 1, wherein the method is applicable to a multi-carrier light source or an optical frequency comb with a loop structure.8.如权利要求1所述的方法，其特征在于，所述方法还适用于非环路结构的多载波光源或光频梳。8. The method according to claim 1, characterized in that the method is also applicable to multi-carrier light sources or optical frequency combs with non-loop structures.

Images