Optical Time Division Multiplexing Transmission Research Articles

Free-space transmission of picosecond-level, high-speed optical pulse streams in the 3 µm band.

The utilization of mid-infrared (mid-IR) light spanning the 3-5 µm range presents notable merits over the 1.5 µm band when operating in adverse atmospheric conditions. Consequently, it emerges as a promising prospect for serving as optical carriers in free-space communication (FSO) through atmospheric channels. However, due to the insufficient performance level of devices in the mid-IR band, the capability of mid-IR communication is hindered in terms of transmission capacity and signal format. In this study, we conduct experimental investigations on the transmission of time-domain multiplexed ultra-short optical pulse streams, with a pulse width of 1.8 ps and a data rate of up to 40 Gbps at 3.6 µm, based on the difference frequency generation (DFG) effect. The mid-IR transmitter realizes an effective wavelength conversion of optical time division multiplexing (OTDM) signals from 1.5 µm to 3.6 µm, and the obtained power of the 40 Gbps mid-IR OTDM signal at the optimum temperature of 54.8 °C is 7.4 dBm. The mid-IR receiver successfully achieves the regeneration of the 40 Gbps 1.5 µm OTDM signal, and the corresponding regenerated power at the optimum temperature of 51.5 °C is -30.56 dBm. Detailed results pertaining to the demodulation of regeneration 1.5 µm OTDM signal have been acquired, encompassing parameters such as pulse waveform diagram, bit error rate (BER), and Q factor. The estimated power penalty of the 40 Gbps mid-IR OTDM transmission is 2.4 dB at a BER of 1E-6, compared with the back-to-back (BTB) transmission. Moreover, it is feasible by using chirped PPLN crystals with wider bandwidth to increase the data rate to the order of one hundred gigabits.

25-GHz dual-wavelength pedestal-free pulse source based on single-driven dual-parallel Mach-Zehnder modulator and Mamyshev reshaper

A dual-wavelength optical Gaussian pulse generation scheme based on a single-driven dual-parallel Mach-Zehnder modulator with subsequent Mamyshev reshaping is proposed. Experimental results show that nearly chirp-free Gaussian pulses with a full width at half maximum of 2.7-ps and a repetition rate of 25-GHz on 2 wavelengths are achieved simultaneously. By changing the central wavelengths of the continuous wave light and the optical bandpass filter, nearly transform-limited optical Gaussian pulses are obtained over the C-band. The pulse source is further employed in a 100-Gbit/s on–off keying optical time division multiplexing transmission system. Error-free bit error rate performance is also achieved, which confirms the high pulse quality.

The Nyquist laser

Nyquist pulses, which are defined as impulse responses of a Nyquist filter, can be used to simultaneously achieve an ultrahigh data rate and spectral efficiency (SE). Coherent Nyquist optical time-division multiplexing transmission increases SE, but the optical signal-to-noise ratio (OSNR) is limited by the amplitude of the original CW beam. To further improve transmission performance, here we describe a new pulsed laser that can emit an optical Nyquist pulse train at a repetition rate of 40 GHz. The Nyquist laser is based on a regeneratively and harmonically mode-locked erbium fiber laser that has a special spectral filter to generate a Nyquist pulse as the output pulse. The pulse width was approximately 3 ps, and the oscillation wavelength was 1.55 μm. The spectral profile of the Nyquist pulse can be changed by changing the spectral curvature of the filter with a roll-off factor, α, between 0 and 1. A Fabry–Perot etalon was also installed in the laser cavity to select longitudinal modes with a free spectral range of 40 GHz, resulting in the suppression of the mode hopping in the regenerative mode locking. A numerical analysis is also presented to explain the generation of a stable Nyquist pulse from the laser. The Nyquist laser is important not only for the direct generation of high-OSNR pulses but also for scientific advances, proving that pulse shapes that differ significantly from the conventional hyperbolic-secant and Gaussian pulse shapes can exist stably in a cavity.

Investigation of Modulators in OTDM System

With the ever-increasing demand for higher speeds and larger capacity brought about by rapid data growth on the Internet, interest in optical time division multiplexing has been growing rapidly in recent years due to its high speed and ability to overcome the “electronic bottleneck” offered by today’s electronic components. Optical time division multiplexing (OTDM) transmits multiple data channels in the form of ultra-short duration optical pulses which are interleaved into a single high-speed data stream by accurate control of their relative delay in the time domain. OTDM transmission system has been a topic of continuous research due to their unique advantages over conventional Pulse sources based transmissions. Among various key high repetition rate, limited pulse source, pulse range still remains as the issues that require further optimization. The performance of OTDM system is analyzed by using BER analyzer in which Q factor is to be measured. In OTDM system the maximum Q factor can be achieved by using different methods which are increasing laser power, using various.. We will focus on performance metrics and parameters used in the topology. We also focused on various modulators related to the topology.

Performance comparison of pre-, post- and symmetrical-dispersion compensation techniques using DCF on 40 Gbps OTDM system for different fibre standards

Various factors like polarization mode dispersion, non-linear effects, Kerr effect, second and third order dispersion impose limit on the performance (transmission distance, pulse broadening) of Optical Time Division Multiplexed (OTDM) transmission system. In this paper, the performance comparison of 40Gbps OTDM transmission system with pre-, post-, and symmetrical-dispersion compensation techniques for different fibre standards has been carried out. It has been observed that for pre compensation, ITU 655 [D=3.78ps/nm/km] came to be best suitable fibre with the dispersion compensating fibre length of 2.36km for maximum reach of 3000km. For post- and symmetrical-compensation, the behaviour of alcatel [D=8ps/nm/km] is almost similar with maximum transmission distance of 3200 and 3050km respectively.

Simultaneous demultiplexing into two 10 Gbit/s using a bidirectionally operated highly nonlinear fiber

A simultaneous two-channel optical time division multiplexing (OTDM) demultiplexing is proposed and experimentally demonstrated by using a bidirectionally operated highly nonlinear fiber followed by a narrow-band offset filter. The performance of the proposed demultiplexer is evaluated in an 80 Gbit/s OTDM transmission system. A maximum power penalty of 2.6 dB is obtained for the worst demultiplexed channel. The proposal might be interesting since it offers a powerful tool for developing ultrafast photonic networks.

A single-channel 192 Tbit/s, 64 QAM coherent optical pulse transmission over 150 km using frequency-domain equalization

We demonstrate a single-channel 1.92 Tbit/s, 64 QAM coherent optical pulse optical time-division multiplexing (OTDM) transmission by utilizing frequency-domain equalization (FDE). FDE makes it possible to compensate precisely for the waveform distortions caused by hardware imperfections thus greatly improving the error vector magnitude (EVM) of the demodulated 64 QAM signal compared with that obtained with a conventional FIR filter. As a result, a coherent 64 QAM OTDM transmission over 150 km with a bit error rate of below the forward error correction limit of 2 x 10⁻³ (requiring 7% overhead) was achieved for the first time.

An all-optical bit-error indicating scheme based on self-phase modulation and filtering

In this paper, a novel all-optical bit-error indicating scheme is numerically studied. The bit-error indicating function is achieved by two all-optical processing stages. Firstly, the amplified original bit stream propagates through a high-nonlinear fiber and experiences self-phase modulation which causes intensity-dependent spectrum broadening and split. And then, the bit stream output from the high-nonlinear fiber is filtered by a band-pass filter with the same central wavelength as the original bit stream to generate an error bit indicating signal. The error bit indicating signal, in which only the “Error” bits have the highest peak power, is synchronous with the delayed original bit stream. Therefore, the position of the “Error” bits in the original bit stream can be identified by setting only one judge threshold in the error bit indicating signal. The scheme is demonstrated for an 80 Gb/s bit stream with return-to-zero format by simulation. The results show that the scheme can be used for the all-optical bit-error indicating of the super high bit-rate systems using the return-to-zero format which is favored in the optical time division multiplexing transmission systems.

Control and Stabilization of bit-wise phase correlation in 160 (4 x 40) Gbit/s OTDM signal and its impact on transmission

Detail of control technique of bit-wise phase correlation in 160 (4 x 40) Gbit/s optical time division multiplexing (OTDM) signal using a phase-correlation monitor based on 1-bit delay asymmetric interferometers (AIFs) is described. The 1-bit delay AIF transforms a bit-by-bit optical phase discontinuity to an optical power variation, so that it enables to quantify the phase-jump between adjacent bits. By use of this unique technique, we experimentally demonstrated stable generation of bitwisely phase-controlled 160 Gbit/s periodical alternate-phase return-to-Zero (APRZ) signal in addition to other different modulation formats such as conventional RZ, carrier suppressed RZ (CS-RZ), pair-wise alternate-phase CSRZ (PAP-CSRZ) and pi/2-APRZ. And long term stability was observed with CS-RZ signal. Also, we show some experimental results of 120 km un-repeatered transmission using standard single mode fiber (SSMF) and then discuss the impact of bit-wise phase change on 160 Gbit/s OTDM transmission performance.

Real-time detection of femtosecond optical pulse sequences via time-to-space conversion in the lightwave communications band

A spectral nonlinear optics time-to-space converter operating in the lightwave communications band is reported for the first time. We demonstrate serial-to-parallel conversion of short frames of femtosecond pulses, for the first time operating at a conversion efficiency level allowing direct electronic readout at a conversion rate of hundreds of megaframes/s in real time, without signal averaging and with good signal-to-noise ratio. The results demonstrate that applications such as real-time measurements of ultrafast optical data sequences and header recognition in ultrafast optical time-division-multiplexed (OTDM) packet networks are approaching feasibility. Moreover, we analyze tradeoffs between optical powers and data rates from a system perspective, which allows us to assess the challenges for scaling to parallel demultiplexing of bit-interleaved OTDM transmission systems.

Interferometric noise in optical time division multiplexing transmission system

A theoretical assessment of the interferometric noise in the optical time division multiplexing (OTDM) transmission system is presented. The impact of such noise on the system performance were investigated in detail. The corresponding system requirements were also revealed by the calculation results. Recommendations on the use of prechirping to reduce the interferometric noise in the OTDM system are given.

Ultrahigh-speed optical time-division multiplexing transmission (OPN Trends Supplement)

Ultrahigh-speed optical time-division multiplexing transmission (OPN Trends Supplement)

Ultrahigh-bit-rate optical transmission research in Japan

Recent progress toward ultrahigh-bit-rate optical fibre transmission systems employing optical time-division multiplexing (TDM) techniques is reviewed. Focus is placed on 100 Gbit s$^{-1}$ optical TDM transmission systems and the related technologies studied in Japan. Successful 100 Gbit s$^{-1}$ TDM transmission experiments over 200-500 km and the key technologies are described, including ultrashort optical pulse generation, all-optical multiplexing-demultiplexing and optical timing extraction techniques, together with state-of-the-art performances and future prospects.