Distributed Feedback Laser Diode Research Articles

A fiber-solid hybrid 1319 nm single-frequency MOPA Laser for sodium Doppler lidar

The narrow linewidth nanosecond pulse 1319 nm laser used to generate 589 nm laser is the core technology of sodium Doppler lidar. Here, a high gain fiber-solid hybrid amplifier seeded by a 1319 nm distributed-feedback laser diode (DFB-LD) is proposed to achieve high-power amplification of small signal 1319 nm pulse laser. A pulsed 1319 nm laser with a repetition frequency of 500 Hz, a pulse duration of 500 ns, an energy of 10.3 mJ and a linewidth of 1.9 MHz was developed by utilizing a three-stage fiber coupled end-pumped amplifier and a two-stage Innoslab amplifier, and the beam quality factor M2 is less than 1.6, the gain of the solid amplification system exceeds 28 dB.

Hybrid integrated narrow-linewidth semiconductor lasers.

Integrated narrow-linewidth lasers are the key devices in compact coherent optical systems of metrology, sensing, and optical microwave generation. Here, we demonstrate a hybrid integrated laser based on an optical negative feedback scheme. The laser is composed of a commercial distributed feedback (DFB) laser diode and an on-chip micro-resonator with a Q-factor of 0.815 million. The feedback optical field is coupled back to the laser cavity through the back facet. Therefore, the laser can maintain the lasing efficiency of the DFB laser diode. The linewidth of the DFB laser diode is compressed from 2MHz to 6kHz, corresponding to the linewidth reduction factor of 25.2dB. The theoretical result shows that the laser performance still has a huge improvement margin through precise control of the detuning between laser frequency and the micro-resonator, as well as the phase delay of the feedback optical field. The hybrid narrow-linewidth laser diode has wide application prospects in coherent optical systems benefitting from the low cost and volume productivity.

Monolithically Integrated Tunable Three- Section All-Active DBR Laser Diodes With 30 nm Tuning Range

We present a monolithically integrated three-section all-active AlGaInAs/InP tunable distributed Bragg reflector (DBR) ridge waveguide laser diode that uses thermal tuning mechanism and mode-hopping tuning principle to achieve wide-range wavelength tuning. It is similar to the traditional three-section DBR laser structure, including a gain section, a phase section, and a DBR grating section. The difference is that the phase section and the DBR section incorporate the same active quantum well structure as the gain section. In this case, weak effective refractive index changes of the three active sections affected by the current injection will occur since the carrier density is clamped by the threshold gain condition of the DBR laser diode. Despite this limitation, a noncontinuous tuning up to ∼30 nm (1564–1594 nm) can be observed using only current injection at a constant temperature of 25 °C. Significant thermal effects occurred during the tuning process. In addition, a discontinuity is introduced in the tuning because it does not contain a passive region for phase adjustment. However, the device still provides a stable single longitudinal mode output with nine channels, a wavelength spacing of about 4 nm, and a side mode suppression ratio (SMSR) of more than 30 dB. Furthermore, the DBR laser diode can be easily fabricated utilizing the conventional distributed feedback laser diode fabrication process without secondary epitaxy and heater metal. The all-active DBR laser diode will be expected to be applied in the coarse wavelength division multiplexing (CWDM) systems with the advantage of low cost.

Two-Way 5G NR Fiber-Wireless Systems Using Single-Carrier Optical Modulation for Downstream and Phase Modulation Scheme for Upstream

Fifth-generation (5G) millimeter-wave (MMW)/sub-THz signals over a two-way fiber-wireless system using single-carrier optical modulation for downstream and phase modulation (PM) scheme for upstream are proposed and implemented for the first time. Compared to multi-carrier optical modulation, using single-carrier optical modulation in downlink is attractive because it can suppress RF power fading due to fiber dispersion and interference caused by optical beating from multiple carriers. Furthermore, compared to intensity modulation scheme, using PM scheme with remotely injection-locked distributed feedback laser diode in uplink is attractive because it enables high robustness to noise and distortion. Through 40-km single-mode fiber, 500-m free-space optical, and 2-m/1-m/0.5-m (downstream)/4-m (upstream) RF wireless cascaded-medium, 5G new radio (NR) MMW/sub-THz signals are transported with low bit error rates and clear constellations in downlink/uplink performance. Such a newly-built two-way 5G NR fiber-wireless system shows promise to perform 5G NR evolution in MMW and sub-THz frequencies, which has significant impacts on fiber-wireless integration.

Wavelength-modulated photoacoustic spectroscopy sensor for multi-gas measurement of acetone, methane, and water vapor based on a differential acoustic resonator

Precise assessment of breath acetone and methane is significant to the medical diagnosis process. A multi-gas sensing system based on wavelength-modulated differential photoacoustic spectroscopy was developed for simultaneous measurement of acetone and methane. A distributed feedback diode laser emitting in the range from 3363 to 3371 nm was employed to scan the absorption lines of acetone and methane. The cross sensitivities in terms of spectral interference among acetone, methane, and water vapor are effectively eliminated by using a linear combination method of reference spectra for accurately determining the concentration of acetone and methane. The positive effect of water vapor on photoacoustic signal resulting from the light absorption of acetone and methane was precisely evaluated. To improve the instrument performance, a differential PA cell companying with a differential amplifier circuit is experimentally demonstrated in providing a better performance of noise suppression compared with a single acoustic resonator. With a low detection limit down to 0.43 ppm and 12 ppb (integration time of 10 s) for acetone and methane, the sensor shows a great potential for medical diagnosis in simultaneous measurement of acetone and methane.

Wavelength-Tunable Narrow-Linewidth Laser Diode Based on Self-Injection Locking with a High-Q Lithium Niobate Microring Resonator.

We demonstrate a narrow linewidth 980 nm laser by self-injection locking of an electrically pumped distributed-feedback (DFB) laser diode to a high quality (Q) factor (>105) lithium niobate (LN) microring resonator. The lithium niobate microring resonator is fabricated by photolithography-assisted chemo-mechanical etching (PLACE) technique, and the Q factor of lithium niobate microring is measured as high as 6.91 × 105. The linewidth of the multimode 980 nm laser diode, which is ~2 nm measured from its output end, is narrowed down to 35 pm with a single-mode characteristic after coupling with the high-Q LN microring resonator. The output power of the narrow-linewidth microlaser is about 4.27 mW, and the wavelength tuning range reaches 2.57 nm. This work explores a hybrid integrated narrow linewidth 980 nm laser that has potential applications in high-efficient pump laser, optical tweezers, quantum information, as well as chip-based precision spectroscopy and metrology.

Development of a Methane-Detection System Using a Distributed Feedback Laser Diode and Hollow-Core Photonic Crystal Fiber

A highly integrated methane-detection system was experimentally established by using a distributed feedback laser diode and hollow-core photonic crystal fiber. The self-developed circuits with a laser diode and essential optical devices were integrated into an instrument that generated a modulated optical signal in a fiber-coupled gas cell that contained the hollow-core photonic crystal fiber. The instrument could also process the return optical signal that contained the gas concentration information. The experiments demonstrated the good performance of the developed system. In the spectrum tests, the center wavelength of the laser diode could be tuned linearly by controlling the laser’s working temperature and driving current. The second harmonic signal could be extracted in order to reflect the gas concentration. According to the Allan deviation method, the low limit of detection of the system was determined to be 29.52 ppm. In addition, a long-term stability test demonstrated that the system has a good stable performance. The proposed system can be further optimized in order to be applied in paddy fields to detect and monitor the methane concentration in a large area by using the optical fibers.

Parametric study of the transient period characteristics of distributed feedback laser diodes

Subject of study. The operating response characteristics for a distributed feedback laser model has presented. Aim of study. A numerical optimization of model parameters is used to reduce the laser transient period by analyzing the effects of the laser injection current, the temperature variation, the dc-bias level, and the gain compression factor on transient period characteristics. Method. The transient period value decreases when the current ratio (i.e., injection current/threshold current) is increased. Main results. Significant reduction is observed in the relaxation oscillation period and the laser turn-on time delay as the effect of increasing the injection current and/or the biasing current. Practical significance. However, varying temperatures resulted in distributed feedback operating in the off-mode region due to increasing the transient period value. Meanwhile, the relaxation oscillation period value is reduced significantly with a faster stabilization period due to the damped sinusoidal oscillations as a result of increasing the ε value.

Excited oxygen kinetics at electronvolt temperatures via 5-MHz RF-diplexed laser absorption spectroscopy.

A multi-MHz laser absorption sensor at 777.2nm (12,863c m -1) is developed for simultaneous sensing of (1)O(5 S 0) number density, (2)electron number density, and (3)translational temperature at conditions relevant to high-speed entry conditions and molecular dissociation. This sensor leverages a bias tee circuit with a distributed feedback diode laser and an optimization of the laser current modulation waveform to enable temporal resolution of sub-microsecond kinetics at electronvolt temperatures. In shock-heated O 2, the precision of the temperature measurement is tested at 5MHz and is found to be within ±5% from 6000 to 12,000K at pressures from 0.1 to 1atm. The present sensor is also demonstrated in a CO:Ar mixture, in parallel with a diagnostic for CO rovibrational temperature, providing an additional validation across 7500-9700K during molecular dissociation. A demonstration of the electron number density measurement near 11,000K is performed and compared to a simplified model of ionization. Finally, as an illustration of the utility of this high-speed diagnostic, the measurement of the heavy particle excitation rate of O(5 S 0) is extended beyond the temperatures available in the literature and is found to be well represented by k(3 P→5 S 0)=2.7×10-14 T 0.5 exp⁡(-1.428×104/T)c m 3⋅s -1 from 5400 to 12,200K.

Photonics-Based Short-Time Fourier Transform Without High-Frequency Electronic Devices and Equipment

A photonics-based short-time Fourier transform (STFT) system is proposed and experimentally demonstrated based on stimulated Brillouin scattering (SBS) without using high-frequency electronic devices and equipment. The wavelength of a distributed feedback laser diode is periodically swept by using a low-speed periodic sawtooth/triangular driving current. The periodic frequency-sweep optical signal is modulated by the signal under test (SUT) and then injected into a section of SBS medium. The optical signal from another laser diode as the pump wave is reversely injected into the SBS medium. After simply detecting the forward transmission optical signals in a low-speed photodetector, the STFT of the SUT is implemented. The system is characterized by the absence of any high-frequency electronic devices or equipment. An experiment is performed. The STFT of a variety of RF signals is carried out in a 4-GHz bandwidth. The dynamic frequency resolution is demonstrated to be around 60 MHz.

Double-enhanced multipass cell-based wavelength modulation spectroscopy CH4 sensor for ecological applications.

A novel CH4 sensor based on wavelength modulation spectroscopy with a multipass cell was developed for the soil respiration measurement of CH4. A home-made double-enhanced Herriot-type multipass cell with an effective absorption length of 73.926 m and a fiber-coupled distributed feedback diode laser emission at 1653.74 nm were used to design the sensor. The double enhancement of the effective optical pathlength of the multipass cell, absorption line locking, laser intensity normalization, and temperature control of the multipass cell were used to improve cell performance and achieve a minimum detection limit of 10 ppbv and a measurement precision of 6.4 ppbv. Finally, the potential of the developed CH4 sensor for ecological applications was verified by measuring the soil respiration of CH4 and monitoring of CH4 in the atmosphere over a long period.

High-gain single-frequency Tm3+-doped ZBLAN fiber amplifier at 2.33 μm.

We report here, to the best of our knowledge, the first high-gain, single-frequency Tm3+-doped fiber amplifier operating at the 2.3-μm band with conventional ground-state pumping transition (3H6→3H4) at 793 nm. The gain fiber is an 8.5-m-long ZBLAN fiber with a Tm3+ doping concentration of 3 mol.%, and the seed is a single-frequency distributed feedback diode laser operated at 2331.9 nm. A gain up to 24.1 dB is generated for ∼14 W of launched pump power with the maximum output power of 246 mW. The competitive 3F4 →3H6 laser transition at ∼2 µm is also investigated, and the prospects for further power scaling are discussed.

Highly Sensitive and Fast Hydrogen Detection Based on Light-Induced Thermoelastic Spectroscopy

As a new energy source, hydrogen (H 2 ) detection is a hot topic in recent years. Because of the weak absorption characteristic, laser spectroscopy-based H 2 detection is challenging. In this paper, a highly sensitive H 2 sensor based on light-induced thermoelastic spectroscopy (LITES) technique is demonstrated for the first time. A continuous-wave, distributed feedback diode laser with emission in the 2.1 μm region was adopted as the excitation source to target the strongest H 2 absorption line of 4,712.90 cm −1 . A Herriott multipass cell with an optical length of 10.1 m was chosen to further improve the H 2 absorption. With the feature of processing the raw input data without data preprocessing and extracting the desired features automatically, the robust shallow neural network (SNN) fitting algorithm was brought in to denoise the sensor. For the LITES-based H 2 sensor, the concentration response was tested, and an excellent linear response to H 2 concentration levels was achieved. A minimum detection limit (MDL) of ~80 ppm was obtained. On the basis of implementation of the H 2 -LITES sensor, a heterodyne H 2 -LITES sensor was further constructed to realize a fast measurement of resonance frequency of quartz tuning fork and H 2 concentration simultaneously. The resonance frequency can be retrieved in several hundred milliseconds with the measurement accuracy of ±0.2 Hz, and the result of 30,713.76 Hz is exactly same as the experimentally determined value of 30,713.69 Hz. After the SNN algorithm was applied, an MDL of ~45 ppm was achieved for this heterodyne H 2 -LITES sensor.

A Width Measurement Method of Line Shape Based on Second Harmonic Peak and Modulation Amplitude.

The line width of different line shapes is a very important parameter in absorption spectroscopy sensing techniques. Based on the high sensitivity and low noise properties of wavelength modulation spectroscopy, we report a novel line width measurement method. After theoretically proving the relationship between line width, modulation amplitude and the amplitude of the second harmonic at the center frequency, the absorption lines of CH4 near 6046.96 cm-1 and CO2 4989.97 cm-1 were chosen for simulation, and the relative errors of the line width between our method and theoretical data were kept at about 1%. A distributed feedback laser diode operating near 1653 nm with three different concentrations of CH4 was used for experimental validation, and the results were consistent with the numerical simulation. Additionally, since only the peaks of second harmonic need to be measured, the advantages of wavelength modulation can be utilized while reducing the difficulty of data acquisition.

High-stability and high-beam-quality single-frequency nanosecond 589 nm laser based on sum-frequency generation

A high repetition rate, high peak power, narrow linewidth nanosecond 589 nm laser based on sum-frequency generation (SFG) of 1064 nm and 1319 nm laser is demonstrated. A 1064 nm single-frequency distributed-feedback laser diode (DFB-LD) externally modulated by an acousto-optic modulator (AOM) and amplified by a fiber-solid hybrid amplifier with three-stage fiber amplifier and six-stage solid-state end-pump Nd:YVO4/Nd:YAG amplifier, a high beam quality laser output with pulse energy of 20 mJ at repetition rate of 500 Hz is achieved, which pulse duration and waveform are adjustable and editable. The ramp–hold–fire detection and dual piezoelectric ceramic (PZT) feedback compensation are employed in the 1319 nm oscillator to achieve high stability and low jitter laser. Then the 1319 nm laser pulse is amplified to 12.2 mJ by three-stage end-pumped Nd:YAG amplifier, with pulse duration of 70 ns. By sum-frequency of the 1064 nm and 1319 nm lasers, finally, 589.1595 nm laser with pulse energy of 10.4 mJ and pulse duration of 62 ns is generated efficiently, the laser beam quality factor M2 is less than 1.3. With the ability of switching frequencies quickly and the characteristic of compatible frequency-stabilized, this laser is believed to be a very potential solution for sodium Doppler lidar.

Measurement and characterization of microwave interaction between integrated distributed feedback laser diode and electro-absorption modulator

Integrated electro-absorption-modulated distributed feedback laser diodes (EMLs) are attracting much interest in optical communications for the advantages of a compact structure, low power consumption, and high-speed modulation. In integrated EML, the microwave interaction between the distributed feedback laser diode (DFB-LD) and the electro-absorption modulator (EAM) has a nonnegligible influence on the modulation performance, especially at the high-frequency region. In this paper, integrated EML was investigated as a three-port network with two electrical inputs and a single optical output, where the scattering matrix of the integrated device was theoretically deduced and experimentally measured. Based on the theoretical model and the measured data, the microwave equivalent circuit model of the integrated device was established, from which the microwave interaction between DFB-LD and EAM was successfully extracted. The results reveal that the microwave interaction within integrated EML contains both the electrical isolation and optical coupling. The electrical isolation is bidirectional while the optical coupling is directional, which aggravates the microwave interaction in the direction from DFB-LD to EAM.

On the Technology of a Laterally Coupled Bragg Grating of Single-Mode Distributed Feedback Laser Diodes

On the Technology of a Laterally Coupled Bragg Grating of Single-Mode Distributed Feedback Laser Diodes

A novel mid-infrared hollow waveguide gas sensor for measuring water vapor isotope ratios in the atmosphere

A novel mid-infrared hollow waveguide gas sensor was developed to target H218O, H216O, H217O, and HDO absorption lines at 3662.9196, 3663.04522, 3663.32128, and 3663.84202 cm−1, respectively, based on wavelength modulation spectroscopy using a 2.73 µm distributed feedback diode laser. A hollow waveguide fiber with a 5-m length and 1-mm inner diameter was used for gas absorption. A dew point generator with liquid water with known water–isotope ratios was used to calibrate the sensor. Detection limits of 35.18 ppbv, 4.69 ppmv, 60.53 ppbv, and 3.88 ppbv were obtained for H218O, H216O, H217O, and HDO, respectively, in a 96-s integration time, which resulted in isotopic ratio measurement precision of 0.85‰, 0.57‰, and 10.48‰ for δ18O, δ17O, and δD, respectively. Field measurements of H218O, H216O, and H217O concentration were conducted on the Nanchang Hangkong University campus to evaluate sensor performance.

All-optical microwave oscillator based on a mutual-injection coupling between DFB-LDs.

An all-optical microwave oscillator (AOMO) is proposed and experimentally demonstrated. It contains only a mutual injection loop consisting of two distributed feedback laser diodes (DFB-LDs) and a few passive components. In this AOMO, the microwave seed signal originates from the period-one (P1) oscillation in one of the DFB-LDs. The functions of microwave envelope detection and feedback modulation are implemented by the other DFB-LD. Due to the optical injection locking and the optical-optical modulated effect in DFB-LD, the P1 signal is enhanced, and the stability of the P1 signal can be improved by coupling the P1 signal with a resonant mode of the mutual injection loop. Meanwhile, since the P1 oscillation is sensitive to injected light, the frequency of the P1 signal can be easily adjusted, which makes the AOMO easy to be tuned. In the experiment, a highly stable single-mode microwave signal with a frequency of 16.69 GHz and a single-sideband (SSB) phase noise of -90.7 dBc/Hz@10 kHz is generated. The frequency can be tuned from 14.48 to 21.45 GHz by adjusting the parameters of DFB-LDs and the injection light.

Experimental demonstration of uncompressed 4K video transmission over directly modulated distributed feedback laser‐based terahertz wireless link

AbstractWe demonstrate the transmission of uncompressed 4K videos over the photonics‐based terahertz (THz) wireless link using a directly modulated distributed feedback laser diode (DFB‐LD). For optical heterodyne mixing and data modulation, a DFB‐LD was employed and directly modulated with a 5.94‐Gb/s non‐return‐to‐zero signal, which is related to a 6G‐serial digital interface standard to support ultra‐high‐definition video resolution. We derived the optimal frequency of the THz carrier by varying the wavelength difference between DFB‐LD output and Tunable LD output in the THz signal transmitter to obtain the best transmission performances of the uncompressed 4K video signals. Furthermore, we exploited the negative laser‐to‐filter detuning for the adiabatic chirp management of the DFB‐LD by the intentional discrepancy between the center wavelength of the optical band‐pass filter and the output wavelength of the DFB‐LD. With the help of the abovementioned methods, we successfully transmitted uncompressed 4K video signals over the 2.3‐m wireless transmission distance without black frames induced by time synchronization error.