Switched laser array modulation with integral electroabsorption modulator

SWITCHED LASER ARRAY MODULATION
WITH INTEGRAL ELECTROABSORPTION
MODULATOR

CROSS-REFERENCE TO RELATED
APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser. No. 60/280,093, entitled SWITCHED LASER ARRAY MODULATION WITH INTEGRAL ELECTROABSORBTION MODULATOR, filed Mar. 30, 10 2001, the disclosure of which is incorporated by reference.

BACKGROUND

The invention relates generally to photonic devices, and more particularly to laser arrays with commonly mounted electro-absorption modulators.

Lasers are often used in telecommunication devices to provide light. The light is generally modulated in some fashion to provide a data transport mechanism. A receiver 20 receives the modulated light and provides the data to other units for processing. A transport media often used is fiber optic cabling. For some systems, such as Dense Wavelength Division Multiplexing (DWDM) system, light at a number of wavelengths is passed simultaneously through the trans- 25 port media to increase data bandwidth.

The light is sometimes modulated by directly varying the laser current. However, in many applications modulation performed by directly varying laser output results in data signals with unsuitable waveforms when received at a 30 receiver. This is often a result of parasitic FM modulation, or chirp, interacting with dispersion due to the fiber serving as a transport medium. Accordingly, in many instances the light is instead modulated by passing the light through a modulator, with the modulator varying the light in accor- 35 dance with a data signal received by the modulator. These modulators are often separate units, which increases system cost. Moreover, individual modulators, such as electroabsorption modulators, may be better adapted to process light at a particular wavelength. As a DWDM system carries 40 light at a number of wavelengths, the use of a common electro-absorption modulator may not provide optimal system performance for all the wavelength channels.

The invention provides a photonic device incorporating an array of lasers with electro-absorption modulators on a common substrate.

These and other aspects of the invention will be more fully comprehended after study of this disclosure including 50 the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a laser array with electro-absorption modulators for each laser in the laser array; 55

FIG. 2 is a schematic of an equivalent circuit for the electro-absorption modulators of FIG. 1;

FIG. 3 is a schematic of a simplified equivalent circuit for the electro-absorption modulators of FIG. 1; gQ

FIG. 4 illustrates an example laser of an array of lasers;

FIG. 5 illustrates a laser array with electro-absorption modulators with an optical switch coupling light from a selected laser to an optical output;

FIG. 6 is illustrates a device including a laser array with 65 electro-absorption modulators with a MEMS mirror coupling light from a selected laser to an optical output; and

FIG. 7 is a semi-block diagram of a device including an array of lasers with the laser grouped into subgroups, with the subgroups having associated electro-absorption modulators.

DESCRIPTION

FIG. 1 illustrates a photonic device in accordance with aspects of the invention. The photonic device includes an array of lasers Ula—d. The lasers are formed on a common substrate 113. Each laser provides light, when the laser is activated, to a corresponding electro-absorption modulator. For example, laser Ilia provides light to electro-absorption modulator 115. The lasers and electro-absorption modulators are formed on a common substrate 113. The common substrate is mounted on a submount 117.

Each of the lasers is provided a drive line, with, for example, laser Ilia provided drive line 121. The drive line is used to activate, or forward bias the laser, causing the laser to lase. Light emitted from the laser is provided to the corresponding electro-absorption modulator. The electroabsorption modulators are provided a common high speed data signal by a data signal line 123, with the electroabsorption modulators coupled in parallel. Also coupled in parallel is a matching resistor 119, which is mounted on the submount.

In one embodiment, the lasers are spaced apart by approximately 10 microns, with the electro-absorption modulators having the same spacing for such a configuration of lasers. In one embodiment the electro-absorption modulators have a band gap appropriate for the output wavelength of the corresponding laser, which may vary from laser to laser in some applications. In other embodiments, however, the electro-absorption modulators have the same band gap.

In one embodiment of the device of FIG. 1 each of the lasers of the array of lasers emit light at different wavelengths. In operation for one embodiment a single laser, for example laser Ilia, is turned on through application of a drive signal to drive line 121. A high speed data signal is applied to the data signal line, which supplies the data signal to all of the electro-absorption modulators. Thus, light from the single laser passes through one of the electro-absorption modulators, and the resulting light is modulated to include the data signal.

As light is passing through a single electro-absorption modulator, the remaining electro-absorption modulators need not receive the data signal. However, compared to lasers electro-absorption modulators are relatively small in size, approximately 100-200 microns in length. Electroabsorption are modulators are operated with reverse bias. Accordingly, electro-absorption modulators have a relatively small capacitance, which allows multiple electroabsorption modulators to receive high speed signals, such as the data signal. Moreover, providing the high speed data signal to all of the electro-absorption modulators removes the need for provision in the data signal line of a switch adapted for switching high speed signals.

Thus, in FIG. 2 a number of electro-absorption modulators 211 are coupled in parallel using line 213. Also coupled in parallel with the electro-absorption modulators is a matching resistor 215, provided for proper termination of the line. In some applications, the capacitance of all the electro-absorption modulators may be excessive for optimal operation. In such a circumstance, or in general, a lumped transmission line may be used. FIG. 3 shows a simplified equivalent circuit for a lumped transmission line version of FIG. 2. As shown in FIG. 3, a line 313, having lumped