Waveguide Diode Research Articles

Compact, Watt-class 785 nm dual-wavelength master oscillator power amplifiers

785 nm micro-integrated, dual-wavelength master oscillator power amplifiers with a footprint of 5 mm × 25 mm are presented. They are based on Y-branch distributed Bragg reflector ridge waveguide diode lasers and anti-reflection coated tapered amplifiers. In order to reduce the impact of potential optical feedback, devices with master oscillator front facet reflectivities of 5% and 30% as well as with an integrated miniaturized optical isolator have been realized. A comparison up to 1 W shows narrowband dual wavelength laser emission with a spectral distance of 0.6 nm (10 cm−1) and individual spectral widths <20 pm. As expected, a higher front facet reflectivity leads to a significant reduction of feedback related mode hops. Longitudinal modes corresponding to the master oscillator resonator length remain within spectral windows <0.15 nm (3 cm−1), suitable for applications such as Raman spectroscopy and especially shifted excitation Raman difference spectroscopy. Integrating a compact 30 dB optical isolator completely eliminates the observed optical feedback effects. Lateral beam propagation ratios of 1.2 (1/e2) enable easy beam shaping and fiber coupling. Outside of the experimental comparison, the developed MOPAs provide up to 2.7 W of optical output power available for applications.

Comparison of individual and common wavelength-operation for 785 nm Y-branch DBR ridge waveguide diode lasers with adjustable spectral distance.

An experimental comparison between individual and common wavelength-operation of a Y-branch distributed Bragg reflector (DBR) ridge waveguide (RW) laser at 785 nm with an electrically adjustable spectral distance is presented. The dual-wavelength Y-branch laser combines two laser cavities via a Y-section to a common output section. DBR gratings with different grating periods are associated with the two cavities, which set the emission wavelengths of the two branches. Implemented resistive heater elements allow separate wavelength tuning of the two branches, which can be operated individually for alternating emission wavelengths in applications such as differential absorption spectroscopy or shifted excitation Raman difference spectroscopy. Common wavelength operation simultaneously generates two emission lines suitable for the generation of THz radiation using difference frequency mixing. Hereby, the devices could potentially be used as single-chip light sources for a combination of Raman and THz applications. For the wavelength-operation comparison presented, the devices were operated up to optical output powers of about 105 and 185 mW in individual and common wavelength-operation mode, respectively. In individual operation mode, the devices show spectral single-mode emission over the whole operation range. In common operation mode, the spectral emission is predominantly single mode up to an optical output power of 65 mW. In both operation modes, mode hops typical for DBR lasers occur. At an optical output power of 50 mW, tuning of the spectral distance between the two wavelengths using the implemented resistor heaters is demonstrated. In both modes of wavelength operation, a flexible frequency difference between 0 and 0.8 THz (0 and 1.6 nm) with predominantly single-mode spectral emission is obtained.

Design of diode laser using slab coupled optical waveguide with graded refractive index structure

Thickness and refractive index of slab layer have major effects in the electro-optical characteristics of slab coupled optical waveguide diode lasers. In this research, ordinary step refractive index profile was replaced by a broadened waveguide with linear graded refractive index profile and optimized doping. The results show such design can significantly improve the power conversion efficiency (PCE). According to these results, by using the asymmetric barrier in the sides of active region, the threshold current decreases and slop efficiency (SE) increases. The PCE and SE in the proposed structure are respectively 12% and 0.21 W/A higher than those in conventional step profile.

Improved light coupling efficiency of organic light-emitting diode and polymer optical waveguide integrated device by grating coupler

Improved light coupling efficiency of organic light-emitting diode and polymer optical waveguide integrated device by grating coupler

High-power single-mode triple-ridge waveguide semiconductor laser based on supersymmetry

To achieve a high-power single-transverse mode laser, we here propose a supersymmetry-based triple-ridge waveguide semiconductor laser structure, which is composed of an electrically pumped main broad-ridge waveguide located in the middle and a pair of lossy auxiliary partner waveguides. The auxiliary partner waveguides are designed to provide dissipative modes that can phase match and couple with the higher-order modes in the main waveguide. By appropriately manipulating the gain–loss discrimination of the modes in the laser cavity, one can effectively suppress all the undesired higher-order transverse modes while keeping the fundamental one almost unaffected, thereby ensuring stable single-mode operation with a larger emitting aperture and accordingly a higher output power than a conventional single-transverse-mode ridge waveguide diode laser.

Distributed feedback lasers using surface gratings in Bragg waveguides.

This Letter presents, to the best of our knowledge, the first report of a narrow-linewidth ∼790-800nm edge-emitting semiconductor distributed feedback Bragg reflection waveguide diode laser (DFB2RL). The DFB2RLs were fabricated using a ridge waveguide structure with 5th order, surface-etched grating forming the wavelength selective element. Unbonded devices with a 500 µm cavity length exhibited continuous wave threshold currents in the region of 25 mA with an output power of 2.5 mW per (uncoated) facet at 100 mA drive current. The devices operated in a single longitudinal mode, with side-mode suppression ratio (SMSR) as high as 49 dB and linewidths as low as 207 kHz. Devices maintained single mode operation with high SMSR over a 9 nm wavelength range as the temperature was swept from 15°C to 50°C.

Emission behavior of distributed Bragg-reflector ridge waveguide lasers exposed to strong optical feedback.

In this work, the influence of strong optical feedback on the emission behavior of distributed Bragg-reflector ridge waveguide diode lasers emitting at 1120 nm with different cavity lengths and facet reflectivities is investigated. Based on measurements of the optical output power, central emission wavelength, and spectral emission width, the different diode laser types are compared while optical feedback up to -8dB is applied. The observed changes of the optical output power and emission wavelength as well as the occurrence of coherence collapse states give insight into the resistance against feedback of the different diode laser types.

A Theoretical Treatment of THz Resonances in Semiconductor GaAs p-n Junctions.

Semiconductor heterostructures are suitable for the design and fabrication of terahertz (THz) plasmonic devices, due to their matching carrier densities. The classical dispersion relations in the current literature are derived for metal plasmonic materials, such as gold and silver, for which a homogeneous dielectric function is valid. Penetration of the electric fields into semiconductors induces locally varying charge densities and a spatially varying dielectric function is expected. While such an occurrence renders tunable THz plasmonics a possibility, it is crucial to understand the conditions under which propagating resonant conditions for the carriers occur, upon incidence of an electromagnetic radiation. In this manuscript, we derive a dispersion relation for a p–n heterojunction and apply the methodology to a GaAs p–n junction, a material of interest for optoelectronic devices. Considering symmetrically doped p- and n-type regions with equal width, the effect of certain parameters (such as doping and voltage bias) on the dispersion curve of the p–n heterojunction were investigated. Keeping in sight the different effective masses and mobilities of the carriers, we were able to obtain the conditions that yield identical dielectric functions for the p- and n-regions. Our results indicated that the p–n GaAs system can sustain propagating resonances and can be used as a layered plasmonic waveguide. The conditions under which this is feasible fall in the frequency region between the transverse optical phonon resonance of GaAs and the traditional cut-off frequency of the diode waveguide. In addition, our results indicated when the excitation was slightly above the phonon resonance frequency, the plasmon propagation attained low-loss characteristics. We also showed that the existence or nonexistence of the depletion zone between the p- and n- interfaces allowed certain plasmon modes to propagate, while others decayed rapidly, pointing out the possibility for a design of selective filters.

Light at the end of the fiber

light at the end of the fiber

Characterization and comparison between two coupling concepts of four-wavelength monolithic DBR ridge waveguide diode laser at 970 nm

Compact laser sources emitting at multiple wavelengths from a single aperture are interesting in a multiple of applications. In this work, we characterize and compare two concepts of four-arm monolithic distributed Bragg reflector (DBR) ridge waveguide (RW) diode lasers emitting at four different wavelengths around 970 nm. The first concept has a single intersection point, where the four arms are joined before being emitted from the output aperture. The second concept has two intersection points: the first where the inner two arms are combined and a second where those are joined by the outer two arms. In the first case, the inner and outer arms show difference in performance, in particular the outer arms show worse opto-electrical and spatial parameters compared to the inner arms. In the second concept, similar performance is observed from all four arms, with smaller deviations between the inner and outer arms in the mentioned parameters. This study suggests that a serial combination of pairs of bends is preferable in this kind of multi-wavelength laser sources.

Annular CPW‐FED directivity‐variable array antenna loaded with Schottky diodes

AbstractA novel high‐speed directivity‐variable array antenna is designed, fabricated and characterized. The passive LC elements and varactor/PIN diodes used in conventional antennas are replaced with an annular coplanar waveguide (CPW) and Schottky diodes, in order to overcome the problem of out‐of‐band radiation. The proposed antenna consists of 3 dipole antennas on the upper side of the substrate, and a CPW with 4 Schottky diodes on the bottom side of the substrate. The antenna was designed and characterized at 2.45 GHz. Measurement results demonstrate that the proposed antenna exhibits beam steering and mirror‐image pattern pairs capability.

Design of the Multi-PIN Diode Waveguide Limiter with Extended Attenuation Bandwidth

Design of the Multi-PIN Diode Waveguide Limiter with Extended Attenuation Bandwidth

Determining the refractive index of a laser diode waveguide from the measured radiation pattern

It is shown that to find the transverse refractive-index profile of a semiconductor laser waveguide, it is sufficient to know the angle of the device’s radiation divergence and two values of the function describing the directional radiation pattern. A calculation technique is proposed and its use in the diagnostics of laser diode degradation is discussed.

InAlGaN superluminescent diodes fabricated on patterned substrates: an alternative semiconductor broadband emitter

We demonstrate InGaN violet light-emitting superluminescent diodes with large spectral width suitable for applications in optical coherence spectroscopy. This was achieved using the concept of nonlinear indium content profile along the superluminescent diode waveguide. A specially designed 3D substrate surface shape leads to a step-like indium content profile, with the indium concentration in the InGaN/GaN quantum wells ranging approximately between 6% and 10%. Thanks to this approach, we were able to increase the width of the spectrum in processed devices from 2.6 nm (reference diode) to 15.5 nm.

Freely Triggerable Picosecond Pulses From a DBR Ridge Waveguide Diode Laser Near 1120 nm

In this letter, we present results on the pulsed operation of a distributed Bragg reflector ridge waveguide diode laser with wavelength close to 1120 nm. Picosecond optical pulses were generated by gain-switching at variable repetition frequencies up to 80 MHz. In single-pulse operation, a pulse width of 92 ps with a pulse peak power of 1.7 W at 10 MHz could be obtained. Investigations in operation at higher injection current pulse amplitude increased the pulse peak power to 2.6 W, but also showed significant trailing pulses which is typical for gain-switched diode lasers. The shape of the pulses is stable over the whole range of the investigated repetition frequencies from 5 to 80 MHz. At an operation temperature of 25 °C, the emitted radiation has a wavelength of 1114.7 nm and increases to 1116.4 nm at 45 °C. The central wavelength does not change significantly at higher output power.

Surface morphology and thermal figure of merit of a new compound thin film

The third nonlinear optical properties of a new compound 4,4′-bis(3-methoxy benzylidene amino) biphenyl doped poly-methyl methacrylate (PMMA) have been studied using Z-scan technique. Experiments are performed using a continuous waveguide (cw) diode laser at 532 nm wavelength and 0.68 kW/cm2 laser intensity. The optical power limiting behavior of sample doped PMMA was also investigated. It also shows a very good optical limiting behavior with a limiting threshold of 4.7 mW. We attribute the nonlinear absorption and optical limiting property of the sample film to two photon absorption effect at 532 nm. The experimental evidences of observing diffraction pattern in compound 4,4′-bis(3-methoxybenzylideneamino) biphenyl doped PMMA has been present. The refractive index change, Δn, and nonlinear refractive index, n 2 determined from the number of observed ring. We obtained good values of Δn = 105.154 × 10−4and n 2 = 154.154 × 10−7 cm2/W. Variation of refractive index with temperature, dn/dT, and figure of merit, H, are found to be 8.858 × 10−6 1/°C and 5.316 × 10−6, respectively. This large nonlinearity is attributed to a thermal effect resulting from linear absorption. Theoretical diffraction pattern that agree well with experimental one are generated using a wave theory.

Comparison of two concepts for dual-wavelength DBR ridge waveguide diode lasers at 785 nm suitable for shifted excitation Raman difference spectroscopy

Two concepts of dual-wavelength 785-nm DBR ridge waveguide (RW) lasers, i.e. RW mini-arrays consisting of two DBR-RW lasers and Y-branch DBR-RW lasers, will be compared with respect to their usability as excitation light sources for shifted excitation Raman difference spectroscopy (SERDS). For both types of devices for each wavelength, output powers up to 215 mW were measured. A stable spectral distance between the laser emissions of the two resonator branches with the targeted value of 0.6 nm, i.e. 10 cm−1, is observed. In the case of the mini-array up to an output power of about 70 mW, the device shows single-mode operation. Although at higher power levels, mode hops and multi-mode operation occur, the emission width smaller than 0.15 nm still meets the requirements for Raman measurements of solids and liquids. Over the whole working range, the spectral distance between the two wavelengths is approximately constant with 0.62 nm. The near field shows two emission spots according to the dimension of the RW and their processed distance of 20 µm. The Y-branch laser shows single-mode operation up to 150 mW with a narrow spectral emission width. At higher powers also, multi-mode operation with an emission width of 0.15 nm occurs. The nearly diffraction-limited emission comes from one output aperture; the far-field emission shows a pronounced asymmetry between the two branches. Both types of devices fulfil the spectral requirements from Raman spectroscopy and SERDS up to 215 mW output power.

Hollow-waveguide-based carbon dioxide sensor for capnography

A CO2 sensor for capnography, based on a hollow waveguide (HWG) and tunable diode laser absorption spectroscopy (TDLAS), is presented; the sensor uses direct absorption spectroscopy and requires neither frequent calibration nor optical filters, giving it a significant advantage over existing techniques. Because of the HWG, the CO2 measurement achieved a concentration resolution of 60 ppm at a measurement rate of 25 Hz, as characterized by Allan variance. The length of the HWG was selected to efficiently suppress the optical fringes. This setup is perfectly suited for the detection of CO2 by capnography, and shows promise for the potential detection of other breath gases.

MHD instability fluctuation measurement on the HL-2A tokamak by using the HCN laser interferometer

The multichannel HCN laser interferometer has been routinely used to measure the electron density (n e ) on the HL-2A tokamak for several years. In order to explore its capability for qualitatively evaluating the Magnetohydrodynamic (MHD) fluctuation in plasmas from the probing signal, we implemented two important modifications on the hardware of channel #3 (r = −10.5 cm): (1) application of the high-response Schottky diode waveguide detector, and (2) utilization of a preamplifier with a broad pass-band of up to 500 kHz so as not to filter the fluctuation component mixed with the intermediate frequency (IF). Many MHD fluctuation phenomena, such as tearing modes (TMs), fishbones, long lived modes (LLMs), have been successfully detected by using the modified channel #3 in the HL-2A experimental campaign, and the results were quite coincident with those derived from the magnetic probe and the soft X-ray systems. We propose to apply this novel approach to more channels of the HCN laser interferometer.

High Brightness, Narrow Bandwidth DBR Diode Lasers at 1120 nm

In this letter, we report on monolithic distributed Bragg reflector ridge waveguide diode lasers. The lasers feature highly strained InGaAs quantum wells and fifth order surface gratings for a stabilized emission wavelength ~1120 nm. Output powers up to 1 W and a maximum conversion efficiency of ~34% were achieved in a spatial and spectral single-mode. In a preliminary reliability test, at 0.4 W a lifetime of could be demonstrated. Therefore, the laser sources should allow for an efficient non-linear frequency doubling to 560 nm.