Sampled-grating Distributed Bragg Reflector Research Articles

Timing jitter reduction of silicon hybrid harmonically mode-locked ring laser using an integrated sampled-grating DBR.

An integrated sampled-grating silicon hybrid mode-locked ring laser is proposed for 20-GHz super-mode noise suppression. The dynamics, phase noise, and timing jitter are investigated using a delay differential equation (DDE) model. The results show that the 20-GHz harmonic regime of the proposed structure is significantly increased when the sampled-grating structure is included. Additionally, a better selectivity of the optical modes by a sampled-grating distributed Bragg reflector (SGDBR) leads to more suppression of super-mode noise compared to the long-ring structures with a spectral filter which were previously reported. Compared to previous works, the phase noise is improved by approximately 6 dB and the timing jitter is decreased to less than a third.

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.

Design of Sampled Grating Distributed Bragg Reflector Laser with Wide Tuning Range in L-band

Design of Sampled Grating Distributed Bragg Reflector Laser with Wide Tuning Range in L-band

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.

Fast Reconfigurable SOA-Based Wavelength Conversion of Advanced Modulation Format Data

We theoretically analyze the phase noise transfer issue between the pump and the wavelength-converted idler for a nondegenerate four-wave mixing (FWM) scheme, as well as study the vector theory in nonlinear semiconductor optical amplifiers (SOAs), in order to design a polarization-insensitive wavelength conversion system employing dual co-polarized pumps. A tunable sampled grating distributed Bragg reflector (SG-DBR) pump laser has been utilized to enable fast wavelength conversion in the sub-microsecond timescale. By using the detailed characterization of the SGDBR laser, we discuss the phase noise performance of the SGDBR laser. Finally, we present a reconfigurable SOA-based all-optical wavelength converter using the fast switching SGDBR tunable laser as one of the pump sources and experimentally study the wavelength conversion of the single polarization quadrature phase shift keying (QPSK) and polarization multiplexed (Pol-Mux) QPSK signals at 12.5-Gbaud. A wide tuning range (&gt;10 nm) and less than 50 ns and 160 ns reconfiguration time have been achieved for the wavelength conversion system for QPSK and PM-QPSK signals, respectively. The performance under the switching environment after the required reconfiguration time is the same as the static case when the wavelengths are fixed.

Design and fabrication of widely tunable sampled grating DFB laser diode integrated with sampled grating distributed Bragg reflector

ABSTRACTA sampled grating distributed feedback (SGDFB) laser diode integrated with a sampled grating distributed Bragg reflector (SGDBR) is designed, fabricated, and characterized. In the proposed laser diode, only two tuning currents, one into the longitudinal mode tuning electrode and the other into the SGDBR tuning electrode, are required, which provides an easier tuning mechanism. A split‐step time‐ domain modeling is used to simulate the designed tunable laser diode and it is shown that a tuning range of about 27 nm with the side mode suppression ratio (SMSR) larger than 50 dB for the particular device. The designed SGDFB‐SGDBR laser diode is fabricated using butt‐coupling interface between the active and passive waveguides in an InGaAsP/InP platform. The tuning range of the fabricated device is about 20 nm with the SMSR of about 30 dB. The fiber‐coupled output power is about 8mW for the tuned lasing modes. The measured results exhibit the proof‐of‐concept of the SGDFB‐SGDBR laser diode despite the room for improvement in the design and fabrication processes. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:252–257, 2017

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.

Mode-locking and frequency mixing at THz pulse repetition rates in a sampled-grating DBR mode-locked laser.

We report a sampled grating distributed Bragg reflector (SGDBR) laser with two different gratings which mode-lock independently at respective pulse repetition frequencies of 640 and 700 GHz. The device operates in distinct regimes depending on the bias conditions, with stable pulse trains observed at 640 GHz, 700 GHz, the mean repetition frequency of 666 GHz, and the sum frequency of 1.34 THz (due to nonlinear mixing). Performance is consistent and highly reproducible with exceptional stability observed over wide ranges of drive bias conditions. Furthermore, a monolithically integrated semiconductor optical amplifier is used to amplify the pulse trains, providing an average output power of 46 mW at 666 GHz.

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.

Pilot-Tone-Aided Transmission of High-Order QAM for Optical Packet Switched Networks

We investigate novel pilot-aided transmission of high-order quadrature amplitude modulation (QAM) modulation formats for optical packet-switched networks. The proposed modulation scheme employs a pilot tone operating at the baud rate for noncoherent reception that is highly immune to laser phase noise. The results show that the system performance equivalent to static operation is achieved 5&#xA0;ns after wavelength switching of a sampled grating distributed Bragg reflector (SG-DBR) tunable laser.

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.