Dominant Lasing Mode Research Articles

High Single-Mode Stability Tunable In-Series Laser Array With High Wavelength-spacing Uniformity

Multi-wavelength distributed feedback laser array based tunable semiconductor lasers have been widely used owing to their high mode stability and simple tuning scheme. Comparing with the in-parallel laser array, the in-series one can avoid a large power loss caused by the optical combiner. However, the single-mode stability of an in-series laser array is vulnerable to the reflections of other lasers. Here we experimentally demonstrated a tunable in-series laser array with high single-mode stability and high uniformity of wavelength spacing. To reduce the impact of such reflections, the Bragg gratings in different lasers were designed in phase, and the grating phase error was reduced by utilizing the reconstruction-equivalent-chirp technique. Besides, a three-section laser structure was applied in each laser to increase the priority of the dominant lasing mode. Four lasers with small wavelength-spacings of 2.5 nm were integrated in the in-series laser array. According to the measurement results of 40 in-series laser arrays (160 lasers), wavelength deviations of 90.6% lasers were within ±0.2 nm, average wavelength spacings of 97.5% of the measured laser arrays were deviated from the design within ±0.2 nm, and SMSRs of 96.3% lasers were above 45 dB. The output power was above 25 mW and the relative intensity noise was below -130 dB/Hz. Like the in-parallel laser array, the proposed laser array can be applied in either continuous wavelength tuning or fast channel switching. For the continuous wavelength tuning applications, the 10-nm tuning range was obtained with a temperature tuning range of less than 20 °C. For the fast channel switching applications, four channels with 2.5-nm spacing are available, and the switching time between two channels was less than 300 ns.

Omnidirectional whispering-gallery-mode lasing in GaN microdisk obtained by selective area growth on sapphire substrate.

The optical properties of hexagonal GaN microdisk arrays grown on sapphire substrates by selective area growth (SAG) technique were investigated both experimentally and theoretically. Whispering-gallery-mode (WGM) lasing is observed from various directions of the GaN pyramids collected at room temperature, with the dominant lasing mode being Transverse-Electric (TE) polarized. A relaxation of compressive strain in the lateral overgrown region of the GaN microdisk is illustrated by photoluminescence (PL) mapping and Raman spectroscopy. A strong correlation between the crystalline quality and lasing behavior of the GaN microdisks was also demonstrated.

Mode-Hopping Phenomena in the InGaN-Based Core–Shell Nanorod Array Collective Lasing

A two-dimensional monolithic InGaN-based core–shell nanorod array was excited under a varying temperature. We observed an abrupt dominant mode hopping from 3.29 to 3.41 eV in the collective lasing as the temperature decreased from T = 240 to 225 K. Photoluminescence under a near-threshold pumping density revealed the splitting of spontaneous emission between the core and the shell with a decreasing temperature. The bandgap evolution of GaN and InGaN showed opposite trends due to the interaction of temperature effects and bandgap renormalization effects. Theoretical simulation revealed the differences of gain spectra evolution between room temperature and low temperature due to the difference in the carrier dynamics. In the optically coupled nanorod array, the dominant lasing mode was not only determined by its structure, but also strongly influenced by external operating conditions. Rather than singular microcavity lasers, the coupled nanorod array demonstrated a broader parameter space for on-chip wavele...

Active control of emission directionality of semiconductor microdisk lasers

We demonstrate lasing mode selection in nearly circular semiconductor microdisks by shaping the spatial profile of optical pump. Despite of strong mode overlap, adaptive pumping suppresses all lasing modes except the targeted one. Due to slight deformation of the cavity shape and boundary roughness, each lasing mode has distinct emission pattern. By selecting different mode to be the dominant lasing mode, we can switch both the lasing frequency and the output direction. Such tunability by external pump after the laser is fabricated enhances the functionality of semiconductor microcavity lasers.

Dielectric-Band Photonic Crystal Nanobeam Lasers

We investigate a mode gap confined dielectric band laser via a 1-D photonic crystal (PhC) nanobeam (NB) nanocavity with lattice gradually shifted PhC mirror. Owing to different modal symmetries, different zeroth-order dielectric mode properties, including quality ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> ) factors, mode volumes, lasing thresholds, and slope efficiencies, in nanocavities with two different cavity sizes are investigated. In experiments, single-mode lasing from dielectric bands with low effective lasing thresholds is obtained. Rising of the high-order modes is also observed when we increase the PhC mirror periods for high Q factor of the zeroth-order dielectric mode. In addition, we observe the bonding and antibonding modes in beamwidth mismatched coupled NB nanocavities and switch the dominant lasing mode via spatially nonuniform carrier injection.

Demonstration of All-Optical nand Gate Using Single-Mode Fabry–Pérot Laser Diode

A novel, simple, and universal all-optical NAND gate using single-mode Fabry-Perot laser diode (SMFP-LD) is demonstrated. The basic operating principle of the proposed NAND gate is the modulation of the dominant lasing mode of SMFP-LD by the injection of external beams. The dominant lasing mode gain is suppressed only when both input beams are high. As SMFP-LD is used to demonstrate the logic function, no additional beam is required as needed in the multimode Fabry-Perot laser diode (MMFP-LD) schemes. The operating principle is explained and the experimental results are presented at 10 Gb/s input data. The logic function is realized with a clear eye opening and an extinction ratio of 14.6 dB with a rising and falling time of 38.3 and 67.1 ps, respectively.

TE-TM coupled mode dynamics in a semiconductor laser subject to feedback with variably rotated polarization

We report on the experimental observation of dynamical collapses which address selectively the TM-mode of a laser subject to optical feedback with variably rotated polarization. Simultaneously, the TE-mode which remains the dominant lasing mode exhibits power bursts. We analyze the relative phase shift between the feedback fields into the TE- and TM-mode and find that the dynamical collapses, observed in a specific range of polarization rotation angles, can be attributed to large phase shift feedback conditions applied on the TM-mode.

Influence of external cavity length on multimode hopping in microchip Nd:YAG lasers

The influence of external cavity length on multimode hopping in microchip Nd:YAG lasers is investigated experimentally. With an optical feedback loop, the threshold gain of different longitudinal modes are all modulated by changing the external cavity length; a lambda/2 change in the external cavity length causes a one-period oscillation. The longitudinal modes can be divided into groups according to different initial threshold gain variations and modulation trends corresponding to different external cavity phases. Because of the initial gain difference, only one mode in each group is the dominant potential lasing mode, while others are suppressed. During the 2 pi change of the external cavity phase, mode hopping occurs among these potential lasing modes from different groups. Both the intensity waveforms and the number of hopping modes strongly depend on the external cavity length. Experimental results agree well with the theoretical analysis of the phenomenon of multimode hopping subjected to optical feedback in microchip Nd:YAG lasers.

Purely loss-coupled distributed feedback lasers based on electromagnetically induced absorption in active photonic band gaps

We utilize electromagnetically induced absorption (EIA) in a one-dimensional functional (active) photonic band gap structure to propose a coherently generated purely loss-coupled distributed feedback (DFB) laser. Such a laser happens when interaction of the photonic band structure with a control laser field totally removes its refractive index perturbation and replaces it with periodic regions of EIA, forming an optical dark lattice. Such a lattice does not have any stop band, but scatters light coherently at the Bragg wavelength. We also show that before the optical dark lattice happens, the photonic band gap structure can act as a coherently generated partly loss-coupled DFB laser with dominant lasing mode at the longer wavelength side of the stop band. We expect such a distinct feature makes this laser quite stable.

Adaptive Mode Selection Based on Chaotic Search in a Fabry–Perot Laser Diode

This paper describes mode-transition dynamics of a compound-cavity, multimode, Fabry–Perot (FP) semiconductor laser and the basic idea of adaptive wavelength selection using chaotic search. In the presence of external feedback, the laser is shown to exhibit different mode-competition dynamics including single-mode, multistability, and chaotic mode-transition states. A chaotic search technique is proposed to adaptively select a dominant lasing mode which fits the environment by switching a control parameter (feedback level or bias injection) between multistability and chaotic mode-transition states. The effectiveness of the adaptive mode selection is verified through a computer simulation and the robustness as well as the experimental implementation of the technique are discussed.

Measurement and modeling of distributed-feedback lasers with spatial hole burning

Longitudinal spatial hole burning (SHB) in semiconductor lasers is examined theoretically and experimentally in index-coupled distributed-feedback (DFB) lasers. The amplified spontaneous emission (ASE), or facet light, below threshold is measured and fitted by a theoretical model in order to extract the parameters such as the phases of optical field reflection at the facets. The ASE spectrum above threshold is also measured and compared with theoretical results using the same parameters. The photon density profile of the dominant lasing mode and the carrier density profile at a bias current above threshold are then calculated. The theoretical results are compared to the experimentally measured change in the spontaneous emission (SE) (or carrier density) profile along the laser stripe using an optical fiber setup with careful calibration between the below and above threshold SE longitudinal profiles. By fitting the experimental ASE spectra from the facet both below and above threshold and the SHB profile from the side of the laser as a function of position to our theoretical results, we show that our procedure is a promising and systematic approach for understanding DFB lasers, especially the SHB effects. It is also shown that the facet reflectivities, phases, and the coupling coefficient have a large impact on the SHB of DFB lasers.

Optical bistability and nearly degenerate four-wave mixing in a GaAlAs laser under intermodal injection

We demonstrate in a GaAlAs laser under intermodal optical injection, the existence of a domain, outside the injection-locking range, where the sidemode becomes the dominant lasing mode and gives rise to nearly degenerate four-wave-mixing processes. It is shown experimentally and by computer simulation that this domain is asymmetric with respect to the frequency detuning, and bistability of its borderline occurs, with a characteristic dependence on the injected light power.

Performance implications of mode partition fluctuations in nearly single longitudinal mode lasers

A statistical model of mode partition fluctuations is developed for semiconductor laser diodes with a single dominant lasing mode and one vestigial side mode. It is the basis of a rigorous analysis of the influence of partition fluctuations on the performance of digital lightwave transmission systems. A Gauss quadrature rule is used to evaluate the average probability of error in the presence of mode-partition-dependent shot noise, photodetector multiplication noise, circuit noise, and intersymbol interference. This methodology permits the determination of reliable performance estimates enabling the establishment of permissible degrees of mode partition fluctuations. >

Twisted-terraced-substrate GaAs/AlGaAs lasers

We present a new structure of AlGaAs/GaAs DH lasers consisting of two oppositely facing terraced-substrate cavities in series. Polarisation change at the junction results in internal reflection and produces a mode-selection effect. A stable single longitudinal mode is observed over a wide current range from 100 to 150 mA. The dominant lasing mode is locked over a 7° temperature variation. The lowest observed threshold current is 50 mA.