Distributed Coupling Coefficient Research Articles

Effect of Injection Current on the Normalized Gain Amplitude, Normalized Detuning Coefficient and the Output Power of Axial Distributed Coupling Coefficient Distributed Feedback Laser Diode (ADCC-DFB-LD)

Effect of Injection Current on the Normalized Gain Amplitude, Normalized Detuning Coefficient and the Output Power of Axial Distributed Coupling Coefficient Distributed Feedback Laser Diode (ADCC-DFB-LD)

Effect of Injection Current on the Normalized Gain Amplitude, Normalized Detuning Coefficient and the Output Power of Axial Distributed Coupling Coefficient Distributed Feedback Laser Diode (ADCC-DFB-LD)

An axial distributed coupling coefficient (ADCC) distributed feedback (DFB) laser diode (LD) in which the coupling coefficient (K) has been distributed axially on both sides of the phase shift region. The effects of injection current on the normalized gain amplitude, normalized detuning coefficient and the output power are investigated using transfer matrix method. The results show that the ADCC DFB laser exhibits high single mode stability at different injection currents above threshold and the main mode operates close to Bragg wavelength at high injected current. For different injection currents the optical output power has been increased with decreased the coupling coefficient.

SPM Response of a Distributed coupling coefficient DFB-SOA All-Optical Flip-Flop

Deriving a dynamic model based on the coupled-mode and carrier rate equations, the effects of coupling coefficient and corrugation position on all-optical flip-flops (AOFF) we have analyzed in this paper. Also the self phase modulation (SPM) in the distributed coupling coefficient distributed feedback semiconductor optical amplifier (DCCDFB-SOA) has been implemented. Then the effects of SPM on the rise and fall times of the flip-flop DFB-SOA are investigated. It has been shown that the application of the optimized coupling coefficient and corrugation position improves the speed limitation in AOFF significantly. The transfer matrix method (TMM) time domain is utilized for the numerical simulations.

Novel DFB laser structure suitable for stable single longitudinal mode operation

This paper shows that a suitable design of a single phase-shift (1PS) distributed coupling coefficient (DCC) distributed feedback (DFB) laser structure can strongly improve both the normalized mode selectivity S and the flatness of the electrical field profile of DFB lasers—usually quantified by a flatness parameter F —in order to ensure the required criteria for single longitudinal mode operation ( S ≥ 0.25 and F ≤ 0.05 ) through an extended range of biasing current injection ( I). It is shown that a symmetric longitudinal laser cavity should be used in order to accomplish the requirements imposed by the modern optical communication systems. Photon and carrier rate equations have been used to evaluate the performance of the proposed laser structure in the above-threshold regime. The variations of the selectivity, the flatness, the lasing-wavelength, the emitted power ( P) and the side-mode suppression ratio (SMSR) versus current have been assessed. For I=5 I th , where I th is the laser threshold current, substantial improvements in S (60% higher), in F (40% better), in P (45% higher) and in the SMSR (about 4 dB higher) are achieved in the proposed 1PS-DCC-DFB laser when compared to similar single phase-shifted DFB structures referred elsewhere. The improvements are even better when compared to the standard QWS-DFB laser.

Optimisation of a corrugation-pitch-modulated DFB laser structure with inhomogeneous coupling coefficient for stable single longitudinal mode operation

This paper shows that a suitable design of a corrugation-pitch-modulated (CPM) distributed-coupling-coefficient (DCC) distributed feedback (DFB) laser structure can strongly improve the mode selectivity $(\mathfrak{G})$ and the flatness $(\mathfrak{F})$ of DFB laser structures in order to ensure the required criteria for single longitudinal mode operation ( $\mathfrak{G}$ ≥ 0.25 and $\mathfrak{F}$ ≤ 0.05), through an extended range of current injection. It is shown that a symmetric structure should be used in order to accomplish the requirements imposed by the modern optical communication systems. Photon and carrier rate equations have been used in order to evaluate the performance of the proposed laser structure in the above-threshold regime. The variations of $\mathfrak{G}$ , $\mathfrak{F}$ , the lasing wavelength, the emitted power ( P ) and the side-mode-suppression-ratio (SMSR) with the current injection ( I ) have been evaluated. For I = 5 I th , where I th is the laser threshold current, substantial improvements in $\mathfrak{G}$ ( 3.8 times better), in $\mathfrak{F}$ ( 2 times better), in P (15% higher) and in the SMSR (about 3.4 dB higher) are achieved in the proposed CPM-DCC-DFB laser when compared to an optimised CPM-DCC-DFB laser referred elsewhere. The improvements are even better when compared to the standard QWS-DFB laser.

Cross-phase modulation response of a DCC-DFB-SOA all-optical flip-flop

Using the coupled-mode and carrier rate equations, we have derived a dynamic model for the distributed feedback semiconductor optical amplifier (DFB-SOA) all-optical flip-flop (AOFF). We have analyzed the effects of the coupling coefficient and the corrugation position on the dynamic response of the device. We have also investigated the effects of cross-phase modulation on the switching speed of the DFB-SOA with the distributed coupling coefficient (DCC), known as the DCC-DFB-SOA AOFF. Furthermore, it is shown that by optimizing the coupling coefficient value and the corrugation position, the AOFF speed limitation is improved significantly. The ON and OFF switching time values, in an optimized condition, are 300 and 100 ps, respectively, while the carrier lifetime is about 780 ps. In comparison with those of a conventional DFB-SOA-AOFF, these values show reductions of more than 2 and 14 times in the ON and the OFF switching times, respectively. Under such conditions, a maximum bit rate of 1.4 GHz is achieved. The finite difference time-domain method is utilized for the numerical simulations.

Steady state analysis of optical bistability in distributed coupling coefficient DFB semiconductor laser amplifiers

In this paper, optical bistability behavior in a distributed feedback (DFB) semiconductor laser amplifier (SLA), with nonuniform-grating is studied. The investigation is focused on distributed coupling coefficient (DCC) structures, in which the corrugation has a nonuniform depth along the cavity. A modified implementation of transfer-matrix method, which takes the longitudinal variation of coupling coefficient along the structure into account, and considers gain saturation, is utilized to examine switching characteristics of DCC DFB SLA’s in the steady state regime. Along with the wavelength dependence of bistability hysteresis, the structural dependence of switching performance in these devices is demonstrated. Low-power switching spectral range and ON–OFF contrast ratio is investigated and the results are discussed.

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.

Axial distribution of coupling coefficient of distributed feedback laser diode

An axial distributed coupling coefficient (ADCC) distributed feedback (DFB) laser diode (LD), in which the coupling coefficient ( K c) has been distributed axially on both sides of the phase shift region (PSR), is proposed to increase the efficiency of QW-DFB LD. The results are compared with that obtained from QW DCC–DFB LD. The present work proposes a new criteria for coupling distribution to decrease the spatial hole-burning (SHB) effect on the single mode (SM) operation.

Analysis of a distributed coupling coefficient phase-controlled distributed feedback optical filter

We have proposed a new phase-controlled distributed feedback wavelength tunable optical filter with distributed coupling coefficient. The analysis, which is based on the transfer matrix method, reveals that an almost constant peak transmissivity (gain) of more than 37dB, tuning range of better than 21.7A and side-mode suppression ratio (SMSR) of more than 17dB can be achieved using this structure.

Distributed feedback lasers with refractive-index-modulated upper cladding layer of the grating for reducing the spatial hole-burning effect

A refractive-index-modulated (RIM) DFB laser, in which the refractive index of the center region of the upper cladding layer of the grating is smaller than that of the side regions, is proposed to obtain an effective λ/4 phase shift in the center region and a distributed coupling coefficient effect simultaneously. Simulation results show that the single-mode gain difference of RIM–DFB lasers is larger than that of corrugation-pitch-modulated (CPM) DFB lasers over the whole range of injection current due to the distributed coupling coefficient effect. The variation of the lasing wavelength of RIM–DFB lasers as a function of injection current is small compared to that of quarter-wavelength-shifted DFB lasers and CPM–DFB lasers. In addition, the effect of the length of the center region of RIM–DFB lasers on the above-threshold characteristics is investigated. © 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 26: 173–176, 2000.

Spectral characteristics of distributed feedback laser diodes with distributed coupling coefficient

A comprehensive investigation of the spectral characteristics of distributed feedback (DPB) laser diodes (LD's) with a distributed coupling coefficient (DCC) is presented. With a proper selection of both the coupling ratio (r) and a corrugation position (CP), the performance of the DCC laser structure is enhanced with an improved single-mode stability as well as a uniform field distribution. In the analysis, the above threshold characteristics and the influence of non-lasing side modes have been investigated using the transfer matrix method (TMM). Based on a DCC laser structure with r=1/3 and CP=0.46, a normalized gain margin (/spl Delta//spl alpha/L)=0.81 and a side mode suppression ratio (SMSR) of 45 dB have been achieved for a DCC LD at biasing current of 4I/sub th/. The introduction of the DCC laser structure opens a new way of stabilizing the single-mode oscillation in DFB LD's. >