Modulation Bandwidth Of Semiconductor Lasers Research Articles

Room‐Temperature Single‐Mode Plasmonic Perovskite Nanolasers with Sub‐Picosecond Pulses

AbstractWith the explosive growth of communication traffic, increasing the modulation bandwidth of semiconductor lasers has attracted significant attention. However, after rapid progress is achieved, further increasing the modulation bandwidth of semiconductor lasers is hampered by the slow charge‐carrier dynamics. Here, a room temperature, single‐mode perovskite nanolaser with sub‐picosecond pulses, enabled by high Purcell enhancement is reported. This enhancement is achieved via transferring an atomically smooth perovskite nanoplatelet onto the surface of an ultra‐smooth SiO2/Ag film. This nanolaser features a low mode volume (V) as low as 0.137 µm3, a high‐quality factor (Q) up to 2180, and a low lasing threshold of 36.65 µJ cm−2. The Q value of the laser is one order of magnitude higher than that of state‐of‐the‐art nanolasers. The smoothness of both the nanoplatelet and the SiO2/Ag film in the laser is critical to achieving a high Purcell enhancement. Polarization analysis reveals that the laser emission consists of a transvere‐magnetic (TM) polarized surface plasmon mode and a transverse‐electric (TE) polarized photonic mode. Furthermore, ultrafast charge‐carrier dynamics indicate the surface plasmon decay time can be as short as 0.6 ± 0.4 ps due to the high Purcell enhancement. This work opens up the possibility of developing nanolasers with high bandwidths and ultra‐small sizes.

Performance of quantum-dot-based tunnel-injection lasers: A theoretical analysis

Tunnel-injection lasers promise advantages in the modulation bandwidth and temperature stability in comparison with conventional laser designs. In this paper, we present results of a microscopic theory for laser properties of tunnel-injection devices and a comparison with a conventional quantum-dot laser structure. In general, the modulation bandwidth of semiconductor lasers is affected by the steady-state occupations of electrons and holes via the presence of spectral hole burning. For tunnel-injection lasers with InGaAs quantum dot emitting at an telecom wavelength of 155 μm, we demonstrate that the absence of spectral hole burning favors this concept over conventional quantum-dot based lasers.

Ultra-Wide-Bandwidth Optically Controlled DFB Laser With External Cavity

Modulation bandwidth enhancement of an optically controlled single-mode semiconductor laser is achieved by introducing an external cavity into the laser. A calculation based on a rate equation model shows that the 3-dB bandwidth of the optically controlled external cavity laser (OC-ECL) can be substantially enhanced by controlling the feedback light intensity and phase properly. A broad 3-dB bandwidth of 59 GHz is experimentally confirmed by using the fabricated OC-ECL. The results suggest that a combination of cross-gain modulation and photon–photon resonance is suitable to enhance the modulation bandwidth of semiconductor lasers.

Enhancing Modulation Bandwidth of Semiconductor Lasers beyond 50 GHz by Strong Optical Feedback for Use in Millimeter-Wave Radio over Fiber Links

We present the modeling on high-speed modulation of semiconductor lasers beyond 50 GHz over a frequency band of 2 GHz by using strong optical feedback (OFB). This ultra high modulation frequency is achieved by adjusting the external-cavity resonance frequency close to the modulation frequency and optimizing strong OFB conditions to achieve stable operation. We show that this optimized strong OFB results in about 20 dB improvement in the link gain of a 55.8 GHz radio over fiber (RoF) link. We also discuss the influence of environmental variations on the simulated modulation characteristics.

Improving the Modulation Bandwidth in Semiconductor Lasers by Passive Feedback

We explore the concept of passive-feedback lasers (PFLs) for direct signal modulation at 40 Gb/s. Based on numerical simulation and bifurcation analysis, we explain the main mechanisms in these devices that are crucial for modulation at high speed. The predicted effects are demonstrated experimentally by means of correspondingly designed devices. In particular, a significant improvement of the modulation bandwidth at low-injection currents can be demonstrated

Modulation bandwidth of semiconductor lasers based on coupled quantum wells

AbstractThe effect of well coupling on differential gain and maximum‐modulation bandwidth for semiconductor lasers based on coupled quantum wells is analyzed using the K‐factor method. We determine differential gain in coupled quantum wells within the self‐consistent solution of the Poisson, Schroedinger, and 4 × 4 Luttinger–Kohn equations. The multiple‐body effects of bandgap renormalization, coulombic scattering interactions, and a nonMarkovian distribution are also included. The analysis has been performed for coupled wells at 1.55 μm in an InGaAsP/InP lattice‐matched system grown in the [001] direction. Our results suggest that in order to maximize modulation bandwidth and differential gain, one should design structures with barrier widths larger than 40 Å. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 42: 272–274, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20275

Nonlinear gain coefficients in semiconductor lasers: effects of carrier heating

Nonlinear gain coefficients due to the effects of carrier heating are derived from the rate equations of carrier energy transfer in semiconductor lasers. We find that, in the modulation responses of semiconductor lasers, stimulated recombination heating will affect the resonant frequency and damping rate in a same form as the effects of spectral hole burning, while free carrier absorption heating will only affect the damping rate. The effects of injection heating and nonstimulated recombination heating are also discussed. The carrier energy relaxation time is calculated from first principles by considering the interactions between carriers and polar optical phonons, deformation potential optical phonons, deformation potential acoustic phonons, piezoelectric acoustic phonons. At the same time, the hot phonon effects associated with the optical phonons are evaluated because their negligible group velocity and finite decay time. We show that the carrier-polar longitudinal optical phonon interaction is the major channel of carrier energy relaxation processes for both electron and holes. We also point out the importance of the longitudinal optical phonon lifetime in evaluating the carrier energy relaxation time. Neglecting the finite decay time of longitudinal optical phonons will significantly underestimate the carrier energy relaxation time, this not only contradicts the experimental results but also severely underestimates the nonlinear gain coefficients due to carrier heating. The effects of spectral hole burning, stimulated recombination heating, and free carrier absorption heating on limiting the modulation bandwidth in semiconductor lasers are also discussed.

Carrier thermalization in sub-three-dimensional electronic systems: Fundamental limits on modulation bandwidth in semiconductor lasers.

Carrier equilibration is essential for semiconductor laser operation since carriers are injected into the active region at energies higher than the effective band edges. While the threshold current of the laser diode can be minimized by quantum confinement in extra dimensions, the quantum effects in carrier capture and thermalization become more pronounced. In this paper, a full treatment of the carrier thermalization in electronic systems of reduced dimensionality for injection conditions relevant to laser operation is given based on ensemble Monte Carlo simulations and the fundamental limits on modulation bandwidth are discussed. Results are presented for quantum wells, quantum wires, and quantum dots. The peculiarities of the relaxation process in each structure are elucidated. It is shown that the relaxation times increase from \ensuremath{\approxeq}1 ps in bulk, to \ensuremath{\approxeq}10 ps in quantum wells, \ensuremath{\approxeq}50 ps in quantum wires, and \ensuremath{\approxeq}200 ps in quantum dots. Since the intraband relaxation times determine the extent of gain nonlinearities in semiconductor lasers, the maximum modulation bandwidth imposed by the intrinsic process of carrier relaxation can be calculated via the dependence of the optical gain on the photon density in the laser structure. For a graded-index quantum-well laser structure, the calculated value of the nonlinear gain coefficient is 1.1\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}17}$ ${\mathrm{cm}}^{3}$ with the maximum -3 dB modulation bandwidth of 78 GHz for a 100-\ensuremath{\mu}m cavity length. The nonlinear gain coefficient in quantum wires is enhanced in comparison with quantum wells, although the differential gain may be increased by as much as an order of magnitude with the exact value of the modulation bandwidth dependent on the details of the design of the quantum wire laser.

Effects of carrier transport on relative intensity noise and critique of K factor predictions of modulation response

The maximum possible intrinsic modulation bandwidth in semiconductor lasers is conventionally written in terms of the K factor. Although this is often sufficient in bulk lasers, it is usually not true in quantum well lasers where carrier transport can significantly affect the high speed properties. Analytical expressions are presented, which include the effects of carrier transport, for the modulation response and the relative intensity noise in quantum well lasers. It is shown that in the presence of significant transport effects, the K factor is not an accurate measure of the maximum possible intrinsic modulation bandwidth.