Some Practical Issues in Deep-Time Multiplexing

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Some Practical Issues in Deep-Time Multiplexing

Michael Peña

Defense Experimentation and Stockpile Stewardship

National Security Technologies, LLC

(2)

►

Deep-time multiplexing

■

Conceptual design

►

Index of refraction variations

■

Wavelength

■

Temperature

►

State of Polarization

■

Stability

■

Control

Outline

(3)

Deep-Time Approach ROADDM

800μs record at detector

= 10km SMF (50us)

16 signals from

MPDV,

2 per ITU21-35

~150km SMF

D W D M

DW

DM

NS 2x2 D W D M 2x1 PD 80km SMF SCOPE

8 Local Oscillators

1 per ITU21-35

Corning

®

SMF-28

®

Ultra

α

_max

≤ 0.18

km

dB

D

_λ

≤ 18.0

(nm·km)

𝑝𝑠

N

_eff

:

1.4682

Pol. Ctrl

(4)

•

Index of Refraction,

n(λ)

•

Phase Velocity,

𝑣

𝑝

𝜔

𝑘

𝑐

𝑜

𝑛(

λ)

•

Group Velocity,

𝑣

𝑔

𝑑𝜔

𝑑𝑘

; 𝑑

λ=

−

λ

2

2𝜋𝑐

_𝑜

𝑑𝜔

𝑐

_𝑜

𝑛(

λ)

1 −

λ

𝑛

𝑑𝑛

𝑑

λ

−1

•

Group Velocity Dispersion, GVD

𝑑

2

𝑘

𝑑𝜔

2

λ

3

2𝜋𝑐

𝑜

2

𝑑

2

𝑛

𝑑

λ

2

•

Group Delay,

𝜏

𝑔

=

𝐿

𝑣

𝑔

=

𝑑𝜑

𝑑𝜔

𝑑𝜑

𝑑𝜔

=

𝑑 𝑘𝐿

𝑑𝜔

𝑛

𝑐

𝑜

1 −

λ

𝑛

𝑑

𝑛

𝑑

λ

𝐿

•

Group Delay Dispersion, GDD

𝑑𝜏

𝑔

𝑑𝜔

=

𝑑

2

(𝑘𝐿)

𝑑𝜔

2

λ

3

2𝜋𝑐

𝑜

2

𝑑

2

𝑛

𝑑

λ

2

𝐿

Wavelength-Dependent Index of Refraction

18

𝑝𝑠

𝑛𝑚 ∙ 𝑘𝑚

× 10[𝑘𝑚] × 1560.61 − 1549.32 [𝑛𝑚]

= 2.032𝑛𝑠

18

𝑝𝑠

𝑛𝑚 ∙ 𝑘𝑚

× 150[𝑘𝑚] × 1560.61 − 1549.32 [𝑛𝑚]

= 30.483𝑛𝑠

(5)

Modulation Phase Shift Dispersion Measurement

Tunable Laser Intensity Modulator PD Sine Wave Generator Compare phase

DUT

f

_m

∆𝜏

𝑔

𝜆 =

𝜑 𝜆 − 𝜑 𝜆

𝑟

360°

1

𝑓

𝑚

𝐷 𝜆 =

1

𝐿

𝑑 ∆𝜏

_𝑔

𝜆

𝑑𝜆

=

1

360°𝐿𝑓

𝑚

𝑑𝜑 𝜆

𝑑𝜆

Measurement setup for fiber chromatic dispersion

Δτ(λ) = 0.00029598λ

2

– 0.7348λ + 440.16

Δτ(1560.61nm) - Δτ(1549.32nm) = 1.97305ns

𝐷λ =

_{11.29𝑛𝑚∙10𝑘𝑚}1973.05𝑝𝑠

= 17.476

𝑝𝑠

(6)

Temperature-Dependent Index of Refraction

LUNA Technical Note EN_FY1406,

∆𝜏

𝜏

=

1

𝐿

𝜕𝐿

𝜕𝑇

∆𝑇 +

1

𝑛

𝜕𝑛

𝜕𝑇

∆𝑇 = 𝛼

𝐿

+ 𝛼

𝑛

∆𝑇

α

L

: thermal expansion coeff

𝛼

𝑛

: thermo-optic coeff

0.55 x 10

-6

°C

-1

~7.0 to 9.0 x 10

-6

°C

-1 (

7.5 x 10-

6

used below)

385

𝑝𝑠

℃ ∙ 10𝑘𝑚

∙ 15 𝑑𝑒𝑙𝑎𝑦𝑠 = 5.78

𝑛𝑠

℃

210

𝑝𝑠

℉ ∙ 10𝑘𝑚

∙ 15 𝑑𝑒𝑙𝑎𝑦𝑠 = 3.15

𝑛𝑠

℉

Observed temps. y=0.393x -8.644 y=0.3798x -8.769

(7)

In situ Cross-Timing Mark

XT-mark



XT-mark in each time window



Follow temp-time fluctuations



XT-mark inherently same λ as

velocity record



Single XT-mark for 16 records (only

8 shown)



Temperature fluctuations ~1–16 ns



Temp gradients = inconsistent

𝛿

t



Compounded effect deeper in time

𝑛=1 15

𝛿𝑡

_𝑖

𝛿𝑡

𝑖

D W D M

DW

DM

2x1

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Static Signal Fluctuations

• All channels seeing same

probe

• 30 m jumpers to firing

chamber

• Shot-to-shot variability

~10 dB

(9)

►

Real single-mode fibers exhibit elliptical birefringence due to

■

Deviations of core shape from circularity

■

Lateral compression

■

Residual twist

■

Bending

Polarization/Induced Birefringence

y

x

y

x

F

(10)

Stokes Parameters vs. 50 min

𝜏

8

𝜏

1

(11)

Tau Windows 1 through 8

(1 millisecond)

(12)

Tau Windows 9 through 16

(1 millisecond)

Stressed Fiber?

(13)

Local Oscillator SOP

(1 millisecond)

(14)

Aligning Local Oscillators with Signals

𝑄𝑊

1

=

𝜋

2

𝑄𝑊

2

=

5𝜋

3

𝑄𝑊

3

=

𝜋

3

𝑄𝑊

4

=

𝜋

3

Dot Products (Signal,LO)

𝜏

1

= 0.3546 𝜏

9

= 0.8797

ITU21

𝜏

2

= 0.4207 𝜏

10

= 0.3000

ITU23

𝜏

3

= −0.1510 𝜏

11

= 0.7326

ITU25

𝜏

4

= 0.5092 𝜏

12

= 0.7100

ITU27

𝜏

5

= −0.3259 𝜏

13

= 0.8980

ITU29

𝜏

6

= 0.2449 𝜏

14

= 0.5950

ITU31

𝜏

7

= 0.8789 𝜏

15

= 0.2652

ITU33

𝜏

8

= −0.8642 𝜏

16

= 0.7807

ITU35

−1 ≤ 𝑆𝑖𝑔𝑛𝑎𝑙 ∙ 𝐿𝑂 ≤ 1

(15)

Polarization Controllers – Fiber Squeezers (EPC-300)

𝑆

_𝑜𝑢𝑡

= 𝑀

_{0°45°0°45°}

1

0

𝑆

_𝑜𝑢𝑡

= 𝑀

_{0°45°0°45°}

0

1

45°

0°

𝑆

_𝑜𝑢𝑡

= 𝑀

_{0°45°0°45°}

0

(16)

Polarization Controllers – PolarRITE (VarRotQWP)

Linear Horizontal

𝑆

_𝑜𝑢𝑡

= 𝑀

_𝜃,𝜑

1

0

Right Circular

𝑆

_𝑜𝑢𝑡

= 𝑀

_𝜃,𝜑°

0

1

Linear +45

𝑆

_𝑜𝑢𝑡

= 𝑀

_𝜃,𝜑

0

1

0

(17)

Polarization Controllers 3-Paddle (RQW-RHW-RQW)

𝑆

_𝑜𝑢𝑡

= 𝑀

_𝜃₁_,𝜃₂_,𝜃₃

0

1

𝑆

_𝑜𝑢𝑡

= 𝑀

_𝜃₁_,𝜃₂_,𝜃₃

0

1

𝑆

𝑜𝑢𝑡

= 𝑀

𝜃1,𝜃2,𝜃3

0

(18)

►

Solution to current systems will need to be:

■

Single- or few-point solution

■

Endless tracking (i.e., no reset or operation discontinuity)

■

Feedback loop, detection and compensation

●

System time constants ~seconds

●

Dynamic excursions from experiment

■

Practical

●

Ease of use

●

Cost

●

Physical footprint

►

Looking at all-optical solutions

■

Based on nonlinear interactions

●

Raman, four-wave mixing, SBS

(19)

►

Timing issues

■

Wavelength- and temperature-dependent Index of Refraction

●

~

21

𝑝𝑠

℉∙𝑘𝑚

/ ~

38

𝑝𝑠

℃∙𝑘𝑚

■

In situ timing marks follow time variations

►

State of Polarization

■

Each time window will have unique state

■

SOP distribution increases with time

■

SOP relatively stable over ~1 hr and ~100s μs

■

Some Practical Issues in Deep-Time Multiplexing