Tunable Twin-guide Laser Diode Research Articles

Widely Tunable Twin-Guide Laser Diodes With Sampled Gratings: Design and Performance

The widely tunable twin-guide laser diode with sampled gratings is a monolithically integrated device that utilizes a vertical integration scheme to realize an electronically and widely tunable distributed feedback (DFB)-type laser. Owing to its DFB- type structure, it possesses many advantages, such as large continuous tuning ranges, simple wavelength tuning scheme, and promising dynamic characteristics. In this paper, we detail on the design of the sampled grating tunable twin-guide laser and discuss its performance. Recent devices achieve tuning ranges over 40 nm along with high side-mode suppression (ges35 dB) as well as large output power (ges10 mW).

Sampled grating tunable twin‐guide laser diodes with wide tuning range (≥40 nm) and large output power (≥10 mW)

The sampled grating tunable twin-guide (SG-TTG) laser diode is a DFB-like tunable laser that employs Vernier-effect tuning to achieve wide wavelength tuning. In contrast to most other monolithic widely tunable lasers (which are usually DBR-type lasers), a phase tuning section is not needed and, hence, the SG-TTG laser requires at least one tuning current less than comparable devices. The devices provide full wavelength coverage over a 40 nm-broad tuning range that is centered at 1.54 µm. Its tuning behavior is quasi-continuous with up to 8.2 nm broad continuous tuning regions. High side-mode suppression (SMSR ≥ 35 dB) as well as large output power (P ≥ 10 mW) are obtained over the whole wavelength range from 1520.5 to 1561.5 nm. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Sampled grating tunable twin-guide laser diodes with over 40-nm electronic tuning range

Device and tuning characteristics of sampled grating tunable twin-guide laser diodes are presented. The vertically integrated, monolithic widely tunable laser requires only two tuning currents to fully cover a wavelength range of more than 40 nm by electrooptic tuning. Its tuning behavior is quasi-continuous with up to 8.2-nm broad continuous tuning regions. High sidemode suppression (SMSR /spl ges/ 35 dB) as well as large output power (P /spl ges/ 10 mW) are obtained over the wavelength range from 1520.5 to 1561.5 nm.

Demonstration of Vernier effect tuning in tunable twin-guide laser diodes

Device and tuning characteristics of superstructure grating tunable twin-guide (SSG-TTG) laser diodes are presented. The devices are based on the distributed feedback (DFB) TTG laser, but comprise sampled or superstructure gratings in order to utilise Vernier effect tuning to extend the tuning range to potentially several tens of nanometres. In contrast to most other existing monolithic widely tunable semiconductor lasers, this device requires only two tuning currents. The first tuning characteristics show distinct regions of high SMSR where continuous wavelength tuning can be carried out. These regions of high SMSR are spaced in agreement with theoretical predictions that are based on the superstructure grating design. Hence, our observations clearly demonstrate Vernier effect tuning for the first time in a TTG-type laser diode.

High output power tunable twin-guide laser diodes with improved lateral current injection structure

Tunable twin-guide laser diodes with improved lateral current injection structure and high output power are reported. By optimising the doping profile of the n-InP layer laterally surrounding the buried stripe, inherent leakage currents are effectively minimised. Thereby, the carrier injection efficiency of the laser diode is significantly increased and high output powers of up to 24 and 3.3 mW are obtained at operation temperatures of 20 and 80°C, respectively.

Tunable twin-guide distributed feedback laser diodes with over 9 nm continuous electro-optic tuning range

Tunable twin-guide laser diodes at 1.55 µm with a record electro-optic tuning range are presented. Employing an optimised device design, continuous tuning ranges of 9.3 and 11.0 nm are achieved in continuous-wave (CW) and pulsed operation, respectively. In CW operation, the output power of 300 µm-long devices remains above 1 mW throughout the whole tuning range.

Wide wavelength tuning of sampled grating tunable twin-guide laser diodes

Tuning characteristics of widely tunable twin-guide (TTG) laser diodes with sampled gratings (SGs) are reported. Two SGs, providing slightly different reflection spectra, enable wide tunability by means of Vernier effect tuning. The device structure is vertically integrated and, hence, a DFB-like laser is obtained, which makes a phase tuning section unnecessary and facilitates easy and fast device characterisation. Although the tuning section can tune the SG reflection spectra by only ∼2 nm, an overall tuning range of 28 nm has been achieved by employing Vernier effect tuning. Within the aforementioned tuning range, five supermodes are usable and can be tuned continuously without any mode-hops. The lasers operate at ∼1.55 µm wavelength and achieve a maximum output power of 12 mW.

Tuning dependent beam characteristics of continuouslytunable laser diodes

The beam characteristic of continuously tunable twin-guide (TTG) laser diodes has been investigated and it was observed that the beam profile is changed during tuning. This affects the coupling of the laser light into a fibre interface, leading to a reduction in transmitted optical power. It is shown how the coupling losses during tuning can be compensated for. An observed shift in the lateral far field has a high potential for the realisation of a continuously beam steering device.

Tunable twin guide laser diodes with high output efficiency fabricated by an improved reactive ion etching technique

An buried heterostructure (BH) tunable twin guide (TTG) laser diode with low threshold current, high output efficiency (over 0.25 W ) and a tuning range around 2.5 nm has been developed. Since BH laser diodes are highly sensitive to the waveguide quality we have improved the dry etching technique for the definition of the ridge in order to enhance the laser performance. Within the developed reactive ion etching (RIE) procedure a plasma with optimized composition has been used alternating with short plasma steps to remove remaining hydrocarbon polymer contamination deposited during the cycles. The first TTG laser diodes fabricated with this process exhibit up to 30% improved output efficiencies as compared to former devices, and show almost no degradation effects during high temperature lifetime stress.

Refractive index and loss changes produced by current injection in InGaAs(P)-InGaAsP multiple quantum-well (MQW) waveguides

We have theoretically estimated the carrier-induced changes in the refractive index /spl delta/n and the optical loss /spl delta//spl alpha/ produced by the injection of free carriers in InGaAs(P)-InP multiple quantum-well (MQW) optical waveguides. MQW structures are specially designed for the tuning layer in carrier injection type tunable laser diodes, such as tunable twin-guide laser diode (TTG-LD), at the lasing wavelength /spl lambda/ of 1.55 /spl mu/m. Anomalous dispersion and plasma effect for /spl delta/n and IVBA (intervalance band absorption) for /spl delta//spl alpha/ were included. A valance-band mixing, an overlap integral of electron-hole, and confinement factors of carriers in the well were considered to include quantum-size effect of carriers in /spl delta/n and /spl delta//spl alpha/. Predictions of /spl delta/n are in reasonably good agreement with the experimental results. Systematic analysis shows that the following InGaAs(P)(well)-InGaAsP (barrier) MQW structures ace promising in order to obtain a large /spl delta/nat a given injection current density J: 1) well materials: InGaAsP alloy with its bulk bandgap wavelength of around 1.55 /spl mu/m, 2) barrier materials: InGaAsP alloy with its bulk bandgap wavelength of around 1.4 /spl mu/m, 3) as many as possible number of wells, typically about 15./spl delta//spl alpha/ is also estimated by calculating the carrier distributions in MQW structures and by fitting experimental data of bulk and MQW waveguides. The maximum well number is limited by the increase of optical loss. According to these results, we have found that 1.55-/spl mu/m InGaAsP (well 1.8-nm thick)/1.40 /spl mu/m InGaAsP (barrier 14-nm thick) MQW, with the well number of around 15, will be the optimum tuning layer structure for 1.55-/spl mu/m band tunable LD's. Over 10 nm continuous tuning range, with moderate output power, is expected for TTG-LD's. >

Phase-noise-limited accuracy of distance measurements in a frequency-modulated continuous-wave LIDAR with a tunable twin-guide laser diode

The realization of a coherent frequency-modulated continuous-wave LIDAR aimed for the accurate measurement of short distances employing a distributed feedback tunable twin-guide laser diode is demonstrated. Theoretical calculations on the ultimate limits in accuracy of distance measurements as determined by the laser phase noise are carried out. A relative accuracy of 8x 10-5 (8 μm) for a single-shot measurement has been achieved at a distance of 10 cm, which is significantly better than expected from the laser linewidth. The results presented here prove the predictions calculated from theory.

FMCW-LIDAR with tunable twin-guide laser diode

The realisation of a coherent frequency modulated continuous wave LIDAR aimed for the accurate measurement of short distances employing a distributed feedback tunable twin-guide laser diode is demonstrated. Theoretical calculations on the ultimate limits in accuracy of distance measurements are carried out. A single shot relative accuracy of 8*10-5 (8gm) has been achieved at a distance of 10cm. The results presented here prove the predictions calculated from theory.

Tunable twin-guide lasers with improved performance fabricated by metal-organic vapor phase epitaxy

Tunable twin-guide (TTG) laser diodes have been fabricated using metal-organic vapor phase epitaxy (MOVPE) exclusively for all epitaxy stages. A significant performance improvement over previous experiments has been achieved with an effective current confinement in a considerably simpler laser structure. As a consequence, continuous wavelength tuning over 4.7 nm is obtained while maintaining a light output power per facet of 3 mW. >

Tunable twin-guide lasers with flat frequency modulation response by quantum confined Stark effect

For the first time results on the frequency modulation response of tunable twin-guide laser diodes utilizing the quantum confined Stark effect in a multiquantum well modulation layer are presented. The structures were grown by metalorganic vapor phase epitaxy and were processed into ridge-waveguide lasers emitting at 1555 nm. Preliminary devices exhibit single-mode output power levels of more than 10 mW and minimum linewidths around 4 MHz. The frequency modulation response is flat up to 2 GHz with a modulation efficiency of 7 GHz/V.

A frequency stabilization arrangement for dense wavelength division multiplexing systems

A frequency stabilization scheme using a tunable twin-guide (TTG) laser diode and a Bragg grating filter on a passive waveguide is proposed. This arrangement is fully compatible with the technologies of monolithic integrated optics. The concept was tested in a hybrid assembly. The frequency drift at laser temperature was 820 MHz/ degrees C and the tuning rate at output power was 310 MHz/mW.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Over 7nm (875GHz) continuous wavelength tuning by tunable twin-guide (TTG) laser diode

The recently developed tunable twin-guide (TTG) laser, which needs only a single control current for continuous wavelength tuning, was fabricated according to an optimised design. Continuous tuning ranges of 7-1 nm (890 GHz) under constant laser current and 5-4 nm (675 GHz) at a constant light output power of 1 mW were achieved at 25 o C