External Cavity Semiconductor Research Articles

Laser threshold magnetometry using green-light absorption by diamond nitrogen vacancies in an external cavity laser

Nitrogen vacancy (NV) centers in diamond have attracted considerable recent interest for use in quantum sensing, promising increased sensitivity for applications ranging from geophysics to biomedicine. Conventional sensing schemes involve monitoring the change in red fluorescence from the NV center under green laser and microwave illumination. Due to the strong fluorescence background from emission in the NV triplet state and low relative contrast of any change in output, sensitivity is severely restricted by a high optical shot noise level. Here, we propose a means to avoid this issue, by using the change in green pump absorption through the diamond as part of a semiconductor external cavity laser run close to lasing threshold. We show theoretical sensitivity to magnetic field on the pT/sqrt(Hz) level is possible using a diamond with an optimal density of NV centers. We discuss the physical requirements and limitations of the method, particularly the role of amplified spontaneous emission near threshold and explore realistic implementations using current technology.

Guided-mode resonance filter extended-cavity diode laser

We characterize a semiconductor external cavity diode laser whose optical feedback is provided by a guided mode resonance filter (GMRF). We focus on the spectral properties. The wavelength of operation falls in the telecom range (1506 nm). The GMRF acting both as a wavelength intracavity filter and feedback mirror allows for a compact laser design. The single-mode operation is verified in a wide range of driving currents. We finely tune the cavity length to adjust the frequency by 14 GHz without mode-hops in agreement with the expected free-spectral range of the resonator ∼20 GHz. The compactness of the cavity allows fast frequency sweeps when modulating the current (90 MHz mA−1 at 100 kHz, the modulation bandwidth). The frequency noise (366 kHz white-noise contribution) is also analysed to evaluate the potential of our design for high-resolution applications.

Infrared laser threshold magnetometry with a NV doped diamond intracavity etalon.

We propose a hybrid laser system consisting of a semiconductor external cavity laser associated to an intra-cavity diamond etalon doped with nitrogen-vacancy color centers. We consider laser emission tuned to the infrared absorption line that is enhanced under the magnetic field dependent nitrogen-vacancy electron spin resonance and show that this architecture leads to a compact solid-state magnetometer that can be operated at room-temperature. The sensitivity to the magnetic field limited by the photonshot-noise of the output laser beam is estimated to be less than 1pT/Hz. Unlike usual NV center infrared magnetometry, this method would not require an external frequency stabilized laser. Since the proposed system relies on the competition between the laser threshold and an intracavity absorption, such laser-based optical sensor could be easily adapted to a broad variety of sensing applications based on absorption spectroscopy.

Flat chaos generated by optical feedback multi-mode laser with filter

<sec> Optical chaos has a wide range of applications in communications, such as secure communication, high-resolution lidar ranging, optical time domain reflectometer, and high-rate physical random bit generator.</sec><sec> In recent years, external-cavity feedback semiconductor lasers (ECLs) are the most common chaotic laser generation systems due to their characteristics of wide bandwidth, large amplitude, and simple structure, and the dynamic characteristics of chaotic signals have attracted much attention. However, limited by the relaxation oscillation of the laser, the energy of the chaotic signal directly generated by ECL is mainly concentrated at high relaxation oscillation frequency. Thus, the low-frequency component encounters the problem of energy loss.</sec><sec> In practical applications, the signal detection/acquisition device usually responds to a 3-dB low-pass filtering characteristic. Therefore, the available effective bandwidth of the chaotic signal should actually be 3-dB bandwidth. The lack of low-frequency components will limit the energy utilization rate of chaotic signals and restrict the relevant performances of chaotic applications (such as reliability and transmission of chaotic secure communication, randomness and generation rate of physical random bits, measurement accuracy and range of lidar ranging or optical time-domain reflectometer).</sec><sec> In the paper, we propose a broadband chaos generation scheme with simple structure and losing no low-frequency components. Specifically, we experimentally analyze the radio frequency (RF) spectra of the single-mode and the multi-mode output from an optical feedback Fabry-Perot (FP) semiconductor laser after and before filtering. The experimental results show that comparing with the multi-mode chaotic signal, the low-frequency energy of the single-mode chaotic spectrum is enhanced by 25 dB, and the 3-dB bandwidth of the single-mode chaotic signal can reach 6 GHz. Further theoretical analysis demonstrates that the enhancement of low-frequency component in the single-mode chaotic signal is caused by the mode-competing in multi-mode laser. It is concluded that this method can well solve the problem of low-frequency energy loss in conventional optical feedback chaotic systems, and is beneficial to improving the energy utilization rate of chaotic signals, which is of great significance for improving the performance of chaotic secure communication, random bit generation, lidar ranging, optical time domain reflectometer, and other relevant applications. </sec>

Influence of feedback strength on the characteristics of the random number sequence extracted from an external-cavity feedback semiconductor laser

Under proper feedback strength, an external-cavity feedback semiconductor laser can operate at a chaos state, and its chaotic output can be used as a physical entropy source to generate a physical random number sequence. In this paper, we focus on the influence of feedback strength on the randomness of the obtained binary code sequence. The simulation results show that with the increase of feedback strength, the time delay characteristic peak of the chaotic signal from an external-cavity feedback semiconductor laser first decreases and then increases gradually, meanwhile, the permutation entropy characteristic value of chaotic signal first increases and then decreases gradually, namely, there exists an optimized feedback strength for obtaining the chaotic signal with the weakest time delay signature and high complexity. The randomness of binary code sequences, generated by the chaotic signal from the external-cavity feedback semiconductor laser under different feedback strengths, is tested by NIST Special Publication 800-22, and the influence of feedback strength on the test results is also discussed.

Modulation of output power in the spatio-temporal analysis of a semi conductor laser

This paper examines the spatio temporal patterns of a set of a (2 + 1) dimensional partial differential equations (PDE) describing the dynamics of semiconductor external cavity THz lasers. The study is conducted in two phases: (a) first we show that the behaviour of the single mode system may be periodic or chaotic; (b) the output power may be optimized by proper choices of parameters, such as cavity length and injected current, which lead to high dimensional spatio-temporal chaotic regimes. This conclusion applies to systems with one and with two external cavities, and is robust with respect to variations of parameter values and initial-boundary conditions.

Packaged, High-Power, Narrow-Linewidth Slab-Coupled Optical Waveguide External Cavity Laser (SCOWECL)

We report the demonstration of an InGaAlAs/InP quantum-well, high-power, low-noise packaged semiconductor external cavity laser (ECL) operating at 1550 nm. The laser comprises a double-pass, curved-channel slab-coupled optical waveguide amplifier (SCOWA) coupled to a narrow-bandwidth (2.5 GHz) fiber Bragg grating passive cavity using a lensed-fiber. At a bias current of 4 A, the ECL produces 370 mW of fiber-coupled output power with a Voigt lineshape having Gaussian and Lorentzian linewidths of 35 and 1 kHz, respectively, and relative intensity noise <; -160 dB/Hz from 200 kHz to 10 GHz.

New Two-Color Laser Concepts for THz Generation

Two-color semiconductor external cavity laser concepts for terahertz (THz) generation are discussed. By defining three critical characteristics, various two-color laser configurations are experimentally classified with respect to the application of THz generation. According to our experimental results, we suggest a new two-color laser configuration. It is based on an external cavity with an etalon.

Fast wavelength switching using digitally tunable external cavity laser

An all-optical fast wavelength switching at 10 Gbit/s between 200 GHz-spaced channels using a digitally tunable external cavity laser and semiconductor optical amplifier-based wavelength converter is demonstrated.

High-power, ultra-stable, single-frequency operation of a long, doped-fiber external-cavity, grating-semiconductor laser

Robust high-power, single frequency operation of semiconductor external cavity lasers is demonstrated in a novel extended two-level dopedfiber absorbing system. Outstanding wavelength and line-width stability is observed in long external cavities.

Longitudinal-mode-partition noise and amplitude squeezing in semiconductor lasers

We have measured the longitudinal-mode-partition noise of free-running, grating-feedback external-cavity and injection-locked semiconductor lasers, using a nonsymmetric Mach–Zehnder interferometer. For an external-cavity laser operated at a high pumping level, the contribution of the longitudinal-mode-partition noise to the total intensity noise was negligible, and 0.9 dB of amplitude squeezing was observed. On the other hand, injection locking suppressed the longitudinal-mode-partition noise by 34 dB, and 1.9 dB of amplitude squeezing was observed when the locking bandwidth was 5 GHz. A further increase in the locking bandwidth reduced the suppression of the longitudinal-mode-partition noise and degraded the amplitude squeezing.

Demonstration of a semiconductor external cavity laser using a UV written grating in a planar silica waveguide

The authors report the first demonstration of a semiconductor external cavity waveguide laser, modulated at 2.5 Gbit/s over 100 km of standard optical fibre using a UV written grating in a planar silica waveguide as the feedback element.

Tunable dual-wavelength continuous-wave diode laser operated at 830 nm

An external grating cavity semiconductor diode laser is made to operate simultaneously at two separately adjustable wavelengths. Lasing is restricted to the vicinity of the solitary laser 6talon resonances.

An overview of optical device research in China

An overview of research activities in China on the following optical communications devices is presented: quantum-well semiconductor lasers; distributed feedback laser diodes; wideband, tunable, narrow-linewidth, external-cavity laser diodes, semiconductor and doped-fiber amplifiers; laser-diode-pumped solid state and single-crystal fiber lasers; doped fiber ring lasers, optical modulators; switches; bistable devices; experimental wavelength-division-multiplexed (WDM) systems; and time-division photonic switching systems. The most important of these technologies are highlighted with respect to demonstrated achievements in China. The potential uses of these technologies in future telecommunications systems are discussed. >