JP2015118245A - Short optical pulse generation device, terahertz wave generation device, camera, imaging device and measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a short optical pulse generation device capable of reducing a pulse interval of a pulse compressed in a pulse compression section.SOLUTION: A short optical pulse generation device 100 includes: an optical pulse generation section 2 generating an optical pulse having a period of time when optical intensity increases longer than a period of time when the optical intensity decreases; and a pulse compression section 5 chirping a frequency of the optical pulse generated by the optical pulse generation section 2 and compressing a pulse width of the optical pulse chirped.

Description

  The present invention relates to a short light pulse generator, a terahertz wave generator, a camera, an imaging device, and a measurement device.

  In recent years, terahertz waves, which are electromagnetic waves having a frequency of 100 GHz to 30 THz, have attracted attention. The terahertz wave can be used for various measurements such as imaging and spectroscopic measurement, non-destructive inspection, and the like.

  A terahertz wave generator that generates a terahertz wave includes, for example, a short optical pulse generator that generates an optical pulse having a pulse width of about sub-picoseconds (several hundred femtoseconds), and an optical pulse generated by the short optical pulse generator. A photoconductive antenna that generates terahertz waves when irradiated.

  As a short optical pulse generator that constitutes a terahertz wave generator, for example, in Patent Document 1, a chirp is imparted to an optical pulse by direct modulation of a semiconductor laser, and the chirped optical pulse is converted into an optical pulse compressor (optical pulse). A short light pulse generator that performs pulse compression by being incident on a compression unit) is disclosed.

Japanese Patent Laid-Open No. 11-40889

  In the short optical pulse generator as described above, since the optical pulse is chirped by direct modulation of the semiconductor laser, the optical pulse incident on the pulse compression unit includes both the down chirp and the up chirp. Therefore, for example, even if the pulse compression unit causes positive group velocity dispersion (or negative group velocity dispersion) in the optical pulse, half of the optical pulses incident on the pulse compression unit are pulse compressed in the pulse compression unit. Not.

  Therefore, even if an attempt is made to shorten the pulse interval of the pulses compressed in the pulse compression unit, there is a portion that is not compressed in the pulse compression unit, so adjacent pulses interfere with each other, and there is a limit to shortening the pulse interval. there were.

  One of the objects according to some aspects of the present invention is to provide a short optical pulse generator capable of shortening the pulse interval of the pulses compressed in the pulse compression unit. Another object of some aspects of the present invention is to provide a terahertz wave generation device, a camera, an imaging device, and a measurement device including the short light pulse generation device described above.

The short optical pulse generator according to the present invention is
An optical pulse generator that generates an optical pulse whose rise time of the light intensity is longer than the fall time of the light intensity;
A pulse compression unit that chirps the frequency of the optical pulse generated by the optical pulse generation unit and compresses the pulse width of the chirped optical pulse;
including.

  In such a short optical pulse generator, for example, the optical pulse generator does not compress the optical pulse in the pulse compressing unit as compared with the case where the optical pulse generating unit generates an optical pulse having the same rise time and falling time. The ratio of can be reduced. Therefore, it is possible to suppress interference between adjacent pulses in a portion that is not subjected to pulse compression, and it is possible to shorten the pulse interval of the optical pulses compressed in the pulse compression unit.

In the short light pulse generator according to the present invention,
The pulse compression unit
A frequency chirp unit for chirping the frequency of the optical pulse generated by the optical pulse generation unit;
A group velocity dispersion unit for generating a group velocity difference according to a wavelength in the optical pulse chirped by the frequency chirp unit;
Including
The group velocity dispersion unit may cause positive group velocity dispersion in the optical pulse chirped by the frequency chirping unit.

  In such a short light pulse generator, the pulse compression unit can pulse-compress an optical pulse whose rise time of light intensity is longer than the fall time of light intensity.

In the short light pulse generator according to the present invention,
The optical pulse generator is
A light emitting element;
A drive circuit for driving the light emitting element so as to generate a light pulse whose light intensity rise time is longer than the light intensity fall time;
May be included.

  In such a short optical pulse generator, the optical pulse generation unit easily generates an optical pulse whose rise time of the light intensity is longer than the fall time of the light intensity without using an optical element or the like, for example. be able to.

The short optical pulse generator according to the present invention is
An optical pulse generator that generates an optical pulse whose light intensity fall time is longer than the light intensity rise time;
A pulse compression unit that chirps the frequency of the optical pulse generated by the optical pulse generation unit and compresses the pulse width of the chirped optical pulse;
including.

  In such a short optical pulse generator, for example, the optical pulse generator does not compress the optical pulse in the pulse compressing unit as compared with the case where the optical pulse generating unit generates an optical pulse having the same rise time and falling time. The ratio of can be reduced. Therefore, it is possible to suppress interference between adjacent pulses in a portion that is not subjected to pulse compression, and it is possible to shorten the pulse interval of the optical pulses compressed in the pulse compression unit.

In the short light pulse generator according to the present invention,
The pulse compression unit
A frequency chirp unit for chirping the frequency of the optical pulse generated by the optical pulse generation unit;
A group velocity dispersion unit for generating a group velocity difference according to a wavelength in the optical pulse chirped by the frequency chirp unit;
Including
The group velocity dispersion unit may cause negative group velocity dispersion in the optical pulse chirped by the frequency chirp unit.

  In such a short light pulse generator, the pulse compression unit can pulse-compress an optical pulse whose light intensity fall time is longer than the light intensity rise time.

In the short light pulse generator according to the present invention,
The short light pulse generator is
A light emitting element;
A drive circuit for driving the light emitting element so as to generate a light pulse whose light intensity fall time is longer than the light intensity rise time;
May be included.

  In such a short optical pulse generator, the optical pulse generator easily generates an optical pulse whose light intensity fall time is longer than the light intensity rise time without using an optical element or the like. be able to.

The terahertz wave generator according to the present invention is
A short light pulse generator according to the present invention;
A photoconductive antenna that generates a terahertz wave by being irradiated with a short light pulse generated by the short light pulse generator;
including.

  Such a terahertz wave generator can include a short optical pulse generator that can shorten the pulse interval of the optical pulses compressed by the pulse compressor. Therefore, for example, high output can be achieved.

The camera according to the present invention is
A short light pulse generator according to the present invention;
A photoconductive antenna that generates a terahertz wave by being irradiated with a short light pulse generated by the short light pulse generator;
A terahertz wave detecting unit that detects the terahertz wave emitted from the photoconductive antenna and transmitted through the object or the terahertz wave reflected from the object;
A storage unit for storing a detection result of the terahertz wave detection unit;
including.

  Such a camera can include a short optical pulse generator that can shorten the pulse interval of the optical pulses compressed by the pulse compression unit.

An imaging apparatus according to the present invention includes:
A short light pulse generator according to the present invention;
A photoconductive antenna that generates a terahertz wave by being irradiated with a short light pulse generated by the short light pulse generator;
A terahertz wave detecting unit that detects the terahertz wave emitted from the photoconductive antenna and transmitted through the object or the terahertz wave reflected from the object;
An image forming unit that generates an image of the object based on a detection result of the terahertz wave detection unit;
including.

  Such an imaging apparatus can include a short optical pulse generator that can shorten the pulse interval of the optical pulses compressed by the pulse compression unit.

The measuring device according to the present invention is
A short light pulse generator according to the present invention;
A photoconductive antenna that generates a terahertz wave by being irradiated with a short light pulse generated by the short light pulse generator;
A terahertz wave detecting unit that detects the terahertz wave emitted from the photoconductive antenna and transmitted through the object or the terahertz wave reflected from the object;
Based on the detection result of the terahertz wave detection unit, a measurement unit that measures the object,
including.

  Such a measuring device can include a short optical pulse generator that can shorten the pulse interval of the optical pulses compressed by the pulse compression unit.

The functional block diagram of the short optical pulse generator which concerns on 1st Embodiment. The figure which shows an example of the optical pulse P1 produced | generated by the optical pulse production | generation part. The figure which shows an example of the optical pulse P1 produced | generated by the optical pulse production | generation part. The figure which shows an example of the optical pulse chirped by the frequency chirp part. The figure for demonstrating the state which produces a group velocity difference in an optical pulse in a group velocity dispersion | distribution part. The figure which shows an example of the optical pulse pulse-compressed by the group velocity dispersion | distribution part. The figure which shows an example of the optical pulse pulse-compressed by the group velocity dispersion | distribution part. The figure which shows typically the short optical pulse generator which concerns on 1st Embodiment. The perspective view which shows typically the light emitting element of the optical pulse generation part of the short optical pulse generator which concerns on 1st Embodiment, and the optical waveguide of a frequency chirp part. Sectional drawing which shows typically the light emitting element of the optical pulse generation part of the short optical pulse generator which concerns on 1st Embodiment, and the optical waveguide of a frequency chirp part. The circuit diagram which shows an example of the drive circuit of an optical pulse production | generation part. The figure which shows an example of the output waveform obtained at the output terminal of an operational amplifier. The figure for demonstrating operation | movement of the short optical pulse generator which concerns on a reference example. The figure which shows typically the short light pulse generator which concerns on the 1st modification of 1st Embodiment. Sectional drawing which shows typically the group velocity dispersion | distribution part of the short optical pulse generator which concerns on the 1st modification of 1st Embodiment. The circuit diagram which shows an example of the drive circuit of the short optical pulse generator which concerns on the 2nd modification of 1st Embodiment. FIG. 17A is a waveform diagram of a square wave signal (input signal), and FIG. 17B is a waveform diagram of a sawtooth wave signal (output signal). The functional block diagram of the short optical pulse generator which concerns on 2nd Embodiment. The figure which shows an example of the optical pulse produced | generated by the optical pulse production | generation part. The figure which shows an example of the optical pulse produced | generated by the optical pulse production | generation part. The figure which shows an example of the optical pulse chirped by the frequency chirp part. The figure which shows the state which produces a group velocity difference in an optical pulse in a group velocity dispersion | distribution part. The figure which shows an example of the optical pulse pulse-compressed by the group velocity dispersion | distribution part. The figure which shows an example of the optical pulse pulse-compressed by the group velocity dispersion | distribution part. The figure which shows typically the short light pulse generator which concerns on 2nd Embodiment. The figure which shows typically the short optical pulse generator which concerns on the 1st modification of 2nd Embodiment. The figure which shows the structure of the terahertz wave generator which concerns on 3rd Embodiment. The block diagram which shows the imaging device which concerns on 4th Embodiment. The top view which shows typically the terahertz wave detection part of the imaging device which concerns on 4th Embodiment. The graph which shows the spectrum in the terahertz band of a target object. The figure of the image which shows distribution of the substances A, B, and C of a target object. The block diagram which shows the measuring device which concerns on 5th Embodiment. The block diagram which shows the camera which concerns on 6th Embodiment. The perspective view which shows typically the camera which concerns on 6th Embodiment.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. The embodiments described below do not unduly limit the contents of the present invention described in the claims. In addition, not all of the configurations described below are essential constituent requirements of the present invention.

1. 1. First embodiment 1.1. First, the short light pulse generator according to the first embodiment will be described with reference to the drawings. FIG. 1 is a functional block diagram of a short optical pulse generator 100 according to the first embodiment.

  As shown in FIG. 1, the short optical pulse generator 100 includes an optical pulse generator 2 and a pulse compressor 5.

  The optical pulse generation unit 2 generates an optical pulse whose light intensity rise time is longer than the light intensity fall time. Here, the light pulse means light whose light intensity changes sharply in a short time. The pulse width (full width at half maximum FWHM) of the optical pulse generated by the optical pulse generator 2 is not particularly limited, and is, for example, 1 ps (picosecond) or more and 100 ps or less.

  2 and 3 are diagrams illustrating an example of the optical pulse P1 generated by the optical pulse generation unit 2. FIG. The horizontal axis Z shown in FIGS. 2 and 3 is the distance, and the direction of the arrow represents the traveling direction of light. The vertical axis I shown in FIG. 2 is the light intensity. The vertical axis shown in FIG. 3 is the electric field strength. FIG. 3 further shows a graph showing the relationship between the frequency of the optical pulse P1 and the distance Z. The light intensity I is proportional to the square of the amplitude of the electric field.

  As shown in FIG. 2, the light pulse P1 has a longer light intensity rise time than a light intensity fall time. That is, the light intensity of the light pulse P1 is longer than the time from when it rises from the intensity baseline until it reaches the maximum value until it falls from the maximum value to return to the baseline value.

In the example of FIG. 2, the light intensity of the light pulse P1 increases linearly (linearly) with time (from the front part of the pulse to the rear part of the pulse), and then rapidly decreases when it reaches a predetermined magnitude. To return to the original value. The shape of the optical pulse P1 in the example of FIG. 2, a triangle, a pulse front side of the angle theta ₁ (angle formed pulse front edge and the horizontal axis Z is) is acute, the angle of the pulse rear side (An angle formed by the side of the rear part of the pulse and the horizontal axis Z) θ ₂ is a right angle.

The optical pulse generator 2 can generate, for example, a series of optical pulses P1 having a sawtooth wave shape by continuously generating the optical pulses P1. Here, the sawtooth wave changes in such a manner that the light intensity increases linearly with time, decreases rapidly when it reaches a predetermined magnitude, and returns to the original value (see FIG. 2). In the case of a waveform (sawtooth wave), the light intensity rapidly changes to a predetermined magnitude, and then linearly decreases with time and returns to the original value (see FIG. 19). If it is a waveform (inverted sawtooth),
Say. The optical pulse generator 2 may generate the optical pulse P1 at a desired time interval without continuously generating the optical pulse P1.

As shown in FIG. 3, the amplitude when the light pulse P1 is viewed as an electromagnetic wave increases linearly (linearly) as time passes. Further, when the light pulse P1 is viewed as an electromagnetic wave, it has a constant frequency (initial frequency ω ₀ ) regardless of the electric field strength.

  The optical pulse generator 2 includes, for example, a light emitting element such as a semiconductor laser and a drive circuit that drives the light emitting element. A specific configuration of the optical pulse generator 2 will be described later.

  The pulse compressor 5 chirps the frequency of the optical pulse P1 generated by the optical pulse generator 2 and compresses the pulse width of the chirped optical pulse. The pulse compression unit 5 includes a frequency chirp unit 4 and a group velocity dispersion unit 6.

  The frequency chirping unit 4 chirps the frequency of the optical pulse P1 generated by the optical pulse generating unit 2. In the frequency chirping unit 4, for example, by propagating the optical pulse P1 through an optical waveguide made of a semiconductor material (GaAs-based material or the like), the frequency of the optical pulse P1 is chirped by the self-phase modulation effect in the semiconductor material. Here, the self-phase modulation effect is phase modulation caused by the optical Kerr effect, and means a phenomenon in which the phase changes depending on the light intensity of the optical pulse itself. Further, chirping the frequency of the optical pulse means changing the frequency of the optical pulse with time.

  The chirp characteristic obtained by the self-phase modulation effect in the semiconductor material is proportional to the light intensity. The following formula (1) is a formula showing the effect of frequency chirp.

Δω is the chirp amount (frequency change amount), c is the speed of light, τ _r is the response time of the nonlinear refractive index effect, n ₂ is the nonlinear refractive index, l is the waveguide length, ω ₀ is the center frequency of the optical pulse, E is the amplitude of the electric field.

  FIG. 4 is a diagram illustrating an example of the optical pulse P2 chirped by the frequency chirping unit 4. FIG. 4 corresponds to FIG.

  As shown in FIG. 4, the frequency chirp unit 4 down chirps the optical pulse P1. Here, down-chirping means that the frequency of the light pulse decreases with time. The frequency of the light pulse P2 decreases linearly with time. This is because the light intensity of the light pulse P1 increases linearly, so that when the frequency chirp is applied in the frequency chirping section 4 as shown in the above equation (1), the frequency of the light pulse P2 is increased. This is because it decreases linearly with the passage of time.

  In the example of FIG. 4, the entire optical pulse of the optical pulse P2 is down-chirped from the front part of the pulse to the rear part of the pulse.

The group velocity dispersion unit 6 causes a group velocity difference corresponding to the wavelength in the optical pulse P2 chirped by the frequency chirp unit 4. Specifically, the group velocity dispersion unit 6 causes positive group velocity dispersion in the down-chirped optical pulse P2 to reduce the pulse width (pulse compression). That is,
The group velocity dispersion unit 6 has a positive group velocity dispersion characteristic. Here, the group velocity dispersion is a phenomenon in which the group velocity changes depending on the frequency because the propagation velocity of the optical pulse varies depending on the wavelength. Positive group velocity dispersion refers to a phenomenon in which the group velocity increases as the wavelength increases. In other words, the positive group velocity dispersion is a phenomenon in which the group velocity increases as the frequency decreases.

  FIG. 5 is a diagram for explaining a state where the group velocity dispersion unit 6 causes a group velocity difference in the optical pulse P2. FIG. 5 corresponds to FIG. 3 and FIG.

  In the group velocity dispersion unit 6, for example, a group velocity corresponding to a graph showing the relationship between the frequency and the group velocity shown in FIG. 5 is given to the down-chirped optical pulse P 2. Accordingly, in the group velocity dispersion unit 6, the rear portion of the light pulse P2 having a low frequency has a higher group velocity than the front portion of the light pulse having a high frequency. Here, in the illustrated example, the entire optical pulse of the optical pulse P2 is down-chirped. Therefore, the group velocity of the optical pulse P2 increases in the group velocity dispersion unit 6 from the front part of the pulse toward the rear part of the pulse. Therefore, the group velocity dispersion unit 6 compresses the entire optical pulse P2.

  6 and 7 are diagrams illustrating an example of the optical pulse P3 pulse-compressed in the group velocity dispersion unit 6. FIG. 6 corresponds to FIGS. 3 to 5, and FIG. 7 corresponds to FIG. 2.

  As shown in FIGS. 6 and 7, the optical pulse P3 has a shape in which the entire optical pulse P1 is compressed. The light intensity of the optical pulse P3 is longer than the falling time as in the optical pulse P1. In the example of FIG. 7, the shape of the optical pulse P3 is a triangle, the angle on the front side of the pulse is an acute angle, and the angle on the rear side of the pulse is a right angle. The pulse width of the optical pulse P3 is not particularly limited, but is, for example, 1 fs (femtosecond) or more and 800 fs or less. As shown in FIG. 6, when the frequency of the optical pulse P3 becomes constant, that is, when the chirp is completely compensated, the shortest pulse width is obtained.

  In the short optical pulse generator 100, for example, when the optical pulse generator 2 generates a sawtooth-shaped optical pulse P1 sequence in which the optical pulses P1 shown in FIG. A sequence of optical pulses P3 having a sawtooth waveform in which the optical pulses P3 are continuous is obtained.

1.2. Next, the configuration of the short optical pulse generator 100 will be specifically described with reference to the drawings. FIG. 8 is a diagram schematically showing the short light pulse generator 100.

  As shown in FIG. 8, the optical pulse generator 2 includes a light emitting element 20 and a drive circuit 22. The frequency chirp unit 4 includes an optical waveguide 40. The group velocity dispersion unit 6 includes a group velocity dispersion medium 60, reflection mirrors 62a and 62b, and antireflection films 64a and 64b. The short light pulse generator 100 further includes a collimating lens 8.

  First, the light emitting element 20 constituting the optical pulse generator 2 and the optical waveguide 40 constituting the frequency chirp part 4 will be described. FIG. 9 is a perspective view schematically showing the light emitting element 20 constituting the optical pulse generation unit 2 and the optical waveguide 40 constituting the frequency chirping unit 4. FIG. 10 is a cross-sectional view schematically showing the light emitting element 20 and the optical waveguide 40. 10 is a cross-sectional view taken along the line XX of FIG.

  The light emitting element 20 and the optical waveguide 40 are integrally provided as shown in FIGS. That is, the light emitting element 20 and the optical waveguide 40 are provided on the same substrate 202.

  The light emitting element 20 includes a substrate 202, a buffer layer 204, a first cladding layer 206, a core layer 208, a second cladding layer 210, a cap layer 212, an insulating layer 220, a first electrode 230, a first electrode 230, 2 electrodes 232. Here, an example in which the light emitting element 20 is a DFB (Distributed Feedback) laser will be described.

  The optical waveguide 40 includes a first cladding layer 206, a core layer 208, and a second cladding layer 210.

  The substrate 202 is, for example, a first conductivity type (eg, n-type) GaAs substrate. The substrate 202 has a first region 202a where the light emitting element 20 is formed and a second region 202b where the optical waveguide 40 is formed.

  The buffer layer 204 is provided on the substrate 202. The buffer layer 204 is, for example, an n-type GaAs layer. The buffer layer 204 can improve the crystallinity of the layer formed thereabove.

  The first cladding layer 206 is provided on the buffer layer 204. The first cladding layer 206 is, for example, an n-type AlGaAs layer.

  The core layer 208 includes a first guide layer 208a, an MQW layer 208b, and a second guide layer 208c.

  The first guide layer 208 a is provided on the first cladding layer 206. The first guide layer 208a is, for example, an i-type AlGaAs layer.

  The MQW layer 208b is provided on the first guide layer 208a. The MQW layer 208b has a multiple quantum well structure in which, for example, three quantum well structures each composed of a GaAs well layer and an AlGaAs barrier layer are stacked. Here, the quantum well structure refers to a general quantum well structure in the field of semiconductor light-emitting devices, and a thin film (nm order) of a material having a small band gap using two or more materials having different band gaps. It is a structure sandwiched by thin films of materials with a large band gap. In the illustrated example, the MQW layer 208b has the same number of quantum wells (the number of stacked GaAs well layers and AlGaAs barrier layers) above the first region 202a and the second region 202b. That is, in the light emitting element 20 and the optical waveguide 40, the number of quantum wells of the MQW layer 208b is the same.

  Note that the number of quantum wells of the MQW layer 208b above the first region 202a may be different from the number of quantum wells of the MQW layer 208b above the second region 202b. That is, the number of quantum wells of the MQW layer 208b constituting the light emitting element 20 and the number of quantum wells of the MQW layer 208b constituting the optical waveguide 40 may be different.

  The second guide layer 208c is provided on the MQW layer 208b. The second guide layer 208c is, for example, an i-type AlGaAs layer. The second guide layer 208c is provided with a periodic structure constituting a DFB type resonator. The periodic structure is provided above the first region 202a. The periodic structure is composed of two layers 208c and 210 having different refractive indexes.

The first guide layer 208a, the MQW layer 208b, and the second guide layer 208c can constitute the core layer 208 that propagates light generated in the MQW layer 208b. The first guide layer 208a and the second guide layer 208c allow injection carriers (electrons and holes) to flow through the MQW layer 2.
It is a layer that confines light in the core layer 208 at the same time that it is confined in 08b.

  The second cladding layer 210 is provided on the core layer 208. The second cladding layer 210 is, for example, a second conductivity type (for example, p-type) AlGaAs layer. In the illustrated example, optical waveguides 218 and 40 are formed by the first cladding layer 206, the core layer 208, and the second cladding layer 210.

  In the light emitting element 20, for example, the p-type second cladding layer 210, the core layer 208 not doped with impurities, and the n-type first cladding layer 206 constitute a pin diode. Each of the first cladding layer 206 and the second cladding layer 210 is a layer having a larger band gap and a lower refractive index than the core layer 208. The core layer 208 has a function of generating light and guiding the light while amplifying the light. The first cladding layer 206 and the second cladding layer 210 have a function of confining injected carriers (electrons and holes) and light (a function of suppressing light leakage) with the core layer 208 interposed therebetween.

  In the light emitting element 20, when a forward bias voltage of a pin diode is applied between the first electrode 230 and the second electrode 232, recombination of electrons and holes occurs in the core layer 208 (MQW layer 208b). This recombination causes light emission. With this generated light as a starting point, stimulated emission occurs in a chain, and the light intensity is amplified in the optical waveguide (gain region) 218.

  The cap layer 212 is provided on the second cladding layer 210. The cap layer 212 can be in ohmic contact with the second electrode 232. The cap layer 212 is, for example, a p-type GaAs layer.

  The cap layer 212 and a part of the second cladding layer 210 form a columnar portion 260. For example, in the light emitting element 20, the current path between the electrodes 230 and 232 is determined by the planar shape viewed from the stacking direction of each layer of the columnar portion 260.

As shown in FIG. 9, the insulating layer 220 is provided on the second cladding layer 210 and on the side of the columnar portion 260. Further, the insulating layer 220 is provided on the cap layer 212 above the second region 202 b of the substrate 202. The insulating layer 220 is, for example, a SiN layer, a SiO ₂ layer, a SiON layer, an Al ₂ O ₃ layer, a polyimide layer, or the like.

  When the above material is used for the insulating layer 220, the current between the electrodes 230 and 232 can flow through the columnar portion 260 sandwiched between the insulating layers 220, avoiding the insulating layer 220. In addition, the insulating layer 220 may have a refractive index smaller than that of the second cladding layer 210. In this case, the effective refractive index of the vertical cross section of the portion where the insulating layer 220 is formed is smaller than the effective refractive index of the vertical cross section of the portion where the insulating layer 220 is not formed, that is, the portion where the columnar portion 260 is formed. Thereby, light can be efficiently confined in the optical waveguides 218 and 40 in the planar direction. Although not shown, the insulating layer 220 may be an air layer without using the above material. In this case, the air layer can function as the insulating layer 220.

  The first electrode 230 is provided on the entire lower surface of the substrate 202. The first electrode 230 is in contact with a layer that is in ohmic contact with the first electrode 230 (the substrate 202 in the illustrated example). The first electrode 230 is electrically connected to the first cladding layer 206 through the substrate 202. The first electrode 230 is one electrode for driving the light emitting element 20. As the 1st electrode 230, what laminated | stacked in order of Cr layer, AuGe layer, Ni layer, Au layer from the board | substrate 202 side can be used, for example. The first electrode 230 may be provided only below the first region 202a of the substrate 202.

  The second electrode 232 is provided on the upper surface of the cap layer 212 and above the first region 202a. Further, the second electrode 232 may be provided on the insulating layer 220. The second electrode 232 is electrically connected to the second cladding layer 210 via the cap layer 212. The second electrode 232 is the other electrode for driving the light emitting element 20. As the second electrode 232, for example, a layer in which a Cr layer, an AuZn layer, and an Au layer are stacked in this order from the cap layer 212 side can be used. In the illustrated example, the first electrode 230 is provided on the lower surface side of the substrate 202, and the second electrode 232 is provided on the upper surface side of the substrate 202. A single-sided electrode structure in which the electrode 232 is provided on the same surface side (for example, the upper surface side) of the substrate 202 may be used.

  The buffer layer 204, the first cladding layer 206, the core layer 208, the second cladding layer 210, and the cap layer 212 are provided over the first region 202a and the second region 202b of the substrate 202. That is, these layers 204, 206, 208, 210 and 212 are layers common to the light emitting element 20 and the optical waveguide 40 and are continuous layers. The first cladding layer 206, the core layer 208, and the second cladding layer 210 which are continuous in the first region 202a and the second region 202b constitute the optical waveguide 218 and the optical waveguide 40. The optical waveguide 218 is provided above the first region 202a, and the optical waveguide 40 is provided above the second region 202b.

  The case where an AlGaAs-based semiconductor material is used as an example of the light-emitting element 20 and the optical waveguide 40 has been described above. However, the present invention is not limited to this. For example, an AlGaN-based, GaN-based, InGaN-based, GaAs-based, InGaAs-based, InGaAsP Other semiconductor materials such as ZnSd and ZnCdSe may be used.

  Moreover, although the example in which the light emitting element 20 is a DFB laser was described, it is not limited to this, For example, semiconductor lasers, such as a DBR laser and a mode synchronous laser, may be sufficient. The light emitting element 20 may be a super luminescent diode (SLD).

  Although not shown, an electrode for applying a reverse bias to the optical waveguide 40 may be provided. Thereby, the absorption characteristic of the optical waveguide 40 can be controlled, and the frequency chirp amount can be adjusted.

  Although the case where the light emitting element 20 and the optical waveguide 40 are provided on the same substrate has been described here, the light emitting element 20 and the optical waveguide 40 may be provided on different substrates.

  Next, the drive circuit 22 of the optical pulse generator 2 will be described. FIG. 11 is a circuit diagram showing an example of the drive circuit 22 of the optical pulse generator 2.

  The drive circuit 22 drives the light emitting element 20 so as to generate the light pulse P1 in which the rise time of the light intensity is longer than the fall time of the light intensity. That is, the light pulse P1 is directly emitted from the light emitting element 20. Here, an example in which the drive circuit 22 drives the light emitting element 20 so as to generate a sawtooth-shaped optical pulse P1 array will be described.

  As shown in FIG. 11, the drive circuit 22 includes operational amplifiers IC1 and IC2, a capacitor C1, diodes D1 and D2, and resistors R1, R2, R3, and R4.

The operational amplifier IC1 operates as a Schmitt circuit. The operational amplifier IC2 operates as an integration circuit. The capacitor charging time in the integrating circuit (op-amp IC2) is different depending on whether the voltage increases or decreases.

  When the output of the operational amplifier IC1 is a positive voltage using the diodes D1 and D2 (when the integrated output voltage is lowered), the battery is rapidly charged with a small resistance value, and when the output of the operational amplifier IC2 is a negative voltage, a large resistance value is obtained. Charge the battery gradually. As a result, the output waveform of the operational amplifier IC2 (integrating circuit) has a sawtooth waveform. In the drive circuit 22, the power supply voltage uses both a positive power source and a negative power source.

  The oscillation frequency of the drive circuit 22 is expressed by the following equation.

  FIG. 12 is a diagram illustrating an example of an output waveform obtained at the output terminal OUT-1 of the operational amplifier IC2. In the output waveform shown in FIG. 12, since the voltage V has a negative region, an offset is applied (applied) by applying a bias or the like. Thereby, a sawtooth waveform voltage waveform is obtained. By applying this sawtooth waveform voltage to the electrodes 230 and 232 of the light emitting element 20, the light emitting element 20 can generate a sawtooth waveform light pulse P1.

  Next, the group velocity dispersion medium 60, the reflection mirrors 62a and 62b, and the antireflection films 64a and 64b constituting the group velocity dispersion unit 6 will be described with reference to FIG.

  The group velocity dispersion medium 60 is incident with the optical pulse chirped by the frequency chirping unit 4. The group velocity dispersion medium 60 is, for example, a glass substrate, a GaN substrate, a SiC substrate, a plastic substrate, or a sapphire substrate. Therefore, the group velocity dispersion medium 60 has a positive group velocity dispersion characteristic. Therefore, in the group velocity dispersion medium 60, it is possible to reduce the pulse width by causing positive group velocity dispersion in the down-chirped optical pulse. The material of the group velocity dispersion medium 60 is preferably a material that absorbs less light pulses. The shape of the group velocity dispersion medium 60 is, for example, a flat plate shape.

  In the illustrated example, the group velocity dispersion medium 60 has a first surface 61a and a second surface 61b opposite to the first surface 61a. The first surface 61a and the second surface 61b are surfaces on the group velocity dispersion medium 60 where the light pulse is incident and the light pulse is emitted. The thickness of the group velocity dispersion medium 60 (the distance between the first surface 61a and the second surface 61b) is, for example, 100 μm or more and 20 mm or less.

  The reflection mirrors 62a and 62b are provided with the group velocity dispersion medium 60 interposed therebetween. The first reflecting mirror 62 a is provided to face the first surface 61 a of the group velocity dispersion medium 60. A gap is provided between the first reflecting mirror 62a and the first surface 61a. The second reflection mirror 62 b is provided to face the second surface 61 b of the group velocity dispersion medium 60. A gap is provided between the second reflecting mirror 62b and the second surface 61b. The two reflecting mirrors 62a and 62b are arranged to face each other with the group velocity dispersion medium 60 interposed therebetween. That is, the two reflecting mirrors 62 a and 62 b are opposed to each other with the group velocity dispersion medium 60 interposed therebetween. The two reflecting mirrors 62a and 62b are arranged in parallel in the illustrated example. The light pulse is obliquely incident on the reflection mirrors 62a and 62b.

The reflection mirrors 62a and 62b are, for example, metal plates whose surfaces are mirror surfaces. As the reflection mirrors 62a and 62b, for example, a metal mirror, a dielectric multilayer mirror, or the like can be used.

  The light pulse incident on the group velocity dispersion medium 60 is reflected a plurality of times by the two reflection mirrors 62 a and 62 b and travels through the group velocity dispersion medium 60. In the illustrated example, the light pulse incident on the second surface 61b of the group velocity dispersion medium 60 propagates through the group velocity dispersion medium 60 and is emitted to the outside from the first surface 61a. The light pulse emitted from the first surface 61a to the outside is reflected by the first reflecting mirror 62a and is incident on the first surface 61a again. The light pulse incident on the first surface 61a propagates through the group velocity dispersion medium 60 and is emitted to the outside from the second surface 61b. The light pulse emitted from the second surface 61b to the outside is reflected by the second reflecting mirror 62b and is incident on the second surface 61b again. By repeating this, the light pulse travels through the group velocity dispersion medium 60. The number of reflections of the light pulse at the reflection mirrors 62a and 62b is not particularly limited.

  Here, the light pulse travels through the group velocity dispersion medium 60 when the light pulse always travels through the group velocity dispersion medium 60 and when the light pulse travels from the group velocity dispersion medium 60 to the outside (as shown in FIG. And after proceeding while repeating the incidence to the group velocity dispersion medium 60 from the outside again.

  The group velocity dispersion unit 6 can obtain a group velocity dispersion value corresponding to the distance that the optical pulse passes through the group velocity dispersion medium 60. That is, in the group velocity dispersion unit 6, a larger group velocity difference can be generated in the optical pulse as the distance that the optical pulse passes through the group velocity dispersion medium 60 is longer. Therefore, in the group velocity dispersion unit 6, a large group velocity difference can be generated in the optical pulse by increasing the number of times the optical pulse is reflected by the two reflecting mirrors 62a and 62b.

  In addition, although the case where the group velocity dispersion | distribution part 6 had two reflection mirrors 62a and 62b was demonstrated here, the number of reflection mirrors will not be specifically limited if it is two or more. For example, in addition to the reflecting mirror facing the first surface 61a and the second surface 61b of the group velocity dispersion medium 60, other surfaces of the group velocity dispersion medium 60 (for example, the first surface 61a and the second surface 61b are connected). A reflecting mirror may be provided so as to face the surface of the group velocity dispersion medium 60 and the side surface of the group velocity dispersion medium 60. Further, for example, reflection mirrors may be provided on all surfaces of the group velocity dispersion medium 60 (except for a region where the light pulse is incident and a region where the light pulse is emitted).

The first antireflection film 64 a is provided on the first surface 61 a of the group velocity dispersion medium 60. The first antireflection film 64a is, for example, a SiO ₂ layer, a Ta ₂ O ₅ layer, an Al ₂ O ₃ layer, a TiN layer, a TiO ₂ layer, a SiON layer, a SiN layer, or a multilayer film thereof. The first antireflection film 64a can reduce the reflectance of the light pulse on the first surface 61a.

The second antireflection film 64 b is provided on the second surface 61 b of the group velocity dispersion medium 60. The second antireflection film 64b is, for example, a SiO ₂ layer, a Ta ₂ O ₅ layer, an Al ₂ O ₃ layer, a TiN layer, a TiO ₂ layer, a SiON layer, a SiN layer, or a multilayer film thereof. The second antireflection film 64b can reduce the reflectance of the light pulse on the second surface 61b.

  The collimating lens 8 is provided on the optical path of the optical pulse between the optical waveguide 40 and the group velocity dispersion medium 60. The material of the collimating lens 8 is, for example, optical glass. The collimating lens 8 can convert an optical pulse emitted from the optical waveguide 40 and incident on the group velocity dispersion medium 60 into parallel light.

1.2. Next, the operation of the short optical pulse generator 100 will be described with reference to FIG.

  The optical pulse generator 2 generates an optical pulse P1 (see FIG. 3) in which the rise time of the light intensity is longer than the fall time of the light intensity. Specifically, the light pulse P <b> 1 is generated by driving the light emitting element 20 by the drive circuit 22. The optical pulse P1 enters the optical waveguide 40 (frequency chirp portion 4) through the optical waveguide 218 (see FIG. 10).

  The frequency chirping unit 4 chirps the frequency of the optical pulse P1 generated by the optical pulse generating unit 2. Specifically, as the optical pulse P1 propagates through the optical waveguide 40, chirp due to the self-phase modulation effect is imparted to the optical pulse P1. The chirp characteristic obtained by the optical waveguide 40 is proportional to the light intensity (see the above formula (1)). Therefore, the optical pulse P1 becomes an optical pulse P2 (see FIG. 4) in which the frequency linearly decreases (down-chirps) with time in the frequency chirp unit 4.

  The light pulse P2 emitted from the optical waveguide 40 is converted into parallel light by the collimator lens 8 and enters the group velocity dispersion medium 60 (group velocity dispersion portion 6).

  The group velocity dispersion unit 6 causes a group velocity difference corresponding to the wavelength in the optical pulse P2 chirped by the frequency chirp unit 4. Specifically, the light pulse P2 incident on the group velocity dispersion medium 60 is reflected a plurality of times by the two reflection mirrors 62a and 62b and travels through the group velocity dispersion medium 60. The group velocity dispersion medium 60 is a positive group velocity dispersion medium, and the down-chirped light pulse P <b> 2 is pulse-compressed while traveling through the group velocity dispersion medium 60. As shown in FIG. 4, since the entire optical pulse is down-chirped as shown in FIG. 4, the entire optical pulse P2 is compressed by the group velocity dispersion unit 6, and the optical pulse P3 (see FIGS. 6 and 7). ) The light pulse P3 compressed by the group velocity dispersion unit 6 is emitted from the group velocity dispersion medium 60 toward the outside.

  The short light pulse generator 100 has the following features, for example.

  The short optical pulse generator 100 includes an optical pulse generator 2 that generates an optical pulse P1 whose rise time of light intensity is longer than a fall time of the light intensity, and an optical pulse P1 generated by the optical pulse generator 2 And a pulse compression unit 5 that compresses the pulse width of the chirped optical pulse P2. Thereby, the pulse interval of the optical pulse P3 compressed in the pulse compression part 5 can be shortened.

  Hereinafter, for this reason, a short light pulse generator (short light pulse generator according to a reference example) including an optical pulse generator that generates an optical pulse having the same rise time and fall time of light intensity will be described as an example. explain. FIG. 13 is a diagram for explaining the operation of the short optical pulse generator 100r according to the reference example.

  In the short optical pulse generator 100r, as shown in FIG. 13, the optical pulse generator 2r has an optical pulse P1r in which the rise time and fall time of the light intensity are equal, that is, a general light intensity such as a Gaussian function. An optical pulse P1r expressed by a wide spread function is generated. In the illustrated example, the optical pulse generator 2r generates an optical pulse whose light intensity is expressed by a Gaussian function as an example of the optical pulse P1r.

The frequency chirp unit 4r chirps the frequency of the optical pulse P1r by the self-phase modulation effect in the semiconductor material. As described above, the chirp characteristic obtained by the self-phase modulation effect in the semiconductor material is proportional to the light intensity. Therefore, the frequency chirp unit 4r down-chirps the front part of the optical pulse P1r and up-chirps the rear part of the optical pulse P1r. Therefore, the optical pulse P1r becomes the optical pulse P2r in which the front part is down-chirped and the rear part is up-chirped in the frequency chirping part 4r. That is, the optical pulse P2r is
Both down chirp and up chirp will be included equally.

  For example, the group velocity dispersion unit 6r causes negative group velocity dispersion in the optical pulse P2r to reduce the pulse width (pulse compression). In the group velocity dispersion portion 6r, the optical pulse P2r has a faster group velocity at the front and rear of the pulse and a slower group velocity at the center of the pulse. Therefore, the optical pulse P2r is compressed at the rear part of the pulse in the group velocity dispersion unit 6r, but is not compressed at the front part of the pulse. Therefore, the pulse compression unit 5r generates an optical pulse P3r in which the rear part of the pulse is compressed and the front part of the pulse is not compressed (expands).

  Although not illustrated, when the group velocity dispersion unit 6r compresses the pulse by causing positive group velocity dispersion in the optical pulse P2r, the optical pulse P2r is divided into the pulse front portion and the group pulse dispersion portion 6r. The group velocity at the rear part of the pulse is reduced, and the group velocity at the central part of the pulse is increased. Therefore, the optical pulse P2r is compressed at the front part of the pulse in the group velocity dispersion unit 6r, but is not compressed at the rear part of the pulse. Therefore, in the pulse compression unit 5r, although not shown, an optical pulse is generated in which the front part of the pulse is compressed and the rear part of the pulse is not compressed (expands).

  Thus, in the short optical pulse generator 100r according to the reference example, the optical pulse generator 2r generates the optical pulse P1r having the same rise time and fall time of the light intensity, and thus the optical pulse incident on the pulse compressor 5r. Half of them are not pulse-compressed in the pulse compressor 5r.

  On the other hand, in the short optical pulse generator 100 according to the first embodiment, the optical pulse generator 2 generates the optical pulse P1 in which the rise time of the light intensity is longer than the fall time of the light intensity. Therefore, compared with the example of the short optical pulse generator 100r, that is, compared with the case where the optical pulse generator 2 generates the optical pulse P1r in which the rise time and the fall time of the light intensity are equal, the pulse compressor 5 It is possible to reduce the proportion of the optical pulse that is not pulse-compressed. Therefore, it is possible to suppress interference between adjacent pulses in a portion not subjected to pulse compression, and the pulse interval of the optical pulse P3 compressed in the pulse compression unit 5 can be shortened.

  Therefore, for example, when the short light pulse generator 100 is used as a light source of a terahertz wave generator that emits terahertz waves by exciting a photoconductive antenna (PCA), more light pulses are photoconductive per unit time. The antenna can be irradiated. As a result, the output of the terahertz wave generator can be increased. For example, when the short optical pulse generator 100 is used for optical communication, more optical pulses can be transmitted per unit time, and high-speed communication is possible.

  Furthermore, in the short optical pulse generator 100r according to the reference example, half of the optical pulses incident on the pulse compression unit 5r are not pulse-compressed by the pulse compression unit 5r, so the optical pulse conversion efficiency is poor (conversion efficiency is 50). %degree). Here, the conversion efficiency of the optical pulse is the ratio of the portion compressed in the optical pulse compression unit among the optical pulses generated in the optical pulse generation unit.

  On the other hand, in the short optical pulse generator 100 according to the first embodiment, the ratio of the portion that is not pulse-compressed in the pulse compressor 5 can be reduced, so that the conversion efficiency of the optical pulse can be increased. Therefore, for example, when the short light pulse generator 100 is used as the light source of the terahertz wave generator, the energy efficiency can be increased.

In the short optical pulse generator 100, the proportion of the portion that is not pulse-compressed in the pulse compressor 5 can be reduced. Therefore, when used as a light source of the terahertz wave generator, the terahertz wave generated by the terahertz wave generator is desired. It is possible to suppress having a peak other than that frequency. For example, if the optical pulse generated by the short optical pulse generator 100 includes a portion that is not pulse-compressed, the terahertz wave generator generates a terahertz wave having a frequency corresponding to the non-pulse-compressed portion.

  In the short optical pulse generator 100, as shown in FIG. 7, the optical pulse P3 generated by being compressed by the pulse compression unit 5 gradually rises at the front part of the pulse and falls sharply at the rear part of the pulse. Here, when the light pulse generated by the short light pulse generator 100 is used as the excitation light of the photoconductive antenna, it is the front part of the light pulse that contributes to the radiation of the terahertz wave. Therefore, the short light pulse generator 100 is good as a light source for a photoconductive antenna.

  In the short optical pulse generator 100, the pulse compression unit 5 includes a frequency chirp unit 4 that chirps the frequency of the optical pulse generated by the optical pulse generation unit 2, and an optical pulse chirped by the frequency chirp unit 4. A group velocity dispersion unit 6 that produces a group velocity difference according to the frequency velocity, and the group velocity dispersion unit 6 causes a positive group velocity dispersion in the optical pulse P2 chirped by the frequency chirp unit 4. Thereby, in the pulse compression part 5, the optical pulse P1 whose rise time of light intensity is longer than the fall time of light intensity can be pulse-compressed.

  In the short light pulse generator 100, the light pulse generator 2 drives the light emitting element 20 so that the light pulse P1 is generated so that the light intensity rise time is longer than the light intensity falling time. Drive circuit 22 to be operated. As a result, the optical pulse generator 2 can easily generate the optical pulse P1 in which the rise time of the light intensity is longer than the fall time of the light intensity without using, for example, an optical element.

1.3. Modified Example Next, a modified example of the short optical pulse generator according to the first embodiment will be described.

(1) First Modification First, a first modification will be described. FIG. 14 is a diagram schematically showing a short optical pulse generator 200 according to the first modification. FIG. 15 is a cross-sectional view schematically showing the group velocity dispersion unit 6 of the short optical pulse generator 200. 15 is a cross-sectional view taken along line XV-XV in FIG.

  Hereinafter, in the short light pulse generation device 200 according to the first modification, members having the same functions as the constituent members of the short light pulse generation device 100 according to the first embodiment described above are denoted by the same reference numerals, and Description is omitted.

  In the short optical pulse generator 100 described above, the group velocity dispersion unit 6 includes a group velocity dispersion medium 60 (for example, a glass substrate) sandwiched between two reflecting mirrors 62a and 62b as shown in FIG. Travels through the group velocity dispersion medium 60 to compress the light pulse.

  On the other hand, in the short optical pulse generator 200 according to the first modified example, the group velocity dispersion unit 6 has two optical waveguides 602a and 602b arranged at a distance for mode coupling. The optical pulse is compressed by the optical pulse traveling through the optical waveguides 602a and 602b. Note that the distance for mode coupling is a distance at which light propagating through two optical waveguides can travel back and forth.

  The two optical waveguides 602a and 602b constitute a so-called coupled waveguide. As shown in FIG. 15, the two optical waveguides 602a and 602b include a substrate 202, a buffer layer 204, a first cladding layer 206, a core layer 208, a second cladding layer 210, a cap layer 212, and an insulating layer. And the layer 220.

  The two optical waveguides 602a and 602b cause positive group velocity dispersion in the optical pulse P2, that is, the two optical waveguides 602a and 602b have positive group velocity dispersion characteristics.

  Although not shown, the light emitting element 20, the optical waveguide 40, and the optical waveguides 602a and 602b may be integrally formed. That is, the light emitting element 20, the optical waveguide 40, and the optical waveguides 602a and 602b may be formed on the same substrate.

  In the short optical pulse generator 200 according to the first modified example, the group velocity dispersion unit 6 has two optical waveguides 602a and 602b arranged at a distance for mode coupling. Thus, a large group velocity difference can be generated. Therefore, for example, the size of the apparatus can be reduced.

(2) Second Modification Next, a second modification will be described. FIG. 16 is a circuit diagram showing an example of a drive circuit 22d of the short optical pulse generator according to the second modification. FIG. 17A is a waveform diagram of a square wave signal (input signal), and FIG. 17B is a waveform diagram of a sawtooth wave signal (output signal).

  In the short optical pulse generator 100 described above, the optical pulse generator 2 generates the optical pulse P1 by driving the light emitting element 20 by the drive circuit 22 shown in FIG.

  On the other hand, in the second modification, the optical pulse generator 2 drives the light emitting element 20 by the drive circuit 22d shown in FIG. 16 to generate the optical pulse P1.

  As illustrated in FIG. 16, the drive circuit 22 d includes an edge detection unit 2011, a charge pump 2012, and an amplification circuit 2013.

  In the drive circuit 22d, the input signal is a pulse-type square wave signal having the same pulse width at both the high level and the low level, as shown in FIG. The edge detection unit 2011 detects rising and falling edges of the square wave signal. The edge detection unit 2011 causes the charge pump 2012 to start charging after resetting the point B voltage to 0 each time a rising or falling edge is detected.

  The charge pump 2012 is a charge pump of a charging circuit including a constant current circuit B1 and a capacitor C10. The amplifier circuit 2013 is a circuit that amplifies the sawtooth wave signal that is the output of the charge pump 2012.

Next, the operation will be described. When a square wave signal (point A signal) as shown in FIG. 17A is input, the edge detection unit 2011 that detects an edge detects the rising and falling edges of the square wave, and outputs an edge detection signal. The On the other hand, in the charge pump 2012, the capacitor C1 is charged from the power supply unit _VCC via the constant current circuit B1. The charging of the capacitor C1 is reset by the rising and falling edge detection signals of the edge detection unit 2011.

Specifically, the capacitor C1 is a square wave signal (input signal) after being discharged instantly corresponding timing edge, by the constant current circuit B1 at a predetermined inclination from 0 (low level) V _{CC (high} level ) And a sawtooth wave signal (point B signal) is generated. The sawtooth wave signal is input to the amplifier circuit 2013, and the sawtooth wave signal shown in FIG. By applying the sawtooth waveform voltage shown in FIG. 17B to the electrodes 230 and 232 of the light emitting element 20, the light emitting element 20 can generate a sawtooth waveform light pulse P1.

2. Second Embodiment Next, a short light pulse generator according to a second embodiment will be described with reference to the drawings. FIG. 18 is a functional block diagram of the short optical pulse generator 300 according to the second embodiment.

  Hereinafter, in the short light pulse generation device 300 according to the second embodiment, members having the same functions as the constituent members of the short light pulse generation device 100 according to the first embodiment described above are denoted by the same reference numerals, and Description is omitted.

  In the short optical pulse generator 100 described above, the optical pulse generator 2 generates the optical pulse P1 whose rise time of the light intensity is longer than the fall time of the light intensity, and the frequency chirp unit 4 reduces the optical pulse P1. The group velocity dispersion unit 6 chirped and caused pulse compression by causing positive group velocity dispersion in the down-chirped optical pulse P2.

  On the other hand, in the short optical pulse generator 300, the optical pulse generator 2 generates an optical pulse P1 in which the light intensity fall time is longer than the light intensity rise time, and the frequency chirp unit 4 has the optical pulse P1. The group velocity dispersion unit 6 performs pulse compression by causing negative group velocity dispersion in the up-chirped optical pulse P2.

  The optical pulse generator 2 generates an optical pulse in which the light intensity fall time is longer than the light intensity rise time.

  19 and 20 are diagrams illustrating an example of the optical pulse P1 generated by the optical pulse generation unit 2. FIG. The horizontal axis Z shown in FIGS. 19 and 20 is distance, and represents the traveling direction of light. The vertical axis I shown in FIG. 19 is the light intensity. The vertical axis shown in FIG. 20 is the electric field strength. FIG. 20 further shows a graph showing the relationship between the frequency of the optical pulse P1 and the distance Z.

  As shown in FIG. 19, the light pulse P1 has a longer light intensity fall time than a light intensity rise time. That is, the light intensity of the light pulse P1 is shorter than the time from when it rises from the baseline of the intensity until it reaches the maximum value until it falls from the maximum value and returns to the baseline value.

In the example of FIG. 19, the light intensity of the light pulse P1 increases rapidly to a predetermined magnitude, and then decreases linearly (linearly) with time (from the front of the pulse to the back of the pulse). Return to the value of. The shape of the optical pulse P1 in the example of FIG. 19, a triangle, a pulse front side of the angle theta ₁ (angle formed pulse front edge and the horizontal axis Z is) is perpendicular, the angle of the pulse rear side (An angle formed by the side of the rear part of the pulse and the horizontal axis Z) θ ₂ is an acute angle.

  The optical pulse generator 2 can generate, for example, an optical pulse P1 array having a sawtooth wave (inverted sawtooth wave) shape by continuously generating the optical pulse P1. The optical pulse generator 2 may generate the optical pulse P1 at a desired time interval without continuously generating the optical pulse P1.

As shown in FIG. 20, the amplitude when the light pulse P1 is viewed as an electromagnetic wave decreases linearly (linearly) as time passes. Further, when the light pulse P1 is viewed as an electromagnetic wave, it has a constant frequency (initial frequency ω ₀ ) regardless of the electric field strength.

  The optical pulse generator 2 includes, for example, a light emitting element such as a semiconductor laser and a drive circuit that drives the light emitting element. A specific configuration of the optical pulse generator 2 will be described later.

  The pulse compressor 5 chirps the frequency of the optical pulse P1 generated by the optical pulse generator 2 and compresses the pulse width of the chirped optical pulse. The pulse compression unit 5 includes a frequency chirp unit 4 and a group velocity dispersion unit 6.

  The frequency chirping unit 4 chirps the frequency of the optical pulse P1 generated by the optical pulse generating unit 2. In the frequency chirping section 4, for example, the optical pulse P1 is propagated through an optical waveguide made of a semiconductor material, so that the frequency of the optical pulse P1 is chirped by a self-phase modulation effect in the semiconductor material.

  FIG. 21 is a diagram illustrating an example of the optical pulse P2 chirped by the frequency chirping unit 4. FIG. 21 corresponds to FIG.

  As shown in FIG. 21, the frequency chirp unit 4 up-chirps the optical pulse P1. Here, up-chirping means that the frequency of the optical pulse increases with time. The frequency of the light pulse P2 increases linearly with time. This is because the light intensity of the light pulse P1 is linearly decreased. Therefore, when a frequency chirp proportional to the light intensity as shown in the above equation (1) is applied in the frequency chirp unit 4, the frequency of the light pulse P2 is given. This is because the value increases linearly with the passage of time.

  In the example of FIG. 21, the entire optical pulse of the optical pulse P2 is up-chirped from the front part of the pulse to the rear part of the pulse.

  The group velocity dispersion unit 6 causes a group velocity difference corresponding to the wavelength in the optical pulse P2 chirped by the frequency chirp unit 4. Specifically, the group velocity dispersion unit 6 causes negative group velocity dispersion in the up-chirped optical pulse P2 to reduce the pulse width (pulse compression). Here, the negative group velocity dispersion refers to a phenomenon in which the group velocity becomes slower as the wavelength becomes longer. In other words, the negative group velocity dispersion refers to a phenomenon in which the group velocity becomes slower as the frequency becomes lower.

  FIG. 22 is a diagram for explaining how the group velocity dispersion unit 6 causes a group velocity difference in the optical pulse P2. FIG. 22 corresponds to FIG. 20 and FIG.

  The up-chirped optical pulse P2 is given a group velocity corresponding to a graph showing the relationship between the frequency and the group velocity shown in FIG. Therefore, in the group velocity dispersion unit 6, the rear portion of the optical pulse P2 with a high frequency has a higher group velocity than the front portion of the optical pulse with a low frequency. Here, in the illustrated example, the entire optical pulse of the optical pulse P2 is up-chirped. Therefore, in the group velocity dispersion unit 6, the group velocity of the optical pulse P2 increases from the front part of the pulse toward the rear part of the pulse. Thereby, in the group velocity dispersion | distribution part 6, the whole optical pulse P2 is compressed.

  23 and 24 are diagrams illustrating an example of the optical pulse P3 that is pulse-compressed in the group velocity dispersion unit 6. FIG. 23 corresponds to FIGS. 20 to 22, and FIG. 24 corresponds to FIG. 19.

As shown in FIGS. 23 and 24, the optical pulse P3 has a shape in which the entire optical pulse P1 is compressed. The light intensity of the optical pulse P3 is longer than the rising time as in the optical pulse P1. The shape of the light pulse P3 is a triangle in the example of FIG. 24, the angle on the front side of the pulse is a right angle, and the angle on the rear side of the pulse is an acute angle. The pulse width of the optical pulse P3 is not particularly limited, but is, for example, 1 fs (femtosecond) or more and 800 fs or less. The frequency of the light pulse P3 is constant (initial frequency ω ₀ ) as shown in FIG.

  In the short optical pulse generator 300, for example, when the optical pulse generator 2 generates an optical pulse P1 sequence having a sawtooth wave shape (inverted sawtooth wave shape) in which the optical pulses P1 shown in FIG. Then, a series of optical pulses P3 having a sawtooth wave shape (inverted sawtooth wave shape) in which the light pulses P3 are continuous is obtained.

2.2. Next, the configuration of the short optical pulse generator 300 will be specifically described with reference to the drawings. FIG. 25 is a diagram schematically showing the short light pulse generator 300.

  As shown in FIG. 25, the optical pulse generator 2 includes a light emitting element 20 and a drive circuit 322. The frequency chirp unit 4 includes an optical waveguide 40. The group velocity dispersion unit 6 includes two prism pairs 66 and 68.

  The configurations of the light emitting element 20 and the optical waveguide 40 are the same as those of the example of the short optical pulse generator 100 shown in FIGS. 9 and 10 described above, and the description thereof is omitted.

  Further, the drive circuit 322 of the short optical pulse generator 300 includes the above-described drive circuit 22 shown in FIG. 11 and an inverting amplifier circuit (op-amp) for inverting the sign of the output signal of the drive circuit 22. Yes. The drive circuit 322 uses the inverting amplifier circuit to invert the output signal shown in FIG. Thereby, a sawtooth wave (inverted sawtooth wave) signal having a longer light intensity fall time than a light intensity rise time can be output.

  Note that the drive circuit 322 of the short optical pulse generator 300 includes the above-described drive circuit 22d shown in FIG. 16 and an inverting amplifier for inverting the sign of the output signal (see FIG. 17B) of the drive circuit 22d. , May be provided. Accordingly, a sawtooth wave (inverted sawtooth wave) signal can be output by inverting the output signal (see FIG. 17B) of the drive circuit 22d using an inverting amplifier circuit.

  The group velocity dispersion unit 6 includes two prism pairs (a first prism pair 66 and a second prism pair 68). The first prism pair 66 includes a first prism 66a and a second prism 66b. The second prism pair 68 includes a third prism 68a and a fourth prism 68b. The first prism pair 66 and the second prism pair 68 are arranged symmetrically. The material of the prisms 66a, 66b, 68a, 68b is, for example, optical glass having a large refractive index, such as SF10 or SF11.

  The group velocity dispersion unit 6 causes the two prism pairs 66 and 68 to generate negative group velocity dispersion in the optical pulse P2 up-chirped in the frequency chirp unit 4, thereby performing pulse compression.

Specifically, in the group velocity dispersion unit 6, when the up-chirped light pulse P2 enters the first prism 66a, the light pulse P2 is spatially dispersed by the first prism 66a. Specifically, among the frequency components (wavelength components) included in the light pulse P2, the high frequency (short wavelength) component is diffracted more than the low frequency (long wavelength) component. In the space between the first prism 66a and the second prism 66b, the high frequency (short wavelength) component propagates over a longer optical distance, and the low frequency (long wavelength) component propagates earlier in time. In the second prism 66b, a low frequency (long wavelength) component propagates a longer optical distance, and a low frequency (long wavelength) component propagates later in time (negative dispersion). The light pulse transmitted through the first prism pair 66 and emitted from the second prism 66b is compensated, for example, by half of the dispersion. The light pulse emitted from the second prism 66b enters the second prism pair 68, and the remaining dispersion is compensated.

  In this way, the two prism pairs 66 and 68 cause negative group velocity dispersion in the light pulse P2 as a whole of the two prism pairs 66 and 68. That is, the two prism pairs 66 and 68 function as a negative group velocity dispersion medium having negative group velocity dispersion characteristics. Therefore, in the two prism pairs 66 and 68, the negative chirp velocity dispersion is generated in the up-chirped light pulse P2, and the pulse width can be reduced.

2.2. Operation of Short Optical Pulse Generator Next, the operation of the short optical pulse generator 200 will be described with reference to FIG.

  The optical pulse generator 2 generates an optical pulse P1 (see FIG. 20) in which the light intensity fall time is longer than the light intensity rise time. Specifically, the light pulse P <b> 1 is generated by driving the light emitting element 20 by the drive circuit 322. The optical pulse P1 enters the optical waveguide 40 (frequency chirp portion 4) through the optical waveguide 218 (see FIG. 10).

  The frequency chirping unit 4 chirps the frequency of the optical pulse P1 generated by the optical pulse generating unit 2 by the self-phase modulation effect. Specifically, as the optical pulse P1 propagates through the optical waveguide 40, chirp due to the self-phase modulation effect is imparted to the optical pulse P1. The chirp characteristic obtained by the optical waveguide 40 is proportional to the light intensity (see the above formula (1)). Therefore, the optical pulse P1 becomes the optical pulse P2 (see FIG. 21) in which the frequency linearly increases (up-chirps) with time in the frequency chirping unit 4.

  The light pulse P2 emitted from the optical waveguide 40 is converted into parallel light by the collimator lens 8, and is incident on the first prism 66a of the two prism pairs 66 and 68 (group velocity dispersion unit 6).

  The group velocity dispersion unit 6 causes a group velocity difference corresponding to the wavelength in the optical pulse P2 chirped by the frequency chirp unit 4. Specifically, since the two prism pairs 66 and 68 have negative group velocity dispersion characteristics, the up-chirped light pulse P2 is pulse-compressed by the two prism pairs 66 and 68. As shown in FIG. 21, since the entire optical pulse is up-chirped, the entire optical pulse P2 is compressed into an optical pulse P3 (see FIG. 23). The compressed light pulse P3 is emitted outward from the two prism pairs 66 and 68 (fourth prism 68b).

  The short light pulse generator 300 has the following features, for example.

  The short optical pulse generator 300 includes an optical pulse generator 2 that generates an optical pulse P1 whose light intensity fall time is longer than the light intensity rise time, and the optical pulse P1 generated by the optical pulse generator 2. And a pulse compression unit 5 that compresses the pulse width of the chirped optical pulse P2. Thus, as in the example of the short optical pulse generator 100 described above, the optical pulse generator 2 generates an optical pulse P1r (see FIG. 13) with the same rise time and fall time of the light intensity. The proportion of the portion that is not pulse-compressed in the pulse compressor 5 can be reduced. Therefore, it is possible to suppress interference between adjacent pulses in a portion not subjected to pulse compression, and the pulse interval of the optical pulse P3 compressed in the pulse compression unit 5 can be shortened.

  In the short optical pulse generator 300, the pulse compression unit 5 includes a frequency chirp unit 4 that chirps the frequency of the optical pulse generated by the optical pulse generation unit 2, and an optical pulse chirped by the frequency chirp unit 4. And a group velocity dispersion unit 6 that produces a group velocity difference corresponding to the frequency velocity. The group velocity dispersion unit 6 causes the optical pulse chirped by the frequency chirping unit 4 to generate negative group velocity dispersion. Thereby, in the pulse compression part 5, the optical pulse P1 whose light intensity fall time is longer than the light intensity rise time can be pulse-compressed.

  In the short light pulse generator 300, the light pulse generator 2 drives the light emitting element 20 so as to generate the light pulse P1 having a light intensity falling time longer than the light intensity rising time. Drive circuit 22 to be operated. As a result, the optical pulse generator 2 can easily generate the optical pulse P1 in which the light intensity fall time is longer than the light intensity rise time without using, for example, an optical element.

  Here, in the short optical pulse generator according to the present invention, the driving method of the light emitting element 20 is changed according to the group velocity dispersion characteristics (positive group velocity dispersion, negative group velocity dispersion) of the group velocity dispersion unit 6. Thus, pulse compression can be performed. Specifically, for example, when the group velocity dispersion unit 6 has a positive group velocity dispersion characteristic, the short light pulse generator 100 according to the first embodiment (that is, the light emitting element 20 has a non-inverted sawtooth wave shape). By applying voltage, pulse compression can be performed. Further, for example, when the group velocity dispersion unit 6 has a negative group velocity dispersion characteristic, the short optical pulse generator 200 according to the second embodiment (that is, the inverted sawtooth voltage is applied to the light emitting element 20) is used. By using it, pulse compression can be performed.

2.3. Modified Example Next, a modified example of the short optical pulse generator according to the second embodiment will be described. FIG. 26 is a diagram schematically showing a short light pulse generator 400 according to a first modification of the second embodiment.

  Hereinafter, in the short optical pulse generator 400 according to this modification, members having the same functions as those of the constituent members of the short optical pulse generator 300 according to the second embodiment described above are denoted by the same reference numerals, and the description thereof is omitted. Is omitted.

  In the short optical pulse generator 300 described above, as shown in FIG. 25, the group velocity dispersion unit 6 generates negative group velocity dispersion in the optical pulse P2 by the two prism pairs 66 and 68.

  On the other hand, in the short optical pulse generator 400, as shown in FIG. 26, the group velocity dispersion unit 6 generates negative group velocity dispersion in the optical pulse P2 by the diffraction grating pair 610. The diffraction grating pair 610 is constituted by a pair of diffraction gratings (a first diffraction grating 610a and a second diffraction grating 610b).

  For example, the first diffraction grating 610a and the second diffraction grating 610b are arranged in parallel to each other. In the diffraction grating pair 610, when the light pulse P2 enters the diffraction grating pair 610, different frequency components (wavelength components) in the light pulse P2 are diffracted in different directions. At this time, in the diffraction grating pair 610, in the space between the first diffraction grating 610a and the second diffraction grating 610b, the low frequency (long wavelength) component propagates a longer optical distance and the low frequency (long) The (wavelength) component is diffracted to propagate slowly in time. Thereby, negative group velocity dispersion can be caused in the light pulse P2.

  Although not shown, a chirp mirror may be used as the group velocity dispersion unit 6. The chirp mirror is a kind of dielectric multilayer mirror, and is formed such that light having a lower frequency (long wavelength) is reflected by a deeper film (depth from the mirror surface). Therefore, the chirp mirror can cause negative group velocity dispersion in the optical pulse.

3. Third Embodiment Next, a terahertz wave generation device 1000 according to a third embodiment will be described with reference to the drawings. FIG. 27 is a diagram illustrating a configuration of the terahertz wave generation device 1000 according to the present embodiment.

  As shown in FIG. 27, the terahertz wave generator 1000 includes a short optical pulse generator according to the present invention and a photoconductive antenna 1010. Here, the case where the short optical pulse generator 100 is used as the short optical pulse generator according to the present invention will be described.

  The short light pulse generator 100 generates a short light pulse (for example, a light pulse P3 shown in FIG. 7) that is excitation light. The pulse width of the short light pulse generated by the short light pulse generator 100 is, for example, not less than 1 fs and not more than 800 fs.

  The photoconductive antenna 1010 generates a terahertz wave when irradiated with the short light pulse generated by the short light pulse generator 100. The terahertz wave means an electromagnetic wave having a frequency of 100 GHz to 30 THz, particularly an electromagnetic wave of 300 GHz to 3 THz.

  In the illustrated example, the photoconductive antenna 1010 is a dipole photoconductive antenna (PCA). The photoconductive antenna 1010 includes a substrate 1012 that is a semiconductor substrate, and a pair of electrodes 1014 that are provided on the substrate 1012 and arranged to face each other with a gap 1016 interposed therebetween. When a light pulse is irradiated between the electrodes 1014, the photoconductive antenna 1010 generates a terahertz wave.

  The substrate 1012 includes, for example, a semi-insulating GaAs (SI-GaAs) substrate and a low temperature growth GaAs (LT-GaAs) layer provided on the SI-GaAs substrate. The material of the electrode 1014 is, for example, Au. The distance between the pair of electrodes 1014 is not particularly limited, and is appropriately set according to conditions. The distance between the pair of electrodes 1014 is, for example, not less than 1 μm and not more than 10 μm.

  In the terahertz wave generation device 1000, first, the short light pulse generation device 100 generates a short light pulse and emits it toward the gap 1016 of the photoconductive antenna 1010. The short light pulse emitted from the short light pulse generator 100 irradiates the gap 1016 of the photoconductive antenna 1010. In the photoconductive antenna 1010, free electrons are excited by irradiating the gap 1016 with a short light pulse. The free electrons are accelerated by applying a voltage between the electrodes 1014. Thereby, a terahertz wave is generated.

  The terahertz wave generation device 1000 includes a short optical pulse generation device 100 that can shorten the pulse interval of the pulses compressed by the pulse compression unit 5. Therefore, in the terahertz wave generator 1000, for example, high output can be achieved.

4). Fourth Embodiment Next, an imaging apparatus 1100 according to a fourth embodiment will be described with reference to the drawings. FIG. 28 is a block diagram illustrating an imaging apparatus 1100 according to the fourth embodiment. FIG. 29 is a plan view schematically showing the terahertz wave detection unit 1120 of the imaging apparatus 1100 according to the fourth embodiment. FIG. 30 is a graph showing the spectrum of the target in the terahertz band. FIG. 31 is a diagram of an image showing the distribution of substances A, B, and C of the object.

As shown in FIG. 28, the imaging apparatus 1100 includes a terahertz wave generation unit 1110 that generates a terahertz wave, and a terahertz wave that is emitted from the terahertz wave generation unit 1110 and is transmitted through the object O or is reflected by the object O. A terahertz wave detection unit 1120 that detects a wave and an image forming unit 1130 that generates an image of the object O, that is, image data based on the detection result of the terahertz wave detection unit 1120 are provided.

  As the terahertz wave generation unit 1110, the terahertz wave generation device according to the present invention can be used. Here, the case where the terahertz wave generation device 1000 is used as the terahertz wave generation device according to the present invention will be described.

  As shown in FIG. 29, the terahertz wave detection unit 1120 includes a filter 80 that transmits a terahertz wave having a target wavelength, and a detection unit 84 that detects the terahertz wave having the target wavelength that has passed through the filter 80. Use things. Further, as the detection unit 84, for example, a detection unit that converts a terahertz wave into heat and detects it, that is, a unit that can convert a terahertz wave into heat and detect the energy (intensity) of the terahertz wave is used. Examples of such a detection unit include a pyroelectric sensor and a bolometer. Note that the configuration of the terahertz wave detection unit 1120 is not limited to the above configuration.

  The filter 80 includes a plurality of pixels (unit filter units) 82 that are two-dimensionally arranged. That is, the pixels 82 are arranged in a matrix.

  Each pixel 82 has a plurality of regions that transmit terahertz waves having different wavelengths, that is, a plurality of regions that have different wavelengths of terahertz waves that pass (hereinafter also referred to as “passing wavelengths”). In the illustrated configuration, each pixel 82 includes a first region 821, a second region 822, a third region 823, and a fourth region 824.

  In addition, the detection unit 84 includes first unit detection provided corresponding to the first region 821, the second region 822, the third region 823, and the fourth region 824 of each pixel 82 of the filter 80. A unit 841, a second unit detection unit 842, a third unit detection unit 843, and a fourth unit detection unit 844. Each first unit detection unit 841, each second unit detection unit 842, each third unit detection unit 843, and each fourth unit detection unit 844 are each a first region 821 of each pixel 82, The terahertz wave that has passed through the second region 822, the third region 823, and the fourth region 824 is converted into heat and detected. Thereby, in each of the pixels 82, terahertz waves having four target wavelengths can be reliably detected.

  Next, a usage example of the imaging apparatus 1100 will be described.

  First, it is assumed that the object O to be subjected to spectral imaging is composed of three substances A, B, and C. The imaging apparatus 1100 performs spectral imaging of the object O. Here, as an example, the terahertz wave detection unit 1120 detects the terahertz wave reflected by the object O.

  In each pixel 82 of the filter 80 of the terahertz wave detection unit 1120, the first region 821 and the second region 822 are used. The transmission wavelength of the first region 821 is λ1, the transmission wavelength of the second region 822 is λ2, the intensity of the component of wavelength λ1 of the terahertz wave reflected by the object O is α1, and the intensity of the component of wavelength λ2 is α2. , The difference (α2−α1) between the intensity α2 and the intensity α1 can be distinguished from each other among the substance A, the substance B, and the substance C, so that the transmission wavelength λ1 and the second of the first region 821 The pass wavelength λ2 of the region 822 is set.

As shown in FIG. 30, in the substance A, the wavelength λ2 of the terahertz wave reflected by the object O
The difference (α2−α1) between the intensity α2 of the component α2 and the intensity α1 of the component of wavelength λ1 is a positive value. In the substance B, the difference (α2−α1) between the strength α2 and the strength α1 is zero. In the substance C, the difference (α2−α1) between the strength α2 and the strength α1 is a negative value.

  When spectral imaging of the object O is performed by the imaging apparatus 1100, first, a terahertz wave is generated by the terahertz wave generation unit 1110, and the object O is irradiated with the terahertz wave. Then, the terahertz wave reflected by the object O is detected by the terahertz wave detection unit 1120 as α1 and α2. This detection result is sent to the image forming unit 1130. Note that the irradiation of the terahertz wave to the object O and the detection of the terahertz wave reflected by the object O are performed on the entire object O.

  In the image forming unit 1130, based on the detection result, the intensity α2 of the component of the wavelength λ2 of the terahertz wave that has passed through the second region 822 of the filter 80 and the wavelength λ1 of the terahertz wave that has passed through the first region 821 The difference (α2−α1) from the intensity α1 of the component is obtained. Of the object O, the part where the difference is a positive value is determined as the substance A, the part where the difference is zero is determined as the substance B, and the part where the difference is a negative value is determined as the substance C.

  Further, the image forming unit 1130 creates image data of an image showing the distribution of the substances A, B, and C of the object O as shown in FIG. This image data is sent from the image forming unit 1130 to a monitor (not shown), and an image showing the distribution of the substances A, B and C of the object O is displayed on the monitor. In this case, for example, the area where the substance A of the object O is distributed is displayed in black, the area where the substance B is distributed is gray, and the area where the substance C is distributed is displayed in white. In this imaging apparatus 1100, as described above, identification of each substance constituting the object O and distribution measurement of each property can be performed simultaneously.

  Note that the use of the imaging apparatus 1100 is not limited to that described above. For example, a terahertz wave is irradiated on a person, the terahertz wave transmitted or reflected by the person is detected, and the image forming unit 1130 performs processing. Thus, it is possible to determine whether or not the person has a handgun, a knife, an illegal drug, or the like.

5. Fifth Embodiment Next, a measuring apparatus 1200 according to a fifth embodiment will be described with reference to the drawings. FIG. 32 is a block diagram showing a measuring apparatus 1200 according to the fifth embodiment. In the measurement apparatus 1200 according to the fifth embodiment described below, members having the same functions as those of the components of the imaging apparatus 1100 described above are denoted by the same reference numerals, and detailed description thereof is omitted.

  As shown in FIG. 32, the measuring device 1200 includes a terahertz wave generation unit 1110 that generates a terahertz wave, and a terahertz wave that is emitted from the terahertz wave generation unit 1110 and is transmitted through the object O or is reflected by the object O. A terahertz wave detection unit 1120 that detects a wave; and a measurement unit 1210 that measures an object O based on the detection result of the terahertz wave detection unit 1120.

  Next, a usage example of the measuring apparatus 1200 will be described. When spectroscopic measurement of the object O is performed by the measuring device 1200, first, a terahertz wave is generated by the terahertz wave generation unit 1110, and the object O is irradiated with the terahertz wave. Then, the terahertz wave transmitted through the object O or the terahertz wave reflected by the object O is detected by the terahertz wave detection unit 1120. The detection result is sent to the measurement unit 1210. The irradiation of the terahertz wave to the object O and the detection of the terahertz wave transmitted through the object O or the terahertz wave reflected by the object O are performed on the entire object O.

  In the measurement unit 1210, from the detection result, each of the terahertz waves that have passed through the first region 821, the second region 822, the third region 823, and the fourth region 824 of each pixel 82 of the filter 80 is measured. The strength is grasped, and the components of the object O and the distribution thereof are analyzed.

6). Sixth Embodiment Next, a camera 1300 according to a sixth embodiment will be described with reference to the drawings. FIG. 33 is a block diagram showing a camera 1300 according to the sixth embodiment. FIG. 34 is a perspective view schematically showing a camera 1300 according to the sixth embodiment. In the camera 1300 according to the sixth embodiment described below, members having the same functions as those of the components of the imaging apparatus 1100 described above are denoted by the same reference numerals, and detailed description thereof is omitted.

  As shown in FIGS. 33 and 34, the camera 1300 emits a terahertz wave that is generated from the terahertz wave and the terahertz wave that is emitted from the terahertz wave generation unit 1110 and reflected by the object O or is transmitted through the object O. The terahertz wave detecting unit 1120 for detecting the terahertz wave thus generated and the storage unit 1301 are provided. These units 1110, 1120, and 1301 are housed in a housing 1310 of the camera 1300. The camera 1300 includes a lens (optical system) 1320 that converges (images) the terahertz wave reflected by the object O on the terahertz wave detection unit 1120, and the terahertz wave generated by the terahertz wave generation unit 1110. A window portion 1330 for injecting the outside is provided. The lens 1320 and the window 1330 are made of a member such as silicon, quartz, or polyethylene that transmits and refracts terahertz waves. Note that the window portion 1330 may have a configuration in which an opening is simply provided like a slit.

  Next, a usage example of the camera 1300 will be described. When imaging the object O with the camera 1300, first, a terahertz wave is generated by the terahertz wave generation unit 1110, and the object O is irradiated with the terahertz wave. Then, the terahertz wave reflected by the object O is converged (imaged) on the terahertz wave detection unit 1120 by the lens 1320 and detected. This detection result is sent to and stored in the storage unit 1301. The irradiation of the terahertz wave to the object O and the detection of the terahertz wave reflected by the object O are performed on the entire object O. The detection result can be transmitted to an external device such as a personal computer. In the personal computer, each process can be performed based on the detection result.

  The above-described embodiments and modifications are merely examples, and the present invention is not limited to these. For example, it is possible to appropriately combine each embodiment and each modification.

  The present invention includes configurations that are substantially the same as the configurations described in the embodiments (for example, configurations that have the same functions, methods, and results, or configurations that have the same objects and effects). In addition, the invention includes a configuration in which a non-essential part of the configuration described in the embodiment is replaced. In addition, the present invention includes a configuration that exhibits the same operational effects as the configuration described in the embodiment or a configuration that can achieve the same object. Further, the invention includes a configuration in which a known technique is added to the configuration described in the embodiment.

DESCRIPTION OF SYMBOLS 2 ... Optical pulse production | generation part, 4 ... Frequency chirp part, 5 ... Pulse compression part, 6 ... Group velocity dispersion | distribution part, 8 ... Collimating lens, 20 ... Light emitting element, 22, 22d ... Drive circuit, 40 ... Optical waveguide, 60 ... Group velocity dispersion medium, 61a ... first surface, 61b ... second surface, 62a ... first reflection mirror, 62b ... second reflection mirror, 64a ... first antireflection film, 64b ... second antireflection film, 66 ... first 1 prism pair, 66a ... 1st prism, 66b ... 2nd prism, 68 ... 2nd prism pair, 68a ... 3rd prism, 68b ... 4th prism, 80 ... filter, 82 ... pixel, 84 ... detection part, 100, DESCRIPTION OF SYMBOLS 200 ... Short light pulse generator, 202 ... Board | substrate, 202a ... 1st area | region, 202b ... 2nd area | region, 204 ... Buffer layer, 206 ... 1st clad layer, 208 ... Core layer, 208a ... 1st guide layer, 208b MQW layer, 208c ... second guide layer, 210 ... second cladding layer, 212 ... cap layer, 218 ... optical waveguide, 220 ... insulating layer, 230 ... first electrode, 232 ... second electrode, 260 ... columnar portion, 300 ... Short optical pulse generator, 322 ... Drive circuit, 400 ... Short optical pulse generator, 602a ... Optical waveguide, 602b ... Optical waveguide, 610a ... First diffraction grating, 610b ... Second diffraction grating, 821 ... First region 822 ... second region, 823 ... third region, 824 ... fourth region, 841 ... first unit detector, 842 ... second unit detector, 843 ... third unit detector, 844 ... 4th unit detection part, 1000 ... Terahertz wave generator, 1010 ... Photoconductive antenna, 1012 ... Substrate, 1014 ... Electrode, 1016 ... Gap, 1100 ... Imaging device, 1110 ... Terahe Wave generation unit, 1120 ... terahertz wave detection unit, 1130 ... image forming unit, 1200 ... measurement device, 1210 ... measurement unit, 1300 ... camera, 1301 ... storage unit, 1310 ... casing, 1320 ... lens, 1330 ... window , 2011... Edge detection unit, 2012... Charge pump, 2013.

Claims (10)

An optical pulse generator that generates an optical pulse whose rise time of the light intensity is longer than the fall time of the light intensity;
A pulse compression unit that chirps the frequency of the optical pulse generated by the optical pulse generation unit and compresses the pulse width of the chirped optical pulse;
A short light pulse generator comprising: The pulse compression unit
A frequency chirp unit for chirping the frequency of the optical pulse generated by the optical pulse generation unit;
A group velocity dispersion unit for generating a group velocity difference according to a wavelength in the optical pulse chirped by the frequency chirp unit;
Including
The short optical pulse generator according to claim 1, wherein the group velocity dispersion unit generates positive group velocity dispersion in the optical pulse chirped by the frequency chirping unit. In claim 1 or 2,
The optical pulse generator is
A light emitting element;
A drive circuit for driving the light emitting element so as to generate the light pulse whose rise time of light intensity is longer than the fall time of light intensity;
The short light pulse generator according to claim 1, wherein the short light pulse generator is included. An optical pulse generator that generates an optical pulse whose light intensity fall time is longer than the light intensity rise time;
A pulse compression unit that chirps the frequency of the optical pulse generated by the optical pulse generation unit and compresses the pulse width of the chirped optical pulse;
A short light pulse generator comprising: The pulse compression unit
A frequency chirp unit for chirping the frequency of the optical pulse generated by the optical pulse generation unit;
A group velocity dispersion unit for generating a group velocity difference according to a wavelength in the optical pulse chirped by the frequency chirp unit;
Including
The short optical pulse generator according to claim 4, wherein the group velocity dispersion unit generates negative group velocity dispersion in the optical pulse chirped by the frequency chirping unit. In claim 4 or 5,
The short light pulse generator is
A light emitting element;
A drive circuit for driving the light emitting element so as to generate the light pulse whose light intensity fall time is longer than the light intensity rise time;
The short light pulse generator according to claim 4, wherein the short light pulse generator is included. The short light pulse generator according to any one of claims 1 to 6,
A photoconductive antenna that generates a terahertz wave by being irradiated with a short light pulse generated by the short light pulse generator;
The terahertz wave generator characterized by including. The short light pulse generator according to any one of claims 1 to 6,
A photoconductive antenna that generates a terahertz wave by being irradiated with a short light pulse generated by the short light pulse generator;
A terahertz wave detecting unit that detects the terahertz wave emitted from the photoconductive antenna and transmitted through the object or the terahertz wave reflected from the object;
A storage unit for storing a detection result of the terahertz wave detection unit;
Including a camera. The short light pulse generator according to any one of claims 1 to 6,
A photoconductive antenna that generates a terahertz wave by being irradiated with a short light pulse generated by the short light pulse generator;
A terahertz wave detecting unit that detects the terahertz wave emitted from the photoconductive antenna and transmitted through the object or the terahertz wave reflected from the object;
An image forming unit that generates an image of the object based on a detection result of the terahertz wave detection unit;
An imaging apparatus comprising: The short light pulse generator according to any one of claims 1 to 6,
A photoconductive antenna that generates a terahertz wave by being irradiated with a short light pulse generated by the short light pulse generator;
A terahertz wave detecting unit that detects the terahertz wave emitted from the photoconductive antenna and transmitted through the object or the terahertz wave reflected from the object;
Based on the detection result of the terahertz wave detection unit, a measurement unit that measures the object,
A measuring device comprising:

Images