We present experimental and theoretical investigations of the temperature dependence of self-pulsation in CD laser diodes. We use a rate equation model to predict the device dynamic behavior over a large temperature range and identify the role of carrier diffusion. We show experimentally and by calculating that the temperature dependence of the threshold current is driven by the carrier diffusion--particularly at low temperature. We experimentally show that for several temperatures the self-pulsation variation with respect to normalized bias current is highly linear. These results call into question whether pulsations in CD laser structures are undamped relaxation oscillations. Our results also suggest that the highly temperature dependent carrier diffusion does not play a first order role in CD laser diode self- pulsation.

We report on the generation of picosecond pulses from a self-mode-locked semiconductor diode laser. The active medium is an InGaAs amplifier whose gain curve extends from 830 to 870 nm. The facets of the amplifier are cut at angle (5 degrees). The amplifier is inserted in a ring cavity with no other component but mirrors and lenses. Mode locking is entirely passive and it takes place when the laser is operated slightly above threshold and misaligned. Trains of counterpropagating pulses are produced, with pulse durations varying from 2 to 5 ps. The counterpropagating pulses have different spectra, with a wavelength difference up to 7 nm. The pulse repetition rate could be adjusted from 0.8 to 6.4 GHz. We discuss the possibility that some nonlinear mechanisms may give rise to the mode-locking action.

The oscillation frequency of semiconductor lasers fluctuates by a temperature or an injection current change. Semiconductor lasers are now used in many application fields such as optical fiber communications systems, compact disk and laser disk systems, and others, because these application fields don't' need the high frequency stability in their light source. Therefore, we must stabilize the oscillation frequency of semiconductor lasers if we use them in a coherent optical communications or other coherent systems. Some frequency stabilization experiments of semiconductor lasers using external frequency references have been reported in recent years. We have also stabilized them using the Rb-D₂ absorption lines as an external frequency reference. Applying a small modulation directly to the injection current usually performs these stabilization methods. But the oscillation spectrum of the semiconductor laser is broadened by the modulation in this method. So we devised two stabilization methods without any direct modulation, which use the magneto-optical effects called the Zeeman and the Faraday effects, and stabilized the oscillation frequency of the semiconductor laser. As a result, we got high frequency stability without any spectrum broadening caused by the modulation. The stabilized frequency was tuned in a wide range at almost the same stability conditions. Moreover, we devised an optical setup, which produces a high sensitive error signal between the reference frequency and the laser oscillation frequency. This method, which we named `PEAK method', is also combined with the Zeeman effect to improve the frequency controllability.

This is a progress report on the realization of a compact and transportable frequency standard at 1556 nm based on a two-photon transition in rubidium at 778 nm. These hyperfine transitions present great metrological interest. They have a narrow theoretical linewidth of 150 kHz when observed with a 1556 nm laser, and their absolute frequency is known with an uncertainty of 5.2 X 10^-12. In this experiment, we use a high power 1556 nm DFB laser and reduce its linewidth to the 10 kHz level using optical feedback from a confocal cavity. We generate its second harmonic in a periodically poled LiNbO₃ crystal and use this signal to injection-lock a Fabry-Perot laser emitting 42 mW at 778 nm. The slave laser is used to observe the Doppler-free two- photon transitions: two counter-propagating beams excite rubidium atoms which emit a blue fluorescence on resonance. This 420 nm light is detected on the side of the Rb cell with a photomultiplier. Such an optical frequency standard at 1556 nm, standing in the multiwavelength telecommunications systems window, becomes an attractive source for absolute frequency calibration of WDM components, optical spectrum analyzers and wavemeters.

For DPSSL applications at low duty cycle (typically 150 microsecond(s) /20 Hz), we have developed a new concept of `High Brightness' stacked arrays, which leads to power density of 10 kW/cm², and to 40 kW/cm² when directly coupled to a lens-duct. The high intensity is made possible thanks to a new proprietary stacking technology that permits a stacking pitch of only 100 micrometers : the principle is to directly stack the arrays without any heat spreaders other than the arrays themselves. When compared to standard commercial QCW stacked arrays, the benefits of using these high brightness laser diodes pumping sources are the following: (1) an important cost reduction related to a drastic simplification in the assembling process, and (2) an improved pumping efficiency associated with an improved brightness (approximately 1 factor 4), consequence of a reduced pitch between linear bar arrays. High-efficiency, frequency-quadrupled, end-pumped 8 mJ, 12-ns-long UV pulses 0.266 micrometers Nd:YAG laser has been developed using these high brightness pump sources. This air-cooled laser is an attractive alterative to the more conventional millijoules-range UV source. A compact high energy 300 mJ Q-switched diode-pumped laser has been developed. Laser performances and integration level demonstration contribute to a preliminary laser design for future airborne laser applications.

Broad-area semiconductor lasers naturally emits on several lateral modes even at injection currents very close to the threshold current. An external cavity terminated by an apodizing holographic grating has been used to favor the oscillation of only one longitudinal mode and one lateral mode. It is possible to obtain laser oscillation on two different wavelengths simultaneously by using a grating that contains two grating periods. The fabrication technique of the apodizing holographic grating is explained. The spectrally-resolved near-field intensity distributions are presented.

In this study, different second harmonic distortion (2HD) levels of a 1.55 micrometers , InGaAsP ridge waveguide laser diode are investigated by using a mathematical model based on multi-mode rate equations. The rate equations with an input current i are solved numerically by using fourth order Runge-Kutta algorithm for frequencies ranging from 1 GHz to 10 GHz with 1 GHz steps and the standard parameter values. The important parameters of 1.55 micrometers . InGaAsP semiconductor lasers such as Auger recombination, non- radiative recombination, spontaneous emission lifetime and gain saturation are taken into account. The effects of some parameters on 2HD for different threshold levels are examined and computed graphically.

Pulsed fiber laser sources are attractive in terms of simpler delivery to a scanning head, small rugged all-fiber design and good power efficiency. For practical systems both high repetition rate and high energy are required along with single spatial mode output. Increasing in practice the pump power launched in a singlemode fiber is not simple and even then, serious pulse sharpening occurs in high gain fiber amplifier. In order to increase the energy with minimal pulse shaping, we have investigate the use of slightly multimode fibers seeded by a singlemode laser source. We achieved more than 40 (mu) J at 10 kHz for a 10 ns pulse with a good spatial mode and small pulse sharpening. Being able to shape the input pulse, we demonstrate that pre- compensation is possible to maintain uniform peak power over the output pulse.

Numerous markets for near-infrared, high-power, multi-mode diode lasers as a direct thermal source have emerged in recent years due to improved device price-to-performance ratios. Diode lasers are currently used as replacement sources in many thermal applications requiring a non-contact heat source and are also utilized in the development of new processes. Industrial applications include welding, epoxy curing, soldering, hardening, sintering, cutting and materials processing. They are also used in graphics, pumping, illumination, and a variety of medical applications. These devices provide high electrical-to- optical efficiency, are compact, virtually maintenance free, easily integrated, and are cost effective.

We present here the work performed by INO and the Canadian Coast Guard in developing a laser range light using a single site to replace conventional range lights requiring two sites. A single laser source and a temporal coding are used to indicate the vessels' position. The laser output power and wavelength are respectively 80 mW and 532 nm. The range covered is 28 km.

Digital speckle pattern shearing interferometry, also called digital shearography, is an optical interferometric technique which have already been applied by industry for the purposes of the nondestructive testing (NDT), strain and stress measurement and vibration analysis. In general, the used laser with a relatively large coherent length has applied in the measuring device. It is obviously that this kind of laser is expensive in price and large in volume. Thus the development of a simple, mobile and inexpensive industrial testing tool is limited. This paper will focus on the application of the simple laser diode without temperature stabilization and without additional expanding lens in the digital shearographic interferometry. The measuring devices using this kind of laser diode is presented. Its applications in the areas of NDT, strain measurement and vibration analysis are demonstrated. The development of a small and mobile measuring device in conjunction with a user guided comfortable program Shearwin enable the digital speckle pattern shearing interferometry to be developed easily into an industrial on line testing tool.

Generation of scanning structured light is an initiative triangulation-based method for acquiring range data. Unlike traditional projection of paten diaphragm, diode laser, rotating mirror and CCD camera are employed into our device. Diode laser is modulated to emit a modulated slit laser beam. Reflected by rotating mirror, the modulated slit laser beam flashes in different frequencies and generates several new type strip structured images in sequence. The strip structured images are characterized with a new pattern code which has higher resolution, speed and robustness than simply binary code. The new, highly efficient, binary code can shorten the measuring time greatly. In order to raise the resolution, the modulated silt laser beam, reflected by rotating mirror, should scanning all the measured space for eight times. As sweeping the measured space, the scanning step of modulated slit laser beam must be synchronized with rotating mirror and CCD camera. When the scanning is completed, the CCD camera take the images and store them in image-storage timely. All these work coordinately under the control of phase-locked loop. By applying the new scanning technique, a depth image with resolution of 1/256 can be obtained in just 0.3 second.

We present comprehensive investigations on the polarization resolved quantum noise behavior of vertical cavity surface emitting lasers (VCSELs) with various cavity designs. These experiments are accompanied by detailed studies using a semiclassical approach, first, to calculate and model theoretically the amplitude fluctuations and correlations of a two orthogonal polarization-mode semiconductor laser as realized by a VCSEL, and second, to explore theoretically the squeezing potential of VCSELs. First, we find that the possible amount of squeezing with VCSELs should be superior as compared to edge emitting lasers for ideal single mode operation and under comparable pumping conditions. Second, we demonstrate that there exists the possibility of squeezing also in the two-mode regime besides sub-shot noise emission in the well known ideal single-mode operation regime configuring the recently published first experimental demonstration of the generation of amplitude squeezed light with VCSELs. Third, we demonstrate for the first time the generation of amplitude squeezed light by a lateral and polarization single mode VCSEL with the achievement of a maximum squeezing of 0.9 dB. Finally the future trends, the applications and the limitations of these non-classical states of light with respect to metrology applications are discussed.

The self-mixing interference is a physical phenomenon well- adapted for sensing applications like range finding or vibration measurements. The optical beam back-scattered by the target into the laser cavity causes fluctuations of the optical output power which allow to determine distances (when the laser wavelength is tuned by a triangular signal) or displacements (for a constant injection current). In this paper, the influence of a weak optical feedback on the spectral characteristics of a semiconductor laser is analyzed for relative and absolute distance measurements. To determine the coherence length of laser diodes with optical feedback, i.e. the maximum range of self-mixing based sensors, the behavior of the spectral linewidth is investigated both theoretically and experimentally. Measurements of the spectral linewidth for several feedback level are made with a Fabry-Perot interferometer. These results are then compared to the theoretical model. The wavelength shift of a Fabry-Perot semiconductor laser due to a current modulation is also studied in the case of a weak feedback. Indeed, the resolution of a self-mixing based laser range finder can be improved by tuning continuously the optical frequency in the greatest region without mode hops. This maximum tuning range without mode hops obviously depends on each laser source but is also modified by the optical feedback. The main characteristics of semiconductor lasers suitable for sensing applications using the self- mixing interference are then deduced.

Spaceborne Fourier-transform spectrometers must use a reliable metrology source to replace the conventional HeNe laser acting as the spatial sampling reference in ground instruments. Because of their lifetime and ruggedness, semiconductor lasers appear to be ideal candidates. However the fringe signal resulting from a semiconductor laser exhibits a noisier behavior than the one from an HeNe laser. This results in more important sampling errors. We present the effect of the phase and intensity noises of semiconductor lasers upon the quality of the reference fringe signal. The semiconductor laser is modelized using a standard rate equations approach, which gives rise to coupled intensity and phase fluctuations. The laser field is sent in a scanning Michelson interferometer modelized as a variable time delay applied to the field in one arm. The recombined field is sent to a fast photodetector, resulting in a noisy fringe signal. We evaluate the signal-to-noise ratio which is used as a measure of the error made when using the zero crossings of the metrology source as a sampling reference. It relies on the noise characteristics of the laser, the optical path differences of the interferometer and the bandwidth of the photodetector. Both theoretical predictions and simulation results are shown.

The increasing complexity of semiconductor devices and corresponding dimensions decreasing till the most advanced semiconductor chips manufactured in 0.35 micrometers or 0.25 micrometers need more cleanliness technological conditions. From this whole field the particles are not even detected or detectable in today's fabs will become killer contaminants of future technology of 0.18 micrometers . The particle must first be detected before they can be eradicated. For this reason the most recommended investigation apparatus are optical particle counters and condensation nucleus counter for determining of airborne particle concentration and as ultrapure water chemicals, gases and vacuum particle counter. In the paper I have analyzed the laser diode application as light sources with the counting results sizing data generation and performance parameters which shown the benefits of their using. All the systems presented can be used for monitoring of particle concentrations for ultrapure fluids from microelectronics fab processes and can be recommended to all microelectronics fabs.

The opto-contact mini-displacement measuring instrument is mainly for mini-displacement measurement. It not only can measure small geometry size, for example silicon chip thickness, but also can measure some other parameters such as small translation, waviness, diameter run-out, vibration. Combining optical, mechanical, electronic and computer technologies, this instrument can do some work automatically like dynamic sampling, real-time processing, on-line measuring. The instrument is based on laser triangulation, it is composed of a CCD, an optical system and a computer, which can sample and process data with high speed. The measuring principle is described as follows: reflected or scattered light by measured surface are received by CCD, since a good relationship between the offset of image point on CCD and the mini-displacement of object located on a reference plane, a mathematical model can be founded, then the mini-displacement may be calculated according to the offset of image point position on CCD. It's measuring range is +/- 500 micrometers , and precision resolution is +/- 0.1 micrometers .

COST 240 is a pan-European action collaborating on the investigation of techniques for modeling and measuring photonic components. This action has concentrated on inter- laboratory comparison of measurement and modeling techniques using round-robin measurement of sample devices. The present paper reviews the work performed within this action on measurement of and parameter extraction from single frequency semiconductor laser diodes. Specifically, those measurements that have been made in order to estimate laser parameters include; Relative Intensity Noise, modulation response, emission linewidth, several static characteristics and amplified spontaneous emission below threshold. Some of the parameters that can be estimated from these measurements include; threshold current, external efficiency, diode resistance, internal loss, characteristic temperature, differential gain, gain compression parameter, facet reflectivities, facet phases, index and gain coupling coefficients, and group refractive index. Following a review of the typical measurements performed on circulated lasers within the COST 240 Action by participating laboratories, a brief description will be presented of the physical models adopted to extract the laser diode parameters. Examples will be presented and conclusions given as to the suitability of certain techniques for the extraction of diode parameters for single frequency lasers.

We study the spectral profile of a semiconductor laser and the Allan variance according to its frequency noise spectral density, particularly in the case of filtered white noise.

The shift, which occurs in the oscillation wavelength of a semiconductor laser in a magnetic field, has been the subject of great interest, since the early 60's. During the course of the investigation, the observed shift was toward the short wavelength side, i.e., a blue shift, which was well accounted for, in terms of the Landau level. At present, we are studying how wavelength shift is affected, by applying, at room temperature, a relatively weak magnetic field, using recently developed visible and infrared diode lasers. By doing so, we have observed a red shift and a decrease in laser output-power, under a certain magnetic field conditions in its strength and direction. Since these two changes in wavelength and output power correspond to those observed at higher temperatures, we assumed that the orientation of the magnetic field affects current density in laser diodes. And then it alters temperatures around the active layer, which in turn influence oscillation wavelength and laser output-power. Also of note, was the fact that the red shift and the decrease in laser output-power occurred simultaneously, revealing an almost linear dependency on one another. This might possibly explain the heat, which developed as the result of applying the magnetic field. However, we recently observed an instance, in which visible MQW laser diodes did not exhibit this linear dependence. Because this phenomenon cannot be traced simply to the effects of heat, we are now examining it in terms of current-density alteration.

The oscillation frequency of a semiconductor laser must be stabilized in coherent optical communications systems that use such devices, because the frequency fluctuates according to variations in either temperature or injection current. Therefore, we set about the task of stabilizing it, using the Rb-D₂ absorption line as an external frequency reference and negative feedback control. This method of stabilization requires the application of small sine wave modulation to obtain error signal by synchronous detection method. While the highly sensitive control ensures improved signal stability, frequency stability is deteriorated under direct FSK (Frequency Shift Keying), because the oscillation spectrum of a semiconductor laser is broadened. We, therefore, devised the `PEAK method', which improves frequency stability under direct FSK. The accurate measurement of frequency stability requires that the beat note between two stabilized laser frequencies, the signal and reference lasers, be measured. But beat note was sometimes outside the limits of our measuring equipment. The reference laser frequency was therefore adjusted by using the magneto-optical effect to control the beat note frequency within measurable limits of this work. We calculated the square root of the Allan variance to estimate the frequency stability, thereby confirming the effectiveness of PEAK method.

In this study, external cavity laser diode has been modeled and non-linear equations of system are being solved by using Volterra series. In the study, linearized laser diodes rate equations are reorganized for external cavity and these equations are solved with harmonic input method using Volterra series. The transfer functions brought about for harmonics are obtained using Volterra-Weiner series approach. The stability analysis of system is compared from output to input using these transfer functions. Nyquist stability criteria have been used in the analysis.