Radio-Frequency Characteristics of

Ultraviolet Optical Links

J. Deng, S. Halder, and J. C. M. Hwang, Lehigh UniversityA. Osinsky, SVT Associates

H. Seigneur, W. V. Schoenfeld, and L. Chernyak, University of Central Florida

• Introduction• Light-emitter diode (LED)

characteristics• Photo-detector (PD)

characteristics• LED-PD link DC characteristics• LED-PD link RF characteristics• Conclusion

Outline

Non-Line-of-Sight Covert Links

Current UV Links

Mercury lamp + photo-multiplier tube= bulky, inefficient and expensive

Proposed UV Links

GaN light-emitting diode +photo-detector diode

= compact, efficient, low cost

5µm

PD2

100µm

PD1

300µm

LED

0

1

2

3

300 350 400 450

Wavelength (nm)

Em

issi

on

In

ten

sity

(a.

u.) I (mA)

100

80

60

40

20

LED Emission Spectra

PD DC Characteristics

-12

-8

-4

0

-6 -4 -2 0 2 4Bias (V)

Lo

g C

urr

ent

(A)

-12

-10

-8

-6

200 400 600 800

Wavelength (nm)

Lo

g C

urr

ent

(A)

Photo Response

Dark Current

Comparable between(■) PD1 & (▲) PD2

0

2

4

6

8

10 100 1000Frequency (MHz)

Cap

acit

ance

(p

F)

Rs+RL

R

C

Distributive R-C Effect

Both (symbol) measurement and (curve) simulation show larger dispersion in PD1

(▲) PD2

(■) PD1

0.0

0.4

0.8

1.2

1.6

0 20 40 60

LED Current (mA)

Det

ecto

r C

urr

ent

(μA

)DC LED-PD Link

Comparable between(■) LED-PD1 & (▲) LED-PD2

-15

-10

-5

0

5

0 20 40 60 80

Frequency (MHz)

No

rmal

ized

Po

ut

(dB

)

(▲) LED-PD2 more wide- band than (■) LED-PD1

Small-Signal LED-PD Link

20

25

30

0 5 10

Detector Bias (V)

Ban

dw

idth

(M

Hz)

0

4

8

12

No

rmal

ized

Gai

n (

dB

)

Bias Dependence of LED-PD1 Link

Bandwidth and gain of LED-PD1 link increase with reverse bias of PD1

LED-PD2 link bandwidth independent of PD2 bias

0

20

40

60

80

0 20 40 60

LED Current (mA)

Ban

dw

idth

(M

Hz)

-4

-2

0

2

No

rmal

ized

Gai

n (

dB

)

Bias Dependence of LED-PD2 Link

• Bandwidth of LED-PD2 link increases with LED current

• Bandwidth of LED-PD1 link independent of LED current

Conclusion

• 370-nm link demonstrated at 60 MHz by using GaN LED and photo-detector

• Link bandwidth is orders-of-magnitude higher than that achieved by using lamp and tube

• Link bandwidth limited by LED instead of photo-detector

• Bandwidth improvement of solar-blind (<280nm) LED in progress

Acknowledgment

• LED supplied by Tekcore Co., Taiwan

• Research sponsored in part by the U.S. Army Research Laboratory and was accomplished under Cooperative Agreement Number W911NF-06-2-0020. The views and conclusions contained in this presentation are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of the Army Research Laboratory or the U.S. Government.