Low-cost Laser Diode Research Articles

All-optical phase modulation for integrated interferometric biosensors

We present the theoretical and the experimental implementation of an all-optical phase modulation system in integrated Mach-Zehnder Interferometers to solve the drawbacks related to the periodic nature of the interferometric signal. Sensor phase is tuned by modulating the emission wavelength of low-cost commercial laser diodes by changing their output power. FFT deconvolution of the signal allows for direct phase readout, immune to sensitivity variations and to light intensity fluctuations. This simple phase modulation scheme increases the signal-to-noise ratio of the measurements in one order of magnitude, rendering in a sensor with a detection limit of 1.9·10⁻⁷ RIU. The viability of the all-optical modulation approach is demonstrated with an immunoassay detection as a biosensing proof of concept.

Broadcast/multicast transmission of video signal in a WDM-PON using a low-cost injection-locked F-P LD with broadband ASE

A broadcast/multicast transmission method in a WDM-PON system using a low-cost Fabry-Perot laser diode with broadband ASE injection is proposed and experimentally demonstrated in this paper. Because of its low front-facet reflectivity (∼0.1%), the F-P LD exhibits a broadband lasing spectrum and reduced mode-partition noise. To demonstrate its performance, the bit error rate and packet loss rate were measured. The proposed optical source provides a cost-effective WDM-PON architecture for a broadcast/multicast service accommodating more than 32×622MBps. For the transmission of MPEG-2 TS packets, zero packet loss could be obtained at an optical power of -32dBm.

Analysis of Er 3+ and Ho 3+ codoped fluoroindate glasses as wide range temperature sensor

The fluorescence intensity ratio technique for two fluoroindate glass samples has been carried out. The green emissions at 523 nm and at 545 nm in a 0.1 mol% of Er 3+ doped fluoroindate glass was studied in a wide range of temperature from 125 K to 425 K with a maximum sensitivity of 0.0028 K −1 for 425 K. In a sample doped with 0.1 mol% of Ho 3+ the emissions at 545 nm and at 750 nm were analyzed as a function of temperature from 20 K to 300 K obtaining a maximum sensitivity of 0.0036 K −1 at 59 K. Using both fluoroindate glass samples a wide temperature range from 20 K to 425 K is easily covered pumping with two low-cost diode laser at 406 nm and 473 nm.

Combless broadband terahertz generation with conventional laser diodes

We present a novel technique to generate a continuous, combless broadband Terahertz spectrum with conventional low-cost laser diodes. A standard time-domain spectroscopy system using photoconductive antennas is pumped by the output of two tunable diode lasers. Using fine tuning for one laser and fine and coarse tuning for the second laser, difference frequency generation results in a continuous broadband THz spectrum. Fast coarse-tuning is achieved by a simple spatial light modulator introduced in an external cavity. The results are compared to multi-mode operation for THz generation.

Self-mixing technique for vibration measurements in a laser diode with multiple modes created by optical feedback

We present experimental and theoretical results obtained from the study of the effects of optical feedback in low-cost Fabry-Perot laser diodes due to the presence of an external cavity created by an external reflective or diffusive vibrating target. Experimental results show that a change in the length of the external cavity produces the well-known amplitude modulation of the optical output power and, depending on the amount of optical feedback, a subperiodicity appears in the amplitude modulation of the output power. The experiments show that the subperiodicity appears independently of the length of the external cavity and is due to mode hopping between different longitudinal laser modes. Numerical analysis focused on the effects observed support that the mode hop occurs between modes whose round-trip phase delay along the external cavity is out of phase, thus producing a subperiodicity of the total amplitude modulation.

Rapid Temperature Jump by Low Cost Laser Diode Irradiation

Thermal TRP ion channels play important functions in somatosensation and pain. Aside from activation by agonist or voltage, they are directly gated by temperature, a novel property unique to these channels. However, the underlying mechanism of the abnormally high thermal sensitivity has remained elusive. Studies on thermal activation of these channels have been challenging, partly because of the difficulty for rapid alteration of ambient temperature in live cells. Existing approaches mostly employ resistive or thermal electric heating/cooling, and have a response time far slower than channel activation. As a result, they only allow for measurement of steady-state properties of the channel. We report here an alternative approach for rapid perturbation of temperature. The approach employs an infra-red laser diode as a heat source, and by restricting laser irradiation around a single cell, it can produce constant temperature jumps over 50oC in sub-milliseconds. Experiments with several heat-gated channels (TRPV1-3) demonstrate its applicability as a general tool for local temperature stimulation of single cells. Compared to other laser heating approaches such as those based on Raman-shifting of the Nd:YAG fundamentals, it is more cost-effective while providing adequate resolution for detection of ion channel kinetics.

Preparation and photoluminescence properties of SrY 2O 4:Yb 3+, Er 3+ powders

Yb 3+/Er 3+ co-doped SrY 2O 4 powders are prepared by developing a nitric-decomposition method. Under 980 nm laser excitation, the green and red up-conversion emissions are observed at around 549 and 661 nm, which are attributed to the transitions of 4S 3/2 → 4I 15/2 and 4F 9/2 → 4I 15/2 of Er 3+ ions, respectively. The intensity ratio of the red emission to the green one increases with Yb 3+ doping concentration. A quadratic dependence of the two emissions on excitation power is obtained, indicating that a two-photon process populates the 4S 3/2 and 4F 9/2 levels for the SrY 2O 4 powders. Especially, it is found that at lower excitation power, Yb 3+ doping concentration has an important influence on the slopes of the emission intensity versus excitation power, similar with the excitation power. The results can be helpful for the design and applications of low-cost near-infrared laser diodes.

Low-Cost Optoelectronic Self-Injection-Locked Oscillators

We demonstrate a new configuration for an optoelectronic self-injection-locked (SIL) oscillator, where a part of the electrical output signal is self-injected after passing through a long optical delay line for output phase-noise reduction. The SIL oscillator consists of an electrical free-running oscillator and a long optical feedback loop. For the compact and low cost configuration, the free-running oscillator is realized with an InP HPT-based monolithic oscillator and electrical-to-optical conversion is carried out by two low-speed and low-cost laser diodes. With this new configuration, we achieve more than 55-dB phase-noise reduction at 10-kHz frequency offset from the center frequency of about 10.8 GHz by injecting 8-dBm optical signals without using any high-speed optoelectronic components.

COMPACT AND EFFICIENT Er–Yb-DOPED FIBER AMPLIFIER

A compact and efficient optical amplifier is demonstrated using an erbium–ytterbium-doped fiber amplifier (EYDFA) with a double-pass configuration. It uses only 3 m of doped fiber with 20 mW pump power. This forward-pumped amplifier achieves a maximum low signal gain of 37 dB and a corresponding noise figure of 5.5 dB. Compared with the backward-pumping double-pass EYDFA, the gain obtained is 7 dB higher, with a lower noise figure of 5.5 dB. In addition, the gain obtained in this study is 17 dB higher than that of a conventional forward-pumping single-pass amplifier, while its noise figure is only 0.5 dB higher. These results show that the forward-pumped double-pass design holds great promise in the development of practical and cost-efficient optical amplifiers which can be pumped by using LEDs or low cost laser diodes.

Energy transfer processes in Yb3+–Tm3+ co-doped sodium alumino-phosphate glasses with improved1.8 µm emission

Sodium alumino-phosphate glasses co-doped withYb3+ andTm3+ ions have been preparedwith notably low OH− content, and characterized from the viewpoint of their spectroscopic properties. In these glasses,Yb3+ acts as an efficient sensitizer of excitation energy at0.98 µm—which can be provided by high power and low cost diodelasers, and subsequently undergoes non-resonant energy transfer toTm3+ ions(2F5/2,, 3H5). Through this process,the emitting level 3F4 is rapidly populated, generating improved emission at1.8 µm (). In order to guarantee the efficiency of such favorable energy transfer, energy lossesvia multiphonon decay, Yb–Yb radiative trapping, and non-radiative transfer toOH− groups were evaluated, and minimized when possible. The dipole–dipole energy transfermicroscopic parameters corresponding to , and transfers, calculated by the Förster–Dexter model, areCYb−Tm = 2.9 × 10−40 cm6 s−1,CYb−Yb = 42 × 10−40 cm6 s−1 and CTm−Tm = 43 × 10−40 cm6 s−1, respectively.

Single-end vibration sensor based on an over-coupled fiber-loop reflector

A single-end fiber-optic vibration sensor based on an over-coupled fused-fiber loop reflector is demonstrated for the first time, which takes advantage of the change of the reflectivity spectrum when the coupling region is applied with a different strain. The interrogation system is designed for the sensor, and consists of a low-cost laser diode, a 3-dB fiber coupler, a detector, and an electronic circuit to the process signal. The output of the sensor system when the sensor is applied with vibration is shown. The system is simple and low cost, and, thus, feasible for practical use.

Single-end vibration sensor based on an over-coupled fiber-loop reflector

A single-end fiber-optic vibration sensor based on an over-coupled fused-fiber loop reflector is demonstrated for the first time, which takes advantage of the change of the reflectivity spectrum when the coupling region is applied with a different strain. The interrogation system is designed for the sensor, and consists of a low-cost laser diode, a 3-dB fiber coupler, a detector, and an electronic circuit to the process signal. The output of the sensor system when the sensor is applied with vibration is shown. The system is simple and low cost, and, thus, feasible for practical use.

Measurement of the pressure broadening coefficients of the oxygen A-band using a low cost, polarization stabilized, widely tunable vertical-cavity surface-emitting laser

Vertical-cavity surface-emitting lasers (VCSELs) are used for oxygen monitoring via tunable diode laser spectroscopy at 760 nm wavelength. For the desired application, novel polarization-stable laser diodes based on AlGaAs were developed. We present measurements of the pressure-broadening coefficients of the electric dipole forbidden oxygen A-band b1 Σ+g → X3 Σ+g transition at 760 nm. The time the pressure-broadening coefficients were determined with a temperature tuned VCSEL. Generally temperature tuning has the disadvantage of frequent mode-hops, but the advantage of a wider tuning range in comparison to current tuning. Because of special techniques of polarization stabilization with a combination of a dielectric surface grating and a surface relief the VCSELs have a mode hop-free tuning range of more than 7 nm and a sidemode suppression of more than 30 dB. This provides a low cost laser diode system with a wide tuning range, which enables the possibility of simultaneous measurement of temperature, pressure and oxygen concentration in air, high pressure measurements and also a higher accuracy of oxygen concentration measurements.

Single, Depolarized, CW Supercontinuum-Based Wavelength-Division-Multiplexed Passive Optical Network Architecture With C-Band OLT, L-Band ONU, and U-Band Monitoring

We propose and experimentally demonstrate a novel bidirectional wavelength-division-multiplexed passive optical network architecture that fully utilizes the superior optical properties of an incoherent continuous-wave (CW) supercontinuum (SC) source. The proposed architecture, which incorporates low-cost Fabry-Perot laser diodes that have been wavelength locked by spectrum-sliced beams from a depolarized 130-nm-bandwidth CW SC source, is based on a unique wavelength band allocation scheme of the C-band for an optical line terminal (OLT), the L-band for optical network units (ONUs), and the U-band for channel monitoring. A cost-effective network that features a single broadband source at the OLT, and no additional wavelength- band-selective monitoring beam reflector at each ONU can be readily achieved. The experimental demonstration presented in this paper is carried out at a data rate of 622 Mb/s over a 25-km standard single-mode fiber.

Detection of a two-photon transition by stimulated emission: Amplification and circular birefringence

We present the detection of a two-photon transition based on stimulated emission. This measurement was performed in rubidium for the 5S-5D{sub 5{approx}}{sub sol{approx}}{sub 2}-5P{sub 3{approx}}{sub sol{approx}}{sub 2} transition, using two low-cost diode lasers. Several detection schemes were tested. We reached the best results by probing the circular birefringence of the excited vapor, with the polarization analysis of the amplified laser beam.

WDM-Based Passive Optical Network Upstream Transmission at 1.25 Gb/s Using Fabry–PÉrot Laser Diodes Injected With Spectrum-Sliced, Depolarized, Continuous-Wave Supercontinuum Source

We experimentally demonstrate the use of low-cost Fabry-Perot laser diodes (FP-LDs) injected with spectrum-sliced beams from our proposed, depolarized, high-power, continuous-wave (CW) supercontinuum (SC) for upstream transmission in a wavelength-division-multiplexed (WDM) passive optical network. A ~500-mW CW SC with a ~130-nm bandwidth is obtained from a narrowband, amplified spontaneous emission (ASE) seed of a pumped erbium fiber by nonlinear effects such as modulation instability and stimulated Raman scattering in a highly nonlinear optical fiber. Through measurements of relative intensity noise at various wavelengths, it is shown that our spectrum-sliced SC offers the same performance as the spectrum-sliced erbium ASE. Error-free 25-km upstream transmission for six WDM signals generated from the CW SC-injected FP-LDs, is readily achieved at 1.25 Gb/s

Total internal reflection fluorescence imaging using an upconverting cover slip for multicolour evanescent excitation

Total internal reflection fluorescence microscopy is well known as a means of studying surface-bound structures in cell biology. It is usually measured either by coupling a light source to the sample using a prism or with a special objective where light passing through the periphery of the lens illuminates the contact region beyond the critical angle. In this study we present a new and simple approach to total internal reflection fluorescence microscopy where the sample is mounted on a cover slip prepared from a high-index upconverting glass-ceramic. Excitation of the cover slip with a low-cost near-infrared laser diode generates intense narrow-band visible emission within the cover slip, some of which is totally internally reflected. This emission gives rise to an evanescent wave at the interface and hence can excite surface-bound fluorescent species. Depending on the excitation conditions the cover slip can generate violet, green and red emission and hence can excite a wide range of fluorescent labels. Fluorescence emission from the sample can be detected in spectral regions where the direct emission from the cover slip is very weak. The advantages and limitations of the technique are discussed in comparison with conventional total internal reflection fluorescence microscopy measurements and prospects for novel total internal reflection fluorescence microscopy geometries are considered.

Aeronautical use of semiconductor lasers for short optical pulses

In this paper, we investigate the feasible schemes to generate periodic optical pulses of width between several picoseconds (ps) and tens ps. Gain-switched semiconductor laser diodes are shown to be more suitable for avionics applications than mode-locked laser diodes. In the experiment, we use a low-cost Fabry-Perot laser diode to generate short optical pulse streams. A simple optical injection-locking scheme is then used to reduce the timing jitter and frequency chirp in such laser diodes, which in turn can improve the transmission performance of the generated optical pulses. It is expected that the use of gain-switched semiconductor lasers can meet the requirement of high-speed airborne communication networks or ground supporting systems at airports. Moreover, we discuss the possibility of using the pulsed semiconductor lasers to generate millimetre-wave (mm-wave) signals for future applications to airborne high-resolution, mm-wave radars.

Excited-state absorption and 1064-nm end-pumped laser emission of Nd:YVO4 single-crystal fiber grown by laser-heated pedestal growth.

We present an investigation of the excited-state absorption and laser emission of a 1.0-at. %-Nd3+-doped YVO4 single-crystal fiber grown by the low-cost and versatile laser-heated pedestal growth technique. Efficient laser emission at 1064 nm was achieved when the fiber was pumped, in an end-pump cavity, by a Ti:sapphire laser at 808 nm. A continuous-wave threshold of 10 mW was observed with an efficiency of 42% with respect to the absorbed pump power and the maximum output power of 200 mW. These results are excellent when compared with those of a commercial bulk crystal adapted to the same cavity (48% efficiency, 250-mW maximum output power). Thus the fibers are characterized as strong candidates for the construction of compact lasers that can also be pumped by low-cost diode lasers.

Optically pumped lead–chalcogenide midinfrared lasers on Si substrates

Double heterostructure (DH) and quantum well (QW) EuSe/PbSe/Pb1−xEuxSe edge-emitting laser structures on Si substrates are grown by molecular-beam epitaxy. They operate up to 250 K when pumped with 870 nm low-cost laser diodes with peak powers of ∼7 W, and emit up to 200 mW peak output power at ∼5 μm wavelength. Differential quantum efficiencies are up to 20%. The threshold powers are limited by Shockley–Read recombination due to the high dislocation densities (108 cm−2) in the active layers. Nearly similar maximum operation temperatures were observed when employing (111)—instead of (100)—oriented layers, as well when using QW rather than DH structures. Reduction of dislocation densities to 107 cm−2 is feasible and will lead to nearly an order of magnitude lower threshold powers.