Single-mode Vertical-cavity Surface-emitting Lasers Research Articles

Reflective-type photonic displacement sensor incorporating a micro-optic beam shaper

A reflective-type photonic displacement sensor has been proposed and realized by taking advantage of a compact optical sensing head that incorporates a micro-optic beam shaper in conjunction with a rotary scale. The miniature beam shaper, which includes a pair of aspheric lenses, plays the role of optimally focusing a light beam emitted by a VCSEL source onto a rotary scale by utilizing efficient collimating optics. The focused beam is selectively reflected by a periodic grating pattern relevant to the scale; the beam then arrives at the photodetector (PD) receiver. Hence, an arbitrary displacement, encoded by the scale, could readily translate into an output signal available from the receiver. The proposed sensor was thoroughly designed through ray tracing based simulations and then analyzed in terms of the alignment tolerance for the VCSEL and code scale. The slim beam shaper was cost effectively constructed using plastic injection molding, and it was precisely integrated with the VCSEL and PD in a passive alignment manner, in order to complete the optical sensing head. In order to construct the displacement sensor, a code-wheel type scale containing alternate patterns of high- and low-reflection, was integrated with the optical head. The sensor was primarily characterized with respect to the evolution of generated beams for single-mode (SM) and multi-mode (MM) VCSELs, taking into consideration that the modulation depth of the output signal is elevated with decreasing focused beam size. For an embodied displacement sensor based on an SM VCSEL, leading to a focused beam spot of ~30 μm, a well-defined output with a modulation depth of 7% was obtained in response to the displacement of the rotary scale engraved with a grating of 10-μm pitch. The linear and angular resolutions were accordingly estimated to be better than 5 μm and 0.02°, respectively.

Single-Mode, High-Speed, and High-Power Vertical-Cavity Surface-Emitting Lasers at 850 nm for Short to Medium Reach (2 km) Optical Interconnects

The vertical-cavity surface-emitting lasers (VCSELs) with high single-mode (narrow linewidth) output power are essential to minimize chromatic dispersion and to further improve the bit-rate distance product in a multimode fiber, which has a significant propagation loss (~3.5 dB/km) at 850 nm wavelength. Here, we demonstrate the detailed design considerations and fabrication of a single-mode, high-power, and high-speed VCSELs at the 850 nm wavelength with oxide-relief and Zn-diffusion apertures for the application of short (0.3 km) to medium reach (2 km) optical interconnects. By optimizing the relative geometric sizes between two such apertures in our demonstrated 850-nm VCSELs, we can not only attain high single-mode output power (~6.5 mW), but also with a reasonable threshold current (<; 2.0 mA). Furthermore, the spatial hole burning effect induced low-frequency roll off can also be minimized in our optimized structure to obtain a maximum data rate up to 26 Gbit/s. The record-high bit rate-distance products for OM4 MMF transmission under ON-OFF keying (14 Gbit/s × 2.0 km) modulation formats have been successfully demonstrated by the use of our VCSEL.

Single-Mode Vertical-Cavity Surface-Emitting Laser Array With High Power and Narrow Far-Field Divergence Angle

We demonstrate novel structures of an 850-nm vertical-cavity surface-emitting laser (VCSEL) array for high output power, single-lobe far-field pattern, and narrow divergence angle. By using the Zn-diffusion process with proper sizes of oxide-current-confined and Zn-diffusion apertures, each unit of VCSEL in the demonstrated array is highly single-mode (side-mode suppression ratio 30 dB) with a narrow far-field divergence angle (9°- 10°) and high maximum single-mode output power ( ~ 6.3 mW). Due to the high uniformity of single-mode performance of each VCSEL unit, the 6 × 6 array exhibits an excellent lasing phenomenon, which includes single-lobe far-field pattern, weak in-phase coupling, narrowing of divergence angle (from 9° to 4°), and output power as high as around 104 mW. Furthermore, by measuring the bias-dependent output optical spectra in different positions of our array, the high similarity of these spectra indicates the excellent uniformity of our fabrication process for single-mode VCSEL.

Modeling and simulation of VCSELs noise and its influence on noise performance of RF fiber links

Abstract In this paper, we present numerical simulations of the dynamics and noise of directly modulated vertical-cavity surface-emitting lasers (VCSELs) as primary light sources in RF links. Contribution of the VCSEL noise to the noise performance of the RF link is evaluated in terms of the noise figure. The VCSEL characteristics are investigated under a variety of conditions, including CW operation and sinusoidal modulation. Both single and two transverse-mode oscillations of VCSELs are studied. The obtained results show that the frequency spectra of the relative intensity noise exhibit peaks at the mode-competition frequency, the modulation frequency and the higher harmonics. The low-frequency level of relative intensity noise is minimum when the modulated VCSEL signal is continuous and uniform, but is pronounced when the signal is pulsing and non-uniform. The noise level of the two-mode VCSELs is almost 20 dB/Hz higher than that of the single-mode VCSEL. The noise factor of the fiber link decreases with the increase of both the modulation frequency and the depth. The contribution of the VCSEL noise to the noise factor of the fiber link is much greater than that of the photodiode.

Polarization axis fluctuations in a single mode VCSEL laser at 780nm

We present a transmission method to determine the polarization axis fluctuations for VCSEL (Vertical Cavity Surface Emitting Laser). The research is focused mainly on commercial lasers operatingat 780 nm, designed forlaser spectroscopy. The angle fluctuation of the laser linear axis polarization iselaborated to be less than 150 mrad. Measurement errors of this method are studied and calculated. The measurement uncertainty is ?1,4 mrad andthis is equivalent to ? 5? of arc.Changes of the linear polarization axis depending on the laser current and temperaturearepresented. Full Text: PDF References T. Ohtoshi et al., "Dependence of optical gain on crystal orientation in surface?emitting lasers with strained quantum wells", Appl. Phys. Lett.63, 1886 (1994). CrossRef K. Tateno et al., "Growth of vertical-cavity surface-emitting laser structures on GaAs (311)B substrates by metalorganic chemical vapor deposition", Appl. Phys. Lett.70, 3395 (1997). CrossRef O. Tadanaga et al., "An 850-nm InAlGaAs strained quantum-well vertical-cavity surface-emitting laser grown on GaAs (311)B substrate with high-polarization stability", IEEE Photon. Tech. Lett.12, 942 (2000) CrossRef K. Choquette, R. Leibenguth, "Control of vertical-cavity laser polarization with anisotropic transverse cavity geometries", IEEE Photon. Tech. Lett. 6, 40 (1994) CrossRef B. Weigl et al., "High-performance oxide-confined GaAs VCSELs", IEEE J. Sel. Top.Quantum Electron. 3, 409 (1997) CrossRef P. Dowd et al., "Complete polarisation control of GaAs gain-guided top-surface emitting vertical cavity lasers", Electron. Lett. 33, 1315 (1997) CrossRef M. Grabherr et al., "Volume production of polarization controlled single-mode VCSELs", Proc. SPIE,6908, 690803 (2008) CrossRef R. Roy et al., "First-Passage-Time Distributions under the Influence of Quantum Fluctuations in a Laser", Phys. Rev. Lett.45, 1486 (1980) CrossRef J. Martin-Regalado et al., "Polarization switching in vertical-cavity surface emitting lasers observed at constant active region temperature", Appl. Phys. Lett. 70, 3350 (1997) CrossRef M. B. Willemsen et al., "Polarization Switching of a Vertical-Cavity Semiconductor Laser as a Kramers Hopping Problem", Phys. Rev. Lett. 82, 4815 (1999) CrossRef M. B. Willemsen et al., "Anatomy of a Polarization Switch of a Vertical-Cavity Semiconductor Laser", Phys. Rev. Lett. 84, 4337 (2000) CrossRef T. Mukaihara et al., "Excess intensity noise originated from polarization fluctuation in vertical-cavity surface-emitting lasers", IEEE Photon. Technol. Lett. 7, 1113 (1995) CrossRef

Polarization axis fluctuations in a single mode VCSEL laser at 780nm

We present a transmission method to determine the polarization axis fluctuations for VCSEL (Vertical Cavity Surface Emitting Laser). The research is focused mainly on commercial lasers operatingat 780 nm, designed forlaser spectroscopy. The angle fluctuation of the laser linear axis polarization iselaborated to be less than 150 mrad. Measurement errors of this method are studied and calculated. The measurement uncertainty is ?1,4 mrad andthis is equivalent to ? 5? of arc.Changes of the linear polarization axis depending on the laser current and temperaturearepresented. Full Text: PDF References T. Ohtoshi et al., "Dependence of optical gain on crystal orientation in surface?emitting lasers with strained quantum wells", Appl. Phys. Lett.63, 1886 (1994). CrossRef K. Tateno et al., "Growth of vertical-cavity surface-emitting laser structures on GaAs (311)B substrates by metalorganic chemical vapor deposition", Appl. Phys. Lett.70, 3395 (1997). CrossRef O. Tadanaga et al., "An 850-nm InAlGaAs strained quantum-well vertical-cavity surface-emitting laser grown on GaAs (311)B substrate with high-polarization stability", IEEE Photon. Tech. Lett.12, 942 (2000) CrossRef K. Choquette, R. Leibenguth, "Control of vertical-cavity laser polarization with anisotropic transverse cavity geometries", IEEE Photon. Tech. Lett. 6, 40 (1994) CrossRef B. Weigl et al., "High-performance oxide-confined GaAs VCSELs", IEEE J. Sel. Top.Quantum Electron. 3, 409 (1997) CrossRef P. Dowd et al., "Complete polarisation control of GaAs gain-guided top-surface emitting vertical cavity lasers", Electron. Lett. 33, 1315 (1997) CrossRef M. Grabherr et al., "Volume production of polarization controlled single-mode VCSELs", Proc. SPIE,6908, 690803 (2008) CrossRef R. Roy et al., "First-Passage-Time Distributions under the Influence of Quantum Fluctuations in a Laser", Phys. Rev. Lett.45, 1486 (1980) CrossRef J. Martín-Regalado et al., "Polarization switching in vertical-cavity surface emitting lasers observed at constant active region temperature", Appl. Phys. Lett. 70, 3350 (1997) CrossRef M. B. Willemsen et al., "Polarization Switching of a Vertical-Cavity Semiconductor Laser as a Kramers Hopping Problem", Phys. Rev. Lett. 82, 4815 (1999) CrossRef M. B. Willemsen et al., "Anatomy of a Polarization Switch of a Vertical-Cavity Semiconductor Laser", Phys. Rev. Lett. 84, 4337 (2000) CrossRef T. Mukaihara et al., "Excess intensity noise originated from polarization fluctuation in vertical-cavity surface-emitting lasers", IEEE Photon. Technol. Lett. 7, 1113 (1995) CrossRef

85-fJ Dissipated Energy Per Bit at 30 Gb/s Across 500-m Multimode Fiber Using 850-nm VCSELs

We present important progress in energy efficiency for oxide-confined 850-nm single mode and quasi single mode vertical-cavity surface-emitting lasers (VCSELs) suitable for optical interconnects. Error-free operation at 30 Gb/s across 500 m of multimode optical fiber is achieved with 85 fJ of dissipated energy per bit. At 25 Gb/s, the maximum multimode fiber distance is 1000 m. These VCSELs are presently the most energy efficient directly modulated light-sources for data transmission across multimode optical fiber distances up to 1 km.

Energy Efficiency of Directly Modulated Oxide-Confined High Bit Rate 850-nm VCSELs for Optical Interconnects

The design, fabrication, and performance of the presently most energy-efficient oxide-confined 850 nm vertical-cavity surface-emitting lasers (VCSELs) for optical interconnects are presented. We employ a novel current spreading layer to reduce differential resistance. Compared to our previous designs, a higher indium content is used in the InGaAs quantum wells to increase the differential gain at low injected current densities. The influence of the oxide aperture diameter on the energy efficiency is determined by comparing the key performance parameters for a batch of VCSELs produced on the same epitaxial wafer, but with varying aperture diameters from 2.5 to 9.0 μm. The static light output power-current-voltage characteristics, small-signal modulation response, and large signal performance of our VCSELs are investigated in detail. The parameters important for energy-efficient operation are analyzed including threshold current, differential quantum efficiency, and differential resistance. We observe that our single-mode VCSELs are more energy efficient than our multimode VCSELs, although our multimode VCSELs typically exhibit a larger maximum static wallplug efficiency. Error-free (defined as a bit error ratio <;1 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-12</sup> ) data transmission at 25 Gb/s with a record-low dissipated heat energy of only 56 fJ/bit is achieved using a single-mode VCSEL with an oxide aperture diameter of 3.5 μm.

All-Optical Inverter Based on Polarization Switching in VCSELs Subject to Single and Dual Optical Injection

All-optical inversion in single-mode vertical-cavity surface-emitting lasers (VCSELs) under single- and dual-polarized optical injection is numerically analyzed. For single optical injection, turn-on delay of the parallel polarized power and spikes of the orthogonally polarized power are similar to those found when gain-switching a multimode semiconductor laser. We consider two different methods for all-optical inversion using dual-polarized optical injection. In the first (second) method, pulses of orthogonally (parallel) polarized light and a CW parallel (orthogonally) polarized beam are injected into the VCSEL. Similar switching times and extinction ratios are obtained with both methods. Faster operation with any of these two methods is obtained than for single injection. We show that both types of dual optical injection produce all-optical inversion and all-optical gating with similar characteristics. All-optical gating and inversion are achieved for a 2.5 Gb/s NRZ signal.

Optimizing Optical Output Power of Single-Mode VCSELs Using Multiple Oxide Layers

The influence of using multiple oxide layers with different positions and aperture sizes on vertical-cavity surface-emitting laser (VCSEL) performance is analyzed to show their effects on the optical output power, single-mode operation, and threshold current. The number of oxide layers, their positions, and aperture sizes are optimized to emit the maximum optical output power and transversally single-mode operation. A comprehensive 3-D optical-electrical thermal-gain self-consistent VCSEL model is used to simulate the continuous-wave operation of the multilayer oxide VCSELs. A comparison between optimized VCSELs possessing for different numbers of oxide layers is proposed. The results show that by using multilayer oxides, high-power single-mode VCSELs could be achieved.

Optimization of Single-Mode Photonic-Crystal Results in Limited Improvement of Emitted Power and Unexpected Broad Range of Tuning

This paper provides a numerical analysis of the influence of photonic crystal etching depth on the confinement factor, slope efficiency, emitted power and tuning range of single mode VCSELs. Several mechanisms were used to determine the level of power emission, namely: selective leakage, thermal focusing, the waveguide effect induced by the photonic-crystal, gain spectrum red shift, and its maximum reduction with the increase of driving currents. We show that careful design of the photonic crystal allows for a 10% increase in the emitted power of a single-mode regime and for a broad range of steering currents from 5 to 50 mA. Such attributes support tuning of a single-mode emission beyond the 20 nm spectrum range.

English

In this paper, a micro electromechanical systems vertical-cavity surface-emitting laser (MEMS-VCSEL) with asymmetric double oxide aperture and highly strained GaInNAsSb quantum wells for widely tunable, single mode and high temperature operation has been investigated. The MEMS-VCSEL is based on an integrated two-chip concept which allows us to extend the single wavelength performance to a continuously tunable, selectively wavelength-addressable spectrum of 40 nm. It has a much larger tuning range as compared with previous works. We present a comprehensive model including electrostatic membrane equation coupled with thermal, spatial and temporal rate equations considering Shockley Read Hall (SRH), Auger and carrier diffusion effects. These coupled equations are solved numerically by finite difference method (FDM). Using the simulation results, we design a single mode, high power, high temperature and tunable VCSEL, which is suitable for C-band dense-wavelength-division- multiplexing (DWDM) optical communication systems. &nbsp; Key words:&nbsp;Micro electromechanical systems (MEMS), tunable&nbsp;vertical-cavity surface-emitting laser (VCSELs), strained GaInNAsSb QWs, single mode operation.

Stochastically sustained population oscillations in high-β nanolasers

Nonlinear dynamical systems involving small populations of individuals may sustain oscillations in the population densities arising from discrete changes in population numbers due to random events. By applying these ideas to nanolasers operating with small numbers of emitting dipoles and photons at threshold, we show that such lasers should display photon and dipole population cycles above threshold, which should be observable as a periodic modulation in the second-order correlation function of the nanolaser output. Such a modulation was recently reported in a single-mode vertical-cavity surface-emitting semiconductor laser.

Energy-Efficient Oxide-Confined 850-nm VCSELs for Long-Distance Multimode Fiber Optical Interconnects

Highly energy-efficient oxide-confined 850-nm singlemode vertical-cavity surface-emitting lasers (VCSELs) for optical interconnects are presented. Error-free (defined as a bit error ratio <; 1 × 10-12) data transmission at 17 and 25 Gb/s across 100 m of multimode optical fiber is achieved with a low dissipated heat energy of only 69 and 99 fJ/bit, respectively. At 17 and 25 Gb/s, the transmission distance is increased to 1000 and 600 m, respectively. To date, our VCSELs are the most energy-efficient directly modulated lasers for data transmission across distances up to 1 km of multimode optical fiber.

Performance comparison of 850-nm and 1550-nm VCSELs exploiting OOK, OFDM, and 4-PAM over SMF/MMF links for low-cost optical interconnects

We experimentally compare the performance of two commercially available vertical-cavity surface-emitting laser diodes (VCSELs), a multi-mode 850-nm and a single-mode 1550-nm, exploiting on–off keying/direct detection (OOK/DD), and orthogonal frequency division multiplexed (OFDM) quadrature phase-shift keying (QPSK)/16-ary quadrature amplitude modulation (16QAM) with direct detection, over SMF (100m and 5km) and MMF (100m and 1km) short-range links, for their potential application in low-cost rack-to-rack optical interconnects. Moreover, we assess the performance of quaternary-pulse amplitude modulation (4-PAM), for the 1550-nm transmitter over SMF and MMF links and we compare it to the data-rate equivalent NRZ-OOK. The extensive performance comparison under various transmission scenarios shows the superiority of 1550-nm single-mode VCSEL compared to its multi-mode 850-nm counterpart. Moreover, OFDM/DD and 4-PAM in conjunction with low-cost, inexpensive VCSELs as transmitters prove to be an enabling technology for next-generation WDM, point-to-point, short-reach, SMF/MMF optical interconnects and potential candidates to substitute NRZ-OOK. Nevertheless, the sensitivity requirements are higher in that case, whereas these advanced, spectrally-efficient modulation formats become severely degraded when transmitted over MMF links, especially, when employing the inexpensive 850-nm VCSELs as transmitter. Finally, we compare the performance of the point-to-point links under investigation to the performance of a semiconductor optical amplifier (SOA)- based, scalable permutation switch fabric, the Optical Shared MemOry Supercomputer Interconnect System (OSMOSIS).

Modelling of vertical-cavity surface-emitting laser beam collimation using a nanostructured gradient index microlens

In this paper we show that the recently developed nanostructured gradient index (nGRIN) rod microlens can be utilised for the collimation of the beam generated by a vertical-cavity surface-emitting laser (VCSEL). The modelling of the nanostructured lens structure is performed using the finite difference time domain (FDTD) method with realistic nGRIN parameters and a Gaussian model of the light source. The large refractive index gradient of the nanostructured microlens allows the final microlens thickness to be only 70 μm with a diameter of 10 μm. Successful collimation of a single-mode VCSEL beam with a waist half-width of 1.53 μm is presented with a reduction in divergence half-angle from 10.1° to 3.3°. We show that the linear polarisation of the incident beam is preserved as well as presenting the tolerance of this type of lens to variations in overall thickness.

Dynamics of 1.55 μm Wavelength Single-Mode Vertical-Cavity Surface-Emitting Laser Output under External Optical Injection

We review the temporal dynamics of the laser output spectrum and polarization state of 1.55 μm wavelength single-mode (SM) vertical-cavity surface-emitting lasers (VCSELs) induced by external optical beam injection. Injection of an external continuous-wave laser beam to a gain-switched SM VCSEL near the resonance wavelength corresponding to its main polarization-mode output was critical for improvement of its laser pulse generation characteristics, such as pulse timing-jitter reduction, linewidth narrowing, pulse amplitude enhancement, and pulse width shortening. Pulse injection of pulse width shorter than the cavity photon lifetime into the SM VCSEL in the orthogonal polarization direction with respect to its main polarization mode caused temporal delay of the polarization recovery after polarization switching (PS), and its delay was found to be the minimum at an optimized bias current. Polarization-mode bistability was observed even in the laser output of an SM VCSEL of a standard circularly cylindrical shape and used for all-optical flip-flop operations with set and reset injection pulses of very low pulse energy of order of the 3.5~4.5 fJ.

Doppler-limited H2O and HF absorption spectroscopy by sweeping the 1,321–1,354 nm range at 55 kHz repetition rate using a single-mode MEMS-tunable VCSEL

A single longitudinal mode micro-electro-mechanical system-tunable vertical cavity surface-emitting laser (VCSEL) was used to measure H\(_{2}\)O and HF absorption spectra in the 1,321–1,354 nm range at 55 kHz repetition rate (\(\sim \)740 MHz/ns tuning rate). Pulse delay referencing was used to achieve an absorbance noise level of 0.004 (RMS), within a factor of 2.6 of the shot noise limit. The measured linewidths approach the low-pressure feature linewidths (\(\sim\)790 MHz) characteristic of the gases studied, highlighting the single-mode nature of the VCSEL throughout each rapid wavelength sweep. At even higher tuning rates, molecular features became asymmetric and broad, consistent with rapid passage and Fourier effects.

Analysis of Relative Intensity to Noise Ratio for Lasers at Different Bias Currents

Abstract In this paper, we have carried out the simulative analysis for averaging out the optimal value of RIN for better performance in high bit rate optical transmission link. We have found that for single mode VCSEL, the bias of 2 mA has the highest Spurious Free Dynamic Range (SFDR) and low RIN. For multimode VCSEL, the bias of 6 mA has the highest SFDR and low RIN.

Comprehensive large-signal analyses of RF modulation of vertical cavity surface emitting lasers

This paper introduces comprehensive numerical simulations of the static and dynamic characteristics of vertical cavity surface emitting lasers (VCSELs) under both continuous-wave (CW) operation and sinusoidal modulation. Both cases of single and two-tone modulations are studied. The VCSEL is assumed to oscillate in two modes, and the obtained results are compared to those of single mode VCSELs. The study is based on a multimode rate equation model of VCSELs, which describes the time evolution of number of the emitted photons and the density of injected electrons in the active and cladding layers. The higher and half harmonic distortions of the single-tone modulated signals as well as the intermodulated distortion of the two-tone modulated signals are investigated and correlated to the characteristics of the signal waveform.