SEMICONDUCTOR LIGHT SOURCE TEMPERATURE CONTROL

Abstract: A heater is fabricated in the same semiconductor substrate (10) with a light source (14) and a temperature sensor (12). A current is passed through the sensor and a voltage across it is sensed, the voltage indicative of actual substrate temperature. This temperature is compared to desired substrate temperature and any difference therebetween drives the heater to appropriately stabilize the substrate temperature at or near the desired temperature. Alternatively, an existing light source (14) fabricated on the substrate (10) has a current passed therethrough and a resulting voltage across the light source is sensed, the voltage and current being indicative of actual substrate temperature. The actual substrate temperature is compared to desired temperature and any difference therebetween drives the heating device (16) to appropriately stabilize the substrate temperature at or near the desired temperature. The circuitry for sensing the voltage across the sensor (12) along with circuitry for comparing the sensed and desired voltages and the heater driver (16) either may be fabricated on the substrate (10) or located external thereto.

Description: Description Semiconductor Light Source Temperature Control Technical Field This invention relates to temperature control devices, and more particularly to such devices for controlling the temperature of a light source fabricated on a semiconductor substrate. Background Art A fiber optic gyroscope (FOG) includes a source of light energy, e.g., a laser diode, which provides coherent light split into two beams that are launched into each end of a coil. When no rotational disturbances are present, the beams propagate equally in opposite directions around the coil and recombine to form an interference fringe pattern at a detector. When the coil is subject to a rotation about an axis normal thereto, a nonreciprocal disturbance occurs known as the Sagnac effect, whereby the opposing light beams take different times to traverse the coil. This causes a phase difference between the beams and a shift of the fringe pattern. The magnitude and direction of the fringe shift is proportional, respectively, to the rate and sense of the rotation applied to the coil. A phase difference between the two beams can be compensated for (i.e., nulled) by imposing a further nonreciprocal phase shift on the beams in an equal and opposite manner by using a phase modulator, e.g., a lithium niobate integrated optic phase modulator. In a serrodyne closed-loop FOG, a phase modulator is driven by a linear ramp or a step ramp signal. The modulator induces a phase shift in the light passing through which is equal and opposite to the Sagnac phase shift. When the magnitude of the ramp is held constant to an amplitude corresponding to one wavelength, and the duration of flyback time is approximately zero, gyro rate information is given by: Ω = (SF) * (f) where Ω is the angular rate of gyro rotation, f is the frequency of the linear ramp, and SF is a scale factor. The ramp frequency can be directly measured, and the scale factor is a function of the source wavelength. In turn, the source wavelength is a function of the source temperature, e.g., 0.03%/ β C for a laser diode. Thus, it is important to know the source temperature so that either a scale factor correction can be made for changes in temperature, or the source temperature may be controlled to maintain a constant wavelength and scale factor. Some known packaged semiconductor light sources comprise a temperature control loop consisting of a thermistor mounted to a substrate or package surface for measuring source temperature, and a means to cool the source package, such as a thermo-electric cooler. The cooler attempts to maintain the source at a constant temperature, thereby removing temperature-induced wavelength variations. However, the thermistor does not directly measure the source's temperature, which results in two types of error. A steady-state error occurs due to the thermal resistance between the thermistor and the source. This error may vary further with the source's efficiency, which can change due to aging. A second type of error is delayed response caused by thermal transport lag and the thermistor time constant. This error is most prevalent during system power up and source power transients. Further, the cooler is part of the thermistor package and not the substrate itself. As such, the cooler is not directly controlling the temperature of the substrate itself, but instead is controlling the temperature of the package to which the substrate is mounted. This adds further thermal time delays in stabilizing substrate temperature. In many high-accuracy device applications, desired warm up time may be given in terms of seconds; however, thermal stabilization times of the source, thermistor and cooler may actually be measured in minutes. This undesirably long warm-up time may seriously affect device accuracies. Disclosure of the Invention Objects of the present invention include provision of an improved semiconductor substrate temperature measurement and maintenance scheme which is directly responsive to substrate temperature in maintaining the substrate at a desired temperature, thereby removing temperature-induced wavelength variations in a light source fabricated on the substrate. According to one aspect of the present invention, a heater is fabricated in the same semiconductor substrate in which a light source and a temperature sensor are fabricated, an electrical current is passed through the sensor and an electrical voltage developed across the sensor is sensed, the voltage being indicative of actual substrate temperature, the actual substrate temperature is compared to desired substrate temperature and any difference therebetween drives the heater to appropriately stabilize the substrate temperature at or near the desired temperature. In further accord with this aspect of the invention, the circuitry for sensing the voltage developed across the sensor along with circuitry for comparing the sensed voltage to desired voltage and circuitry for driving the heater are fabricated on the substrate. In still further accord with this aspect of the present invention, the circuitry for sensing the voltage developed across the sensor along with circuitry for comparing the sensed voltage to desired voltage and circuitry for driving the heater are located external to the substrate. According to a second aspect of the present invention, an existing light source fabricated on a semiconductor substrate has an electrical current passed therethrough and a resulting electrical voltage developed across the light source is sensed, the voltage and current being indicative of actual substrate temperature, the actual substrate temperature is compared to desired temperature and any difference therebetween drives the heating device to appropriately stabilize the substrate temperature at or near the desired temperature. The present invention represents an advancement over previous semiconductor substrate temperature maintenance schemes, such as an external thermistor and cooler. This is due to reduction in thermal resistance between the light source, temperature sensing device, and heater, which now are all fabricated in the same substrate. Therefore, steady state errors and transport lags due to thermal resistance are greatly reduced. Thus, more accurate temperature information can be supplied to a control loop to better maintain the light source at a constant desired temperature. In addition, warm up time of high accuracy devices employing the present invention is reduced due to the rapid response time to changes in source temperature. Further, the heater operates more efficiently than prior art external coolers since the heater, by being fabricated on the substrate, is heating a significantly smaller thermal mass, i.e., that of the substrate, instead of both the substrate and cooler device package. This results in further power savings. Also, by fabricating the heater on the substrate, the added weight and volume of prior art external coolers are avoided. The foregoing and other objects, features and advantages of the present invention will become more apparent in the light of the following detailed description of an exemplary embodiment thereof, as illustrated in the accompanying drawings. Brief Description of the Drawings Fig. 1 is a schematic block diagram of circuitry fabricated on an integrated circuit (IC) in accordance with the present invention; Figs. 2(a)-(d) are structural diagrams of the IC of Fig. 1 in various stages of an epitaxial-diffused fabrication process; Fig. 3 is a structural diagram of the IC of Figs. 2(a)-(d) completely fabricated; Fig. 4 is a graph of the voltage versus temperature relationship for a GaAs diode fabricated on the IC of Fig. 3; Fig. 5 is a schematic block diagram of circuitry fabricated on an IC in accordance with an alternative embodiment of the present invention; Fig. 6 is a schematic block diagram of circuitry fabricated on an IC in accordance with another alternative embodiment of the present invention; and Fig. 7 is a schematic block diagram of a detailed portion of the circuitry of the alternative embodiments of Figs. 5 and 6. Best Mode for Carrying Out the Invention In Fig. 1 is illustrated a schematic diagram of circuitry fabricated on a portion of semiconductor substrate material 10; more particularly, the material comprising a monolithic IC 10. The IC has fabricated thereon, in accordance with the present invention, a temperature sensitive semiconductor device 12, e.g., a Gallium Arsenide (GaAs) diode 12, a semiconductor light source 14, e.g., a GaAs laser diode 14, and a semiconductor heating device 16, e.g., a semiconductor resistor 16. Other well known electronic components, some of which are described hereinafter, are fabricated onto the substrate as well. The sensing and light source diodes, heater and other components may all be fabricated onto the IC substrate using known epitaxial-diffused IC fabrication processes. Referring to Fig. 2(a) , the IC is formed by first providing a thin layer of substrate material 20, e.g., GaAs, doped with a high concentration of n-type donor atoms (i.e., atoms having excess free electrons), one side of the layer 20 being lapped and polished. Next, an epitaxial growth process is used to grow a second layer 22 on the substrate 20. The epitaxial layer 22 has a different type or concentration of impurity atoms, e.g., a lower concentration of n-type impurity atoms. In the epitaxial growth process, the substrate is exposed to a high temperature gaseous environment; the gas containing the substrate crystal material having a different concentration or different type of impurity material. The crystal material in the gas is deposited on the polished side of the substrate. An oxide layer 24 is then formed on the epitaxial 22 layer by exposing the IC to a high temperature oxygen or steam atmosphere. Referring to Fig. 2(b), an etching and diffusion process is performed where sections 26 of the oxide layer 24 are removed. Next, isolation diffusion takes place by exposing the assembly to an atmosphere containing the same impurities as the substrate impurities. The time and temperature of exposure is controlled to allow the impurities to penetrate the epitaxial layer and reach the substrate 20, thereby forming isolation regions 28 which allow electrical isolation between different circuit components. A new oxide layer 24 is then formed and sections 30 of the layer are removed (Fig 2(c)) to form the circuit components 32 (e.g., the sensing and light source diodes 12,14 and heater resistor 16). Component formation is accomplished using the aforementioned isolation diffusion process with a variety of diffusion atoms, such as n-type donor atoms or p-type acceptor atoms (i.e., atoms having excess free holes), to form the desired circuit components. In addition to oxide layer formation and subsequent removal for isolation diffusion, sections of oxide layer may be removed for formation of additional epitaxial growth layers 34, as illustrated in Fig. 2(d). Once the diffusion and epitaxial growth steps are complete, a new oxide layer 24 is formed, and sections of the layer are again removed for deposition of metal to form oh ic contacts 36 (Fig. 3) with the components formed in the assembly. In Fig. 3 is illustrated the completed IC. Referring again to Fig. 1, a DC power supply (not shown) external to the IC 10 provides plus (+) and minus (-) DC Volts (+V, -V) on lines 40,42 to the circuitry inside the IC. The light source 14 typically comprises a laser diode and is connected by signal lines 44 to known driver circuitry (not shown) external to the IC. The driver circuitry, which forms no part of the present invention, provides the appropriate current for proper diode operation. Alternatively, the light source driver circuitry may, if desired, be fabricated on the IC. +V is also provided to a reference voltage generator 46, e.g., a zener diode, which generates a stable voltage, VREF, on a line 48 for use by other components on the IC. VREF supplies a junction current (i.) to forward bias the sensing diode 12. The junction current flows from VREF through a resistor 50 and the diode 12 to ground. The value of the resistor 50 connected between VREF and the diode is selected so that the junction current (i.) is greater than the sensing diode saturation current (Is) . A sensing voltage (V 'S) is the voltage across the sensing diode at the junction (node) 52 between the sensing diode and the resistor 50, and is a function of junction current (i.) and sensing diode temperature (T) , as given by: V s = (kT/q)(ln(i j /I s )) (Eq. 1) where k is Boltzmann's constant and q is the charge of an electron. Fig. 4 is a graph of voltage, Vs, versus temperature, T, for a GaAs diode having a 10 micro-amp junction current. The relationship is approximately linear in the temperature range of 25 β C to 300 β C, and is given by: T = 434.65 β C - (444.42 β C/volt) (V β ) (Eq. 2) Thus, by knowing the voltage across the sensing diode, the temperature of the diode may be calculated. Further, because the diode is fabricated on the substrate, the temperature of the diode represents the temperature of the substrate. Referring again to Fig. 1, a non-inverting terminal of a first operational amplifier (op-amp) 56 is connected to the node 52 through a resistor 58. A shunt resistor (R ) 60 is connected between an inverting terminal of the op-amp 56 and ground. A feedback resistor (R f ) 62 is connected between the inverting terminal and an output terminal of the op-amp. An offset resistor (R ) 64 is connected between the inverting terminal and VREF to cancel any nominal sensing diode offset voltage. The sensing voltage (V ) is applied at the non-inverting terminal. An output voltage (V ) generated at the output terminal is a function of V , Rr */ Rs- Γ Ro- and VREF as given by: V Q = V g *[l+R f (R s +R 0 )/(R s *R 0 )3 - VREF(R f /R o ) (Eq. 3) Thus, V , which is an amplified version of V , is indicative of the temperature of the substrate as sensed by the sensing diode. V is supplied on a line 66 through a resistor 68 to an inverting terminal of a second op-amp 70 configured as an error amplifier. Additional resistors 72,74 on the IC, along with an adjustable resistor 76 external to the IC, provide a voltage indicative of a constant desired IC temperature. The second op-amp 70 compares the desired voltage (temperature) with the sensed voltage, V , (temperature) and provides a signal indicative of any difference therebetween on a line 78 to a third op-amp 80. The second op-amp 70 has a capacitor 82 external to the IC connected across the op-amp output and inverting input, and connected in parallel with an internal resistor 84. The external capacitor 82 serves as a filter capacitor to set the loop response. The output of the third op-amp 80 is connected through a resistor 86 and diode 88 to a transistor 90. In turn, the transistor 90 is connected to the heater resistor 16. Together, the third op-amp 80, the resistor 86, diode 88 and transistor 90 serve as a simple linear heater driver. In this exemplary embodiment of the present invention, the efficiency of the heater driver is not a factor since the heater driver is fabricated on the same IC as the heater 16; hence, it can be considered a part of the heater. During operation, a bias current signal energizes the laser diode 14. The temperature of the laser changes as it is operated, thereby changing the wavelength of the light emitted by the laser. As described hereinbefore, the changing laser wavelength may have adverse consequences for high accuracy devices. The temperature of the substrate changes in response to changes in the laser temperature. The sensing diode 12 is responsive to these changes in laser temperature and the error amp 70 indicates the difference between actual and desired temperatures. The error amp commands the heater driver, which drives the heater 16 to heat the substrate 10 until the sensed substrate temperature equals the desired constant substrate temperature. The response time of the sensing diode and heater to changes in substrate temperature is significantly faster than the aforementioned prior art schemes since the laser, the sensing diode, and the heater are fabricated on the same substrate, thereby reducing the thermal resistance between the elements. It is to be understood that the aforementioned circuitry fabricated on the IC is purely exemplary; any other circuitry may be used, if desired, for sensing the temperature of the substrate as provided for by the sensing diode, for comparing the sensed temperature with the desired temperature, and for driving the heater in response thereto. Referring to Fig. 5, an alternative embodiment of the present invention is illustrated in which the sensing diode 12, laser diode 14, and the heater resistor 16 are fabricated on the IC 10, while any controlling circuitry is external to the IC. As with Fig. 1, external laser control circuitry is not illustrated since this circuitry is well known and forms no part of the present invention. Current through the sensing diode is provided on a pair of signal lines 100,102 by a current source 104, which is illustrated in detail in Fig. 7 and described hereinafter with reference thereto. The sensed voltage across the sensing diode is fed on the lines 100,102 to a buffer amplifier 106, which may comprise one or more op-amps arranged in the well known instrumentation amplifier configuration. The buffer output voltage is indicative of the sensed substrate temperature. The buffer output is fed on a line 108 to an analog to digital converter 110 (ADC) which converts the analog buffer output voltage to a corresponding digital signal. Also fed to the ADC, as well as to the current source, is a stable reference voltage, VREF, provided by, e.g., a zener diode 112 in a similar manner to that of Fig. 1. The output of the ADC 110 is provided on a set of signal lines 114 (i.e., data bus) to a known microprocessor 116 (UPROC) . The UPROC 116 converts the digital voltage signal into a corresponding temperature signal using a look-up table which may contain a graphical relationship between voltage and temperature similar to that of Fig. 4. The look-up table may comprise a plurality of memory or register locations within the UPROC or in external memory (not shown) for storing corresponding temperature signal information. Also input on a line 118 to the UPROC is a signal indicative of a desired constant substrate temperature. The signal may be generated from other circuitry (not shown) , which may be responsive to other parameters in arriving at a desired substrate temperature. • The UPROC compares the desired and sensed substrate temperatures and provides a signal indicative of any difference therebetween on a line 120 to heater driver circuitry 122. The signal to the heater driver 122 may be a pulse width modulated (PWM) signal to minimize wasted power in the heater driver. The heater driver may comprise a simple transistor responsive to the PWM signal for driving the heater with the pair of signal lines 123 accordingly so as to closely match desired and sensed substrate temperatures, thereby reducing temperature-induced laser wavelength variations. Also included may be current control circuitry 124 for the current source 104. The circuitry 124 may comprise a known digital to analog converter 124 (DAC) . The DAC is responsive to a signal on a line 126 from the UPROC and provides a signal on a line 128 to the current source, as illustrated in greater detail in Fig. 7. VREF is also fed to the DAC. Specifically, the UPROC may contain a modelling algorithm for the sensing diode 12. As a result, the UPROC may adjust, through the DAC, the current source output for proper operation of the sensing diode, depending on the particular diode used. Or, the UPROC may adjust the current source output to compensate for unit to unit variations in sensing diodes. Referring to Fig. 6, another alternative embodiment of the present invention is illustrated in which only the laser diode 14 and a heater resistor 16 are fabricated on the IC 10, while any controlling circuitry is external to the IC. However, it is to be understood that, in this alternative embodiment, a portion or all of the controlling circuitry may be fabricated on the IC, if desired. The controlling circuitry is similar to that of Fig. 5 in that it comprises a similar current source 104, buffer 106, reference voltage generator 112, ADC 110, UPROC 116, and heater driver 122. However, because there is no sensing diode 12 fabricated on the IC, the controlling circuitry must monitor the voltage across the laser as well as the current through it. A voltage indicative of the current generated by the current source is provided on a line 130 to one input of a multiplexer 132 (mux) . The buffer voltage output on the line 108 is fed to a second input of the mux 132. The mux alternately chooses one of the two inputs to pass through to the mux output on a line 134. The mux output is fed to the ADC, which provides the digital value of the mux output to the UPROC. Software inside the UPROC contains a well known detailed model of light source temperature versus light source current and voltage, similar to the graph of Fig. 4. From this model the UPROC calculates the temperature of the laser diode, and thus, the temperature of the substrate. The UPROC compares the calculated actual light source temperature with the desired temperature provided on the line 118 and provides a signal indicative of any difference therebetween on the line 120 to the heater driver 122. The heater driver then commands the heater with appropriate signals on the pair of lines 123 to heat the substrate accordingly to match actual and desired substrate temperatures. The current through the laser may be controlled by the UPROC as part of a separate control loop. The control loop may operate on a sensed laser parameter such as optical intensity or wavelength. The sensed parameter (sensor not shown) is input to the UPROC on a line 140. Software inside the UPROC calculates a commanded laser operating current in response thereto and provides a signal indicative thereof on the line 126 to a light source control circuit 124. The circuit may comprise a DAC 124, similar to that of Fig. 5, responsive to the commanded current on the line 126 in controlling the current supplied to the laser in the current source. VREF is also fed to the DAC. In Fig. 7 is illustrated in more detail the current source 104 of both Figs. 5 and 6. A fixed resistor 150 and a variable resistor 152 are connected between VREF and ground and provide a voltage indicative of a desired laser operating current on a line 154 to a non-inverting input of an op-amp 156. The output of the op-amp is connected through a resistor 158 to a transistor 160. The collector of the transistor 160 is pulled up to +V through a resistor 162. The emitter of the transistor is connected by the line 100 to the anode of either the sensing diode 12 (Fig. 5) or the laser diode 14 (Fig. 6) . The cathode of either device 12,14 is connected by the line 102 to the inverting input of the op-amp 156, such input also being connected through a resistor 164 to ground. For the mux 132 of Fig. 6 only, the non-inverting op-amp input is also connected to a non-inverting input of a second op-amp 166. The second op-amp 166 is configured as a voltage follower, and its output is fed on the line 130 to the mux of Fig. 6. Further, the laser current control output on the line 128 from the DAC 124 of Figs. 5 and 6 is fed through a resistor 168 to the non-inverting input of the first op-amp 156. In operation, current source operating current is indicated by the voltage at the non-inverting input of the first op-amp 156. This voltage is trimmed as necessary by the UPROC 116 through the DAC 124. The op-amp output is converted to a current through the transistor 160, the current being used to control either the sensing diode 12 of Fig. 5 or the laser diode 14 of Fig. 6. Although the invention is illustrated with the temperature sensor 12 implemented as a diode fabricated on the IC, other temperature sensitive semiconductor devices may be fabricated thereon without departing from the spirit and scope of the present invention. A zener diode, a semiconductor resistor, and the base-emitter or base-collector junction of a transistor are examples of semiconductor devices having suitable temperature characteristics. Also, it is to be understood that the GaAs laser diode 14 used as the semiconductor light source is exemplary; other light sources may be used; e.g., a light emitting diode (LED) , an edge-emitting diode (ELED) , a super luminescent diode (SLD) , or a distributed feedback (DFB) laser diode. Further, the semiconductor resistor used as the heater 16 is exemplary; other heaters may be used; e.g., a semiconductor diode or a zener diode. If fabricated other than as a semiconductor resistor, the heater driver circuitry must be changed from that illustrated herein so as to match the characteristics of the heater implementation. The UPROC is described as converting the digital voltage signal into a temperature signal using a look-up table. However, other signal conversion methods could be used such as a subroutine which performs a calculation using a relationship which defines the curve of the light source voltage versus temperature characteristic. In addition, although the the IC is described as being fabricated using the epitaxial-diffused fabrication process, other integrated circuit fabrication techniques could be employed; e.g., crystal growth techniques and alloy or fused construction. Although the invention has been illustrated and described with respect to exemplary embodiments thereof, it should be understood by those skilled in the art that the foregoing and various other changes, omissions and additions may be made therein and thereto, without departing from the spirit and scope of the invention. I claim:

Claims: Claims 1. Apparatus, comprising: a substrate of semiconductor material; a light source, fabricated in said substrate, a temperature of said light source varying as said light source is operated, a temperature of said substrate varying as the temperature of said light source varies; sensing means, fabricated in said substrate; heating means, fabricated in said substrate; current means, for providing an electrical current through said sensing means, said sensing means responsive to said electrical current for providing a voltage signal indicative of a voltage across said sensing means, said voltage signal varying as a function of the temperature of said substrate; control means, responsive to said voltage signal, for comparing said voltage signal to a signal indicative of a desired value of a temperature of said substrate and for providing an error signal indicative of any difference therebetween; and heater driver means, for varying an amount of current passing through said heating means in an amount proportional to the value of said error signal, said heating means responsive to said varying amount of current therethrough for heating said substrate accordingly. 2. The apparatus of claim 1, wherein said heater driver means comprises a linear circuit. 3. The apparatus of claim 1, wherein said heater driver means comprises a pulse width modulator circuit. 4. The apparatus of claim 1, wherein said control means further comprises means for varying said electrical current provided for said sensing means by said current means. 5. The apparatus of claim, 1, wherein said heating means comprises a semiconductor resistor. 6. The apparatus of claim 1, wherein said heating means comprises a semiconductor diode. 7. The apparatus of claim 1, wherein said heating means comprises a zener diode. 8. The apparatus of claim 1, wherein said sensing means comprises a semiconductor diode. 9. The apparatus of claim 1, wherein said sensing means comprises a zener diode. 10. The apparatus of claim 1, wherein said sensing means comprises a transistor base-emitter junction. 11. The apparatus of claim 1, wherein said sensing means comprises a transistor base-collector junction. 12. The apparatus of claim 1, wherein said sensing means comprises a semiconductor resistor. 13. The apparatus of claim 1, wherein said light source comprises a laser diode. 14. The apparatus of claim 1, wherein said light source comprises a light emitting diode. 15. The apparatus of claim 1, wherein said light source comprises an edge-emitting light emitting diode. 16. The apparatus of claim 1, wherein said light source comprises a super luminescent diode. 17. The apparatus of claim 1, wherein said light source comprises a distributed feedback laser diode. 18. The apparatus of claim 1, wherein one or more of each of said current means, said control means, and said heater driver means are fabricated in said substrate. 19. Apparatus, comprising: a substrate of semiconductor material; a light source, fabricated in said substrate, a temperature of said light source varying as said light source is operated, a temperature of said substrate varying as the temperature of said light source varies; heating means, fabricated in said substrate; current means, for providing an electrical current through said light source, said light source responsive to said electrical current for providing a voltage signal indicative of a voltage across said light source, said voltage signal varying as a function of the temperature of said substrate; control means, responsive to said voltage signal and to the amount of said electrical current provided for by said current means for calculating therefrom a signal indicative of the actual substrate temperature and for comparing said actual temperature signal to a signal indicative of a desired value of a temperature of said substrate and for providing an error signal indicative of any difference therebetween; and heater driver means, for varying an amount of current passing through said heating means in an amount proportional to the value of said error signal, said heating means responsive to said varying amount of current therethrough for heating said substrate accordingly. 20. The apparatus of claim 19, wherein said heater driver means comprises a linear circuit. 21. The apparatus of claim 19, wherein said heater driver means comprises a pulse width modulator circuit. 22. The apparatus of claim 19, wherein said heating means comprises a semiconductor resistor. 23. The apparatus of claim 19, wherein said heating means comprises a semiconductor diode. 24. The apparatus of claim 19, wherein said heating means comprises a zener diode. 25. The apparatus of claim 19, wherein said light source comprises a laser diode. 26. The apparatus of claim 19, wherein said light source comprises a light emitting diode. 27. The apparatus of claim 19, wherein said light source comprises an edge-emitting light emitting diode. 28. The apparatus of claim 19, wherein said light source comprises a super luminescent diode. - 29. The apparatus of claim 19, wherein said light source comprises a distributed feedback laser diode. 30. The apparatus of claim 19, wherein said control means further comprises means for varying said electrical current provided for said light source by said current means. 31. The apparatus of claim 19, wherein one or more of each of said current means, said control means, and said heater driver means are fabricated in said substrate.

Inventors: WINSTON CHARLES R JR, WINSTON, CHARLES, R., JR.
Applicants: HONEYWELL INC, HONEYWELL INC.
Application year: 1992
Main classification: G01K7
IPC codes: G01K7, H01L27, H01S5