Μm Vertical-cavity Surface-emitting Laser Research Articles

Analysis of Internal Optical Loss of 1.3 μm Vertical-Cavity Surface-Emitting Laser Based on n++-InGaAs/p++-InGaAs/p++-InAlGaAs Tunnel Junction

Analysis of Internal Optical Loss of 1.3 μm Vertical-Cavity Surface-Emitting Laser Based on n++-InGaAs/p++-InGaAs/p++-InAlGaAs Tunnel Junction

Experimental demonstration of 1.3 μm VCSEL‐based optoelectronic oscillator at 12 GHz using optical injection‐locking technique

The experimental validation is presented of an optical injection-locked (OIL) vertical-cavity surface-emitting laser (VCSEL)-based optoelectronic oscillator (VBO) to overcome the direct-modulation bandwidth limitations of packaged VCSELs. A 1.3 μm VCSEL under OIL is directly modulated at 12 GHz. The carrier phase noise value is −97.7 dBc/Hz at 10 kHz offset. A time domain characterisation of the oscillator based on Allan variance is proposed. The performed measurements showed that the OIL technique allows an increase in the optoelectronic oscillator (OEO) carrier frequency in comparison with free-running VBOs while maintaining high spectral purity. The results for a 12 GHz delay-line OEO with amplitude modulation are also compared with the proposed approach.

Interrogation of fiber-Bragg-grating temperature and strain sensors with a temperature-stabilized VCSEL

The interrogation of fiber-Bragg-grating (FBG) sensors using a vertical-cavity surface-emitting laser (VCSEL) is discussed. A long-wavelength (1.54 μm) VCSEL was used as a wavelength-tunable source by variation in the current. Temperature stabilization was performed with a thermoelectric device. Characteristics of temperature and strain sensing were investigated. FBGs with different reflectivities were compared. For temperature sensing, the root-mean-square error in the measurement was reduced to 1/3 that without temperature stabilization. The dependence of the measurement error on the reflectivities of the FBGs was investigated. The measurement error was larger for FBGs with lower reflectivities in both temperature and strain sensing. Improvement on the sensing with low-reflectivity FBGs is discussed.

Evaluation of 1.3-㎛ Wavelength VCSELs Grown by Metal Organic Chemical Vapor Deposition for 10 Gb/s Fiber Transmission

We have evaluated a 1.3 μm vertical-cavity surface-emitting laser (VCSEL), whose bottom mirror and central active layer were grown by metal organic chemical vapor deposition (MOCVD) and whose top mirror was covered with a dielectric coating, for 10 Gb/s data transmission over single-mode fibers (SMFs). Successful demonstration of error-free transmission of the directly modulated VCSEL signals at data rate of 10 Gb/s over a 10 km-long SMF was achieved for operating temperatures from 20°C to 60°C up to bit-error-rate (BER) of 10-12. The DC bias current and modulation currents are only 7 mA and 6 mA, respectively. The results indicate that the VCSEL is a good low-power consuming optical signal source for 10 GBASE Ethernet applications under controlled environments.

12.5 Gbit/s VCSEL-based transmission over legacy MMFs by centre-launching technique

1.3 µm vertical-cavity surface-emitting laser (VCSEL)-based transmission in legacy standard multimode fibre (MMF) by using the mode-field matched centre-launching technique is experimentally demonstrated. A transmission bit rate of 12.5 Gbit/s is realised at 1.3 µm by direct modulation of a VCSEL suitable for high-speed applications. Performances without significant penalties, also compared with singlemode fibre (SMF) propagation, are measured up to 10 km MMF coils, simply connected by fusion splicing, without SMF patchcords. The explored VCSEL-based solution can be exploited for the low-cost development of next-generation multi-Gbit/s LANs over already installed MMFs.

Two-Axis MEMS Lens Alignment System for Free-Space Optical Interconnect

We present a two-axis microelectromechanical systems (MEMS) lens aligner with a 260 μm × 220 μm translation range that positions a 6.35 mm lens with focal length f = 12.1 mm for alignment compensation of free-space optical interconnects (FSOIs) between computer servers separated by 50 mm spacing. Efficient ultrasonic linear piezoelectric motors (PMs) provide actuation with zero power required to hold the lens alignment. A four-channel FSOI is demonstrated with 1 × 4 vertical cavity surface-emitting laser (VCSEL) and photodiode (PD) arrays capable of 10 Gb/s transmission bandwidth. Demonstrated minimum step size of 1.68 μm is sufficient for aligning the 20 μm VCSEL spots onto the 40 μ m PD receivers. Force transmission between PMs and a silicon MEMS flexure stage is accomplished using a 1-mm steel ball bearing in a magnetic groove, providing compliance in the nondriven axis. The ball-coupling design has 15 μm backlash and induces a maximum of 8 μm of cross-axis motion.

Broadband MEMS-Tunable High-Index-Contrast Subwavelength Grating Long-Wavelength VCSEL

A widely-tunable single-mode 1.3 μm vertical-cavity surface-emitting laser structure incorporating a microelectromechanical system-tunable high-index-contrast subwavelength grating (HCG) mirror is suggested and numerically investigated. A linear tuning range of 100 nm and a wavelength tuning efficiency of 0.203 are predicted. The large tuning range and efficiency are attributed to the incorporation of the tuning air gap as part of the optical cavity and to the use of a short cavity structure. The short cavity length can be achieved by employing a HCG design of which the reflection mechanism does not rely on resonant coupling. The absence of resonance coupling leads to a 0.59 λ-thick penetration depth of the HCG and enables to use a 0.25 λ-thick tuning air gap underneath the HCG. This considerably reduces the effective cavity length, leading to larger tuning range and efficiency. The basic properties of this new structure are analyzed, and shown to be explained by analytical expressions that are derived in the paper. In this context, the penetration depth of the HCG is introduced and shown to be an important characteristic length scale. Throughout the tuning wavelength range, strong single mode operation was maintained and uniform output power is expected.

Different forms of wavelength polarization switching and bistability in a 155 μm vertical-cavity surface-emitting laser under orthogonally polarized optical injection

Different forms of wavelength polarization switching and bistability are reported in a 1550 nm vertical-cavity surface-emitting laser (VCSEL) operated just above threshold and subject to orthogonally polarized optical injection into the subsidiary orthogonal polarization mode. This diversity of behavior at the wavelength of 1550 nm offers promise for the use of VCSELs in optical signal processing and optical switching applications.

Wavelength modulation spectroscopy with a widely tunable InP-based 23 μm vertical-cavity surface-emitting laser

We report on the successful application of recently developed 2.3 microm InP-based vertical-cavity surface-emitting lasers with a buried tunnel junction in a wavelength modulation spectroscopy measurement for carbon monoxide (CO) detection. The electrically pumped devices operate at room temperature under cw operation with stable single-mode emission and should allow for parts in 10(6) (ppm) level resolution measurement of CO with a standard optical setup.

Long-wavelength vertical-cavity surface-emitting laser using an electro-optic index modulator with 10nm tuning range

We demonstrate an original approach to achieving a tunable 1.55μm vertical-cavity surface-emitting laser. The tunability is based on an electro-optic index modulator using nanosized droplets of liquid crystal as a phase layer. Such an approach can produce a robust and a low-cost device. A 10nm tuning range with less than 170V applied voltage has been demonstrated. The device is formed by a conventional InP-based active region with an epitaxial and a dielectric Bragg mirror. This optically pumped device exhibits an excellent side-mode suppression ratio of higher than 20dB over the whole spectral range.

Nanofocusing probe limitations for a ultra-high density optical memory

The limitation aspects of nanofocusing recording probes are discussed in this paper. Thedefinitions of nanophotonics and nanofocusing are underlined. In this nano-age opticalnanophenomena are described for nanometric architectures and nanostructural photonicdevices. The nanofocusing probe limitations are connected with the wave-optics diffractionlimit, geometrical beam tiny focusing, electromagnetic wave design, fabricationerrors, nanoprobe energetic efficiency, near-field air gap and optical disk surfaceconditions. The micro-structure of the designed near-field optical head is discussed.The obtained nanofocused spot size is about 20 nm for the near-field space. Thecomputed finite differential time domain (FDTD) power density spot is under 200 nmwithout any optical optimization. The far-field functions have a diffraction limit of150 nm. The energy intensity can be elevated by more than 70 times in the FDTDcalculated focal point using a convex microlens (ML) surface for focusing of a8 µm vertical-cavity surface-emitting laser (VCSEL) beam. The optical power density iscompressed up to 1024 times to the exact nanofocused spot in comparison with theentrance VCSEL micro-beam. The experimentally fabricated ML arrays and single lensesare presented. The optical quality and ML radius control with an AFM method isfulfilled. The optical integration technology for the proposed nanofocusing probefabrication is announced. The nanofocusing probe spots are 10–13 nm for thecentral zone of the ML surface. The merit spot sizes are 10–18 nm for the entireML nanofocusing diameter. For a single ML nanofocusing near-field head theenergy spots have sizes from 9 to 15 nm, limited by technological aberrations.

Nonlinear optical input–output characteristics of 1.55 μm injection-locked vertical-cavity surface-emitting lasers

The optical input–output characteristics of a 1.55 μm vertical-cavity surface-emitting laser (VCSEL) with external light injection to its fundamental mode were investigated. Appropriate wavelength detuning of external light enables abrupt modal switching in an injection-locked VCSEL. We found that the obtained nonlinear transfer function is strongly dependent on the distance between a VCSEL and an input lensed fiber. As the distance was changed, different optical input–output characteristics were observed, demonstrating that such a VCSEL can be employed in various optical signal-processing schemes, for example as an optical regenerator or an optical inverter.

Chirp and linewidth enhancement factor of 1.55 [micro sign]m VCSEL with buried tunnel junction

Chirp characteristics of a 1.55 µm vertical-cavity surface-emitting laser (VCSEL) employing a buried tunnel junction are reported for the first time. From the measurements the linewidth enhancement factor αH is derived and presented.

1.8 µmvertical-cavity surface-emitting laser absorption measurements of HCl, H2O andCH4

A 1.8 µmwavelength single frequency InGaAlAs–InP vertical-cavity surface-emittinglaser (VCSEL) was used successfully for the first time for highresolution absorption spectroscopic measurements. As a demonstrationof the multi-species measurement capability, spectra of HCl, CH4 andH2Ogases were measured at pressures ranging from 0.07 to 1.5 bar andcompared with calculations based on the HITRAN2000 database. Ingeneral, good agreement was observed. The laser threshold was 0.9 mA,the temperature tuning rate was 0.125 nm K−1(0.38 cm−1 K−1)and the current tuning rate was 0.9 nm mA−1(2.75 cm−1 mA−1). Acontinuous mode-hop-free single frequency current tuning range of 8.4 cm−1(2.8 nm) was achieved using a 0–4.1 mA driving current. Single frequencyVCSELs show a variety of advantages compared to edge emitting semiconductorlasers, such as wide current tuning range, very high tuning speeds (MHz)and therefore very good time resolution, little susceptibility to opticalfeedback and low manufacturing costs. The availability of long wavelengthsingle frequency VCSELs (1.3–2 µm)should make VCSEL the preferred choice for diode-laser gas sensing and processcontrol applications and help to significantly expand the application fields forinfrared diode-laser gas sensors.

Low-threshold optically pumped λ=4.4 μm vertical-cavity surface-emitting laser with a PbSe quantum-well active region

We report pulsed emission from an optically pumped lead-salt vertical-cavity surface-emitting laser with a PbSe/PbSrSe quantum-well active region. The lasing wavelength of λ=4.44 μm is nearly constant over the temperature range 200–280 K, and the threshold is only 10.5 kW/cm2 at 260 K, where the gain peak and cavity mode are in resonance. Over 330 mW of peak power is emitted at 260 K, into a circular beam whose divergence angle increases with pump intensity.

88 °C, continuous-wave operation of apertured, intracavity contacted, 1.55 μm vertical-cavity surface-emitting lasers

We demonstrate a lattice-matched 1.55 μm vertical-cavity surface-emitting laser operating continuous wave up to 88 °C. The laser employs AlAsSb-based mirrors, which provide high reflectivity and lattice matching to InP. The poor electrical and thermal conductivity of these mirrors is circumvented by utilizing an InP double-intracavity contacted structure. Benefits of the intracavity contacts are addressed by comparing the characteristics with the alternative contact scheme where current is injected through the Sb-based mirrors. Current and optical confinement is provided by an undercut aperture. The device shows a threshold current of 800 μA, a differential efficiency of 23%, and a maximum output power of over 1 mW at 20 °C.

Submilliamp long-wavelength InP-based vertical-cavity surface-emitting laser with stable linear polarisation

A 1.5 µm vertical-cavity surface-emitting laser operating with high efficiency under continous wave conditions at room temperature is demonstrated with threshold current and voltage below 1 mA and 1 V, respectively. The singlemode emission spectrum exhibits stable linear polarisation with a sidemode suppression ratio of 30 dB.

Control of wet-etching thickness in the vertical cavity surface emitting laser structure by in situ laser reflectometry

We have investigated the use of in situ laser reflectometry for etch depth control in vertical cavity surface emitting laser (VCSEL) structures. We can obtain the precise etch depth by simply counting the number of oscillations during the wet-etching process. After calibration on an AlGaAs/GaAs 20-period distributed Bragg reflector (DBR) structure, this technique was applied to the monolithic 1.55 μm VCSEL device process that is required to etch epilayers of several μm thickness. In the 1.55 μm VCSEL structure, the mesa was generated by monitoring the number of peaks in the bottom DBR that corresponded to an etch depth of about 11 μm. The overall spatial uniformity of the etched sample was within a layer (1000 Å) by the distinction between layers. This process offers the possibility of precise control of etch depth for any multilayer structure.

Precise control of 1.55 μm vertical-cavity surface-emitting laser structure with InAlGaAs/InAlAs Bragg reflectors by in situ growth monitoring

The vertical-cavity surface-emitting laser (VCSEL) structure designed at 1.55 μm was grown by a low-pressure metalorganic chemical vapor deposition method. In situ laser reflectometry, using both 0.633 and 1.53 μm wavelengths simultaneously, was employed to control the exact optical thickness over the whole growth time. The distributed Bragg reflectors (DBRs) were grown with alternate In0.53Al0.13Ga0.34As and In0.52Al0.48As λ/4 wavelength layers. The oscillatory reflection signals obtained by the monitoring laser at 1.53 μm gave information for designing the center wavelength of the DBR. The reflectance spectrum of the VCSEL structure showed an excellent square shaped wide flatband (greater than 90 nm) where the reflectivity reached a plateau as expected by the in situ monitoring data.

1.55 [micro sign]m vertical-cavity surface-emitting lasers with wafer-fused InGaAsP/InP-GaAs/AlAs DBRs

The authors propose a novel 1.55 µm vertical-cavity surface-emitting laser (VCSEL) structure with wafer-fused InGaAsP/InP-GaAs/AlAs distributed Bragg reflectors. The resonant-cavity wavelength before water fusion is in exact accord with the emission wavelength, and a 25 µm diameter VCSEL exhibits CW operation at 27°C.