Distributed Feedback Semiconductor Laser Research Articles

Synchronous achievement of laser frequency stabilization and tunability via modulation transfer spectroscopy on the rubidium D1 line

In the Spin Exchange Relaxation Free (SERF) magnetometer, the laser frequency must be stabilized at the alkali D1 line and tunable within a range of several gigahertz (GHz). We theoretically and experimentally analyzed the modulated sideband and resonant frequencies on the D1 transition line of rubidium (Rb) atoms using a modulation transfer spectroscopy (MTS) frequency stabilization system. The laser's self-estimated frequency stability shows the Allan deviation of 1.5 × 10−12/τ for resonance peak stabilization and 1.4 × 10−12/τ for sideband stabilization. The spectrum of the modulated laser interacting with the rubidium D1 line exhibits several absorption peaks and MTS signals across a 6 GHz scanning frequency range, which can be used to lock and tune the laser. This method enhances the application of distributed feedback semiconductor lasers in Rb atom-based magnetometers.

Simplified 1.5 μm Distributed Feedback Semiconductor Laser (DFB-LD) Frequency Stabilization System Based on Gas Absorption Chamber

The classical 1.5 μm band frequency-stabilized laser using acetylene gas saturated absorption can achieve high frequency stability and reproducibility, but its system design is complex and bulky. For some practical applications, a simple, compact system containing anti-interference abilities is preferred. In this study, a low-cost and simple-structured 1.5 μm frequency-stabilized laser is constructed using digital control methods, wavelength modulation technology, and acetylene gas absorption. The fiber input and output optical devices of the system significantly simplify the optical path and reduce the volume of the system. The error signal is obtained by the first-order differential method, and a combination of the high-speed comparator circuit and the microcontroller unit (MCU) is used to detect the error signal. Through the feedback control method of coarse temperature adjustment and fine current adjustment, the second-level frequency stability of the laser is stabilized within 100 kHz, that is, the frequency stability reaches 10​−10. The designed system achieved continuous and stable operation for more than 6 h, and the long-term frequency stability reached 10​−9.

Robust low-noise 795-nm single-frequency fiber laser with continuous frequency tuning

This study presents a highly efficient and low-noise all-fiber single-frequency (SF) 795-nm laser system realized using a simple and robust single-pass frequency-doubling configuration. The foundation of the system is a 1590-nm erbium-doped fiber amplifier operating in a master oscillator power amplifier configuration seeded by a distributed feedback semiconductor laser at 1590.52 nm. The main amplifier exhibits an exceptional amplification efficiency of 30.5 %. By utilizing a periodically poled lithium niobate waveguide, the 795-nm laser is frequency-doubled with an output power reaching 2.3 W, corresponding to an optical efficiency of 44 % of the fundamental laser. Crucial to its application in precision measurements and quantum technologies, the SF 795-nm laser exhibits a relative intensity noise close to −150 dBc/Hz in the frequency range of 0.1 to 10 MHz. Additionally, a continuous frequency-tuning range of 11.7 GHz is achieved by modulating the current with a 2.5-mA 1-Hz triangular wave. Notably, this is the first report on an all-fiber SF 795-nm laser system.

Interferometric Optical Pumping of an InGaN/GaN-Based Gain-Coupled Distributed Feedback Multi Quantum Well Laser

We describe an all-optical method to achieve—prior to further advanced processing steps—a perfect match of the relevant wavelength-sensitive parameters of an InGaN/GaN semiconductor distributed feedback laser. Instead of permanently etching and epitaxially over-growing a waveguide-based diffraction grating for the definition of an index-coupled distributed feedback laser, we suggest here—by employing a powerful ultraviolet pump laser—a non-permanent, photoinduced generation of an optical diffraction grating. The resulting complex refractive index modulation then forms a gain-coupled distributed feedback laser. Such an approach has the advantage of remaining flexible as long as possible—both in terms of the correct grating period and the ideal coupling constant. This flexibility is maintained until the definitive etch and the epitaxial over-growth of the diffraction grating are completed. Such devices can—like their dye laser counterparts in the early seventies—also be used as ultra-broadly tunable single-mode sources.

Research on an Enhanced Detuned-Loading Effect in Integrated Two-Section DFB Lasers with High Modulation Bandwidths.

A novel high-speed directly modulated two-section distributed-feedback (TS-DFB) semiconductor laser based on the detuned-loading effect is proposed and simulated. A grating structure is designed by the reconstruction-equivalent-chirp (REC) technique. A π phase shift is introduced into the reflection grating, which can provide a narrow-band reflection region with a sharp falling slope on both sides of the reflection spectrum, thus enhancing the detuned-loading effect. Owing to its unique dual-falling-edges structure, the bandwidth can be improved even when the lasing wavelength shifts beyond the left falling edge due to a thermal effect in the actual test, in which condition the detuned-loading effect can be used twice, which greatly improves the yield. The modulation bandwidth is increased from 17.5 GHz for a single DFB laser to around 24 GHz when the lasing wavelength is located on the left falling edge of the TS-DFB laser based on the detuned-loading effect, and it can be increased to 22 GHz for the right side. An eight-channel laser array with precise wavelength spacing is investigated, with a side-mode suppression ratio (SMSR) >36 dB. In addition, TS-DFB lasers with uniform reflection gratings are studied, and simulated results show that the modulation characteristic is far inferior to the laser with a phase-shifted grating reflector.

High-coherence hybrid-integrated 780 nm source by self-injection-locked second-harmonic generation in a high-Q silicon-nitride resonator

Visible, high-coherence optical sources are important to a wide range of applications spanning spectroscopy to precision timing. Integration of these sources on a semiconductor chip is a necessary step if the systems that use these devices are to be made compact, portable, and low power. Here, by self-injection-locking a 1560 nm distributed feedback semiconductor laser to a high-Q silicon-nitride resonator, a high-coherence 780 nm second-harmonic signal is generated via the photogalvanic-induced second-order nonlinearity. A record-low frequency noise floor of 4Hz2/Hz is achieved for the 780 nm emission. The approach can potentially generate signals over a wide range of visible and near-visible bands, and thereby help transition many table-top systems into a fieldable form.

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.

Simple multi-band linearly frequency-modulated signal generation with a multiplying bandwidth based on a gain-switching laser.

Multi-band linearly frequency-modulated (LFM) signal generation with a multiplying bandwidth is proposed and experimentally demonstrated. It is a simple photonics method based on the gain-switching state in a distributed feedback semiconductor laser without a complex external modulator and high-speed electrical amplifiers. With N comb lines, the carrier frequency and bandwidth of generated LFM signals are N times those of the reference signal. (N is the number of comb lines.) The number of bands and time-bandwidth products (TBWPs) of the generated signals could be easily adjusted by tuning the reference signal from an arbitrary waveform generator. Three-band LFM signals with carrier frequencies ranging from the X-band to K-band are given as an example, and the TBWP up to 20000. The results of auto-correlations of the generated waveforms are also given.

Research on application of local oscillator power locking method to laser heterodyne radiometer

Laser heterodyne radiometer has the advantages of low cost, small size, and high spectral resolution. It can expand the existing ground carbon measurement network, verify satellite observation results, and provide data coverage outside the satellite observation area. Using the existing laser heterodyne radiometer, is presented a prototype of near-infrared laser heterodyne radiometer based on the erbium-doped fiber amplifier that can realize local oscillator power locking. In the laser heterodyne radiometer a distributed feedback semiconductor laser with a center wavelength of 1.603 μm is used as a local oscillator light source. The erbium-doped fiber amplifier is used to enhance the local oscillator power, and the automatic power control circuit is adopted to lock the output optical power of the erbium-doped fiber amplifier. The baseline slope caused by the change of the local oscillator power is eliminated, and the whole layer atmospheric transmittance spectrum without baseline fitting is measured. The instrument performance of a highly integrated laser heterodyne radiometer based on an erbium-doped fiber amplifier is evaluated in detail, and the atmospheric CO<sub>2</sub> transmittance spectrum is measured in the Science Island (31.9°N, 117.2°E) of Hefei. Six groups of atmospheric CO<sub>2</sub> transmittance spectra are obtained during the measurement period of one day, which are compared with the simulation results from an atmospheric radiation model, showing that they are consistent with each other. The experimental results show that the application of erbium-doped fiber amplifier can improve the performance of laser heterodyne radiometer, optimize its structure, and provide equipment supplement for realizing unattended long-term atmospheric CO<sub>2</sub> concentration observation and building a comprehensive carbon observation network.

Monolithic Integrated Two-Section Dual-Wavelength Distributed Feedback Semiconductor Laser

Monolithic Integrated Two-Section Dual-Wavelength Distributed Feedback Semiconductor Laser

Experimental demonstration of a photonic convolutional accelerator based on a monolithically integrated multi-wavelength distributed feedback laser.

We propose and experimentally demonstrate a simple and energy-efficient photonic convolutional accelerator based on a monolithically integrated multi-wavelength distributed feedback semiconductor laser using the superimposed sampled Bragg grating structure. The photonic convolutional accelerator operates at 44.48 GOPS for one 2 × 2 kernel with a convolutional window vertical sliding stride of 2 and generates 100 images of real-time recognition. Furthermore, a real-time recognition task on the MNIST database of handwritten digits with a prediction accuracy of 84% is achieved. This work provides a compact and low-cost way to realize photonic convolutional neural networks.

Microwave photonics scanning channelizer with digital image-reject mixing and linearization

Microwave photonics scanning channelizer with digital image-reject mixing and linearization is investigated by employing a cascaded distributed feedback semiconductor laser (DFB) operating at stable locking dynamics when subjected to flat optical frequency comb (OFC) injection. The OFC injection locking (OIL) provides a high-quality coherent optical local oscillator with ultra-broadband tuning capability by demultiplexing and amplifying individual comb from densely spaced OFC. The channelizer receiver scans the whole frequency range at discrete steps through a single tunable heterodyne receiver and a single ADC, thus reducing the SWaP and increasing agility. By introducing the digital Hartley structure image-reject mixing (IRM), the amplitude and phase imbalance of the IQ channel are easily compensated, resulting in a high image rejection ratio (IRR) up to around ∼50 dB for all channels. Furthermore, a novel digital linearization technique is employed to suppress third-order intermodulation components by more than 19.43 dB while improving the spurious free dynamic range (SFDR) by 16.1 dB The analysis confirms the scheme’s capability for detecting signals from 1.5 GHz to 43.5 GHz and beyond with excellent performance. The proposed channelizer can find applications in future wideband RF systems, including 5G and beyond wireless communications, electronic warfare, and radars.

Detection of trace carbon monoxide based on cantilever enhanced photoacoustic spectroscopy at 2.33 μm

The composition gases internal SF6 insulation equipment is closely related to the insulation state of the equipment. According to relevant regulations, CO is an important component, and its concentration can be used as the basis for judging the internal insulation state of SF6 equipment. Gas detection based on photoacoustic spectroscopy is an effective means of online monitoring. The study adopts the 2.33 μm distributed feedback semiconductor laser as light source and the cantilever as acoustic sensor to develop the photoacoustic spectroscopy detection system, performs the photoacoustic spectroscopy detection of CO, and studies the influence mechanism of the background gas and temperature on the excited photoacoustic signals. The results show that the signal has high stability and a good linear relationship with the gas concentration. The lowest detection limit of CO in SF6 is 5.1 ppm, and the background gas and temperature mainly affect the excited signals by the difference of the cell constant.

QAM-DMT of Hybridly Integrated EAM-DFBLD Chip-on-Board With Adaptive Machine Learning Algorithm for 149.6-Gbit/s BtB and 138-Gbit/s 10-km-SMF Transmission

By using the generalized frequency division multiplexing (GFDM) and the machine learning algorithm for self-feedback amplitude/phase pre-distortion, the electro-absorption modulator integrated distributed-feedback semiconductor laser diode (EAM-DFBLD) is encoded with improved transmission quality and capacity. Both back-to-back (BtB) and 10-km single-mode fiber (SMF) transmissions are preliminarily demonstrated for inter-data-center applications. Optimizing the EAM-DFBLD transmitter at 1306.8 nm with a bias current of 100 mA and a bias voltage of −1.5 V can provide a 34.5-GHz bandwidth for 16-QAM discrete multitone (DMT) and GFDM formats. The parametric comparison reveals that the 16-QAM GFDM with <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</i> = 16 can improve its performance from BtB to 10-km SMF transmission with decoding BER slightly increasing from 1.44 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> to 2.82 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> . The EAM-DFBLD carried GFDM data also provides a better power penalty by -0.25 dB. This enables higher raw data rates of 149.6 Gbit/s under BtB case and 138 Gbit/s in 10-km SMF transmission link below the forward error correction (FEC) criterion. The GFDM format carried by the EAM-DFBLD transmitter thus becomes the more suitable candidate than the DMT to implement ultra-high-speed inter-data-center and data access link applications.

Dual-linear chirp microwave signal generation by using single-beam injection to a DFB semiconductor laser and optical heterodyne technique.

Based on a single-beam injection distributed feedback semiconductor laser (DFB-SL) combining with optical heterodyne, a photonic scheme for generating dual-linear chirp microwave (dual-LCM) signal with identical or complementary chirp is proposed and experimentally demonstrated. For such a scheme, a continuous-wave (CW) light with a frequency of finj is split into two parts. One part is passing through a Mach-Zehnder modulator (MZM) driven by a modified sawtooth signal, and then its intensity varies with time as a sawtooth wave. Such a light is injected to a DFB-SL for generating a single linearly chirped microwave (single-LCM) signal. The other part of the CW light with frequency of finj is sent to a phase modulator (PM) driven by a sinusoidal signal, and one of higher-order sidebands is selected by a tunable optical filter and taken as the referenced light. Through heterodyning the referenced light with the single-LCM signal, a dual-LCM signal with identical (or complementary) chirp can be obtained. The experimental results demonstrate that, by adjusting the injection parameters and the frequency of the sinusoidal signal loaded on the PM, the central frequency of the generated dual-LCM signal can be widely tuned. For the period of the sawtooth signal at 10 µs, the bandwidth for each frequency band included in the generated dual-LCM signal is 19.36 GHz under identical chirp and 16.98 GHz under complementary chirp, respectively. Correspondingly, the time bandwidth product (TBWP) for each frequency band can reach 1.936 × 105 under identical chirp and 1.698 × 105 under complementary chirp, respectively.

The effect of the convex lens focal length and distance between the optical devices on the photoacoustic signals in gas detection

Photoacoustic (PA) spectroscopy has been extensively applied in gas detection field due to its high sensitivity. However, the stability and repeatability are unsatisfactory in some cases. Herein, it is proposed that the PA signals intensity is associated with the focal length F of the convex lens (CL), the distance l1 between the CL and the window of the PA cell, and the distance l2 between the CL and the laser head. Then, the experimental setup was constructed with a distributed feedback semiconductor laser (DFB LD) as the light source, and a cylindrical cavity with its length and diameter are 95 mm and 6 mm, respectively, as the PA cell. And the influence of the above three factors on the PA signals has been analyzed. The results show that the strongest PA signals can be obtained when the F, l1, and l2 are 20 mm, 0 mm and 9 mm, respectively. Additionally, l1 and l2 both have an impact on the PA signals and the influence of l2 seems to be more regular and can be approximately ignored except when F is 20 mm. Especially, the PA signals weaken with the increase of the F, but the l1 and l2 have the least effect on the PA signals intensity when the focal length is 50 mm and 63 mm based on the calculation of variance. The results provide a reference for the selection of convex lens and the optical devices positions to improve the stability and sensitivity of the PAS gas detection device.

Chaotic characteristics of output light from semiconductor laser with self-chaotic phase modulation and optical feedback

&lt;sec&gt;Distributed feedback semiconductor lasers (DFB-SLs) are the class B lasers, and would output chaotic laser under the external disturbances, such as external optical feedback and optical injection. Chaotic laser are widely used in many fields, including optical fiber sensing, chaotic laser secure communication, and better entropy sources for generating high-speed random number. However, the chaotic laser outputted from the semiconductor lasers with external cavity optical feedback produces a time delay signature (TDS) , which limits the applications of chaotic laser. On the other hand, the bandwidth (BW) of chaotic carrier signal plays the important role in determining the transmission rate of information signal. Therefore, the TDS and BW are two important parameters that will affect chaotic laser’s applications, and they are usually used to describe the chaos characteristics of chaotic laser.&lt;/sec&gt;&lt;sec&gt;In this paper, we present a new scheme used to describe the TDS and investigate the BW of chaotic laser from semiconductor laser. For this scheme, the output laser from a DFB-SL with external single optical feedback is injected in double ways into another DFB-SL with phase modulation optical feedback by self chaos light. Thus they form a semiconductor laser system with external double optical injection and phase modulation optical feedback by self chaos light (SL-EDOI-PMOFBSCL). We investigate numerically the influences of the system parameters on TDS, such as the injection coefficient and feedback coefficient. Then the suppression effects on TDS are contrasted and analyzed with two other systems, that is to say, the semiconductor laser with external double optical injection and optical feedback (SL-EDOI-OF) and the semiconductor laser with external single optical injection and phase modulation optical feedback by self chaos light (SL-ESOI-PMOFBSCL). The results indicate that the proposed scheme in this work has the better suppression effect on TDS. Then the BW of the chaotic laser is investigated under the parameters conditions of effectively suppressing TDS. The simulation results show that the scheme proposed in this work can enhance the BW of chaotic laser by appropriately selecting the parametric values, and the maximum BW value of the obtained chaotic laser reaches about 16 GHz.&lt;/sec&gt;

Fabrication Technology of Distributed Feedback Semiconductor Laser Based on Buried Metal Mask

Fabrication Technology of Distributed Feedback Semiconductor Laser Based on Buried Metal Mask

Picosecond hybrid laser based on semiconductor laser, fibre and Nd: YVO4 amplifiers. Investigation of effects limiting the peak power

Based on a distributed-feedback (DFB) semiconductor laser, an ytterbium fibre amplifier, an Nd : YVO4 amplifier, and a frequency converter, we designed a hybrid picosecond laser for satellite laser ranging. A gain exceeding 108 is achieved while maintaining the temporal shape and spectrum of the pulses, with a low noise level and a divergence close to the diffraction limit. The pulse energy after conversion to the second harmonic at λ = 532 nm is 2.2 mJ with a duration of 27 ps and a repetition rate of 1 kHz. It is shown that the main effects limiting the peak power are spectrum broadening due to self-phase modulation in a fibre amplifier and large-scale self-focusing in the Nd : YVO4 amplifier. Optimisation of the amplifier geometry and the use of a uniform profile of the pump radiation intensity make it possible to reduce the effect of self-focusing and increase the energy efficiency of the amplifier.

Measurement of Laser Phase Noise for Ultra-Long Period of 0.8 Seconds With 800-ps Temporal Resolution Using Optical Coherent Detection With FPGA-Implemented Data Acquisition

In this study, we demonstrate laser phase noise measurement with a 0.8-s period and an 800-ps temporal resolution. An optical carrier is received by heterodyne detection, and the detected electrical signals are acquired using field programmable gate array circuits with 1.25-GSample/s analog-to-digital converters and 1-GByte memory. The laser phase noise is visualized using a field spectrogram and a very wide FM noise spectrum from near the DC, which is constructed using our proposed phase-compensating interleaved fast Fourier transformation. We compare the phase noise characteristics of an external cavity laser with those of a distributed feedback semiconductor laser.