[Show abstract][Hide abstract] ABSTRACT: An alternative segmented-contact method for accurate measurement of the optical gain and absorption of quantum-dot and quantum-dash active materials with small optical gain is reported. The usual error from unguided spontaneous emission is reduced by subtracting signals acquired from three independently controlled sections as opposed to just two found in the conventional technique. The quantum-dot gain spectra are measured to a precision of less than 0.2 cm<sup>-1</sup> at nominal gain values below 2 cm<sup>-1</sup>, and gain spectrum of quantum-dash sample is calculated with an error less than 0.3 cm<sup>-1</sup> at a gain less than 1 cm<sup>-1</sup>. These accuracies are checked with a self-calibrating method. The internal optical mode loss measurement is also described
[Show abstract][Hide abstract] ABSTRACT: Novel InAs/InGaAs quantum dots-in-a-well (DWELL) infrared photodetectors are described. These detectors, in which the active region consists of InAs quantum dots embedded in an InGaAs quantum well, represent a hybrid between a conventional quantum well infrared photodetector (QWIP) and a quantum dot infrared photodetector (QDIP). Like QDIPs, the DWELL detectors display normal incidence operation without gratings or optocouplers while demonstrating reproducible dial-in recipes for control over the operating wavelength, like QWIPs. We report the first demonstration of a two-color infrared focal plane array based on a voltage-tunable quantum dots-in-well (DWELL) design. The active region consists of multiple layers of InAs quantum dots in an In0.15Ga0.85As quantum well. Spectral response measurements yielded a peak at 5.5 mum for lower biases and at 8-10 mum for higher biases. Using calibrated blackbody measurements, the mid-wavelength and long wavelength specific detectivity (D*) were estimated to be 7.1 × 1010 cmHz1/2 /W (Vb = 1.0 V) and 2.6 × 1010 cmHz1/2 /W (Vb = 2.6 V) at 78 K, respectively. This material was processed into a 320 × 256 array and integrated with an Indigo 9705 readout chip and thermal imaging was achieved at 80 K.
physica status solidi (c) 03/2006; 3(3):439-443. DOI:10.1002/pssc.200564162
[Show abstract][Hide abstract] ABSTRACT: We present wavelength conversion using nondegenerate four-wave mixing in loss-coupled distributed feedback lasers based on InAs quantum dots (QDs) grown on a GaAs substrate. The conversion efficiency is measured to be -15 to -30 dB for a signal-pump detuning range from 0.33 to 8 nm. The third-order optical susceptibility (χ<sup>(3)</sup>) normalized to the optical linear gain in the QDs is estimated to be 3×10<sup>-20</sup> m<sup>3</sup>/V<sup>2</sup> to 9×10<sup>-20</sup> m<sup>3</sup>/V<sup>2</sup> for the signal-pump detuning range.
[Show abstract][Hide abstract] ABSTRACT: We report the demonstration of a two-color infrared focal plane array based on a voltage-tunable quantum dots-in-well (DWELL) design. The active region consists of multiple layers of InAs quantum dots in an In0.15Ga0.85As quantum well. Spectral response measurements yielded a peak at 5.5 μm for lower biases and at 8–10 μm for higher biases. Using calibrated blackbody measurements, the midwavelength and long wavelength specific detectivity (D*) were estimated to be 7.1×1010 cm Hz1/2/W(Vb = 1.0 V) and 2.6×1010 cm Hz1/2/W(Vb = 2.6 V) at 78 K, respectively. This material was processed into a 320×256 array and integrated with an Indigo 9705 readout chip and thermal imaging was achieved at 80 K.
[Show abstract][Hide abstract] ABSTRACT: We measure, for the first time, the gain compression coefficient and above-threshold linewidth enhancement factor (alpha parameter) in quantum dot (QD) distributed feedback lasers (DFB) by time-resolved-chirp (TRC) characterization. The alpha parameter is measured to be 2.6 at threshold and increases to 8 when the output power of the QD DFB is increased to 3 mW. The dependence of the above-threshold alpha parameter on the optical power is found to be stronger than the optical gain compression effect alone can predict. The inhomogeneous gain broadening, gain saturation at the ground states and carrier filling in the excited states in QDs are proposed to explain the results.
Proceedings of SPIE - The International Society for Optical Engineering 04/2005; 5722:72-79. DOI:10.1117/12.591105 · 0.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Sub-picosecond timing jitter is demonstrated for 5 GHz, <10 ps optical pulses generated from monolithic passively mode-locked quantum dot lasers. Their low cost, compact size and DC-biased operation make them ideal for high speed optical interconnects.
Optical Fiber Communication Conference, 2005. Technical Digest. OFC/NFOEC; 04/2005
[Show abstract][Hide abstract] ABSTRACT: For understanding the fundamental processes in QDs and optimizing the design of QD optical devices, it is essential to obtain accurate optical gain and absorption spectra. An improved segmented-contact method is described that subtracts the unguided spontaneous emission that normally introduces error into the calculated gain and absorption. Using the technique a QD gain spectrum is measured to an accuracy of less than 0.2/cm at nominal gain values below 2/cm. This capability also enables precise measurement of waveguide internal loss, unamplified spontaneous emission spectra and Stark shift data.
Proceedings of SPIE - The International Society for Optical Engineering 04/2005; 5722. DOI:10.1117/12.591241 · 0.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We report the first two-color 320 x 256 infrared Focal Plane Array (FPA), based on a voltage-tunable InAs/InGaAs/GaAs DWELL structure. The detectors, grown by solid source molecular beam epitaxy (MBE) comprise of a 15–stack asymmetric DWELL structure sandwiched between two highly doped n-GaAs contact layers, grown on a semi-insulating GaAs substrate. The DWELL region consists of a 2.2 monolayer deposition of n-doped InAs quantum dots (QDs) in an In 0.15 GaAs 0.85 As well, itself placed in GaAs. The well widths below and above the dots are 50Å and 60Å, respectively. The absorption region asymmetry results in a bias dependent spectral response, with the peak wavelength varying from 5.5 to 10 µm. Using calibrated black body measurements, mid-wavelength and long wavelength specific detectivities (D*) of top-illuminated test pixels at 78K were estimated to be 7.1 x 10 10 cmHz 1/2 /W (V b = 1.0V) and 2.8 x 10 10 cmHz 1/2 /W (V b = 2.5V), respectively. Subsequently, a 320 x 256 QDIP FPA array was fabricated on a 30 µm pitch and was hybridized with an Indigo 9705 ROIC. Thermal imaging was successfully carried out at an estimated FPA temperature of 80K, using different optical filters between 3-5 µm, and 8-12 µm, so as to demonstrate two-color operation. The operability of the FPA was greater than 99%, and the noise-equivalent temperature difference was estimated to be less than 100 mK for f#1 (3-5 µm) and f#2 (5-9 µm) optics.
Proceedings of SPIE - The International Society for Optical Engineering 01/2005; 5897. DOI:10.1117/12.617775 · 0.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The performance and applications of 1.3 to 1.6 micron quantum dot optoelectronic devices will be presented, including semiconductor lasers for data communications, mode-locked lasers, and semiconductor optical amplifiers suitable for high power, high speed operation.
Indium Phosphide and Related Materials, 2004. 16th IPRM. 2004 International Conference on; 07/2004
[Show abstract][Hide abstract] ABSTRACT: The performance and applications of Quantum Dot optoelectronic devices will be presented, including infrared photodetectors for space imaging, diagnostics and sensing, and semiconductor lasers for communications, clock distribution, optical time division multiplexing, marking and printing.
[Show abstract][Hide abstract] ABSTRACT: This study reports on the fabrication and lasing characteristics of InAs quantum dot (QD) lasers on GaAs substrates grown by metalorganic chemical vapor deposition (MOCVD). Continuous wave lasing at room temperature with low threshold (6.7 mA) has been achieved at the wavelength of 1.18 μm. The threshold current of 6.7 mA is the lowest value so far achieved in QD lasers grown by MOCVD. The observed lasing wavelength is also the longest. Comparison with photoluminescence spectra of InAs QD lasers indicate that the observed lasing originates mainly from the ground state of InAs QDs.
Lasers and Electro-Optics Society, 2003. LEOS 2003. The 16th Annual Meeting of the IEEE; 11/2003
[Show abstract][Hide abstract] ABSTRACT: We have reported the temperature and high-speed performance for DWELL FP and DFB lasers at wavelengths near 1310 nm. The positive gain-offset clearly improves the temperature performance of the QD DFB lasers, resulting in a constant threshold current and slope efficiency in the temperature range from 10 to 50°C. A threshold current as low as 10.5 mA with a 3 mW output power at 100°m and 9 GHz 3-dB bandwidth at room temperature were obtained. By utilizing the p-doped active region, which improves both T<sub>0</sub> and the bandwidth, low-threshold temperature-independent QD FP and DFB lasers with 3-dB modulation bandwidth well above 10 GHz can be expected in the near future for 1310 nm uncooled applications.
[Show abstract][Hide abstract] ABSTRACT: The characteristics of DFB lasers, external cavity tunable lasers, and semiconductor optical amplifiers are presented to demonstrate the versatility of GaAs-based quantum dot materials technology. For the DFB laser, a temperature-insensitive slope efficiency, low threshold, and feedback resistance are primary advantages. The external cavity tuned device has a 90 nm range, and the SOA demonstrates 18 dB gain and 9 ps gain recovery time.
[Show abstract][Hide abstract] ABSTRACT: The first self-assembled InAs quantum dash lasers grown by molecular beam epitaxy on InP (001) substrates are reported. Pulsed room-temperature operation demonstrates wavelengths from 1.60 to 1.66 μm for one-, three-, and five-stack designs, a threshold current density as low as 410 A/cm<sup>2</sup> for singlestack uncoated lasers, and a distinctly quantum-wire-like dependence of the threshold current on the laser cavity orientation. The maximal modal gains for lasing in the ground-state with the cavity perpendicular to the dash direction are determined to be 15 cm<sup>–1</sup> for single-stack and 22 cm<sup>–1</sup> for five-stack lasers.
[Show abstract][Hide abstract] ABSTRACT: Design and growth of oxide-confined self-assembled InAs quantum dash ridge waveguide lasers on InP substrates were discussed. Molecular beam epitaxy was used for the deposition of p-type lattice-mismatched InGaAs to facilitate low-resistance ohmic contact. The laser cavity was aligned along  direction to maximize tranverse electric gain. Testing of the device under pulsed conditions suggested that no significant current leakage occurred through the oxide layer thereby validating the results of V-I curve.
Lasers and Electro-Optics Society, 2001. LEOS 2001. The 14th Annual Meeting of the IEEE; 02/2001
[Show abstract][Hide abstract] ABSTRACT: Self-assembled quantum ash laser diodes fabricated on semiconducting indium phosphide substrates as demonstrated. Molecular beam epitaxy was used to grow the self-assembled nanostructures. The devices were tested under pulsed conditions with a 0.5 μs pulse width and a 0.5% duty cycle at 15 °C. The threshold current was found to depend on the orientation of the laser cavity. A threshold current of 410 A/cm2 as measured on a 4 mm long cavity cleaved facet laser diode. The quantum dash lasers had low threshold current density, ground state wavelength of operation near 1.62 μm and a clear quantum-like dependence of the threshold current on laser cavity orientation.
Lasers and Electro-Optics, 2001. CLEO '01. Technical Digest. Summaries of papers presented at the Conference on; 02/2001
[Show abstract][Hide abstract] ABSTRACT: The optical performance of quantum dot lasers with different
dots-in-a-well (DWELL) structures is studied as a function of the well
number and the indium composition in the InGaAs quantum well (QW)
surrounding the dots. While keeping the InAs quantum dot density nearly
constant, the internal quantum efficiency η<sub>i</sub>, modal gain,
and characteristic temperature of 1-DWELL and 3-DWELL lasers with QW
indium compositions from 10 to 20% are analyzed. Comparisons between the
DWELL lasers and a conventional In<sub>0.15</sub>Ga<sub>0.85</sub>As
strained QW laser are also made. A threshold current density as low as
16 A/cm<sup>2</sup> is achieved in a 1-DWELL laser, whereas the QW
device has a threshold 7.5 times larger. It is found that η<sub>i
</sub> and the modal gain of the DWELL structure are significantly
influenced by the quantum-well depth and the number of DWELL layers. The
characteristic temperature T<sub>0</sub> and the maximum modal gain of
the ground-state of the DWELL structure are found to improve with
increasing indium in the QW It is inferred from the results that the QW
around the dots is necessary to improve the DWELL laser's η<sub>i
</sub> for the dot densities studied
[Show abstract][Hide abstract] ABSTRACT: A grating-coupled external-cavity quantum dot laser is tuned
across a 201 nm range at a maximum bias of 2.87 kA/cm<sup>2</sup>. One
order of magnitude less than the bias required for comparable tuning of
quantum well lasers. The tuning range increases for higher cavity losses
of the quantum dot laser
[Show abstract][Hide abstract] ABSTRACT: An antireflection (AR) coated single-stack quantum-dot (QD) laser in a grating-coupled external cavity is shown to operate across a tuning range from 1.095 /spl mu/m to 1.245 /spl mu/m. This 150-nm range extends from the energy levels of the ground state to excited states. At any wavelength, the threshold current density is no greater than 1.1 kA/cm/sup 2/. This large tunable range is the product of the rapid carrier filling of the higher energy states under a low pumping current and homogeneous broadening in the QD ensemble. The possibility of a larger tuning range is discussed with the further improvement of the AR-coating.