External Optical Pulse Research Articles

Storage and release of femtosecond laser pulses in a resonant photonic crystal

Femtosecond laser pulses with suitable pulse areas are shown to decelerate and stop inside a resonant photonic crystal. The release of the stored fields can be achieved through pulse collision by use of an external optical pulse as a control field. The duty cycle efficiency of the storage and release of light is shown to be as much as 96%. The proposed technique is applied to a real photonic system with finite thickness of atomic layers.

50-GHz, ultrastable, polarization-maintaining semiconductor fiber ring laser

We demonstrate a highly stable, all-polarization-maintaining fiber semiconductor ring laser source. It uses a semiconductor optical amplifier (SOA) to provide both gain and gain modulation from an external 5-GHz optical pulse train. The laser source generates 3.5-ps pulses up to a 50-GHz repetition rate with negligible amplitude pattern.

Application of an optical pulse stretcher to coherent anti-Stokes Raman spectroscopy

An external optical cavity pulse stretcher for nanosecond-long laser pulses has been applied to coherent anti-Stokes Raman spectroscopy (CARS). An increased signal-to-noise ratio was achieved for both vibrational and pure rotational CARS, while the power density of the laser beams remained constant. Moreover, it was demonstrated that the use of the pulse stretcher also leads to improved precision of the determined temperatures and concentrations as a result of repeated excitation of the dye laser.

Pulsewidth-Variable Relaxation-Free Optical Millimeter-Wave Generation From a Semiconductor Fiber Ring Laser

Optical pulses of 10-50-GHz repetition frequencies have been generated by rational harmonically mode locking a semiconductor fiber ring laser using cross-gain modulation by 10-GHz external double optical pulses. The output is pulsewidth-variable from 6.4 to 14 ps, wavelength-tunable from 1530 to 1560 nm, and remains relaxation-free even though the injected external optical pulses have large relaxation oscillation noise.

40-GHz Mode-Locked Fiber-Ring Laser Using a Mach–Zehnder Interferometer With Integrated SOAs

A 40-GHz mode-locked fiber-ring laser based on an optically controlled modulator is presented and analyzed in detail. The modulator is a monolithic InGaAsP-InP Mach-Zehnder interferometer with integrated semiconductor optical amplifiers, which allows optical pulse generation synchronized to an external optical clock pulse stream. The laser generates nearly transform-limited Gaussian pulses of 2.5-ps width and up to 9-mW mean output power with less than 130 fs of timing jitter, and it is wavelength tunable over more than 30 nm. The relationship between key laser parameters and the output pulse characteristics is analyzed experimentally and numerically. An improved cavity design permits the generation of shorter pulses of 1.0-ps width.

Nonlinear dynamics of current-modulated vertical-cavity surface-emitting lasers

A numerical analysis of the nonlinear dynamics of weakly index-guided vertical-cavity surface-emitting lasers (VCSELs) subject to high-frequency current modulation is performed. Chaotic behavior appears in the multi-mode regime due to transverse-mode competition. Chaotic operation is such that multi-stability of the chaos–chaos type is observed. Injection of appropriate optical pulses can switch between different chaotic solutions. The analysis of the nonlinear dynamics of high-frequency current-modulated single-mode VCSELs indicates that the chaotic behavior is not present for the considered range of current modulation amplitudes and frequencies. Only periodic behaviors are observed in such a way that multi-stability of different periodic solutions is also observed. Switching between different stable periodic solutions can be obtained by injecting external optical pulses. Finally, we show that spontaneous emission noise increases the number of available channels in chaotic optical communication systems in which frequency division multiplexing with multi-transverse-mode VCSELs is used.

Sensitivity improvement of spectral phase interferometry for direct electric-field reconstruction for the characterization of low-intensity femtosecond pulses

A modified-SPIDER (spectral phase interferometry for direct electric-field reconstruction) technique where external powerful optical pulses are employed as a light source of chirped reference pulses for sum-frequency generation is proposed and is demonstrated experimentally. It provides great improvements in sensitivity and signal-to-noise ratio, and will enable a single-shot measurement for a weak pulse, such as 1 nJ/THz-bandwidth. The technique demonstrates high accuracy for determining the delay-time, t, for weak pulse characterization, which greatly affects the group-delay dispersion of the reconstructed spectral phase.

All-optical electron spin quantum computer with ancilla bits for operations in each coupled-dot cell

A quantum cellular network with a qubit and ancilla bits in each cell is proposed. The whole circuit works only with the help of external optical pulse sequences. In the operation, some of the ancilla bits are activated, and autonomous single- and two-qubit operations are made. In the sleep mode of a cell, the decoherence of the qubit is negligibly small. Since only two cells at most are active at once, the coherence can be maintained for a sufficiently long time for practical purposes. A device structure using a quantum dot array with possible operation and measurement schemes is also proposed.

Experimental and theoretical studies of a high repetition rate fiber laser, mode-locked by external optical modulation

An experimental and theoretical study of a high repetition rate laser source operating on a novel mode-locking technique is presented. This technique relies on the fast saturation and recovery of a semiconductor optical amplifier induced by an external optical pulse and has been used to obtain 4.3 ps pulses at 20 GHz. A complete mathematical model of the fiber ring laser is presented describing the mode-locking process in the laser oscillator and providing solutions for the steady-state mode-locked pulse profile. The critical parameters of the system are defined and analyzed and their impact on the formation of the mode-locked pulses is examined. The comparison between the theoretical results and the experimental data reveals very good agreement and has allowed the optimization of the performance of the system in terms of its critical parameters.

10 x 30 GHz pulse train generation from semiconductor amplifier fiber ring laser

A multiwavelength, fiber ring laser source, is demonstrated. It generates 10 wavelength channels, simultaneously mode-locked and synchronized at 30 GHz, each producing 7-ps pulses. The mode-locking technique relies on the gain saturation of the semiconductor amplifier from an external optical pulse train to impose the simultaneous mode-locking of the 10 wavelengths.

20-GHz broadly tunable and stable mode-locked semiconductor amplifier fiber ring laser

We present an actively mode-locked fiber ring laser that uses a single active semiconductor optical amplifier device to provide both gain and gain modulation from an external optical pulse train. The laser source generated 4.3-ps pulses at 20 GHz over a 16-nm tuning range and is stable against environmental changes and simple to build.

Optical clock repetition-rate multiplier for high-speed digital optical logic circuits

Repetition-rate multiplication has been shown by use of a fiber ring oscillator with a semiconductor optical amplifier as the gain medium and by use of fast saturation and recovery of the amplifier from an external optical pulse train. Repetition-frequency multiplication up to 6 times and up to 34.68-GHz frequency have been achieved.

Optical multi-stable set-reset functions of optoelectronic integrated device composed of six heterojunction phototransistors over two laser diodes

An optoelectronic integrated device composed of six heterojunction phototransistors epitaxially integrated over two buried crescent laser diodes is developed. The integrated device provides internal electro-optical coupling among constituent components. The coupling has an important role to achieve several optical functions quite appropriate for the fields of neural network and optical information processing. With a proper combination of the constituent devices, the integrated device exhibits tetra-stable set-reset function (extendable to penta-stable set-reset function) when external optical pulses are incident to the device. Physics and mechanism of the device operation are discussed in detail and the experimental results are presented.

Optical and electrical oscillations in double-heterojunction negative differential resistance devices

The observation of optical and electrical oscillations is reported in a GaAs/AlGaAs digital optoelectronic switch (DOES) structure. The oscillations are correlated to the negative differential resistance (NDR) region typically observed in the current-voltage (I-V) characteristics of this heterostructure. Plateaulike DC I-V characteristics in the NDR region and an apparent enhancement of the DC luminescence are shown to be a direct result of device oscillations in the NDR regime. External and intrinsic circuit parameters are demonstrated to determine the temporal characteristics of both the electrical and optical oscillations. These oscillations can be of sufficient magnitude to induce lasing at apparently very low DC current levels. It is shown that an external optical pulse can be used to induce the extent of the NDR region and thereby quench optical oscillations. In this manner, an optically controlled free-running optical oscillator is demonstrated. >

Gain-switched semiconductor laser amplifier as an ultrafast dynamical optical gate

A gain-switched semiconductor laser is shown to act as an optical gate with picosecond resolution and amplification for light pulses from another laser source. The amplification mechanism and the gate width change qualitatively when the gate laser undergoes a transition from a pumping rate slightly below the dynamic laser threshold to slightly above the dynamic threshold. If the gate laser is pumped below but close to its dynamical threshold, unsaturated amplification of an external signal pulse occurs over a delay time range between the external optical pulse and the electrical driving pulse of about 100–200 ps which is equivalent to the optical gate width. The signal amplification is observed to increase by two orders of magnitude and the gate width decreases by one order of magnitude if the gate laser is pumped slightly above the dynamical threshold. Amplification then occurs for input signals injected much earlier. A detailed theory of coherent, time-dependent amplification including the nonlinear dynamics of the semiconductor laser is shown to account for the observations. Both amplification regimes, below and above threshold, are reproduced in the numerical simulations. The extremely short and highly sensitive gate range above threshold is identified as being due to the gain maximum related with the first relaxation oscillation of the laser.