Dynamic Single Mode Research Articles

Electrical single mode switching in coupled microcavity

Flexible lasing mode regulation is significant for optoelectronic applications, such as on-chip communication and optoelectronic integration. However, reversible and dynamic single mode lasing output is still a challenge. Herein, reversible lasing modes tuning is demonstrated in whispering gallery mode microcavity controlled by bias voltages. Especially in coupled microcavity consisting of two microrods, applied electrical fields cause lasing modes shifting of one microrod, and the optical field coupling process with the other microrod occurs simultaneously to select distinct single mode lasing. Hence, the switchable single mode lasing can be achieved. The mechanisms of Vernier effect, electro-optic effect, and their synergy on lasing mode modulation are analyzed via experimental results and theoretical analysis. Synergistically running the two effects, the high quality factor of the single mode indicates an effective coupling process, providing an effective way for controllable lasers.

The Theory and Experimental Study on the Long-External Cavity Semiconductor Lasers

Long-External Cavity Laser (L-ECL) is a kind of new and promising type laser because of its dynamic single mode performance. In this paper, firstly, the theory model of L-ECL is discussed; Secondly, the influence of coupling coefficient on the threshold gain of L-ECL is studied based on equivalent external cavity theory; Thirdly, utilizing the theory of equivalent cavity length, combined rate equations, the high frequency response characteristic of L-ECL is analyzed; Lastly, optical spectrums of L-ECL on different grating peak reflectivity are obtained by experiment.

Dynamic Single-Mode Lasers

The 40-year history of research on semiconductor lasers for high-speed long-distance optical fiber communications, so-called dynamic single-mode (DSM) lasers, is reviewed. DSM lasers include phase-shift distributed feedback (DFB) lasers, uniform DFB lasers, wavelength tunable (WT) distributed Bragg reflector lasers, WT distributed reflector lasers, and external reflector lasers. The vertical cavity surface emitting laser is also a type of DSM laser that is applied for rather short-distance communication. Photonic-integrated circuits with monolithic integration of DSM lasers with other devices, as well as photonic crystal lasers, have advanced significantly to support stable operation of photonic subsystems. The DSM laser is currently essential for most long-haul optical communications and transoceanic submarine cables, as well as medium-distance local area networks. Its application to sensing systems is another interesting area.

Dynamic single-mode and modulation characteristics analyses for λ/4 phase-shifted distributed feedback lasers with chirped grating

The dynamic single-mode and modulation performance of λ/4 phase-shifted distributed feedback laser diode with chirped grating (QWS-CG-DFB) are analyzed theoretically. The numerical simulation shows that, in contrast to purely QWS-DFB laser, the enhanced dynamic single-mode suppression ratio (SMSR) can be reached by QWS-CG-DFB laser. Under the smaller biasing current, the modulation band-width in presence of chirped grating is narrower, this difference shrinks for larger biasing current. For large signal modulation, the chirped grating is helpful to increase the output extinction ratio, but worsens the frequency chirping. The good dynamic characteristic can be obtained by selecting system parameters reasonably.

Detailed modulation response analyses on enhanced single-mode QWS-DFB lasers with distributed coupling coefficient

By using the coupled mode equations, the dynamic characteristics of λ/4 phase-shifted distributed feedback laser diode with distributed coupling coefficient (QWS-DCC-DFB) is analyzed. The numerical simulation indicates that, compared with purely QWS-DFB laser, the better dynamic single-mode can be achieved by QWS-DCC-DFB laser; Under the smaller biasing current, the modulation band-width is narrower, this difference shrinks for larger biasing current; For large-signal modulation, the distributed coupling coefficient is helpful to increase the output extinction ratio, but worsens the wavelength chirping. The good dynamic characteristic can be obtained by selecting system parameters reasonably. QWS-DCC-DFB laser would have potentials in optics communications because of better dynamic SMSR.

Design and Analysis of a Widely Tunable Sampled Grating DFB Laser Diode with High Output Power

A widely tunable SG-DFB (Sampled Grating Distributed Feedback) laser diode is proposed and its feasibility is confirmed through simulation. The new SG-DFB laser diode is composed of a pair of sampled gratings, some parts of which are gain sections and the other parts of which are phase control sections. It is shown that a few tens of nanometers can be tuned through the adjustment of two currents into the phase control sections. Higher output power is expected compared with a SG-DBR laser diode with similar parameters. The dynamic single mode operation is also observed in the time-domain simulation.

Large signal dynamics of distributed feedback lasers with spatial modulation of their coupling coefficient and grating pitch

A multimode time domain model is used to study the large signal dynamics of complex distributed feedback lasers with nonuniform grating pitch and coupling coefficient. Lasers with longitudinal variation of their grating pitch Λ (corrugation-pitch-modulated lasers) can exhibit poor steady-state side mode suppression ratios. Numerical simulations show that an adequate profile of the coupling coefficient κ (stronger coupling at the center of the cavity) can help to achieve improved steady-state single mode operation with respect to conventional Bragg-detuned cavities (uniform coupling coefficient). However, it is found that in such lasers (z-dependent κ), side modes are liable to be excited during the turn-on transient interval. A careful study of the turn-on transient is needed to determine the maximum (keeping dynamic single mode regime) bias current.

Linewidth reduction of DSM lasers due to effects of composite cavity and distributed reflectors

Spectral properties of dynamic single-mode (DSM) lasers are theoretically analyzed in terms of the effects of composite cavity and distributed reflectors. Unique reduction mechanisms of adiabatic chirp and linewidth are found in distributed reflector (DR) lasers and complex-coupled (CC) (i.e., gain+index-coupled) DSM lasers, which are explained from the viewpoints of modal phase and modal gain behaviours. For CC-DSM lasers, it is shown that the arrangement of index and gain corrugation, namely, antiphase or in-phase combination, will suppress or enhance, respectively, an effective linewidth enhancement factor, alpha /sub eff/. Numerical results show that DR structures are much superior in spectral and single-mode properties to distributed-feedback (DFB) and distributed-Bragg-reflector (DBR) structures.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Advanced semiconductor lasers

Recent research activities in the field of advanced semiconductor lasers are reviewed with emphasis on highly stable single-wavelength lasers and surface-emitting (SE) lasers for wideband lightwave communication systems and optical parallel information processing. The operational characteristics of DSM (dynamic single-mode) lasers are summarized and requirements for high-performance operation as light sources for high-speed transmission or coherent communications are described. A type of DSM laser called the distributed-reflector (DR) laser is described as an advanced DSM laser which enables high efficiency, high power, and narrow linewidth operations. Specific features and the potential of SE lasers are summarized. Research activities and remaining problems to be solved for a breakthrough in optical parallel information processing are presented. The potential of multidimensional quantum-well structures, such as QW lasers and quantum-box lasers, is discussed in terms of superior characteristics in both stationary and dynamic operations. The present fabrication technologies for realizing high-performance lasers based on multidimensional QW structures are also presented. >

Dynamic mode stability in gain-switched quarter wave shifted distributed feedback lasers

The dynamic single-mode stability of 1.5- mu m quarter-wave-shifted distributed-feedback lasers is compared to that of conventional distributed feedback lasers by measuring the time-averaged spectra under gain switching. The experimentally observed relation between the threshold gain difference and the peak intensity ratio in the spectra is well explained by the analysis based on rate equations. The measurements show that quarter-wave-shifted lasers exhibit superior single-mode stability, and their threshold (field) gain difference between main modes and submodes is estimated to exceed 8 cm/sup -1/. >

Widely tunable active Bragg reflector integrated lasers in InGaAsP-InP

Monolithic InGaAsP-InP lasers comprising an active Bragg reflector integrated with a separately pumped wide-band gain region have been developed. The lasers operate in a dynamic single mode in the 1.55 μm wavelength region. By adjusting the current through the Bragg reflector, the wavelength can be tuned. The maximum tuning range is 11.6 nm.

Dynamic-single-mode(DSM) lasers by integrated optical waveguides.

Long wavelength GaInAsP/InP dynamic-single-mode (DSM) lasers with distributed reflector integrated by bundle-integrated-guide (BIG) structure are reviewed from the points of their fabrication process and operation performances.The optical coupling efficiency in the BIG structure as well as lasing properties of the BIGD-DBR lasers are discussed from aspects of a low threshold current, a high side-mode-suppression ratio, narrow line-width, and stable single-mode operations under high-speed direct modulation.

Flat-surface buried heterostructure distributed feedback lasers operating in a single longitudinal mode at 1.5 μm with low chirp

Distributed feedback lasers emitting in a stable dynamic single mode at 1.5 μm wavelength in a temperature range of more than 50 °C have been developed using the so-called flat-surface buried heterostructure. Threshold currents as low as 14 mA in cw (8 mA in pulse) operating and output powers as high as 20 mW/facet were obtained. By detuning the Bragg wavelength to the shorter wavelength side of the gain peak, and by reducing the confinement factor, a wavelength chirp as a function of modulation current as low as 0.003 nm/mA has been obtained. This value corresponds to a total chirp of 0.1–0.2 nm under normal modulation conditions.

Yield analysis of second-order DSM DFB lasers and implications for design

The results of yield analysis of dynamic single-mode (DSM) second-order distributed feedback (DFB) lasers are presented. Design implications of this analysis are discussed. Three ways of achieving DSM operation which, depending on the design, can operate simultaneously are considered: radiation loss, asymmetric end cavity reflections, and phase shifting of a grating. The interplay among these mode selection mechanisms is analyzed under conditions of random facet cleaving. The calculated expected yield is subjected to three constraints: a minimum side-mode suppression ratio, a maximum threshold current, and a minimum external quantum efficiency. A comparison of DSM performance between first-order and second-order DFB lasers of analogous designs is also included.

Integrated optics approach for advanced semiconductor lasers

Recent advances in the field of semiconductor integrated optics are reviewed from the point of view of monolithic integration of semiconductor lasers and other optical components and/or devices. Emphasis is placed on dynamic-single-mode (DSM) lasers, such as DFB and DBR lasers, intended for highly stable single-wavelength light sources for such monolithic integration. The realization of high-performance DSM lasers and the fabrication techniques of monolithically integrated optical devices and circuits are briefly reviewed. A variety of potential applications is discussed.

Injection Locked Dynamic Single Mode Lasers for Fibre and Integrated Optic Applications

The structure and fabrication procedure of a fully integrated injection locked distributed Bragg reflector semiconductor laser (∼ 1.5 μm) have been discussed. Initial studies confirm the occurrence of injection locking phenomenon. The problems connected with the integrated structures have been discussed.

Wavelength stabilisation of 1.5 μm GaInAsP/InP bundle-integrated-guide distributed-Bragg-reflector (BIG-DBR) lasers integrated with wavelength tuning region

The temperature dependence of the lasing wavelength was stabilised in wavelength-tunable 1.5 μm GaInAsP/InP bundle-integrated-guide distributed-Bragg-reflector (BIG-DBR)-type dynamic-single-mode (DSM) lasers. The lasing wavelength was controlled to maintain a fixed wavelength over a temperature range of 40 deg C.

Lasers and Photodetectors in Europe

This paper reviews the European activities on fiber optic semiconductor devices for optical communication. Progress in the development of lasers, LED's, and photodetectors and also first attempts of monolithic integration are reported. Emphasis is put on materials and devices for the wavelength range of 1200-1600 nm and for high-speed transmission. Results of recent work are highlighted. So, for example, extremely high reliability and high optical output power of LED's and Fabry-Perot lasers have been achieved. MOCVD growth techniques are increasingly applied for device fabrication; for lasers, highly reproducible characteristics have been demonstrated. Development of dynamic singlemode lasers (DSM) is under progress with low threshold currents and good optical characteristics reported. First electrically tunable single-mode lasers and DSM lasers with parallel coupled cavities have been realized. Long wavelength p-i-n photodetectors have reached maturity. InGaAsP and CdHgTe avalanche photodiodes show excellent properties for high-speed long-haul transmission. First steps of monolithic integration of several optical and electrical functions have been made and specifically for p-i-n-FET combinations good results have been achieved. The plans of European PTT authorities to implement fiber optics in trunk lines and subscriber loops will further push the activities on optoelectronic device technology.

Dynamic-single-mode Lasers

Recent progress in the dynamic-single-mode (DSM) semiconductor laser for long wavelength optical fibre communications is reviewed, and applications to wide-band optical fibre communication in the lowest loss wavelength region of 1·5–1·65 μm are studied. A DSM laser consists of a mode selective resonator and a transverse-mode-controlled waveguide, such as the narrow-striped distributed Bragg reflector (DBR) laser, to maintain a fixed axial mode under rapid direct modulation. The technology of monolithic integration for optical circuits is applied to realize some DSM lasers. The structures and properties of DSM lasers are reviewed.

Power and frequency modulation characteristics of a coupled cavity dynamic single mode GaAlAs laser

A commercially available GaAlAs diode laser has been modified to provide a stable dynamic single longitudinal mode laser. The laser was modulated with a power modulation index of more than 50 percent at microwave frequencies while operating in a single mode. Small signal modulation efficiency for optical power and frequency was measured together with the corresponding phase delays relative to the modulation current, in the frequency range 0.5 to 4 GHz. As predicted by the standard rate equation model, the laser frequency modulation index normalized to the power modulation index was a constant, independent of laser drive current and modulation frequency, and had a value of about 4. The phase advance of the frequency modulation relative to the power modulation was close to 90 deg over most of the frequency range, also in agreement with the rate equation model.