Time-domain Optical Fourier Transformation Research Articles

320 Gb/s Nyquist OTDM received by polarization-insensitive time-domain OFT

We have demonstrated the generation of a 320 Gb/s Nyquist-OTDM signal by rectangular filtering on an RZ-OTDM signal with the filter bandwidth (320 GHz) equal to the baud rate (320 Gbaud) and the reception of such a Nyquist-OTDM signal using polarization-insensitive time-domain optical Fourier transformation (TD-OFT) followed by passive filtering. After the time-to-frequency mapping in the TD-OFT, the Nyquist-OTDM signal with its characteristic sinc-shaped time-domain trace is converted into an orthogonal frequency division multiplexing (OFDM) signal with sinc-shaped spectra for each subcarrier. The subcarrier frequency spacing of the converted OFDM signal is designed to be larger than the transform-limited case, here 10 times greater than the symbol rate of each subcarrier. Therefore, only passive filtering is needed to extract the subcarriers of the converted OFDM signal. In addition, a polarization diversity scheme is used in the four-wave mixing (FWM) based TD-OFT, and less than 0.5 dB polarization sensitivity is demonstrated in the OTDM receiver.

OTDM-to-WDM Conversion Based on Time-to-Frequency Mapping by Time-Domain Optical Fourier Transformation

This paper reports on the utilization of the time-domain optical Fourier transformation (OFT) technique for serial-to-parallel conversion of optical time division multiplexed (OTDM) data tributaries into dense wavelength division multiplexed (DWDM) channels. The OFT is implemented by using a dispersive medium followed by phase modulation; the latter being achieved by a four-wave mixing process with linearly chirped pump pulses. Both numerical and experimental investigations of the OTDM-to-WDM conversion technique are carried out. Experimental validations are performed on 320- and 640-Gbit/s OTDM data with error-free performance.

Ultra-high-speed optical serial-to-parallel data conversion by time-domain optical Fourier transformation in a silicon nanowire

We demonstrate conversion from 64 × 10 Gbit/s optical time-division multiplexed (OTDM) data to dense wavelength division multiplexed (DWDM) data with 25 GHz spacing. The conversion is achieved by time-domain optical Fourier transformation (OFT) based on four-wave mixing (FWM) in a 3.6 mm long silicon nanowire. A total of 40 out of 64 tributaries of a 64 × 10 Gbit/s OTDM-DPSK data signal are simultaneously converted with a bit-error rate (BER) performance below the 2 × 10(-3) FEC limit. Using a 50 m long highly nonlinear fiber (HNLF) for higher FWM conversion efficiency, 43 tributaries of a 64 × 10 Gbit/s OTDM-OOK data signal are converted with error-free performance (BER<10(-9)).

256 Tbit/s/ch polarization-multiplexed DQPSK transmission over 300 km using time-domain optical Fourier transformation

We demonstrate a 2.56 Tbit/s/ch polarization-multiplexed single-carrier transmission over 300 km using subpicosecond DQPSK signals. We adopted an ultrafast time-domain optical Fourier transformation technique to reduce waveform distortions. For such an ultrashort optical pulse, depolarization components resulting from second-order polarization-mode dispersion (PMD) become a dominant factor as regards signal distortion because of the broad signal bandwidth. The influence of inter-polarization crosstalk induced by second-order PMD, is presented in detail.

Single-Channel 1.28 Tbit/s-525 km DQPSK Transmission Using Ultrafast Time-Domain Optical Fourier Transformation and Nonlinear Optical Loop Mirror

We demonstrate a single-channel 1.28Tbit/s-525km transmission using OTDM of subpicosecond DQPSK signals. In order to cope with transmission impairments due to time-varying higher-order PMD, which is one of the major limiting factors in such a long-haul ultrahigh-speed transmission, we newly developed an ultrafast time-domain optical Fourier transformation technique in a round-trip configuration. By applying this technique to subpicosecond pulses, transmission impairments were greatly reduced, and BER performance below FEC limit was obtained with increased system margin.

High Time-Resolution 640-Gb/s Clock Recovery Using Time-Domain Optical Fourier Transformation and Narrowband Optical Filter

We present a novel scheme for subharmonic clock recovery from an optical time-division-multiplexing signal using time-domain optical Fourier transformation and a narrowband optical filter. High-resolution 640-Gb/s clock recovery is successfully demonstrated with no pattern dependence. The clock recovery is also applied to a 640-Gb/s differential phase-shift-keying transmission, and error-free performance is achieved over 300 km.

640-Gb/s/Channel Single-Polarization DPSK Transmission Over 525 km With Ultrafast Time-Domain Optical Fourier Transformation

A single-channel 640-Gb/s differential phase-shift-keying transmission over 525 km was successfully demonstrated in a single polarization. A new ultrafast time-domain optical Fourier transformation (OFT) circuit was developed, in which the strong chirp required for the OFT of a subpicosecond optical pulse was realized with a phase modulator operated in a round-trip configuration. By applying this technique to a 640-Gb/s transmission, the tolerance to higher order polarization-mode dispersion was greatly improved and error-free transmission was achieved.

Low-Penalty 5$\,\times \,$320 Gb/s/Single-Channel WDM DPSK Transmission Over 525 km Using Time-Domain Optical Fourier Transformation

Ultrahigh-speed wavelength-division-multiplexing transmission at 5times320 Gb/s/single channel is successfully demonstrated over 525 km using time-domain optical Fourier transformation (OFT). The modulation format is optical time-division multiplexing/differential phase-shift keying. We first suppressed signal distortions by using dispersion management and principal state of polarization launch, where the power penalty was 3.3-4.2 dB. Then, by further applying OFT, the transmission performance was greatly improved, in which a power penalty as small as 1.3-2.1 dB was achieved for all channels without using forward-error correction.

160-Gb/s 200-km Field Transmission Experiment With Large PMD Using a Time-Domain Optical Fourier Transformation Technique

A 160-Gb/s single-polarization differential phase-shift-keying transmission using time-domain optical Fourier transformation (OFT) was demonstrated over a 200-km installed fiber link with large polarization-mode dispersion (PMD). First, we suppressed differential group delay (DGD) by coupling to the principal state of polarization (PSP) launch, where the power penalty was 2.8 dB. Then, by further applying OFT, which enables us to reduce time-dependent DGD and second-order PMD that cannot be removed with the PSP launch alone, excellent error-free performance with a power penalty of 1.5 dB has been successfully achieved.

320-Gb/s Single-Polarization DPSK Transmission Over 525 km Using Time-Domain Optical Fourier Transformation

A 320-Gb/s single-polarization differential phase-shift keying transmission is successfully demonstrated over a 525-km straight transmission line using time-domain optical Fourier transformation (OFT). The tolerance to higher order polarization-mode dispersion is greatly improved and long-term stable transmission performance is achieved with OFT.

A Straight-Line 160-Gb/s DPSK Transmission Over 1000 km With Time-Domain Optical Fourier Transformation

A straight-line 160-Gb/s 1000-km differential phase-shift keying transmission was successfully demonstrated with time-domain optical Fourier transformation (OFT) without employing polarization multiplexing or Raman amplification. The OFT greatly reduced the transmission impairments caused by linear perturbations, and transmission performance close to the amplified spontaneous emission limit was achieved.

Bright and dark 40 GHz parabolic pulse generation using a picosecond optical pulse train and an arrayed waveguide grating

We demonstrate parabolic optical pulse generation by manipulating the intensity and phase of individual longitudinal modes of a 40 GHz picosecond optical pulse train in the spectral domain. Bright and dark parabolic pulses were generated from a 40 GHz mode-locked fiber laser using a 64-channel arrayed waveguide grating pulse shaper. The obtained parabolic pulse, which can easily generate a linear chirping, is useful for a number of applications to optical signal processing applications, including pulse compression and time-domain optical Fourier transformation.

Optical adaptive equalization of high-speed signals using time-domain optical Fourier transformation

This paper describes a new distortion-free optical transmission method that can eliminate any kind of linear perturbation including jitter, polarization-mode dispersion, and higher order dispersion as well as time-varying dispersion. This method uses transform-limited pulses and time-domain optical Fourier transformation (OFT). With this technique, particular attention is given to the spectral envelope profile of the transmitted signal, which is unchanged regardless of the type and magnitude of the linear perturbation in the transmission fiber. OFT converts the unchanged spectral profile into the time domain and allows to obtain undistorted original waveforms at the output. Experimental and analytical results to show the effectiveness of this method are presented, especially when the method is applied to high-speed signals up to 160 Gb/s, which are sensitive to both higher order and time-varying dispersions. This paper also describes a new all-optical time-domain Fourier transformation technique that uses an optical parabolic pulse. This technique is promising, with a view to improving the elimination of distortion at 160 Gb/s and above.

ABCD matrix formalism of time-domain optical Fourier transformation for distortion-free pulse transmission

An analytical description of distortion-free transmission using time-domain optical Fourier transformation (OFT) is newly developed by using a time-domain ABCD matrix formalism. The analysis is based on an analogy with a spatial Fourier transformation in diffraction through lenses. The theory enables us to derive the pulse width and chirp at the OFT output explicitly and to evaluate the effect of dispersion inaccuracy in OFT by using only simple algebra.

Comparison of 40GHz optical demultiplexers using SMZ switch and EA modulator in 160Gbit/s-500km OTDM transmission

We compare two types of optical demultiplexers, one with a symmetric Mach-Zehnder (SMZ) switch and the other with an electro-absorption modulator (EAM), when used for 160Gbit/s (4 × 40Gbit/s) OTDM transmission over 500km. By combining the SMZ switch with a time-domain optical Fourier transformation technique, we succeeded in obtaining slightly better bit-error rate performance than with the EAM.

A New Adaptive Equalization Scheme for a 160-Gb/s Transmitted Signal Using Time-Domain Optical Fourier Transformation

We demonstrate a new adaptive equalization scheme at 160 Gb/s using time-domain optical Fourier transformation. In this technique, we take advantage of the fact that the spectral profile does not change even when the transmission fiber has linear perturbations such as jitter, polarization-mode dispersion, and higher order dispersions. The unchanged spectral profile is then converted into the time-domain waveform at the output, resulting in the reconstruction of the original undistorted waveform. With the present scheme, a 160-Gb/s optical time-division-multiplexing signal was successfully transmitted over 120 km by simultaneously equalizing both second- and third-order dispersions even when they varied with time.