Ing-Fa Jang

Monolithically integrated multiwavelength sampled grating DBR lasers for dense WDM applications

For accurate control of the channel spacing in fabricating multiwavelength laser arrays or discrete multicolor lasers, we proposed a novel approach that exploits sampled grating distributed Bragg reflector (DBR) mirrors to vary the laser wave length across the wafer. This approach can realize a set of lasers with a wavelength spacing that meets the ITU recommendations for dense wavelength-division multiplexing systems and a wavelength range that can cover up to 40 nm or more. The wavelength variation across an array is achieved by changing the sampling periods of the DBR mirrors from laser to laser. The accuracy on the channel spacing of sampled grating DBR laser arrays was shown to be the same as that of conventional distributed feedback or DBR laser arrays, but their wavelengths can be better controlled for the gratings are fabricated with single holographic exposure. Arrays of 21 lasers have been successfully fabricated and have around 0.8-nm wavelength spacing with a simple tuning mechanism.

Two-section Bragg-wavelength-detuned DFB lasers and their applications for wavelength conversion

We propose to include a Bragg-wavelength-detuned (BWD) layer in a portion of the cavity of an index-coupled distributed feedback (DFB) laser to overcome the mode degeneracy problem. The new two-section DFB (TSDFB) lasers are experimentally demonstrated to have comparable device dimension and output characteristics as conventional DFB lasers but have much better spectral stability. High side-mode suppression ratio can be obtained over a wide range of current injection and temperature conditions when the laser is coated with anti-reflection coatings on both output facets. Wavelength tuning over 5.4 nm can be obtained by adjusting the heatsink temperature and levering the bias currents. With excellent mode stability, the TSDFB lasers are demonstrated to perform wavelength conversion with large extinction ratio, high conversion efficiency, and waveform reshaping capability. The wavelength conversion can cover 30-THz of input frequency that matches the frequency grid of the dense wavelength division multiplexing systems. Penalty-free conversion is also demonstrated.

Simple approaches of wavelength registration for monolithically integrated DWDM laser arrays

A simple approach is proposed to allocate the wavelengths of monolithically integrated sampled grating distributed Bragg reflector (SGDBR) laser arrays for applications in dense wavelength-division-multiplexing (DWDM) systems. The lasers in an array are thermally controlled altogether and each laser is operated with two electrodes. Arrays of accurate wavelengths can be realized by fine adjusting the bias current and phase current of each laser to output a uniform wavelength comb, and then varying the heat sink temperature to align all channels to the desired wavelength grid. Such procedures can provide arrays of high sidemode suppression ratio (SMSR) and no mode hopping over a wide range of operation condition. We demonstrated 50-GHz spaced arrays of accurate and stable wavelengths.

Wavelength-selectable lasers with Bragg-wavelength-detuned sampled grating reflectors

Tunable laser arrays covering forty 50-GHz-spaced channels are realized with novel sampled grating reflectors. The grating design can realize lasers to cover different wavelength bands with simple fabrication and allows high-reflection coating to increase power.

Design of DWDM laser arrays based on sampled grating DFB lasers

This paper presents a study on sampled grating DFB semiconductor laser array design for application as dense WDM transmitters.

Multiwavelength laser arrays with 0.4/0.8-nm wavelength spacing

We report the results of laser arrays with 32 wavelengths in 0.8- or 0.4-nm wavelength spacing. For the 0.8-nm spaced arrays, we demonstrate that a much larger range of reflection peak spacing can be realized in sampled grating DBR (SGDBR) mirrors, in comparison with previous designs. For the 0.4-nm spaced arrays, we show to our knowledge the best as-fabricated wavelength control for MWLAs that are feasible for DWDM applications.

Novel techniques for realizing SGDBR DWDM sources without coarse tuning

The multi-wavelength transmitters for DWDM systems can be built with either multiple discrete lasers (DLs) or monolithically integrated multi-wavelength laser arrays (MWLAs). The output wavelengths of these sources must match a specified wavelength grid, so the critical issues of fabricating DWDM sources are wavelength accuracy and stability. We have demonstrated a simple approach for fabricating MWLAs using SGDBR lasers of which the sampling period varies from laser to laser. Arrays of 32 wavelengths with good wavelength uniformity and controllability have been demonstrated. However, the multi-wavelength output was achieved by tuning one of the two SGDBR mirrors to align the reflection spectra at their first order peaks. To simplify the wavelength control for each laser, we demonstrate here the laser arrays that can generate multiwavelength output without any current tuning. This approach may be even more advantageous for fabricating DL-type DWDM sources such that multiple wavelengths can be obtained from the same wafer to save the manufacture cost. The previous approach for fabricating DL-type sources is to vary the wavelength in the wafer scale, i.e., one wavelength from one wafer.

Adjustable multiwavelength laser arrays with sampled grating DBR mirrors

Multiwavelength InP-InGaAsP MQW laser arrays with 100-GHz wavelength spacing were designed using sampled grating DBR lasers. Arrays of eight wavelengths, each has better than 30 dB MSR, have been obtained with a simple tuning mechanism.

Wavelength selectable lasers with Bragg-wavelength detuned sampled-grating reflectors

Wavelength-selectable lasers (WSLs) with a novel type of grating reflectors are proposed for realizing fast tunable lasers that can cover a wide range of wavelengths. Each WSL includes an array of distributed-Bragg-reflection (DBR)-type lasers that are combined with a multimode-interference (MMI) coupler. In order to cover different wavelength bands with simple fabrication, the grating reflector is formed of two sampled-grating (SG) subsections on waveguides of different thicknesses. The resultant Bragg-wavelength detuning from the thickness difference between the two SG subsections causes the maximal refection shift to the high-order reflection peaks. A laser array where each laser covers a different wavelength band is realized by varying the corresponding wavelength position of the second-order peak from laser to laser. Each laser has one-side SGs for allowing one-electrode fast tuning. It can also allow high-reflection facet coating to increase output power. Four-laser WSLs, where each laser can be tuned to cover at least 3.5 nm of wavelength span with a side-mode suppression ratio that is better than 30 dB, are designed and demonstrated. Forty 50-GHz-spaced channels can be covered with the four-laser array

Integrated DWDM laser arrays with stable and high-SMSR wavelengths

We demonstrate monolithically integrated 16-wavelength laser arrays of which the wavelengths are arranged to meet the ITU channel spacing. High side mode suppression ratio (SMSR) and no mode hopping can be achieved over a wide range of operation current and temperature.