Noise performance and nonlinear distortion of semiconductor laser under two‐tone modulation for use in analog CATV systems

Abstract

We introduce numerical modeling of noise performance and distortion of semiconductor lasers subject to two‐tone modulation according to the National Television Standards Committee NTSC plan for the cable television (CATV) signal transport. The waveform of the laser signal is simulated over wide ranges of the modulation index and placements of the modulation channel. The power and frequency spectra of the relative intensity noise (RIN) are characterized, and the associated second‐order harmonic distortion (2HD), and the second‐order (IMD2) and third‐order intermodulation distortions (IMD3) are calculated. The calculated data are used to predict the measures of the CATV system performance. The dynamic range of linearity of the laser is evaluated in terms of the spurious‐free dynamic range SFDR. We show that under weak modulation, the low‐frequency RIN is constant at −168 dB/Hz regardless the modulation frequency. Within this accepted noise level, IMD2 is 4 dBm higher than 2HD and 10 dBm higher than IMD3. When the modulation index exceeds 25%, the laser emits clipped signals associated with large values of signal distortions. Accepted values of the carrier to noise ratio and distortions correspond to lower modulation index and/or channel frequency. Copyright © 2015 John Wiley & Sons, Ltd.

Influence of Fiber Properties on Harmonic and Intermodulation Distortions of Semiconductor Lasers

“…IMDs have two types; namely, IMD2 and IMD3, which describe the spectral power at the sum and difference between the modulation two-tone frequencies, respectively. These intermodulation components are located very close to the modulation frequencies and can fall within the narrow transmission band of an optical link [15][16][17][18][19].…”

“…In analog optical fiber applications and for the purpose of increasing the transmission speed, the laser is modulated by two signals with adjacent frequencies. This type of two-tone modulation happens to results in intermodulation distortions (IMDs) in additions to HDs [15][16][17][18][19]. IMDs have two types; namely, IMD2 and IMD3, which describe the spectral power at the sum and difference between the modulation two-tone frequencies, respectively.…”

“…Also, it is essential to minimize the signal distortions in order to increase the transmitted information capacity in analog fiber links [20]. Intensive research works were reported on investigating HDs and IMD3 and determining the corresponding spurious free spectral range (SFDR) of the laser [9,10,13,[15][16][17][18][19][20][21]. Mendis et al [22] showed that such intermodulation distortions are lowered by large gain compression.…”

Effect of fiber properties and dispersion management on distortions associated with two subcarriers modulation of laser diode in radio over fiber systems

“…These nonlinear laser dynamics create undesired distortion products associated with the modulated laser signal, which degrades the transmission quality [14,15]. Typically, the nonlinear distortions associated with analog two subcarriers modulation of LDs are harmonic distortions (HDs) and intermodulation distortions (IMDs) [16][17][18][19]. These distortions are exacerbated when the frequency of the fundamental signals approaches the relaxation frequency of the laser (f _r) [20][21][22].…”

Post-detection modulating signal power reduction due to optical feedback

“…IN fiber-optic communication, IM-DD is, by far, the simplest and cost-effective scheme. In IM-DD communication [1][2][3][4][5][6][7], nonlinear signal distortion [1][2][3][4][5][6] is detrimental on one hand while undesired circuit reflection is an adverse effect on the other hand. Reflection in optical circuits often plays a detrimental role in the process of reception of an IM-DD fiber optic link.…”