Modulated Semiconductor Lasers Research Articles

Researching the 915 nm high-power and high-brightness semiconductor laser single chip coupling module

Based on the high-speed development of the fiber laser in recent years, the development of researching 915 nm semiconductor laser as main pumping sources of the fiber laser is at a high speed. Because the beam quality of the laser diode is very poor, the 915 nm laser diode is generally based on optical fiber coupling module to output the laser. Using the beam-shaping and fiber-coupling technology to improve the quality of output beam light, we present a kind of high-power and high-brightness semiconductor laser module, which can output 13.22 W through the optical fiber. Based on 915 nm GaAs semiconductor laser diode which has output power of 13.91 W, we describe a thoroughly detailed procedure for reshaping the beam output from the semiconductor laser diode and coupling the beam into the optical fiber of which the core diameter is 105 μm and the numerical aperture is 0.18. We get 13.22 W from the output fiber of the module at 14.5 A, the coupling efficiency of the whole module is 95.03% and the brightness is 1.5 MW/cm2 -str. The output power of the single chip semiconductor laser module achieves the advanced level in the domestic use.

Tunable Ultra-Broadband Microwave Frequency Combs Generation Based on a Current Modulated Semiconductor Laser Under Optical Injection

We have demonstrated and characterized the generation of ultra-broadband microwave frequency combs (MFCs) based on a current modulated distributed feedback semiconductor laser (DFB-SL) subject to optical injection, and the comb spacing of MFCs can be tuned easily through adjusting the modulation frequency $\text{f}_{m}$ . For the DFB-SL under only current modulation with modulation frequency $\text{f}_{m }= 1.2$ GHz and modulation power $\text{P}_{m }= 22$ dBm, the generated MFC has a bandwidth of about 15.6 GHz within ±5.0 dB amplitude variation. Further, introducing continuous-wave optical injection into the current modulated DFB-SL with injection power $\text{P}_{i }= 1170~\mu \text{W}$ and no frequency detuning between the injection light frequency and the oscillation frequency of the free-running DFB-SL, the bandwidth of MFC can be increased to 57.6 GHz. Through measuring the single sideband (SSB) phase noises of some representative comb lines, the performances of the MFCs generated before and after introducing optical injection are compared, and the SSB phase noises at 10 kHz offset frequency can be increased by 10 dB for the harmonics with frequencies of more than $40\text {f}_{m}$ after adopting optical injection. Moreover, the influences of operation parameters on the bandwidths of MFCs are analyzed, and the optimized parameter range for generating ultra-broadband MFCs has been determined.

Cover Image, Volume 7, Issue 4

Optical fiber has a long and rich history. Even before the electromagnetic wave equation was revealed by Maxwell in 1865, Tyndall – building on the efforts of Colladon and Babinet – popularized total internal reflection to a broad audience, thanks in part to our ability to ‘see’ light. Proposed for use in several imaging applications in the early 20th century, a pivotal moment in the development of optical fiber was the invention of the fiber cladding, which enabled the control of a dielectric waveguide's mode distribution. The 1960's saw the development of the technologies, such as single mode fiber and semiconductor lasers, required to build a prototypical optical communication system, while developments in fiber fabrication processes in the 1970's led to the very first low‐loss fiber. With further reductions in the transmission loss in fibers, coupled with the development of the erbium doped fiber amplifier (EDFA) which obviated the need for electrical repeaters, the world became ‘fiberized’ by the 1990's. The systems of today continue to scale in both power and bandwidth, enabled in part by new developments in optical fibers, from the perspective of both the waveguide and the materials comprising them. For further information see “Glass: The Carrier of Light – A Brief History of Optical Fiber” in this issue by J. Ballato and P. Dragic. Cover credits: Christie Klinger and Payton Focken, Visualization Lab Graphics Services, University of Illinois at Urbana‐Champaign. image

Transversely diode-pumped -switched Nd : YAG laser with injection of radiation from a single-frequency semiconductor laser

A -switched Nd : YAG laser with a high-power transverse diode pumping and injection of seed radiation generated by a single-frequency semiconductor laser is described. The threshold seed radiation power at which the -switched Nd : YAG switches to the single-frequency mode is (radiation intensity . With increasing injection power, the spectral and power characteristics of the -switched laser almost do not change at a constant excitation of its active medium. The spectral linewidth of the -switched Nd : YAG laser with injection from a TLD-1060-14BF single-frequency semiconductor laser module does not exceed (wavelength .

Theoretical analysis of an optoelectronic oscillator based on a directly modulated semiconductor laser

We numerically simulated the performance of an optoelectronic oscillator (OEO) based on a directly modulated (DM) semiconductor laser. The standard coupled rate equations were used to describe the DM-OEO modulation process. A rate-equation-based analysis is a means of analyzing OEO performance that is a variation of the method used to assess standard OEOs that employ external modulators. We modeled an OEO with an open-loop response and calculated the oscillation threshold gain and amplitude of the DM-OEO as functions of the DC bias current. By using this method, we were able to optimize OEO operation conditions for a given laser DC bias level in both gain- and amplitude-limited operating environments.

Towards high-order modulation using complex modulation of semiconductor lasers.

Optical communication using high-speed on-off-keying signal by directly modulated semiconductor lasers (DML) was one of the most significant breakthroughs for telecommunication in 1960s. The wide deployment of 2.5-Gb/s per-channel transoceanic optical fiber links in 1990s drove the internet as a global phenomenon. However, the detrimental frequency chirp of DML prevents its application to the subsequent internet capacity evolution. Today, the state-of-the-art long-haul optical transponder uses external modulators to support high-order complex modulation. In contrast, this paper shows that the "detrimental" chirp effect can be exploited to generate complex modulation with a single DML, which achieves dramatic sensitivity gain of signal-to-noise-ratio compared to the conventional intensity modulation of DML. By using large chirp parameters, complex-modulated DML paves an attractive pathway towards high-order pulse-amplitude modulation with an ultra-low transmitter cost, which has great potential in future medium reach optical communications.

Enhancement of the phase-modulation range by using cascaded injection-locked semiconductor lasers

The phase modulation of an injection-locked semiconductor laser can be controlled by tuning the injection-locking parameters. However, the phase-modulation range is limited to 180°, which significantly hinders its widespread application. In this study, we investigated the phase-modulation characteristics of a single stage of an injection-locked laser configuration by considering a slave laser’s bias control as a tuning parameter. Herein, we propose cascaded injection-locked laser configurations to enhance the phase-modulation range and theoretically demonstrate that the achievable phase-modulation range can be increased. The output of the slave laser is used as the input of the next slave laser to produce an accumulated phase modulation. The results show that a phase modulation of 360° can be achieved using the cascaded configurations; moreover, the number of cascaded configurations required to achieve this range is determined for specific laser parameters.

Harmonic and intermodulation distortions and noise associated with two-tone modulation of high-speed semiconductor lasers

We present results of modeling and simulation of the harmonic and intermodulation distortions as well as the intensity noise of high-speed semiconductor lasers under two-tone modulation. Multiple quantum-well lasers are considered, which are characterized by large differential gain and a modulation bandwidth of about 25GHz. The study is based on the rate equation model of semiconductor lasers excited by injection current with two sinusoidal tones separated by a radio frequency. The modulated laser signal is modeled in both the time and frequency domains. The time domain characteristics include the fluctuating waveform, while the frequency domain characteristics include the frequency spectrum of the relative intensity noise (RIN), carrier-to-noise ratio, modulation response, harmonic distortion, and the second- and third-order intermodulation distortions (IMD2 and IMD3). The analysis is performed for three frequencies of 5, 15, and 24 GHz, which are, respectively, lower, comparable, and higher than the laser relaxation frequency. The range of the modulation depth covers the regimes of small and large-signal modulation. We show that both RIN and IMD3 of two-modulated laser are minimum when the modulation frequency is 5GHz, and maximum when the modulation frequency is 24 GHz. The second-order harmonic distortion, IMD2, and IMD3 values are larger in the vicinity of relaxation oscillations and increase with the modulation index, especially under large-signal modulation.

光谱稳定的低功耗980 nm单模泵浦源半导体激光器

Due to many special applications,the 980 nm pumping source semiconductor lasers should have the characteristics of spectrum stability,low power consumption. Based on the optimization design of a 980 nm single mode semiconductor laser cavity length,cavity reflectivity and fiber Bragg grating reflectivity,the low threshold,high power 980 nm fiber Bragg grating external cavity semiconductor lasers with wavelength stability are developed. The pigtail output power of the low power consumption single mode semiconductor lasers with wavelength stability can reach 51 m W under 100 m A,3 d B bandwidth of 0. 16 nm. The side mode suppression ratio( SMRS) is greater than40 d B. The pigtail output power of the device can reach 120 m W under 250 m A.

Dual-Mode Semiconductor Lasers and Their Applications in Optical Clock Recovery and Photonic Microwave Generation

As a compact multi-functional device, monolithic integrated multi-section semiconductor laser has a wide range of applications in optical communication systems and microwave photonics with its advantages in cost, size, power consumption and integration possibilities with other components. In this paper, we will review the design and characteristics of monolithically integrated dual mode semiconductor laser, with special emphasis on amplified feedback lasers (AFL). Then, their application in optical clock recovery and high frequency photonic microwave generation will be discussed

Transient mode competition in directly modulated DFB semiconductor laser

A new effect of transient mode competition in directly modulated DFB laser based on equivalent phase-shift (EPS) technique is presented and studied. Since there are multi-order reflections in EPS structure and if the 0th order subgrating is properly designed, the transient lasing of 0th order will occur during the rising time of the injection current. As a result, transient mode competition between -1st order (main mode) and 0th order will occur accordingly. This can consume redundant carrier and suppress the transient relaxation oscillation, which may be applied in some areas like on-off switching modulation of DFB semiconductor lasers. As an example, an equivalent π phase shift (π-EPS) is carefully designed to realize the effect. In such a laser the 0th order wavelength is in the margin of the material gain region and the -1st order wavelength is around the gain peak, while the stable single longitudinal mode (SLM) operation of the -1st order is guaranteed. The simulation investigation is performed. Good results with suppressed relaxation oscillation and 1.25 Gb/s directly on-off modulation (32 dB extinction ratio) are demonstrated. We believe it provides a new kind of method for on-off switching with high extinction ratio and weak relaxation oscillation.

Analysis of the Spike Rate and Spike Correlations in Modulated Semiconductor Lasers With Optical Feedback

We investigate experimentally how changes in the external cavity length and dc current affect the mean interspike-interval (ISI) in a modulated semiconductor laser with optical feedback operating in the low-frequency fluctuations regime. The variation of the mean ISI with the modulation frequency is shown to be more pronounced when time delay and dc current allow for low spike rate. We use the method of ordinal symbolic analysis to examine how time correlations (among three, four and five consecutive laser spikes) change with the spike rate. This method is able to capture subtle changes, otherwise hidden in the dynamics. We find that higher spike rates wash out the effects of the modulation in the time correlations. Simulations using the Lang and Kobayashi model are in good qualitative agreement with the experimental observations.

Rate Equation Analysis of <italic>Q</italic>-Modulated Strongly Injection-Locked Whistle-Geometry Ring Lasers

In a monolithically integrated strongly injection-locked whistle-geometry semiconductor ring laser, modulating the photon lifetime or the optical losses in the cavity can lead to higher modulation bandwidth and complete elimination of low-frequency roll-off, which is commonly observed during the current modulation of injection-locked semiconductor lasers. Rate equation analysis is performed to show that modulating the photon-lifetime is significantly more advantageous than the conventional injection-current modulation. Different schemes to achieve photon-lifetime or optical-loss modulation in a strongly injection-locked whistle-geometry ring laser are discussed.

Calibration-free absolute frequency response measurement of directly modulated lasers based on additional modulation.

A calibration-free electrical method is proposed for measuring the absolute frequency response of directly modulated semiconductor lasers based on additional modulation. The method achieves the electrical domain measurement of the modulation index of directly modulated lasers without the need for correcting the responsivity fluctuation in the photodetection. Moreover, it doubles measuring frequency range by setting a specific frequency relationship between the direct and additional modulation. Both the absolute and relative frequency response of semiconductor lasers are experimentally measured from the electrical spectrum of the twice-modulated optical signal, and the measured results are compared to those obtained with conventional methods to check the consistency. The proposed method provides calibration-free and accurate measurement for high-speed semiconductor lasers with high-resolution electrical spectrum analysis.

The mode competition in a two-mode semiconductor laser

In this paper the dynamics of a two-mode semiconductor laser model is considered. The dynamic evolution of a two -mode semiconductor laser can be described by nonlinear rate equations, which take in account the gain saturation. Changes in parameters of the system can lead to changes of the character of the solutions. Qualitative analysis of the system is used for investigating the typical bifurcations and allowed conditions for the existence of different types of mode oscillations in the system. The phase portraits of steady state solution of system are plotted using numerical methods. The competition phenomenon between modes is observed.

Simultaneous Computation of Two Independent Tasks Using Reservoir Computing Based on a Single Photonic Nonlinear Node With Optical Feedback.

In this brief, we numerically demonstrate a photonic delay-based reservoir computing system, which processes, in parallel, two independent computational tasks even when the two tasks have unrelated input streams. Our approach is based on a single-longitudinal mode semiconductor ring laser (SRL) with optical feedback. The SRL emits in two directional optical modes. Each directional mode processes one individual task to mitigate possible crosstalk. We illustrate the feasibility of our scheme by analyzing the performance on two benchmark tasks: 1) chaotic time series prediction and 2) nonlinear channel equalization. We identify some feedback configurations for which the results for simultaneous prediction/classification indicate a good performance, but with slight degradation (as compared with the performance obtained for single task processing) due to nonlinear and linear interactions between the two directional modes of the laser. In these configurations, the system performs well on both tasks for a broad range of the parameters.

High-Capacity Directly Modulated Optical Transmitter for 2-μm Spectral Region

The 2-μm wave band is emerging as a potential new window for optical telecommunications with several distinct advantages over the traditional 1.55 μm region. First of all, the hollow-core photonic band gap fiber (HC-PBGF) is an emerging transmission fiber candidate with ultra-low nonlinearity and lowest latency (0.3% slower than light propagating in vacuum) that has its minimum loss within the 2-μm wavelength band. Second, the thulium-doped fiber amplifier that operates in this spectral region provides significantly more bandwidth than the erbium-doped fiber amplifier. In this paper, we demonstrate a single-channel 2-μm transmitter capable of delivering >52 Gbit/s data signals, which is twice the capacity previously demonstrated. To achieve this, we employ discrete multitone modulation via direct current modulation of a Fabry-Perot semiconductor laser. The 4.4-GHz modulation bandwidth of the laser is enhanced by optical injection locking, providing up to 11 GHz modulation bandwidth. Transmission over 500-m and 3.8-km samples of HC-PBGF is demonstrated.

Theoretical analysis of semiconductor ring lasers with short and long time-delayed optoelectronic and incoherent feedback

We report results on the asymptotic, bifurcation and numerical analysis of semiconductor ring lasers with negative optoelectronic feedback or incoherent optical feedback. We find that the dynamical behavior of both systems can be adequately described by two differential equations and one map with time delay on time-scales longer than the relaxation oscillations. On these timescales, the dynamics for both types of feedback is identical. We study the stationary solutions of this model and are able to obtain the analytical expressions of all local bifurcations. As we vary the feedback strength for small delay times comparable to the period of relaxation oscillations, the devices under consideration in the paper display both continuous wave operation and a period-doubling route to chaos. The intensities of two counter propagating modes of both systems exhibit in-phase chaotic behavior similar to single mode semiconductor lasers. However, for long delay times, the counter propagating modes show anti-phase chaotic oscillations. This anti-phase chaotic regime does not involve carrier dynamics and is a result of the bistable character of the semiconductor ring laser.

Modulator-free quadrature amplitude modulation signal synthesis.

The ability to generate high-speed on–off-keyed telecommunication signals by directly modulating a semiconductor laser’s drive current was one of the most exciting prospective applications of the nascent field of laser technology throughout the 1960s. Three decades of progress led to the commercialization of 2.5 Gbit s−1-per-channel submarine fibre optic systems that drove the growth of the internet as a global phenomenon. However, the detrimental frequency chirp associated with direct modulation forced industry to use external electro-optic modulators to deliver the next generation of on–off-keyed 10 Gbit s−1 systems and is absolutely prohibitive for today’s (>)100 Gbit s−1 coherent systems, which use complex modulation formats (for example, quadrature amplitude modulation). Here we use optical injection locking of directly modulated semiconductor lasers to generate complex modulation format signals showing distinct advantages over current and other currently researched solutions.

High-Bandwidth Operation of Optically Controlled Semiconductor Laser With External Cavity

A high-speed optically controlled semiconductor laser was numerically and experimentally demonstrated by integrating a phase controllable external cavity with a single mode semiconductor laser. It was numerically confirmed that the laser source can be operated at up to 50 GHz when the lasing-mode gain was directly controlled by an optical signal. The optically controlled semiconductor laser, which has an optimally designed structure using the results from the numerical analysis, was fabricated. A broad 3-dB bandwidth of >30 GHz was experimentally confirmed, which was the limit of the measurement system bandwidth of the experimental setup.