Laser Diode Modulation and Noise

Laser diodes represent a key element in the emerging field of opto­ electronics which includes, for example, optical communication, optical sensors or optical disc systems. For all these applications, information is either transmitted, stored or read out. The performance of these systems depends to a great deal on the performance of the laser diode with regard to its modulation and noise characteristics. Since the modulation and noise characteristics of laser diodes are of vital importance for optoelectronic systems, the need for a book arises that concentrates on this subject. This book thus closes the gap between books on the device physics of semiconductor lasers and books on system design. Complementary to the specific topics concerning modulation and noise, the first part of this book reviews the basic laser characteristics, so that even a reader without detailed knowledge of laser diodes may follow the text. In order to understand the book, the reader should have a basic knowledge of electronics, semiconductor physics and optical communica­ tions. The work is primarily written for the engineer or scientist working in the field of optoelectronics; however, since the book is self-contained and since it contains a lot of numerical examples, it may serve as a textbook for graduate students. In the field of laser diode modulation and noise a vast amount has been published during recent years. Even though the book contains more than 600 references, only a small part of the existing literature is included.

1 Introduction.- 2 Basic Laser Characteristics.- 2.1 Double heterostructure characteristics.- 2.2 Direct and indirect semiconductors.- 2.2.1 Energy- and momentum conservation.- 2.2.2 Semiconductor materials for direct and indirect semiconductors.- 2.3 Emission and absorption.- 2.3.1 Density of photon oscillation states.- 2.3.2 Principal mechanisms of radiative transitions.- 2.3.3 Carrier lifetime and lifetime of spontaneous emission.- 2.3.4 Gain and stimulated emission.- 2.4 Lasing characteristics of Fabry—Perot-type lasers.- 2.4.1 Lasing conditions.- 2.4.2 Dynamic characteristics of laser operation.- 2.4.3 Light current characteristics, threshold current and quantum efficiency.- 2.4.4 Basic laser structures.- 2.4.5 Modifications for the spontaneous emission term.- 2.5 Dynamic single-mode laser structures.- 2.5.1 DFB laser characteristics.- References.- 3 Longitudinal Mode Spectrum of Lasing Emission.- 3.1 Multimode rate equations.- 3.2 Spectral envelope for Fabry—Perot-type lasers (linear gain).- 3.3 Influence of nonlinear gain on the spectral characteristics.- 3.3.1 Symmetric nonlinear gain.- 3.3.2 Asymmetric nonlinear gain.- 3.3.3 Nonlinear gain, conclusions.- References.- 4 Intensity-Modulation Characteristics of Laser Diodes.- 4.1 Modulation characteristics by studying single-mode rate equations.- 4.1.1 Turn-on delay.- 4.1.2 Rate equations, small signal analysis.- 4.1.3 Relaxation oscillation damping.- 4.1.4 Upper limits for the modulation bandwidth of laser diodes.- 4.2 Influence of lateral carrier diffusion on relaxation oscillation damping.- 4.3 Modulation bandwidth limits due to parasitic elements.- 4.4 Examples for high speed modulation of laser diodes.- 4.5 Modulation and longitudinal mode spectrum.- 4.5.1 Transient spectra of laser diodes.- 4.5.2 Lasing spectra under high speed modulation.- 4.5.3 Dynamic single-mode condition.- 4.6 Modulation with binary signals.- 4.7 Harmonic and intermodulation distortions (without fibre interaction).- 4.7.1 Harmonic and intermodulation distortions for low modulation frequencies.- 4.7.2 Harmonic and intermodulation distortions for high modulation frequencies.- References.- 5 Frequency-Modulation Characteristics of Laser Diodes.- 5.1 Relation between intensity-modulation and frequency modulation.- 5.2 Current/frequency-modulation characteristics.- 5.3 Chirp effects in directly modulated laser diodes.- 5.3.1 Spectral line broadening due to laser chirping.- 5.3.2 Chirp-reduction by proper pulse shaping.- 5.3.3 Time-bandwidth product of chirped pulses.- 5.3.4 Transmission of chirped pulses over single-mode fibres.- 5.4 Possibilities of modifying the chirp parameter ?.- 5.4.1 Dispersion of the chirp parameter ?.- 5.4.2 Chirp of laser diodes, coupled to optical cavities.- References.- 6 Instabilities and Bistability in Laser Diodes.- 6.1 Repetitive self-pulsations due to lateral instabilities.- 6.2 Instability and bistability in laser diodes with segmented contacts.- References.- 7 Noise Characteristics of Solitary Laser Diodes.- 7.1 Relative intensity noise (RIN).- 7.1.1 Basic properties of noise signals.- 7.1.2 Definition and measurement of RIN.- 7.1.3 Requirement of RIN for intensity modulated systems.- 7.2 Introduction of the spontaneous emission noise.- 7.3 Intensity noise of laser diodes.- 7.3.1 Intensity noise of laser diodes by studying single-mode rate equations.- 7.3.2 Mode partition noise.- 7.3.3 Mode partition noise analysis for nearly single-mode lasers.- 7.3.4 Mode-hopping noise.- 7.3.5 1/f-intensity noise.- 7.4 Statistics of intensity noise.- 7.4.1 Statistics of amplified spontaneous emission.- 7.4.2 Probability density distribution for the total laser light output.- 7.4.3 Statistics of mode partition noise.- 7.4.4 Turn-on jitter in laser diodes.- 7.5 Mode partition noise for the transmission of pulse-code modulated (PCM)-signals.- 7.5.1 Multimode lasers.- 7.5.2 The mode partition coefficient k.- 7.5.3 Nearly single-mode lasers.- 7.6 Phase and frequency noise.- 7.6.1 Phase and frequency noise characterization in general.- 7.6.2 Spectral line shape for white frequency noise.- 7.6.3 Spectral line shape for 1/f-frequency noise.- 7.6.4 Frequency noise and spectral linewidth for single-mode laser diodes.- 7.6.5 Power-independent contribution to the linewidth of laser diodes.- 7.6.6 Correlation between FM-noise and AM-noise.- References.- 8 Noise in Interferometers Including Modal Noise and Distortions.- 8.1 Noise in interferometers.- 8.1.1 Complex degree of coherence.- 8.1.2 Interferometric noise analysis for single-mode lasers.- 8.1.3 Interferometric set-ups for measuring the linewidth and the degree of coherence.- 8.1.4 Interferometric noise analysis for multimode lasers.- 8.2 Modal noise.- 8.2.1 Modal noise for monochromatic light sources.- 8.2.2 Modal noise for single-mode lasers with finite spectral linewidth.- 8.2.3 Modal noise for multimode laser diodes.- 8.2.4 Modal distortions.- 8.3 Modal noise and distortions in single-mode fibres.- References.- 9 Semiconductor Lasers with Optical Feedback.- 9.1 Amplitude and phase conditions for laser diodes with external cavities.- 9.1.1 Short external reflectors for longitudinal mode stabilization.- 9.1.2 Emission frequency shifts due to optical feedback.- 9.1.3 Single external cavity mode condition.- 9.1.4 Spectral linewidth for laser diodes with external optical feedback.- 9.2 Dynamics of laser diodes with external reflections.- 9.2.1 Derivation of the time-dependent electric field.- 9.2.2 Modulation characteristics of external-cavity lasers.- 9.3 Laser diodes with distant reflections.- 9.3.1 Classification of feedback regimes.- 9.3.2 Phase and frequency noise of laser diodes with distant reflectors.- 9.3.3 Intensity noise in laser diodes with distant reflectors.- 9.3.4 Coherence collapse.- 9.3.5 Tolerable feedback levels.- References.- 10 Laser Diodes with Negative Electronic Feedback.- 10.1 Modulation characteristics of laser diodes with negative electronic feedback.- 10.2 Linewidth narrowing and phase noise reduction with negative electronic feedback.- References.- 11 Circuitry for Driving the Laser Diode.- 11.1 Schemes for stabilizing the bias current.- 11.2 Laser drivers with optoelectronic integration.- References.