Polarization dependent parametric gain in amplifiers with orthogonally multiplexed optical pumps

Abstract

508 / VOL. 2 / OFC 2003 / THURSDAY MORNING to 2 dBm when the gain is increased to 23.5 dB.Note that the XGS effect can be reduced by a gain clamping principle, i.e. by launching high power CW signal into the FOPA. ConclusloosWe have presented, to ow knowledge, the fmt expenmental results on FOPA as in-line amplifier for WDM systems. We.have quantified the impairments from both XGS and FWM and found them -101 -30 -20 t 1 Fif -90 1540 1550 1560 1570 1580 Wavelength, nmFig. 2 Typical spectra with and without pump after the HNLF. -. . equal channel spacing -~ Fig 3 O m l l o r c o~e e x e s showing how a hit seque$ [unequ<l channel spacing __ ~c e on channel 1 LS deterioratedbv XGS and FWM from adjacent chhels. -14 -12 -10 -8 -6 -4 -2 0 2 4 -6 -4 -2 0 2 4 6 8 10 12 Channel output paver, dBm Channel OW w e r , dBm . .Fig. 4 Power penalty versus channel output power for WO diNerent amplifier gains. Inset shows BERcurves at 1.8 dBm output power and verifies error-free performance.The results from the penalty measurements at 15.8 dB bump power 31.0 dBm) and 23.5 dB (pump power 32.0 dBm) small signal gain are shown in Fig. 4. At low input power levels, the signal-to-noise ratio at the FOPA output will limit the performance, and the penally is comparable for identical input power levels independent of the gain and the number of channels. At high power IcveIs, channel interaction from XGS and F W M will induce a penalty. However, the latter will only OCCLV when more than two channels are present. The penally from FWM is caused by the appearance of an idler wave from W O signals on the same wavelength as the third. This effect can thereby be removed if the signal wavelengths are carefully chosen, and in Fig. 4, the dashed linesshow the penalty when one of the wavelengths is changed. In this case, the penalty from XGS in a three channel WDM-system is isolated. At high gain, a substantial penalty is caused by XGS alone, while at moderate gain, the penalty is mainly caused by FWM. To verify that there were no error-floors, the inset BER-curves in Fig. 4 were measured for one channel at I .8 dBm oulput power bath with and without the presence of the other channels. Furthermore, the sensitivities for the other two channels were measured to be within 0.5 dB from the presented channel.From the results in Fig. 4, we can see that the maximum channel power with three channels present and < 3 dB power penalty is approximately 0 dBm at 15.8 dB gain. This is enhanced . . Aekno\;ledgementsSumitamo Electric Industries are acknowledged for providing the HNLF and Jonas Hansryd at CENiX Inc. i s acknowledged for sharing his exoenise in the area of FOPAs. Riferenees: [I] 1. Hanslyd and P. A. Andrekson "Wavelength tunable 40 GHz pulse source based on a fiber optical paramemc amplifier," Electronics Letters, Vol. 37, pp. 584-585, (Apr2001). [2] J. Hansryd and P. A. Andrekson "Broadband CW pumped fiber optical paramemc amplifier with 49 dB gain and wavelength conversion eficiencv." IEEE Photonics Technoloev Letters. Vol. I , 13,p~.'194-196, (2001...

Fiber Optic Parametric Amplifiers for Lightwave Systems

“…PDG increases as the signal wavelength gets closer to either of the pumps. The same behavior was also observed in a 2003 experiment [72]. In physical terms, the reason why the largest PDG occurs for a signal close to pump wavelength can be understood as follows.…”

“…It is thus evident that both of these schemes will introduce polarization-dependent gain (PDG). This was also observed experimentally when second method was implemented [72].…”

“…Such birefringence fluctuations induce polarization-mode dispersion (PMD) and randomize the SOP of any optical wave propagating through the fiber [69,70]. They change the relative orientation of the four waves, affect the angular-momentum conservation among the four photons during the FWM process, and thus seriously degrade the performance of FOPAs [6], [71], [72]. Because, the nonlinear processes contributing to parametric amplification depend on the SOPs of the fields, a vector theory of FWM is needed.…”

Current status of fiber optical parametric amplifiers

“…Then if the two orthogonal pumps are aligned with the Received Power (dBm) PSPs, they have propagation constants that differ because of the fiber birefringence. As a result, ∆β now contains an extra term, which has a linear dependence on ∆ω s , and this renders the gain spectrum asymmetric [28].…”

Second-order effects in fiber optical parametric amplifier

“…In recent years, impressive performance has been demonstrated by the author's research group and different researchers in fiber OPAs in several respects: 1) Gain in excess of 60-dB has been obtained [1] [2]; 2) fiber OPAs can exhibit a large variety of gain spectra: a gain bandwidth of 400-nm or beyond has been demonstrated [xx]; tunable narrowband gain regions can also be generated [3]; 3) Noise figure of 3.7-dB [4], limited by other third-order nonlinear process [5]; 4) Polarization-insensitive operation in both one-pump [6] and two-pump configurations [7]; 5) Due to the inverted spectrum of the idler with respect to that of the signal; thus by placing an OPA in the middle of a fiber span one can realize midspan spectral inversion (MSSI) which counteracts the effect of fiber dispersion and some nonlinear effects [8]. Besides using fiber OPA in continuous-wave regime as in typical systems, pulsed-pump has also been demonstrated to achieve larger bandwidth and higher peak gain by combining with optical filtering technique [9].…”