WO2013107165A1

WO2013107165A1 - Deflection detection method and system for output signals of coherent optical receiver

Info

Publication number: WO2013107165A1
Application number: PCT/CN2012/078638
Authority: WO
Inventors: 朱亚敏
Original assignee: 中兴通讯股份有限公司
Priority date: 2012-01-16
Filing date: 2012-07-13
Publication date: 2013-07-25
Also published as: CN102546026A; CN102546026B

Abstract

A deflection detection method and system for the output signals of a coherent optical receiver. The deflection detection method comprises: normalizing the sampling values of the output signals of a coherent optical receiver; pairwise multiplying of all the normalized output signals, and integral averaging of the pairwise multiplying results in a signal cycle; and solving the integral averaging result to obtain the deflection amount between the output signals. The solution can achieve deflection detection for output signals of a coherent optical receiver.

Description

Method and system for detecting skew of output signal of coherent optical receiver

Technical field

The present invention relates to the field of optical fiber communication, and in particular to a method and system for detecting skew of an output signal of a coherent optical receiver.

Background technique

With the rapid development of optical devices and microwave devices in recent years, coherent optical communication technology has become a hot spot in optical communication research. Among them, the coherent optical receiver is one of the most important optical devices in coherent optical communication. The coherent optical receiver uses optical coherent demodulation, and its detection signal contains the amplitude and phase information of the transmitted signal, which improves the receiving sensitivity of the conventional optical receiver, and is widely used in 40 Gb/s and higher speed and large-capacity light. In the transmission system.

In the 100G transmission system using the PM-QPSK modulation method, the front section of the coherent optical receiver obtains two polarized lights after polarization separation, and then optically demodulates the two polarized lights through two 90's. The mixer mixes to get four component outputs. However, in the coherent demodulation process, the phase deviation between the four output signals is caused by the different path paths through which the four outputs pass. The magnitude of the skew is mainly determined by the device characteristics and the link traces, and the change with the environment is small. However, there is no technical solution for how to detect the skew of the four signals. Summary of the invention

In view of the above, it is a primary object of the present invention to provide a method and system for detecting a skew of an output signal of a coherent optical receiver, which can solve the problem of the inability to detect the amount of skew of the output signal of the coherent optical receiver in the prior art.

In order to achieve the above object, the technical solution of the present invention is achieved as follows:

The invention provides a skew detection method for an output signal of a coherent optical receiver, comprising: normalizing a sample value of an output signal of a coherent optical receiver;

Multiplying the normalized output signals by two and two, and integrating and averaging the two-two multiplied results in one signal period; The result of averaging the integrals is solved to obtain the amount of skew between the output signals of the respective channels. Preferably, after the skew amount is obtained, the method further includes: performing skew compensation on the output signals of the respective channels according to the skew amount.

Preferably, the output signal includes four analog electrical signals; the method further includes:

The four analog electrical signals are converted into corresponding four digital electrical signals, and the sample values of the four digital electrical signals are normalized.

Preferably, the coherent optical receiver outputs the four analog electrical signals, including:

The coherent optical receiver divides the received one signal light and one local oscillator light into one X-direction and one Y-direction polarized light signal;

The polarized light signal of the signal light in the X direction and the polarized light signal of the local oscillator light are mixed by 90 degrees to obtain two orthogonal optical signals in the X direction; and the polarized light signal of the signal light in the Y direction is obtained. After 90-degree mixing with the polarized light signal of the local oscillator, two orthogonal optical signals in the Y direction are obtained; two orthogonal optical signals in the X direction and two orthogonal optical signals in the Y direction are obtained. The photoelectric conversion is performed to obtain a corresponding four-way analog electrical signal.

The present invention also provides a skew detection system for a coherent optical receiver output signal, comprising: a coherent optical receiver, an analog to digital converter (ADC), and a digital signal processing unit;

The coherent optical receiver is configured to: receive signal light and local oscillator light, and output a signal after coherent reception;

The ADC is configured to: acquire and output a sample value of the output signal of the coherent optical receiver; the digital signal processing unit is configured to: receive a sample value of the output signal, and perform the following processing: Normalizing the sample values of the signals; multiplying the normalized output signals by two and two, and integrating and averaging the two-two multiplied results in one signal period; The results of the averaging of the integrals are solved to obtain the amount of skew between the output signals of the respective channels.

Preferably, the system further comprises: a compensation unit, configured to: perform skew compensation on the output signals of the respective channels according to the skew amount.

Preferably, the coherent optical receiver comprises: a polarization beam splitter (PBS), a 90 degree mixer and a photoelectric converter; wherein: The PBS is configured to divide the received one signal light and one local oscillator light into one X-direction and one Y-direction polarized light signal, and output the same to the 90-degree mixer;

The 90-degree mixer is configured to: after the polarized light signal of the signal light in the X direction and the polarized light signal of the local oscillator light are mixed by 90 degrees, obtain two orthogonal optical signals in the X direction; And performing a 90-degree mixing of the polarized light signal of the signal light in the Y direction and the polarized light signal of the local oscillator light to obtain two orthogonal optical signals in the Y direction; and outputting the four optical signals to the photoelectric conversion The photoelectric converter is configured to: photoelectrically convert the four optical signals to obtain corresponding four analog electrical signals, and output the signals to the ADC.

Preferably, the ADC is configured to: perform analog-to-digital conversion on the four analog electrical signals to obtain a sample value of the corresponding four digital electrical signals.

Preferably, the system further comprises: a laser, configured to: generate the signal light and the local oscillator light, and output the light to the coherent optical receiver.

The skew detection method and system of the coherent optical receiver according to the embodiment of the present invention introduces a digital signal processing unit, which uses a process of normalization processing, integral averaging, etc., and can accurately calculate a coherent receiver, a PCB trace, and a signal pass. The cable is biased into the ADC. In addition, the digital signal processing unit makes the implementation of the skew calculation and compensation algorithm more convenient and less expensive. BRIEF abstract

1 is a flow chart of a skew detection method for an output signal of a coherent optical receiver according to an embodiment of the present invention; FIG. 2 is a block diagram of a skew detection system for an output signal of a coherent optical receiver;

Figure 3 is a schematic diagram showing the internal structure of a coherent optical receiver. Preferred embodiment of the invention

The technical solutions of the present invention are further elaborated below in conjunction with the accompanying drawings and specific embodiments.

As shown in FIG. 1, the skew detection method for the output signal of the coherent optical receiver of the present invention includes: Step 101: Normalize the sample value of the output signal of the coherent optical receiver.

Step 102, multiplying the normalized output signals by two and two, and in one signal week During the period, the results of the two-two multiplication are integrated and averaged; the signal period here refers to the signal period corresponding to the signal obtained after multiplication.

Step 103: Solving the result of averaging the points to obtain the amount of skew between the output signals of the respective channels.

During this skew detection process:

The output signal of the coherent optical receiver includes four analog electrical signals. After converting four analog electrical signals into corresponding four digital electrical signals, the sampled values of the four digital electrical signals are normalized.

After the skew amount is obtained, the output signal of each channel is compensated by the interpolation algorithm according to the skew amount, which is implemented in the prior art, and is not described here.

In addition, the process of outputting signals by a coherent optical receiver includes:

The coherent optical receiver separates the received one signal light and one local oscillator light into one X-direction and one Y-direction polarized light signal;

The polarized light signal of the signal light in the X direction and the polarized light signal of the local oscillator light are mixed by 90 degrees to obtain two orthogonal optical signals in the X direction; and the polarized light signal of the signal light in the Y direction is After the vibrating polarized light signal is mixed by 90 degrees, two orthogonal optical signals in the Y direction are obtained;

The two orthogonal optical signals in the X direction and the two orthogonal optical signals in the Y direction are photoelectrically converted to obtain corresponding four analog electrical signals and output.

The above method will be specifically described below with reference to Figs. 2 and 3.

First, a laser (Integrable Tunable Laser Assembly, ITLA for short) is used as a signal source to generate signal light (Signal), and another laser (ITLA) is used to generate local oscillator (LO), signal light and local oscillator light. Access to the coherent optical receiver.

In order to more clearly illustrate the skew detection process of the present invention, here:

The signal light is expressed as: exp (i3⁄4 + (0) ( 1 ) ; The local oscillator is expressed as: exp (i3⁄4/ + .(0) ( 2 ). Where is the frequency of the signal light signal, indicating the local oscillator The frequency of the optical signal, (0 indicates the phase of the signal optical signal, and 6U0 indicates the phase of the local optical signal. The coherent optical receiver processes the signal light signal and the local oscillator light signal as shown in Figure 3: Polarization Beam Splitter (PBS):

After an optical signal enters the PBS, it is divided into two polarized optical signals with orthogonal polarization states. For the convenience of subsequent description, it is recorded as a polarized light signal in the X direction and a polarized light signal in the Y direction. Then the signal light signal is divided into Xc and Yc whose polarization states are orthogonal; the local oscillator signal is divided into Xlo and Ylo which are orthogonal to the polarization state, and the PBS outputs four optical signals: Xc, Yc, Xlo, Ylo.

90 degree mixer section:

The input two-direction polarized light signals (Xc and Xlo) in the X direction are subjected to 90-degree coherent mixing, and the input two-direction polarized light signals (Yc and Ylo) are subjected to 90-degree coherent mixing.

The polarized light signal in the X direction after mixing includes: a polarized light signal XQ of the signal light and a polarized light signal XI of the local oscillator light, XQ and XI are orthogonal; the polarized light signal in the Y direction includes: a polarized light signal YQ of the signal light and The polarized light signals YI, YQ of the local oscillator are orthogonal to YI.

After mixing, the four optical signals XQ, XI, YQ and YI are output.

Photoelectric converter part:

The four channels of the mixed optical signals are photoelectrically converted to obtain four analog electric signals, which are outputs, that is, four output signals of the coherent optical receiver according to the present invention.

In order to implement the skew detection method, the present invention increases the operation of the ADC and the digital signal processing unit as follows:

First, an analog-to-digital converter (ADC) performs analog-to-digital conversion on four analog electrical signals output by the coherent optical receiver, including: performing sampling and quantization processing, and finally obtaining sample values of four digital electrical signals.

Based on formula (1) and formula (2), if the four signals output by the coherent optical receiver are in an ideal state, that is, no skew occurs, the corresponding sample values of the four digital electrical signals can be expressed as:

XI: Re exp ]{{ω _α -ω _1ο )ί + θ _ΰ {ί)-θ _1ο {ί)} ( 3.1 )

XQ: lm{^ exp Μω _α - ω _1ο )t + θ _α (t) -0 _lo {t)} (3.2) YI: Re{y ₂ exp - ω _1ο ) ί + θ _α (ί) - θ _1ο (ί)} ( 3.3 )

YQ: lm{y ₂ exp Μω _α -ω _1ο )ΐ + θ _α {ΐ)-θ _1ο {ΐ)} ( 3.4 ) where ₂ is the difference in the split ratio of the polarized light signals in the X direction and the Υ direction of the PBS output. , It can be considered that and ₂ is a real number; in addition, in a relatively short period of time, it can be considered

Αω=ω _€ -ω _1ο , Δ = — _ο () Α Another ¹ J is - often.

However, in practical applications, there is a skew between the four signals output by the coherent optical receiver, so the above formulas (3.1), (3.2), and (3.3) (3.4) need to be corrected. Specifically, the six skewness between the two signals is set, but the three skew amounts are redundant, so any three skew amount pairs (3.1), (3.2), (3.3) (3.4) Amendment.

For example, the amount of skew between the XI and XQ 4 Jia is provided, the amount of skew between the YI and YQ is _δ Ί, ΥΙ skew amount between 4 and XI. Then, when γ ₂ , Α ω = ω _€ - ω ₁₀ . ΑΘ = θ _ε (ή - θ _1ο (ή^ is a constant, the corrected value of the four-way digital electrical signal can be expressed as:

XI: r, ∞s(Acot + Ae) (4.1)

XQ: γ^m{^ωt + ^θ+δ,) (4.2 )

YI: r ₂ cos(A ot + A0+S ₃ ) (4.3)

YQ: r ₂ sm(A ot + A0+S ₂ + S ₃ ) (4.4 ) Then, the digital signal processing unit performs skew detection based on the sample values of the four digital electrical signals. The specific process is as follows:

1. Normalize the sample values of the four digital electrical signals to obtain:

XI: cos(A<3⁄4i + A(9) (5.1 )

XQ: smiA ot + AO+S,) (5.2)

YI: cos(AiW + A<9+ ₃ ) (5.3)

YQ: sin(Aox + ΑΘ + S ₂ + S ₃ ) (5.4)

2. Multiply (5.1), (5.2), (5.3), and (5.4) by two and two, and perform integration and averaging in one signal period, that is, [0, T]. Where T = .

Αω

It should be pointed out that after multiplying two pairs and performing integral averaging, up to six nonlinear equations can be obtained, but only three skew amounts are used in the skew detection process. Therefore, six nonlinear equations Three of the programs are redundant, and only need to solve with any three of the six nonlinear equations to get the value of the three skew amounts.

For example, multiply (5.1) by (5.2) and integrate the averaging in the [0, T] interval to obtain a nonlinear equation:

1 τ

Al=—J _o sin(2Airf + 2ΑΘ+δ)άί+- where τ = .

, Αω.

Since the laser can output lasers with substantially the same frequency, phase and running direction, the frequency of the local oscillator signal is approximately equal to the frequency of the signal light signal, that is, Δ« is very small, and in the case of a relatively large ,, formula (6) Approximate equal to: Obtain a nonlinear equation:

_Λ1 — sin

(7) Similarly, multiply (5.3) and (5.4), and average in the interval [0, T] to obtain a non-linear

Sin(^ ₂ )

A2= (8)

2

For the same reason, multiply (5.1) and (5.4), and obtain the nonlinear equation by integrating the average in the [0, T] interval:

The above three nonlinear equations form a system of equations, and the solution can be obtained. After δ ₂ . δ ₃ obtains the skew amount, the skew compensation can be performed by the interpolation method.

In order to achieve the above skew detection method, the present invention also proposes a skew detection system, as shown in FIG. 2, including: a coherent optical receiver, an ADC, and a digital signal processing unit; wherein: a coherent optical receiver for receiving signal light and The local oscillator, and outputs the signal after coherent reception; the ADC is used to obtain the sample value of the output signal and output; a digital signal processing unit, configured to receive a sample value of the output signal, and perform the following processing: normalizing the sample value of the output signal;

Multiplying the normalized output signals by two and two, and integrating and averaging the results of the two-two multiplication in one signal period;

The result of averaging the integrals is solved to obtain the amount of skew between the output signals of the respective channels.

Among them, the digital signal processing unit can use DSP or FPGA.

As shown in FIG. 2, the system further includes: a compensation unit, configured to perform skew compensation on each output signal according to the skew amount interpolation algorithm.

A coherent optical receiver includes: a polarization beam splitter (PBS), a 90 degree mixer, and a photoelectric converter;

PBS is configured to separately divide the received one-way signal optical signal and one local-acoustic optical signal into one X-direction and one-way Y-direction polarized light signal, and output the same to the 90-degree mixer;

a 90-degree mixer for mixing a polarized light signal of the X-direction signal light with a polarized light signal of the local oscillator light by 90 degrees to obtain two orthogonal optical signals in the X direction; and The polarized light signal of the signal light and the polarized light signal of the local oscillator light are mixed by 90 degrees to obtain two orthogonal optical signals in the Y direction, and the four optical signals are output to the photoelectric converter;

The photoelectric converter is used for photoelectrically converting four optical signals to obtain corresponding four-way analog electrical signals, and outputs the signals to the ADC.

The ADC is used to perform analog-to-digital conversion on four analog electrical signals to obtain the sample values of the corresponding four-way digital electrical signals.

The system also includes: a laser for generating signal light and local oscillator light, and outputting to the coherent optical receiver.

The above is only the preferred embodiment of the present invention and is not intended to limit the scope of the present invention.

Industrial Applicability The method and system for detecting skew of a coherent optical receiver according to an embodiment of the present invention introduces a digital signal The unit, using normalization processing, integral averaging, etc., can accurately calculate the deflection of the coherent receiver and PCB traces and signals connected to the ADC through the cable. In addition, the digital signal processing unit makes the implementation of the skew calculation and compensation algorithm more convenient and less costly.

Claims

Claim

1. A method for detecting skew of an output signal of a coherent optical receiver, comprising:

Normalizing the sample value of the output signal of the coherent optical receiver;

Multiplying the normalized output signals by two and two, and integrating and averaging the two-two multiplied results in one signal period;

2. The method of detecting a skew of an output signal of a coherent optical receiver according to claim 1, wherein, after obtaining the skew amount, the method further comprises: interpolating the respective paths according to the skew amount The output signal is skew compensated.

The method for detecting a skew of an output signal of a coherent optical receiver according to claim 1 or 2, wherein the output signal comprises four analog electrical signals; the method further comprising:

4. The method of detecting a skew of an output signal of a coherent optical receiver according to claim 3, wherein the outputting the four-way analog electrical signal by the coherent optical receiver comprises:

5. A skew detection system for a coherent optical receiver output signal, comprising: a coherent optical receiver, an analog to digital converter (ADC), and a digital signal processing unit;

The coherent optical receiver is configured to: receive signal light and local oscillator light, and output after coherent reception Signal

6. The skew detection system of the output signal of the coherent optical receiver according to claim 5, wherein the system further comprises: a compensation unit, configured to: output an output signal to each of the channels according to the skew amount Perform skew compensation.

7. The skew detection system for output signal of a coherent optical receiver according to claim 5 or 6, wherein said coherent optical receiver comprises: a polarization beam splitter (PBS), a 90 degree mixer, and a photoelectric converter; among them:

The PBS is configured to divide the received one signal light and one local oscillator light into one X direction and one Y direction polarized light signal, and output the same to the 90 degree mixer;

8. The skew detection system of the output signal of the coherent optical receiver according to claim 7, wherein the ADC is configured to: perform analog-to-digital conversion on the four analog electrical signals to obtain a corresponding four-way digital electrical signal.釆 sample value.

9. The skew detecting system of the output signal of the coherent optical receiver according to claim 8, wherein the system further comprises: a laser, configured to: generate the signal light and the local oscillator light, and output the Coherent optical receiver.