光谱稳定的低功耗980 nm单模泵浦源半导体激光器

Theoretical investigation into spectral characteristics of a semiconductor laser with dual-FBG external cavity

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

The attainment of a high power, diffraction limited output from semiconductor laser arrays is currently a subject of great interest for many applications such as increasing optical fiber launch efficiency and improvement of solid state laser pumping. The output from a single stripe, single mode semiconductor laser is essentially diffraction limited but power output from these devices is limited due to problems with dissipation of heat from the lasing region, the current highest cw operating power being 100 mW. Diode laser arrays and bars present a solution to the problem of higher output powers but their output is generally far from diffraction limited.

With a proper perturbation, even a single-mode semiconductor laser can exhibit highly complex dynamical characteristics ranging from stable, narrow-linewidth oscillation to broadband chaos. In recent years, three approaches to invoke complex nonlinear dynamical states in a single-mode semiconductor laser have been thoroughly studied: optical injection, optical feedback, and optoelectronic feedback. In each case, the nonlinear dynamics of the semiconductor laser depends on five intrinsic laser parameters and three operational parameters. The dynamical state of a given laser can be precisely controlled by properly adjusting the three operational parameters. This ability to control the dynamical behavior of a laser, combined with the understanding of its characteristics, opens up the opportunity for a wide range of novel applications. This paper illustrates the utilization of the rich nonlinear dynamics of single-mode semiconductor lasers by focusing on the period-one oscillation for its applications in tunable photonic microwave generation, AM-to-FM conversion, and dual-frequency precision Doppler lidar.

High single-mode selectivity V-cavity tunable semiconductor laser based on GaAs

We report a self-injection-locked InAs/InP quantum-dash tunable laser with ∼11 nm (∼1602–1613 nm) tuning window for next generation multiuser ultrahigh capacity fiber/free-space optics (FSO)/hybrid fiber-FSO-based optical networks. A tunability of >18 independently locked subcarriers with ∼28 dB side mode suppression ratio (SMSR) and stable (±0.1 dBm) mode power is exhibited, and an estimated small injection ratio of ∼–22 dBm is found to sustain locking and SMSR. Error free transmission of 100 and 128 Gb/s externally modulated dual-polarization quadrature phase shift keying (DP-QPSK) signals over 20 km single mode fiber (SMF) and 16 m indoor FSO links are demonstrated across 8 and 4 individual subcarriers, respectively, thus covering the entire tuning range. Moreover, up to 168 (192) Gb/s successful transmission over 10 km SMF (BTB) and 176 Gb/s over 16 m FSO link is achieved on a ∼1610 nm subcarrier. Finally, a 128 Gb/s DP-QPSK transmission over 11 km SMF–8 m FSO–11 km SMF hybrid system is accomplished, thus paving the potential deployment of this single-chip, cost-effective, and energy efficient tunable light source in terabits/s next-generation passive optical networks.

Single-mode semiconductor lasers are desirable for fiber-optic communications because their narrow spectrum translates into minimal pulse spreading in a dispersive fiber. Unfortunately, simple Fabry-Perot semiconductor lasers tend to oscillate in several longitudinal modes, particularly under high-frequency modulation. To combat this problem, more complicated laser structures have been proposed, including distributed feedback lasers, distributed Bragg reflectors, and coupled cavity lasers.1 These last are of particular interest due to their relative ease of fabrication. Thus far, most work has focused on longitudinally coupled lasers. In these devices, the gap between the lasers plays a critical role in determining gain selectivity, and it must be altered mechanically. Recently, we demonstrated operation of a laterally coupled laser pair, in which the coupling between two lasers of dissimilar lengths occurs via the evanescent fields of the individual lasers.2 In this paper we solve for the threshold gains of a laterally coupled cavity (LC2) laser and present experimental verification of single-mode operation.

There are a number of approaches to inducing chaotic behavior in a single-mode semiconductor laser. We have investigated the following three approaches: (a) optical injection, (b) optical feedback, and (c) optoelectronic feedback. The nonlinear dynamics of a semiconductor laser depend on five intrinsic laser parameters and three operational parameters. We have studied unidirectional chaotic synchronization between two remote injection-locked semiconductor lasers to achieve chaotic communications.

Results of a long-term research in spectral narrowing and transverse mode selection in semiconductor lasers by means of volume Bragg gratings recorded in a photo-thermo-refractive (PTR) glass are described. PTR glass is a multicomponent silicate optical glass which changes its refractive index after UV exposure followed by thermal development. This feature enables recording of volume holograms with efficiency exceeding 97% in visible and near IR spectral regions which tolerate high temperatures up to 400°C, high power laser radiation. Transmitting and reflecting volume Bragg gratings recorded in such manner have spectral and angular selectivity down to 0.01 nm and 0.1 mrad, respectively. These spectral and angular selectors were used as transmitting and reflecting elements of external resonators for high-power semiconductor laser diodes (LDs). Transmitting Bragg gratings provide tunability of LDs in the range up to 60 nm, spectral narrowing down to 200 pm, stabilization of wavelength within 500 pm. Reflecting Bragg gratings allow spectral narrowing down to 20 pm, stabilization of wavelength below 100 pm at temperature variations up to 75 K. A single transverse mode emission for wide stripe LDs is observed at pumping currents exceeding 10 thresholds. Narrowing and stabilization of emission spectra of LD bars is demonstrated. It is important that all these features are achieved by passive elements with efficiency exceeding 97% and unlimited lifetime while actual brightness increase exceeded two orders of magnitude.

Bidirectional single longitudinal mode fiber ring laser have advantages and potential in optical sensing, especially angular velocity sensing. The current methods for implementing bidirectional single longitudinal mode fiber ring laser cannot ensure complete reciprocity in the optical path, and the side mode suppression ratio needs to be increased, while the laser linewidth is relatively wide. This paper proposes a combined filtering structure using a bandpass filter and a cascaded add-drop type fiber ring filter. When realizing bidirectional single longitudinal mode output, the optical path structure is fully reciprocal including polarization state reciprocity, while the side mode suppression ratio is relatively high. The linewidth of the bidirectional laser is around 1.1 kHz, far lower than the previous report of tens of kHz. The fully reciprocal combined filter structure proposed in this paper does not require special devices, and its theoretical system is mature, which is conducive to the subsequent application and improvement of bidirectional single longitudinal mode fiber ring laser.

We report on our design and fabrication of 1064-nm laterally-coupled distributed feedback (LC-DFB) semiconductor lasers, in which, a 9 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> order grating with λ/4 phase shift was incorporated, as well as investigating the effect of asymmetric phase shift (APS) on the device characteristics. It was found that the laser exhibited significantly higher output power when the phase-shifted position was closer to the rear facet. The results indicate that under the conditions of continuous-wave (CW) operation and the ambient temperature of 20°C, the output power reaches 362.3 mW when the injection current is 1 A, and the slope efficiency is about 0.4 W/A. The side-mode suppression ratio (SMSR) > 40 dB can be achieved for operation current in the range of 0.2 A to 1 A, which meets the requirement of single mode operation. This study provides valuable insights for the development of high-power LC-DFB semiconductor lasers with simple high-order grating fabrication process.

High power single-mode pump laser diodes operating around 980nm are key components for Erbium-doped devices. Much effort is still currently devoted to improve both their wavelength stability and their achievable output power, while maintaining a stable single-mode operation. Usually, the emission wavelength is stabilized by an external Fiber Bragg Grating (FBG). This configuration requires free-space optics between the laser diode output facet and the fiber or a lensed fiber to ensure an efficient coupling efficiency. This constraint increases fabrication costs, dimensions and mechanical instabilities. Moreover, the maximum achievable output power is limited because a high optical power density can damage the laser facets. To increase the achievable output power, a solution consists in using Broad-Area Laser Diodes (BALD), which are multimode emitters that are composed of large active ribbons with width of some hundreds of micrometers. The objective is then to improve the beam quality by locking the BALD emission on its transverse fundamental mode. We propose in this article to insert an integrated adiabatic transition between the multimode laser and a single-mode FBG. This taper, made by ion-exchange in glass, provides a coupling efficiency of -22.0dB from the multimode laser emission to the single-mode fiber. An optical feedback of -34dB demonstrates the stabilization of the BALD spectrum at the Bragg wavelength. The spectrum of the device is characterized by a maximum side-mode suppression ratio of 35dB, a RMS spectral width of (0.16 ± 0.04) nm and a frequency shift with current of -12GHz/100mA.

A coupled-wave rate-equation model, including multiple-order stimulated Brillouin scattering (SBS), is used to study power scaling of hybrid Brillouin/ytterbium fiber lasers. To validate the model, a single-frequency, Brillouin/ytterbium fiber laser was built with a laser output of 40 mW and an optical signal-to-noise ratio greater than 50 dB. The numerical model simulation agrees with the measurements in both fully and partially injection locked regimes. To scale up the laser's output power, a dual-clad architecture is proposed. In this new configuration, the active Yb-doped fiber provides the nonlinear SBS gain as well as the gain resulting from the excited Yb ions. Numerical modeling including three Stokes orders shows that over 5 W of single-frequency laser output can be achieved with a side-mode suppression ratio (SMSR) of greater than 80 dB. Beyond this power, multi-order SBS affects the laser efficiency and SMSR.

Semiconductor lasers are particularly well suited for the implementation of pump-noise suppression, yielding a reduction of the intensity noise in the laser. In this simple picture, the maximal amount of squeezing is equal to the quantum efficiency. However, experimental results on intensity noise reduction by pump-noise suppression are usually above this limit. This discrepancy suggests that additional noise sources must be involved. Here we successfuly interpret the full noise behavior of a single-mode laser diode far above threshold by considering two excess noise sources: the leakage current fluctuations across the laser and the Petermann excess noise. We have estimated the contribution of each noise source using the results of the correlations between the laser output intensity noise and the voltage fluctuations across the laser diode (light-voltage correlations) and obtained good agreement between our theory and experimental results.

Results of direct laser recording on a two-component medium consisting of deposited layers of amorphous silicon and silver on a glass substrate by magnetron sputtering are presented. A single-mode semiconductor laser with λ = 405 nm for amorphous silicon film on glass substrate with a power of 120 mW is used for direct laser recording on amorphous silicon. Formation of the relief on the silver film with direct recording pulses of a semiconductor laser with λ = 405 nm at the a-Si layer is taken on the electron microscope TESCAN VEGA 3 LMH.