Spectrally Equalized Frequency Comb Generation in Multistage Parametric Mixer With Nonlinear Pulse Shaping

A Survey of Optical Carrier Generation Techniques for Terabit Capacity Elastic Optical Networks

“…The performance of the comb based transmitter exceeded that of the standard tunable coherent device, while providing lower frequency uncertainty and drift [68]. In continuation to previous work on spectral flatness improvement through re-shaping, in addition to NOLM, Ataie et al introduced the use of nonlinear optical amplifying loop mirror (NALM) in the regeneration stage [143]. The difference between the two can be understood by looking into the mathematical representations of transfer function for NOLM and NALM.…”

“…In the time domain, an OFC corresponds to a pulse train, which can be expressed in general by g(t) = A(t) e jϕ(t) (15) where, A(t) is amplitude and φ(t) is phase of the pulse. The Fourier transform of the pulse train represents the spectrum of a band-limited OFC and can be expressed as [143]: (16) where, denotes the Fourier transform, δ(t − t 0 ) is Dirac delta function centered at t 0 , ∆T is the pulse repetition rate and G( f ) is the Fourier transform of the pulse waveform [143]. Therefore, any periodic temporal pulsed emission can also be Figure 16: Combs based on polarization modulators (a) Generic OFC scheme using PolM (b) Comb using cascaded PolM [138] (c) OFC scheme based on cascaded PolM and PM [139] (d) Single PolM based comb with additional flatness improvement block [135] (e) PolM based combs with optoelectronic oscillator (OEO) [140], [141] (f, h) Complementary frequency shifter using PolMs and its used in RFS loop [142].…”

“…The difference between the two can be understood by looking into the mathematical representations of transfer function for NOLM and NALM. The NOLM power transfer function can be expressed as [143]:…”

“…However the amplifier introduces additional noise. The transfer function of the NALM is given by [143]:…”

“…In principle, multiple NOLMs/NALMs can be cascaded to increase the spectral flatness of the comb. Two different combs with coarse (100 GHz) and dense (10 GHz) tone spacing, exhibiting a 4 dB flatness over 100 nm and sub-2 dB spectral flatness over 120 nm bandwidth (1500 lines), were produced respectively [143]. Subsequently, a comb based 20 Gbaud 16QAM transmitter was demonstrated using carriers from an OFC (based on the principle described above) providing 126 lines with a FSR of 100 GHz.…”