Narrow linewidth laterally-coupled 1.55 [micro sign]m DFB lasers fabricated using nanoimprint lithography

Abstract

A report is presented on the use of nanoimprint lithography for the fabrication of InP-based laterally-coupled ridge waveguide distributed feedback laser (DFB) diodes emitting around 1550 nm. At room temperature the uncoated lasers exhibited a sidemode suppression ratio of 50 dB at an output power of 6 mW. The lasers showed extremely pure singlemode spectrum with the Lorentzian part of the measured linewidth being 200 kHz. The results prove that nanoimprint lithography is suitable for the low-cost manufacturing of high performance singlemode laser diodes.Introduction: Conventional distributed feedback (DFB) lasers make use of buried Bragg gratings for achieving selective optical feedback. They require epitaxial regrowth [1], which complicates the fabrication process and can degrade device performance. Another possibility to implement the distributed feedback is to etch lateral gratings on the surface of the device enabling a regrowth-free process [2]. Typically, such surface gratings have been realised by means of electron-beam lithography. We have recently devised an approach to process high aspect-ratio surface gratings using nanoimprint lithography (NIL) and plasma etching [3]. The method consists in defining a laterally-corrugated ridge waveguide (LC-RWG) structure, in a single step, by using a cost-effective and high-throughput soft stamp UV-NIL technology. With this method a full wafer can be patterned in a few minutes at an extremely high resolution. The soft and flexible stamp accommodates locally to micro-particle presence [3] and enables large area imprinting even for wafer surfaces with curvatures caused by the internal strain of the epitaxial layers. This fabrication technique is easily applicable to different material systems; we have used it before for GaAs [3,4] and GaSb [5]. In this Letter, we present results of the first InP-based LC-RWG DFB lasers based on UV-NIL.

Laterally‐coupled distributed feedback laser with first‐order gratings by interference lithography

“…Among the LC-DFB lasers reported, grating definition and fabrication have been achieved using e-beam lithography (EBL) [1,2], interference lithography [3], stepper technology [4], or nanoimprint lithography [5,6]. Among all LC-DFB lasers reported without using EBL, only higher-order Bragg gratings have been achieved [3][4][5][6], which result in low grating efficiency. EBL has been used to pattern a first-order grating LC-DFB laser [2].…”

Narrow Linewidth 1550 nm Corrugated Ridge Waveguide DFB Lasers

“…The selection of the Voigt fitting arises from the fact that some broadening in the RF DSH beat note lineshape is observed near the center. This broadening can mainly be attributed to 1/f frequency noise (including environmental noise sources and injection current noise) whose corresponding lineshape is Gaussian [5], [14], [15]. Fig.…”

“…The development of distributed feedback (DFB) lasers that use surface rather than buried gratings brings compatibility with low-cost production, high performance, and ease integrability. Indeed, surfacegratings DFB or laterally coupled DFB (LC-DFB) lasers [1]- [5] make use of gratings that are patterned and etched along the sidewalls of the ridge waveguide (i.e. a corrugated ridge waveguide (CRW)), as shown in our design in Fig.…”

“…In particular, we demonstrate single mode and narrow linewidth InGaAsP multiple quantum well (MQW) CRW-DFB lasers at 1550 nm. Although such DFB-based structures have been fabricated using different techniques [1]- [5], only a few publications have reported the linewidth of these lasers. Reid et al [4] claimed a linewidth < 1MHz and Telkkälä et al [5] reported a linewidth of 203 kHz at a particular current.…”

“…Although such DFB-based structures have been fabricated using different techniques [1]- [5], only a few publications have reported the linewidth of these lasers. Reid et al [4] claimed a linewidth < 1MHz and Telkkälä et al [5] reported a linewidth of 203 kHz at a particular current. However no experimental study has shown the variations of the linewidth for wide injection current ranges.…”