JP4417937B2 - Semiconductor laser inspection equipment - Google Patents

Description

  The present invention relates to an apparatus for inspecting change and deterioration with time of output characteristics of a semiconductor laser.

  In the manufactured semiconductor laser, there may be a defective element such as an element including a defect in a semiconductor crystal or an element damaged during a manufacturing process. Many of such defective elements deteriorate in characteristics at a relatively early stage during use even if there is no problem in the initial characteristic evaluation immediately after energization. Therefore, in the final manufacturing process, the manufactured semiconductor laser is extracted and evaluated for a long time of about 200 hours to 1000 hours, or it is selected by continuously driving for a relatively short time within 100 hours, A so-called aging test is performed.

  As an aging apparatus for performing an aging inspection, a light output is detected by a detection unit having a light receiving element provided in the vicinity of the semiconductor laser to be inspected, and a drive circuit for the semiconductor laser to be inspected is set so that the detected value becomes a predetermined value There is known a technique in which a semiconductor laser to be inspected emits light for a long time by APC (Automatic Power Control) driving for feedback (see, for example, Patent Document 1).

  Such an aging apparatus normally inspects a large number of n (for example, several hundred) semiconductor lasers at the same time, and includes a drive circuit and a detection unit, and a laser inspection unit to which a semiconductor laser to be inspected is mounted. A large number n is provided. However, since there is a variation in light receiving sensitivity among the light receiving elements of each detection unit, even if each semiconductor laser to be inspected is APC-driven, the optical output of the semiconductor laser to be inspected can be made constant between the laser inspection units. There is a problem that you can not. Also, when a neutral density filter is interposed between the semiconductor laser to be inspected and the light receiving element, the attenuation filter has variations in attenuation characteristics. There is a problem that the light output cannot be made constant.

  To solve this problem, the gain of the amplifier that converts the optical output of the semiconductor laser under test into a current-voltage converter is adjusted by a semi-fixed resistor for each optical output detector, thereby calibrating variations in light reception sensitivity. However, it is very complicated to make adjustments for all of the n detection units. Moreover, if the light receiving element and the neutral density filter are input at different emission wavelengths, the sensitivity of the photosensitive element and the attenuation characteristics of the neutral density filter change, and the sensitivity of the photosensitive element and variations in the attenuation characteristics of the neutral density filter also vary. Every time a semiconductor laser with a different wavelength band is inspected, the gain of the current-voltage conversion amplifier must be adjusted.

On the other hand, it is conceivable to automatically calibrate variations in the light reception sensitivity of the light output detection unit by setting a reference signal for feedback control with a DA converter. It is necessary to provide an expensive high-resolution DA converter, which is a problem due to the manufacturing cost.
JP 2005-142184 A

  The present invention has been made in view of the above problems, and an object thereof is to provide a semiconductor laser inspection apparatus capable of automatically calibrating variations in light receiving sensitivity of a light output detection unit at a low cost. To do.

A semiconductor laser inspection apparatus according to the present invention includes a plurality of n laser inspection units provided corresponding to each of a plurality of n semiconductor lasers, and a reference for setting a reference signal for each of the plurality of n laser inspection units. A reference signal generator configured to input a reference signal set for each of the plurality of n laser inspection units to the corresponding laser inspection unit, and the plurality of n laser inspection units, Based on the reference signal input from the reference signal generation unit, the corresponding semiconductor laser is APC-driven, and the semiconductor laser inspection apparatus that inspects the operating characteristics of the corresponding semiconductor laser, the reference signal generation unit includes: a-bit first DA converter, a plurality of n b-bit (a> b) second DA converters provided corresponding to each of the plurality of n laser inspection units, and the plurality of n laser inspection units A plurality of n adder circuits provided corresponding to the plurality of n adder circuits, wherein the first DA converter inputs a common voltage to the plurality of n adder circuits in common, and the plurality of n second DA converters include: A calibration voltage is input to the corresponding adder circuit, and the plurality of n adder circuits add the common voltage input from the first DA converter and the calibration voltage input from the corresponding second DA converter. A reference signal is set for each of the plurality of n laser inspection units. In this invention, the first DA converter is preferably 12 bits or more, and the second DA converter is preferably 8 bits or less.

  According to the semiconductor laser inspection apparatus of the present invention, it is possible to automatically calibrate variations such as the light receiving sensitivity of the light output detector at a low cost.

  Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a block circuit diagram of a semiconductor laser inspection apparatus 10 according to the present embodiment, and FIG. 2 is a block diagram showing a reference voltage output unit.

  The semiconductor laser inspection apparatus 10 according to the present embodiment outputs a plurality of n semiconductor lasers 1-1, 1-2, 1-3..., 1-n (collectively referred to as 1) to be inspected. A so-called aging device that inspects the characteristic change (deterioration) of the semiconductor laser 1 by driving it for a predetermined period by APC control that continues to be driven at a predetermined time and periodically recording the drive current and optical output value of the semiconductor laser 1. It is.

  As shown in FIGS. 1 and 2, the inspection apparatus 10 includes a plurality of n laser inspection units 20-1, 20-2, 20-3,..., 20- to which a semiconductor laser to be inspected is mounted. n (collectively 20), a reference signal generator 50 for generating a reference signal to be output to the laser inspection unit 20, and the laser inspection unit 20 and the reference signal generator 50 are controlled in accordance with a predetermined operation program. A control unit 80 that records the detection result input from the laser inspection unit 20 is also included.

Each laser inspection unit 20 detects the optical output from the semiconductor laser element 1 by driving the mounted semiconductor laser 1, and includes a drive circuit 22 that inputs a drive current to the semiconductor laser 1, and a drive current The light receiving element 24 such as a PIN photodiode for detecting the light output emitted from the semiconductor laser 1 receiving the input via the neutral density filter 23 and the differential amplifier 28 are extracted from the mounted semiconductor laser 1. drive current _{I OP-1 was, I OP-2, I OP} -3, ···, I OP-n and (collectively referred to as _{I OP),} light detected by the light receiving element 24 outputs the signal _{P O-1} , _PO-2 , _PO-3 ,..., _PO-n (collectively referred to as _PO ) are output to the control unit 80, and the control unit 80 records these signals _IOP and _PO . To do.

The laser inspection unit 20 includes a switching control can switch 30 by the controller 80, the switch 30 includes an optical output signal P _O detected by the light receiving element 24, the current - the semiconductor laser via the voltage conversion circuit 26 The drive current I _OP extracted from 1 is input, and the optical output signal _PO and the voltage signal corresponding to the drive current I _OP are switched and input to one input terminal of the differential amplifier 28.

  As shown in FIG. 2, the reference signal generation unit 50 includes a first DA converter 52 and a plurality of n second DA converters 54-1, 54-2, 54-2, 54 corresponding to the plurality of n laser inspection units 20. 54-3... 54-n (collectively referred to as 54) and adder circuits 56-1, 56-2, 56-3..., 56-n (collectively referred to as 56), The first DA converter 52 has a higher resolution than the second DA converter 54. For example, the first DA converter 52 is a 12-bit DA converter and the second DA converter 54 is an 8-bit DA converter.

The 1DA converter 52, and inputs the tone the common voltage V _C depending on the data value of the common data signal S _C that is input from the control unit 80 to each adder circuit 56. Further, the second DA converters 54-1, 54-2, 54-3,..., 54-n are respectively supplied with calibration data signals S _P-1 , S _P-2 , S _P-3 inputted from the control unit 80. _, ···, _{S P-n} calibration voltage _{V P-1} according to the data values of (collectively referred to as _{S P), V P-2} , V P-3, ···, V P-n ( collectively inputs, respectively) that _{V P} corresponding adder circuit 56-1,56-2,56-3 ... and toned, the 56-n and. This means that each adder circuit 56, and the common voltage _{V C,} the calibration voltage _{V P} from the 2DA converter 54 corresponding to the respective adder circuits 56, are input.

Each adder circuit 56, the reference signal voltage obtained by adding the input and the common voltage _{V C} and the calibration voltage _{V P V ref-1, V} ref-2, V ref-3, ···, V _ref-n (collectively referred to as V _ref ) is input to the other input terminal of the differential amplifier 28 of the corresponding laser inspection unit 20.

As a result, the control unit 80 switches and controls the switch 30 so that the optical output signal _PO is input to one input terminal of the differential amplifier 28, so that the differential amplifier 28 converts the optical output signal _PO into the reference signal _Vref. The drive current output from the drive circuit 22 is APC controlled so that the optical output signal _PO becomes a predetermined value. Further, the control unit 80 switches the switch 30 and inputs a voltage signal corresponding to the drive current I _OP to one input terminal, whereby the voltage signal is compared and amplified with the reference signal V _ref to drive the drive current of the semiconductor laser 1. I _OP becomes a driving current outputted from the driving circuit 22 to a predetermined value so as to control ACC (Automatic current control).

In such an inspection apparatus 10, each adder circuit 56 of the reference signal generation unit 50 includes a common voltage V _C input in common to each adder circuit 56 and a calibration voltage V _P that can be adjusted for each adder circuit 56. adding, to output the obtained voltage as a reference signal V _ref, the calibration voltage even first 2DA converter 54 is relatively small resolution to output a V _P, the reference signal while maintaining a predetermined resolution over a wide range V _ref can be set.

More specifically, the first DA converter 52 inputs 9 V as the common voltage V _C to each adder circuit 56, and the second DA converter 54 adjusts the calibration voltage VP adjusted in the range of 0 V to 2 V for each adder circuit 56. In the case of input, by using an 8-bit DA converter as the second DA converter 54, the range from 0V to 2V can be adjusted with a resolution of 0.1 mV or less, and thereby the range from 9V to 11V as the reference voltage. Can be adjusted with a resolution of 0.1 mV or less. Further, by changing the common voltage _{V C} output from the first 1DA converter 52, it is possible to set the reference voltage while maintaining a resolution of 0.1mV range other than 9V～11V.

As described above, in the inspection apparatus 10, the reference signal generator 50 that generates the reference signal V _ref input to the other input terminal of the differential amplifier 28 includes a plurality of n high-resolution DA converters for each laser inspection unit 20. There is no need to use a single circuit, and the circuit configuration can be reduced in cost.

  Next, a method for automatically calibrating the attenuation rate of the received light amount of each laser inspection unit 20 caused by variations in the light receiving sensitivity of the detection element 24 and the attenuation characteristics of the neutral density filter in the inspection apparatus 10 will be described.

First, n standard samples, which are semiconductor lasers with known current-light output characteristics, that is, the relationship between the drive current value and the light output value, are prepared and attached to each laser inspection unit 20. The n number of standard sample (semiconductor laser) production conditions equal light output value _{P S} (e.g., 120 mW) reference at the time of driving the drive current value _{I s-1, I s-} 2, I s-3 ···, I _s-n (generally called I _s ) and average differential efficiency value η are measured in advance by another measuring device, and the data values are stored in the control unit 80.

Then, the semiconductor laser 1 to be inspected and ACC driven at the minimum value of _{I s,} light output signal _{P OA-1} detected by the light receiving element 24 for each laser inspection unit _{20, P OA-2, P} OA-3 ,..., P _OA-n (collectively referred to as P _OA ) is recorded by the control unit 80. As a method for setting the drive current during the ACC drive, only the first DA converter 52 is controlled to adjust the common voltage V _C, and all the calibration voltages V _p are set to 0.

Next, a minimum value is obtained from each optical output signal _POA , and the semiconductor laser 1 is APC driven with that value. At this time, only the common voltage V _C is controlled, and each calibration voltage V _p is set to zero. The control unit 80, the drive current extracted from the semiconductor laser 1 that is APC driven I _OP and the current of the standard sample was stored in the control unit 80 - corresponding to from determined light output value P _S optical output characteristic drive current I A reference signal V obtained by causing the second DA converter 54 to output a calibration voltage V _p calculated from _s (for example, 180 mA) and the differential efficiency value η based on the following equation (1), and adding the calibration voltage V _p to the common voltage V _{C. The} standard sample is again APC driven by _ref (= V _c + V _p ), and the driving current I _OP at that time is extracted.

_{V p = (I s -I OP} ) × η (1)
Then, the calculation of the calibration voltage V _p and the extraction of the drive current I _OP are repeated until I _s −I _OP becomes sufficiently small, and then the light output signal P _OB− detected by the light receiving element 24 for each laser inspection unit 20. ₁ , P _OB-2 , P _OB-3 ,..., P _OB-n (collectively referred to as P _OB ) are recorded.

Next, the control unit 80 divides the optical output signal P _OB by the optical output signal P _s and calibrates the calibration coefficients C-1, C-2, C-3,. (Collectively referred to as C). The calibration coefficient C (= P _OB / P _s ) calculated in this way is an attenuation rate of the received light amount of each laser inspection unit 20 caused by variations in the light receiving sensitivity of the light receiving element 24 and the attenuation characteristics of the neutral density filter 23. Become.

  In the inspection apparatus 10 according to the present embodiment, since a control unit such as a computer can automatically calculate the calibration coefficient C in a very short time, it is not affected by changes in characteristics of the semiconductor laser due to heat generation, and is accurate. Calibration coefficient C can be obtained.

Then, remove the standard sample from the laser inspection unit 20, by mounting the semiconductor laser 1 to be inspected, the light output value of each of the semiconductor laser 1 is APC controls the driving current so that P _S. At this time, if the minimum value of each calibration coefficient is C _min , V _ref is set as shown in the following equation (2).

_{V ref = V c + V p} = P S × C min + P S × (C-C min) (2)
Thus, by inputting the calibration reference voltage multiplied by the calibration coefficient C as the reference signal V _ref input to the other input terminal of the differential amplifier 28, it does not depend on the attenuation rate of the received light amount of each laser inspection unit 20. In all the laser inspection units 20, the semiconductor laser 1 to be inspected can be driven under a uniform load condition.

1 is a block circuit diagram of a semiconductor laser inspection apparatus according to an embodiment of the present invention. It is a block diagram which shows the reference voltage output part of the inspection apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser 10 ... Inspection apparatus 20 ... Laser inspection part 22 ... Drive circuit 23 ... Neutral filter 24 ... Light receiving element 26 ... Current-voltage conversion circuit 28 ... Differential amplifier 52 ... 1st DA converter 54 ... 2nd DA converter 56 ... Adder circuit 80 ... control unit

Claims (2)

  A plurality of n laser inspection units provided corresponding to each of the plurality of n semiconductor lasers, and a reference signal generation unit that sets a reference signal for each of the plurality of n laser inspection units,
  The reference signal generation unit inputs a reference signal set for each of the plurality of n laser inspection units to the corresponding laser inspection unit,
  Inspection of a semiconductor laser in which the plurality of n laser inspection units drive APC of the corresponding semiconductor laser based on the reference signal input from the reference signal generation unit and inspect the operating characteristics of the corresponding semiconductor laser In the device
  The reference signal generator includes an a-bit first DA converter, a plurality of n b-bit (a> b) second DA converters provided corresponding to the plurality of n laser inspection units, and the plurality a plurality of n adder circuits provided corresponding to each of the n laser inspection units,
  The first DA converter inputs a common voltage to the plurality of n adder circuits in common,
  The plurality of n second DA converters input calibration voltages to the corresponding adding circuits,
  The plurality of n adder circuits add the common voltage input from the first DA converter and the calibration voltage input from the corresponding second DA converter, and each of the n n laser inspection units. Set the reference signal to
  A semiconductor laser inspection apparatus.   2. The semiconductor laser inspection apparatus according to claim 1, wherein the first DA converter is 12 bits or more and the second DA converter is 8 bits or less.

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