Frequency-converted dilute nitride laser diodes for mobile display applications
© Konttinen and Korpijärvi; licensee Springer. 2014
Received: 19 November 2013
Accepted: 31 January 2014
Published: 17 February 2014
We demonstrate a 1240-nm GaInNAs multi-quantum well laser diode with an integrated saturable electro-absorber whose wavelength is converted to 620 nm. For conversion, we used a MgO:LN nonlinear waveguide crystal with an integrated Bragg grating in direct coupling configuration. Broadened visible spectral width and reduced speckle as well as a high extinction ratio between the below and above threshold powers were observed in passively triggered pulsed operation with smooth direct current modulation characteristics. The demonstration opens a new avenue for developing 620-nm semiconductor lasers required for emerging projection applications.
KeywordsSemiconductor laser Second harmonic generation Visible III-V semiconductors Dilute nitride GaInNAs Mobile display Semiconductor lasers Laser diodes 42.55.Px Second harmonic generation 42.65.Ky
Red laser light sources emitting in the wavelength range of 610 to 620 nm are particularly interesting for mobile display applications due to increased luminous efficacy and higher achievable brightness within eye-safety regulations . Unfortunately, this wavelength range is difficult to achieve by using traditional GaInP/AlGaInP red laser diodes (LDs) . Another well-known drawback of GaInP/AlGaInP diodes is the reduction of characteristic temperature of threshold current (T0) with wavelength. High T0 values have been demonstrated with red laser diodes emitting at wavelengths above 650 nm , while shorter wavelength diodes suffer from poor temperature characteristics . These features render impossible the use of standard AlGaInP laser diodes in embedded projection displays, where large operating temperature range is typically required.
Frequency conversion of infrared laser emission is an attractive solution for the generation of short-wavelength red light . While GaInAs quantum well (QW) emission wavelength is practically limited to approximately 1200 nm , by using dilute nitride GaInNAs QWs with a tiny fraction of nitrogen added to the highly strained GaInAs, the emission wavelength can be extended to 1220-1240 nm for high luminosity red light generation at 610 to 620 nm by frequency conversion . In addition, excellent temperature characteristics and high power operation have been demonstrated with GaInNAs laser diodes in this wavelength range .
The processed laser chips employed a single transverse mode RWG process with ridge width of 3.5 μm and cavity length of 1250 μm. The laser diode further comprised an 85-μm reverse-biased saturable electro-absorber section to passively trigger short pulses for enhancing frequency conversion efficiency in the nonlinear waveguide. The front and rear facets of the laser diode were AR/HR coated with reflectivities of <1% and >95% at 1240 nm, respectively.
A nonlinear waveguide crystal made of MgO-doped LiNbO3 with high nonlinear coefficient was used for frequency doubling to visible wavelengths. The crystal had a surface Bragg grating implemented near the output end of the waveguide. The function of the surface Bragg grating is to provide self-seeding to frequency lock the IR laser diode in order to maintain sufficient spectral overlap with acceptance spectrum of quasi-phase-matched (QPM) grating over an extended temperature range.
Results and discussion
A transversally single-mode frequency-converted GaInNAs-based 620-nm laser diode is demonstrated with high single pass conversion efficiency and extinction ratio. Further improvements of threshold current and conversion efficiency are expected by optimizing the laser diode manufacturing process and optical coupling configuration.
JK is CTO at EpiCrystals. VMK is a PhD student at the Optoelectronics Research Centre of Tampere University of Technology.
full-width at half maximum
lithium niobate (LiNbO3)
molecular beam epitaxy
characteristic temperature of threshold current.
Authors wish to thank Prof. Mircea Guina for the support in proofreading of the manuscript as well for the numerous helpful comments. VMK acknowledges the financial support of the Graduate School of Electronics, Telecommunications and Automation (GETA) and HPY Research Foundation.
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