Compound Cavity Modes Research Articles

Wavelength Jumps and Multimode Instabilities in Integrated Master Oscillator Power Amplifiers at 1.5 <inline-formula><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula>m: Experiments and Theory

We analyze the large ( $>$ 10 nm) and abrupt jumps in emission wavelength, together with the multimode instabilities associated with them, which are observed in monolithically integrated master oscillator power amplifiers emitting at 1.5 $\mu$ m. The physical origin of such phenomena is investigated in the framework of a travelling-wave model which phenomenologically incorporates thermal effects via self and cross-heating of the different sections of the device. The occurrence of the wavelength jumps and the instabilities as a function of the injected currents in the two sections is interpreted in terms of a thermally tuned competition between the modes of the master oscillator and the compound cavity modes.

Emission Characteristics of a 1.5- <inline-formula> <tex-math notation="TeX">$\mu$</tex-math></inline-formula>m All-Semiconductor Tapered Master Oscillator Power Amplifier

We present experimental results on the emission characteristics of a 1.5-μm distributed feedback (DFB) tapered master oscillator power amplifier (MOPA) in a wide range of steady-state injection conditions, showing different dynamical behaviors. A detailed analysis of the optical and radio-frequency spectra has allowed the identification of three different emission regimes: i) stable amplified DFB emission, but with wavelength jumps when sweeping the injection currents; ii) multimode Fabry-Perot (FP) operation of the complete MOPA cavity; and iii) self-pulsed operation at frequencies between 5 and 8 GHz. The quasi-periodic occurrence of these emission regimes as a function of the injected currents is interpreted in terms of a thermally tuned competition between the modes of the master oscillator and the compound cavity modes. The physical origin of the wavelength jumps and of the alternation between regimes is discussed.

Refractive Index Sensing Based on Plasmonic Waveguide Side Coupled With Bilaterally Located Double Cavities

Based on a metal-dielectric-metal (MDM) plasmonic waveguide side coupled with a single cavity, we propose a resonator system by placing double cavities on each side of the MDM waveguide. The coupling between two cavities provides an additional degree of freedom to engineer the resonant transmission response. By decomposing the compound cavity modes into two decoupled resonances, we obtain the theoretical transmission response of the resonator system and optimize the geometric parameters to improve the performance of refractive index sensing. At last, we conduct numerical experiments on the theoretically optimized resonator system and find that the resonant wavelength is linearly related with the refractive index of the material filled in the cavities and waveguide. A high sensitivity of 1030 nm/RIU (refractive index unit) is realized in a nanoscale structure (several hundred nanometers). This refractive index sensing configuration is easy to be integrated into lab-on-a-chip and find potential application in plasmonic circuits.

Flat-Top Reflection Characteristics in Metal-Dielectric-Metal Plasmonic Waveguide Structure Side Coupled with Cascaded Double Cavities

Based on a metal-dielectric-metal (MDM) plasmonic waveguide side coupled with a single cavity, we rebuild such resonator system by cascading double side-coupled cavities to obtain flat-top reflection response over a frequency bandwidth. The increased coherent scattering path provides an additional freedom to engineer the complex interference between the cavity modes and the waveguide mode. By decomposing the compound cavity modes into two decoupled resonances, we analyze the conditions to realize flat-top reflection response. The physics behind the flat-top reflection characteristics is found to be originated from the interference interaction between the two cavities through examining the cavity excitations and the reflected power response. Temporal coupled-mode theory and finite difference time domain method are utilized as theoretical and numerical tools which convince each other.

Widely frequency tunable amplified feedback laser as 20 GHz optical microwave source

Optical microwave sources are required in optical signal processing. Amplified feedback laser (AFL) which can generate high frequency self-pulsation due to compound cavity modes beating are used as optical microwave sources. In this paper, we fabricate a four-section AFL consisted of a different distribute feedback (DFB) section, a phase control section, an amplifier section, and a transparent section. This AFL generate continuously tunable microwave in the range 19.87–26.30 GHz with 3 dB linewidth about 3 MHz. Microwave with narrow linewidth is obtained by injecting quarter frequency modulated light experimentally.

Influence of free-running characteristics on optical clock in all-optical clock recovery using a self-pulsating semiconductor laser

All-optical clock recovery is performed using a multisection semiconductor laser that can generate two kinds of self-pulsation due to compound cavity mode beating and passive mode locking. To investigate factors to influence quality of optical clock, optical clocks recovered from an optical data are compared by using various self-pulsations with different characteristics. It is experimentally demonstrated that characteristics of optical clock depend on free-running characteristics of a RF linewidth and amplitude noise. In particular, optical clock with a subpicosecond jitter is recovered by use of a self-pulsation with a narrow linewidth and low amplitude noise of the monolithic semiconductor laser in the 10GHz regime. The free-running characteristics can be utilized as a criterion of a potential of self-pulsating semiconductor lasers for all-optical clock recovery.

Dependence of self-pulsation characteristics of multisection index-coupled distributed feedback lasers on section lengths

We investigate the effect of section lengths on the self-pulsation (SP) characteristics of a multisection index-coupled distributed feedback (DFB) laser that is composed of two spectrally detuned DFB sections and a phase-tuning section between them. Compound-cavity modes in multisection DFB lasers can be obtained by the concept of Fabry-Perot cavity modes. The simple equation for a CS number, which represents the number of compound-cavity modes within the stop-band width of a DFB section, is derived. By using the CS number, we were able to predict the SP characteristics such as abrupt changes of SP frequency due to mode hopping. Stable SP characteristics without abrupt changes of SP frequency for the variation of the spectral detuning and the phase shift in a phase-tuning section were obtained in cases with small CS numbers, which can be obtained by adjustment of section lengths.

Bistable polarization switching in mutually coupled vertical-cavity surface-emitting lasers

We theoretically investigate the polarization-resolved dynamics of two vertical-cavity surface-emitting semiconductor lasers that are mutually coupled through coherent optical injection. We find a sequence of bistable polarization switchings that can be induced by changing either the coupling strength or the optical propagation phase. The successive polarization switchings are correlated with the creation of new compoundcavity modes when these parameters are continuously varied.

Self-pulsation in multisection laser diodes with a DFB reflector

A novel self-pulsation regime is observed in multisection laser diodes which consist of a loss-coupled distributed-feedback (DFB) section, a phase control section, and gain sections, where 10-GHz self-pulsation due to compound cavity mode beating has been reported with the DFB section operated as a single-mode laser. When the DFB section is below threshold current, the devices give the self-pulsation in a very wide operating range. We attribute the pulsation to passive mode-locking and also confirm that this structure is applicable to 40-GHz operation.

다중 전극 Index-Coupled DFB 레이저에서 결합 세기 및 각 영역의 길이가 Self-Pulsation 동작 특성에 미치는 영향

As the number of compound cavity modes within the stopband of DFB sections decreases, the frequency of mode hopping decreases for the variation of λ, which represents the difference between the Bragg wavelengths of two DFB sections, so that the number of abrupt changes of pulsation frequencies decreases. In addition, the pulsation frequency varies continuously for the variation of the phase in a phase tuning section for a fixed λ. The number of compound cavity modes within the stopband decreases as the length of DFB sections increases and the length of a phase tuning section decreases. Thus stable self-pulsation operations for the variation of λ and the phase in a phase tuning section could be obtained by proper selection of the coupling strength and the length of each section.ction.

Spatio-Temporal Dynamics in Semiconductor Lasers with Delayed Optical Feedback

We investigate the influence of delayed optical feedback (DOF) on the dynamics of semiconductor lasers. In the case of the narrow single-stripe laser, we find that the presence of DOF leads to a wealth of dynamical phenomena in the coherence-collapsed regime, including mode-hopping between compound-cavity modes induced by DOF. Focusing on the twin-stripe laser — the most simple system with inherent spatio-temporal instabilities — we show that feedback may both induce and suppress spatio-temporal instabilities. Eigenmode analysis enables us to determine and identify the underlying spatio-temporal "supermodes". For appropriately chosen parameters, regular regimes including continuous wave operation can be obtained from an originally chaotic regime. For moderate to strong feedback, interaction between the spatial degrees of freedom in the twin-stripe laser and the compound cavity modes leads to a new phenomenon which we term "spatio-temporal mode-hopping".

Modeling multiple-longitudinal-mode dynamics in semiconductor lasers

We present a time-dependent coupled-wave equation analysis for simulating both single- and multilongitudinal-mode dynamics in semiconductor lasers, while incorporating frequency-dependent gain in a particularly simple way. In our first application, we analyze the response of Fabry-Perot semiconductor lasers to feedback levels ranging from -60 to -30 dB. This allows us to anchor, continuously, from single-mode phenomena at weak feedback levels to multimode behavior at stronger feedback levels. To our knowledge, this is the first simulation of multilongitudinal-mode dynamics that are induced in a laser at feedback levels exceeding -30 dB, Feedback-induced phenomena provide a significant test of both the single-mode and multimode capabilities of our coupled-wave model. In our second application, we analyze a modern, large-scale device for which multiple longitudinal modes, as well as compound cavity modes, are a significant possibility. Specifically, we consider facet-coating requirements for a new class of monolithic master-oscillator power-amplifier (MOPA) devices.

Turn-on transient dynamics in a multimode, compound-cavity laser

The turn-on-time statistics for an individual longitudinal mode and the total intensity of a multimode laser are shown to be very different. In both experiment and theory we find that the differences are due mainly to transitory modes that decay as a result of frequency-dependent losses and gains. Associated with this phenomenon is a kink in the time evolution of the mode intensity, but not in the total intensity, that represents a transition in the dynamics from domination by independent growth of all modes to domination by competition between modes with different net gains. This unequal competition increases the average and the standard deviation of the individual mode turn-on time. The experimental dye-laser system has a thin gain medium (100 µm) that is strongly coupled to a short cavity (2.5 cm) and is adjacent to one of the cavity mirrors. The opposite cavity mirror serves as a relatively weak output coupler. The presence of the thin gain medium in the cavity causes the effective pump and loss rates to be frequency dependent. The result is a transient spectrum in which the cavity modes that have the highest net gain dominate the system more as the turn-on transient progresses. The gain spectrum is found to be strongly affected by the frequency dependence of the compound-cavity modes. Using realistic laser parameters, numerical simulations of a multimode laser model {developed in companion paper [J. Opt. Soc. Am. B14, 191 (1997)]} yield turn-on dynamics and statistics that agree well with those measured experimentally.

Spectral characteristics of vertical-cavity surface-emitting lasers with strong external optical feedback

We study the spectral optical properties of vertical-cavity surface-emitting lasers (VCSEL's) in the presence of strong optical feedback from an external reflecting surface. When the feedback strength exceeds 1%, multicompound-cavity-longitudinal-modes are observed. The output spectral width increases significantly as the feedback increases. Besides the normal compound-cavity modes, high-loss compound-cavity modes are also observed for the first time. The experimental observations are well explained by a compound-cavity laser theory.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Antimode dynamics and chaotic itinerancy in the coherence collapse of semiconductor lasers with optical feedback.

Low-frequency fluctuations observed in the coherence collapse of semiconductor lasers are numerically investigated based on the Lang-Kobayashi model. It is found that the attractor in the compound cavity mode loses its stability due to a crisis with an antimode. Chaotic itinerancy among the destabilized compound cavity modes is also found.

High-frequency oscillations and self-mode locking in short external-cavity laser diodes

An effect of compound-cavity mode competition for a laser diode with a short external cavity is investigated analytically and numerically on the basis of a round-trip approximation for emitted photons in the external cavity. Due to the noncoincidence of the compound-cavity modes with possible frequencies of stationary lasing, such competition may cause self-locking of two compound-cavity modes with deep high-frequency oscillations of the laser output for a short (typically /spl les/5 mm) external cavity. Simple analytical expressions for critical feedback parameters and the frequencies of self-oscillations are given, as well as a generalized diagram of different dynamic regimes of a short external-cavity laser, which shows these regimes of high-frequency self-oscillations as well as coherence collapse instability. The results may be considered a guideline for the design of high-speed laser diodes with an integrated passive cavity. In particular, such a device may be a very efficient pulse source in the microwave (>20 GHz) region.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Fabrication and spectral characteristics of a 1.55-μm distributed feedback laser with a tunable integrated external cavity

The fabrication and lasing characteristics of a 1.5-μm distributed feedback laser with a butt-coupled tunable integrated resonator are described. An additional modulation of the distributed feedback laser spectrum introduced by the external cavity is clearly demonstrated. Optical bistability has been observed in the power versus tuning current characteristic. The device has a limited continuous tuning range of 4.2 Å. Tuning current change allows for the selection of compound cavity mode and one of the distributed feedback laser modes, while maintaining single-mode operation. Linewidth reduction due to the integrated cavity is clearly demonstrated, and linewidths &amp;lt;10 MHz have been obtained.

Compound cavity modes in semiconductor lasers with asymmetric optical feedback

We describe a static model for determining the oscillating modes of an external cavity semiconductor laser with asymmetric feedback induced by external mirror misalignment. The most significant prediction of this model, the existence of double loss minima leading to compound cavity mode splitting, has been confirmed directly by spectral measurements. This result is important for analyzing complex dynamical phenomena in semiconductor lasers with optical feedback.

Multiple feedback effects in asymmetric external cavity semiconductor lasers

Multiple feedback effects on the output power and spectral characteristics of an external cavity semiconductor laser with asymmetric feedback induced by misalignment of an external mirror are discussed. The external mirror tilt modifies the round-trip phase condition as well as the coupling efficiency. Undulation in power as a function of external mirror tilt have been observed. At particular tilt angles where strong interaction between odd-order round-trip beams and even-order round-trip beams occurs, unique optical spectra featuring double peaks within a compound-cavity mode spectrum or uneven compound-cavity mode spacings have been observed. A quasi-static model for asymmetric external cavity systems explains qualitatively the power undulations and complex spectral characteristics. The model also predicts the existence of two nearby phase-matched mode groups, which may result in complex and chaotic instabilities. >