JP2007027154A - High peak power output optical amplifier for light source, laser apparatus, processing apparatus, and inspection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical amplifier obtaining an output signal of a high peak pulse when performing optical amplification by using an EDFA. <P>SOLUTION: A light pulse to be amplified is input into an optical encoding apparatus 1 and is converted to pseudo random light in time series. The light enters an EDFA2 to be optically amplified. The amplified light is made to enter an optical encoding apparatus 3 having reverse characteristics to those of the optical encoding apparatus 1 and is decoded into a light pulse. By converting the amplified light pulse to the pseudo random light in time series, light having low peak and long continuation time is yielded, so that a peak of the light output from the optical amplifier is increased without increasing the peak of the light output from the EDFA2. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a high peak power output optical amplifier for a light source, a laser device, a processing device, and an inspection device.

  Some processing devices and inspection devices that use laser light for processing and inspection amplify the laser light emitted from the laser light source by an amplifier (EDFA) using an optical fiber, and convert the wavelength as necessary. There is something to use. An example of such an apparatus is described in, for example, WO 2004/086121 A1 (Patent Document 1).

WO2004 / 086121 A1

  However, in the EDFA, when the peak power of the amplified optical pulse becomes strong, nonlinear effects such as self-phase modulation and four-wave mixing appear, so the peak power of the amplified optical pulse cannot be increased beyond a certain level. There is a problem. In order to cope with this problem, a method has been proposed in which the peak power is lowered by chromatic dispersion of the input pulse, and color synthesis is performed after amplification by the EDFA, thereby obtaining an output pulse having a high peak power.

  However, with this method, when the pulse to be amplified is not in a Fourier limit state, the pulse does not necessarily spread and the peak power before amplification does not necessarily decrease. Furthermore, this method is not very effective when the wavelength band of the original pulse is narrow. In addition, if the spectral distribution of the original pulse changes, the chirp state must be changed accordingly.

  The present invention has been made in view of such circumstances, and when performing optical amplification using an EDFA, an optical amplifier capable of obtaining an output signal having a high peak pulse, and a laser device using the optical amplifier, It is an object to provide a processing apparatus and an inspection apparatus.

  A first means for solving the above problem is an optical amplifier that amplifies an optical pulse by using an EDFA, and converts the input optical pulse into pseudo-random light in time series for each pulse. An optical encoding device, an EDFA that amplifies pseudo-random light in time series, and an optical decoding device that decodes the amplified light and has characteristics opposite to those of the optical encoding device. A high peak power output optical amplifier for a light source.

  Here, the optical encoding device is a device in which the input light is pseudo-random in time series (having periodicity when viewed in a long period, but can be regarded as random within one period when viewed in a long period. For example, a random FBG (fine Bragg grating element) in which a random diffraction grating is formed in an optical fiber is well known. Thereby, the input optical pulse is converted into pseudo-random light having a low peak and a long time. Since this light is amplified by EDFA, the peak of the light output from EDFA becomes low. That is, the power of the input optical pulse can be increased to increase the peak, and the amplification degree of the EDFA can be increased.

  The light amplified by the EDFA is input to an optical decoding device having characteristics opposite to those of the optical encoding device. This optical decoding device is also composed of, for example, a random FBG, and is designed to output light corresponding to the input of the optical encoding device when light having a waveform corresponding to the output of the optical encoding device is input. Therefore, according to the present means, since non-linearity of the peak due to EDFA can be avoided, high peak (for example, 30 KW or more) pulsed light, which has been difficult with conventional EDFA, can be obtained as an output. Also, noise components generated during amplification by the EDFA are reduced in the optical decoding device, so that the optical amplifier is resistant to noise. Furthermore, since it does not depend on the original pulse signal waveform or frequency range, it is not necessary to change the apparatus even if the pulse width or wavelength band is changed.

  A second means for solving the above-mentioned problem is an optical amplifier that amplifies an optical pulse using an EDFA, and the input optical pulse is converted into pseudo-random light that is different in time series for each pulse. Corresponding to each of the plurality of types of optical decoding devices, the EDFA for amplifying pseudo-random light in time series, and the plurality of types of optical decoding devices for decoding the amplified light, respectively, A plurality of types of optical decoding devices having characteristics opposite to those of the optical encoding device and a circulator, and all of the optical decoding devices are reflection type optical decoding devices, and each of the reflection type optical decoding devices A high peak power output optical amplifier for a light source, wherein each of the circulators is provided on the input side.

  In this means, a plurality of types of pseudo-random light are generated by using a plurality of types of optical encoding devices having different performances, and each pseudo-random light is synthesized by a coupler and then amplified by FDFA. The amplified light passes through the first circulator, is decoded by the first reflective optical decoding device, is reflected, and is taken out to the output side through the first circulator. The remaining light that has not been decoded by the first reflective optical decoding device passes through the first reflective optical decoding device, passes through the second circulator, and is decoded by the second reflective optical decoding device. And reflected and taken out to the output side through the second circulator. Hereinafter, such light decoding and extraction are performed by the number of reflection type optical decoding devices.

  A third means for solving the above-described problem is an optical amplifier that amplifies an optical pulse using an EDFA, and the input optical pulse is converted into pseudo-random light that is different in time series for each pulse. Corresponding to each of the plurality of types of optical decoding devices, the EDFA for amplifying pseudo-random light in time series, and the plurality of types of optical decoding devices for decoding the amplified light, respectively, A plurality of optical decoding devices having characteristics opposite to those of the optical encoding device, and a circulator. The optical decoding device is a reflection type optical decoding device except for one, and one is a transmission type optical decoding device. The reflection type optical decoding device is provided in the preceding stage, the circulator is provided on the input side to each reflection type optical decoding device, and the transmission type optical decoding is provided via the circulator in the final stage. Equipment It is a light source high peak power output optical amplifier for which said being.

  In this means, only the decoding device connected to the final stage is a transmissive type, and the essential operation is the same as the second means. Therefore, the same effect as the second means can be achieved.

  A fourth means for solving the above problems includes a laser oscillation unit that outputs an optical pulse, a high peak power output optical amplifier for a light source of any one of the first to third means, and the amplified signal. And a wavelength converter that converts the wavelength of the optical pulse.

  In this means, wavelength conversion of light having a large peak wavelength can be performed.

  A fifth means for solving the above problem is a processing apparatus having the laser device of the fourth means.

  In this means, processing can be performed using light having a large peak wavelength.

  A sixth means for solving the problem is an inspection apparatus having the laser device of the fourth means.

  In this means, the inspection can be performed using light having a large peak wavelength.

  According to the present invention, an optical amplifier capable of obtaining an output signal having a high peak pulse when optical amplification is performed using an EDFA, and a laser apparatus, a processing apparatus, and an inspection apparatus using the optical amplifier are provided. be able to.

Hereinafter, an example of an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an outline of the configuration of the optical amplifier according to the first embodiment of the present invention. The amplified optical pulse is input to the optical encoding device 1 and converted into pseudo-random light in time series. As described above, a random FBG (Fine Bragg Grating Element) can be used as the optical encoding device 1, which is also known as SSFBG (Superstructured Fiber Bragg Grating). For example, Journal of Lightwave Technology Vol.19, No.9 (September 2001) is described in detail as `` A Comparative Study of the Performance of Seven and 63-Chip Optical Code-Division Multiple-Access Encoders and Decorders Based on Superstructured Fiber Bragg Grating '' . Also on the web
There is also a description in http://www.khn-openlab.jp/bunkakai-gw/kokino-net/et_al_pj/files/et_al_oshiba.pdf. By giving a random refractive index change in the length direction of the optical fiber, the pulsed light can be changed to pseudo-random light, which is a well-known one mainly used in the field of multiplexed optical communication It is.

  This light enters the EDFA 2 and is optically amplified. The optically amplified light is input to an optical decoding device 3 having characteristics opposite to those of the optical encoding device 1 and is decoded into optical pulses. It is described in the Journal of Lightwave Technology that the optical decoding device 3 can also be constituted by a random FBG and can use the SSFBG. That is, for example, when an SSFBG having the same refractive index pattern as that of the SSFBG used as the optical encoding device 1 is used and the input / output direction of light is reversed as compared with the case where the SSFBG is used as the optical encoding device 1, the optical code It is possible to decode the pseudo-random light generated by the converting apparatus 1 into the original pulse waveform shape.

  By converting the amplified light pulse into pseudo-random light in time series, it is possible to obtain light with a low peak and a long duration, so that this peak can be increased without increasing the peak of light output from the EDFA 2. The peak of light output from the optical amplifier can be increased.

  In FIG. 1, a transmission type is used as the optical encoding device 1. That is, the output of the optical encoding device 1 is obtained as light transmitted through the optical encoding device 1. On the other hand, as an optical encoding device, there is a reflection type that extracts output light as reflected light, and such a device can also be used. An example is shown in FIG. In FIG. 2, an optical pulse to be amplified passes through a circulator 4 and is input to an optical encoding device 5 (reflection type). Then, pseudo-random light in time series is obtained as a reflected signal from the optical encoding device 5. This light is extracted through the circulator 4 and input to the EDFA 2 shown in FIG. If the configuration of the subsequent apparatus is the same as that shown in FIG. 1, the same effects as those of the apparatus shown in FIG. 1 can be obtained.

  Similarly, as an optical decoding device, there is a reflection type that extracts output light as reflected light, and such a device can also be used. An example is shown in FIG. In FIG. 3, the pseudo-random light amplified by the EDFA passes through the circulator 6 and is input to the optical decoding device 7 (reflection type). Then, the decoded pulse light is obtained as a reflected signal from the optical decoding device 7. This light is extracted through the circulator 6.

  FIG. 4 is a diagram showing an outline of the configuration of the optical amplifier according to the second embodiment of the present invention. The optical pulse to be amplified is input to the splitter 11 and divided into three. The divided first light is input to the first optical encoding device 12A, and the second light is input to the second optical encoding device 12B. The third light is input to the third optical encoding device 12C. The same optical encoders 12A, 12B, and 12C as those shown in FIGS. 1 and 2 can be used. The optical encoding devices 12A, 12B, and 12C have different characteristics, and output different pseudo-random light when the same optical pulse is input. These lights are combined into one by the coupler 13 and amplified by the EDFA 14. The amplified light passes through the circulator 15 and is input to the first optical decoding device 16A. The optical decoding device 16A has a reverse characteristic to that of the optical encoding device 12A, and is a reflective optical decoding device. Therefore, the pseudo-random light formed by the optical encoding device 12A is decoded and reflected by the optical decoding device 16A, and is extracted through the circulator 15.

  The remaining light passes through the circulator 17 and is input to the second optical decoding device 16B. The optical decoding device 16B has a reverse characteristic to that of the optical encoding device 12B, and is a reflective optical decoding device. Therefore, the pseudo-random light formed by the optical encoding device 12B is decoded and reflected by the optical decoding device 16B, and is extracted through the circulator 17.

  The remaining light is input to the third optical decoding device 16C. The optical decoding device 16C has a reverse characteristic to the optical encoding device 12C, and is a transmission type optical decoding device. Therefore, the pseudo-random light formed by the optical encoding device 12C is decoded by the optical decoding device 16C, and transmitted through the optical decoding device 16C and output. By combining these three outputs, pulsed light having a large peak can be obtained.

  In FIG. 4, the optical decoding device 16C is a transmissive type. However, as a reflection type, a circulator is placed between the optical decoding device 16B and the optical decoding device 16C and reflected by the optical decoding device 16C. You may make it take out pulsed light through this circulator. Although the light is divided into three in FIG. 4, it may be divided into two, four or more, and the device configuration at that time will be obvious to those skilled in the art.

  FIG. 5 is a diagram illustrating an outline of an example of an optical encoding device using an optical system. The amplified optical pulse is emitted from the end face of the optical fiber 21, converted into a parallel light beam by the collimator lens 22, reflected by the diffraction grating 23, and chromatically dispersed. The chromatically dispersed light is collected on the random phase filter 25 by the condenser lens 24. The random phase filter 25 has different optical thickness depending on its position, and the phase of the transmitted light is changed. The relationship between the position and the optical thickness is random. The light transmitted through the random phase filter 25 is reflected by the diffraction grating 27 through the lens 26 to return to a parallel light beam, and is collected on the end face of the optical fiber 29 by the condenser lens 28. Since the position incident on the random phase filter 25 differs depending on the color, the light passes through different optical distances depending on the color. As a result, the light collected on the end face of the optical fiber 29 is time-sequentially. It is pseudo-random light. The above is the description of the optical encoding device, but this optical system can be used as it is as an optical decoding device by reversing the light traveling direction.

  The wavelength conversion device according to the embodiment of the present invention may be obtained by modifying the optical amplification unit described in Patent Document 1 as in the embodiment of the present invention, and the wavelength conversion unit should be used as it is. Therefore, Patent Document 1 is cited and its description is omitted. A laser device having a wavelength conversion unit as described in Patent Document 1 and using an optical amplifier according to an embodiment of the present invention as an optical amplification unit is hereinafter referred to as a “laser device”.

  Next, a mask defect inspection apparatus configured using such a laser apparatus 20 (light source) will be described below with reference to FIG. The mask defect inspection apparatus optically projects a device pattern precisely drawn on a photomask onto a TDI sensor (Time Delay and Integration), compares the sensor image with a predetermined reference image, and determines the pattern from the difference. Extract defects. The mask defect inspection apparatus 120 includes the laser apparatus 20 described above, an illumination optical system 112, a mask support base 113 that supports the photomask 110, a drive device 116 that horizontally moves the mask support base, a projection optical system 114, And a TDI sensor 125. In this mask defect inspection apparatus 120, the laser beam output from the laser apparatus 20 described above is input to an illumination optical system 112 composed of a plurality of lenses, through which a photo supported on the mask support 113 is passed. A predetermined area of the mask 110 is irradiated. The light thus irradiated and passed through the photomask 110 has an image of a device pattern drawn on the photomask 110, and this light is coupled to a predetermined position of the TDI sensor 125 via the projection optical system 114. Imaged. The horizontal movement speed of the mask support 113 and the transfer clock of the TDI sensor 125 are synchronized.

  FIG. 7 is a schematic diagram of a processing apparatus for polymer crystals constructed using the laser device 20 (light source) of the present invention. The ultraviolet short pulse laser beam 139 emitted from the laser device 20 passes through the shutter 132, the intensity adjusting element 133, the irradiation position control mechanism 134, and the condensing optical system 135 and enters the polymer crystal 138 placed in the sample container 136. Focused irradiation. The sample container 136 is mounted on the stage 137 and can move in the three-dimensional direction of the x-axis, y-axis, and z-axis in the xyz orthogonal coordinate system with the optical axis direction as the z-axis, It can rotate around the z-axis. The polymer product is processed by the laser beam focused on the surface of the polymer crystal 138.

  By the way, when processing a workpiece which is a polymer crystal, it is necessary to confirm where the laser beam is irradiated on the workpiece. However, since laser light is usually not visible light and cannot be visually observed, it is preferably used in combination with an optical microscope.

  An example is shown in FIG. In the optical system shown in FIG. 8, the laser light from the ultraviolet short pulse laser system 141 (corresponding to reference numerals 20 and 132 to 134 in FIG. 7) is condensed at a predetermined point via the condensing optical system 135. The stage 137 has a function as described in FIG. 8, and a sample container 136 containing a polymer crystal 138 is placed on the stage 137. Visible light from the illumination light source 142 is reflected by the reflecting mirror 143, and the sample container 136 is Koehler illuminated. The polymer crystal 138 is viewed by the eye 146 through the objective lens 144 and the eyepiece 145 of the optical microscope.

  A cross-shaped mark is formed at the optical axis position of the optical microscope so that the optical axis position can be visually observed. The focus position of the optical microscope (the in-focus position, that is, the object surface that is in focus when viewed) is fixed. The laser light condensed by the condensing optical system 135 is condensed at the optical axis position of the optical microscope and at the focal position of the optical microscope. Therefore, when a workpiece is placed on the stage 137 and the image is observed with an optical microscope, the laser beam from the laser system 141 is focused at a position that is in focus and at the center of the cross mark. It has come to be. The relative positional relationship among the laser system 141, the condensing optical system 135, and the optical microscope unit is fixed, and only the stage 137 is movable relative to these fixed systems.

  Therefore, by processing while moving the stage 137 so that the place to be processed is the optical axis position of the optical microscope and the in-focus position, processing at a desired place and processing of a desired shape are performed. Can do. If it is desired to perform processing automatically, an automatic focus adjustment device is attached to the optical microscope and the stage 137 is driven by the command, and a predetermined portion of the stage 137 is placed on the optical axis of the optical microscope. In this way, the stage 137 may be driven. Alternatively, the stage 137 may be driven two-dimensionally or three-dimensionally by a servo mechanism after the reference position is first adjusted.

It is a figure which shows the outline | summary of a structure of the optical amplifier which is the 1st Embodiment of this invention. It is a figure which shows the example of an encoding using a reflection type encoding apparatus. It is a figure which shows the example of a decoding using a reflection type decoding apparatus. It is a figure which shows the outline | summary of a structure of the optical amplifier which is the 2nd Embodiment of this invention. It is a figure which shows the outline | summary of the example of the optical encoding apparatus which uses an optical system. It is a figure which shows the outline | summary of the mask inspection apparatus which is an example of embodiment of this invention. It is a figure which shows the outline | summary of the processing apparatus of the polymer crystal which is an example of embodiment of this invention. It is a figure which shows the example which combined the processing apparatus of the polymer crystal which is an example of embodiment of this invention with the optical microscope.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Optical encoding apparatus, 2 ... EDFA, 3 ... Optical decoding apparatus, 4 ... Circulator, 5 ... Optical encoding apparatus, 6 ... Circulator, 7 ... Optical decoding apparatus, 11 ... Splitter, 12A, 12B, 12C ... Optical encoding device, 14 ... EDFA, 15 ... circulator, 16A, 16B, 16C ... optical decoding device, 17 ... circulator

Claims (6)

An optical amplifier for amplifying an optical pulse using an EDFA, an optical encoding device that converts an input optical pulse into pseudo-random light in time series for each pulse, and pseudo-random in time series A high peak power output optical amplifier for a light source, comprising: an EDFA that amplifies light; and an optical decoding device that decodes the amplified light and has characteristics opposite to those of the optical encoding device. An optical amplifier that amplifies an optical pulse by using an EDFA, and a plurality of types of optical encoding devices that convert input optical pulses into different pseudo-random light in time series for each pulse, and time A plurality of types corresponding to each of the plurality of types of optical decoding devices that decodes the amplified light and EDFAs that sequentially amplify pseudo-random light and have characteristics opposite to those of the respective optical encoding devices All of the optical decoding devices are reflection type optical decoding devices, and each circulator is provided on the input side to each of the reflection type optical decoding devices. A high peak power output optical amplifier for a light source. An optical amplifier that amplifies an optical pulse by using an EDFA, and a plurality of types of optical encoding devices that convert input optical pulses into different pseudo-random light in time series for each pulse, and time A plurality of types corresponding to each of the plurality of types of optical decoding devices that decodes the amplified light and EDFAs that sequentially amplify pseudo-random light and have characteristics opposite to those of the respective optical encoding devices The optical decoding device and a circulator, the optical decoding device except for one is a reflection type optical decoding device, one is a transmission type optical decoding device, and the reflection type optical decoding device is in the preceding stage. The circulator is provided on the input side to each reflective optical decoding device, and the transmissive optical decoding device is provided via the circulator at the final stage. For high pea Power output optical amplifier. The laser oscillation part which outputs an optical pulse, The high peak power output optical amplifier for light sources of any one of Claims 1-3, The wavelength conversion part which carries out wavelength conversion of the said amplified optical pulse, A laser device comprising: A processing apparatus comprising the laser device according to claim 4. An inspection apparatus comprising the laser apparatus according to claim 4.

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