Distributed Feedback Laser Research Articles

Single-mode GaSb-based laterally coupled distributed-feedback laser for CO2 gas detection

We report on a GaSb-based laterally coupled distributed feedback (LC-DFB) laser with Cr gratings operating at 2004 nm for CO2 detection application. Butterfly packaged with single-mode fiber pigtailed, the laser diode operates in the continuous-wave mode in a temperature range from −10 °C to 60 °C, with a maximum output power of 2 mW and a maximum side-mode suppression ratio over 30 dB. Wavelength-modulated absorption spectroscopy of CO2 demonstrates the applicability of the LC-DFB laser to tunable diode laser absorption spectroscopy. Furthermore, the diode junction temperature, which is measured by using the wavelength shift method, exhibits a maximum value of 17 °C in the single-mode operation range.

On-line measurement of atmospheric oxygen by an open-path OA-ICOS based sensor with high accuracy at ambient pressure

In this paper, a compact optical oxygen (O2) sensor system was demonstrated based on off-axis integrated cavity output spectroscopy (OA-ICOS). Light from a distributed feedback laser near 761 nm was coupled into an open-path F-P cavity by off-axis configuration. To address the challenges of changing field environments for open-path configuration, the influence of pressure on the sensor system was studied. A linewidth enhancement factor (δ) was proposed to measure the ambient pressure and a pressure correction method was developed to improve the measurement accuracy. A minimum detection limit of 0.0038% was obtained for an optimum averaging time of 20 s under 760 Torr. Indoor and outdoor O2 concentration measurements were conducted and the sensing applicability of the sensors system at ambient pressure was verified. The demonstrated sensor system allows operation without a vacuum pump and a pressure controller combine with the self-developed laser driver and digital lock-in amplifier, which has advantages of reduced size, low power consumption, low cost and has wide application prospect for O2 sensing in field environments.

Research on Very-Low-Frequency Hydroacoustic Acoustic Velocity Sensor Based on DFB Fiber Laser

We have conducted a study on a very-low-frequency acoustic-velocity sensor which is based on a cantilever of distributed-feedback (DFB) fiber laser immersed in castor oil. A mathematical model of the frequency dependent response of the proposed sensor to the acoustic pressure signal influenced by the fluid viscosity is established. We have fabricated the proposed sensor and conducted experimental measurements in the standing wave tube. The results show that the sensor has an average phase sensitivity of −179.5 dB (0 dB = 1 rad/μPa) with ±1.45 dB fluctuation over the frequency range of 20–38 Hz. It has good cosine directivity with a directivity index of 32.5 dB and axial maximum asymmetry of 0.4 dB. The sensor presents promising applications for detecting very-low-frequency underwater acoustic signals.

Distributed feedback laser grating order effects on optical systems with NRZ-RZ line coding scheme performance signature

Abstract This work demonstrated the distributed feedback laser grating order effects on optical system in the presence of NRZ-RZ line coding schemes. Max lighted signal form power variations are studied with spectral base wavelength band variations through optical fiber based on first various distributed based band feedback laser (DFB) grating order. The total lighted form base power band through optical fiber based on first different DFB laser grating order is estimated. The max electrical base signal band power form variations with spectral base frequency form band variations through photo-detector based on various DFB laser grating order is demonstrated. Total electrical based power band form through photo-detector based on various DFB laser grating order is also clarified. Max base band power form band amplitude with time through photo-detector based on different DFB laser grating order is clarified. Max Q base band form is studied numerically with DFB laser grating order variations.

High Speed All-Optical Polarization Scrambler Based on Polarization Beam Splitting Delayed Fiber Loop

Polarization scramblers are widely employed to mitigate polarization fluctuation-related effects for optical signals propagating in fiber systems. We propose an all-optical polarization scrambler configuration based on a polarization beam splitting delayed fiber loop. By deteriorating the coherence of one beam, and controlling the intensity ratio of two orthogonal beams, the polarization scrambler operates in a chaotic regime. The effect on polarization scrambling of loop structure is tested by a home-made narrow-linewidth laser with linewidth of 500 Hz. We investigate the polarization scrambling performance for a commercial distributed feedback laser with linewidth of 3 MHz in various operating regimes. Scrambling speeds under chaotic regime reach 42 Mrad/s with a degree of polarization <0.1 at the maximum sampling rate of 100 MSa/s. We also characterize the dependence of the scrambling speed and average degree of polarization on delay fiber length and wavelengths within the C-band. The output performance of the proposed scrambler for scrambling 40 MHz and 6 GHz modulated signals are tested and waveform distortions are identified due to polarization scrambling.

Narrow linewidth semiconductor multi-wavelength DFB laser array simultaneously self-injection locked to a single microring resonator.

We experimentally demonstrate a narrow linewidth semiconductor multi-wavelength distributed feedback (DFB) laser array by simultaneously injection locking each laser to the corresponding resonance of a single on-chip microring resonator. The white frequency noises of all the DFB lasers is reduced by more than 40 dB once they are simultaneously injection locked to a single microring resonator with a quality factor (Q-factor) of 2.38 million. Correspondingly, the instantaneous linewidths of all the DFB lasers are narrowed by a factor of 104. In addition, frequency combs originating from non-degenerate four-wave mixing (FWM) between the locked DFB lasers are also observed. Simultaneously injection locking multi-wavelength lasers to a single on-chip resonator may enable the possibilities of integrating a narrow-linewidth semiconductor laser array on a single chip and having multiple microcombs in a single resonator, which are in high demand in wavelength division multiplexing coherent optical communication systems and metrological applications.

Spectral behavior of high-power distributed feedback lasers

The mode hopping behavior of high-power distributed feedback lasers emitting near 780,hbox {nm} is studied. The lasers have highly reflective rear and anti-reflection coated front facets. The influence of the phase of the grating at the rear facet is investigated by means of numerical simulations in the time domain taking into account spatial hole burning and self-heating effects. The simulation results are in agreement with experimental findings.

A new magnetic state selection method in high-performance optically detected compact cesium beam clocks

We perform a new scheme of magnetic state selection in optically detected compact cesium beam clocks. Unlike the conventional method, we select atoms in the ground state |F = 4, mF ≠ −4⟩ by pointing the atomic collimator to the convex pole of the magnet realizing the two-wire magnetic field and detect atoms in |F = 3⟩ after interacting with the microwave field using a distributed feedback laser. The fluorescence background is greatly reduced as the inherent residual atoms |F = 4, mF = −4⟩ are avoided in this reversed scheme. The velocity distribution is narrowed, and the most probable velocity is decreased, since atomic trajectories are close to the weak-field region. We also investigate the relationship between the position of the atomic collimator and the distributions of the atomic beam, which is consistent with the Monte Carlo-based simulation model. By applying the reversed scheme and setting the deviated position of the collimator to 1.3 mm, the signal contrast is improved from 0.7 to 3, and the short-term frequency stability reaches 3.0 × 10−12 τ−1/2, nearly three times better than that of the high-performance version of Microsemi 5071A.

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.

An analog fiber optic link developed for electrical pulse signal transmission

The electromagnetic interference (EMI) around the devices for ionizing radiation experiments is a serious concern. In order to reduce EMI and enhance the signal-to-noise ratio, a new type of analog fiber optic link (FOL) has been developed for fast pulse signal transmission under complicated electromagnetic fields. Electrical signals are converted to optical signals through an electro-optical conversion process using the amplitude modulation mechanism. After long-distance transmission, optical signals can also be restored via photoelectric conversion. Each link has a transmitter unit connected via a fiber optic cable to the receiver unit. The transmitter unit consists of a distributed feedback laser, a driver circuit made of amplifiers, and an automatic temperature control module, while the receiver unit consists of a PIN detector, a transimpedance amplifier, a main amplifier, and a third order active low-pass filter. A prototype of this link has been fabricated and tested. The test results show that the transmission bandwidth of the analog signals is DC ∼ 155 MHz, the transmission delay is a typical 21 ns, the linear dynamic range is greater than 56 dB (692 times larger), the output noise is less than 4.5 mV, and the transmission distance is up to several kilometers, which can meet the requirements of ionizing radiation experiments. The FOL demonstrates great performance in transmission for scientific research with high quality in terms of transmission bandwidth, linearity, security, and stability.

Regrowth-free AlGaInAs MQW polarization controller integrated with a sidewall grating DFB laser

Polarization control is at the heart of high-capacity data optical communication systems, such as polarization-division multiplexers and Stokes vector modulation transmitters. Despite passive polarization control being mature, the realization of monolithically integrated polarization controllers and single longitudinal mode light sources, such as distributed-feedback (DFB) lasers, is of importance. In this research, we report an AlGaInAs multiple-quantum-well photonic integrated circuit device which can control the state of polarization of the output light source, consisting of a polarization mode converter (PMC), a differential phase shifter (DPS), and a sidewall grating DFB laser. We demonstrate an asymmetrical stepped-height ridge waveguide PMC to realize TE to TM polarization conversion and a symmetrical straight waveguide DPS to enable polarization rotation from approximately counterclockwise circular polarization to linear polarization. Based on the identical epitaxial layer scheme, all the PMC, DPS, and DFB lasers can be integrated monolithically using only a single step of metalorganic vapor-phase epitaxy and two steps of III-V material dry etching. For the DFB-PMC device, a high TE to TM polarization conversion efficiency (98.4%) over a wide range of DFB injection currents is reported at 1555 nm wavelength. For the DFB-PMC-DPS device, a nearly 60° rotation of the Stokes vector on the Poincaré sphere was obtained with a range of bias voltage from 0 to −3.0 V at a laser drive current of 170 mA.

High-speed directly modulated distributed feedback laser based on detuned loading and photon–photon resonance effect

A monolithic integrated two-section distributed feedback (TS-DFB) semiconductor laser for high-speed direct modulation is proposed and analyzed theoretically. The grating structure of the TS-DFB laser is designed by the reconstruction-equivalent-chirp (REC) technique, which can reduce the manufacturing cost and difficulty, and achieve high wavelength controlling accuracy. The detuned loading effect and the photon–photon resonance (PPR) effect are utilized to enhance the modulation bandwidth of the TS-DFB laser, exceeding 37 GHz, while that of the conventional one-section DFB laser is only 16 GHz. When the bit rate of the non-return-to-zero (NRZ) signal reaches 55 Gb/s, a clear eye diagram with large opening can still be obtained. These results show that the proposed method can enhance the modulation bandwidth of DFB laser significantly.

Noninvasive Skin Respiration (CO2) Measurement Based on Quartz-Enhanced Photoacoustic Spectroscopy.

A noninvasive method for disease diagnosis that does not require complex specialized laboratory facilities and chemical reagents is particularly attractive in the current medical environment. Here, we develop a noninvasive skin respiration sensor based on quartz-enhanced photoacoustic spectroscopy (QEPAS) that can monitor the skin elimination rate of carbon dioxide (CO2). A 3.8 mW distributed feedback laser emitting at 2.0 μm is used as an excitation source, and a three-dimensional (3D)-printed acoustic detection module is designed to apply to the skin as a sensor head. The performance of the noninvasive skin respiration sensor is assessed in terms of detection sensitivity, linearity, long-term stability, and water effect. A minimum detection limit of 35 ppb is achieved at the optimal integration time of 670 s. The skin respiration measurements from eight healthy volunteers are recorded, and the real-time results are analyzed.

High-power tapered two-section distributed feedback laser based on a chirped sampled grating.

We propose and theoretically study a two-section high-power distributed feedback (DFB) laser with three equivalent phase shifts (3EPSs). A tapered waveguide with a chirped sampled grating is introduced to amplify the output power and keep a stable single-mode operation. The simulation exhibits the maximum output power and side mode suppression ratio of a 1200µm length two-section DFB laser as high as 306.5mW and 40dB, respectively. Compared with traditional DFB lasers, the proposed laser has a higher output power, which may benefit wavelength division multiplexing transmission systems, gas sensors, and large-scale silicon photonics.

Optical pressure sensing at MHz rates via collisional line broadening of carbon monoxide: uncertainty quantification in reacting flows

An optical method for high-speed line-of-sight pressure measurements using infrared laser absorption spectroscopy is presented with detailed uncertainty analysis related to thermodynamic and compositional variation in combustion environments. The technique exploits simultaneous sub-microsecond sensing of temperature and mole fraction to extract pressure from collisional line broadening at MHz rates. A distributed-feedback quantum-cascade laser near 5 upmu m in a bias-tee circuit is used to spectrally resolve multiple rovibrational transitions in the P-branch of the fundamental band of carbon monoxide, which may be seeded or nascent to reacting flows. A comprehensive approach for estimating collisional line broadening in complex combustion gas mixtures is presented. Uncertainty is quantified for a wide range of conditions, reflecting different fuels, equivalence ratios, reaction progress, and combustion modes (deflagration and detonation), which influence gas composition and temperature. The sensor was evaluated for accuracy and precision in both a high-enthalpy shock-tube facility in hydrocarbon–air ignition experiments and behind ethylene–oxygen detonation waves in a detonation-impulse tube facility at temperatures from 1500 to 3000 K and pressures from 0.5 to 10 bar. Pressure measurements were compared to measurements by piezoelectric pressure transducers and to theoretical estimates from normal-shock and Chapman-Jouguet simulations. The high-speed path-integrated optical pressure measurement offers an alternative to traditional electromechanical transducers that are constrained to values at wall boundaries and have proven unreliable in some harsh reacting flows.

Suppression of Nonlinear Optical Effects in DWDM-PON by Frequency Modulation Non-Coherent Detection

We propose a simple and cost-effective method, using a direct frequency modulation (FM) and noncoherent detection (NCD) scheme, to suppress the nonlinear optical effects in dense wavelength division multiplexed (DWDM) optical communication. The FM transmitter comprises a directly modulated distributed feedback laser and a saturable semiconductor optical amplifier. In the NCD receiver, an optical slope filter as the FM to intensity modulation (IM) signal convertor is placed before a conventional photodetector. Because the FM signal has more evenly distributed optical power, bit-pattern-dependent nonlinear effects are consequently suppressed. After analyzing the nonlinear effects in the FM-NCD system and traditional IM direct detection (IM-DD) system, we found that the minimum achievable BER of the proposed FM-NCD scheme is 40 dB smaller. Moreover, a 2 Tbps (10 Gb/s × 200 channels) capacity was achieved by the FM-NCD system in 100 km DWDM passive optical networks (PONs), which is twice the capacity of the IM-DD system (10 Gb/s × 100 channels) under the same condition. These results indicate that WDM-PONs with the cost-effective FM-NCD scheme are strong candidates for future broad access networks and show great potential for the combination of optical access and metro networks for future generations of PONs.

High Speed Directly Modulated DFB Lasers Having MQW Based Passive Reflectors

We have fabricated <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.3~\mu \text{m}$ </tex-math></inline-formula> band InP based high speed directly modulated distributed feedback (DFB) lasers having passive distributed Bragg reflector (DBR). Because of the feed back from the DBR section, the modulation bandwidth of the lasers is over 25 GHz, which is notably larger than the 19 GHz for a normal single section DFB laser. The reflector of the devices has the same multi-quantum wells (MQWs) as the DFB section, which simplifies the device fabrication greatly, helping to lower the device cost. For the DBR integrated DFB lasers, experimental results show that a larger modulation current efficiency can be obtained when the DFB wavelength is more positively detuned relative to the reflection peak of the DBR reflector. This indicates that a static detune between the DFB wavelength and the DBR reflection peak can be introduced into a distributed reflector laser to get a good detune condition, helping to lower the device cost of high speed directly modulated lasers.

Dynamic intrinsic spectrum reconstruction of narrow-linewidth laser based on band-extended frequency noise

Narrow-linewidth lasers have extensive applications due to advantages of low phase noise and high coherence. To explore the dynamics of narrow-linewidth lasers, the intrinsic spectrum is a kernel parameter which can show the dynamical coupling strength between the spontaneous emission and the stimulated emission in a laser cavity. Herein, we propose an intrinsic spectrum measurement method of narrow-linewidth lasers based on the band-extended frequency noise, which can improve the spectrum resolution. In the experiment, we successfully apply the method to the measure the linewidth compression dynamics of external-cavity distributed feedback lasers. The proposed measurement method can dynamically characterize the fast evolution process of the laser intrinsic spectrum with wide-range linewidth fluctuations, which will benefit for the dynamics research of narrow-linewidth lasers and tunable lasers.

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.

Enhanced Modulation Bandwidth by Delayed Push–Pull Modulated DFB Lasers

The bandwidth of a distributed feedback (DFB) directly modulated laser (DML) is limited by its carrier-photon resonance (CPR) frequency. A viable approach to break the bottleneck is to introduce a photon-photon resonance (PPR), since the PPR can happen at a much higher frequency than the CPR. Among the many structures that can possibly generate the PPR, the dual-sectional push-pull modulated (PPM) DFB is of particular interest for its fabrication cost-effectiveness as no regrowth is required. The PPR in the PPM DFB, however, usually shows a rapid roll-off on both edges, which brings in an indentation on the lower frequency side of the PPR peak and, consequently, cuts off the bandwidth. To compensate for this dip, we introduce a detuned PPR and restart the CPR response by exploiting a time delay between the differential signals applied to the PPM DFB. Our simulation result shows that the broadened PPR peak and the restarted CPR response indeed mitigate the dip and effectively expand the PPM-DFB's bandwidth to approximately 50 GHz, a value double that of the conventional (single-sectional) DFB DML.