Relative Intensity Noise Characteristics Research Articles

Correlation between emission and relative intensity noise spectral profiles of an Er-doped fiber superfluorescent source

The spectral characteristics of the relative intensity noise (RIN) of two amplified spontaneous emission (ASE) sources are experimentally measured. An Er-doped fiber superfluorescent source (EDF-SFS) is investigated and compared with a super-luminescent diode (SLD) source, using a simple tunable fiber Bragg grating filter-based system. Experimental results based on normal ASE operation conditions showed that the RIN distribution of the EDF-SFS is correlated with its emission spectral profile, which is different from the results observed using the SLD source. This finding shows for the first time that an EDF-SFS based ASE has fundamentally different RIN characteristics from other known existing spontaneous emission broadband sources. The amplifying process of the EDF-SFS is discussed and confirmed using a rate equation-based simulation.

Quantum-dot semiconductor lasers with prominent relative intensity noise and spectral characteristics.

Relative intensity noise (RIN) behavior of a quantum dot laser (QDL) at free running and under optical injection locking (OIL) has been reported in detail. Considering the mutual effects of the inhomogeneous and homogeneous broadenings, different and also non-routine RIN characteristics of a QDL at low, intermediate, and high homogeneous broadening regimes have been discussed. Results demonstrate that an injection-locked quantum dot laser exhibit enhanced characteristic over free-running operation along with low-frequency noise behavior in a wide range of homogeneous broadening values. RIN reduction of about 25, 55, and 7 dB/Hz have been achieved for low, intermediate, and high values of homogeneous broadening which implies the spontaneous emission noise suppression even at low injection power. The promising impact of the OIL on side-mode suppression for the intermediate homogeneous broadening regime has also been discussed. Our results guarantee the single-mode and low-noise operation of the OIL-QDL at any homogeneous broadening value.

Multi-Objective Laser Rate Equation Based Parameter Extraction Using VCSEL Small Signal Response and RIN Spectra

Rate equation parameters used to simulate semiconductor lasers must be carefully chosen in order to accurately model high-speed laser characteristics in optical link simulations. Previous parameter extraction methods have largely characterized these lasers through their small signal frequency response. We show that capturing both the small signal frequency response and relative intensity noise (RIN) spectrum of the laser is crucial for accurate parameter extraction. We present a multi-objective parameter extraction method alongside a stochastic rate equation model to account for a vertical cavity surface emitting laser's (VCSEL's) bandwidth and RIN characteristics. A genetic algorithm extracts VCSEL parameters from a set of experimentally measured small signal responses and RIN spectra at multiple drive currents. Through Pareto sorting we can extract a single set of parameters which accurately captures the laser's BW and RIN characteristics.

Improved noise characteristics of mutually injection locked semiconductor lasers in a weak coupling regime

Noise characteristics of stable mutual injection locking under weak coupling is studied by a theory based on noise correlation analysis. Both relative intensity noise (RIN) and frequency noise are investigated in detail. It is found that the RIN characteristics of mutual injection locked lasers under weak coupling are similar to that of unidirectional injection locking, except for the oscillation caused by coupling delay. Different from unidirectional injection locking, however, an extremely narrow linewidth can be obtained by mutual injection locking, and the injection parameters have a significant influence on the linewidth.

Experimental Demonstration of Amplified Feedback DFB Laser With Modulation Bandwidth Enhancement Based on the Reconstruction Equivalent Chirp Technique

A novel amplified feedback DFB laser with extended modulation bandwidth is experimentally demonstrated in this paper. All the three sections of laser cavity, including DFB section, phase section, and amplified feedback section, have the same active layer, which can avoid the butt-joint regrowth process. The gratings in both DFB section and amplified feedback section are fabricated by the reconstruction equivalent chirp technique, which can significantly decrease the difficulties in realizing precise grating structure. An enhanced −3 dB bandwidth of 19 GHz is achieved by means of a normal low-frequency wafer. Modulation linearity and relative intensity noise characteristics are experimentally investigated. 20 MSymbol/s 32-QAM signal with 19 GHz carrier is transmitted via 25-km radio-over-fiber link using the as-fabricated directly modulated DFB laser, and the average error vector magnitude of the whole link is 3.91%.

Relative intensity noise of temperature-stable, energy-efficient 980 nm VCSELs

The relative intensity noise (RIN) of temperature-stable, energy-efficient oxide confined vertical-cavity surface-emitting lasers (VCSELs) have been investigated. Low energy consumption data transmission is achieved by using small oxide-aperture diameter VCSELs biased at small currents. We demonstrate that energy efficiency is not in conflict with our VCSELs’ RIN characteristics. The experimental results indicate that small oxide-aperture diameter VCSELs, which are most suitable for energy-efficient, temperature-stable operation, exhibit lower laser RIN due to less mode competition inside the smaller optical cavity volume. Our energy-efficient VCSELs fulfill the RIN requirements of the 32G Fibre Channel standard.

Design Methodology for Reducing RIN Level in DFB Lasers

The relative intensity noise (RIN) characteristics in distributed feedback (DFB) lasers are analyzed theoretically by proposing a new methodology. In addition to temperature variation (T), the effect of other model parameters such as injection current (Iinj), active layer volume (V), spontaneous emission (βsp) and gain compression (ε) factors on RIN characteristics is investigated. The numerical simulations shows, the peak RIN level can be reduced to around –150 dB/Hz, while relaxation oscillation frequency (ROF) is shifted towards 5.6 GHz. In addition, the RIN level is increased with temperature by the rate of 0.2 dB/ºC and ROF is reduced by the rate of 0.018 GHz/ºC. Results show, the low RIN level can be obtained by selecting model parameters reasonably.

External cavity diode laser based upon an FBG in an integrated optical fiber platform

An external cavity diode laser is demonstrated using a Bragg grating written into a novel integrated optical fiber platform as the external cavity. The cavity is fabricated using flame-hydrolysis deposition to bond a photosensitive fiber to a silica-on-silicon wafer, and a grating written using direct UV-writing. The laser operates on a single mode at the acetylene P13 line (1532.83 nm) with 9 mW output power. The noise properties of the laser are characterized demonstrating low linewidth operation (< 14 kHz) and superior relative intensity noise characteristics when compared to a commercial tunable external cavity diode laser.

Effect of carrier transition mechanisms and gain compression on relative intensity noise of 1.55 µm QD lasers

The impacts of gain compression and direct carrier transition on relative intensity noise (RIN) characteristics of 1.55µm QD lasers have been investigated theoretically. The auto and cross correlation coefficients are calculated through small signal linearization of rate equations for carriers and photon numbers in presence of Langevin noise sources. Calculations reveal that gain nonlinearity reduces RIN level of QD lasers while increases damping factor. These results show good agreement with experimental measurements of RIN spectrum in 1.55µm QD lasers which is flat up to 10GHz. Evaluations demonstrate that among wetting layer, Quantum and Photon shot noises, the second and third one have essential role in overall value of RIN in both linear and nonlinear QD lasers. Moreover, calculations indicate that by increasing the direct carrier transition time, RIN level of auto and cross correlations resulted from wetting layer and ground state carriers increases. Finally, it is shown that the RIN level declines in nonlinear QD lasers by working at higher injection currents which is in confirmation with recent experimental reports. Though, it is demonstrated that considering nonlinear gain and direct carrier transition play essential role on correct modeling of RIN characteristics in 1.55µm QD lasers.

Relative Intensity Noise Reduction by Optimizing Fiber Grating Fabry–Perot Laser Parameters

A set of nonlinear rate equations that can describe an external cavity laser with any arbitrary external optical feedback (OFB) level are derived. A comprehensive study on the relative intensity noise (RIN) characteristics of a fiber grating Fabry-Perot is performed numerically. In this paper, fiber Bragg grating (FBG) is used as a wavelength lasing selective element to control the external OFB level, thereby control the RIN. In addition to the external OFB level, the effect of other external cavity parameters such as temperature, injection current, cavity volume, gain compression factor, and FBG parameters on RIN characteristics is investigated. The temperature dependence (TD) of RIN is calculated according to TD of laser parameters instead of well-known Parkove relationship. Results show that by optimization, the peak value of the RIN can be reduced down to around -150 dB/Hz. The optimum and the shortest external cavity length that provides the minimum RIN is found to be around 3.1 cm. In addition, by optimization, the relaxation oscillation frequency of RIN spectra is shifted toward around 5.6 GHz.

Dynamic Characteristics and Linewidth Enhancement Factor of Quantum-Dot Vertical-Cavity Surface-Emitting Lasers

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This study explores the relative intensity noise characteristics of quantum-dot vertical-cavity surface-emitting lasers (QD VCSELs). The resonance frequency and eye diagram are presented. The linewidth enhancement factor (<formula formulatype="inline"><tex Notation="TeX">$\alpha$</tex></formula> factor) of QD VCSEL is also investigated experimentally. The values of <formula formulatype="inline"><tex Notation="TeX">$\alpha$ </tex></formula> factor were measured to be between 0.48 and 0.60. Moreover, a photonic RF phase shifter is examined using the QD VCSEL. A phase shifter with a total phase shift of 2<formula formulatype="inline"><tex Notation="TeX">$\pi$</tex> </formula> was demonstrated. These investigations and demonstrations will be useful in the field of QD VCSEL. </para>

Self-Consistent Analysis of the Relative Intensity Noise Characteristics in the Strained AlGaInN Laser Diodes with the High Frequency Current Modulation Effects

The relative intensity noise (RIN) characteristics in 405 nm blue laser diodes grown on wurtzite AlGaInN multiple quantum well structures were investigated using the rate equations with the quantum Langevin noise model. The device parameters were extracted from the optical gain properties of the MQW active region using the self-consistent numerical method developed for calculating the multiband Hamiltonian in the strained wurtzite crystal. These methods have been applied to laser diodes for various conditions including the external feedback and the high frequency current injection.

Relative intensity noise characteristics of frequency stabilised grating-coupled modelocked semiconductor laser

Relative intensity noise (RIN) characteristics of a frequency stabilised grating-coupled modelocked semiconductor laser (MSL) have been experimentally investigated. Reported is the first measurement, to the authors&apos; knowledge, of general RIN characteristics as well as RIN reduction in the frequency stabilised MSL system showing the relationship between RIN and mode coherency in the MSL.

External Feedback Effects on the Relative Intensity Noise Characteristics of InAIGaN Blue Laser Diodes

The external feedback effect on the relative intensity noise (RIN) characteristics of blue InAlGaN laser diode has been analyzed taking into account the spontaneous emission noise and the injection current for the high frequency modulation. A Langevin diffusion model was exploited to characterize its relative intensity noise. The simulation parameters were quantitatively evaluated from the optical gain properties of the InAlGaN multiple quantum well active regions by using the multiband Hamiltonian for the strained wurtzite crystals. The extracted parameters were then applied to the rate equations taking into account the external feedback and the high frequency modulation current. The RIN characteristics were investigated to optimize the low frequency laser diode noise characteristics.

Relative intensity noise characteristics of injection-locked semiconductor lasers

An experimental and theoretical study of relative intensity noise (RIN) spectra of side-mode injection-locked Fabry–Pérot semiconductor lasers is reported. It is shown that the injection-locking technique effectively increases the relaxation oscillation frequency from 4.5 GHz (free-running mode) to 12 GHz (injection-locked mode) and enhances relaxation peaks of the slave laser RIN spectra. Results from our theoretical model, which include the key parameters for semiconductor quantum-well lasers, such as the linewidth enhancement factor, the nonlinear gain saturation coefficients, and optical confinement factor, show good agreement with our experimental results.

Relative intensity noise for laser diodes with arbitrary amounts of optical feedback

A unified study of the noise characteristics of semiconductor lasers with optical feedback and short external cavity length is presented. A new set of nonlinear rate equations that can describe a laser diode with any amount of optical feedback is proposed. The relative intensity noise (RIN) is calculated by using a numerical solution of these equations. This paper concentrates mainly on the moderate and strong feedback regimes. The spectral phenomena observed during the transition from the weak feedback to the coherence collapse regime and then to the strong feedback regime are studied and explained. The effect of the variation of some of the laser diode parameters on the RIN characteristics is also investigated.

Explanation of low-frequency relative intensity noise in semiconductor lasers

For the first time, the enhanced low-frequency relative intensity noise characteristics of semiconductor lasers is explained. It is shown, by multimode rate equation analysis, that the enhanced low-frequency noise is caused by coupling between longitudinal modes which can renormalize the resonance frequency of the individual modes to very low values. It is further shown that a single-mode laser will also exhibit enhanced low-frequency noise unless the side-mode suppression is high.