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Fig. 5. Ultrafast amplitude (top row) and phase (bottom row) dynamics of the QD (left column), QDash (middle column), and QW (right column) SOAs, measure over 8 ps, for varying bias currents. Dotted lines show the measured data and thin solid lines show the double-exponential fits to the data. The labeled bias current are the minimum applied, transparency, and maximum applied currents.

Figure 5 Ultrafast amplitude (top row) and phase (bottom row) dynamics of the QD (left column), QDash (middle column), and QW (right column) SOAs, measure over 8 ps, for varying bias currents. Dotted lines show the measured data and thin solid lines show the double-exponential fits to the data. The labeled bias current are the minimum applied, transparency, and maximum applied currents.

Related Figures (8)

Fig. 1. Normalized ASE spectra of the three SOA samples at maximum bias (QD—thick solid line, FWHM = 164 nm; QDash—dotted line, FWHM = 66 nm; QW—dash-dotted line, FWHM = 72 nm) and the spectrum of the 150 fs OPO pulses (thin solid line, FWHM = 25 nm). The normalized OPO spectrum has been arbitrarily scaled by a factor of 0.5 in the figure.
Fig. 1. Normalized ASE spectra of the three SOA samples at maximum bias (QD—thick solid line, FWHM = 164 nm; QDash—dotted line, FWHM = 66 nm; QW—dash-dotted line, FWHM = 72 nm) and the spectrum of the 150 fs OPO pulses (thin solid line, FWHM = 25 nm). The normalized OPO spectrum has been arbitrarily scaled by a factor of 0.5 in the figure.
SAMPLE STRUCTURES in [18], its core consisting of five stacked layers of self-assem- bled InAs dots, grown in Ino.s05Gao,.195ASo.405P 0.595 1.15-m -bandgap barrier layers and InP cladding layers by chemical beam epitaxy on an InP substrate. It has a ridge width of 2 zm, a length of 1 mm, and it is antireflection (AR)-coated to create a single-pass amplifier. Compared with the structure in [18], it has a slightly reduced active region width and increased p-type dopant concentration to lower the series resistance and improve hole injection, allowing for higher injected currents and more gain. The QD growth conditions were also nominally similar, thus we estimate the dot characteristics to be similar to those in our previous reports, with a planar density of 1.5 x 10!° cm~? and approximate average lateral diameter and height of 25 and 5 nm, respectively, as confirmed by TEM and AFM measure- ments [19], [20]. We believe the dots are on average slightly larger than those in [18], however, because of the slightly longer observed amplified spontaneous emission (ASE) peak wave- length of 1620 nm (see Fig. 1), which is due to a small in- crease in the amount of InAs deposited. The QW SOA has been made as similar to the QD SOA as possible, for comparison. It has identical cladding layers and doping, but has a core con- sisting of five Ing,g95;Gag.195AS0.gPo.2 compressively strained QWs in place of the InAs dot layers. The widths of the wells and Ino.g95Gao.195ASo.405P0.595 barriers were adjusted to pro- vide an electroluminescence peak near 1550 nm. The waveguide is 2 ym wide, 1 mm long, and is AR-coated, as with the QD SOA. The QDash sample structure is the same as described in [21] and of the type also reported in [22], [23], consisting of five layers of InAs quantum dashes (highly elongated with axes aligned perpendicular to the waveguide) each embedded in com- pressively strained Alp.2Gao,1¢INo.g4As QWs, and separated by tensile-strained 30-nm-thick Alp.43Gag.32Ing.5As barriers. The dimensions of the dashes were estimated to be 300, 25, and 5 nm for the length, width, and height, respectively, and the dash density to be ~ 1 x 10!° cm~? [23]. This dash-in-a-well layer structure is surrounded with Alg.oGao,.ogIno,52As guiding layers to complete the intrinsic active region, which is then bounded by doped AlInAs upper and lower cladding layers. The entire struc- ture is grown on an InP substrate. The sample has a 5-j.m ridge width and is 1 mm in length. The value of A for each sample in Table I is the ridge width multiplied by the sample length and is the cross-sectional areas of the current flow into the active re- gion, neglecting current spreading effects. TABLE I
SAMPLE STRUCTURES in [18], its core consisting of five stacked layers of self-assem- bled InAs dots, grown in Ino.s05Gao,.195ASo.405P 0.595 1.15-m -bandgap barrier layers and InP cladding layers by chemical beam epitaxy on an InP substrate. It has a ridge width of 2 zm, a length of 1 mm, and it is antireflection (AR)-coated to create a single-pass amplifier. Compared with the structure in [18], it has a slightly reduced active region width and increased p-type dopant concentration to lower the series resistance and improve hole injection, allowing for higher injected currents and more gain. The QD growth conditions were also nominally similar, thus we estimate the dot characteristics to be similar to those in our previous reports, with a planar density of 1.5 x 10!° cm~? and approximate average lateral diameter and height of 25 and 5 nm, respectively, as confirmed by TEM and AFM measure- ments [19], [20]. We believe the dots are on average slightly larger than those in [18], however, because of the slightly longer observed amplified spontaneous emission (ASE) peak wave- length of 1620 nm (see Fig. 1), which is due to a small in- crease in the amount of InAs deposited. The QW SOA has been made as similar to the QD SOA as possible, for comparison. It has identical cladding layers and doping, but has a core con- sisting of five Ing,g95;Gag.195AS0.gPo.2 compressively strained QWs in place of the InAs dot layers. The widths of the wells and Ino.g95Gao.195ASo.405P0.595 barriers were adjusted to pro- vide an electroluminescence peak near 1550 nm. The waveguide is 2 ym wide, 1 mm long, and is AR-coated, as with the QD SOA. The QDash sample structure is the same as described in [21] and of the type also reported in [22], [23], consisting of five layers of InAs quantum dashes (highly elongated with axes aligned perpendicular to the waveguide) each embedded in com- pressively strained Alp.2Gao,1¢INo.g4As QWs, and separated by tensile-strained 30-nm-thick Alp.43Gag.32Ing.5As barriers. The dimensions of the dashes were estimated to be 300, 25, and 5 nm for the length, width, and height, respectively, and the dash density to be ~ 1 x 10!° cm~? [23]. This dash-in-a-well layer structure is surrounded with Alg.oGao,.ogIno,52As guiding layers to complete the intrinsic active region, which is then bounded by doped AlInAs upper and lower cladding layers. The entire struc- ture is grown on an InP substrate. The sample has a 5-j.m ridge width and is 1 mm in length. The value of A for each sample in Table I is the ridge width multiplied by the sample length and is the cross-sectional areas of the current flow into the active re- gion, neglecting current spreading effects. TABLE I
Fig. 2. Net gain coefficient gye_ versus wavelength for the QD SOA for ir creasing bias currents. The maxima in the gain curves at high bias correspon to the QD energy levels, indicated by the arrows. Inset: Fit to the ASE spectrut from Fig. 1 (solid line) using a sum of four Gaussian functions (dotted lines centered at the GS, ES1, and ES2 wavelengths determined from the gain curve: plus an ES3 centered at 1535 nm. An optimum fit was obtained using a FHW) of 49 nm for the Gaussian curves.
Fig. 2. Net gain coefficient gye_ versus wavelength for the QD SOA for ir creasing bias currents. The maxima in the gain curves at high bias correspon to the QD energy levels, indicated by the arrows. Inset: Fit to the ASE spectrut from Fig. 1 (solid line) using a sum of four Gaussian functions (dotted lines centered at the GS, ES1, and ES2 wavelengths determined from the gain curve: plus an ES3 centered at 1535 nm. An optimum fit was obtained using a FHW) of 49 nm for the Gaussian curves.
Fig. 3. Net gain coefficient g,.; versus applied current density, for the three SOAs. The QD gain curve is measured at 1620 nm, and the QDash and QW at 1560 nm.
Fig. 3. Net gain coefficient g,.; versus applied current density, for the three SOAs. The QD gain curve is measured at 1620 nm, and the QDash and QW at 1560 nm.
Fig. 4. (a), (c), (e) Long-lived amplitude and (b), (d), (f) phase recoveries over 2 ns for the QD (a), (b), QDash (c), (d), and QW (e), (f) SOAs. Dotted lines are the measured data, and thin solid lines are multi-exponential fits. The bias current in mA and long-lived 1/e lifetime in ps of the fit are given for each measured curve.
Fig. 4. (a), (c), (e) Long-lived amplitude and (b), (d), (f) phase recoveries over 2 ns for the QD (a), (b), QDash (c), (d), and QW (e), (f) SOAs. Dotted lines are the measured data, and thin solid lines are multi-exponential fits. The bias current in mA and long-lived 1/e lifetime in ps of the fit are given for each measured curve.
Fig. 6. Magnitudes of the step changes, a,, (amplitude—left axis of the three plots) and a.) (phase—right axis of the three plots), in the fits to the curves ir Fig. 5, versus normalized bias current I/ It,.
Fig. 6. Magnitudes of the step changes, a,, (amplitude—left axis of the three plots) and a.) (phase—right axis of the three plots), in the fits to the curves ir Fig. 5, versus normalized bias current I/ It,.
Fig. 7. 1/e lifetimes of the CH (7c4) and SHB (7s) components in the fits to the amplitude (solid curves) and phase (dotted curves) curves in Fig. 5 versu normalized bias current. No SHB dynamic was observed in the phase traces, which is consistent with hole burning symmetric about the center frequency [6], [32]
Fig. 7. 1/e lifetimes of the CH (7c4) and SHB (7s) components in the fits to the amplitude (solid curves) and phase (dotted curves) curves in Fig. 5 versu normalized bias current. No SHB dynamic was observed in the phase traces, which is consistent with hole burning symmetric about the center frequency [6], [32]
Fig. 8. Magnitudes of the CH component, acy (amplitude—solid curves, left axes) and acHp (phase—dotted curves, right axes), in the exponential fits to the curves in Fig. 5 versus normalized bias current.
Fig. 8. Magnitudes of the CH component, acy (amplitude—solid curves, left axes) and acHp (phase—dotted curves, right axes), in the exponential fits to the curves in Fig. 5 versus normalized bias current.
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