WO2012167447A1 - 光频率间隔为25GHz的外腔式可调谐激光器 - Google Patents

光频率间隔为25GHz的外腔式可调谐激光器 Download PDF

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Publication number
WO2012167447A1
WO2012167447A1 PCT/CN2011/075682 CN2011075682W WO2012167447A1 WO 2012167447 A1 WO2012167447 A1 WO 2012167447A1 CN 2011075682 W CN2011075682 W CN 2011075682W WO 2012167447 A1 WO2012167447 A1 WO 2012167447A1
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Prior art keywords
laser
optical
tunable
acousto
mirror
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PCT/CN2011/075682
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English (en)
French (fr)
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高培良
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天津奇谱光电技术有限公司
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Publication of WO2012167447A1 publication Critical patent/WO2012167447A1/zh
Priority to US13/974,585 priority Critical patent/US9048610B2/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/005—Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping
    • H01S3/0085—Modulating the output, i.e. the laser beam is modulated outside the laser cavity
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/106—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity
    • H01S3/1068—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity using an acousto-optical device
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
    • H01S5/14—External cavity lasers
    • H01S5/141—External cavity lasers using a wavelength selective device, e.g. a grating or etalon
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/08—Construction or shape of optical resonators or components thereof
    • H01S3/08013—Resonator comprising a fibre, e.g. for modifying dispersion or repetition rate
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/08—Construction or shape of optical resonators or components thereof
    • H01S3/081—Construction or shape of optical resonators or components thereof comprising three or more reflectors
    • H01S3/0813—Configuration of resonator
    • H01S3/0817—Configuration of resonator having 5 reflectors, e.g. W-shaped resonators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/106—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity
    • H01S3/107—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity using electro-optic devices, e.g. exhibiting Pockels or Kerr effect
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
    • H01S5/14—External cavity lasers
    • H01S5/141—External cavity lasers using a wavelength selective device, e.g. a grating or etalon
    • H01S5/142—External cavity lasers using a wavelength selective device, e.g. a grating or etalon which comprises an additional resonator
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
    • H01S5/14—External cavity lasers
    • H01S5/141—External cavity lasers using a wavelength selective device, e.g. a grating or etalon
    • H01S5/143—Littman-Metcalf configuration, e.g. laser - grating - mirror

Definitions

  • the invention belongs to the field of optoelectronics, especially an external cavity tunable laser with an optical frequency interval of 25 GHz. Background technique
  • an ideal tunable laser should include the following features: wide tunable range, covering C and/or L-band (approximately 1520 nm to 1620 nm); small size; any two International Telecommunications Union (ITU) frequencies Fast switching between intervals (on the order of sub-milliseconds); long-term stability (over 25 years of operation); high reliability under extreme environmental conditions; low power consumption; easy to manufacture and low cost.
  • ITU International Telecommunications Union
  • DWDMs wavelength division multiplexers
  • optical communication systems have evolved from systems with channel spacings of 400 GHz and 200 GHz to channel spacing of 100 GHz and 50 GHz. Even 25 GHz and higher density systems; at the same time, the optical communication system transmission rate has also evolved from the past 2.5 Gbps to 10 Gbps, 40 Gbps and 100 Gbps systems.
  • An external cavity tunable laser with a high-sharp optical etalon is one of the good choices for a new generation of dynamic, high transmission rate and high spectral density optical communication systems because of its ability to meet these requirements.
  • a matching tunable narrowband optical filter is required. If the laser output optical frequency interval is required to be Af, the optical filter filtering bandwidth should not exceed twice the frequency interval, that is, ⁇ 2 (to avoid the laser operating in a multi-mode state, thereby improving the stability of the laser operation; If the laser output optical frequency interval is 50 GHz, the optical filter filtering bandwidth should be ⁇ 10 «»3 ⁇ 4 ; if the output optical frequency interval is further required to be 25 GHz, the optical filter filtering bandwidth should be ⁇ 5 «»3 ⁇ 4.
  • Optical filters For narrower bandwidth Optical filters, the more difficult it is to make, the higher the cost, such as the commonly used optical grating filters and acousto-optic filters. Similarly, for optical etalons with narrower transmission spectral spacing, the larger the size, the more difficult it is to make. The higher, the higher the cost.
  • An external cavity tunable laser with an optical frequency interval of 25 GHz comprising a laser cavity end mirror mounted on a laser gain medium and a laser gain medium sequentially mounted in the laser cavity, an intracavity collimating lens, and an active optical phase modulation , tunable acousto-optic filter and endoscopic full-mirror, also includes:
  • An active polarization rotator placed after the tunable acousto-optic filter, receives a beam that is diffracted twice by the tunable acousto-optic filter to control the polarization direction of the incident linearly polarized light;
  • a polarizing beam splitter placed in the active polarization rotator, totally transmitting the incident parallel polarized light, and reflecting the incident vertically polarized light to a direction 90 degrees from the incident light;
  • the first optical etalon and the first total reflection mirror are placed in a direction perpendicular to the optical axis of the two diffracted beams of the tunable acousto-optic filter, receive the vertically polarized light output from the polarization beam splitter, and output to the first
  • the total reflection mirror, the first total reflection mirror and the laser cavity end mirror constitute a first laser resonator cavity, and the second diffracted light of the tunable acousto-optic filter forms a laser oscillation in the first laser cavity;
  • a second optical etalon and a second total reflection mirror are disposed in the optical axis direction of the two diffracted beams of the tunable acousto-optic filter, receive parallel polarized light output from the polarization beam splitter, and output to the second total reflection mirror,
  • the second total reflection mirror and the laser end mirror form a second laser resonator cavity, and the second diffracted light of the tunable acousto-optic filter forms a laser oscillation in the second laser cavity;
  • An RF signal source for supplying RF energy to the tunable acousto-optic filter and adjusting the oscillation wavelength of the laser cavity by changing the RF frequency;
  • a pumping device for a laser gain medium a driving device for an active optical phase modulator, a driving device for an active polarization rotator, and a laser drive control circuit.
  • first optical etalon and the second optical etalon have the same sharpness factor.
  • first optical etalon and the second optical etalon have the same spectral range as the laser gain medium, and the first optical etalon and the second optical etalon have a transmission spectrum peak interval of 50 GHz, the second optical The peak frequency of the transmission spectrum of the etalon differs from the peak frequency of the transmission spectrum of the first optical etalon by 25 GHz.
  • the first total reflection mirror, the second total reflection mirror, and the intracavity total reflection mirror are one of the following types of mirrors: a plane mirror, a convex mirror, and a concave mirror; the first total reflection mirror, The second total reflection mirror and the intraluminal full mirror have the same spectral range as the laser gain medium.
  • the laser cavity end mirror is a full mirror or a partial mirror in a specified spectral range
  • the The optical cavity end mirror has the same spectral range as the laser gain medium.
  • the tunable acousto-optic filter comprises an acousto-optic crystal and an acoustic transducer.
  • the tunable acousto-optic filter is a narrow-band optical filter
  • the spectral range of the tunable acousto-optic filter is the same as the spectral range of the laser gain medium
  • the FWHM of the filtered spectrum is not greater than the first optical etalon or
  • the second optical etalon has twice the peak frequency of the transmission spectrum.
  • the active optical phase modulator is one of the following types: an electro-optic phase modulator, or a magneto-optical phase modulator, or a liquid crystal phase modulator, or an acousto-optic phase modulator, or based on Other forms of phase modulators of physical optical effects, or combinations of phase modulators as described above, and have the same spectral range as the laser gain medium.
  • the active polarization rotator is one of the following types: an electro-optic active polarization rotator, or a magneto-optical active polarization rotator, or a liquid crystal active polarization rotator, or an acousto-optic active A polarization rotator, or other form of active polarization rotator based on physical optical effects, or a combination of the above-described active polarization rotators and having the same spectral range as the laser gain medium.
  • the laser drive control circuit comprises: a digital signal microprocessor, four digital-to-analog conversion modules, a laser pump source, an active optical phase modulator drive source, a tunable acousto-optic filter drive source, and an active polarization
  • the rotator drive source, the digital signal microprocessor receives the external command signal command and realizes the laser by the laser pump source, the active optical phase modulator drive source, the tunable acousto-optic filter drive source and the active polarization rotator drive source Drive control for gain media, active optical phase modulators, tunable acousto-optic filters, and active polarization rotators.
  • the invention has reasonable design, and adopts an active polarization rotator, a polarization beam splitter, two optical etalons with transmission peaks of 50 GHz and two total reflection mirrors to form sub-cavities of two laser resonators.
  • Interval tunable acousto-optic filters and optical etalon with a 50 GHz transmission spectrum to achieve a stable laser output with a spectral separation of 25 GHz, reducing the filter bandwidth requirements for tunable acousto-optic filters and optical etalon transmission spectra
  • the requirement of peak frequency spacing density greatly reduces the difficulty of making tunable acousto-optic filters and optical etalons. It has the characteristics of stable and reliable
  • DRAWINGS 1 is a schematic diagram of a conventional tunable acousto-optic filter
  • FIG. 2 is a schematic diagram of a conventional tunable acousto-optic filter for realizing frequency offset compensation
  • FIG. 3 is a wave vector diagram of an incident beam, an acoustic wave field, and a diffracted beam of primary and secondary diffraction in an acousto-optic crystal;
  • Figure 4 is a schematic illustration of the structure of an external cavity tunable laser employing a tunable acousto-optic filter and a single optical etalon;
  • Figure 5 is a schematic view of the structure of the present invention.
  • Figure 6 is a schematic view of a device for performing laser resonant mode switching using an active polarization rotator and a polarization beam splitter;
  • Figure 7 is a schematic view showing a transmission path of a polarized light beam of parallel light in the device of Figure 6;
  • Figure 8 is a schematic view showing the transmission path of the polarized light beam of the vertical light in the device of Figure 6;
  • FIG. 9 is a transmission spectrum diagram of a first optical etalon and a second optical etalon, wherein FIG. 9-1 is a transmission spectrum of the first optical etalon with an interval of 50 GHz, and FIG. 9-2 is a second optical etalon Transmission spectrum, the interval is 50 GHz, but the peak frequency of the transmission spectrum and the peak frequency of the transmission spectrum of the first optical etalon are 25 GHz;
  • FIG. 10 is a schematic diagram of the output spectrum of the tunable laser with a transmission spectral interval of 25 GHz;
  • FIG. 11 is a block diagram showing the principle of the laser drive control circuit of the present invention.
  • FIG. 1 shows a conventional tunable acousto-optic filter 100.
  • the tunable acousto-optic filter 100 includes a transducer 22, a radio frequency signal source 20, and an acousto-optic crystal 26.
  • the transducer 20 is mounted on the acousto-optic crystal, and the incident beam 2 is incident on the acousto-optic crystal 26 at a Bragg angle to generate zero.
  • the working principle of the acousto-optic filter is based on a phenomenon called Bragg diffraction.
  • Bragg diffraction involves the interaction of photons (quantum of light energy) and phonons (quantum of acoustic energy). In this interaction, energy and momentum are conserved.
  • the Acousto-Optical Tunable Filter (A0TF) is a solid-state band-pass optical filter that can be electrically tuned. Compared to traditional technologies, AOTF provides continuous, fast adjustment and narrow spectral bandwidth.
  • Non-collinear and non-paraxial filters with high RF frequencies enable narrowband filtering.
  • the formula indicates that the magnitude of the optical wave frequency offset is equal to the frequency of the acoustic wave.
  • the tunable acousto-optic filter 200 includes a transducer 22, an acousto-optic crystal 26, a radio frequency signal source 20, and a total reflection mirror 28,
  • the incident beam 2 is incident on the acousto-optic crystal 26 at a Bragg angle, producing a zero-order diffracted beam 4 and a first-order diffracted beam 6, which is passed through a total reflection mirror through the acousto-optic crystal 26 to produce a zero-order diffracted beam 10 and a first order Diffracted beam 12
  • Figure 3-1 and Figure 3-2 show the incident relationship of ⁇ J, diffracted light ( ⁇ d ) and sound wave ( ⁇ J , respectively. As mentioned above, this relationship is always true, using the plus sign (+ Or the minus sign (-) is determined by the direction of the incident sound wave.
  • the acousto-optic crystals employed are anisotropic and have birefringence characteristics.
  • One of the materials is cerium oxide (Te0 2 ), which is widely used in such applications due to its high optical uniformity, low light absorption and high optical power resistance in shear mode.
  • Other substances such as lithium niobate (LiNb0 3 ), gallium phosphide (GaP), and lead bis(PbMo0 4 ) are also frequently used in various acousto-optic devices. There are many factors that influence the selection of specific substances.
  • FIG 4 shows an external cavity adjustable with a single optical etalon and a tunable acousto-optic filter as shown in Figure 2.
  • Harmonic laser 300 includes a laser cavity end mirror 32 directly plated on a laser gain medium 34, a laser gain medium 34, an intracavity collimating lens 36, an active optical phase modulator 40, a tunable acousto-optic filter 100, a cavity The inner full mirror 28, the optical etalon 42, and the full mirror 44. Among them, the laser cavity end mirror 32 and the full mirror 44 constitute a laser cavity.
  • Laser output mirrors typically have different reflectivities for different wavelengths or colors of light, and the reflectivity referred to herein is the reflectance corresponding to the wavelength bandwidth at which the laser operates.
  • the laser cavity end mirror 32 can be a partial mirror or a full mirror depending on the situation. If the laser gain medium is a semiconductor gain medium, since there is generally a relatively large output dispersion angle, the intracavity collimating lens of the tunable laser 300 is generally used when the laser gain medium is a semiconductor gain medium. When the laser gain medium is a gas, liquid or some solid medium, the intracavity collimating lens is generally not used, but a non-planar cavity mirror is used to achieve a reasonable distribution of the intracavity beam. When such a laser is used for fiber optic communication, the output beam 4 needs to be coupled into the fiber, and the collimating lens 38 is indispensable.
  • the broadband fluorescent light beam 36 emitted by the laser gain medium 34 is collimated by the intracavity collimating lens 38 and transmitted through the active optical phase modulator 40 to enter the acousto-optic crystal 26 at a Bragg angle.
  • the diffracted first-order diffracted light 6 is incident on the intracavity full-mirror 28 at a Bragg angle, and the reflected beam 8 enters the acousto-optic crystal 26 at a Bragg angle.
  • the diffracted first-order diffracted light 12 is reflected by the full refracting mirror 44 back into the laser cavity through the optical etalon 42, and laser oscillation and amplification are formed in the laser cavity.
  • beams 4 and 10 respectively serve as zero-order diffracted beams of the laser beam 2, 8; the zero-order diffracted beam of beam 13 as the reflected beam of beam 12 becomes the loss in the laser cavity, and beam 4 has the largest
  • the energy is chosen as the laser output beam.
  • Beams 10 and 13 can be used to monitor the optical power and wavelength within the laser cavity.
  • the tunable acousto-optic filter 100 is caused in the structure of the tunable laser 300.
  • the wavelength of the light is offset by zero.
  • a laser oscillation narrower than the primary diffraction bandwidth is formed in the laser cavity.
  • Laser output tuning is achieved by active optical phase modulator 40 and tunable acousto-optic filter 100.
  • Changing the RF frequency of the RF signal source 20 of the tunable acousto-optic filter changes the resonant frequency of the light wave within the laser cavity.
  • the active optical phase modulator 40 modulates the phase of the light wave such that a particular light wave produces laser oscillations and amplification in the laser cavity.
  • Optical etalon 42 determines the spacing and bandwidth of the laser output spectrum.
  • An optical etalon with a high sharpness factor can reduce the spectral bandwidth of the output beam and increase the side mode rejection ratio. If it is desired to reduce the interval of the laser output spectrum, it is necessary to simultaneously reduce the filter bandwidth of the tunable acousto-optic filter 100 and reduce the peak frequency of the transmission spectrum of the optical etalon 42. Interval to avoid mode hopping and to ensure single mode oscillation of the laser.
  • the interval of the output spectrum of the laser is required to be 25 GHz, and not only the spectrum interval of the optical etalon 42 is required to be 25 GHz, but also the FWHM (spectral half-width) parameter of the filter bandwidth of the tunable acousto-optic filter 100 is at least less than 50 GHz.
  • the technical difficulty and manufacturing cost of the optical etalon 42 will also increase.
  • the filter bandwidth FWHM of the tunable acousto-optic filter is less than 2 Af (assuming that the transmission bandwidth of the optical etalon is A f).
  • the filter bandwidth of the tunable acousto-optic filter is greater than 2 ⁇ , it is easy to form multimode oscillation, resulting in multimode output or mode hopping.
  • the filter bandwidth FWHM value of the tunable acousto-optic filter is required to be narrower.
  • the external cavity tunable laser 400 of the present invention is described in detail below:
  • the external cavity tunable laser 400 provides a method for solving the above problems by using two optical optical etalons and placed in sub-chambers of two laser cavities.
  • the external cavity tunable laser 400 includes a laser cavity end face mirror 32 directly plated on the laser gain medium 34, a laser gain medium 34, an intracavity collimator lens 38, an active optical phase modulator 40, Tunable acousto-optic filter 100, intracavity full mirror 28, active polarization rotator 50, polarization beam splitter 52, first optical etalon 62, first total reflection mirror 64, second optical etalon 56, second The total reflection mirror 58 and the laser drive control circuit.
  • An active polarization rotator 50 is mounted behind the tunable acousto-optic filter 100 for rotating the polarization direction of the incident linearly polarized light 12 by 90 degrees, and the active polarization rotator 50 is followed by a polarization splitter 52 for incident parallel polarization.
  • the light is totally transmissive, and the incident vertically polarized light is reflected in a direction 90 degrees from the incident light;
  • the first optical etalon 62 is mounted in a direction perpendicular to the laser beam 12 in the laser cavity for receiving the secondary polarizing beam splitter 52 outputs the vertically polarized light 60 and outputs it to the first total reflection mirror 64.
  • the first total reflection mirror 64 and the laser cavity end mirror 32 constitute a first laser resonator sub-cavity.
  • a second optical etalon 56 is mounted in the direction of the beam 12 in the laser cavity for receiving the parallel polarized light output from the polarization beam splitter 52 and outputting it to the second total reflection mirror 58.
  • the second total reflection mirror 58 and the laser cavity end mirror 32 constitute a second laser resonator sub-cavity.
  • the tunable laser 400 differs from the tunable laser 300 in that the optical etalon 34 and the full mirror 36 in the tunable laser 300 (Fig.
  • a dual optical path system 500 consisting of a mirror 52, a first optical etalon 62, a first total reflection mirror 64, a second optical etalon 56 and a second total reflection mirror 58 is shown in FIG.
  • the function of the active polarization rotator 50 is to change the polarization direction of the incident beam 12: when the active polarization rotator is in an inoperative state, the incident beam 12 does not change the polarization state, directly passes through the polarization beam splitter 52, The two-light etalon 56 then reaches the second total reflection mirror 58 and is reflected back into the laser cavity by the second total reflection mirror 58, as shown in FIG.
  • the polarization state of the incident beam 12 is rotated by 90 degrees to become vertically polarized light, which is reflected by the polarization beam splitter 54 and reaches the second total reflection through the first optical etalon 62.
  • Mirror 64 then The second total reflection mirror 64 is reflected back into the laser cavity as shown in FIG. Since the light reflected back through the second total reflection mirror 64 passes through the active polarization rotator 50 again, the polarization state is rotated by 90 degrees again, so that the polarization direction of the output beam of the laser does not change.
  • the tunable laser 400 of FIG. 5 can be formed into sub-cavities of two laser resonators: the first sub-cavity is comprised of a laser cavity end mirror 32 and a first total reflection mirror 64, The second sub-cavity is composed of a laser cavity end mirror 32 and a second total reflection mirror 58.
  • Figures 9-1 and 9-2 show the transmission spectra of the first optical etalon 62 and the second optical etalon 56, respectively.
  • the two second all-optical etalons 56 and 62 have the same transmission spectral spacing of 50 GHz and a sharpness factor, but the transmission spectral peaks differ by 25 GHz.
  • the output spectrum of the tunable laser 400 is a combination of two sub-cavities to achieve a 25 GHz spectral peak spacing and a tunable laser output with uniform polarization, as shown in FIG.
  • the first optical etalon 62 and the second optical standard 56 have the same sharpness coefficient, and the first optical etalon 62 and the second optical etalon 56 have the same spectral range as the laser gain medium, first The transmission spectroscopy peak spacing of the optical etalon 62 and the second optical etalon 56 is 50 GHz, and the transmission spectrum peak frequency of the second optical etalon 56 differs from the transmission spectrum peak frequency of the first optical etalon 62 by 25 GHz.
  • the transmission spectrum peaks of the first optical etalon 62 should meet the International Optical Communication Standard (ITU GRID).
  • ITU GRID International Optical Communication Standard
  • the peak of the transmission spectrum of the first optical etalon 62 can be designed to different values depending on the particular application.
  • the peak of the transmission spectrum and the peak interval of the transmission spectrum of the second optical etalon should also meet the above conditions.
  • the tunable laser 400 With the structure of the tunable laser 400, as long as the filter bandwidth FWHM of the tunable acousto-optic filter is less than 2Af (assuming that the optical etalon has a transmission bandwidth of Af), a tunable output with a denser optical frequency interval can be realized.
  • the first optical etalon 62 and the second optical etalon 56 may have a transmission spectral peak interval of 25 GHz and satisfy the difference between the transmission spectrum peak frequency of the second optical etalon 56 and the transmission spectrum peak frequency of the first optical etalon.
  • the tunable laser 400 can achieve a tunable output with a spectral frequency interval of 12. 5 GHz as long as the filter bandwidth FWHM of the tunable acousto-optic filter is less than 50 GHz.
  • the fluorescence output from a semiconductor laser gain medium is linearly polarized light.
  • no polarizer is required in the cavity.
  • a polarizer must be used to enable the tunable laser 400 to perform the above functions.
  • the DWDM optical communication network is developing in the direction of 25 GHz and even higher density of optical channels.
  • the requirement for a tunable acousto-optic filter with a narrower filter bandwidth also makes it more difficult to manufacture such a tunable acousto-optic filter and a tunable laser that requires miniaturization, and is more expensive.
  • the laser's output beam is required to have a higher tunable spectral density, and the overall laser cost and technical difficulty will be further improved. Therefore, the tunable laser 400 can be flattened in an existing 50 GHz spectrally spaced external cavity laser.
  • On-stage, a novel approach to tunable output with 25 GHz spectral spacing and even smaller spectral spacing is provided without significant cost and manufacturing difficulties.
  • the tunable laser 400 described above is also equipped with a laser drive control circuit.
  • the laser drive control circuit includes a digital signal microprocessor (DSP) 112 with an embedded software program, four digital to analog conversion (D/A) devices 102, 106, 110 and 116, a laser pump source 101, and an active source.
  • the optical phase modulator drives source 104, RF signal source 108, and active polarization rotator drive source 114.
  • a digital signal microprocessor (DSP) 112 with an embedded software program controls the laser pump source 101, the active optical phase modulator drive source, respectively, through digital to analog conversion (D/A) devices 102, 106, 110, and 116. 104.
  • the digital signal microprocessor 112 can also receive external commands to control the tunable laser 400.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Optics & Photonics (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Lasers (AREA)

Abstract

公开了一种频率间隔为25GHz的外腔式可调谐激光器（400）。激光器（400）包括镀在激光增益介质（34）上的激光腔端面镜（32）和依次安装在激光腔内的激光增益介质（34）、准直透镜（38）、有源光相位调制器（40）、可调谐声光滤波器，和全反射镜（28）。激光器（400）还包括放置在可调谐声光滤波器后的有源偏振旋光器（50）、放置在有源偏振旋光器（50）后的偏振分束器（52）、第一光学标准具（62）、第一全反射镜（64）、第二光学标准具（56）、第二全反射镜（58）。激光器（400）具有高频谱密度、窄频谱带宽，输出稳定，性能稳定，成本低，尺寸小，易于安装和生产的优点。

Description

光频率间隔为 25GHz的外腔式可调谐激光器 技术领域
本发明属于光电子领域， 尤其是光频率间隔为 25GHz的外腔式可调谐激光器。 背景技术
目前， 大多数现代通迅系统都是基于光纤通信网络， 而光纤通信网络提供了前所未有 的大容量和安装的灵活性， 可以支持不断发展的各种宽带应用。 宽带和多通道的可调谐激 光器可以帮助最大限度的利用现有的光纤网络资源。 通过动态提供带宽可以将流量从拥挤 通道转移到未使用的通道， 从而满足互联网的需求。 使用可调谐激光器使快速建立或改变 光路变得容易， 它是实现动态光纤网络的重要器件之一。
针对这种应用,理想的可调谐激光器应当包括以下特性：可调谐范围宽，覆盖 C和（或） L波段（大约 1520纳米至 1620纳米）； 尺寸小； 任何两个国际电信联盟（ITU)频率间隔 之间的切换速度快 （亚毫秒量级）； 长期工作稳定性好 （超过 25年的运行时间）； 在极端 环境条件下的高可靠性； 低功耗； 易制造和低成本。
随着高密度波分复用器（DWDM)的和其他高密度频谱相关器件的开发成功， 现代光 通迅系统已从过去的频道间隔为 400GHz和 200GHz 的系统， 发展到频道间隔为 100GHz 和 50GHz,甚至 25GHz和更高密度的系统；同时，光通迅系统传输速率也从过去的 2.5Gbps 发展到 10Gbps、 40Gbps和 lOOGbps系统。 这就对用于光通迅系统的小型可调谐激光器 提出了相应的要求， 特别是在激光器输出光的光谱密度和光谱宽度提出了更高的要求。 采 用高锐度的光学标准具的外腔式可调谐激光器， 因其能够实现上述要求， 是用于新一代动 态， 高传输速率和高光谱密度的光通迅系统的好的选择之一。
在外腔式可调谐激光器中， 特别是用于光通讯的这类器件， 除了用具有高锐度的光学 标准具来压缩激光输出带宽外， 还需要有相匹配的可调谐的窄带光滤波器。 如果要求激光 器输出光频率间隔为 Af, 则光滤波器滤波带宽应不超过该频率间隔的两倍， 即<2 (， 方可 避免激光器工作在多模状态， 从而提高激光器工作的稳定性； 如果要求激光器输出光频率 间隔为 50GHz, 则光滤波器滤波带宽应<10«»¾; 如果进一步要求输出光频率间隔为 25GHz, 则光滤波器滤波带宽应<5«»¾。对于带宽越窄的光滤波器， 制作难度就越高， 造 价也就越高， 如常用的光学光栅滤波器和声光滤波器等。 同样， 对于透射光谱间隔越窄的 光学标准具， 尺寸就越大， 制作难度就越高， 造价也就越高。
发明内容 本发明的目的在于克服现有技术的不足， 提供一种低成本、 尺寸小、 易于生产且性能 高的可调谐激光器。
本发明解决现有的技术问题是采取以下技术方案实现的：
一种光频率间隔为 25GHz的外腔式可调谐激光器，包括安装在激光增益介质上的激光 腔端面镜和依次安装在激光腔内的激光增益介质、 腔内准直透镜、 有源光相位调制器、 可 调谐声光滤波器和腔内全反镜， 还包括：
一个有源偏振旋光器， 放置在可调谐声光滤波器后， 接收经可调谐声光滤波器两次衍 射的光束， 控制入射的线偏振光的偏振方向；
一个偏振分束器， 放置在有源偏振旋光器后， 对入射的平行偏振光全透射， 而对入射 的垂直偏振光反射到与入射光成 90度的方向上；
第一光学标准具和第一全反射镜， 放置在与可调谐声光滤波器两次衍射光束的光轴相 垂直的方向上， 接收从偏振分束器输出的垂直偏振光并输出到第一全反射镜， 第一全反射 镜与激光腔端面镜构成第一激光谐振子腔， 可调谐声光滤波器二次衍射的光线在第一激光 腔中形成激光振荡；
第二光学标准具和第二全反射镜， 放置在可调谐声光滤波器两次衍射光束的光轴方向 上， 接收从偏振分束器输出的平行偏振光并输出到第二全反射镜， 第二全反射镜与激光端 面镜构成第二激光谐振子腔， 可调谐声光滤波器二次衍射的光线在第二激光腔中形成激光 振荡；
一个射频信号源， 用于提供给可调谐声光滤波器射频能量并通过改变射频频率来调节 激光谐振腔的振荡波长；
激光增益介质的泵浦设备、 有源光相位调制器的驱动设备和有源偏振旋光器的驱动设 备及激光器驱动控制电路。
而且， 所述的第一光学标准具和上述第二光学标准具具有相同的锐度系数。
而且，所述的第一光学标准具、第二光学标准具具有与激光增益介质相同的光谱范围， 上述第一光学标准具和第二光学标准具的透射光谱峰值间隔均为 50GHz,第二光学标准具 的透射光谱峰值频率与第一光学标准具的透射光谱峰值频率相差为 25GHz。
而且， 所述的第一全反射镜、 第二全反射镜和腔内全反镜为以下几种类型的反射镜之 一： 平面镜、 凸面镜和凹面镜； 所述的第一全反射镜、 第二全反射镜和腔内全反镜具有与 激光增益介质相同的光谱范围。
而且， 所述的激光腔端面镜是在指定光谱范围内的全反镜或或部分反射镜， 所述的激 光腔端面镜具有与激光增益介质相同的光谱范围。
而且， 所述的可调谐声光滤波器包括一个声光晶体和一个声波换能器。
而且， 所述的可调谐声光滤波器为窄带光滤波器， 该可调谐声光滤波器的光谱范围与 激光增益介质的光谱范围相同， 且其滤波光谱的 FWHM不大于第一光学标准具或第二光 学标准具透射光谱峰值频率的二倍。
而且， 所述的有源光相位调制器是以下几种类型之一： 电光相位调制器， 或者是磁光 相位调制器， 或者是液晶相位调制器， 或者是声光相位调制器， 或者是基于物理光学效应 的其他形式的相位调制器， 或者是上述相位调制器的组合并具有与激光增益介质相同的光 谱范围。
而且， 所述的有源偏振旋光器是以下几种类型之一： 电光有源偏振旋光器， 或者是磁 光有源偏振旋光器， 或者是液晶有源偏振旋光器， 或者是声光有源偏振旋光器， 或者是基 于物理光学效应的其他形式的有源偏振旋光器， 或者是上述有源偏振旋光器的组合并具有 与激光增益介质相同的光谱范围。
而且， 所述的激光器驱动控制电路包括： 数字信号微处理器、 四个数模转换模块、 激 光泵浦源、有源光相位调制器驱动源、可调谐声光滤波器驱动源和有源偏振旋光器驱动源， 数字信号微处理器接收外部指令信号指令并通过激光泵浦源、 有源光相位调制器驱动源、 可调谐声光滤波器驱动源和有源偏振旋光器驱动源实现对激光增益介质、 有源光相位调制 器、 可调谐声光滤波器和有源偏振旋光器的驱动控制功能。
本发明的优点和积极效果是：
本发明设计合理， 其采用了有源偏振旋光器、 偏振光分束镜、 两个透射光谱峰值间隔 同为 50GHz的光学标准具和两个全反射镜构成两个激光谐振腔的子腔，实现在宽频谱范围 内的频谱间隔为 25GHz的高密度、窄频谱带宽和可调谐的稳定激光输出，将对可调谐声光 滤波器的滤波带宽的要求降低了一倍，将适用于输出为 50GHz频谱间隔的可调谐声光滤波 器和透射光谱间隔为 50GHz的光学标准具来实现频谱间隔为 25GHz 的稳定激光输出， 降低了对可调谐声光滤波器的滤波带宽的要求以及对光学标准具透射光谱峰值频率间隔 密度的要求， 从而大大降低了可调谐声光滤波器和光学标准具的制作难度， 具有性能稳定 可靠、 成本低廉、 尺寸小、 易于安装及生产等特点， 可满足光纤通信对于小尺寸和极端工 作环境下的可靠运行。 并且在生物、 医疗器械和光纤传感器网络等其他领域中也有着广泛 的应用。
附图说明 图 1是现有的一种普通可调谐声光滤波器的示意图；
图 2是现有的一种实现频率偏移补偿的可调谐声光滤波器示意图；
图 3是在声光晶体中一次衍射和二次衍射的入射光束、 声波场和衍射光束的波矢关系 图；
图 4是一种采用了可调谐声光滤波器和单一光标准具的外腔式可调谐激光器的结构示 意图；
图 5是本发明的结构示意图；
图 6是利用一个有源偏振旋光器和一个偏振光分束镜进行激光谐振模切换的装置示意 图；
图 7 是显示了图 6装置中平行光偏振光束的传输路径示意图；
图 8 是显示了图 6装置中垂直光偏振光束的传输路径示意图；
图 9是第一光学标准具和第二光学标准具的透射光谱示意图， 其中图 9-1 是第一光学 标准具的透射光谱， 其间隔为 50GHz, 图 9-2 是第二光学标准具的透射光谱， 其间隔为 50GHz, 但透射光谱峰值频率和第一光学标准具的透射光谱峰值频率相差为 25GHz; 图 10是透射光谱间隔为 25GHz的可调谐激光器输出光谱示意图；
图 11是本发明的激光驱动控制电路的原理框图。
具体实施方式
以下结合附图对本发明实施例做进一步详述。
图 1显示了一种普通的可调谐声光滤波器 100。 该可调谐声光滤波器 100包括换能器 22、 射频信号源 20、 声光晶体 26, 换能器 20安装在声光晶体上， 入射光束 2以布拉格角 入射到声光晶体 26, 产生零级衍射光束 4和一级衍射光束 6
声光滤波器的工作原理是基于一种叫做布拉格衍射的现象。 布拉格衍射涉及了光子 (光能的量子）和声子 （声能的量子） 的相互作用过程。 在这个互作用的过程中， 能量和 动量都是守恒的。 动量守恒要求 ϋ K d = ^ K ^ + ^ K s, 其中 ϋ K d是衍射光子的动量， 是入射光子的动量， 是互作用的声子的动量。 约分去掉 ^后得到：
这就给出了布拉格衍射最基本的波矢等式， 它表明了衍射光的波矢是入射光波矢与声波波 矢的矢量和， 如图 3-1所示。
能量守恒要求 ϋ ο^ = + Ω ,其中 是衍射光的角频率， ω是入射光的角频率， Ω是声波的角频率。 约分去掉 ϋ 后得到： = ω + Ω。 这表明衍射光子的角频率被声 波的角频率轻微改变， 即光线的频率产生了多普勒频移。 声光可调谐滤波器（A0TF) 是一种固态的、 可采用电调谐的带通光滤波器。 与传统的 技术相比， A0TF提供了连续、 快速的调节能力和窄的光谱带宽。 声光滤波器有两种类型： 共线型与非共线型。 其中具有高射频频率的非共线型和非近轴滤波器可以实现窄带滤波。 然而根据上面的公式， = ω + Ω , 公式表明光波频率偏移的大小等于声波的频率。
尽管因为光线频率和声波频率相差很多个数量级， 从而产生的偏移量很小， 但是在一 些激光器系统中还是会引起不稳定的运行。这个问题的一个解决办法是使用两个 A0TF,其 中第二个 A0TF用来抵消第一个 A0TF所带来的频率偏移； 另一个解决办法是在同一个声光 晶体上使用两个换能器。 但是这些解决办法都有几个缺点： 1、 增加了系统的体积； 2、 使 得光学对准更为困难； 3、 引起运行的不稳定性； 4、 增加成本， 对大批量生产来说尤为重 要。
图 2显示了一种可以有效消除频率偏移的可调谐声光滤波器 200, 该可调谐声光滤波 器 200包括换能器 22、 声光晶体 26、 射频信号源 20、 全反射镜 28, 入射光束 2以布拉格 角入射到声光晶体 26, 产生零级衍射光束 4和一级衍射光束 6, —级衍射光束 6经全反射 镜经声光晶体 26后产生零级衍射光束 10和一级衍射光束 12
图 3-1和图 3-2分别显示了入射光（ κ J、 衍射光（ κ d)和声波（ κ J 的波矢关系。 正如上面提到的， 这个关系永远成立， 使用加号 （+ )还是减号 （-) 由入 射声波的方向决定。在图 3-1中， 光线 2 ( K 2)、 光线 6 ( κ 6)和声波 24 ( κ J 的关系是： κ 2 + s = κ 4。 声波 ^不仅仅使得衍射光的方向向上偏移， 光线的角频率 ω 也向上偏 移了 Ω = Vs I κ 其中 ^是声波的速度。 在图 3-2中， 光线 8 8)、 光线 12 ( κ 12) 和声波 24 ( κ J 的关系是： κ 5 - K s = K l2。 在这种情况下， 声波使得衍射光的方向向 下偏移， 并且将第二次衍射的光线 12的角频率 ω 也向下偏移了 Vs I K s |。 因为向上和向 下的偏移量基本相同， 当光线 12从声光滤波器 200中射出时， 整体频率偏移被充分的消 除了。
在一些具体实施中， 例如需要窄带调节时， 采用的声光晶体是各向异性并有双折射特 性。其中一种物质为二氧化碲（Te02), 由于其运行在剪切模式时具有高光学均匀性、低光 吸收度和耐高光功率能力的特点，广泛使用于这类应用中。其他物质例如铌酸锂（LiNb03)、 磷化镓（GaP)和钥酸铅（PbMo04)也经常用于各种声光器件中。 影响选择特定物质的因素 有很多， 下面仅列出几种， 如： 声光器件的类型、 高质量晶体是否容易获得以及应用的类 型和需求， 例如衍射效率功率损耗、 入射光与衍射光的分散度和整体器件的大小等。
图 4显示了一种采用单一光学标准具和如图 2所示的可调谐声光滤波器的外腔式可调 谐激光器 300。 该可调谐激光器 300包括直接镀在激光增益介质 34上的激光腔端面镜 32、 激光增益介质 34、 腔内准直透镜 36、 有源光相位调制器 40、 可调谐声光滤波器 100、 腔 内全反镜 28、 光学标准具 42、 全反镜 44。 其中， 激光腔端面镜 32和全反镜 44构成了激 光谐振腔。
激光输出镜通常对不同波长或颜色光的反射率不同， 这里提到的反射率是与激光器运 行的波长带宽相对应的反射率。 激光腔端面镜 32可以根据不同的情况， 采用部分反射镜 或全反镜。 如果激光增益介质是半导体增益介质时， 由于一般都有比较大的输出分散角， 因此， 可调谐激光器 300的腔内准直透镜一般是针对激光增益介质是半导体增益介质时使 用。 当激光增益介质是气体、 液体或有些固体介质时， 一般不用腔内准直透镜， 而是采用 非平面腔镜以实现腔内光束的合理分布。 当这类激光器用于光纤通讯时， 需要将输出光束 4藕合到光纤中， 准直透镜 38是必不可少的。
在可调谐激光器 300中， 由激光增益介质 34发出的宽带荧光光束 36经腔内准直透镜 38准直后的光束 2透过有源光相位调制器 40, 以布拉格角进入声光晶体 26, 被衍射后的 一级衍射光 6 以布拉格角入射到腔内全反镜 28, 反射后的光束 8又以布拉格角进入声光 晶体 26。 被衍射后的一级衍射光 12经光学标准具 42后由全反镜 44反射回激光腔内， 在 激光腔内形成激光振荡和放大。 在这个过程中， 光束 4和 10分别作为激光腔内光束 2, 8 的零级衍射光束； 光束 13作为光束 12的反射光束的零级衍射光束成为激光腔内的损耗， 光束 4因其具有最大的能量被选择作为激光输出光束。光束 10和 13 可用于监控激光腔内 的光功率和波长。
正如前面分析的， 由于第一次衍射光波长偏移和第二次衍射所产生的光波长偏移正好 相反， 因此， 可调谐声光滤波器 100在可调谐激光器 300中的结构中所造成的光波长偏移 为零。 又由于经可调谐声光滤波器 100的两次衍射， 因此， 在激光腔内形成了比一次衍射 带宽更窄的激光振荡。
激光输出调谐是通过有源光相位调制器 40和可调谐声光滤波器 100来实现。 改变可 调谐声光滤波器的射频信号源 20 的射频频率， 可改变激光腔内的光波谐振频率。 根据不 同的光波谐振频率， 有源光相位调制器 40通过调节光波的相位使得某一个特定的光波在 激光腔内产生激光振荡和放大。
光学标准具 42决定激光器输出频谱的间隔和带宽。 采用高锐度系数的光标准具能起 到压缩输出光束的频谱带宽和提高边模抑制比。 如需要减小激光器输出频谱的间隔， 则需 要同时减小可调谐声光滤波器 100的滤波带宽和减小光标准具 42的透射光谱峰值频率的 间隔， 才能避免发生跳模现象和保证激光器的单模振荡。 如激光器的输出频谱的间隔要求 为 25GHz , 不仅需要光标准具 42 的频谱的间隔为 25GHz, 还要求可调谐声光滤波器 100的 滤波带宽的 FWHM (频谱半宽度）参数至少小于 50GHz。 这就大大提高了可调谐声光滤波 器 100的技术难度和制造成本。 光标准具 42 的技术难度和制造成本也会增加。 对于激光 增益介质是均匀增益介质的情况下， 一般要求可调谐声光滤波器的滤波带宽 FWHM值小于 2Af (假设光标准具的透射带宽为 A f)。 如果可调谐声光滤波器的滤波带宽大于 2Α〖 ， 容 易形成多模振荡， 导致多模输出或跳模现象。 对于激光增益介质是非均匀增益介质的情况 下， 要求可调谐声光滤波器的滤波带宽 FWHM值更窄。
下面对本发明的外腔式可调谐激光器 400进行详细说明：
本外腔式可调谐激光器 400通过采用两个光光学标准具， 并放置在两个激光腔的子腔 内为解决上述问题的提供了一个方法。 如图 5所示， 本外腔式可调谐激光器 400包括直接 镀在激光增益介质 34上的激光腔端面镜 32、激光增益介质 34、腔内准直透镜 38、有源光 相位调制器 40、 可调谐声光滤波器 100、 腔内全反镜 28、 有源偏振旋光器 50、 偏振分光 器 52、 第一光学标准具 62、 第一全反射镜 64、 第二光学标准具 56、 第二全反射镜 58及 激光器驱动控制电路。
在可调谐声光滤波器 100后安装一个有源偏振旋光器 50用于将入射的线偏振光 12的 偏振方向旋转 90度， 有源偏振旋光器 50后安装偏振分光器 52对入射的平行偏振光全透 射， 而对入射的垂直偏振光反射到与入射光成 90度的方向上； 在与激光腔内光束 12相垂 直的方向上安装第一光学标准具 62, 用于接收从偏振分光器 52输出的垂直偏振光 60, 并 输出到第一全反射镜 64, 第一全反射镜 64与激光腔端面镜 32构成第一激光谐振子腔。在 激光腔内光束 12的方向上安装第二光学标准具 56,用于接收从偏振分束器 52输出的平行 偏振光并输出到第二全反射镜 58。第二全反射镜 58与激光腔端面镜 32构成第二激光谐振 子腔。 可调谐激光器 400与可调谐激光器 300不同之处在于： 可调谐激光器 300 (图 4) 中的光标准具 34和全反镜 36, 被换成了由有源偏振旋光器 50、偏振光分束镜 52、第一光 学标准具 62、 第一全反射镜 64、 第二光学标准具 56和第二全反射镜 58组成的双光路系 统 500, 如图 6所示。 有源偏振旋光器 50的功能是改变入射光束 12的偏振方向： 当有源 偏振旋光器处在非工作状态时，入射光束 12不改变偏振态，直接通过偏振光分束镜 52后， 经第二光标准具 56后到达第二全反射镜 58, 再经第二全反射镜 58反射回激光腔中， 如图 7所示。 当有源偏振旋光器处在工作状态时， 入射光束 12 的偏振态旋转 90度， 变成垂直 偏振光， 通过偏振光分束镜 54反射后， 经第一光学标准具 62到达第二全反射镜 64, 再经 第二全反射镜 64反射回激光腔中， 如图 8所示。 由于经第二全反射镜 64反射回的光再次 通过有源偏振旋光器 50后，偏振态再次旋转 90度，所以激光器的输出光束偏振方向不变。
因此， 通过控制有源偏振旋光器 50可以使图 5中的可调谐激光器 400形成两个激光 谐振腔的子腔： 第一子腔是由激光腔端面镜 32和第一全反射镜 64组成，第二子腔是由激 光腔端面镜 32和第二全反射镜 58组成。 图 9-1、 图 9-2分别显示了第一光学标准具 62 和第二光学标准具 56的透射光谱。 两个第二全光标准具 56和 62具有相同的透射光谱间 隔 50GHz和锐度系数， 但透射光谱峰值相差 25GHz。 这样， 可调谐激光器 400的输出光谱 是两个子腔的综合， 即可实现 25GHz光谱峰值间隔， 并且偏振态一致的可调谐激光输出， 如图 10所示。
本发明中， 第一光学标准具 62和第二光学标准 56具有相同的锐度系数， 而且， 第 一光学标准具 62、 第二光学标准具 56具有与激光增益介质相同的光谱范围， 第一光学标 准具 62和第二光学标准具 56的透射光谱峰值间隔均为 50GHz ,第二光学标准具 56的透射 光谱峰值频率与第一光学标准具 62的透射光谱峰值频率相差为 25GHz。对于应用于光纤通 讯的这类可调谐激光器， 第一光学标准具 62的透射光谱峰值应满足国际光通讯标准（ITU GRID)。 对于其他的应用， 第一光学标准具 62 的透射光谱峰值可以根据具体应用设计不 同的值。 而对第二光学标准具的透射光谱峰值和透射光谱峰值间隔也应符合上述条件。
利用可调谐激光器 400的结构， 只要满足可调谐声光滤波器的滤波带宽 FWHM值小于 2Af (假设光学标准具的透射带宽为 Af), 可以实现光频率间隔更密的可调谐输出。 例如， 第一光学标准具 62和第二个光学标准具 56透射光谱峰值间隔可以是 25GHz , 并满足第二 光学标准具 56 的透射光谱峰值频率与第一个光学标准具的透射光谱峰值频率相差为 12. 5GHz时，可调谐声光滤波器的滤波带宽 FWHM值只要满足小于 50GHz ,可调谐激光器 400 即可实现光谱频率间隔为 12. 5GHz 的可调谐输出。
一般来说， 半导体激光增益介质输出的荧光即是线偏振光。 对这类激光增益介质， 腔内不需要使用起偏器。 对其他输出为非线偏振光的激光增益介质， 必须使用起偏器才能 使可调谐激光器 400实现上述功能。
随着光通讯技术的发展， DWDM光通讯网正向 25GHz ,甚至光频道密度更高的方向发展。 就要求有滤波带宽更窄的可调谐声光滤波器， 也使得制作这样的可调谐声光滤波器和要求 小型化的可调谐激光器的难度进一步提高， 价格更加昂贵。 对于一些其它的可调谐激光器 的应用， 要求激光器的输出光束有更高的可调谐频谱密度， 其整体激光器的成本和技术难 度将更加提高。 因此， 可调谐激光器 400 可在已有的 50GHz频谱间隔的外腔式激光器的平 台上，提供了一种可以实现 25GHz频谱间隔，甚至频谱间隔更小的可调谐输出的新颖方法， 并且不显著增加成本和制造难度。
上述可调谐激光器 400还安装有一个激光器驱动控制电路。 如图 11所示。 该激光器 驱动控制电路包括带有嵌入式软件程序的数字信号微处理器 （DSP) 112 、 四个数模转换 (D/A) 设备 102、 106, 110和 116、 激光泵浦源 101、 有源光相位调制器驱动源 104、 射 频信号源 108和有源偏振旋光器驱动源 114。 带有嵌入式软件程序的数字信号微处理器 (DSP) 112通过数模转换（D/A) 设备 102、 106, 110和 116来分别控制激光泵浦源 101、 有源光相位调制器驱动源 104、 射频信号源 108和有源偏振旋光器驱动源 114。 数字信号 微处器 112也可以接收外部指令来对可调谐激光器 400进行控制。
上述说明仅起演示和描述的作用， 并不是一个详细无遗漏的说明， 也没有意图将 本发明限制在所描述的具体形式上。 经过上面的描述， 对本发明的许多改动和变化都 可能出现。 所选择的具体实施仅仅是为了更好的解释本发明的原理和实际中的应用。 这个说明能够使熟悉此领域的人可以更好的利用本发明， 根据实际需要设计不同的具 体实施和进行相应的改动。

Claims

权利要求书
1、 一种光频率间隔为 25GHz的外腔式可调谐激光器， 包括安装在激光增益介质 上的激光腔端面镜和依次安装在激光腔内的激光增益介质、 腔内准直透镜、 有源光相 位调制器、 可调谐声光滤波器和腔内全反镜， 其特征在于： 还包括：
一个有源偏振旋光器， 放置在可调谐声光滤波器后， 接收经可调谐声光滤波器两 次衍射的光束， 控制入射的线偏振光的偏振方向；
一个偏振分束器， 放置在有源偏振旋光器后， 对入射的平行偏振光全透射， 而对 入射的垂直偏振光反射到与入射光成 90度的方向上；
第一光学标准具和第一全反射镜， 放置在与可调谐声光滤波器两次衍射光束的光 轴相垂直的方向上， 接收从偏振分束器输出的垂直偏振光并输出到第一全反射镜， 第 一全反射镜与激光腔端面镜构成第一激光谐振子腔， 可调谐声光滤波器二次衍射的光 线在第一激光腔中形成激光振荡；
第二光学标准具和第二全反射镜， 放置在可调谐声光滤波器两次衍射光束的光轴 方向上， 接收从偏振分束器输出的平行偏振光并输出到第二全反射镜， 第二全反射镜 与激光端面镜构成第二激光谐振子腔， 可调谐声光滤波器二次衍射的光线在第二激光 腔中形成激光振荡；
一个射频信号源， 用于提供给可调谐声光滤波器射频能量并通过改变射频频率来 调节激光谐振腔的振荡波长；
激光泵浦源、 有源光相位调制器的驱动源和有源偏振旋光器的驱动源及激光器驱 动控制电路。
2、 根据权利要求 1所述的光频率间隔为 25GHz的外腔式可调谐激光器， 其特征 在于： 上述的第一光学标准具和上述第二光学标准具具有相同的锐度系数。
3、 根据权利要求 1或 2所述的光频率间隔为 25GHz的外腔式可调谐激光器， 其 特征在于： 所述的第一光学标准具、 第二光学标准具具有与激光增益介质相同的光谱 范围， 上述第一光学标准具和第二光学标准具的透射光谱峰值间隔均为 50GHz, 第二 光学标准具的透射光谱峰值频率与第一光学标准具的透射光谱峰值频率相差为
25GHz。
4、 根据权利要求 1所述的光频率间隔为 25GHz的外腔式可调谐激光器， 其特征 在于： 所述的第一全反射镜、 第二全反射镜和腔内全反镜为以下几种类型的反射镜之 一： 平面镜、 凸面镜和凹面镜； 所述的第一全反射镜、 第二全反射镜和腔内全反镜具 有与激光增益介质相同的光谱范围。
5、 根据权利要求 1所述的光频率间隔为 25GHz的外腔式可调谐激光器， 其特征 在于： 所述的激光腔端面镜是在指定光谱范围内的全反镜或或部分反射镜， 所述的激 光腔端面镜具有与激光增益介质相同的光谱范围。
6、 根据权利要求 1所述的光频率间隔为 25GHz的外腔式可调谐激光器， 其特征 在于： 所述的可调谐声光滤波器包括一个声光晶体和一个声波换能器。
7、 根据权利要求 1或 6所述的光频率间隔为 25GHz的外腔式可调谐激光器， 其 特征在于： 所述的可调谐声光滤波器为窄带光滤波器， 该可调谐声光滤波器的光谱范 围与激光增益介质的光谱范围相同，且其滤波光谱的 FWHM不大于第一光学标准具或 第二光学标准具透射光谱峰值频率的二倍。
8、 根据权利要求 1所述的光频率间隔为 25GHz的外腔式可调谐激光器， 其特征 在于： 所述的有源光相位调制器是以下几种类型之一： 电光相位调制器， 或者是磁光 相位调制器， 或者是液晶相位调制器， 或者是声光相位调制器， 或者是基于物理光学 效应的其他形式的相位调制器， 或者是上述相位调制器的组合并具有与激光增益介质 相同的光谱范围。
9、 根据权利要求 1所述的光频率间隔为 25GHz的外腔式可调谐激光器， 其特征 在于： 所述的有源偏振旋光器是以下几种类型之一： 电光有源偏振旋光器， 或者是磁 光有源偏振旋光器， 或者是液晶有源偏振旋光器， 或者是声光有源偏振旋光器， 或者 是基于物理光学效应的其他形式的有源偏振旋光器， 或者是上述有源偏振旋光器的组 合并具有与激光增益介质相同的光谱范围。
10、根据权利要求 1所述的光频率间隔为 25GHz的外腔式可调谐激光器， 其特征 在于： 所述的激光器驱动控制电路包括： 数字信号微处理器、 四个数模转换模块、 激 光泵浦源、 有源光相位调制器驱动源、 可调谐声光滤波器驱动源和有源偏振旋光器驱 动源， 数字信号微处理器接收外部指令信号指令并通过激光泵浦源、 有源光相位调制 器驱动源、 可调谐声光滤波器驱动源和有源偏振旋光器驱动源实现对激光增益介质、 有源光相位调制器、 可调谐声光滤波器和有源偏振旋光器的驱动控制功能。
PCT/CN2011/075682 2011-06-09 2011-06-13 光频率间隔为25GHz的外腔式可调谐激光器 WO2012167447A1 (zh)

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