CN101095269A - Temperature control for coarse wavelength division multiplexing systems - Google Patents

Abstract

Optoelectronic devices and methods are used to maintain a CWDM transmitter operating within design parameters over an extended ambient temperature range. In order to avoid excessive wavelength drift with temperature shifts, lasers in the CWDM transmitters are heated or cooled to a selected temperature, for example by using a thermoelectric cooler. By heating and cooling the lasers, any wavelength drift that an ambient temperature variation might inflict on the laser is minimized to the range hotter or colder than the selected temperature. As the temperature range of the laser increases above the selected temperature, the AC swing driving the laser is increased to maintain a sufficient extinction ratio for acceptable transmitter performance.

Description

Temperature Control for CWDM Systems

technical field

In general, the present invention relates to optoelectronic components. More specifically, the present invention relates to systems and methods for maintaining a CWDM transmitter transmitting in a target wavelength channel over an extended temperature range.

Background technique

Computer and data communication networks continue to evolve and expand due to decreasing costs, increasing performance of computer and networking equipment, the dramatic growth of the Internet, and the resulting increased demand for communication bandwidth. Such increased demand occurs within and between urban areas, and within communication networks. Moreover, as organizations have realized the economic benefits of using communication networks, network applications such as e-mail, voice and data transfer, mainframe access, and shared and distributed databases are increasingly being used as a means to increase user productivity. This increased demand, along with the increased number of distributed computing resources, has led to a rapid expansion of the number of fiber optic systems required.

With fiber optics, digital data in the form of light signals is formed by lasers or light-emitting diodes and then propagated through fiber optic cables. Such optical signals allow high data transfer rates and high bandwidth capacities. The light signal is then received at a photodiode, which converts the light signal back into an electrical signal. Current optical designs typically include both a laser and a photodiode within a single transceiver module that can be connected at one end via a compatible connection port to, for example, a host computer, switching hub, network router, switch box, The main device for computer I/O etc. and connects to the fiber optic cable at the other end. In addition to the laser and photodiode, each transceiver module typically contains all other optical and electrical components needed to convert electrical signals to optical signals via the laser and back to electrical signals received at the photodiodes.

Another advantage of using light as a transmission medium is that light of multiple wavelength components can be transmitted through a single communication path such as an optical fiber. This process is generally referred to as wavelength division multiplexing (WDM), in which the bandwidth of the communication medium is increased by the number of independent wavelength channels used. Several wavelength channels can be transmitted using coarse wavelength division multiplexing (CWDM) applications to achieve higher channel densities and overall channel counts in a single communication line.

Figure 1 illustrates eight wavelength channels typically used in a CWDM system. As shown, CWDM typically implements a channel spacing of 20 nanometers. Thus, CWDM allows a modest number—typically 8 or less—of channels to be stacked around the 1550nm region of fiber. Figure 1 illustrates how CWDM transmission can occur at one of eight wavelengths: typically 1470nm, 1490nm, 1510nm, 1530nm, 1550nm, 1570nm, 1590nm and 1610nm.

To save cost and reduce power consumption, CWDM transmitters typically use uncooled lasers with a loose room temperature tolerance of ±3nm. The wide spacing accommodates uncooled laser wavelength drift due to ambient temperature changes within a relatively small acceptable range.

Figure 2 illustrates three adjacent channels in a CWDM system in more detail. Each channel uses a filter with a passband approximately 11 nm wide. Operation outside the allowable permissible passband results in high attenuation of the transmitted signal and, in extreme cases, in potential crosstalk with adjacent channels. The light emitted from the transmitter does not need to occupy the entire channel, it just needs to stay within it. Thus, it can be seen that the spectral lines of the light transmitted from the transmitter may occupy the wavelength range illustrated by the wavelength range 12 in the center of the passband. It is also acceptable if the transmitted light is on one side of the wavelength channel, eg wavelength range 14. However, if the transmitter emits light outside the specified passband or within a wavelength range that overlaps an adjacent passband, such as wavelength range 16, then the CWDM system will not work properly.

There are several factors that determine the wavelength of the signal generated by a conventional laser source. These factors include, for example: current density, temperature of the optical transmitter, and specific intrinsic characteristics of the optical transmitter. Referring to FIG. 3, this graph shows the wavelength (λ) shift (wavelength shift) over a varying temperature range. The wavelength range is shown along the y-axis, no wavelength is specifically indicated, while the temperature range is shown along the x-axis, from -40°C to 85°C. Line 20 illustrates the characteristic wavelength shift as temperature increases. For distributed feedback ("DFB") laser sources commonly used in CWDM applications, a wavelength shift of 0.1 nm per degree Celsius change is generally acceptable given a good approximation of motion. It can thus be seen how the wavelength of the emitted light shifts by about +12.5nm within a temperature change of 125 degrees. This is shown by the linearity of curve 20, the low point 22 of the slope at -40°C being 12.5nm lower than the high point 24 at 85°C.

To control the effects of temperature-induced wavelength shifts, CWDM transceivers are typically cooled by equipment external to the transceiver, such as fans or placed in a temperature-controlled room. The controlled environment keeps the transceiver components within a reasonable temperature range so that the laser emits over a range of wavelengths within the specified wavelength channel.

However, using CWDM transceivers only in controlled environments can be very restrictive and expensive. As a result, more attention has been paid to how to operate CWDM transceivers in less expensive or more convenient locations. For example, if a CWDM transceiver can work in the field such as a data relay station in a remote location, it will reflect the advanced nature of the CWDM technology. In fact, the expected operating conditions for CWDM transceivers are currently from -40°C to 85°C.

Therefore, there is a need for devices and methods that enable CWDM transceivers to operate in environments with large temperature variations without excessive wavelength drift. In particular, enabling a CWDM transceiver to operate without a fan or without placing it in a temperature-controlled room would represent an advance in the art.

Contents of the invention

The present invention relates to methods and systems for maintaining CWDM transmitter operation within design parameters over an extended ambient temperature range. More specifically, in order to avoid excessive wavelength drift moving with ambient temperature, the laser in the CWDM transmitter is heated and cooled to a selected set-point temperature. The set point temperature is preferably a temperature at which the laser temperature can be locked within the maximum ambient temperature range. By heating and cooling the laser, any wavelength shift of the laser that could be caused by changes in ambient temperature is minimized to a tolerable level. As the temperature of the laser increases or decreases from the set point temperature, the AC swing (AC Swing) driving the laser can be adjusted to maintain a sufficient extinction ratio for acceptable transmitter performance.

Thus, a first example embodiment of the present invention is a method of maintaining the wavelength of light emitted by a laser diode within a desired tolerance range. The method generally includes providing a laser diode operable from at least a first selected temperature to a second selected temperature, wherein the wavelength shift of light emitted by the laser diode is greater than the desired amount; and heating or cooling the laser diode as needed so that the laser diode does not drop below a third temperature, which is between the first temperature and the second temperature, or so that the laser diode does not rise above the first temperature Above four temperatures, the fourth temperature is between the third temperature and the second temperature, wherein the wavelength shift of the light emitted by the laser diode is shifted to a desired content in the temperature range from the third temperature to the fourth temperature amount within the range. In a variation on this embodiment, the AC swing of the laser diode is adjusted to minimize the extinction ratio from the set point over the temperature of the laser diode falling below a third temperature or rising above a fourth temperature Variety.

Another example embodiment of the present invention is also a method of operating an optoelectronic component for use in a CWDM system. The method generally includes: heating the laser diode in the optoelectronic component to a set point temperature above the typical optoelectronic component ambient temperature; operating the laser diode to emit light; heats or cools the laser diode to within the selected range of the setpoint when the laser diode is identified as being above or below the setpoint temperature and there is not enough power available to further heat or cool the laser diode AC swing to drive the laser diode to minimize extinction ratio variation.

Yet another example embodiment of the invention is an optoelectronic device. The optoelectronic device generally includes: an optoelectronic assembly including a laser diode for emitting light; a laser driver for controlling the operation of the laser diode; a temperature controller coupled to the laser diode for controlling the temperature of the laser diode; at least one temperature sensor that detects a temperature associated with the laser diode; a memory configured to store a look-up table for controlling the AC swing of the laser diode based on the detected laser diode temperature; and one or more control devices configured to for generating: a command signal to a temperature controller for controlling operation of the temperature controller such that the temperature controller maintains the laser diode temperature within a temperature range around a set point; and a command signal to a laser driver for Controls the AC swing of the laser diode.

These and other objects and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by practice of the invention hereinafter described.

Description of drawings

In order to make the above and other advantages and features of the present invention more apparent, a more specific description of the present invention follows with reference to specific embodiments shown in the accompanying drawings. It is to be noted that the drawings depict only typical embodiments of the invention and therefore should not be considered limiting of its scope. The invention is described and explained below with additional characteristics and details by using the figures.

Figure 1 illustrates eight wavelength channels typically implemented in a CWDM system;

Figure 2 illustrates more specific details related to several wavelength channels typically implemented in a CWDM system;

Figure 3 illustrates a wavelength diagram of light emitted by a laser diode over the laser diode temperature range;

Figure 4 illustrates an optoelectronic transceiver according to one embodiment of the invention;

Figure 5 illustrates a transmitter optical subassembly according to one embodiment of the invention;

6 illustrates a graph of wavelengths of light transmitted by a laser diode over a range of laser diode temperature and ambient temperature, according to an embodiment of the invention;

FIG. 7 illustrates several curves of laser diode temperature moving as the ambient temperature changes according to an embodiment of the present invention;

Figure 8 illustrates a method of operating an optoelectronic device within the laser diode temperature range according to another embodiment of the invention.

Detailed ways

The present invention relates to methods and systems for maintaining a CWDM transmitter operating within design parameters over an extended ambient temperature range. To avoid excessive wavelength drift with ambient temperature changes, the laser in a CWDM transmitter is heated and cooled to a range around a selected set-point temperature. By heating and cooling the transmitter, any wavelength shift that ambient temperature changes may cause to the lasers in the transmitter is minimized to tolerable limits.

Various aspects of exemplary embodiments of the invention are now described with reference to the accompanying drawings. It is to be understood that the drawings are diagrammatic and schematic representations of these exemplary embodiments and are not intended to limit the invention, nor are they necessarily drawn to scale.

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known aspects of optoelectronic systems and devices have not been described in detail in order to avoid unnecessarily obscuring the present invention.

Reference is now made to FIG. 4 which shows a schematic representation of an embodiment of an optoelectronic transceiver 100 usable in a CWDM system according to the present invention. It should be understood by those skilled in the art, given the disclosure herein, that aspects of the invention may be practiced outside the context of transceiver 100 and the accompanying discussions herein. As illustrated in Figure 4, the transceiver 100 includes a receiver optical subassembly (ROSA) 106 that includes a mechanical fiber receptacle 107 and coupling optics, as well as a photodiode and pre-amplifier (pre-amplification) circuitry. The ROSA 106 is in turn connected to a post-amplifier (post-amplification) integrated circuit 108, the function of which is to take relatively small signals from the ROSA 106 and amplify and limit them to produce a digital electronic output of equal amplitude, which is routed via the RX+ and RX- pin 110 to connect to external circuitry. Post-amplification circuit 108 provides a digital output signal known as Signal Detect or Loss of Signal to indicate the presence or absence of a suitable strong light input.

Transceiver 100 also includes a transmitter optical subassembly (TOSA) 114 and a laser driver integrated circuit 116 that takes signal inputs from RX+ and RX− pins 118 . The TOSA 114 contains a mechanical fiber optic receptacle 109 and coupling optics, as well as a thermoelectric cooler (TEC) and a laser diode or LED. Laser driver circuitry 116 provides AC drive and DC bias current to the laser. Signal inputs for the drivers are taken from I/O pins (not shown) of the transceiver 100 . In other embodiments, the TEC is external to the TOSA 114. In another embodiment, the TEC is integrated in a laser transistor-outline (TO, transistor-outline) package.

Because there are a large number of potential designs for enabling transceivers to interface with host equipment and optical fibers, international and industry standards defining the physical size and shape of optical transceiver modules have been adopted to ensure compatibility between different manufacturers. For example, in 1998, a group of optical component manufacturers developed a set of standards for optical transceiver modules called the Small Form Factor Pluggable Transceiver Multisource Agreement (SFP Transceiver MSA). In addition to the details of the electrical interface, the standard also defines the physical size and shape for the SFP transceiver module, the amount of power that the transceiver module can use, and the corresponding components that are mounted on the host's printed circuit board and accommodate the transceiver module. The module box (module cage), thus ensuring interoperability between products of different manufacturers.

As data rates increase and transceiver packages become smaller, the heat generated by transceivers also typically increases. However, the use of heat dissipation mechanisms increases the complexity and cost of the transceiver assembly, reduces the space otherwise available for the functional optical and electrical components of the assembly, and increases the amount of power required to operate the transceiver. For this reason, traditional CWDM systems rely on wide channel spacing and/or moderately controlled environments without cooling.

One approach for cooling the transceiver is to use a thermoelectric cooler (TEC). A TEC is a device capable of maintaining the temperature of a component at a predetermined point. If the part gets too hot, power flows in one direction in the TEC to cool it down. If the part gets too cold, power is delivered in the other direction and the TEC becomes a heater. Unfortunately, the TEC requires more power in cooling mode than in heating mode. As the temperature of the module increases, the amount of power consumed to keep the module at a constant temperature increases exponentially. Because transceiver standards strictly control the amount of power that can be supplied to the transceiver, TECs are utilized over a wide range of ambient temperatures to provide the amount of cooling required to maintain the transceiver within a narrow range of desired temperatures, in Routinely not feasible.

TECs are successfully used in Dense Wavelength Division Multiplexing (DWDM) systems, where the TEC is used in conjunction with other temperature control systems - primarily temperature-controlled chambers - to fine-tune laser operation. Therefore, the TEC is not responsible for large temperature regulation.

According to the invention, it is possible to use TECs or other temperature control devices in CWDM transceivers by limiting the maximum amount of heating or cooling. This limits the power usage required by the transceiver while enabling the CWDM module to be used over a wide range of ambient temperatures. Thus, in this embodiment, optoelectronic transceiver 100 includes a temperature controller (e.g., a thermoelectric cooler (TEC)) disposed in or near TOSA 114 for controlling the temperature of the laser diode therein. The optoelectronic transceiver 100 also includes a TEC driver 120 and additional circuitry not shown for controlling the temperature of the TOSA 114.

Also shown in FIG. 4 is the microprocessor 130 , which may include one, two or more chips and is configured to control the operation of the transceiver 100 . Suitable microprocessors include PIC16F873A, PIC16F8730, PIC16F8718-bit CMOS FLASH microcontrollers manufactured by Microchip Technology, Inc. Microprocessor 130 is coupled to provide control signals to post amplifier 108, laser driver 116, and other components, and to receive feedback signals from ROSA 106 and TOSA 114. For example, microprocessor 130 provides signals (e.g., bias and amplitude control signals) to control the DC bias current level and AC modulation level of laser driver circuit 116 (which thereby controls the extinction ratio (ER) of the optical output signal). , while the post-amplifier circuit 108 provides a Signal Detect output to the microprocessor 130 to indicate the presence or absence of a suitable strong light input.

Importantly, both the bias current level and the AC modulation level affect the optical output wavelength of the transceiver 100 . Those skilled in the art understand that an increase in bias current, and to a lesser extent, AC modulation, increases the temperature of the active region of the laser chip. More specifically, as the bias current and AC modulation increase, the power dissipation of the laser chip also increases. And as the power dissipated in the laser chip increases, the temperature of the laser chip with a fixed thermal resistance also increases. This is true even when the temperature of the base of the laser chip is typically controlled by the TEC 120.

The temperature and/or other physical conditions of various components of transceiver 100 may be acquired using sensors coupled to microprocessor 130 . In some embodiments, the condition of the optical link may also be acquired using sensors.

Microprocessor 130 may handle a number of other tasks in addition to, and sometimes in combination with, these control functions. These tasks include, but are not necessarily limited to, the following: setup functions, which typically involve required adjustments made in the factory on a part-by-part basis to account for variations in part characteristics such as: laser diode threshold current and slope efficiency; identification functions , which controls the storage of identification codes, subcomponent revisions, factory test data, etc., in general-purpose memory (e.g., EEPROM); eye safety and general fault detection for proper identification of abnormal and potentially unsafe operating parameters , and report it to the master and/or perform laser shutdown; receiver input optical power measurement; laser diode drive current function to set the output optical power level of the laser diode; and laser diode temperature monitoring and control. Additionally, microprocessor 130 is responsible for providing control signals to the temperature controller to maintain the temperature of housing 112 and TOSA 114 of transceiver 100 at a desired set point.

With continued reference to FIG. 4 , the transceiver 100 has an interface 132 for communicating with a host device, such as a link card to which a transceiver is attached and/or a host system computer to which a transceiver provides an optical connection. The host system may be a computer system, network attached storage (NAS) device, storage area network (SAN) device, optical router, and other types of host systems and devices.

In some embodiments, optoelectronic transceiver 100 includes an integrated circuit controller that can perform some of the functions listed above. For example, the integrated circuit controller performs the tasks of identification and eye safety and general fault detection, while the microprocessor provides control signals to the temperature controller and may perform other tasks as well.

All components of the transceiver 100 may be located in the protective case 112 except for the connector, which may protrude from the case. In addition, transceiver 100 includes at a minimum transmit and receiver circuit paths as well as one or more power connections and one or more ground connections.

Referring now to FIG. 5, the defined features of TOSA 200 are shown in block diagram form to further illustrate the present invention. In one embodiment, TOSA 114 may be substantially the same as TOSA 200. TOSA 200 includes a laser assembly 202 (e.g., a laser transistor form factor package), which in turn includes an optical emitter (e.g., an edge-emitting laser diode, such as a distributed feedback laser (DFB)) that operates at a forward-biased It is activated when the setting current and laser bias are applied to its p-n junction. FIG. 5 also shows a laser temperature sensor 204 and a thermoelectric cooler (TEC) 206 , each of which is coupled to the laser assembly 202 . In other embodiments, the laser temperature sensor 204 and/or the TEC 206 are integrated in the laser assembly 202. In other embodiments, TEC 206 is external to TOSA 106. In other embodiments, the laser temperature sensor may be located spaced apart from the laser subassembly 202, such as elsewhere in the TOSA 200 (e.g., TOSA temperature sensor 208), or external to the TOSA (e.g., external temperature sensor 210 ).

In some embodiments, the laser temperature sensor 204 is a thermistor. Any other device suitable for measuring the temperature of a laser diode may also be used. Laser diode temperature sensor 204 produces a signal that varies according to the temperature of the laser diode. As mentioned above, and as is well known to those skilled in the art, the wavelength of the optical signal produced by a laser diode varies according to the temperature of the laser diode. Therefore, in addition to the laser temperature sensor 204, a device is used that measures the operating conditions of the laser diode, which vary according to the temperature of the laser diode. For example, since the wavelength of emitted light varies with temperature, measurement of the wavelength of emitted light can be used to determine temperature changes and thereby coordinate changes in TEC operation.

Although the laser temperature sensor 204 is preferably placed near the laser diode, because the laser temperature sensor 204 is physically separated from the laser diode, the temperature read from the laser temperature sensor 204 will generally differ from the actual temperature of the laser diode. Therefore, the temperature read from the laser temperature sensor 204 and its signal vary according to the external temperature. By receiving ambient temperature signals, eg, from TOSA temperature sensor 208 and/or external temperature sensor 201, microprocessor 130 (or similar device) can compensate for the effect of ambient temperature on the temperature read from the laser temperature sensor.

Referring now to FIG. 6 , a graph similar to that of FIG. 3 is shown. As previously mentioned, curve 20 in Figure 3 shows a steady wavelength shift over the entire temperature range of -40°C to 85°C. Curve 30 in FIG. 6 roughly corresponds to curve 20 of FIG. 3, except that curve 30 also reflects that the laser has a temperature that varies directly from point 32 to point 34 as the ambient temperature changes. Of course, those skilled in the art will appreciate that the actual laser temperature may vary slightly from the ambient temperature due to heat generated by operating the transmitter or other factors.

Figure 6 also shows how heating or cooling the laser temperature to a set point can reduce the wavelength shift experienced by the laser. In one embodiment of the invention, TEC 206 is used to provide heating or cooling of the laser as needed based on measurements from laser temperature sensor 204, TOSA temperature sensor 208, and/or external temperature sensor 210.

Curve 54 shows the wavelength shift of light over the same 125 degree temperature change experienced by the laser as shown in curve 30 . In this example, the TEC is set to heat the transmitter up to 50°C. However, cooling operation is not enabled. As a result, any wavelength shift with temperature below 50°C is eliminated, as shown by the lack of a slope on curve 54 to the left of the 50°C ambient temperature. In this embodiment, the TEC or other heat source is capable of heating the laser diode by at least 90°C. Since the TEC does not control the laser temperature above the 50°C point, there is still a wavelength shift with ambient temperature above 50°C. This is shown by the sloped line on curve 54 to the right of 50°C. Thus, as used herein, the term "temperature lock" is used to refer to how the temperature of the transmitter (and thus the emitting laser) is maintained at 50°C when the ambient temperature is at or below 50°C. In FIG. 6, the wavelength shown on curve 54 is temperature locked below an ambient temperature of 50°C and drifts approximately 3.5 nm above 50°C. A wavelength drift of 3.5nm is generally acceptable in CWDM systems.

In a heating-only implementation, such as the embodiment shown in curve 54, the TEC may be replaced by a resistive heater. This feature is preferred in certain embodiments because resistive heaters cost less than TECs. Heat-only techniques work well in embodiments where the laser can operate at relatively high temperatures. This is because most conventional CWDM distributed feedback lasers have performance and/or reliability issues if operated above 50°C for extended periods of time.

Of course, the same benefit of locking the transmitter at a selected temperature can be enhanced by enabling cooling operation. A TEC is required for cooling operation with the benefit of less wavelength variation over a larger lock-in temperature range. In other words, by cooling the laser diode to 50°C when the ambient temperature exceeds 50°C, the wavelength shift can be avoided. Additionally, device hardware, such as distributed feedback lasers, has fewer performance and/or reliability issues if it is not operated above 50°C for extended periods of time.

In one embodiment of the invention not shown in Fig. 6, the temperature of the laser diode is locked at 50°C over an ambient temperature range from -40°C to a temperature above 50°C, eg 70°C. However, because of the limited power available to the TEC, the temperature of the laser diode loses lock when the ambient temperature exceeds 70°C. In this case, there is a relatively small wavelength shift of about 1.5 nm for the temperature range from 70°C to 85°C.

The same benefit of locking the transmitter to a selected temperature can be maintained by heating the transmitter to other temperatures, eg 70°C. Curve 50 shows the wavelength shift of light over a 125 degree ambient temperature change when the transmitter temperature is locked to 70°C. In the illustrated embodiment, the TEC is set to heat the transmitter to 70°C. As a result, any wavelength shift with temperature is eliminated below 70°C, as shown by the lack of a slope on curve 50 to the left of the ambient temperature of 70°C. Since the TEC does not control the laser temperature above this point, there is still a wavelength shift with ambient temperature above 70°C. This is shown by the sloped line on curve 50 to the right of 70°C. In Figure 6, the wavelength shown on the curve is locked below 70°C and drifts by about 1.5nm above 70°C. A drift of 1.5nm is generally acceptable in a CWDM system.

As previously discussed, for this embodiment, cooling operation of the TEC can be achieved to lock the laser diode temperature at 70°C even when the ambient temperature exceeds 70°C. The exact amount of cooling available depends on the power available to the transceiver.

Curve 58 also shows the wavelength shift of light experienced by the laser over the same 125 degree temperature change as shown by curve 30 . In this example, the TEC is set to heat the transmitter up to 70°C. Although a cooling operation could be added by one skilled in the art in view of the disclosure herein, no cooling operation is implemented in the illustrated embodiment. As a result, any wavelength shift with temperature is eliminated in the range immediately below the ambient temperature of 70°C, as shown by the missing slope on curve 58 to the left of the ambient temperature immediately following 70°C. Since the TEC does not control the laser temperature above this point, there is still a wavelength shift with ambient temperature above 70°C. This is shown by the sloped line on curve 58 to the right of 70°C. In FIG. 6, the wavelength shown on curve 58 is temperature locked in the range immediately below 70°C ambient temperature and drifts about 1.5 nm above 70°C.

Additionally, in this embodiment, the transmitter also loses lock below -20°C (where maximum heating is limited by module power constraints). The lower end temperature at which a particular device can unlock can vary from device to device. As shown by the slash portion of curve 58 to the left of -20°C and ending at point 56 at -40°C ambient temperature, the device loses lock below -20°C such that at an ambient temperature of -40°C, the transmitter operates at 50°C. The exact amount of laser temperature drop due to temperature loss will vary from device to device. In this example, the wavelength shifts by about 2.0 nm below -20°C. As a result, a transmitter operating in the manner of curve 58 experiences a net wavelength shift of 3.5 nm over the range -40°C to 85°C. As mentioned earlier, a wavelength drift of 3.5nm is generally acceptable in CWDM systems.

In general, operating the laser diode above ambient temperature makes the TEC work more efficiently because the TEC is more efficient when heated than when cooled. TECs are more effective at heating than cooling because the thermoelectric effect and resistive heating work together when the TEC is heating the laser diode, but are in conflict when the TEC is cooling the laser diode. Efficiency is particularly important in pluggable transceiver applications, where the available power, and thus the capability of the TEC to function, is limited to a specified level. Running a CWDM module with a TEC in heating-only mode is acceptable under current CWDM transceiver standards because the limited current draw does not exceed the allowable maximum.

Referring now to FIG. 7, three additional examples of ambient temperature versus laser temperature are shown for other heating and cooling configurations. In particular, curve 500 shows a heat-only embodiment where the laser temperature is locked to 60°C in a heat-only implementation. As previously mentioned, since this is a heat only embodiment, TEC or resistive heaters could be used. In curve 500 and in each of curves 502 and 504 described below, the maximum heating that can be provided to the laser by a TEC or resistive heater is 75°C. Because the temperature is locked at 60°C, the device loses temperature lock below the ambient temperature of -15°C, as indicated by the slash to the left of -15°C of line 500 . At an ambient temperature of -60°C, the laser is still at 35°C. As a result, reduced temperature variation reduces wavelength shift. Moreover, because no cooling is implemented, the temperature of the laser rises gradually with the increase of the ambient temperature above the ambient temperature of 60°C. This is shown by the upward sloping line to the right of the 60°C ambient temperature of line 500 .

Similarly, curve 502 shows another heat only embodiment where the temperature lock is set at 45°C. In this case, there is a smaller temperature shift (and thus a smaller wavelength shift) at the cold end of the ambient temperature range because it does not lose lock until the ambient temperature drops to -30°C. However, at the high end of the ambient temperature range, the device loses lock at 45°C. Because no cooling is implemented, the laser temperature rises gradually as the ambient temperature rises. Therefore, there is a large temperature and wavelength shift at high temperature.

Next, curve 504 shows an example where both heating and cooling are performed and the temperature is locked at 45°C. In this example, the maximum cooling performed by the TEC is 15°C. Thus, the device loses lock at the cold end of -30°C, but at the hot end of only 60°C (45°C plus 15°C cooling). Thus, it is easy to see how implementing heating and cooling in the device maximizes the range over which temperature lock can be maintained.

In various implementations of the invention, heating the laser to a set temperature is not sufficient to ensure accurate operation of the transmitter over a wide temperature range. This is because when the laser temperature drifts upwards, when most conventional CWDM distributed feedback lasers operate above 50°C for extended periods of time, not only will there be performance and/or reliability issues, but the slope efficiency will decrease and the extinction ratio will also decrease. decrease accordingly.

Generally, optical transmitters are configured to transmit at various power levels to enable the transmission of binary data. More specifically, a relatively high optical power transmission level P1 represents a binary one, while a relatively low optical power transmission level P0 represents a binary zero. Therefore, the optical transmission of binary data is achieved by modulating the output power of the optical transmitter. Such optical power delivery levels have certain implications regarding the performance of the optical transmitter.

For example, optical transmitters typically have a characteristic "extinction ratio", defined as P1/P0 (for power expressed in dBm). An ideal optical transmitter would have a P0 of 0, and the optimal extinction ratio is thus infinite. In practice, however, the optical transmitter must be so biased that P0 lies near the laser threshold such that P0 must be somewhat greater than zero. This means that at least some optical power is sent at P0, while the actual extinction ratio is not infinite.

The specific value of the extinction ratio, as well as the fluctuation of the extinction ratio, relates to the bit error rate (BER) associated with the transmitted data stream. Generally, BER is derived by counting the number of data errors that occur in a predetermined sequence of bits. While the ideal BER should be zero, this is generally not achievable in practice, and therefore, a certain BER must be accepted in fact. In any case, maintaining the BER at an acceptable level is important because a relatively constant BER brings a degree of predictability to the performance of the optical system and also contributes to the reliability of the system.

Not only are relatively low ERs problematic, but high ERs or ER fluctuations are also worthy of consideration. In particular, it is desirable to keep the extinction ratio as constant as possible at the factory calibrated setting. In particular, a decrease in the extinction ratio can lead to problems with the signal-to-noise ratio, while an increase in the extinction ratio has even more detrimental effects, where transmission performance can be severely degraded at high extinction ratios.

In particular, it is necessary to correct for undesired variations in the extinction ratio as a function of ambient temperature. Extinction ratio correction is based on temperature error, that is, how much it deviates from the calibrated temperature at which the laser is actually operating, rather than absolute temperature. Since the calibration temperature can vary in some cases, it is important to base the correction on the temperature error, not the measured temperature. For extinction ratio correction, embodiments of the present invention incorporate firmware with a lookup table setting the AC swing that drives the AC current for the laser. As the laser temperature rises above or below the set point, the AC swing is increased or decreased as directed by a lookup table to keep the extinction ratio constant. In one embodiment, the lookup table would conceptually have columns such as temperature error, laser bias current, and AC modulation, combined with a row for the corresponding laser temperature.

Referring again to Figures 1 and 2, the current CWDM standard uses passbands of approximately 11nm, with passive bandpass filters producing steep shoulders on the edge of each passband. Therefore, it is necessary to keep the light emitted from the laser within the specified 11nm passband. Embodiments of the present invention ensure that the wavelength of emitted light does not shift outside a specified passband as the ambient temperature moves over a wide range by temperature locking the laser.

The preferred lock temperature is chosen so that loss of lock is minimized and balanced. For example, if the operable ambient temperature range is from -40°C to 85°C, and the TEC can provide 20°C cooling and 65°C heating, the optimal laser setting temperature would be at each of the high and low ends. The temperature at which the equilibrium loses lock is about 45°C. In other words, the device will lose lock at 20 degrees on the low end and 20 degrees on the high end. Except for the case where the maximum cooling is zero degrees, the calculations of this method are also correct for the heating-only design.

Alternatively, where extremely low temperatures are not a concern, a higher temperature can be chosen as the set point to avoid spending too much energy on cooling. For example 50°C may be chosen as the set point since it is the maximum operating temperature at which many conventional transceiver components currently operate. However, in cases where transceiver components that can withstand higher temperatures are used, high laser temperatures can be used as set points, such as 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C .

An example method of calibrating a transmitter according to an embodiment of the present invention includes: first causing a computer or other device in communication with the transceiver 100 to set the target wavelength in the desired CWDM channel; and instructing the microprocessor 130 to set the TOSA 114 The setpoint temperature of the laser diode (via the TEC Command signal).

Additionally, the computer in communication with microprocessor 130 may also set the AC modulation and I _{laser bias} for laser operation to default values. If the operating temperature of the laser exceeds or falls below the set temperature, these values can be changed later as needed by consulting a lookup table or other methods.

Since the wavelength produced by the transceiver at a specified laser diode temperature and current density varies from one laser diode to another, the transceiver 100 can be initially calibrated prior to being installed in an optical network, as shown in block 306 Show. Calibration involves monitoring the wavelength of the optical signal produced by the laser diode while varying its temperature and other operating conditions, and then storing the calibration information in microprocessor 130 memory. It also includes receiving an analog signal from a sensor in the optoelectronic device and converting the analog signal to a digital value, which is also stored in the memory. Using this data, the device generates control signals based on digital values in the microprocessor to control the temperature of the laser diode to maintain the desired emission wavelength.

Referring now to FIG. 8, another example method of operating a CWDM transceiver is shown in block diagram form. Initially, the computer or other device commands the microprocessor 130 to set the set point temperature of the laser diode in the TOSA 114 (via the TEC Command signal), as shown in block 402.

The operating temperature of the laser diode is then continuously or repeatedly determined, as shown in block 404 , such as by reference to one or more temperature sensors 204 , 208 , and 210 , or by using other methods known in the art to determine the temperature. For example, the microprocessor 130 then continuously checks the laser diode temperature to see if it is above or below the set point temperature. If the laser diode temperature is above or below the set point temperature, the operation of the TEC (or other temperature controller) is adjusted as needed, as shown in block 406, and temperature monitoring continues. If the laser diode temperature is above the set point temperature, the TEC operates in cooling mode. If the laser diode temperature is below the set point temperature, the TEC operates in heating mode.

However, due to the standards applicable to the transceiver, there may not be enough power available to heat or cool the laser diode to the set point over the entire operating ambient temperature range of the transceiver. Thus, before sufficient heating or cooling occurs to bring the laser diode temperature back to the set point, the microprocessor or other device monitors whether power consumption is being maximized, as shown in block 408 . If power consumption is maximized, then the laser diode will operate above or below the set point and thus wavelength drift will occur. To avoid extinction ratio issues, for example, a microprocessor or other device consults a lookup table in the TOSA firmware and adjusts the AC swing as needed to achieve target values for laser power and extinction ratio operation, as shown in block diagram 410 .

In some embodiments, a transceiver controller (not shown) is used to perform certain functions that might otherwise be performed by the microprocessor 130 . For example, a transceiver controller can be used to look up values in a table and output those values through one or more digital-to-analog converters. Thus, the look-up table (or portions of the look-up table) may also be accessed or stored by the transceiver controller such that it may output certain control signals while the microprocessor 130 outputs other control signals.

Embodiments within the scope of the present invention also include computer-readable media for carrying or having computer-executable instructions or data structures stored thereon. Such computer-readable media can be any available media that can be accessed by a general purpose or special purpose computer. By way of example and not limitation, such computer-readable media may be embodied in transceiver firmware, and/or include RAM, ROM, EEPROM, or any other form to carry or store the required program code means and be accessible by the microprocessor 130 or a general or special purpose computer. Computer-executable instructions comprise, for example, instructions and data which cause microprocessor 130, a general purpose computer, special purpose computer, or special purpose processing device to perform a certain function or group of functions. Although not required, the invention may be described or claimed in the general context of such computer-executable instructions, such as program modules, being executed by a computer. The particular sequence of such associated data structures or executable instructions represents examples of corresponding acts for implementing the functions described in those acts. Accordingly, the methods of the present invention disclosed above may be configured to operate as computer-executable instructions by a computing device.

The present invention may be embodied in other specific forms without departing from the spirit and essential characteristics of the invention. The described embodiments should be considered in all respects as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than the foregoing description. All changes within the meaning and range of equivalence of the claims are intended to be embraced therein.

Claims (20)

1. method that will maintain by the optical wavelength that laser diode is launched in the required range of tolerable variance, described method comprises:

Providing can be from the laser diode of the selected temperature work of at least the first selected temperature to the second, is wherein moved greater than desired amount by described laser diode institute wavelength of light emitted in the temperature range from first temperature to second temperature; And

Desirably described laser diode is heated or cools off, make described laser diode:

Do not drop to below the 3rd temperature, described the 3rd temperature is between described first temperature and described second temperature; Or

Rise to more than the 4th temperature, described the 4th temperature is between described the 3rd temperature and described second temperature;

Wherein in from described the 3rd temperature to the temperature range of described the 4th temperature, move amount that falls in the desired range of tolerable variance of skew by described laser diode institute wavelength of light emitted.

2. method as claimed in claim 1, wherein said laser diode comprise the part of Coarse Wavelength Division Multiplexing (CWDM) module.

3. method as claimed in claim 1 wherein is used for the temperature controller that the temperature of described laser diode is controlled is carried out by being coupled to described laser diode to the action that described laser diode heats.

4. method as claimed in claim 3, wherein said temperature controller comprises thermoelectric (al) cooler.

5. method as claimed in claim 1 further comprises: when the temperature of described laser diode surpasses described the 3rd temperature, the AC amplitude of oscillation to described laser diode is regulated, so that extinction ratio is maintained more than the lower limit of regulation.

6. method as claimed in claim 6, the wherein said AC amplitude of oscillation is regulated by the look-up table that comes the index AC amplitude of oscillation based on the laser diode temperature is consulted.

7. method as claimed in claim 1, the temperature of wherein said laser diode is determined by selected equipment from the following group that constitutes: the temperature sensor of communicating by letter with described laser diode; Be arranged in the temperature sensor of photoelectric subassembly; And the temperature sensor that is positioned at the photoelectric subassembly outside.

8. method as claimed in claim 1, wherein said first temperature and described second temperature are separated by a temperature range, and the wavelength that the described laser diode operation of working in whole described temperature range will be experienced greater than 8nm moves.

9. method as claimed in claim 1, wherein said first temperature comprise approximately negative 40 ℃ or following, and described second temperature comprise about 85 ℃ or more than.

10. method as claimed in claim 1, wherein said the 3rd temperature comprises at least about 50 ℃.

11. method as claimed in claim 1, wherein said the 3rd temperature comprises at least about 70 ℃.

12. an operation is used for the method for the photoelectric subassembly of Coarse Wavelength Division Multiplexing (CWDM) system, comprising:

Laser diode in the photoelectric subassembly is heated to set point temperatures, and this set point temperatures is more than the typical ambient temperature of described photoelectric subassembly;

Move described laser diode and launch light;

Described laser diode is heated or cools off, described laser is remained in the selected scope of described set point temperatures; And

, when described set point is above, the AC amplitude of oscillation that drives described laser diode is regulated in the temperature that identifies described laser diode, maintain more than the lower limit of regulation with the extinction ratio of the light signal that will be launched by described laser diode.

13. the method as claim 12 further comprises: by from described laser diode temperature being monitored: the temperature sensor of communicating by letter with described laser diode by selected equipment the following group that constitutes; Be arranged in the temperature sensor of described photoelectric subassembly; And the temperature sensor that is positioned at described photoelectric subassembly outside.

14. as the method for claim 12, wherein the action that described laser diode is heated is carried out by thermoelectric (al) cooler.

15. as the method for claim 12, the wherein said AC amplitude of oscillation is by regulating coming the look-up table of the described AC amplitude of oscillation of index to consult based on described laser diode temperature.

16. as the method for claim 12, wherein said set point temperatures comprises at least about 50 ℃.

17. an optoelectronic device comprises:

Comprise the photoelectric subassembly that is used for radiative laser diode;

Be used for laser driver that the operation of described laser diode is controlled;

Be coupled to described laser diode and be used for temperature controller that the temperature of described laser diode is controlled;

Be used at least one temperature sensor that the temperature that is associated with described laser diode is detected;

Memory is configured to store and is used for the look-up table the described AC amplitude of oscillation of described laser diode controlled based on the laser diode temperature that is detected; And

One or more control device, be used for producing: to the command signal that the operation of described temperature controller is controlled of being used for of described temperature controller, this command signal makes described temperature controller with near the scope of described laser diode temperature maintenance set point temperatures; And to the command signal that the AC amplitude of oscillation of described laser diode is controlled of being used for of described laser driver.

18. as the optoelectronic device of claim 17, wherein:

Described at least one temperature sensor comprises and is used for the laser temperature transducer that monitors from described photoelectric subassembly temperature inside and is used for the external temperature sensor that the ambient temperature to described photoelectric subassembly outside monitors; And

Described microprocessor is configured to that the two generates the command signal of described temperature controller according to the temperature in the described photoelectric subassembly and the ambient temperature that monitored.

19. as the method for claim 17, wherein said temperature controller comprises thermoelectric (al) cooler.

20. method as claim 17, wherein said optoelectronic device comprises Coarse Wavelength Division Multiplexing (CWDM) module, wherein said Coarse Wavelength Division Multiplexing (CWDM) block configuration becomes to come work from first temperature to second temperature, wherein said first temperature and described second temperature are separated by a temperature range, and the wavelength that the laser diode operation of working in whole described temperature range will be experienced greater than 8nm moves.

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