Method and apparatus reducing electrical and thermal crosstalk of a laser array

Abstract

Active compensation techniques are used for control of temperature, wavelength, and other characteristics of lasers within a laser array. The laser array includes a plurality of lasers and a plurality of dissipation elements. The dissipation elements can be interstitial to the lasers and can be implemented as non-lasing diodes. The dissipation elements are selectively activated (i.e., turned “on” to dissipate power) to adjust the temperature at the laser junctions. The change in junction temperature allows the lasers to operate at their specified wavelengths. The dissipation elements can be individually controlled and two or more bits of resolution can be provided. Active compensation can be used to adjust (i.e., to compensate) the temperature of selected lasers when one or more lasers are deselected. Active compensation can also be used to adjust (i.e., “tweak”) the wavelengths of the lasers within the laser array to be within their specified wavelengths.

Description

BACKGROUND OF THE INVENTION [0001] This invention relates to lasers, and in particular to a method and apparatus for providing active compensation for a semiconductor laser array. Active compensation can be used for control of temperature, wavelength, and other characteristics of each individual laser within the laser array. [0002] Optical communications systems are used to provide high-speed communication, including voice and data services. Conventionally, only one optical signal at one wavelength (or one channel) is transmitted per optical fiber. While demand for bandwidth soars, this one optical wavelength per optical fiber design has limited the capacity of optical communications systems. [0003] Wavelength division multiplexing (WDM) is a technology that greatly increases the information transmission capacity of optical fibers in communications systems. In a WDM system, a multiplicity of independently modulated lasers, each with a unique but precisely controlled wavelength, gene...

AI Technical Summary

Benefits of technology

[0008] The invention provides techniques for active compensation for a semiconductor laser array. Active compensation can be used for control of temperature, wavelength, and other characteristics of the lasers within the laser array. Through active compensation, operating performance and manufacturer yields can be improved.

Problems solved by technology

While demand for bandwidth soars, this one optical wavelength per optical fiber design has limited the capacity of optical communications systems.

Unfortunately, several problems can render the use of simultaneously driven WDM laser arrays impractical.

One problem with conventional WDM laser arrays is the shift in laser wavelengths caused by changes in temperature at the laser sites when one or more particular lasers are turned “on” (i.e., selected for use) or “off” (i.e., deselected).

Typically, the data bit rate is high and results in an average duty cycle of approximately fifty percent and a steady-state power dissipation of approximately one half peak power.

The problematic temperature change generally occurs when one or more lasers is “deselected” (i.e., the data stream input to the laser is removed).

Specifically, the problem arises because the operating wavelength of semiconductor lasers is dependent on temperature.

Unfortunately, because of the substantial power levels at which WDM lasers typically operate (e.g., PL=0.2 to 0.5 watts per laser), when one or more lasers in the array are deselected, the thermal crosstalk between these devices in practical array packaging configurations leads to temperature changes much greater than the allowable temperature range.

This problem makes it extremely difficult to use laser arrays in applications (e.g., WDM) involving simultaneous and selectable operation of lasers in the array.

In fact, for many applications, this problem can preclude the use of laser arrays altogether.

Another problem with conventional WDM laser arrays relates to manufacturing yields.

However, with an array of lasers sharing only one TE cooler / controller, the temperature of each of the lasers cannot be independently adjusted to obtain the specified operating wavelengths for all lasers.

This translates to poor manufacturing yields and increased costs for WDM laser arrays, as compared to individually packaged devices.

The poor manufacturing yields make the use of laser arrays prohibitively expensive.

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