We investigate the dynamical response of a quantum dot photonic integrated circuit formed with a combination of eleven passive and active gain cells operating when these cells are appropriately biased as a multi-section quantum dot passively mode-locked laser. When the absorber section is judiciously positioned in the laser cavity then fundamental frequency and harmonic mode-locking at repetition rates from 7.2GHz to 51GHz are recorded. These carefully engineered multi-section configurations that include a passive wave-guide section significantly lower the pulse width up to 34% from 9.7 to 6.4 picoseconds, as well increase by 49% the peak pulsed power from 150 to 224 mW, in comparison to conventional two-section configurations that are formed on the identical device under the same average power. In addition an ultra broad operation range with pulse width below ten picoseconds is obtained with the 3rd-harmonic mode-locking configuration. A record peak power of 234 mW for quantum dot mode-locked lasers operating over 40 GHz is reported for the first time.
proper operation of the proposed UWB circuit. Experimental results show that the pulse generator can yield an output pulse of 235 ps duration which has a bandwidth of 4.3 GHz at the center frequency of 2.15 GHz. The circuit is easy to implement and have low profile. It can be used for mobile UWB applications where space requirements are stringent. ACKNOWLEDGMENTSThe authors thank Ayhan Bozkurt during implementation of the circuit and Sertac Yilmaz for the time measurements of the UWB pulse generator. APPENDIX: TRANSMISSION LINE LENGTH RELATION AND THE TIME DELAYTo obtain the desired monopulse with no zero-frequency component, pulse width, or equivalently time delay between even and odd mode pulses, and the transmission line length should be both taken into consideration as design parameters. Basically, the odd mode and even mode propagate at different velocities, and the difference in velocities will create the time difference between the even and odd mode pulses at a specific point on the transmission line. So, for the desired pulse, the transmission line length should be a design parameter as well as the time duration of the pulse. To obtain a monopulse, the difference between time delays (t 2 Ϫ t 1 ) should be equal to the pulse width ⌬t. This statement can be expressed as,Assume that the length of the transmission line is l, then, the time duration that it takes for the odd and even mode voltages to reach the output port [port 3 in Fig. 3(a)] will be given by,where e ϭ c/ ͱ eff,e and o ϭ c/ ͱ eff,o are the velocities of the even and odd modes. Using Eqs. (A1)-(A3), we can obtain the transmission line length versus desired time delay between even and odd pulses relation as, l ϭ ⌬t ϫ c 1 ͱ eff,e Ϫ ͱ eff,oAs an example, for the same FR4 substrate of r ϭ 4.6, the calculated values of effective dielectric constants for the odd and even modes are given in Eq. (17), and if the desired time delay is taken as 75 ps, then, the transmission line length is calculated as 9.3 cm using Eq. (A4). Note that for a higher dielectric constant material and using meander trace, the area of the transmission line circuit could be made a few square-cm. Actually, antenna performances with respect to phase variation of the far-field, transfer function, and transient response in time-domain also pose a serious impact on antenna application. In this article, a printed SWB antenna is proposed and studied. It is composed by a corner-rounded ground plane, a tapered microstrip feeder and a patch made by a half-disc and a half-ellipse. Then various antenna characteristics are experimentally analyzed in detail by building a transceiving antenna system, including VSWR, radiation patterns, gain, group delay, and antenna transfer function. In addition, transient response is carefully investigated and presented by using four different signals, which provides designers with much useful information on true application of the antenna behind its more than 25:1 impedance bandwidth. DESCRIPTION OF THE ANTENNAConfiguration of the proposed SWB antenna is ...
By extending the net-gain modulation phasor approach to account for the discrete distribution of the gain and saturable absorber sections in the cavity, a convenient model is derived and experimentally verified for the cavity design of two-section passively mode-locked quantum dash (QDash) lasers. The new set of equations can be used to predict functional device layouts using the measured modal gain and loss characteristics as input. It is shown to be a valuable tool for realizing the cavity design of monolithic long-wavelength InAs/InP QDash passively mode-locked lasers.
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