Superstructure-grating Distributed Bragg Reflector Research Articles

Quasi-continuous tuning of a 1.3-µm-wavelength superstructure grating distributed Bragg reflector laser by enhancing carrier-induced refractive index change.

To overcome the limitation of the small tuning range of 1.3-µm-wavelength distributed Bragg reflector (DBR) lasers using the carrier-plasma effect, we designed a DBR structure with InAlAs carrier confinement layers and an InGaAlAs core layer. We found that the enhanced carrier density and small effective mass of electrons in the core layer of the DBR regions resulted in a wide Bragg wavelength shift. The enhanced refractive-index change due to the new structure enabled us to fabricate the world's first 1.3-µm-wavelength superstructure-grating DBR laser with a quasi-continuous tuning range of over 30 nm.

Tuning of successively scanned two monolithic Vernier-tuned lasers and selective data sampling in optical comb swept source optical coherence tomography

Monolithic Vernier tuned super-structure grating distributed Bragg reflector (SSG-DBR) lasers are expected to become one of the most promising sources for swept source optical coherence tomography (SS-OCT) with a long coherence length, reduced sensitivity roll-off, and potential capability for a very fast A-scan rate. However, previous implementations of the lasers suffer from four main problems: 1) frequencies deviate from the targeted values when scanned, 2) large amounts of noise appear associated with abrupt changes in injection currents, 3) optically aliased noise appears due to a long coherence length, and 4) the narrow wavelength coverage of a single chip limits resolution. We have developed a method of dynamical frequency tuning, a method of selective data sampling to eliminate current switching noise, an interferometer to reduce aliased noise, and an excess-noise-free connection of two serially scanned lasers to enhance resolution to solve these problems. An optical frequency comb SS-OCT system was achieved with a sensitivity of 124 dB and a dynamic range of 55-72 dB that depended on the depth at an A-scan rate of 3.1 kHz with a resolution of 15 μm by discretely scanning two SSG-DBR lasers, i.e., L-band (1.560-1.599 μm) and UL-band (1.598-1.640 μm). A few OCT images with excellent image penetration depth were obtained.

Rapid High-Precision In Situ Wavelength Calibration for Tunable Lasers Using an Athermal AWG and a PD Array

This letter presents a simple and rapid high-precision in situ calibration technique for tunable superstructure grating distributed Bragg reflector (SSG-DBR) lasers using a laser driver board with an athermal arrayed waveguide grating (AWG) and a photodetector (PD) array. The experiment demonstrates laser calibration for seven wavelength channels completed in 23 s with a precision of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\pm$</tex> </formula> 0.015 nm. This letter describes the details of the system calibration method, the mode competition detection technique, and the calibration time analyses. The presented technique can also apply to other tunable lasers with suitable modification in the laser driver interfaces. <?Pub _bookmark="" Command="[Quick Mark]"?>

140-nm Quasi-Continuous Fast Sweep Using SSG-DBR Lasers

We demonstrate a single-mode and fast wavelength swept light source by employing superstructure-grating distributed Bragg reflector (SSG-DBR) lasers for use in optical frequency-domain reflectometry optical coherence tomography. A noteworthy feature is that our laser employs a thermal drift compensator (TDC). By utilizing the TDC, we achieved a fast wavelength sweep without any unexpected mode hopping. We newly designed and fabricated SSG-DBR lasers covering the following four wavelength bands: 1496-1529, 1529-1564, 1564-1601, and 1601-1639 nm. We achieved a stable operation for the whole wavelength range. A wide wavelength tuning of 143 nm was achieved within 1.4 ms. A single-mode, wide, and fast wavelength sweep was demonstrated.

Suppression of Thermal Wavelength Drift in Super-Structure Grating Distributed Bragg Reflector (SSG-DBR) Laser with Thermal Drift Compensator

Thermal wavelength drift in a super-structure grating distributed Bragg reflector (SSG-DBR) laser is suppressed by introducing a thermal drift compensation waveguide into a DBR laser. Injecting a compensatory current into the thermal drift compensation waveguide greatly suppresses the drift, and also prevents SSG mode hopping during rapid wavelength switching.

Optical frequency-domain reflectometry with a rapid wavelength-scanning superstructure-grating distributed Bragg reflector laser

Superstructure-grating distributed Bragg reflector lasers are particularly suited for optical frequency-domain reflectometry optical-coherence tomography with wide wavelength tunability and frequency agility. We report theoretical estimates of and experimental results for the data acquisition speed, the observable depth range, the resolution, and the dynamic range of an optical frequency-domain reflectometry system that uses a superstructure-grating distributed Bragg reflector laser whose wavelength can be tuned from 1533 to 1574 nm with a tuning speed of 10 micros/0.1-nm step.

Control of widely tunable SSG-DBR lasers for dense wavelength division multiplexing

This paper presents a general discussion on the control of widely tunable super structure grating distributed Bragg reflector (SSG-DBR) lasers. A feedback control scheme is presented that ensures frequency stability and accuracy (better than /spl plusmn/0.5 GHz), as well as high side mode suppression ratio (>35 dB). The active section voltage is monitored to maintain mode stability and a highly stable Fabry-Perot etalon is used as a reference to lock the laser frequency to a specific ITU channel. It is shown that stability can even be maintained when directly modulating the laser at 1.244 Gb/s. Furthermore, a characterization scheme is demonstrated that uses the voltage monitoring to generate a look-up table of operation points very efficiently and accurately. For all operation points, the frequency accuracy is better than /spl plusmn/0.5 GHz and the side mode suppression ratio is above 35 dB.

Measurement for Scattering Media by Synthesis of Optical Coherence Function with Super-Structure Grating Distributed Bragg Reflector Laser Diode

The application of the technique of synthesis of optical coherence function for detection in scattering media is investigated. By modulating the optical frequency, the technique synthesizes the coherence function into a delta-function-like peak at an arbitrary location, and thus can select interferometrically the information at that location. The location is adjustable by the modulation parameter or additional phase modulation. A multi-section super-structure grating distributed Bragg reflector laser diode (SSG-DBR-LD) of THz-order tunable range is employed to enhance the spatial resolution for suppressing the multiple scattering from locations other than that detected. In a preliminary experimental demonstration, a reflectometry of 550 μm spatial resolution was achieved and was used to detect scattering media.

Finely tunable wavelength conversion of high bit-rate signals by using a superstructure-grating distributed Bragg reflector laser

Finely tunable wavelength conversion of high bit-rate signals is analyzed numerically and demonstrated experimentally-to a wavelength range from 1530 to 1560 nm-by using a superstructure-grating distributed Bragg reflector laser. Transmission of a 10 Gb/s converted signals over a 100 km-long optical fiber is also demonstrated using a dispersion-shifted optical fiber.

Complete single mode wavelength coverage over 40 nm with a super structure grating DBR laser

The spectral characteristics of a widely tunable super structure grating distributed Bragg reflector (SSG-DBR) laser are investigated and the design considerations of the grating reflectors are given. By systematically adjusting the control currents of the two reflector sections and the phase section it is experimentally shown that every wavelength in an interval of 40 nm can be reached with a side-mode suppression usually better than 30 dB.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Characteristics of super structure grating (SSG) DBR lasers under broad range wavelength tuning

Spectral characteristics of the super structure grating (SSG) distributed Bragg reflector (DBR) lasers under broad range wavelength tuning are discussed. SSG DBR lasers show good spectral characteristics with broad range wavelength tunability. Under the directly intensity modulated condition, stable single longitudinal mode oscillations are also obtained over the broad wavelength tuning range.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Broad-range wavelength-tunable superstructure grating (SSG) DBR lasers

A broad tuning range is demonstrated in tunable DBR lasers with a novel superstructure grating (SSG). These SSG reflectors were fabricated by electron-beam lithography, and grating performance was evaluated by measuring the transmittance characteristics of a ridge-type SSG reflector. Incorporating this SSG reflector into distributed-Bragg-reflector (DBR) laser results in lasers that can be tuned over a wide wavelength range by using coarse and fine tuning mechanisms. Wavelength-tunable SSG DBR lasers were fabricated and operated under low-threshold CW conditions. Wavelength tuning ranges of 50 and 100 nm were designed and experimentally measured to be 50 and 83 nm, respectively, with single-mode operation. >