Delayed-interference Signal-wavelength Converter Research Articles

Improvement in the Performance of a Semiconductor Optical Amplifier Based Delayed Interference Signal-Wavelength Converter With Phase Offset of a Mach-Zehnder Delay Interferometer and BPF Detuning

We investigated the improvement in the wavelength conversion performance of a semiconductor optical amplifier-based delayed interference signal-wavelength converter with the phase offset of a Mach-Zehnder delay interferometer and band pass filter (BPF) detuning. In the experiments, the power penalty of the wavelength converted output was improved using negative phase offset due to the suppression of double pulse and reduction of zero level power, and the transmission characteristics were improved using negative detuning of a BPF because of the elimination of the degraded components in the output signal. Moreover, the power penalty was optimized using a -0.12 rad phase offset and -0.15 nm BPF detuning at a bit rate of 10 Gb/s. We also investigated its effect via simulations by solving rate equations. The waveform and Q-factor of the wavelength converted signal were in good qualitative agreement with the experimental results. We studied the principle of the impact of both phase offset and BPF detuning on output signal improvement by a comparison of the optical spectrum of the wavelength converted output with that of the return-to-zero signal. Waveform improvement can be achieved by positioning the intensity of the two sidebands symmetrically on both sides of the carrier.

Recent Progress in High-Speed All-Optical Wavelength Converters Based on SOAs

Recent patents and progress on all-optical wavelength converters (WCs) based on semiconductor optical amplifiers (SOAs) are reviewed. Differential schemes utilizing the nonlinear optical effects of SOAs in the configurations such as the Mach-Zehnder interferometer (MZI), the delayed-interference signal-wavelength converter (DISC), detuned narrow filter and novel turbo-switch structure are discussed and compared, which overcome the limitation of operation speed of WCs due to the SOA recovery time(~100 ps). It is shown that, by using the chirp effect or turbo-switch schemes, the WCs can be operated at the range of 160-320Gb/s, which will be good candidates for the applications in the next generation all-optical fiber networks.

Investigation of Improvement of Dynamic Switching Operation for Wavelength Switch With Super-Structure-Grating (SSG)-DBR-LD, Delayed-Interference Signal-Wavelength Converter (DISC), and Bandpass Filter

We demonstrate dynamic wavelength switching operation using a super-structure grating (SSG)-DBR-LD and a semiconductor optical amplifier (SOA)-delayed-interference signal-wavelength converter (DISC) for optical packet switch and buffering systems. The wavelength conversion-type optical switch has the advantage of lowering packet blocking probability and reducing numbers of the required SOAs in the DISC-type wavelength converter. However, we confirmed that large optical spikes occur at the timing of wavelength switching due to the optical chirping. By detuning the center wavelength of a bandpass filter to suppress optical chirped wavelength component, we could reduce the intensity of the spikes. We also observed the alternate wavelength switching operation with small optical spikes with fixed detuning of the bandpass filter and the fixed optical phase bias of the Mach-Zehnder Delayed Interferometer (MZDI) by setting the small current variation of the SSG-DBR-LD for wavelength switching. Error free performance was also achieved under back-to-back and 50 km single mode fiber transmission.

Novel 160-GHz wavelength converter based on a SOA and a long period grating

The proposed converter is based on cross-phase modulation (XPM) in a semiconductor optical amplifier (SOA). The predominantly phase-encoded signal at the SOA output is converted to a purely amplitude-modulated signal using a long period grating. First, we design the converter in terms of power conversion efficiency and pulse pedestal suppression. Subsequent analysis for the delayed-interference signal-wavelength converter (DISC) revealed that our device offers 5dB higher power conversion efficiency and gives shorter pulses at the converter output. In the proof-of-principle experiment, good agreement with the theoretical predictions is obtained.

200-Gb/s wavelength conversion using a delayed-interference all-optical semiconductor gate assisted by nonlinear polarization rotation

The pattern-induced intensity fluctuation (PIF) of output signals with a bit-rate above 160Gb/s has been one of the major issues regarding all-optical semiconductor gates. We have demonstrated that the nonlinear polarization rotation (NPR) in the semiconductor optical amplifier (SOA) plays a significant role in the high-frequency operation of a delayed-interference signal-wavelength converter (DISC). We did this using a cross-correlation system whose temporal resolution is 1.5ps which was developed to monitor our 200-Gb/s, 4992-bit-long binary-patterned waveforms. When we experimentally optimized the NPR effect inside our DISC specially for our 200-Gb/s wavelength conversion, the PIF was significantly improved (from 5.0 to 1.5, for example). Our systematically measured dependence of the PIF on the polarization settings was qualitatively explained with the new gate model that we developed earlier in this work.

Analysis of Subpulse Generation from Delayed-Interference Signal-Wavelength Converter for Wide Carrier Recovery Rate Range

The generation of subpulses in delayed-interference signal-wavelength converters (DISCs) had been suspected as a cause of waveform degradation in their application in ultrafast (∼160 GHz) optical time division multiplexing (OTDM) communication systems. We reported its first observation in our previous letter. In this paper, after a detailed explanation of our model, experimental method and improved results with respect to those in the previous letter, we discussed the applicability of our model in a wide range of carrier recovery rates in the semiconductor optical amplifier (SOA). Subpulse waveforms were systematically measured for several carrier recovery rates (carrier lifetimes τeff=11–280 ps), and an increase in subpulse intensity with recovery rate was observed. The calculated intensities showed good agreement with measured data for most recovery rates, which supports our model. Using this model, we numerically showed the trade-off between subpulses and pattern-induced intensity noise, in the same recovery rate range. This trade-off suggests that part of the DISC structure needs improvement.

Optical-spectrum-synthesizer design within an all-optical semiconductor gate to reduce waveform distortion induced by carrier-cooling relaxation at sub-Teraherz frequencies

In frequency ranges above 200-300 GHz, the second slowest relaxation in the optical response (such as carrier-cooling relaxation having a time constant of 1-2 ps) of a semiconductor optical amplifier inside the conventional delayed-interference signal-wavelength converter (DISC) scheme is thought to start the distortion of all-optically gated waveforms. In this work, we design a digital optical-spectrum-synthesizer block that is part of the expanded DISC scheme. Our numerically calculated spectra, waveforms, and eye diagrams with assumed pseudorandom digital data pulses indicate that this synthesizer significantly removes strong distortion from the gated waveforms. A signal-to-noise ratio of 20 dB was obtained from our random-data eye diagram, providing proof of effectiveness in principle.

Symmetric Mach‐Zehnder‐type all‐optical switches and ultrafast all‐optical signal processing

AbstractSymmetric Mach‐Zehnder (SMZ) type all‐optical switches, namely, the SMZ, polarization‐discriminating SMZ (PD‐SMZ), and delayed interference signal wavelength converter (DISC), are described in detail. All of these all‐optical switches are characterized by push–pull operation and allow ultrafast switching not limited by the relaxation time of high‐efficiency nonlinear optical materials that are suitable for low‐power operations. They make possible a low‐chirp switching window of a quasi‐square type that is important in practice. Ultrafast all‐optical signal processing with an SMZ, namely, 168 → 10.5 Gbit/s error‐free DEMUX (using a hybrid‐integrated SMZ, HI‐SMZ), zero‐penalty optical signal pulse regeneration at 84 and 168 Gbit/s, and error‐free all‐optical wavelength conversion are reported. In experiments with pulse regeneration and wavelength conversion, the error rate is evaluated after DEMUX to 10.5 Gbit/s by HI‐SMZ because the signal light after signal processing has ultrahigh speed. © 2002 Scripta Technica, Electron Comm Jpn Pt 2, 85(2): 1–17, 2002

BER estimation for all-optical regenerators influenced by pattern effects

An efficient method is presented for the estimation of the bit-error rate (BER) of a system employing all-optical regenerators influenced by pattern effects. We theoretically study noise accumulation and noise redistribution in long distance transmission systems employing a delayed interference signal wavelength converter for all-optical regeneration. The BER is studied for return-to-zero signals at bit rates of 2.5 Gb/s (no patterning) up to 40 Gb/s (strong patterning). The calculation of the BER is based on pattern dependent transfer functions, which may be obtained numerically or measured.

168-Gb/s all-optical wavelength conversion with a symmetric-Mach-Zehnder-type switch

Error-free all-optical wavelength conversion at 168 Gb/s, which is the highest repetition rate ever reported, has been achieved by using a symmetric-Mach-Zehnder (SMZ)-type switch. Low-power-penalty 84-Gb/s operation is also demonstrated. The push-pull switching mechanism of the SMZ switch enables such ultrafast operation based on cross-phase modulation associated with the carrier depletion in a semiconductor optical amplifier. The configuration of the delayed-interference signal-wavelength converter, which is a simplified variant of the SMZ switch, is used in this experiment.

3.8-THz wavelength conversion of picosecond pulses using a semiconductor delayed-interference signal-wavelength converter (DISC)

A new all-optical semiconductor-band-filling-based wavelength converter, named delayed-interference signal-wavelength converter (DISC), is proposed. Its speed is not restricted by the carrier lifetime and its structure is very simple: it consists of only two essential components, namely, a semiconductor optical amplifier and a passive split-delay. Using this converter, 3.8-THz-shifted (from 1530 to 1560-nm) 14-ps-long pulses are generated from 1530-nm 140-fJ 0.7-ps pulses with high-conversion efficiency.