In-line Phase-sensitive Amplifiers Research Articles

Long-haul optical transmission link using low-noise phase-sensitive amplifiers

The capacity and reach of long-haul fiber optical communication systems is limited by in-line amplifier noise and fiber nonlinearities. Phase-sensitive amplifiers add 6 dB less noise than conventional phase-insensitive amplifiers, such as erbium-doped fiber amplifiers, and they can provide nonlinearity mitigation after each span. Realizing a long-haul transmission link with in-line phase-sensitive amplifiers providing simultaneous low-noise amplification and nonlinearity mitigation is challenging and to date no such transmission link has been demonstrated. Here, we demonstrate a multi-channel-compatible and modulation-format-independent long-haul transmission link with in-line phase-sensitive amplifiers. Compared to a link amplified by conventional erbium-doped fiber amplifiers, we demonstrate a reach improvement of 5.6 times at optimal launch powers with the phase-sensitively amplified link operating at a total accumulated nonlinear phase shift of 6.2 rad. The phase-sensitively amplified link transmits two data-carrying waves, thus occupying twice the bandwidth and propagating twice the total power compared to the phase-insensitively amplified link.

PPLN-Based Low-Noise In-Line Phase Sensitive Amplifier with Highly Sensitive Carrier-Recovery System

PPLN-Based Low-Noise In-Line Phase Sensitive Amplifier with Highly Sensitive Carrier-Recovery System

Phase squeezing and dispersion tolerance of phase sensitive amplifier using periodically poled LiNbO_3 waveguide

The phase squeezing property of phase sensitive amplifiers (PSAs) is a useful feature to recover signal quality. Chromatic dispersion of transmission fiber largely affects the performance of PSAs when they are used as in-line amplifiers in long-haul transmission systems. In this work, we demonstrated that phase variation such as chirping can be reduced by phase squeezing in a periodically poled LiNbO3 (PPLN)-based PSA. We also examined the dispersion tolerance of a PPLN-based in-line PSA. Theoretical analysis and experiment revealed that we can relay the received data with negligible power penalty utilizing the phase squeezing capability of the PSA, if the phase variation due to dispersion within the data bandwidth is below π/2.

In-line phase-sensitive amplification of QPSK signal using multiple quasi-phase matched LiNbO₃ waveguide.

Phase-sensitive amplifiers (PSA) using periodically poled (PPLN) LiNbO₃ waveguides are promising as low-noise optical amplifiers. However, it is difficult to realize in-line operation for multi-level phase modulated signals using a PPLN based PSA with the conventional configuration. In this paper, we report a PPLN based in-line PSA that can regenerate quadrature phase shift keying (QPSK) signals. Multi-stage frequency mixing in a multiple quasi-phase matched LiNbO₃waveguide allows carrier phase recovery from a QPSK signal. Non-degenerate parametric amplification enables the phase-sensitive amplification of a QPSK signal. Amplitude and phase regeneration is examined utilizing gain saturation and phase squeezing capability.

Multi-span transmission using phase and amplitude regeneration in PPLN-based PSA

We demonstrated multi-span transmission using a periodically poled LiNbO(3) (PPLN) based phase sensitive amplifier (PSA). An in-line PSA with a carrier recovery and phase locking system is implemented as a repeater amplifier in a recirculating loop. We achieved a PSA gain as high as + 18 dB and a high external gain of + 12 dB for the in-line PSA as a black box. The impairments caused by phase noise resulting from fiber nonlinearity and intensity noise caused by the amplified spontaneous emission (ASE) of an optical amplifier are largely suppressed using the phase and amplitude regeneration capabilities of the PSA. The ultra long-haul transmission of a 28-Gb/s binary phase shift keying (BPSK) signal over 5400 km was achieved with phase and amplitude regeneration.

In-line phase sensitive amplifier based on PPLN waveguides

We demonstrate a χ(2)-based in-line PSA with a carrier-recovery and phase-locking system for a phase shift keying (PSK) signal. By doubling the signal phase using a wavelength conversion technique, the carrier was recovered from a PSK signal. The carrier phase was synchronized to a local oscillator using optical injection locking. Phase sensitive amplification with a wide phase sensitive dynamic range of 20 dB was achieved using degenerate parametric amplification in a periodically poled LiNbO(3) (PPLN) waveguide. The phase regeneration effect was examined for a degraded signal by means of constellation analyses and bit-error rate measurements. The in-line PSA also operated successfully as a repeater amplifier in a 160 km fiber link without a power penalty. Finally, we demonstrate the regeneration of non-linear impairments induced by fiber non-linearity.

Theoretical analysis of system limitation for AM-DD/NRZ optical transmission systems using in-line phase-sensitive amplifiers

This paper shows the theoretically derived performance of single channel, amplitude modulation/direct detection optical transmission systems using in-line optical phase-sensitive amplifiers (PSA's). The calculations take into account the degradation of the signal-to-noise power ratio (SNR) and intersymbol interference (ISI) due to the distortion of transmitted signal pulses. The SNR is analyzed by considering not only amplifier noise and fiber loss but also noise enhancement by four-wave mixing in the transmission fiber. The ISI is estimated by eye-pattern degradation of the transmitted signal numerically calculated using the nonlinear Schrodinger equation. The regenerative repeater spacing of in-line PSA systems limited by SNR and ISI can be expanded by approximately 3 to 10 times that of in-line EDFA systems, in the case of |D|/spl les/0.1 ps/mn/km dispersion fiber systems transmitting a 40-Gb/s signal.

Error-free operation of in-line phase-sensitive amplifier

Optical phase-sensitive amplifiers (PSAs) are promising circuit elements for expanding the regenerative repeater spacing of optical transmission systems. The authors first demonstrate error-free operation of in-line PSAs with a 10 dB net gain by using an injection-locked pump with a compensation phase-locked loop.

In-line phase-sensitive amplifier with optical-PLL-controlled internal pump light source

Randomly modulated signal pulses from an independent source are successfully amplified by a phase-sensitive amplifier with an internal pump light source whose optical phase is locked to that of the injected signal using an optical phase-locked loop.

Reduction of fiber-nonlinearity-enhanced amplifier noise by means of phase-sensitive amplifiers

In optical fiber transmission systems near the zero-dispersion wavelength that use in-line erbium-doped fiber amplifiers (EDFA's), the enhancement of optical amplifier noise caused by four-wave mixing (FWM) in transmission fibers degrades signal-to-noise ratio (SNR) excessively. We theoretically show that the enhancement of amplifier noise by the FWM in transmission fibers can be effectively eliminated by implementing in-line phase-sensitive amplifiers (PSA's). Small-signal analysis of the nonlinear Schrödinger equation shows that the transmission distance limited by the SNR of an in-line PSA system is expanded four times more than that of an in-line EDFA system.