JPH10242580A - Semiconductor pulsed light source device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor pulsed light source device wherein the repeated frequency of its generated optical pulse is created with a good reproducibility according to its design, and its optical pulse width is varied slightly to the variation of its modulation frequency in a high repeated frequency not lower than 10GHz to make possible the generations of pulses with widths not lower than 10ps. SOLUTION: A semiconductor gain control portion 1, a semiconductor modulator 2, and an optical filter 3 with a grating are integrated into an optical resonator. Further, a distributed Bragg reflector(DBR) is integrated into a chirped grating. The resonance frequency of the optical resonator which is determined by its optical resonator length is varied by the integrated DBR to make possible the generations of pulses in such a wide high-frequency range as to be conventionally impossible.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor pulse light source device, and is particularly useful when applied to a semiconductor pulse light source device having a chirped grating. 2. Description of the Related Art FIG. 4A is a diagram for explaining a configuration of a conventional semiconductor pulse light source device, where 01 is an optical modulator,
02 is a gain part, and 03 is a distributed Bragg reflector (DBR) made of a diffraction grating. Conventionally, a uniform diffraction grating is used for the DBR. FIG. 2B is a diagram for explaining another conventional semiconductor pulse light source device, wherein reference numeral 04 denotes an optical gain unit, and reference numeral 05 denotes a fiber on which a chirped grating 06 is formed. In the semiconductor pulse light source device, the repetition frequency of the generated pulse is equal to the resonance frequency given by the reciprocal of the time required for the light pulse to reciprocate through the resonator. Is fixed for each element. In order to obtain the required repetition frequency, it is necessary to accurately manufacture the resonator length. However, due to variations in the resonator length at the time of cleavage and variations in the group refractive index that determines the resonance frequency, the resonator is manufactured with high reproducibility. It was difficult. Further, in the active mode-locked laser, if the modulation frequency is slightly shifted from the resonance frequency, there is a problem that the pulse width increases, the power of the pulse decreases, and the noise increases. The semiconductor pulse light source device shown in FIG. 4B combines a fiber 05 having a chirped grating 06 and an optical gain unit 04. In this device, the repetition frequency is wide due to the chirped grating 06. It has been reported that it can be varied over a range (PA Morton, et. Al., "Mode-
locked solute pulse sour
ce with fibercavity and i
integrated chipped Bragre
factor, "OFC / IOOC '93 Tech
medical Digest, pp. 57-58). [0005] However, the semiconductor pulse light source device, the fiber 05 and the optical gain section 04 is coupled with the external cavity length is increased for that, 10GH _Z over high repetition frequency has been difficult. Further, in the fiber 05 having the chirped grating 06, the reflectance cannot be ensured unless the grating portion is made longer than 1 mm, so that the wavelength band becomes narrow and it is difficult to generate a pulse having a small time width. [0006] The present invention, the view of the prior art, to create good reproducibility with respect to designing the repetition frequency of the generated light pulses, also in the above high repetition frequency 10GH _Z, the optical pulse with respect to the change of the modulation frequency It is an object of the present invention to provide a semiconductor pulse light source device capable of generating a light pulse of 10 ps or less with a small variation in width. [0007] The structure of the present invention that achieves the above object has the following features. 1) A semiconductor gain section having a gain in a certain wavelength range, a semiconductor modulator section in which a light absorption coefficient or an optical gain coefficient changes in the wavelength range by applying a voltage or a current, and a diffraction grating. In a semiconductor pulse light source device in which an optical semiconductor pulse generating element and an optical filter unit are formed as a set is formed on the same semiconductor substrate,
The optical filter section is composed of a diffraction grating having periodicity, the period of the diffraction grating is reduced at a certain rate in the light emitting direction, and the length of the filter section is 200 microns or less. 2) A semiconductor gain section having a gain in a certain wavelength range, a semiconductor modulator section in which a light absorption coefficient or an optical gain coefficient changes in the wavelength range by applying a voltage or a current, and a diffraction grating. In a semiconductor pulse light source device in which an optical semiconductor pulse generating element and an optical filter unit are formed as a set is formed on the same semiconductor substrate,
The optical filter section includes a chirped grating configured by a diffraction grating having periodicity and configured such that a large number of constant negative phase shifts are inserted and the insertion interval decreases as going in the light emitting direction, and The length of the filter section is 200 microns or less. 3) a semiconductor gain section having a gain for a certain wavelength range, a semiconductor modulator section for changing a light absorption coefficient or an optical gain coefficient for the wavelength range by applying a voltage or a current, and a diffraction grating. In a semiconductor pulse light source device in which an optical semiconductor pulse generating element and an optical filter unit are formed as a set is formed on the same semiconductor substrate,
The optical filter section includes a chirped grating configured to include a diffraction grating having periodicity, and a large number of fixed positive phase shifts are inserted, and the insertion interval is increased with an increase in a light emitting direction, and The length of the filter section is 200 microns or less. [0011] 4) In the semiconductor pulse light source device of 1) to 3), a non-reflection film having a reflectance of at least 1% or less is coated on an emission end face. Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a structural diagram showing a basic configuration of the present embodiment. As shown in the figure, a semiconductor pulse light source device according to the present embodiment includes a semiconductor gain unit 1 having a gain in a certain wavelength range, and a semiconductor modulator in which a voltage is applied to increase a light absorption coefficient in the wavelength range. The unit 2 and the optical filter unit 3 having a diffraction grating are formed on the same semiconductor substrates 8 and 11. At this time, the optical filter unit 3 is configured such that the period of the diffraction grating is reduced at a certain rate in the light emitting direction and the length is 200 microns or less. In the drawings, reference numeral 4 denotes a gain portion electrode, 5 denotes a modulator portion electrode, 6 denotes a DBR electrode, 7 denotes a lower electrode, 9 denotes a modulator multiple quantum well, 10 denotes a gain portion multiple quantum well, and 12 denotes a DB.
R and 13 are high reflection films, and 14 is a non-reflection film. The optical filter section 3 is composed of a diffraction grating having a periodicity, and a chirp configured such that a large number of fixed negative phase shifts are inserted and the insertion interval decreases as going in the light emitting direction. It may have a doping grating, or may have a chirped grating configured such that a large number of fixed positive phase shifts are inserted and the insertion interval increases in the light emitting direction. FIG. 2 shows a calculation result regarding the wavelength dependence of the reflectance and effective length of the optical filter unit 3. When a sine wave voltage is applied to the semiconductor modulator section 2, the absorption coefficient changes, and the loss changes with time. The repetition frequency at this time needs to match the resonance frequency given by the reciprocal of the time required for the optical pulse to reciprocate in the resonator. Distributed Bragg reflector (DBR) constituting optical filter unit 3
The effective length in the range changes depending on the wavelength as shown in FIG. 2 because the period of the diffraction grating decreases at a certain rate in the light emission direction. As the optical pulse oscillating wavelength with changing the modulation frequency is changed within a DBR matches the resonance frequency given by the inverse of the time required for reciprocation, to vary the effective length automatically, 10GH _Z or And a stable pulse is obtained at the repetition frequency. On the other hand, in the conventional structure shown in FIG. 4A, the wavelength dependence of the effective length is small, and the above-mentioned effect is hardly obtained.
In the conventional structure shown in FIG. 4B, a fiber 05 on which a chirped grating 06 is formed and an optical gain section 04 are coupled, and the chirped grating 06 is formed.
Although the repetition frequency is reported to be varied over a wide range, since a bond structure at the outside of the optical gain section 04, the resonator length becomes longer, high repetition frequencies above 10GH _z is difficult by . Further, in the fiber 05 having the chirped grating 06, it is difficult to generate a pulse having a small width because the reflectance cannot be ensured unless the grating portion is as long as 1 mm or more. Next, a more detailed embodiment of the present invention will be described. The semiconductor gain section 1, the electroabsorption type semiconductor modulator section 2 and the optical filter section 3 are integrated on the same semiconductor substrate 8 made of n-type InP and the same semiconductor substrate 11 made of p-type InP. A resonator is formed. In the semiconductor gain section 1, the well layer is made of InGaAs or InGaAsP, and the barrier layer is made of InGaAs.
It consists of a GaAsP multiple quantum well 9 for the gain section, and its photoluminescence wavelength is around 1.55 microns. The semiconductor modulator section 2 is composed of a semiconductor multiple quantum well 10 having a well layer of InGaAs or InGaAsP and a barrier layer of InGaAsP, and has a photoluminescence wavelength of about 1.49 microns.
The length of the semiconductor gain section 1 is 1800 microns, and the length of the semiconductor modulator section 2 is 100 microns. Semiconductor gain unit 1
And the semiconductor modulator section 2 are separated from each other by electrodes 50 over a length of 50 microns, and the resonator length is about 2200.
Micron. DB having a chirped grating
R is 150 microns. Char plate is 7250
Å / cm. The chirped grating used the multiple phase shift pattern shown in FIG. These patterns were realized using an electron beam exposure apparatus. Here, “phase shift” means that the phase of a diffraction grating having periodicity is shifted by a predetermined amount in a direction opposite to the light emission direction (this is called a negative phase shift, and FIG. 3 shows the case of this negative phase shift). Or a phase shift of the diffraction grating having a periodicity in the light emitting direction by a predetermined amount (this is referred to as a positive phase shift). Further, “multiple phase shifts” refers to providing a plurality (four in FIG. 3) of “phase shifts”. 3A schematically shows the period of the diffraction grating, FIG. 3B schematically shows the phase shift, and FIG. 3C conceptually shows the diffraction grating formed at this time. In the case shown in FIG.
_c is given by r _c = 4n _eq (△ Λ / Λ) / m ² . Here, n _eq is the equivalent refractive index of the optical waveguide,
ΔΛ is the amount of phase shift, Δ is the period of the diffraction grating, and m is the number of periods at the position where the phase shift is first inserted. As shown in FIG. 3, when the phase shift is negative, the value is obtained by multiplying the square root of the number i by m with respect to the number i of the phase shift from the opposite side (left side in FIG. 3) with respect to the emission end face. A phase shift is inserted at the position. The insertion position of this phase shift is shown in FIG.
This is indicated by a downward arrow in (a). The resulting diffraction grating has a negative phase shift △, as shown in FIG.
Λ are inserted, and the insertion intervals T _{1 to} T ₄ decrease in the light emitting direction. That is, a _{T 1> T 2> T 3} > T 4. If the phase shift is positive, a phase shift is inserted from the emission end face to a position where the value is obtained by multiplying the square root of the number i by m with respect to the number i of the phase shift, and the insertion interval is equal to the light emission interval. The insertion may be performed so as to increase in the direction, that is, T ₁ <T ₂ <T ₃ <T ₄ . The antireflection film 14 on the end face on the DBR side is made of SiO ₂ and Ti.
It is formed by a multilayer anti-reflection coating made of O ₂ and has a reflectance of 0.2% or less. As described in detail with the above embodiments, according to the present invention, the pulse repetition frequency is
In order to be variable in effective length self-alignment of at the inner, it facilitates the pulse generation frequency in a wide range and it is possible to obtain a 20GH _Z frequency higher than for being integrated into small .

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a configuration diagram of a semiconductor pulse light source device according to an embodiment of the present invention. FIG. 2 is a characteristic diagram showing characteristics based on a calculation result regarding the wavelength dependence of the reflectance and effective length of the optical filter unit 3. FIG. 3 is an explanatory diagram for explaining a phase shift in an optical filter unit of the device according to the embodiment of the present invention. FIG. 4 is a structural view showing a conventional semiconductor pulse light source device. [Description of Signs] 1 Semiconductor gain unit 2 Semiconductor modulation unit 3 Optical filter unit

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Yasuhiro Kondo             3-19-2 Nishi Shinjuku, Shinjuku-ku, Tokyo Japan             Telegraph and Telephone Corporation (72) Inventor Yamamoto ▲ Mitsu ▼ Husband             3-19-2 Nishi Shinjuku, Shinjuku-ku, Tokyo Japan             Telegraph and Telephone Corporation

Claims (1)

1. A semiconductor gain section having a gain in a certain wavelength range, and a semiconductor modulator section changing a light absorption coefficient or an optical gain coefficient in the wavelength range by applying a voltage or a current. And an optical semiconductor pulse generating element having a pair of an optical filter unit having a diffraction grating, in a semiconductor pulse light source device formed on the same semiconductor substrate, wherein the optical filter unit is composed of a diffraction grating having periodicity. And a period of the diffraction grating is reduced at a certain rate in the light emitting direction, and a length of the filter portion is not more than 200 microns. 2. A semiconductor gain section having a gain for a certain wavelength range, a semiconductor modulator section for changing a light absorption coefficient or an optical gain coefficient for the wavelength range by applying a voltage or a current, and a diffraction grating. In a semiconductor pulse light source device in which an optical semiconductor pulse generating element as one set of an optical filter unit is formed on the same semiconductor substrate, the optical filter unit is constituted by a diffraction grating having periodicity, and has a constant negative phase shift. A semiconductor pulsed light source device having a chirped grating configured so that a large number of holes are inserted and the insertion interval decreases in the light emitting direction, and the length of the filter portion is 200 μm or less. . 3. A semiconductor gain section having a gain for a certain wavelength range, a semiconductor modulator section for changing a light absorption coefficient or an optical gain coefficient for the wavelength range by applying a voltage or a current, and a diffraction grating. In a semiconductor pulse light source device in which an optical semiconductor pulse generating element as a pair with an optical filter section is formed on the same semiconductor substrate, the optical filter section is constituted by a diffraction grating having a periodicity, and has a constant positive phase shift. A semiconductor pulsed light source device having a chirped grating configured so that a large number of holes are inserted and the insertion interval increases in the light emitting direction, and the length of the filter portion is 200 μm or less. . 4. The semiconductor pulse light source device according to any one of claims 1 to 3, wherein the light-emitting end face is coated with a non-reflection film having a reflectance of at least 1% or less. Light source device.