Accurate Estimation of Chromatic Dispersion for Non-Degenerate Phase-Sensitive Amplification

Abstract

A phase-sensitive amplifier (PSA) has the potential of low-noise optical amplification and nonlinear phase noise mitigation. For PSA operation, the chromatic dispersion (CD) that causes gain ripple must be compensated before amplification. We propose an accurate CD estimation method for non-degenerate PSAs (ND-PSAs). We experimentally demonstrated its effectiveness by using periodically poled LiNbO3 waveguides as amplification mediums. We first modified the conventional formula for the gain spectrum under residual CD conditions to be applicable to ND-PSAs by considering phase locking. We then experimentally described the effect of passband narrowing due to the gain ripple on the signal quality using a probabilistically shaped 64QAM signal. Furthermore, we applied the modified formula to CD estimation and compensation. As a result, accurate CD estimation on the sub-ps/nm order and gain-flattened spectrum over 3.5 THz were demonstrated with our method. We also propose a method for estimating residual CD from the gain variation among wavelength division multiplexing (WDM) channels. The possibility of adaptive compensation for CD was shown by carrying out WDM amplification.

Inter-band non-degenerate phase-sensitive amplification scheme for low-noise full C-band transmission

“…This ripple was the result of a superposition between the signal and idler and thus demonstrates phase-sensitive amplification characteristics. The CD can be estimated using the bandwidth between peaks in the spectrum, and the residual CD in our setup was calculated to be 0.522 ps/nm [9]. The envelope of the rippled spectrum a potential gain spectrum with complete CD compensation and shows gain fluctuation within 1.2 dB in the 8-THz bandwidth.…”

PPLN-Based Optical Parametric Amplification for Wideband WDM Transmission

“…However, to perform wider-band phasesensitive amplification, it is necessary to accurately compensate for the CD generated during fiber transmission. To overcome this problem, we proposed a method for accurately estimating and compensating for the residual CD of the transmission link [47]. Recently, using this proposed method, we demonstrated 80-km unrepeated transmission with a 20-ch.…”

Wideband PPLN-Based Phase-Sensitively Amplified Transmission of 20-Channel 96-Gbaud WDM Signal

“…In addition, although one of the operational requirements of the PSA link is the ability to handle slight changes in the CD (e.g., caused by the connection of fiber-patch codes and changes in environmental temperature), adaptive and precise CD compensation using these methods is difficult. A spectral shaper using a spatial light modulator (SLM), such as a wavelength selective switch, can adaptively and precisely control the CD over a wideband [23], and a PSA link configuration that accurately measures the slight residual CD and compensates for it with an SLM have been proposed [18]. Because the control range of a CD is limited by the frequency resolution and the modulation depth of the SLM, large CDs must be roughly compensated using RDF or FBG apart from the compensation by the SLM.…”

“…In the ND-PSA, a PLL monitors an optical channel arranged at a different frequency from f0. Because the frequency that serves as a reference for the relative phase is that monitored by the PLL, the gain spectrum is modified as follows [18]:…”

“…We proposed a method to accurately estimate CD from the gain characteristic of PSA and experimentally showed a proof of concept [18]. Recently, an 80-km single-span transmission of a 2-THz WDM signal with the PPLN-based PSA supported by our proposed method was reported as a demonstration of the widest-band simultaneous phase-sensitive amplification [19].…”