Polarization Of Vertical-cavity Surface-emitting Lasers Research Articles

Chaos synchronization of VCSELs with common injection of polarization-random light.

We propose and numerically demonstrate chaos synchronization of two vertical-cavity surface-emitting lasers (VCSELs) induced by common injection of constant-amplitude random-polarization light for physical key distribution. Results show that synchronization is sensitive to polarization rotation of injection light, and synchronization coefficients larger than 0.9 can be achieved as the rotation-degree mismatch is smaller than ±10°. Therefore, polarization rotation degree can serve as a hardware key parameter. Furthermore, each laser's output has no correlation to the constant amplitude of the injected light. Their components with identical polarization state, e.g. x or y polarization of VCSEL, also have low correlation coefficient smaller than 0.2. It is therefore believed that this synchronization scheme can provide a security-enhanced method of physical key distribution.

Study and Application of Birefringent Nanoporous GaN in the Polarization Control of Blue Vertical-Cavity Surface-Emitting Lasers

III-Nitride vertical-cavity surface-emitting lasers (VCSELs) have attracted much attention during the last two decades. Control of the laser polarization in VCSELs is one of the main challenges that needs to be addressed for real applications. In this work a novel polarization locking technique for GaN VCSELs is presented by employing birefringent nanoporous distributed Bragg reflectors (DBRs). The birefringence arises from a nanophotonic effect of evanescent field enhancement in the anisotropically aligned nanopores. Furthermore, the birefringence dependence over the nanopores morphology is explored. A fully electrically injected blue VCSEL with polarization locking is demonstrated. As presented, this technique allows to individually define the polarization angle in a planar array, opening the path to novel applications.

VCSEL mode and polarization control by an elliptic dielectric mode filter.

In this paper, we demonstrate the effectiveness of polarization mode control in vertical-cavity surface-emitting lasers (VCSELs) with integrated elliptic dielectric mode filters. The single-mode single-polarization laser operation is obtained by an irregularly shaped oval dielectric mode filter, aimed at cost-effective mass production. The orthogonal polarization suppression ratio was measured to be 16.7 dB, and the side-mode suppression ratio exceeded 30 dB. A single fundamental mode power of 0.55 mW was achieved at a bias current of 4 mA. We compared the spectra and near-field intensities of the dielectric mode filter VCSEL with a reference device. The comparison clearly indicates the effectiveness of our dielectric mode filter in controlling the transverse- and polarization-mode properties of VCSELs.

VCSEL polarization modulation for pulse-per-second clock signal transfer in optical frequency distribution systems

In this paper, a novel vertical cavity surface emitting laser (VCSEL) polarization modulation technique based on polarization switching due to thermal heating in a single transverse mode class 10 G VCSEL at 1 310 nm is demonstrated experimentally. The inherent orthogonal polarization switching of the VCSEL carrier with changing bias is exploited in the transmission of pulse-per-second (PPS) timing clock signal. Experimental results show that PPS pulse widths of 9.97 μs and 9.98 μs are measured for back-to-back analysis and over 3.21 km of G 652 urban fibre transmission, respectively. This work provides a novel alternative for adoption in optical frequency and time transfer applications.

Lasing Polarization Characteristics in 1.55- $\mu \text{m}$ Spin-Injected VCSELs

Circular polarization characteristics in vertical-cavity surface-emitting lasers (VCSELs) with InAlGaAs quantum wells injected by spin-polarized electrons were investigated. A degree of circular polarization of 10% was obtained in a reduced birefringence VCSEL at a lasing wavelength of 1544 nm at room temperature under optical pumping of spin-polarized electrons. Strong birefringence originally introduced to stabilize the lasing polarization was confirmed to be undesirable for a high degree of circular polarization in spin-injected VCSELs. A spin-flip rate equation analysis fairly reproduced the experimental results and supported our conclusions.

Asymmetric dwell-time statistics of polarization chaos from free-running VCSEL.

We experimentally report on asymmetric dwell-time statistics of polarization chaos dynamics generated from free-running vertical-cavity surface-emitting lasers (VCSELs). Theoretically, we explain this behavior by introducing a misalignment between the phase and amplitude anisotropy within the spin-flip model for VCSELs. It induces an asymmetry in the VCSEL polarization behavior which is then responsible for significant changes in the statistics of the chaotic mode-hopping with an increase in the average residence time and an inversion of the dominant mode.

Impact of optical feedback on current-induced polarization behavior of 1550 nm vertical-cavity surface-emitting lasers

Polarization switching (PS) between two orthogonal linearly polarized fundamental modes is experimentally observed in commercial free-running 1550 nm vertical-cavity surface-emitting lasers (VCSELs) (Raycan). The characteristics of this PS are strongly modified after introducing a polarization-preserved (PP) or polarization-orthogonal (PO) optical feedback. Under the case that the external cavity is approximately 30 cm, the PP optical feedback results in the PS point shifting toward a lower injection current, and the region within which the two polarization modes coexist is enlarged with the increase of the PP feedback strength. Under too-strong PP feedback levels, the PS disappears. The impact of PO optical feedback on VCSEL polarization behavior is quite similar to that of PP optical feedback, but larger feedback strength is needed to obtain similar results.

Vertical cavity surface emitting laser transverse mode and polarization control by elliptical hole photonic crystal

The polarization of traditional photonic crystal (PC) vertical cavity surface emitting laser (VCSEL) is uncontrollable, resulting in the bit error increasing easily. Elliptical hole photonic crystal can control the transverse mode and polarization of VCSEL efficiently. We analyze the far field divergence angle, and birefringence of elliptical hole PC VCSEL. When the ratio of minor axis to major axis b/a = 0.7, the PC VCSEL can obtain single mode and polarization. According to the simulation results, we fabricate the device successfully. The output power is 1.7 mW, the far field divergence angle is less than 10°, and the side mode suppression ratio is over 30 dB. The output power in the Y direction is 20 times that in the X direction.

Optically-pumped dilute nitride spin-VCSEL

We report the first room temperature optical spin-injection of a dilute nitride 1300 nm vertical-cavity surface-emitting laser (VCSEL) under continuous-wave optical pumping. We also present a novel experimental protocol for the investigation of optical spin-injection with a fiber setup. The experimental results indicate that the VCSEL polarization can be controlled by the pump polarization, and the measured behavior is in excellent agreement with theoretical predictions using the spin flip model. The ability to control the polarization of a long-wavelength VCSEL at room temperature emitting at the wavelength of 1.3 µm opens up a new exciting research avenue for novel uses in disparate fields of technology ranging from spintronics to optical telecommunication networks.

Polarization synchronization in unidirectionally coupled vertical-cavity surface-emitting lasers with orthogonal optical injection

We analyze theoretically the polarization dynamics in unidirectionally coupled vertical-cavity surface-emitting lasers (VCSELs). The master VCSEL is subject to an isotropic optical feedback. The slave VCSEL is subject to an orthogonal optical injection from the master VCSEL, i.e., only the linearly polarized mode orthogonal to the dominant linearly polarized mode of the free-running slave VCSEL is injected into the slave VCSEL. This laser configuration may lead the slave VCSEL polarization to switch to that of the injected master laser field. The injected power required for polarization switching depends on the frequency detuning. We identify in the plane of the injection parameters two regions of enhanced synchronization between the injected LP mode and the corresponding slave LP mode. In the so-called region II the slave VCSEL exhibits anticorrelated dynamics in its two LP modes while in the so-called region I the slave VCSEL exhibits dynamics in only one LP mode, which corresponds to the polarization of the injected field. The two regions exhibit different synchronization properties in both the LP mode dynamics and total intensity dynamics. We furthermore analyze the dependency of the synchronization quality on the parameter mismatch between master and slave VCSELs and on the polarization switching properties of each VCSEL.

Polarization-preserved and polarization-rotated synchronization of chaotic vertical-cavity surface-emitting lasers

The synchronization process in a vertical-cavity surface-emitting laser (VCSEL) based master-slave configuration, where the master laser has been destabilised by optical feedback from an external mirror, has been investigated. The dynamics of both VCSEL polarization modes have been modeled and used to study the chaos synchronization mechanism in both polarization preserved, and polarization rotated unidirectionally coupled master and slave configurations. Two types of synchronization have been identified in the polarization rotated case, one of which may afford an opportunity to effect multiplexed message encoding using orthogonal laser modes.

Two-mode injection locking in vertical-cavity surface-emitting lasers

We report on the dynamics that accompany polarization switching induced by orthogonal optical injection in a vertical-cavity surface-emitting laser (VCSEL). As the injection strength increases, the VCSEL bifurcates to injection-locked steady states and time-periodic and possibly chaotic dynamics. Of particular interest is a two-mode injection-locking solution, i.e., locking of the two VCSEL polarization modes. A detailed stability analysis unveils new bistability mechanisms in optical injection problems.

Investigation of polarization bistability in vertical-cavity surface-emitting lasers subjected to optical feedback

Polarization bistability in vertical-cavity surface-emitting lasers (VCSELs) subject to optical feedback has been studied both experimentally and theoretically. Optical feedback is shown to reduce the width of the bistability hysteresis loop and, hence, suppress the bistability. It is also demonstrated experimentally that polarization-selective optical feedback can be utilized to eliminate VCSEL polarization switching without inducing instabilities in the device.

Suppression of polarization switching in vertical-cavity surface-emitting lasers by use of optical feedback.

The polarization properties of vertical-cavity surface-emitting lasers (VCSELs) subject to optical feedback are studied experimentally. It is thereby demonstrated that polarization-selective optical feedback can be utilized to entirely eliminate VCSEL polarization switching over the entire device operating range.

VCSEL polarization control by optical injection

The stability of the polarization-resolved (PR) light output of a commercial vertical-cavity surface-emitting laser (VCSEL) has been studied with and without the presence of external optical injection in a master-slave configuration. Pulsations in the PR light output are observed in the solitary laser at certain bias current. It has been observed here for the first time that optical injection can stabilize the polarization of a VCSEL operating in a pulsation regime.

Coupled mode theory: A powerful tool for analyzing complex VCSELs and designing advanced device features

Vertical-cavity surface-emitting lasers (VCSELs) have become leading light sources in plenty of applications due to their good characteristics and low costs. There are, however, some features that need improvements; therefore, optimized or new designs ideas are necessary. To this aim, an electromagnetic simulation tool, which is fast and precise at the same time, is desirable; to cover all the possible requirements, it should be fully three-dimensional (3-D) and vectorial. A model with such features was first proposed by Bava et al. ("Three-Dimensional Model for Vectorial Fields in Vertical-Cavity Surface-Emitting Lasers", Phys. Rev. A, vol. 63, p. 23816, 2001), based on coupled-mode theory. Here, a review of its applications will be given, related to particular devices: nonperfectly circular VCSELs and phase-coupled arrays. The comparison with the corresponding experimental results turns out to be very satisfactory. Therefore, we were encouraged to use the model for obtaining design criteria of polarization maintaining VCSELs by using a small relief grating. The capability of gratings to pin the VCSEL polarization was already demonstrated; however, the different configurations do not allow one to have a clear overview of this technique. Moreover, to the best of our knowledge, a full simulation of a VCSEL with a grating was never presented, due to the complexity of treating the corresponding fully 3-D and vectorial problem. For the first time, we have the possibility of comparing different configurations on the same footing; in particular, we will evaluate the performances of dielectric and metal gratings. With the design we propose here, single-transverse and single-polarization-mode operation are predicted with a suppression of the other polarization easily in the order of 45 dB.

Impact of in-plane anisotropic strain on the polarization behavior of vertical-cavity surface-emitting lasers

We experimentally demonstrate that the presence of switching between two fundamental modes with orthogonal linear polarization in vertical-cavity surface-emitting lasers and the current at which this phenomenon occurs depend on both the magnitude and the orientation of an externally induced in-plane anisotropic strain. We interpret this behavior by considering the anisotropy in gain and in refractive index, both induced by the in-plane strain, and by accounting for a redshift of the two gain curves as a result of current-induced heating.

Polarization control of vertical-cavity surface-emitting lasers by electro-optic birefringence

Polarization of vertical-cavity surface-emitting lasers (VCSELs) grown on (001) GaAs substrate has been controlled by electro-optic birefringence. Birefringence was induced at the top distributed Bragg reflector by applying an electric field along the [001] direction. The cavity resonance of the polarized light along the [110] or [11̄0] direction shifted to shorter and longer wavelength, depending on the direction of the applied electric field. By varying the direction and strength of the electric field, we actively controlled the polarization of VCSELs. The dominant polarization mode occurred along the [110] direction for the negative electric field, and along the [11̄0] direction for the positive electric field.

Polarization selection in VCSELs due to current carrier heating

The problem of polarization switching of light from a vertical cavity surface emitting laser (VCSEL) is discussed. It is shown that heating of holes in the p-type distributed Bragg reflector and of electrons and holes in the quantum wells of the active region lead to switching of the polarization of the VCSEL. The model developed here makes it possible to explain the results of experiments on switching of the polarization of VCSELs at fixed active region temperatures.

High-bit-rate generation of low chirped pulses from vertical-cavity surface-emitting lasers via external axial magnetic field

The possibility of generating low chirped, fast optical pulses with linear polarization in vertical-cavity surface-emitting lasers (VCSELs) is numerically explored. We show that, under the influence of an axial magnetic field, polarization modulation at gigahertz rates can be achieved with possible applications in optical clock generation/extraction and optical communications.