Modulated Laser Diode Research Articles

Discrete multitone transmission for underwater optical wireless communication system using probabilistic constellation shaping to approach channel capacity limit.

Probabilistic constellation shaping (PCS) is utilized to approach the channel capacity limit in discrete multitone (DMT) transmission for underwater optical wireless communication (UOWC) system. A fixed quadrature amplitude modulation (QAM) format with various probabilistic distributions is individually allocated for different subcarriers to obtain achievable maximum channel capacity in accordance with the pre-estimated signal-to-noise ratio. By using a 450-nm directly modulated laser diode (LD) with an available modulation bandwidth of ∼2.75 GHz, DMT with PCS technique is experimentally realized with a net data rate of 18.09Gbit/s over 5m, 17.21Gbit/s over 25m, and 12.62Gbit/s over 35m underwater transmission, giving substantial capacity improvement of 32.22%, 30.03%, and 27.55%, respectively, in comparison with the widely used regular QAM formats in DMT with bit-power loading scheme. The figure of merit of the UOWC system in terms of entropy, generalized mutual information (GMI), and normalized GMI are also presented. To the best of our knowledge, this is the first time to employ PCS-QAM-DMT in a UOWC system, and it is also the highest data rate ever reported for a single LD in UOWC.

An Electronic Dispersion Compensation Transceiver for 10- and 28-Gb/s Directly Modulated Lasers-Based Optical Links

This paper presents an electronic dispersion compensation (EDC) transceiver to encompass extended reach of both 10- and 28-Gb/s directly modulated lasers (DMLs). In DML-based links, direct modulation of laser diodes induces power-dependent frequency chirp on the generated optical signals, which causes severe chromatic dispersion as well as pattern dependence on the received signal after optical fiber transmission. Such time-varying nature of the dispersion makes conventional equalization methods ineffective for compensation. The proposed EDC-based clock and data recovery (CDR) IC overcomes the chirp-induced dispersion via a linear equalizer followed by a double-sampling decision feedback equalizer (DFE) at the receiver and a pattern-dependent pulse shaping filter at the transmitter. The chirp-managed EDC improves the receiver sensitivity at a bit error rate (BER) of 10−6 by 1.3 dB in a 3-km link using a DML at a modulation rate of 28 Gb/s, where transient chirp is dominant, and by more than 7 dB in a 105-km link at 10 Gb/s, where adiabatic chirp is dominant. The chip prototype is fabricated in a 40-nm CMOS process and packaged in a flip-chip ball grid array (BGA). The single-chip IC containing dual-lane transceivers and a global clock generator (CG) occupies an active area of 2.8 mm2. The test chip consumes 236 mW, wherein a single-lane transceiver consumes 105.5 mW and a global CG consumes 25 mW from a 0.9-V supply at 28 Gb/s.

Calculation of a fiber laser diode module of the spectral range 445-450 nm with an optical output power of more than 100 W

Calculation of a fiber laser diode module of the spectral range 445-450 nm with an optical output power of more than 100 W

Clinical Evaluation of a Novel Blended Mode Diode Laser for Hair Removal

Introduction: Photoepilation by lasers is a popular procedure in aesthetic dermatology for removing unwanted body and facial hair. The use of the most appropriate laser wavelength is crucial as it affects treatment depth and melanin absorption. The three commonly used hair removal lasers are of specific wavelengths: 755 nm, 810 nm, and 1064 nm, each preferred certain types of skin and hair characteristics. The current evaluation reports the safety and efficacy of unique blended modes 755/810 nm and 810/1064 nm diode lasers for hair removal. Methods: Hair removal results from 50 patients treated with the 755/810 nm handpiece and 50 patients treated with the 810/1064 nm handpiece were gathered from a few clinics. 3 treatments on various body areas were conducted 6 weeks apart and patients were followed up with 6 months after the last treatment. Results were evaluated by baseline, follow-up photographs, and hair counts. Results: Treatment area photos demonstrated hair reduction in the treated body and facial areas. Average hair count reduction at 6 months follow-up was 84% for the 755/810 nm handpiece and 81% for the 810/1064 nm handpiece. No significant or unexpected adverse events were detected in any of the patients. Conclusions: The novel blended mode hair removal diode lasers are proven to be safe and effective for hair removal in facial and body areas for patients of various skin types and hair characteristics.

Demonstration of a 10 Mbit/s quantum communication link by encoding data on two Laguerre-Gaussian modes with different radial indices.

We experimentally demonstrate a 10Mbit/s free-space quantum communication link using data encoding on orthogonal Laguerre-Gaussian (LG) modes with the same azimuthal index but different radial indices. Data encoding on two LGℓp modes (i.e., for ℓ=0, we encode ["0", "1"] as [p=0, p=1], and for ℓ=1, we encode ["0", "1"] as [p=0, p=1]) is demonstrated by employing directly modulated laser diodes and helical phase holograms. The quantum symbol error rate (QSER) of <5% is achieved at an encoding rate of 10Mbit/s. Moreover, the influence of the circle radius (R) of the receiver phase pattern on registered photon rates and QSERs is investigated. Our results show that a receiver phase pattern whose R does not match the beam size of the LG modes would induce higher cross talk between the two encoded quantum branches.

High order DBR GaSb based single longitude mode diode lasers at 2 μm wavelength * * Project supported by the National Basic Research Program of China (Nos. 2016YFB0402403, 2014CB643903) and the National Natural Science Foundation of China (Nos. 61790583, 61435012).

The GaSb-based distributed Bragg reflection (DBR) diode laser with 23rd-order gratings have been fabricated by conventional UV lithography and inductively coupled plasma (ICP) etching. The ICP etching conditions were optimized and the relationship among etching depth, duty ratio and side-mode suppression ratio (SMSR) was studied. The device with a ridge width of 100 μm, gratings period of 13 μm and etching depth of 1.55 μm as well as the duty ratio of 85% was fabricated, its maximum SMSR reached 22.52 dB with uncoated cavity facets under single longitudinal operation mode at room temperature.

A hybrid cooling system combining self-adaptive single-phase mechanically pumped fluid loop and gravity-immune two-phase spray module

Although single-phase mechanically pumped fluid loop (MPFL) and two-phase spray cooling technologies have been investigated independently for decades, there is a lack of understanding on the combined operation of these two modules. The MPFL has been extensively utilized in the space thermal control system due to its technological maturity and gravity immunity. The spray cooling, which is characterized by the speciality in thermally dealing with the high heat flux equipment, has not gone that far owing to its complexity in the management of the two-phase flow in the space environment. It is also acknowledged that the MPFL, as an overall cooling strategy in the space thermal control system, will not be replaced completely in the foreseeable future because the primary on-board electronic devices require normal heat dissipation demand and only a few equipment such as on-board laser diode and multi-chip modules demand extreme high heat removal technologies. Therefore, a combination of the MPFL and spray cooling technologies, which constitutes the biggest innovation in this paper, is imperatively needed. A hybrid cooling system (HCS) combining the single-phase self-adaptive MPFL and gravity-immune two-phase spray module which satisfies various cooling demands is proposed in the present study. A validating system as a prototype was established on the basis of the optimal design method. Three test cases were conducted to verify the coordinated operation between the single-phase module and two-phase one and investigate thermal performances of both modules. In all the experiments, the controlled temperature of the cold plate in the MPFL remains within a range between 35.9 °C and 41.9 °C under the heat load from 50 W to 150 W. The highest heat flux acquired by the spray cooling module can be up to 468.8 W/cm2 with the superheat level being 70.0 °C. Results can be drawn that the two modules can be operated simultaneously and independently. Systematic operation efficiency of the proposed HCS is calculated to be 17.7 which displays a high economy of the proposed system.

Long-reach 60-GHz MMWoF link with free-running laser diodes beating

With the remote beating of two mutually incoherent laser carriers, the local-oscillator-free long-reach millimeter-wave over fiber (MMWoF) link at 60-GHz band is demonstrated. The unique schemes of the proposed MMWoF are the wavelength-locked colorless laser diode (CLD) modulator, the mutually incoherent optical carrier for heterodyne MMW generation, and the square-law power envelope detection at receiving end. By directly encoding the single-mode with the CLD modulator, the single-carrier modulated QAM-OFDM data is achieved to release the RF power fading after fiber transmission. The mutually incoherent laser beating enables the optical heterodyne MMW generation with two independent optical carriers, which provides the advantages of local-oscillator-free operation and rules out the requirement of dual-mode optical carrier delivery from central office. At the wireless receiving end, the received QAM-OFDM data is self-down-converted to the baseband by employing the square-law power envelope detection. This eliminates the requirement of local oscillator and rules out the influence of the MMW carrier frequency fluctuation between two mutually incoherent lasers (used at central office and remote node), which effectively provides the MMW carrier immunity against the down-conversion instability caused by clock jitter or carrier incoherence. This architecture ensures the transmission of 16.5-Gbit/s 32-QAM OFDM data over 50 km in SMF and 3 m in free-space with the FEC certificated error vector magnitude of 12%, signal-to-noise ratio (SNR) of 18.4 dB, and bit error rate of 3.8 × 10−3. For multi-channel DWDM-PON applications, the proposed local-oscillator-free MMWoF link can successfully perform 11 DWDM channels of 32-QAM OFDM data access at 16.5 Gbit/s per channel via the wavelength controlling of the CLD modulation stage and the detuning of the beating carrier at remote node.

Highly sensitive and selective CO sensor using a 2.33 μm diode laser and wavelength modulation spectroscopy.

A ppm-level CO sensor based on a 2f wavelength modulation spectroscopy (2f-WMS) technique was developed for the application of SF6 decomposition analysis in an electric power system. A detailed investigation of the optimum target line selection was carried out to avoid spectral interference from high purity SF6 in a wide wavelength range. A diode laser emitting at 2.33 μm and a 14.5-m multipass gas cell (MGC) was employed to target the R(6) line of the CO first overtone band and increase the optical path, respectively, thus resulting in a minimum detection sensitivity of 1 ppm. A Levenberg-Marquardt nonlinear least-squares fit algorithm makes full use of the information from all data points of the 2f spectrum and as a result, a measurement precision of ~40 ppb was achieved with a data update rate of 0.6 s. The sensor performance was also evaluated in terms of the gas flow rate, stability, and linearity. The results showed that the best operating condition with a precision of 6 ppb can be achieved by increasing the gas flow rate to the value that matches the optimum averaging time of 48 s.

Partial scanning frequency division multiplexing for interrogation of low-reflective fiber Bragg grating-based sensor array

Interrogation using partial spectrum scanning for a low-reflective fiber Bragg grating (FBG)-based sensor array is proposed. The sensor head is a Fabry–Perot interferometer (FPI) consisting of low-reflective fiber Bragg gratings. An FPI consisting of low-reflective FBGs (FBG-FPI) has a spectrum with a sinusoidal structure with a period determined by the length of the FBG-FPI. Multiple point sensing is possible by installing multiple low-reflective FBG-FPIs on one fiber and analyzing the reflection spectrum of that fiber by the frequency division multiplexing method. A coherent wavelength-swept light source is necessary to acquire the reflection spectrum; however, but the sweep speed of a commercially available wavelength-swept light source that satisfies the condition is only approximately several tens of hertz. Therefore, we propose to conduct a wavelength sweep by injection current modulation of a laser diode. Wavelength sweeping with a modulated laser diode allows fast sweeping at 100 Hz or more, and the sweep range is as narrow as several hundred picometers. Reading only a part of the reflection spectrum of a low-reflective FBG-FPI sensor array using a modulated laser diode enables high-speed multipoint measurement through frequency analysis. Theoretical requirements for successful interrogation using the partial reflection spectrum are shown. A demonstration experiment to simultaneously measure strain applied to two low-reflective FBG-FPI sensors with a measurement time of 10 ms is reported.

High-efficiency LD-pumped all-fiber Raman laser based on a 100 µm core graded-index fiber

We demonstrate a high-power, high-efficiency Raman laser based on a 100 µm core graded-index (GRIN) fiber directly pumped by 915 nm multimode laser diode modules in all-fiber configuration. Optimization of GRIN fiber length and pumping scheme was performed. As a result, 62 W of CW power has been obtained at a wavelength of 954 nm with a slope efficiency of 85%. The joint action of Raman clean-up effect and mode-selection properties of special fiber Bragg gratings inscribed in the central part of the GRIN fiber core results in significant beam quality enhancement for the generated Stokes beam ( < 3) in comparison with that of the pump radiation ( > 30). In addition, the exact value of the operating wavelength near the Raman gain maximum was varied. To the best of our knowledge, this is the first study of the impact of a Raman gain spectral profile on the power, spectrum and beam quality parameter M2 of multimode Raman laser. It appears that they very much dependent on the spectral region of Raman gain at which we work, when the wavelength is selected by a fiber Bragg grating inscribed in a multimode GRIN fiber.

Fast interrogation using sinusoidally current modulated laser diodes for fiber Fabry–Perot interferometric sensor consisting of fiber Bragg gratings

A fast interrogation method using a sinusoidal modulated laser diode for a fiber Fabry–Perot interferometric sensor consisting of Bragg gratings (FBG–FPI) is proposed.. The FBG–FPI has sharp transmittance peaks in the reflection band of the FBGs. Wavelength sweep produced by current modulation of a laser diode can be used to detect the peak position. This enables high-resolution strain or temperature measurement. To precisely control the current, the current modulation is realized using a laser diode controller (LDC) with external modulation function. In the modulation by a sawtooth wave, the possible speed of wavelength sweeping is limited to 100 kHz or less due to the bandwidth limitation of an LDC and thermal effect in a laser diodeUsing a sinusoidal wave as a modulation waveform enables wavelength sweeping at speeds exceeding 100 kHz. The modulation characteristics of the laser wavelength is evaluated experimentally and the operating wavelength is monitored using an asymmetric Mach–Zehnder interferometer. The resolution of 0.2 fm/\(\sqrt{\mathrm{Hz}}\) and measurement time of 1 \(\upmu\)s were experimentally demonstrated in the present sensor.

Compact femtosecond 10 μJ pulse energy fiber laser with a CFBG stretcher and CVBG compressor

Abstract In this work, a compact high energy fiber chirped pulse amplification system with matched pair of a chirped fiber Bragg grating stretcher and a chirped volume Bragg grating compressor is presented. Chirped pulses of 230 ps duration were amplified in a single mode Yb-doped fiber amplifiers to 10 µJ pulse energy and re-compressed to 349 fs duration corresponding to the peak power of 26 MW. Gain saturation was demonstrated when pumping with tandem of single mode laser diodes due to small mode area of the single mode fiber. Such laser source could be used in applications where high peak power is required but moderate average power is sufficient.

High power narrow linewidth discrete mode laser diode integrated with a curved semiconductor optical amplifier emitting at 2051 nm.

We report on a 2.051μm InxGaAs/InP-based discrete mode laser diode monolithically integrated with a curved tapered semiconductor optical amplifier for CO2 sensing applications. At a heat-sink temperature of 0°C, the laser emits a record InP value of more than 35mW continuous-wave output power in a single longitudinal mode.

Rancang-bangun prototipe mesin CNC laser engraving dua sumbu menggunakan diode laser

The development of industrial technology can help the manufacturing industry for producing quality products. One tool that can help produce such quality products is CNC machines. As we know that the price of CNC machines is not cheap. Therefore, in this article, the researchers suggest how to design a prototype CNC laser engraving machine for the acrylic workpiece. The machine is designed as cheaply as possible but provide great benefits. The machine frame is designed using aluminum extrusion, the laser uses a laser diode type, the actuators of axis uses the stepper motor, and the control software uses a USB CNC controller. The dimension of workpiece that can be machined is 600 mm x 300 mm x 2 mm. The optimization of the stepper motor movement system is chosen 1/8 micro stepping after testing full-step method, half-step, 1/8 micro stepping, and 1/16 micro stepping. Using a 2.5 watt diode laser module, the radiant heat received by the acrylic workpiece during the engraving process is 558.8 x 10-5 cal/sec.

Photoacoustic for Oral Soft Tissue Imaging based on Intensity Modulated Continuous-Wave Diode Laser

We built the photoacoustic imaging (PAI) systems to image oral soft tissue. To reduce the cost and size significantly, the PAI system used an intensity-modulated continuous-wave (CW) diode laser with a wavelength of 532nm and output peak power of 200mW as an excitation source, combined with a condenser microphone as photoacoustic signals detector. The Pulse Width Modulation technique was applied to form a square wave fluctuation of laser radiation by using certain duty cycle on single-frequency of 17.8 kHz. Sample of this study was Sprague Dawley rats tongue on plasticine media, irradiated by modulated CW diode laser. The result of this study showed that modulated laser exposure on one certain spot of the sample produced PA-signals in polynomial correlation with a duty cycle of laser modulation. Based on it, the photoacoustic imaging then was done by using gradual duty cycles, i.e., 20%, 30%, and 40%. This study also showed that using CW diode laser which is modulated with low duty cycle can produce most accurate PA image, as well as keeping the sample from the high energy of laser exposure that may cause biological changes. Furthermore, the maximum duty cycle to modulate laser for oral soft tissue imaging in this system was 30%.

12-W continuous-wave green output from a 200-μm fiber-coupled diode laser based on TO-Can packaged emitters.

A 12-W green laser diode module with fiber-coupled output is developed. The high-power fiber-coupled output of a green diode laser is realized by using the technologies of beam collimation, spatial beam combining, beam shaping, and fiber coupling based on TO-Can packaged emitters. According to the optical fiber parameters, the detailed beam combination method is described and the maximum quantity of a single emitter in beam combination is calculated theoretically. In the experiment, as many as 16 green laser diode emitters with output power of 1W each were combined and coupled into a fiber with core diameter of 200μm and a numerical aperture of 0.22. A total of 12.2W continuous-wave output at the wavelength of 520nm was achieved with a coupling efficiency of 86.5% and an electro-optical efficiency of 10.6%.

Use of pump current modulation of diode laser for increased sensitivity of detection of 13СO2 in human exhaled breath

This paper reports that the use of a lock-in detection technique, when the pump current modulation of a diode laser is operating near the wavelength of 2 µm, allows the improvement of the sensitivity of the online detection of 13СO2 in expired air by more than three orders of magnitude. The sensitivity of the 13СO2 detected in the paper is 60 ppb with an error of 13СO2 concentration measured in the exhaled breath at the level of 2.9% for an optical path length of 60 cm.

Compact burst-mode Nd:YAG laser for kHz-MHz bandwidth velocity and species measurements.

A compact-footprint (0.18 m2) flash-lamp-pumped, burst-mode Nd:YAG-based master-oscillator pulsed-amplifier laser is reported with a fundamental 1064nm output of over 14J per burst. A directly modulated diode laser seed source is used to generate 10ms duration arbitrary sequences of 500kHz doublet or MHz singlet pulses for flow-field velocity or species measurements, respectively. Flexible pulse widths are used to balance the energy distribution of pulse doublets and achieve second-harmonic conversion efficiencies up to 42%. Burst-mode laser performance characteristics, measurement accuracies in turbulent flows, and prospects for kHz-MHz flow-field diagnostics are discussed.

Compact Deep UV System at 222.5 nm Based on Frequency Doubling of GaN Laser Diode Emission

Laser light sources emitting in the deep ultraviolet wavelength range between 210 and 230 nm are of great interest for spectroscopic applications. Here, a compact DUV diode laser system emitting at a wavelength of 222.5 nm is presented. The system is based on frequency doubling of the laser radiation from a micro-integrated GaN external cavity diode laser module (μECDL) emitting at 445 nm. The μECDL has an optical pump power of 1.4 W with an emission bandwidth of 35 pm. Narrowband laser radiation in continouos wave operation with an output power of 160 μW at 222.5 nm is generated in a single-pass frequency doubling stage with a β-BaB 2 O 4 crystal. The results are suitable to address applications such as spectroscopic investigations of biological samples. The presented concept of a compact and efficient deep ultraviolet laser light source enables the realization of portable systems for which a small footprint and a low power consumption is essential.