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Athermal AWG Module1.

the transmission wavelength for an AWG, which is represented by Equation ⑴.

INTRODUCTION

Arrayed waveguide grating (AWG) which handles thefunction of wavelength multiplexer/demultiplexer is extensively used in configuring optical communication networks that are becoming more diversified. Since thetransmission wavelength of an AWG is temperaturedependent, it was a common practice to control its temperature using heaters or Peltier elements. But thiscaused problems of power consumption increase in thewhole system in addition to limiting the installation locations of AWGs, thus making it difficult to respond to various needs of the next-generation optical communication
networks, despite the fact that system performance
upgrading and function enhancement are required inrecent years.
To solve these problems, Furukawa Electric has developed an athermal (temperature independent) AWG module of PS701 series that do not require, based on its proprietary structure and principle, any temperature control
and power supply. The product will be introduced in thisreport.

2.

FEATURES

The AWG consists of input waveguides, arrayed waveguide, slab waveguide and output waveguides, constituting a diffraction grating that takes advantage of the optical
path difference in the arrayed waveguide. Figure 1 showsa schematic of AWG circuitry.
As ambient temperature changes, the phase front at
each wavelength generated by the arrayed waveguide will
tilt due to the change in the refractive index of the opticalwaveguide and the linear expansion of the silicon substrate, causing a shift of the focusing point on the output
waveguide within the slab waveguide. This constitutes themain factor determining the temperature dependence ofλ ��� ��λ� �λ� �� ����⑴where: nc is the effective refractive index of the arrayedwaveguide; and αs is the thermal expansion coefficient of
the silicon substrate.
Letting dnc/dT = 8×10-6/℃ and αs = 3×10-6/℃, thetemperature dependence of the AWG is estimated to be
0.011 nm/℃.
In order to solve such a problem of temperature dependence for the transmission wavelength, we have devised
a structure in which the AWG circuit is cut at the slab
waveguide.
The AWG circuit is cut at one of the slab waveguides
into two pieces --one larger and one smaller, and thesepieces are connected by a compensating plate made ofcopper. Figure 3 shows the slab waveguide, schematically illustrating the mechanism of temperature compensation.
In an ordinary AWG, when ambient temperature changes from the middle temperature, the focus point will shift
as shown in Figure 3. In an athermal AWG, on the otherhand, the focus point shift as the temperature changes,
but the expansion or contraction of the copper plate
Slab waveguideCompensating plate（Copper）

Figure 2

Structure of athermal AWG circuitry.

Low temp.

Arrayed waveguide

Output slab waveguide

Input slab waveguide
Input waveguides
λ1, λ2, λ3…λnFigure 1

Output waveguides
λ1 λ2
λ3

Structure of AWG circuitry.

Mid.

High temp.

Conventional
AWG
Focus point shifts.

Focus point shifts.

Waveguide is moved

Waveguide is moved

AthermalAWG

λnFigure 3

Principle of temperature compensation for athermal
AWG.

Furukawa Review, No. 31

200723Athermal AWG Module

Table 1 summarizes typical optical characteristics of thePS701 series athermal AWG module developed here. Theinsertion loss is 3.5 dB or less for the Gaussian type, 4.5
dB or less for the semi-flat type, and 6.5 dB or less for theflat-top type --excellent results, together with the otheroptical characteristics. The package measures 130 x 65 x
8.5 mm3, a very compact size. See Photo 1.

moves the output waveguide to the new focus point, sothat the same wavelength can be output.

3.

CHARACTERISTICS

Center wavelength shift（nm）

3.1 Optical Characteristics
Figure 4 shows a typical temperature dependence of thecenter transmission wavelength of the athermal AWG
product based on Furukawa Electric’s proprietary principle and structure, and Figure 5 a typical temperaturedependence of the transmission spectrum. Both the center wavelength with respect to the ITU-T Grid wavelengthand the transmission spectrum show no fluctuation anddegradation against ambient temperature changes,
achieving good results.
0.05
0.04
0.03
0.02
0.01
0.00
-0.01
-0.02
-0.03
-0.04
-0.05
-10

3.2 Reliability Tests
Reliability tests in conformity with Telcordia GR-1209 and1221 were carried out, and the results are shown in Table
2. It can be seen that the changes in the insertion loss
and in the center wavelength before and after the tests
are 0.3 dB or less maximum and 0.022 nm or less,respectively, achieving a high level of reliability.

4. CONCLUSION
Based on its proprietary structure and principle, Furukawa
Electric has launched an athermal AWG module of PS701
series that needs no temperature control and power sup-01020304050607080

Temperature（℃）

Transmission (dB)Figure 4

Temperature dependence of center wavelength.

0-5-10-15-20-25-30-35-40-45-50
1540

70℃
20℃0℃

1542

1544

1546

1548

1550

Wavelength（nm）

Figure 5

Photo 1

Temperature dependence of transmission spectrum.
Table 1

Typical optical characteristics of athermal AWG module.
Gaussian

Type
Item

Min

Appearance of athermal AWG module,measuring 130 x 65 x 8.5 mm3.

Typ

Semi-flatMaxMin

TypFlatMax

Min

TypUnitMax

Number of channel

40

40

40Ch

Channel spacing

100

100100GHz

ITU-grid frequency

C-band or L-band…

Pass band-0.1

0.1-0.10.1-0.1

0.1

nm

Center wavelength accuracy

-0.05

0.05

-0.05

0.05

-0.05

0.05

nm

1-dB bandwidth

0.2

0.3

0.4

3-dB bandwidth

0.4

0.5

0.6

Insertion loss at ITU-grid

2.0

Uniformity of insertion loss

3.5

4.0

4.5

nm
nm
5.5

6.5

dB

1.0

1.0

1.0

dB

Adjacent crosstalk

-25.0

-25.0

-25.0

dB

Non-adjacent crosstalk

-30.0

-30.0

-30.0

dB

Total crosstalk

-21.0

-21.0

-21.0

dB

Polarization dependent loss

0.5

0.5

0.5

dB

Polarization mode dispersion0.50.50.5

ps

20.0

ps/nm

24.0

dBm

Chromatic dispersion-15.0

Return loss

45.0

Optical input power
Package size

15.0

-20.0

20.0

45.0

-20.0
45.0

24.0

24.0

dB

130×65×8.5

mm

Furukawa Review, No. 31

2007

24

Athermal AWG Module

Table 2
Reliability Test
Vibration
ImpactCondition
20 G, 20~2000 Hz
4 min/cycles
4 cycles/axis
500 G
5 times/direction
6 directions

Results of reliability tests.
n14
14

Temperature cycling-40~85℃
500 cycles

14Damp heat

85℃・85%RH
2000 hours

15Low temperature storage-40℃
2000 hours3Temperature-humidity cycling-40~85℃
20~85%RH
42 cycles

3Cable retention

1.5, 0.45 kgf
60 sec11Side pull

0.23 kgf
5 sec
90° 2 directions

11ply. In terms of transmission spectrum, the Gaussian,semi-flat and flat-top types are available, provided withexcellent optical characteristics and reliability.
Hereafter, we plan to successively launch athermal
AWG modules with outdoor specification for WDM-PON
applications.

ResultInsertion loss change (dB)
Ave
Worst
Std
Ave
Worst
Std
Ave
Worst
Std
Ave
Worst
StdAveWorst
StdAveWorst
Std
Ave
Worst
Std
Ave
Worst
Std

0.00
-0.10
0.031
-0.01
0.11
0.025
0.00
0.17
0.051
0.10
0.30
0.087
-0.06
-0.11
0.023
0.02
0.09
0.018
0.00
0.00
0.000
0.00
0.00
0.000

Center wavelength change (nm)
Ave
Worst
Std
Ave
Worst
Std
Ave
Worst
Std
Ave
Worst
Std
Ave
Worst
Std
Ave
Worst
Std

0.002
-0.0150.00560.000
0.011
0.0046-0.0030.013
0.00600.012
0.022
0.0050-0.011-0.0180.0075-0.014-0.0200.0057-For more information, please contact:
New Business Promotion Unit, Optical Components
Section, FITEL Products Department,
Telecommunications Company.
TEL: +81-436-42-1676
FAX: +81-436-42-1789

Furukawa Review, No. 31

200725