Sampled-grating Distributed Bragg Reflector Laser Research Articles

Dual Laser Indium Phosphide Photonic Integrated Circuit for Integrated Path Differential Absorption Lidar

An indium phosphide photonic integrated circuit (PIC) was demonstrated for integrated path differential absorption lidar of atmospheric carbon dioxide (CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ). The PIC consists of two widely tunable sampled grating distributed Bragg reflector (SGDBR) lasers, directional couplers, a phase modulator, a photodiode, and semiconductor optical amplifiers (SOAs). One SGDBR laser, the leader, is locked to the center of an absorption line at 1572.335 nm using the on-chip phase modulator and a bench-top CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Herriott reference cell. The other SGDBR laser, the follower, is stepped in frequency over ±15 GHz around 1572.335 nm to scan the target CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> absorption line. The follower laser is offset locked to the leader laser with an optical phase lock loop. An SOA after the follower laser generates a pulse at each frequency step to create a train of pulses that samples the target CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> absorption line. The PIC components and subsystem are characterized and evaluated based on target performance requirements. The leader laser demonstrated a 236-fold improvement in frequency stability standard deviation when locked compared to free running and the follower laser frequency stability standard deviation compared to the leader laser was 37.6 KHz at a 2 GHz programmed offset.

Indium Phosphide Photonic Integrated Circuit Transceiver for FMCW LiDAR

We present a photonic integrated circuit (PIC) transceiver for frequency modulated continuous wave (FMCW) LiDAR applications. The transmitter consists of a widely tunable sampled grating distributed Bragg reflector laser (SGDBR) and a frequency discriminator which combines multimode interference couplers, a tunable asymmetric Mach–Zehnder Interferometer (a-MZI), and balanced photodiodes. The frequency discriminator converts frequency fluctuations of the laser to amplitude fluctuations of the photodiode currents. This provides an error signal for feedback into the laser cavity for frequency stabilization. Frequency modulation is obtained by a phase shifter in the a-MZI which tunes the quadrature point of the filter and the frequency where the error is zero. An on-chip receiver couples power from the transmitter to self-heterodyne with the time-delayed echo of a distant object. The generated beat frequency of the self-heterodyne measurement gives the echo signals time-of-flight to obtain the distance and velocity of the reflecting object. The theory of the components is described, and characterization of the transmitter and receiver is presented.

Indium Phosphide Photonic Integrated Circuits for Free Space Optical Links.

An indium phosphide (InP)-based photonic integrated circuit (PIC) transmitter for free space optical communications was demonstrated. The transmitter consists of a sampled grating distributed Bragg reflector (SGDBR) laser, a high-speed semiconductor optical amplifier (SOA), a Mach-Zehnder modulator, and a high-power output booster SOA. The SGDBR laser tunes from 1521 nm to 1565 nm with >45 dB side mode suppression ratio. The InP PIC was also incorporated into a free space optical link to demonstrate the potential for low cost, size, weight and power. Error-free operation was achieved at 3 Gbps for an equivalent link length of 180 m (up to 300 m with forward error correction).

Parallelized Kalman Filters for Mitigation of the Excess Phase Noise of Fast Tunable Lasers in Coherent Optical Communication Systems

Numerical and experimental investigations are carried out on the performance of parallelized Kalman filters applied for mitigation of the excess phase noise of fast tunable lasers. Based on the characterization of the phase noise of a sampled grating distributed Bragg reflector (SG-DBR) laser, the proposed carrier phase recovery (CPR) scheme using Kalman filters is introduced. By performing simulations of data transmission with various advanced modulation formats in the presence of the excess phase noise, the Kalman filter based CPR scheme shows its ability to overcome the excess phase noise and this method is suitable for parallel processing. Then the results are further demonstrated by 12.5 Gbaud QPSK and 16-QAM transmission experiments employing the SG-DBR laser. We find that the Kalman filters have better performance than the 2nd-order phase-locked loop in parallel systems due to a better phase noise tolerance. The bit error rate performance is also examined in the whole tuning range (∼30 nm) of the tunable laser, which further proves the feasibility of the proposed scheme.

Highly tunable heterogeneously integrated III-V on silicon sampled-grating distributed Bragg reflector lasers operating in the O-band.

We report on the design, fabrication and performance of the first hetero-integrated III-V on silicon sampled-grating distributed Bragg reflector lasers (SGDBR) operating in the O-band and based on direct bonding and adiabatic coupling. Two devices with different geometric parameters are presented both showing an output power in the Si waveguide as high as 7.5 mW and a continuous tuning range of 27 and 35 nm respectively with a side mode suppression ration higher than 35 dB.

Numerical Analysis on Thermal Tuning Efficiency and Thermal Stress of a Thermally Tunable SG-DBR Laser

Thermally tunable sampled grating distributed Bragg reflector (SG-DBR) lasers are very attractive for applications of optical coherent systems, where light sources with narrow linewidth are key requirements. In this paper, we focus on the thermal tuning efficiency and the thermal stress field of such lasers. The influence of a thermal isolation (air trench) design on the tuning efficiency of the laser is analyzed by using a thermal model based on the finite-element method (FEM) at first. The thermal tuning efficiency is found to be tenfold improved if the air trench is used. Influences of the air trench geometry configurations on temperature and thermal stress field are then examined in detail. Simulation results indicate that the most dangerous positions that can crack always appear at the output port and the corner of the air trench structure contact with the n-InP layer. The air trench geometry configuration of an SG-DBR laser is finally optimized (with a width of 70 $\mu\text{m}$ and a thickness of 1 $\mu\text{m}$ ) to ensure the reliability and the quasi-continuous wavelength tuning range of the device at the same time. With the optimized design, by using a developed temperature-dependent transfer matrix method-based optical model, optical output characteristics of the thermally tunable SG-DBR laser are demonstrated, including the output wavelength for the tuning range (1525–1585 nm covering C band) and the linewidth for all the channels (several tens to several hundreds of kilohertz). The simulated results have been found to be in good agreement with the experimental measurements previously reported, which are helpful to the thermal management and the design optimization of such devices.

Thermal analysis of an SOA integrated in SG-DBR laser module

In this paper, we developed a temperature-dependent thermal-optical model of a semiconductor optical amplifier (SOA) integrated in sampled grating distributed Bragg reflector (SG-DBR) laser module by extending our pervious works. By numerically solving the thermo-optical coupling equations, static and transient temperature distributions of the integrated module were simulated based on finite element method (FEM). Furthermore, thermal effects on optical output properties of the module were obtained by using a temperature-dependent dynamic transfer matrix method (DTMM) based optical model. Phenomenon of thermal crosstalk was clearly observed. Induced by the thermal transients in the SOA, the wavelength drift is as large as 39 pm and the power decrease is over 5 %. Our results could be helpful to the design optimization and the thermal management of relevant integrated devices.

Numerical Analysis of Phase Noise Characteristics of SGDBR Lasers

Detailed analyses of the phase noise characteristics of tunable sampled grating distributed Bragg reflector (SGDBR) lasers are presented in this paper. Based on the transmission line laser model, we derive the Langevin rate equations for the photon number and the electric-field phase in the cavity of SGDBR lasers. This model includes the spontaneous emission white noise in active section and the carrier shot noise in passive tuning sections, both of which contribute to the enhancement of the laser phase noise. Based on this model, the frequency modulation (FM) noise spectrum is calculated from the instantaneous laser phase fluctuation. The white noise linewidth and carrier shot noise linewidth are then calculated according to the FM noise spectrum. The linewidth tuning curves as a function of the currents in passive sections are simulated and the laser linewidth is strongly dependent on the tuning currents. Lower white noise linewidth is obtained when the longitudinal mode is located on the longer wavelength side of the total reflection-peak wavelength of the front and back gratings. However, the carrier shot noise linewidth increases with the increase of the injected current within each longitudinal mode. Finally, the impact of structural parameters on the linewidth is discussed.

BER Performance of Coherent Optical Communications Systems Employing Monolithic Tunable Lasers With Excess Phase Noise

We analyze the bit error rate (BER) performance of optical coherent communication systems employing multi-section monolithic tunable lasers with large excess phase noise. The BER of the coherent system utilizing a second-order decision-directed digital phase-locked loop (DD-PLL) for phase tracking was computed numerically. Experimental results have also been demonstrated with a 16-quadratic-amplitude modulation coherent system deploying a sampled-grating distributed Bragg reflector laser at 16 Gbaud that confirms the performance of the second-order DD-PLL in tracking the excess phase noise.

Simple analytical model for low-frequency frequency-modulation noise of monolithic tunable lasers

We employ simple analytical models to construct the entire frequency-modulation (FM)-noise spectrum of tunable semiconductor lasers. Many contributions to the laser FM noise can be clearly identified from the FM-noise spectrum, such as standard Weiner FM noise incorporating laser relaxation oscillation, excess FM noise due to thermal fluctuations, and carrier-induced refractive index fluctuations from stochastic carrier generation in the passive tuning sections. The contribution of the latter effect is identified by noting a correlation between part of the FM-noise spectrum with the FM-modulation response of the passive sections. We pay particular attention to the case of widely tunable lasers with three independent tuning sections, mainly the sampled-grating distributed Bragg reflector laser, and compare with that of a distributed feedback laser. The theoretical model is confirmed with experimental measurements, with the calculations of the important phase-error variance demonstrating excellent agreement.

Two-Dimensional Optical Beam Steering With InP-Based Photonic Integrated Circuits

Two-dimensional optical beam steering using an InP photonic integrated circuit has been demonstrated. Lateral beam steering controlled by a 1-D phased array has been made easier through on-chip interferometer monitors. Longitudinal beam steering controlled by the input wavelength has demonstrated an efficiency of 0.14 °/nm. Very fast beam steering (>107 °/s) in both dimensions has been demonstrated as well. As the latest development, a widely tunable sampled-grating distributed Bragg reflector laser has been monolithically integrated and 2-D beam steering has been demonstrated with this on-chip tunable laser source.

Monolithic Integration of a High-Speed Widely Tunable Optical Coherent Receiver

In this letter, a monolithically integrated widely tunable optical receiver is demonstrated. A sampled-grating DBR (SG-DBR) laser, an optical 90-degree hybrid, four high-speed uni-travelling-carrier photodetectors and microstrip transmission lines are integrated on a single InGaAsP/InP chip. A 42-nm tuning range and a 35-GHz detector bandwidth are achieved. Experiments show real-time reception of 40 Gb/s BPSK data.

Phase Noise Characterization of SGDBR Lasers Using Phase Modulation Detection Method With Delayed Self-Heterodyne Measurements

This study employed the coherent phase modulation (PM) detection method to characterize the phase noise of a Sampled-Grating Distributed Bragg Reflector (SGDBR) laser via delayed self-heterodyne (DSH) measurements. We derived the formula for phase-error variance from the FM noise spectrum of the laser and performed measurements on the Distributed Feedback (DFB) and SGDBR lasers. The results confirmed that the DFB laser phase noise is well described by white FM noise while the SGDBR laser has additional frequency fluctuations below 400 MHz. The measurement and simulation results also demonstrated that the low frequency excess noise significantly broadens the linewidth of SGDBR lasers and can degrade the performance of coherent optical communication systems.

Dynamic Modeling of PID Temperature Controller in a Tunable Laser Module and Wavelength Transients of the Controlled Laser

Temperature controllers based on proportion-integration-differentiation (PID) control strategy are widely used in tunable semiconductor laser modules for optical communication systems. A properly designed temperature controller (consisting of a thermoelectric cooler, a thermistor, and control circuits) can maintain a nearly constant laser temperature regardless of the variation of environment temperature ( <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${-}{\rm 20}^{\circ}{\rm C}$</tex> </formula> to 70 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{\circ}{\rm C}$</tex></formula> ). However, it cannot avoid the thermal transients arising from fast changes of tuning-section currents in fast wavelength-switching applications. In these cases, the behavior of the thermal transients in the laser is closely related to characteristics of the temperature controller. In this paper, a dynamic 3-D thermal model of a packaged sampled grating distributed Bragg reflector (SG-DBR) laser module containing a PID temperature controller is presented. This model is based on finite element method. It can simulate the dynamic working process of the temperature controller when the laser is wavelength-switched by current change and the corresponding transient temperature in the laser chip. Transient temperature variations and wavelength drifts of the SG-DBR laser after switching for different PID coefficients are simulated and discussed. Wavelength stabilization times and their influences on the laser's actual application in dynamic optical networks are also discussed.

Influence of facet reflection of SOA on SOA-integrated SGDBR laser

A combined model of the transmission-line laser model (TLLM) and the digital filter approach is developed to simulate the shuttering characteristic of a semiconductor optical amplifier (SOA), which is integrated with a sampled grating distributed Bragg reflector (SGDBR) laser, to create a so called SOA-SGDBR laser. The SOA section acts as a shutter to blank the laser output during wavelength switching events. Simulated results show that the turn-on edge of the SOA blanking process will oscillate when the facet reflection of SOA is relatively high. This phenomenon is also observed by experiments.

Modulation response analysis for a SOA-integrated SGDBR laser by microwave lumped-element circuit modeling approach

A small-signal microwave lumped-element circuit model of a sampled grating distributed Bragg reflector (SGDBR) laser monolithically integrated with a semiconductor optical amplifier (SOA) has been derived from the rate equations of electron and photon density. Compared with the classical circuit model for semiconductor lasers, our model takes into account series cascade action of the SGDBR laser and the SOA. The circuit parameters are extracted by a synthetical approach, which combines the global numerical optimization technique with the analytical extraction method using the measured S-parameters of the integrated device for a determined operating wavelength. The modulation response of the SOA-integrated SGDBR laser has been analyzed by this model including parasitic effect.

New Theoretical Model to Analyze Temperature Distribution and Influence of Thermal Transients of an SG-DBR Laser

A theoretical model capable of calculating transient temperature distribution and simulating the dynamic lasing behavior of a sampled grating distributed Bragg reflector (SG-DBR) tunable laser with the influence of thermal effects into account is described in this paper. Transient 3-D temperature distribution of an SG-DBR laser is modeled by numerically solving heat transfer equations using finite element method. Then, a temperature-dependent dynamic transfer matrix method based model of the laser is developed, which can take thermal effects into account. In this paper, we pay special attention to thermally induced wavelength drift and spectrum evolution under different combinations of tuning currents. Simulated results show that the wavelength drifts are usually in the order of several tens of picometers. Furthermore, when the tuning currents are switched to some certain values, thermal transients may cause mode hop or dual modes lasing. In these cases, total wavelength change induced by thermal effects can be as large as 0.6 nm.

Modeling of Tunable DBRs Lasers Based on Transmission-Line Laser Model

The transmission-line laser model (TLLM) is extended to simulate the three-section distributed Bragg reflector (DBR) lasers, while a combined model of TLLM and digital filter approach is developed to study the sampled grating DBR (SGDBR) lasers. We integrate time-domain TLLM method and frequency-domain transfer matrix method (TMM) in the combined model. Characteristics of tunable DBR lasers and SGDBR lasers are all successfully simulated, such as L-I curve, and static tuning characteristics, which are in good agreement with the published experimental results. This new method is also used to study transient response and lasing spectrum of the devices, which are difficult to be obtained by the frequency domain models.

A Sampled Grating DBR Laser Monolithically Integrated by Using SOAs with 22 mW Output Power and 51 ITU 100 GHz Channels over 43 nm

A sampled grating distributed Bragg reflector (SG-DBR) laser monolithically integrated with semiconductor optical amplifiers (SOAs), which has a tuning range over 43 nm from 1514.05 nm to 1557.4 nm covering 49 continuous and totally 51 ITU 100 GHz standard channels and an output power more than 22 mW for all output wavelengths, is successfully demonstrated.

Frequency drift and instantaneous linewidth broadening of phase-section tuned SG-DBR laser

We experimentally investigate the spectral dynamics of a phase-section tuned sampled-grating distributed Bragg reflector (SG-DBR) laser by using optical heterodyne method. The measured time-resolved spectra of the beat signal illustrate that the beat signal suffers from both frequency drift and instantaneous spectrum broadening, which indicates that the wavelengths of the lightwaves experience drift and jitter. We study the variation of frequency drift and instantaneous linewidth broadening with applied voltages. It is helpful in selection of optimum operating conditions and design of experimental setup. Experimental results demonstrate that the pulse-waveform can be used to reduce the frequency drift by shorting the beating time.