Quadrature Imbalance Compensation for PDM QPSK Coherent Optical Systems

Petrou, C.S.; Vgenis, A.; Roudas, I.; Raptis, L.

doi:10.1109/lpt.2009.2034750

Cited by 36 publications

(25 citation statements)

References 9 publications

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“…Since BER is the main concern in coherent communication systems, it represents a fairer approach for estimating hybrid's operation bandwidth via simulation. Besides, notice that although several imbalance compensation algorithms have been proposed so far [15], [16], the goal of PIC designers is to maximize performance at the optical level. By designing low imbalance and highly resilient coherent transmitters and receivers, the computing effort wasted in compensating for these impairments could eventually be removed.…”

Section: System Level Evaluationmentioning

confidence: 99%

“…At most, 1-D sweeps at a single wavelength of some geometrical features have been performed in 2 Â 2 [14] and 4 Â 4 MMIs [13]. On the other hand, previous works on imbalance compensation algorithms have considered generic imbalance values without resorting to either numerical results or experimental data from manufactured devices [15], [16]. In this paper, we aim to bridge the gap between these two abstraction levels.…”

Section: Introductionmentioning

confidence: 99%

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Dual Photonic Generation Ultrawideband Impulse Radio by Frequency Shifting in Remote-Connectivity Fiber

Beltrán

Llorente

2011

J. Lightwave Technol.

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A numerical study of the impact that manufacturing tolerances have on the performance of an InP 4 Â 4 MMI working as a 90 optical hybrid is presented, including simultaneous variations of width, thickness, and refractive index over the C and L bands. Simulation results for different figures of merit, such as optical common-mode rejection ratios (CMRRs) and phase errors, are provided for both nominal and worst case scenarios. Additionally, system simulations are performed to compute imbalance-induced power penalty. Our results indicate that the combined effect of realistic foundry tolerances on device performance is significant. In particular, a fourfold reduction is predicted between nominal ('40 nm) and worst cases ('10 nm) when optical CMRRs and phase errors are compared against Optical Internetworking Forum specifications. By contrast, a much greater bandwidth is expected at the system level (! 40 nm) if a power penalty of less than 1 dB ð@BER ¼ 10 À3 Þ is to be allowed. In fact, worst case power penalties lower than 0.25 dB are predicted over the full C band, which further proves the great potential of integrated 4 Â 4 MMIs as wide-bandwidth devices for mass production of coherent receivers using state-ofthe-art integration technologies.

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Section: System Level Evaluationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Dual Photonic Generation Ultrawideband Impulse Radio by Frequency Shifting in Remote-Connectivity Fiber

Beltrán

Llorente

2011

J. Lightwave Technol.

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“…Since digital signal processing (DSP) circuits are becoming increasingly faster, providing simple and efficient compensation of linear and, possibly, non-linear impairments, it is important to assess their potential for the compensation of this detrimental loss of orthogonality in the receiver. It has already been demonstrated that IQ imbalance in coherent QPSK systems can be corrected by applying different methods such as the Gram-Schmidt orthogonalization procedure (GSOP) [3], the ellipse correction method (EC) [4] or an IQ compensation based on the constant modulus algorithm [5].In this paper, we propose an alternative method for IQ imbalance compensation based on the definition and estimation of a suitable signal-to-noise ratio (SNR) metric for the detected signal. This approach, called maximum SNR estimation method (MSEM), provides an attractive alternative to existing algorithms thanks to its reduced complexity.…”

mentioning

confidence: 99%

IQ imbalance compensation based on maximum SNR estimation in coherent QPSK systems

Nguyen

Gomez-Agis

Gay

et al. 2014

2014 16th International Conference on Transparent Optical Networks (ICTON)

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We present a simple alternative method for the compensation of quadrature imbalance in optical quadrature phase-shift-keying (QPSK) coherent systems. The method is based on the determination and the compensation of the phase mismatch by the introduction of a relevant signal-to-noise ratio metric. The principle is validated numerically and the algorithm is validated experimentally through bit-error-rate (BER) and error vector magnitude (EVM) measurements. A 20 Gb/s optical QPSK experiment reveals a good agreement of the proposed method with the Gram-Schmidt orthogonalization procedure (GSOP). Moreover, the robustness of both methods was verified with up to 30° phase misalignment by comparing the signal after phase imbalance compensation to that without compensation. A 10% reduction of EVM is achieved with our method for a high phase misalignment of 30 . Keywords: in-phase/quadrature imbalance, digital signal processing, fiber optic communications, coherent communications. INTRODUCTIONOver the last decade, there has been a renewed interest in coherent optical communication systems because of their improved receiver sensitivity and spectral efficiency, and ability to mitigate transmission impairments in the digital domain [1]. In particular, the quadrature phase-shift-keying (QPSK) format has been the object of intensive investigations and 100 Gb/s transmission systems using this format are now commercially available. Ideally, in a QPSK system, the in-phase and quadrature components of the optical field should be orthogonal to each other. However, hardware implementation imperfections such as incorrect bias-points settings in the modulator, imperfect splitting ratio of couplers, photodiodes responsivity mismatch and misadjustment of polarization splitters in the optical coherent receiver can create amplitude and phase imbalance, known as quadrature imbalance (or IQ imbalance), which destroys the orthogonality of the received signal [2]. Since digital signal processing (DSP) circuits are becoming increasingly faster, providing simple and efficient compensation of linear and, possibly, non-linear impairments, it is important to assess their potential for the compensation of this detrimental loss of orthogonality in the receiver. It has already been demonstrated that IQ imbalance in coherent QPSK systems can be corrected by applying different methods such as the Gram-Schmidt orthogonalization procedure (GSOP) [3], the ellipse correction method (EC) [4] or an IQ compensation based on the constant modulus algorithm [5].In this paper, we propose an alternative method for IQ imbalance compensation based on the definition and estimation of a suitable signal-to-noise ratio (SNR) metric for the detected signal. This approach, called maximum SNR estimation method (MSEM), provides an attractive alternative to existing algorithms thanks to its reduced complexity. Indeed, the proposed method requires simple mathematical functions such as exponentiation or division, whereas the GSOP method requires other more complex mathematical ...

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“…This effect is called quadrature imbalance (QI) [10] . QI affects the performance of all subsequent DSP algorithms in a receiver and diminishes the performance of a QPSK system [11] . To correct QI, many compensation algorithms have been proposed: in Ref.…”

mentioning

confidence: 99%

“…[9], the Gram-Schmidt orthogonalization procedure (GSOP) was used to correct nonorthogonality; in Ref. [11], a QI compensation scheme based on the constant modulus algorithm was proposed; in Ref. [12], the least-squares algorithm was applied to fit constellation to an ellipse, after which the ellipse parameters were extracted and then used to estimate the amplitude and phase imbalance parameters.…”

mentioning

confidence: 99%

Quadrature imbalance compensation algorithm based on statistical properties of signals in CO-QPSK system

Qiao¹,

Xu²,

Li³

et al. 2012

中国光学快报

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We propose a blind quadrature imbalance (QI) compensation algorithm based on the statistical properties of I and Q signals in a receiver. The algorithm estimates the QI parameters of a receiver by calculating the mean, variance, and correlation coefficient of I and Q components. Then, the estimated imbalance parameters are adopted to compensate for the QI in the receiver. Simulation results show that the Q factor is considerably optimized by the application of the QI compensation algorithm in an 80-Gb/s PolMux coherent optical quadrature phase-shift keying (CO-QPSK) system. Compared with conventional algorithms, the proposed algorithm exhibits better performance when the phase deviation from QI exceeds ±15• . Coherent detection technology for long-haul and highspeed transmission has recently attracted considerable attention because such technology presents high receiver sensitivity [1] and spectral efficiency [2] . Coherent detection can obtain complete optical field information, including that amplitude and phase, thereby enabling the compensation of dispersion and nonlinearity in the electrical domain by digital signal processing (DSP) [3] . Multilevel optical modulation formats with high spectral efficiency and robust resistance to linear impairments have also been extensively investigated [4] . Quadrature phase-shift keying (QPSK) with a coherent detection scheme is widely used in high-speed optical communications [5−7] , and is one of the most promising modulation formats because of its superior transmission characteristics [8] . Ideally, the amplitudes of the I/Q channel signals of a receiver are equal, and the phase difference between channels is 90• in a QPSK system with a coherent receiver. However, an imperfect optical 90• hybrid may cause amplitude and phase imbalances [9] . This effect is called quadrature imbalance (QI) [10] . QI affects the performance of all subsequent DSP algorithms in a receiver and diminishes the performance of a QPSK system [11] . To correct QI, many compensation algorithms have been proposed: in Ref.[9], the Gram-Schmidt orthogonalization procedure (GSOP) was used to correct nonorthogonality; in Ref.[11], a QI compensation scheme based on the constant modulus algorithm was proposed; in Ref. [12], the least-squares algorithm was applied to fit constellation to an ellipse, after which the ellipse parameters were extracted and then used to estimate the amplitude and phase imbalance parameters. Real-time QI compensation has also been recently reported [13] . In this letter, we propose a blind QI compensation algorithm based on the statistical properties of received signals. The algorithm calculates the mean, variance, and correlation coefficient of I and Q components. Then, the calculated parameters are applied to estimate imbalance parameters. With given amplitude and phase imbalance parameters, QI compensation is performed. The proposed algorithm is tested by simulation in an 80-Gb/s back-to-back (B2B) coherent optical (CO)-QPSK system. The performance of the proposed algorith...

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Quadrature Imbalance Compensation for PDM QPSK Coherent Optical Systems

Cited by 36 publications

References 9 publications

Dual Photonic Generation Ultrawideband Impulse Radio by Frequency Shifting in Remote-Connectivity Fiber

Dual Photonic Generation Ultrawideband Impulse Radio by Frequency Shifting in Remote-Connectivity Fiber

IQ imbalance compensation based on maximum SNR estimation in coherent QPSK systems

Quadrature imbalance compensation algorithm based on statistical properties of signals in CO-QPSK system

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