Gain-coupled Distributed Feedback Research Articles

Two-Segment Gain-Coupled Distributed Feedback Laser

A two-segment regrowth-free gain-coupled distributed feedback (DFB) laser monolithically integrated different gain contrast segments was proposed, realizing both wavelength-tunable (5 nm) and wavelength stabilization characteristics, controlled by a single electrode only. At current larger than 320 mA, side mode suppression ratio reached >30 dB with 3 dB linewidth μ m-width ridge were patterned merely by one-step i-line lithography. It provides a novel method for low-cost practical gain-coupled DFB laser fabrication, which can be used in either/both wavelength-tunable applications such as sensing and detection, or/and wavelength stabilization fields such as pumping fiber lasers.

Theorical analysis of a monolithic all-active three-section semiconductor laser

We propose a novel semiconductor laser structure. It is composed of three cascaded active sections: a Fabry-Pérot laser section sandwiched between two gain-coupled distributed feedback (DFB) laser sections. We have modeled this multi-section structure. The simulation results show that compared with index- and gain-coupled DFB lasers, a significant reduction in the longitudinal spatial-hole burning can be obtained with the proposed device, and that this leads to a stable single longitudinal mode operation at relatively high optical power with a SMSR exceeding 56dB. Full Text: PDF ReferencesL.A. Coldren, "Monolithic tunable diode lasers", IEEE J. Select. Topics Quant. Electron. 6, 988 (2000) CrossRef O. Kjebon, R. Schatz, S. Lourdudoss, S. Nilsson, B. Stalnacke, L. Backbom, "30 GHz direct modulation bandwidth in detuned loaded InGaAsP DBR lasers at 1.55 [micro sign]m wavelength", Electron. Lett. 33(6), 488 (1997). CrossRef N. Kim, J. Shin, E. Sim, C.W. Lee, D.-S. Yee, M.Y. Jeon, Y. Jang, K.H. Park, "Monolithic dual-mode distributed feedback semiconductor laser for tunable continuous-wave terahertz generation", Opt. Expr. 17(16), 13851 (2009). CrossRef M.J. Wallace, R. ORreilly Meehan, R.R Enright, F. Bello, D. Mccloskey, B. Barabadi, E.N. Wang, J.F. Donegan, "Athermal operation of multi-section slotted tunable lasers", Opt. Expr. 25(13), 14426 (2017). CrossRef J.E. Carroll, J.E.A. Whiteaway, R.G.S. Plumb, "Distributed Feedback Semiconductor Lasers", Distributed feedback semiconductor lasers (IEE and SPIE, 1998). CrossRef H. Ghafour-Shiraz, Distributed Feedback Laser Diodes and Optical Tunable Filters (Wiley, 2003). CrossRef D.D. Marcenac, Ph.D dissertation (University of Cambridge, 1993). DirectLink L.M. Zhang, J.E. Carroll, C. Tsang, "Dynamic response of the gain-coupled DFB laser", IEEE J. Quant. Electr. 29, 1722 (1993). CrossRef W. Li, W.-P. Huang, X. Li, J. Hong, "Multiwavelength gain-coupled DFB laser cascade: design modeling and simulation", IEEE J. Quant. Electro. 36(10), 1110 (2000). CrossRef B.M. Mehdi, H. Rachid, in Proc. 3rd Intern. Conf. on Embedded Systems in Telecomm. and Instrument., Annaba, Algeria (2016). DirectLinkC. Henry, "Theory of the linewidth of semiconductor lasers", IEEE J.Quant. Electr. QE-18, 259 (1982). CrossRef K. Takaki, T. Kise, K. Maruyama, N. Yamanaka, M. Funabashi, A. Kasukawa, "Reduced linewidth re-broadening by suppressing longitudinal spatial hole burning in high-power 1.55-/spl mu/m continuous-wave distributed-feedback (CW-DFB) laser diodes", IEEE J. Quant. Electr. 39, 1060 (2003) CrossRef

Nonlinear emission from an InGaAs/AlGaAs quantum-wire array

Gain-coupled distributed-feedback (GC-DFB) effects in a V-grooveIn0.2Ga0.8As/Al0.2Ga0.8As quantum-wire (QWR) array are investigated by comparison with those in aGaAs/Al0.2Ga0.8As QWR array. Temperature-dependent photoluminescence (PL) spectra are measured forboth samples, showing that the PL spectra from the QWRs are much stronger than thosefrom the quantum wells (QWs) in the entire temperature region. Then, InGaAs/AlGaAsQWR GC-DFB lasers are fabricated by one-step metallorganic chemical vapour deposition(MOCVD) growth and characterized. As a result, strong nonlinearity in the emissionspectra by optical feedback along the DFB directions is clearly observed near the thresholdcurrent, indicating that a V-groove InGaAs QWR array is a good candidate for again-coupled DFB laser.

Self-consistent Simulation of self-pulsating two-section gain-coupled DFB lasers

The role of cavity conditions in the dynamics of two-section gain-coupled distributed feedback (DFB) lasers is investigated using a self-consistent model. Self-sustained pulsation (SSP) exists only for devices with strongly coupled DFB gratings. As the coupling strength increases, multiple SSP regimes are developed. The SSP frequency tuning range increases as cavity length decreases. The frequency and modulation index predicted by the model agree well with experimental results. The facet condition of each section is found to affect SSP differently because of the asymmetrical behavior of the modes responsible for SSP.

Effects of self-mixing interference on gain-coupled distributed-feedback lasers

The effects of self-mixing interference on gain-coupled (GC) distributed-feedback (DFB) lasers are analyzed. From coupled-wave theory, the oscillation frequency and threshold gain variations are theoretically deduced. The influences on self-mixing from the coupling length coefficient, the linewidth enhancement factor of the GC DFB laser, and the reflection coefficient of the external reflector are discussed along with numerical analysis and are compared with the effects of self-mixing interference of lambda/4 phase-shifted DFB lasers and Fabry-Perot (F-P) lasers. Our results show that high-accuracy self-mixing sensors can be obtained with GC DFB lasers.

AlGaAs/InGaAs DFB Laser by One-Time Selective MOCVD Growth on a Grating Substrate

A gain-coupled distributed feedback (DFB) laser is realized using a high-density InGaAs/AlGaAs quantum wire (QWR) array formed within a finite area of 6×500 µm by electron beam lithography and one-time selective metalorganic chemical vapor deposition (MOCVD). The stable gain-coupled DFB mode is confirmed at 812 and 830 nm from the 360 and 370 nm pitch gratings, respectively. The mode analysis of the actual cross-sectional structure using a finite element method verified that modal gain has a single peak at the Bragg wavelength of the grating.

Enhanced wavelength shift in partly gain-coupled distributed feedback lasers using quantum well intermixing

In this paper, we present a theoretical study on the properties of wavelength shift due to quantum well (QW) intermixing in the partly gain-coupled distributed feedback (DFB) lasers. A maximum possible wavelength red-shift of 9.2 nm is predicted if using a proper DFB grating, whose period is smaller than that in the conventional DFB lasers. In contrast to the index-coupled λ/4-shifted DFB lasers, no increase in carrier density is required to compensate for the gain reduction due to QW intermixing, as the threshold gain in the partly gain-coupled DFB laser decreases with the QW intermixing because of the increase in the coupling coefficient. The injected threshold current density for lasing is considerably flat in the wavelength red-shift range. The result is important as it indicates that the QW intermixing technique may be used in the fabrication of the equal threshold DFB lasers with different wavelengths in the monolithically integrated laser arrays.

Fabrication of AlGaAs-GaAs quantum-wire gain-coupled DFB lasers by a single MOCVD growth step

AlGaAs-GaAs quantum-wire (QWR) gain-coupled distributed-feedback (GC-DFB) lasers have been fabricated by a single metal-organic chemical vapor deposition growth step on 0.36-/spl mu/m pitch V-groove arrays of GaAs. A record low-threshold current of 13 mA is achieved via DFB lasing from QWR gain at room temperature. The consistency of the photon energies of the lasing and the photoluminescence peaks from QWR, and about 4-nm-wide stopband with a large threshold gain difference observed in the near-threshold spectrum are presented as possible evidence for GC-DFB effects in these devices.

Optical generation of microwave/millimeter-wave signals using two-section gain-coupled DFB lasers

We report the first analysis and experimental demonstration of tunable microwave/millimeter-wave signal generation in two-section gain-coupled distributed-feedback (DFB) lasers. Continuous tuning from 20 to 64 GHz was directly observed and characterized both in the electrical and optical domain. The mechanism of microwave generation in two-section gain-coupled DFB lasers is different from that of two-section index-coupled DFB lasers previously reported. As a result, gain coupling can lead to simultaneous large modulation indexes and high frequencies in two-section DFB lasers.

High Output Power Operation of a 1.3 µm Gain-Coupled Distributed Feedback Laser with Narrow Spectral Linewidth

High output power and narrow spectral linewidth operation of 1.3 µm gain-coupled distributed feedback (DFB) lasers with InAsP buried absorptive grating is reported. In this study, we have investigated the effect of the thickness of a separate-confinement-heterostructure (SCH) layer on the single-mode stability and the spectral-linewidth property of 1.3 µm gain-coupled DFB lasers. As a result, we clarified that decreasing the thickness of the SCH layer led to stable single-mode operation at high output power and the reduction of the product of the spectral linewidth and the output power. For the fabricated gain-coupled DFB laser, a record high output power of 230 mW and a minimum spectral linewidth of 100 kHz at an output power of 150 mW were realized.

Reduction of second- and third-order harmonic distortion by nonlinear absorption in gain-coupled distributed-feedback laser diodes

We have calculated the characteristics of second- and third-order harmonic distortion in gain-coupled distributed feedback (DFB) lasers using a set of three rate equations. In these calculations, the relaxation oscillation, nonlinear gain compression, and nonlinear loss compression are taken into account. We have found that modulation distortion due to nonlinear gain compression is reduced significantly in the gain-coupled DFB laser of absorptive-grating type. This improvement occurs because gain compression is compensated by loss compression within the grating.

Circuit model for absorption grating gain-coupled distributed feedback semiconductor lasers

A circuit model for absorption grating (AG) gain-coupled (GC) distributed feedback (DFB) semiconductor laser diodes (LD) is presented, based on the rate equations of carrier densities in active region and absorption grating, as well as the photon density. The relation of photon lifetime to cavity loss and facet loss, and the relation of light power to average photon density are derived. As an example, self-pulsation in AG–GC–DFB–LD is studied.

Threshold current of quantum-disk and quantum-wire gain-coupled distributed feedback lasers

This numerical study shows that an effective way to reduce the threshold current density (Jth) in the quantum well (QW) and bulk types of gain-coupled distributed feedback (DFB) lasers is to reduce the active volume. Although the threshold current per unit cavity width (Ith) is smaller for the quantum-disk type than it is for the quantum-wire or QW type of gain-coupled DFB laser, both the optimum number of vertically stacked quantum structures (Nst) for minimizing Ith when cavity length (L) is fixed and the optimum L for minimizing Ith when Nst is fixed are the largest for the quantum-disk type. When L=500 μm, for example, the optimum Nst is 7 for the quantum-disk type, 5 for the quantum-wire type and 3 for the QW type. Threshold current density (Jth) is almost independent of facet reflectivity (r), and this implies that all these lasers oscillate at the Bragg mode. The Jth of the bulk laser, however, is influenced most by r because this type has the smallest differential gain.

Effect of p-contact metallization on the performance of gain-coupled DFBs with oxide-defined surface gratings

The effect of p-contact metallization on the performance of a single-growth-step ridge waveguide InGaAs-GaAs distributed feedback (DFB) laser with a silicon dioxide defined titanium surface grating is analyzed. The metallic surface grating introduces a periodic variation of the loss in the cavity to promote single-frequency emission. Device characteristics for DFBs with 50, 150, and 300 /spl Aring/ of titanium are compared. Under continuous-wave (CW) conditions, the devices with a titanium adhesion layer of only 50 /spl Aring/ operate on single-longitudinal and single-lateral modes, with threshold currents of roughly 14 mA, slope efficiencies of 0.16 W/A and sidemode suppression ratios (SMSRs) of greater than 40 dB.

The symmetry of the amplified spontaneous emission spectrum in complex-coupled DFB lasers

We present relations between facet reflections and coupling coefficient for the amplified spontaneous emission (ASE) spectrum of a complex-coupled, an index-coupled, and a gain-coupled distributed feedback (DFB) laser to have a mirror image with respect to the Bragg wavelength. We show that the ASE spectrum of a complex-coupled DFB laser cannot be symmetric in general with respect to the Bragg wavelength. The index-coupled and gain-coupled DFB lasers can have symmetric ASE spectrum for some values of the phase of the facet reflection coefficient that are determined.

Transient side-mode suppression in gain-coupled DFB lasers

Based on the spatially dependent multimode rate equations, we investigate the transient side-mode suppression in the gain-coupled distributed feedback (DFB) lasers. A simplified but accurate multimode dynamic analysis of gain-coupled DFB lasers is developed. To first order of perturbation approximation, the study includes various spatial effects, such as the distributed complex coupling, the nonuniform carrier distribution, and the nonlinear gain compression. It is found that gain coupling introduces high decay rates and low dynamic differential gains for the side modes, which effectively suppress their transient fluctuation and shorten the rise time of the transient side-mode suppression ratio (SMSR).

Self-consistent analysis of side-mode suppression in gain-coupled DFB semiconductor lasers

Based on a set of spatially dependent multimode rate equations derived from Maxwell's equations, a self-consistent analysis of gain-coupled distributed feedback (DFB) lasers is developed. By introducing the modal net gain into the coupled wave equations, we also obtain a closed form formula of the side-mode suppression ratio (SMSR) for DFB lasers. It is shown that, associated with the distributed feedback, the longitudinal spatial hole burning, and the nonlinear gain compression effects, gain coupling produces significant effects on the SMSR of DFB lasers.

Impact of random facet phases on modal properties of partly gain-coupled distributed-feedback lasers

A first comprehensive study of impact of random phase at cleaved facet on modal properties of partly in-phase gain-coupled distributed-feedback (GC DFB) lasers is carried out both theoretically and experimentally. It is shown that, variation of grating phase of antireflective (AR) facet has a relatively small impact on lasing properties, while that of cleaved facet has a significant influence not only on modal properties such as threshold, efficiency, front-to-back facet efficiency ratio (FB ratio), side-mode-suppression-ratio (SMSR), and transient SMSR (TSMSR), but also on DFB lasers' long term stability against longitudinal mode-switching. Correlation among different laser properties is revealed for GC DFB lasers, and compared with that of index-coupled ones. It is found that FB ratio provides a good description of long-term longitudinal mode stability against CL facet phase variation and equivalent external feedback in GC DFB lasers, while TSMSR reveals their dynamic properties for a fixed facet phase. It is shown that devices with a possible stable operation will exhibit both a large TSMSR and a large FB ratio in GC DFB lasers. Lasers that are located within the transition region between left Bragg mode region and the stably operated right Bragg mode region in phase-space will have either a low TSMSR or a small FB ratio, and, therefore, are susceptible to longitudinal Bragg mode-switching. The combination of TSMSR and FB ratio as a screening criteria provides a simple and yet powerful tool to single out the potentially unstable devices due to random facet phase distribution in AR/CL GC DFB lasers.

Fluctuations of the laser characteristics and the effect of the index-coupling component in the gain-coupled DFB laser

The normalized oscillation frequency /spl delta/L and threshold gain /spl alpha/L of gain-coupled distributed feedback (DFB) lasers with an AR/AR (symmetric) structure vary significantly with a variation in the corrugation phase at the facets when the facet reflectivity |r| is large, even though the spatial-hole-burning-corrected yield is 100%. For example, the standard deviation for the /spl delta/L, /spl sigma/(/spl delta/L), increases from 0.018 to 0.40 when |r| is increased from 0.03 to 0.30. The magnitude of /spl sigma/(/spl delta/L) and /spl sigma/(/spl alpha/L) are small, however, for the gain-coupled, index-coupled, and complex-coupled DFB lasers when the |r| is kept small. For the HR/AR (asymmetric) structure, these two values are more than an order of magnitude larger than those for the AR/AR structure, except for the /spl sigma/(/spl alpha/L) for the index-coupled laser, even though yields of each of these lasers are relatively large. In the AR/AR structure, the contamination by the index-coupling and gain-coupling components always degrades the device characteristics because of the difference in the phase shifter and when the amount of contamination is small this degradation is particularly severe for the index-coupled laser. Several properties of the index-coupled laser with the HR/AR structure can be improved, however, by introducing the gain-coupling component.

16-wavelength gain-coupled DFB laser array with fine tunability

16-wavelength semiconductor laser array with fine wavelength tunability is demonstrated, utilizing gain-coupled distributed feedback (DFB) lasers with different ridge waveguide widths. Besides the coarse tuning by the ridge widths, the fine post-fabrication tunability for individual lasers in the array is achieved with a Ti thin-film resistor integrated on the chip. Due to the gain-coupling effect, 16 single-mode lasing wavelengths around 1.55 μm in /spl sim/1 nm spacing are obtained simultaneously. An effective fine-tuning up to 1 nm is observed at a moderate heating power of 100 mW.