90° optical hybrids
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i n f o @ k y l i a . c o m

COH1 – Description
The COH24 is a single polarization 90° optical hybrid that enables to extract phase and amplitude from asingle polarization signal by performing four 90° phase stepped interferences between the signal and a Local
Oscillator (LO). The COH24-X is a new generation optical hybrid with improved performances (among otherthings, a wider operating wavelength range and much better dual uniformities).
The COH28 and COH28-X are based on two single polarization 90° optical hybrids that enable to extract
phase, amplitude and polarization from a signal with any polarization.
These products are purely passive and athermal.
The COH24-X and COH28-X also feature a phase tunability option in order to perfectly adjust the 90° of thehybrid depending on the wavelength used.
Kylia also offers a dual polarization 180° hybrid named COH22.

COH packaging

COHX packaging

COHX phase tunable packaging

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COH1

COH: 90° optical hybrids

2 – Block diagram
Below is a block diagram showing how the four 90° phase stepped. Interferences are done in the opticalhybrid.

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COH2COH: 90° optical hybrids

3 – Absolute maximum ratings
Parameter
Maximal optical input power
Storage temperature range
Humidity
Fiber bend radius
1
Maximal input voltage
1Symbol
OpIn
STR
RH

Min

Typ.

-40
520U

Max
300
8085
4UnitmW°C%mm
V

Remarks/Conditions

Non condensing

for phase tunability option only (COH24-X and COH28-X)

4 – Operating conditions
Parameter

SymbolCOH
COH-X
Operating temperature range
Operating wavelength

Typ.

OTRMin1520
15200Symbol

Min

Typ.
7.0
7.0
7.0
10.0
1.0
0.5
0.5
0.2

OWR

Max
1570
1625
70

Unit

Remarks/Conditions

nm°C

5 – Specifications
Parameter
Insertion Losses
2from Signal

COH24/COH24-X
COH28/COH28-X
COH24/COH24-X
Insertion Losses
2
from LO
COH28/COH28-X
COH
2,3
IL uniformity
COH-X
COH
IL dual2,3uniformity
COH-X
2
Phase shift between I and Q
4Skew
Optical return loss
5
Polarization splitting ratio

2,6

Phase shift tunability
COH
7Packaging size
COH-X
Fiber Pigtail Type

IL→SIL→LO
ΔIL
ΔdualMax
8.5
8.5
8.5
11.5
2.0
1.0
1.0
0.5
95
1UnitdBdBdB

Without connectorsdB

Between balanced outputs
Without connectors

φ85

ORLPSR

3520deg
psdB
dB

Δφ+/-20deg

0.5SMPM

Fiber Pigtail Length

70 x 52 x 10180 x 32 x 19.5
SMF-28PANDA PM
0.9
1.0
1.1

Remarks/Conditions
Including 6dB of natural losses
Including 6dB of natural losses
Including 6dB of natural losses
Including 9dB of natural lossesmm

Measured at connectors end
Separation of X and Y
polarization at the Signalinput by the PBS
For a 3V voltage
3

With 900µm loose tubem

Other lengths on request

2

measured over OTR and OWR for all states of polarizationfrom Signal or LO
4
for all outputs
5for COH28 and COH28-X only
6for phase tunability option only
7
excluding fiber boots
3

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COH

3

COH: 90° optical hybrids

6 – COH-X and COH dual uniformities
3.5

3.5
IL uniformity (dB)

2.5
2IL unifomity (dB)

Signal ch 1 & 2Signal ch 3 & 4
LO ch 1 & 2LO ch 3 & 4

3

1.5
13Signal ch 1 & 2

2.5Signal ch 3 & 4
LO ch 1 & 2

2LO ch 3 & 4

1.5
10.5

0.5

00197
196195
194193192
191
190
189188
187
186
185
184

197
196
195
194
193
192
191
190
189
188
187
186
185
184

Frequency (THz)

Frequency (THz)

COH24 IL dual uniformities vs frequency

COH24-X IL dual uniformities vs frequency

The graphs above compare the dual uniformities, a key parameter of 90° optical hybrids, for the Signal andLO of a standard hybrid (COH) and a new generation one (COH-X). We can clearly see that COH-X exhibits
much better dual uniformities over a wider range.

7 – Phase tuning option
The 90° phase shift of the hybrids depends slightly on the wavelength. For example, it increases of about 2°
to 3° over the C-band. That means that if at 191THz the phase shift is 88.5° it will be approximately 91.5° at
197THz (see next paragraph for some typical measurements).
For some applications it can be useful to have a very precise 90° phase shift whatever the wavelength you
are working at. That is what the phase tunability option on COH-X enables. With this option, two voltages(V1 and V2) between 0V and 4V can be applied on the hybrid. One will increase the phase shift when thesecond one will decrease it. Hence for any wavelength in the OWR the phase shift can be adjusted to beprecisely equal to 90°.
Below are the packaging of a COH24-X with the phase tuning option and a typical measurement of the phaseshift versus voltage for a COH24-X device:

Phase tuning V2Phase tuning V1

COH24-X with phase tuning option packaging

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COH4

phase shift (deg)COH: 90° optical hybrids

1801651501351201059075604530
150

V1 (V2=0V)
V2 (V1=0V)

00.5

11.5

22.5

33.5

4

voltage applied (V)Graph: phase vs voltage for a COH24-X with phase tuning option

8 – Typical measurements

phase (deg)The two following diagrams show the typical behavior of the 90° phase shift. On the first one, one can seethat the variation of the phase shift versus the temperature is very small (less than 1°). Hence the hybrid
does not need any temperature control to ensure a precise, stable 90° phase shift. On the second diagram,one can see that the variation of the phase shift versus the wavelength is small (less than 3°). However if forsome particular application one need to have a very precise 90° phase shift, the phase tunability option
available on COH-X will enable to adjust it precisely for any wavelength of the OWR.
9594939291
90
8988
X polarization

87

Y polarization

86
85
-100

10

20

30

40

50

60

70

80

90
T (°C)

Graph: COH28 phase variation vs temperature

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COH5

phase (deg)COH: 90° optical hybrids

9594
93
929190898887

X polarization86

Y polarization

85
191

192

193

194

195

196

197

frequency (THz)Graph: COH28 phase variation vs frequency
The third diagram shows the IL variations versus the temperature. One can see that each output do not haveexactly the same variation but they all remain small, as well as dual and total uniformities.
T (°C)
01020

30

40

50

60

70

-7
-7.1
-7.2
-7.3
-7.4
-7.5
-7.6
-7.7
-7.8
-7.9
-8

IL SIGNAL (dB)

-8.1
-8.2
-8.3
-8.4

ch #1
ch #2
ch #3
ch #4
ch #5
ch #6ch #7
ch #8-8.5

Graph: insertion losses variation vs temperature (SIGNAL → OUTPUTS of a COH28-X)

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COH

6

COH: 90° optical hybrids

9 – Application note: full tunable 90° hybrid
In order to have the possibility to control all the parameter of a COH24-X or a COH28-X, we propose in a
19inches-2U rack a system where the user can adjust:-the phase
the insertion losses uniformity
the skew
phase adjustment

output 4

differential
photodetector

differential
photodetector

micrometer headfor IL attenuation(IL uniformity control)

micrometer headfor IL attenuation(IL uniformity control)

micrometer headfor delay tuning(skew control)

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output 3

output 1
output 2

SIGNAL and LOCALOSCILLATOR inputs

micrometer headfor delay tuning(skew control)

COH

7

COH: 90° optical hybrids

10 – Dual-Polarization 180° hybrid
Kylia offers a dual-polarization 180° hybrid based on the following block diagram and specifications:
LO(oriented @ 45°)
PM fiber.

SM fiber.

INOUT1. .

OUT2.
.
PBS

50/50 plate

mirrorOUT4Parameter
1
Insertion Losses from Signal
1Insertion Losses from LO
1,2IL uniformity
IL dual uniformity

1,2

OUT3

SymbolIL→SIL→LOΔILMin

Δdual
1

Phase shift between I and Q
3Skew
Optical return loss
4Packaging size
SM
Fiber Pigtail TypePM
Fiber Pigtail Length

φ85

ORL

35

Typ.
4.0
7.0
0.8

Max
5.0
8.0
1.5

Unit
dB
dB
dB

0.2

0.8

dB

0.5

95
1deg
ps
dB
3mm

70 x 52 x 10
SMF-28PANDA PM
0.9
1.0
1.1

Remarks/Conditions
Including 3dB of natural losses
Including 6dB of natural losses
Without connectorsBetween balanced outputs
Without connectors
Measured at connectors end

With 900µm loose tubem

Other lengths on request

1

measured over OTR and OWR for all states of polarizationfrom Signal or LO
3
for all outputs
4
excluding fiber boots
2

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COH

8

COH: 90° optical hybrids

11 – Fiber type and connectors
For the single polarization hybrids (COH24 and COH24-X) both the Signal and Local Oscillator have PM fiber.
The outputs have SM fiber.
For the dual polarization hybrids (COH22, COH28 and COH28-X), the Local Oscillator has PM fiber and theSignal has SM fiber. The outputs have SM fiber.
For all of these products, the outputs can optionally have PM fiber with a PER of 20dB.
For COH22, COH28 and COH28-X, the Signal input can optionally have a PM fiber aligned such that the slow
and fast axes are split by the input PBS. Eventually the fiber can be aligned in a different way upon customer
request.
The devices can be proposed with any kind of connectors (FP/UPC, FC/APC, SC/PC, SC/APC, LC/PC, E2000/PC,
E2000/APC).
All our COH products are offers with 1m fiber lengths. Other fiber lengths, down to 10cm are available onrequest.

12 – Wavelength range
Both COH-X can be proposed at different wavelength range, from the visible to the IR. The device will be
operational on a wavelength range of a tens of nanometers centered on the wavelength required bycustomer. Products at 1300nm, 1064nm and 800nm have already successfully been manufactured.

13 – Splitting ratio
For a standard COH we have 50% of the optical power from SIGNAL (or LO) on I and 50% on Q.
This splitting ratio can be customized. For instance, we can split the optical power from SIGNAL (or LO) inorder to have 10% on I and 90% on Q. Splitting ratio of SIGNAL and LO can be different.

14 – Custom productThanks to our free-space technology we can easily customize most of our product and so it is for the 90°
optical hybrids. Customer can feel free to ask for any customization they need. We will examine the requestand do our best to have a positive answer.

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COH9COH: 90° optical hybrids

15 – Package layout

COH28 packaging

COH-X packaging

16 – Revisiondate
March 27, 2013
rdFebruary 3 , 2015
thFebruary 24 , 2015

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version
COH V1.0
COH V1.1
COH V1.2

ObjectCreation
Added COH22 (dual-polarization 180° hybrid)
COH22 specification update

COH10