PAM-XIAMEN offers 850nm laser diode wafer, which is a SLD (superluminescent diode) structure. It can be used as the light source of fiber optic gyroscope. Super-luminescent diode is a kind of semiconductor optoelectronic devices between laser diodes (LDs) and light-emitting diodes (LEDs). More detail information on the SLD structure, please see:
1. GaAs Epi-structure of Superluminescent Diode
850nm SLD Structures
P+ GaAs P>5E19, d=0.15um
P- AlGaAs and undoped AlGaAs d~1.4um
Undoped GaAsP or AlGaInAs active layer, PL: 850+-15nm
Undoped AlGaAs and N- AlGaAs, d~1.5um
N GaAs buffer
N GaAs substrate N=(0.4~4)×10^18, d=350~625um(100)2° off
2. What is SLD?
Superluminescent Diode is a semiconductor light-emitting device. Superluminescent light is obtained by the process of stimulated amplification of spontaneously emitted photons propagating in the gain medium. So, we call the amplified spontaneous emission (ASE) superradiance.
Compared with semiconductor lasers, superluminescent light-emitting diodes have a wider luminescence spectrum, that is, a shorter coherence length, which can significantly reduce the noise caused by fiber Rayleigh scattering and nonlinear optical Kerr effect, as well as fiber transmission modes noise. Device fabricated on GaAs based superluminescent diode laser structure have higher output power, smaller divergence angle, higher coupling efficiency and faster response speed than that of general light-emitting diodes. The superluminescent light emitting diode with performance between LD and LED can meet the requirements of high optical power and small coherence length at the same time.
Figures 1 and 2 are comparisons of the optical power and spectral characteristics of LD, LED, and SLD. From the perspective of spectral full-width-at-half-maximum (FWHM), the spectrum of LED is the widest, followed by SLD, and the spectrum of LD is the narrowest.
Fig. 1 Optical Power Comparison of LD, SLD and LED
Fig. 2 FWHM Spectrum of LD, SLD and LED
From the working wavelength of SLD, it can be a short-wave device working around 850nm, or a long-wave device working around 1310nm and 1550nm. Compared with the 1300nm SLD, the device fabricated on 850nm superluminous diode wafer requires a shorter fiber length for the same sensitivity, and the 850nm SLD structure has better optical power stability and does not require cooling, which simplifies the system drive circuit. This can greatly reduce the cost of fiber optic gyroscopes, meet the requirements of fiber optic gyroscopes, and the 850nm superluminescent diode epitaxial structure is an ideal light source for low-to-medium-precision, low-cost fiber optic gyroscopes.