Items and Definitions

1. Absolute Maximum Ratings for Laser Diode

Specifications are given for a case temperature Tc of 25 °C. However, note that the thermistor temperature (Tth) is used for devices with an internal Peltier element, and the cooling water temperature (Tw) for water-cooled packages.

Item Symbol Definition of maximum rating Remarks
Optical
power output
Pomax Maximum allowable output defined for continuous operation or pulse operation. This optical power output or less does not have the degradation as shown in the figure.

Graph Po/If

 
Reverse
voltage
VR Maximum allowable voltage when the reverse bias is applied to the semiconductor laser and the photodiode.  
Operating
temperature
Topr Allowable temperature when the device is operated. It is given for the case temperature.  
Storage
temperature
Tstg Allowable ambient temperature when the device is stored.  

2. Laser Diode Electrical and Optical Characteristics (1)

Item Symbol Definition Remarks
Oscillation
start current
Ith The diagram below can be divided into two regions; a spontaneous emission region A and a laser oscillation region B.The oscillation start current is called "threshold current".

Graph Ith, Iop

 
Operating
current
Iop Forward current required to maintain the specified optical power output.  
Operating
voltage
Vop Forward voltage at the specified optical power output.  
Wavelength λp It is the peak oscillation wavelength when the laser diode is operated at the specified optical power output. In the case of plural spectra, this is the wavelength of the center line of the set of spectral lines that have 1/2 of maximum intensity. The laser oscillation spectrum is classified into two kinds, that is, single longitudinal mode or multi mode according to the feature.

Graph Single and Multi mode

 

2. Laser Diode Electrical and Optical Characteristics (2)

Item Symbol Definition Remarks
Monitor current Imon Current value which flows when the specified reverse voltage is applied to the photodiode at the specified optical power output Po.  
Radiation
angle
Perpendicular to junction θ⊥ Light emission from the laser diode extends as shown in Fig. (a). The measurement results of the light intensity along the X and Y axis are shown in Fig. (b) and Fig. (c). The width that have 1/2 of peak intensity (FWHM) are called extension angle θ// in the horizontal direction and extension angle θ⊥ in the vertical direction. The unit is degrees.

Figure (a), (b), (c), (d)

 
Parallel
to junction
θ//
Asymmetry ΔSr

2. Laser Diode Electrical and Optical Characteristics (3)

Item Symbol Definition Remarks
Emission
point
accuracy
Positional
accuracy
ΔX
ΔY
ΔZ
Displacement of the laser diode emission point in the direction of X, Y and Z. ΔX and ΔY indicate the displacement from the center of the package, ΔZ indicates the displacement from the reference plane of the package.

Figure Emission point accuracy,Optical axis

ΔΦ⊥ indicates the optical axis deviation from perpendicular plane to the junction plane.
The emission point accuracy causes the variation of the optical coupling efficiency, which is provided by the radiation angle and the collimator, and becomes the factor of instability of other items.
Angular
accuracy
ΔΦ⊥
ΔΦ//

Figure Optical axis

ΔΦ// indicates the optical axis deviation from parallel plane to the junction plane.
 
Differential
efficiency
ηD This indicates the value of the incremental change in optical power output for an incremental change in forward current; represented by the slope in the region B in the figure of "Optical Power Output vs. Forward Current Characteristics". The larger the differential efficiency, the steeper the curve of the optical power output vs. current characteristics becomes. The smaller the differential efficiency, the gentler the curve becomes. Because the larger the differential efficiency, the steeper the curve of the optical power output vs. current characteristics, the width between the oscillation start current and the rated operating current becomes small. On the contrary, because the smaller the differential efficiency, the gentler the curve of the optical power output vs. current characteristics, the width between the oscillation start current and the rated operating current becomes large.

2. Laser Diode Electrical and Optical Characteristics (4)

Item Symbol Definition Remarks
Astigmatism As Apparent emission point deviation on the planes between parallel and perpendicular to the P-N junction plane in the direction of the optical axis.  
Polarization
ratio
P1 Ratio of the optical power of the linearly polarized component parallel to the P-N junction plane to that of the linearly polarized component perpendicular to it.  
Relative
intensity
noise
RIN Ratio of the optical intensity noise to the average optical power output per unit frequency. Actually, the light fluctuations are measured and calculated using a photodetector such as a photo diode and an amplifier. Therefore, RIN is obtained by eliminating the shot noise generated by the photodetector and the thermal noise generated by the amplifier from noise detected in the specified frequency, and dividing the remaining noise by the average output of the semiconductor laser (generally detected by the optical current of the photodetector) and the measurement frequency bandwidth.  
Photodiode
dark
current
ID Current value flowing to the optical monitor output when the semiconductor laser is not in the emitting state.