Boolean logic device done with DFB laser diode

We present simulation results on how power output-input characteristic Instability in Distributed FeedBack -DFB semiconductor laser diode SLA can be employed to implemented Boolean logic device. Two configurations of DFB Laser diode under external optical injection, either in the transmission or in the reflective mode of operation, is used to implement different Optical Logic Cells (OLCs), called the Q- and the P-Device OLCs. The external optical injection correspond to two inputs data plus a cw control signal that allows to choose the Boolean logic function to be implement. DFB laser diode parameters are choosing to obtain an output-input characteristic with the values desired. The desired values are mainly the on-off contrast and switching power, conforming shape of hysteretic cycle. Two DFB lasers in cascade, one working in transmission operation and the other one in reflective operation, allows designing an inputoutput characteristic based on the same respond of a self-electrooptic effect device is obtained. Input power for a bit'T' is 35 uW(70uW) and a bit "0" is zero for all the Boolean function to be execute. Device control signal range to choose the logic function is 0-140 uW (280 uW). Q-device (P-device)

Laser diode bistability as sensor of optical signals pameters

Laser Diodes have been employed many times as light sources on different kinds of optical sensors. Their main function in these applications was the emission of an optical radiation impinging onto a certain object and, according to the characteristics of the reflected light, some information about this object was obtained. Laser diodes were acting, in a certain way, just as passive devices where their only function was to provide the adequate radiation to be later measured and analyzed. The objective of this paper is to report a new concept on the use of laser diodes taking into account their optical bistable properties. As it has been shown in several places, different laser diodes as, for example, DFB lasers and FP lasers, offer bistable characteristics being these characteristics a function of different parameters as wavelength, light polarization or temperature. Laser Bistability is strongly dependent on them and any small variation of above parameters gives rise to a strong change in the characteristics of its non-linear properties. These variations are analyzed and their application in sensing reported. The dependence on wavelength, spectral width, input power and phase variations, mainly for a Fabry-Perot Laser structure as basic configuration, is shown in this paper.

Distance measurement using the change in junction voltage across a laser diode due to the self-mixing effect

Conventional detection scheme for self-mixing sensors uses an integrated photodiode within the laser package to monitor the self mixing signal. This arrangement can be simplified by directly obtaining the self-mixing signals across the laser diode itself and omitting the photodiode. This work reports on a Vertical-Cavity Surface-Emitting Laser (VCSEL) based selfmixing sensor using the laser junction voltage to obtain the selfmixing signal. We show that the same information can be obtained with only minor changes to the extraction circuitry leading to potential cost saving with reductions in component costs and complexity and significant increase in bandwidth favoring high speed modulation. Experiments using both photo current and voltage detection were carried out and the results obtained show good agreement with the theory.

Pulse tail suppression in laser diode output by tunable notch filter

Efficient suppression of relaxation oscillations in the output signal from an overdriven gain-switched laser diode was demonstrated. Several quantum-well distributed feedback laser diodes from different manufacturers were used for experimental analysis. A five-fold increase in the peak power was achieved for the tail-free operation. It was found that spectral filtering removed the nonlinearly chirped components resulting in pulse shortening by a factor of three.

Talbot-like bands for a laser diode below threshold

We report on the problems encountered when replacing a tungsten filament lamp with a laser diode in a set-up for displaying Talbot bands using a diffraction grating. It is shown that the band pattern is rather complex and strong interference signals may exist in situations where Talbot bands are not normally expected to appear. In these situations, the period of the bands increases with the optical path difference (OPD). The visibility of bands as dependence on path imbalance is obtained by suitably obstructing halfway into the arms of a Michelson interferometer using opaque screens.

A frequency locked laser diode for interferometric sensing systems

Interferometric sensors for slowly varying measurands, such as temperature or pressure, require a long term frequency stability of the source. We describe a system for frequency locking a laser diode to an atomic transition in a hollow cathode lamp using the optogalvanic effect.

Self-seeded gain-switched operation of an InGaN MQW laser diode

Self-seeded, gain-switched operation of an InGaN multi-quantum-well laser diode has been demonstrated for the first time. An external cavity comprising Littrow geometry was implemented for spectral control of pulsed operation. The feedback was optimized by adjusting the external cavity length and the driving frequency of the laser. The generated pulses had a peak power in excess of 400mW, a pulse duration of 60ps, a spectral linewidth of 0.14nm and maximum side band suppression ratio of 20dB. It was tunable within the range of 3.6nm centered at a wavelength of 403nm.

Talbot-like bands for a laser diode below threshold

We report on the problems encountered when replacing a tungsten filament lamp with a laser diode in a set-up for displaying Talbot bands using a diffraction grating. It is shown that the band pattern is rather complex and strong interference signals may exist in situations where Talbot bands are not normally expected to appear. In these situations, the period of the bands increases with the optical path difference (OPD). The visibility of bands as dependence on path imbalance is obtained by suitably obstructing halfway into the arms of a Michelson interferometer using opaque screens.

A novel tunable all-optical incoherent negative-tap fiber-optic transversal filter based on a DFB laser diode and fiber Bragg grating

We demonstrate experimentally a novel and simple tunable all-optical incoherent negative-tap fiber-optic transversal filter based on a distribution feedback laser diode and high reflection fiber Bragg gratings (FBGs). In this filter, variable time delay is provided by cascaded high reflection fiber Bragg gratings (FBGs), and the tuning of the filter is realized by tuning different FBG to match the fixed carrier wavelength, or adjusting the carrier wavelength to fit different FBG. The incoherent negative tapping is realized by using the carrier depletion effect in a distribution feedback laser diode.

THz emission from quantum dot-based THz antennas pumped by a tunable quantum-dot laser diode

The THz optoelectronics field is now maturing and semiconductor-based THz antenna devices are becoming more widely implemented as analytical tools in spectroscopy and imaging. Photoconductive (PC) THz switches/antennas are driven optically typically using either an ultrashort-pulse laser or an optical signal composed of two simultaneous longitudinal wavelengths which are beat together in the PC material at a THz difference frequency. This allows the generation of (photo)carrier pairs which are then captured over ultrashort timescales usually by defects and trapping sites throughout the active material lattice. Defect-implanted PC materials with relatively high bandgap energy are typically used and many parameters such as carrier mobility and PC gain are greatly compromised. This paper demonstrates the implementation of low bandgap energy InAs quantum dots (QDs) embedded in standard crystalline GaAs as both the PC medium and the ultrafast capture mechanism in a PC THz antenna. This semiconductor structure is grown using standard MBE methods and allows the device to be optically driven efficiently at wavelengths up to ~1.3 µm, in this case by a single tunable dual-mode QD diode laser.

Orange light generation from a PPKTP waveguide end pumped by a cw quantum-dot tunable laser diode

A compact all-room-temperature frequency-doubling scheme generating cw orange light with a periodically poled potassium titanyl phosphate waveguide and a quantum-dot external cavity diode laser is demonstrated. A frequency-doubled power of up to 4.3 mW at the wavelength of 612.9 nm with a conversion efficiency exceeding 10% is reported. Second harmonic wavelength tuning between 612.9 nm and 616.3 nm by changing the temperature of the crystal is also demonstrated. © Springer-Verlag 2010.

Efficient yellow-green light generation at 561 nm by frequency-doubling of a QD-FBG laser diode in a PPLN waveguide

A compact high-power yellow-green continuous wave (CW) laser source based on second-harmonic generation (SHG) in a 5% MgO doped periodically poled congruent lithium niobate (PPLN) waveguide crystal pumped by a quantum-dot fiber Bragg grating (QD-FBG) laser diode is demonstrated. A frequency-doubled power of 90.11 mW at the wavelength of 560.68 nm with a conversion efficiency of 52.4% is reported. To the best of our knowledge, this represents the highest output power and conversion efficiency achieved to date in this spectral region from a diode-pumped PPLN waveguide crystal, which could prove extremely valuable for the deployment of such a source in a wide range of biomedical applications.

Optical trapping with superfocused high-M2 laser diode beam

Many applications of high-power laser diodes demand tight focusing. This is often not possible due to the multimode nature of semiconductor laser radiation possessing beam propagation parameter M2 values in double-digits. We propose a method of 'interference' superfocusing of high-M2 diode laser beams with a technique developed for the generation of Bessel beams based on the employment of an axicon fabricated on the tip of a 100 μm diameter optical fiber with highprecision direct laser writing. Using axicons with apex angle 140º and rounded tip area as small as 10 μm diameter, we demonstrate 2-4 μm diameter focused laser 'needle' beams with approximately 20 μm propagation length generated from multimode diode laser with beam propagation parameter M2=18 and emission wavelength of 960 nm. This is a few-fold reduction compared to the minimal focal spot size of 11 μm that could be achieved if focused by an 'ideal' lens of unity numerical aperture. The same technique using a 160º axicon allowed us to demonstrate few-μm-wide laser 'needle' beams with nearly 100 μm propagation length with which to demonstrate optical trapping of 5-6 μm rat blood red cells in a water-heparin solution. Our results indicate the good potential of superfocused diode laser beams for applications relating to optical trapping and manipulation of microscopic objects including living biological objects with aspirations towards subsequent novel lab-on-chip configurations.