Intensity modulation technique using a directly frequency-modulated semiconductor laser and an interferometer

Abstract

Harmonic distortion in semiconductor laser direct frequency modulation is described with the aid of a nonlinear differential equation for the photon density including gain damping. Curves are presented showing the fundamental, secondorder harmonic and third-order harmonic FM responses. It is found that systems using a frequency-modulated laser and an interferometer would exhibit lower distortion levels than those using direct intensity modulation of the laser diode.

Linear, Low Noise Microwave Photonic Systems using Phase and Frequency Modulation

“…The analysis assumed that derivatives of the transmission spectrum of the interferometer (in the Fourier-frequency domain) with respect to the instantaneous optical frequency were proportional to overall link nonlinearity. Similar (inaccurate) theoretical analyses using Taylor series were published by [48] and [49]. However, these papers did include new models for the nonlinearities in the lasers' FM and included the effects of residual IM.…”

“…[94][95][96] used Bessel function and perturbation models to solve for harmonic and intermodulation distortion in laser IM and FM. In [48,[97][98][99][100][101][102], the authors used Taylor-series analyses to estimate the harmonic and intermodulation distortion of an FM laser after a Mach Zehnder interferometer. Unfortunately, none of these papers applied their theory to multi-section devices.…”

Output intensity noise of lightwave transmitters employing chirp demodulation

“…1 as decibels versus frequency when the MZI is assumed to operate in quadrature. The parameter of the curves is the free-spectral range (FSR), which is most conveniently defined as the frequency offset between a maximum transmission and the next-neighboring minimum [2]. The noise is seen to show a resonant behavior.…”

“…We have carried out a theoretical investigation of this technique and have shown its ability in improving the signal linearity [2]- [4]. However, the nonlinear distortion is not the only figure of merit for an optical transmitter.…”

“…The laser diode is described by the well-known single-mode rate equations including Langevin noise functions. For a device operated at a reasonable power far enough below saturation, the rate equations can be expressed in terms of normalized quantities [2] as…”