Correlation between polarization modes in VCSEL with optical 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.

As a key part of vertical cavity surface emitting laser (VCSEL), active region will seriously affect the threshold and efficiency of the device. To obtain the appropriate laser wavelength and material gain, the design of In<sub>0.18</sub>Ga<sub>0.82</sub>As strain compensated quantum well is optimized. The relationship between the lasing wavelength of multiple quantum wells (MQWs) and the thickness is calculated. Considering the influence between the active region temperature and the lasing wavelength, the thickness of the quantum well is chosen as 6 nm, and the quantum barrier thickness is chosen as 8 nm, corresponding to the lasing wavelength of 929 nm. The material gain characteristics of the MQWs at different temperatures are simulated by Rsoft. The material gain exceeds 3300/cm at 300 K, and the temperature drift coefficient of the peak wavelength is 0.3 nm/K. In this work, Al<sub>0.09</sub>Ga<sub>0.91</sub>As and A<sub>l0.89</sub>Ga<sub>0.11</sub>As are chosen as the high- and the low-refractive index material of distributed Bragg reflector (DBR), and 20 nm graded layer is inserted between two types of materials. The influence of the graded layer thickness of DBR on the valence band barrier and reflection spectrum are calculated and analyzed. The increase of graded layer thickness can lead the band barrier peak and the reflection spectrum bandwidth to decrease. The reflection spectrum and phase spectrum of P-DBR and N-DBR are calculated by the transmission matrix mode (TMM): the reflectance of DBR is over 99% and the phase shift is zero at 940 nm. The optical field distribution of the whole VCSEL structure is simulated, in which the standing wave peak overlaps with the active region, and the maximum gain can be obtained. Using the finite element method (FEM), the effect of oxidation confined layer on the injection current is simulated. The current in the active region is effectively limited to the position corresponding to the oxidation confined hole, and its current density is stronger and more uniform. The optical field distributions in different modes of photonic crystal-vertical cavity surface emitting laser (PC-VCSEL) are simulated, and different modes have different resonant wavelengths. The values of quality factor Q in different modes of VCSEL and PC-VCSEL are calculated, Q of the fundamental mode is higher than that of higher transverse mode. It is demonstrated that the photonic crystal air hole structure can realize the output of basic transverse mode by increasing the loss of high order transverse mode. The VCSEL and PC-VCSEL with oxidation hole size of 22 μm are successfully fabricated, in which the photonic crystal period is 5 μm, the air pore diameter is 2.5 μm, and the etching depth is 2 μm. Under continuous current test, the maximum slope efficiency of VCSEL is 0.66 mW/mA, the output power is 9.3 mW at 22 mA, and the lasing wavelength is 948.64 nm at 20 mA injection current. Multiple wavelengths and large spectrum width are observed in the spectrum of VSCEL, which is an obvious multi-transverse mode. The maximum fundamental transverse mode output of PC-VCSEL reaches 2.55 mW, the side mode suppression ratio (SMSR) is more than 25 dB, and the spectrum width is less than 0.2 nm, indicating that the photonic crystal air hole has a strong control effect on the transverse mode, and the laser wavelength is 946.4 nm at 17 mA.

This paper is going to review the state-of-the-art of the high-speed 850/940-nm vertical cavity surface emitting laser (VCSEL), discussing the structural design, mode control and the related data transmission performance. InGaAs/AlGaAs multiple quantum well (MQW) was used to increase the differential gain and photon density in VCSEL. The multiple oxide layers and oxide-confined aperture were well designed in VCSEL to decrease the parasitic capacitance and generate single mode (SM) VCSEL. The maximal modulation bandwidth of 30 GHz was achieved with well-designed VCSEL structure. At the end of the paper, other applications of the near-infrared VCSELs are discussed.

The aim of this work is to fabricate high-power, single mode vertical cavity surface emitting lasers (VCSELs). Multiple junction VCSELs provide a pathway towards scaling optical output power. However, especially in the case of oxide confinement, these lasers have a greater tendency to exhibit multimode behavior when compared to their single junction counterparts. To achieve high-power, single mode multi-junction VCSELs, more advanced single mode strategies must be employed. A two-dimensional complex refractive index model was applied to model the transverse modes of photonic crystal VCSELs in order to determine the most suitable designs. Oxide confined VCSELs were fabricated using 850 nm single and double junction wafers, as well as 940 nm double and triple junction wafers. We report a maximum single mode power of 8.0 mW from the 850 nm double junction VCSELs and 10.7 mW from the 940 nm triple junction VCSELs. Double junction implant/oxide VCSELs were also fabricated and produced a peak single mode power of 8.1 mW.

Locking bandwidth and birefringence effects for polarized optical injection in vertical-cavity surface-emitting lasers

Random source is important for the security of key distribution. In this paper, a novel secure key distribution scheme based on unidirectional injection of vertical cavity surface emitting laser (VCSEL) system is proposed. In the proposed scheme, a chaotic signal without time delay signature is generated by a VCSEL subject to unidirectional optical injection, which is regarded as a master laser. The chaotic signal generated by the master VCSEL is further injected into two slave VCSELs to obtain synchronized bandwidth-enhanced chaotic signals. After that, by sampling, quantizing and XOR operation on the two synchronized chaotic signals, two key streams can be obtained. Based on the well-known spin-flip model, the time delay signature of chaotic signals generated by master VCSEL and the synchronization performance between the master VCSELs and two slave VCSELs are numerically investigated in detail. It is shown that by the unidirectional injection, the chaotic outputs can be achieved in the master VCSEL in a wide range of frequency detuning and coupling strength. More importantly, no time delay signature can be observed in the auto correlation function of the chaotic intensity time series generated by the master VCSEL. Besides, we find that high quality synchronization is achieved between the bandwidth-enhanced chaotic signals generated by two slave VCSELs under the common driving of master VCSEL. The synchronization coefficient between two slave VCSELs increases up to 0.99, and the synchronization coefficient between master VCSEL and salve VCSEL is only 0.74. Note that such a high quality synchronization between two slave VCSELs while relatively low quality synchronization between the master and slave VCSEL is conducible to ensuring the security of key distribution. In addition, the effects of tunable parameters on key bit error rate are considered, and two quantization methods are employed for comparison. Numerical simulation results show that the key bit error rate between two legitimate users is as low as 1%, and the key bit error rate between legitimate user and eavesdropper is higher than 10% in the single-threshold case; the bit error rate can even be as low as 10-6 in the double-threshold case. The influence of parameter mismatch on key bit error rate is also discussed, and it is suggested that two salve VCSELs should be finely matched to ensure low bit error rate. Finally, NIST randomness test is performed for the generated key streams. Hence, the proposed scheme enhances the security of key distribution, which is valuable for further developing the chaos communication systems.

In this paper, the influence of the rotating polarization-preserved optical feedback on the chaos synchronization of a vertical-cavity surface-emitting laser (VCSEL) is investigated experimentally. Two VCSELs' polarization modes (XP) and (YP) are gradually rotated and re-injected back into the VCSEL. The anti-phase dynamics synchronization of the two polarization modes is evaluated using the cross-correlation function. For a fixed optical feedback, a clear relationship is found between the cross-correlation coefficient and the polarization angle θp. It is shown that high-quality anti-phase polarization-resolved chaos synchronization is achieved at higher values of θp. The maximum value of the cross-correlation coefficient achieved is -0.99 with a zero time delay over a wide range of θp beyond 65° with a poor synchronization dynamic at θp less than 65°. Furthermore, it is observed that the antiphase irregular oscillation of the XP and YP modes changes with θp. VCSEL under the rotating polarization optical feedback can be a good candidate as a chaotic synchronization source for a secure communication system.

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

Based on the framework of the spin-flip model (SFM) for GHz level modulation frequency, the polarization performances of current-modulated vertical-cavity surface-emitting lasers (VCSELs) subject to weak optical feedback have been theoretically investigated. The results show that, for type 1 polarization switching (PS), the influences of optical feedback intensity and the current modulation amplitude on the high-frequency modulation response is not obvious. For low-frequency modulation, optical feedback will result in the output of a VCSEL having rich dynamics. A new style PS can be obtained under large-signal modulation through adjusting the modulation frequency. For type 2 PS the situation is more complex, and optical feedback increases the probability of polarization conversion and competition, while also affecting the PS point. The modulation amplitude also affects the output dynamics of the VCSEL.

We report a new graphical tool to analyze optical injection-locked vertical-cavity surface-emitting lasers (VCSELs). It predicts the resonant frequency enhancement and cavity mode behavior for both single- and multi- mode VCSELs under injection locking. Calculations based on this model show excellent agreement with experimental results.

The small-signal modulation response of multiple transverse modes in a vertical-cavity surface-emitting laser was studied numerically. The overlap between the modal distribution of the field and the carrier distribution in the active region is fundamental to determining the modulation response, According to the injection current level, the modulation response curve in several configurations and parameters used can display peaks and notches that may impair the frequency response of the device. These features reflect the competition of carrier by the operating modes in a way that can be described as interference. Therefore, the total modulation response curve cannot be evaluated from the modulation response of the individual modes.

Multimode VCSEL(Vertical Cavity Surface Emitting Laser) coupling into MMF (Multimode Optical Fiber) and its influence on MMF link has been numerically studied. Considering the transverse misalignment between VCSEL and MMF, coupling efficiency between VCSEL higher-order modes and modes of MMF is calculated and the Mode Power Distribution in the MMF is obtained. Simulation of MMF link with multimode VCSEL indicates that the higher-order VCSEL modes lead to decreasing of the eye opening of received signal. The transverse misalignment of VCSEL between MMF greatly deteriorates the eye opening. With 300m OM3-MMF link , the EOP (eye-opening-penalty) is greater than 14dB when the misalignment between VCSEL and MMF is lager than 5μm.

This paper presents for the first time the transmission of LTE signal based-on Radio-over-Fiber (RoF) scheme by using SiGe Hetero-junction Photo-Transistor as photo-receiver. The photo-transistor is fabricated based-on the commercial bipolar transistor technology. An 850 nm single mode Vertical Cavity Surface Emitting Lasers (VCSELs) and Standard Single Mode Fiber (SSMF) are used to complete the link so that makes the total cost of the system very low. The transmission of 20 MHz bandwidth LTE signal with high modulation format is achieved. The performance of the system is evaluated through the measurement of Error Vector Magnitude (EVM) under different operation conditions of the photo-transistor (in photodiode mode, photo-transistor mode and two terminals mode). We reach an EVM below 8% for the input power of -25 dBm to -2 dBm when the photo-transistor operates under two terminals condition. This EVM value fulfills the requirements of the LTE standard for 64-QAM modulation. The stability of the system with regard temperature variation and modal noise is also presented.

Remarkable progress made in performance characteristics and reliability of high-speed (> 10 GHz) 850-nm multi-mode (MM) oxide-confined vertical cavity surface emitting lasers (VCSELs) during the last decade has led them to find applications in space satellite systems. The main advantage of deploying high-speed VCSELs in space satellites over directly modulated 850-nm edge emitting lasers is the absence of COMD (catastrophic optical mirror damage). In recent years, leading VCSEL manufacturers introduced higher speed (~ 20 GHz or 25 Gbps) VCSELs with encouraging characteristics. However, little has been reported on reliability and failure modes of these state-of-the-art VCSELs although it is crucial to understand failure modes and degradation mechanisms in these VCSELs through physics of failure investigation and subsequently develop VCSELs that exceed lifetime requirements for space satellite systems. For the present study, we performed short-term and long-term accelerated life-tests on 25 Gbps oxide-confined MM VCSELs to study reliability of these devices. Our goal is to extract credible reliability model parameters (thermal activation energy and current exponent factor) from these life-tests to determine suitability of these lasers for future space satellite systems. We also performed failure mode analysis on VCSELs at different stages of degradation using various techniques. We employed nondestructive techniques including optical beam induced current (OBIC) and electron beam induced current (EBIC) techniques as well as destructive techniques including focused ion beam (FIB) and high-resolution TEM techniques. Our detailed reliability and failure mode analysis results are reported along with our understanding on the physical origin of degradation in high-speed VCSELs with strained InGaAs quantum wells.

Vertical cavity surface emitting laser (VCSEL) is an important laser source for their evident plentiful applications in optical communication. The present investigation reports a comparison of the modeling and optimization of long wavelengths 1310 nm and 1550 nm high speed short cavity VCSEL for continuous wave operation at various temperature (283-3230K) for various diameters. The continuous wave lasing is demonstrated for the device diameter from 2 to 5 μm with threshold current of 1.07-1.33 mA with threshold power consumption of 1.86-2.57 mW for 1310 nm and threshold current of 0.94-1.24 mA and threshold power consumption 1.67-2.1 mW for 1550 nm VCSEL. The results demonstrate that the threshold current, peak emitted power and power consumption increases with the increase in device diameter. The results confirm that VCSELs with 2 μm diameter is most suitable to achieve energy-efficient operation. Although rollover current increases with the diameter, but, due to the advantage of lower threshold current and power consumption, VCSEL having smaller diameter is best suited. The power conversion efficiency for proposed long wavelength VCSELs is approximately 50% which is extremely useful for low power applications. The proposed VCSELs are suitable for very short reach (<2 m) optical interconnects such as chip-to-chip and board-to-board communication in high performance computers.