Optical phase shifting device

Optical: systems and elements – Optical modulator – Light wave temporal modulation

Reexamination Certificate

Rate now

  [ 0.00 ] – not rated yet Voters 0   Comments 0

Details

C359S288000, C385S123000, C385S003000

Reexamination Certificate

active

06825966

ABSTRACT:

The present invention relates to an adjustable optical phase-shifting device according to claim
1
.
More particularly, the present invention relates to an adjustable optical phase-shifting device created for use in directional couplers, optical ring resonators, dispersion compensating devices, Mach-Zehnder interferometers, add-drop multiplexers, optical wavelength converters or amplitude-shift keying (ASK) as well as phase-shift keying (PSK) modulators operating particularly in low wavelength regions.
BACKGROUND OF THE INVENTION
Optoelectronic integrated circuits made in thin-film technology often comprise phase-shifting devices used for the adjustment of the phase of an optical signal guided in a first waveguide relative to the phase of an optical signal guided in a second waveguide.
According to Govind P. Agrawal, Fiber Optic Communication Systems, Wiley Series in microwave and optical engineering, New York 1992, chapter 6.2.1, pages 232-234, optical signals can be modulated by means of a Mach-Zehnder interferometer comprising two arms wherein the phase of optical carrier signals is shifted relatively to each other according to electrical binary data. As long as the phase of the optical carrier signals, which originate from the same source, is identical, then the corresponding optical fields interfere constructively. An additional phase shift of adequate size introduced in one of the arms destroys the constructive nature of the interference of the optical carrier signals which are superpositioned on an output line of the ASK-modulator. The additional phase shift in the given example is introduced through voltage-induced index changes of the electro-optic materials (e.g. LiNbO
3
) used for said arms of the Mach-Zehnder interferometer as described in [2], Richard C. Dorf, THE ELECTRICAL ENGINEERING HANDBOOK, CRC Press LLC, Boca Raton 1997, chapter 31.3, pages 829-837.
Phase shifting devices are also used in directional couplers. An optical waveguide directional coupler filter with waveguides in LiNbO
3
which is tunable with electrical control signals is disclosed in U.S. Pat. No. 4,146, 297.
In C. K. Madsen, G. Lenz, A. J. Bruce, M. A. Capuzzo and L. T. Gomez, Phase Engineering Applied to Integrated Optical Filters, IEEE Lasers and Electro-Optics Society, 12
th
annual meeting, San Francisco 1999, allpass filter rings and linear delay response architectures for dispersion compensations are described. A basic ring architecture consists of a tunable optical waveguide ring which is coupled to an optical waveguide through which optical signals are transferred. A thermo-optic effect is used to shift the phase of the signals within the ring. In order to obtain a desired filter response, it is critical to accurately fabricate the desired coupling ratio. To reduce the fabrication tolerances on the couplers and simultaneously to obtain a fully tunable allpass response, the basic ring architecture is preferably enhanced with a Mach-Zehnder interferometer (see FIG.
1
). This enhanced ring structure, below called ring resonator, is briefly explained with reference to
FIGS. 1 and 2
.
FIG. 1
shows a prior art directional coupler with a first and a second waveguide
3
,
4
aligned in parallel, with a first and a second coupler
301
,
302
, through which optical signals can be exchanged between said waveguides
3
,
4
, and with one thin film heater
100
covering a part of the first waveguide
3
lying between the couplers
301
,
302
. An optical signal entering the first waveguide
3
at port A will partially be coupled from the first coupler
302
to the second waveguide
4
. Between the couplers
301
,
302
the phase of the remainder of the optical signal transferred in the first waveguide
3
will be shifted according to the thermal energy applied to the first waveguide
3
by means of the thin film heater
100
. The optical signal in the first waveguide
3
then interferes in the second coupler
302
with the optical signal of the second waveguide
4
. Depending on the phase relationship between the optical signals the signal intensity in the second waveguide
4
will be increased or reduced accordingly.
In case that the second waveguide
4
is formed as a ring and enhanced with a thin film heater
101
for phase-shifting purposes, then the architecture shown in
FIG. 1
corresponds to the tunable ring resonator shown in
FIG. 2
respective,
FIG. 1
which may be used for dispersion compensation.
In order to obtain a desired shift of the phase of the optical signal in the first waveguide
3
relative to the phase of the optical signal in the second waveguide
4
thermal energy provided by the thin film heater
100
is applied to the first waveguide
3
and not to the second waveguide
4
. In the region of the thin film heater
100
the waveguides
3
,
4
are therefore spaced apart at a distance which is sufficient to avoid a transfer of thermal energy from the thin film heater
100
to the second waveguide
4
. Thermal energy provided by the thin film heater
100
is absorbed by the substrate
5
acting as a heat sink in such a way that the thin film heater
100
forces a temperature gradient with respect to the substrate
5
.
Since the waveguides
3
,
4
of the tunable ring resonator are kept apart from each other between the couplers
301
,
302
over a relatively long distance, the architectures shown in
FIGS. 1
and
2
are difficult to realise in small sizes as required for high frequency applications operating for example in the range of 25 GHz to 75 GHz.
As described above the temperature gradient will depend on the temperature and nature of the substrate
5
which may not be homogeneous over the whole circuit. With a change of the ambient temperature the operating conditions of the discussed circuit may vary considerably. Information regarding the temperature and hence the refractive index of the related waveguide is not provided by the circuit so that means for controlling the function of the circuit are limited. In addition shifting only the phase of the optical signal guided in the first waveguide of the device shown in
FIG. 1
by establishing a temperature gradient between the heater
100
and the substrate
5
appears to be inefficient.
It would therefore be desirable to improve the described phase-shifting devices. It would be desirable to create an easily controllable phase-shifting device operating with high efficiency. It would be desirable to create a phase-shifting device which operates independently of changes of the ambient temperature. It would further be desirable to create a phase-shifting device which, besides the phase-shifting function, comprises a coupling function.
It would be desirable in particular to create a phase-shifting device for tunable ring resonators, directional couplers, add-drop multiplexers, Mach-Zehnder interferometers, optical filters, dispersion compensating devices, optical wavelength converters or amplitude-shift keying (ASK) as well as phase-shift keying (PSK) modulators suitable for operating in high frequency ranges.
It would also be desirable to control the adjusted temperature in order to reach and hold a selected phase shift in a narrow range.
It would further be desirable to create a phase-shifting device which in conjunction with related circuitry can be fabricated at reduced cost and in high packing density.
SUMMARY OF THE INVENTION
The above and other objects of the present invention are achieved by a device according to claim
1
.
A phase-shifting device, which is electrically adjustable, is arranged on a substrate comprising at least a first waveguide and a thermoelectric element arranged adjacent to the first waveguide in order to shift the phase of an optical signal in the first waveguide by means of a thermo-optic effect according to a control voltage applied to the thermoelectric element which, according to the present invention, is a Peltier element comprising during operation a cold and hot side.
In a preferred embodiment of the invention the cold side of the thermoelectric element is arranged adj

LandOfFree

Say what you really think

Search LandOfFree.com for the USA inventors and patents. Rate them and share your experience with other people.

Rating

Optical phase shifting device does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Optical phase shifting device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical phase shifting device will most certainly appreciate the feedback.

Rate now

     

Profile ID: LFUS-PAI-O-3327091

  Search
All data on this website is collected from public sources. Our data reflects the most accurate information available at the time of publication.