Journal of Microscopy, Vol. 229, Pt 3 2008, pp. 496–502
Received 28 September 2006; accepted 27 June 2007
Experimental research on the performance of a very-small-aperture
laser
HONGFENG GAI
∗
, JIA WANG
∗
,QIANTIAN
∗
,WEIXIA†,
XIANGANG XU†,SHUOHAN‡ & ZHIBIAO HAO‡
∗
State Key Laboratory of Precision Measurement Technology and Instruments, Department of
Precision Instruments, Tsinghua University, Beijing 100084, P. R. China
†Shandong University, Jinan 250100, P. R. China
‡State Key Laboratory of Integrated Optoelectronics, Department of Electronic Engineering, Tsinghua
University, Beijing 100084, P. R. China
Key words. Aperture, confinement effect, front facet reflectivity, lasing ability,
very-small-aperture laser (VSAL).
Summary
Very-small-aperture lasers (VSALs) with different aperture
shapes are fabricated. Their far-field and near-field
performance is analyzed experimentally. The far-field
performance, including the threshold current, the slope
efficiency, the lasing ability and the linear frequency
modulation property, is found to be influenced by the front
facet reflectivity. A new factor is tentatively proposed to
analyze the lasing abilities of VSALs with different aperture
shapes. This factor can diminish the discrepancies among the
same type laser diodes. The near-field performance focusses
on the confinement effect of the VSAL aperture. A near-field
scanning optical microscopy is used to measure the near-
field intensity distribution from a VSAL. The experimental
results indicate that the near-field performance is affected
by the aperture shape. A 100-nm C-aperture is proved to be
superior to a 100 × 300 nm
2
rectangular aperture on both
power throughput and peak intensity. These two apertures
are fabricated on the same VSAL facet for the fairness of
comparison. An optical spot beyond the diffraction limit
is also obtained by fabricating a 70-nm C-aperture on a
VSAL facet.
Introduction
Near-field optics has gained a huge advancement in recent
years. As one of the key technologies in this researching field,
a nanometric light source has also developed from a passive
device to an active device.Theformertypeisdelegatedbyafibre
probe and the latter one is delegated by a very-small-aperture
Correspondence to: Hongfeng Gai.Tel: +86 10 6278 8610; fax: +86 10 6278 4691;
e-mail: gaihf99@mails.tsinghua.edu.cn
laser (VSAL) (Partovi et al., 1999). A VSAL is usually fabricated
by creating a sub-wavelength aperture on a metal-coated laser
diode (LD) facet to expose the active region beneath the coating
(Partovi et al., 1999; Chen et al., 2001). Another type of
VSAL is fabricatedfrom a vertical-cavity surface-emitting laser
(Shinada et al., 1999). When the aperture is small enough, an
optical spot beyond the diffraction limit can be obtained in the
near-field region. The diameter of the optical spot can be as
small as 30 nm (Partovi et al., 1999). The small optical spot
makes it possible to use a VSAL in the ultra-high density optical
data storage (Partovi et al., 1999), heat-assisted magnetic
recording (Challener et al., 2003), super resolution near-field
imaging (Gan, Song, Yang, et al., 2006) and so on.
The far-field performance of a VSAL usually focusses on the
threshold current and the slope efficiency, which are changed
during the fabrication processes of the VSAL (Shinada et al.,
1999; Chen et al., 2001; Ohno et al., 2004). These changes
are due to the front facet reflectivity change (Gan, Song, Xu,
et al., 2006) and the light absorption by the metal coating
(Shinada et al., 1999). It has also been observed that the
emitting wavelength from a VSAL is larger than the emitting
wavelength from an LD (Gan et al., 2005). This was attributed
to the strong optical feedback caused by the metal coating and
heataccumulationinside the resonant cavity(Gan et al., 2005;
Gan, Song, Xu, et al., 2006).
The near-field performance of a VSAL mostly lies on
the aperture shape (Chen, Itagi, Stebounova, et al., 2003;
Chen, Stancil & Schlesinger, 2003). Regular aperture shapes,
such as a square aperture and a circular aperture, suffer
from low power throughput when the apertures are small
enough (Bethe, 1944; Bouwkamp, 1950). To solve this
problem, researchers have proposed various aperture shapes,
for example, a C-aperture (Shi et al., 2002; Sun & Hesselink,
2006; Tang et al., 2006), an I-aperture (Tanaka & Tanaka,
C
2008 The Authors
Journal compilation
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2008 The Royal Microscopical Society