JP5448666B2 - Pulsed light generator - Google Patents

Description

  The present invention relates to a pulsed light generator suitable for generating an ultrashort pulse of about several femtoseconds.

  An optical pulse is indispensable in optical information transmission and various optical measurements. In general, one pulse of light carries information corresponding to one bit. In addition, this light pulse is also used in various optical measurements such as time-resolved spectroscopy, etc., in addition to various basic research and applied research to investigate the optical response and electronic dynamics of the substance as the measurement target, The present invention is also applied to performance evaluation of manufactured electronic devices.

  Among these optical pulses, ultrashort pulse light with a pulse width in the time domain from picoseconds to femtoseconds is particularly used as a light source for observing ultrafast phenomena with very high time resolution. It is used in a wide range of academic fields such as solid state physics, plasma physics, and chemistry, and has been applied as an ultrafast optical technology in various engineering fields such as optical communication and optical information processing.

  Conventionally, such an ultra-short pulse light is obtained by inserting an element called a mode locker such as a saturable absorber, an electro-optic modulation element, or an acousto-optic modulation element into an optical resonator, and the resonance frequency of the optical resonator. In general, the frequency is generated in combination with the frequency of the mode locker (see, for example, Patent Documents 1 and 2). However, with this generation method, the pulse width of light emission is limited to the saturable absorber, electro-optic modulation element, acousto-optic modulation element, or gain medium bandwidth, and only a very short pulse up to 50 femtoseconds is generated. I can't. Light pulses of 50 femtoseconds or less can be generated using nonlinear phenomena such as self-phase modulation, but a strong and stable light source is required to induce such nonlinear phenomena, which is large and expensive. Equipment is required. For this reason, an apparatus capable of easily generating a high-speed pulse width of 50 femtoseconds or less has been desired.

JP 2007-115811 A JP 11-330597 A

  Accordingly, the present invention has been devised in view of the above-described problems, and an object of the present invention is to provide a simple and inexpensive pulsed light generator capable of generating a pulse width of 50 femtoseconds or less. It is to provide.

  The invention according to claim 1 of the present application has a light emitting means for emitting continuous (CW) light, and CW light emitted from the light emitting means, and has an asymmetric shape with respect to the incident direction of the CW light. A polarization converting means in which nanometer-sized polarizers are arranged in a glass plate, and a polarizing plate that generates a pulsed light every predetermined time by transmitting a predetermined polarization component of the light that has passed through the polarization converting means. It is characterized by providing.

  The invention according to claim 2 of the present application is characterized in that, in the invention according to claim 1, the polarizer has a convex portion projecting in a direction substantially orthogonal to the incident direction of the CW light.

  The invention according to claim 3 of the present application is the invention according to claim 2, wherein the polarization conversion means generates near-field light in the vicinity of the convex portion based on the incident CW light, and is continuously incident. The magnetic field oscillation direction of the CW light is changed based on the generated near-field light.

  According to the pulse light generator to which the present invention having the above-described configuration is applied, a nanometer-size polarizer having an asymmetric shape with respect to the incident direction is arranged in the glass plate. Then, near-field light is generated in the vicinity of the asymmetric shape based on the incident CW light, and the magnetic field oscillation direction of the continuously incident CW light is changed based on the generated near-field light. . As a result, it is possible to make the major axis and minor axis of the polarization component not orthogonal to each other, and it is possible to take out a periodic peak caused by the generated phase jump as a pulse. This pulsed light can generate a very high-speed pulse by setting the pulse width to the femtosecond order. In addition, the pulse interval can be configured in the femtosecond order, and ultrahigh-speed modulation can be realized.

It is a figure which shows the structure of the pulsed light generator to which this invention is applied. It is a figure which shows the structure of the polarizer of the polarization conversion part in the pulsed light generator to which this invention is applied. (a) is a figure which shows the polarization component of the CW light which injected into the polarization conversion part, (b) is a figure which shows the polarization component of the light radiate | emitted from the polarization conversion part. It is a figure which shows the near-field light generated based on CW light irradiated to the polarizer. FIG. 5 is a diagram showing the polarization component with the horizontal axis representing the phase of light (× π) and the vertical axis representing the amplitude. It is the figure which represented the light intensity of the light radiate | emitted from the polarization conversion part in the pulsed light generator to which this invention was applied in time series.

  Hereinafter, a pulsed light generator that generates an ultrashort pulse of about several femtoseconds will be described in detail with reference to the drawings as a mode for carrying out the present invention.

  A pulsed light generator 1 to which the present invention is applied includes, for example, as shown in FIG. 1, a light source 11 that emits continuous (CW) light and a CW light emitted from the light source 11 and passes through a polarization conversion process described later. And a polarization plate 13 that transmits a predetermined polarization component of the light that has passed through the polarization conversion unit 12.

  The light source 11 oscillates CW light having a predetermined wavelength based on a driving power supply received via a power supply device (not shown). The light source 11 may be composed of, for example, a solid-state laser such as Nd: YAG, a semiconductor laser such as GaAs, a gas laser such as ArF, or an LED or a xenon lamp.

  The polarization converter 12 receives CW light emitted from the light source 11. The polarization conversion unit 12 includes a glass plate 21 and a polarizer 22 arranged in the glass plate 21. The polarizer 22 is not limited to be embedded in the glass plate 21, and may be formed on the surface of the glass plate 21. Further, as an alternative to the glass plate 21, for example, a resin substrate may be used.

  FIG. 2A shows an enlarged perspective view of one polarizer 22, and FIG. 2B shows an enlarged plan view of the polarizer 22. The polarizer 22 includes a main body portion 31 and a convex portion 32 that protrudes outward from the main body portion 31. The polarizer 22 is made of a material such as Al, Cr, Au, or Pt. The polarizer 22 may have any shape, but the example of FIG. 2 shows a case where the main body 31 is formed in a rectangular parallelepiped shape. Moreover, the polarizer 22 is comprised by nanometer size, for example, you may make it the one side of the main-body part 31 consist of 250 nm or less. Further, as a method of arranging the polarizer 22 in the glass plate 21, pattern transfer by EB lithography, photolithography, near-field lithography, and processing by etching are performed.

  The convex portion 32 is provided so as to protrude in a direction substantially orthogonal to the incident direction A of the CW light incident from the light source 11. As shown in FIG. 2 (b), the convex portion 32 is formed in a shape protruding from one side of the main body portion 31 when viewed in plan. By forming the convex portion 32, the polarizer 22 has an asymmetric shape when viewed from the incident direction of the CW light, as shown in the plan view of FIG. 2B. The upper surface of the convex portion 32 is configured to form the same plane as the upper surface of the main body portion 31. On the other hand, the bottom surface of the convex portion 32 is configured to be higher than the bottom surface of the main body portion 31.

  The protrusion 32 may be provided at any location as long as it has an asymmetric shape when viewed from the incident direction of the CW light, and may be formed at a plurality of locations. Good. In addition, as a fine processing method of this polarizer 22, you may make it produce the shape of the convex part 32 and the main-body part 31 by laser processing etc., for example.

  Next, the operation of the pulsed light generator to which the present invention is applied will be described.

  First, CW light is emitted from the light source 11. The emitted CW light is incident on the polarization converter 12.

  The CW light incident on the polarization conversion unit 12 reaches the polarizer 22.

  FIG. 3A shows the polarization component of the CW light incident on the polarization converter 12. In FIG. 3, the direction of the magnetic field of CW light is shown, and the horizontal axis corresponds to TE (Transverse Electric) and the vertical axis corresponds to TM (Transverse Magnetic). If the incident CW light is circularly polarized light, as shown in FIG. 3 (a), the TE and TM polarized electric fields have substantially the same amount of change in the oscillating magnetic field. The short axes are perpendicular to each other.

  When the polarizer 22 is irradiated with CW light, near-field light is generated in the vicinity of the convex portion 32 as shown in FIG. If the CW light is continuously irradiated in a state where such near-field light is generated, the direction of the current changes almost in synchronization with the frequency of the near-field light. The direction of this current is further changed by the generated near-field light, and when the electric field vibration of light for several cycles is repeated as shown in FIG. 3B, the electric field vibration of the light and the polarizer 22 The difference from the polarization vibration inherent in the structure increases, and the amount of change in the vibration direction of the polarization vibration increases. As a result, after a certain period, the incident CW light and the polarization of the corresponding polarization vibration generated based on this polarizer 22 change, and the so-called phase as shown in FIG. A jump will occur.

  Such light having a polarization component as shown in FIG. 3B is emitted from the polarization conversion unit 12. The outgoing polarization component has a shape in which the major axis and minor axis of the polarization component are not orthogonal. In FIG. 5A, the horizontal axis represents the phase of light (× π) and the vertical axis represents the amplitude of the polarization component shown in FIG. It can be seen that peaks occur periodically due to the change in the polarization component described above.

  In the present invention, the light emitted from the polarization converter 12 is made incident on the polarizing plate 13 in order to take out a periodic peak generated by the generated phase jump as a pulse. The polarizing plate 13 is set so that only a polarized component corresponding to the phase of the peak to be extracted as a pulse can be transmitted. As a result, the light transmitted through the polarizing plate 13 becomes a pulse generated every predetermined time as shown in FIG.

  FIG. 6 shows the light intensity of the light emitted from the polarization conversion unit 12 in the pulsed light generator 1 to which the present invention is actually applied in time series. In FIG. 6, the horizontal axis represents time (femto (f) seconds), and the vertical axis represents light intensity (W). In general, since the polarization period is in the femtosecond order, peaks based on phase jumps that occur periodically occur at femtosecond order intervals. In FIG. 6, it can be seen that peaks occur at time intervals of 10 femtoseconds or less. In addition, the peak width is even smaller and can be reduced to 1 femtosecond or less. For this reason, it is possible to generate pulsed light of 1 femtosecond or less at a time interval of 10 femtoseconds or less by taking out this peak using the polarizing plate 13.

  Thus, according to the pulsed light generator 1 to which the present invention is applied, the nanometer-sized polarizers having an asymmetric shape with respect to the incident direction are arranged in the glass plate. Then, near-field light is generated in the vicinity of the asymmetric shape based on the incident CW light, and the magnetic field oscillation direction of the continuously incident CW light is changed based on the generated near-field light. . As a result, it is possible to make the major axis and minor axis of the polarization component not orthogonal to each other, and it is possible to take out a periodic peak caused by the generated phase jump as a pulse. This pulsed light can generate a very high-speed pulse by setting the pulse width to the femtosecond order. In addition, the pulse interval can be configured in the femtosecond order, and ultrahigh-speed modulation can be realized.

  In addition, according to the present invention, it is possible to generate a femtosecond order optical pulse from CW light with a very simple structure, thereby reducing the manufacturing cost. In addition to its use as a pulse generator, it can also function as a mode locker, and can be expected to be used in various applications.

DESCRIPTION OF SYMBOLS 1 Pulse light generator 11 Light source 12 Polarization conversion part 13 Polarizing plate 21 Glass plate 22 Polarizer 31 Main-body part 32 Convex part

Claims (3)

Light emitting means for emitting continuous (CW) light;
Polarization conversion means in which CW light emitted from the light emission means is incident and nanometer-size polarizers having an asymmetric shape with respect to the incident direction of the CW light are arranged in or on the substrate;
A pulsed light generator comprising: a polarizing plate that generates pulsed light at predetermined time intervals by transmitting a predetermined polarized light component of the light that has passed through the polarization converting means. The pulsed light generator according to claim 1, wherein the polarizer has a convex portion that is projected in a direction substantially orthogonal to the incident direction of the CW light. The polarization conversion unit generates near-field light in the vicinity of the convex portion based on the incident CW light, and based on the generated near-field light in the direction of magnetic field oscillation of the continuously incident CW light. The pulsed light generator according to claim 2, wherein

Images