Clock Recovery Scheme Research Articles

5–10 Gb/s 70 mW Burst Mode AC Coupled Receiver in 90-nm CMOS

A low power burst mode receiver architecture is presented which can be used for AC coupled links where low frequency signal components are attenuated by the channel. The nonlinear path comprises a hysteresis latch that recovers the missing low frequency content and a linear path that boosts the high frequency component by taking advantage of the high pass channel response. By optimally combining them, the front-end recovers NRZ signals up to 13 Gb/s burning only 26 mW in 90 nm CMOS. A low power- and area-efficient clock recovery scheme uses the linear path to injection lock an oscillator. A simple theory and simulation technique for ILO-based receivers is discussed. The clock recovery technique is verified with experimental results at 5-10 Gb/s in 90 nm CMOS consuming 70 mW and acquiring lock within 1.5 ns.

Single and Multiwavelength All-Optical Clock Recovery Using Fabry–PÉrot Semiconductor Optical Amplifier

We experimentally demonstrate an all-optical clock recovery scheme for the return-to-zero data with single- and multiwavelength. This scheme is mainly based on clock-like pulse generation from an active filter with a multiquantum-well Fabry-Perot semiconductor optical amplifier and amplitude-equalization with self-nonlinear polarization switching. We obtain stable and low jitter optical clock signals in single and dual channels using this scheme, which has some distinct advantages including easy integration, free preamplification, convenient tuning, good tolerance to long ldquo0srdquo data, and greater tolerance to the stability of the input wavelength.

Optical Clock Recovery Using a Polarization-Modulator-Based Frequency-Doubling Optoelectronic Oscillator

We propose and demonstrate a flexible optical clock recovery scheme using a polarization-modulator-based frequency-doubling optoelectronic oscillator (OEO). The proposed system can extract both prescaled clock and line-rate clock from a degraded high-speed digital signal using only low-frequency devices. A simple theory is developed to study the physical basis of the optical clock recovery. The OEO operation from a free-running mode to an injection-locking mode is investigated. The locking range is quantitatively predicted. An experiment is then implemented to verify the proposed scheme. A prescaled clock at 10 GHz and a line-rate clock at 20 GHz are successfully extracted from a degraded 20 Gb/s optical time-division-multiplexed (OTDM) signal. The locking range and the phase noise performance are also experimentally investigated. Clock recovery from data signals that have no explicit subharmonic tone is also achieved. The proposed system can be modified to extract prescaled clock and line-rate clock from 160 Gb/s data signal using all 40-GHz devices.

64.5L: Late‐News Paper: A Clock Embedded Differential Signaling (CEDS™) for the Next Generation TFT‐LCD Applications

AbstractA CEDS™ (Clock Embedded Differential Signaling) interface for the next generation TFT‐LCD applications is proposed. The proposed intra‐panel interface reduces the number of signal lines in the TFT‐LCD panel by embedding the clock signal in transmitted data without explicit clock lines, and it provides low EMI, low power consumption and high data rate. The CEDS protocol provides an embedded clock recovery scheme which is based on the delay‐locked loop (DLL). The CEDS interface is verified on a 42‐inch full‐HD (1920×1080) TFT‐LCD panel with the 10‐bit RGB and 120Hz driving technology. The maximum data rate is measured as higher than 1.405Gb/s, with a pixel clock frequency of up to 330MHz.

Experimental demonstration of a clock recovery scheme utilizing nonlinear relaxation oscillation in directly modulated lasers

AbstractAn experimental demonstration was presented for a clock recovery scheme suitable for low‐cost short‐haul optical communications. This scheme utilizes the nonlinear relaxation oscillation in a directly modulated laser, which creates clock information in modulated nonreturn‐to‐zero optical signals. At the receiver, an injection locked oscillator is employed to extract and restore the clock. Eye diagrams of both received data signal and recovered clock demonstrate the capability of recovering clock from the data signal with an almost closed eye at ∼9 Gbps. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 1654–1657, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24436

基于受激布里渊效应的新型高速OTDM时钟提取技术

A new but simply implemented optical clock recovery scheme for optical time-division multiplexing (OTDM) systems based on stimulated Brillouin scattering (SBS) effect is presented and demonstrated experimentally. According to the unequal-amplitude even-multiplexed OTDM signals, the frame clock is extracted. In addition, the clock with multiple tributary rates is recovered from 160-Gb/s OTDM signal in simulation by utilizing the clock recovery module.

A High-Speed Multiwavelength Clock Recovery Scheme for Optical Packets

We present a novel scheme for high-speed multiwavelength clock recovery using a low finesse Fabry-Perot filter and a quantum-dot semiconductor optical amplifier. Performance evaluation based on extensive numerical analysis reveals that the proposed configuration can acquire clock from 40- and 160-Gb/s input data packet streams at four wavelengths with very short rise- and fall-times.

An Iterative Algorithm for Joint Symbol Timing Recovery and Equalization of Short Bursts

In this work a joint clock recovery (CR) and equalization scheme for short burst transmissions is pre- sented. The joint optimization performance may be pur- sued by means of both data aided and decision directed solutions. The novel algorithm is based on an iterative scheme, exploiting a timing error function sampled at symbol rate. The symbol timing adjustment is implemented by an interpolation filter, built according to the Farrow structure. Equalization is obtained by baud spaced zero forcing (ZF) and minimum mean square error (MMSE) linear filtering. Performance is evaluated by simulating a QPSK transceiver and simulations results are compared with the ideal solutions, for both symbol timing recovery and channel equalization, under frequency selective multipath fading channel conditions.

Burst-Mode Clock Recovery Utilizing Relaxation Oscillation in Directly Modulated Lasers

A novel clock recovery scheme utilizing the relaxation oscillation in a directly modulated laser (DML) for burst-mode transmission is proposed for the first time. In this scheme, the DML generates the clock tone along with the transmitted non-return-to-zero data in the optical signal. An injection-locked oscillator (ILO) is employed in the receiver to extract the clock tone and restore the clock. The proposed scheme is investigated systematically and verified by simulations with different laser modulation currents as well as some nonideal characteristics of the system. The simulation results show that the low cost clock recovery method using an ILO in an optical link using a regular DML is highly efficient for burst-mode transmission at 10 Gbps.

A Novel Clock Recovery Scheme for ATSC Receivers

This paper presents a method of using the field sync signal to perform clock recovery for ATSC receivers. This approach ensures a fast, reliable, and accurate receiver clock recovery even under severely distorted channel conditions.

A Clock Recovery Scheme utilizing Fiber Dispersion for Burst Mode Transmission

A novel clock recovery scheme for burst mode (BM) transmission is proposed and analyzed. The method utilizes the characteristics of the non-return-to-zero (NRZ) signals propagating through a dispersive single mode optical fiber (SMF) at wavelength around 1550 nm to extract the clock information. The amplified photocurrent carrying the generated clock information by the fiber dispersion is fed directly into the injection locked oscillator (ILO) without perfonning conversions between currents and voltages. The proposed scheme is investigated systematically by simulation and the trade-offs between the transmission reach and the locking time is examined. It is shown that the clock recovery method is highly effective for burst mode transmission reach of 17 -38 km at 10 Gbit/s, which is typical of access networks.

Single and Multiwavelength All-Optical Clock Recovery in Single-Mode Fiber Using the Temporal Talbot Effect

We introduce and demonstrate an all-optical clock recovery scheme for return-to-zero transmission systems based on the buffering property of the temporal Talbot effect. This linear, dispersive, and, in principle, lossless phenomenon allows us to generate a regular pulse train from a pseudorandom (aperiodic) input train. Proof-of-principle operation at one and two simultaneous wavelengths is demonstrated using the single-mode fiber as the dispersive medium to implement the temporal Talbot effect. We examine both the limitations and the tolerance of our approach.

Performance investigation of all-optical clock recovery circuit based on Fabry-Pérot filter and semiconductor optical amplifier assisted Sagnac switch

A theoretical model is developed and exploited for characterizing the behavior of an all-optical circuit that deploys a Fabry-Perot filter (FPF) and a semiconductor optical amplifier (SOA)-assisted Sagnac switch driven by an intense continuous wave (cw) holding beam to extract the clock signal from a received ultra-fast data stream. The role of each unit is thoroughly studied, and its understanding allows us to identify the critical operational parameters, which include the cw power, the energy of the data pulses, the SOA small signal gain, carrier lifetime and linewidth enhancement factor, the Sagnac loop asymmetry, and the finesse of the FPF. By means of numerical simulation, an extensive set of diagrams is derived, and from their interpretation the impact of these key factors on the amplitude modulation of the extracted clock pulses is investigated and evaluated. This process enables us to appropriately select and combine them to ensure enhanced performance concerning the defined quality metric, first at 10 Gb/s and then at 40 Gb/s. The final outcome demonstrates the technological feasibility and effectiveness of the proposed clock recovery scheme. The obtained results may be useful for theoretically addressing various all-optical signal processing tasks, whose proper execution relies decisively on clock recovery.

Phase Noise Analysis of Clock Recovery Based on an Optoelectronic Phase-Locked Loop

A detailed theoretical analysis of a clock-recovery (CR) scheme based on an optoelectronic phase-locked loop is presented. The analysis emphasizes the phase noise performance, taking into account the noise of the input data signal, the local voltage-controlled oscillator (VCO), and the laser employed in the loop. The effects of loop time delay and the laser transfer function are included in the stochastic differential equations describing the system, and a detailed timing jitter analysis of this type of optoelectronic CR for high-speed optical-time-division-multiplexing systems is performed. It is shown that a large loop length results in a higher timing jitter of the recovered clock signal. The impact of the loop length on the clock signal jitter can be reduced by using a low-noise VCO and a low loop filter bandwidth. Using the model, the timing jitter of the recovered optical and electrical clock signal can be evaluated. We numerically investigate the timing jitter requirements for combined electrical/optical local oscillators, in order for the recovered clock signal to have less jitter than that of the input signal. The timing jitter requirements for the free-running laser and the VCO are more relaxed for the extracted optical clock (lasers's output) signal

Photonic crystal fibre based all-optical modulation format conversions between NRZ and RZ with hybrid clock recovery from a PRZ signal

Several all-optical modulation format-converting schemes are described for non-return-to-zero (NRZ) and return-to-zero (RZ) modulation formats that make use of spectral filtering of either self-phase modulation (SPM) or cross-phase modulation (XPM) broadened signal spectrum in a highly-nonlinear dispersion-flattened photonic-crystal fibre. Format conversions have been performed between the most widely used modulation formats - NRZ and RZ. In addition, a hybrid clock recovery scheme is proposed to obtain the data rate of the NRZ signal for NRZ-to-RZ format conversion. All format-converting schemes are based on the extraction of the spectral components in a nonlinear phase modulation broadened signal spectrum. In NRZ-to-RZ format conversion, a periodic pulse train, at a repetition rate similar to the NRZ data rate, is used as a control that induces a nonlinear phase shift to the NRZ probe signal and broadens its spectrum. The spectral components, contributed by different time instances of the control pulse, can be extracted as the converted RZ signal output. In RZ-to-NRZ format conversion, the RZ signal serves as a control that induces a nonlinear phase shift to a continuous wave probe light, where a logic-inverted NRZ signal can be extracted by filtering out the chirped components. Format conversions between NRZ and RZ signals at 9.95328 GB/s (OC-192) are demonstrated. As the proposed optical signal-processing schemes make use of the fibre nonlinearity (SPM/XPM), it is possible to extend it to a high-speed operation <160 Gb/s. Therefore the proposed format-converting schemes can serve as a format converter between the optical time-division multiplexed networks and the wavelength division multiplexed networks

Polarization-Insensitive Low Timing Jitter and Highly Optical Noise Tolerant All-Optical 40-GHz Clock Recovery Using a Bulk and a Quantum-Dots-Based Self-Pulsating Laser Cascade

We report on the experimental assessment of an all-optical clock-recovery scheme at 40-Gb/s cascading a polarization-insensitive bulk-based self-pulsating (SP) laser and a high spectral purity quantum-dots-based SP laser. It is demonstrated experimentally that such a clock-recovery scheme is polarization insensitive, efficient in the jitter filtering, and tolerant for an input optical signal-to-noise ratio (OSNR) as low as 15 dB/0.1 nm. It is shown theoretically that the jitter-filtering function of the cascade is the product of the transfer functions of both lasers. The contributions of the phase noise of these two lasers to the final jitter are also identified and quantified. The influence of the degradation of the OSNR to the total timing jitter is also analyzed. The approach proposed in this paper offers the real opportunity to realize an all-optical clock recovery with a performance compatible for system applications

Polarization Independent All-optical Clock Recovery Scheme based on Birefringent Resonator

We introduce a polarization insensitive scheme for all-optical clock recovery and demonstrate how it works with data signals highly distorted by chromatic dispersion and self-phase modulation. The scheme which is known for its multi-wavelength and multi-data-rate capabilities is based on a birefringent fiber resonator and a polarizer. In this article we show how it can handle data signals which have undergone distortion due to transmission over dispersive and nonlinear fiber-optic propagation paths and which come in with arbitrary polarization orientation. Bit-pattern dependent amplitude fluctuations of the recovered clock signal are equalized by means of a semiconductor optical amplifier operated in saturation. The experimental results which, as a proof-of-concept, are obtained from single-wavelength channel 10 Gbit/s return-to-zero data agree well with numerical simulations.

All-Optical Clock Recovery for NRZ-DPSK Signals

We experimentally demonstrate an optical clock recovery scheme for nonreturn-to-zero differential phase shifting keying (NRZ-DPSK) data. By using an optical circuit made by a proper fiber Bragg filter and a Fabry-Peacuterot based clock extraction circuit, we obtain a stable and low jitter 10-GHz optical clock signal. This signal shows comparable performance with the original electrical clock in bit-error-rate measurements and oscilloscope triggering operation

Investigation of multiwavelength clock recovery based on heterodyne beats of sideband-filtered signal

We investigate a new parallel all-optical clock recovery scheme based on heterodyne beats of an optical sideband-filtered signal. The oscillating clock signal is recovered when the filtered sideband is combined with a stable local oscillator. The filtering is performed with an optical resonator, which by nature provides possibility for multiwavelength operation. The local oscillator could be realized by a multiwavelength laser, whose emission wavelengths are injection seeded with carrier wavelengths of the input data. The output signal of such a configuration benefits from a reduced bit-pattern effect and a stable offset level. The sideband filtering is demonstrated for 23 simultaneous channels at 100GHz DWDM grid, each hosting a data stream of 10Gbit/s.

Study of phase-noise properties and timing jitter of 40-GHz all-optical clock recovery using self-pulsating semiconductor lasers

This paper reports on timing-jitter analysis of an all-optical clock-recovery scheme at 40 GHz using self-pulsating (SP) lasers. Based on the analogy with injection locking of oscillators, theoretical investigations on phase-noise properties of the recovered clock lead to the demonstration of a filtering function with slope that is compliant with the International Telecommunications Union (ITU) standards and allow us to underline the dependence of the cutoff frequency of the filtering transfer function on the spectral linewidth of the free running SP laser. From this phase-noise analysis, an analytical expression of the timing jitter of the recovered clock is derived, including the optical signal-to-noise ratio (OSNR) of the injected signal. A set of experiments on all-optical clock recovery at 40 GHz is then presented and demonstrates the crucial role of the spectral linewidth on the timing-jitter-filtering function of the SP laser. In good agreement with theoretical results, the impact of the OSNR degradation of the injected signal on the timing jitter is also demonstrated. Finally, the all-optical clock-recovery operation using a quantum-dot SP laser is shown to be standard compliant in terms of timing jitter, even for highly degraded OSNR.