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Response to comment on “Optical characterization of quantum dots entrained in microstructured optical fibers”
ARTICLE IN PRESS
Physica E 31 (2006) 109–110 www.elsevier.com/locate/physe
Response to comment on ‘‘Optical characterization of quantum dots entrained in microstructured optical fibers’’ K.E. Meissnera,, C. Holtonb, W.B. Spillman Jr.c a
Texas A&M University, College Station, TX, USA b Virginia Tech, Blacksburg, VA, USA c University of Vermont, Burlington, VT, USA
Received 17 October 2005; accepted 30 October 2005 Available online 20 December 2005
Corresponding author.
E-mail address: [email protected] (K.E. Meissner). 1386-9477/$ - see front matter r 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.physe.2005.10.006
within a logarithmic intensity axis in order to provide easy viewing of both the probe light as well as low level, broad QD emission extending from approximately 537 to 624 nm (at the 10% level). This seems to have caused some confusion and it is suggested that the light output with both pump and probe could be the sum of the probe light plus the QD emission. Here, Fig. 2 is reproduced with a linear intensity axis. The probe only is shown in black, and the probe with pump in gray. It is clear that the sum does not account for the additional light observed with both the pump and probe. This observation was repeated numerous times over extended periods of time.
Intensity
We appreciate the comments by C.E. Finlayson and the opportunity to respond. Our recent paper describes the entraining of CdSe/ZnS core/shell semiconductor quantum dots (QDs) in the cladding of a ‘‘holey’’ optical fiber and interesting observed optical properties. The QDs are entrained in liquid media and thus remain mobile within the fiber capillaries. This discussion arises from our observation of additional probe light on the low-energy side of the QD emission when the QDs are pumped in their absorption band. We refer to this increase in probe light as apparent amplification or optical gain. As we outlined in the paper, there a number of reasons the data presented are not definitive with respect to this point. Thus, we attempted to make no definitive claims as to the exact mechanism of this apparent amplification. At this point, it is best to briefly review the data in the paper. As expected, light from a laser source (the probe) may be coupled to and propagated down the core of the optical fiber. Fig. 1b in the paper demonstrates this process. When a pump laser is coupled to the fiber, the QDs in the clad are excited and emit as expected. Fig. 1c in the paper shows that some emission from the QDs entrained in the cladding region of the fiber couple to the core of the fiber. Undoubtedly, this coupling will occur with both short-range propagation and long-range propagation within the fiber. These data do not seem to be in dispute. Fig. 2 in the paper shows the spectra of light emerging from the core of the fiber with the probe only and with both the pump and probe. The figure was plotted
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Wavelength (nm)
Thus, we believe the additional probe light observed when pumping the QDs is real and needs to be explained. However, the exact mechanism is certainly not known at this time. As indicated in the paper, the major issue with
ARTICLE IN PRESS 110
K.E. Meissner et al. / Physica E 31 (2006) 109–110
this system for us was the spatial instability of the modal pattern due to the QD colloid mobility within the capillaries of the fiber clad. At this time, we have been unable to immobilize the QDs within the clad structure.
Until this issue is overcome, we do not believe the exact mechanism of this apparent gain can be determined. Therefore in the paper, we did not speculate on the precise nature of the apparent optical gain.
Physica E 31 (2006) 109–110 www.elsevier.com/locate/physe
Response to comment on ‘‘Optical characterization of quantum dots entrained in microstructured optical fibers’’ K.E. Meissnera,, C. Holtonb, W.B. Spillman Jr.c a
Texas A&M University, College Station, TX, USA b Virginia Tech, Blacksburg, VA, USA c University of Vermont, Burlington, VT, USA
Received 17 October 2005; accepted 30 October 2005 Available online 20 December 2005
Corresponding author.
E-mail address: [email protected] (K.E. Meissner). 1386-9477/$ - see front matter r 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.physe.2005.10.006
within a logarithmic intensity axis in order to provide easy viewing of both the probe light as well as low level, broad QD emission extending from approximately 537 to 624 nm (at the 10% level). This seems to have caused some confusion and it is suggested that the light output with both pump and probe could be the sum of the probe light plus the QD emission. Here, Fig. 2 is reproduced with a linear intensity axis. The probe only is shown in black, and the probe with pump in gray. It is clear that the sum does not account for the additional light observed with both the pump and probe. This observation was repeated numerous times over extended periods of time.
Intensity
We appreciate the comments by C.E. Finlayson and the opportunity to respond. Our recent paper describes the entraining of CdSe/ZnS core/shell semiconductor quantum dots (QDs) in the cladding of a ‘‘holey’’ optical fiber and interesting observed optical properties. The QDs are entrained in liquid media and thus remain mobile within the fiber capillaries. This discussion arises from our observation of additional probe light on the low-energy side of the QD emission when the QDs are pumped in their absorption band. We refer to this increase in probe light as apparent amplification or optical gain. As we outlined in the paper, there a number of reasons the data presented are not definitive with respect to this point. Thus, we attempted to make no definitive claims as to the exact mechanism of this apparent amplification. At this point, it is best to briefly review the data in the paper. As expected, light from a laser source (the probe) may be coupled to and propagated down the core of the optical fiber. Fig. 1b in the paper demonstrates this process. When a pump laser is coupled to the fiber, the QDs in the clad are excited and emit as expected. Fig. 1c in the paper shows that some emission from the QDs entrained in the cladding region of the fiber couple to the core of the fiber. Undoubtedly, this coupling will occur with both short-range propagation and long-range propagation within the fiber. These data do not seem to be in dispute. Fig. 2 in the paper shows the spectra of light emerging from the core of the fiber with the probe only and with both the pump and probe. The figure was plotted
585
590
595
600
605
Wavelength (nm)
Thus, we believe the additional probe light observed when pumping the QDs is real and needs to be explained. However, the exact mechanism is certainly not known at this time. As indicated in the paper, the major issue with
ARTICLE IN PRESS 110
K.E. Meissner et al. / Physica E 31 (2006) 109–110
this system for us was the spatial instability of the modal pattern due to the QD colloid mobility within the capillaries of the fiber clad. At this time, we have been unable to immobilize the QDs within the clad structure.
Until this issue is overcome, we do not believe the exact mechanism of this apparent gain can be determined. Therefore in the paper, we did not speculate on the precise nature of the apparent optical gain.