SYSTEMS FOR DEPLOYING AN OPTICAL NETWORK
A transmitter on an integrated circuit chip is disclosed that employs a laser, modulator, and a dispersion compensator module and a modulator for overcoming chromatic dispersion and polarization dependent loss effects. With the present invention, the dispersion compensator module is placed on a chip, either integrated or monolithic, for operation with a laser and a modulator without the need to compensate for dispersion within a separate unit that is not part of the chip. The dispersion compensator module can be implemented, for example, with a ring resonator, an etalon or a Mach-Zehnder interferometer. In a first aspect of the invention, the optical transmitter module of the present invention provides a cost-effective solution for upgrading from an existing optical network to a faster optical network, such as upgrading from a 2.5 Gbps to a 10 Gbps network. In a second aspect of the invention, the optical transmitter module of the present invention provides a means to deploy an optical network at the transmission rate of 10 Gbps, 40 Gbps and faster.
This application is a divisional of co-pending U.S. patent application Ser. No. 11/098,837, filed Apr. 4, 2005, which is herein incorporated by reference.
BACKGROUND OF THE INVENTION1. Field of the Invention
The invention relates generally to the field of fiber optic networks and systems and more particularly to dispersion compensation in optical and photonic networks.
2. Description of the Related Art
The evolution of optical technologies intersecting with the industrial drive to utilize material science in designing an integrated circuit chip as a compact and cost-effective solution creates a platform for an innovative approach in addressing properties associated with optics and electronics. Traditional optical theories provide an understanding to make a purely optical-based device but the resulting product is frequently bulky in size, while electronic theories push relentlessly for a greater integration and miniaturization of integrated circuits by following the so-called Moore's Law. Emerging trends from this phenomenon present a new set of circumstances requiring optical solutions on a small chip that are able to compensate sporadic optical signal variations or perturbations.
A common well-known problem in high-speed transmission of optical signals is chromatic dispersion. Chromatic dispersion refers to the effect in which the various physical wavelengths of an individual optical channel either travel through an optical fiber or component at different speeds—for instance, longer wavelengths travel faster than shorter wavelengths, or vice versa—or else travel different path lengths through a component. This particular problem becomes more acute for data transmission speeds higher than 2.5 gigabits per second (Gbps). The resulting pulses of the signal will be stretched, will possibly overlap, and will cause increased difficulty for optical receivers to distinguish where one pulse begins and another ends. This effect seriously compromises the integrity of a signal. Therefore, for fiber optic communication systems that provide a high transmission capacity, the system must be equipped to compensate for chromatic dispersion.
In
Further, a conventional wavelength division multiplexer (WDM) system 200 for transmitting a plurality of optical channels over a single optical fiber is shown in
In both systems 100 and 200, the physical dimension of the DCF 130 in the system 100 and the DCF 260 in the system 200 is too bulky to fit on a chip. Accordingly, there is a need to design optical systems and methods that solve the dispersion effects functionally but, at the same time, significantly reduce the dimension of a dispersion compensation component for placement on an integrated circuit for operating with a laser-modulator combination.
SUMMARY OF THE INVENTIONThe invention discloses and optical transmitter module disposed upon an integrated circuit chip that employs a laser, modulator, and a dispersion compensator module and a modulator for overcoming chromatic dispersion and polarization dependent loss effects. With the present invention, the dispersion compensator module is placed on a chip, either integrated or monolithic, for operation with a laser and a modulator without the need to compensate for dispersion within a separate unit that is not part of the chip. The dispersion compensator module can be implemented, for example, with a ring resonator, an etalon or a Mach-Zehnder interferometer.
In a first aspect of the invention, the optical transmitter module of the present invention provides a cost-effective solution for upgrading from an existing optical network to a faster optical network, such as upgrading from a 2.5 Gbps to a 10 Gbps network. In a second aspect of the invention, the optical transmitter module of the present invention provides a means to deploy an optical network at the transmission rate of 10 Gbps, 40 Gbps and faster.
A first preferred embodiment of an optical transmitter module in accordance with the present invention comprises a laser coupled to a modulator through a dispersion compensator module where the dispersion compensator module is designed so as to have an angle associated with a single polarized light that will either minimize the polarization dependent loss, or keep the polarization dependent loss unchanged or substantially the same. A second preferred embodiment of an optical transmitter module in accordance with the present invention comprises a laser coupled to a modulator that is further coupled to a dispersion compensator module wherein a polarization maintaining fiber is placed on either side of the modulator for maintaining the polarization of the single polarized light. Each of the transmitter embodiments can be designed as a stand-alone transmitter, as a component in a transceiver, or as a component in a transponder.
Advantageously, the present invention facilitates a simpler apparatus and method for upgrading an existing optical network at a central office by swapping, for example, a 2.5 Gbps line card with a 10 Gbps line card without the cumbersome and costly need, for instance, to install new dispersion compensating fiber within a fiber optic transmission system.
Other structures and methods are disclosed in the detailed description below. This summary does not purport to define the invention.
The invention is defined by the claims.
Referring to
The significance in keeping the polarization dependent loss substantially the same or unchanged as the light travels through the transmitter 300 (from the laser 310 to the modulator 330 and to the dispersion compensator module 330) eliminates the dependency on polarization dependent loss variations. Generally, the polarization of an optical signal is subject to environmental factors such as temperature which will cause the optical signal to fluctuate throughout a day. When the optical signal exceeds a certain maximum power (P.sub.max), the optical signal determined by a receiver is truncated at or above P.sub.max. Conversely, when the optical signal falls below or near the minimum power (P.sub.min), a receiver may have difficulty ascertaining the integrity of the optical signal that may be distorted by noise.
Turning now to
The dispersion compensator module 330 or 430 can be implemented, for example, with a ring resonator, an etalon, a Virtually Imaged Phased Array (VIPA) or a Mach-Zehnder interferometer. These types of dispersion compensator modules are sufficiently compact for incorporation onto an integrated chip with a laser and a modulator. However, the conventional chips made with dispersion compensator modules suffer from high polarization dependent loss (PDL) that is introduced into an optical signal.
One objective of the present invention is to minimize or eliminate the polarization dependent loss of a device. The use of polarization maintaining fibers ensures that a light or signal of a single polarization is propagated from a first optical component to a second optical component, thereby removing the effect of PDL on an optical signal.
In
The design of the transmitter 300 or the transmitter 400 can be incorporated into an optical transceiver 700 which comprises and optical transmitter 710 and an optical receiver 720 as shown in
Moreover, the transmitter 300 or the transmitter 400 can be incorporated into a transponder 800 as shown in
Those skilled in the art can now appreciate, from the foregoing description, that the broad techniques of the embodiments of the present invention can be implemented in a variety of forms. Therefore, while the embodiments of this invention have been described in connection with particular examples thereof, the true scope of the embodiments of the present invention should not be so limited since other modifications, whether explicitly provided for or implied by this specification, will become apparent to the skilled artisan upon a study of the drawings, specification and following claims.
While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
Claims
1. A system, comprising:
- a laser for generating a single polarized light of a wavelength λ to an output;
- a first polarization maintaining fiber;
- a modulator having an input and an output, the first polarization maintaining fiber optically coupled between the laser and the input of the modulator for preserving the polarization of the single polarized light between the laser and the modulator;
- a second polarization maintaining fiber; and
- a dispersion compensating module having an input and an output, the second polarization maintaining fiber optically coupled between the output of the modulator and input of the dispersion compensating module for preserving the polarization of the single polarized light between the modulator and the dispersion compensating module, the dispersion compensator generating a single polarized output light signal.
2. The system of claim 1, wherein the single polarized light from the laser has a polarization dependent loss that is substantially the same as the single polarized output light signal.
3. The system of claim 1, wherein the single polarized light from the laser has a polarization dependent loss that is unchanged as the single polarized output light signal.
4. The system of claim 1, wherein the dispersion compensating module comprises a ring resonator.
5. The system of claim 1, wherein the dispersion compensating module comprises an etalon.
6. The system of claim 1, wherein the dispersion compensating module comprises a Virtually Image Phased Array (VIPA).
7. The system of claim 1, wherein the dispersion compensating module comprises a Mach-Zehnder interferometer.
8. The system of claim 1, wherein the system comprises a transmitter, a transceiver or a transponder.
9. The system of claim 1, wherein the laser, the first polarization maintaining fiber, the modulator, the second polarization maintaining fiber and the dispersion compensating module are integrated on a chip.
Type: Application
Filed: Aug 18, 2009
Publication Date: Dec 17, 2009
Inventors: Giovanni Barbarossa (Saratoga, CA), Roger A. Hajjar (San Jose, CA)
Application Number: 12/543,261
International Classification: H04B 10/04 (20060101);