Page 456 - Tunable Lasers Handbook

4 1 6 Paul Zorabedian

modulation index of the emission spectrum. The magnitude of the round-trip
amplification factor is given by

For an uncoated laser, RflRf2. = RZ where R, = 0.3 1 is the Fresnel reflectance of
an uncoated facet. By definition, when the uncoated laser is driven at threshold,
I a I = 1. After coating, the value of I a I at the same current and wavelength is
reduced to

The modulation index nz of 1.x subthreshold eniission is given -y

m= 'mas - Pmin (89)
Pmax + Pmm '

where Pmm and Pmin are, respectively, the local maximum and minimum at the
peak of the emission spectrum. When the coated device is driven at the original
uncoated-laser threshold current, 1 a I is related to in by

nz=-. 214
1 +(a('

T=20'C
L=190pm
h= 1.51 pm
E I

0 50 100 150
Pulse current, rnA
FIGURE 39 Light output versus current curves before and after AR coating. (Reproduced with
permission from Wyatt and Devlin [118] and IEE Publishing.)