SG-DBR Laser Research Articles

Temperature distribution of an SG-DBR laser cooled by a thermoelectric cooler

We introduce a one-dimensional analytical model to determine the steady-state thermal behavior of a sampled grating distributed Bragg reflector laser coupled to a thermoelectric element cooler. The governing equations are a system of ordinary differential equations that can be solved analytically. This method can easily be used when the laser is integrated with more functional elements, e. g., semiconductor optical amplifiers and amplitude modulators. The results are verified by the numerical finite element method and experimental data reported by other researchers. A comparison between the results of the analytical and numerical methods reveals the high consistency between them.

Photonic integrated circuit with sampled grating lasers fabricated on a generic foundry platform for broadband terahertz generation.

We demonstrate a monolithically integrated photonic integrated circuit (PIC) for terahertz spectroscopy with wide spectral bandwidth. The PIC includes two widely tunable sampled grating DBR (SG DBR) lasers, semiconductor optical amplifiers (SOAs), and passive components to combine signals. The SG DBR lasers cover 22 nm and 24 nm tuning range, respectively, with 4 nm overlap in the C band. The side mode suppression ratio (SMSR) exceeds 37 dB with a linewidth below 4.3 MHz. We used the PIC to generate THz radiation with a state-of-the-art photodiode emitter. The measured THz power spectrum between 0.03 and 1 THz compares well with the spectrum generated with commercial tunable laser sources. This demonstrates the suitability of our PIC for future miniaturized continuous wave (cw) THz systems.

Demonstration of high output power DBR laser integrated with SOA for the FMCW LiDAR system.

We demonstrated a high output power distributed-Bragg-reflector (DBR) laser integrated with semiconductor optical amplifier (SOA) for the frequency-modulated continuous-wave (FMCW) light detection and ranging (LiDAR) system. In order to acquire higher output power, different from the conventional SG-DBR laser, the front mirror in this work is a section of uniform grating to get higher transmissivity. Therefore, the output power of the laser reaches 96 mW when the gain current and SOA current are 200 mA and 400 mA, respectively. Besides, we fabricated a spot size converter (SSC) at the laser output port to enhance the fiber coupling efficiency, which reached 64% coupled into the lensed fiber whose beam waist diameter is 2.5 μm. A tuning range of 2.8 nm with free spectral range (FSR) of 0.29 nm and narrow Lorentzian linewidth of 313 kHz is achieved. To realize distance and velocity measurement, we use the iterative learning pre-distortion method to linearize the frequency sweep, which is an important part of the FMCW LiDAR technology.

Widely Tunable Laser on an InP Photonic Integrated Circuit

We present a widely tunable laser design based on three intra-cavity Mach-Zehnder interferometers. The laser has been fabricated in a multi-project wafer run and does not require high precision lithography, as needed for SGDBR lasers. We demonstrate 20 nm of tuning range with output powers of approximately 1 mW in fiber. With an excess of 30 dB in side-mode suppression ratio, the laser can find applications in gas spectroscopy, which is also supported by an absorption measurement in an HCN-filled gas cell. Tuning has been demonstrated solely relying on electro-optical phase modulators, providing a potentially faster tuning scheme than temperature or current based tuning mechanisms.

High-power sampled-grating-based master oscillator power amplifier system with 23.5 nm wavelength tuning around 970 nm.

Tunable high-power diode lasers are key components in various established and emerging applications. In this work, we present a compact hybrid master oscillator power amplifier (MOPA) laser system. The system utilizes a tunable GaAs-based sampled-grating (SG) distributed Bragg reflector (DBR) laser as the master oscillator (MO), which emits around a wavelength of 970nm in a single longitudinal mode with a spectral width below 20pm. The SG-DBR laser consists of two SGs, each of which can be thermally tuned with microheaters. By tuning one of the two SGs, a discrete wavelength tuning of 21.1nm can be obtained with a Vernier mode spacing of about 2.3nm. By tuning both SGs, 23.5nm of quasi-continuous tuning is obtained, with a mode spacing of about 115pm. The coupling of the beam emitted by the MO into a tapered power amplifier provides an amplified output power in the watt range having a nearly diffraction-limited beam with a propagation factor of M1/e22=1.6. The combination of high power and wide wavelength tuning in a compact system makes this light source ideal for, among other things, nonlinear frequency conversion.

Investigation Into the Phase Noise of Modulated Grating Y-Branch Lasers

Theoretical and experimental investigations of the phase noise of modulated grating Y-branch (MGY) lasers are presented, mainly focusing on influence of the additive Vernier effect. A comprehensive simulation model based on transmission line model is developed, taking into account the spontaneous emission noise in the active section, the carrier shot noise in the passive sections, the 1/f noise for the injection currents and the detuned-loading effect induced by the grating reflectors. The phase noise characteristics of the MGY laser and the SGDBR laser are simulated, and compared to find the difference between the additive and multiplicative Vernier effects. The results clearly indicate that the MGY laser exhibits more serious phase noise due to using the additive Vernier effect. It has been found that different super-mode selection methods lead to different reflection characteristics, which play an important role in determining the phase noise. Finally, the phase noise of the MGY laser and the SGDBR laser are measured by using a coherent phase noise measurement technique, the experimental results turn out to be in agreement with the simulations.

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 (>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.

Concept and numerical simulations of a widely tunable GaAs‐based sampled‐grating diode laser emitting at 976 nm

Tunable diode lasers are essential components in various optical systems. The authors present a concept and simulations of a four-section, widely tunable GaAs-based sampled-grating (SG) distributed-Bragg reflector (DBR) laser emitting at 976 nm. This work includes the design approach of the SG reflectors and the simulation of the behaviour of the modes in the active cavity during the wavelength tuning process. Parameters such as the lasing wavelength, threshold current and the gain of the lasing and of the adjacent side modes during the tuning are presented. The numerical results presented suggest a tunability of at least 17 nm, with a threshold current change of only 2.5 mA and single-mode operation over the entire tuning range, without the need of simultaneous adjustments of the phase section. Finally, the authors present early experimental results of a developed GaAs-based vertical structure, providing a high coupling coefficient of $\kappa = 240 \, \hbox{c}\hbox{m}^{ - 1}$κ=240 cm-1, thus suitable for implementation of an SG-DBR laser design.

Effects of phase noise of monolithic tunable laser on coherent communication systems

We investigate the effects of different phase noise processes of SGDBR laser on coherent systems. The SGDBR device operated well with QPSK modulation at 5 Gbaud, while the performance of 16-QAM was significantly degraded due to excess noise. The white FM noise mainly defines the ultimate performance of coherent reception, but the low frequency excess noise can potentially degrade the performance of systems that employ 16-QAM format at 5 Gbaud.

Characterization of a tunable three-section slotted Fabry–Perot laser for advanced modulation format optical transmission

In this paper we report on the characterization of a narrow linewidth three-section tunable slotted Fabry–Perot laser. The SMSR of the 25 available 100-GHz ITU channels is above 30 dB, whereas their average linewidth is 538 kHz with a maximum below 800 kHz. The RIN spectra of six different channels are also measured and a maximum average RIN of −135 dB/Hz is obtained. The linewidth effect of the laser in a 1.25 Gb/s DPSK transmission system is investigated by comparing the performance between the slotted Fabry–Perot laser and a commercial SG-DBR laser respectively. Error free transmission of the slotted Fabry-Perot laser shows the benefit of the narrow linewidth of the device for systems employing advanced modulation formats.

Linewidth of SG-DBR laser and its effect on DPSK transmission

In this paper the linewidth of widely tunable SG-DBR lasers has been investigated theoretically and experimentally. We demonstrate experimentally the importance of obtaining low linewidth operation for the application of SG-DBR laser with advanced modulation format transmission. This is achieved by choosing two sets of tuning currents for an SG-DBR laser that give the same wavelength channel and good SMSR, but different linewidths. When the laser is employed in a DPSK system only the operating point (the set of drive currents used to obtain specific output characteristics) that portrays low linewidth achieves error free transmission. This work shows that although calibration of tunable lasers is normally based on achieving sufficient SMSR and output power, it will be important to consider the linewidth parameter as these lasers begin to be used in more spectrally efficient WDM systems employing advanced modulation formats. The simulation results illustrate that the operating points which achieve narrow linewidth are correlated with those that exhibit low threshold current. This finding may be used for calibration of SG-DBR lasers to achieve minimum linewidth at each operating wavelength.

Effects of the electrical signals generated in passive sections of SG-DBR lasers

We investigate electrical signals generated in passive sections of a sampled-grating distributed Bragg reflector laser. A DC voltage is applied to one of the passive sections, and a negative current in the circuit is observed with a low voltage biased. Experimental results demonstrate that the negative current is generated due to photovoltaic effect. This effect could be enhanced or suppressed by adjusting the parameters of p–n junctions in the passive sections. On account of this effect, the passive sections can be utilized as inner photodetectors to control the laser power, which greatly simplifies the laser packaging and reduces the cost.

Time-Resolved $Q$-factor Measurement and Its Application in Performance Analysis of 42.6 Gbit/s Packets Generated by SGDBR Lasers

We demonstrate a novel time-resolved Q-factor measurement technique and demonstrate its application in the analysis of optical packet switching systems with high information spectral density. For the first time, we report the time-resolved Q-factor measurement of 42.6 Gbit/s AM-PSK and DQPSK modulated packets, which were generated by a SGDBR laser under wavelength switching. The time dependent degradation of Q-factor performance during the switching transient was analyzed and was found to be correlated with different laser switching characteristics in each case.

Direct modulation bandwidth enhancement of strongly injection-locked SG-DBR laser

Significant enhancement in the direct amplitude modulation bandwidth of an SG-DBR laser has been demonstrated under strong injection-locking conditions, where the wavelength detuning between the master and the free-running SG-DBR slave laser is varied from −8.58 to 13.6 nm. It is demonstrated that the relaxation resonance frequency of a strongly injection-locked SG-DBR laser increases from 1.05 GHz for the free-running case to over 20 GHz.

Analysis on steady-state characteristics of widely tunable SG-DBR laser with residual facet reflectivity model

An efficient way to model the distributed Bragg reflector type of semiconductor devices with residual facet reflectivity is presented. Particularly, to improve the performance of such laser from two different ways of tuning—the differential or simultaneous tuning of two reflectors—the impacts of residual facet reflectivity on the sampled grating, and the static characteristics of such laser, including tuning behavior, output power, and side mode suppression ratio, are discussed. It revealed that the position of the facet relative to the gratings as well as their reflectivities are important parameters and should be carefully designed and fabricated to ensure good performance for such devices.

Widely Tunable Separate Absorption and Modulation Wavelength Converter With Integrated Microwave Termination

A widely tunable wavelength converter utilizing a separate absorption and modulation configuration and only dc bias connections is demonstrated. The device integrates an SG-DBR laser with a traveling-wave electroabsorption modulator and an optically pre-amplified receiver and introduces a simplified bias scheme by the inclusion of passive resistor and capacitor circuit elements. We discuss a the design of these passive elements and their compatibility with fabrication of photonic integrated circuits. The device demonstrates over 12 GHz optical bandwidth and error free 10 Gb/s wavelength conversion is achieved with less than 2.5 dB power penalty over 25 nm of output tuning.

A single regrowth integration platform for photonic circuits incorporating tunable SGDBR lasers and quantum-well EAMs

A monolithic integration platform is demonstrated for high functionality photonic circuits that include quantum-well electroabsorption modulators, semiconductor optical amplifiers, and widely tunable lasers. The platform is based on the selective removal of a set of active quantum wells located above an optical waveguide layer. The waveguide layer contains a second set of quantum wells to be used in modulator regions. Fabrication requires only a single blanket InP regrowth

Less than 5-ns wavelength switching with an SG-DBR laser

We achieve fast wavelength switching between all channel combinations of a 64-channel sampled-grating distributed Bragg reflector laser in less than 5 ns. The laser was designed to have low tuning currents and efficient heat extraction in order to reduce parasitic thermal effects. We also report on the behavior of the front and back mirror pre-emphasis amplitudes required for the fast switching.

High efficiency widely tunable SGDBR lasers for improved direct modulation performance

We report on two novel approaches to improve the differential quantum efficiency (DQE) of widely tunable 1.55-/spl mu/m lasers: the bipolar cascade sampled grating distributed Bragg reflector (BC-SGDBR) laser and the gain-levered SGDBR (GL-SGDBR) laser. Each is fabricated on a robust InGaAsP/InP photonic integrated circuit platform. The lasers demonstrate improved direct modulation performance over conventional SGDBR lasers. The BC-SGDBR laser was also monolithically integrated with a semiconductor optical amplifier and photodetector receiver in order to perform wavelength conversion. Error free wavelength conversion at 2.5 Gb/s and improvements in conversion efficiency are demonstrated.

Widely tunable monolithically integrated all-optical wavelength converters in InP

Design, fabrication, and characterization of monolithically integrated widely tunable all-optical wavelength converters in InP is reported. The devices are based on the SGDBR laser integrated with different MZI-SOA wavelength converters. Error-free wavelength conversion at 2.5 Gbps was demonstrated over 50 nm input and 22 nm output wavelength range. Static operation, extinction ratio enhancement, signal reamplification, dynamic range, and chirp properties were characterized as well.