Mode Vertical-cavity Surface-emitting Laser Research Articles

Polarization Bistability Induced by Orthogonal Optical Injection in 1550-nm Multimode VCSELs

We have analyzed experimentally the optical power polarization bistability induced in a long-wavelength multitransverse mode vertical-cavity surface-emitting laser (VCSEL) under orthogonal optical injection. Bistability with very wide hysteresis cycles is measured for both the fundamental and the high-order transverse mode of the device. The shape of the associated hysteresis cycle is different for each of the two transverse modes. The power of the parallel polarized high-order (fundamental) transverse mode remains constant (gradually decreases) as the injected power is increased. Both powers suddenly drop to low levels at large values of the injected power. The squared shape measured for the I/O characteristic of the high-order transverse mode is of particular interest for obtaining good quality all-optical inversion and all-optical regeneration for use in optical telecommunication networks.

Electro-optical resonance modulation of vertical-cavity surface-emitting lasers

Optical and electrical investigations of vertical-cavity surface-emitting lasers (VCSEL) with a monolithically integrated electro-optical modulator (EOM) allow for a detailed physical understanding of this complex compound cavity laser system. The EOM VCSEL light output is investigated to identify optimal working points. An electro-optic resonance feature triggered by the quantum confined Stark effect is used to modulate individual VCSEL modes by more than 20 dB with an extremely small EOM voltage change of less than 100 mV. Spectral mode analysis reveals modulation of higher order modes and very low wavelength chirp of < 0.5 nm. Dynamic experiments and simulation predict an intrinsic bandwidth of the EOM VCSEL exceeding 50 GHz.

Dynamics of vertical-cavity surface-emitting laser subject to optical injection and positive optoelectronic feedback

Based on the spin-flip model (SFM), we theoretically investigate the dynamics of a vertical-cavity surface-emitting laser (VCSEL) subject to optical injection and positive optoelectronic feedback. The results show that under the joint action of positive optoelectronic feedback and optical injection from a master VCSEL (M-VCSEL), two polarization modes of a slave VCSEL (S-VCSEL) will show many dynamic states such as period one, period two, multi-period and chaos, and the evolution routes of these states are different for two polarization modes. Mapping of dynamic region as a function of feedback strength f and injection strength is varied with frequency detuning between M-VCSEL and S-VCSEL (=m-s, where m ands are the free-running frequencies of M-VCSEL and S-VCSEL, respectively). Compared with the case for zero or negative frequency detuning, the region of chaotic state is expanded significantly under positive . For a fixed , the influences of f and on the chaotic bandwidth of S-VCSEL are discussed. Through selecting proper f and , chaotic bandwidth of S-VCSEL can be improved obviously.

Transverse-Mode Characteristics of GaSb-Based VCSELs With Buried-Tunnel Junctions

We report the transverse-mode characteristics of GaSb-based vertical-cavity surface-emitting lasers (VCSELs) with buried-tunnel junctions (BTJs). The optical-index guiding in the devices is achieved by an effective refractive index step due to the presence of a laterally structured BTJ in the cavity. All lasing modes in VCSELs of different active diameters are experimentally measured. Then the experimental results are compared against the theoretical data for two different VCSEL designs emitting at 2.3 and 2.6 μm yielding a good agreement. The transverse-mode spacing between the excited modes is also determined and the results are compared with the theory. The far-field patterns ensure that devices with reasonable aperture diameters operate in single-fundamental LP01 mode, showing that the devices are well-designed.

Current-dependence of polarisation switching and locking in an optically injected 1550 nm vertical-cavity surface-emitting laser

The authors have studied the effects of polarised optical injection in a 1550 nm vertical-cavity surface-emitting laser (VCSEL) operated at currents up to 4.5 times threshold. Regions of stable injection locking have been measured for cases where the injected signal is polarised to match one of the two polarisations of the fundamental transverse mode of the solitary VCSEL. In addition regions of polarisation switching have been found for the case where the input polarisation is matched to that of the subsidiary mode of the solitary VCSEL. The variation of this behaviour with current has been investigated.

Transverse Mode Selection and Bistability in Vertical-Cavity Surface-Emitting Lasers Induced by Parallel Polarized Optical Injection

Modal selection induced by parallel polarized optical injection in a vertical-cavity surface-emitting laser (VCSEL) emitting in two transverse modes is analyzed from a theoretical point of view. We show that the selection of the fundamental transverse mode can be achieved when the two transverse modes have parallel polarizations. This selection is accompanied by locking of the fundamental mode to the optically injected signal for large enough values of the wavelength detuning between the fundamental mode and the externally injected signal. The injected power needed to induce modal selection grows as the VCSEL bias current is increased for small positive wavelength detunings, while it is independent on the bias current for larger wavelength detunings. That power exhibits a minimum with respect to the injection wavelength at a value λ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">min</i> that is slightly longer than the wavelength of the fundamental mode of the solitary VCSEL. We also show that the selection process exhibits bistable behavior when the wavelength of the optically injected signal increases beyond λ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">min</i> . The width of the bistable region increases linearly with the wavelength of the optically injected signal. Our results show that λ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">min</i> also increases linearly with the VCSEL bias current. Higher order transverse mode selection and bistability, similar to those found for the fundamental mode, are obtained when the optical injection wavelength is close to that of the higher order mode. Our results are in agreement with the experimental results reported earlier.

Wavelength-induced polarization bistability in 1550 nm VCSELs subject to orthogonal optical injection

We report on a theoretical and experimental investigation of the bistable behavior of the polarization of long-wavelength single-transverse mode vertical-cavity surface-emitting lasers (VCSELs) when subject to orthogonal optical injection. We have studied the bistability properties of the polarization switching that appear when changing the master laser wavelength with a fixed master laser power. Two bistable regions are found for polarization switchings appearing at short and long wavelengths. The directions of the obtained hysteresis cycles are in agreement with the experimental results. The widths of both bistable regions are also found to be similar and nearly independent of the injected power. The width of the region where polarization switching takes place is shown to increase as the injected power is increased. A good overall qualitative agreement is found between our theoretical and experimental results.

Behavior of the relaxation oscillation frequency in vertical cavity surface-emitting laser with external feedback

The influence of weak optical feedback on the dynamics of a single longitudinal mode vertical-cavity surface-emitting laser (VCSEL) is studied experimentally under conditions when the feedback power is sufficiently low so as to avoid the onset of chaos. The VCSEL dynamics divides into two regimes depending on the ratio of the relaxation oscillation frequency to the external cavity mode spacing. In the long cavity regime, the modulation frequency response of the VCSEL exhibits resonances corresponding to the frequencies of the external cavity modes, while for the short cavity regime the modulation response of the VCSEL at the cavity resonances remains very low while the relaxation oscillation frequency is shifted and the modulation response at the shifted frequency exhibits a sharpened and enhanced resonance.

Experimental Study of Transverse Mode Selection in VCSELs Induced by Parallel Polarized Optical Injection

Modal selection induced by parallel polarized optical injection is studied experimentally in a vertical-cavity surface-emitting laser (VCSEL) with emission in two transverse modes. We report that the selection of the fundamental transverse mode can be achieved when the two transverse modes have parallel polarizations. The selection of the fundamental mode is accompanied by locking of that mode to the optically injected signal for large enough values of the wavelength detuning between the fundamental mode and the externally injected signal. The injected power needed to induce modal selection grows as the VCSEL bias current is increased and exhibits a minimum with respect to the injection wavelength at a value ?min that is slightly longer than the wavelength of the fundamental mode of the solitary VCSEL. We also report that the selection process exhibits a bistable behaviour when the wavelength of optical injection increases beyond ?min. The width of the observed bistable region grows linearly with the wavelength of the optically injected signal. Selection of the higher order transverse mode is achieved when the optical injection wavelength is close to that of the higher order transverse mode. The qualitative behavior associated with the selection of the higher order mode is similar to that of the fundamental mode.

Very Wide Hysteresis Cycles in 1550-nm VCSELs Subject to Orthogonal Optical Injection

A first experimental observation of three different types of frequency-induced polarization bistabilities in 1550-nm single transverse and polarization mode vertical-cavity surface-emitting lasers (VCSELs) subject to orthogonal optical injection is described. The hysteresis width of the bistable region that appears at longer wavelegth detunings increases as the injected power or the VCSEL current increases. Very large hysteresis widths are obtained. These widths are more than seven times larger than previously reported widths.

Analysis and Design of Antiresonant Reflecting Optical Waveguide Vertical-Cavity Surface-Emitting Lasers for Above-Threshold Operation

Modal characteristics of antiresonant reflecting optical waveguide (ARROW) vertical-cavity surface-emitting lasers (VCSELs) are studied under high current injection. It is found that the influence of carrier spatial hole burning increases the radiation loss margin of ARROW at low injection current, while the thermal lensing effect significantly reduces radiation loss margin of ARROW at high injection current. Hence, the excitation of multiple-transverse modes in VCSELs is inevitable under high injection current even if the dimensions of the ARROW have been optimized to maximum radiation loss margin. Therefore, it is proposed to modify the refractive index profile of the ARROW to compensate against the influence of thermal lensing in VCSELs. It can be shown that the radiation loss margin of the modified ARROW can remain unchanged under the influence of thermal lensing if the dimensions and refractive index profile of the ARROW are properly designed. Hence, stable single-mode operation can be obtained in ARROW VCSELs at high injection current.

Theoretical study on phase conjugation in weakly injected vertical-cavity surface-emitting lasers

This paper gives a detailed theoretical investigation on phase conjugation induced by nearly degenerate four-wave mixing in single mode vertical-cavity surface-emitting lasers (VCSELs) with weak optical injection. Considering VCSELs that can work in linearly polarized or elliptically polarized states, it derives the theoretical expression of the conjugated field by small signal analysis based on the vectoral rate equations—the spin-flip model. For linearly polarized state, VCSELs show similar conjugate spectra to edge-emitting semiconductor lasers. For the elliptically polarized state, dichroism and birefringence parameters as well as the spin-flip rate can change the conjugate spectra. Especially, when frequency detuning of the probe and pump waves is between the positive and negative relaxation oscillation frequency, changes are evident. For specific values of parameters, conjugate efficiency between 20dB to 40dB are obtained.

Single mode high-contrast subwavelength grating vertical cavity surface emitting lasers

We present a single mode vertical-cavity surface-emitting laser (VCSEL) utilizing a single-layer, high-contrast subwavelength grating (HCG) based top mirror, which provides both the ultrahigh reflectivity and lateral transverse modes control. Experimentally, we demonstrate that merely 11 HCG stripes with a thickness of 230nm are required to achieve lasing operation. The finite area of HCG, in combination with an oxide aperture of 2–6μm, effectively discriminates the higher-order transverse modes in VCSELs with a side mode suppression ratio of ⩾40dB. Furthermore, a single (first high-order transverse) mode, high output power of 2.3mW laser was achieved from a VCSEL with a 10μm oxide aperture.

Noise, distortion and dynamic range of single mode 1.3 µm InGaAs vertical cavity surface emitting lasers for radio-over-fibre links

The analogue modulation characteristics, including second order harmonic and third order intermodulation distortion, relative intensity noise (RIN) and spurious free dynamic range (SFDR), of single mode, GaAs-based 1.28 μm vertical cavity surface emitting laser (VCSELs) with highly strained InGaAs quantum wells have been investigated. The VCSELs utilise an oxide aperture for current and optical confinement and an inverted surface relief (SR) for suppression of higher order transverse modes. The inverted SR structure also has the advantage of suppressing oxide modes that, otherwise, appear in VCSELs with a large detuning of the cavity resonance with respect to the gain peak, which is needed to extend the emission wavelength. RIN levels comparable with those of single mode VCSELs emitting at 850 nm are demonstrated, with values from 140 to 150 dB/Hz in the 2 5 GHz range. SFDR values of 100 and 95 dBHz2/3 are obtained at 2 and 5 GHz, respectively. These values are in the range of those required in radio-over-fibre links.

Various high-order modes in vertical-cavity surface-emitting lasers with equilateral triangular lateral confinement

Large-aperture vertical-cavity surface-emitting lasers with an equilateral triangular lateral confinement are fabricated to investigate the formation of high-order resonant modes. The experimental lasing patterns are composed of the superscar mode, honeycomb eigenstate, and chaotic mode. Experimental results confirm the theoretical predictions that tiny symmetry breaking can cause the high-order modes to reveal miscellaneous states of integrable and chaotic systems.

Irregular Pulsating Polarization Dynamics in Gain-Switched Vertical-Cavity Surface-Emitting Lasers

In this paper, we report on experimental and theoretical investigation on the nonlinear dynamics of the two orthogonal linearly polarized fundamental transverse modes of vertical-cavity surface-emitting lasers (VCSELs) under sinusoidal current modulation. Irregular pulses of the power of individual polarizations are measured with a period equal to twice the modulation period. In contrast with individual polarizations, total power displays regular pulsing at twice the modulation period. The variability of pulse streams is characterized by using residence times distributions. We show that the residence time distributions for individual linear polarizations display an exponential decay for large values of that time. Those results are well reproduced by using a theoretical model that includes spontaneous emission fluctuations. However the previous qualitative features remain even in the absence of spontaneous emission noise. Our results therefore suggest that the irregular polarization dynamics have a deterministic origin and can be defined as deterministic chaos.

Polarization Bistability in 1550 nm Wavelength Single-Mode Vertical-Cavity Surface-Emitting Lasers Subject to Orthogonal Optical Injection

In this paper, we report on an experimental investigation of the bistable behavior of a 1550 nm single transverse and polarization mode vertical-cavity surface-emitting laser (VCSEL) when subjected to orthogonal optical injection. As the master laser wavelength is scanned near the resonance wavelength of the depressed linearly polarized fundamental mode, and for a fixed injected power, the VCSEL exhibits two successive polarization switchings (PSs). Both PSs exhibit bistable regions in such a way that a pure-frequency-induced polarization bistability is found. The width of both bistable regions has been measured as a function of the injected power and for different values of the VCSEL current. While the injection power is lesser than a certain value, the hysteresis width fluctuates around a constant level. Further increase of the injection power leads to a smaller constant value of the hysteresis width. The value of that transition value is independent of the VCSEL current. Power-induced polarization bistability - by fixing the master laser wavelength - is found near the transition value. Clockwise and anticlockwise power-hysteresis cycles are observed for short and long master laser wavelengths, respectively.

Nonlinear dynamics of the polarization of multitransverse mode vertical-cavity surface-emitting lasers under current modulation

In this paper we report on a theoretical investigation of the nonlinear dynamics of the polarization of multitransverse mode vertical-cavity surface-emitting lasers (VCSELs) under current modulation. Special attention is given to the comparison with a previously studied case of single-transverse mode VCSEL emitting in two orthogonal polarizations. The consideration of spatial effects in VCSEL modifies the polarization dynamics that accompanies the period doubling route to chaos for large modulation amplitudes. Depending on the modulation parameters, the excitation of a higher order transverse mode may either induce chaotic pulsing in an otherwise regularly pulsating VCSEL, or induce a time-periodic pulsing dynamics in an otherwise chaotic VCSEL. Bifurcation diagrams obtained for different modulation frequencies, several values of the dichroism, and different transverse mode characteristics allow us to identify the different scenarios of polarization dynamics in a directly modulated VCSEL. Temporal analysis of carrier number radial profile reveals considerable changes for the multitransverse mode case only constituting the physical origin of the reported changes in the temporal and polarization dynamics.

The use of spatially ordered arrays of etched holes for fabrication of single-mode vertical-cavity surface-emitting lasers based on submonolayer InGaAs quantum dots

To suppress the generation of high-order modes in vertical-cavity surface-emitting lasers based on submonolayer InGaAs quantum dots, the method of formation of a spatially ordered array of etched holes in the upper distributed Bragg reflector was used. Single-mode vertical-cavity surface-emitting lasers for spectral region of 990 nm with current-aperture diameter of 20 μm, threshold current 0.9 mA, and maximum output power 3.8 mW at room temperature were demonstrated. Single-mode lasing with the coefficient of side-mode suppression in excess of 35 dB is retained in the entire range of pump currents. A decrease in the current oxide aperture to sizes that are close to those of the optical aperture brings about an increase in the external quantum efficiency; however, in this case, the transition to the multimode of lasing is observed at high pump currents.

Polarization control of 0.85μm vertical-cavity surface-emitting lasers integrated with gold nanorod arrays

In this letter, the authors unambiguously demonstrate the polarization control of 0.85μm single transverse mode vertical-cavity surface-emitting lasers (VCSELs) using plasmonic nanorod arrays fabricated on the top surface of VCSELs. The strong direction dependent scattering of light from anisotropic gold nanorods enables stable polarization operations of VCSELs with suppressing the absorption in gold layer and leads to high differential quantum efficiencies. These nanorod arrays integrated VCSELs show negligible penalties in laser performances having the maximum output power of nearly 1mW with the side mode suppression ratio of 45dB and the orthogonal polarization suppression ratio of 21dB.