Showing papers by "Mohammed N. Islam published in 1989"
TL;DR: It is shown experimentally the trapping of orthogonally polarized solitons in birefringent optical fibers with polarization dispersions as high as 90 psec/km.
Abstract: We show experimentally the trapping of orthogonally polarized solitons in birefringent optical fibers with polarization dispersions as high as 90 psec/km. Solitons along two axes of a fiber compensate for the polarization dispersion by shifting their frequencies, and we observe frequency splitting up to 1.03 THz for a polarization dispersion of 80 psec/km. For a 20-m fiber the energy required to compensate for the polarization dispersion is ~84 pJ, and for a 76-m fiber the energy required reduces to ~64 pJ.
193 citations
TL;DR: In this article, a femtosecond distributed soliton spectrum with τ ≳ 100 fsec covering a wide spectral range between 1.55 < λ < 1.85 μm is presented.
Abstract: By pumping a fiber in the anomalous group-velocity dispersion regime with a color-center laser, we generate a femtosecond distributed soliton spectrum with τ ≳ 100 fsec covering a wide spectral range between 1.55 < λ < 1.85 μm. We present a theory to explain the spectrum and use autocorrelations and cross correlations to verify the results experimentally. Modulation instability and the soliton self-frequency shift effect initiate a multisoliton collision process that results in narrow, high-intensity solitons. An ensemble average over these solitons, which start from noise and frequency shift by different amounts, yields the observed broad spectra. We use the fiber output in pump–probe experiments, measuring the exciton ionization time in InGaAs/InP multiple quantum wells for the first time to our knowledge.
145 citations
TL;DR: All-optical, ultrafast switching at an energy of 55 pJ in a fiber nonlinear-optICAL loop mirror and the soliton self-frequency shift lowers the peak transmission and splits the output pulse at higher powers, in agreement with numerical simulations.
Abstract: We observe all-optical, ultrafast switching at an energy of ∼55 pJ in a fiber nonlinear-optical loop mirror. The entire 310-fsec soliton waveform switches with 90% peak transmission. The soliton self-frequency shift lowers the peak transmission and splits the output pulse at higher powers, in agreement with numerical simulations.
112 citations
TL;DR: Ultrafast all-optical soliton-trapping logic gates, including an inverter, exclusive OR, and AND, are experimentally demonstrated in birefringent fibers and numerical simulations show that the output from the inverter can be cascaded to other trapping gates.
Abstract: Ultrafast all-optical soliton-trapping logic gates, including an inverter, exclusive OR, and AND, are experimentally demonstrated in birefringent fibers The soliton-trapping logic gates are three terminal devices with orthogonally polarized inputs, phase-insensitive nonlinear operation, and switching energies of ~42 pJ Using a 02-THz bandpass filter, the contrast ratio for the exclusive-OR gate is ~8:1, but the output pulses are ~10 times broader than the input pulse width By widening the filter bandpass to 058 THz, an inverter is demonstrated with an ~4:1 contrast ratio and output pulses that can propagate as solitons in a fiber Numerical simulations show that the output from the inverter can be cascaded to other trapping gates
101 citations
TL;DR: Computer simulations show that modulation instability and the soliton self-frequency-shift effect initiate a multisoliton collision process that results in narrow, high-intensity, fundamental solitons.
Abstract: By pumping a fiber in the anomalous group-velocity-dispersion regime with a color-center laser we generate pulses with τ ≳ 100 fsec covering a wide spectral range of 1.55 μm < λ < 1.85 μm. Cross-correlation measurements show the lack of correlation between different parts of the spectrum. Computer simulations show that modulation instability and the soliton self-frequency-shift effect initiate a multisoliton collision process that results in narrow, high-intensity, fundamental solitons. The observed broad spectra correspond to an ensemble average over these solitons, which start from noise and frequency shift by different amounts.
99 citations
TL;DR: In this paper, a NaCl color center was passively mode locked to produce 275fs transform-limited, pedestal-free pulses with a peak power as high as 3.7 kW.
Abstract: Using multiple-quantum-well (MQW) saturable absorbers, a NaCl color center was passively mode locked to produce 275-fs transform-limited, pedestal-free pulses with a peak power as high as 3.7 kW. The pulses are tunable from lambda =1.59 to 1.7 mu m by choosing MQWs with different bandgaps. The output pulses from the laser were shortened to 25 fs using the technique of soliton compression in a fiber. The steady-state operation of the laser requires the combination of a fast saturable absorber and gain saturation. >
85 citations
Patent•
25 Sep 1989TL;DR: In this article, a Fabry Perot etalon centered at the center frequency of both the first and second signals is utilized to realize a exclusive-OR operation whereas centering the etalon on the frequency related to the spectral shift caused by soliton trapping realizes an AND operation.
Abstract: Combinatorial (Boolean) logic functions are provided by ultrafast optical logic devices which utilize soliton trapping between two optical signals propagating in a birefringent fiber. The logic devices are three terminal devices having orthogonally polarized soliton input signals and a single output signal. Optically filtering the output from the fiber permits the desired combinatorial logic operation to be performed on the input optical signals. Logic operations include AND, exclusive-OR, NOT, and NOR functions. In operation, the devices exhibit phase insensitivity, low switching energy, high contrast ratio between output logic levels, and cascadability. In one embodiment of the invention, a first optical signal and a second optical signal are optically coupled into the principal axes of a birefringent fiber. A Fabry Perot etalon centered at the center frequency of both the first and second signals is utilized to realize a exclusive-OR operation whereas centering the etalon on the frequency related to the spectral shift caused by soliton trapping realizes an AND operation.
68 citations
Proceedings Article•
24 Apr 1989TL;DR: In this article, the authors experimentally observe soli ton trapping in birefringent fibers and find that the solitons frequency shift by more than 1 THz to compensate for polarization dispersion as high as 90 psec/km.
Abstract: We experimentally observe soli ton trapping in birefringent fibers and find that the solitons frequency shift by more than 1 THz to compensate for polarization dispersion as high as 90 psec/km.
60 citations
Patent•
13 Oct 1989TL;DR: Combinatorial logic devices are presented in which data signals interact with an enable signal in the device to move the enable signal outside its prescribed time slot when one or both of the data signals are present.
Abstract: Combinatorial logic devices are presented in which data signals interact with an enable signal in the device to move the enable signal outside its prescribed time slot when one or both of the data signals are present. Data signals are discarded within the device to avoid propagation through subsequent logic device stages. Such logic devices are particularly well suited to all-optical realizations in which soliton pulse signals are used. These devices exhibit high gain, cascadability and potentially large fanout capability.
39 citations
34 citations
TL;DR: In this article, the authors reported room temperature confinement and photoluminescence near 3 μm in a mercury cadmium telluride multiple quantum well, where the absorption spectra show transitions from the first heavy and light hole confined levels to the first conduction electron confined level.
Abstract: We report room‐temperature confinement and photoluminescence near 3 μm in a mercury cadmium telluride multiple quantum well. The absorption spectra show transitions from the first heavy and light hole confined levels to the first conduction electron confined level. Photoluminescence is present even at room temperature. The transition energies and temperature dependence of our data can be described by a square well model provided that a temperature‐independent value of approximately 400 meV is used for the HgTe‐CdTe valence‐band offset.
Proceedings Article•
01 Jan 1989TL;DR: Using multiple quantum well (MQW) saturable absorbers, the authors passively mode locked a NaCl color center laser to produce transform-limited, pedestal-free pulses with τ as short as 275 fs and peak power as high as 3.7 kW.
Abstract: Using multiple quantum well (MQW) saturable absorbers, we passively mode locked a NaCl color center laser to produce transform‐limited, pedestal‐free pulses with τ as short as 275 fs and peak power as high as 3.7 kW. Because of exciton ionization with a 200±30 fs time constant, the MQW shows a fast absorption recovery that is comparable to our pulse widths. This fast component plays a major role in pulse shaping and may limit the pulse width. We also show that the wavelength for the short pulses can be tuned from 1.59 to 1.7 μm by choosing MQWs with different band gaps.
TL;DR: Using multiple quantum well (MQW) saturable absorbers, the authors passively mode locked a NaCl color center laser to produce transform-limited, pedestal-free pulses with τ as short as 275 fs and peak power as high as 3.7 kW.
Abstract: Using multiple quantum well (MQW) saturable absorbers, we passively mode locked a NaCl color center laser to produce transform‐limited, pedestal‐free pulses with τ as short as 275 fs and peak power as high as 3.7 kW. Because of exciton ionization with a 200±30 fs time constant, the MQW shows a fast absorption recovery that is comparable to our pulse widths. This fast component plays a major role in pulse shaping and may limit the pulse width. We also show that the wavelength for the short pulses can be tuned from 1.59 to 1.7 μm by choosing MQWs with different band gaps.
TL;DR: In this paper, the authors observed photoluminescence from 2 K to room temperature, and the low-temperature peak width is consistent with layer thickness fluctuations limited to one monolayer.
Abstract: HgCdTe multiple quantum wells with transition energies near 3 μm have been grown by molecular‐beam epitaxy. We observe photoluminescence from 2 K to room temperature, and the low‐temperature peak width is consistent with layer thickness fluctuations limited to one monolayer. High‐resolution transmission electron microscopy shows that there is some roughness at the interfaces, but that there is good layer thickness uniformity throughout the structure. The absorption spectra contain sharp, steplike features due to carrier confinement in the wells at energies that can be described by a square‐well model, provided that a temperature‐independent HgTe/CdTe valence‐band offset near 400 meV is assumed.
TL;DR: In this paper, a new class of optical correlator which is integrable and potentially compatible with semiconductor laser diodes is experimentally tested and shown to be a broad band correlator capable of correlating pulse trains with average power in the correlator in sub-mW range with wavelengths at least ranging from 1.06 to 1.7 μm.
Abstract: A new class of optical correlator which is integrable and potentially compatible with semiconductor lasers is experimentally tested. The correlator proposed earlier (a special GaAs/AlGaAs waveguide) is shown to be broad band capable of correlating pulse trains with average power in the correlator in sub‐mW range with wavelengths at least ranging from 1.06 to 1.7 μm. To show compatibility with semiconductor laser diodes the correlator device was also used to generate sum frequency signal from mixing a 400 μW cw beam of a 1.06 μm Nd:YAG laser with a 400 μW cw beam of a 1.3 μm semiconductor laser diode. The latest result shows the potential of direct measurement of optical pulses from semiconductor laser diodes at different wavelengths with a single integrable compact correlator without any mechanical translation.
TL;DR: An active fiber polarization-rotation switch based on modulation instability operating near 1.5 microm that exhibits contrast ratios of up to 40:1 and small-signal gains of upto 40 dB is demonstrated.
Abstract: We demonstrate an active fiber polarization-rotation switch based on modulation instability operating near 1.5 μm that exhibits contrast ratios of up to 40:1 and small-signal gains of up to 40 dB. Modulation instability generates upper and lower sideband frequencies with different states of polarization from the pump at the fiber output. The high contrast ratio is achieved in part because intensity fluctuations with the pump alone do not lead to an output from the device.