Transcript PosterEECS_time_stre.. - School of Electrical Engineering and

Jiejun Zhang
Microwave Photonics Research Laboratory, School of Electrical Engineering and Computer Science, University of Ottawa, Ontario K1N 6N5, Canada
[email protected]
y  t    x   t  exp   j  t d

2
0
DC bias
DCF
1
ATT
EDFA1
MLL
OBPF
MZM
PD
AWG
Synchronization
SG
OSC
Mixer
The transfer function of a single LCFBG is:
 C 2 
H LCFBG    exp   j  
2


E
2
 N C 2 
H loop   

exp   j
 
Ei
2
2


(N )
o
The main problem is the lack of dispersion devices
with large dispersion coefficient, limiting the
stretching factor and the length of the signal that
can be sampled. This limitation is in analogy to the
magnifying factor and the aperture of a lens
imaging system. Here we proposed an fiber optic
structure that can achieve the largest dispersion
ever reported, which enable us to sample electrical
field at a time resolution of 347 fs.
20
The stretch factor is deduced as:
M  1  N C  D
It is seen that, by adopting the recirculating loop, an
equivalent dispersion coefficient N times as large as
the original LCFBG dispersion coefficient is
achieved, i. e., the time stretching ability is enhance
by N times. In the dispersive loop, the propagation
loss can be compensated by the EDFA. Early work
has demonstrated that N can be over 200.
This work has been published in: J. Zhang and J. P. Yao, Optica, vol. 1, no. 2, pp. 64-69, Aug. 2014
(b)
50
30
(c)
30
20
10
-2
-1
0
1
Time (ns)
2
30
306
(d)
20
10
921
The transfer function of the dispersive loop is:
 Current challenges
40
0
2X2
coupler
(a)
60
Voltage (mV)
The pace-time duality of light indicates that
magnification can also be realized in time domain,
i. e., very fast temporal feature of signal can be
sampled if we use a temporal magnifier, or, time
stretching. Similarly, the function can be realized
by a dispersion device, of which the transfer
function is given by:
3
922
923 924
Time (ns)
925
24
20
16
12
1840
1845
1850
Time (ns)
1855
308 309
Time (ns)
310
(e)
25
20
15
926
(g)
307
1225
615 616
Time (ns)
18
14
2160
617
618
(f)
20
15
1535
(h)
2155
Time (ns)
614
25
1230
1235
Time (ns)
22
2150
613
Voltage (mV)
 Time stretching
2
EDFA2
The original electrical signal sampled by the oscilloscope. Left:
As the signal bandwidth exceeds the bandwidth of sampling
system, only the envelope of the pulse is detected; right: the
fast oscillations are successfully resolved with the same PD
and oscilloscope, after the pulse is temporally stretched.
Voltage (mV
LCFBG
400 ps
Voltage (mV)
0
2 ns
Voltage (mV)
2
A 36-GHz sinusoidal electrical pulse is modulated
to the optical pulse, which is then detected by a 20GHz PD and sampled by a 32-GHz oscilloscope.
Voltage (mV)
y  r   2  x    r  exp   jDr d 

A microwave waveform is modulated on a predispersed optical pulse which is sent to a
recirculating dispersive loop consisting of an
LCFBG and an erbium-doped fiber amplifier
(EDFA). The LCFBG is used to achieve repetitive
pulse stretching and the EDFA is used to
compensate for the loss in the loop. By controlling
the gain of the EDFA to compensate for the loop
loss, the optical waveform can recirculate in the
loop and a repetitive use of the LCFBG for
accumulated pulse stretching is realized.
Voltage (mV)
The magnification of a target is realized by a lens
which has a transfer function given by:
4. Experiment
Voltage (mV)
 Magnifying glass
2. PRINCIPLE
Voltage (mV)
1. INTRODUCTION
1540
Time (ns)
1545
(i)
18
16
14
2455
2460
2465
Time (ns)
2470
The detail output waveforms after different number of round
trips. (a)-(i) correspond to 0 to 8 round trip respectively. Note
that the time scale is 1 ns/div in (a) to (d), and 5 ns/div in (e) to
(i).
6. CONCLUSION
In the experiment, the electrical pulse recirculates
for 8 round trips in the loop, which leads to an
equivalent dispersion coefficient of 12 000 ps/nm,
which is the largest that have ever been reported.
The stretching factor is 36, which enables the
sampling of terahertz signal with traditional
electrical equipment. The application can be
numerous.