Laser Module Research Articles

A Simplified Volterra Equalizer Based on System Characteristics for Direct Modulation Laser (DML)-Based Intensity Modulation and Direct Detection (IM/DD) Transmission Systems

The nonlinear Volterra equalizer has been proved to be able to solve the problem of nonlinear distortion, but it has high computational complexity and is difficult to implement. In this paper, a simplified second-order Volterra nonlinear equalizer designed for intensity modulation/direct detection systems based on direct modulated laser is proposed and demonstrated, taking into account the characteristics of the system. It has been proved that the received signal of direct modulation laser/direct detection system can be expressed in Volterra series form, but its form is too complex, and the device parameters should also be considered. We re-derived it and obtained a more concise form. At the same time, we proposed a method to simplify the second-order Volterra nonlinear equalizer without relying on device parameters. The performance of the proposed Volterra nonlinear equalizer is evaluated experimentally on a 56 Gb/s 4-ary pulse amplitude modulation link implemented by using a 1.55 µm direct modulation laser. The results show that, compared with the traditional Volterra nonlinear equalizer, the receiver sensitivity of the equalizer is only reduced by 0.2 dB at most, but the complexity can be reduced by 50%; compared with diagonally pruned Volterra nonlinear equalizers, the complexity of the equalizer is the same, but the reception sensitivity can be improved by 0.5 dB.

Order transfer in a hybrid Raman-laser-optomechanical resonator.

Order is one of the most important concepts to interpret various phenomena such as the emergence of turbulence and the life-evolution process. The generation of laser can also be treated as an ordering process in which the interaction between the laser beam and the gain medium leads to the correlation between photons in the output optical field. Here, we demonstrate experimentally in a hybrid Raman-laser-optomechanical system that an ordered Raman laser can be generated from an entropy-absorption process by a chaotic optomechanical resonator. When the optomechanical resonator is chaotic or disordered enough, the Raman-laser field is in an ordered lasing mode. This can be interpreted by the entropy transfer from the Raman-laser mode to the chaotic motion mediated by optomechanics. Different order parameters, such as the box-counting dimension, the maximal Lyapunov exponent, and the Kolmogorov entropy, are introduced to quantitatively analyze this entropy transfer process, by which we can observe the order transfer between the Raman-laser mode and the optomechanical resonator. Our study presents a new mechanism of laser generation and opens up new dimensions of research such as the modulation of laser by optomechanics.

Photoelectric performance of InSe vdW semi-floating gate p–n junction transistor

Semi-floating gate transistors based on vdW materials are often used in memory and programmable logic applications. In this paper, we propose a semi-floating gate photoelectric p–n junction transistor structure which is stacked by InSe/h-BN/Gr. By modulating gate voltage, InSe can be presented as N-type and P-type respectively on different substrates, and then combined into p–n junction. Moreover, InSe/h-BN/Gr device can be switched freely between N-type resistance and p–n junction. The resistance value of InSe resistor and the photoelectric properties of the p–n junction are also sensitively modulated by laser. Under dark conditions, the rectification ratio of p–n junction can be as high as 107. After laser modulation, the device has a response up to 1.154 × 104 A W−1, a detection rate up to 5.238 × 1012 Jones, an external quantum efficiency of 5.435 × 106%, and a noise equivalent power as low as 1.262 × 10−16 W/Hz1/2. It lays a foundation for the development of high sensitivity and fast response rate tunable photoelectric p–n junction transistor.

Design and modelling of modulated cw laser generation in lidar application

In this work, we designed a configuration that may be used for direct detection of light, detection and ranging sensing method based on generated continuous wave laser and characterized by range measurements. The generation of modulated laser distance is studied and analysed by several distances where modulation of laser signal is utilized. The modelling configuration consisted of transmission module that comprises of signal generator, modulator, and propagation module, object target, and receiver modules comprises of photodetector, amplifier, filter, and visualizers. The design and configuration were developed by Optisystem layout, and the study and analysis are done by simulation using the developed model. A subsystem of range measurement was designed to detect varied distances of detection of target object by the generated modulation of continuous wave laser at 10, 50, 100 and 200 meters respectively. The results discussed were based on the power received and frequency given by different detection ranges. Analysis shows that the detection scheme is sensitive to the received electromagnetic radiation and the signal is better at shorter haul based on the generated modulation of the continuous wave source and the signal deteriorated as target distance is increased.

Thermal Modulation of a Chaotic Fiber Laser by Using a Phase-Shifted Fiber Bragg Grating

Thermal Modulation of a Chaotic Fiber Laser by Using a Phase-Shifted Fiber Bragg Grating

Introducing TiO2 to design high-reflectivity AlN composite substrates to synthesize green/white converters for high-brightness reflective laser illumination☆

Phosphor-in-glass (PiG) has been prepared into various types of phosphor films owing to its simplicity process, exceptional color purity, and convenient color adjustability. Nevertheless, existing reflective PiGs films have encountered limitations in terms of stability and feasibility as reliable color converters, mainly attributed to issues related to thermal deposition and insufficient optical efficiency. Herein, we propose to use AlN substrate with superior thermal conductivity to coat the TiO2 layer to obtain TiO2–AlN (TA), which enhances the reflectivity of blue light to facilitate the light conversion process. By incorporating highly thermally stable LuAG:Ce-PiGs on a TA substrate, the LuAG:Ce-PiTA converter exhibits a luminous flux of 1102 lm@6.4 W, and maintains a relative intensity of 94.6% at 473 K benefiting from the high thermal conductivity of 34.1 W/(m·K). The addition of CASN3:Eu to the color converter 50 L&10C-PiTA enables an impressive CRI of 90.7. Relative luminescence intensities of LuAG:Ce-PiTA and 50 L&10C-PiTA only decrease by 5.35% and 3.28%, respectively, in the 24 h illumination aging decay test of the reflective laser module. The results confirm the suitability of the optimally designed TA substrate for LuAG:Ce color converter applications in high-power reflective laser illumination.

Research on absolute ranging technology of resampling phase comparison method based on FMCW

Abstract As an advanced optical precision ranging method, FMCW (frequency-modulated continuous-wave) laser interferometric ranging technology can achieve a large-scale and high-precision absolute distance measurement, so it has high research and application value in the field of coordinate measurement in large space. How to improve the resolution and stability of laser interferometry is a research difficulty in this technology. Based on FMCW laser interferometry relative distance technology, a method for achieving absolute distance measurement through phase comparison after repeated sampling is proposed. Using the FMCW laser distance measuring system, two interference optical paths of measuring interferometer and auxiliary interferometer are constructed, respectively. Synchronous sampling is performed on two interference signals, and the phase ratio of the two interference signals is obtained through the extracted frequency information. The optical path difference of the unknown measurement interferometer is derived from the known auxiliary interferometer information. This method uses a triangular wave modulation laser to reduce the influence of Doppler frequency shift and eliminate quantization errors. By using the fixed-point repeated sampling, the optical path difference information is quickly extracted, and the nonlinear error of laser interference frequency modulation is effectively reduced.

Noise Suppression of Nitrogen-Vacancy Magnetometer in Lock-In Detection Method by Using Common Mode Rejection.

Nitrogen-vacancy (NV) centers in diamonds are promising solid-state magnetic sensors with potential applications in power systems, geomagnetic navigation, and diamond NV color center current transformers, in which both high bandwidth and high magnetic field resolution are required. The wide bandwidth requirement often necessitates high laser power, but this induces significant laser fluctuation noise that affects the detection magnetic field resolution severely. Therefore, enhancement of the magnetic field resolution of wide-bandwidth NV center magnetic sensors is highly important because of the reciprocal effects of the bandwidth and magnetic field resolution. In this article, we develop a common mode rejection (CMR) model to eliminate the laser noise effectively. The simulation results show that the noise level of the light-detected magnetic resonance signal is significantly reduced by a factor of 6.2 after applying the CMR technique. After optimization of the laser power and modulation frequency parameters, the optimal system bandwidth was found to be 75 Hz. Simultaneously, the system's detection magnetic field resolution was enhanced significantly, increasing from 4.49 nT/Hz1/2 to 790.8 pT/Hz1/2, which represents an improvement of nearly 5.7 times. This wide-bandwidth, high-magnetic field resolution NV color center magnetic sensor will have applications including power systems, geomagnetic navigation, and diamond NV color center current transformers.

Investigating the effect of laser modulation and input energy on bending mechanism and bending angle in the multi-pass laser forming process through real-time monitoring

Laser forming is a non-contact type process used for bending, spatial forming, and alignment of metallic components through a controlled application of laser energy. The process involves localized rapid heating and cooling, inducing thermal strains exceeding the elastic strain of the material resulting in plastic deformation. The process is broadly governed by the temperature gradient mechanism (TGM), buckling mechanism (BM), and upsetting mechanism (UM). However, in the case of multi-pass laser forming process, heat accumulation and variation in the flow stress because of consecutive thermal cycles and strain hardening due to multiple bending cycles makes the process highly complicated. While operating laser in modulated mode may be a wise choice to handle the heat accumulation, inter-pulse cooling cycles along with variation in peak and average power with change in duty cycle affects the bending mechanism and angle significantly. Therefore, in the present study, a real-time monitoring system was developed to investigate the bending mechanism for a multi-pass laser forming process carried out in laser modulated mode. Also, the effect of average power, peak power, heat accumulation, strain hardening on bending mechanism and bending angle were investigated. Keeping the peak power constant, variation in duty cycle from 100% to 40% resulted in reduced average energy and strain hardening was found to be dominant, decreasing bending angle per pass. On contrast, variation in duty cycle by keeping the average power constant resulted in heat accumulation dominating the bending mechanism.

Integrated near-infrared fiber-optic photoacoustic sensing demodulator for ultra-high sensitivity gas detection

An integrated near-infrared fiber-optic photoacoustic sensing demodulator was established for ultra-high sensitivity gas detection. The demodulator has capacities of interference spectrum acquisition and calculation, laser modulation control as well as digital lock-in amplification. FPGA was utilized to realize all the control and signal processing functions, which immensely improved the integration and stability of the system. The photoacoustic signal detection based on fiber-optic Fabry–Perot (F-P) acoustic sensor was realized by applying ultra-high resolution spectral demodulation technique. The detectable frequency of photoacoustic signal achieved 10 kHz. The system integrated lock-in amplification technology, which made the noise sound pressure and dynamic response range of sound pressure detection reached 3.7 μPa/√Hz @1 kHz and 142 dB, respectively. The trace C2H2 gas was tested with a multi-pass resonant photoacoustic cell. Ultra-high sensitivity gas detection was accomplished, which was based on high acoustic detection sensitivity and the matching digital lock-in amplification. The system detection limit and normalized noise equivalent absorption (NNEA) coefficient were reached 3.5 ppb and 6.7 × 10−10 cm−1WHz−1/2, respectively. The devised demodulator can be applied for long-distance gas measurement, which depends on the fact that both the near-infrared photoacoustic excitation light and the probe light employ optical fiber as transmission medium.

Monolithic Saturable Absorber with Gallium Arsenide Nanowires Integrated on the Flexible Substrate for Optical Pulse Generation.

In this work, we demonstrated a kind of flexibly monolithic saturable absorber (SA) with GaAs nanowires (NWs) on polyimide (PI) plastic substrate for broadband optical modulation at 1.0 and 1.5 µm, separately. The monolithic SA sample was prepared by the metalorganic vapor phase epitaxy (MOVPE) method. The crystal structure and element analysis were examined carefully by high-resolution scanning transmission electron microscopy (HRSTEM) and energy-dispersive X-ray spectroscopy (EDX). We observed a high-density distribution of NWs on the flexible substrate by scanning electron microscopy (SEM). In addition, linear and nonlinear optical properties of the sample were examined by testing the photoluminescence and absorption properties, which showed its potential application as an optical switch due to the pure semiconducting properties. After the characterizations, we experimentally demonstrated this monolithic SA for laser modulation at 1.0 and 1.5 µm, which yielded the minimum optical pulse widths of 1.531 and 6.232 µs, respectively. Our work demonstrated such a kind of monolithic flexible NW substrate-integrated device used for broadband optical modulation, which not only eased the integration process of NWs onto the fiber endface, but also proved the potential of easily integrating with more semiconducting nanomaterials (e.g., graphene, MoS2, …) to realize monolithic active flexible photonic systems, such as a microscale phase modulator, delay-line, and so on, paving an easy avenue for the development of both active and flexible photonic devices.

Controllable experimental modulation of high-order Laguerre-Gaussian laser modes.

High-order helical and sinusoidal Laguerre-Gaussian (LG) laser modes have uneven energy distribution among their multiple concentric vortex core rings and lobes, respectively. Here, we explore an experimental method to reshuffle the optical energy among their multiple concentric vortex core rings and lobes of high-order LG modes in a controllable manner. We numerically designed a diffractive optical element displayed over a spatial light modulator to rearrange optical energy among multiple concentric vortex core rings. This changes outer low-intensity concentric vortex core rings into high-intensity vortex core rings of high-order helical LG modes at the Fourier plane. The precise generation of a high-order modulated helical LG laser mode has a maximum number of highly intense concentric vortex core rings compared to known standard helical LG modes. Further, this method is extended to high-order sinusoidal LG modes consisting of both low- and high-intensity lobes to realize modulated sinusoidal LG modes with a maximum number of highly intense lobes in a controllable manner. We envisage that the modulated helical and sinusoidal high-order LG modes may surpass standard LG modes in many applications where highly intense rings and lobes are crucial, as in particle manipulation of micro- and nanoparticles, and optical lithography.

Spectrum Extreme Purification and Modulation of DBR Fiber Laser With Weak Distributed Feedback

Highly coherent lasers with spectral hyperpurity can further advance the fields of science and engineering. Especially, a light source with controllable frequency domain parameters can be adapted to a variety of emerging application scenarios. Herein, we report on an implementation of a novel ultra-high spectral purity distributed Bragg reflector (DBR) all-fiber laser based on weak distributed feedback, and its spectrum can be modulated in a certain extent by precisely controlling the intensity of the distributed feedback signal. Eventually, an ultra-high spectral purity laser with a spectral signal-to-noise ratio of 64 dB, a side mode suppression ratio (SMSR) of 83 dB, an output Lorentz linewidth of 115 Hz and a relative intensity noise of less than -122 dB/Hz is successfully obtained under normal conditions. Also, the frequency noise limit of the fiber laser with weak distributed feedback in the high frequency white noise flat region is 4.8 Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /Hz, corresponding to a fundamental linewidth of ∼15.1 Hz. In particular, the SMSR and Lorentz linewidth of the laser can be continuously adjusted from 53 dB to 83 dB and 115 Hz to 8.2 kHz, respectively. In addition, we also investigated the effect of different pumping configurations on the performance of the DBR fiber laser. The proposed controllable mechanism of laser spectrum also provides a new perspective for extreme regulation of other laser parameters.

Improvement on stability of direct modulation laser with integrated active feedback by partial corrugated gratings.

Researchers have developed a uniform grating DFB with an integrated active optical feedback waveguide (UG-AFDFB) to enhance the modulation speed of direct modulation lasers (DMLs) while reducing costs based on identical active layer designations. However, this design has difficulties in obtaining high single mode yield (SMY) and low relative intensity noise (RIN) as a result of the strong optical feedback caused by the integrated active feedback waveguide (AFW) and the random phase of the facet phase. In this paper, a partial corrugated grating DFB with an integrated active optical feedback waveguide (PG-AFDFB) is proposed to address this issue. Comparison of SMY, S21, RIN, modulation eye pattern, and frequency chirp parameters between UG-AFDFB and PG-AFDFB based on time-domain transmission line laser mode reveals that PG-AFDFB with an optimized grating couple parameter κ performs significantly better than UG-AFDFB under the same conditions. Furthermore, the performance of PG-AFDFB is not sensitive to the random phase of the rear facet phase. Even when κ ranges from 6000 /m to 12000 /m, the current in the AFW is between 0 mA and 20 mA, and the length of the AFW ranges from 50 µm to 100 µm; the SMY of PG-AFDFB remains above 80%.

ИЗМЕРЕНИЕ ФАЗОВЫХ И АМПЛИТУДНЫХ ШУМОВ ПОЛУПРОВОДНИКОВЫХ ЛАЗЕРОВ. МЕТОДИКА ИЗМЕРЕНИЙ. КАЛИБРОВКА. РЕЗУЛЬТАТЫ

The application of the frequency detector method for measuring the phase noise spectrum of semiconductor lasers has been experimentally demonstrated. The frequency detector is based on an unbalanced Mach-Zehnder interferometer and a photodetector. Analytical relations are obtained that allow one to choose the parameters of the Mach-Zehnder interferometer and perform experimental calibration of the measuring system. A technique is proposed for measuring the spectral components of the phase noise of lasers in the presence of a slow drift of the delay in fiber-optic lines and the frequency of the laser under study. The results of measuring the phase noise of a low-noise DX-1 laser module and high-noise laser diodes LSDLD155 (DFB) and LSFLD155 (FP) are presented. A strong correlation between the amplitude and phase noise levels of these lasers is found. The decisive influence of the noise of LSDLD155 and LSFLD155 lasers on the level of phase noise of optoelectronic (OE) microwave generators built using them is shown. It has been suggested that the low-noise laser module DX-1, which has a phase noise level 20–60 dB lower (in different parts of the spectrum), is not decisive in the level of phase and amplitude noise of an optoelectronic microwave generator. The investigated OE generator was built during the research in this work. The generator has low phase noise: −120 dBc/Hz at a frequency detuning of 10 kHz. Oscillation frequency 6.8 GHz; fiber optic delay line length 200 m.

Coherent control of mid-infrared frequency comb by optical injection of near-infrared light

We demonstrate the use of a low power near-infrared laser illuminating the front facet of a quantum cascade laser (QCL) as an optical actuator for the coherent control of a mid-infrared frequency comb. We show that with appropriate current control of the QCL comb and intensity modulation of the near-infrared laser, a tight phase lock of a comb line to a distributed feedback laser is possible with 2 MHz of locking bandwidth and 200 mrad of residual phase noise. A characterization of the whole scheme is provided, showing the limits of the electrical actuation, which we bypassed using the optical actuation. Both comb degrees of freedom can be locked by performing electrical injection locking of the repetition rate in parallel. However, we show that the QCL acts as a fast near-infrared light detector such that injection locking can also be achieved through modulation of the near-infrared light. These results on the coherent control of a QCL frequency comb are particularly interesting for coherent averaging in dual-comb spectroscopy and for mid-infrared frequency comb applications requiring high spectral purity.

Uncooled Tunable Laser Based on High-Density Integration of Distributed Feedback Semiconductor Lasers

Most types of tunable lasers are sensitive to the ambient temperature and require thermoelectric coolers (TECs) for temperature control. For conventional tunable laser modules, high power consumption of cooling is required for stabilizing the laser temperature and complex hermetic packages are normally used to avoid moisture condensation problems, which are expensive and difficult to manufacture. To overcome these drawbacks, we demonstrated an uncooled tunable laser via the monolithically integrated multi-wavelength distributed feedback (DFB) laser array based on the reconstruction-equivalent-chirp technique. Totally sixteen DFB semiconductor lasers are densely integrated with a 4-by-4 matrix laser array. To ensure the uncooled laser operates properly, the active material of the laser chip is designed to work at high temperatures without TEC cooling. Therefore, an uncooled wavelength-tuning range of 33.8 nm is achieved during the whole commercial operating temperature range from 0 °C to 70 °C.

Fluorescence lifetime measurements using photon pair correlations generated via spontaneous parametric down conversion (SPDC).

We have used photon pair correlations generated via spontaneous parametric downconversion (SPDC) to measure the fluorescence lifetime of the organic dye rhodamine 6 G, demonstrating that fluorescence lifetime measurements can be achieved using a continuous wave (CW) laser, without pulsed or modulated lasers. Our entangled photon method, quantum fluorescence lifetime (Q-FL) measurements, uses one photon to excite fluorescence and the resulting fluorescence photon is timed and referenced to the arrival time of the other entangled photon. Thus, we can exploit the short timescale of photon pair correlations to conduct experiments that are typically carried out with pulsed lasers and we show that the inherent timing of the photons is fast enough to resolve the nanosecond scale fluorescence lifetime of the sample. This measurement paves the way towards using the time correlations of entangled photons for fluorescence imaging; capitalizing on the presence of fast, sub-100 ps correlations that have not been demonstrated classically.

CMOS Linear Laser Driver for Intermediate Frequency over Fiber (IFoF) Links

The main objective of the proposed linear laser driver (LLD) is to reduce signal distortion in an analog direct modulation laser configuration used for intermediate frequency over fiber links. This work draws on an open-loop configuration featuring two differential pair blocks in a cascade arrangement to achieve a bandwidth measurement of 415 MHz at the half-power point, a total harmonic distortion of 4.57% for a fundamental frequency of 100 MHz, and an amplitude of 100 mVpp. The LLD provides a gain of 12.3 dB for a differential output and an output impedance of 46 Ω. The design, layout, and integration correspond to the process design kit for TSMC 65-nm CMOS technology. Experimental results show the advantage over other previously reported laser drivers.

Methane detection with a near-infrared heterodyne phase-sensitive dispersion spectrometer at a stronger frequency modulation using direct injection-current dithering.

Heterodyne phase-sensitive dispersion spectrometer (HPSDS) retrieves the concentration of gas samples by measuring the refractive index fluctuations near the molecular resonance. Compared to previous HPSDS studies focusing on pure intensity modulation, it is attractive to investigate the performance of HPSDS sensor based on a distributed feedback (DFB) laser under conditions where frequency modulation is much higher than intensity modulation. In this work, we report the implementation of a near-infrared HPSDS for methane detection based on the direct modulation of a DFB laser. The performance of our HPSDS is assessed using the characteristic absorption peak of methane near 1653.7 nm. Long-time measurements show that our HPSDS has a detection limit (MDL) of 1.22 ppm at standard atmospheric pressure and room temperature. In the same experimental conditions, we have experimentally compared HPSDS to wavelength modulation spectroscopy (WMS) to evaluate the dynamical range, long-term stability, and precision limits of the two methods.