JPS637687A - Semiconductor laser wavelength stabilizer - Google Patents

Abstract

PURPOSE:To miniaturize a semiconductor laser while stabilizing oscillation frequency by a method wherein a transmitted light from an absobing part enclosing a reference material which absorbs light of specific wavelength is converted to an electric signal, and the semiconductor laser is controlled corresponding to the electric signal obtained. CONSTITUTION:An outgoing light from a photowaveguide 32 enters into a photoabsorber 2 to enclose a reference material (Cs in this invention) photoabsorbing in specified wavelength while another outgoing light from the photoabsorber 2 enters into a photodetector PD 2. Any output electric signal from the photodetector PD 2 enters into a controller 2. This controller 2 is provided with a lockin amp circuit LA 2 wherein an output from the photodetector PD2 is connected to input, a current circuit CT3, a signal transmitting circuit (oscillation circuit) SG3 in frequency fm wherein one of output becomes a reference signal input of lockin amp LA2 and the second signal transmitting circuit (oscillating circuit) SG4 in frequency fn wherein an output modulated by another output from the signal transmitting circuit SG3 is connected to an acoustic optical modulator UM2. Through these procedures, a semiconductor laser can be integrated into one chip to be miniaturized.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to improvements in the characteristics of a semiconductor laser wavelength stabilizing device that stabilizes the wavelength of a semiconductor laser by controlling it to the absorption line of atoms or molecules.

(Prior Art) FIG. 11 is a block diagram illustrating a prior art of a semiconductor laser wavelength stabilizing device described in Japanese Patent Application No. 118-11898 filed by the present applicant.

LDl is a semiconductor laser, PE1 is this semiconductor laser LD
1. A Bertier element CT1 for cooling or heating the semiconductor laser LD1 drives the Bertier element PEI to cool or heat the semiconductor laser LD1.
TBl is a constant temperature bath that stores these to reduce temperature fluctuations, BSl is a beam splitter that separates the output light of the semiconductor laser LD1 into two directions, and tJIVM is this beam splitter. BS1
An acousto-optic modulator, CL1, which receives the output light from one of the acousto-optic modulators and constitutes a modulation means, receives the diffracted light output of the acousto-optic modulator UM1 and encloses a standard material (here, Cs) that absorbs light of a specific wavelength. The absorption cell PDl is this absorption cell CL
A1 is a photodetector into which the transmitted light of I is incident, and A1 is this photodetector P.
An amplifier that inputs the output electrical signal of D1, LA1 a lock-in amplifier that inputs the electrical output of this amplifier A1, and CT
2 is a PID controller that inputs the output of this lock-in amplifier LA1 and constitutes a control means for controlling the current of the semiconductor laser LDI, and SWl is the acousto-optic modulator UM.
1, SG1 is a signal generator whose output turns the switch SW1 on and off at a frequency fm (for example, 2kHz), and SG2 is the switch SW1.
Frequency fo connected to the other end (e.g. 80MHz>
is the second signal generator.

The operation of the grooved semiconductor radar wavelength stabilizing device as described above will now be described. The semiconductor laser LD1 is controlled to a constant temperature by a control means CT1 which inputs a temperature detection signal in a constant temperature bath TBl via a Vertier element PE1. The output light of the semiconductor laser LD1 is split into two by the beam splitter BS1.
The reflected light becomes output light to the outside, and the transmitted light enters the acousto-optic modulators U to 11. switch SW
1 is on, the acousto-optic modulator IJM1 is the signal generator SG
2, most of the incident light with frequency ν0 is diffracted and undergoes a frequency (Doppler) shift, and light with frequency νO+f□ enters absorption cell CL1 as first-order diffracted light. When the switch SW1 is off, all the incident light has a frequency of 0-order diffracted light and enters the absorption cell CL1 at a frequency of 0.

Since the switch SW1 is driven by the clock of the signal generator SG1 at the frequency f, the light incident on the absorption cell CL1 is subjected to frequency modulation at the modulation frequency f and the modulation depth fO. When this modulated light enters the absorption cell CL1,
As shown in the operation explanatory diagram of FIG. 12, since the amount of transmitted light is modulated only at the location of the absorption signal of the Cs atoms, a signal appears in the output. If this signal is converted into an electric signal by the photodetector PD1, locked-in amplified by the amplifier A1, and synchronously rectified at the frequency f at 81, a first-order differential waveform as shown in the frequency characteristic curve diagram in Fig. 13 is obtained. is obtained. The current of the semiconductor laser LD1 is controlled by the PrD controller CT2, and the output of the lock-in amplifier LA1 is locked to the center of the first-order differential waveform (control O>, then the output light of the semiconductor laser becomes 5-fo/2). This becomes a stable frequency. Here, νS indicates the center frequency of absorption of C5 atoms.

According to the semiconductor laser wavelength stabilizing device having such a configuration, since the excavation frequency of the laser is not modulated, it becomes an extremely stable light source even instantaneously.

(Problems to be Solved by the Invention) However, each element of the semiconductor laser wavelength stabilization device having the above configuration is composed of a single component, so it has the disadvantage that the configuration is complicated and large. .

The present invention has been made to solve these problems, and an object of the present invention is to miniaturize and realize a semiconductor laser wavelength stabilizing device with a stable oscillation frequency.

(Means for Solving the Problems) The present invention relates to a semiconductor laser wavelength stabilization device that stabilizes the wavelength by controlling the wavelength of a semiconductor laser according to the absorption spectrum line of a standard substance. an absorption section that includes a standard substance that enters light related to the output light of the semiconductor laser through an optical waveguide and causes absorption at a specific wavelength;
a light detection section that converts the transmitted light of the absorption section into an electrical signal;
The advantage of the present invention is that the current or temperature of the semiconductor laser is controlled in response to an electrical signal related to the output electrical signal of the photodetector, and a part that controls the current or temperature of the semiconductor laser is provided on the same substrate. (Example) The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. 1 is an optical integrated circuit (optical IC>
The substrates formed on the optical IC substrate 1 will be explained below. LD2 is a semiconductor laser section, 31 is an optical waveguide into which the output light of this semiconductor laser section is input, and UM2 is an optical waveguide that receives the output light of this optical waveguide 31. The input acousto-optic modulator (ultrasonic light modulator) 32 is an optical waveguide into which the output light of this acousto-optic modulator UM2 is input, and CL2 is an optical waveguide into which the output light of this optical waveguide 32 is input and which outputs light of a specific wavelength. PD2 is an absorption part CL in which a standard substance to be absorbed (Cs in this case) is enclosed.
2 is a light receiving section into which the emitted light is input, and 2 is a control section into which an output electrical signal of this light receiving section PD2 is input. In the control section 2, L.DELTA.2 is a lock-in amplifier circuit whose input is connected to the output of the light receiving section PD2, and CT3 is a lock-in amplifier circuit whose input is connected to the output of this lock-in amplifier circuit L.DELTA.2, whose output is connected to the semiconductor laser section LD2. S03 is a signal generation circuit (oscillation circuit) having a frequency fm (for example, 2kHz), one of whose outputs is the reference signal input of the lock-in amplifier circuit LA2. , SG4 is a second signal generating circuit (oscillation circuit) having a frequency fo (for example, 80 MHz>) which is modulated by the output of the signal generating circuit SG3 and whose output is connected to the acousto-optic modulator UM2.

The operation of the device having the above configuration is similar to that of the semiconductor laser wavelength stabilizing device shown in FIG.

According to the semiconductor laser wavelength stabilizing device having such a configuration, since mv4 can be implemented in one chip, it has the advantage of being compact, mass-producible, and easy to adjust.

Further, even if the diffraction efficiency of the acousto-optic modulator UM2 changes, the light component (O-order diffracted light) that does not contribute to modulation increases, and the signal intensity only decreases, and the center wavelength is not affected.

In the above embodiment, the modulation frequency *f was used as the reference frequency of the lock-in amplifier LA2, but a frequency that is an integral multiple of the modulation frequency *f may be used.

In addition to Cs, for example, Rb, NHs, H2O, etc. may be used as a standard substance for the absorption cell CL2.

Further, in the above embodiment, an acousto-optic modulator is used as the modulation means, but the present invention is not limited to this, and a phase modulator using an electro-optic element may be used, for example.

These include, for example, vertical modulators, horizontal modulators, traveling waveform modulators, etc. (Amnon Yarif: Fundamentals of Optoelectronics (Maruzen), p. 247-p. 253).

Further, in the above embodiment, the current of the semiconductor laser is controlled by the output of the control section, but the present invention is not limited to this, and the temperature of the semiconductor laser may be controlled.

FIG. 2 is a table showing a concrete implementation method of each component of the apparatus shown in FIG. For example, if the electrical circuit part is a silicon substrate, it will have a monolithic structure, but in other cases, it will have a hybrid structure. This will be explained in more detail below using specific examples.

FIG. 3 is a perspective view of a main part showing a specific example in which the semiconductor laser LD2 is monolithically realized on the optical IC substrate 1 in the apparatus shown in FIG.

4 and 5 are a perspective view and a sectional view of a main part showing a specific example of a hybrid configuration in which a semiconductor laser LD2 is externally attached to the apparatus shown in FIG.
(See Optical Communication Handbook J 4991501). Figure 4 shows light I.
A configuration in which the end face of the waveguide 31 formed on the C substrate 1 is directly irradiated with the output of the semiconductor laser LD2, FIG.
The configuration is such that the output light of the semiconductor laser LD2 is introduced into the waveguide 31 via R.

FIG. 6 shows that in the device shown in FIG. 1, the absorption section OL2 is an optical IC!
! Plate 1 Table Figure 1 A cross section showing a specific example of a structure in which a glass pattern 4 is formed by glass coating or thermal oxidation in a recess made by surface tinting, etc., and a glass erodible plate 5 containing a standard substance is fused and sealed. It is a diagram.

FIG. 7 is a sectional view showing another specific example of the absorption section CL2 in the apparatus shown in FIG. The standard substance sealed in the lid 51 above the waveguide 32 absorbs the output light from the waveguide 32 by an evanescent effect. Compared to the configuration shown in FIG. 6, this has the advantage of being easier to manufacture.

In each of the above specific examples, the photodetector can have a monolithic or hybrid configuration (see "Optical Communication Handbook J
433/434).

The eighth factor is a structural plan view showing a second embodiment of the semiconductor laser wavelength stabilizing device, which is a roughly narrower spectrum version of the device shown in FIG. An optical resonator FP1 consisting of an optical branching unit OBI that branches part of the output light of the semiconductor laser LD2, a Fabry-Perot etalon into which the branched output light of the optical branching unit OB1 enters, and an output of the optical resonator FP1. A second photodetector PD3 into which light is incident, and a broadband amplifier A2 which amplifies the electrical output of the photodetector PD3 and returns it to the injected current of the semiconductor laser 02 are connected to an optical IC! i! It is additionally provided on the board 1, where the wideband amplification section A2 is provided within the control section 21 (shown in a simplified manner in FIG. 8). The resonance curve of the optical resonator FP1 (position shifted from the center frequency) is aligned with the oscillation wavelength of the semiconductor laser LD2, and the semiconductor laser L
After converting the phase noise contained in the output light of D2 into a ti width modulation signal, it is detected by a photodetector PD3, and the electrical output is transmitted to a semiconductor laser via a broadband amplifier A2 having a band wider than the spectral width of the semiconductor laser light. By providing negative feedback to the drive current (injected current) of D2, the semiconductor laser LD2
This suppresses phase noise and narrows the spectrum. (Reference: Furutashima et al.; IEICE Technical Report, 0QE84-13
0. (1984)) Figure 9 shows the light I
9A and 9B are a perspective view of a main part (FIGS. 9A and 9B) and a plan view of a main part (FIG. 9C) showing a specific example of a Fabry-Perot resonator FP1 provided on a C substrate 1. FIG. 9 (A> shows a resonator constructed by providing a hole 7 in a part of the waveguide 61 provided on the substrate 1 and coating two opposing surfaces 81 of the hole 7 with a reflective film. Figure (B) shows a resonator in which two ridge portions 62 are provided as waveguides on a substrate 1 in series and separated from each other, and reflective films are formed on opposing end surfaces 82 of the ridge portions 62. , FIG. 9(C) shows a structure in which a part of the waveguide 63 provided on the ?4 plate 1 is doped with a high refractive index material to form a resonant part 83.

FIG. 10 shows the optical resonator part FP1 in the device shown in FIG. 9(C).
This is a perspective view of a main part configuration showing a specific example of a means for adjusting the resonant frequency to the v4 node. changing the effective resonator length of the resonant section 83 by changing the refractive index;
It is something that makes you

Another method for adjusting the resonant frequency is to form a heater thin film resistor near the optical resonator FP1 on the substrate and change the resonance frequency by thermal expansion.

There is also a method in which a ferroelectric material is doped as a high refractive index material in a structure similar to that shown in FIG. 10(C), and the refractive index is changed by an applied electric field.

Further, when controlling the semiconductor laser LD2 and the optical resonator FP1 to a predetermined temperature, a resistor 7a or the like is used as a heater, but it is preferable that both heaters are placed as far away as possible so as not to interfere with each other.

In each of the above embodiments, the linear absorption method is used to control the wavelength of the semiconductor laser to the absorption line of atoms or molecules, but instead, a part of the light emitted from the acousto-optic modulator UM2 is converted into pump light. The other part enters the absorption part CL2 as a probe light from the opposite direction as a thin beam of light.
Saturation absorption method in which the saturated absorption signal is detected by entering L2 (Hori, Tsunoda, Kitano, Yabusaki, Frequency stabilization of semiconductor lasers using small 22 saturation absorption spectroscopy, IEICE Technical Report 0QE82-116)
If you use more stable semiconductor laser wavelength stabilization IUI
can be realized.

(Effects of the Invention) As described above, according to the present invention, it is possible to miniaturize and integrate a semiconductor laser wavelength stabilizing device with a stable oscillation frequency and easy adjustment.

[Brief explanation of the drawing]

FIG. 1 is a structural perspective view showing an embodiment of a semiconductor laser wavelength stabilizing device according to the present invention, FIG. 2 is a table showing an outline of specific means for each component of the device in FIG. 1, and FIGS. FIG. 7 is a diagram for explaining a specific example of the components of the device shown in FIG.
The figure is a configuration plan view showing a second embodiment of the present invention, FIGS. 9 and 10 are diagrams showing a specific example of the optical resonator part FP1 of the device shown in FIG. 8, and FIG. 11 is a semiconductor laser wavelength stabilizing device. FIG. 12 is an operation explanatory diagram for explaining the operation of the device shown in FIG. 11, and FIG.
Characteristic song I to explain the operation of the device! It is a diagram. DESCRIPTION OF SYMBOLS 1... Substrate, 2... Control part, 31.32... Waveguide, LD2... Semiconductor laser, Cl3... Absorption part,
PO2...light detection section. Figure 3 Tail 4 Figure 5 M6 Figure Moon 7 Figure Tail 8 Crack 1 Vi UΔ

Claims (8)

[Claims] (1) In a semiconductor laser wavelength stabilization device that stabilizes the wavelength by controlling the wavelength of a semiconductor laser to the absorption spectrum line of a standard material, light related to the output light of the semiconductor laser is input through an optical waveguide and a specific an absorption section enclosing a standard substance that causes absorption at a certain wavelength; a photodetection section that converts the transmitted light of the absorption section into an electrical signal; 1. A semiconductor laser wavelength stabilizing device, characterized in that a control section for controlling laser current or temperature is provided on the same substrate. (2) The semiconductor laser wavelength stabilizing device according to claim 1, which uses Rb or Cs as a standard substance. (3) Wavelength stabilization of the semiconductor laser according to claim 1, in which the absorber has a structure in which a glass film is formed by glass coating or thermal oxidation in a recess provided on the substrate surface, a standard substance is placed therein, and the glass film is sealed with a glass plate. conversion device. (4) Claim 1, wherein the absorption section is configured to include a waveguide on a glass substrate, and to absorb light related to the output light of the semiconductor laser by means of an evanescent effect using a standard substance on the waveguide. Semiconductor laser wavelength stabilization device. (5) The semiconductor laser wavelength according to claim 1, comprising a modulation means for externally modulating the output of the semiconductor laser, and a lock-in amplifier that performs synchronous rectification at a frequency related to the modulation frequency of the modulation means in the control section. Stabilizer. (6) A semiconductor laser wavelength stabilizing device according to claim 5, which uses an acousto-optic modulator as the modulation means. (7) A semiconductor laser wavelength stabilizing device according to claim 5, which uses a phase modulator made of an electro-optical element as the modulation means. (8) An optical branching section that branches part of the output light of the semiconductor laser, an optical resonator that receives the branched output light of this optical branching section, and a second photodetector that receives the output light of this optical resonator. Department and
2. The semiconductor laser wavelength stabilizing device according to claim 1, further comprising a broadband amplifying section provided on the substrate for amplifying the electrical output of the photodetecting section and feeding it back to the injection current of the semiconductor laser.