Distributed Feedback Device Research Articles

Purely Gain-Coupled Distributed Feedback Bragg Semiconductor Laser Emitting At 795 Nm With a Wide Tunable Range

We demonstrate a distributed feedback (DFB) semiconductor laser based on i-line lithography and surface periodic current injection technologies with a lasing wavelength of 795 nm, which corresponds to the D1 spectrum of Rb and has many applications with respect to alkali vapor lasers and atomic clocks. The maximum output power, side mode suppression ratio (SMSR), and single-longitudinal-mode tunable range of our device are 50.89 mW (at 20 °C), 34.56 dB, and 12.792 nm, respectively. The rate of change in wavelength with temperature of the laser is 0.401 nm/°C, which is equivalent to that of a Fabry-Perot (FP) laser and much better than that of a general DFB device. This device has a cavity the same as an FP laser without any etching gratings, meanwhile the lasing spectrum behaves a single longitudinal mode characteristic as a DFB laser.

The Leap from Organic Light-Emitting Diodes to Organic Semiconductor Laser Diodes

In recent years, organic light-emitting device technology has expanded from organic light-emitting diodes (OLEDs) to organic semiconductor laser diodes (OSLDs) with the progress of sophisticated mo...

Femtosecond tuning dynamics of organic amplifiers based on injection into DFB resonators of slant gratings

We report regenerative amplification of femtosecond laser pulses locked by injection of supercontinuum spectrum into a distributed feedback (DFB) microcavity constructed by slant gratings. Destroying the symmetry of the DFB resonance modes about the normal injection, the slant grating not only enabled concentration of the energy amplification on single modes, but also facilitate continuously tuning of the amplification in a broad band. The injection has locked efficiently the amplification spectrum, the transverse mode and the direction of the output beam, as well as the pulse length. In-plane amplification using a thin-film DFB device and injection locking supplies an important approach to produce high-quality ultrashort-pulsed laser beam from organic semiconductors. Advantages of injection-locked amplification techniques are also largely extended.

Tunable organic distributed feedback dye laser device excited through Förster mechanism

Tunable organic distributed feedback (DFB) dye laser performances are re-investigated and characterized. The slab-type waveguide DFB device consists of air/active layer/glass substrate. Active layer consisted of tris(8-quinolinolato)aluminum (Alq3), 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM) dye, and polystyrene (PS) matrix. Effective energy transfer from Alq3 to DCM through Forster mechanism enhances the laser emission. Slope efficiency in the range of 4.9 and 10% is observed at pump energy region higher than 0.10–0.15 mJ cm−2 (lower threshold), which is due to the amplified spontaneous emission (ASE) and lasing. Typical slope efficiency for lasing in the range of 2.0 and 3.0% is observed at pump energy region higher than 0.25–0.30 mJ cm−2 (higher threshold). The tuning wavelength for the laser emission is ranged from 620 to 645 nm depending on the ASE region.

Design and operation of distributed feedback transistor lasers

The design and fabrication methods utilizing soft photocurable nanoimprint lithography to realize single longitudinal mode distributed feedback transistor lasers are investigated. Coupled-mode theory and the effective index method are used to determine accurately the periodic dimensions necessary to integrate a surface grating in the top emitter AlGaAs confining layers of an InGaP/GaAs/InGaAs heterojunction bipolar transistor laser. Electrical and optical device data confirm the design methods. The distributed feedback device produces continuous wave laser operation with a peak wavelength λ=959.75 nm and threshold current IB=13 mA operating at −70 °C. For devices with cleaved ends a side mode suppression ratio >25 dB has been achieved.

First Approach to the Analysis of the Lasing Conditions in POLIPHEM© Structures

We report a study devoted to the creation of a distributed feedback device on a basis of waveguide with periodical composition polymer – liquid crystal. Due to the refractive indices difference between the components the Bragg diffraction grating is formed, which provides coupling of the forward and backward propagating waves. The influence of the gain and conditions of laser oscillation threshold are analyzed for gain-type reflection grating. The conclusion is done on the advantage of second-order Bragg diffraction exploitation. Numerical simulations demonstrated the stability of the waveguide mode.

High-resolution gas phase spectroscopy with a distributed feedback terahertz quantum cascade laser

The quantum cascade laser is a powerful, narrow linewidth, and continuous wave source of terahertz radiation. The authors have implemented a distributed feedback device in a spectrometer for high-resolution gas phase spectroscopy. Amplitude as well as frequency modulation schemes have been realized. The absolute frequency was determined by mixing the radiation from the quantum cascade laser with that from a gas laser. The pressure broadening and the pressure shift of a rotational transition of methanol at 2.519THz were measured in order to demonstrate the performance of the spectrometer.

Spectral linewidth and tuning requirements of sources for gas sensing in space-based applications at 935 nm

The spectral linewidth and tuning requirements of an external cavity laser (ECL) in the Littrow architecture and a distributed feedback (DFB) device for space-based gas sensing were investigated. The wavelengths of both devices were in the 935 nm range and different linewidth measurment techniques were explored for the two sources. The linewidth of the ECL was measured using a short-arm homodyne technique, while the linewidth of the DFB was measured with a het- erodyne technique using the ECL as a local oscillator. The spectral linewidth of the ECL was measured to be ,300 kHz with ,5 MHz for the DFB device. The emission wavelength tuning characteristics, including the overall tuning range and the free running stability of the ECL, were also examined. The full frequency drift of the ECL measured over a 36-hour period was found to be approximately 540 MHz, while it showed approximately 0.4 nm continuous mode-hop free wavelength tuning. The objective of this work is the stabilisation of four laser frequencies to four specific predefined wavelengths that are associated with water absorption lines in the 935- 940 nm range for space-based gas sensing. A list of these water absorption lines, with their wavelengths and line- strengths, is shown in Table 1. The experimental set-up involves locking one injection seed laser (ISL) to the stron- gest water line via a water vapour reference gas cell. This laser is then used as a reference to stabilise the other lasers, each to one of the three remaining lines. Locking by means of gas absorption is the preferred technique as the absorption wavelength at a fixed temperature and pressure is constant. The stabilisation technique used for the three remaining lasers employs a Fabry-Perot interfe- rometer to reference from the locked ISL by a fixed detun- ing. The work performed in this research is a portion of a wider study being carried out by the European Space Agency (ESA). The overall project is termed the WALES (water vapour light detection and ranging (LIDAR) exper- iment in space) mission and its objective is to provide

Self-organization in semiconductor lasers with ultrashort optical feedback.

The dynamical behavior of a single-mode laser subject to optical feedback is investigated in the limit, when the delay time is much shorter than the period of the relaxation oscillations. Use of an integrated distributed feedback device allows us to control the feedback phase. We observe two kinds of Hopf bifurcations associated with regular self-pulsations of different frequencies.

High-speed directly modulated fabry-perot and distributed-feedback spot-size-converted lasers suitable for passive alignment, unisolated operation, and uncooled environments up to 85 °C

Semiconductor lasers with narrow far fields are highly desirable because they can be directly coupled to fiber with high-coupling efficiency, eliminating the cost of lenses and extra packaging. Because of their smaller size, they facilitate more compact transmitters, and since they can be used unpackaged, they enable complex integrated optoelectronic devices. We describe the design, fabrication, and performance characteristics of our family of spot-size-converted (SSC) devices with narrow far fields designed for directly modulated (2.5 and 10 Gb/s) uncooled (85/spl deg/C) use. The design consists of a conventional active region buried heterostructure laser coupled to an expander region (consisting of a loosely confining waveguide) through a laterally tapered etch of the active layers. This basic design achieves far fields of /spl sim/16/spl times/10 degrees, suitable for coupling /spl sim/50 percent of the emitted light into a flat cleaved fiber. Distributed feedback (DFB) 1.3- and 1.5-/spl mu/m devices, and 1.3-/spl mu/m Fabry-Perot (F-P) lasers have been implemented in this technology. The devices have dc thresholds from 8-12 mA at 25/spl deg/C and 35-45 mA at 85/spl deg/C, with peak power of >15 mWs over temperature, all similar to non-SSC devices with the same active regions. Both SSC F-Ps and DFBs demonstrate bandwidths of >7 GHz and wide-open eyes at 85/spl deg/C, and reliability suitable for uncooled use. With the DFB device, we also demonstrate a wide open 10-Gb/s eye pattern at room temperature. The laser on a submount demonstrates coupling to a fiber in a v-groove of /spl sim/25% using passive alignment, and sufficient tolerance to back reflection to enable transmission over at least 15 km with typical drive circuitry. Analysis shows that these lasers also have a factor of two improvements in alignment tolerance compared to standard devices in a typical lensed system. The expander impacts the dc and dynamic characteristics of the SSC F-P through the increase in cavity size. The dc and dynamic characteristics of SSC DFBs and standard DFBs are very similar, demonstrating that expander-related absorption and mode transition loss has been almost eliminated in this structure. The SSC-DFBs are, thus, the preferred device for high-speed applications. To our knowledge, the 1.3-/spl mu/m lasers described are the first SSC devices fully suited for use as an uncooled 2.5-Gb/s transmitters up to 85/spl deg/C. The combination of a tailored narrow far field with an edge emitting structure rivals vertical cavity lasers in alignment tolerance for low-cost packaging with superior dynamic and thermal performance.

Single-longitudinal-mode emission from interband cascade DFB laser with a grating fabricated by interferometric lithography

A distributed-feedback, type-II interband cascade laser is demonstrated in pulsed mode, emitting near 3.145 µm at temperatures between 50 and 80 K. Feedback is provided by a surface-etched grating formed using interferometric lithography. Between 50 and 80 K, the device's single longitudinal mode red-shifts with temperature at ∼0.1 nm/K. At 70 K and 190 mA of pulsed injection current, side-mode suppression exceeds 30 dB. The characteristics of related Fabry–Perot IC lasers are also described and contrasted with those of the distributed feedback device.

Low-chirp and enhanced-resonant frequency by direct push-pull modulation of DFB lasers

The first long haul experiment on the use of a new direct modulation scheme is reported. This scheme in principle permits simultaneous tailoring of the chirp and enhancement of the resonant frequency of a distributed feedback (DFB) laser. Numerical and analytical results are presented that demonstrate the properties of push-pull modulation along with supporting experiments. Measurement of the time resolved chirp shows that push-pull modulation results in a low-chirp and a unique-chirp shape, which improves pulse transmission along a dispersive fiber. Initial experiments, using a bulk active region unoptimized DFB device driven directly by push-pull modulation, demonstrate operation over 150 km transmission at a bit rate of 2.5 Gb/s with a practical system receiver giving 10/sup -9/ bit-error rate at a dispersion penalty of -0.5 dB. Significant improvements are foreseen using quantum-well material. Simulations indicate that with appropriately optimized devices and drives, direct modulation at 10 Gb/s may give transmission over 100 km of standard fiber comparable to existing externally modulated systems.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Optical bistability in a multiple-quantum-well structure with Fabry-Pérot and distributed-feedback resonators.

The system we analyze has the structure of a planar optical waveguide containing a multiple quantum well, with the planes of the wells parallel to the direction of propagation. We consider the two different configurations of a Fabry-P\'erot cavity and distributed-feedback device. The optical nonlinearities are described by means of the first-principles theory developed by Haug, Koch, Schmitt-Rink, and co-workers, generalized to include the finite width of the wells. The dynamics of the system is described by the equations that govern the evolution of the two counterpropagating fields, coupled with the carrier-density equation, and accompanied by the appropriate boundary conditions. The steady-state behavior is analyzed as a function of the control parameters of the system for the case of a GaAs/${\mathrm{Al}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ga}}_{\mathit{x}}$As/AlAs structure. The system develops bistability even when the input field is in resonance with the excitonic peak, but the phenomenon becomes more pronounced in the detuned configuration. The hysteresis cycles obtained in the case of distributed-feedback device turn out to be competitive with those displayed by the Fabry-P\'erot system.

Distributed feedback device characterization using a continuous wave model

The second-order cw equation for a medium having gain and a modulated index of refraction is solved to characterize an aperiodic distributed feedback structure. The solutions are compared with those of a coupled-wave model for the cases of tapered, chirped, and phase-shifted structures. A correlation is observed between the solutions, endorsing the validity of the cw approach.

The effect of end reflections and mirror positioning on the optical response of a nonlinear distributed feedback device

We study the transmission characteristics of a distributed Bragg reflector and include the effect of end reflections. Analytical expressions are developed for the linear response, and numerical results are presented for the nonlinear response. In each case it is shown that the positioning of the Bragg grating relative to the end reflectors has a significant effect on the device characteristic. We consider bistable action and show that it is important to choose the position of the grating so that the critical switching intensity may be decreased below that which obtains when end reflections are absent.