JP4714177B2 - Jitter reduction apparatus and test apparatus - Google Patents

Description

  The present invention relates to a jitter reduction apparatus and a test apparatus. More specifically, the present invention relates to a jitter reducing device that reduces jitter generated in an optical signal when a pulsed optical signal is generated, and a test apparatus including the jitter reducing device.

  There is a test apparatus for processing a test signal in a device under test such as a semiconductor integrated circuit and evaluating its function and performance. Many of the devices under test are semiconductor circuits or the like that handle electrical signals, but recently, devices that process optical signals are also being tested.

  Patent Document 1 below describes that a test optical signal generated by a test optical signal generator is supplied to a test head through an optical fiber. Thereby, the connection to the test head is simplified, and a test signal with little deterioration can be transmitted. However, in the apparatus described in Patent Document 1, the test signal input to the device under test to be tested is an electrical signal converted from an optical signal in the test head.

Further, Patent Document 2 below describes an optical signal generator that generates a stable test optical signal by combining two intensity-modulated optical signals. Thereby, it is possible to evaluate jitter tolerance in a device under test that processes an optical signal.
JP 2000-249746 A JP 2006-041681 A

  A test signal used for testing a device under test that handles an optical signal is once generated as an electrical signal by an electronic circuit of a test apparatus, and then converted into an optical signal and applied to the device under test. However, since there are limitations on the transmission bands of circuits, elements, transmission paths, connectors, and the like that form the test apparatus, jitter may occur in the test signal even within the test apparatus. For this reason, in the test for the device under test for processing the optical signal, the jitter generated in the test apparatus and the jitter generated in the device under test are superimposed, which hinders the improvement of the test accuracy.

  In order to solve the above problems, as a first embodiment of the present invention, in the signal light having a specific wavelength generated by the optical signal generation unit, a control optical signal having a wavelength corresponding to the jitter included in the optical signal is generated. Wavelength conversion including a control light signal generation unit and a wavelength conversion element that outputs a wavelength conversion light that is input by superimposing the signal light and the control light signal and converted to a conversion wavelength different from a specific wavelength according to the wavelength of the control light signal And a delay generation unit that has a plurality of optical paths having different path lengths and outputs wavelength-converted light through different individual paths according to the respective wavelengths. Among them, there is a jitter reduction device that injects signal light into an optical path that generates a delay amount that cancels jitter in each pulse included in the signal light, and reduces and outputs the jitter included in the signal light for each pulse. It is subjected.

  Further, as a second aspect of the present invention, a control light signal generator that generates a control light signal having a wavelength corresponding to jitter included in the signal light in the signal light having a specific wavelength generated by the optical signal generator; A wavelength conversion unit including a wavelength conversion element that outputs a wavelength-converted light that is input by superimposing the signal light and the control light signal, and converted to a conversion wavelength different from the specific wavelength according to the wavelength of the control light signal, And a delay generation unit that outputs wavelength-converted light via different individual paths according to the respective wavelengths, and the delay generation unit includes signal light in the optical path. A jitter reduction device that injects signal light into an optical path that generates a delay amount that cancels jitter in each pulse to be output, reduces the jitter contained in the signal light for each pulse, and outputs it as an optical test signal The test apparatus is provided.

  The above summary of the invention does not enumerate all necessary features of the present invention. Also, a sub-combination of these feature groups can be an invention.

  Hereinafter, the present invention will be described through embodiments of the invention. However, the following embodiments do not limit the invention according to the scope of claims, and all combinations of features described in the embodiments are included. It is not necessarily essential for the solution of the invention.

  FIG. 1 is a diagram showing the overall structure of the test apparatus 100. As shown in the figure, the semiconductor test apparatus 100 includes a handler 170, a test head 180, and a host apparatus 150.

  The handler 170 has a function of physically operating the device under test 130 to be tested. This automates the work of sequentially supplying a number of devices under test that can be processed by the semiconductor test apparatus 100 from a large number of devices under test. In some cases, after the test, a function of separating and storing the device under test 130 according to the test result may be provided.

  The test head 180 includes a performance board 160 serving as an interface according to the specifications of the device under test 130, and forms a signal transmission path between the test apparatus 100 and the device under test 130. The test head 180 accommodates a plurality of pin electronics boards 182 (see FIG. 2) and supplies test signals to the device under test 130 via the performance board 160.

  The host device 150 is connected to the handler 170 and the test head 180 via the connection cable 140. As a result, the overall operation of the test apparatus 100 is controlled, and the control signal and the data signal are supplied to the handler 170 and the test head 180 to execute the test of the device under test 130. The connection cable 140 may accommodate an optical fiber cable for transmitting an optical signal in addition to a metal cable for transmitting an electrical signal.

  FIG. 2 is a diagram schematically showing the internal structure of the test head 180 in the semiconductor test apparatus 100. As shown in the figure, a performance board 160 is mounted on the top of the test head 180. A plurality of pin electronics boards 182 are accommodated in the test head 180.

  The performance board 160 includes a socket 162 on which the device under test 130 can be mounted on the upper surface, and a connector 164 used for connecting the performance board 160 to any one of the pin electronics boards 182 on the lower surface. The connector 164 is electrically connected to the connector 184 of the pin electronics board 182 via a collective cable 168 having connectors at both ends. The device under test 130 and the pin electronics board 182 can also input and output optical signals to each other via the optical fiber cable 166.

  The pin electronics board 182 generates an optical test signal and sends it to the device under test 130. The pin electronics board 182 receives the optical test signal output after the device under test 130 processes the test operation and receives the optical test signal of the device under test 130. Each includes an optical comparator unit 120 for evaluating the operation. The optical driver unit 110 includes a pattern generator 112 that generates a signal pattern of a test signal, and an electro-optical conversion unit 116 that converts the signal pattern supplied from the pattern generator 112 via an amplifier 114 into an optical signal. The optical test signal output from the electro-optical conversion unit 116 is supplied to the device under test 130 via a jitter reduction unit 200 described later.

  On the other hand, the optical comparator section 120 receives the signal output from the photoelectric conversion section 122 that converts the received optical test signal into an electric signal and the photoelectric conversion section 122 via the amplifier 124, and is processed by the device under test 130. And a digital signal capturing unit 126 for extracting a signal pattern from the received signal. Thereby, the function, performance, characteristics, etc. of the device under test 130 mounted on the performance board 160 can be evaluated.

  When testing a device under test 130 having different specifications, the same test head 180 can be used by replacing the performance board 160. Further, the function of the existing test head 180 can be changed or added by replacing or adding the pin electronics board 182.

  However, in the test apparatus 100 as described above, the elements, transmission paths, connectors, and the like that form the optical driver unit 110 are limited in bandwidth. In addition, each element and transmission line has parasitic capacitance or parasitic reactance. For these reasons, jitter is inevitably generated in the optical test signal generated by the optical driver unit 110. Further, jitter that depends on the output signal pattern by the pattern generator 112 is also generated in the optical test signal.

  As described above, jitter generated in the test apparatus 100 itself is also superimposed on the signal light 21 output from the optical driver unit 110. For this reason, the jitter generated in the optical driver 110 and the jitter generated in the device under test 130 are superimposed on the optical test signal output from the device under test 130, and it is difficult to distinguish them. However, the test head 180 illustrated in FIG. 2 includes a jitter reduction unit 200 that reduces jitter generated in the optical driver unit 110.

  FIG. 3 is a block diagram schematically showing the structure of the jitter reduction unit 200 by the signal path 101 of the test signal related to one pin electronics board 182. As shown in FIG. In each of the following drawings, a hatched signal line indicates a signal line that transmits an optical signal.

  As shown in the figure, the jitter reduction unit 200 receives a control signal generation unit 210 that receives a pattern signal generated by the optical driver unit 110 and generates a control signal, and a signal light 21 generated by the optical driver unit 110. A wavelength conversion unit 220 that converts the wavelength and a delay generator 230 that generates a delay in the signal light 21 so as to cancel jitter by an operation described later are provided. The output of the delay generator 230 is supplied to the device under test 130 as the output light 24 of the jitter reduction unit 200. The optical test signal processed in the device under test 130 is received by the optical comparator unit 120. The operations of the optical driver unit 110 and the optical comparator unit 120 are as described above. Thus, the optical comparator unit 120 can detect the jitter generated in the device under test 130.

  FIG. 4 is a block diagram illustrating the structure of the jitter reduction unit 200 in more detail. As shown in the figure, the jitter reduction unit 200 is formed by sequentially connecting a control signal generation unit 210, a wavelength conversion unit 220, and a delay generation unit 230.

  As described above, the control signal generator 210 receives the pattern signal, which is an electrical signal generated by the pattern generator 112, and outputs the control optical signal 22, which is an optical signal corresponding thereto, via the optical fiber 202. Thereafter, the wavelength conversion unit 220 and the delay generation unit 230 handle the optical signal consistently.

  The wavelength conversion unit 220 includes an optical coupler 222 and a wavelength conversion element 224 connected in series. The optical coupler 222 receives the signal light 21 output from the optical driver unit 110 through the optical fiber 201 together with the control optical signal 22 output from the control signal generation unit 210, and combines and outputs them. The wavelength conversion element 224 will be described later. The delay generation unit 230 includes an optical demultiplexer 240 and an optical delay line 250.

  The optical demultiplexer 240 includes a channel waveguide 242 that branches the wavelength-converted light 23 received via the optical fiber 203 into different optical waveguides 241, 243, and 245 according to the wavelength. Further, the branched propagating light is individually coupled to the optical waveguides 251, 253, and 255 of the optical delay line 250 coupled via the channel waveguide 244. Since the optical waveguides 251, 253, and 255 of the optical delay line 250 have different optical path lengths, the propagation time of the propagation light is also different.

  With such a structure, the wavelength-converted light 23 incident on the delay generation unit 230 has a delay with a different delay amount depending on the wavelength. Further, the propagating light propagated through the optical waveguides 251, 253, and 255 is guided to one optical fiber 204 by the optical multiplexer 254. The optical fiber 204 is also an output port of the jitter reduction unit 200, and the output light 24 is output toward the device under test 130 via the optical fiber 204.

FIG. 5 is a perspective view showing a structure of a PPLN (Periodically Poled LiNbO ₃ : periodic polarized lithium niobate) optical waveguide that can be used as the wavelength conversion element 224. As shown in the figure, the PPLN optical waveguide includes a LiNbO ₃ substrate 223 that is a nonlinear optical crystal whose polarization is inverted at a very short period, and an optical waveguide formed on the LiNbO ₃ substrate 223 so as to cross the polarization distribution that is inverted. 225. When two laser beams having different wavelengths are injected into the wavelength conversion element 224 having such a structure, difference frequency light between one second harmonic of the laser beams and the other is emitted.

FIG. 6 is a diagram for explaining the operation of the wavelength conversion element 224 having the PPLN optical waveguide as described above. As shown in the figure, the wavelength conversion element 224 is injected with _one of the control light signals 22 having different wavelengths ε ₁ , ε ₂ , and ε ₃ and the signal light 21 having the specific wavelength λ ₁ . Here, when the light intensity of the signal light 21 is sufficiently high, the second harmonic of the signal light 21 is generated, and the wavelengths λ ₂ and λ ₂₂ corresponding to the difference frequency between the control light signal 22 and the second harmonic are generated. , Λ _23, and converted light 23 is emitted. Therefore, by selecting the wavelengths ε ₁ , ε ₂ , and ε ₃ of the control light 22 via the control signal generator 210, the wavelength of the converted light 23 is converted to any of the wavelengths λ ₂ , λ ₂₂ , and λ _23. be able to.

LiNbO ₃ is known to be damaged by visible light at room temperature. Therefore, it is preferable to add magnesium oxide or the like to increase the stability of the material. In addition to LiNbO ₃ , examples of the material of the wavelength conversion element 224 include LiB ₃ O ₅ , BaB ₂ O ₄ , KTiOPO _{4, and the} like. Further, in the wavelength conversion element as described above, the signal light 21 and the control light 22 which are linearly polarized light in the TM mode, or the TM included in the signal light 21 and the control light signal 22 are to be converted. It is the linear polarization component of the mode.

  Furthermore, the wavelength conversion element 224 can also be formed using a nonlinear optical element such as a semiconductor optical amplifier SOA (Semiconductor Optical Amplifier). A nonlinear optical fiber, an electroabsorption modulator, or the like can also be used.

  FIG. 7 is a block diagram illustrating an example of the internal structure 300 of the control signal generation unit 210. As shown in the figure, the control signal generator 210 converts the control electric signal 11 described above into an optical signal and outputs it. That is, the control signal generator 210 includes a control light source element 214 that always emits light and an optical switch 216 that can couple the output of the control light source element 214 to the optical fiber 202. Therefore, by driving the optical switch 216 with the control electrical signal 11 described above, the fact that the occurrence of jitter has been detected is output as the control optical signal 22.

FIG. 8 is a diagram showing the timing of the signal light 21, the control light signal 22, the wavelength conversion light 23, and the output light 24 in the jitter reduction unit 200 including the control signal generation unit 210 having the internal structure 300 described above. is there. As shown in the figure, the signal light 21 having the specific wavelength λ ₁ and the control light signal 22 having the specific wavelength ε ₁ are input to the wavelength conversion element 224. However, some of the pulses X of the signal light 21 are delayed from the original timing indicated by the dotted line.

This for the control light signal 22 has a constant pulse width encompasses a portion of the pulses of the signal light 21, a repetitive pulse signal having a wavelength epsilon _1. However, the control signal generator 210 does not generate a pulse at the same timing as the delayed pulse X based on the signal pattern of the signal light 21 generated by the pattern generator 112.

The signal light 21 and the control light signal 22 are combined by the optical coupler 222 and input to the wavelength conversion element 224. Therefore, among the pulses of the signal light 21, pulses other than the delayed pulse X are combined with the control light signal 22, converted in wavelength by the wavelength conversion element 224, and output as wavelength converted light 23 having the wavelength λ _2. The On the other hand, since for the pulse X the timing was delayed not generated pulse of the control light signal 22, the signal light 21 is entered solely in the wavelength conversion element 224, while the initial wavelength lambda _1, the wavelength converted light 23 is output. Thus, the pulse timing of the wavelength conversion light 23 is not changed from the signal light 21, a pulse except the delayed pulse X timing is converted to the wavelength lambda _2. In this case, the wavelength of the pulse X is not converted, but for convenience, it is also described as wavelength converted light 23.

As described above, when the wavelength-converted light 23 including the pulses of the wavelengths λ ₁ and λ ₂ is input to the delay generation unit 230, the optical demultiplexer 240 individually transmits the optical waveguides 241, 243, and 245 for each wavelength. Propagated to. In this embodiment, for example, an optical signal with a wavelength λ ₁ is propagated to the optical waveguide 245, and an optical signal with a wavelength λ ₂ is propagated to the optical waveguide 243.

The optical waveguides 243 and 245 of the optical demultiplexer 240 are individually connected to the optical waveguides 253 and 255 of the optical delay line 250. Accordingly, the optical delay line 250, the wavelength lambda ₁ of the signal to the optical waveguide 255, the signal of wavelength lambda ₂ is propagated respectively to the optical waveguide 253. Here, the optical waveguides 253 and 255 in the optical delay line 250 have different path lengths, and the optical waveguide 255 has a longer path length. For this reason, the optical signal having the wavelength λ ₂ propagating through the optical waveguide 255 reaches the optical multiplexer 254 later than the optical signal having the wavelength λ ₁ propagating through the optical waveguide 253. As a result, all the timings of the pulses of the optical signal are aligned with the timing of the delayed pulse X, so that the jitter is effectively eliminated.

  In this way, the jitter reduction unit 200 including the control signal generation unit 210, the wavelength conversion unit 220, and the delay generation unit 230 can reduce the pattern-dependent jitter included in the signal light 21, so that the test apparatus shown in FIG. In 100, it is possible to execute a highly accurate test that eliminates the influence of the pattern-dependent jitter generated in the optical driver unit 110.

  When only the signal light 21 is input to the wavelength conversion unit 220 provided with the wavelength conversion element 224, the signal light 21 is output to the optical fiber 203 while maintaining the original waveform. On the other hand, the wavelength-converted signal light 21 does not change the timing, but the signal amplitude becomes small. Therefore, it is preferable that the wavelength conversion element 224 is always operated to align the pulse height of the wavelength converted light 23. Therefore, it is preferable that the control signal generator 210 can generate a plurality of control optical signals 22 having different wavelengths.

FIG. 9 is a block diagram showing another internal structure 301 of the control signal generator 210. As shown in the figure, the control signal generator 210 includes a plurality of control light source elements 214 that always emit light at mutually different wavelengths ε _1, ε _{2, and} ε ₃ . Each of the control light source elements 214 is coupled to the optical multiplexer 218 via the optical switch 216, and the output of the optical multiplexer 218 is coupled to the optical fiber 202. One of the optical switches 216 is selectively turned on by the control electrical signal 11, and the light generated by the control light source element 214 corresponding to the turned on optical switch 216 is output to the optical fiber 202 as the control light signal 22. The

As described above, the control signal generator 210 that generates the control light signal 22 having different wavelengths has the control light signal 214 and the control light signal 22 that always emit light at different wavelengths ε _1, ε _{2, and} ε _3. When it is to be generated, it can be formed using an optical switch 216 that couples the emitted light of any one of the control light source elements 214 to the optical fiber 202 as the control optical signal 22. In addition, since the wavelength conversion light 23 having a plurality of different wavelengths can be generated by the control light signal 22, the optical waveguides 241, 243, 245, 251, and 253 of the optical demultiplexer 240 and the optical delay line 250 can be generated. By increasing the number of H.255, the delay amount can be changed variously.

  As the control light source element 214, a semiconductor laser or the like can be used. In the above-described embodiment, the structure using the optical switch 216 is exemplified. However, a structure in which the control light signal 214 is directly driven by the control electrical signal 11 to generate the control light signal 22 may be employed. In this case, since the optical switch 216 is not used, the number of parts can be reduced.

  FIG. 10 is a block diagram for explaining still another internal structure 302 of the control signal generator 210. As shown in the figure, the internal structure 302 is similar to the internal structure 300 shown in FIG. However, in the internal structure 302, the control light source element 214 is replaced with a wavelength tunable semiconductor laser 215. Thereby, the control optical signal 22 having an arbitrary wavelength can be generated by a circuit having a simple structure.

  FIG. 11 is a block diagram illustrating another internal structure 303 of the control signal generator 210 viewed from another aspect. As shown in the figure, the control signal generator 210 has a pattern jitter table 212. The pattern jitter table 212 includes data that associates a signal pattern with jitter generated according to the signal pattern. Therefore, when the control signal generation unit 210 that receives the pattern signal detects a specific signal pattern in which pattern-dependent jitter corresponding to the pattern is generated, the control signal generation unit 210 generates the control electric signal 11 that notifies the fact. As a result, the control signal generator 210 detects the occurrence of pattern dependent jitter corresponding to the signal pattern generated by the pattern generator 112.

FIG. 12 is a diagram showing a comparison of timings of the signal light 21, the control light signal 22, the wavelength conversion light 23, and the output light 24 in the jitter reduction unit 200 having any one of the internal structures 301, 302, and 303 as described above. It is. As shown in the figure, as shown in the figure, the wavelength conversion element 224 receives the signal light 21 having the specific wavelength λ ₁ and the control light signal 22 having the specific wavelength ε ₁ . However, some of the pulses X of the signal light 21 are delayed from the original timing indicated by the dotted line. In addition, other pulses Y that have a small delay amount but are delayed from the original timing are also included.

This for the control light signal 22 has a constant pulse width including the pulse of the signal light 21, a repetitive pulse signal having a wavelength epsilon _1. However, the control signal generator 210 generates pulses with different wavelengths ε ₂ and ε ₃ for the delayed pulse X and pulse Y, respectively, based on the signal pattern of the signal light 21 generated by the pattern generator 112. .

The signal light 21 and the control light signal 22 are combined by the optical coupler 222 and input to the wavelength conversion element 224. Therefore, of the wavelength converted light 23 output from the wavelength conversion element 224, the pulse X of the signal light 21 is combined with the control light signal 22 and then wavelength-converted by the wavelength conversion element 224. Here, the pulse in which the timing delay has not occurred in the signal light 21 is converted by the control light signal 22 having the wavelength ε ₁ to become the wavelength converted light 23 having the wavelength λ ₂ . Further, the pulses X and Y in which the timing delay has occurred in the signal light 21 are wavelength-converted by the control light signal 22 having the wavelength ε ₂ or ε ₃ and output as the wavelength-converted light 23 having the wavelength λ ₂₂ or λ _23. The

As described above, when the wavelength-converted light 23 including pulses having wavelengths λ ₂ , λ ₂₂ , and λ ₂₃ is input to the delay generation unit 230, the individual optical waveguides 241, 243, 245 individually propagated. In this embodiment, for example, an optical signal having a wavelength λ ₂ is propagated to the optical waveguide 245, an optical signal having a wavelength λ ₂₂ is propagated to the optical waveguide 243, and an optical signal having a wavelength λ ₂₃ is propagated to the optical waveguide 245.

The optical waveguides 241, 243 and 245 of the optical demultiplexer 240 are individually connected to the optical waveguides 251, 253 and 255 of the optical delay line 250. Therefore, in the optical delay line 250, the signal of wavelength λ ₂ is propagated to the optical waveguide 255, the signal of wavelength λ ₂₂ is propagated to the optical waveguide 253, and the signal of wavelength λ ₂₃ is propagated to the optical waveguide 251. Here, the optical waveguides 251, 253, and 255 in the optical delay line 250 have different path lengths, and the optical waveguide 255 has a longer path length. Therefore, the optical signal having the wavelength λ ₂₂ propagating through the optical waveguide 253 arrives at the optical multiplexer 254 later than the optical signal having the wavelength λ ₂₃ propagating through the optical waveguide 251. Further, the optical signal having the wavelength λ ₂ propagating through the optical waveguide 255 reaches the optical multiplexer 254 with a delay later than the optical signal having the wavelength λ ₂₂ propagating through the optical waveguide 253. As a result, all the timings of the pulses of the optical signal are aligned with the timing of the delayed pulse X, so that the jitter is effectively eliminated. In the optical delay line 250, if the difference in path length between the optical waveguides 251, 253, and 255 is several hundred μm, the jitter can be effectively reduced.

  FIG. 13 is a block diagram schematically illustrating the structure of the jitter reduction unit 200 according to another embodiment using another signal path 600 of the test signal according to the pin electronics board 182. In FIG. Note that the same reference numerals are assigned to the same components as those in FIG. 3 and redundant description is omitted.

  As shown in the figure, the jitter reduction unit 200 includes a control signal generation unit 210, a wavelength conversion unit 220, and a delay generation unit 230, similarly to the test apparatus 100 shown in FIG. However, the control signal generation unit 210 has a unique feature in that the optical driver unit 110 receives the output of the amplifier 114 as a drive signal.

  FIG. 14 is a diagram showing an internal structure 304 of the control signal generation unit 210 in the jitter reduction unit 200 shown in FIG. As shown in the figure, the control signal generator 210 includes an integrator 211, and receives the output of the amplifier 114 from the integrator 211. Thereby, the control light signal 22 corresponding to the jitter can be generated without using the pattern jitter table 212.

  That is, it is known that when a laser diode such as VCSEL is used as the light source element of the optical driver unit 110, a light emission delay occurs due to accumulation of carriers. For this reason, jitter increases in a signal input subsequent to a signal pattern in which the extinction time becomes long. Therefore, the drive signal of the optical driver unit 110 can be monitored by the integrator 211 to predict the increase in jitter and generate the control light signal 22.

  As described above, the control signal generation unit 210 can generate the control optical signal 22 based on the accumulated amount of carriers in the light emitting element of the optical driver unit 110 that outputs the optical signal. As a result, the control light signal 22 can be generated without preparing the pattern jitter table 212 in advance, so that even if the signal pattern of the test signal is changed, the control signal generator 210 can be effectively used without changing the specifications. Jitter can be reduced.

  FIG. 15 is a diagram schematically illustrating the structure of a jitter reduction unit 401 according to another embodiment. As shown in the figure, the jitter reduction unit 401 also includes a control signal generation unit 210, a wavelength conversion unit 220, and a delay generation unit 230. Here, the structure of the control signal generation unit 210 and the wavelength conversion unit 220 is the same as that of the jitter reduction unit 200 shown in FIG.

  In contrast, the delay generation unit 230 includes an optical circulator 410 that receives the wavelength-converted light 23, an optical fiber grating 420 connected to the optical circulator 410, and an optical fiber 204 as an output port. The optical circulator 410 has a function of sequentially outputting input optical signals from adjacent ports. Therefore, in this embodiment, the wavelength converted light 23 input from the optical fiber 203 is input to the optical fiber grating 420, and the optical signal input from the optical fiber grating 420 to the optical circulator 410 is output to the optical fiber 204. .

  The optical fiber grating 420 has a plurality of fiber Bragg gratings (hereinafter referred to as “FBGs”) 422, 424, and 426 formed at different positions along the light propagation direction. Each of the FBGs 422, 424, and 426 is formed by periodically changing the refractive index along the light propagation direction, and has high efficiency for light in a narrow band centered on a specific wavelength (called a Bragg wavelength). Reflect on. Accordingly, since the FBGs 422, 424, and 426 have different Bragg wavelengths, the optical signal input to the optical fiber grating 420 can be returned to the incident end with a different path length for each wavelength. The optical signal returned to the optical circulator 410 again from the incident end of the optical fiber grating 420 is output as output light 24 from the optical fiber 204 serving as an output port.

Therefore, in the optical fiber grating 420, when the reflected wavelength of the FBG 426 is set to λ ₂ , the reflected wavelength of _the FBG 424 is set to λ _{22, and} the reflected wavelength of _the FBG 422 is set to λ ₂₃ , respectively, Jitter can be effectively eliminated by outputting a pulse with a large delay amount to the optical fiber 204 with a small path length.

  As the optical fiber grating 420, a chirped FBG in which the pitch of the FBG continuously changes in the axial direction can also be used. In the case of chirped FBG, the reflection position for determining the delay amount of the optical signal can be continuously changed by continuously changing the wavelength. Therefore, various timing controls can be executed by combining with the control signal generator 210 that can generate the control light signal 22 that changes continuously. Further, it is preferable to provide a filter 430 at the output from the optical circulator 410 to the optical fiber 204 to remove the control light signal 22 component included in the output light 24.

  FIG. 16 is a diagram schematically illustrating the structure of a jitter reduction unit 402 according to still another embodiment. As shown in the figure, the jitter reduction unit 402 also includes a control signal generation unit 210, a wavelength conversion unit 220, and a delay generation unit 230. The structures of the control signal generation unit 210 and the wavelength conversion unit 220 are the same as those of the jitter reduction unit 200 shown in FIG.

  On the other hand, the delay generator 230 includes an optical demultiplexer 512 formed as a bulk optical waveguide on the optical waveguide substrate 510, and a plurality of optical fibers 521, 523, 525 coupled to the optical demultiplexer 512, respectively. Is provided. The optical demultiplexer 512 has a function of separating an incident optical signal according to its wavelength. The separated optical signal for each wavelength is propagated to one of the optical fibers 521, 523, and 525. The optical fibers 521, 523, and 525 are individually coupled to one ends of optical fibers 541, 542, and 543 having different lengths. Optical signals incident from the optical fibers 541, 542, and 543 are output to one optical fiber 204.

In such a delay generation unit 230, the wavelength converted light 23 having the wavelength λ ₂ is applied to the optical fiber 543, the wavelength converted light 23 having the wavelength λ ₂₂ is applied to the optical fiber 542, and the wavelength converted light 23 having the wavelength λ ₂₃ is applied to the optical fiber 541. When the wavelength-converted light 23 shown in FIG. 11 is input by propagating each of them, it is possible to output the pulse having a larger delay amount to the optical fiber 204 with a smaller path length, thereby eliminating the jitter. In this embodiment, the delay amount of the optical signal generated in the delay generation unit 230 can be easily changed by exchanging the optical fibers 541, 542, and 543.

  As described above, the jitter reduction unit 200 according to each of the above embodiments can reduce the jitter generated in the signal light generated in the optical driver 110 at a high speed by the control optical signal 22 that is itself an optical signal. Therefore, it is possible to remove the influence of jitter generated on the test signal in the optical driver unit 110 and perform the test of the device under test 130 with high accuracy.

  As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. It will be apparent to those skilled in the art that various modifications or improvements can be added to the above-described embodiment. It is apparent from the scope of the claims that the embodiments added with such changes or improvements can be included in the technical scope of the present invention.

1 is a schematic diagram showing a structure of a test apparatus 100 according to one embodiment. 2 is a diagram schematically showing the structure of a test head 180. FIG. 2 is a block diagram schematically showing a signal path 101 in the test apparatus 100. FIG. 3 is a block diagram showing a structure of a jitter reduction unit 200. FIG. 3 is a perspective view showing a structure of a wavelength conversion element 224. FIG. 5 is a graph for explaining the operation of a wavelength conversion element 224. It is a figure which shows the internal structure 300 of the control signal generation part 210. FIG. FIG. 10 is a timing chart for explaining the operation of the jitter reduction unit 200. 5 is a block diagram illustrating another internal structure 301 of the control signal generator 210. FIG. It is a figure which shows the other internal structure 302 of the control signal generation part. FIG. 10 is a diagram showing another internal structure 303 of the control signal generator 210. FIG. 5 is a timing diagram for explaining the operation of a jitter reduction unit 200 including a control signal generation unit 210 having internal structures 301, 302, and 303. 2 is a diagram illustrating a signal path 600 of the entire test apparatus 100 including a jitter reduction unit 200. FIG. It is a figure which shows the other internal structure 304 of the control signal generation part 210. FIG. It is a figure which shows typically the structure of the jitter reduction part 401 which concerns on other embodiment. It is a figure which shows typically the structure of the jitter reduction part 402 which concerns on other embodiment.

Explanation of symbols

11 control electrical signal, 21 signal light, 22 control light signal, 23 wavelength conversion light, 24 output light, 100 test equipment, 101, 600 signal path, 110 optical driver unit, 112 pattern generator, 114, 124 amplifier, 116 electrical Optical conversion unit, 120 optical comparator unit, 122 photoelectric conversion unit, 126 digital signal capture unit, 130 device under test, 140 connection cable, 150 host device, 160 performance board, 162 socket, 164 connector, 168 collective cable, 166 light Fiber cable, 170 handler, 180 test head, 182 pin electronics board, 184 connector, 200, 401, 402 Jitter reduction unit, 201, 202, 203, 204 Optical fiber, 210 Control signal generation unit, 211 Integrator, 212 P Turn jitter table, 214 Control light source element, 215 wavelength tunable semiconductor laser, 216 optical switch, 218 optical multiplexer, 220 wavelength converter, 222 optical coupler, 223 LiNbO ₃ substrate, 224 wavelength converter, 225 optical waveguide, 230 Delay generation Part, 240, 512 optical demultiplexer, 241, 243, 245 optical waveguide, 242 channel waveguide, 250 optical delay line, 241, 243, 245, 251, 253, 255 optical waveguide, 254 optical multiplexer, 300, 301 , 302, 303, 304 Internal structure, 410 Optical circulator, 420 Optical fiber grating, 422, 424, 426 (FBG) Fiber Bragg grating, 430 Filter, 521, 523, 525, 541, 542, 543 Optical fiber

Claims (15)

It includes a pattern generator and the light emitting element, a light signal generating unit for converting the pattern signal the pattern generator is generated in the signal light is generated, with the optical signal having a specific wavelength, the optical signal generating unit A control optical signal generating unit that generates a control optical signal having a wavelength corresponding to at least one of the characteristics of the element and the transmission path, the pattern of the pattern signal, and the carrier accumulation amount of the light emitting element ;
And a wavelength conversion portion including the signal light and is input by superimposing the control light signal, the wavelength conversion element that outputs a wavelength-converted light converted into conversion wavelength different from the specific wavelength according to the wavelength of the control light signal,
A plurality of optical paths having different path lengths from each other, and a delay generator that outputs the wavelength-converted light via different individual paths according to the respective wavelengths,
In the delay generator, said one of the plurality of optical paths, characteristics of the device and the transmission path you have to the optical signal generating unit to each of the pulses included in the signal light, the carrier pattern and the light emitting element of the pattern signal A jitter reduction apparatus for injecting the signal light into an optical path in which a delay amount that cancels at least one jitter caused by the accumulated amount is generated, and reducing and outputting the jitter of the signal light for each pulse. The control light signal generating unit, according to claim 1 having a control light source device that emits light at the same wavelength as the control light signal, a control signal drive circuit for emitting the control light source device in the case to be generated the control light signal The jitter reduction apparatus described in 1. The control light signal generation unit is configured to couple a control light source element that always emits light at the same wavelength as the control light signal and externally output light of the control light source element as the control light signal when the control light signal is to be generated. jitter reducing device according to claim 1 or claim 2 and an optical switch.   4. The jitter reduction apparatus according to claim 2, wherein the control light source element is a wavelength tunable light emitting element capable of changing a light emission wavelength. 2. The jitter reduction apparatus according to claim 1 , wherein the control light signal generation unit includes a plurality of control light source elements that emit light at different wavelengths, and a control signal drive circuit that selectively emits the control light signal. The control light signal generator includes a plurality of control light source elements that always emit light at mutually different wavelengths, and, when the control light signal is to be generated, the emitted light of any of the plurality of control light source elements as the control light signal The jitter reduction apparatus according to claim 1 , further comprising an optical switch coupled to the outside. The wavelength conversion element has a periodic polarization inversion structure, and outputs the converted light having a sum frequency or a difference frequency wavelength between the specific wavelength of the input signal light and the wavelength of the control optical signal. The jitter reduction apparatus according to any one of claims 1 to 6 , comprising a PPLN (Periodically Poled LiNbO ₃ : periodic polarized lithium niobate) optical waveguide. The delay generation unit includes: an optical demultiplexer that demultiplexes an input optical signal according to a wavelength; a plurality of optical waveguides having different path lengths that individually propagate the demultiplexed optical signal; and the plurality of optical waveguides jitter reducing device according to any one of claims 1 and a optical multiplexer for multiplexing the optical signals emitted from the optical waveguide to a single optical waveguide to claim 7. The jitter reducing apparatus according to claim 8 , wherein the optical demultiplexer is an AWG optical demultiplexer, and the optical multiplexer is an AWG optical demultiplexer. The jitter reducing apparatus according to claim 8 , wherein the plurality of optical waveguides are channel waveguides having different lengths. The jitter reducing apparatus according to claim 8 , wherein the plurality of optical waveguides are optical fibers having different lengths. The delay generating unit, a jitter reducing device according to any one of claims 1 to 11 including a wavelength dispersion medium. 13. The jitter according to claim 12 , wherein the chromatic dispersion medium is an optical fiber grating having a plurality of fiber Bragg gratings that are arranged at different positions along the propagation direction of the signal light and reflect optical signals having different wavelengths. Reduction device. The delay generating unit, according to any one of claims 1 is a chirped optical fiber grating spacing along the propagation direction of the signal light has a continuously varying fiber Bragg grating to claim 11 Jitter reduction device. It includes a pattern generator and the light emitting element, a light signal generating unit for converting the pattern signal the pattern generator is generated in the signal light is generated, with the optical signal having a specific wavelength, the optical signal generating unit A control optical signal generating unit that generates a control optical signal having a wavelength corresponding to at least one of the characteristics of the element and the transmission path, the pattern of the pattern signal, and the carrier accumulation amount of the light emitting element ;
And a wavelength conversion portion including the signal light and is input by superimposing the control light signal, the wavelength conversion element that outputs a wavelength-converted light converted into conversion wavelength different from the specific wavelength according to the wavelength of the control light signal,
A plurality of optical paths having different path lengths from each other, and a delay generator that outputs the wavelength-converted light via different individual paths according to the respective wavelengths,
In the delay generator, said one of the plurality of optical paths, characteristics of the device and the transmission path you have to the optical signal generating unit to each of the pulses included in the signal light, the carrier pattern and the light emitting element of the pattern signal by injecting the signal light to the optical path delay to cancel the jitter caused by the least one accumulation occurs, the test device having a jitter reducing device and outputs the reduced pulse to pulse jitter of the signal light .

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