Uncooled Laser Research Articles

Development of S-domain experimental correlation thermal control model and rapid enumeration PID tuning method for uncooled Laser chip module

Uncooled semiconductor lasers are sensitive to ambient temperature variation which makes the PID thermal control for the uncooled semiconductor is complicated. In this work, a kind of enumeration PID tuning method based on S-domain experimental correlation thermal control model for the uncooled semiconductor lasers is introduced. Numeric validation and enumeration PID tuning of S-domain experimental correlation model for uncooled semiconductor are conducted. Results shows that the control accuracy prediction result of the S-domain experimental correlation model has a deviation of 3.6% in contrast with CAE simulation result. The PID tunning speed of rapid enumeration S-domain experimental correlation method is 17,000 times that of CAE method.

High-Reliability Uncooled InGaAlAs Lasers with Unpumped Current Blocking Regions Near Cavity Facets

The facet heating of high-power laser diodes significantly influences device reliability. To mitigate facet temperature, current blocking (CB) regions are employed at both cavity facets of the laser. In this paper, we investigate the device characteristics of uncooled InGaAlAs lasers with CB facets. We observe two types of light versus current (LI) curves and propose corresponding physical models. Our findings demonstrate the high reliability performance of uncooled lasers with proper engineering design and CB process.

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.

Silicon Photonic Phase-Diverse Receiver Enabling Transmission of >Net 250 Gbps/λ Over 40 km for High-Speed and Low-Cost Short-Reach Optical Communications

The fast growth of data traffic in short-reach optical communications drives the demand for high-speed and low-cost optical modules. Here we demonstrate a silicon photonic (SiP) phase-diverse receiver based on our recently proposed asymmetric self-coherent detection (ASCD) scheme with Mach-Zehnder interferometers (MZI). The SiP MZI-ASCD receiver has a hardware-efficient architecture and recovers complex double-sideband signals via the beatings between a signal portion and a delayed signal portion from an asymmetric MZI using only 2 single-ended photodiodes and 2 analog-to-digital converters. The removal of the local oscillator in the direct detection receiver enables low-cost uncooled lasers, whereas the phase diversity closes the gap with coherent detection in terms of electrical spectral efficiency (ESE). Using a SiP MZI-ASCD receiver with a 15 ps delay, we detect a 60 Gbaud single-polarization 16-QAM signal transmitted over 40 km of single-mode fiber (SMF) below 20% overhead (OH) SD-FEC threshold of 2×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> with a net bit rate of 200 Gbps and a record net ESE of 5.86 b/s/Hz per wavelength per polarization. Using a SiP MZI-ASCD receiver with a different delay of 7.5 ps, transmission of single-polarization 16-QAM DSB signal up to 80 Gbaud over 40 km is achieved below 24% OH SD-FEC threshold of 4.5×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> with a record net bit rate of 258 Gbps and a net ESE of 5.31 b/s/Hz per wavelength per polarization.

Deep-learning-enabled high-performance full-field direct detection with dispersion diversity.

Data center interconnects require cost-effective photonic integrated optical transceivers to meet the ever-increasing capacity demands. Compared with a coherent transmission system, a complex-valued double-sideband (CV-DSB) direct detection (DD) system can minimize the cost of the photonic circuit, since it replaces two stable narrow-linewidth lasers with only a low-cost un-cooled laser in the transmitter while maintaining a similar spectral efficiency. In the carrier-assisted DD system, the carrier power accounts for a large proportion of the total optical signal power. Reducing the carrier to signal power ratio (CSPR) can improve the information-bearing signal power and thus the achievable system performance. To date, the minimum required CSPR is ∼7 dB for all the reported CV-DSB DD systems having electrical bandwidths of approximately half of baud rates. In this paper, we propose a deep-learning-enabled DD (DLEDD) scheme to recover the full optical field of the transmitted signal at a low CSPR of 2 dB in experiment. Our proposal is based on a dispersion-diversity receiver with an electrical bandwidth of ∼61.0% baud rate and a high tolerance to laser wavelength drift. A deep convolutional neural network enables accurate signal recovery in the presence of a strong signal-signal beat interference. Compared with the conventional method, the proposed DLEDD scheme can reduce the optimum CSPR by ∼8 dB, leading to a significant signal-to-noise ratio improvement of ∼5.8 dB according to simulation results. We experimentally demonstrate the optical field reconstruction for a 28-GBaud 16-ary quadrature amplitude modulation signal after 80-km single-mode fiber transmission based on the proposed DLEDD scheme with a 2-dB optimum CSPR. The results show that the proposed DLEDD scheme could offer a high-performance solution for cost-sensitive applications such as data center interconnects, metro networks, and mobile fronthaul systems.

High-reliability, High-performance 25 Gb/s Directly Modulated Uncooled Lasers for 5G Wireless Communications

Semiconductor laser diodes are important components for fifth-generation wireless technologies. To meet 5G wireless specifications, ever increasing performance and reliability requirements of each component become necessary to guarantee uptime air service. In this paper, we present highly reliable 25G DFB uncooled lasers that exhibit low threshold current, high single-mode, high bandwidth, and excellent eye pattern for uncooled operations of -40 to 85°C. Ultra-high component reliability is demonstrated to ensure stable operations for 5G mobile communications.

Carrier-assisted differential detection

To overcome power fading induced by chromatic dispersion in optical fiber communications, optical field recovery is a promising solution for direct detection short-reach applications, such as fast-evolving data center interconnects (DCIs). To date, various direct detection schemes capable of optical field recovery have been proposed, including Kramers−Kronig (KK) and signal−signal beat interference (SSBI) iterative cancellation (IC) receivers. However, they are all restricted to the single sideband (SSB) modulation format, thus conspicuously losing half of the electrical spectral efficiency (SE) compared with double sideband (DSB) modulation. Additionally, SSB suffers from the noise folding issue, requiring a precise optical filter that complicates the receiver design. As such, it is highly desirable to investigate the field recovery of DSB signals via direct detection. In this paper, for the first time, we propose a novel receiver scheme called carrier-assisted differential detection (CADD) to realize optical field recovery of complex-valued DSB signals via direct detection. First, CADD doubles the electrical SE compared with the KK and SSBI IC receivers by adopting DSB modulation without sacrificing receiver sensitivities. Furthermore, by using direct detection without needing a precise receiver optical filter, CADD can employ cost-effective uncooled lasers as opposed to expensive temperature-controlled lasers in coherent systems. Our proposed receiver architecture opens a new class of direct detection schemes that are suitable for photonic integration analogous to homodyne receivers in coherent detection.

Compact GaSb/silicon-on-insulator 2.0x μm widely tunable external cavity lasers.

2.0x µm widely tunable external cavity lasers realized by combining a GaSb gain chip with a silicon photonics waveguide circuit for wavelength selection are demonstrated. Wavelength tuning over 58 nm from 2.01 to 2.07 µm is demonstrated. In the silicon photonic integrated circuit, laser feedback is realized by using a silicon Bragg grating and continuous tuning is realized by using two thermally tuned silicon microring resonators (MRRs) and a phase section. The uncooled laser has maximum output power of 7.5 mW and threshold current density of 0.8 kA/cm2. The effect of the coupling gap of the MRRs on tunable laser performance is experimentally assessed. A side mode suppression ratio better than 52 dB over the full tuning range and in the optimum operation point of more than 60 dB is achieved for the laser with weakly coupled MRRs.

MIMO DWDM System Using Uncooled DFB Lasers With Adaptive Laser Bias Control and Postphotodetection Crosstalk Cancellation

A proof-of-principle demonstration of a multiple input-multiple output (MIMO) dense wavelength division multiplexing (DWDM) system is reported. It uses standard uncooled distributed feedback lasers with intensity modulation-direction detection (IM-DD), in which the temperature of each laser is allowed to drift independently within a 50 °C temperature range. A feedback-based laser bias control algorithm is introduced to guarantee acceptable wavelength spacing and a postphotodetection minimum mean square error decoder is applied to cancel the interchannel crosstalk. The relative sensitivity of the MIMO receiver in both a random laser temperature drift scenario and a worst-case scenario are investigated by simulations in MATLAB. Experimental results for a 40-channel × 12.5 Gb/s DWDM system transmitting over 28 km of single-mode fiber with worst possible wavelength distribution prove the feasibility of the technique.

Power-efficient III-V/Silicon external cavity DBR lasers

We report the design and characterization of external-cavity DBR lasers built with a III-V-semiconductor reflective-SOA with spot-size converter edge-coupled to SOI waveguides containing Bragg grating mirrors. The un-cooled lasers have wall-plug-efficiencies of up to 9.5% at powers of 6 mW. The lasers are suitable for making power efficient, hybrid WDM transmitters in a CMOS-compatible SOI optical platform.

Linewidth characteristics of un-cooled fiber grating Fabry–Perot laser controlled by the external optical feedback

The effect of external optical feedback (OFB) on the linewidth characteristics of un-cooled laser module is theoretically investigated. This laser that consists of a Fabry–Perot (FP) laser diode and fiber Bragg grating (FBG) realizes stable operation and relatively low-cost solution. The effects of external OFB and temperature on linewidth are calculated according to their effect on threshold carrier density (Nth). The temperature dependence (TD) of linewidth characteristics is calculated according to TD of laser parameters instead of well-known Parkovin relationship. Results show that, linewidth decreases as the external OFB reflectivity (Rext) increases. A narrow linewidth which is less than 3kHz is obtained for Rext≥0.5. In addition, the linewidth is not largely affected by temperature as compared to the DFB lasers. Also, we found that the linewidth temperature coefficient is 0.04kHz/°C, which is small enough in comparison to 18.5kHz/°C for the DFB laser.

Continuous-wave uncooled interband cascade lasers for gas sensing

Continuous-wave uncooled interband cascade lasers for gas sensing

Pulse Input Response of Uncooled Laser Diodes

Pulse Input Response of Uncooled Laser Diodes

Performance Study of a 980 nm GaAs Based Laser Diode Chip in a Moisture Condensing Environment

This paper presents a performance study done on a semiconductor laser diode in a moisture condensing environment. Devices with laser diodes are used in a wide variety of electronic applications and in the various climatic conditions. The motivation behind this study is a common environmental exposure, where a device using a laser diode is brought into a relatively humid building from a dry, cold, outside environments. Under such conditions, condensation occurs on various components of the device, including the diode, which could affect the laser output power. Device performance could be affected since the laser diode and the lens are susceptible to degradation due to such repetitive condensation conditions. The test vehicle chosen for this study was an optoelectronic package using a 980 nm laser diode. These are used in products for a broad range of markets, including data communications, aerospace, material processing, scientific, and defense industries [Pliska et al., "Wavelength Stabilized 980nm Uncooled Pump Laser Modules for Erbium-Doped Fiber Amplifiers," Opt. Lasers Eng., 43, pp. 271–289; Righetti, 1996, “Amplifiers Pumped at 980 nm in Submarine Applications,” European Conference on Optical Communication, Vol. 3, pp. 75–80; Pfeiffer et al., 2002, "Reliability of 980 nm Pump Lasers for Submarine, Long-haul Terrestrial, and Low Cost Metro Applications," Optical Fiber Communication Conference and Exhibit, pp. 483–484]. These products may be used in environmental conditions that could result in condensation within the product. A hermetic package could address this concern, but it is an expensive option. Nonhermetic packaging for the laser component could help to lower the cost of these devices; however, these packages have important failure mechanisms that are a potential concern. Prior research reported performance studies conducted on similar packages at elevated temperature, humidity, and power conditions using accelerated tests [Pfeiffer et al., 2002, "Reliability of 980 nm Pump Lasers for Submarine, Long-haul Terrestrial, and Low Cost Metro Applications," Optical Fiber Communication Conference and Exhibit, pp. 483–484; Park and Shin, 2004, “Package Induced Catastrophic Mirror Damage of 980nm GaAs High Power Laser,” Mater. Chem. Phys., 88(2-3), pp. 410–416; Fukuda et al., 1992, “Reliability and Degradation of 980nm InGaAs/GaAs Strained Quantum Well Lasers,” Qual. Reliab. Eng., 8, pp. 283–286]. However, studies conducted that specifically addressed condensation measurements have not been previously reported. Hence, an attempt was made to study package performance with condensation, to address the identified concern for the current package. A test method based on a military standard specification was used for this purpose. Elevated temperature and humidity (without condensation) were found to affect the laser power. These were characterized to isolate the effect of condensation alone. The package was subjected to repetitive condensing cycles and laser output power was recorded as a function of time, temperature and humidity. The variation in laser output power due to condensation was observed and quantified. Results showed a temporary power degradation of approximately 5% with condensation. This was a repeatable effect throughout the test time. Visible water droplets were found in various areas of the package after the test cycle. This could lead to potential failure mechanisms during the device life time.

The Effect of Temperature on the Performance of Uncooled Semiconductor Laser Diode in Optical Network

Problem statement: The characteristics of a laser diode are highly dependent on the temperature of the laser chip. Thus, the effect of temperature on the network performance of uncooled semiconductor laser diode are studied by simulating its equivalent electrical circuit, developed from the rate equations that governing optical components directly into an electrical simulation framework. Approach: The simulations are carried out using circuit analysis program named OptiSPICE and Opti System. On this simulation study, the analysis is done based on three parameters in order to determine the quality of received signal which are; center wavelength, bandwidth and output power. Results: As the temperature variance is fed to the laser diode through an external thermal noise, the result will shows that the ambient temperature of laser diode is varied with time. In this case, the performance of laser diode will decreases as the operating temperature increases or, conversely the performance increases as the operating temperature decreases. Conclusion: The circuit design must be simulated using a SPICE engine that incorporates both electrical and optical models, which is Opti SPICE software. It cannot be simulated using traditional software packages because they do not provide sufficient coupling between electrical and optical devices.

Performance of an optical equalizer in a 10 G wavelength converting optical access network

A centralized optical processing unit (COPU) that functions both as a wavelength converter (WC) and optical burst equaliser in a 10 Gb/s wavelength-converting optical access network is proposed and experimentally characterized. This COPU is designed to consolidate drifting wavelengths generated with an uncooled laser in the upstream direction into a stable wavelength channel for WDM backhaul transmission and to equalize the optical loud/soft burst power in order to relax the burst-mode receiver dynamic range requirement. The COPU consists of an optical power equaliser composed of two cascaded SOAs followed by a WC. Using an optical packet generator and a DC-coupled PIN-based digital burst-mode receiver, the COPU is characterized in terms of payload-BER for back-to-back and backhaul transmission distances of 22, 40, and 62 km. We show that there is a compromise between the receiver sensitivity and overload points that can be optimized tuning the WC operating point for a particular backhaul fiber transmission distance. Using the optimized settings, sensitivities of -30.94, -30.17, and -27.26 dBm with overloads of -9.3, -5, and >-5 dBm were demonstrated for backhaul transmission distances of 22, 40 and 62 km, respectively.

Real-time experimental demonstration of low-cost VCSEL intensity-modulated 1125Gb/s optical OFDM signal transmission over 25km PON systems

The feasibility of utilising low-cost, un-cooled vertical cavity surface-emitting lasers (VCSELs) as intensity modulators in real-time optical OFDM (OOFDM) transceivers is experimentally explored, for the first time, in terms of achievable signal bit rates, physical mechanisms limiting the transceiver performance and performance robustness. End-to-end real-time transmission of 11.25 Gb/s 64-QAM-encoded OOFDM signals over simple intensity modulation and direct detection, 25 km SSMF PON systems is experimentally demonstrated with a power penalty of 0.5 dB. The low extinction ratio of the VCSEL intensity-modulated OOFDM signal is identified to be the dominant factor determining the maximum obtainable transmission performance. Experimental investigations indicate that, in addition to the enhanced transceiver performance, adaptive power loading can also significantly improve the system performance robustness to variations in VCSEL operating conditions. As a direct result, the aforementioned capacity versus reach performance is still retained over a wide VCSEL bias (driving) current (voltage) range of 4.5 mA to 9 mA (275 mVpp to 320 mVpp). This work is of great value as it demonstrates the possibility of future mass production of cost-effective OOFDM transceivers for PON applications.

Writing wide bandwidth nonchirped fiber Bragg gratings with high sidelobe suppression ratio by linearly scaling apodization

A linearly scaling optical apodization method for laser beam power profile modulation is induced. Changing an amplitude mask position between the beam-focusing cylindrical lens and the fiber can linearly scale the vertical apodization profile; this, in turn, enables the optimization of the grating apodization. By using this method, an apodized fiber Bragg grating (FBG) that is designed as an uncooled pump laser diode stabilizer with the specifications of 4.5% reflectivity, 1.6 nm bandwidth, and the side-lobe suppression ratio (SLSR) of 30 dB was UV-imprinted with a tiny Gaussian amplitude mask. Using the same apodization method, a nonchirped-type FBG edge filter was written with a very smooth spectrum. The grating specifications of 0.5-dB attenuation bandwidth of 3.6 nm and 96.5% reflectivity were achieved. The half-spectrum ascending bandwidth in the longer wavelength side is 2.2 nm with 27-dB SLSR. The linearly scaling apodization method is highly beneficial for optimizing the apodization process of UV-writing shorter FBGs with strong apodization.

Temperature dependence of turn-on time delay of semiconductor laser diode: Theoretical analysis

AbstractTemperature dependence of the turn-on time delay (ton) of uncooled semiconductor laser diodes biased below and above threshold is analyzed in presence of data pattern effect. We show that even when the laser is biased at or slightly above threshold, the increase in temperature of operation will lead to increase in the threshold carrier (Nth) and consequently the laser diode will be biased below the threshold again and a significant value of ton will be produced. Thus, knowledge about a value of dc-bias current required to achieve zero ton within wide range of temperature degrees is important when considering uncooled laser diode in high-speed optical communication systems. The temperature dependence of ton is calculated according to the temperature dependence of Nth and Auger recombination coefficient (C) and not by the well-know exponentional relationship of threshold current with temperature. The temperature dependence of Nth is calculated according to the temperature dependence of laser cavity parameters. Advanced analytical model is derived in term of carrier density, recombination coefficients and the injection current (Iinj). The validity of proposed model is confirmed by a numerical method. In addition, approximated models are included where under specified assumptions the proposed model reduces to the well-known approximate models of ton. According to our typical values and at a specified value of modulation current, the dc-bias one (Iib) should be increased from Iib = Ith to Iib ≈ 1.25 and 1.5Ith in order to achieve approximately zero ton when the temperature increases from 25°C to 55°C and 85°C, respectively.

Architecture to integrate multiple PONs with long reach DWDM backhaul

This paper demonstrates the feasibility of an architecture that consolidates a number of deployed Passive Optical Network (PON) infrastructures into a long-reach, high-split ratio system which further increases equipment sharing between users. The demonstrated system allows the use of uncooled lasers with possible wavelength drift across a CWDM band (20 nm) with optical amplification and narrow optical filtering with no performance degradation. A complete study of potential implementations was performed with experimental results showing that a target performance of 10-10 could be achieved over 120 km of standard fiber with transmitter wavelengths from 1542 to 1558 nm and DWDM backhaul wavelengths from 1520 to 1535 nm. This gives the potential to support up to 2560 users.